China's Refractories

Abstract: To utilize coal gangue solid waste as a resource, a slurry was prepared by mixing coal gangue powder (d₅₀=75 μm), CaCO₃ powder (d₅₀=75 μm), and α-Al₂O₃ powder (d₅₀=5 μm) at a mass ratio of 6 : 3 : 1, with 35 mass% distilled water added. Then, 2 mass% composite foaming agent NS-Ⅲ was added to the slurry to form a foamed slurry. The foamed slurry was poured into a 100 mm×100 mm×50 mm mold. The demolded green bodies were first dried at 100 °C for 24 h and then fired at different temperatures (1 200, 1 250, 1 300, and 1 350 °C) for 3 h to fabricate anorthite insulating refractories. The effects of the firing temperature on the phase evolution, microstructure and properties were investigated. The results show that (1) with the increasing firing temperature, the diffraction peak intensity of anorthite and mullite gradually increases, the anorthite crystals increase and gradually develop from short columnar to lamellar; the crystal bonding gradually enhances; the bulk density, linear shrinkage and thermal conductivity of the samples decrease firstly and then increase, while the apparent porosity shows an opposite trend, and the cold compressive strength gradually rises; (2) when the firing temperature is 1 300 °C, the sample exhibits the optimal overall performance, with the bulk density of 0. 48 g·cm^-3, apparent porosity of 84.3%, cold compressive strength of 1.80 MPa, and thermal conductivity of 0.139 W·m^-1·K^-1 at 1 000 °C, and the anorthite crystals in the sample show lamellar morphology and bond closely, which makes the sample suitable for long-term service at high temperatures.

Key words: insulating refractories, anorthite, coal gangue, phase composition, microstructure, thermal conductivity