SOME OBSERVATIONS ON THE CRYSTALLIZATION OF BERYLLIUM OXIDE FROM A GASEOUS PHASE

The growth of single crystals of refractory BeO at atmospheric pressure has been observed in argon at 1900, 1800 and even 1600 deg C. Compacted beryllium oxide 99.9% pure is maintained in a hollow graphite block for 10 hours or more at constant temperature in a graphite resistance furnace. The erystals of BeO are grown on the inner surface of the cover which is at a temperature 10 to 50 deg C below the temperature of the sample. Dendritic growths or whiskers are noted at angles of 60, 90 or 100 deg with the primary crystal. In a number of cases the crystals are not transparent because of the presence of a film of carbon evaporated from the graphite vessel (the film is not Be/sub 2/C, since carbon and BeO react only above 1950 deg C). Single crystals of BeO are very strong and can undergo large elastic deformations without breaking (the strength of BE0 whiskers is 150,000 kg/cm/sup 2/ on bending). This method of growing oxide crystals would be very satisfactory, if the rate of growth could be increased, and if the condensation process could be controlled better at high temperatures. (TTT)