In order to clarify the sintering process of the ferroelectric or antiferroelectric ceramics when the hot-pressing was applied, and the relation between the sintering conditions and the electrical properties, systematic experiments were made on the following solid reactions containing PbO,
4PbO+Ta₂O₅+Fe₂O₃→4Pb(Ta_0.5-Fe_0.5)O₃ (PTF)…(1)
PbO+ZrO₂→PbZrO₃…(2)
0.94PbO+0.06SrCO₃+0.53ZrO₂+0.47TiO₃→Pb_0.94Sr_0.06(Zr_0.53-Ti_0.47)O₃(PZT)…(3)
At first, the variations of apparent density, when the raw powders of reactions (1)-(3) were heated, were examined as functions of the maximum firing temperature (T_m), the hot-pressing pressure (P_h) and of the duration of hot-pressing at T_m (t_p). In this report, the following procedures were mainly taken for hot-pressing:
SP method; P_h was applied for t_p (min) after the temperature reached to T_m in the firing process.
OP method; P_h was applied from a certain temperature (T_s) (T_s<T_m) in the firing process, and after the temperature reached to T_m, P_h was successively applied for t_p (min).
DP method; P_h was applied during all firing process.
The results obtained are summarized as follows.
(1) When the mixture of raw powder of equation (1) was heated by normal sintering, remarkably anomalous expansion was observed at 600°-900°C with the maximum linear expansion of 22% and the reduction of density was occurred in this temperature range. However, when P_h of 100-700kg/cm² was applied to the specimen by SP method, the densification was considerably promoted from about 500°C. Almost sintered ceramic was obtained by hot-pressing of (SP) P_h=500kg/cm², T_m=800°C and t_p=30 min.
This hot-pressing temperature is 400°C lower than the temperature of normal sintering. The specimens prepared by hot-pressing at relatively lower temperature and higher pressure (e.g. T_m=800°C, P_h=700kg/cm²) showed the broad temperature dependency of permittivity at about ferroelectric Curie temperature.
(2) PbZrO₃ has been known as antiferroelectrics. When the normal sintering was used for the reaction (2), it was very difficult to obtain the dense ceramic body because of the strong evaporation of PbO. However, when the SP method was applied to PhZrO₃, the remarkable effect on the increase of the densification was observed, and very dense body with 99.2% of theoretical density was obtained by the hot-pressing of T_m=1200°C, P_h=200kg/cm² and t_p=30 min.
The measurements of the permittivity (ε_s) vs. temperature characteristics during heating and cooling and of D-E hysteresis characteristics were made, and also X-ray diffraction analysis and electron micrographic observation of the etched surfaces were made on the specimens prepared by various hot-pressing conditions.
In PbZrO₃ prepared by hot-pressing, the second transition (T_t) occurred at the lower side of the Curie point (T_c) and the ferroelectric behaviors were observed in the temperature range between T_c→T_t. These properties were considerably differed from the result of normally sintered PbZrO₃ reported by Sawaguchi. When the hot-pressing was applied to PbZrO₃ containing a few mole

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This work was undertaken as a part of the research program of development of good opaque porcelain enamels for aluminum alloys. In the present study the efforts were made on the identification of crystalline phases in these enamels. Furthermore, the relation between variety of crystals depositted and chemical durability of the enamel was studied.
The results obtained are summarized as follows:
1) Two kinds of crystalline phases were detected by X-ray diffraction method. One of them was apatite type hexagonal leadsilicovanadate, 5 PbO⋅SiO₂⋅V₂O₅, and another was KBrO₃ type hexagonal phase. Although the exact formula of the latter phase could not be determined, it might be reasonably concluded from many synthetic experiments that the chemical composition corresponds with that of Pb₂SiO₄-x Pb(Na_y⋅K_1-y) VO₄ solid solution.
2) X-ray peak intensities of (00l) reflections of apatite type crystals and of (h00) reflections of KBrO₃ type crystals on the surface of enamels were abnormally strong. Preferred orientation of these crystals might be inferable from the facts mentioned above.
3) Acidity of the frit glazes used might be one of factors determining which phase between the two would be crystallized in enamels. In general, apatite type phases were preferred to crystallize in more acidic enamels, while the KBrO₃ type phases were developed in more basic enamels.
4) Chemical durability of crystalline phases and glass matrix in enamels were compared with each other. It was found from the results of immersion experiments that chemical durability decreases in the following order: glass matrix>apatite type crystalline phase>KBrO₃ type crystalline phase.
5) Good opaque enamels having a nearly pure white tone were established by using a frits contained higher RO₂ components, but in this case, it was necessary to fire at about 600°C.

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Guaranteed reagent grade magnesium basic carbonate with 0, 2, 5 and 10 wt% of ZnO and extra pure grade magnesium basic carbonate and natural magnesite with 0, 2 and 5 wt% of ZnO were calcined at temperatures of 600°C to 1400°C for periods of 7.5 to 240 minutes. The MgO obtained was studied by means of X-ray diffraction and electron microscopy.
In the calcined products of E. P. magnesium basic carbonate the shape of original material was broken at temperatures higher than 800°C and converted clearly into the separated spherical particles of MgO, in contrast with the fact that pseudomorphs were observed over the whole ranges of calcination temperatures on the calcined products of G. R. magnesium basic carbonate and magnesite.
Evidences were also obtained from X-ray analysis that the solid solutions were formed from MgO and added ZnO, and the lattice constants of MgO increased continuously with the increase of the content of ZnO.
The relation between crystallite size (D) of MgO and calcination time (t) could be described by the equation D=Ktⁿ (K: a constant).
The values of n for G. R. magnesium basic carbonate and magnesite increased with the addition of ZnO, but in the case of E. P. magnesium basic carbonate, the variations of n was not almost observed.
The obtained values of n were as follows:
G. R. magnesium basic carbonate: 0.10-0.16
E. P. magnesium basic carbonate: 0.10-0.11
Natural magnesite: 0.22-0.34
The activation energies (Q) for crystallite growth of MgO showed two values in low and high temperature regions for each mixture.
The obtained Q values for low temperature region were 41 to 46kcal/mol and almost constant for all mixtures.
The Q values for high temperature region were decreased with the addition of ZnO and the obtained values were as follows:
G. R. magnesium basic carbonate: 126-59kcal/mol
E. P. magnesium basic carbonate: 180-149kcal/mol
Natural magnesite: 143-81kcal/mol

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