I N D E X

Section 1.Introduction

1.1Bulk solids in industry

1.2Rand Reports on the performance of plants that handle bulk solids

1.3General terms

Section 2.Particle Technology

2.1Particle Size

2.2Particle Shape

2.3Particle Surface

2.4Particle Pores

a.Physical

b.Chemical

2.5Particle Testing Methods

a. of Image Analysis

b. other Particle Tests

Section 3.Bulk Technology

3.1Bulk Properties, physical

3.2Bulk Stress systems

3.3Bulk Behaviour

3.4Health & Safety Issues

3.5Bulk Testing Methods

Section 4.Storage and Handling

4.1Flow Regimes and Flow Stresses

4.2Bulk Storage

4.3Feeders

a.for Bulk Discharge

b.for Metering

4.4Conveyors

4.5Elevators

4.6Pneumatic Conveying

Section 5.Solids Processing

Appendices

(i). Andrew Jenike

(ii).Relevant Standards

The terms are broken down into the sections below to aid the review of specific fields of interest.

Descriptions in relevant sections are followed by an alphabetic list of the terms with page reference.

Note:- Words shown in Italics in the definitions are defined elsewhere is the glossary.

Some text is included that is not part of the definition, but is added to aid understanding. ■

Section 1 – Introduction

1.1Bulk solids in industry

Approximately half of all materials that are used and consumed by society are solid materials that are handled and processed in a loose particulate form. During their passage from source to ultimate use most are stored and handled many times. They are subjected to a wide range of ambient and operational conditions and almost invariably incur significant changes in their physical nature during their route. The particles of composition of these materials span an enormous scale of physical and chemical properties, many bearing the same title existing in radically different conditions because of variations and changes that occur during their lifetime, due either to the natural unstableness of the product or changes induced during handling and processing. Bulk solids are also mixed, blended and treated in ways that change the way in which the bulk behaves. The influences of scale and time also bear on behavioural aspects.

The make-up of any bulk material comprises of at least two phases, the essential mass of the solid component and that of the fluid, most usually air, that occupies the void space between the particles. Where moisture or another liquor is present there are three phases, two of which tend to vary in quantity. Considering that the subject of particle size alone is difficult to define and that particle size distribution has a considerable influence on the behavioural nature of a bulk material, it is not surprising that the rheological behaviour of particulate solids is the most complex of all material masses. In respect to deformation characteristics of a bulk material under stress, loose solids can be classed with gases, liquids and mass solids as a fourth state of matter.

The subject is both exceptionally comprehensive and diffuse at the same time, as no individual can possibly encounter all the conditions and circumstances what fall within the field. The scientific disciplines involved include organic and physical chemistry, mechanical engineering, soil mechanics, physics, electrostatics, solid and fluid mechanics and many topics relating to heath and safety, economics and numerous other concerns. Education in the subject is seriously handicapped by it being an emerging technology in a mature field of application and falling between the many schools of scientific interest.

1.2Rand Reports on the performance of plants that handle bulk solids

Two detailed surveys were conducted at different times to compare the commissioning and operating performance of substantial industrial plants that were constructed to carry out a various types of production processes. The conclusions clearly showed that the results on plants that involved the handling of bulk solids incurred far more difficulties at the commissioning stage and seldom attained the level of efficiency that was regularly secured with equipment that handled liquids and gasses. In most cases, plants that handled particulate materials took far longer to bring into production and ran further over budget than those dealing with fluids, and that they rarely achieved their full design rating of output. Another finding of some significance was that, despite the considerable advances made in the technology, plants that were built in the 1980's did not measurable show improvements in these respects over plants built in the 1960's. See Appendix.1

There is much evidence that, with a few notable exceptions, this situation still persists. ■

1.3General Terms

accuracyThe closeness of the agreement between the result of a measurement and the true value.

aerosolA dispersion of fine particles (solids or liquids) suspended in a gas.

adsorbed waterwater attracted to the particle surface by physiochemical forces, having properties that may differ from the pore water at the same temperature and pressure due to the altered molecular arrangement. Adsorbed water does not include water that is chemical combined within the particles.

aeration The action of injecting gas, usually air, to a bulk material to weaken the particulate structure by dilatation. The process induces the material to adopt a fluid or highly agitated state. (See quiescent and boiling bed)

anistropic Not of the same composition, structure or condition in all axial directions.

attritionUnwanted reduction in particle size caused by the collision of particles with other particles or with a surface, resulting in abrasion, causing fines, or fracture that creates ‘mother’ and ‘daughter’ particles.

barrel sectionThe upper, parallel section of a circular storage hopper. See body section.

bed An assembly of particles in a contained state.

biaxial compressionCompression of a bulk mass by the application of normal stresses in two directions at right angles to each other

biaxial state of stressState of stress in which one of the three principal stresses is zero

big bagSee FIBC

binA bulk storage container, usually of small or medium size. Synonymous with hopper and, to a limited extent, with silo. May be mobile or transportable, See IBC

binder An additive that coheres a loosely assembled particulate mass.

Bingham plasticA form of deformation that exhibits Newtonian behaviour once a threshold shear stress is exceeded.

body forceA force, such as gravity, magnetic force or inertia, whose effect is distributed throughout a material body by direct action on each elementary part of the body independent of others.

body sectionThe upper, parallel part, of largest cross section, of a storage container. ■

bunkerGeneric term for a fixed container for bulk storage. Typically of shallow construction with a large, open top. See hopper, bin.

capillarityA phenomenon associated with surface tension and angle of contact that leads to the migration of fluids through narrow channels, as the interstitial voids of closely packed particulate beds.

cavitationThe formation of a cavity

clean roomA room with control of particulate contamination to a defined level.

C/M/R substancesMaterials classified as category 1 or 2 carcinogens, mutagens or toxic to reproduction. (Related to points 29, 30 and 31 pf Annex 1 of Directive 76/769/EEC. (A Consolidated, 100 page, list of materials is given ).

coagulantAn agent causing coagulation.

colloidA state of matter comprising a system with two or more phases, in which one phase exists as discrete particles of the order of 100 to 100,000 nanometers densely permeating a continuous phase. Physical characteristics related to the enormous surface area of the bulk tend to dominate the behaviour of such materials

compression indexThe slope of the linear portion of the pressure-void ratio curve on a semi-log plot.

compressive stressA normal stress that tends to shorten the body to which it is applied, in the direction in which it acts. In solids, the effect is termed compaction.

consolidationThe reduction in volume of a bulk particulate mass resulting from the effect of gravity over time, or of a compacting stress. It is useful to consider consolidation as a state, rather than a process of volume reduction, which is better distinguished by the term ‘compaction’.

creep A slow, plastic deformation under stress lower than the failure stress.

critical densityThe unit weight of a unit volume of a granular material that will deform in a specific state of stress without change of volume. Below this value of density the bulk will gain strength when subjected to deformation, i.e. it is under-consolidated, and above which it will loose strength when deformed, an over-consolidated condition. Critical density reflects the condition of a material in instantaneous equilibrium during gravity flow.

deliquescent The ability to absorb moisture from the atmosphere, to the extent that the product dissolves in the absorbed fluid.

dilatant suspensionA material that increases in shear strength with the rate of shear. ■

dilatation A conditions of expanded particulate structure that may be brought about by such as agitation, aeration or shear. The opposite of compaction.

disintergrantMaterials incorporated within compacts of dry powders or granules to promote separation to the primary particles, on addition to a liquid.

elastic limitPoint on the stress-strain curve beyond which deformation will not fully recover on the removal of stress.

elastic state of equilibriumState of stress within a stressed mass when the internal resistance to permanent deformation is not fully mobilised.

elastic strain energyPotential energy stored within a strained solid equal to the work done in deforming the solid from its unstrained condition, less any energy dissipated by inelastic deformation.

elasto-plasticA deformation that will partially recover on relaxation of the applied stress

emulsionA dispersion of immiscible liquids.

entrainment patternThe flow velocity contours that are generated over the cross section of the interface from a hopper outlet by a feeder used to discharge the container.

equivalent surface levelThe level that the contents of a hopper would reach if the material were evenly spread across the surface.

failureA state of dis-equilibrium brought about by stresses exceeding the elastic limit of deformation of a powder compact. (See shear failure, yield).

failure criterionSpecification of the mechanical conditions under which a bulk solid will fail to support the applied stress.

feeder A device used to discharge a bulk storage container in a controlled manner. Typical equipment for this purpose are screw feeders, belt conveyors, scraper type conveyors, vibratory feeders, table feeders, rotary valves and disc type feeders.

FIBCA Flexible Intermediate Bulk Container, See IBC.

filter porosityThe ratio (or percentage) of the void volume within the filter material to the total volume of the filter material.

flocc, floc; flocculateAn assemblage of particles which, having been initially dispersed, have become loosely coherent.

fluidA liquid or gas. ■

fractions Portions of the mass that fall into a certain defined category, usually a particle size range.

fumeCloud of airborne particles, generally visible, that arise from condensing vapours from either a chemical or physical reactions

Gausian distribution(See normal distribution)

health hazard rankingFor substances within EU classification as a dangerous substance are ranked in five groups of acute health hazard with respect to corrosive/irritation and organ toxicity. These classes are ranked 1 – 5 ( with 0 for unidentified products).

Class 0No data available relevant to human heath hazard

Class 1Very high risk. (e.g. very acute toxicity).

Class 2High risk. (e.g. acute toxicity).

Class 3Moderate risk, (e.g. mild toxicity).

Class 4Low risk, (e.g. low toxicity).

Class 5No reasonable concern with regard to health hazard effects

Five sub-chronic/chronic health hazards relating to allergy, neurotoxicity, carcinogenicicity, genotoxicity and rproductive toxicity are, ranked A – E, as below

Class 0No relevant data available

Class ASevere effects from low exposure

Class BSevere effects after medium exposure, or mild effects with low exposure

Class CSevere effect only from extensive exposure, or to limited cases

Class DEffects limited or applies to isolated cases.

Class ENo reason for concern with regard to heath effects.

HEPA filterAcronym for High Efficiency Particulate Air filter, for particles in air, having a specified minimum collection efficiency to the D O P test.

heterogeneous material Material in which a spot sample will have a significantly different value of the characteristics under consideration from the mean value of that characteristic of the bulk material. ■

homogeneous materialMaterial in which a spot sample will have the same value of the characteristic under consideration as the mean value of that characteristics for the bulk material.

homogeneous suspensionA suspension in which the particles are uniformly distributed in a liquid.

homogenisation

1.(Relating to a fluid based product).

Mixing using a high shear rate.

2.(Relating to a particulate solid).

Re-ordering the particle distribution of a heterogeneous material to the condition of a homogeneous material.

hopper

1.Generic term for a bulk storage container.

2.The converging section of a bulk storage container.

(The ambiguity of this term demands that, for appropriate clarity, the meaning is clarified within the context in which it is used).

hopper half angleThe inclination of the wall of a symmetrical hopper from the vertical axis.

hopper section (of bulk storage container)The converging section of a bulk storage container leading to the outlet. See hopper.

Hvorslev surfaceThe envelope of a family of yield loci on a three dimensional axis of shear stress, normal stress and bulk density. The boundary conditions are: -

-The line of tensile strength on the axis of density.

-The critical state line, being the limiting shear strength of a bulk mass against its density.

-The envelope of the yield loci at each condition of bulk density.

-The bulk density condition at zero shear strength. (Maximum density for fluidity).

-The bulk density condition of maximum consolidation.

hygroscopic Possessing the tendency to absorb moisture from the atmosphere. In the case of particulate solids this leads to many potential flow problems as the effect of moisture changes the bulk strength and slip characteristics of the bulk, sometimes dramatically with only a small change of water content.

Equilibrium atmospheric moisture conditions depend upon the ambient temperature, pressure and relative humidity.

Changes in ambient conditions can cause moisture content variations according to the boundary surface contact conditions of the bulk mass. Moisture migration and condensation conditions can give rise to massive imbalances in moisture distribution, leading to caking or surface adhesion problems. (See moisture content).

hysteresis Incomplete recovery of shape on the relaxation of stress. i.e. A partial elastic recovery inhibited by a degree of permanent deformation. ■

IBCIntermediate bulk container.

intensity of variationThe degree to which a variation of a physical property deviates from defined bounds, the average value of a batch or from adjacent product, whichever is significant. (See Scale of scrutiny and Scale of variation).

interstice The space between particles in a mass. (See preferred term void).

interstitialOccurring in the space between the particles of composition.

isotropic Pertaining to axial directional differences. This applies to individual particles, their structure in a bulk arrangement of particles, to stresses and to strains. A sphere is isotropic, whereas elongated particles and flakes are not. Fluids are, whilst wood, by virtue of its grain, is not. Strain, Shear and uniaxial compaction are essentially anistotropic (non-isotropic) processes that produce anistropic states in the bulk material.

The feature is relevant to both the preparation and loading of a sample of bulk material for testing, as the failure conditions depend upon how the bulk will shear. This in turn depends on the orientation of the constituents of the particulate structure in relation to the direction of stresses that produced the specific state of the bulk and the direction of stresses applied to cause the bulk to fail. The isotropy of a particulate structure is essentially disturbed when shear takes place.

Jenike, AndrewSee Appendix II. (Recommended reading).

laminar flowFlow in which the head loss is proportional to the first power of the velocity. It is characterised by the lack of turbulence.

latex particlesParticles of natural latex or other polymer; usually spherical and of a narrow size range; often used for calibration purposes.

liquefactionThe process whereby a powder bed is transformed from a solid state to a liquid state, usually as a result of the restructuring of particles in a fully saturated bed to a higher packing density arrangement or the introduction of excess fluid. Additional fluid separates the particles, whereas closer particle packing allows the pore pressure of the incompressible fluid to support the applied stresses. Either change relaxes the particle-to particle contact pressure and resulting in a much greater freedom for the particles to shear with little resistance. Fluidisation is an equivalent process with a gas, instead of a liquid, providing the void pressure to reduce the contact pressure between particles.

Log-normal distributionA distribution which results in a straight line when a cumulatively

quantity on a probability axis is plotted against particle size on a logarithmic axis. ■

measuring rangeThe range over which an instrument as set-up can give results within a specified uncertainty.

(Note: – Some instruments have many measuring ranges).

micrometre (m)One millionth part (10-6) of a metre.

micron(See micrometre)

monolithA block of material; a very large particle.

nanometre (nm)One thousand millionth part (10-9) of a metre.

nano technologyThe study of particles in the size region of one nanometre or less.

(This is an area of intense interest because of some useful physical characteristics of ultra fine particles, such as their large surface area in relation to mass).

normal distributionA distribution which results in a straight line when cumulative quantity on a probability axis is plotted against particle size on a linear axis.

normal stressThe stress acting at 90 degrees to the considered plane. (usually that of shear failure).

particleA discrete piece of matter.

particle adhesionThe tendency for neighbouring particles to hold together by attraction forces, such as surface tension, Van der Waal forces at the molecular level, surface sintering, thermal fusion or by electrostatic forces.

particle, effectiveA particle as perceived by a measuring technique that discriminates between the constituent elements of a powder.

particle, primaryThe basic particle within a agglomerate or flocculate.

particulateConsisting of particles.

particulate bedA particulate solid occupying a given space.

particulate solidA crowd of particles, the number of particles being sufficient for the statistical mean of any property to be independent of the number of particles present. The mass assumes a behaviour due to their interaction such that the assembly may be considered as a continuum. Particulate solids may be called bulk solids, granular solids or powders although, in certain contexts, these terms have different meanings from one another.

particulate structure The manner of composition of touching particles in a bed. ■

period of scrutinyThe time interval over which variations of a given property are significant. A typical example is for defining the time interval over which a weighed sample should be collected to determine the relevant accuracy of a Loss-in-weight feeder output. Typically, for this duty, the period is of the order of 60 seconds. Whereas feedback control can ensure that the average feed rate is relatively accurate, there are circumstances, such as metering the feed into a high-speed mill where the residence time is very short, that place a high premium on the very short-term feed evenness, rather than the precise accuracy, in relation to the mill power demands and consistency of the product produced.

phaseA physical state that constitutes all or part of a material mass, such as a liquid, gas or solid. Particulate solids comprise a minimum of two phases, the solid and the medium occupying the voids. There are three phases if a loose fluid is present in addition to a gas in the void space.

points of co-ordinationThe points of contact between particles in a particulate bed.

Poison’s ratioThe ratio between linear strain changes perpendicular to, and in the direction of, a given uniaxial stress change.

porosity, filter(See filter porosity).

powderA bulk solid consisting of particles less than 1 mm.

primary consolidationThe reduction of volume that occurs in a dilated powder due to the escape of excess gas from the voids.

relative humidity The proportion of moisture that can be held in air as a vapour compared with the maximum vapour holding capacity at the given temperature.

Reynolds numberThe dimensionless number which defines the flow pattern of a fluid surrounding a particle,

where Re = v.d. /

Re is the Reynolds number

v is the relative velocity

d is the diameter of spherical particles

is the density of fluid

= viscosity



All values being in the same system of units.

rheology The subject of deformation and flow.

rheopecticThe behaviour of materials that set or increase in viscosity when shaken or tapped. ■

risk phrasesLegends used in the Countries of the EU to denote category of risk related to dangerous substances and preparations. See Attributes.

Rosin-Rammler distibution A mathematical function to describe particle size distribution

(The expression was originally developed for broken coal).

safetySee attributes, risk phases, MSDS, CMR substances, and Directives 99/45/EC, 67/548/EEC (in Appendix of standards)

scale of scrutinyThe amount, volume or mass, that is sufficient to ensure that specific determined qualities of interest in a bulk material sample will satisfy the requirement for purpose. A common use is to define the size of a mixture sample that must be taken, to ensure that the ratio of constituents falls within acceptable bounds for the application. In the case of a mix prepared for making pharmaceutical tablets, this should be no more than that required for an individual tablet to confirm that the amount of active ingredient per dose is within prescribed bounds.

A larger sample may be appropriate for a detergent for use in domestic appliances and a different again scale for a solid fuel supply to a power station, where the average calorific value on a large scale is of interest.

Some circumstances demand that more than one scale of scrutiny be considered, for each of which different levels of tolerances can apply.

(See Scale of variation, intensity of variation, period of scrutiny).

An analogy may be considered with colour differences in a fabric or sheet, where a small, intense spot is obvious, but a small shade difference at that scale would be un-noticed. However, a similar fine shade difference on a much large scale would be immediately apparent and un-acceptable.

scale of variationThe size of region over which a significant variation of an interesting physical property is detected. This may be from defined bounds or from the average in the universal sample. (See scale of scrutiny and Intensity of variation). Note that this term relates to the scale of causal occurrence of a variation, whereas the scale of scrutiny applies to the scale of significance relevant to an application, as with the suitability of the material to subsequent processing or for its ultimate use.

shear failure The permanent disturbance of a particulate structure by the application of a shear stress. Interest may focus on incipient failure and/or sustained failure.

silo A bulk storage container, usually of large volumetric capacity and tending to have a slender, cylindrical body section with a conical hopper section. May be built in banks and constructed of metal or concrete. Broadly synonymous with hopper and, to a limited extent, with bin and bunker.

solidA state of matter in which the constituent molecules or ions possess no translational motion, but can only vibrate about fixed mean positions. A solid has definite shape and offers resistant to changes in shape and/or volume. ■

spot sample A sample taken at random from a bulk mass.

state,(of a bulk material) The condition of dilatation of a bulk material, as characterised by the

packing arrangement of the constituent particles.

Material state is normally quantified by its condition of density, although strictly, this does not take account of any anisotropy in the system.

Stokes-Einstein equation The equation relating the pace of Brownian motion to the diameter of the particle in motion, expressed as: -

D = kT/3π.. d

where: D is the diffusion coefficient of the particle.

K is the Boltzmann’s constant.

T is the temperature.

is the viscosity of the surrounding fluid

d is the particle diameter (diffusion diameter).

and where D is determined in photo correlation spectroscopy using the equation: -

k = 4 π.n. sin (/2) /

where n is the refractive index of the suspending field

. is the scattering angle

is the wavelength of incident light.

Stoke’s lawThe equation which determines the free falling velocity, v, (terminal velocity), attained by a particle in viscous flow conditions and allows a calculation to be made of the particle size.

v = d2.g ( ∂s - ∂f ) / 18 in SI Units,

Where: -v is the free-falling velocity.

d is the Stoke’s diameter of particle.

g is the gravitational acceleration.

∂s is the density of particle.

∂f is the density of fluid.

is the viscosity..

strain ellipsoidRepresentation of strain in the form of an ellipsoid into which a sphere of unit radius deforms and whose axis are the principal axis of strain.

stress The value of an applied force divided by the area of its application.

stress ellipsoidThe representation of the state of stress in the form of an ellipsoid whose semi-axes are proportional to the magnitude of the principal stresses and lie in the principal directions. The coordinates of a point, P, on this ellipse are proportional to the magnitudes of the respective components of the stress along the planes normal to the direction, OP, where O is the centre of the ellipsoid. ■

stress history The sequence of stress conditions that have brought a bulk material to the state in which it now resides.

stress relaxationThe reduction in stress due to creep or the reduction in confinement during flow. See Sigma Two relief.

surfactantA substance which reduces surface tension.

suspensionA dispersion of particles in a fluid.

tangent modulusThe slope of the tangent to the stress-strain curve at a given stress value. (generally taken at a stress equal to half the compressive strength).

thixotropic suspension A condition that requires an initiating stress to commence

deformation, but then resistance decreases with increased strain.

turbitity The light scattering properties of particles suspended in a fluid.

ullageThe space in the upper part of a bulk storage container that cannot be filled because of the surface contours formed by the repose conditions acting from the point of fill.

unconfined failureThe failure of a particulate bed that is not supported on a boundary by a confining surface, therefore no normal force or shear force is acting on this surface. Such is the situation at the underside of an arch.

under-consolidatedA state of consolidation and applied stress where shearing causes compaction of the particulate structure in the shear plane

uniaxial state of stress State of stress in which two of the principal stresses are zero.

unloading moduleSlope of the tangent to the unloading stress-strain curve at a given stress value.

van der Waal forcesMolecular attractive forces between closely aligned fine particles.

viscous flowOf permeability. A form of flow in which adjacent layers of fluid do not mix except at the molecular level and when the velocity at the particle interface is zero.

void Space in a particulate bed that is not occupied by particulate matter. This volume may be occupied by air, water or any other liquid or gas in any combination. If the void space is totally occupied by a liquid, the bed is said to be ‘fully saturated’.

void pressure The pressure of the fluid, usually air, in the interstitial voids between the particles in a bed.

void ratioThe ratio of the volume of the void space to the volume of the solid particles in a given particulate mass.

At higher normal loads, with a particular condition of preparation, the shear strength will not peak, and continue to increase accompanied by an increase in the density of the sample to a different bulk condition, where it has a greater shear strength. See underconsolidated. ■

void pressure The pressure of the fluid, usually air, in the interstitial voids between the particles in a bed.

void ratioThe ratio of the volume of the void space to the volume of the solid particles in a given particulate mass.

At higher normal loads, with a particular condition of preparation, the shear strength will not peak, and continue to increase accompanied by an increase in the density of the sample to a different bulk condition, where it has a greater shear strength. See underconsolidated. ■

Section 2 - Types of Powder

Arizona test (road dust)A powder of specified size distribution used for calibration, quality

control or filter testing.

atomised powderA powder produced by the dispersion of molten material sprayed under conditions such that it solidifies as a finely divided powder.

ballotiniSolids glass spheres, graded in size ranges.

calcined powderA powder produced or modified by dry heat treatment.

calibration materialA powder or suspension used to standardise instruments and methods.

carbonyl powderA metal powder produced by thermal decomposition of a metal carbonyl, generally nickel or iron or a combination of the two.

cenospheres Fine, hollow glass spheres, a fractional component of fly ash.

certified reference materialA reference material that is accompanied by, or traceable to, a certificate stating the property value(s) concerned, issued by an organisation that is generally accepted as technically competent.

clay Fine grained soil that exhibits plasticity, ( putty-like properties), within a range of water contents and that exhibits considerable strength when dry. (The term has been used to designate the percentage of particles finer than 0.002 mm, (even 0.005 mm in some cases), but it is recommended that this definition is not used as, from the engineering standpoint, the properties described in the initial definition above are many time more important).

CRM 116A standard powder (ground limestone) used for the verification of consistency and tester calibration with a Jenike shear cell. See SSCT. Samples are available from BCE, ( Community Bureau of Reference to the European Union, together with certified yield loci for the Jenike test).

crystalline powderA powder produced by the process of crystallisation.

‘C’ test dustA powder of specified size distribution, coarse or fine, for calibration, quality control or filter testing. (Air cleaner tests).

diatomatious earthA siliceous deposit occurring as a whitish powder, consisting essentially of the frustules of diatoms. It is resistant to heat and chemical action, so is used in fireproof cement, insulating materials and as an absorbent in the manufacture of explosives. ■

dust (of occupational hygiene). A definition given in health and safety manual is: -

‘A particulate material that is, or has been, airborne and would pass through a 75 m sieve’.

This description takes no account of the particle density and shape factor. The term may be more appropriately applied to - ‘Particles of low aerodynamic diameter, that tend to become airborne in low velocity air currents and are slow to settle’.

In general, particles above 20 m are captured in the primary air passages of inhalation and are absorbed, if soluble, or eventually expelled by the system, if insoluble. Particles in the general aerodynamic particle size range of 7 to 20 m tend to move through to upper airways of the respiratory tree and have more significant effects in irritation or asthmatic sensitisation. Particles of sub 5 m aerodynamic size tend to pass to the foundations of the respiratory system and cause accumulative damage.

Suspended particles less than 200 m can represent an explosion hazard if a potential ignition source is present and the particle concentration is such that a flame front can propagate itself. Settled dust carries a serious hazard of causing a secondary explosion when the disturbance of a primary explosion mobilises this dust to an airborne cloud.

Fugitive dust is a major source of mess, spillage and product loss, as well as raising health hazards, handling difficulties and quality issues of the product from which it originated.

Typical materials in this category are: -

Carbon black, tobacco smoke, paint pigments, insecticides, milled flour, coal dust and fly ash.

Coarse particles can be removed from entrainment by cyclones, intermediate size dust particles are generally collected by fabric or sintered sheets and very fine particles captured by electrostatic filters.

filter cakeA packed bed formed by a filtering process and held together by cohesive strength if dry and by surface tension of residual moisture if the result of filtering from an initially saturated mass.

fly ashFinely divided ash composed of fused silica and glass, collected from electrostatic precipitators of power stations burning pulverised coal.

fumed powderA powder recovered from fume. ■

grit(Of occupational hygiene). Particulate material which is or has been airborne and which would be retained on a 75 m sieve.

hydrogen reduced powderPowder produced by the hydrogen reduction of a metallic oxide or other compound.

hydrophilic The property that defines a material as attracting water. Water exhibits an obtuse contact angle with hydrophilic materials.

hydrophobicThe property that defines a material as water repellent. Water exhibits an obtuse contact angle with hydrophobic materials. This property favours the use of such materials, for example sheets of ultra-high molecular density polyethylene, as contact surfaces for damp and wet bulk products, to minimise the wall cohesive effects of surface tension,

hydrostatic pressureA state of stress in which all the principal stresses are equal, (there is no shear stress), as in a fluidised powder where the pressure in the voids is due to the head of product and acts in all directions.

milled powderA powder produced by comminution in a mill.

natural powderMaterial occurring naturally as a fine powder.

precipitated powderA powder produced by chemical or electrostatic precipitation.

reference materialA material, the relevant properties of which are sufficiently established and consistent for it to be used for the calibration of a measuring instrument. (See also certified reference material, CRM116).. ■

Section 3 - Powder properties

absolute powder density The mass of powder per unit of absolute powder volume.

absolute powder volume The volume occupied by the solid content of a powder, excluding

all pores and voids.



absorption 1.Penetration of a substance, usually a fluid, into the body of another.

2.The attachment of water molecules to the surface of particles

aerated bulk density ( See density, aerated bulk)

agglomerate An accumulated cluster of many particles that are rigidly bonded together by inter-particle forces, partial fusion, sintering or by growing together, such that they act as a single, larger particle.

apparent powder density The mass of powder per unit of apparent powder volume.

apparent powder volume The total volume occupied by solid matter, including open and closed pores.

bed porosity( See powder bed porosity ).

blindingThe building up of small particles on a screening surface reducing the aperture size or closing them completely.

bulkA mass of particles.

coefficient of compressibilityv = (L 2 F –1 ). The secant slope, for a given pressure increment, of the pressure-void ratio curve. Where a stress-strain curve is used, the slope of this curve is equal to v/(1+e).

coefficient of consolidationv (L 2 T –1 ). A coefficient utilised in the theory of consolidation, containing the physical constant of the loose solid affecting its volume change. cv = k(1+e)/ vw , where: -

k = coefficient of permeability, LT-1

e = Voids ratio,

v = coefficient of compressibility, (L 2 F –1 ).

w = unit weight of water, FL-3

coefficient of friction, The relationship between normal stress and the corresponding shear stress at which sliding takes place between two surfaces. (Between a loose solid and a contact surface, this behaviour is referred to as wall friction). See static friction and dynamic friction. ■

coefficient of permeabilityThe rate of passage of a fluid under laminar flow conditions through a unit cross section of a media under a unit pressure drop at standard temperature conditions.

coefficient of uniformityCu (D), The ratio D60/D10, where D60 is the particle diameter corresponding to 60 % finer on the cumulative particle-size distribution curve, and D10 is the particle diameter corresponding to 10 % finer on the cumulative particle-size distribution curve.

compression ratioThe ratio of the loose poured density to the pressed density.

dynamic frictionThe frictional resistance to sustained sliding. See friction.

friabilityThe tendency of particles and granules to break down in size during handling and storage under the influence of light physical forces.

gravelMineral particles greater in size than 2000 microns

Hausner ratioThe ratio of tapped density to loose poured bulk density.

hydrodynamic clusterThe phenomenon of multiple, closely-grouped, individual particles falling through a fluid with a higher terminal velocity than that of the individual particles. Note that a focused flow stream achieves a higher fall velocity than the terminal velocity of an individual particle

major principal stressThe largest principal stress acting on a bulk solid.

minor principal stressThe principal stress acting on a bulk solid at 90 degrees to the major principal stress.

oscillating hopperA method of securing a representative sample by oscillating feed from a

sample divider hopper over two contiguous chutes leading into separate collectors.

parent populationThe overall bulk system from which a powder sample is taken.

permeabilityThe ease with which a porous mass e.g. a powder bed or compact, permits the passage of a fluid such as air. This feature has a major influence on the flow behaviour of fine powders. Changes in volume of the bulk essentially are reflected in changes in the voidage. This must initially respond to the volume variation by pressure change of the ambient fluid. A positive void pressure acts to partially support the particle mass. This support reduces particle-to-particle contact pressures and surface interferences that resist shear. In extreme circumstances, the shear strength of the bulk is negated and a highly dilated mass behaves as a fluid. A void pressure less than ambient, as generated by the shear of a settled bed, opposes the expansion of the bulk and hence increases its resistance to expansion and flow. ■

powder density, absolute( See absolute powder density).

powder density, apparent( See apparent powder density).

powder density, bulk( See bulk density).

powder density, tapped ( See tapped density).

powder volume, apparent( See apparent powder volume).

pressed density( See density, pressed).

principal stress A stress acting in a plane that is not subjected to a shear stress

principal stress, majorSee major principal stress

principal stress, minorSee minor principal stress

pyrophoricThe property of a powder to self combust when exposed to oxygen

ratio, compression( See compression ratio).

recovery factorThe change in dimension of a non-metallic compact on ejection from its die or mould.

representative sampleA quantity taken from a larger amount, that fairly reflects the qualities relative to the conditions of interest of the whole.

sampling tableA device for taking a small powder sample from a large quantity by pouring the material through a series of divided chutes that successively reject 50% of the material flowing.

sandMineral particles in the size range 200 to 2000 microns

sand, fineMineral particles in the size range 20 to 200 microns.

siltMineral particles in the size range 2 to 20 microns. (Mineral particles less than 20 microns are usually referred to as ‘clay’).

sliding frictionSee dynamic friction

static frictionThe friction value developed when resistance to slip is fully mobilised prior to relative movement taking place between the material and the contact surface. Note that friction is dependent upon both the nature of the bulk solid and its interaction with a specific contact surface. The magnitude of frictional resistance is then a function of the normal stress acting between the bulk material and the contact surface. See surface friction, co-efficient of friction, dynamic friction. ■

surface adhesionThe result of attractive mechanisms between a particulate solid and a contact surface. These will give rise to surface cohesion effects according to the frictional nature of the interface. See adhesion, cohesion.

surface cohesion The resistance to slip offered by internal forces between a particulate solid and a contact surface, separate from any frictional effect due to a normal force acting on the surface. These forces may be generated by such effects as surface tension, in the case of a damp powder, electrostatic forces or molecular forces. The effect may be exacerbated by a negative void pressure differential with ambient pressure. See adhesion. Cohesion.

surface frictionSee static friction, dynamic friction

tortuosity bedA measure of the convoluted path followed by an element of fluid passing through the intensities of a packed powder

volume, absoluteThe volume of the solid matter after exclusion of all the spaces (pores and voids).

volume, apparent powder ( See apparent powder volume)

volume, powderThe apparent volume of a powder as measured under specific conditions. ■

Section 4 - Powder Processing.

blending The placing together of different materials in a prescribed ratio at a scale of scrutiny that is significant to the application by way of low energy mechanisms, such as by intermingling gravity flow streams or layering onto a moving belt. (See mixing and homogenising).

‘boiling’ fluid bedA fluid bed where the quantity of the fluidising media agitates the mass by passing through the bed in large bubbles.

calciningA process of modifying the properties of a powder by subjecting it to a high temperature.

capture zoneThe converging region between the rollers of a roll press where the surface friction on the product causes the material to move towards the nip point without slipping on the roller surfaces.

cementationThe binding together of particles by precipitation at their points of contact.

cold pressingThe compaction of a powder carried out at room temperature.

comminutionThe reduction of particles size by intensive fracture.

compactA form prepared by compressing powder in a mould or die.

compact, green( See green compact)

compact, sinteredA green compact after sintering.

cutThe division point for separating a flow stream in which particles are preferentially directed to each side of the ‘cut’ according to some physical attribute.

dilated bed A bed of powder that is expanded to a dilate condition by a gas pressure in the voids in excess of ambient. (See settling bed, expanded bed).

dry inertial collectorsA type of dust collector that disengages particles from a gas by virtue of exploiting their physical dynamics.

electrostatic precipitators A dust collecting system that imparts an electric charge to particles in a dust laden stream and subsequently collects them on plates maintained at a high voltage.

expanded bedA bed of particulate solids held in a state of dilatation by the upwards passage of a second phase media such that the particle-to-particle contact pressure is reduced from that of a settled bed. (See dilated bed) ■

fabric filtersA dust collecting system that uses porous fabric as a barrier to collect dust particles.

fluid bedA suspension of particles suspended in an upward flow of fluid (or downward flow if the particles are less dense than the fluid).The bed may be quiescent or boiling, according to the quantity of the fluidising fluid.

fluidising The process of injecting a gas underneath a bed of particulate solids , to dilate the material in a rising gas stream such that it behaves like a liquid. See fluid bed.

granulationThe process of combining particles into larger agglomerates (granules)

green compactA formed compact intended for sintering, or which hardens with time or other treatment.

Haultain infrasizerA vertical air elutriator similar to the roller elutriator.

homogenisingThe rendering of components that were initially separate or varied in nature throughout the volume of a mass, to a compound of uniform composition at a scale of scrutiny that is significant to the application. (See blending and mixing).

hot pressingThe compaction of a powder under heat and pressure, to result in sintering of the mass to a strongly bound mass.

minimum fluidising velocityThe minimum gas velocity required to fluidise a bed of powder. The value depends mainly upon the particle size and effective particle density.

pegging The conditions which occurs when particles wedge in the apertures of a sieving medium.

pelletAn agglomerate of particles produced by specialised techniques, such as pressing.

pre-sinteringA heat treatment carried out at a temperature below a final sintering temperature to strengthen a powder compact.

pressingThe compaction of a powder under pressure in a mould or die.

pressing, cold( See cold pressing).

pressing, hot( See hot pressing).

pressing, warm( See warm pressing). ■

quiescent bedA bed of particulates held in a steady, tranquil state of suspended dilatation by the passage of a second phase media

roller elutriatorA vertical air elutriator used for fractionating powder in the size range 5 to 300 microns

roll press A compacting device that consolidates powder between two contra-rotating rollers under a nip pressure acting on the small gap between the rollers. The rollers may have flat surfaces, to produce flakes, or have mould indentations that form pellets or nodules.

scalpingThe separation of a small amount of oversize lumps or particles from a bulk material by size classification.

settled bedA stable bed of particulates where particle to particle contact pressure is fully developed and not relieved by internal void pressure or the counter-flow of a fluid.

settling bedA transient condition, where a bed of dilated particles has an increasing density condition and a decreasing void pressure as the media in the interstitial volume at a higher pressure than ambient percolates from the bed, ultimately to allow particle-to-particle contact pressures to develop to those of a fully-settled bed where the void pressure is ambient.

shrinkageThe reduction in size of a compact on drying or sintering, expressed as a percentage of the final volume or stated linear dimension.

sinteringThe bonding of contiguous particles in a mass of powder or a compact by partial fusion at temperatures below the melting point of the particles.

spiral flow classifierA device for fractionating fine particles by moving a fluid stream in which the particles are suspended through a cylindrical vessel from a tangential inlet to a more centrally located outlet. The extend to which centripetal forces on the particles overcome fluid drag is related to the physical characteristics of the individual particles and determines the ability of the particles to exit at specific radially located outlets of the equipment. The division between outlet positions being terms the ‘cut’.

tabletA small compact.

trajectory The path taken by a particle with an initial component of horizontal motion under the influence of gravity and/or prevailing air flow.

warm pressingThe compaction of a powder under pressure above room temperature and below sintering temperature.

wet scrubbersA dust collecting system that employs a spray system to capture particles. ■

Section 5 - Particle Properties

abrasiveness The ability of a particle to cause wear on a contact surface. This quality is determined by its hardness factor and sharpness of the points of contact. The actual degree of wear then depends on power factors of both the contact pressure and the relative velocity of the contact surfaces. Hard, sharp, angular shaped particles may be expected to be highly abrasive.

aerodynamic diameterThe diameter in m, of a unit density sphere that has thesame terminal velocity in air as the particle in question.

apparent particle density( See density, apparent particle).

Blain finenessThe fineness of a particulate material, expressed as the surface area per unit of mass.

Bond work indexThe energy required to reduce the size of unit mass of material from infinity to 100 m in size.

Brownian motionThe random movement of small particles in a disperse phase caused by the bombardment of molecules of the surrounding media.

classificationGrading in accordance the particle size, shape, density or other attribute.

cleavageThe tendency to cleave, or split, along definite parallel, closely spaced, particle planes of least cohesion.

coagulationThe change from a fluid to a more or less irregular solid state.

coalescenceThe joining together of fluids originally separated by boundaries.

de-flocculationThe breaking down of flocculates.

density, apparent particleThe mass of a particle divided by its volume.

density, effective particleThe mass of a particle divided by its volume including open pores and closed pores.

density, immersed particleThe mass of a particle per unit volume of suspension fluid displaced.

density, trueThe mass of a particle divided by its volume, excluding open pores and closed pores.

dispersionThe separation and distribution of one phase in another.

effective particle density( See density, effective particle). ■

electrokinetic potentialSee zeta potential

flocculationThe coalescence of particles into floccs.

foulingThe building up of particles onto surfaces because of the particles stronger attraction to the surface than to the fluid in which they are dispensed.

free-fall velocityVelocity of fall of a particle though a still fluid at which the affective weight of the particle is balanced by the drag exerted by the fluid on the particle.

hardness Hardness is characterised, in general, by the resistance of a material to deformation. This property reflects a material’s susceptibility to abrasion by other material of contact and its ability to abrade other materials. As such, the value is a measure of its resistance to wear and aggressiveness to cause wear on other materials. When the surface is sufficiently large, absolute hardness is normally measured by determining the resistance to indentation, as in Brinell, Rockwell, Vickers diamond pyramid and scleroscope hardness tests. For particles and powders hardness, it is generally described in relation to its capacity to scratch or wear other materials, without itself suffering surface degradation. Ten materials of different hardness are defined by Mohr’s scale of hardness, to act as a basis for comparison and interpolation.

immersed particle density( See density, immersed particle).

Mohr’s scaleA scale that gives a comparative order of hardness by expressing it

of hardnessin terms of the ability of one material to scratch another, without itself being affected. A set of reference materials is listed with which others may be compared.

In ascending order of hardness, these are: -

1.TalcIt should be noted that some material

2.Gypsumsurfaces are an-isotopic in hardness,

3.Calcitethe resistance to scratching being

4.Fluoride‘tougher’ in one direction than

5.Apatiteanother.

6.OrthoclaseThe ability to mark another surface is

7.Quartzdependent upon the intensity of local

8.Topazpressure, therefore a particle that has

9.Corundumsharp corners will concentrate any

10.Diamond.given contact force on a smaller area.

Ostwald ripeningThe growth of some particles in a suspension at the expense of others as a result of dissolution and re-crystallisation.

particle density( See density, apparent density, or density, effective particle). ■

particle density, true( See density, true).

sedimentationThe settling of particles in a still fluid, resulting in grading by mass.

settling velocityThe distance per unit time that a particle falls in a still fluid. Stokes’ law has been developed, at low Reynolds number, to relate settling velocity to particle size.

temperature Generally, most materials are handled in ambient temperature conditions. In sensitive cases, the physical properties of the bulk material may be affected at high ambient temperatures, and almost certainly so at elevated temperatures. High temperature also affects the gas in the voids, almost invariably to increase the gas viscosity and thereby significantly influence the effects of bulk volume changes. See porosity.

Hot, fine powders from driers and kilns are considerably more prone to sustained aeration and fluidity than the same material at normal ambient temperature. This is because of the increased resistance to loss of excess air from the voids by virtue of the reduced permeability of the mass to the higher viscosity gas.

Changes of temperature also cause secondary effects of moisture holding capacity of the gas, condensation migration and ‘thermal ratcheting’, a process of repeated change of volume due to fluctuating thermal variations, as between day and night conditions, that alternately contract a bulk volume in a silo to cause settlement, and then expand to stress the container walls.

terminal velocity1 - See free-falling velocity. 2. - See terminal gas velocity

velocity, free fallingSee free-falling velocity.

viscous dragThe resistance to movement of a particle through a fluid.

zeta potentialThe potential difference between the surface of a solids particle

immersed in water or a conducting liquid and the fully dissociated ionic concentration in the body of the liquid.

It can be determined using the Smoluchowski equation:

= 4 π..U / Eoo



Where is the zeta potential

is the viscosity of the liquid

U is the velocity of a particle under an applied electric field Eoo. ■

Section 6 - Particle Size

apparent particle volumeThe total volume of the particle, excluding open pores, but including closed pores.

boulder A rock fragment, usually rounded by weathering or abrasion, normally larger than 300 mm.

chipcrushed, angular rock fragment smaller than a few centimetres.

classified gradingThese are bulk materials for which the ratio between the sizes of

(of lump size)the biggest and the smallest lump is less than or equal to 2.5. (This includes material of a single dimension). A classified material is adequately defined by the values of dmax and dmin.

cumulative oversize A plot obtained by recording the amount of the oversized

distribution plotparticles (y axis) against particle size (x axis) for several different size levels.

cumulative undersizeA plot obtained by recording the amount of the undersize

distribution plotparticles (y axis) against particle size (x axis) for several different size levels.

D10 The diameter of a particle at which 10 % by weight (dry) of the constituent particles of a sample are finer.

D60 The diameter of a particle at which 60 % by weight (dry) of the constituent particles of a sample are finer.

density distributionOf size distribution. (See frequency distribution plot).

diameter, diffusionThe diameter of a particle calculated from photon correlation spectroscopy, using the Stokes-Einstein equation.

diameter, equivalentThe diameter calculated from light diffraction observations.

diffraction

diameter, equivalentThe diameter of a sphere which has the same free-falling

free-fallingvelocity in a given fluid as the particle when determined under similar conditions.

diameter, equivalentThe diameter of a circle with a perimeter equal to that of

perimeterthe particle.

diameter, equivalentThe diameter of a sphere which behaves like the observed particle

sphererelative to or deduced from a chosen property. ■

diameter, equivalentThe diameter of a sphere which has the same effective

surface surface as the particle when determined under similar conditions.

diameter, equivalent The diameter of a sphere which has the same effective

volumevolume as the particle when determined under similar conditions.

diameter, Ferrets The distance between two parallel tangents on opposite sides of the image of a particle.

diameter MartinsThe length of a line which bisects the particle image.

diameter, maximum chord.Maximum length of a line limited by the particle contour .

diameter, meanSeveral mean diameters can be presented of particle size distribution data. To understand them, consider an experimental study (for example, by microscopy) where the population of particles is counted within several finite size classes. It is found that there are i particles within any size interval (i), which has an arithmetic mean diameter of d i . The full size distribution is obtained by accumulating data over several size intervals, becoming more accurate if the intervals are small, so that di becomes a better estimate of the real average particle size within the interval.

e.g diameter meanLet any mean, mq, be represented by mq = ni (di )q / ni

The more commonly used mean diameters of the size distributions are:

Systematic codeNomenclature Calculated from

D1,0

D2,0

D3,0

D2, 1

D3, 2

D4, 3

Number mean diameter

Surface mean diameter

Volume* mean diameter

Diameter-weighted mean diameter

Surface-weighted mean diameter

Volume*-weighted mean diameter

m1

m2

m3

m2/ m1

m3 m2

m4 m3

*Note . Mass means are equal to volume means if all of the particles have the same density.

diameter , medianThe middle of a number of observations of diameters. ■

diameter, modalThe most commonly occurring particle diameter.

diameter, projected The diameter of a circle which has the same area of projection as the

area projected area of the particle.

diameter, sievingThe diameter of the aperture of the mesh of the sieve which just allows the passage of the particle.

diameter, specificThe diameter of a sphere having the same surface area as the particle.

surface

diameter, specificThe diameter of a sphere having the same volume as the particle.

volume

diameter, Stokes’The diameter of a sphere with the same settling velocity as the particle, calculated according to Stokes’ law. This is of the form: -

d = [ 18 .H / ( ∂s – ∂f) g.t ]1/2 where: – d = diameter of sphere

= viscosity coefficient of the fluid

H = distance moved by the sphere in the time interval - t

g = acceleration due to gravity

H/t = falling velocity = v

∂s = density of the particle

∂f = density of the fluid

differential distribution plot( See frequency distribution plot).

diffusion diameter( See diameter, diffusion).

dispersity( See monodisperse system and polydisperse system).

distribution, mass( See mass distribution).

distribution, number( See number distribution).

distribution, particle( See particle size distribution).

size

distribution, volume( See volume distribution).

dynamic rangeThe ratio of the sizes of the largest and smallest particles.

envelope volumeThe external volume of a particle, powder, or monolith such as would be obtained by tightly shrinking a film to contain it. ■

equivalent free-( See diameter, equivalent free-falling)

falling diameter

equivalent settling( See diameter, equivalent settling).

diameter

equivalent surface( See diameter, equivalent surface)

diameter

equivalent volume( See diameter, equivalent volume)

diameter

Feret’s diameter( See diameter, Ferret’s)

finesParticles that are smaller than a given size.

Fisher numberAn indication of average particle size as given by a Fisher sub-sieve sizer.

free-falling diameter,( See diameter, equivalent free-falling)

equivalent

frequency distributionA plot exhibiting a series of observations of values as a

plot function of the frequency of occurrence.

gradingSeparation of a powder into particles size fractions. See classified

and non-classified materials

heterodisperse systemA bulk powder or suspension containing particles with a range of sizes.

lengthThe longest Feret’s diameter of a particle.

lump size (grading)The size of the lump is denoted by the longest edge, d, of the cuboid in which it can be contained. Materials are distinguished as classified or non-classified. Note – Whatever the grading might be, an indication should be made as to whether is can be considered as a regular average. If the grading differed over a period of time, the limits of probable variations and their duration shall be defined, especially if repeated periods are anticipated where concentrations of big lumps will occur. The size of a piece is the minimum rectangular parallel box in which it can be contained of length, l, (the longest dimension), thickness (the smallest dimension) t, and width, w.

lump form, (shape)See particle shape. Section 7.

Martin’s diameter( See diameter, Martin’s). ■

mass diameterThe distribution by mass of particles as a function of their size.

mean particle sizeDimension of a hypothetical particle such that, if the total mass of the particulate system was wholly composed of such identical particles, they would all have that dimension.

median diameter( See diameter, median).

modal diameter( See diameter, modal).

monodisperse systemA dispersion having particles all of effectively the same size.

non-classified gradeThese are materials for which the ratio between the size of the largest and

(of lump size)smallest lump is greater than 2.5. These materials normally require a complete grading analysis, made by section in which the extreme ratios of the lump size should not exceed 2.5. The grading should at least indicate the proportion, (by mass), of the lumps between 0.8 dmax and dmax, dmax being the size of the biggest lump which can be found in the material.

number distributionThe distribution by number of particles as a function of their size.

oversizeThe fraction of a powder composed of particles which are larger than a specified size, e.g. the fraction of the test portion retained on a sieve.

perimeter diameter,( See diameter, equivalent perimeter).

equivalent

particle size A description of the size and frequency of particles in a population.

distribution

particle size, mean( See mean particle size).

particle volume,( See apparent particle volume).

apparent

polydisperse systemA dispersion having particles of significantly different sizes.

projected area( See diameter, projected area).

diameter

range, dynamic( See dynamic range).

sedimentation analysisParticle size characterisation based upon Stoke’s diameter

techniquesstudies.

sedimentation diameter,( See diameter, equivalent free-falling ).

equivalent ■

sieve size of a particleThe smallest sieve aperture through which a particle will pass if presented in the most favourable attitude.

size distribution, particle( See particle size distribution).

size fraction The portion composed of particles between two given size limits, expressed in terms of mass, volume, surface area or numerical frequency.

size, mean particle( See mean particle size).

Stokes’ diameter( See diameter, Stokes’)

undersizeThe portion of a powder composed of particles which are smaller than a chosen size. e.g. the fraction of the test portion passing through the sieve.

volume, apparent particle( See particle volume, apparent)

volume, distributionThe distribution by volume of particles as a function of their size.

volume, equivalent diameter,( See diameter, equivalent volume). ■

Section 7 - Particle shape

acicularLong, thin shape, like a stiff thread or needle.

angularSharp edged, or having approximately polyhedral or irregular shape.

aspect ratioThe ratio of the longest Feret’s diameter of a particle to the largest width measured at right angles.

cavity A natural opening in the body of the particle that may be small or large.

convex perimeter(Of image analysis.) The shortest perimeter that will circumscribe the object. (Like the length of a piece of string tied around the object).

crystal A particulate body, generally solid, whose atoms are arranged in a definite pattern, the outer faces being an expression of the regular structure of the atomic composition. Usually formed from a solution.

crystallineHaving geometric or multi-faceted, regular shape characteristic of the substance, as grown from a crystal, such as granular sugar and salt.



cylindrical Shaped like a cylinder. Extruded plastic pellets typically take this form.

dendriticHaving a branched crystalline shape with the branches extending in a tributary manner from the faces of the body.

fibrousThreadlike, either regular formed or not, with a flexible structure.

flakeA thin, broad particle. May be flat or of convoluted form.

flakiness ratioThe ratio of the breadth of a particle to its thickness.

flakyConsisting of flakes, usually of irregular form. (See lamellar).

globularOf rounded composition, such as a coastal pebble.

granularA large particle with approximately equal dimensions, but of irregular shape with the surface characterised by angular points or irregularities.

Hausner shape factorThe ratio of the two sides of a rectangle constructed with minimum area to contain the profile of a particle viewed at right angles to its position of maximum stability, inscribed within the minimum circle required to contain the particle boundaries.

Heywood elongation ratioThe ratio length/breadth of the Heywood shape factor.

Heywood flakiness ratioThe ratio breadth/thickness of the Heywood shape factor. ■

Heywood shape factor A method of defining particle dimensions based upon the ‘thickness’ defined as the minimum distance at which two parallel plates can contain the particle. The ‘breadth’ being the minimum distance at which two parallel plates set at 90 degrees to those defining the ‘thickness’ can contain that plane of the particle. ‘Length’ being the minimum distance required for two parallel plates set at 90 degrees to those capturing the thickness to contain the largest dimension across the particle in that plane.

irregularHaving different measurements in the three dimensions.

isometricHaving the same measurement in three dimensions.

lamellarPlate like, usually of flat, regular form in contrast to flakes, which as usually of irregular profile and/or surface flatness

modularHaving a rounded irregular shape.

needle-likeLong, thin rigid, straight and pointed shaped particles

noduleA large rounded particle.

out-of-roundA flattened sphere or oblate spheroid.

rod-likeStraight, smooth, extended length particles

rugosityA measure of the degree of wrinkling on a surface of a particle.

shape coefficient, The ratio of the resistance to motion of a given particle in a fluid to that

dynamicof a spherical particle of the same volume.

shape elongationThe ratio of the length of a rectangle, with two sides parallel to the

factorlongest dimension of a particle, to its width.

shape sphericity1.A means to express the deviation from spherical uniformity of the

factor particle. One such is the sphericity factor.

2.The name is also given to the factor correlating different values of a particle parameter that is secured by different methods; such as the ratio of the mean diameter of a particle as separately determined by microscope and sedimentation analysis.

spherical Ball or globe shaped, of perfect symmetry.

sphericity factor,The ratio of the surface area of the particle to that of a sphere that has

the same volume as the particle.

spheroidOf basically globular or spherical shape. ■

Section 8 - Pore Size and Shape

closed poreA cavity with no access to an external surface.

‘ink bottle’ pore( See pore, ‘ink bottle’).

lattice structureA framework of pores in thin shell (as with a spray dried product)

macroporeA pore with a width greater than approximately 50 nm.

mesoporeA pore with a width between approximately 2 nm and 50 nm.

microporeA pore with width less than approximately 2 nm.

multi-poreA particle with multiple, discrete cavities – closed or open

open poreA cavity or channel with access to an external surface.

poreA cavity in a particle.

pore, closed( See closed pore).

pore, ‘ink bottle’A narrow-necked open pore.

pore, macro ( See macropore ).

pore, meso ( See mesopore ).

pore, micro( See micropore ).

pore, multi( See multi-pore ).

pore, open( See open pore).

pore size distributionThe distribution of pore width in a porous body, as determined by a specific method.

pore volumeThe volume of open pores, measured by a specific method

porosity (of particle)The ratio of the volume of any open pores and voids to the envelope volume. ■

Section 9 - Particle Surface Area

adsorbateA substance in the absorbed state.

adsorbentA substance on whose surface adsorption of another substance take place.

adsorptionThe taking up of a substance, usually gas or liquid, on the surface of another

adsorption hysteresisThe phenomenon which occurs when the amount of substance desorbed is not the same as the amount absorbed.

adsorption isothermThe relation, at constant temperature, between the amount of substance adsorbed and he equilibrium pressure of the adsorptive.

adsorption surface area See surface area, adsorption.

adsorptiveThe surface to be adsorbed.

area, calculated surface(See surface area, calculated.

area, permeability surface See permeability surface area.

BET surface areaThe surface area calculated from the Brunauer, Emmett and Teller theory for the multi-layer adsorption of a gas on a solid surface.

calculated surface area See surface area, calculated.

chemisorption Adsorption in which the adsorbate is held on the surface by chemical forces.

dead-space (adsorbate)The amount of gas required to fill the space around the adsorbent.

desorbtionThe giving up of one substance, usually gas or liquid, at the surface of another

effective permeability, The effective surface area divided by the effective solids density, as

mass specific surface determined by permeametry.

effective permeability, The effective surface area divided by the effective solids volume, as

volume specific surface determined by permeametry.

equilibrium adsorption The pressure of the gas in equilibrium with the adsorbate.

pressure

isotherm, adsorption( See adsorption isotherm).

Knudsen flow( See molecular Knudsen flow). ■

Kozeny-CarmanOf permeametry. An equation used to calculate a surface area of a

equation packed bed from its permeability.

molecular cross-Of gas adsorption. The average area occupied by an adsorbate

sectional areamolecule in the monolayer.

molecular KnudsenThe flow of low pressure gas through a pore or interstice, whose

flowdiameter is much smaller than the mean free path of the molecules.

monolayer amountThe number of moles of adsorbate that forms a monomolecular layer over the surface of an adsorbent.

monolayer capacityThe amount of adsorbate needed to cover an absorbent surface with a complete monolayer of molecules.

permeability surfaceThe surface area of a powder calculated from the permeability of a

areapowder bed under stated conditions.

pressure, equilibriumThe pressure of a gas in equilibrium with an adsorbate.

adsorption

pressure, relativeThe ratio: - equilibrium adsorption pressure to saturation vapour pressure.

pressure, vapourThe vapour pressure of the bulk liquefied adsorptive at the temperature of the adsorption.

slip flow,(of permeability). The enhanced airflow caused by the air velocity at the air/powder interface not being zero, as assumed for viscous flow. This feature becomes significant at low pressures or for very fine powders, and can affect permeability measurements.

specific surface areaThe surface area of the particles in a unit mass of powder, determined under stated conditions.

surface area,The surface area of a powder calculated from an adsorption method.

adsorption

surface area,The surface area of a powder calculated from its particle size

calculateddistribution.

surface area,The surface area of a powder calculated from the permeability of a

permeabilitypowder bed under stated conditions.

surface area,See specific surface area.

specific

vapour pressureSee pressure vapour ■

Section 10 - Particle Test Methods (of Image Analysis)

backgroundThe regions of an image that are not currently considered as objects.

binary imageA processed image having two levels of intensity.

blobAn object.

Boolian operationA logical procedure where two binary images are compared, pixel by pixel, to produce a third binary image.

closeTo dilate, and then erode, objects in a binary image to reduce the roughness of their edges.

cutThe intervention by an operator, to insert a line of non-object pixels in a binary image to separate overlapping objects.

delineationAn image processing operation which introduces abrupt changes in grey level at the boundaries of objects in a grey level image. Its main use is to prevent errors in measuring sizes of objects having different grey levels in the same image.

detection( See segmentation).

dilateTo add pixels uniformly to the periphery of an object in a binary image.

dispersative quotientThe variation or refractive index with wavelength.

edgeThe boundary between regions of interest and background (also see segmentation).

edge enhancement( See delineation).

erode To remove pixels uniformly from the periphery of an object.

eyepiece graticuleA scale or grid inserted in the eyepiece of a light microscope, for the purpose of measurement.

false colour( See pseudo-colour)

fieldThe area which can be viewed simultaneously by an imaging device e.g. a camera or microscope.

filling ( See hole filling). ■

frame The area of an image over which image analysis operations are executed.

graticule, eyepiece( See eyepiece graticule).

grey areaA number representing the brightness of a pixel in an image.

halo(Of light microscopy and image analysis). The apparent grey perimeter surrounding a dark abject caused by the finite resolution of the imaging system.

halo error(Of light microscopy and image analysis). The over-sizing of objects due to a halo effect.

Helos diffractionA proprietary particle size measuring device based upon laser

pattern analyser diffraction.

hole fillingThe process of filling gaps left in objects within a binary image.

iconometrics The scientific study of image analysis.

image analysisThe process of producing numerical or logical results from an image, which can be expressed in non-image terms.

image enhancement( See image processing)

image frame( See frame).

image processingOperations on an image which produces a different image.

inversionThe reversal of a binary image by the conversion of all the 1’s to 0’s and the 0’s to 1’s. Inversion is an example of a Boolean operation.

measurement frame( See frame)

micrometerA fabricated scale used to measure magnification. The micrometer is placed in the object plane of the microscope and compared with a length in the plane.

objectA region in which all the pixels in the binary image are connected and which are surrounded by pixels of the alternative state. It is sometimes referred to as a feature or a blob.

openTo erode, and then dilate, objects in a binary state.

picture point( See pixel).

pixelThe smallest spatially-digitised unit of an image. ■

pseudo-colourA technique for enhancing grey level differences by converting them into different colours and displaying the result on a colour monitor.

relaxationSee smoothing

retro-diffusionThe optical diffusion which takes place in the half space containing the pencil of incident light and limited by the plane tangent to the diffusion at the point of incidence of the beam.

‘salt and pepper’The spurious unwanted fluctuations in an electronic signal as shown on a video screen.

scannerThe image device for an image analyser, usually a video camera or an electron microscope.

segmentationThe process of distinguishing from the background those parts of a grey level image that are of interest.

shadingThe variation in electrical output from a video scanner when scanning across areas of identical brightness in different parts of the image. Shading can be caused by optical effects and scanner deficiencies.

shading correctorA device which compensates for uneven scanner output using an image from a blank field, i.e. one with no particles present.

skeletonisingThe process of successive erosion from the periphery of an object unless this would destroy connectivity. The resulting skeleton has no pixel in it with more than two intermediate neighbours, unless it is at a junction.

slicing( See segmentation).

smoothingThe process of digitising an image whereby each pixel is considered in turn, and its value modified by reference to its neighbours.

stereologyThe study of three dimensional structures from two dimensional sections or projections of them.

thinning( See skeletonising).

thresholdA grey level value which separates regions of interest from background in a grey level image. (See also slicing and segmentation).

threshold settingThe voltage level at which a particle counter detection circuit is set in order to identify a particle of a specific size.

video signal The analogue signal from a scanner. ■

Section 11 - Particle Test Methods - (others)

analysis sample( See sample, test portion).

Andreasen pipetteA device to determine particle size distribution by gravitational liquid sedimentation by taking sample from fixed depths by means of a pipette. BS 3406 Part 2 1980

aperture sizeThe dimensions of an opening

attrition test The measurement of particle fracture or abrasion characteristics

autocorrelation( See photo correlation spectroscopy).

spectroscopy

BCIRA dustBritish Cast Iron Research Association gravimetric size- selection

samplerpersonal dust sampler

BCURA samplingAn apparatus for sampling dusty gasses in gaseous streams. (British

trainCoal Utilisation Research Association).

BCURA sedimentationA sedimentation column for a cumulative method of grametational sedimentation size analysis, (British Coal Utilisation Research Association).

Blain permeameter An instrument for estimating a specific surface area of a powder.

Bostock’s sedimentationA sedimentation balance for determining the Stoke’s diameter

balanceof particles.

Boundbrook photsedimentometerA commercial photosedimentometer.

bridge width The distance between the nearest edges of two adjacent holes in a

perforated plate.

bubble point The differential gas pressure at which, under specified conditions, the

first, steady stream of gas bubbles is emitted from a horizontal disc of

porous medium when immersed in, or pre-wetted with, a liquid. The

bubble point is used to estimate the diameter of the largest pore present.

buffered line start The use of a small density gradient between the layer of suspension

method and the beginning of the column of clear liquid in a sedimentation

balance.

calibration The determination of a bias conversion factor of an analytical process,

under specified conditions, in order to obtain meaningful results. ■

calibration factor A factor used to adjust measurements after calibration.

cascade impactor A device for separating particles from a fluid by leading the fluid

stream through a series of jets.

centrifugal The grading of particles by size, shape and density in a fluid,

classification accelerated by centrifugal forces.

centrifugal disc A commercial photosedimentometer that uses centrifugal force to

photosedimentometer accelerate the sedimentation process.

centrifugal The classification of particles by their movement relative to a rising

elutriation fluid, accelerated by centrifugal force.

centrifugal The classification of particles by their rate of fall in a fluid, accelerated

sedimentation by centrifugal force.

cone and quartering A method of sub-dividing a dry powder sample. ( See BS 3406: part 1)

contamination Levels of particulate contamination according to various standards.

classes Example 1. Particles in air (clean rooms): BS 5259 Part 4.

Example 2. Particles in hydraulic fluids: BS 5540 Part 4.



Coulter Counter An electrical sensing zone method of determining particle size, named after the inventor. The size of a particle is indicated by the change of potential caused by the particle flowing through a small cross section of flow channel in dilate suspension in an electrolytic solution.

cyclosizer A form of inverted cyclone used for the fractionation of particles.

diffraction The deviation of light caused by it interaction with the edges of a

particle.

diffraction pattern The pattern of varying light intensity resulting from the diffraction of

light by particles.

direct method of measurementA method by which the value of a measurement is

obtained directly, rather than form estimation of other functionally related quantities.

DOP testAn air filter efficiency test, using an aerosol of dioctylphthalate (of approximately 0.3m diameter).

dry sieving(See Sieving, dry).

Eagle Pincher photosedimentometer A commercial photosedimentometer. ■

Eel photosedimentometerA commercial photosedimentometer

electrical sensing zone methodThe measurement of number and volume of individual

particles suspended in an electrolytic solution as they pass through a small aperture in an electrical field.

electrophorietic mass transportThe migration of particles in a fluid caused by an

applied electrical filed.

elutriationClassification of particles effected by their upwards movement relative to a rising fluid. (A specific particle will achieve a terminal velocity in free fall, hence classification is determined by the velocity of gas required to generate a viscous drag on the particle that is greater than its mass, (i.e. gravitational attraction). Note that the gas velocity to dilate or fluidise a bed of particles, fluidisation velocity, is lower than the elutriation, or terminal velocity of the constituent particles.

elutriation, centrifugal(See centrifugal elutriation).

end-point, (of test)The stage in a test when continuation of the procedure fails to alter the result significantly.

Fisher sub-sieveA device for estimating particle size based upon permeability

sizer measurements

Fox and Parekh A device for estimating surface area by permeability techniques

permeamenter

frame, (of particle sizing) A rigid framework which supports the sieving medium and limits

the spread of the material being sieved.

Fraunhofer diffraction Measurement of special distribution of laser light scattering patterns from particle assemblies using Fraunhofer diffraction theory.

Gooden and SmithAn early instrument to estimate particle size from the permeability of a

permeameter packed powder bed comparing the gas flow rate to a reference bed of sand.

Goring-Kerr photosedimentometerA commercial photosedimentometer.

gravity sedimentationA method of analysis of particle size distribution of a

suspension by measuring the rate of settling of particles under gravity.

Hitatchi scanning photosedimentometerA commercial photosedimentometer. ■

impaction samplingThe process of selectively removing particles from a gas-borne stream by obstructing the flow of gas so that particles of higher momentum collect on a solid surface.

impactorA device to remove particles selectively from a gas-borne stream by means of a solid collecting surface.

impact test The generation of impact forces to determine particle fracture or surface wear characteristics.

impinger A device to remove particles selectively from a gas stream into a liquid medium

indirect method A method in which the value of a measurement is obtained from

of measurementestimation of other functionally related quantities.

inversion procedureA back-calculation method used to obtain a result (e.g. of particle size distribution from light diffraction energy pattern).

isokinetic sampleSample taken at the same velocity as that in the process under test.

ISO scale number A contamination class level in hydraulic fluids, as specified in

International Standards Organisation document ISO 4406. BS 5540

Part 4.

jet impacter A device for separating particles from an aerosol by deflecting the fluid

stream by a surface on which the particles are deposited.

Joyce-Loebel centrifuge A commercial version of an I.C.I. developed disc centrifuge type

Photosedimentometer.

Kaye disc centifuge A photosedimentometer that utilises centrifugal force to accelerate

Sedimentation. After Brian Kaye.

Knudsen flow A method of measuring specific surface by the steady-state diffusion

permeametry flow of a gas through a uniformly packed powder bed.

konimeter A device in the class of ‘impingers’, for measuring the particle size

distribution of dusts.

Lee and Nurse An instrument for measuring the specific surface area of a powder by

permeameter air permeability. The Lee and Nurse equation enables specific surface

area to be calculated from the flow rate and pressure drop across the

powder.

Leschonski pipette A variant of the Andreasen method of sample extractions from

equipment sedimentations by means of pipettes with graduated positions of

extraction holes ■

levigation The classification of particulates according to their movement through a

separating fluid. (See also sedimentation and elutriation).

lid, cover A cover which fits snugly over a sieve to prevent the escape of the

material above the mesh,

line start technique A technique in which a thin layer of a homogeneous suspension is

floated on the surface of the sedimentation liquid.

Lotzch Permeameter An instrument to measure permeability through a packed bed of

powder using a rotometer to measure the gas flow directly.

manometer A device for measuring fluid pressure.

margin The region between the outside edges of the outside row of holes and the

edges of a perforated plate.

micromerograph A commercial sedimentation balance where the particles sediment

through a column of gas from a line start system, in which a well defined

cloud of particles is blown onto the top of a column of gas.

noise The spurious unwanted fluctuation in an electronic signal.

percentage open (1) For woven wire, cloth and wire screen:

area The proportion of the total area of the aperture to the total area of the

cloth or screen, expressed as a percentage.

(2)For perforated plate:

The proportion of the total area of holes to the total area of perforated part of the plate (excluding any non-perforated part), expressed as a percentage.

perforated plate A sieving medium, consisting of a plate with uniformly sized holes in a

symmetrical arrangement.

permeameter An instrument for estimating a surface area by measuring the resistance

offered to a flowing fluid by a packed bed of particles.

photo correlation A method of estimating diffusion diameter from Brownian motion.

photosedimentometer An instrument which combines sedimentation with the

photoelectrical determination of concentration, for measuring

particle size distribution. In simple cases, Lambert-Beer law is used

to relate the concentration to the transmission levels. (Sometimes

referred to as Beer’s law). More refined interpretation hypotheses

utilise the Mie theory of light scattering, often using wide angle

light collectors, such a with fibre optics and scanning systems.

pipette centrifuge Centrifugal settling in a spinning disc of suspension. ■

pitch The distance between corresponding points of two adjacent holes in a

perforated plate.

plain weave The weave in which every warp wire crosses alternately above and below

every weft wire and vice versa.

plate thickness The thickness of the plate sieving medium after perforation.

porosimeter, The estimation of porosity and pore size distribution by means of the

intrusion of mercury under pressure.

pycnometer A vessel, of accurately defined volume, used for determining the density of

liquids or particles.

quasi-electric ( See photon correlation spectroscopy).

light scattering

rate method of A procedure of measuring the weight of powder retained by a sieve at

sieve analysis given time intervals and calculating the ultimate residue from the

logarithmic decay of the weight .

receiver; pan A pan which fits snugly under a sieve to collect fine particles.

repeatability The closeness of the agreement between the results of successive

measurements of the same sample that are carried out subject to all of the

following conditions: -

-The same measuring instrument;

-The same method of measurement;

-The same conditions of use;

-The same observer;

-The same location;

-Repetition over a short period of time.

reproducibility See repeatability

resolution A quantitative expression of the ability of a measuring device to distinguish

meaningfully between closely adjacent values of the quantity indicated.

riffler A device for dividing a stream of particles into representative samples.

riffler, spinning A rotary sample divider that collects a multiple series of consecutive samples from a flow stream as a means to secure a representative sample as a specific proportion of the total amount passing. ■

Rigden permeameterA device in which the powder bed under test is connected across the two arms of a U-tube manometer when the liquid columns of the manometer are displaced with respect to each other. The rate at which air flows through the powder bed is a measure of the permeability of the bed.

Rose photosedimentometer An early type of photosedimentometer.

sample analysis( See sample, test portion).

sample, grossSample obtained or prepared from the bulk material under the sampling plan, from which subdivision for testing, reference or storage can be made.

sample, laboratoryThe sample delivered to the laboratory.

sample, testThe sample prepared from the laboratory sample from which the test portions are drawn.

sample, test portionPortion taken from test sample, for use entirely in the observed test.

Sartorius sedimentation balance A commercial, high-accuracy, sedimentation balance.

screenA sieve or sieving medium used for separating particulate material in a manufacturing process.

sedimentation balance An instrument used to determine the Stoke’s diameter distribution of

particles.

sedimentation,The grading of mass of suspended particles accelerated by centrifugal

centrifugalforce.

sedimentation, The grading of mass of suspended particles accelerated by means of

gravitational gravitational force.

segregation testerA device that reflects a segregation mechanism and shows its effect.

sensorThat part of an instrument which captures the information relevant to the dimension being measured.

Shimadzu sedimentation A low-sensitivity sedimentation balance used for quality control.

balance

sieve mesh numberThe number of apertures occurring in the surface of a sieve per linear inch.

Note 1. - Unless the size of the wire used in forming the mesh is specified,

the mesh number does not specify the aperture size.

Note 2. - This term is still recognised in industry, but the preferred designation of test sieves is by aperture size. See Appx E of BS 410 1986 ■

sieves, nest ofA set of test sieves assembled together.

sieves, testA frame supporting a sieving medium intended for particle size analysis, and conforming to a standard specification.

sieving aidsThe addition of foreign bodies to sieve surfaces, to promote the motion of particles through the sieve mesh. A process to be used with caution, as the induced mechanism may cause crushing and generate fines.

sieving, air jetA device in which a portion of powder in a sieve is fluidised by air passing upward through it from a rotating slit. At the same time a negative pressure is applied to the bottom of the sieve which removes fine particles to a collecting device.

sieving, dryThe sieving of powders without the aid of a liquid.

sieving mediumA network or perforated sheet used for separating particles according to their size.

sieving, testThe use of test sieves in a prescribed manner to perform separation of particles into size classes.

sieving, wetThe sieving of particles with the aid of a liquid.

sifterA type of screening machine having a rotary motion substantially in the plane of the screening surface, used for the screening of powders.

sonication( See ultrasonic agitation).

spatualtionThe gentle working and kneading with a flexible spatula of a powder after the addition of a few drops of dispersant.

SpillaneAn automated version of the Blain permeameter.

spinning rifflerSee riffler, spinning

test portion( See sample, test portion).

test sample( See sample, test).

test sieve( See sieve, test).

turbidimeter An instrument which measures turbidity, from which surface area can be estimated.

ultrasonic agitationThe vibration of particles in a fluid by means of ultrasonic waves, thereby assisting their dispersion. ■