Familiarity with refractories
There is no doubt, that the most important family member of materials engineering is the  refractories; Without them, manufacturing any metal would be impossible and not cost-effective.
Non-metallic materials with high melting and mushing points (at least 1500 ℃) have been introduced as an independent industry since the 18th century;
It is approximately estimated that the refractories have been assigned 23 billion dollars (equals 27500 kilotons of refractories) of the world’s trade exchanges in 2020, and it is expected that it will be raised to 27.5 billion dollars in 2025.
It should be mentioned that this number is underestimated, because China as the largest manufacturer of the refractories declared that with a growth rate of 4%, they will manufacture 30 billion dollars refractories, individually. The refractory manufacture status in many countries is not clear. Generally, the share of countries in refractory manufacturing is as described below.
From an overall and commercial view, refractories are considered a small part of the steel industry which includes 3 to 4 percent of the steelmaking costs. Among these costs, 43 percent of the refractory utilization is allocated to the steel industry crucibles.
The issue can be analyzed by this point of view that all the metals (translator suggestion: Metal industries) require refractories to stay alive, even though; refractories get used in petrochemical industries, glass production, power plants, concrete, ceramics, as well. However, the steel industries are the consumers of 60 percent of the world’s refractory productions. The consumption of other industries is shown in the figure below.
If consider refractories a family, different species of these categories of materials exist and come to life second by second.
Silica, alumina, magnesia, titania are the main members of this family that alongside concretes and additives are introduced as powerful bodyguards to fight against the slag and melt. The variety in refractories masses are vast, according to their chemical composition, phases, production method, and utilization methods, so it can be said that there are 1000 species of refractories are produced worldwide.
The most famous and the most used materials among refractories are based on six oxides SiO2, Al2O3, ZrO2, Cr2O3, CaO, and MgO, also their compositions between them which are recently mixed with carbon. Out of 24 inorganic materials, 5% of the total inorganic materials are involved in refractory production. Which places them in the rank ten of inorganic materials consumers, after the glass production industry.
. To study the main components of the refractories, as it said before, each refractory material (either mass or block), is made of ceramic, concrete, or additive material.
Ceramic materials play the role of a skeleton and give the main performance to the material. These materials are used sometimes purely or sometimes with impurities. At any temperature according to their nature and other environmental conditions, they act differently which can be useful or harmful. Sometimes, at a specific temperature phase transition caused mass destruction and must be avoided.
Sometimes we are looking for heat to sinter the material. Also, conditions such as humidity can influence the material’s behavior. Other conditions like electromagnetic radiation (e.g. UV), heating rate, tension rate affect the material’s behavior. Although there are many ceramic-based and inorganic-based materials to produce refractories, chamotte-based (SiO2 and Al2O3 composition) and magnesia-based materials are mostly used globally; other kinds of refractories are shown in the figure.
Even though ceramic materials are known as the main component of the refractories, concretes are needed to work as binders to maintain the desired strength.
Concretes are known as the most strategic part of refractories, and even the most important problem of our country in the refractory scope is to produce and become self-sufficient in producing them
. Portland concrete 80, Portland concrete 70, Fondo, Polonium, A700, and Secar are some kinds of concrete that are used in this industry. The most utilized ones are Portland concrete 80, Portland concrete 70. Besides mentioned applications, increasing performance and reducing the cost are other advantages of concretes.
The last components of the refractories are the additives; they are the competing factor of the refractory manufacture companies, presently. Additives alongside the consumption percent and method of adding, are confidential secrets of companies that cannot be introduced precisely. Micro-silica, citric acid, sodium hexametaphosphate, and phosphoric acid are some of the additives that are meaningful alongside their consumption percent.
The water absorption percent, sintering temperature, pressure strength, thermal expansion coefficient, shock resistance, and phase transitions are some of the reasons why additives are used.
The refractory categories especially about the mass of refractories are so various. They can be categorized based on their, chemical compositions, producing methods, physical shapes, and used materials (compositions).
In the Iran industry, the refractories are usually categorized and known by the way they are manufactured:
Binder - Shaped Refractories- Ramming- Castable- Gunning- Fetting
we will more discuss the technical details of the refractories.
Other things about refractories that are must be mentioned; are the condition of producing them in our country.
The refractory industry in Iran; is among industries that have grown well and along with the primary industry (key industry) in the last decades. More than 60 production units in the refractory industry in Iran are working which can produce 95 percent of the refractory species, but 50 percent of the country’s production is done by 7 to 8 large companies which have the production capacity of 600,000 tons in a year.
This number from the perspective of 2025 is low. For instance, for producing each ton of steel, 10 to 20 kilograms of refractories are used, on average.
In other words, for the annual production of 33 million tons of steel in the country (from 2025 perspective), only for steelmaking, 500,000 tons of refractories are required. Whereas, other industries also require refractories. The refractory consumption of the other industries is given in the table below.
|Average consumption of the refractories for each ton of production (kg)
|Iron and Steel
|Aluminum and alloys
The three industries of steelmaking, concrete production, and glass production are the most important applicants of the refractory industry in Iran, respectively. The refractories due to their high weight are having some problems in the transportation. However, due to the growth of the refractory industry, the exportation especially to the countries of the region (Iraq, Kuwait, Russia, Belarus, Ukraine) has significantly grown.
China, the USA, and India are the largest producers in this scope, in the world. Among these three countries, China due to the government laws based on pollution reduction; has decreased the growth rate of refractory production and some raw materials production.
In these countries for every labor force employed in the refractory industry, 220 to 250 tons of refractories are produced annually. Whereas in Iran this number is 85 tons. This difference is mostly because of the equipment used in the factories, and back down Iran in the global market.
The figure below shows the shares of different regions of the world in the refractory market, Asia is ahead due to China’s mass production.