In the previous paper (J. Ceram. Assoc. Japan, 68 [10] 223 (1960)) the authors reported that some glasses of low lithium content (4%) in the system Li₂O-MgO-Al₂O₃-SiO₂ could be converted, by the heat treatment, into a polycrystalline material without showing any appreciable deformation even if no special nucleating agent, such as platinum, was added. The present paper contains the results of experiments designed to determine the optimum conditions of heat treatment of the glass of this type for producing a polycrystalline material of high mechanical strength.
(1) Chemical composition of the glass studied The glasses of the composition, MgO x, Al₂O₃ y, SiO₂ z, Li₂O 4, where x+y+z=100 by weight, were melted and formed into a specimen of the size 2.5×5×50mm. They were heated from room temperature to 1200°C with the rate of 5°C/min. and then held there for two hours. Among the polycrystalline materials, the one produced from a glass of the composition of Li₂O 4, MgO 15, Al₂O₃23, SiO₂62 showed the highest modulus of rupture (1, 550kg/cm²).
(2) Process of cristallization of the glass during heat treatment Thermal differential and X-ray analysis made with the glass specimen of above composition showed that, during its heat treatment, β-eucryptite was first precipitated at about 850°C and then β-spodumene at about 1000°C (Fig. 9). Microscopic examination showed that β-spodumene, after its precipitation, decreased its grain size by fission, by still unknown reason, with increasing temperature (Fig. 10, b, c, d). Above 1000°C the marked increase in specific density of the specimen with increasing temperature was also observed (Fig. 12).
(3) Effects of heat treatments on strength The conditions of heat treatment such as the heating rate and the maximum holding temperature were varied and their effects on the modulus of rupture of the resultant polycrystalline materials were determined. The slow heating with the rate at least below 5°C/min. in the temperature interval of 800 to 900°C, in which β-eucryptite was first precipitated in the specimen, was found to be necessary increasing the strength (Fig. 6). The specimen which missed this heat treatment had poor strength (Fig. 5). The strength was also found to increase with increasing the maximum holding temperature (Fig. 7). This change was attributed to the decrease in grain size of β-spodumene and also to the compacting of microstructure.

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There are many papers published concerning the mineralizers used to drop the sintering temperature of MgO, for example, to around 1500°C.
In order to carry out the studies along these lines the authors concentrated their attension to the compounds CaO⋅Fe₂O₃ and 2CaO⋅Fe₂O₃ existing in the system CaO-Fe₂O₃. The mixtures, x CaO+Fe₂O₃, where x=1, 1.25, 1.5 and 1.75, where heated and the X-ray patterns of the compounds as well as their hydrates were studied.
It was confirmed that d=2.533 Å belongs to CaO⋅Fe₂O₃, and d=2.71 and d=2.80 Å to 2CaO⋅Fe₂O₃, MgO prepared by calcining Mg(OH)₂ at 800°C for 3 hours showed the growth of periclase crystals to 0.03mm by the addition of 3% by weight of calcium ferrites. In this case X-ray analysis disclosed that Fe₂O₃ of calcium ferrites reacted with MgO to form MgO⋅Fe₂O₃, while microphotograph showed that CaO was occluded in periclase crystals.
The mixtures 2CaCO₃+MgO+Fe₂O₃, and CaCO₃+MgO+Fe₂O₃ were heated at 1000°-1300°C for 5 hours. From the results of X-ray analysis it has been found that the compound 2CaO⋅MgO⋅Fe₂O₃, reported by Hansen, is the mixture of CaO⋅Fe₂O₃, 2CaO⋅Fe₂O₃, and MgO⋅Fe₂O₃. Also the authors consider that CaO⋅MgO⋅Fe₂O₃ does not exist.

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From the ceramic point of view the systems Al₂O₃-ZrO₂ and Na₂O-ZrO₂ were studied. The results show that in the system Al₂O₃-ZrO₂ there exists no compound as well as solid solution, and that a eutectic point is 1890°±5°C at the composition 45% Al₂O₃, 55% ZrO₂.
The rate of the growth of Al₂O₃ crystals is the highest at 80% Al₂O₃⋅20% ZrO₃, and in this case, the transformation of ZrO₂ from high to low temperature modification is kept in check most efficiently.
In the system Na₂O-ZrO₂ there is a compound Na₂O⋅ZrO₂, and its temperature of formation is lower than the decomposition temperature of Na₂CO₃.
The rate of reaction is expressed by
{1-(1-α)^1/3}²=-0.3715+0.0023t
in which α is the rate of formation, and t is time. This compound melts incongluently at about 1180°C in which the quantity decomposed may be expressed by a logarithmic function of time.
In Na₂O-ZrO₂ system the vapour pressure of Na₂O which does not take part of the formation of compound is so large that it makes impossible to draw a melting curve.

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The tests of capillary water absorption and of the strength of the mortar of portland cement blended with (1) 20-70% of fly ash, and with (2) 20-50% of siliceous earth mined, respectively, from Yorii and Beppu districts, were carried out.
The fly ash from a coal power station was used partly as it was, and partly after grinding in laboratory.
The siliceous earths, sun dried, or dried at 110°C, were ground to a finer size than portland cement, and a part of which was calcined at 750°-840°C.
All these materials, after passing through the respective pretreatments were subjected to the tests.
The blending with fly ash gave a by far larger absorption than pure portland cement, partly because of the same mix-proportion by volume used for preparing mortar regardless of the substitution ratio, which made W/C by weight of blended cements larger.
The siliceous earths, both Yorii and Beppu, showed by far smaller absorption than pure cement at the age of 4 and 5 weeks. The effect of calcination on the reduction of the absorption of blended cement was obvious in Yorii brand, while it is not clear in Beppu brand. When the blending with siliceous earth decreased the absorption of cement the ratio of absorption to evaporation (A/E) decreased with decreasing absorption, indicating that the smaller absorption does not run parallel with smaller evaporation. In other words it may be concluded that a blended portland cement will tend to dry when exposed to air. It may be said that the cements blended with Yorii or Beppu earth are suitable to use in wet surroundings.
Bending strength of Yorii-earth mortar after 3 weeks was nearly the same with, or larger than that of pure cement, but its compressive strength showed less development.
Calcination of Yorii earth made the strength larger. The strength of the simply dried Beppu earth at the age of 5 or 6 weeks was larger than that of pure cement. Calcination showed no good effect on the strength in the case of blending with Beppu earth.

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