Zircon refactories are severely attacked by potassium salt vapors at high temperature. However, the mechanism of the disintegration and products formed in the refractories corroded by potassium salts are not clear.
In the present paper, the process and products of the reaction between zircon and potassium salts such as K₂CO₃ and K₂SO₄ are studied. In the initial stage of reaction of zircon and K₂CO₃ vapor, K₂⋅ZrO₂⋅3SiO₂ and ZrO₂ were formed, and subsequently they reacted with K₂CO₃ to form K₂⋅ZrO₂⋅2SiO₂ which was found in this paper. Finally, K₂O⋅ZrO₂⋅SiO₂ was formed. The zircon refractories greatly expanded owing to the formation of K₂⋅ZrO₂⋅3SiO₂, K₂O⋅ZrO₂⋅2SiO₂ and K₂O⋅ZrO₂⋅SiO₂ during exposure to K₂CO₃ vapor. K₂O⋅ZrO₂⋅SiO₂, however, was not detected in the reaction of zircon and K₂SO₄ vapor.

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The liquidus curve in the system Al₂O₃-La₂O₃ was determined by the use of a heliostat type solar furnace. The cooling curves of melt specimens were obtained in the black body centrifugal cavity with an optical pyrometer. The quenched specimens were examined by X-ray technique and petrographic microscopy.
Anomalies in the liquidus curve of the system were found in the region of 60.0 and 99.0mol% of La₂O₃. A composition of 80.0mol% La₂O₃ was further examined by high-temperature X-ray diffractometry, and the presence of a new orthorhombic phase was established.
A tentative phase diagram for the Al₂O₃-La₂O₃ system at high temperatures is presented.

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Composition and concentration dependence of the decay time constant of the Nd³⁺ emission for the ⁴F_3/2-⁴I_11/2 transition in glasses were investigated, and dominant factors regulating these results were discussed.
The changes of the decay time constant in different glasses are summerized as follows; the constants increase in the series silicate-, phosphate-, germanate- and borate-glasses, with the ionic radius of network modifier and the content of network former, and with the content of SiO₂ and the ratio of Na₂O in borosilicate glasses. These results may be explained in connection with strength of the influence of the environment on Nd³⁺, which could be described as the function of the vibrational frequency of network, and the nature of the bonding and the distance between Nd-O.
About the quenching concentration, the tendency to be different within the range of about six times and to increase with the ionic radius of network modifier were recognized.
From the view point of the concentration dependence of the total transition probability from the ⁴F_3/2level and the Nd-Nd distance at which the quenching begins, it was considered that the nature of interaction between Nd³⁺ causing the quenching is mainly of the electrostatic multipolar. Since the concentration dependence of the probability in phosphate glass was described by the Stern-Volmer model, the quenching is regarded to proceed in the presence of migration of the excitation energy.
Although the quenching rate largely depends on the Nd³⁺ concentration, it shows also the composition dependence. This means that the increase of the coupling of Nd³⁺ with the environment has a definite contribution for that of Nd³⁺-Nd³⁺ interaction.

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Reaction of monoaluminum phosphate Al(H₂PO₄)₃ with alumina and magnesia and thermal change of the phosphate as well as of the reaction products were studied for fundamental research of the phosphate as a combining material of refractories. On heating, the phosphate changed to an amorphous material and then to Al(PO₃)₃ (type B) above 450°C and type A above 550°C (Figs. 1 to 3). By treating an aqueous solution of the phosphate with aluminum hydroxide at a ratio of P/Al=2, AlH₃(PO₄)₂⋅3H₂O crystallized whose thermal change is shown in Figs. 4 and 5. Thermal change of amorphous AlPO₄⋅nH₂O is shown in Fig. 6. Much AlPO₄ (Tridymite form) appeared at 140°C while Berlinite appeared predominantly when P/Al ratio was larger than 1 (Fig. 7).
Magnesia reacted rapidly with the solution of the phosphate; the setting of the mixtures of the solution, aluminum hydroxide and magnesia occurred more rapidly with increasing amount of magnesia (Table 3 and Fig. 8). The reaction products consisted of MgHPO₄⋅3H₂O and amorphous AlPO₄⋅nH₂O when P/(Al+Mg) ratio was 1. Magnesia interrupted the crystallization of AlPO₄ (Tridymite form), which appeared mainly at 650°C as Mg₂P₂O₇ crystallized (Fig. 9). When the ratio was smaller than 1, Mg₃(PO₄)₂ formed above 900°C while Mg(PO₃)₂ formed above 400°C when the ratio was larger than 1 (Figs. 10 and 11).

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[in Japanese]

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