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13598-37-3
futurechemical
13598-37-3
Zinc dihydrogen phosphate (also known as zinc acid phosphate, zinc dihydrogen phosphate dihydrate, chemical formula Zn(H2PO4)2·2H2O, CAS 13598-37-3) is an acid phosphate of zinc, a white triclinic crystalline or white solidified substance. It is the key ingredient in the "phosphating treatment" before painting automobile bodies and appliance casings—steel parts form a grayish-white zinc phosphate crystalline film in a phosphating solution containing zinc dihydrogen phosphate, which both prevents rust and allows paint to adhere firmly. It is also a corrosion inhibitor in the electroplating industry, a white pigment for ceramics, a clarifying agent for glass, and a compliant additive and analytical reagent in plastic packaging—from automobile manufacturing to everyday ceramics, zinc dihydrogen phosphate is the unsung hero behind the scenes in protecting metals from rust.
Basic information: Chemical formula Zn(H2PO4)2·2H2O (dihydrate), molecular weight 295.38, CAS number 13598-37-3 (some sources also mention 14485-28-0), EINECS number 237-067-2; produced by reacting phosphoric acid with zinc oxide at 100-120℃, followed by concentration, cooling crystallization, and solid-liquid separation. Note the distinction from zinc phosphate (Zn3(PO4)2, CAS 7779-90-0): zinc dihydrogen phosphate is a water-soluble acidic salt and an active component in phosphating solutions and chemical conversion membranes.
Physically, it is a white triclinic crystal or a white solid; it has a low melting point, starting to decompose at about 100℃; it is readily soluble in water (about 1000 g/L at 20℃, hydrolysis occurs upon dissolution), soluble in hydrochloric acid and alkali; it is hygroscopic, stable in air at room temperature; its aqueous solution is acidic (acidity coefficient about 4.7); its boiling point is about 158℃ (760 mmHg, accompanied by decomposition).
Chemically, zinc dihydrogen phosphate contains a high amount of free acid, making its solution highly corrosive. In water, it hydrolyzes to release phosphate and zinc ions, releasing acidity. It can react with steel surfaces to form an insoluble zinc phosphate crystalline film (hopéite type). When heated above 100°C, it decomposes and releases water vapor at high temperatures, which can participate in glass clarification. It exhibits the chemical activity of a weakly acidic salt, capable of neutralizing alkalis and reacting with metal oxides. Storage requires sealing to prevent moisture, and keeping away from fire and alkaline substances.
From the perspective of mechanism of action, industrial-grade zinc dihydrogen phosphate plays an irreplaceable role through the "dissolution-film-forming chemistry of acid phosphates," and its mechanism of action in different applications is as follows:
Zinc dihydrogen phosphate hydrolyzes in water to release phosphate and zinc ions, which micro-etch the steel surface and form an insoluble zinc phosphate crystalline film (hopéite). This film is dense and porous, which not only isolates the corrosive medium to prevent rust, but also provides anchoring points for paint. It is the core reaction of the pretreatment before coating.
Treating the surface of ferrous metals with zinc dihydrogen phosphate solution before electroplating generates a uniform phosphate base film, which can improve the adhesion of the coating and enhance the overall anti-corrosion performance (its effect is better than that of manganese dihydrogen phosphate).
Zinc dihydrogen phosphate forms a stable white zinc phosphate phase (CI Pigment White 32) in ceramic glaze and body, which appears as a pure white, opaque color after high-temperature firing.
Zinc dihydrogen phosphate decomposes at high temperatures during glass melting, releasing gases and altering the color and particle morphology of oxides, which can promote the removal of bubbles and clarification of the molten glass.
Zinc dihydrogen phosphate is permitted for use in various food contact plastics according to GB 9685—2008 (migration limit 25 mg/kg). Within the limit, its use as an additive does not affect food safety.
In summary, industrial-grade zinc dihydrogen phosphate is an "acidic phosphate that protects metals from rust." Based on the solubility and film-forming chemistry of acidic salts, it is used in a wide range of fields, including surface treatment, electroplating, coatings, ceramics, glass, plastics, and analytical chemistry, from steel phosphating to electroplating corrosion protection, from ceramic white pigments to glass clarification, and from plastic packaging additives to analytical reagents.
Industrial-grade zinc dihydrogen phosphate has applications in steel phosphating, electroplating corrosion protection, anti-corrosion coatings, ceramic coloring, glass clarification, plastic additives, and analytical reagents, as detailed below:
Application Areas: Metal surface treatment and pre-coating treatment.
Corresponding Products: Zinc phosphating solution, steel rust-preventive phosphating solution, pre-coating phosphating agent, low-temperature phosphating agent, spray phosphating solution, immersion phosphating solution, phosphating primer, automotive body phosphating agent, appliance casing phosphating agent, etc.
Why it works for this purpose:Zinc dihydrogen phosphate hydrolyzes in water to release phosphate and zinc ions, forming an insoluble zinc phosphate crystalline film on the steel surface. This film both prevents rust and enhances paint adhesion, making it a core component of pre-coating treatment (its phosphating performance is superior to manganese dihydrogen phosphate).
Application areas: Electroplating and metal corrosion protection.
Corresponding products: Pretreatment agents for ferrous metal electroplating, anti-corrosion base film treatment agents for electroplating, pre-galvanizing phosphating agents, fastener anti-corrosion treatment agents, phosphating anti-corrosion agents for hardware parts, etc.
Why it works for this purpose: Treating the surface of ferrous metals with zinc dihydrogen phosphate solution before electroplating generates a uniform phosphating base film, which improves the adhesion of the coating and enhances the overall anti-corrosion performance.
Application areas: Anti-corrosion coatings and heavy-duty anti-corrosion applications.
Corresponding products: Hard anti-corrosion coating additives, anti-rust primer components, metal anti-corrosion coatings, anti-rust coatings for bridge steel structures, anti-corrosion coatings for storage tanks, etc.
Why it works for this purpose: Zinc dihydrogen phosphate, added to coatings as an anti-rust component, reacts with the steel surface to form a zinc phosphate passivation layer, inhibiting corrosion and improving coating adhesion. It represents a potential alternative to environmentally friendly anti-rust pigments.
Application areas: Ceramics and glazes.
Corresponding products: White ceramic glazes, white ceramic tile glazes, sanitary ware glazes, white colorants for ceramic bodies, CI pigment white 32, enamel glazes, etc.
Why it works for this purpose: Zinc dihydrogen phosphate forms a stable white zinc phosphate phase in ceramic glazes and bodies. After high-temperature firing, it exhibits a pure white, opaque color, making it a commonly used white colorant in the ceramic industry.
Application Areas: Glass manufacturing industry.
Corresponding Products: Glass melting clarifying agent, flat glass clarifying agent, bottle and jar glass clarifying agent, glass material clarifying aid, optical glass formulation components, etc.
Why it works for this purpose: Zinc dihydrogen phosphate decomposes at the high temperatures of glass melting, releasing gases and changing the color and particle morphology of oxides. This promotes the removal and clarification of bubbles in the molten glass, improving glass transparency.
Application areas: Plastics and food packaging materials.
Corresponding products: PE plastic additives, PP plastic additives, AS/PS/ABS plastic additives, PET/PC/PA plastic additives, food container packaging material additives, plastic masterbatch components, etc.
Why it can be used for this purpose: According to GB 9685—2008, zinc dihydrogen phosphate is permitted for use in various plastics used in food container packaging materials (used in appropriate amounts as needed for production, with a maximum migration limit of 25.0 mg/kg in the SML range). Within this limit, it can be safely used as a plastic additive.
Application areas: Analytical chemistry and laboratory fields.
Corresponding products: Analytical grade zinc dihydrogen phosphate, zinc content determination reagent, phosphate determination reagent, chemical analysis standard reagent, laboratory teaching reagent, preservative, etc.
Why it is suitable for this purpose: Reagent-grade zinc dihydrogen phosphate has a defined composition and controllable purity, making it suitable as an analytical reagent for zinc and phosphate and a laboratory preservative to ensure accurate detection (acid corrosion prevention is required during handling).
industrial-grade zinc dihydrogen phosphate (CAS 13598-37-3) is an acidic phosphate that acts as a "metal coating for rust prevention." Leveraging its acidic salt dissolution-film-forming chemistry, it has seven applications, including steel phosphating agents, electroplating corrosion protection, anti-corrosion coatings and rust inhibitors, ceramic white colorants, glass clarifying agents, plastic packaging material additives, and analytical reagents. Steel phosphating and electroplating corrosion protection are the core areas with the largest consumption. Note: Zinc dihydrogen phosphate contains high levels of free acid, its solutions are highly corrosive, and it is hygroscopic. Handling must be protected against acid mist and corrosion. Applications in plastic food packaging must comply with migration limits specified in GB 9685.
