Journal of the Ceramic Association, Japan

Solid State Reaction between Y₂O₃ and Nb₂O₅

Noriyasu HOTTA, Yasuhiko MATSUSHITA, Shigetomo MATSUO

1978 Volume 86 Issue 989 Pages 7-11
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.7

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Solid state reactions between sintered Y₂O₃ and Nb₂O₅ have been studied from 1275°C to 1350°C, in which two kinds of sintered Y₂O₃, 70 and 95% dense, were employed. Techniques used were electron microscopy, EPMA, X-ray diffraction and dilatometry.
A layer of Y₂O₃⋅Nb₂O₅ formed at the Y₂O₃-Nb₂O₅ interface, of which growth was controlled by the one-way diffusion of Nb₂O₅ across the product layer. The apparent activation energies of the diffusion for 70% and 95% dense Y₂O₃ are 150 and 200kcal/mol, respectively.
EPMA of 1350°C-specimen showed the concentration gradient of Nb across the reaction layer ranging from 50 to 55mol% of Nb₂O₅ increasing towards the Y₂O₃⋅Nb₂O₅-Nb₂O₅ interface. The observed separation of diffusion couples is probably due to the difference of thermal expansion coefficients between the product and Nb₂O₅.

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Nitrides Formed by Reducing Process of the Shirasu Glass with Carbon

Kinji SHIMADA, Yasuo FUKUSHIGE, Yoshihiro HIRATA

1978 Volume 86 Issue 989 Pages 11-18
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.11

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The mixtures of silicious volcanic glass (shorten as v.g., 74.76% SiO₂, 13.36% Al₂O₃, 0.60% Fe₂O₃, 1.73% CaO, 0.69% MgO, 4.00% Na₂O, 3.27% K₂O, 0.61% Ig. loss) separated from the original Shirasu and carbon black (shorten as C) were heated at temperatures from 1300 to 1450°C for 1 to 10h under N₂ gas flow. As the reaction products, Si₂ON₂*, β′-Si₃N₄, α-Si₃N₄, AlN and β-SiC were observed. Si₂ON₂* and β′-Si₃N₄ are solid solutions appeared in the system of Si₃N₄-AlN-SiO₂-Al₂O₃.
The kinds of reaction products and their amounts were altered according to C/v.g. value, reaction temperature, reaction time and impurities. Each of Si₂ON₂*, β′-Si₃N₄ and α-Si₃N₄ was mainly formed in a range of C/v.g. value, 0.2-0.3, 0.3-1 and above 1, respectively. Relative amounts of α-Si₃N₄ were increased with increasing C/v.g. value.
The nitridation of the volcanic glass by reducing process with carbon is induced below 1300°C and this temperature is lower than that of pure silica. β′-Si₃N₄ is considered to be formed via Si₂ON₂* from the volcanic glass but α-Si₃N₄ is accounted to be formed through vapour phase by the reaction between the volcanic glass and carbon under N₂ atmosphere.

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Evaluation of TiO₂ Powders and Effects of Calcination in the Sintering of BaTiO₃ Ceramics

Takeshi NOMURA, Takashi YAMAGUCHI

1978 Volume 86 Issue 989 Pages 19-25
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.19

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Effects of TiO₂ raw material powders and calcination conditions on the sintering of BaTiO₃ ceramics have been studied. Techniques used are dilatometry, X-ray diffraction analysis and SEM. Four kinds of equimolar mixtures in the system BaCO₃-TiO₂ were prepared mainly by partial precipitation mixing using three different TiO₂ powders. The partial precipitation mixing consists of precipitating BaCO₃ in the TiO₂-suspension, and this method was of advantage for observing the effect of TiO₂ powders. It is shown that the aggregation state of TiO₂ powder has marked effects on the solid state reaction during calcination and also on the subsequent sintering. The presence of Ba₂TiO₄, of which formation is pronounced in aggregated mixtures, has a deleterious effect on the sintering. Another effect of calcination on the sintering has been understood by the pressed density of calcined materials. It is suggested that aggregated TiO₂ powders may be used by appropriate processing such as ball-mill mixing or preliminary disintegration of secondary particles prior to the precipitation mixing.

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Growth of Si₂ON₂ Needle Crystals by Nitriding Process on Silicon-Silica System in Powder Compacts

Nobuyuki AZUMA, Tomeru YAMADA, Hiroshi HAYASHI

1978 Volume 86 Issue 989 Pages 26-33
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.26

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(1) Si₂ON₂ needle crystals were obtained by heating the compacts of the mixture of Si and SiO₂ with the addition of Mg and a small amount of Cu, in nitrogen atmosphere at 1380 to 1420°C for 3h. The needle crystals grew mainly on the surface of the compact.
(2) The role of Mg and Cu metals for the growth of Si₂ON₂ is explained as follows;
The formation of a liquid phase in Mg-Cu-Si system promotes the reaction between Si and SiO₂. SiO phase formed by the reaction, subsequently reacts with nitrogen to result in the growth of Si₂ON₂ needles through VLS mechanism.
(3) The optimum growth condition were as follows; molar ratio: Si/SiO₂/Mg/Cu=2.2/1.0/0.3/0.003 initial heat treatment: _??_650°C (30min)→650°C (30min) grain size of Si: 10-30μm reaction temperature: 1420°C reaction time: 3h nitrogen flow rate: 50ml/min
(4) The size of the Si₂ON₂ needles obtained under the optimum conditions were 5-6mm in length and 1-3μm in diameter.

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Effects of Oxygen Partial Pressures on Vaporization Rates in the System MgO-Cr₂O₃

Hong Lim LEE, Toshiyuki SATA

1978 Volume 86 Issue 989 Pages 34-40
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.34

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The vaporization mechanisms of the system MgO-Cr₂O₃ were studied at 1600°C as functions of oxygen partial pressure. It was found that the vaporization mechanisms of the system MgO-Cr₂O₃, at low oxygen partial pressures, are decomposition reactions as given by MgO(s)=Mg(g)+1/2O₂(g) Cr₂O₃(s)=2Cr(g)+3/2O₂(g) MgCr₂O₄(s)=Mg(g)+2Cr(g)+2O₂(g) and, at high oxygen partial pressures, oxidation reactions as given by Cr₂O₃(s)+3/2O₂(g)=2CrO₃(g) MgCr₂O₄(s)+3/2O₂(g)=MgO(s)+2CrO₃(g).
The minimum rate of vaporization was obtained at about 10^-5atm of oxygen partial pressure at 1600°C for both Cr₂O₃ and MgCr₂O₄.
The rate of vaporization in gas flow could be correlated with those in vacuum by assuming diffusion in gaseous boundary layer.

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Physical and Chemical Characteristics of Some Clays from Jammu Region, India

S. N. KHOSLA, C. S. GUPTA, R. K. BEDI

1978 Volume 86 Issue 989 Pages 40-44
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.40

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The physico-chemical characteristics related to the working properties of three Indian clays have been studied. While two of the samples are fairly plastic and good to work at, the third is highly silicious. Results on various physical properties coupled with base exchange capacity and chemical analysis of clays indicate that all the samples are Ca-Mg based bentonites, though associated with other impurities in varying proportions.

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Synthesis of Hydrated Alumina Gel by the Homogeneous Precipitation Method Using NaAlO₂ as Starting Material and Its Phase Change by Heating

Kazumi FUJITA, Kunihiko YANAGIHARA, Jin KAWAZU, Isao KAYAMA

1978 Volume 86 Issue 989 Pages 45-47
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.45

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Sintering of TiO

Katsuya KUDAKA, Takashi HANAZAWA, Hidenori TAKAI

1978 Volume 86 Issue 989 Pages 47-49
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.47

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Erratum

1978 Volume 86 Issue 989 Pages 49a
Published: 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.989_49a

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Erratum

1978 Volume 86 Issue 989 Pages 49b
Published: 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.989_49b

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[title in Japanese]

1978 Volume 86 Issue 989 Pages A1-A4
Published: January 01, 1978
Released on J-STAGE: April 30, 2010

DOIhttps://doi.org/10.2109/jcersj1950.86.A1

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