Structure sensitive measurements on phosphate glass fibers

Abstract As in the case of E-glass fibers the following properties of fibers continuously drawn from a nozzle have been measured over a broad range of drawing parameters (temperature, pressure on the nozzle and drawing speed): birefringence, density, thermal shrinkage and X-ray diffraction patterns. The structure of the metaphosphate glass fibers (25Na 2 O 25Li 2 O 50P 2 O 5 and 25CaO 25BaO 50P 2 O 5 , mol%) is influenced mainly by three parameters: nozzle temperature, cooling rate (thermal prehistory) and drawing stress (mechanical prehistory). Thermal prehistory produces an open structure corresponding to fictive temperatures of up to more than 100 K above the T g of the bulk glass. The mechanical prehistory causes orientation of anion chains and stretched flaws and anisotropic frozen-in structural strains or network deformations, respectively. For the alkali metaphosphate glass fibers the high values of birefringence up to 10 4 nm/mm indicate a high degree of orientation of linear phosphate chains. The temperature dependence of the properties and the low shrinkage values (maximum 4%) point to intensive entanglements and to a bond-switching mechanism when the structure relaxes at elevated temperatures. The alkaline earth metaphosphate fibers are strongly cross-linked, showing much less orientation of chain-like fragments and more similarity to the structure of E-glass fibers than to that of alkali metaphosphate glass fibers. The change from the oriented to the disoriented state of all fibers is connected with a drastic decrease of strength.