Types of Refractory Materials and Their Applications
Dolomite Refractory Materials
Dolomite refractory materials are formed from a mineral known as dolomite, a combination of magnesium and calcium carbonates. This is one of the most common refractory products for aluminium foundries. The raw material must be impregnated with tar or pitch before being used for refractory purposes. The resulting bricks are used in various industries. They are resistant to thermal shock and exhibit low expansion when heated. They are used in the glass, cement, iron, and steel industries.
High-temperature processes require significant energy, much of which escapes into the environment. Refractory materials, in particular, can minimize the amount of energy escaping from the furnace by reducing the rate at which heat moves through the wall. The thermal conductivity of a refractory depends on its chemical and mineral composition and operating temperature.
Another factor to consider is its dimensional accuracy. The size of the refractory material must be precise to ensure proper fit and minimize the number of joints. The porosity of a refractory material is measured as the average percentage of open pore space in its overall volume. Materials with high porosity trap a large volume of air, which is a poor thermal conductor. Low-porosity materials are used for hotter zones, whereas materials with high porosity are used for thermal backup and colder zones.
Silica refractories are silicon oxide and contain at least 93 percent SiO2. These refractories are manufactured from high-quality rock. Silica bricks are commonly used in furnaces in the steel and iron industries. Silica bricks are durable, do not soften before the fusion point, and have excellent spelling and flux resistance.
The thermal conductivity of refractory materials depends on their size and porosity. High porosity means they are unsuitable for direct flame impingement or high temperatures. Pores of a refractory material should be uniformly tiny. If the refractory material is too porous, it may crack easily or break.
Bricks are used in the internal lining of furnaces. The brickwork inside a furnace must be heated to a high temperature before it can begin functioning. The amount of heat energy needed to raise the brickwork’s temperature will vary, depending on the time cycle of the furnace. Even if the furnace is shut down every night, the initial heat up of the brickwork will still consume a significant amount of energy.
Carbon graphite refractory materials are materials that are made of carbon. They are used in high-temperature-reducing environments. They are a perfect choice for refractory purposes because they do not oxidize or lose their properties in extreme temperatures. On the other hand, Alumina refractories contain at least 50 percent alumina (Al2O3).
The use of carbon-graphite refractory materials dates back thousands of years. The Celts used it in producing fireproof crucibles, and today, it is a widely used refractory material. Because it is oxidation resistant, offers excellent thermal conductivity, and is chemically inert, graphite plays a critical role in the refractory industry. Large-flake graphite, for example, is known for its outstanding thermal conductivity, which ensures its service life even under extremely high temperatures.
The carbon content of refractory graphite materials is determined through various methods. For example, it can be classified by fixed carbon content, which gives a better understanding of the materials’ properties. Fixed carbon content affects several properties of the refractory material, such as cold crushing strength and apparent porosity.
Non-oxide Refractory Materials
Non-oxide refractory materials do not contain oxygen or a mixture of these gases. They are often used in highly reducing environments and offer excellent resistance to slags. They are also lightweight. These refractories are primarily comprised of carbon.
They can be classified by chemical composition, the properties of their constituent substances, and their applications. The essential characteristics of non-oxide refractories include their ability to resist high temperatures and low thermal conductivity. Their dimensional stability at high temperatures is another essential property. They can also resist chemical action and contamination.
These materials can be used to build ovens and kilns. They are available in different forms, including fibers, blankets, castables, bricks, and modules.