Transparent MgAl^sub 2^O^sub 4^ Spinel from a Powder Prepared by Flame Spray Pyrolysis

The densification of an ... spinel powder prepared by flame spray pyrolysis was examined in order to determine whether it is suitable for fabricating transparent parts using a sinter/HIP approach. It was found that the powder exhibits excellent sinterability. Firing pressed powder compacts to 1650...C/2 h in air increases the bulk density to 99.9% TD. Similar densification, within the precision range of He picnometry, but a higher level of light transmission, is obtained by firing for 80 h at 1400...C. By HIPing, both specimens, sintered at 1650... and 1400...C, are made transparent but the level of transparency attained is higher in the case of specimens presintered according to the latter conditions. Such specimens (2 mm thick) exhibit, after HIPing at 1500...C./3 h (Ar, 200 MPa), a real in-line transmission (RIT) of 63% (635 nm), an average grain size of 2.2 ...1/4m, and a hardness of 13.2 CPa. After HIPing at 1700...C, the Rh attains a value of 77%, while the average grain increases to 17 ...1/4m and the Vickers hardness slightly decreases to 12.8 GPa. (ProQuest: ... denotes formulae/symbols omitted.)