As a part of the studies on the oxidation of silicon-carbide powders the oxidazability of Si and β-SiC, both found in the market products of silican carbide, as well as the influence of Fe₂O₃, Al₂O₃ and MgO on the oxidation of pure green silicon carbide were investigated. The results obtained are summarized as follows:
(1) Although it was confirmed that metallic silicon was oxidized much easier than α-SiC, the small volume increase accompanied by the reaction would play no more roll than to reduce the SiC content as long as the silicon carbide is used as refractories.
(2) β-SiC is fine powder showing a very slow oxidation compared favourably with α-SiC in this respect. Consequently, it showed no trend to become porous, since no volume increase occured even though it was exposed to oxidizing atmosphare for a long time. The contamination of β-SiC in raw material is not only harmless but rather favourable.
(3) It was confirmed that Fe₂O₃ did not give any serious influence on the oxidation of SiC at a temperature lower than 1200°C, and that there was no appreciable volume increase even in contact with water vapour. At about 1400°C the reaction became violent, which however, did not continue long, showing that Fe₂O₃ is not so harmful an admixture as it is universally believed.
(4) At all temperatures Al₂O₃ held back more or less the oxidation of SiC. It was observed that a violent oxidation occured at 1150°C under the coexistence of water vapour, accompanying large volume and porocity increase. It was thus confirmed that Al₂O₃ is an impurity to which we should use due precaution against its contamination.
(5) MgO is an impurity accerelating the oxidation of SiC at the temperatures higher than 700°C, it is one of the most undesirable impurities.
(6) The influence of oxides on the oxidation of SiC is governed:
(a) by the stability discriminated by the free energy of the formation of oxides,
(b) by the location of the melting points in the binary system [metal oxide]-SiO₂,
(c) by the reactivity of metal oxide with SiO₂,
(d) by the properties of the reaction products.
Referring to the influence of the addition of Pb₃O₄, V₂O₅, and Li₂CO₃ on the oxidation of SiC such conditions as above were explained satisfactory.
(7) The prolonged oxidation of SiC is governed mainly by the nature of the oxide film covering the crystal surface. The fact that even the pure green silicon carbide behaved like an ordinary black silicon carbide when mixed with Al₂O₃ or MgO may be attributed to the nature of accerelating the crystallization of amorphous silica to quartz and cristobaite.

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This paper concerns with the theory and experimental procedure for finding out the thermal diffusivity κ (thermometric conductivity) and thermal conductivity λ by means of so-called periodical wave of temperature as initiated by Ångstrom.
From the initial condition θ=f(λ) when t=0 and the boundary condition θ=βcosωt at x=-l, x=l, the temperature θ₀ at the central layer of an infinite plane may be represented as
θ₀=η₀βcos(ωt-φ₀)
where
η₀=1/[cosh²√π/Fcos²√π/F+sinh²√π/Fsin²√π/F]^1/2
the attenuation of amplitude,
φ₀=tan^-1{tanh√π/Ftan√π/F}
the phase difference,
F₀=τκ/l²
the Fourier number corresponding to l and τ (τ=2π/ω period of one cycle), θ the temperature, τ the time, and β the initial amplitude.
From this result the functional relation between F-η, F-φ are decided, and then F corresponding to h or φ can be worked out provided η or φ are measurable, so that κ is calculable from the retation F=τκ/l² since τ and l are given as the experimental conditions.
In the same way λ can be calculated from the equation λ=cρκ, provided the specific density ρ and the specific heat c are known.
There are, however, some difficulties, i.e. (1) it is very difficult to generate perfect sine waves, (2) the relations of infinite plane given above can not always be satisfied by the finite plane, (3) owing to many reasons one dimensional heat flow may not be realized.
For the first case the author used the wall of a nichrom furnace as the filter through which a rectangular or a triangular wave may be transformed to a simple sine wave under the conditions, F_b≤1/4, where F_b is the Fourier number for the depth and the thermal diffusivity of the wall material.
For the second case, the end effect can be neglected under the condition, 0.6<F₀<1.2.
For the third case the devices and techniques for the correction to the one dimensional flow are given in the text.
It was found out that the range of the limits of F_b and F₀ confind the measurable range of κ to about κ<0.009cm²/sec, which cover from common ceramic products and materials to the heat insulators.

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In succession to the investigation on the crystallization of mullite needles in large feldspar particles this paper concerns on the microstructure of the bodies consisting of coarse feldspar grains embedded in kaolinite powder.
Complicated Becke's lines were observed at the boundary between the molten feldspar grain and the matrix phase suggesting that there was diffusion between the two phases.
The photomicrograph (photo 2) indicates that the molten feldspar showed the trend of approaching each other by forming the veins in the matrix, or by the deformation of the grains.
During these processes the pores included in the grains joined together to become larger (photo 2, 3). At higher temperatures the reduction of viscosity made the reaction more and more rapid until the bubbles suddenly open. This may be a mechanism of the formation of bubbling in over-fired bodies.
Feldspar grains locating next to cracks indicate that the molten mass pushed into the cracks through the veins by the pressure of expansion of feldspar with melting and pores in the grains.
It was thus observed that the pores near the cracks are larger than ordinary size, suggesting that the bubbles in the molten feldspar had the potential power of further expansion puhsing out the matrix, changing the shape of the grains to promote the intrusion of molten feldspar through the veins.
If the body was heated further after the cracks had closed the expanding gases found their way in the weak points to form large pores in the feldspar grains locating near the cracks. It is highly probable that a part of pores in porcelain bodies were formed in this way.
The needle crystals came out earlier and far greater in number in feldspar melts being sandwiched in the crack.
In a few specimens fired at as high as 1450°C it was observed that the needle crystals were concentrating at the surface of large bubbles showing that they were pushed back by expanding gases after the deposition of the crystals. It was also observed that the crystals were accumlating at the surface which was pushed back by expanding gases enclosed in the crack. This is the positive proof of the author's conclusion that the needle crystals in feldspar appears in the heating up period.
Moreover, it was concluded that the deposition of the crystals in molten feldspar begins in the heating up period when the expansion of gases and the penetration of feldspar into the crack have just come to an end.

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In order to obtain zirconia refractories, sufficiently stabilized and yet having high registance to spalling the influence of CaO on the bending strength of fired zirconia refractories was investigated.
Up to 8% of CaO was added to the unstabilized oxide to fire in an electric furnace at various temperatures. It was confirmed that the binding power of Ca(OH)₂ developed sufficiently at lower temperatures, while the lowering of the strength at about 600°C due to the decomposition of Ca(OH)₂, and the falling off at 1000°C due to the transformation of ZrO₂ did not fail to come out.
It was then tried to add the necessary amount of CaO in two steps interposing the calcination of the mixture between the first and second step. Although this method lowered the low temperature strength it kept away, to some extent, the transition at 1000°C.
The first addition of 4-6% followed by the second 6-2% gave the best results. The authors consider that the present method would open the door to the new processes of producing zirconia refractories with the addition of CaO as a stabilizing agent.

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