Tailoring tactics for preparation of superior thermal insulation materials from blast furnace ferronickel slag: Control of sintering temperature

Abstract

Blast furnace ferronickel slag (BFFS) was converted to thermal insulation materials by sintering of its mixture with 15 wt% fly ash cenosphere (FAC) from 1000 °C to 1200 °C. The influence of sintering temperature on the phase compositions, microstructures, and properties of the materials was investigated based on both thermodynamic and experimental analyses. It was demonstrated that increasing sintering temperature from 1000 °C to 1200 °C led to linear increases of contents of diopside (CaMgSi2O6; y = 0.039T – 21.5, where y and T denote the content and temperature, respectively), anorthite (CaAl2Si2O8; y = 0.0504T – 46.54), and magnesium aluminate spinel (MgAl2O4; y = 0.043T – 30.86) in the thermal insulation materials. Meanwhile, there existed linear decreases of contents of akermanite (Ca2MgSi2O7; y = -0.0352T + 66.18) and gehlenite (Ca2Al2SiO7; y = -0.0914T + 129.96), which could form a solid solution above 1100 °C, suppressing the expansion associated with the generation of magnesium aluminate spinel. Along with the phase transformation, the macroporous structure was also identified. By sintering at 1100 °C for 2 h, an optimal high-quality thermal insulation material with apparent porosity of 46.04%, water absorption of 42.12%, bulk density of 1.35 g/cm3, linear shrinkage of 0.82%, compressive strength of 6.83 MPa, thermal conductivity of 0.31 W/(m·K) at 25 °C and 0.42 W/(m·K) at 800 °C, and refractoriness of 1259 °C could be obtained.