Powder wetting

In a comparison of shock-modified powder to powder subjected to other intense deformation, data on shock-modified TiC was compared to a well annealed TiC powder wet milled for many hours to similar values of residual strain. As depicted in Fig. 7.4 the anisotropies observed in residual strain and crystallite size in the two cases are quite different. The shock-modified powders show less anisotropy in strain and more anisotropy in crystallite size... 

ZIRCONIUM POWDER, wetted with not <25% water (UN 1358) (DOT) see ZOAOOO ZIRCONIUM SCRAP (UN 1932) (DOT) see ZOAOOO ZIRCONIUM(IV) SIUCATE (1 1) see ZSSOOO ZIRCONIUM(I 0 SULFATE (1 2) see ZTJOOO ZIRCONIUM TETRACHLORIDE (DOT) see ZPAOOO ZIRCONIUM TETRACHLORIDE, soUd (DOT) see ZPAOOO... 

Tablets are produced directly by compression of powder blends or granulations, which include a small percentage of fine-particle powders. Wet granulation is used for drugs that are not sensitive to moisture and heat. The powdered drug is mixed with the filler. The mixture is then wetted and blended with the binder, forming a solution [16, 17]. The coarse granules are dried on trays in hot air ovens or fluid-bed dryers. Granules are mixed with lubricants such as magnesium stearate and then compressed into tablets [16, 17].

Burning rate test Substanees and mixtures other than metal powders wetted zone does not stop fire and burning time < 45 seconds or burning rate >2.2 mm/s Metal powders burning time < 5 minutes. Symbol ... 

A low surface tension value correlates with a small contact angle. The binder with the smaller contact angle has improved spreadabiiity and can wet powders more effectively (65,84). A surfactant can also be added to the binder solution to improve wettability, especially for hydrophobic powders, and functions to lower both the surface tension as well as the contact angle of the liquid. If the contact angle, 6, is less than 90, then the powder wetting is spontaneous. However, if the contact angle is closer to 180 then the powder would be considered unwettable by the liquid. The pore space within a particle assembly can be simplistically considered as a model capillary. The capillary pressure, Pc, of a liquid is related to the surface tension by the following equation ... 

The adsorption of surfactants at the solid/liquid (S/L) interface determines their efficiency in powder wetting and dispersion. A reduction of the S/L interfacial tension by surfactant adsorption leads to a reduction of the contact angle, which in turn ensures complete wetting of the powder by the Hquid. In addition, the... 

For agglomerates (as represented in Figure 11.2), which are found in aU powders, wetting of the internal surface between the particles in the structure requires liquid penetration through the pores. Assuming that the pores behave as simple capillaries of radius r, Ap is given by the following equation ... 

The above molecule has a higher cmc (1 gdm ) than Aerosol OT, but it is less effective in lowering the surface tension of water, reaching a value of 30 mN m at and above the cmc. It is, therefore, not as effective as Aerosol OT for powder wetting. 

Most processes of powder wetting operate under dynamic conditions, and improvements in their efficiency require the use of surfactants that lower the liquid surface tension Yiy under these circumstances. The interfaces involved (particles separated from aggregates or agglomerates) are freshly formed and have only a small effective age of some seconds, or even less than a millisecond. 

---