Influence of the amount of Na2O and SiO2 on the sintering behavior and on the microstructural evolution of a Bayer alumina powder

Louet, Nicolas; Gonon, Maurice; Fantozzi, G.

doi:10.1016/j.ceramint.2004.10.013

Cited by 25 publications

(21 citation statements)

References 18 publications

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“…This effect increases with the silica content and seems to start from the beginning of the sintering (first and/or intermediate stages) as already reported in the literature. [15][16][17][18][19] Nevertheless, only the density values of samples sintered above 1500 • C are displayed in Fig. 3 because the Archimedes's method cannot be used in materials sintered at lower temperatures.…”

Section: Resultsmentioning

confidence: 99%

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

Louet

Reverón

Fantozzi

2008

Journal of the European Ceramic Society

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Section: Resultsmentioning

confidence: 99%

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

Louet

Reverón

Fantozzi

2008

Journal of the European Ceramic Society

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“…The Al 2 O 3 powders were doped with up to 1000 ppm Na 2 O using sodium acetate (NaC 2 H 3 O 2 ·3H 2 O, ACS grade, BDH, West Chester, PA), based on the procedure reported by Louet et al The Al 2 O 3 powders were dispersed in a solution of sodium acetate dissolved in deionized water. The suspension was stirred on a magnetic stir plate for 5 h at room temperature, and held at 80°C for 24 h while stirring until the mixture was too viscous to stir, and then dried at 100°C for 24 h.…”

Section: Methodsmentioning

confidence: 99%

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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“…It is well known that trace amounts (ppm) of dopants or impurities can have a significant influence on the sintering of alumina . Since Coble's discovery of MgO doping to produce high‐density translucent alumina, there has been high academic and commercial interest in understanding how small concentrations of dopants and impurities characteristic of specialty aluminas affect sintering …”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3] Since Coble's discovery of MgO doping to produce high-density translucent alumina, there has been high academic and commercial interest in understanding how small concentrations of dopants and impurities characteristic of specialty aluminas affect sintering. [4][5][6][7][8] In our previous work, the influence of Na 2 O and SiO 2 on the sintering of MgO-free specialty alumina was investigated. 9 Na 2 O was shown to initially retard the densification of MgO-free specialty alumina samples, but no effect was observed after extended sintering time (>30 minutes) at 1525°C, whereas the addition of SiO 2 to MgO-free specialty alumina formed a liquid phase and significantly retarded densification throughout the entire sintering process.…”

Section: Introductionmentioning

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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Influence of the amount of Na2O and SiO2 on the sintering behavior and on the microstructural evolution of a Bayer alumina powder

Cited by 25 publications

References 18 publications

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

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

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

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Influence of the amount of Na2O and SiO2 on the sintering behavior and on the microstructural evolution of a Bayer alumina powder

Cited by 25 publications

References 18 publications

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

Sintering behaviour and microstructural evolution of ultrapure α-alumina containing low amounts of SiO2

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

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

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Product

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

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