Thermodynamic modeling of the (Al2O3+Na2O), (Al2O3+Na2O+SiO2), and (Al2O3+Na2O+AlF3+NaF) systems

Lambotte, Guillaume; Chartrand, Patrice

doi:10.1016/j.jct.2012.09.002

Cited by 34 publications

(25 citation statements)

References 192 publications

(380 reference statements)

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“…Since the global Na 2 O:SiO 2 ratio in most of the samples investigated in this work is either >0.5 or <0.25, the liquid in those samples had compositions of 0.5 or 0.25, respectively. As the Na 2 O:SiO 2 ratio in the liquid increases from 0.25 to 0.5, the solubility of Al 2 O 3 in the liquid increases from 18.4 to 21.6 vol% . The increased Al 2 O 3 solubility leads to higher densification rates and higher densities in Na 2 O/SiO 2 co‐doped samples compared to singly SiO 2 ‐doped samples, regardless of the rate‐limiting process.…”

Section: Discussionmentioning

confidence: 99%

“…To understand the above effects, we first note from the Al 2 O 3 –Na 2 O phase diagram that Na 2 O is insoluble in α‐Al 2 O 3 . A few platelet‐shaped grains with high aspect ratios were observed in the microstructures of sintered Na 2 O‐doped samples (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Because the main impurities in Bayer aluminas are SiO 2 and Na 2 O, the Al 2 O 3 –SiO 2 –Na 2 O ternary phase diagram was utilized to evaluate the effects of dopant type and concentration on solubility of Al 2 O 3 in the grain‐boundary liquid. It is assumed that the system approaches thermodynamic equilibrium upon holding at 1525°C, and thus the equilibrium composition of the liquid at 1525°C can be calculated from the ternary phase diagram (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…) can be used to determine the stability and equilibrium composition of a liquid since the volume fractions of Na 2 O and SiO 2 are known. Lambotte and Chartrand calculated isoplethal sections of the ternary phase diagram, and based on their calculations, the solubility of Al 2 O 3 in the liquid at 1525°C in the samples was estimated based on the respective Na 2 O:SiO 2 ratios (assuming a constant liquid density of 2.45 g/cm 3 ) . Likewise, the volume fractions of liquid and solid phases can be estimated since the doping and impurity concentrations of SiO 2 and Na 2 O are known.…”

Section: Discussionmentioning

confidence: 99%

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The Effects of Na₂O and SiO₂ on Liquid Phase Sintering of Bayer Al₂O₃

Frueh

Kupp

Compson³

et al. 2016

J. Am. Ceram. Soc.

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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 Na 2 O and 603 ppm SiO 2 and heated at 1525°C up to 8 h. Na 2 O 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 Al 2 O 3 , Na 2 Odoped samples sinter to 98% density with average grain sizes of~3 lm after 8 h. Increasing SiO 2 concentration significantly retards densification at all hold times up to 8 h. The estimated viscosities (20 -400 PaÁs) 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 Na 2 O/SiO 2 ratios, densification of Bayer Al 2 O 3 at 1525°C is controlled by diffusion of Al 3+ through the grain-boundary liquid, whereas for high Na 2 O/SiO 2 ratios, densification can be governed by either the interface reaction (i.e., dissolution) of Al 2 O 3 or diffusion of Al 3+ . Increasing Na 2 O in SiO 2 -doped samples increases diffusion of Al 3+ and Al 2 O 3 solubility in the liquid, and thus densification increases by 1%. Based on these findings, we conclude that Bayer Al 2 O 3 densification can be manipulated by adjusting the Na 2 O to SiO 2 ratio.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

The Effects of Na₂O and SiO₂ on Liquid Phase Sintering of Bayer Al₂O₃

Frueh

Kupp

Compson³

et al. 2016

J. Am. Ceram. Soc.

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“…3H 2 O, ACS grade, BDH, VWR International LLC, West Chester, PA) and tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ), 98%, Aldrich Chemical Company, Inc. Milwaukee, WI), respectively, to obtain chemistries similar to commercial high purity specialty aluminas with different liquid volume fractions and different Na 2 O/SiO 2 ratios, as shown in Table . The amount of liquid in the samples at 1525°C was estimated from the Al 2 O 3 ‐Na 2 O‐SiO 2 and Al 2 O 3 ‐MgO‐SiO 2 phase diagrams based on the concentrations of SiO 2 , Na 2 O and MgO. The detailed doping procedures are described in previous work …”

Section: Methodsmentioning

confidence: 99%

Powder chemistry effects on the sintering of MgO‐doped specialty Al₂O₃

et al. 2018

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In this work, we investigate the effects of powder chemistry on the sintering of MgO‐doped specialty alumina. The stages at which MgO influences densification of Al2O3 were identified by comparing dilatometry measurements and the sintering kinetics of MgO‐free and MgO‐doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO2 in alumina grains near the boundaries using EDS. First‐principles DFT calculations demonstrate that the co‐dissolution of MgO and SiO2 in alumina is thermodynamically favored over the dissolution of MgO or SiO2 individually in alumina. This study experimentally demonstrates for the first time that removal of SiO2 from the grain boundaries is a key process by which MgO enhances the sintering of alumina.

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