Temperature changes of the template structure in MCM-41 type materials; positron annihilation studies

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• 作者：Zaleski ; Radoslaw ; Wawryszczuk ; Jan ; Boró ; wka ; Anna ; Goworek ; Jacek ; Goworek ; Tomasz
• 关键词：MCM-41 ; Template structure ; Template removal ; Positron annihilation
• 刊名：Microporous and Mesoporous Materials
• 出版年：2003
• 出版时间：August 14, 2003
• 年：2003
• 卷：62
• 期：1-2
• 页码：47-60
• 全文大小：472 K

文摘

The lifetime spectra of positrons annihilating in MCM-41 ordered silica were measured as a function of temperature. It was found that in alkyltrimethylammonium templates degradation in vacuum begins at 380–400 K, that consists in breaking the long micelle cylinders, rise of gaps between the fragments and finally pore evacuation. The latter process is not completed and particularly in C12TAB the spectrum component belonging to fragmented template preserves its high intensity up to 520 K (the highest temperature in our experiment). The pore surface area over 1000 m²/g is achieved already at temperatures about 490 K. The lifetime of the longest-lived component indicates that practically all ortho-positronium atoms leave the pores before annihilation.