Final Stage Densification in Vacuum Hot-Pressing of Alumina

Abstract

Temperature and oxygen pressure limits on the oxidation of molybdenum in MoSiz and MogSi3 are a consequence of thermodynamic and diffusion considerations for the pertinent systems and were derived independently of observations of nonprotective oxidation behavior. For a given oxygen pressure, molybdenum can oxidize only at temperatures below these limits. Since nonprotective oxidation is expected to occur exclusively at temperatures and pressures where molybdenum oxidizes, the theoretical and experimental results zre in reasonable agreement. Molybdenum oxidation is a necessary condition for nonprotective oxidation in both cases arid i t is a sufficient condition for nonprotective oxidation of Mo&.

Analysis of Trace Amounts of Emitted Gases during Fracture of High-Purity Alumina under Ultrahigh Vacuum. Effects of Sintering Atmosphere and Sintering Time on Gas Emission Behavior.

“…Equation (2) means that the number of pores decreases during grain growth. Furthermore, assuming that a pore of radius r0 contains n0 moles of nondiffusive gas and that the pressure inside the pore balances the capillary pressure of 2/r0,11) where is the solid-vapor surface tension; then the pores coalesce and re-equilibrate under a second set of conditions of G1, r1 and n1, the Nv and the equilibrium of a pore derived from the gas laws of Boyle and Charles can be written as follows.…”

Development and testing of matrices for the encapsulation of glass and ceramic nuclear waste forms.

“…Hot pressing temperatures considerably greater than the 1200°C upper limit assumed for this work are generally required to attain alumina densities in this range. However t densities up to 99% of theoretical have been achieved by vacuum hot pressing at 1200°C and 41.4 MPa for five hours t using Linde A alumina (0.3 ~m) that had been treated in isopropyl alcohol t vacuum dried for 40 hours and handled in a moisture-free atmosphere until it was hot pressed (Rossi and Fulrath 1965).…”

FABRICATION AND CHARACTERIZATION OF HOT PRESSED Al2O3

“…That an obeervable amount of such gaseous impurities can be reained from the starting powders is not serprising when one considers the tenacity of the last monomolecular layer of such impurities (5,10,13,14), the rapid, relatively low-temperature densification, and the difficulty of diffusing released gases out of such fine powders (10,11,14). Both atmospheric contamination and its tenacity are shown by Scott's (2?)…”

“…The most extensively studied materials were Lindet A and B powders (designated A ýnd B AI 2 0 3 ), since they were most commonly used by other investigators (1)(2)(3)(4)(5)(6). Limited tests were also made on three other alumina powders, designated as R A1 2 0 3 1 BM A1 2 0 3 , § and C A1 2 0 3 ".…”

“…These findings have, in turn, stimulated further use and study of the pressure-sintering process occurring during hot pressing (4)(5)(6).…”