Types and physical properties of common refractories

1、 What is a refractory?

Refractory materials generally refer to inorganic non-metallic materials with fire resistance above 1580℃. It includes natural ores and various products produced by certain processes according to certain requirements of use. It has certain high temperature mechanical properties and good volume stability. It is a necessary material for all kinds of high temperature equipment. It has a wide range of uses.

2、 Types of refractories

1. Acid refractories generally refer to refractories with a SiO2 content above 93%. Its main characteristic is that it can resist the erosion of acid slag under high temperature, but it is easy to react with alkaline slag. Silica bricks and clay bricks are commonly used as acid refractories. Silica brick is a siliceous product containing more than 93% silicon oxide. The raw materials used include silica and waste silica bricks. It has strong acid slag erosion resistance, high load softening temperature, and does not shrink or expand even slightly after repeated calcination; However, it is easy to be eroded by alkaline slag and has poor thermal vibration resistance. Silica brick is mainly used in coke ovens, glass furnaces, acid steel furnaces and other thermal equipment. The clay brick takes fireclay as the main raw material and contains 30%~46% alumina. It is a weakly acid refractory with good resistance to thermal vibrations and good resistance to corrosion by acid slag. It is widely used.

2. Alkali refractories generally refer to refractories containing magnesium oxide or magnesium oxide and calcium oxide as main components. These refractories have a high refractoriness and a strong resistance to alkaline slag. For example, magnesia brick, chrome magnesia brick, chrome magnesia brick, aluminum magnesia brick, dolomite brick, forsterite brick, etc. It is mainly used in alkali steel making furnaces, non-ferrous metal smelting furnaces and cement kilns.

3. Aluminum silicate refractories refer to refractories with SiO2-Al2O3 as the main component. According to the Al2O3 content, they can be divided into semi-siliceous (Al2O3 15~30%), clayey (Al2O3 30~48%) and high alumina (Al2O3 above 48%).

4. Melting and casting refractory refers to refractory products with a certain form cast after the batch is melted at high temperature by a certain method.

5. Neutral refractories refer to refractories that do not react easily with acidic or alkaline slag at high temperature, such as carbon refractories and chromium refractories. Some also attribute high alumina refractories to this category.

6. Special refractories are new inorganic non-metallic materials developed on the basis of traditional ceramics and general refractories.

7. Amorphous refractory is a mixture composed of refractory aggregates, powder, binder or other additives in a certain proportion, which can be used directly or after suitable liquid preparation. Unshaped refractory is a new type of non-calcination refractory, and its fire resistance is not lower than 1580℃.

3、 What are the frequently used refractories?

Commonly used refractories include silica brick, semi-silica brick, clay brick, high alumina brick, magnesia brick, etc.

Special materials often used include AZS brick, corundum brick, directly bonded magnesium chrome brick, silicon carbide brick, silicon nitride bonded silicon carbide brick, nitride, silicide, sulfide, boride, carbide and other non-oxide refractories; Calcium oxide, chromium oxide, alumina, magnesium oxide, beryllium oxide and other refractory materials.

Frequently used heat insulation and refractory materials include diatomite products, asbestos products, heat insulation boards, etc.

Frequently used amorphous refractory materials include furnace repair materials, fire resistant ramming materials, fire resistant concretes, fire resistant plastics, fire resistant mud, fire resistant blasting materials, projectiles fire-resistant, fire-resistant coatings, light fire-resistant castables, gun mud, ceramic valves, etc.

4、 What are the physical properties of refractories?

The physical properties of refractories include structural properties, thermal properties, mechanical properties, service properties and operational properties.

Structural properties of refractories include porosity, bulk density, water absorption, air permeability, pore size distribution, etc.

Thermal properties of refractories include thermal conductivity, coefficient of thermal expansion, specific heat, heat capacity, thermal conductivity, thermal emissivity, etc.

The mechanical properties of refractories include compressive strength, tensile strength, bending strength, torsion strength, shear strength, impact strength, wear resistance, creep, bond strength, modulus of elasticity, etc.

Service performance of refractories include fire resistance, load softening temperature, reheat line change, thermal shock resistance, slag resistance, acid resistance, alkali resistance, resistance to hydration, resistance to CO erosion, conductivity, resistance to oxidation, etc.

The workability of refractory materials includes consistency, slump, fluidity, plasticity, cohesion, resilience, coagulability, hardenability, etc.

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