The effect of an increased pyrophyllite component on the bulk specific gravity, compressive strength, linear shrinkage and thermal conductivity was mainly investigated for insulating materials of the system expanded vermiculite-bond clay. The vermiculite from Fukushima Pref. was expanded at about 1050°C, and was used as an aggregate. The bond clays used with the aggregate were Mitsuishi-pyrophyllite from Okayama Pref., kibushi-clay from Aichi Pref., bentonite from Gumma Pref. and acid clay from Niigata Pref. In hand mixing, the bond clays and vermiculite were mixed dry until the resultant mass had a uniform color; after the addition of water to the mass, a further mixing was made for about 5 min. until a uniform consistency was obtained; the mixture was shaped, dried at 110°C, and then fired at temperatures of 800, 1000 and 1100°C for 4 hours.
The results obtained are as follows: (a) Short mixing time is preferable for the vermiculite-clay specimens. Long mixing time and intensive mixing action have the tendency to crush the vermiculite granules and to cause the increase in both bulk specific gravity and linear shrinkage. (b) The bulk specific gravity is little different between both groups of specimens predominantly including pyrophyllite and predominantly including plastic clays as bonding materials. (c) The compressive strength is largely increased by the firing operation at temperatures ranging from 800 to 1100°C for the group of specimens predominantly including pyrophyllite. (d) The linear shrinkage is decreased with increasing the pyrophyllite content of bonding material. (e) The thermal conductivity is increased with temperature for the specimens investigated here.
From the data presented, the following ranges of batch compositions are recommended for general insulating purposes at temperatures near 1000°C: 75-80 parts of Mitsuishipyrophyllite, 10 parts of kibushi-clay, 10-15 parts of expanded vermiculite and 30-40 parts of water by weight. The characteristics of the specimens obtained by firing the batches of the above range of compositions at a temperature of about 1000°C were as follows: Thermal conductivity (kcal/m, hr, °C) at the mean temperature of 350°C, 0.121-0.146; bulk specific gravity, 0.71-0.97; compressive strength (kg/cm²), 14.9-18.4; linear shrinkage (%), 0.80-0.86.

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Magnesia bricks were fired at 1600° to 1700°C and changes in their properties, especially the volume contraction due to sintering and the grain growth of periclase, were examined. Effects of temperature and firing time on the rate of sintering contraction were investigated.
The volume change of refractories in reheating has been examined usually by the repeat contraction measurements. In this investigation, the reheat linear change of magnesia bricks was considered as a kind of rate process including sintering reaction.
The reheat linear changes for two kinds of burnt magnesia bricks from sea-water magnesia were measured at 1600° to 1700°C, and the correlation among reheat change, temperature and reheating time was analysed. It was found that the repeat contraction (S) will be approximately expressed by the following equation including reheating temperature (T), time (t) and activation energy for sintering contraction (E_s);
S=k_s√texp(-E_s/RT)
This correlation may be applied to the estimation of brick contraction in furnace linings during service and also to adjust the firing condition for making bricks.
Reheating promotes the grain growth of periclase in magnesia bricks approximately proportionally to reheating temperatures, where silicates will retard the grain growth of periclase.
The standardized methods for reheat change measurements prevailing at present will not be always fit to bricks of these grades. The authors propose an example of optimum condition for reheat change test: 10hrs reheating at 1700°C.

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To obtain excellent glass ceramics, having either highly heat resisting properties or strong mechanical strength, glasses of the system CaO⋅Al₂O₃⋅2SiO₂(anorthite)-2MgO⋅2Al₂O₃⋅5SiO₂(cordierite)-CaO⋅TiO₂⋅SiO₂-(sphene), the composition of which is shown in Table 1, were studied. By X-ray analysis it was observed that anorthite crystallized more easily than cordierite or sphere during the heat treatment from 850° to 1300°C (Fig. 1). These crystallized samples were, however, brittle because of the rapid crystallization and of the inadequate crystal growth of anorthite, no matter how slowly the temperature of heat treatment was raised. To improve it a part of SiO₂ was replaced by B₂O₃ in some of them (Table 2).
The effects of B₂O₃ addition were as follows.
1) It improved the bending strength, especially by the successive heat treatment from about 750°C (Fig. 10).
2) It facilitated the crystallization of rutile or anatase beside anorthite even at the lower temperature (Fig. 7, 8, 9). This co-crystallization prevents the crystal growth of anorthite (Electronmicrophotograph 4-8).
3) The characteristic domain structures appeared in this glass base at about 800°C (Electronmicrophotograph 4). The crystal seemed to grow only within these domains (Electronmicrophotograph 5, 6). Therefore the size of these crystals is limitted by the size of these domains.
4) Crystals of another kind of lattice structure, anatase and hexagonal anorthite in place of rutile and triclinic anorthite respectively, were observable when B₂O₃ was added.
Numerous small cracks, corresponding to the Griffith flaw on the surface, were found to grow inward and the gross crystals seemed to grow along these cracks (Photo. 1-3). These cracks lower the bending strength. The successive heat treatments were effective to decrease the formation of these cracks.
Thus, with the addition of B₂O₃ and with appropriate heat treatment, it was possible to obtain highly strengthened glass ceramics, having the bending strength of 42kg/mm² on average.

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