Méthode de dopage au chrome dans la préparation du rubis hydrothermal

Abstract

Hydrothermal growth of ruby single crystals, on {1¯22} oriented seeds, has been carried out, using silver cans in a 150 cm3 autoclave. Chromium doping using potassium dichromate in an aqueous solution of potassium carbonate with sapphire as source material, caused inhomogeneous chromium distribution with unequally colored bands in the crystal. The use of ruby both as nutrient and doping reagent yielded a more regular chromium distribution. Both the two preceding methods generally produced heavy chronium accumulation at the seed-crystal interfaces and chromium rich green deposits on seeds have often been observed; in the latter case no further growth occured. In order to greatly reduce the initial chromium concentration in solution during the warm-up period, gibbsite was added to the ruby nutrient; in the same way, an experiment performed with sapphire instead of gibbsite was not satisfactory. First, the starting crystallisation temperature of ruby was determined, then the gibbsite solubility was determined, so that the useful amount of gibbsite could be correctly estimated. With the use of an appropriate gibbsite-ruby nutrient mixture, optically clear and uniformally doped ruby single crystals have been prepared.