HOT-PRESSING CERAMICS IN ALUMINA DIES

Exploratory experiments showed that it was possible to prepare a wide variety of polycrystalline ceramic oxides of very high density and fine grain size by hot pressing in high density alumina dies. The contaminating and reducing atmosphere of conventional graphite dies was eliminated. Higher pressures and hence lower temperatures were allowed; and the fabrication of otherwise easily reduced oxides was possible. The use of a dial indicator permitied continuous monitoring and measurement of ceramic body compression, sintering and densification effects and stages, and specific control, where desired, of porosity levels. A hot ejectio chamber allowed the molding of materials whose expansions were less than that of the die body. Examples are given of the ceramic oxides successfully fabricated to high density by this technique: the refractory oxides Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 3/, M gO, Y/ sub 2/O/sub 3/; defect oxides such as NiO, ZnO, TiO/sub 2/, Nb/sub 2/O/sub 5/, WO/ sub 3/, and a number of rare earth oxides. (auth)