The high SiO2 content in ash is very harmful. First of all, the introduction of a large amount of SiO2 will inevitably change the CaO/SiO2 ratio of high-quality magnesia, so that the original high-temperature binding phase C2S or C3S (melting points of 2130°C and 1900°C, respectively) of magnesia is transformed into CMS and C3MS2 (melting points of 1490°C and 1575°C, respectively), thereby significantly reducing the high-temperature performance of bricks. Secondly, SiO2 can also reduce the stability of magnesia and carbon coexistence, and promote the volatilization of MgO. This is due to the fact that SiO2 reacts with MgO during heating, forming a thin layer of magnesia olivine (M2S) on the surface of magnesia; When the temperature rises, SIO2 in M2S is easy to react with C and volatilize (SiO2+C→SiO+CO), and the surface of magnes after SiO2 volatilization is activated, which promotes the MgO-C redox reaction. At the same time, it is easy to undergo redox reaction with C at high temperatures. The consequence is that the magnesia carbon brick is thermally lost and the tissue structure is loose.
1. The use of magnesia carbon bricks on the converter lining
Since the use conditions of each part of the converter working lining are different, the use effect of magnesia carbon bricks is also different.
The furnace mouth part of the furnace lining is constantly impacted by cold and hot steel liquid, so the refractory material used for the furnace mouth must be resistant to high-temperature slag and high-temperature exhaust gas washout, and it is not easy to hang steel and easy to clean in time. The furnace cap part is not only subjected to serious slag erosion, but also subject to rapid cold and hot temperature changes, and due to the combined effect of high-temperature air flow of carbon oxidation and high-temperature waste gas washout of dust, magnesium-carbon bricks with strong slag erosion resistance and peeling resistance are used. The charging side requires magnesia carbon bricks in addition to high slag erosion resistance, but also has a high high temperature strength and has quite good anti-spalling performance, so usually use metal antioxidant high-strength magnesia carbon bricks, studies show that the high temperature strength of magnesia carbon bricks added to metal aluminum at lower temperatures is lower than the composite addition of metal aluminum and silicon metal samples, and at high temperatures, its high temperature strength increases. The slag line is the three-phase junction of furnace lining refractory material, high-temperature slag and furnace gas, which is the most serious part of slag erosion, so it is necessary to build magnesia carbon bricks with excellent slag erosion resistance, and magnesia carbon bricks with high carbon content are required at the slag line part.