Change of Infrared Absorption Spectra in the Range 3660-3740cm<sup>-1</sup> by the Dehydration and Rehydration of Clay Minerals

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  • KATO Chuzo
    School of Science and Technology, Department of Applied Chemistry, Waseda University

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  • 粘土鉱物の脱水と再水和による赤外線吸収スペクトルの変化-特に3660-3740cm<sup>-1</sup>の吸収について
  • ネンド コウブツ ノ ダッスイ ト サイスイワ ニ ヨル セキガイセン キュウシュウ スペクトル ノ ヘンカ トクニ 3660 3740cm-1 ノ キュウシュウ ニ ツイテ

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Abstract

The change of infrared absorption band, especially in the range of 3740-3660cm-1, of clay minerals (pyrophyllite, montmorillonite, kaolinite, halloysite, illite and muscovite) by dehydration and rehydration were measured. Clay minerals were rehydrated by keeping in air or in water after the removal of lattice OH at 500°-800°C. The temperatures of dehydration of all rehydrated samples were about 550°C, being 30°-200°C lower than the dehydration temperatures of original clay minerals.<br>The author discussed about the origin of the drop of dehydration temperatures of rehydrated samples, the bond state of rehydrated water, and the assignment of two separated spectra at 3740-3660cm-1, as follows:<br>(1) The absorption band of all specimens due to OH in 3740-3660cm-1 separated into two spectra by dehydration and rehydration.<br>(2) The spectra at 3740-3720cm-1 (2.67-2.69μ) disappeared when the lattice OH was dehydrated by heating at 550°-800°C, but appeared again by hydrothermal treatment (300°C, 85atm., 1-10hrs.). It seems that this absorption comes from lattice OH.<br>(3) The absorption at 3680-3660cm-1 (2.72-2.73μ) did not change much by heat treatment up to 700°C. The higher the heating temperature the lower became the intensity of the spectra, but did not disappear easily. The spectra, however, disappear or almost faded away by the treatment which makes the surface area of the crystals to decrease by calcination at the temperatures higher than 800°C. The author posturates that the spectra originate from OH of water bonding directly to the crystal surface or the edges by hydrogen bond.<br>(4) The water of the rehydration dehydrated at the temperatures lower than dehydration temperature of lattice OH did not entered as lattice OH in octahedral layer, but bonded directly to the crystal surface or the edges by hydrogen bond. However, the water of rehydration can enter as lattice OH in octahedral layer by stronger rehydration method, for example, by the hydrothermal treatment (300°C, 85atms., 1-10hrs.).

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