Special Grade Phosphate Bricks

Special Grade Phosphate Bricks Description

Phosphate bricks have been recognized as high quality linings for cement kilns and lime kilns. Phosphate bricks include two types: one is phosphate bonded high alumina brick (referred to as phosphate brick), and the binder is phosphoric acid solution with a concentration of 42.5% ~ 50%; the other is phosphate bonded high alumina wear resistant bricks ( wear-resistant bricks), and the binder is aluminum phosphate solution prepared from industrial phosphoric acid and industrial aluminum hydroxide. Among them, phosphate brick has good chemical stability, high thermal strength and good wear resistance. It is often used at expansion port of machine shaft kiln and high temperature zone kiln lining, rotary cement kiln cooling zone and transition zone. The corrosion resistance of wear-resistant bricks is better than that of phosphate bricks. It is commonly used in areas of machine shaft kiln where abrasion is severe,  as well as cooling machine an and kiln preheating parts of the rotary kiln.

Special grade high alumina bricks contain zirconium, their thermal shock stability and anti-stripping property are good, Special grade phosphate brick is developed and produced in recent years. Special grade phosphate brick is made from phosphate solution binder with a concentration of 42.5%~50%, alumina clinker aggregate calcined above 1600 °C in rotary kiln. During the application of the special grade phosphate brick, the phosphoric acid and the calcined bauxite fine powder react with the refractory clay to form a bond mainly composed of cristobalite-type orthophosphate.

Special Grade Phosphate Bricks Characteristics

High normal temperature compressive strength, good thermal shock stability, high Refractoriness under load temperature, accurate dimensions, large bulk density and good wear resistance.

Special phosphate brick has the advantages of ordinary phosphate brick: high normal temperature compressive strength, good wear resistance, refractoriness under load temperature is basically equivalent to semi-direct combined magnesia chrome brick, superior to anti-spalling high alumina brick, and has good thermal shock stability.

For transition zone with large temperature fluctuation, special grade phosphate bricks have obvious performance advantages: high temperature strength and strong resistance to thermal stress and mechanical stress in the kiln, excellent adaptation to cylinder body ellipticity changes at wheel belt parts.

Secial grade phosphate brick has higher bulk density and lower permeability, which greatly improves its thermodynamic performance and chemical corrosion resistance. The harmful components in coal powder fluctuate greatly, especially the SO3 component is high and unstable. Special grade phosphate brick is almost neutral and not sensitive to alkali corrosion, so it is more suitable for the transition zone where lining coating is frequently sprayed and damaged.

Special Grade Phosphate Bricks Physiochemical Index

Special Grade Phosphate Bricks Applications

Special grade phosphate bricks are suitable for transition zone kiln mouth of rotary kiln and other parts that firebricks are easy to fall off, and are suitable for sintering zone. The use of special phosphate bricks in the transition zone, the service life of the bricks is basically matched with the magnesia chrome bricks.  Special grade phosphate bricks are also used in mechanical shaft kiln, lime kiln, carbon industry rotary kiln and so on.

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.