The main methods to improve the thermal shock performance of products as following:
- Reasonable particle size composition and porosity
- Appropriately increase micro cracks
- Fiber toughened refractories
- Choose raw materials with better thermal performance
Thermal shock performance is the ability of refractory materials to maintain a certain strength without failure under thermal stress. Thermal stress causes cracks in refractory products, and gradually leads to crack propagation and partial peeling of products, and finally damages the products. Therefore, the thermal shock performance of refractory materials is an important index to evaluate its high-temperature performance, and the excellent thermal shock performance is directly related to the service life of refractory materials.
Material resistance to thermal shock damage is divided into two types: thermal shock fracture resistance and thermal shock damage resistance. The former theory only considers the generation of new cracks in the product and the fracture of the product, and does not consider the expansion of the original cracks in the product. However, in the actual preparation process of refractory products, due to the difference in thermal expansion coefficient of the raw materials used, the products There will inevitably be some microcracks inside, and the existence of these microcracks can delay the damage of thermal stress to the product, so the thermal shock performance of the product can be improved to a certain extent, so the thermal shock damage resistance mechanism of refractory products should be Thermal shock damage.
Resistance to thermal shock damage
The theory of thermal shock damage resistance points out that under the action of thermal shock, the degree to which microcracks are generated in the product and thus expand and spread is related to the elastic modulus of the product itself.
The increase of R value is conducive to the improvement of thermal shock performance, so it can be clearly seen from the formula that the influence of various factors on the thermal shock performance of materials provides a certain reference for the preparation of refractory products.
The improvement of the thermal shock stability of refractory materials can directly lead to the improvement of the service life of products. Therefore, many high-temperature industries pay more and more attention to the indicators of thermal shock stability of refractory materials, especially in the use environment with frequent temperature changes. Thermal shock stability becomes particularly important. Nowadays, the main methods to improve the thermal shock performance of products are:
01 Reasonable particle size composition and porosity
Refractory products are generally compounded by combining multi-level particle sizes, especially for castables, the particle size can reach more than 5 grades. With the continuous development of micropowder and nanopowder technology, research on the use of ultrafine powder to improve the performance of refractory castable products has also been gradually carried out. Whether the particle gradation is reasonable directly affects the bulk density, porosity and pore size of the product, and the appropriate porosity is conducive to the improvement of the thermal shock performance of the refractory material.
02 Appropriately increase micro cracks
If there is a certain amount of fine cracks with a uniform network structure inside the refractory product, it can effectively improve the product’s ability to resist thermal shock damage. Therefore, many researchers are trying to add some substances that can increase the network micro-cracks in the refractory products to improve the thermal shock stability of the products. Using the difference in thermal expansion coefficient between different raw materials, a certain amount of micro-cracks can be generated inside the product, thereby improving the thermal shock stability of the product.
03 Fiber toughened refractories
Fibers have a prominent pull-out or bridging effect in refractory products. Research in this area has also been carried out, and now it is mainly focused on research on heat-resistant steel fibers and silicon carbide fibers. In addition, studies on the bridging effect by the formation of fibrous minerals are being paid attention to. The formation of the required new minerals can not only achieve the effect of improving the thermal shock performance of the product, but also have important significance for the improvement of other high-temperature properties.
04 Choose raw materials with better thermal performance
The thermal expansion of raw materials is one of the main factors that generate thermal stress. Raw materials with low thermal expansion coefficient have good volume stability and are not easy to generate large thermal stress in the process of rapid temperature changes. Raw materials with high thermal conductivity can quickly heat up and cool down when the temperature changes sharply, thereby minimizing the generation of thermal stress. Therefore, for refractory materials with excellent thermal shock stability, it is also very important to choose suitable raw materials. Over the years, the research on raw materials for refractory products has not stopped. The successful application of non-oxides with low thermal expansion coefficients in refractory products has become a new breakthrough in the study of improving thermal shock performance. In recent years, oxide-non-oxide composite materials have become a research hotspot, and research on Al2O3-SiC and MgO-SiC castables has achieved good results. Studies have shown that adding such materials on the basis of the original oxide can significantly improve the thermal shock performance of the product.