2023

Composition and Properties of Refractory Materials (Ⅱ)

Source: Network

1.1.2.3 Magnesia refractories

Magnesia refractories are alkaline refractories with magnesia as the main raw material, periclase as the main crystal phase, and MgO content (mass fraction) greater than 80%. It is usually divided according to its chemical composition:

(1) Magnesium products. w(MgO)≥ 87%, the main mineral is periclase.

(2) magnesium aluminum products. W (MgO)>75%,w(Al,0,) is generally 7% ~ 8%, and the main mineral components are periclase and magnesium aluminate spinel (MgO, Al,O,).

(3) magnesium chromium products. W (MgO)>60%,w(CrQ) is generally below 20%, and the main mineral components are periclase and chromium spinel.

(4) olivine and magnesium siliceous products. In addition to the main component Mg0 in this magnesium material, the second chemical component is Si0,. Forsterite brick contains more Si0 than magnesia brick, the main mineral composition of the former is forsterite and periclase, the main mineral of the latter is periclase and forsterite.

(5) magnesium calcium products. This magnesium material contains a certain amount of CaO, the main mineral composition in addition to periclase also contains a certain amount of calcium silicate (2CaO · SiO,).

1.1.2.4 Dolomite Refractory

Alkaline refractories produced with natural dolomite as the main raw material are called dolomite refractories. The main chemical composition is 30% ~ 42% MgO and 40% ~ 60% Ca0, and the sum of the two should generally be greater than 90%. Its main mineral composition is periclase and periclase (calcium oxide).

1. 1. 2.5 'Carbon-containing refractories

Carbon-containing refractory materials, also known as carbon composite refractory materials, refers to the different forms of carbon materials and refractory oxide composite production of refractory materials. Carbon-containing refractory materials mainly include magnesium carbon materials, magnesium aluminum carbon materials, aluminum carbon materials, aluminum silicon carbide carbon materials.

1.1.2.6 Zirconium-containing refractories

Zirconium-containing refractories refer to refractories produced from zirconium-containing materials such as zirconia (ZrO_) and zircon. Zirconium-containing refractory products typically include zircon products, zirconium mullite products, zirconium corundum products, and the like.

1.1.2.7 Special refractory materials

Materials that cannot be included in the above classification, in addition to their special chemical composition, should not be classified into the above categories, usually they also have their own more prominent characteristics, such as excellent thermal shock stability, slag resistance, etc., these characteristics are often used for specific conditions of use. Special refractory products can be divided into the following varieties:

(1) Carbon products. Carbonaceous products include carbon bricks and graphite products.

(2) pure oxide products. Pure oxide products include alumina products, zirconia products, calcium oxide products, and the like.

(3) Non-oxide products. Non-oxide articles include silicon carbide, boron carbide, silicon nitride, boron nitride, zirconium boride, titanium boride, SiAION, AION, magnesium-AlON, and the like.

1.1.3 Other classification methods

(1) According to the supply form of refractory materials, it can be divided into shaped refractory materials and unshaped refractory materials. Shaped refractories refer to refractory products with fixed shapes, which are divided into two categories: dense shaped products and heat preservation shaped products. The former is products with a total porosity of less than 45%, and the latter is products with a total porosity of more than 45%. Including standard bricks, special-shaped bricks, special-shaped bricks, as well as laboratory and industrial crucibles, tubes, utensils and other products with complex shapes. Unshaped refractory material refers to the mixture composed of aggregate (particle), fine powder, binding agent and additives, which is directly used in bulk delivery state, or is used after adding one or more suitable liquids that do not affect the performance of refractory materials. Small amounts of metallic, organic or inorganic fibrous materials may also be added to certain monolithic refractories. There are many varieties of unshaped refractory materials, mainly castable, plastic, ramming material, dry material, injection material, joint material, extrusion material, paint, stemming, mud and so on. The details will be discussed in the chapter on monolithic refractories. It should be noted that the so-called shaped and unshaped refractory materials are relative. The precast block obtained by casting or molding the monolithic refractory into a certain shape and pre-treatment is supplied in the form of a shaped product, but its entire production process is the same as that of the monolithic refractory, so it can also be included in the monolithic refractory.

(2) according to the fire resistance, can be divided into ordinary refractory products (1580~1770 ℃), advanced refractory products (1770~2000 ℃), super refractory products (>2000 ℃), super refractory products (>3000 ℃).

(3) According to the production process, it can be divided into fired products, cast products and non-fired products.

(4) according to different shapes and sizes, it can be divided into s & p type: 230mm × 113mm × 65mm, no more than 4 measuring scales, Max:Min <4 :1 (size ratio); Special type: no more than 2 concave angles, Max:Min <6:1 (size ratio), or an acute angle of 50~70; Special type Max:Min < 8 :1 (size ratio), or no more than 4 concave angles, or an acute angle of 30 ° ~ 50 °, etc. For refractory materials, its use conditions are more complex, compared with metal materials, polymer materials and other ceramic materials, its composition is relatively complex, is a multi-phase heterogeneous material, to bring many difficulties to the research work. In recent years, due to advances in materials science and research methods and equipment, there has been a greater understanding of the microstructure and composition of refractory materials and their relationship to the properties of refractory materials.

Key words:

Composition and properties of refractory materials