Study of Alumina as a Raw Material for Synthetic Gems (Process of Thermal Decomposition of Alum).

摘要

The foregoing are the results of an X-ray investigation of alumina produced by the thermal decomposition of alum. It is a part of a study of alumina as a raw material for synthetic gems. A summary of the conclusions of this study is as follows: (1) Ammonium alum, when heat treated, decomposes into gamma-alumina after going through anhydrous alum, aluminum sulfate, and an amorphous stage. It goes into the amorphous stage at 800 C. (2) A heat treatment at 1200 C for 5 hours is not sufficient to shift gamma-alumina formed by the thermal decomposition of alum into alpha-alumina. (3) The shift into alpha-alumina may be via the kappa-phase or the theta-phase, depending upon the condition of the sample when it is in the gamma-phase, especially upon the degree of the water content. (4) the theta-phase is considered to be easier to stabilize than the kappa-phase.