Background【1】【2】
As a high-temperature binder, aluminum dihydrogen phosphate has the characteristics of strong chemical bonding, room temperature hardening, high temperature resistance and erosion resistance under high temperature conditions. As early as the 1980s, the foundry industry began to use aluminum dihydrogen phosphate as a binder in the shell-making process. In recent years, some experts have also conducted research in this area. Liu Weilai and others modified the phosphate binder by adding magnesium oxide and M agent to obtain a self-hardening casting binder with good moisture resistance and high strength. Xing Jinlong and others modified the phosphate binder for casting and achieved good process performance and self-stability.
Pure aluminum dihydrogen phosphate is needle-shaped crystals or large rod-shaped crystals, belonging to the hexagonal crystal system, with a density of 2. 19. It is highly hygroscopic and soluble in water. The pH value of 1% aqueous solution is 2. 4 or so. Industrial products are divided into two states: liquid and solid. The liquid is a colorless, odorless and viscous syrup, and the solid is white powdery crystal. Material grade aluminum dihydrogen phosphate has good room temperature adhesion, high temperature adhesion, high temperature resistance, earthquake resistance, corrosion resistance, and airflow resistance. It is an ideal chemical bonding agent. Two tests have been done: one was to add 3% aluminum dihydrogen phosphate to corundum powder to make a slurry, and bond three pairs of test blocks. One group was dried at 110°C for 12 hours, and the other set was heated to 1°C. After being kept for 2 hours and cooled to room temperature, the flexural bonding strengths were measured to be 2.12MPa and 8. 3MPa. Another time, 50% aluminum dihydrogen phosphate, 85% aluminum oxide, and high-quality pottery were used in the Xuzhou Iron and Steel Works for the coating of the tundish nozzle in induction furnace steelmaking. When the molten steel was around 1650°C, the leakage nozzle worked intermittently. Each time for 3 minutes, about 50kg of molten steel flows through, and it still has good high-temperature thermal stability. In addition, when combined with high-temperature-resistant fillers, the performance of high-temperature-resistant materials can be improved and made into various refractory coatings, flame-retardant coatings, high-temperature-resistant cementitious materials, refractory cement, etc. Therefore, it is widely used in high-temperature furnaces, high-temperature-resistant equipment, electrical, metallurgy, building materials and other industries.
Properties【3】
There are two types: anhydrous and liquid. The anhydrous product is powdery crystal, and the pure product is hexagonal needle-shaped or rod-shaped crystal with a relative density of 2.19. The liquid is a colorless, odorless, viscous syrupy liquid with a relative density of 1.44 to 1.47. Both liquids and solids have strong chemical bonds and are easily soluble in water. Easy to solidify at room temperature. The cured body is resistant to high temperatures, vibration, and peeling, and has good infrared absorption capabilities and insulation properties. When heated to 236°C, aluminum dihydrogen pyrophosphate is generated; when heated to 300°C, aluminum dihydrogen tripolyphosphate is generated; above 900°C, aluminum metaphosphate is generated.
Purpose
Used as adhesive, high-temperature resistant joint material and insulating material in high-temperature kilns, heat treatment electric furnaces, etc. Also used as intumescent flame retardant coating for fiber, wood, etc. Used in the production of ceramic products, it can improve the high temperature compressive strength and flexural strength of the products. Mixed into cement, it can improve the strength of cement products and shorten the setting time. Used as a silicone bonding material or surface coating with good dielectric properties in electrical appliance production.
Packaging
Liquid products are packed in plastic barrels, with a net weight of 30 kg per barrel. Powdered products are packed in polyethylene woven bags lined with plastic bags, with a net weight of 50 kg per bag.
Notes
Should be stored in a ventilated and dry place. Prevent it from being knocked upside down during transportation, handle it with care, and be careful not to break the packaging barrel. In case of fire, water and sand can be used to put out the fire.
Production process【4】【5】
Produced by the neutralization method of phosphoric acid and aluminum hydroxide.
Main chemical reactions:
The process flow is shown in Figure 13.17-1.
(1) Neutralization Add 85% phosphoric acid into the reaction kettle, heat it to 120 C with steam, stir, and press H. PO. with A1(OH). Add AI(oH) at a molar ratio of 3:1. , and add an appropriate amount of water. The reaction time is about 2 hours. After the solution is clear, measure and adjust the pH value of the reaction solution to 2.4 and the relative density to about 1.47. (2) Filter the reaction liquid and send it to the high-level tank with a pump, and obtain the liquid aluminum dihydrogen phosphate product after filtration. (3) Drying If you produce powdered aluminum dihydrogen phosphate products, you need to send the liquid aluminum dihydrogen phosphate from the reactor to the high tank, then let it flow into the spray drying tower, and spray it into a mist with compressed air. And the gas sent from the gas system is used as the heat source, so that the mist aluminum dihydrogen phosphate is dried into powdery and granular anhydrous matter and falls into the bottom of the tower, and comes out through the discharge port at the bottom of the tower. Strictly control the temperature of the spray material at 160°C. C, the tower top temperature is about 180 C, and the exhaust gas leaving the tower is about 100 C. (4) The granular materials coming out of the lower part of the crushing tower are sent to the crusher for crushing and screening. When the fineness requirements are met, the finished product is packaged. After the exhaust gas is separated from dust by the cyclone separator, it is then exhausted by the induced draft fan. Recycle dust into products. The main production equipment is a spray drying tower, and other common equipment. The drying tower is cylindrical and the lower part is conical. There is a nozzle on the top, and the liquid at the nozzle outlet is sprayed into mist by compressed air, and there is a gas inlet on the side. In order to prevent the gas and air in the tower from mixing and exploding, when driving, you must first turn on the air compressor and induced draft fan to drain the gas in the tower before igniting the gas for spray drying.
Neutralization method neutralizes phosphoric acid and aluminum hydroxide to prepare aluminum dihydrogen phosphate. The reaction formula is as follows:
References
[1] Liu Jiabin, Yuan Zizhou, Lu Shisheng, Zhou Zigang, Jia Shaowei. Dihydrogen phosphate.�Research on the reinforcement of bauxite clinker shell[J]. Casting, 2016, 65(03):258-261+266.
[2]Zhang Zhenxing, Zhang Yanbin. Production and application of material-grade aluminum dihydrogen phosphate[J]. Chemical Engineering Times, 2011, 25(09):20-22.
[3] Zhu Hongfa, editor-in-chief Zhu Yuxia, Inorganic Chemical Products Handbook, Golden Shield Publishing House, 2008.12, page 466
[4] Editor-in-Chief Pan Changhua, Encyclopedia of Practical Small Chemical Production Volume 1: Inorganic Chemical Products &middosolvents; Compound Fertilizers, Pesticides, and Veterinary Drugs, Chemical Industry Press, September 1996, 1st edition, page 517
[5] Tianjin Chemical Industry Research Institute of the Ministry of Chemical Industry, etc., Chemical Product Manual Inorganic Chemical Products, Chemical Industry Press, July 1982, 1st edition, page 337
