The sintering process of a porcelain body has been studied from a view point of rate-process by following the change of α difined as under:
α=ρ_a-ρ₀/ρ_t-ρ₀
where ρ_a: apparent density of sintered body
ρ₀: apparent density before sintering
ρ_t: true density after sintering
It has been found that the following velocity equation is generally valid.
dα/dt=K(1-α)ⁿ
or by putting p=100α,
dp/dt=K(T)(100-p/100)^n(T)
By determining graphically the following two values ψ and φ, the order of the reaction (n) and the reaction constant (K) of the sintering process can be expressed as follows:
n=2/ψ-φ
K=exp{n(2-φ)}=exp{2(2-φ)/ψ-φ}
where
φ=log(100-p) when logdp/dt=0 or dp/dt=1
and
ψ=log(100-p) when logdp/dt=2 or dp/dt=100
To the contrary of the conclusion given by many other researchers that n is a constant, we found by sintering samples at several constant temperatures that n as well as φ are dependent on temperature as follows:
n(T)=A/T-B=6.35/T⋅10⁴-36
φ(T)=C/T-D=0.921/T⋅10⁴-4.62
therefore
logK(T)=(A/T-B)(2+D-C/T)=-5.85/T²⋅10⁸+75.2/T⋅10⁴-238
We found further that the sintering proceeded in forming a zonal structure. The growth of vitrified outer layer with the rise of sintering temperature or the increase of sintering time was traced by the change in its thickness or the area of inner part which remained porous and therefore easily stained with graphite or polishing powder such as chrome oxide, but such an observation satisfied not for the explanation of the process.
The development of hardness within the samples was successfully measured on its section by means of the Rockwell Tester “Superficial” 15 N and 15 T. The relation between the hardness in inner part (H_s) and the mean apparent density (ρ_a) is given by:
ρ_a=8.6×10^-3H_s+1.58

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The pH of Japanese ceramic raw materials suspended in H₂O (10 gm in 30cc H₂O) were determined with calibrated antimony electrode. Relations between the pH and the viscosity, plasticity, contents of organic matters in clays, etc. were discussed. Effect of time of ageing of slips upon the pH and the difference of the pH between suspensions and clear parts of suspensions (separated by centrifuging) were also determined.
The conclusions are as follows: (1) The pH, determined after 5-hours-standing, is (a) 4.2 to 6.4 in kaolins, (b) 4.5 to 6.6 in Kibushi-clays (plastic, humus-bearing clays), (c) 5.2 to 6.2 in Gaerome-clays, (d) 4.9 to 6.4 in stoneware clays, (e) 1.1 to 5.8 in sericites (high acidity is because of the presence of much sulphides), (f) 5.3 to 6.2 in crushed and ball-milled pottery stones, (g) 5.0 to 5.3 in pyrophyllites, (h) 7.4 to 10.0 in bentonites, and other raw materials 5.0 to 6.0 (2) Changes in the pH of slip by ageing are different in clay sorts, but the pH of relatively pure clay is generally become constant after two-days-standing. (3) From the pH of clay suspension, no relations are found between the pH and the viscosity, plasticity, and other characteristics of raw clay. (4) The change of viscosity and plasticity of clay by ageing is independent with the pH-change. (5) Acid-clay show high acidity in suspension than the clear part of suspension, and alkali-clay is vice versa. (6) Clays which show little pH difference between suspension and clear part have high dispersity. (7) Humus content and the pH has no relation.

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Glasses containing high percentage of lead oxide show oxidizing effect when they are dissolved in acid solution. This oxidizing power was measured precisely by means of a modified thiosulfate method, for glasses containing various amounts of PbO. The value for the oxidizing power from 0.06 to 0.01% as PbO₂ was found for glasses in the system PbO-SiO₂-B₂O₃ containing 90, 87 or 84% PbO. While no oxidizing effect was observed in those glasses containing less than 80% PbO. As the value of the oxidizing power depends on the factors governing the condition under which these glasses were melted, it was measured quantitatively by changing four inportant factors among them.
This oxidizing power of high-lead glasses seems to be caused by the high valency lead ion introduced into glass from Pb₃O₄ which was used as the raw material. The results of the experiments concerning the re-melting of the glass in oxygen atmosphere show that it may be supposed that the quantity of PbO₂ should converge to an equilibrium value, and hence a part of it could exist stably in glass.

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