Magnesia chrome

MgO-spinel clinker is obtained by the same procedure, but with a substantial proportion of free MgO (75-85%). MgO-spinel is produced by sintering at temperatures of 1600-1800°C and a dense product is obtained. MgO-spinel refractory has better high temperature mechanical properties in arc furnace roof application compared to magnesia-chrome refractories, but it has lower strength than a high-alumina refractory. 

Direct-bonded magnesia-chrome ore materials exhibit a high strength at high temperatures, superior resistance to slags and volume stability up to 1800 C. They also show a much lower tendency to expansion and subsequent spalling as a result of interaction with iron oxides (cf. the follow ing section on chromite materials). Direct--bonded ware finds application in open-hearth furnaces, in electric arc furnaces, in secondary steelmaking processes, in rotary cement kilns, etc. 

Chemical composition silica-based and silica-alumina-based materials, chrome, magnesia, chrome-magnesia, spinel, SiC, materials containing carbon (more than 1% carbon or graphite), and special materials (containing other oxides or materials such as zircon, zirconia, Si3N4, etc.)... 

Refractories. Aluminosilicates, silica and aluminous material, basic materials such as magnesite, chrome-bearing materials such as magnesia-chrome bricks, zirconia-bearing materials, and silicon carbide. There are also raw materials such as fireclay, ferrosilicon, and graphite. 

Refractory-grade chromite is used for manufacturing magnesia-chrome bricks used in the extractive metallurgy of platinum group metals. Foundry sands made of chromite fines are used for making mould used for casting nonferrous metals. 

Basic products consist of magnesia, doloma, magnesia-chrome, chrome ore, and spinel. 

Figure 33 Slag-brick interface in a magnesia-chrome brick after a rotary slag test.

As with chrome ore, magnesia-chrome grains, in the presence of calcium-containing contaminants, may lead to the formation of soluble, hexavalent chromium compounds and carcinogenic concerns. 

Various combinations of magnesia and chrome ore can be produced. The properties of both a typical sintered and a fused magnesia-chrome raw material used for producing a number of different refractory products appear in Table 4 (24). 

Table 4 Properties of Sintered and Fused Magnesia-Chrome Grains...

Sintered magnesia-chrome grain tnagnesia-chrotne grain... 

Carbon, not only classifies by refractory type, but also by MgO content or principal oxides content this classification is shown in Table 10 (52). ISO 1927-1984 covers the ISO classification for dense and insulating monolithic refractories Class IV applies to basic materials, but, like the SIC standards, this standard uses only general types of products with differentiation within the class limited to the principal basic material of the monolithic mixtures—magnesia, chrome ore, spinel, forsterite, dolomite, or other alkaline earth oxides (53). 

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