長石-石英系素地薄片中の気泡と黄色斑点

陶磁器素地の微構造に関する研究 (第8報)

抄録

In order to study the origin of yellow spots usually found in thin section of fired bodies, size and amount of pores, uniform glassy like spheres and the yellow spots developed in the bodies were microscopically observed. The specimens set for the experiment consisted of 97% feldspar with 3% quartz fired at 1150-1450°C. Regular relationships were found between the size and firing conditions, but not between the amount and firing conditions (Figs. 1-6).
Distribution of the yellow spots and pores are microscopically compared and found that they show a marked similarity in the followings; (1) the lowest temperature at which they are detected in the thin section, (2) the aspect of the variation of their size and shape with firing schedule, and characteristics of their distribution, (3) irregularity between their amounts and firing conditions.
Furthermore, (4) in the case of total amounts of the pores and yellow spots, regular relationship between their amounts and firing condition can be found (Figs. 7, 8).
(5) Volume changes of the yellow spots with rising temperature and holding time are of the same order with that of pores which contain water vapour, air and other gases.
(6) Size of small yellowish brown particles included in the yellow spots is not changed with firing conditions, but rather with grinding conditions of the thin section. Moreover, their compactness to fill up the yellow spots is highly irregular. Appearance of the small yellowish brown particles closely resembles with that of the abrasive powders used in grinding the thin sections (Photo 4).
(7) Yellow spots can not be found in the powder of the specimens observed with oil immersion method.
(8) Content of Fe₂O₃ in the raw materials used for this experiments, is too low to produce such a number of dark yellowish spots. There are no conditions to produce carbon deposits on the specimens during firing schedule.
From the results mentioned above, following is to be concluded: The yellow spots are not actually present in the fired bodies, but derived from a part of the pores, which are filled with abrasive matters such as carborundum or emery powders, used during grinding the thin section.
In order to corroborate these conclusions, yellow spots are artificially produced in optical glass, FaK, which is ground into a thin section. Photo 5 shows the very one.
Besides the yellow spots which forms the chief subject of this paper, we rarely meet with similar ones, such as yellowish brown glasses, in the fired bodies. The writer also briely refers to them.