Nano-porosity in silica reinforced methyltrimethoxysilane coatings studied by positron beam analysis

• Published in: Composites science and technology Vol. 63; no. 8; pp. 1133 - 1139
• Main Authors: Escobar Galindo, R., van Veen, A., Schut, H., Falub, C.V., Balkenende, A.R., de With, G., De Hosson, J.Th.M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2003; Elsevier
• Subjects: A. Ceramic-matrix composites; A. Porosity; Applied sciences; B. Mechanical properties; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; E. Sol–gel methods; Exact sciences and technology; Positron beam analysis; Structural ceramics; Technical ceramics; B. Mechanical properties; A. Ceramic-matrix composites; Positron beam analysis; A. Porosity; E. Sol–gel methods; Ceramic matrix composite; Coating material; Mechanical properties; Organic siloxane; Dispersion reinforced material; Positron beam; Experimental study; Coatings; Silica; Composite material; Optimization; Structural ceramic; Nanometer scale; E. Sol-gel methods; Sol gel process; Porosity; Colloid particle; Structural analysis; Organic silicate
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/S0266-3538(03)00034-4

The porosity in particle reinforced sol-gel coatings has been studied. Silica particles (Ludox-TM40) are introduced into methyl silicate coatings to increase the hardness, the elastic modulus and the fracture toughness. The methyl silicate has a relatively low density (about 1.2 g/cm 2), while the silica particles are known to be porous. However, the porosity of the silica particles is not accurately known. For model calculations on mechanical properties like the E-modulus this porosity should be known. Positron Beam Analysis (PBA), using the Doppler Broadening (DB) and 2D-Angular Correlation of Annihilation Radiation (2D-ACAR) techniques, was therefore performed for analysis of the porosity. Samples with different weight fractions (0, 20 and 63 wt.%) of silica particles of typically 40 nm in diameter and treated at different curing temperatures (623 and 723 K) were measured. With increasing filler content we observed a decrease in the positron annihilation S-parameter and a broadening of the para-positronium (p-Ps) fraction. By neglecting positron diffusion we can separate porosity in the matrix from that in the particles. This assumption is valid as long as the expected positron diffusion length is short compared to the size of the filler particles, as in the present case. A more detailed description takes into account the local environment of the filler particles affecting their adhesion to the matrix. It is concluded that the density of the silica particles is about 1.4 g/cm 2.