Production of highly pure hexagonal crystals of cadmium and zinc chalkogenides by sublimation

Claim 1

A PROCESS FOR THE PRODUCTION OF HIGHLY PURE HEXAGONAL CRYSTALS OF METAL CHALKOGENIDES SELECTED FROM THE GROUP CONSISTING OF CADMIUM, SULFIDE, CADMIUM, SELENIDE, CADMIUM SULFOSELENDIE AND ZINC SULFIDE BY SUBLIMATION WHICH COMPRISES SUBLIMING IMPURE METAL CHALOGENIDE CONTAINING VOLATILE AND NON-VOLATILE IMPURITIES BY HEATING IN A FIRST ZONE TO A TEMPERATURE OF BETWEEN 750-1200*C. WHILE CONTINUOUSLY MAINTAINING AN ABSOLUTE PRESSURE IN SAID FIRST ZONE OF LESS THAN 0.1 MM. OF HG TO FORM A VAPOR MIXTURE OF METAL CHALKOGENIDE AND VOLATILE IMPURITIES, PASSING SAID VAPOR MIXTURE INTO A CONTIGUOUS SECOND ZONE, MAINTAINING A DECREASING TEMPERATURE GRADIENT OF ABOUT 10*C. PER CENTIMETER IN SAID SECOND ZONE AND A THIRD CONTIGUOUS ZONE PROGRESSING AWAY FROM THE FIRST ZONE MAINTAINING A TEMPERATURE DROP IN SAID SECOND ZONE RELATIVE TO THE TEMPERATURE IN SAID FIRST ZONE OF BETWEEN 5 AND 15*C., THEREBY CRYSTALLIZING HIGHLY PURE HEXAGONAL METAL CHALKOGENIDE CRYSTALS FROM SAID VAPOR MIXTURE IN SAID SECOND ZONE AT A CRYSTALLIZING TEMPERATURE WHICH IS LOWER THAN THAT AT WHICH SAID MIXTURE IS EVAPORATED, CONTINUOUSLY WITHDRAWING THE VOLATILE IMPURITIES FROM THE SECOND ZONE INTO THE THIRD CONTIGUOUS ZONE BY MAINTAINING SAID THIRD ZONE AT A PRESSURE SUBSTANTIALLY LESS THAN THE PRESSURE IN SAID SECOND ZONE, MAINTAINING A TEMPERATURE IN THE THIRD ZONE SUFFICIENTLY LOWER THAN THE TEMPERATURE IN THE SECOND ZONE TO PRECIPITATE SAID VOLATILE IMPURITIES IN THE THIRD ZONE, CONTINUOUSLY WITHDRAWING ANY NON-CONDENSED GASES FROM THE THIRD ZONE INTO A FOURTH CONTIGUOUS ZONE BY MAINTAINING SAID FOURTH ZONE AT A PRESSURE SUBSTANTIALLY LESS THAN THE PRESSURE IN SAID THIRD ZONE, THE VAPOR FLOW THROUGH THE SECOND AND THIRD ZONES BEING INDUCED BY A VACUUM IMPOSED ON SAID FOURTH ZONE, AND THE PRESSURE DROPS BETWEEN THE SECOND AND THIRD, AND THIRD AND FOURTH ZONES BEING MAINTAINED BY THROTTLING THE VAPORS FLOWING BETWEEN THE ZONES SO AS TO IMPOSE A SUBSTANTIAL REDUCTION IN PRESSURE BETWEEN THE ZONES.