For the purpose of investigating the effective way of preventing the thermal fracture of various bricks for bottom casting pit in teeming of molten steel, the equation of thermal shock resistance has been deduced from thermal stress equation, and the physical-mechanlcal properties of various bricks have been determined by testing. On the basis of the results obtained, considerations have been made concerning the effect of these properties and the size of each brick on thermal shock resistance.
Important results obtained are summarized as follows:
i) In the thermal stress equation σ=Eα/(1-μ)⋅(θ₀-Θ)⋅f, thermal shock resistance (R) are expressed in σ_max/σ′, putting σ′ as max. thermal stress in tension, f′ as factor f corresponding to σ′, σ_max as max. tensile strength of a brick.
ii) Heat-transfer coefficient from molten steel flowing at temperature θ₀ to the surface of the brick at temperature Θ being in contact with molten steel flow is very large, and therefore, thermal shock resistance is expressed by the following two equations.
In the earliest stage, when heat does'nt begin to flow within a brick:
R₂′=σ_max/E⋅(1-μ)/α⋅1/(θ₀-Θ)
In the next stage, when heat flows within a brick:
R₁′=σ_max/E⋅(1-μ)/α⋅1/(θ₀-Θ)⋅(kt^1/2/γ)^a
or R₁′=σ_max/E⋅(1-μ)/α⋅1/(θ₀-Θ)⋅(K/γh)^a′
iii) The relation between the mechanical properties and porosity may be expressed by a hyperbolic curve.
iv) The ratio of bending strength to Young's modulus, an effective factor for increasing thermal shock resistance, is larger in pyrophillite-clay brick than that in grog-clay brick. This ratio shows a trend to decrease with increasing porosity. It is presumed from the data in technical literatures that this ratio is approximately constant at high temperature below the critical temperature of pyroplastic property.
v) Based on the equation of thermal shock resistance determined in the case of runner brick, it is estimated that bending strength/Young's modulus ratio, linear thermal-expansion coefficient (α), poisson's ratio (μ) and temperature difference (θ₀-Θ) have an influence of first power. On the other hand, the thermal conductivity (K), specific heat (C_ρ), density (ρ) and wall thickness (γ) have an infiuence of 0.040 and 0.081 powers, respectively, on thermal shock resistance. In addition, considerations have been made concerning the degree of the effect of porosity, which is in functional relation to mechanical properties and thermal conductivity, on the thermal shock resistance.
vi) It is presumed that there is a limit in the improvement of thermal shock resistance by changing the properties of a fire clay brick and that most important factor for the prevention of thermal fracture is the moderate pyroplastic property.

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The mixture composed of dunite, fused corundum and sillimanite or magnesia were melted in an electric furnace under reducing condition in order to study the reactions during the melting and the change of the structure of the body.
The addition of corundum was found to promote the so called the “liberation of silica” which was due partly to the evaporation of the reduction products (Si), (SiO), and (SiC), etc., and partly to the elimination of silica as iron alloy, and thus paving the way to the increase spinel formation. On the contrary, corundum remained in the ingot practically unaffected to the reducing action.
By the simultaneous addition of corundum and magnesia a compact structure composed of periclase, forsterite and spinet were formed. And it was found that the proportion of the quantity of the crystals as well as their grain size may be controlled through the change of batch composition. Furthermore, the mixed crystals of periclase-forsteritespinel were obtained.
The addition of the powder of pig iron promoted still more the liberation of silica, and the crystallization of spinel became so remarkable that, under some suitable conditions, the synthesis of pure spinel by electrocast seemed to be possible.

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The previous work (J. Ceram. Assoc., Japan, 68 [778] 237 1960) was extended to the investigation of the reaction during the melting and the change of the structure of the electro-molten dunite when magnesia, dolomite and lime were added to the batch.
Magesia crystallized into periclase, the qantity and grain size of which were growing with increasing amount of MgO making the body more compact and stronger. In this case, however, a considerable amount of magnesia frew off during the melting.
The addition of lime showed the trend of separating periclase.
With less than 30% lime a low melting CaO-MgO-SiO₂ compound was formed, which was unstable at high temperatures. It is, therefore, possible to control the condition of melting-by selecting a suitable reducing agent and the time of melting-for the purpose of eliminating the unstable compounds by the decomposition and vaporization, leaving the body composed of lime silicate, being stable at high temperatures.
With more than 30% lime periclase and 2CaO⋅SiO₂ were produced, and showed dusting.
Using the radio isotope ⁴⁵Ca* it was confirmed that Ca was existing in the glass phase between the crystals.

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In order to investigate the hydration product of blast furnace slag under the coexistence of stimulating agents such as Ca(OH)₂, Ca(OH)₂ and CaSO₄, Ca(OH)₂ and CaSO₃⋅1/2H₂O the slag and synthetic gehlenite were subjected to hydration during a month, and the reaction products appeared were studied using several methods.
(A) Both in blast furnace slag and gehlenite the hydration products, 2CaO⋅SiO₂⋅H₂O, 3CaO⋅Al₂O₃ 8-12H₂O, 4CaO⋅Al₂O₃⋅13H₂O, 3CaO⋅Al₂O₃⋅CaSO₃⋅7H₂O, etc., the same compounds in the hydration of portland cement, were confirmed by X-ray analysis.
(B) Using quantitative X-ray analysis and the measurement of ignition loss the rate of chemical reaction was estimated. It was found that the hydration of slag came to only 20% after 28 days, while gehlenite was so active that 50-60% hydration was observed after 3 hours.
(C) The differential thermal analysis of hydrated gehlenite showed the increase of the amount of heat absorption at 100-200°C along with the progress of hydration, which indicates the formation of the hydrates losing water at lower temperatures.
(D) Slag and gehlenite were remelted and quenched to form disks of 3/4″ in diameter. The disks were polished to mirror surface in order to observe the change of appearance during the hydration under electron microscope. In the initial stage the hydration products crystallized out leaving the mirror surface unchanged. After 3 days in slag, and 5 hours in gehlenite the film of the hydration products separated out on the surface with the appearance of silk crape or fish scale. The authors consider that these film takes part in the increase of adhesive strength.
(E) Suspension of slag powder in solution containing stimulating agents showed the increase with time of sedimentation volume, the trend becomming more remarkable with increasing basicity. Based on this fact the authors have worked out a new method of estimating the hydrauric property of blast furnace slag.

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