Fabrication of Submicron Alumina Ceramics by Pulse Electric Current Sintering Using Mg~(2+)-Doped Transition Alumina Powders

摘要

Dense submicron-grained alumina ceramics were fabricated by pulse electric current sintering (PECS) using Mg~(2+)-doped transition alumina powders at 1200-1350 deg C under a uniaxial pressure of 40 or 80 MPa. The Mg~(2+)-dopei transition alumina powders (0-0.50 mass percent MgO base) were prepared through a new sol-gel route using high-purity polyhydroxoaluminum (PHA) and MgCl_2 solutlonS as starting materials. The composite gels obtained were calcined at 900 deg C and ground by planetary ball-milling. Upon heating, the composite gels transformed into a single-phase gamma-alumina or mixed phase of gamma- and chi-aluminas, depending on the MgO content. The resultant transition alumina powders were solid solutions, in which Mg~(2+) cations were substitnted into the crystal lattice. The powders were re-calcined to increase the content of alpha-alumina particles, which act as seeding for low-temperature densification. Densification depended on the MgO content and loading pressure. The critical Mg~(2+)-doping for suppressing grain growth was found to be 0.10 mass percent MgO. Higher loading pressures led to full densification at lower temperatures, resulting in a more uniform and finer microstructure. Thus, dense alumina ceramics (relative density >= 99.6 percent) with a uniform microstructure composed of fine grains with an average size of 0.47 mu m could be obtained by PECS at 1250 deg C under 80 MPa.