Direct combination of magnesium chromium bricks for detailed explanation

The performance indicators of fused cast magnesium chromium bricks are refractory products made from magnesia and chromium ore through electric melting and casting. The production process of fused cast magnesium chromium bricks is shown in the following figure.

Its characteristics are large and isolated pores, dense products, high strength, corrosion resistance, and sensitivity to temperature changes. The chemical properties of magnesium chromium bricks are alkaline. Compared with magnesium bricks and chromium bricks, they have good thermal shock resistance, stable volume at high temperatures, and high load softening temperature.

Magnesium chromium bricks are alkaline refractory products containing 55% 80% MgO and 8% 20% Cr₂O₃, composed of periclase, composite spinel, and a small amount of silicate phase. Composite spinel includes spinel solid solutions such as MgAl₂O₄, MgFe₂O₄, MgCr₂O₄, and FeAl₂O₄.

Magnesium chromium bricks developed rapidly after the 1960s due to the improvement of raw material purity and firing temperature. Currently, magnesium chromium bricks can be divided into ordinary bricks, directly bonded bricks, co fired bricks, rebonded bricks, and fused cast bricks according to different production methods.

(1) Ordinary magnesium chromium bricks

This is a traditional product that uses chrome ore as coarse particles and magnesia as fine powder. Alternatively, the two materials are composed of graded particles, and the firing temperature is generally 1550 ℃ -1600 ℃. The microstructure of this type of brick is characterized by little direct bonding between chromite particles and periclase, and mostly silicate (CMS) cementation or crack isolation; There are few dissolved phases in periclase and few direct bonding in the matrix. This type of brick has poor mechanical properties and poor slag corrosion resistance.

(2) Directly bonded magnesium chromium bricks

Direct combination of magnesium chromium bricks is developed on the basis of ordinary magnesium chromium bricks, and its production characteristics mainly include two aspects: the use of purer raw materials and the use of higher firing temperatures. The so-called direct bonding refers to the direct contact between chromium ore particles and periclase in bricks, as there is less SiO₂ in the raw material (controlled below 1% -25%) and less silicate generation. By high-temperature sintering, the silicate is squeezed into the corners of the solid particles. Thus improving the direct binding of the solid phase.

Directly bonded magnesium chromium bricks have high high-temperature strength, slag resistance, corrosion resistance, erosion resistance, corrosion resistance, excellent thermal shock stability, and volume stability at 1800 ℃ due to their high degree of direct bonding.