Dispersing WC-Co to water

[kthomas]

Hello!

I have a problem with dispersing tungsten carbide-cobalt to water. I try to make hard metal-water dispersion to spray drying. Aim is to use polyvinylalcohol as a binder. I use propeller mixer and I add powder slowly to fluid. Problem is following: If I have slow mixing speed, powder sedimentates to the bottom of vessel. With high speed, air is mixed to dispersion and it makes viscosity of dispersion very high (not able to pump). What kind of mixer should I use and what chemicals would make dispersing easier (wetting, antifoam)?

 

[m777182]

You need a mixer with good dispersion effectivness and low power input with no sucking vortex. You gave little data about material properties- densities, viscosity and particle size distribution and dimensions of your vessel, but never mind, EKATO Germany had an excellent series of multistage mixers of MIG or INTERMIG type. They had fine mixing characteristics with complex flow patterns by very low power input.
m777182

 

[kthomas]

Thanks for answer m777182, theoretical density of WC-Co is about 15kg/dm3. Powder's d0.5 to be dispersed is about 1µm and d0.9 is 2.5µm. Dimensions of my vessel are height 560mm and diameter 600mm. Should vessel's bottom be hemisphere? Powder tend to sedimentate to corner of vessel bottom.

 

[m777182]

I have never calculated power consumption for such a dense material, mine was usually abou 2oookg/m**3. However there is a good book by Shinji Nagata ,Wiley 1975(ISBN 0-470-62863-4), where you can find basic calculations, though regretfully not including MIG type impellers of EKATO. Additionaly there are many articles about suspending powders.
Your vessel will be probably dished bottom type with side baffles, slightly higher to correspond to the standard proportions. You must not allow your particles to settle down because you will need an enormous power, up to 15 to 20 times the normal one to suspend it again!
If you do not want to be involved in calculations yourself, contact vendors of equipment and do not forget to point out very high density of your particles!
m777182