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Transcript of Chromite Refractories
Chromite has long been used in basic refractories in conjunction with magnesia 'mag-chrome' refractories. Mag-chrome refractories are preferred in sectors of non-ferrous metallurgy, because of their excellent corrosion resistance and high flexibility and low thermal conductivity are key factors for using magnesia chromite bricks. Available for different applications.
Uses of Chromite refractories
Modern refractories technology began in the late 18th century with the growth of the iron and steel industry during the Industrial Revolution. The greater demands placed on refractories required materials other than alumino-silicates and silica; magnesite and chrome brick were all introduced in the late 1880s. It was only in 1931 that the superior hot strength of blends of chromite and magnesite was recognized and chrome-magnesite bricks were introduced with electric steel-making furnaces.
In the mid-1960s low-silica, magnesia-chrome and reconstituted fused-grain magnesia-chrome refractories were introduced worldwide, in 1967
History of Chromite Refractories
The largest producers are South Africa (44%), India (18%), Kazakhstan (16%), Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world production. A very small amount of chromite ore is also found in the district regions of Afghanistan and the district of Balochistan in Pakistan.
Occurrence of Chromite
Copper refining furnaces
In recent years in copper refining furnaces, instead of silica refractories, more extensive use of chromite refractories are being made. The life of furnace has been increased. Even though many reactions occur in this furnaces but the refractories scarcely diminishes. This suggests low probability of wear even with the many fusible compounds formed during the reactions. Although a considerate amount of copper is found in the chromite refractory bricks afterwards.
History of refractories
The history of refractory materials goes back to the times of ancient China, medieval and Renaissance . Refractory materials and high technology company, roughly originated in the middle of the Bronze Age. China during the eastern Han dynasty had made porcelain kiln burning clay refractory material, known to be one of the first refractory materials.
Suitability of chromite as a refractory raw material The usefulness of chromite as a refractory is based on four factors: --Its a high melting point. Because of their unique properties the Marico chromites, with a higher proportion of Mg than Fe, are postulated to have an even higher liquidus temperature than other Chromites. Chromite has a linear expansion of about 1.3% at 1400°C, which is almost 50% of that of magnesia (MgO). As a consequence, when added to magnesia refractories, chromite will improve the thermal shock resistance of the refractory.
Relatively high corrosion resistance, chromite has exceptionally good resistance to pyrometallurgical slags. The resistance of chromite against fayalitic slags which are common in many non-ferrous metallic smelting processes is exceptional. Neutral chemical behaviour. In addition to refractoriness, a lining material must be compatible with the process slag chemistry. Chromite-containing materials can tolerate slags ranging from slightly acid to basic.
How they are made?
1. The crude chrome ore, ground to a suitable mesh ratio for the manufacture of refractory shapes may be mixed with the desired amount of barium oxide or strontium oxide (yielding materials), tempered (after premixing in a dry mixer), pressed into brick and then dried and burned, the desired refractory is formed during the burning of the brick.
2. The crude chrome ore may be exposed to a heat treatment preferably in a rotary kiln and at a temperature above 3100 F, by which treatment the chromite of the ore is recrystallized and the gangue minerals redistributed so as to surround the chromite in thin films. After cooling, the ore is ground to a suitable mesh ratio for the manufacture of refractory shapes then we can add yielding material, apply tempering, pressing, drying and burning processes.
Burnt magnesia-chrome bricks are made from high quality magnesia and chrome concentrate, Cr2o3 content can be adjusted according to different requirements. The bricks have good thermal stability and high temperature performance, and are widely used in cement kilns and non-ferrous rnetal metallurgical furnaces.
Chrome magnesite bricks are mainly used as chequer bricks of the regeneration zone. Chrome magnesite bricks find use in various applications like rotary kiln, furnaces and open heart. They have high anti-erosion ability and optimum resistance.
igh density i.e low porosity.
esistant to the altering effects of temperature.
xcellent wear resistance.
ncredibly low thermal expansion.
xidation in the furnace with others rarely occurs
hermal conductivity is extremely low.
elting is exceptionally high.