Effects of Fe 2+ /Fe 3+ molar ratio from raw basalts on the production and properties of continuous fibers

Due to the fluctuation and uncertainty of composition content in raw basalts, the discontinuous production process and the unpredictable mechanical properties presented by existing basalt fibers always limit their developments and applications. Herein, to promote the utilization of ore composition homogenization strategy for achieving high-quality and stable development of basalt fibers, the effects of Fe2+/Fe3+ ratio from basalt ore on the production and properties of continuous basalt fibers were studied to establish the standardized ore formulation. The Fe2+/Fe3+ ratio in ore was adjusted from 0.25 to 1.50 by adding sodium nitrate (NaNO3) as oxidant and magnesium powder (Mg) as reductant. After crushing, blending, and melt-spinning, the basalt ore with different Fe2+/Fe3+ ratios were fabricated into continuous basalt fibers. The study characterized both the viscosity and crystallization temperature variations of different basalt melts, as well as the mechanical properties, thermal stability (high- and low-temperature resistance), alkali durability, and dielectric performance of the resulting basalt fibers. These experimental results indicated that the increase of Fe2+/Fe3+ ratio from 0.25 to 1.50 leaded to the linear decreases of basalt melt viscosity (from 4.5 Pa·s to 3.2 Pa·s) and related crystallization temperature (from 1080 °C to 1010 °C). When the Fe2+/Fe3+ ratio was 1.0, the tensile strength of responding basalt fiber reached maximum value (2650 MPa). When the ratio decreased to 0.25, the tensile modulus increased to 89.2 GPa, while the basalt fiber maintained a volume resistivity of 1.2 × 1012 Ω·m and a high-frequency dielectric loss of 0.008. Therefore, the basalt fibers with the Fe2+/Fe3+ ratio ranged from 0.25 to 0.50 can be used in the field of electronic communications, and the fibers with higher Fe2+/Fe3+ ratio (0.80–1.20) showed better mechanical strength and temperature resistance.