THE IMPORTANT ROLE OF MAGNESIUM-CALCIUM REFRACTORY RAW MATERIALS AND ADDITIVES ON PRODUCT PERFORMANCE

Magnesium-calcium-based refractories have a series of excellent properties, especially the function of purifying molten steel. At present, magnesia-calcium refractories are mainly used for continuous casting tundish lining, out-of-furnace refining ladle AOD, VOD furnace, electric furnace, converter and firing zone of large dry-process cement kiln, etc. In the future, this type of material will have a wider range of applications. application prospects. Magnesium-calcium sand is the main raw material for the production of magnesia-calcium refractories, and its properties directly affect the use of products. Therefore, the effects of different contents of dolomite ultrafine powder and different firing temperatures on the microstructure of magnesia-calcium sand are studied. High-quality magnesium-calcium refractories with low thermal conductivity, good mechanical properties and corrosion resistance play an important role.
1 trial
1.1 Raw materials and test plan
In this experiment, lightly burned dolomite powder was used as the main raw material, and different contents of dolomite ultrafine powder were added, and the chemical composition of the raw materials and additives was determined by X-ray fluorescence analyzer.
The ground light calcined powder was passed through a 180-mesh sieve, and the light calcined powder without additives was used as a blank sample, and then the dolomite ultrafine powder with a particle size of about 300-500 nm was ball-milled by a ball mill for 48 hours at 3%. , 6% and 9% of the addition amount (w) was added to the lightly burned powder.
1.2 Test process and performance testing
The ingredients are mixed according to the test plan, and the mixed materials are put into the tableting molds respectively, and the dry pressing method is adopted. mm and a cylindrical specimen with a height of 10 mm. Mark the serial number, put it in a drying oven and dry it at 95 °C for 24 h. The dried samples were calcined in a high-temperature furnace, kept at 1500 and 1600 °C for 2 h, and cooled to room temperature naturally. The Zeiss-ΣIGMA HD field emission scanning electron microscope produced by Zeiss Company in Germany was used to observe the microstructure and morphology, and the Nano Measurer software was used to analyze the pore size of the electron microscope pictures after firing at 1600 °C.
2 Results and discussion
It can be seen from the 500 times electron microscope pictures of the samples without additives treated at 1500 and 1600 ℃ that with the increase of calcination temperature, the porosity of magnesia-calcium sand does not change much, and it can be seen that the temperature has no effect on the structure of magnesia-calcium sand. big impact.
It can be seen from the 500x electron microscope pictures of the samples that the additive is dolomite superfine powder and its content (w) is 3%, 6%, and 9% at 1500 ℃, the addition of superfine dolomite fine powder is higher than that without the addition of superfine dolomite powder. The distribution of dolomite fine powder is more uniform, the apparent porosity is increased, and the effect is the best when 6% (w) of ultra-fine dolomite is added. The image is processed with Nano Measurer software, and the stomatal diameter in the electron microscope image can be analyzed to obtain a histogram (see Figure 2). It can be seen from the histogram: when the dolomite content is 3% (w), about 88.53% of the pores have a pore diameter of 1 to 6 μm, and the remaining pore diameters are all 6 to 11 μm; when the dolomite content is 6% (w), about 86.37 μm % of the pores are concentrated in 1-3.8 μm, about 12.13% of the pores are in the 3.8-5.9 μm, and 1.52% of the pores are in the 7.3-9 μm; when the dolomite content is 9% (w), about 82.35% The pore diameter of 1-8.2μm, about 17.64% of the pore diameter is 8.2-13μm. When the content of dolomite ultrafine powder is 6% (w), the number of pores is the largest, and compared with 3% and 9% (w), at this time, the pores are smaller and the distribution is more uniform.
From the 500-fold SEM pictures of the samples with dolomite ultrafine powder content (w) of 3%, 6%, and 9% at 1600 °C, the pictures were processed with NanoMeasurer software, and the pore diameter of the pores in the SEM pictures could be analyzed, and the columnar shape was obtained. picture. It can be seen from the histogram: when the dolomite content is 3% (w), about 84.78% of the pores are 1-5.8 μm in diameter, and the remaining pores are 5.8-17 μm; when the dolomite content is 6% (w), about 82.61% of the pores are concentrated in 1-6 μm, about 13.05% of the pores are in 6-11 μm, and 1.45% of the pores are in the range of 23.5-26 μm, which may be due to the uneven distribution of additives during mixing. It is more concentrated; when the content of dolomite is 9% (w), about 87.18% of the pores have a pore diameter of 1-9 μm, and about 12.81% of the pores are 9-17 μm in diameter.
It can be seen from the above analysis that the pores in the magnesia-calcium sand sintered with dolomite ultrafine powder are mostly circular pores, the pores are small in diameter, uniform in distribution, and mostly located in the crystal; Grade micropowder has a large specific surface area and high activity, which can promote sintering. When the sintering temperature is 1500 and 1600 °C, the addition amount of dolomite ultrafine powder is 6% (w), which is more suitable. Compared with the content of 3% and 9% (w), the pore diameter is smaller and the distribution is more uniform. , it can be seen that the temperature has little effect on it.
3 Conclusion
The light-fired dolomite powder in Dashiqiao area was used as the raw material matrix, and the superfine dolomite powder was used as the additive. After tableting and molding, it was calcined at a temperature of 1500 and 1600 °C, and its microstructure was observed by scanning electron microscopy. The effect of superfine powder content on the microstructure of magnesia-calcium sand. When the addition of dolomite superfine powder is 6%, the number of pores is large, the pore diameter of pores is relatively small, and the distribution is relatively uniform.