Performance and Construction Methods of Acid-Resistant Castables for the Petrochemical Industry

Acid-resistant castables are those that can resist corrosion from colloidal media such as nitric acid, hydrochloric acid, sulfuric acid, and acetic acid at temperatures ranging from 80 to 1200℃. Acid-resistant castables are typically made from acid-resistant aggregates, such as silica, cast stone, wax stone, and diabase particles, as well as acid-resistant material powders from waste silica bricks, silica, waste porcelain, and cast stone, using water glass as a binder.

Performance and Applications of Acid-Resistant Castables

The modulus of water glass is between 2.6 and 3.2, and the density is between 1.38 and 1.42 g/m³. The addition amount is typically between 13% and 16%. Sodium fluorosilicate is used as a settling accelerator, added at 10% to 12% of the water glass solution mass. This type of acid-resistant castable is low in cost and has good acid resistance, making it widely used in furnace linings or chimneys in metallurgy and chemical industries. However, it has poor resistance to phosphoric acid, hydrofluoric acid, and high-fatty acid corrosion.

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Technical Performance of Acid-Resistant Castables

Acid-resistant castables possess the following properties:

1. Acid-resistant castables are a new type of anti-corrosion material with strong prestress, composed of multiple components including potassium silicate as a binder, inorganic molecular materials as curing agents, and silicates as acid-resistant fillers.
2. Acid-resistant castables have high mechanical strength and excellent bonding properties. Especially in the construction of granite blocks, acid-resistant ceramic tiles, and ceramic slabs, the adhesion between the castable and cement is greater than that of the base material.
3. The acid-resistant castable exhibits stable performance in various concentrations of organic and inorganic acids. Particularly in dilute acids, industrial water, and neutral aqueous solutions, it does not produce crystalline salts and possesses high impermeability.
4. It has good heat resistance and can be used in titanium dioxide rotary kiln linings at temperatures as high as 950℃-1000℃.
5. The acid-resistant castable uses a non-toxic curing agent, posing no harm to operators and construction personnel. It has been certified by medical and health departments as suitable for corrosion protection in food, pharmaceutical, and other equipment.
6. Compared with organic acid-resistant materials, the acid-resistant castable is inexpensive. In addition to possessing the same acid and corrosion resistance as organic materials, it also has the unique property of resisting corrosion from strong oxidizing media.
7. It cures at room temperature, is simple to construct, convenient to use, easy to transport, and requires moisture-proof storage.

Applications of Acid-Resistant Castables

Acid-resistant castables can be used in various concentrations of sulfuric acid, hydrochloric acid, nitric acid, chromic acid, hypochlorous acid, chlorosulfonic acid, formic acid, oxalic acid, acetic acid, and other acids; various organic solvents; various acidic salts; oxidizing media such as chlorine and hydrogen peroxide; and mixtures of the above media. Rongsheng acid-resistant materials are widely used in corrosion protection projects for reaction vessels, storage tanks, towers, floors, trenches, electrolytic cells, etc., in industries such as petroleum, chemical, metallurgy, power, pesticides, food, fermentation, hydrolysis, and pickling.

Acid-resistant castable refractory construction requirements:

1. Acid-resistant castable refractory, 10-20 mm thick, should be applied in sections. The spacing between sections should be 2-3 meters, and the joint width should be 15-20 mm. The joints should be completely filled with a suitable sealant.
2. Acid-resistant castable refractory can also be used to line granite blocks. The bonding layer and joint width are generally 10-15 mm.
3. The construction requirements for acid-resistant castable refractory are the same as those for mortar application.
4. Acid-resistant castable refractory can be used for integral casting linings of reaction vessels, storage tanks, towers, electrolytic cells, trenches, floors, fermentation tanks, etc., in chemical, light industry, metallurgical, pickling, petroleum, pesticide, food, electroplating, and electrolysis industries. With the addition of reinforcing steel, it can serve as a structural corrosion-resistant material.
5. When casting inside carbon steel equipment, the surface of the carbon steel equipment should be sandblasted to remove rust. When casting inside cement concrete equipment, the surface of the equipment should be thoroughly cleaned of oil and dust.
6. The formwork structure used for casting must be tight, dimensionally accurate, and possess sufficient rigidity; a height of 50 cm is recommended.
7. Before construction, the formwork surface should be coated with oil, then a plastic film should be placed on the formwork surface, extending 5-10 cm beyond the joints.
8. Mixing containers and tools must be clean and dry.
9. The temperature at the construction site must be above 15℃. Rain shelters should be erected during the rainy season.
10. Mix the concrete and potassium silicate thoroughly according to the mixing ratio.
11. Pour the mixed material into the formwork and compact it manually or with mechanical vibration.
12. The filling depth should be 30 cm each time.
13. If the ambient temperature is above 35℃, the formwork can be removed after seven days. After demolding, strictly prevent impact and localized high-temperature welding.
14. If casting load-bearing structural equipment, reinforcement should be designed accordingly.

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Precautions for Acid-Resistant Castable Resin Construction

1. Carbon steel equipment should be sandblasted to remove rust before construction. For concrete equipment, surface dust should be cleaned and uneven areas repaired. The moisture content of concrete tanks and pools should be less than 6%.
2. The surfaces of acid-resistant bricks and granite used for lining should be clean and dry.
3. Containers and tools for mixing acid-resistant materials should be clean and dry.
4. The temperature at the construction site should be between 15°C and 35°C, and the ambient air temperature should be below 80°C before construction. If it exceeds 80°C, ventilation and dehumidification facilities should be added.
5. Weigh potassium silicate according to the acid-resistant castable resin mix ratio and add it to the mixer or mixing container. Then add the weighed powder and mix thoroughly. Each batch of mixture should be used within 30 minutes.
6. During construction, it is strictly forbidden to add powder or potassium silicate to the acid-resistant castable resin. If the mortar hardens, it should be discarded.
7. When lining brick slabs, the mortar should be applied fully and compacted with a spatula, squeezing the mortar out of the brick joints. Excess mortar should be scraped away with a knife. The bonding layer and joint should generally be 3- 5 mm.
8. When lining large acid-resistant bricks, they should be supported and secured to prevent movement.
9. After successful lining, the equipment must be cured in an environment above 15 degrees Celsius for at least 14 days. During curing, contact with water and water vapor is strictly prohibited.
10. For open-air construction, a rainproof and sun-protective shed should be erected.

What is the difference between acid-resistant and alkali-resistant castables?

Alkali-resistant castables are castables that resist the corrosion of alkali metal oxides at medium to high temperatures. They can be classified into medium-temperature and high-temperature types according to their service temperature, and into lightweight and heavyweight types according to their bulk density. Medium-temperature alkali-resistant castables typically use aluminosilicate materials as aggregates or fine powders, such as clay clinker, waste porcelain powder, and expanded perlite. Their resistance to alkali corrosion works by reacting with alkali metal oxides to form a high-SiO2, high-viscosity glaze layer on the surface of the refractory castable, thus preventing further penetration of alkali metal oxides into the interior of the refractory castable and improving its corrosion resistance.

Alkali-resistant castables are divided into high-strength alkali-resistant castables and ordinary alkali-resistant castables. They are used extensively in cement rotary kiln preheaters, with SiO2 content around 60% and Al2O3 content between 45% and 75%. High-strength alkali-resistant castables use high-voltage electrical porcelain materials, while ordinary alkali-resistant castables use low-voltage electrical porcelain materials. The higher the operating temperature, the higher the Al₂O₃ content. Depending on the application, calcium aluminate cement, silica powder, etc., can be selected to adjust the process proportions.

For excessively high temperatures, alkali-resistant castables are also made using chromium corundum, zircon, fused spinel, etc., as aggregates or fine powders. These types of alkali-resistant castables are mostly used in hazardous waste incinerators.

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.

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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.

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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.

Performance Advantages of Silicon Carbide Lithium Battery Saggers

Against the backdrop of the rapid development of new energy vehicles and energy storage industries, the demand for lithium batteries has exploded. As the core container in the sintering process of lithium battery cathode materials (such as ternary materials and lithium cobalt oxide), the performance of the sagger directly affects sintering efficiency, material quality, and production costs. Traditional alumina saggers are gradually becoming insufficient to meet the demands due to problems such as rapid high-temperature wear and short lifespan. Silicon carbide (SiC) lithium battery saggers, with their unique material properties, are becoming a key direction for industry upgrading. This article will analyze silicon carbide lithium battery saggers from two dimensions: performance advantages and market prospects.

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Performance Advantages of Silicon Carbide Lithium-ion Battery Saggers: High-Efficiency Sintering

Silicon carbide is a ceramic material composed of silicon (Si) and carbon (C), whose crystal structure endows it with excellent physicochemical properties. It exhibits significant advantages in the field of lithium-ion battery saggers:

1. Ultra-High Temperature Resistance and Thermal Stability

The sintering temperature of lithium-ion battery cathode materials typically needs to reach 800-1000℃ (some high-nickel ternary materials even exceed 1200℃). Traditional alumina saggers are prone to crystal phase transformation at this temperature, leading to volume shrinkage and cracking. Silicon carbide, however, has a melting point as high as 2700℃ and almost no crystal structure change below 1400℃. Its coefficient of thermal expansion is only 4.5×10⁻⁶/℃ (compared to 8×10⁻⁶/℃), enabling it to withstand extreme high temperatures for extended periods without deformation or cracking, significantly extending its service life.

2. Extreme Corrosion Resistance: Resistant to Molten Salt and Atmosphere Erosion

During sintering, the sagger needs to come into contact with molten materials such as lithium salts (e.g., lithium carbonate) and transition metal oxides, while being exposed to air or an inert atmosphere. Alumina saggers are prone to reacting with alkaline substances, gradually corroding their surface, leading to rough inner walls and material contamination. Silicon carbide has extremely strong chemical stability, resisting acid and alkali erosion from room temperature to high temperatures (except for hydrofluoric acid), and does not react with lithium salts, maintaining a smooth inner wall for a long time, preventing impurities from contaminating the cathode material and improving product purity.

3. High Thermal Conductivity and Low Energy Consumption: Accelerated Sintering, Cost Reduction and Efficiency Improvement

Silicon carbide has a thermal conductivity as high as 120-150 W/(m·K) (compared to only 20-30 W/(m·K) for alumina), enabling rapid heat transfer, resulting in a more uniform temperature distribution within the sintering furnace, shortening heating time, and improving production efficiency. Meanwhile, its low heat capacity reduces heat accumulation and lowers sintering energy consumption (actual energy savings of approximately 15%-20%), meeting the cost reduction and efficiency improvement needs of the lithium battery industry.

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4. Ultra-long lifespan: Overall cost reduction of over 60%

Traditional alumina crucibles, due to high-temperature wear and corrosion during continuous use, have an average lifespan of only 30-50 cycles. Silicon carbide crucibles, with their high-temperature and corrosion resistance, can achieve a lifespan of 200-300 cycles (some high-end products exceed 500 cycles). Although the cost per crucible is 30%-50% higher than alumina, the overall cost of use is reduced by over 60%, resulting in significant economic benefits.

Application Areas of Silicon Carbide Saggers

1. Explosive Downstream Demand: A “Must-Have” for New Energy Vehicles and Energy Storage

According to data from GGII (Gaogong Lithium Battery Research Institute), global lithium battery shipments are growing, with power lithium batteries accounting for over 70%. As the core cost unit of lithium batteries (accounting for approximately 40%), the cathode material requires a huge amount of saggers during its sintering process. Estimating the demand of tens of millions of saggers per GWh of ternary cathode material, the annual demand in the power lithium battery sector alone is enormous. With the rapid growth of global energy storage installations, the sagger market will further expand.

2. Dual Catalysts of Policy and Technology: Accelerated Replacement Process

High-nickel content and single-crystal material are becoming the upgrade directions for cathode materials. High-nickel materials require higher sintering temperatures (above 1200℃), placing more stringent demands on sagger performance. Traditional alumina can no longer meet these requirements, making silicon carbide saggers the inevitable choice. Furthermore, leading battery manufacturers (such as CATL and BYD) and cathode material manufacturers (such as Ronbay Technology and Dangsheng Technology) have accelerated the adoption of silicon carbide crucibles, driving the industry’s substitution process.

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3. Technological Iteration: Breakthroughs in Cost Reduction and Scale

Early silicon carbide crucibles were limited in large-scale application due to their complex manufacturing process (requiring high-temperature sintering and surface coating treatment) and high cost. In recent years, companies have reduced the cost per unit by optimizing sintering processes (such as pressureless sintering + reactive infiltration) and developing low-cost raw materials (recycled silicon carbide micropowder). Simultaneously, some manufacturers have achieved higher production capacity, and large-scale production further reduces costs.

Core Carrier for Industrial Upgrading

Silicon carbide lithium-ion battery crucibles, with their advantages of high temperature resistance, corrosion resistance, and long lifespan, have solved the pain points of traditional crucibles, becoming the “upgraded standard” in the sintering process of lithium-ion battery cathode materials. With the rapid growth of the downstream lithium-ion battery industry, policy support for high-end materials, and continuous breakthroughs in manufacturing technology, the silicon carbide crucible market is poised for explosive growth. According to industry forecasts, the global lithium-ion battery crucible market size will increase, with silicon carbide crucibles also accounting for a larger share, becoming a key link in the new energy industry chain that combines technological barriers and market potential.