Effects of CaO added to raw basalt on producing continuous basalt fibers and their mechanical properties

• Continuous basalt fibers (CBFs) were produced from basalt mixtures. • The dosage of CaO inhibits the crystallization of spinel. • CaO promotes the crystallization of pyroxene and plagioclase. • The spinnability (capability of being spun) was improved. • The tensile strength of CBF was enhanced grealy. The influence of CaO on spinnability (the capability of being spun) of continuous basalt fibers (CBF) and strength property were investigated. The addition of CaO in raw basalts was found to eliminate spinel crystals (magnesioferrite), and to reduce frequency of fiber breaks during the fiber-drawing. The tensile strength of CBF was enhanced by 13% after addition 3% wt. of CaO to the starting materials. Excessive addition of CaO (>5.0%) would result in less spinnability and inferior mechanical strength. The structure of basaltic glass fibers with varying CaO contents was studied by various characterizations. Doping of CaO reduced the degree of fiber polymerization and increased the amount of non-bridging oxygen. Results showed that increase of CaO changes the crystallization behavior of fibers, inhibits the crystallization of spinel, and promotes the crystallization of pyroxene and plagioclase.