TY - JOUR
T1 - The Effects of Na2O and SiO2 on Liquid Phase Sintering of Bayer Al2O3
AU - Frueh, Tobias
AU - Kupp, Elizabeth R.
AU - Compson, Charles
AU - Atria, Joe
AU - Messing, Gary L.
PY - 2016/1/1
Y1 - 2016/1/1
N2 - To determine how grain-boundary composition affects the liquid phase sintering of MgO-free Bayer process aluminas, samples were singly or co-doped with up to 1029 ppm Na2O and 603 ppm SiO2 and heated at 1525°C up to 8 h. Na2O retards densification of samples from the onset of sintering and up to hold times of 30 min at 1525°C compared to the undoped samples, but similar to the as-received, MgO-free Al2O3, Na2O-doped samples sinter to 98% density with average grain sizes of ~3 μm after 8 h. Increasing SiO2 concentration significantly retards densification at all hold times up to 8 h. The estimated viscosities (20−400 Pa·s) of the 0.3 to 1.8 nm thick siliceous grain-boundary films in this study indicate that diffusion greatly depends on the composition of the liquid grain-boundary phase. For low Na2O/SiO2 ratios, densification of Bayer Al2O3 at 1525°C is controlled by diffusion of Al3+ through the grain-boundary liquid, whereas for high Na2O/SiO2 ratios, densification can be governed by either the interface reaction (i.e., dissolution) of Al2O3 or diffusion of Al3+. Increasing Na2O in SiO2-doped samples increases diffusion of Al3+ and Al2O3 solubility in the liquid, and thus densification increases by 1%. Based on these findings, we conclude that Bayer Al2O3 densification can be manipulated by adjusting the Na2O to SiO2 ratio.
AB - To determine how grain-boundary composition affects the liquid phase sintering of MgO-free Bayer process aluminas, samples were singly or co-doped with up to 1029 ppm Na2O and 603 ppm SiO2 and heated at 1525°C up to 8 h. Na2O retards densification of samples from the onset of sintering and up to hold times of 30 min at 1525°C compared to the undoped samples, but similar to the as-received, MgO-free Al2O3, Na2O-doped samples sinter to 98% density with average grain sizes of ~3 μm after 8 h. Increasing SiO2 concentration significantly retards densification at all hold times up to 8 h. The estimated viscosities (20−400 Pa·s) of the 0.3 to 1.8 nm thick siliceous grain-boundary films in this study indicate that diffusion greatly depends on the composition of the liquid grain-boundary phase. For low Na2O/SiO2 ratios, densification of Bayer Al2O3 at 1525°C is controlled by diffusion of Al3+ through the grain-boundary liquid, whereas for high Na2O/SiO2 ratios, densification can be governed by either the interface reaction (i.e., dissolution) of Al2O3 or diffusion of Al3+. Increasing Na2O in SiO2-doped samples increases diffusion of Al3+ and Al2O3 solubility in the liquid, and thus densification increases by 1%. Based on these findings, we conclude that Bayer Al2O3 densification can be manipulated by adjusting the Na2O to SiO2 ratio.
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U2 - 10.1111/jace.14206
DO - 10.1111/jace.14206
M3 - Article
AN - SCOPUS:84963750553
VL - 99
SP - 2267
EP - 2272
JO - Journal of the American Ceramic Society
JF - Journal of the American Ceramic Society
SN - 0002-7820
IS - 7
ER -