市販磁器の透光度と微構造について

抄録

As samples, we used three kinds of commercial porcelain dinner-ware (A, B and C), an experimental porcelain body (A′), a commercial bone china, and a synthetic magnesium silicate-ware (commercial name: Magna China). To measure translucency, sections of each sample, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2mm thick, were placed between thin optical glass plates with a slight coating of cedar wood oil. Translucency of these specimens within the range of light wave length of 400 to 700 mμ was measured by using a spectrophotometer.
The translucency of the bone china and the Magna China bodies was found to be good in the range of both short and long wave lengths. The translucency in the long wave range of the dinner-ware porcelain bodies was as good as, or better than, that of the bone china and the Magna China bodies, but the translucency in the short wave range of these porcelain bodies decreased and became poorer than that of the bone china or the Magna china bodies.
Trilinear coordinates x and y of CIE chromaticity diagram were calculated from the measured transmission spectra. The colorimetric purity of the Magna China and the bone china bodies was higher than that of the dinner-ware porcelain bodies. Among the last, the sequence of purity was A, A′, C and B. The dominant wave length of each sample was around 580mμ. The relationship between the logarithm of translucency at 580mμ and the thickness of specimen was expressed by the formula log (I/I₀)=a-kt, where k is the extinction coefficient, t the thickness of specimen and a a term relating to surface reflection. The values of k of the bone china and the Magna China bodies were smaller than those of the dinner-ware porcelain bodies, and among the latter the value of k increased in a sequence of A′, A, C and B. Angular distribution of scattered light from sample bodies showed that the light scattering of the Magna China body was more than that of the dinner-ware porcelain bodies.
The microstructures of sample bodies were examined under a petrographic microscope and by X-ray diffractometer. The bone china body had a compact texture composed mainly of very minute crystals of β-calcium orthophosphate with small amounts of anorthite. High refractive indices and the minute size of β-calcium orthophosphate may be the main cause of the good surface reflectivity and milk-white appearance of bone china.
The Magna China body was composed of a large amount of magnesium metasilicate, a considerable amount of free silica particles and a small amount of glass. The free silica particles were coarse, and more than half of the original quartz had been converted to cristobalite and tridymite. The magnesium metasilicate phase was composed of minute crystals of clinoenstatite and protoenstatite. The good surface reflectivity and milk-white appearance of the Magna China body may be caused by high refractive indices and the minute size of magnesium nietasilicate, as same as with the bone china.
Among the three dinner-ware porcelain bodies A, B and C, A had the largest amount of free quartz and the smallest amount of mullite crystals, together with a small amount of glass. A′ was prepared by adding a small amount of talc to A composition. The contents of quartz and mullite in the porcelain body decreased considerably and the glass content increased when talc was added, which seems to answer for the increased translucency of A′ as compared with A.
Quartz particles of B were coarser than those of A and C. The quartz content of B was the smallest and the mullite content was the largest among the three porcelain bodies. The fact that B has the largest content of mullite is responsible for having the least translucency, although B contained nearly the same amount of glass as A.
The quartz particles in C were about the same in size as those in A. The quartz