Process for making powder alloys containing cadmium and selenium
A process for preparing alloy products powders is described using a self-sustaining or self-propagating SHS-type combustion process. Binary, ternary and quaternary alloy having cadmium, selenium and optionally a third element X or Y selected from Group VIA (such as S or Te) or from group IIB (such as Zn or Hg). The alloy products may be doped or not with a wide variety of other elements. The process involves heating to ignition, maintaining an elevated temperature less than melting for homogenization, followed by cooling and crushing. An optional de-oxidation process may follow to further purify the alloy and balance the stoichiometry.
1. A process for making powder alloys containing cadmium and selenium, comprising
blending a mixture of cadmium particles and selenium particles, the cadmium and selenium particles having a size ranging from about 1 to about 600 microns;
blending into the mixture a quantity of quenchant particles having a size ranging from about 1 to about 1000 microns;
heating the mixture to an ignition temperature at a rate allowing the reaction to establish a self-propagation mode to form an alloy product;
maintaining an inert environment at an elevated temperature less than a melting point of the alloy product for a time sufficient to ensure homogenization of the alloy product; and
cooling and crushing the alloy product to form a homogeneous alloy powder.
2. The process according to claim 1 , further comprising blending particles of an additional element into the mixture to form a ternary alloy of the formula CdSe u X (1-u) , or Cd w Y (1-w) Se, in which X is an element selected from group VIA; Y is an element selected from group IIB; u and w are numbers from 0.05 to 0.99.
3. The process according to claim 2 , wherein Y is selected from Cd, Zn, and Hg and wherein X is selected from S and Te.
4. The process according to claim 1 , further comprising blending particles of two additional elements into the mixture to form a quaternary alloy of the formula:
CdSe u X (v) X′ (1-v-u) or Cd w Y (z) Y′ (1-z-w) Se or Cd w Y (1-w) Se u X (1-u)
in which X and X′ are independently selected from elements in group VIA; Y and Y′ are independently selected from elements in group IIB; u and w are independently a number from 0.05 to 0.98; and v and z are independently a number from 0.001 to 0.75.
5. The process according to claim 4 , wherein Y is selected from Cd, Zn, and Hg and wherein X is selected from S and Te.
6. The process according to claim 1 , wherein the quenchant particles are binary compounds selected from CdSe particles and CdTe particles.
7. The process according to claim 1 , wherein the quenchant particles are ternary compounds selected from CdSeTe, CdSeS, CdTeS, ZnSeTe, ZnSeS, ZnTeS, ZnCdSe, ZnCdS, and ZnCdTe particles.
8. The process according to claim 1 , wherein the quenchant particles are blended into the mixture in a weight percentage from about 0.1% to about 60%.
9. The process according to claim 1 , wherein the particle size of the quenchant particles is from about 10 to about 300 microns.
10. The process according to claim 1 , further comprising blending dopant particles into the mixture to form a doped alloy, the dopant particles comprising one or more elements selected from those in groups IA, IIIA, IVA, VA, VIA, VIIA, IB and IIB, and compounds thereof.
11. The process according to claim 10 , wherein the dopant particle is blended into the mixture at a concentration from about 0.1 ppm to about 10,000 ppm.
12. The process according to claim 1 , wherein the particle size of the cadmium particles and the selenium particles is less than about 200 microns.
13. The process according to claim 1 , wherein maintaining an inert environment includes maintaining a reducing inert environment.
14. The process according to claim 1 , wherein maintaining an inert environment is at an elevated temperature in the range from about 40% to about 85% of the melting point of the alloy product.
15. The process according to claim 1 , further comprising cooling the alloy product in an inert, reducing environment.
16. The process according to claim 1 , further comprising subjecting the alloy powder to a deoxidation step comprising heating the alloy powder in a reducing atmosphere.
17. The process according to claim 16 , wherein the deoxidation step removes oxygen or unreacted elements or both.
18. The process according to claim 1 , further comprising adding heat to the mixture at a rate from about 2° C./min to about 100° C./min.
19. The process according to claim 18 , further comprising adding heat to the mixture at a rate from about 10° C./min to about 25° C./min.
20. The process according to claim 1 , wherein the ignition temperature is between about 100° C. and about 450° C.
21. The process according to claim 1 , wherein the quenchant particles comprise a product of a reaction between cadmium and selenium.