When we speak of a material, we mean just what the adjective suggests: resistant. A refractory material is therefore a material that is able to withstand high temperatures. Not only that, but another ability of a refractory material is that it does not react chemically with other materials with which it comes into contact.
They generally consist of materials composed of simple oxides or oxide-based compounds, the raw materials including clay, silicon-aluminium compounds and magnesium compounds silicon, aluminium, magnesium, calcium, boron, chromium and zirconium and carbon
The refractory product retains its mechanical properties despite the external shocks to which it is subjected during the processing cycle
It is therefore obvious that refractory materials are widely used in the industrial sector, given the frequent high temperatures. They are well suited for use in the industrial production of glass metals and chemical and petroleum products, and their ability to withstand heat, temperature changes and compression makes them ideal candidates for various types of industrial furnaces The choice of a refractory oven is in fact a crucial point for a restaurant business, for example; this is because clearly the use of refractory materials influences the thermal performance and, therefore, the cooking of food (consider, for example, that the refractory oven tends to cook the lower part of the food without initial and sudden heat pushes that tend to give annoying burns in the lower part of the food).
In this article, however, we want to focus on the industrial sector; this is because refractory materials are also the best choice for the production of various types of kilns. Clearly, the kilns and the material used differ according to use. Consider, for example, the industrial use of refractory bricks. There are five types most commonly used: clay, chromite, magnesite, bauxite, etc. As far as clay is concerned, let us point out that they are the most widespread. Chromite bricks (which are highly insulating), on the other hand, are used in furnaces for the production of ferrous alloys and cement. Magnesite bricks boast excellent mechanical properties but tend to lose some volume while those made of bauxite Sillimanite and Mullite are used to line industrial furnaces for glass production
Clearly, this is a rather general overview, but what is important to understand about industrial furnaces is that there are essentially different types of furnaces: e.g. furnaces for the treatment of metals, plants for the production of lime and cement, furnaces for the production of glass, all plants related to the petrochemical sector from boilers to the FCCU system, refractory materials can be used for the production of cast iron to steel and ceramics. They are also suitable for melting operations, thus for chemical and nuclear production.
In summary, it is clear that the choice of the specific refractory material must take into account a number of variables, the most important of which is precisely the operating temperature of the required application, but not only that. A first general classification that must be made is the chemical classification; in fact, depending on its composition, a refractory may react with the substances with which it comes into contact.
Hence we have :
A-Refractory Acids (Reacts with basic oxides at high temperatures) E.G: Silicic-Aluminous B-Basic Refractories (Reacts with acid oxides at high temperatures) E.G: Magnesian, Dolomitic C- Neutral Refractories that do not react with either of the above two categories
E.G : Chromitics and Carbon-based Another classification is based on the physical appearance of the product :
Another classification is based on the physical appearance of the product :
The first Monolithic Refractories in turn are divided into castable, plastic, and ramming materials The latter A- precast cement and fused or sintered refractory products Third and last but not least: They are formed mostly from glassy or crystalline filaments formed into mats flakes felts or mixed with other elements to make rigid components Each one of the listed categories has its own properties at room temperature and at operating temperature When choosing a material for the construction or repair of an installation, consideration must be given to the product’s natural properties and properties under operating conditions -Chemical composition – Mineralogy and microstructure – Porosity – Permeability