Porosity is the basic technical indicator of most refractories. It affects almost all properties of the refractories, in particular strength, thermal conductivity, slag resistance and thermal shock resistance.
Keywords: refractories, magnesium-chromite bricks.
The porosity of refractory bricks increases, and the strength decreases. This is not only due to the reduction of the solid cross-sectional area, but also to the actual stress increase, and more importantly, the porosity is a defect of the material, which causes stress concentration and decreases the strength, and the effect of the rough atmosphere is more significant. The increase in porosity can significantly reduce the thermal conductivity, the porosity of the slag to increase the penetration of the product. Therefore, we are here to introduce you to magnesium-chromite bricks.
Low porosity refractory brick
Magnesium-chromium bricks are refractory products with magnesium oxide (MgO) and chromium oxide (Cr2O3) as the main components, periclase and spinel as main mineral components. Such bricks have high refractoriness, high temperature strength, strong resistance to alkaline slag, excellent thermal stability, and a certain degree of adaptability to acidic slag. The main raw materials for the manufacture of magnesia-chrome bricks are sintered magnesia and chromite. The purity of magnesia raw materials should be as high as possible. The requirements for the chemical composition of chromite are: Cr2O3: 30-45%, CaO: ≤ 1.0-1.5%.
The method of using the fine powder produced after the calcination of the chrome ore-magnesia co-grinding compact and the coarse granulation of the magnesia is an effective measure to eliminate the loosening effect. Compared with ordinary magnesium-chromium bricks, the magnesia-chromite bricks made by this method have low porosity, high compressive strength, load softening temperature and flexural strength. The magnesium-chromite bricks made from chrome ore-magnesite powder compacts and the high-temperature calcined synthetic magnesium-chromium sands have better slag resistance and high-temperature strength than other magnesium-chromium bricks.
In addition, high-grade refractories with low porosity have fused cast magnesium-chromite bricks obtained by direct casting of fused magnesium-chromium materials in electric furnaces, and fused fused-magnesia-chrome materials produced by the brick-making process in combination with magnesite-chrome bricks.
It can be seen from the study that the change rules of high temperature strength of magnesium chrome refractories with different processes are as follows: silicate combined with magnesium-chromium refractories <direct combination with magnesium-chromium refractories < semi-recombination with magnesium-chromium refractories < electrofusion recombination with magnesium-chrome refractory material. Since the high temperature flexural strength mainly represents the combination of various minerals in the brick, this shows that the combined strength of the electrofusion and the combination of the magnesium and chrome bricks is the largest, and thus the erosion resistance at the high temperature is the best.
Since the permeability of the liquid phase between different grains is lower than the permeability between the same grains, when the liquid content is fixed, the occurrence of the second solid phase will increase the solid-solid contact, which can increase the high temperature of the brick. strength. In the production of electro-magnetized recombined magnesium chrome bricks or semi-recombined magnesium chrome bricks, pre-synthesized magnesium chromite sand is used as a raw material, thereby increasing the content of the second solid phase and increasing the high-temperature strength of the bricks.