Low Thermal Conductivity Sic Mullite Bricks

Low Thermal Conductivity Sic Mullite Bricks Description

Silicon carbide mullite bricks are the most preferred refractory material for non-sintering zone of middle and large scale cement rotary kiln. Silicon carbide mullite bricks usually adopts high Al2O3 content natural bauxite clinker as main raw material, which has corundum principle phase and good thermal conductivity. The second largest component, silicon carbide, also have good thermal conductivity, so the thermal conduction coefficient of silicon carbide mullite bricks is high and lead to the over high temperature of rotary kiln surface temperature. which in turn,results in the increase of fuel consumption and the decline of energy efficiency. To decrease the thermal conductivity while maintaining the high temperature performance of silicon carbide mullite bricks, low thermal conductivity multi-layer composite mullite bricks ae developed.

Low Thermal Conductivity Sic Mullite Bricks Production Crafts

Low thermal conductivity SiC mullite bricks adopt multi-layer composite structure design which is composed of working layer, insulation layer and a heat preservation layer. Instead of natural bauxite clinker, bauxite-based sintered mullite is used as the main raw material. Its main mineral phase is mullite, so that the overall thermal conductivity of the SiC mullite brick is reduced, and the high-temperature structural strength is effectively enhanced. In light of the poor basic slag erosion resistance of mullite, some composite additives is added into the raw material to improve matrix property, the alkali corrosion resistance of the refractory brick is enhanced. In order to further reduce the thermal conductivity of the working layer, 97# silicon carbide fine powder with good crystal development and andalusite fine powder are added to strengthen the matrix, which not only reduces the thermal conductivity, but also improves the high-temperature structural strength , as well as thermal shock resistance of SiC mullite brick.

Working layer: M70 alumina-based sintered mullite is used as the main raw material, homogenized bauxite is used as aggregate and powder, multi-element additives such as andalusite and silicon carbide are added to prolong the service life.

The Physiochemical Index of Working Layer

Insulation layer: mainly mullite phase, using M60 alumina-based sintered mullite as the main raw material, added with some composite additives to adjust the expansion coefficient to make it close to the working layer, avoiding cracks from the joint during sintering or application. Under the premise of satisfying the strength requirement, thermal insulation effect is maximally improved.

Insulation: Thermal conductivity is an important indicator for thermal property of refractory materials. By adding a composite material with a lower thermal conductivity to the insulating layer, the overall thermal conductivity of silicon carbide mullite brick is reduced.

Low Thermal Conductivity Silicon Carbide Mullite Bricks Application

Low thermal conductivity silicon carbide mullite bricks is especially suitable for the fore- transition zone of medium & large scale rotary cement kilns. In the area where Silicon carbide mullite composite bricks are used, the cylinder temperature can be reduced by 50~80 °C. The average temperature of the fore transition zone is 250 °C, and the thermal insulation effect is very significant. The service life of low thermal conductivity SiC mullite bricks is not lower than that of spinel brick, silicon carbide mullite bricks and silicon carbide andalusite bricks. Apart from being applied to the fore transition zone of the rotary kiln, low thermal conductivity SiC mullite bricks are also used in the tertiary air duct, grate cooler side wall and so on.

Fused Cast Mullite Bricks

Fused Cast Mullite Bricks Description

Fused cast mullite bricks are aluminao-silicate series refractories, mainly composed of mullite crystalline phase. Since the principle crystalline phase of fused cast mullite brick is mullite, which has a refractoriness of about 1850°C, high refractoriness under load temperature, small high temperature creep rate, good thermal shock resistance is and acid corrosion resistance. Fused cast mullite bricks have excellent high temperature performances.

Fused  cast mullite bricks are made from high alumina bauxite, different grades of bauxite are mixed  proportionally to have identical components with mullite (3Al2O3·2SiO2, the mass percentage of Al2O3 is 72%,  and that of SiO2 is 28%). The raw material is melted at about 2300 °C, casted in sand mold at 1850°C, and then annealed to eliminate stress. The main crystalline phase is mullite and corundum, with glass phase filled between the crystalline phases.

Fused cast mullite bricks have better molten glass corrosion resistance compared with sintered mullite bricks, but not so good as other fused refractories. So if a small amount of zirconia (7%~8.5%) can be added into the raw material, which can make the mullite crystal smaller, brick structure will be denser, mullite phase can reach to 60%~70%, correspondingly, glass phase content will decline, so there will be lower cracks in fused cast mullite bricks.

Fused Cast Mullite Bricks Properties

High refractoriness and refractoriness under load  temperature.

Low thermal expansion coefficient.

Good thermal shock resistance and strong resistance to molten glass corrosion.

Fused cast mullite bricks physiochemical index

Fused Cast Mullite Bricks Application

When making fused cast mullite bricks, corundum crystal is first precipitated during the cooling, and then mullite crystal. A small amount of SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O and other oxides finally form glass phase. The glass phase accounts for 25% of the bricks. It contains many low-melting substances, so the corrosion resistance is weaker than other fused bricks. Bubbles and reducing substances are also present in the glass phase, which can contaminate the glass during application.

Fused cast mullite bricks are mainly used for parts that need wear-resistant and high-temperature resistant materials, such as sliding-rail bricks of metallurgical Pusher-type heating furnace, walking-type heating furnace tapping platform (tapping spout) and garbage incinerator lining.

High Zirconia Blocks

High Zirconia Blocks Description

High zirconia blocks are also called pure zircon bricks, their principle crystalline phase is zircon. Raw material of high zirconia block is zircon sand, with about 90% of zircon by weight. Zircon fine ore has very small granularity, so is not suitable to produce refractory bricks directly. To make coarse granule pure zircon firebricks, zircon fine ore should be pre-sintered or fused into zircon clinker. After sintering, the density of zircon fine ore is increased, bulk density can reach to 3.5g/cm3.

High Zirconia Blocks Characteristics

The weight percent of ZrO2 in pure zircon refractory is about 65%. High zirconia block is almost completely consisted of zircon crystals, only a little amount of glass phase and free ZrO2 appears in it. The true density of high zirconia blocks is about 4.55g/cm3, max. 4.62g/cm3. Ordinary zirconia block’s bulk density is between 3.6~3.8g/cm3, apparent porosity is higher than 13%. Dense zirconia brick’s bulk density is between 3.8~4.0g/cm3, apparent porosity is about 5%. High dense zirconia brick’s bulk density is larger than 4.0g/cm3, apparent porosity is less than 1.0%.

High zirconia blocks have very high viscosity even in high temperature, so its refractoriness is high, usually higher than 1825℃. The cold crushing strength of high zirconia bricks is between 100~430Mpa, modulus of rupture can reach to 17.8~76.3Mpa, refractoriness under load(RUL) is higher than 1650℃. With the reduce of mineralizer quantity and the increasement of sintering temperature, RUL can reach to 1750℃. So high zirconia bricks is a high grade firebricks which can resist high temperature load action and mechanical abrasion.

Zircon has low thermal expansion rate, so high temperature sintered zirconia blocks or fused cast zirconia blocks has good volume stability. From room temperature to 1400℃, its thermal expansion rate is only 0.5%. Refiring for 2 hours at 1500℃, residual shrinkage rate is only 0.04%~0.20%.

High dense zircon refractory will have lower thermal shock resistance if there is no corase granules. But if it is composed of multi-granularity particles, thermal shock resistance will be significantly improved.

 High zirconia blocks have good resistance to molten metals & molten slag corrosion and permeation. High dense zirconia refractory has more better performance, for example, the extent of basic molten slag corrosion is only 1/3 of mullite refractory.

Fused high zirconia blocks have the characteristics of high corrosion resistance, low foaming rate and stone rate, almost no pollution to the glass liquid.

High Zirconia Blocks Physiochemical Index

High Zirconia Blocks Application

Zircon refractory are mainly used in continuous casting ladle inner lining and other parts where suffers severe molten slag corrosion. High zirconia blocks are also used for the masonry of copper and aluminum smelting furnaces casting nozzles. Besides, high zirconia blocks can also be used in glass kilns, where contacts with glass liquid directly and upper structure, as well as separation bricks between fused cast zirconia corundum bricks and silica bricks. Fused high zirconia blocks are suitable for various glass furnaces, especially high quality glass furnaces and special glass furnaces, such as glass bath wall, throat, electrode bricks and so on.

Sialon Bonded Sic Refractories

Sialon Bonded Sic Refractories Description

Sialon bonded SiC refractories are normally β-Sialon bonded SiC material. Sialon is the general name of compounds consisted of Si, Al, O, N and other elements. β-Sialon has many similar properties of Si3N4 based ceramic material, such as high rigidity, excellent mechanical performance, corrosion resistance, thermal shock resistance, low linear expansion coefficient. Its thermal conductivity is lower than β-Si3N4, but oxidization resistance is better than β-Si3N4, as well as better corrosion resistance to Al, Fe and Zn molten liquid and alkali.

Sialon bonded SiC bricks are mainly used as inner lining of blast furnace bosh or furnace belly. It is regarded as the second generation of SiC bricks used  for blast furnaces. The principle crystalline phase of Sialon bonded SiC material is SiC, secondary phase is β-Sialon. Sialon bonded SiC bricks have relatively more Al2O3 compared with Si3N4 bonded SiC bricks.

For blast furnace SiC refractory, SiC content is usually between 70%~80%. With the SiC content, Sialon bonded SiC refractory has slightly higher linear expansion coefficient than Si3N4 bonded SiC refractory, while slightly lower thermal conductivity.

Sialon Bonded Sic Refractories Characteristics

Sialon bonded SiC refractory has very excellent high temperature and high temperature mechanical performances, most Sialon bonded SiC refractory’s 1400℃ modulus of rupture(MOR) is higher than cold MOR.

Sialon bonded SiC refractory also has excellent alkali corrosion resistance. Its alkali corrosion resistance is significantly better than Si3N4 bonded SiC refractory, which makes it more suitale to be used in places of blast furnace where have severe alkali corrosion.

Sialon bonded SiC has excellent oxidization resistance.

Sialon bonded SiC has excellent thermal shock resistance.

Sialon bonded SiC has excellent blast furance slag corrosion resistance.

Generally speaking, compared with Si3N4 bonded SiC material, Sialon bonded SiC has better basic slag corrosion resistance, iron, aluminum and other molten metal corrosion resistance.

Sialon Bonded Sic Refractory Application

Sialon bonded SiC products have been applied in many large scale blast furnaces, molten reduction iron smelting furances (COREX furnace lining, where has severe corrosion damage). Sialon bonded SiC are also used in nonferrous metals industry, such as zinc smelting, aluminum smelting and so on.

The Application Of Silicon Carbide Refractories

Silicon Carbide Refractory Description

Due to the excellent high temperature performances of silicon carbide refractory, they are widely used in steel industry, nonferrous metals industry, petrol industry, power plant, chemical industry and so on.

The Advantages of Silicon Carbide Refractory

High mechanical strength.

Good thermal conductivity.

Excellent thermal shock resistance and abrasion resistance.

Good slag corrosion resistance and alkali corrosion resistance.

Excellent oxidization resistance.

Good erosion resistance to some molten metals.

 SiC refractories applications

Silicon Carbide Refractory Used In Steel Industry

Si3N4 and Sialon bonded SiC & corundum SiC composite refractories are mainly used in steel industry. For example, the lower part of blast furnace bosh, belly, tuyere combination bricks, tuyere sleeve, iron runner, cupola inner lining, coke oven head, heating furnace sliding rail, converter and electric furnace tapping hole.

Silicon Carbide Refractory  Used In Nonferrous Metals Industry

Oxide bonded SiC, Si3N4, Sialon, Si2N2O bonded SiC refractories are widely used in nonferrous metals ( aluminum, zinc and copper, etc) smelting. Aluminum electrolysis cell inner lining, aluminum refinery furnace lining, zinc retort vessel lining, zinc fine distillation tower tray, ISP furnace condenser and rotor, fine copper smelting stand furnace, ASARCO furnace bosh lower part working lining and holding furnace inner lining, molten metals tube, metal smelting crucible, iron powder reduction smelting sagger, aluminum and zinc liquid temperature testing thermocouple protection tube, aluminum casting ceramic raiser tube and so on.

In Ceramics Industry

Oxide bonded SiC, Si3N4 and Si2N2O bonded SiC refractoryies can be used as muffle board and kiln furniture of ceramics kilns, high temperature burning nozzle, glass annealing furnace lining, ceramic sintering furnace lining, muffle furnace inner lining, rotary cement kiln clinker cooler, radiation heating tube, cyclone separator inner lining, etc.

Silicon Carbide Refractory Used In Metallurgy

The protective coating tube of radioactive pyrometer, thermocouple pyrometer and pyrophotometer. The blades of ore selecting stirrer. Sand pump inner lining and swirler nozzle.

Silicon Carbide Refractory Used In Chemistry

Fertilizer nitriding furnace inner lining, petrol vaporizer, desulfurization furnace and organic scrap incinerator inner lining, heat exchanger and so on.

Silicon Carbide Refractory Used In Chemical Fiber Industry

Sand furnace inner lining.

Silicon Carbide Refractory Used Petroleum Industry

Spray nozzle, encapsulation element, valve plates and so on.

Wear Resistant Firebrick

Wear Resistant Firebricks Description

High strength wear resistant firebricks, or also called abrasion resistant firebricks are shaped refractory materials. Refractory bricks has standard sizes and can be processed as per required dimensions during construction. High strength wear resistant refractory bricks have been very popular in recent years. Abrasion resistant firebricks are usually made by corundum, silicon carbide or other abrasion resistant materials, and processed by special crafts. Wear resistant firebricks have high mechanical strength, high density, good abrasion resistance and so on. Abrasion resistant firebricks are widely used in various kinds of industrial furnaces and kilns, such as high temperature zone, strong mechanical abrasion zone and so on. Among them, silicon nitride bonded silicon carbide bricks has the best wear resistance (room temperature wear resistance is about 1.8cm3).

Wear Resistant Firebricks Characteristics

1. Strong wear resistance and good eolation resistance, ideal for strong abrasion area.
2. The thermal conductivity is good because of pores in refractory brick. Under the unit temperature gradient, the unit heat flow rate through the material is related to the porosity.

3, good slag resistance, can resist high temperatures slag erosion and corrosion.

4. High-strength wear-resistant firebricks have good impact resistance, high strength and long service life.

Wear Resistant Firebricks Physiochemical Index

Wear Resistant Firebricks Applications

Wear-resistant  refractory bricks are mainly used for circulating fluidized bed boilers, boiling furnaces and other industrial furnaces. In the past two decades, with the popularization and application of industrial furnaces such as circulating fluidized bed boilers and boiling furnaces, high requirements have been placed on the wear resistance of refractory materials. Traditional refractory materials, such as clay bricks and ordinary high-aluminum bricks, could not meet service life demand. For example, the service life of a typical clay brick in a serious abrasion part of the circulating fluidized bed is only about 3 to 6 months. So wear-resistant refractory bricks are developed, their wear resistance are far better than that of ordinary refractory bricks. Wear resistant firebricks’ service life is between 1 and 2 years.

Silicon Carbide Bricks

Silicon carbide bricks are high grade refractory material, its main chemical composition is SiC. Silicon Carbide Fire Bricks have both normal temperature and high temperature mechanical strength, good thermal conductivity, small linear change rate, excellent thermal shock resistance, excellent high temperature abrasion resistance and fairly good chemical corrosion resistance. The Fire Bricks in RS Refractory Manufacturer are popularly used in steel industry, nonferrous metal industry, chemical industry, power plants, ceramics industry and so on. 

Silicon Carbide Bricks Classification

Silicon carbide bricks can be divided into different categories based on SiC content, binder types and quantity. According to binder types, SiC bricks can be divided into:

1. Oxide bonded SiC bricks. The bonding phase is Al2O3-SiO2 series silicate, including clay bonded silicon carbide brick, mullite bonded silicon carbide brick and silica bonded SiC brick.
2. Nitride bonded silicon carbide brick. The bonding phases are Si3N4, Si2N2O, Sialon and other covalance compounds.
3. Self bonded SiC bricks. Including β-SiC bonded SiC bricks and re-crystallization SiC bricks.
4. Siliconizing reaction sintered SiC bricks. SiC and free Si consisted engineering ceramics material.

Normally, SiC products with less than 50% SiC are called semi SiC refractory, including clinker SiC refractory, high alumina SiC refractory, zircon SiC refractory, mullite SiC refractory and Corundum SiC refractory, etc.

Oxide Bonded Silicon Carbide Brick

The mineral phases of oxide bonded silicon carbide bricks are quartz, mullite and silicate glass phase. Based on the difference of bonding phases, oxide bonded SiC bricks can be divided into SiO2 bonded SiC bricks, mullite bonded SiC bricks and clay bonded SiC bricks.

Clay Bonded Silicon Carbide Brick

Clay bonded silicon carbide bricks contain 50%~90% SiC, binding material is binding clay, usually added in sillimanite, andalusite, kyanite and other mineral fine powder. The sintering temperature is between 1350~1450℃. The quantity and types of binding material can directly affect the performance of clay bonded SiC bricks. With the increase of clay content, oxidization resistance is improved, but thermal conductivity, refractoriness under load temperature, thermal shock resistance and high temperature strength will all decrease.

Clay bonded SiC refractory are mainly used as muffle boards of various kinds of industrial kilns and furnaces, ceramic kiln furniture ( refractory slab, sagger and so on). But due to the clay bonding phase in SiC refractory, Clay bonded SiC refractory high temperature performance is greatly affected.

Mullite Bonded Silicon Carbide Brick

Mullite bonded silicon carbide bricks developed on basis of clay bonded SiC refractory. The bonding raw material are high purity Al2O3 and SiO2 micro powder or fine powder, sometimes sillimanite, andalusite and kyanite fine powders are also added. The bonging phase are mainly mullite, with low glass phase. In mullite bonded SiC bricks, SiC content is between 65%~85%, sintering temperature is between 1350~1500℃. Mullite bonded SiC bricks have significantly better high temperature performance than clay bonded SiC bricks. Mullite bonded SiC bricks are widely used in ceramic industry, nonferrous metals industry, machinery industry and so on.

Silica Bonded Silicon Carbide Brick

SiO2 bonded SiC bricks has far better high temperature performance than clay bonded SiC refractory, high temperature modulus of rupture is higher than mullite bonded SiC refractory. Silica bonded SiC bricks are mainly used as kiln furniture.

Oxide Bonded Silicon Carbide Brick Specification

Silicon Carbide Bricks Manufacturer

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Silicon Nitride Bonded Silicon Carbide Bricks

Silicon Nitride Bonded Silicon Carbide Bricks Description

Silicon nitride bonded silicon carbide bricks are the most widely used nitride boned SiC refractories. Nitride bonded SiC materials have many excellent high temperature performances such as high mechanical strength, good thermal conductivity, small linear expansion coefficient, good thermal shock resistance, alkali corrosion resistance, oxidization resistance, molten metal liquid( zinc, copper, aluminum, lead,etc) corrosion resistance, as well as high temperature abrasion resistance. Si3N4 bonded SiC bricks are composite refractory, main crystalline phase is SiC, secondary crystalline phase is α-Si3N4 and β-Si3N4.

Si3N4 Bonded SiC Bricks Characteristics

Low apparent porosity.

Excellent high temperature mechanical strength.

Good high temperature creep resistance, at 0.2 Mpa load condition, RUL beginning temperature is higher than 1800℃.

High modulus of rupture.

Good thermal conductivity.

Very high alkali corrosion resistance.

Excellent oxidization resistance.

Prominent thermal shock resistance.

Excellent slag corrosion resistance.

Have strong cryolite corrosion resistance , ZnO corrosion resistance and electrolyte permeation resistance.

Si3N4 Bonded SiC Bricks Physiochemical Index

Si3N4 Bonded SiC Bricks Application

Si3N4 bonded SiC refractories are widely used in steel industry, nonferrous metals industry, ceramics industry and so on. Blast furnace refractory materials corrosion reasons include: alkali corrosion, CO, Zn, SiO and water vapor oxidization, abrasion, low thermal conductivity, thermal shock and slag corrosion. In light of this condition, Si3N4 bonded SiC bricks are the ideal products for blast furnace inner lining. The service life of silicon nitride bonded silicon carbide bricks inner lining can reach to 10~15 years. It is the first choice of large scale blast furnace inner lining refractory material.

SiN4 bonded SiC refractory is the best choice of new generation aluminum reduction cell inner lining. It can decrease horizontal electric current, increase side part heat diffusion, decline cell temperature, enhance electric current efficiency and save energy. Besides, the service life of aluminum reduction cell is greatly prolonged. SiN4 bonded SiC bricks have good thermal conductivity, cryolite corrosion resistance, oxidization resistance and scouring resistance. During using, SiN4 bonded SiC bricks inner lining can form a thick and stable protective layer, which in turn effectively prolongs the service life of aluminum electrolysis cell.

Si3N4 bonded SiC bricks are also used as kiln furniture of ceramic kilns.