Bricks (Refractory)
| Infobox on Bricks (Refractory) | |
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| Example of Bricks (Refractory) |  |
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| Humidity / moisture | - |
| Ventilation | - |
| Risk factors | See text |
Bricks (Refractory)
Description / Application
A fire brick, firebrick, or refractory brick is a block of refractory ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency. Usually dense firebricks are used in applications with extreme mechanical, chemical, or thermal stresses, such as the inside of a wood-fired kiln or a furnace, which is subject to abrasion from wood, fluxing from ash or slag, and high temperatures. In other, less harsh situations, such as in an electric or natural gas fired kiln, more porous bricks, commonly known as "kiln bricks" are a better choice. They are weaker, but they are much lighter, easier to form, and insulate far better than dense bricks. In any case, firebricks should not spall under rapid temperature change, and their strength should hold up well during rapid temperature changes.
Fire bricks are made from clays which contain 30-40% Aluminium Oxide or alumina and 50% silicon dioxide or silica. For bricks of extreme refractory character, the aluminium oxide content can be as high as 50-80% (with correspondingly less silica).
These bricks are of varying constituent chemicals, consistency, etc., according to intended usage, e.g. blast furnace linings, kilns, industrial boilers, power plants, etc., many purposes involving very high and sustained temperatures.
High temperature applications
The silica firebricks that line steel-making furnaces are used at temperatures up to 1650°C, which would melt many other types of ceramic, and in fact part of the silica firebrick liquefies. HRSI, a material with the same composition, was used to make the insulating tiles of the space shuttle.
Lower temperature applications
A range of other materials find use as firebricks for lower temperature applications. Magnesium oxide is often used as a lining for furnaces. Silica bricks are the most common type of bricks used for the inner lining of furnaces and incinerators. As the inner lining is usually of sacrificial nature, fire bricks of higher alumina content may be employed to lengthen the duration between re-linings. Very often cracks can be seen in this sacrificial inner lining shortly after being put into operation. They revealed more expansion joints should have been put in the first place, but these now become expansion joints themselves and are of no concern as long as structural integrity is not affected. Silicon carbide, with high abrasive strength, is a popular material for hearths of incinerators and cremators. Common red clay brick are used for chimneys and wood-fired ovens.
Shipment / Storage / Risk factors
Fire bricks are susceptible to mechanical damage. Absorption of salt water can render the bricks hazardous when heat is applied.
Chrome magnesite bricks are porous and will absorb moisture; this will cause a breakdown of the fabric, causing crumbling.
Susceptibility to damage of this nature is well known to users of this class of brick, and steps are usually taken to protect the bricks from the elements while on open quays, etc. Chrome magnesite bricks vary considerably in colour, due to the nature and type of chrome used in the manufacture. Colour will vary from a light yellow to a dark brown, and contact with fresh water should not materially affect the original colour of the bricks.
Damaged bricks, if of no value for their original purpose, have a salvage value as ‘Hot Repair Cement’.