<P> In the making of firebrick, fireclay is fired in the kiln until it is partly vitrified, and for special purposes may also be glazed . There are two standard sizes of fire - brick; one is 9 × 41⁄2 × 3 inches (229 × 114 × 76 mm) and the other is 9 × 41⁄2 × 21⁄2 inches (229 × 114 × 64 mm). 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 9 × 41⁄2 × 11⁄4 inches (229 × 114 × 32 mm). Fire brick was first invented in 1822 by William Weston Young in the Neath Valley of Wales . </P> <P> Fire bricks have an aluminium oxide content that can be as high as 50--80% (with correspondingly less silica). </P> <P> The silica firebricks that line steel - making furnaces are used at temperatures up to 1648 ° C (3000 ° F), 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 . </P> <P> 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 (depending on the relative ratios of magnesite and chromite ores used in their manufacture). </P>

Why is silica used to make bricks for high temperature furnaces