FACTORS INFLUENCING THE MECHANICAL-PROPERTIES OF SILICATE FIBERS

Eight fibre materials (three basalt wools, three kaolin wools, a glass wool and an SiO2-based sample) were used to study the relationship be tween the tensile strength and other characteristics (fibre diameter, chemical composition, structural homogeneity and order, surface porosi ty). Based on the porosity investigation size ranges of the macropores (ca, greater than or equal to 0.15 mu m), mesopores (ca. 0.15 to 0.00 6 mu m) and micropores (ca. less than or equal to 0.006 mu m) were dis tinguished. Considerable macroporosity was shown by the SiO2 sample on ly. On the basis of the specific pore volume the amorphously structure d glass wool may be considered to have a relatively defectless surface , while the surfaces of the glass-ceramic structured kaolin wool and o f the SiO2 fibres contain several potential defect points. It was show n that the porosity and the diameter of mesopores of basalt wool sampl es manufactured by different techniques increase with the reduction of Fe(III), i.e. with the Fe(lI)/Fe(II)+ Fe(III) ratio. There is no dire ct connection between the chemical composition of inorganic fibrous ma terials and their mechanical properties. For instance, the tensile str ength of d less than or equal to 12 mu m) diameter basalt and glass wo ol samples produced in tank furnaces is similar, in the case of thicke r fibres (n greater than or equal to 12 mu m. however, the strength of the basalt fibres, due to their more inhomogeneous structure, is smal ler than that of the glass fibres. While the changes in tensile streng th of a given Fibre material are mainly determined by the fibre diamet er those of samples of similar type and of identical diameter are firs t 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-size d mesopores (ca. 0.15 to 0.03 mu m) are most beneficial.