Application of Microsilica Powder in Refractory Materials

Silica powder is a kind of powder that will produce a part of solid waste tail gas in the process of smelting ferrosilicon alloy and metal silicon, which is collected by dust removal equipment.

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The raw materials for smelting ferrosilicon alloy are quartz rock crushed stone and pig iron, adding coke as a reducing agent, reacting in a high-temperature electric furnace close to 2000 ℃, the quartz is reduced to silicon, and reacts with pig iron to form ferrosilicon alloy. During this process, due to the high temperature, the flue gas brings 10% to 15% silicon (Si) vapor, which combines with oxygen in the flue to form silicon monoxide, and reacts with oxygen in the cold air to form silicon monoxide after exiting the flue. The silica vapor then condenses and crystallizes in air to form fine particles.

Properties of microsilica powder

(1) Good insulation. Silica powder has the advantages of high purity, stable performance and good electrical insulation, so that the cured product after solidification also has the characteristics of good insulation and high arc resistance.
(2) Add silicon micropowder to the epoxy resin to reduce its exothermic peak temperature during curing, which can also reduce the linear expansion coefficient and shrinkage rate of the cured product, reduce the internal stress of the cured product, and avoid cracking.
(3) Microsilica powder is an inert substance, it is difficult to react with other substances, and it does not react much with acid and alkali. If a layer of microsilica powder particles is covered on the surface of the object, it can effectively improve the corrosion resistance.
(4) The particle gradation is reasonable, which can reduce and eliminate precipitation and stratification during use; it can increase the tensile and compressive strength of the cured product, improve the wear resistance, increase the thermal conductivity of the cured product, and increase the resistance flammability.
(5) Silica powder treated with silane coupling agent has good wettability to various resins, good adsorption performance, easy mixing, and no agglomeration.
(6) Adding silicon micropowder filler to the organic resin can improve the properties of the cured product and reduce the cost.

Modification of silica powder

The surface modification of silica powder mainly relies on silane coupling agent to achieve compatibility with polymer materials. In the modification process, special attention should be paid to the types of silanes, their dosage and usage. In addition, the best treatment time, temperature and pH value can be mastered through experiments. By measuring the wetting angle, penetration time and wetting point of modified powdered quartz to water droplets, compared with unmodified powdered quartz, it shows that modified powdered quartz has better compatibility and affinity with organic polymers. The viscosity of the silane-modified powder quartz in the epoxy resin mixing system is significantly reduced, the processing performance of the filler and polymer mixing system is improved, a uniform mixture is obtained, the filling amount is increased, and the production cost is reduced.

Application of silica powder in refractory industry

Application of silica powder in refractory industry
Microsilica powder is mainly used in unshaped refractories in the refractory industry. The action mechanism of microsilica powder is complex, and it is generally considered to be the combined action of filling and coagulation. Although the refractory aggregate and powder gradation of traditional refractory castables have higher bulk density and denser, many pores are still filled by excess water. After the water is removed, many pores are left; when microsilica powder is used, these pores are filled by microsilica powder, and a very small amount of micropores are filled by water. In this way, the amount of mixing water for refractory castables is reduced, and after the water in the molded body is removed, there are fewer pores left. That is to say, the addition of microsilica powder can reduce the water consumption for mixing, increase the bulk density and reduce the apparent porosity at the same time.
There are two main types of SiO2 powder used in castables: one is made of high-purity silica, and the other is a by-product of the production of metallic silicon or ferrosilicon, both of which are amorphous amorphous materials. The former is granular and inactive; the latter is hollow spherical, active, non-agglomerated, and has good filling properties. After being mixed with castables and condensed, silanol groups are formed on the surface of SiO2, and after drying and dehydration, a siloxane network structure is formed, which is not easy to break when the temperature rises, and the medium temperature strength is improved, and mullite is formed with Al2O3 at high temperature, which is also Conducive to the improvement of material strength. Therefore, silica powder is widely used in low cement, ultra-low cement and cement-free castables.
SiO2 is used together with an appropriate dispersant and added to the castable. Since silicon micropowder is a particle with an obvious spherical shape, it is easy to enter the tiny gaps in the castable, and the particle size is small, so it not only has a good water reducing effect, but also improves The compactness of the refractory castable reduces the porosity and porosity left after drying, thereby improving the strength and high-temperature performance. At the same time, the active silica powder forms a colloid in water, and the colloid particles absorb the dispersant around it to form a solvent layer, thereby increasing the fluidity of the castable and improving its molding performance. In addition, due to the small particle size, large surface free energy, many lattice defects, and high activity of silicon micropowder, solid-state sintering reaction and mullite reaction with Al2O3 in high-alumina refractories are more likely to occur at medium and high temperatures. Thereby improving the post-firing strength and high temperature performance of the low cement refractory castable.

Microsilica is an indeterminate micropowder with spherical structure, with large specific surface area and high chemical activity, which is widely used in refractory materials. As the microsilica can fill the pores between cement particles, and at the same time generate gels with hydration products, it can also react with alkaline material magnesium oxide to generate gels.

    In cement-based concrete, mortar, exterior wall insulation, grout and refractory castables, the addition of appropriate amount of microsilica can realize excellent performance and economic benefits. Our ACC microsilica products provide you with excellent cost performance and reliable quality, helping your building materials to achieve outstanding performance levels.

 Refractory materials with microsilica to improve its performance has been more than 40 years of history, refractory materials with microsilica  will have the following characteristics and performance:

1, improve the fluidity of cast refractories, reduce water consumption, so that it is easy to mold, greatly improving production efficiency;.

2, because of its ultra-micro-structure of the gap-filling effect, the denseness and strength of the refractory material to get a substantial increase;.

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3, microsilica ash with high activity, in the presence of Al2O3 components under the premise, easier to generate mullite phase, so that the high temperature strength of refractory materials, thermal shock stability significantly improved.

 Microsilica is a commonly used micropowder in castables. Microsilica with small particle size can fill the pores between particles in the castables and reduce the water consumption of the castables; microsilica has a standard spherical structure, which has the "rolling ball effect". When it is filled between particles, the relative sliding friction between particles is changed to rolling friction, which reduces the friction between particles, resulting in the viscosity of the castables being reduced and the fluidity being improved.

ACC® undensified microsilica is a by-product of the production of ferrosilicon alloys or silicon metal, with SiO₂ content range from 85% to 96%, bulk density around 300-400kg/m³, and light grey color.

 

 

Due to its special production process, microsilica has an amorphous crystal structure, which is easy to form broken bonds on the surface of the particles. Due to the existence of broken bonds, microsilica in aqueous solution can easily adsorb OH- in water to form Si-OH, and dissociate into Si-O- and H+ in aqueous solution. Due to its relatively small particle size (micron level), microsilica can easily form a colloidal structure with a double electric layer in aqueous solution. Highly active microsilica can adsorb OH- in aqueous solution, forming a large number of hydroxyl groups on the surface of its particles.

In the low-temperature maintenance, the microsilica can be dehydrated to form -Si-O-Si-bonds between the particles, which improves the mold release strength of the castables. Microsilica can become liquid phase at high temperature, which reduces the viscosity of mass transfer between particles, and thus enhances the mass transfer rate and promotes the sintering between particles. Therefore, the castables doped with microsilica can promote the sintering between the matrix in the castables at 800℃, which enhances the interlocking bonding ability between the particles, and improves the mid-temperature strength of the castables.

  According to the different properties of refractory raw materials, orthogonal design, through the comparison test, select the best formula, microsilica manufacturers of technical experts can assist refractory factory to carry out the work of coordinated nature. Refractories usually use undensified microsilica. In addition to its wide use in castables for non-crystallized refractories, it is now also being used in a large number of applications in electrofused and sintered refractories.

For example, it is used as low cement castable: low cement castable is a new type of high-performance refractory castable developed in the 1970s, which was firstly developed successfully by France. It is widely used in various industrial high temperature furnaces, with good technical and economic results. 1983 Pittsburgh City, the United States general refractory company will be used for low cement castables for blast furnace main iron out of the ditch ditch cover lining, the service life of the original ordinary castables is three times, from 75-100 furnaces up to 300-400 furnaces.

  Both low cement castables and ordinary castables use calcium aluminum cement. However, after the former is equipped with microsilica and high-efficiency water reducing agent, the amount of cement added is 4-8%, and the amount of water added is only 5-8%, which is 15-20% of the amount of cement and 10-15% of the amount of water added than the latter, and there is a substantial reduction. Low-cement castables not only save 50-70% of expensive aluminate cement, but also the performance of microsilica for refractory materials has been greatly improved.

The test results of the General Research Institute of Architecture of the Ministry of Metallurgy on low cement castables are as follows:

  (1)Porosity and pore structure tuning: low cement castables and ordinary castables in 1400 ℃ heating after the apparent porosity comparison, the former is 20.4%, while the latter is 26.4%, an increase of nearly 30%. The total porosity in low cement castables is lower than that in ordinary castables as determined by the pressure pump method. The increase was nearly 40% in ordinary castables after heating at 800°C compared to 110°C drying. From the pore size distribution, the pore size in ordinary castables greater than 100A is 2-3 times of that in low cement castables, and the pore size in less than 1000A is only 30-50% of that in low cement castables.

  (2)Refractory materials with microsilica strength change characteristics: low cement castables strength regardless of low, medium and high temperature stage can continue to grow, while the ordinary castables have a significant decline in the strength of the medium temperature. At present, refractory products, ceramic dampers and ceramic inner cylinders have been widely used. And according to the available information, low cement castables are widely used in foreign countries, and have been applied in coke oven, sintering, iron making, steel making, steel rolling, non-ferrous metallurgy, petroleum and chemical industry, cement, glass ceramics and power generation and other industries.

We proudly announce that in the field of refractory applications, many of our collaborative clients have chosen our ACC microsilica and reported significant success. We adhere to our commitment to product quality ensuring that each order represents outstanding performance and superior quality. Trust in us as we continue to provide excellent  microsilica. We look forward to our collaboration, delivering exceptional service and top-tier products for you.

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