ハロイサイトの熱的特性,特に示差走査熱量分析(D.S.C.)による脱水エネルギーについて

Abstract

Halloysite (10 A), one species of kaolin minerals, changes to metahalloysite by heating at 30-120°C with the loss of water and also changes to metakaolin by heating at 350-550°C with the loss of water or hydroxyl ion. Halloysite shows two different shapes under the electron microscope, such as tubular and spherical, and is formed by two different geological conditions, by hydrothermal reaction and weathering reaction. The differences of thermal properties on halloysites of different shapes and different modes of occurrence are investigated by means of thermogravimetry and differential scanning calorimetry. And dehydration energies of the first and the second stages are measured as cal/gram for the following five halloysite specimens. Two tubular materials from Tawara, Naegi, Gifu Prefecture and Mikuni, Kato-gun, Hyogo are tested, the former one is formed by hydrothermal reaction and the latter one is formed by weathering reaction. The other two materials of spherical shape from Ookuchi mine, Kagoshima Prefecture and from ma mine, Nagano Prefecture are also tested, the former one is formed by hydrothermal reaction and the latter one is formed by weathering reaction. The purified four materials are measured by the same methods, and the first stage dehydration energies are nearly the same value for the four specimens and the values are nearly equal to that of the latent heat of water evaporation. The values of the second stage dehydration energy for the four materials are different and the materials formed by hydrothermal reaction have higher value than that of the materials formed by weathering reaction in the both crystal forms. And the spherical materials have higher values than of tubular shape ones. These differences caused by their crystallinity, shapes of crystal, modes of occurrences, etc. Halloysite material with high grade of crystallinity occurred from the Dragon mine, Utah, U.S.A.. It is also tested by the same methods for the dehydration energies in the first stage and the second stage; both the values are higher than that of the four materials above mentioned.