A refractory brick is built primarily to withstand high heat, but should also usually have a low thermal conductivity to save energy. 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 a natural gas fired kiln, more porous 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.
To make firebrick, fireclay is baked in the kiln until it is partly vitrified, and for special purposes may also be glazed. Fire-bricks usually contain 30-40% aluminium oxide or alumina and 50% silicon dioxide or silica. They can also be made of chamotte and other materials. For bricks of extreme refractory character, the aluminium oxide content can be as high as 50-80% (with correspondingly less silica), and silicon carbide may also be present. The standard size of fire-brick is 9 x 4.5 x 2.5 in. (228 mm x 115 mm x 64 mm)
The silica firebricks that line steel-making furnaces are used at temperatures up to 1650 °C (3000 °F), which would melt many other types of ceramic, and in fact part of the silica firebrick liquifies. HRSI, a material with the same composition, is used to make the insulating tiles of the space shuttle.
The first application of silica "tiles" within ceramic brick kilns or furnaces is credited to William Harry of the Swansea Valley, Glamorganshire, Wales in 1817. Harry's invention served to vitrify the interior surface of ceramic brick built blast furnace. In 1820 however Quaker entrepreneur William Weston Young began experimenting with silica clay recipes, at his pottery in Nantgarw, also in Glamorganshire, for the creation of a robust, heat-proof brick from which a whole blast furnace could durably be made.
In 1822, Young, with three further investors, including David Morgan, John Player and (Young's brother) Joseph Young established The Dinas Firebrick Co. in the Vale of Neath, Glamorganshire, Wales and the first batches of firebricks began to be exported for the construction of blast furnaces across the industrialized world.
The Welsh word "Dinas," a reference to the hill where the silica was quarried in the upper Neath Valley, (Craig-y-Dinas, at Pontneddfechan) is synonymous with the word firebrick in many foreign languages, as a result of the extensive influence of this industry in South Wales.
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