Magnesia carbon refractory is a kind of furnace lining material mainly used in converter, electric furnace and ladle. Carbon plays a very key role in smelting molten steel at high temperature. This is because carbon has the characteristics of high thermal conductivity, low thermal expansion coefficient and low wettability to slag, so as to improve the corrosion resistance of slag and improve the thermal shock resistance.
Due to the high content of carbon, the traditional magnesia carbonaceous refractories have great heat loss and easy oxidation in the process of use, which is not conducive to the production of high-quality steel such as clean steel and special steel, and thus cannot meet the requirements of use. Therefore, low carbonization is the main development trend of magnesia - carbon refractories. However, for low carbon magnesia carbonaceous refractory, in view of the low carbon content, the slag resistance and thermal shock resistance becomes worse, which leads to the main form of damage is slag erosion and material surface cracking or spalling.
1.Improve slag resistance of magnesia carbon refractories
Low carbon magnesia carbon refractories are mainly composite materials composed of magnesia, graphite, carbon bond, antioxidant and other components. Among them, the research on strengthening slag resistance of low carbon magnesia carbon bricks with nanotechnology mainly focuses on two aspects: nano carbon strengthening matrix structure and nano catalyst modifying carbon bond.
In the low carbonization process of magnesia carbon refractories, nano carbon is often introduced as a raw material to improve the slag resistance and thermal shock resistance of products. The reason is that nano carbon has the characteristics of large specific surface area, high reactivity and small particle size, which enhances the direct bonding strength between particles.
In the traditional carbon magnesia refractories, the combination between different particles is through the chemical crosslinking reaction of carbon binders such as coal tar, asphalt, phenolic resin, etc. The cross-linked network structure acts as a bridge to make the particles cross link with each other, forming a certain interlocking network structure. However, due to the low carbon content of low-carbon magnesia carbon refractories, it is difficult to achieve a continuous network structure, which reduces the direct bonding strength between particles. Therefore, the modification of carbon binder is one of the key factors affecting the performance of low-carbon magnesia carbon refractories.
2.Improve the thermal shock resistance of magnesia carbon refractories
Low carbon magnesia carbon refractories require not only good slag resistance, but also good thermal shock resistance of products, which is due to the sharp decline of thermal shock resistance due to the reduction of carbon content. The thermal shock resistance is not only an important indicator of refractories, but also a key research direction of magnesia carbon bricks in the use of low carbon. Due to the characteristics of small size, large surface energy and large dispersion, nano powder particles are conducive to relative slip between particles and can improve their thermal shock resistance.
Using nanotechnology to improve the thermal shock resistance of low-carbon magnesia carbon refractories is essentially to increase the fracture toughness of the materials. The resistance to crack propagation can be further improved by adjusting the microstructure of the materials. Low carbon magnesia carbon refractories are mainly toughened in two ways:
- For crack deflection toughening, nano powder is introduced in the form of raw materials or additives, and the introduced nano powder is dispersed within or between particles, forming a large number of secondary interfaces, and plays a role in pinning dislocations, making the crack growth path more tortuous, extending the crack growth path, leading to increased capacity consumed in the crack growth process and increased fracture toughness of materials.
- Cracks are bridged and toughened. Nanoparticles are introduced into the refractory aggregate, which can form bridging components of fibers, whiskers and ceramic phases in situ. When large bridging components are encountered during crack propagation, the existence of larger bridging components is equivalent to a bridge between two opposite crack surfaces, increasing the resistance to crack propagation. If the crack continues to expand further, the bridge component will be destroyed by pulling out of the matrix. This pulling out process will consume a lot of energy, improve the fracture toughness of the product, and thus improve the thermal shock resistance.