01.AL2O3
The melting point of corundum (AL2O3) is 2050℃, the density is 3.85~4.0lg·cm-3, and it has good thermal conductivity and chemical stability. Corundum is often used as aggregate particles in iron ditch materials. It is generally believed that AL2O3 can reduce the activity of slag and prevent slag from corroding aggregates.
In terms of the selection of corundum particles, sub-white corundum has a very high volume density and water absorption rate; dense corundum has few impurities and a relatively low water absorption rate; and brown corundum has a relatively low water absorption rate although it has more residues. When using dense corundum and brown corundum as aggregates, the amount of water added to refractory castables is relatively low, which has a great effect on the density and baking of the castable. From the perspective of microstructure, dense corundum crystals are mature and highly dense; brown corundum crystals grow and develop relatively well, but are not dense; sub-white corundum contains not only a lot of residues, but also a lot of large cracks and closed pores, which adversely affect the thermal shock stability of the material. From the perspective of water absorption and microstructure, dense corundum and brown corundum are more suitable for iron ditch castables.
02.SiC
Silicon carbide is also called corundum or refractory sand, with a density of 3.17-3.47g·cm-3, a Mohs hardness of 9.2-9.6, and a melting point of up to 2827℃. Silicon carbide has high impact toughness, with a toughness modulus of 4.76x10 5MPa at 25℃, a tensile strength of 1.75x100MPa, and an elastic modulus of 2.8x10 5MPa at 1500℃. In addition, silicon carbide should be a semiconductor material with high thermal conductivity and low thermal expansion coefficient. As an economical raw material, SiC is widely used in refractory materials due to its excellent performance.
SiC will oxidize at high temperature to form SiO2 and CO2. At 800℃, SiC gradually oxidizes to form SiO2; when the temperature is 1000℃, SiC reacts violently with O2, forming more silicon oxide liquid phase to form SiO2 glass protective film; at 1300℃, the glass protective film gradually precipitates quartz and absorbs water and expands, causing the protective film to crack and the oxidation rate of SiC to increase. At 1500℃-1600℃, the SiO2 glass protective film has a certain thickness, which can weaken the continued oxidation of SiC; when the temperature is 1627℃, SiO2 reacts with SiC to generate SiO and CO, so the use temperature of SiC shall not exceed 1600℃.
In the iron ditch refractory castable, SiC's high wear resistance and high mechanical strength can resist the erosion and damage of the castable by continuous high-temperature molten iron and slag; at the same time, SiC's high thermal conductivity and low thermal expansion coefficient can resist the repeated thermal shock of continuous high-temperature molten iron on the castable, and weaken the thermal damage of molten iron to the castable; in addition, the chemical reaction between SiC and air can reduce the oxidation of C in the castable, and the glass protective film formed after SiC oxidation can also protect the carbon material in the castable, thereby weakening the oxidation damage of the castable.
03.C
C has poor wettability, and C-based materials have good resistance to slag erosion and are not easy to stick to iron; at the same time, C has a large thermal conductivity, which can resist the thermal shock of high-temperature molten iron and slag on the castable, thereby improving the thermal stability of the castable; in addition, under certain conditions, C and Si react to form SiC fibers, which have a reinforcing effect on the castable. However, C-based materials are easy to oxidize at high temperatures, and they contain certain volatile substances, which have an adverse effect on the density of the castable. Therefore, in the development of Ah03-SiC-C iron ditch castables, C materials with relatively low evaporation should be used, and a certain amount of antioxidants should be added to the castables.
There are many carbon sources for iron ditch refractory castables, including asphalt, graphite, carbon black and coke. Except for asphalt, other carbon source materials are hydrophobic materials, and they use more water during construction; while asphalt belongs to hydrophilic materials, and they use less water during construction, and have good dispersion properties. It is usually used as an important carbon source for Ah03-SiC-C iron ditch castables. However, asphalt evaporates after heating, and as the asphalt addition increases, the apparent porosity in the castable also increases. Therefore, it is very important to control the amount of asphalt added to the iron ditch castable.
