Factors influencing the mechanical properties of silicate fibres

Abstract

Eight fibre materials (three basalt wools, three kaolin wools, a glass wool and an SiO₂-based sample) were used to study the relationship between the tensile strength and other characterisdcs (fibre diameter, chemical composidon, structural homogeneity and order, surface porosity). Based on the porosity investigation size ranges of the macropores (ca. ≥0.15 µm), mesopores (ca. 0.15 to 0.006 µm) and micropores (ca. ≤0.006 µm) were distinguished. Considerable macroporosity was shown by the SiO₂ sample only. On the basis of the specific pore volume the amorphously structured glass wool may be considered to have a relatively defectless surface, while the surfaces of the glass-ceramic structured kaolin wool and of the SiO₂ fibres contain several potential defect points. It was shown that the porosity and the diameter of mesopores of basalt wool samples manufactured by different techniques increase with the reducdon of Fe(III), i.e. with the Fe(II)/(Fe(II)+Fe(III)) rado. There is no direct connection between the chemical composition of inorganic fibrous materials and their mechanical properties. For instance, the tensile strength of of d ≤ 12 µm diameter basalt and glass wool samples produced in tank furnaces is similar, in the case of thicker fibres (d ≥ 12 µm), however, the strength of the basalt fibres, due to their more inhomogeneous structure, is smaller than that of the glass fibres. While the changes in tensile strength of a given fibre material are mainly determined by the fibre diameter, those of samples of similar type and of identical diameter are first of all determined by their surface porosity. From the point of view of the mechanical properties of fibres, the possible smallest specific pore volume and within this the possible minimal extent of large-sized mesopores (ca. 0.15 to 0.03 µm) are most beneficial.