Dehydration Phenomena of Some Crystalline Hydrates, Mainly of Borax

Abstract

Department ofApplied Chemistry, Faculty of Engineering, Kyushu University Hakozaki, Fukuoka-shi, Japan Dehydration phenomena observed in four crystalline hydrates were investigated by means of polarization microscope using thin single crystal specimens. Dehydration were observed from CuSO, 5 H₂O to tri-hydrate, similarly, Na₂CO₃ 10 H₂O ---+- hepta-hydrate, H₂C_2CO^2-2 H₂O anhydrate, and Na₂13407 10 H₂0--di-hydrate. In the former three cases, dehydration extended from a few original points isotropically to the single crystal plates, while an apparent anisotropy was observed in the last case.
Further measurement of the anisotropy in the dehydration of Na₂1340710 H₂O, using specimens having various orientations, revealed the anisotropy to be most marked in the (100) plane, and the dehydration to proceed preferentially along 001 direction. This direction coincides with that of {Na(H₂0)4} chains in the crystal structure of Na₂13, 07.10 H₂O, and, therefore, it is considered that the existence of such a chain structure may bring about the anisotropy in its dehydration.