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Unburned refractory bricks are refractory materials that can be directly used without firing. They have advantages such as energy saving, good thermal shock stability, and simple processing, which allow them to replace fired refractory products in a wide range of applications. Unburned refractory bricks have many characteristics different from fired refractory products in terms of processing. These are mainly reflected in the following aspects: Good Raw Material Calcination: Unburned refractory bricks do not undergo firing processes and are used directly after drying. Well-calcined raw materials can minimize volume changes during use, preventing cracking of the furnace body. Reasonable Particle Size Distribution and High Molding Pressure: It is best to use granules with a flaky or angular shape, with a ratio of granules to fine powder of 7:3 or 75:25. A molding pressure of over 630 tons with more than 6 strikes is recommended. Selection of Suitable Binders: Based on current usage, a single binder usually cannot meet the requirements, and composite binders are commonly used. Selection of Additives: Unburned bricks undergo significant shrinkage during use, and delayed sintering on the surface may cause structural flaking, reducing the performance of the bricks. This can be partially addressed by selecting appropriate additives. Control of Drying System: Proper control of the drying system is essential. The binding methods of unburned refractory materials are ceramic bonding or direct chemical bonding, where the hardening of the binder provides sufficient strength for the refractory material's use without the need for complex firing processes. The use of unshaped refractory materials eliminates the firing and molding processes, resulting in energy savings, increased production, improved product qualification rates, and reduced raw material consumption. The simplification of production processes and elimination of complex processing restrictions inherent in ceramic or direct bonding have led to improvements in certain properties. The critical particle size of ingredients for unburned bricks or unshaped materials can be appropriately increased, significantly improving the products' thermal stability. Using binders such as phosphate salts, high-purity alumina cement, tar, resin, etc., not only reduces or eliminates the introduction of foreign impurities but also enhances the performance due to the advantageous final reaction products such as Al2O3, CA2, and C formed by chemical bonding. Additionally, the use of various additives and reinforcing materials such as steel fibers can produce unburned refractory materials with excellent properties such as slag resistance, resistance to CO and H2 gases, volume stability, high thermal strength, anti-spalling, and anti-creep. The Utilization Value of Unburned Magnesia-Calcium Carbon Bricks: 1.Due to their lack of firing requirements and superior performance, as well as their flexibility in structural design, unburned magnesia-calcium carbon bricks will become the main direction of development for this series of refractory materials. 2.The development of unburned magnesia-calcium bricks is not only due to their superior technical performance but also because of their high economic benefits. 3.The use and development of unburned refractory materials are of significant importance in the current situation of energy shortage.

Magnesia-carbon bricks have been widely used in converters, electric furnaces, and ladles due to their excellent high-temperature resistance, slag corrosion resistance, and good thermal shock stability, making them highly suitable for steelmaking requirements. The utilization of carbon materials, which are difficult to wet by slag and molten steel, along with the high refractoriness, high slag resistance, solubility resistance, and low temperature creep properties of magnesia, allows magnesia-carbon bricks to be applied in severely worn areas such as slag lines and ladle mouths. So far, due to the extensive use of magnesia-carbon bricks in steelmaking processes and the improvement of iron and steel smelting technology, significant economic benefits have been achieved. However, magnesia-carbon bricks have shown disadvantages such as high graphite consumption, increased heat consumption, continuous carbon increase in the molten steel, and pollution of the molten steel, resulting in high costs. To reduce raw material costs and obtain clean molten steel, the low-carbonization of magnesia-carbon bricks can effectively address these issues.   The characteristics of magnesia-carbon bricks mainly include the following aspects: 1.Microstructure: Denseness of Structure: The denseness of magnesia-carbon bricks depends on the types and amounts of binders and antioxidants, the type of magnesia, the particle size, and the addition of graphite. In addition, the molding equipment, brick pressing technology, and heat treatment conditions also have certain influences. To achieve a visible porosity rate of less than 3.0% and ensure a molding pressure of 2t/cm2, it is necessary to use magnesia-carbon bricks with a particle size of less than 1mm for tuyere bricks and ladle mouth bricks. Different binders have certain effects on the denseness of magnesia-carbon bricks, and binders with higher residual carbon rates result in higher bulk densities. The addition of different antioxidants has significantly different effects on the denseness of magnesia-carbon bricks. Below 800 degrees Celsius, the visible porosity rate increases with the oxidation of antioxidants. Above 800 degrees Celsius, the visible porosity rate of non-metallic magnesia-carbon bricks remains unchanged, while that of metallic magnesia-carbon bricks decreases significantly, reaching only half of the rate at 1450 degrees Celsius. Among them, magnesia-carbon bricks containing metallic aluminum have the lowest visible porosity rate. Heating Rate: The heating rate during the use of magnesia-carbon bricks also affects the change in visible porosity rate. Therefore, when using magnesia-carbon bricks for the first time, it is recommended to increase the temperature slowly to ensure complete decomposition of the binder at a lower temperature. During the use of magnesia-carbon bricks, the impact of temperature difference on the porosity rate is also significant. The greater the temperature difference, the faster the increase in porosity rate.   2.High-Temperature Performance: High-Temperature Mechanical Properties: The effectiveness of different additives in improving the high-temperature strength of magnesia-carbon bricks varies. Studies have shown that for flexural strength above 1200°C, the sequence is: no additives < calcium boride < aluminum < aluminum-magnesium < aluminum + calcium boride < aluminum-magnesium + calcium boride, with aluminum-magnesium + boron carbide falling between aluminum-magnesium and aluminum-magnesium + calcium boride.   Thermal Expansion Performance: The participation expansion value of magnesia-carbon bricks without added metals is much lower than that with added metals, and the participation expansion value increases with the increase in metal addition. Anisotropy: The thermal expansion and high-temperature flexural strength of magnesia-carbon bricks vary in different directions due to the orientation of flake graphite. The bricks have higher high-temperature strength and lower thermal expansion in the vertical direction.

When purchasing refractory materials for glass melting furnaces, in addition to the high-temperature performance discussed earlier, their physical properties are also crucial. The physical properties of the product are closely related to its actual service life, and specific items to consider include:   1.Microstructure: Porosity: Refractory materials typically contain various sizes and shapes of pores. Porosity is often categorized into open pores (or visible pores), connected pores, and closed pores. Porosity rate reflects the density of refractory materials, indicating the percentage of pore volume in the total volume of the brick. Lower porosity rates generally correspond to better erosion resistance and higher structural strength.   Bulk Density: This refers to the mass of refractory material per unit volume, including pores. It directly reflects the density of the refractory product and is a significant indicator of its quality. Higher bulk densities usually indicate lower porosity rates and better performance in terms of strength and resistance to high temperatures.   True Density: True density represents the ratio of the mass of porous materials to their true volume (excluding pores). It's related to the chemical mineral composition of refractory materials and is independent of porosity and density. 2.Thermal Properties: Thermal Expansion: Refractory materials expand with increasing temperature. Thermal expansion properties are usually expressed using coefficients of linear or volumetric expansion. It's crucial to consider these properties when designing furnace structures to accommodate thermal expansion and prevent damage.   Thermal Conductivity: This property measures the ability of refractory materials to conduct heat and is represented by thermal conductivity. It depends on the material's chemical composition and microstructure.   Heat Capacity: Heat capacity, also known as specific heat capacity, refers to the amount of heat required to raise the temperature of one kilogram of refractory material by one degree Celsius under constant pressure. It's significant for designing and controlling the heating process and heat storage capacity of furnaces.   These physical properties play essential roles in determining the performance and lifespan of refractory materials in glass melting furnaces. Therefore, they should be carefully evaluated when selecting refractory products for specific applications.