TiO2 is of course, very cohesive and very affected by aeration and by the degree of compaction or consolidation. It is also very flow rate sensitive. You could evaluate flowability as a function of each of these factors by using an instrument such as the FT3 Powder Rheometer.

You could expect to obtain various flowability indices for each of your different TiO2 materials with clear indications of how they compared. The FT3 is very sensitive and the measurements are exceptionally repeatable.

For info see website www.freemantech.co.uk

For contact or sample testing, email; as below

Regards,

Reg Freeman reg@freemantech.co.uk ■

To answer this question properly, we need to know what the purpose of your measurements is.

If you want to measure the flow properties as properly defined, then the only thing is a shear cell, whether Jenike or Walker type (or for that matter Peschl or Schwedes, which are nothing more than developments of Walker). No other means will give you actual flow property measurements. We use both here and have done measurements of many grades of TiO2 with great success, for hopper designs, comparative benchmarking, QC etc.

Instruments such as the Freeman FT3 or the Indiciser will only give you comparative indications and not true flow properties. In my experience the Hausner Ratio is every bit as good and much cheaper to measure (tapped bulk density divided by poured bulk density).

Find us at www.bulksolids.com for further information. ■

Yes, TiO2 is challenging in dry or high-solids liquid form. I have done engineering work in this area, as a traveling tech service engineer for a major TiO2 manufacturer. High density; abrasive; sticky in humid environment. What specifically is the issue? ■

jstiverson raises an excellent point. Different grades from various suppliers flow differently. If, for instance, you are looking for >98% TiO2 to supply Ti, rather than an optical pigment, there are "glass grades" available which have better flow characteristics than the pigment-quality version of the same product. Reason is effective particle size of 2 rather than 0.2 ■

Brian Rutledge is exactly right with regard to the different grades. We have measured the flowability of many different grades, of both the two different mineral habits and with different coatings, sizes etc.

If you want a grade which is free flowing, but not too bothered by dispersability, then there are some plastics grades which are actually granulated - Tioxide makes one - and these handle almost like dry sand. They are well worth looking at depending on your application.

On the other hand, if you have to use a less free flowing grade it is actually not a problem as long as you invest in a properly designed MASS FLOW hopper or silo. We've designed lots of silos for TiO2 using this approach, it requires measurement of flowability but you finish up with something cheap to build, easy to maintain, no need for vibration or large aoounts of fluidisation (though some SMALL amount of air injection is desirable) and it ALWAYS discharges reliably and in a controlled condition of bulk density and discharge rate. That's more than you can say for any other approach!

If you don't want to cross the pond to talk to us, then J&J can do this for you closer to home. That proves this is not just a sales pitch! But there is no doubt that a proper mass flow silo will deal with TiO2 with absolutely no problem whatsoever. It really works like a dream and so many people are amazed to see how easy a material TiO2 is to handle - IF you have the right equipment!

Mike. ■

Of course, there is the possibility that you do not use enough to install a silo or engineer a storage system. In those cases, bulk bags may be right for you.

They can be stored almost indefinitely, and keep airborne moisture out. Hoist them into place above the container to be filled, then untie the bottom of the bag manually from the side. Several types of closures. Some double-closed. Some pull-tab-to-open. In general, if you have to use two hands to open it, you are not doing it right, or it wasn't closed properly to begin with.

Some are anti-static for explosion-proof environments. Most can be recycled back to the supplier, providing you don't yield to temptation and use a knife to cut the bag open or cut the ties off. You don't want to do that anyway, since a tie fragment in a mixer can plug things up, or a piece of bag in a batch of material can contaminate a lot of product.

Available in different weights in metric and British units.

If bulk bags sound right to you, I suggest talking to several suppliers, choosing the right combination of product and bulk-bag. Not all products may be available in bulk bags, or in the size you want, so you may have to shop around or compromise.

If "it can't be done that way", then you may resort to a contract repacker, such as Technical Industries in Peacedale RI, USA who can formulate, disperse, or simply repack.

One last comment: once the bulk bags are open, or the TiO2 exposed to air, it tends to become less free-flowing than you would expect. I had a customer in Singapore that had a seasonal moisture problem when a bag or one-bag hopper was filled for to long a time. Bag emptied batch-wise to hopper. Hopper to rest of equipment. It worked well if the TiO2 was used approximately immediately, but they had trouble if the hopper was left full over the weekend in the un-air-conditioned manufacturing area.

Hope this helps.

Brian ■