Patent GB-878096-A (GB)
Title: Selenides of copper zinc and cadmium
IPC: H01J29/20
Filed: 1958-01-13
Abstract: Copper, zinc or cadmium selenides, particularly suitable for electronic applications, are prepared by reacting an aqueous solution of an ammine selenite of the desired metal with a preheated aqueous solution containing a stoichiometric excess of hydrazine.  The aqueous solution of ammine selenite preferably contains an excess of ammonia; ammonium carbonate may also be present to increase the solubility of the ammine complex.  The reaction may be effected in the presence of a catalyst providing a small amount of an organic carboxylic acid ion such as the formate, acetate, propionate, butyrate or benzoate ion, provided either by the free acid or by an appropriate salt.  In the case of the zinc and cadmium, an intermediate zinc or cadmium selenide hydrazinate of formula MSe.N2H4 is formed, which is subsequently converted by heat or acid to the corresponding selenide, preferably by digesting the hydrazinate with excess acetic acid at 70-85 DEG C.  The selenides may be activated by effecting their formation in the presence of a copper or silver activator which is normally provided as a water soluble salt.  The initial ammine selenites may be prepared by treating a salt such as sulphate or acetate, or an oxide of the metal with selenious acid and ammonia, optionally in the presence of ammonium carbonate.  According to examples (1) zinc acetate dihydrate solution was ammoniated and a selenious acid solution was added thereto at about 40 DEG C. and the pH adjusted to 7.8 with glacial acetic acid.  Solid zinc selenite formed was filtered off and after washing was dissolved in water by the addition of gaseous ammonia to form zinc ammine selenite solution.  An 85% hydrazine hydrate solution containing a minor amount of zinc acetate was heated to 80 DEG C. and the zinc ammine selenite solution prepared above was slowly added at 85-95 DEG C.  A wet selenide hydrazinate cake was obtained on filtration and after washing was digested in glacial acetic acid solution; the resulting zinc selenide was washed with water and methanol.  If 0.01 % mole of silver acetate is added to the aqueous ammine selenite solution, the corresponding quantity of silver is obtained in the final zinc selenide.  (3) Cadmium selenite was dissolved in water containing ammonia and ammonium carbonate and on further ammoniating, a solution of cadmium ammine selenite was obtained which was slowly added to hydrazine hydrate containing glacial acetic acid which had been pre-heated to 80 DEG C.  On the completion of nitrogen evolution, a solid cadmium selenide hydrazinate/cadmium selenide mixture was obtained which was slurried with acetic acid, washed and dried to yield cadmium selenite.  (5) A mixture of copper acetate and selenious acid in water was treated with ammonia to form a tetrammine copper complex which was added slowly to a preheated mixture of hydrazine hydrate and glacial acetic acid at 80-85 DEG C. until nitrogen evolution ceased.  The solid copper selenide was filtered off and dried.  Dependent upon the molar proportion of copper acetate and selenious acid employed, the copper in the selenide may be mono or divalent.  Specifications 875,773, 875,774 and 875,775 are referred to.