Concrete is the most important material used in the construction sector. However, its strength decreases when concrete is subjected to high temperatures. In the event of temperatures over 200 °C, significant damage starts to occur in the structure of concrete and its service life shortens. Therefore, other materials must be used in production conditions including processes that require high temperatures. Refractory materials refer to materials resistant to fire. They resist high temperatures for a long time. Thus, they have various areas of use in various industries. Refractory materials can be described as all kinds of non-metallic materials which can be used in temperatures over 538 °C without losing their chemical and physical properties. In this series, we will examine refractory materials which are also used in cement industry, and their properties and their areas of use. In the following posts of the series, we will further point out how to use calcium aluminate cement as a refractory material and experimental studies conducted in this area.
What is a Refractory Material?
ISO International Standards Organization defines refractory materials as “materials whose chemical and physical properties allow them to be used in a high temperature environment and resist physical and chemical impacts of solids, liquids and gases at these temperatures.”. In short, refractories are fire-resistant materials. They resist high temperatures for a long time. Fire bricks can be given as an example for refractory materials. Refractory furnaces lined with these bricks are used for various purposes in industry. However, refractory materials do not only refer to fire bricks. The description includes all kinds of non-metallic materials which can be used in temperatures over 538 °C without losing their chemical and physical properties. Refractory materials do not shrink or expand when subjected to high temperatures. They preserve their chemical structures, and they do not crack. Main materials used in the production of refractory materials are aluminum, silicon and magnesium. However, decision on which of these materials should be used and their composition depends on the area of use and purpose. Refractories:
- Artificially, where they are manufactured as a single material directly from raw materials.
- Naturally, where they are composed of oxides found in nature.
Image 1. Fire Bricks
Significance of Refractory Materials
The demand for construction materials increases every day. Hence it becomes a necessity for development of innovative technologies. Concrete is the most important material used in construction sector. Concrete is subjected to various external factors during its service life such as wearing, freezing, thawing, chemical environments and dynamic loads. One of these external factors is high temperatures. Concrete’s strength decreases when subjected to high temperatures. Especially at temperatures above 200 °C, the structure of concrete starts to get damaged. Therefore, high thermal resistance is required in case concrete will be used in production conditions including high temperatures since it will be subjected to high temperatures. Concrete types used in many industrial processes are also subjected to wearing and harmful chemical impacts in addition to high temperatures. Mechanical and chemical wearing in addition to high temperatures cause deterioration mechanism to accelerate. As a result, service life of concrete shortens, and high-cost repairs would be required. In order to prevent this situation, it is important to use refractory materials at places with high temperatures.
What are the Properties of Refractory Materials?
Properties of refractory materials vary depending on their chemical strength and production process. Refractory materials are divided into three groups, i.e., acidic, neutral and alkaline. Acidic refractories are the ones that predominantly include aluminum and silica. They will not be affected by other acidic materials. However, they can easily be damaged by alkaline materials. On the other hand, the contrary is true for alkaline refractories. The rate of SiO2 in proportion to alkaline components determines the acidity degree of the material. Neutral refractories, on the other hand, have resistance to both acidic and alkaline materials. Refractories are divided into various categories depending on their production methods. Main production methods are dry-pressing, hand-made, melting and monolithic.
Where to Use Refractory Materials
Refractories are frequently used in industries which require high temperatures. They are preferred in places where metallic materials are expensive or cannot be used. Today, iron steel industry uses approximately 70% of materials produced as refractory. However, refractories are generally used in construction of furnaces, reactors, igniters and quarries. They can also be used in glass production, fire shields and rocket platform constructions. Main areas of use are;
- Furnaces used to melt and process metals,
- Glass melting and ceramic kilns,
- Incineration plants,
- Furnaces used to temper and harden iron,
- Cement industry.
Image 2. Materials Produced as Refractories
What is a Refractory Material? Why is it Important to Use Refractory Materials?
Refractory is the industrial term used for materials with temperature and acid resistance. It can insulate high temperatures as well as acid. Therefore, it has a wide range of industrial usage areas. Examples of these areas would be thermal processing furnaces, refineries, chimneys, pre-heating units, industrial kilns, glass melting furnaces, frit furnaces, lime kilns, tunnel kilns in cement industry, many heavy-duty industrial furnaces such as melting and holding raw materials such as copper and iron. Properties of refractory materials also vary depending on their areas of use due to the wide range. Today, properties of refractory materials are extremely developed, and their types and areas of use are increased. Cement industry is one of these. Calcium aluminate cement based refractory materials are also frequently used in areas requiring high thermal resistance. In addition, calcium aluminate cement sets slowly and gains strength very rapidly. Thanks to this property, it is widely used in construction applications where rapid hardening and early strength are required. Check out our blog post titled Everything You Need to Know About Calcium Aluminate Cement to find further information on CAC.
In this article, we talked about what refractory is. In the next post of the series, we will discuss how to use calcium aluminate cement as refractory in detail.
References:
- Refractory Materials, Metallurgical
- Development Overview of Refractory Materials
- Alümi̇na Esasli Şeki̇lli̇ Refrakterlerde Katki Malzemeleri̇ni̇n Alümi̇nyum Penetrasyonuna Etki̇ler
