Single crystals of perovskite-type Pb(Zn_1/3Nb_2/3)O₃ were grown from PbO flux. Their thermal stability, ferroelectric property, and phase transition were studied.
(1) Single crystals with a dimension of approximately 3×3×2mm were obtained from the 50 to 55 wt% PbO flux at a cooling rate of 25°C/hr after the 1150°C soaking. The crystal growth rate along the [100] direction was about 0.5mm/hr from 1100 to 900°C. Addition of SiO₂, Al₂O₃, or B₂O₃ to the PbO flux prevented the formation of a perovskitetype Pb(Zn_1/3Nb_2/3)O₃ crystal.
(2) The single crystals prepared were confirmed to have a Nb rich composition deviating from a stoichiometric ratio of Zn/Nb and to have a perovskite-type structure with rhombohedral lattice parameters, a=4.063±0.003Å and α=89°55′±5′ at room temperature. The super-lattice due to an ordered arrangement of Zn and Nb ions was not observed.
(3) The Pb(Zn_1/3Nb_2/3)O₃ crystals showed a thermal decomposition only near the surface at 1000°C in air, resulting in conversion into Pb₂Nb₂O₇ss, PbOss, and ZnO. On the other hand, the pulverized crystals completely decomposed into the above-mentioned three phases at the same conditions. Pb(Zn_1/3Nb_2/3)O₃ is nstable in solid equilibrium at ordinary atmosphere, but becomes stable in liquid state, or molten solution with PbO.
(4) The temperature of maximum dielectric constant increases with increasing the atomic ratio of Zn/Nb. The Single crystals with Zn/Nb ratio of 0.463, 0.481 and 0.485 showed temperatures of maximum dielectric constant of 135°C, 144°C, and 147°C, respectively, at the frequency of 10³Hz. The temperature of high pressure-sintered specimens was 188°C at the same frequency.
(5) The ferroelectric-paraelectric transition is presumed to be a higher order-transition, because of no domain structure, no hysteresis in thermal expansion, and gradual and uniform change of optical anisotropy throughout the crystal.

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ポルトランド・セメント・クリンカーの構成鉱物の1つであるアルミネート相の原形化合物3CaO・Al₂O₃への鉄の固溶は古くから研究されているが, 1965年Nature誌上で, 顕微鏡的相平衡の結果から, 3CaO・(Al_0.965Fe_0.035)₂O₃が限界組成であるとするC. M. Schlaudt, D. M. Royと, X線的格子定数の変化から, 3CaO・(Al_0.90Fe_0.10)₂O₃までのひろがりがあるとするP. Tasteの実験事実が対立した. この論争にA. E. Mooreは自身の実験値をも加味して, ‘3CaO・Fe₂O₃’の固溶限界濃度は処理温度が低いと, 高い濃度を示すとする温度依存の仮説を提唱した. しかし, この仮説でP. Tarte, A. J. Majumdar, A. E. Mooreの実験値が説明されても, C. M. Schlaudt, D. M. Royの相平衡状態図が矛盾することをA. E. Mooreも認めている. 当報では先行者の手法を追跡しつつ, この対立, 矛盾は3CaO・Al₂O₃に対応する固溶系の相違にあるとして, 3CaO・Al₂O₃-‘3CaO・Fe₂O₃’, 3CaO・Al₂O₃-2CaO・Fe₂O₃, 3CaO・Al₂O₃-CaO・Fe₂O₃, 3CaO・Al₂O₃-Fe₂O₃の4つの系につき, X線的に格子定数の精密測定を行ない, この結果から, 上記の矛盾を充分に説明することができた.
同一処理温度では, 対象とする系に固溶濃度限界が依存し, 処理温度が高くなるにつれて固溶濃度限界がひろがっていく通常形の固溶関係のあることを明らかにした. 3CaO・Al₂O₃-2CaO・Fe₂O₃系で一番大きな固溶量を示すが, 他の系では格子定数変化の折曲点からさらに漸次的膨脹を示し, 真の限界値を決定するに際し困難があったが, 先行者A. E. Moore, A. J. Majumdarの方法にならって, 一応, 折曲点をそれぞれの系の固溶濃度限界と見なした. 折曲点からの漸次的膨脹は最終系3CaO・Al₂O₃-2CaO・Fe₂O₃系への移行過程にあるため起った現象と推定した. この系にみられるように, 3CaO・Al₂O₃構造への鉄固溶量の大きい原因は, 固溶鉄イオンの分布がアルミニウムイオン席だけでなく, カルシウムイオン席にまで及ぶためと考えられる.

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The effect of doped aluminium on thermal stability of basic structures was studied experimentally in the range from 2000°C to 2400°C. The results were summarized as follows;
(1) The 4H type SiC was stabilized by aluminium, and it could be changed 4H to 6H and 6H to 4H by exclusion and inclusion of the aluminium respectively.
(2) The distortion of the lattice was caused by the aluminium and the stability of 4H structure in this temperature range was attributed to this distortion.
(3) The 15R type seemed to be unstable in these conditions.

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The purpose of this work is to show the polishing mechanism of the cerium oxide and water slurry polishing process, most commonly used.
We observed:
Using the polishing of 18 different kinds of optical glasses, the relationship between microvickers hardness, softening point and chemical durability of the glass, and the rate of polishing; and the relationship between the change of surface roughness and that of the weight before and after polishing. The glass surface was observed with an electron microscope. In order to compare the water polishing with the oil polishing or the dry polishing, each type of glass was polished three ways: with cericm oxide and water slurry, with cerium oxide and kerosene slurry, and with cerium oxide alone.
Our observations follows:
1) There is no relationship between the rate of polishing glass and microvickers hardness and softening point.
2) The rate of polishing for each type of glass is dependent upon the chemical durability of the glass. In other words, the rate of polishing using cerium oxide and water slurry is mainly dependent upon the rate at which hydrated layers formed as a result of the chemical reaction between the polishing solution and the glass surface. The rate of polishing also depends upon the hardness of the hydrated layers.
3) Many scratches are observed on the polished surface. The progressive polishing is accompanied by a nearly proportional weight loss through the polishing process. These observations are conclusive evidence that the cerium oxide granules in the polisher physically remove outside layer of glass.
4) Using the cerium oxide and water slurry the polishing rate is much faster than either the cerium oxide and kerosene slurry or the dry cerium oxide. Because the polishing is accelerated by hydration, which makes the surface of the glass softer than the bulk glass.
Our observations conclude that optical glass polishing is both chemical and physical processes, i.e. chemical, in that hydration is a chemical reaction to the cerium oxide and water slurry, and mechanical, in that the cerium oxide granules physically remove the rough surface from the glass layers softend by hydration. The heat generated in the process of polishing does no more than accelerated hydration in the cerium oxide and water slurry polishing process.

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In spite of the fact that periclase is one of the most stable minerals to alkali, magnesia brick, mainly made up of periclase, is subjected to attack of alkaline vapors. The reason is that the silicate minerals, mainly f orsterite, forming the bond between the periclace grains are not so resistant to alkaline vapors as periclase.
In this present paper, the processes of corrosion of forsterite brick by Na₂CO₃ and K₂CO₃ vapor, respectively, were studied.
When forsterite was exposed to Na₂CO₃ vapor, at the initial stage the following reaction took place:
2MgO⋅SiO₂+Na₂CO₃→2Na₂O⋅2MgO⋅3SiO₂+MgO
and with increasing of pick-up of Na₂O their reaction products were replaced by the final products, i.e. Na₂O⋅MgO⋅SiO₂ and MgO.
On the other hand, in the reaction beteween K₂CO₃ vapor and forsterite, K₂O⋅MgO⋅SiO₂ and MgO were produced. The products were the final in K₂CO₃ vapor.

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