Thermodynamic Assessment of the System MgO–Al₂O₃

Abstract

The system MgO-AI2O3 was assessed with the CALPHAD technique using a computerized optimization procedure called PARROT. ' h o of the solid phases, MgO and spinel, showed extensive solid solubility at high temperature and were modeled with the compound energy model. The third solid phase, a-Al2O3, was modeled as a stoichiometric phase. For the liquid phase, an ionic two-sublattice model was used. In total, 13 adjustable parameters were optimized: 3 for the MgO, 8 for the spinel, and 2 for the liquid. This resulted in a consistent thermodynamic description for most of the available experimental data points on the phase diagram as well of the thermodynamic properties.

Hardness and friction behavior of bulk CoAl2O4 and Co–Al2O3 composite layers formed during Spark Plasma Sintering of CoAl2O4 powders

“…50 nm) with some large pores. These observations are in reasonable agreement with the XRD and specific surface area data and with earlier works [10][11][12].…”

“…In reaction (1), the precipitation is not total and an aluminum-rich spinel [10,11] is formed. For the surface of the specimens, or even the bulk of the sample from the more reactive powder (CA), the aluminum-rich spinel becomes unstable and the precipitation proceeds with the formation of aAl 2 O 3 along with more Co particles.…”

“…the Co 2+ ions are located in the tetrahedral sites of the cubic close-packing of O 2À ions whereas the Al 3+ ions occupy the octahedral sites. Moreover, a considerable solidsolution range exists on the Al 2 O 3 -rich side of the stoichiometric spinels [10,11]. The second aim is to investigate the microhardness and friction behavior of the Co-Al 2 O 3 composite layers and of the core of the specimens, made up of bulk CoAl 2 O 4 .…”

Magnesium aluminate (MgAl2O4) spinel produced via self-heat-sustained (SHS) technique

“…The only other phase detected was ␣-alumina and within the detectable limit of the XRD, MgO could not be found even in trace quantity at this stage. This could possibly be due to small yet finite solid solubility of Al 2 O 3 and MgO in MgAl 2 O 4 as predicted by phase diagram [23][24]. A comparison of Figs.…”

Microstructural development in Al/MgAl2O4 in situ metal matrix composite using value-added silica sources

“…The anion is usually oxygen. The MgAl 2 O 4 phase exhibits a congruent melting point at 2315 • C in the MgO-Al 2 O 3 binary phase diagram [2]. MgAl 2 O 4 exhibits a unique combination of properties such as a low thermal conductivity, a low coefficient of thermal expansion, good thermal shock resistance, a low dielectric constant and high electric resistivity [3].…”