Fire brick
A fire brick, firebrick, fireclay brick, or refractory brick is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. Made of primarily oxide materials like silica and alumina in varying ratios, these insulating materials are able to withstand extremely high temperatures, and have a low thermal conductivity for greater energy efficiency. Refractory bricks generally range from 25-45% alumina, and ~60% silica, with additional magnesium, calcium, potassium oxides.
Usually dense fire bricks 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 and easier to form and insulate far better than dense bricks. In any case, firebricks should not spall, and their strength should hold up well during rapid temperature changes.
Manufacturing
There are three main manufacturing methods for firebrick: firing, cementing and geopolymerization. In the first method, clay is fired in the kiln until it is partly vitrified. For special purposes, the brick may also be glazed. Firing is the most conventional process, with easy execution using traditional equipment. However, it is an energy intensive process, consuming a significant amount of energy - on the scale of 2.0 kWh per brick. Firing also releases around 0.41 kg of CO2 from the decomposition of carbonate materials and combustion of fuel.To cement, refractory brick is combined with refractory cement. Portland cement is not able to withstand high temperatures and is therefore not recommended. High-temperature refractory cements include furnace cements or high-heat mortar. These mixtures are applied to the brick surfaces and pressed together, and allowed to cure with time - taking anywhere from days to weeks.
A technique with the potential to replace firing and cementing is geopolymerization. Firing and cementing both require huge amounts of energy and release large amounts of greenhouse gases, thus motivating research into additional methods of production. Efforts to incorporate up to 30 wt% of waste materials into clay ceramics have been shown. Clay ceramics with 17 wt% additives displayed the highest bending strength of 30 MPa. Although these waste materials are inert, they could be responsible for structural defects that change the material properties and therefore applications of these bricks.
There are two standard sizes of fire brick: and . Also available are firebrick "splits" which are half the thickness and are often used to line wood stoves and fireplace inserts. The dimensions of a split are usually. Fire brick was first invented in 1822 by William Weston Young in the Neath Valley of Wales.
High temperature applications
The silica fire bricks that line steel-making furnaces are used at temperatures up to, which would melt many other types of ceramic, and in fact part of the silica firebrick liquefies. High-temperature Reusable Surface Insulation (HRSI), a material with the same composition, was used in the insulating tiles of the Space Shuttle.Non-ferrous metallurgical processes use basic refractory bricks because the slags used in these processes readily dissolve the "acidic" silica bricks. The most common basic refractory bricks used in smelting non-ferrous metal concentrates are "chrome-magnesite" or "magnesite-chrome" bricks.