The effect of chromium ore on the performance of magnesia-chrome brick

Chromium ore is the main raw material for the production of magnesia-chrome bricks, and its main impurity content varies depending on the source. In addition, the amount of chrome ore added will also affect the performance of the chrome brick. Next, I will give you a detailed introduction to the effect of the source and amount of chrome ore on the performance of the directly combined magnesia-chrome brick.
 

1. The effect of chrome ore particle size

Domestically produced high-chromium ore w (Cr2O3)> 53%) Although the content of iron oxide is much lower than that of South African chromium ore, the content of silicon dioxide is higher. To this end, the effect of the particle size composition of domestic high-chromium ore on the performance of directly combined magnesia-chromium bricks was mainly studied. The compressive strength of the product increased with the reduction of the critical particle size of chrome ore, and the high-temperature bending strength (1400 ° C, 0.5h ) Decreases with the decrease of the critical particle size of the chrome ore. When the critical particle size of the chrome ore is 1.5 mm, the thermal shock stability peaks.
 

2. Influence of chromium ore addition

The fused magnesia and South African chromium ore are prepared in different proportions to form directly combined magnesium-chromium samples with different Cr2O3 contents, and fired in a high-temperature 1740 ° C kiln.

The chemical composition of the fused magnesia, South African chrome ore and magnesium-chromium samples used for firing in a high-temperature kiln at 1740 ℃.
 

As the content of chromium ore increases, the apparent porosity of the sample directly combined with magnesium and chromium decreases, the bulk density increases, and the thermal shock stability increases. Optical microscopy, SEM and EDAX analysis showed that after calcination at high temperature, most of the iron oxide in the chromium ore of South Africa entered into the brucite phase to form (MgO, FeO) solid solution or secondary spinel of magnesium ferrite. As mentioned in the previous analysis, when (Mg, Fe) O is formed, the volume shrinks by 20%, and in the presence of CaO, a liquid phase appears at 1500 ° C, which promotes dense sintering. One of the reasons why the bulk density increases and the porosity decreases.
 

EDAX analysis of the composition of the magnesium-rich ferrite phase shows that the order of the solid solution amount of each sesquioxide in the cristobalite is: Fe2O3> Cr2O3> Al2O3, although there is also a certain amount of magnesium oxide that diffuses into the ferrochrome spinel, but the comparison In particular, the amount of sesquioxides (especially Fe203) in ferrochrome spinel entering human periclase is greater than the amount of magnesia entering ferrochrome composite spinel. Therefore, after calcination at high temperature, the composition of magnesia and chrome ore changes, and more secondary spinel is formed in the brucite.

Its typical composition (EDAX analysis, mass fraction) is: MgO 75.90%, Al2O3 3.21 %, Fe2O3 15.49%, Cr2O3 5.42%. The composition of chromium ore particles also varies greatly. The typical chemical composition of chromium ore particles is (direct boundary); MgO 21.69%, Cr2O3 47.35%, A12O3 12.31%, Fe2O3 12.73%, so this direct combination High degree of integration. Therefore, with the increase of chromium ore content, the physical properties of magnesium chromium samples have been significantly improved.