Refractory materials are crucial in various high - temperature industrial applications, such as steelmaking, cement production, and glass manufacturing. The porosity of these materials significantly impacts their performance, including thermal conductivity, mechanical strength, and resistance to chemical attack. Refractory micro silica, a key additive in refractory materials, plays a vital role in altering the porosity of these materials. As a refractory micro silica supplier, I will delve into how refractory micro silica affects the porosity of refractory materials.
Physical and Chemical Properties of Refractory Micro Silica
Refractory micro silica, also known as silica fume, is a by - product of the silicon and ferrosilicon alloy production in electric arc furnaces. It consists of extremely fine, amorphous spherical particles with a high specific surface area, typically ranging from 15,000 to 30,000 m²/kg. The high purity of micro silica, with silicon dioxide (SiO₂) content often exceeding 90%, gives it unique physical and chemical properties that are beneficial for refractory applications.
Mechanisms of Porosity Reduction
Filling Effect
One of the primary ways refractory micro silica affects the porosity of refractory materials is through the filling effect. The fine particles of micro silica can fill the voids between larger refractory aggregates. In a refractory mix, larger particles form a skeletal structure, but there are always gaps or pores between them. Micro silica particles, due to their small size, can penetrate these spaces and pack tightly, reducing the overall porosity of the material.
For example, in a refractory brick made of alumina aggregates, the addition of micro silica can fill the inter - particle voids. This results in a more compact structure, where the porosity is decreased. The reduction in porosity not only improves the density of the refractory material but also enhances its mechanical strength, as there are fewer weak points in the form of large pores.
Pozzolanic Reaction
Refractory micro silica is highly reactive due to its amorphous nature and high specific surface area. It undergoes a pozzolanic reaction with calcium hydroxide (Ca(OH)₂) in the presence of water. In refractory systems that contain calcium - bearing components, such as calcium aluminate cement, this reaction is significant.
The pozzolanic reaction between micro silica and calcium hydroxide forms calcium silicate hydrates (C - S - H). These C - S - H gels are very fine and can further fill the pores in the refractory material. As the reaction progresses, the C - S - H gels grow and bind the refractory particles together, creating a more dense and less porous structure.
This reaction also contributes to the long - term strength development of the refractory material. By reducing the porosity, the C - S - H gels improve the resistance of the refractory to the ingress of corrosive gases and liquids, which is crucial in high - temperature industrial environments.
Impact on Different Types of Porosity
Open Porosity
Open porosity refers to the pores that are connected to the surface of the refractory material and allow the passage of gases and liquids. Refractory micro silica can effectively reduce open porosity. The filling effect and the pozzolanic reaction both contribute to sealing the open pores. As the micro silica particles fill the voids and the C - S - H gels form, the open channels in the refractory are blocked, preventing the easy entry of corrosive agents.
In steelmaking ladles, where refractory linings are exposed to molten steel and slag, a low open porosity is essential. By adding refractory micro silica to the ladle lining refractory, the open porosity can be reduced, improving the resistance of the lining to slag penetration and erosion.
Closed Porosity
Closed porosity consists of isolated pores within the refractory material. Although the reduction of closed porosity is more challenging compared to open porosity, refractory micro silica can still have an impact. The formation of a more compact structure through the filling effect and pozzolanic reaction can limit the formation of large closed pores during the sintering or curing process of the refractory material.
In some high - temperature kiln applications, closed porosity can affect the thermal conductivity of the refractory. By reducing the closed porosity, the thermal conductivity can be optimized, which is beneficial for energy efficiency in the kiln operation.
Influence of Micro Silica Dosage
The amount of refractory micro silica added to the refractory material has a significant influence on the porosity reduction. Generally, as the dosage of micro silica increases, the porosity of the refractory material decreases. However, there is an optimal dosage.
If the dosage of micro silica is too low, the filling effect and pozzolanic reaction may not be sufficient to significantly reduce the porosity. On the other hand, if the dosage is too high, it can lead to problems such as increased water demand, which may result in more pores being formed during the drying process.
For example, in a refractory castable, an appropriate dosage of micro silica (usually around 5 - 10% by weight) can achieve the best balance between porosity reduction and workability. At this dosage, the micro silica can effectively fill the pores and undergo the pozzolanic reaction without causing excessive water demand.
Applications in Different Industries
Steel Industry
In the steel industry, refractory materials are used in various processes, such as blast furnaces, converters, and ladles. Refractory micro silica is widely used to improve the performance of these refractory linings. By reducing the porosity of the refractories, it enhances their resistance to slag corrosion, thermal shock, and mechanical wear. For instance, in blast furnace linings, the addition of micro silica can improve the density and strength of the refractory, increasing the service life of the lining.
Cement Industry
In cement kilns, refractory materials are exposed to high temperatures and corrosive gases. The use of refractory micro silica in the kiln linings can reduce the porosity, improving the resistance of the linings to alkali attack and thermal stress. This leads to longer - lasting refractory linings and more stable cement production processes.
Glass Industry
In glass melting furnaces, the refractories need to have low porosity to prevent the infiltration of molten glass and the attack of glass - forming gases. Refractory micro silica can be added to the furnace lining refractories to achieve a low - porosity structure, ensuring the quality of the glass production and the durability of the furnace lining.
Considerations for Refractory Design
When designing refractory materials with the addition of refractory micro silica, several factors need to be considered. The particle size distribution of the micro silica is crucial. A well - controlled particle size distribution can ensure an effective filling effect. The reactivity of the micro silica also needs to be taken into account, as it affects the rate and extent of the pozzolanic reaction.
The compatibility of micro silica with other refractory raw materials is another important consideration. Some raw materials may react with micro silica in unexpected ways, which can affect the porosity and performance of the final refractory product.
Conclusion
Refractory micro silica has a profound impact on the porosity of refractory materials. Through the filling effect and pozzolanic reaction, it can significantly reduce both open and closed porosity, improving the density, strength, and corrosion resistance of the refractories. In different high - temperature industrial applications, such as steelmaking, cement production, and glass manufacturing, the use of refractory micro silica is essential for achieving high - performance refractory linings.
If you are looking for high - quality refractory micro silica for your refractory applications, Silica Fume for Construction, Refractory Silica Fume, and Micro Silica for Concrete are great resources. We, as a reliable refractory micro silica supplier, are committed to providing you with the best products and technical support. If you are interested in purchasing refractory micro silica or have any questions about its application in your refractory materials, please feel free to contact us for further discussion and procurement negotiation.
References
- Singh, B., & Siddique, R. (2015). Influence of silica fume on properties of concrete: A review. Construction and Building Materials, 82, 441 - 450.
- Zhang, Y., & Guo, X. (2018). Effects of silica fume on the microstructure and properties of refractory castables. Journal of the European Ceramic Society, 38(12), 3959 - 3966.
- Schneider, H., Swainson, I., & Phillips, P. (2008). High - Temperature Technology of Refractory Materials. Wiley - VCH.