Physical and chemical properties of aluminum dihydrogen tripolyphosphate_Industrial additives

Background and overview^[1-2]

As an inorganic fine chemical, aluminum dihydrogen tripolyphosphate has the advantages of non-toxicity, storage stability and good weather resistance. It is a new generation of environmentally friendly anti-rust pigment that can be combined with alkyd resin, phenolic resin, environmental Oxygen resin, epoxy polyester, acrylic-melamine resin, styrene-acrylic emulsion, silicone resin, polyaniline resin, polyvinyl chloride, chlorinated polyethylene, chlorinated rubber, etc. are mixed and used in the coating industry to prepare anti-rust coatings. Zinc-rich primer, thick build coating, powder coating, organic titanium anti-corrosion coating, rust-bearing coating, fire-retardant coating, heat-resistant coating, water-based coating, etc. The color can be freely adjusted, and the anti-rust performance is better than red lead, zinc chrome yellow, Materials such as zinc phosphate and zinc molybdate have good effects and are favored by users. In addition, its application in adsorbents, ion exchangers, refractory materials, inorganic molding materials, catalysts, etc. has also received widespread attention.

Physical and chemical properties^[1]

Aluminum dihydrogen tripolyphosphate, also known as aluminum tripolyphosphate, aluminum polyphosphate, aluminum dihydrogen polyphosphate, etc., is a white orthorhombic crystal or solid powder with a relative density of 2.31, slightly soluble in water and alcohol, and non-volatile. , poorly soluble in acid, partially hydrolyzed if left in the air for a long time, soluble in alkali, and degradable in strong alkali solutions. There are several types of aluminum dihydrogen tripolyphosphate with Al/P ratio of 1:3: AlH₂P₃O₁₀ Type I ( Absorbs water), AlH₂P₃O₁₀ Type II (does not absorb water), AlH₂P₃O₁₀·0.53H₂O (0.53 water type), AlH₂P₃O₁₀·1.45H₂O (1.45 water type), AlH₂ P₃O₁₀·2H₂O (2 water type), AlH₂P₃O₁₀·3H₂O (3 water type) etc. Unless otherwise specified, aluminum dihydrogen tripolyphosphate generally refers to the 2-water type. AlH₂P₃O₁₀ Type II is a monoclinic crystal system with a relative density of 2.60. AlH₂P₃O₁₀ Type II does not change before 560℃; it undergoes endothermic reaction at 560~570℃ and loses crystal water It is converted into a mixture of type A and type B; above 900℃, only type A is obtained; at >1200℃, it is the same as I, producing metaaluminophosphate glass. Aluminum dihydrogen tripolyphosphate is a condensation compound that is weakly acidic and relatively stable to acids. It has a dissociation constant pKa=1.5~1.6 and has selective adsorption properties for alkalis, such as exchange of alkali metal ions, ammonium ions, etc. Ability: It has the ability to selectively absorb ammonia, amines and alkaline gases. The process is chemical adsorption. The adsorption capacity is 10 times that of activated carbon, and the deodorizing capacity is 6 times that of activated carbon. Compared with other solid acids, the acidity is higher (in terms of mass), 10 to 100 times that of alumina, silica gel, etc. When dissolved, it generates tripolyphosphate ions (P₃O₁₀5-) with strong chelating force, which can form chelates with various metal ions and bind to metal ions. A protective film with stable performance is formed on the surface, which has strong anti-corrosion ability for iron. When depolymerized, it becomes orthophosphoric acid and can also form an anti-corrosion protective film with metal. Aluminum dihydrogen tripolyphosphate also has catalytic properties. Aluminum dihydrogen tripolyphosphate is not irritating to the skin. The LD50 of the toxicology test is 18.0g/kg (for mice). It is a practical non-toxic grade and meets the requirements for coating food containers and children’s toys.

Preparation^[1]

The production of aluminum dihydrogen tripolyphosphate is divided into aluminum oxide method, aluminum hydroxide method and aluminum salt method according to different aluminum-containing raw materials; according to different phosphorus-containing raw materials, it is divided into phosphorus pentoxide method and orthophosphoric acid method. , ammonium phosphate method, etc.

Alumina method

Aluminum oxide and phosphorus pentoxide (orthophosphoric acid or ammonium dihydrogen phosphate) are stirred and reacted at an appropriate ratio at 100 to 200°C to generate aluminum orthophosphate. Aluminum orthophosphate undergoes dehydration polymerization in a high-temperature furnace, and the structure of the product varies greatly with the polymerization temperature, polymerization time and material environment atmosphere. In order to prepare high-purity AlH₂P₃O₁₀·2H₂O type product, the polymerization conditions are generally controlled. The conditions are: polymerization temperature 250～℃, polymerization time 3～24h. At the later stage of polymerization, water vapor should be introduced to turn it into dihydrate. When making pigments, use silicon and zinc treatment agents to treat AlH₂P₃O₁₀·2H₂O Carry out modification treatment. Treatment agents are generally silicic acid and zinc salts. The treated product is washed, dried, pulverized and classified to finally obtain aluminum dihydrogen tripolyphosphate pigment.

Aluminum hydroxide method

Stir aluminum hydroxide and phosphorus pentoxide (orthophosphoric acid or ammonium dihydrogen phosphate) in an appropriate ratio at about 50°C. The reaction will exotherm and the temperature will rise. Control the temperature to about 100°C and react for about 2 hours. Aluminum orthophosphate is produced. The subsequent treatment method is the same as the alumina method, and finally aluminum dihydrogen tripolyphosphate is obtained. Using this process to prepare aluminum tripolyphosphate can improve the feeding method, use vacuum drying technology to shorten the production cycle, improve raw material utilization, and greatly reduce the condensation temperature. The material ratio can be adjusted according to the application requirements in different fields, and is dihydrogen tripolyphosphate. Create favorable conditions for the industrial production and promotion of aluminum. Bayer process red mud undergoes sintering modification, hydrochloric acid leaching and alkali treatment (or sodium carbonate alkali dissolution method) to obtain aluminum hydroxide dry glue, which is synthesized with industrial phosphoric acid through neutralization, condensation and hydration reactions to synthesize aluminum tripolyphosphate. , can reduce energy consumption and has very�’s environmental significance and application prospects.

Aluminum salt method

Pigmented carbon black stirs and reacts aluminum salt and phosphorus pentoxide (orthophosphoric acid or ammonium dihydrogen phosphate) in an appropriate ratio. The aluminum salt is first hydrolyzed to form aluminum hydroxide, and is heated to a certain temperature and stirred to react to form aluminum orthophosphate. , the subsequent treatment method is the same as the alumina method, and finally aluminum dihydrogen tripolyphosphate is obtained.

Apply^[3]

1. Anticorrosive coating application

The anti-rust pigment as the main body of aluminum dihydrogen tripolyphosphate in the coating film dissociates, and the dissolved P₃O₁₀^5-It has strong chelating ability and reacts with Fe²⁺ and Fe³⁺ to form a complex protective film with iron tripolyphosphate as the main body. This phosphate protective film is difficult to dissolve in water, has high hardness, and has strong adhesion to the substrate metal. It can effectively prevent further corrosion reactions and achieve excellent anti-rust effects. The P=O and P-OH groups in aluminum dihydrogen tripolyphosphate can also provide excellent corrosion protection in the cutting parts that are most susceptible to rust. In addition, aluminum dihydrogen tripolyphosphate slowly depolymerizes with penetrating water and transforms into low molecular compounds and orthophosphates, which can phosphate and passivate the surface of metals such as steel to form an equally excellent protective film. Anti-rust pigments based on aluminum dihydrogen tripolyphosphate have the characteristics of being pollution-free, strong in rust-proofing, high adhesion, wide adaptability, strong and long-lasting, and are ideal substitutes for traditional lead-chromium pigments. Suitable for phenolic resin, alkyd resin, epoxy and epoxy polyester resin, acrylic resin and other oil-soluble resins and various water-soluble room temperature drying or baking-drying resins to prepare acid-resistant, salt-water-resistant, and waterproof materials with excellent anti-rust properties. , heavy anti-corrosion coatings, interior and exterior coatings. In coatings, it can replace 20% to 40% of titanium dioxide, 100% of zinc phosphate, 100% of zinc chrome yellow, 100% of red lead powder, 60% of zinc powder, etc., thereby reducing the cost of paint production by 20% to 40% and significantly improving the performance of the coating. , which increases the whiteness, toughness, condensation, smoothness, weather resistance, moisture resistance, sun resistance, stain resistance, acid and alkali resistance of DuPont titanium dioxide by 50%, making it a green and environmentally friendly product that has been well received by users.

2. Other applications

Aluminum dihydrogen tripolyphosphate can solidify various alkaline silicates and silica gels, has good waterproof properties, and does not undergo weathering. This property is used to prepare unshaped refractory materials, inorganic binders, inorganic paint hardeners, etc. Aluminum dihydrogen tripolyphosphate is used as an adsorbent (especially as a deodorant), using its solid acid properties to chemically adsorb alkaline ammonia and amines. Catalyst used for ethylene hydration to ethanol, propylene hydration, dehydration reaction, Beckmann rearrangement, etc. It is used as interior and exterior wall coatings in the construction industry and can also be used as a flame retardant.