Special Refractories: Overview, Classifications, and Applications

Special Refractories: Overview, Classifications, and Applications
As described in material science, a refractory or refractory material is a material that can combat the highest level of heat, chemical attacks, and pressure with an ability to retain its original form showing no proneness to decomposition at all. Refractory solutions are considered to be the lifeblood of many industries particularly those that work under extreme temperatures. Whatever we see around us has either a direct or indirect connection with refractory materials or simply refractories.
Refractories are non-metallic, porous, polycrystalline, polyphase, inorganic, and heterogeneous. They are typically made up of oxides or carbides, nitrides etc. of the materials that include the following: 
Chromium, and
As per ASTM C71, refractories are "non-metallic materials with incredible chemical and physical properties. These materials make the perfectly suitable to be applied in structures exposed to environments above 1,000 °F (811 K; 538 °C)". Refractory solutions find applications in the following:
In the making of crucibles and molds for casting glass and metals, and
Surfacing flame deflector frameworks for rocket launch structures.

The metal casting sector is the biggest consumer of approximately 70% of all refractories produced 

As per the latest information available, approximately 70% of all refractories produced are used by the metal casting sectors and the iron and steel industry the world over. Refractories find applications in high-temperature processes due to their heat-safe properties and dependability at high temperatures. They are mainly utilized as linings for high-temperature furnaces and other handling units, for example, kilns, incinerators and reactors since they can endure physical wear, extreme temperatures, and erosion by different types of chemical agents. They are also used to make melting pots. They serve broad purposes in the iron and steel industry. 

Some salient general requirements that form the refractories

The characteristics of refractories are reliant upon their substance, and physical, mineralogical and thermal properties. Refractory solutions have a scope of properties to meet the necessities imposed by a large number of processes. 

The general requirements that form the refractories include the following:

Capacity to endure high temperatures and trap heat inside a restricted region like a furnace
Capacity to endure unexpected changes in temperature
Capacity to endure load in a variety of service conditions
Capacity to endure chemical and harsh activity of the materials like fluid metal, fluid slag, hot gases and so on interacting with the refractories
Capacity to resist tainting of the material with which it comes into contact
Capacity to keep up with adequate layered security at high temperatures and in the wake of/during rehashed heat cycling
Capacity to conserve/save heat
Capacity to endure load and grating powers, and low coefficient of thermal extension.

The concept of special refractories

When it comes to special refractories, they are produced through special refractory casting methodology and often include the following:
High melting point oxides 
High melting point non-oxides
Derived composite compounds
High-temperature coating
High-temperature fibre, and
Reinforcing materials.
Non-oxides having a high melting point are often known as refractory compounds that also include borides, silicides, carbides, nitrides, and sulfides. 

The cost quotient associated with special refractories

Although the cost quotient of special refractories is high when compared to standard refractory materials, they are considered to be indispensable and irreplaceable solutions in a large number of industrial sectors because of their versatile properties. Special refractories replace standard refractory solutions in many significant parts in various new technologies as well as fields, which can incredibly improve not only the service life but also increase the economic advantages. 

The classification of special refractories at a glance

When it comes to the classification of special refractories, it can be roughly made based on the following aspects concerning many different properties of raw materials:
Oxides having a very high melting point as well as their specific composites
Compound materials that mainly include carbides, nitrides, borides, silicides, etc. along with their composites
Oxides’ composite materials and refractory metals having a high melting point (cermet)
Inorganic coating and high-temperature amorphous material, and
High-temperature fibre as well as its reinforcing material.

Classification of refractories based on the method of manufacture

Un-formed (monolithic-plastic, ramming and gunning mass, castables, mortars, dry vibrating cement.)
Dry press process
Fused cast
Hand moulded
Formed (normal, fired or chemically bonded)
Un-formed dry refractories.

Classification based on the place of use

As stated earlier, the iron and steel industry is one of the major consumers of refractory solutions as more than 70% of total refractories produced are consumed by this industry. The primary reason lies in the fact that different manufacturing processes in this industry are heavily exposed to extreme temperatures, slags, and sulfur gases. This variety in the operating conditions associated with different tools and equipment calls for different grades of refractory solutions. Apart from it, each production floor has specific refractory requirements that need special shapes and technical particulars to fulfill the process requirements of the particular shop. Therefore, the refractories often get names after the shop names. 

Under this category of classification, they are classified in the following ways:

Coke oven refractories
Blast furnace refractories
Steelmaking refractories
Ladle refractories
Tundish refractories
Calcining plant refractories, and
Reheating furnace refractories etc.
As refractories have always been the lifeline of many industries, Indian refractory producers have risen to the occasion to meet the demand of their customers both in India and around the globe. These Indian manufacturers have got unmatched abilities to produce refractories as per the exacting requirements of their customers.

Concluding Remarks 

RHI Magnesita India is one of the top producers and suppliers of high-grade refractory products, systems and solutions. The refractory solutions provided by the company are indispensable for industrial high-temperature processes exceeding 1,200°C. These refractory materials find applications in a comprehensive range of industries that include non-ferrous metals and glass, steel, and cement. Right since its inception, the company has been a frontrunner concerning all the leading innovations within the field and always strives hard to come up with new kinds of products. For more details, get in touch with the company.