Contrast and comparison of several magnesia
The magnesia suitable for the production of magnesia-carbon bricks is basically large crystal fused magnesia, ordinary fused magnesia and high-purity magnesia (high-purity balls), among which the magnesium content of large crystalline magnesia is generally above 97%, and the magnesium content of ordinary fused magnesia The magnesium content of high-purity magnesia is generally above 96%, and the magnesium content of high-purity magnesia is generally above 96.5%. Only such content of magnesia can be used to produce magnesia-carbon bricks. If the magnesia taste is lowered, it will easily cause product quality problems. The selection of magnesia is not the same. There is also a big difference in product quality.
The content of magnesia is only one factor when choosing magnesia, and the density of magnesia is also an extremely important factor. Under the same premise of the production process of fused magnesia, theoretically, the higher the magnesia content, the smaller the pores. The higher the density. However, driven by economic interests, some situations are not so, so when we choose magnesia, we must pay attention to it. In addition to the content of magnesia, it also depends on the density of magnesia, especially for the purchase of granular materials. Especially important for manufacturers.
Fuel cost is the most important cost for the production of magnesia, whether it is fused magnesia or sintered magnesia, so now many manufacturers have greatly reduced the time of electric melting and sintering in order to reduce production costs. To reduce energy consumption, this will bring a lot of negative effects, the most prominent is the under-burning of raw materials. For magnesia, under-burning is manifested in the small grain size of magnesia, the density is not up to standard, and fine grains after crushing Lots of powder.
When magnesia-carbon bricks first appeared, most of the foreign production used sintered magnesia, but after research, it was found that magnesia and graphite had the following reactions at high temperatures:
MgO(s)+C(s)=Mg(g)+CO(g)
Studies have shown that this reaction begins to occur at 1600°C, and the reaction speed increases as the temperature increases. This process is one of the important reasons for the oxidation of graphite and the loss of magnesia-carbon bricks. Its damage is firstly caused by the oxidation of graphite on the working surface under the action of various oxides in the slag and O2, CO2 in the environment, forming loose bricks. Then the molten slag infiltrates into the loose decarburized layer and reacts with magnesia to form a low-melt material that reduces its strength and accelerates damage. Impurities contained in magnesia, such as SiO2, Fe2O3, etc., can accelerate the entire reaction process, so when we choose magnesia, we hope that the impurities are as low as possible.
Compared with sintered magnesia, fused magnesia has larger crystal grains, better density, lower porosity, and strong slag resistance, especially the effect of large crystal magnesia is better. In addition, the higher the content of magnesium oxide, the lower the corresponding amount of harmful impurities, especially silicon dioxide, the lower the content of silicon dioxide, the less low-melting silicate produced in the product at high temperature, and the less low-melting , the lower the probability of reaction with graphite, the better the performance of the product. The larger the grain size, the higher the degree of direct bonding of the product, and the less the liquid phase at the grain boundary, so as to prevent the slag from eroding the product from the liquid phase at the grain boundary.
Therefore, with the development of magnesia carbon bricks, in order to improve the performance of products, fused magnesia began to be used in production. However, due to the high density of fused magnesia, low porosity, and poor wettability of the binder, sintered magnesia can make up for this problem, so sometimes fused magnesia and sintered magnesia are used together. Due to the poor market conditions in recent years, the share of sintered magnesia in production is increasing.
According to the results of use in steel mills, magnesia-carbon bricks with relatively good on-site use effects are generally produced with magnesia with high magnesia content, high density, large crystal particles, and high calcium-silicon ratio.