The Thermal Behavior of Surface Hydroxyl Groups of Silica and Alumina Gels Studied by IR-TG Simultaneous Measurement

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  • IR-TG同時測定によるシリカおよびアルミナゲル表面水酸基の熱的振舞
  • IR TG ドウジ ソクテイ ニヨル シリカ オヨビ アルミナ ゲル ヒョウメ

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An instrument for the simultaneous measurement of thermogravimetry and IR spectroscopy of porous adsorbents was developed in this laboratory, in order to obtain the accurate and real-time information on the thermal change of the surface and pore structures of these materials. This apparatus consists of a vacuum electrobalance of Cahn RG having the sensitivity of 2 × 10-6g and an infrared spectrophotometer of JASCO IRA-2 having the resolution of 1 cm-1 at 3000 cm-1, together with a vacuum cell being capable of heating the sample up to about 850°C in situ. This instrument was used to study the thermal behavior of the surface hydroxyl groups of silica and alumina gels. These materials were synthesized by the hydrolysis of the alkoxides. These samples are transparent and have thin plate-like shapes whose transmittance are more than about 75% at 4000 cm-1. The simultaneous measurements of IR and TG were made on these samples by stepwise elevation of the heat-treatment temperatures. The results obtained were such that the curves of IR integral intensities of the OH stretching absorption bands versus the surface OH density of these materials (Figures 6 and 10) consist of roughly two straight lines having slightly different gradients. This result indicates that the free OH groups have a different oscillator strength from those of other types of OH groups.

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