Analysis of composition of magnesia chrome brick

1) Composition of magnesia chrome brick

Magnesia chrome bricks are alkaline refractories containing 55% - 80% MgO and 8% - 20% Cr203, with periclase and composite spinel XO · Y2O3 as the main crystal phase, wherein XO is mainly MgO and FeO; Y203 mainly includes Cr203, Al203 and Fe203. The mole numbers of XO and Y2 () 3 are equal, and the surplus Y203 is dissolved in the composite spinel. There is also a small amount of silicate phase (forsterite and forsterite).

(2) Raw materials and production process

Magnesia chrome bricks are mainly made of high-quality sintered magnesia and chromite (Cr203 30% - 15%, CaO 1% - 5%). The production process of magnesia bricks is similar to that of magnesia bricks. Inorganic magnesium salt solution is used as binder for unfired magnesium inscription bricks. The loose effect caused by the expansion of spinel formed by the reaction of MgO and CrO3, Al2O3 or iron oxides during the firing process can be used to make bricks with pre synthesized magnesium inscription sand, which must be fired in an oxidizing atmosphere above 1600 ℃. If the nature of atmosphere changes, Fe203 in chromite is affected by oxidation and reduction reaction, forming various valence oxides of iron. At the same time, Cr203 is also reduced to produce compounds with different valence. Under repeated reaction, bricks will be damaged, so products with high MgO and low Cr203 shall be used as far as possible.

According to the raw materials and process characteristics of the products, they can be divided into cast magnesium inscription bricks, directly bonded magnesium inscription bricks, silicate bonded magnesium inscription bricks, re bonded magnesium inscription bricks, semi re bonded magnesium inscription bricks, pre reaction magnesium inscription bricks and unburned magnesium inscription bricks.

① Cast magnesium inscription brick: Cast magnesium inscription brick is a refractory product made from magnesia and chrome ore by electric melting and pouring. The production process of cast magnesium inscription brick is shown in Figure 1. It is characterized by large and isolated pores, dense products, high strength, corrosion resistance and sensitivity to temperature changes. The chemical property of magnesia brick is alkaline. Compared with magnesia brick and chrome brick, it has good thermal vibration resistance, stable volume at high temperature and high load softening temperature.

② Direct bonded magnesia bricks: The direct bonded magnesia bricks are made by mixing sintered magnesia and chromite. It is required that the content of SiO2 in raw materials is low, and the raw materials are fired at a high temperature above l700 ℃ to form a direct combination between periclase and chromite particles. The typical physical and chemical properties of directly bonded magnesia fused brick are: MgO 82.61%, Cr203 8.72%, SiO2 2.02%, apparent porosity 15%, and bulk density 3.08g/cm3. The compressive strength is 59.8MPa, the load softening temperature is 1765 ℃, the thermal shock resistance is 11OO ℃, water cooling for 14 times, and the bending strength is 8.33MPa.

③ Silicate bonded magnesia chrome bricks: Silicate bonded magnesia chrome bricks are sufficient to sinter magnesia and chrome ore as raw materials, and are prepared by mixing them in proper proportion and firing at high temperature. The mineral composition of the product is periclase, spinel and a small amount of silicate. Silicate bonded magnesia bricks are produced with magnesia for brick making and ordinary refractory chrome ore as raw materials. SiO2 in magnesia is less than 4%, Mg0 is more than 90%, and Cr203 in magnesia is 32% - 45%. After being mixed and formed with sulfite as the binder, they are fired at about 1600 ℃. In order to prevent abnormal expansion of products during firing, a weak oxidation atmosphere must be maintained in the kiln. Chemical composition of the product: SiO2 2.98% - 4.50%, MgO 61.75% - 72.69%, Cr203 10.04% - 14.90%. Physical properties: apparent porosity 18% - 21%, normal temperature compressive strength 36.1-50 OMPa, load softening temperature 16001640 ℃.