The effect of the H2O/TEOS ratio on the structure of gels derived by the acid catalysed hydrolysis of tetraethoxysilane
Creators
- 1. Sheffield Univ. (UK). Dept. of Ceramics, Glasses and Polymers
- 2. Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro
Description
Silica gels were produced by the acid catalysed hydrolysis of tetraethoxysilane (TEOS) using H2O/TEOS ratios from 2 to 50. After heat treatment the structure of the gels was studied using nitrogen adsorption, small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and bulk density measurements. All the gels possessed microporosity in the region of 30 A or less. For H2O/TEOS = 25 and 50 the matrix density was found to be uniform, but for gels from solutions with H2O/TEOS = 2, 4 and 10, density fluctuations in the matrix were detected from a Porod analysis of the SAXS data. These results indicate that in high water content solutions, rearrangement of the polymeric chains leads to small densified particles, but for lower water content solutions, gelation results from the entanglement of linear chains leaving free volume on a molecular scale between the chains. (Author)
Availability note (English)
MF available from INIS under the Report Number.Abstract (Portuguese)
Gels de silica foram produzidos pela hidrolise catalizada por acido do tetraetoxisilano (TEOS) usando razoes de H2O/TEOS de 2 a 50. Estuda-se, apos tratamento termico, a estrutura dos gels usando adsorcao de nitrogenio, espalhamento de raios X a baixo angulo (SAXS), microscopia de eletron de transmissao e medidas de densidade do volume. Todos os gels possuem microporosidade na regiao de 30 A ou menos. Para H2O/TEOS = 25 e 50 a densidade de matriz e uniforme mas, para gels de solucoes com H2O/TEOS = 2, 4 e 10, existem flutuacoes de densidades de SAXS. Esse resultados indicam que em solucoes contendo maior quantidade de agua o re-arranjo das cadeias polimericas leva a pequenas particulas densificadas mas, para solucoes contendo menor quantidade de agua, gelatinacao resulta de um emaranhamento de cadeias lineares deixando volume livre sobre uma escala molecular entre as cadeias. (L.C.)Files
17010840.pdf
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Additional details
Publishing Information
- Imprint Pagination
- 38 p.
- Report number
- CBPF-NF--030/85
INIS
- Country of Publication
- Brazil
- Country of Input or Organization
- Brazil
- INIS RN
- 17010840
- Subject category
- S75: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY;
- Resource subtype / Literary indicator
- Numerical Data
- Descriptors DEI
- ADSORPTION; EXPERIMENTAL DATA; HEAT TREATMENTS; HIGH TEMPERATURE; MICROSTRUCTURE; NITROGEN; POROSITY; SILICA GEL; SMALL ANGLE SCATTERING; TRANSMISSION ELECTRON MICROSCO; VERY HIGH TEMPERATURE; X RADIATION
- Descriptors DEC
- ADSORBENTS; CRYSTAL STRUCTURE; DATA; ELECTROMAGNETIC RADIATION; ELECTRON MICROSCOPY; ELEMENTS; INFORMATION; IONIZING RADIATIONS; MICROSCOPY; NONMETALS; NUMERICAL DATA; RADIATIONS; SCATTERING