Refractory bricks (bricks that do not decompose due to high heat or pressure) are an integral component of any large-scale kiln or furnace operation. These bricks are important because they are used to line the interior of furnaces and kilns due to their low thermal conductivity.
Low thermal conductivity, in this case, means a high degree of thermal insulation, which keeps furnaces and kilns at a consistent temperature while doing little or no damage to the brick at those temperatures. While many materials are used in the refractory industry, some of the best material is known as “alumina”, which is used to make a product most manufacturers refer to as “high alumina brick”.
Understanding High Alumina Brick
Alumina is a material composed of powdered bauxite. As we’ve discussed in previous articles, bauxite is a raw material typically harvested from topsoil. The bauxite is refined further into aluminum oxide (aka "alumina") where it is then sintered with ceramic to produce something called alumina ceramic.
The manufacturing of high alumina brick is very similar; powdered bauxite is sintered with ceramic and fired at temperatures upwards of 1,470C, producing an enhanced fire brick with properties that defer greatly from both conventional ceramic and clay.
Beneficial Properties of High Alumina Brick
High alumina brick touts a low iron content, which gives it a high bulk density of the brick thereby increasing its lifespan making it an excellent material for kiln lining brick. High alumina bricks are great in industrial applications where fewer lining changes are preferred. High alumina brick is extremely durable, resistant to friction, and has very a high degree of thermal shock resistance as your furnace heats and cools. Due to its resistance to these phenomena, high alumina brick is less likely to crack, crumble, or otherwise fail for a considerably longer time than conventional fire brick.
Moreover, alumina’s natural corrosion and wear resistance makes it an excellent material to use in processes that deal with corrosive or abrasive chemicals. Many laboratories and industrial plants use these kinds of chemicals, so high alumina brick is highly regarded in these industries.
Common Applications of High Alumina Brick
Anyone can take advantage of the benefits of high alumina brick. However, the most common applications are in large-scale industrial processes. These are just a few of the industries that rely heavily on this type of refractory brick:
- Refractory Industry
- Cement Manufacturing
- Liquid-steel ladles
To put it simply, any industry that relies on either a furnace or kiln and wishes to get the most out of their refractory lining can benefit from using high alumina brick; it lasts longer, insulated better, and is overall more energy-efficient than conventional brick.
How High Alumina Bricks Are Manufactured
The most common way to manufacture high alumina brick is through the firing of bauxite, which naturally contains a blend of both aluminum oxide and something called “kaolinitic clay”, which is a clay composed of layered silica. Once this material is fired it creates a composition of alumina and mullite, which is used as-is to create bricks.
High alumina brick typically contains between 50-88% alumina, which is more than enough to lend the robust benefits of alumina to the refractory brick.
Alternatives to High Alumina Brick
Refractory brick is an entire industry on its own. Many materials can be used in fire brick applications, some are as simple as clay or ceramic. We'll dive into the most common varieties.
Made of hydrated aluminum silicates, fireclay is one of the most inexpensive and widespread types of firebrick on the market.
Composed of at least 85% magnesium oxide, magnesite is best used in metallurgical applications due to its poor durability but high resistance to lime and iron slag.
Most often used in glassmaking and steel working, silica is typically composed of at least 93% SiO2. Its primary benefit is its high mechanical strength.
Zirconia can maintain its high durability even at temperatures from a hot blast furnace, which can be more than 15,000C. Most of all, it has one of the lowest thermal conductivities of any of the refractories. It also does not typically react with either liquid metal or molten glass, making it a great material for both metallurgy and glassmaking.
High Alumina Brick; an Industry Favorite
While there are many alternatives to high alumina brick, many do not stand up to alumina’s multiple material benefits that make it the perfect choice for when you need high-temperature performance. It’s durable, non-reactive, and will withstand high-temperature and pressure.