常圧塩類水溶液中におけるα型半水セッコウの生成におよぼす塩類の作用

抄録

The effects of salts, such as NaCl, NH₄C1, NaNO₃, NH₄NO₃ and CH₃COONH₄ were investigated experimentally on the formation of α-hemihyrates when heated in these aqueous salts solution with concentrations ranging from 8 to 15 wt % at the boiling point under the atmospheric pressure.
The formation time of α-hemihydrates, elevation of the boiling point and change of the transformation temperature were measured in these conditions, respectively.
The transformation temperature was determined as an intersection of the solubility curve of gypsum and that of α-hemihydrate.
The results obtained are summarised as follows :
1) Decrease of the transformation temperature in the aqueous salts solution affects predominantly the formation of α-hemihydrate.
Namely, the more the decrease of the temperature is, the more readily α-hemihydrate is formed. On the contrary, the effect of the elevation of the boiling point is small compared with the abovementioned.
2) Assuming that the solubility at the boiling point of gypsum is Ds and that of a-hemihydrate is as, the difference of both solubilities, Ds-as, is inversely correlated with the readiness of the formation of α-hemihydrates when heated at the boiling point.
This gives a criterion to choose a suitable salt which accelerates the formation of a-hemihydrates under the atmospheric pressure.