Replacing Fossil Carbon in Mold Fluxes: Carbon-Neutral Straw-derived Biochar as a Renewable Resource for Tailoring Melting Behavior

The physicochemical properties of carbon significantly influence the melting behavior of mold fluxes. In this study, straw-derived biochar is proposed as a carbon-neutral alternative to carbon black and considers its influence on the melting behavior of mold flux. The structural and physicochemical characteristics of the carbon were systematically investigated using proximate and elemental analyzer, laser particle size analyzer, and scanning electron microscope. The melting behavior was evaluated using the single hot thermocouple technique. The results show that compared with carbon black, straw-derived biochar exhibits a larger specific surface area of 1267.42 m2·g-1 and a lower sulfur and nitrogen content of 0.13% and 0.62%, respectively, reducing the release of nitrogen and sulfur pollutants. Additionally, straw-derived biochar exhibits a lower fixed carbon of 80.51%, reducing the emissions of CO₂ and CO. The melting experiments show that the regulatory effects on the melting temperature progressively enhance with carbon increasing from 4 to 10%. While, the controlling effectiveness reduces as the carbon increase to 12%. Carbon enhances the viscosity of molten slag, and the degree to which carbon black increases the viscosity is greater than that of straw-derived biochar. Q0Si and Q1Si decreased, and Q2Si and Q3Si increase with an addition of carbon, elevating the degree of polymerization from 0.58 to 0.73, and ultimately increasing the complexity of silicate network structure. Straw-derived biochar is a sustainable carbon-neutral carbon source, and can replace the traditional fossil carbon and effectively regulate the melting behavior of mold flux.