The Influence of Al2O3-Cr2O3 Solid Solution Particles on the Performance of High-Chromium Bricks
High-chromium bricks are shaped refractory products made primarily from industrial-grade chromium trioxide and alumina, with the addition of small amounts of zirconium oxide, etc., and fired at high temperatures. The chromium trioxide content is not less than 75%, and the combined content of chromium trioxide, alumina, and zirconium oxide is not less than 98%. Some even have a chromium trioxide content as high as approximately 90%. This high chromium trioxide content endows high-chromium bricks with excellent refractory properties and high-temperature stability.
Advantages and Characteristics of High-Chromium Bricks
High-chromium bricks possess the following characteristics:
- (1) High Refractoriness: High-chrome bricks have a refractoriness far exceeding that of ordinary refractory products, maintaining structural stability at high temperatures and resisting softening and deformation. Therefore, they can be used in thermal equipment such as industrial furnaces and kilns with extremely high temperature requirements.
- (2) High High-Temperature Strength: Under high-temperature conditions, high-chromium bricks maintain high strength and possess excellent wear and impact resistance. They can resist the erosion and friction of materials inside the furnace, extending the service life of the furnace lining.
- (3) Strong Corrosion Resistance: They have good resistance to some acidic and alkaline chemicals and are not easily corroded by molten slag and gases inside the furnace, thus ensuring the integrity and stability of the furnace lining.
- (4) High Thermal Conductivity: They have high thermal conductivity, enabling rapid heat transfer within the furnace, improving energy utilization efficiency, and reducing energy consumption.
Due to their excellent refractoriness and high-temperature stability, high-chrome bricks can be widely used in various high-temperature environments. In steelmaking, high-chromium bricks are widely used in the linings of high-temperature furnaces such as blast furnaces, converters, and electric furnaces, including the belly and waist of blast furnaces. High-chromium bricks effectively resist the erosion of high-temperature gas and slag, improving the service life and production efficiency of the blast furnace. In glass melting furnaces, high-chromium bricks can be used in the pool walls and furnace bottom, resisting the erosion and scouring of molten glass while possessing good heat insulation properties, thus contributing to improved glass melting quality and production efficiency. High-chrome bricks also have important applications in the smelting of non-ferrous metals such as copper, aluminum, and zinc. In areas like the tuyeres and slag line of copper smelting furnaces, high-chromium bricks effectively resist the erosion of high-temperature melt and slag, extending the service life of the furnace lining.
The Influence of Al2O3-Cr2O3 Solid Solution Particles on the Performance of High-Cr Bricks
By optimizing particle size distribution, increasing the sintering temperature, and adding novel accelerators and binders, the strength of high-chromium bricks can be improved.
Specific experimental schemes for adding different fused Al2O3-Cr2O3 solid solutions to high-chromium bricks in granular form are presented. K1, K2, K3, K4, K5, and K6 represent the aggregate portions of the samples, which are 100%, 95%, 90%, 75%, 10%, and 0% aluminum-chromium, respectively.
The changes in bulk density and apparent porosity of various samples with different Al2O3-Cr2O3 solid solutions added to high-chromium bricks in granular form are also shown. It can be seen that as the Al2O3 content in the added Al2O3-Cr2O3 solid solution increases, the bulk density of the product initially decreases. Then, in scheme K6, i.e., with 0% Aluminum-Cr2O3, the apparent porosity increases, and correspondingly, it first increases, then decreases again with 0% Aluminum-Cr2O3. In this part of the experiment, because the bulk density and apparent porosity of the product are affected not only by the degree of sintering densification but also by the properties of the particles themselves and the theoretical density of different compounds, they do not have a significant effect on predicting local variation trends.
The cold strength of each sample with different Al2O3-Cr2O3 solid solutions added to high-chrome bricks in granular form was measured. It can be seen that the room-temperature flexural strength and room-temperature compressive strength have the same trend, i.e., first decreasing and then increasing. At scheme K4, i.e., with 75% Aluminum-Cr2O3 particles, the minimum values of 23.8 MPa and 126.3 MPa were reached, respectively. The strengths of schemes K6 and K1, with 0% and 100% aluminum-chromium particles, respectively, were the highest and second highest among all samples, at 42.8 MPa and 192.9 MPa, and 30.4 MPa and 172.1 MPa, respectively. The differences in the physical properties of the products were very significant.
The high-temperature flexural strength variation trends of the high-chromium brick samples with different Al2O3-Cr2O3 solid solutions in granular form were clearly shown. Scheme K4, with 75% aluminum-chromium particles, had the lowest high-temperature flexural strength at 15.5 MPa. This was significantly lower than Scheme K1 (24.5 MPa) with 100% aluminum-chromium particles and Scheme K6 (24.2 MPa) with 0% aluminum-chromium particles. The high-temperature flexural strength showed a trend of first decreasing and then increasing.
The residual flexural strength of high-chrome bricks with different Al2O3-Cr2O3 solid solutions added in granular form after thermal shock initially decreased and then increased, reaching a minimum at scheme K4 with 75% aluminum chromium material particles added.
The effect of Al2O3-Cr2O3 solid solution particles on the static slag resistance of high-chromium bricks. After comparison, it is clear that the thickness of the residual slag layer gradually decreases and disappears from scheme K1 to scheme K5, while a significant slag layer reappears in scheme K6, with an average thickness of approximately 1 mm.
The effect of Al2O3-Cr2O3 solid solution particles on the resistance to coal slag erosion of high-chromium bricks. Macroscopically, the resistance to coal slag erosion increases from 10.1% to 19.4% in scheme K1 to scheme K5, then decreases to 13.3% in scheme K6.
The distribution of Si, Ca, and Fe element contents at different distances from the slag surface after static slag resistance tests for schemes K1, K3, K5, and K6, based on the effect of Al2O3-Cr2O3 solid solution particles on the resistance to coal slag erosion of high-chrome bricks. Comparing schemes K1, K3, and K5, it can be seen that the penetration depth and amount of SiO2, CaO, and Fe2O3 in coal slag gradually increase from K1 to K5. Taking the penetration depth of SiO2, CaO, and Fe2O3 as an example, the penetration depths in scheme K1 are 2mm, 3mm, and 1.5mm, while in scheme K5 they are 7mm, 7mm, and 2.5mm, showing a significant increase in penetration depth. Comparing schemes K5 and K6, it can be seen that the penetration depth and amount of SiO2, CaO, and Fe2O3 in scheme K6 are relatively small. Again, taking penetration depth as an example, the values in scheme K6 are 5mm, 5mm, and 2mm, significantly smaller than the corresponding values in scheme K5. Considering the influence trend of different Al2O3-Cr2O3 solid solution particles on the apparent porosity of high-chromium bricks, it can be concluded that the apparent porosity of high-chromium bricks is one of the key factors determining the penetration depth and amount of SiO2, CaO, and Fe2O3 in coal slag.
The decrease in chromium oxide content is not the cause of the decline in the physical properties of high-chromium bricks; the changing trends in these indicators are due to differences in densification caused by varying degrees of sintering.
Except for slightly different trends in bulk density and apparent porosity among the sample groups due to interference from other factors, the cold strength, high-temperature flexural strength, and residual flexural strength after thermal shock of high-chromium bricks with different Al2O3-Cr2O3 solid solutions added in granular form all showed the same trend: first decreasing and then increasing, reaching a minimum at scheme K4 using 75% aluminum chromium particles. These analyses show that the changing trend is consistent with theoretical predictions. That is, the increase in mixing entropy results in a smaller decrease in Gibbs free energy, which is not conducive to effective sintering.
From the perspective of differentiated high-chrome bricks based on location configuration, compared to K1 and K6, the samples from other schemes all showed a decline in sintering performance (expressed as apparent porosity and bulk density), thermal shock stability, and slag erosion resistance, and therefore cannot be applied. However, compared to K1, while K6 exhibits reduced resistance to slag erosion, it demonstrates improved strengths such as room-temperature flexural strength, room-temperature compressive strength, and thermal shock resistance. Therefore, this design can be used at the cone bottom of a Texaco gasifier, or at the upper part of the cylinder and the cone bottom of a four-nozzle opposed gasifier.
The fire-facing bricks produced using the K6 design, when used at the cone bottom of a Texaco gasifier, initially had a service life of approximately 6500 hours. After trials, the service life increased by nearly 1000 hours, reaching 7564 hours. Similar results were achieved in industrial applications at the cone bottom of a four-nozzle opposed gasifier. Therefore, the use of high-chromium bricks with 0% aluminum-chromium particles at the cone bottom of a gasifier is effective in improving service life.
Improving the Sintering Densification of the Matrix
Improving the sintering densification of the matrix can significantly improve various physical properties of the product, such as room temperature flexural strength and room temperature compressive strength. From the perspective of the structural composition and performance of high-chrome bricks, the entire system can be simply divided into two parts: an aggregate part with a particle size greater than 1 mm and a matrix part with a particle size less than 1 mm. Therefore, the overall mechanical properties of the material will likely be a combination of the following three parts:
- (1) Mechanical properties of the aggregate part.
- (2) Mechanical properties of the matrix part.
- (3) Mechanical properties of the aggregate-matrix bond.
The sintering conditions of the aggregate particles and matrix bond at the same particle size in schemes K1 and K6 show that, compared to K1, the product in scheme K6 has a tighter bond between the aggregate particles and the matrix, resulting in higher sintering density. Through the comparison of schemes K1 and K6, it can be found that improving the sintering densification between the aggregate and the matrix can improve various physical properties of the product. The photographs of the fracture surfaces of K1 and K6 products show that the fracture does not occur entirely in the matrix or along the edges of the aggregate particles, but rather spans both the matrix and aggregate portions.
Based on the above analysis, it can be concluded that improving the performance of the aggregate particles, improving the sintering of the matrix, or promoting the densification of the sintering between the aggregate particles and the matrix will all contribute to improving the various physical properties of high-chromium brick products.
Rongsheng Refractory Materials Manufacturer
Refractory materials are indispensable for ensuring the stable operation of kilns. As the “heart” of the kiln, the configuration and quality of refractory materials determine the service life and production efficiency of the kiln. With the comprehensive development of the refractory industry, higher requirements are being placed on refractory materials, which in turn promotes the development and technological progress of refractory materials. Rongsheng Refractory Materials Manufacturer will continue to provide reliable refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free samples and quotations.