Chrome magnesite refractories

Semler, C.E. and Bradt, R.C., Thermal shock damage of magnesite chrome refractories in the ribbon test , Am. Ceram. Soc. Bull, 1984 63(4) 605-9. 

Refractory Magnesite, 92% MgO Magnesite—chrome, CB CB Fired Forsterite, stabih2ed Chrome, fired 90% 70%... 

In technological practice, refractories are usually classified according to content of SLO2 and divalent oxides, as acid, neutral or basic types. The acid types comprise silica refractories and siliceous fireclay neutral refractories are alumina, mullite and chromite refractories magnesite, chrome-magnesite and dolomite refractories are... 

The term basic refractories is used for materials with a high MgO and CaO content they include magnesite, chrome-magnesite, magnesite-chrome and dolomite refractories as the main types. 

FIG. 210. High-temperature deformation curves of refractories obtained from the standard test (after the prospectus of the Didier Corp.) ) fireclay, (2) silltmanite, (i) chrome-magnesite, 4) silica for crowns, (J) coke-oven silica, (6) magnesite-chrome. 

Chrome refractories were first introduced in about 1880 as a neutral zone between the acid and basic courses of steel-making furnaces. Nowadays, chrome ore is usually mixed with dead-burned magnesite for the production of chrome-magnesite, a very important basic refractory, which has made the all-basic open-hearth steel furnace an economic possibility. 

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. 

Chrome-bearing refractories are particularly difficult to fuse, and, although not entirely satisfactory, a flux mixture of 10 parts of lithium metaborate and 12.5 parts of lithium tetraborate to one part of sample is generally used for chrome-magnesite, chrome-magnesia—zirconia and chrome ore samples, but not metallvugical chrome ore, which requires further dilution in MgO. 

Basic Refractory. A general term for those types of refractory material that contain a high proportion of MgO and/or CaO, i.e. oxides that at high temperatures behave chemically as bases. The term includes refractories such as magnesite, chrome-magnesite, dolomite, etc. 

Chrome Refractory. A refractory brick made from chrome ore without the addition of other materials the Cr203 content is 25%. and the MgO content is 25%. Chrome refractories are neutral, chemically, and find use as a separating course of brickwork between silica refractories and basic refractories their R.u.L. q.V.) is considerably lower than that of chrome-magnesite refractories. Chemical composition (per cent) Si02 4-7 Fc203, 12-15 AI2O3,16-20 Cr203, 38-42 CaO, 1-2 MgO, 15-20. 

The cost of the lining amounts to between 1 and 2% of the cost of construction if the rate of consumption of refractory material is about 0.5-1.5kg per tonne of Portland cement clinker produced. About 35% of the lining in a modern kiln typically consists of dolomite brick, 35% of magnesite-chrome brick, and the remainder (30%) of fireclay brick, lightweight refractory brick, special brick and monolithic refractories. 

According to Konopicky (1957), the expansion joints should, as a rule of thumb, be designed to absorb half the thermal expansion that develops up to the service temperature of the refractory lining. Approximate values to be adopted are 0.5% for fireclay and silicon carbide brick, and 1.2% for magnesite-chrome and dolomite brick. The expansion joints are filled with cardboard, which burns away when the kiln is heated, leaving the joints clear. In general, it is more favourable to provide a larger number of narrower expansion joints than a smaller number of wider ones. 

Basic refractories react with acidic slags. Therefore, they are not useful in acidic enviroiunents. They are used under basic conditions and are based on MgO. Examples are magnesite, dolomite, chrome-magnesite, magnesite-chrome, alumina, and mullite. 

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