窯業協會誌
Online ISSN : 1884-2127
Print ISSN : 0009-0255
ISSN-L : 0009-0255
各種炭化珪素粉末の酸化に対する水蒸気の作用と色彩あるいは多形の影響
炭化珪素粉末の酸化に関する研究, 続報
鈴木 弘茂
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ジャーナル フリー

1959 年 67 巻 761 号 p. 157-164

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The green silicon carbide powder of classified and purified grains was oxidized at 1200°C by the mixture of water vapour and oxygen in the volume ratios of H2O: O2=25:75, 50:50, 75:25, 90:10, and also by steam containing 10% of nitrogen (>99.99%). The degree of oxidation was measured by weight increase, from which the oxidation ratio was worked out.
Similar experiments were carried out at 1000° and 1400°C using the mixture 50:50 to compare the results with those of the oxidation by dry oxygen (J. Ceram. Assoc., Japan, 65 [736] 88, 1957), and to discuss the role of water vapour.
To investigate the influence of the colour and polytype composition of silicon carbide crystals the samples, home and foreign origin, were subjected to the similar experiments, i.e., the oxidation at 1000°, 1200° and 1400°C for long hours by dry oxygen, and also by the 50:50 mixture. Especially, those oxidized at 1200°C were put to the tests such as X-ray analysis, dilatometry, and the observation of thin section under microscope.
The results are summarized as follows:
(1) Silicon carbide powder was oxidized strongly by water vapour containing oxygen when heated above 1000°C. At comparatively lower temperatures the powder was sintered, while at such a high temperature as 1400°C it was swollen to a porous mass caused by the increase of oxidation velocity. Up to 90 vol.% the increasing steam content accelerated the reaction velocity.
(2) The same formula as before, {R0(1-3√1-x)}N=Kt, the rate of oxidation with dry oxygen, where R0 is the average radius, x the oxidation ratio, t the time, and N and K are constants, was established. The value of K increased and N decreased with increasing temperature.
(3) Generally, the colour and the polytype composition of the powder exerted no appreciable influence on the function of dry oxygen.
(4) In the current of 50:50 mixture, a marked difference was observed between the oxidation at 1200°C of the green and greenish black powders, containing, respectively, more than 83 and 74% of 6 H type, and of the black and dark grey domestic products, each containing more than 47 and 52% 4 H type. Especially, the silica formed by the oxidation of the black powder turned comparatively early to cristobalite which developed to form a porous mass. In this case the rate was represented by the first order equation.
(5) An infinitesimal quantity of impurity contained in above samples would lower the temperature of crystallization, of silica which together with the acceleration of the velocity of crystal growth by water vapour, would be the most important source of bringing about such a difference in the oxidation characteristics.

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