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| - Surface Energy and Thermodynamic Stability of γ-Alumina: Effect of Dopants and Water
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| - The objective of this work is to show the thermodynamic basis of using additives, such as Zr and Mg, to control the γ-Al2O3 surface and bulk energetics and manipulate the transformation temperature to the α modification. Direct measurements of heats of solution in a lead borate melt of pure and doped alumina as a function of surface area enabled us to experimentally derive trends in surface energies of hydroxylated surfaces. Accounting for heats of water adsorption measured on pure and doped alumina surfaces allowed us to delineate the thermodynamic effects of hydration on surface energies.
- Retaining large surface areas in alumina powders during high-temperature annealing is a major challengein applications as catalyst supports and ceramic precursors. This is because the alumina surface areadrastically decreases with transformation from the γ modification (defect spinel structure) into the αmodification (corundum structure). The objective of this work is to show the thermodynamic basis ofusing additives, such as Zr and Mg, to control the γ-Al2O3 surface and bulk energetics and to manipulatethe transformation temperature and surface area. These additives are observed to change the pattern ofphase transformation and densification. Direct measurements of heats of solution in a lead borate meltof pure and doped alumina as a function of surface area enabled us to experimentally derive trends in thesurface energies of hydroxylated surfaces. Accounting for heats of water adsorption measured on pureand doped alumina surfaces allowed us to delineate the thermodynamic effects of hydration on surfaceenergies. Zr-doped γ-alumina showed a higher energy of the hydroxylated surface than did pure γ-aluminabut showed a lower energy of the anhydrous surface. Mg addition does not change surface energiessignificantly but decreases the energetic instability of the bulk γ phase.
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