We calcined six kinds of limestone from various localities up to 900, 1000, 1100, 1200, 1300 and 1400°C with or without NaCl, and observed the growth of CaO crystals in their thin sections. The CaO crystals occurring in the specimens calcined with NaCl are, as usual, better grown than those without NaCl, and it is more evident at lower temperature calcination. In the case of higher temperature calcination, the formers are hardly over-burnt.
With regard to the limestones, those of cryptcrystalline make finer CaO crystals. Especially it is evident at higher temperature calcination. This may show to have larger range for optimum calcination, that is easy to work with.

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In order to find out the best firing condition of Barium Titanate ceramics for use as electro-acoustic transducer, we measured at first the thermal expansion and shrinkage characteristics of Barium Titanate at high temperature. Our method of measurement was to observe the variation in length of the test piece continuously as a function of both temperature and time, over the temperature range from room temperature to 1400°C, by means of telescope. The results obtained are summarized as follows.
(1) When the temperature was raised from room temperature to 1400°C at the constant rate of 275°C/hr., we found there was an abnormal expansion at 1000°C amounting maximal to 7.5%. This phenomenon seems to be caused by the decomposition of Barium Carbonate.
(2) Considering that the sintering phenomenon is the result of the completion of diffusion reaction among particles of solids, we calculated inversely, the reacted quantity of Barium Titanate by the rate of shrinkage and found that Jander's diffusion formula can be applied here. Applying this result, the activation energy of reaction was calculated to be 98kcal/mol.
(3) The calculated results with respect to the shrinkage characteristics of Barium Titanate in the firing process nearly coincided with experimental results.
(4) By the above mentioned results, we found that when Barium Titanate ceramics are to be fired, sufficient attention must be paid not only for the highest firing temperature and it's duration but also for the raising rate of temperature, especially over the temperature range of abnormal expansion and rapid shrinkage.
On applying the obtained results, we made next some further experiments with regard to the difference between the calcined and not calcined material in electrical and acoustic properties of Barium Titanate. We found by the experimental results that the materials which were not calcined had approximately the same quality as those which were calcined, though the former showed slightly higher value than the latter with respect to frequency constant of radial mode vibration.

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UO₂, ThO₂の添加がZrO₂の性質におよぼす影響について, 熱膨脹により判定すると共に, ガス炉で焼結したUO₂-ZrO₂系の混合物の二, 三の性質を測定し, 研究した. その結果の要点は下記のようであった.
(1) UO₂をZrO₂に添加すると, ZrO₂の単斜晶系→←正方晶系の結晶転移に基づく異常膨脹収縮が減少し, 約30%以上UO₂を含有させると安定化を達成することが出来る.
(2) 添加するUO₂の量が増加するにつれて正方晶系のZrO₂固溶体が生じ, さらにU0₂量が増加すると等軸晶系のZrO₂固溶体が生成して行くものと考えられる.
(3) 曲ゲ強サはUO₂-ZrO₂系の場合, UO₂添加量の増大によって大きくなるが, CaO 5%の安定化ジルコニアより小さい. 弾性率はUO₂の添加量と大体直線的に増大する.
(4) ThO₂の添加はZrO₂の安定化に良効果を与えなかった.

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The mechanism of chemical erosion of cement materials against the alumina brick has been studied. The resistance of the brick against the erosion is very strong, but during long using time, the brick is slowly eroded or permeated by the molten cement, and the materials produced after erosion consist of the low melting substances, namely gehlenite and glass. The porosity of the brick has an influence to the permeation of molten materials against the brick, and depends on the amount of diaspore that is mixed for making the brick.
In the brick that contains much diaspore, the resistance against the erosion and the permeation is weaker than the brick that contains less diaspore.

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The authors have studied on the non-slaking lime refractories and obtained the following summaries.
(a) Non slaking lime clinker can be prepared by sintering at 1600°C for 20-30 min. under addition of a few percentage of titanium slag.
(b) At this case precipitated calcium carbonate, lime stone and dolomite, passed through 200 mesh sieve about the latter two, are available as raw materials.
(c) Lime refractories have an excellent resistance against chemical corrosion at high temperature and especially are very good for blast furnace slag, molten phosphate fertilizers and portland cement.
(d) Coefficient of thermal expansion of lime clinker increases linearly to temperature rise up to 1000°C, and shows somewhat large values, i.e., 1.2-1.4%.
(e) By adding titanium slag the lime clinker is sufficiently able to use for stamp materials of basic furnaces and for making other special crucibles as well as bricks.

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The relation between sintering mechanism and electrical conductivity of zinc oxide, a typical representative of oxide semi-conductor, was studied from a view point of rate-process. On the degree of sintering P and velocity equation of sintering, expressions (1) and (2) were examined.
P=ρ_a-ρ₀/ρ_t-ρ₀…(1)
dP/dt=K(100-P/100)ⁿ…(2)
Where symbols denote:-
ρ_a=bulk densities of specimens after sintering.
ρ₀=bulk densities of specimens before sintering
ρ_t=true density of specimens
K=velocity constant
n=order of reaction
t=duration of sintering
Now it was established that the expressions (6) and (7) are valid between n and K as functions of φ and ψ which are indentically equal to values of log (100-P) when the reaction velocity (dP/dt) becomes unity or 100, respectively. (Fig. 4)
n=2/(ψ-φ)…(6)
log K=n(2-φ)…(7)
For simple one component system such as metallic oxides, to which zinc oxide used in the experiment also belongs, or metal and glass powders., order the of reaction n will be constant over the range of sintering temperature. In the case of zinc oxide, n was found to be 5.7 in a range of 800-1250°C, while the value of φ was expressed as a certain function of temperature. In two or more components system, n is not a constant but a function of temperature. For instance, it was found with powdered clayey raw material for electric insulating porcelain that value of n decreases lineally with temperature.
As expressed in equation (8), the velocity constant K, has a physical meaning of reciprocal of n′th power of q₀, “degree of not-sintering” which is equal to the percentage of remainder of sintering.
K=(q₀)^-n
where, q₀=(100-P₀)/100…(8)
Result of experiments with zinc oxide show their activation Energy E to be 74.6kcal/mol. in case of firing at 800-1250°C in common air atomosphere and its sintering process can be expressed as follows
dP/dt=K(100-P/100)^{5, 7}
log₁₀K=14.9-1.6×10⁴/T}………………………………(9)
The electrical resistivity of zinc oxide is predominantly determined by diffusion of zinc atom librated by dissociation of ZnO in oxide lattice. Electrical resistivity, ρ decreases with increase of sintering time as expressed by the equation, ρ=At^-B, obtained experimentally, where A and B are constants depending on sintering temperature. But the resistivity attains finally at a saturation value after some time of firing, necessary duration of which is also some function of temperature. (Fig. 7) The logarithm of saturation value is found to be a linear function of the ratio, (γ) of sintering and melting temperature as shown in equation (11).
log ρ_sat.=15.4-20.3γ……………………………………(11)
Then the relation between velocity constant K and the saturated value of electrical conductivity, σ_sat. is expressed as
σ_sat.=4.47×10^-6[K]^1.15…………………………………(12)
In this equation, it is seen that σ_sat. is nearly proportional to K. This means that amounts of intersticial zinc atom diffused in oxide

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