Berrier Elise, Zoller Carine, Beclin Franck, Turrell Sylvia, Bouazaoui Mohamed, Capoen Bruno
Laboratoire PhLAM (CNRS, UMR 8523), Université des Sciences et Technologies de Lille, Villeneuve d'Ascq F-59655, France.
J Phys Chem B. 2005 Dec 8;109(48):22799-807. doi: 10.1021/jp053089+.
Silica xerogels were synthesized and annealed at 1000 degrees C for different durations to yield stable silica materials. The samples were prepared through base-catalyzed hydrolysis and condensation of tetramethyl orthosilicate in methanol. After aging and drying steps, clear and solid xerogels exhibiting a narrow pore size distribution were achieved. The annealing treatment of these xerogels was performed at 1000 degrees C and proved in the present study to lead to a monolithic glass when a progressive heat-treatment procedure was employed to attain 1000 degrees C. In addition to the expected glass, silica foams and ordered phases were observed when the samples were instantaneously heat-treated at 1000 degrees C. Raman spectra of the foamed materials exhibit the classical features of amorphous silica, whereas transmission electronic microscopy pictures reveal the presence of crystallized domains within the vitreous matrix. These crystallites are prone to nucleation and growth processes, which jeopardize the believed stability of the silica foam. The assessment of the hydroxyl content by IR spectroscopy reveals the role played by the latter polycondensation of silanols. The occurrence of foaming process was thus found to result from two competitive phenomena occurring at 1000 degrees C: evacuation of water-related species and viscous sintering.
合成了二氧化硅干凝胶，并在1000℃下进行不同时长的退火处理，以制备稳定的二氧化硅材料。样品通过原硅酸四甲酯在甲醇中的碱催化水解和缩合反应制备。经过老化和干燥步骤后，得到了孔径分布狭窄的透明固体干凝胶。这些干凝胶在1000℃下进行退火处理，本研究证明，当采用逐步热处理程序达到1000℃时，会形成整体玻璃。当样品在1000℃下进行瞬间热处理时，除了预期的玻璃外，还观察到了二氧化硅泡沫和有序相。泡沫材料的拉曼光谱显示出非晶态二氧化硅的典型特征，而透射电子显微镜图像则揭示了玻璃基质中存在结晶区域。这些微晶易于发生成核和生长过程，这危及了人们认为的二氧化硅泡沫的稳定性。通过红外光谱对羟基含量的评估揭示了硅醇后缩合所起的作用。因此发现，发泡过程的发生是由在1000℃下发生的两种竞争现象导致的：与水相关物种的逸出和粘性烧结。
