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Phosphate-Bonded Refractory Castables The composition of phosphate-bonded refractory castables is similar to that of general castables. Aggregates and powders include high-alumina, clay, silica, and magnesia. Phosphates such as aluminum phosphate and phosphoric acid react slowly with neutral and acidic aggregates and powders at room temperature. To enable hardening at room temperature, hardeners like active aluminum hydroxide, talc, ammonium fluoride, magnesium oxide, alkaline aluminum chloride, and calcium aluminate cement are added. Magnesium oxide is particularly effective as a hardener, but the resulting magnesium phosphate reduces refractoriness and lowers hot strength. The hardening time varies significantly with ambient temperature. When phosphates react with aggregates, the formation of insoluble products can lead to aging effects. Reactions involving iron content in raw materials may also impact aging. Additionally, the mixing process can corrode mixing equipment, necessitating the addition of aging inhibitors and mitigating additives.   Phosphate-bonded castables must be dried at 450–500°C to form aluminum phosphate or metaphosphates. At lower drying temperatures, hygroscopic compounds such as pyrophosphoric acid (H₄P₂O₇) may form, which absorb moisture from the air and revert to orthophosphoric acid, compromising bonding properties. Aluminum Sulfate-Bonded Refractory Castables Common aluminum sulfate solutions have a density of 1.20–1.30 g/cm³ and are added in amounts ranging from 12% to 18%. Being acidic, these solutions contain sulfate and bisulfate ions, which react with iron and other components in aggregates and powders, releasing hydrogen gas and causing expansion. To counteract this, the material is left to rest for over 24 hours before forming. Initially, 70–80% of the total aluminum sulfate solution is added, with the remainder added after resting.   After forming, the castables are naturally cured in dry air and at 50°C for three days to meet strength requirements. Accelerators such as bauxite cement (2–4%) can be added to speed up hardening. To enhance high-temperature performance, 5–10% of fine clay powder or expansion agents can be incorporated to counteract shrinkage. The strength of aluminum sulfate-bonded castables fluctuates with temperature. At room temperature, hardening is slow, but with the addition of accelerators, compounds like calcium sulfate, ferric sulfate, and magnesium sulfate form. These compounds interact to produce needle-like or columnar precipitates (e.g., calcium sulfoaluminate or aluminoferric sulfate), promoting hardening. At 500–600°C, the strength remains similar to that after drying. However, at 700–800°C, decomposition of aluminum sulfate and its salts releases SO₂ gas, reducing density and strength. Above 1000°C, active Al₂O₃ from decomposition reacts with SiO₂, forming mullite and other compounds, which significantly increase strength.   To address the structural loosening and strength reduction around 800°C, composite binders with 25–50% phosphoric acid can be used. The service temperature of aluminum sulfate-bonded castables depends on the material type: clay-based at 1300–1350°C, high-alumina at 1350–1550°C, and corundum-based at 1500–1650°C. Sodium Silicate-Bonded Refractory Castables Sodium silicate-bonded castables use aggregates and powders from diverse sources, including aluminosilicate, silica, semi-silica, magnesia, and magnesia-alumina materials. Due to the high viscosity of sodium silicate, mixing and vibration times are extended. In the 1970s, fast-dissolving solid sodium silicate was introduced, allowing refractory aggregates and powders to be mixed on-site with water for convenient casting. However, at 800–1000°C, sodium fluoride and sodium oxide melt, increasing the liquid phase and reducing the effect of silica gel, leading to lower softening temperatures under load. The service temperature of sodium silicate-bonded castables is relatively low: 1400°C for high-alumina, 1000°C for clay and semi-silica, and 1600°C for magnesia. To address these limitations, the addition of sodium silicate and sodium fluosilicate must be minimized, or high-modulus sodium silicate should be used.   Despite these challenges, sodium silicate-bonded castables exhibit high room-temperature strength and minimal strength reduction during heating, providing excellent high-temperature wear resistance. They are particularly effective in resisting acid media (except hydrofluoric acid) and sodium salt melts. The acid resistance of clay and semi-silica sodium silicate castables exceeds 93%, meeting the requirements for acidic thermal equipment. About Us Henan Rongsheng Xinwei New Materials Research Institute Co., Ltd. is affiliated to Henan Rongsheng Refractory Group and we have been a leading manufacturer and supplier of high-performance refractory materials for more than 20 years. As a national high-tech enterprise, we specialize in research, development, production, and technical services of advanced refractory materials.   Our product range includes refractory castables, high-alumina bricks, corundum bricks, AZS bricks, fireclay bricks, insulating bricks, and unshaped materials such as refractory cement and mortar. These products serve industries like iron and steel, cement, glass, petrochemical, and non-ferrous metals, with exports to over 100 countries worldwide.   We are committed to providing innovative, energy-efficient, and environmentally friendly solutions for high-temperature industries.   Contact Us Today!

In the early 1970s, Lafarge in France successfully developed low cement castables, followed by the development of ultra-low cement castables, which gained global application in the 1980s. In China, there is no unified standard for categorizing these castables. According to ASTM standards in the United States, they are defined based on the CaO content in the product.   Unlike conventional refractory castables, low cement and ultra-low cement castables partially or largely replace calcium aluminate cement with ultrafine powders of the same or similar chemical composition as the castable's main material. Additionally, small amounts of dispersants (water reducers) and delayed-setting accelerators are added. Cement-free castables use ultrafine powders or oxide sol entirely as binders.   The setting and hardening mechanisms of low cement, ultra-low cement, and cement-free castables differ from those of conventional calcium aluminate cement. While traditional cement relies primarily on hydration bonding, low cement castables exhibit both hydration and coagulation bonding, ultra-low cement castables are predominantly coagulation-bonded, and cement-free castables rely entirely on coagulation bonding. The principle behind coagulation bonding is as follows: in silica-alumina castables containing SiO₂ ultrafine powder, mixing the powder with water forms colloidal particles due to the high activity of SiO₂ ultrafine powder. The surface of these colloidal particles dissociates Si-OH groups into Si-O⁻ and H⁺, giving the particles a negative charge. These negatively charged particles adsorb Al³⁺ and Ca²⁺ ions slowly released during the hydrolysis of calcium aluminate, leading to a decrease in the zeta potential of the colloidal particles. When adsorption reaches the isoelectric point (where the colloidal particles are neutral), coagulation occurs, forming bonds that harden through drying. Advantages of Low Cement, Ultra-Low Cement, and Cement-Free Castables: Reduced CaO Content: Lower CaO content reduces the formation of low-melting phases, enhancing refractoriness, high-temperature strength, and slag resistance, with cement-free castables offering superior performance. Lower Mixing Water Requirement: The water needed for mixing is only 1/2 to 1/3 of that for conventional refractory castables (about 4%–6%), resulting in lower porosity and higher bulk density. Improved Strength: After forming and curing, minimal or no cement hydration products are generated. This avoids significant strength reduction due to the breakdown of hydration bonds during heating. Instead, strength gradually increases with sintering at higher temperatures. Aggregate and Powder Materials Low cement, ultra-low cement, and cement-free castables can use aggregates and powders made of clay, high alumina, mullite, corundum, carbon-containing materials, or silicon carbide. The choice of binders such as ultrafine powder or silica/alumina sol depends on the chemical composition of the aggregate. For example: Corundum-based castables should use alumina ultrafine powder or a combination of alumina and silica ultrafine powder. Silica-alumina castables can use silica ultrafine powder alone, a combination of silica and alumina ultrafine powder, or silica sol as the binder. These innovative castables represent a significant advancement in refractory material technology, providing enhanced performance and broader applications across high-temperature industries.

Detailed Analysis of the Classification of Refractory Properties and Their Application Fields 1. Detailed Classification of Properties 1.1 Chemical Composition and Mineral Composition Silica Refractories: Primarily composed of silicon dioxide (SiO₂), silica refractories have excellent acid slag resistance and are commonly used in blast furnaces, hot blast stoves, and coke ovens. Aluminosilicate Refractories: Composed of alumina (Al₂O₃) and silicon dioxide, these refractories offer good heat resistance and thermal shock stability, making them widely used in high-temperature equipment such as blast furnaces, hot blast stoves, and glass melting kilns. Corundum Refractories: Made from high-purity alumina (Al₂O₃), corundum refractories exhibit a high melting point, high hardness, high strength, and excellent chemical stability, suitable for a variety of high-temperature industrial kilns. Magnesia Refractories: Composed mainly of magnesium oxide (MgO), magnesia refractories offer excellent alkali slag resistance and are commonly used in steelmaking converters, electric furnaces, and other alkaline environments. Chromium Refractories: Made from chromium oxide (Cr₂O₃), chromium refractories provide superior high-temperature and oxidation resistance, suitable for industrial kilns operating in high-temperature oxidative atmospheres. Carbon Refractories: Composed of carbon, carbon refractories maintain structural stability and resist deformation at high temperatures, commonly used in blast furnaces, converters, and other areas subject to high-temperature shock. Zirconium Refractories: Made from zirconium oxide (ZrO₂), zirconium refractories have an extremely high melting point and excellent chemical stability, ideal for industrial kilns operating in ultra-high temperatures and corrosive environments. 1.2 Physical Properties and Functional Characteristics High-Temperature Stability: Refractory materials can maintain their physical and chemical properties at high temperatures without significant deformation or melting. Corrosion Resistance: The ability of refractory materials to resist acids, alkalis, salts, and other chemical media, including slag resistance and permeability. Thermal Shock Resistance: Refractories maintain structural integrity and performance stability despite rapid temperature changes, preventing cracking or spalling. Thermal Conductivity: The heat conductivity of refractory materials varies depending on their composition and structure, used to control heat transfer and distribution. Density and Porosity: The density and porosity of refractory materials significantly impact their performance. Lightweight refractories have lower density and higher porosity, suitable for insulation, while dense refractories, with lower porosity, are used in high-temperature and heavy-load environments. 2. Detailed Analysis of Application Fields 2.1 Construction Industry In the construction industry, refractory materials improve the fire resistance and safety of buildings. Materials like fire-resistant walls, doors, and windows help prevent the spread of fire, while refractory coatings and fire-resistant glass enhance the fire performance of building components. 2.2 Metallurgical Industry The metallurgical industry is a primary field for the application of refractory materials. Refractories are used as linings and insulating layers in high-temperature equipment such as blast furnaces, hot blast stoves, converters, and electric furnaces to protect the furnace body from high-temperature and slag erosion. Additionally, refractories are used for linings in slag pots and ladles during the smelting process. 2.3 Glass and Ceramic Industries Glass melting furnaces and ceramic firing kilns are key application areas for refractory materials. In glass melting furnaces, refractories are used in parts such as the melting pool, flow channels, and clarification pools for insulation and load-bearing. In ceramic kilns, refractories are used for the walls, roof, and bottom to provide insulation and heat retention. 2.4 Chemical and Petrochemical Industries High-temperature, high-pressure equipment and reactors in the chemical and petrochemical industries often use refractories as linings and insulating layers. Refractory materials in devices like cracking furnaces, hydrogenation reactors, and synthesis towers resist high temperatures and corrosive media, ensuring stable operation of equipment. 2.5 Power Industry In the power industry, boilers, steam turbines, and generators widely use refractories. Refractories improve heat efficiency and reduce heat loss in the furnace chambers, flue gas ducts, and water-cooled walls of boilers, while high-temperature components in steam turbines rely on refractories to withstand high temperatures and friction from high-speed rotation. 2.6 Aerospace and New Energy Industries In the aerospace industry, high-temperature components such as rocket engines and aircraft engines use refractory materials to enhance heat resistance and stability. For example, refractory materials are used in rocket engine nozzles and combustion chambers to withstand high temperatures and high-speed airflow erosion, while turbine blades in aircraft engines use refractory alloys or composites to improve high-temperature and oxidation resistance. In the new energy sector, refractory materials improve the thermal stability and lifespan of components such as solar panels and fuel cells. For instance, the backplates of solar panels use refractories to prevent deformation and aging under high temperatures, and electrolytes and electrodes in fuel cells are made from refractory materials to enhance high-temperature and corrosion resistance. With over 20 years of experience as a leading manufacturer and supplier of refractory materials, we offer a wide range of high-performance products designed to meet the demands of various industries, including steel, cement, glass, petrochemical, and energy. Whether you require silica, aluminosilicate, magnesia, corundum, or other specialized refractory products, we have the expertise and resources to provide solutions that ensure long-lasting durability and efficiency.   Contact us today for more information and inquiries!   Tel/Whatsapp: +86-13903810769 Email: Jackyhan2023@outlook.com Website: https://www.bricksrefractory.com   Let us help you find the perfect refractory solution tailored to your needs!