電融マグネシアの水和

オートクレーブ・テストによる水和量のバラツキについて

抄録

In recent years, considerable interest has developed in the conversion of high-purity magnesium oxide of sea-water origin into dense crystalline periclase. This periclase has found increasing use in such applications as refractory materials, electrical insulation in heaters and electronics parts.
At the present time, most high-purity periclase is manufactured either by the fusion of magnesia in an electric arc or by heating the magnesia in a furnace at 1800°C or higher.
Periclase, however, has the nature susceptible to hydration and this deteriorates the quality of periclase.
The initial objective of this study was to evaluate the hydration resistance of fused magnesia by autoclaving at 9 atm for 3 hr. The samples used were grains (125-250μ) obtained by grinding and screening, after crushing the electrically fused magnesia blocks.
But the autoclave tests revealed that there was a fairly great dispersion in the weight increases by hydration among the samples of all the same kind, even in the very same batch.
That is to say, the experimental results showed that the reproducibility of the weight increases by autoclaving on fused magnesia was very poor.
Accordingly, an investigation was conducted of certain factors which influence this dispersion of values of hydration by autoclave test on fused magnesia. In the process of series of test, these facts were observed that a disturbance of water and steam occurred during operation in an autoclave, the degree of the disturbance was different according to every location in the space inside the autoclave, and the reproducibility of disturbance was also very poor.
By this disturbance, in the tests of open method using crucibles as sample vessels, some samples were dipped in water and some got wet during operation and the samples dipped or wet with water resulted in low values of the weight increase by hydration, compared with ones which were not dipped or wet, thus being hydrated rather in dry conditions.
On the contrary, in the static hydration tests such as the glass-tube tests or the dipping tests in water, the dispersion of the weight increases by hydration was very little, as was to be expected.
But the hydration test by saturated vapor at room temperature revealed the abnormally great dispersion of the weight increases, contrary to our expectation. It may probably be due to the condensation of water in some samples, because of the fluctuation of room temperature and this fact also suggests the difference of the effects to hydration on fused magnesia between water and steam.
From these experimental results, the main factor that influences the dispersion of values of hydration by autoclave test on fused magnesia, is probably the complex disturbance of water and steam occurred inside the autoclave during operation.