Why We Hate Titanium Dioxide
by Joseph Marinelli
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What is it about titanium dioxide (TiO2) that causes it to
be one of the most hated bulk solid to handle? Titanium dioxide is one of the
best pigments, providing one o the best whiteness, opacity and refractive index
improvements to paints, coatings, plastics, paper, inks, fibers, food and cosmetics.
The reason we all hate it is with it's small particle size and irregular shape, it
sticks everywhere, to everything and to everyone!
Most commercially available TiO2 is nearly 100% minus 325
mesh and has a bulk density of about 50 lb./cu.ft. Curiously, of the various grades
of TiO2 supplied by the major manufactures, the better the grade, the more difficult it
is to handle! My experience has been that it is a fine, cohesive solid that
clings and sticks to any surface. TiO2 has enough cohesive strength (i.e., it forms
a "snowball" upon compaction) to cause bridging and rat-holing problems in
improperly designed bins and hoppers.
TiO2 can bridge over circular outlets of 12-inches to up
to 5-feet. Equally important is it's ability to cling to any surface!
One of the best surface for solids to slide is a 2B finish
stainless steel. TiO2 can even adhere to this smooth finish and effect a hopper's
ability to flow properly. Remember to measure and evaluate your specific material's
properties to ensure proper bin and feeder design. Properties vary from manufacture
to manufacture.
Another area of critical concern is maintenance.
There are not many machines that work well when product builds up on the sliding
surfaces. A material as "sticky" as TiO2 presents an even greater problem.
It's propensity to cling creates constant work for those who maintain equipment
that stores, feeds, mixes or conveys it. Work, not on a semi-annual or quarterly
basis, but weekly or even daily!
Mechanical assistance for stubborn-flowing TiO2 is not
out of the question. Devices such as air blasters, air sweeps and vibrators, if
designed, strategically-placed and used properly, will lengthen the time between scheduled
maintenance. Some users have even gone so far as to pelletize their TiO2 to improve
it's handling characteristics.
In summary, it is important to:
- 1) Respect TiO2's ability to bridge, rathole and cling
2) Test for and be aware of the flow properties of the TiO2 you use
3) Allow time for scheduled maintenance
4) Use flow-enhancing devices, when needed, but with caution
Help others by posting your comments, suggestions and
experiences with bulk solids feeding or any other materials handling concerns you may have
on our On-Line Help Forum. For
past Ask Joe ! Articles, visit the Ask Joe! Archived Articles.
Guest articles for the Ask Joe! Column are always welcome,
for more information please contact Joe Marinelli directly at his email address:
joe@solidshandlingtech.com.
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