Magnesia bricks

The thermal shock resistance of magnesia bricks can be improved by adding chrome ore. Sintering at 1750°C leads to so-called direct bonding upon formation of the spinels Mg0 Cr203 and Mg0 Fe203. Such bricks are utilized in open hearth furnaces, in the rotary kilns of the cement industry and in the furnaces of the nonferrous metals industry. 

Chrome brick is made fromnaturally occurring chrome ore. It contains 34% AI2O3 and 30% Cr203. Often MgO is added to produce chrome-magnesia brick. 

Refractory Lining - Type Choma/Magnesium bricks are used in the hearth, the sides of the furnace are water cooled jackets. Chrome Magnesia Brick ... 

The temperatures at which the silicate minerals in burned magnesia brick begin to melt... 

All burned magnesia brick contain CaO and Si02 as impurities. Table 1 illustrates the mineral phases that exist at equilibrium in a burned magnesia brick at various hme-to-silica ratios the temperatures of initial liquid formation of those minerals are included in the table. 

A major U.S. float glass manufacturer used a burned magnesia brick as part of the furnace regenerator package in a gas-fired furnace. After approximately 5 years service, the checkers experienced a partial coUapse. Several pieces of broken brick were pulled from the debris pile under the checkers for analysis. Table 2 contains chemical analysis data on a representative sample of the used brick, on the original unused brick, and of buildup taken from the surface of the brick. The unused brick had a CaO content of 2.05% while samples taken from the exterior and interior of the used brick had much lower CaO contents of 0.19 and 0.14%, indicating depletion of CaO during service. The buildup on the surface of the brick contained... 

Table 3 contains the chemical analyses of the brick samples tested in the simulative checker test. A high-purity magnesia brick, two intermediate-purity magnesia brick, and a magnesia-zircon brick were tested. 

High Purity Burned Magnesia Brick Intermediate-Purity Burned Magnesia Brick 1 Intermediate-Purity Burned Magnesia Brick 2 Magnesia-Zircon Brick... 

As shown in Table 13, the magnesia-zircon brick exhibited 6.7% volume expansion during the test, while the magnesia-forsterite brick without zirconia exhibited only 0.93% voiume expansion. The volume expansion of the magnesia-forsterite brick without zirconia approached the 0% volume expansion exhibited by the burned magnesia brick sample, which was known to have good alkali resistance. 

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