The Matrix Of Refractory Materials

The matrix of refractory materials refers to the substances present in the gaps of large crystals or aggregates.

Matrix has a decisive impact on the properties of refractory products. During the use, the samage of refractories always starts from the matrix. Changing the matrix of refractories is an effective way to improve the properties of products.

Most refractory materials, according to the main crystal phase and matrix, can be divided into two types: refractories containing crystal phases and glass phase and refractories only containing crystals. The former includes fireclay brick, silica brick, etc.. The latter includes magnesia brick, magnesia chrome brick, etc..

These products are fired at high temperature and contain a certain amount of liquid phase. The liquid will not form glass phase when cooled but the crystalline matrix which is bonded together with the main crystal phase. The matrix crystal phases are different from the main crystal phase.

Application of corundum brick

Corundum refractory refers to the refractory with Al2O3 as the main compostion and corundum(α- Al2O3) as the main crystal phase. Since it can withstand high temperature and has high hardness, good resistance to oxidization, corrosion and eletricity and good air tightness, it finds a wide application.

Natual corundum is rare in the nature and not . It is mainly used to produce abrasive materials for the machinery industry and precious crafts. So far, it has not been reported to be used produce refractory materials. Corundum used in the refractory industry is made from alumina exacted fron the minerals containing Al2O3.
Refractory brick containing more than 90% Al2O3 are called corundum brick, or pure alumina refractory brick. Corundum has high hardness (Mohs hardness 9) and high melting point. Those properties are related to the Al-O bond. Therefore, it is an excellent mateial to produce high temperature refractory bricks and electrical insualtion materials.
Corundum brick has good resistance to acid and basic slags, molten mental and glass. It can work well in both oxidizing atmosphere and reducing atmosphere. The basic raw material for corundum brick is fused or sintered corundum.
Since it has excellent high temeprature properties and suitable to various conditions, it can not only used in the belly of the blast furnace, but also the hot stove of the blast furnace and other furnaces. It can be used at 1500～1700℃ in furnace walls, roofs and checker bricks, gas preheater, linings in direct contact with methane, natural gas and coke oven gas, vaccum and continuous casting devices and the roof and inner lining of glass furnaces.

The use of Fused Cast refractories in glass furnaces

AZS brick is also called fused cast AZS block. It is made by melting raw materials in an electric arc furnace, then cating the melt into a mold and cooling it into solid. It is mainly used in glass furnaces. What should pay attention to during the manufacruring process is the voids caused by the volume shrinkage.

There are four casting ways for AZS refractory bricks: PT, QX, ZWS and WS. The different cating ways of AZS bricks can meet the requirements of different pats in different glass furnaces. It has great corrosion resistance and a long service life.
Currently, there are three important driving forces of the development of AZS refractory. The first is the requirement to maintain or improve the quality of glass quality. The second is the longer service life. And the final one is the effect of the oxygen-fuel system. The three aspects determine the selection of refractory bricks.
Fused cast alumina block has been used in the crown of glass furnaces. Before the emergency of oxygen-fuel technology, only beta alumina bricks are used in the crown. Nowadays, beta or alpha-beta fused cast blocks are also used in the crown of TV glass furnaces, float glass furnaces and borosilicate glass furnaces.
Fused cast AZS bricks can be used at 1600-1650℃, while fused cast alumina bricks can be used at 1700℃. This provides a better promise for the production of high-melting glass.

The Manufcturing Process Of Fire Clay Bricks

The manufcturing process of fire clay bricks includes seven steps.

1) Obtain raw materials. The clay for manufacturing bricks is obtained from the ancient soil deep under the earth’s surface. The soil in this layer is slightly deeper in color than the topsoil and was formed about 80,000 to 120,000 years ago. At that time, the climate is warm and humid and plants are diverse and lush , which mades the soil in this period soft and sticky and a good raw material for fire clay bricks.

2) The clay is stacked in the open air for up to six months to make its inner structure loose. Then it is crushed and screened to get the pure fine clay.

3) Add water to the clay and then repeat kneading to make it into thick mud. This step is very important for the finished products.

4) Puur the mud into the mold. Compact it and then remove the remaining mud with a wire bow.

5) Release the green body from the mold and dry it in the shadow to avoid cracks and deformation caused by exposure to the sun.

6) After drying, fire the bricks in the kiln. This process is the most important part of the brick-making process.

7) After ten days of firing, the green body is basically sintered. if stopping heating at this time, the outside air may come into the kiln and make the bricks oxidized into red bricks. in order to prevent oxidazing, seal the kiln roof with clay.

The Manufcturing Process Of Fire Clay Bricks

The manufcturing process of fire clay bricks includes seven steps.
1) Obtain raw materials. The clay for manufacturing bricks is obtained from the ancient soil deep under the earth’s surface. The soil in this layer is slightly deeper in color than the topsoil and was formed about 80,000 to 120,000 years ago. At that time, the climate is warm and humid and plants are diverse and lush , which mades the soil in this period soft and sticky and a good raw material for fire clay bricks.
2) The clay is stacked in the open air for up to six months to make its inner structure loose. Then it is crushed and screened to get the pure fine clay.
3) Add water to the clay and then repeat kneading to make it into thick mud. This step is very important for the finished products.
4) Puur the mud into the mold. Compact it and then remove the remaining mud with a wire bow.
5) Release the green body from the mold and dry it in the shadow to avoid cracks and deformation caused by exposure to the sun.
6) After drying, fire the bricks in the kiln. This process is the most important part of the brick-making process.
7) After ten days of firing, the green body is basically sintered. if stopping heating at this time, the outside air may come into the kiln and make the bricks oxidized into red bricks. in order to prevent oxidazing, seal the kiln roof with clay.

Four Factors For The Production Of Magnesia Carbon Brick

Magnesia carbon brick is mde of magnesium oxide (melting point 2800 ℃) and carbon material with a high melting point that is difficult to be infiltrated by slags by adding a variety of non-oxide additives. It is mainly used in the converter, AC arc furnace, DC arc furnace lining, ladle slag lines and other parts.

The factors for the production of magnesia carbon brick incldue raw materials, binding agents and additives.

1) Magnesia sand

Magnesia sand should have high purity. Compared to sintered magnesia brick, fused magnesia brick has more complete crystal structure and stable reducing effect on carbon, so the production of magnesai brick turns to fused magnesia bricks. Given the binding state of carbon and infiltration of binding agents, fused magnesia can be mixed with sintered magnesia.

Magnesia carbon brick made of magnesia sand with high MgO content, large periclase particles and a lime-silica ratio of greater than 2 has the best quality.

2) Graphite

Graphite is another raw material for magnesia carbon bricks. it has good basic refractory properties. It contains 85%-98% fixed carbon and 13%-2% ash nd has a relative density of 2.09-2.23 and a melting point of 3640K ( volatile).

There are three reasons for the oxidization of graphite during use:

a. Oxygen in the air

b. Oxides in the slag

c. Oxides in graphite itself

Oxide impurities can react with graphite and make the structure loose, permeability increased and strength reduced, which is the main reason for the damage of magnesia carbon brick. Therefore, graphite with high purity and large flake crystals is mainly used for the production of magnesia carbon brick.

3) Binding agent

Binding agent is important for magnesia carbon brick and other carbon refractory products. Graphite and refractory oxides are not miscible. Thwy rely on binding agents to bond. At high temperature, the binding agent will be carbonized and form carbon bond with graphite. These binding agents are typically phenolic resins, modified bitumen, petroleum cracking by-products. Among them, phenolic resin has the best performance.

4) Additives

During the damaging process of magnesia carbon bricks, the oxidization of graphite is the main reason. The oxidation and carbon loss result in loose structure and weak strenth. In order to improve the oxidation resistance of magnesia carbon bricks, a certain amount of additives are added, including silica powder, alumina powder, FeSi alloy, CaSi alloy, SiC, Si3N4 and B4C. another function of additives is to build a bridge between refractory oxides and graphite and reinforce the binding between refractory oxides and graphite.

Four Factors For The Production Of Magnesia Carbon Brick

Magnesia carbon brick is mde of magnesium oxide (melting point 2800 ℃) and carbon material with a high melting point that is difficult to be infiltrated by slags by adding a variety of non-oxide additives. It is mainly used in the converter, AC arc furnace, DC arc furnace lining, ladle slag lines and other parts.
The factors for the production of magnesia carbon brick incldue raw materials, binding agents and additives.
1) Magnesia sand
Magnesia sand should have high purity. Compared to sintered magnesia brick, fused magnesia brick has more complete crystal structure and stable reducing effect on carbon, so the production of magnesai brick turns to fused magnesia bricks. Given the binding state of carbon and infiltration of binding agents, fused magnesia can be mixed with sintered magnesia.
Magnesia carbon brick made of magnesia sand with high MgO content, large periclase particles and a lime-silica ratio of greater than 2 has the best quality.
2) Graphite
Graphite is another raw material for magnesia carbon bricks. it has good basic refractory properties. It contains 85%-98% fixed carbon and 13%-2% ash nd has a relative density of 2.09-2.23 and a melting point of 3640K ( volatile).
There are three reasons for the oxidization of graphite during use:
a. Oxygen in the air
b. Oxides in the slag
c. Oxides in graphite itself
Oxide impurities can react with graphite and make the structure loose, permeability increased and strength reduced, which is the main reason for the damage of magnesia carbon brick. Therefore, graphite with high purity and large flake crystals is mainly used for the production of magnesia carbon brick.
3) Binding agent
Binding agent is important for magnesia carbon brick and other carbon refractory products. Graphite and refractory oxides are not miscible. Thwy rely on binding agents to bond. At high temperature, the binding agent will be carbonized and form carbon bond with graphite. These binding agents are typically phenolic resins, modified bitumen, petroleum cracking by-products. Among them, phenolic resin has the best performance.
4) Additives
During the damaging process of magnesia carbon bricks, the oxidization of graphite is the main reason. The oxidation and carbon loss result in loose structure and weak strenth. In order to improve the oxidation resistance of magnesia carbon bricks, a certain amount of additives are added, including silica powder, alumina powder, FeSi alloy, CaSi alloy, SiC, Si3N4 and B4C. another function of additives is to build a bridge between refractory oxides and graphite and reinforce the binding between refractory oxides and graphite.