Zinc crystalline powders

The physical and chemical characteristics of zinc oxide powders are known to affect cement formation (Smith, 1958 Norman et al., 1964 Crisp, Ambersley Wilson, 1980 Prosser Wilson, 1982). The rate of reaction depends on the source, preparation, particle size and surface moisture of the powder. Crystallinity and lattice strain have also been suggested as factors that may change the reactivity of zinc oxide powders towards eugenol (Smith, 1958). 

Rhodium dissolves in molten zinc at dull redness, and on treating the product with concentrated hydrochloric acid, the excess of zinc dissolves, leaving a crystalline powder of composition corresponding to the formula RhZns. The formation of this insoluble alloy affords a convenient method of purifying rhodium (see p. 15-1). 

Zinc Gluconate occurs as a white or nearly white, granular or crystalline powder and as a mixture of various states of... 

Zinc Sulfate occurs as colorless, transparent prisms or small needles, or as a granular, crystalline powder. It contains one or seven molecules of water of hydration. The monohydrate loses water at temperatures above 238° the heptahydrate effloresces in dry air at room temperature. Its solutions are acid... 

The Rate of Heterogeneous Reactions. A heterogeneous reaction takes place at the surfaces (the interfaces) of the reacting phases, and it can be made to go faster by increasing the extent of the surfaces. Thus finely divided zinc reacts more rapidly with acid than does coarse zinc, and the rate of burning of a perchlorate propellant is increased by grinding the potassium perchlorate to a finer crystalline powder. 

Nitro-2-aminophenylarsinic acid is diazotised and treated in alkaline solution with sodium arsenite in the presence t)f copper ])owdcr. The diarsinie acid thus obtained is purified by means of its zinc salt, a pale yellow, crystalline powder. The acid crystallises in large, prismatic rosettes of needles, containing 1 molectilc of water. It is sparingly soluble in cold water, readily soluble in hot water, moderately soluble in alcohols, fairly soluble in acetone aird acetic acid, insoluble in benzene and chloroform. When heated above 100° C. it pas.ses into the anhydride. 

The copper sulphide is filtered off and zinc acetate added to the filtrate, the zinc salt of m-arsanilic acid separating out. After filtering and washing, this is boiled with 275 c.c. of water and 160 c.c. of 10 per cent, sodium carbonate solution, the zinc carbonate filtered off, and the solution nearly neutralised with concentrated hydrochloric acid. 13-5 c.c. of glacial acetic acid are added to acidify the solution, and the amino compound is precipitated as a faintly red, crystalline powder. Yield, 65 per cent. It may be purified by dissolving in dilute ammonium hydroxide, boiling with animal charcoal, and reprecipitating with acetic acid. 

Red crystalline powder or small, tabular crystals, d 6.094. Crystal structure tetragonal. Space group D on heating to 70°C, the color changes to chocolate brown with simultaneous enantiotropic structure transformation to cubic tyiie B3 (zinc-blende) in which the cation distribution is random. 

Reaction with tellurium powder in alkaline solution yields red crystalline zinc telluride, ZnTe. 

Zinc sulfide is white to gray-white or pale yellow powder. It exists in two crystalline forms, an alpha (wurtzite) and a beta (sphalerite). The wurtzite form has hexagonal crystal structure refractive index 2.356 density 3.98 g/cm3 melts at 1,700°C practically insoluble in water, about 6.9 mg/L insoluble in alkalis soluble in mineral acids. The sphalerite form arranges in cubic crystalline state refractive index 2.368 density 4.102 g/cm changes to alpha form at 1,020°C practically insoluble in water, 6.5 mg/L soluble in mineral... 

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