FREEZE DRYING OF SILICA GELS PREPARED FROM SILICIUMETHOXID
1989; EDP Sciences; Volume: 24; Issue: C4 Linguagem: Inglês
10.1051/jphyscol
ISSN2777-3418
Autores Tópico(s)Glass properties and applications
ResumoThe freeze dried gels were prepared by acid catalysed hydrolysis of Si(OEt)4 diluted by ButOH. The acids used include H3PO4 and oxalic acid. Oxalic acid has DCCA-properties. Freeze drying without prior solvent exchange results in disintegration of the gels into mm size flakes. The fracturing of the gels becomes less severe as the concentration of EtOH in the liquid phase is reduced by solvent exchange. Pure ButOH shows only a very small volume change upon crystallization, but air saturated ButOH expand about 5 vol% upon freezing. This volume expansion is presumably the cause of the crack-pattern observed in the solvent exchanged monolithic pieces.
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