98% Zinc Dihydrogen Phosphate CAS 13598-37-3

 What is Zinc Dihydrogen Phosphate? How does it work?

Zinc dihydrogen phosphate (also known as zinc acid phosphate, zinc dihydrogen phosphate dihydrate, chemical formula Zn(H2PO4)2·2H2O, CAS 13598-37-3) is a white triclinic crystal or a white solidified substance, which is an acid phosphate of zinc. It is the main ingredient in the "phosphating treatment" that automobile bodies and appliance casings undergo before being painted. In a phosphating solution of zinc dihydrogen phosphate, steel parts develop a grayish-white zinc phosphate crystalline film that both prevents rust and provides a firm base for paint. In electroplating it functions as a corrosion inhibitor, in ceramics it is a white pigment, in glass it is a clarifying agent, in plastic packaging it is a compliant additive, as an analytical reagent, and as a raw material for the synthesis of zinc compounds. Zinc dihydrogen phosphate is the unsung hero behind the scenes, protecting metals from rust in everything from automobile manufacturing to everyday ceramics.

Basic information Chemical formula Zn(H2PO4)2·2H2O(Dihydrate) Molecular weight 295.38 CAS number 13598-37-3 (some sources also 14485-28-0) EINECS number 237-067-2 Production method React zinc oxide with phosphoric acid at 100-120℃, concentrate, crystallise by cooling and separate solid and liquid. Note the difference to zinc phosphate (Zn3(PO4)2, CAS 7779-90-0) Zinc dihydrogen phosphate is a water soluble acidic salt and an active ingredient in phosphating solutions and chemical conversion membranes.

It is a white triclinic crystal or a white solid. It has a low melting point (begins to decompose at approximately 100℃). It is easily soluble in water (approximately 1000 g/L at 20℃, hydrolyses during dissolution) and soluble in hydrochloric acid and alkali. It is hygroscopic. It is stable in air at room temperature. Its aqueous solution is acidic (acidity coefficient approximately 4.7). Its boiling point is approximately 158℃ (760 mmHg, with decomposition).

Chemically zinc dihydrogen phosphate has a high free acid content and the solution is highly corrosive. In water it hydrolyses to liberate phosphate and zinc ions with release of acidity. It can react with steel surfaces to form an insoluble zinc phosphate crystalline film (type hopéite). When heated above 100°C, it decomposes and gives off water vapour, which can assist in the clarification of glass. It has chemical activity of a weakly acid salt, is capable to neutralise alkalis, to react with metal oxides and to be used as a source of zinc in preparation of other compounds of zinc (zinc oxide, zinc carbonate, zinc phosphate etc. Sealed storage to protect from moisture Keep away from fire and alkali substances

From the mechanism of action, zinc dihydrogen phosphate plays an irreplaceable role in “dissolution of acid phosphate - film-forming chemistry+ zinc source chemistry”. The mechanisms of action in different applications are:

1. Mechanism of the phosphating film formation

In water, zinc dihydrogen phosphate hydrolyses to phosphate and zinc ions, which micro-etch the steel surface and form a film of insoluble crystalline zinc phosphate (hopéite). This film is dense and porous and not only isolates the corrosive medium to avoid rust, but creates anchoring points for paint. It is the basic pretreatment reaction before coating.

2.Principle of the anti-corrosive electroplating treatment

Electroplating surface treatment of ferrous metals with zinc dihydrogen phosphate solution can form a uniform phosphate base film, which improves the adhesion of the coating and enhances the overall anti-corrosion performance (its effect is better than manganese dihydrogen phosphate).

3.Ceramic white colouring & glass clarification mechanism

As a stable white zinc phosphate phase (CI Pigment White 32) zinc dihydrogen phosphate is used in ceramic glazes and bodies. During glass melting at high temperature it decomposes releasing gases, alters the colour and particle morphology of oxides, and helps to remove bubbles and to clarify.

4. Plastic Additives and Compliance Systems

Zinc dihydrogen phosphate may be used in food-contact plastics, as per GB 9685—2008 (migration limit 25 mg/kg). Within the limit its use as an additive is safe for food safety.

5. Synthesis Mechanism of Zinc Source

Zinc dihydrogen phosphate in aqueous solution provides zinc ions and phosphate groups, which can be used as a zinc source for the preparation of other zinc compounds such as zinc oxide, zinc carbonate and zinc phosphate by neutralisation, precipitation and other reactions.

To summarise, zinc dihydrogen phosphate is a “acidic phosphate that prevents rust on metals.” It is used in steel phosphating, electroplating corrosion protection, ceramic white pigments, glass clarification, plastic packaging additives, analytical reagents and zinc compound synthesis. It extends to widely different fields including surface treatment, electroplating, coatings, ceramics, glass, plastics, analytical chemistry and fine chemicals through the dissolution-film-forming chemistry of acidic salts and zinc source chemistry.

What are the uses of Zinc Dihydrogen Phosphate?

Zinc dihydrogen phosphate is a common additive for steel phosphating, electroplating corrosion protection, anti-corrosion coatings, ceramic colouring, glass clarification, plastic additives, analytical reagents and synthesis of zinc compounds. Particularly:

1.Steel phosphating agent (major application in metal surface treatment)

Application areas：Metal Surface Treatment & Pre Coating Treatment.

Corresponding products:Zinc phosphate passivation solution, steel anti-rust phosphate passivation solution, pre-coating phosphate passivation agent, low temperature phosphate passivation agent, spray phosphate passivation solution, immersion phosphate passivation solution, phosphate passivation primer, automobile body phosphate passivation agent, appliance shell phosphate passivation agent, etc.

Why it works for this purpose: Zinc dihydrogen phosphate hydrolyses in water to liberate phosphate and zinc ions, and forms an insoluble zinc phosphate crystalline film on the steel surface. This film can prevent rust and promote paint adhesion, and is the core component of pre-coating treatment (its phosphating performance is superior to manganese dihydrogen phosphate).

2.Corrosion protection in electroplating industry (electroplating field)

Application Areas: Electroplating and corrosion protection of metals.

Corresponding products: pretreatment agents for electroplating of ferrous metals, 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: The application of zinc dihydrogen phosphate solution on the surface of ferrous metals before electroplating forms a uniform phosphating base film, which enhances the adhesion of the coating and improves the overall anti-corrosion performance.

3.Anti-corrosion coatings and rust prevention components (coating sector)

Application areas: Anti-corrosion coatings, heavy-duty anti-corrosion applications. Corresponding products: Hard anticorrosive additives for coatings, anticorrosive primers components, metal anticorrosive coatings, anticorrosive coatings for steel structures of bridges, anticorrosive coatings for storage tanks, etc.

Why it works for this purpose:As an anti-rust additive in coatings, zinc dihydrogen phosphate reacts with the steel surface to form a zinc phosphate passivation film to prevent corrosion and enhance coating adhesion. It may be an alternative to environmentally friendly anti-rust pigments.

4. Ceramic white colourant (ceramic industry)

Application areas:Ceramics and glazes.

Corresponding products:: White ceramic glaze, white ceramic tile glaze, sanitary ware glaze, white colourants for ceramic bodies, CI pigment white 32, enamel glaze, etc.

Why it works for this purpose:Zinc dihydrogen phosphate creates a stable white zinc phosphate phase in ceramic glazes and bodies. It shows pure white opaque colour after being fired at a high temperature. It is a common white colourant in the ceramic industry.

5. Glass setters (the glass 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, components of optical glass formulation, etc.

Why it works for this purpose: Zinc dihydrogen phosphate decomposes at the high temperatures involved in glass melting to release gases and to alter the colour and particle morphology of oxides. This helps to remove and clarify the bubbles in the molten glass and therefore the transparency of the glass is improved.

6. Plastic packaging material additives (plastics industry)

Application fields: Plastics and Food

Corresponding products:Packaging Materials Matching Product PE plastic additive, PP plastic additive, AS/PS/ABS plastic additive, PET/PC/PA plastic additive, food container packing material additive, plastic masterbatch component and so on.

Why it works for this purpose:Use of zinc dihydrogen phosphate in plastics used in food packaging materials (as required for the production of the appropriate amount, the SML range of the maximum migration limit of 25.0 mg/kg) in accordance with GB 9685-2008. It can be used as a plastic additive safely within this range.

7. Analytical Chemistry (Analytical Reagents and Laboratory Use)

Application areas： Analytical chemistry and laboratory disciplines.

Corresponding products:Zinc dihydrogen phosphate, analytical reagent, reagent for zinc content determination, reagent for phosphate determination, standard reagent for chemical analysis, laboratory teaching reagent, preservative, etc.

Why it works for this purpose: Reagent-grade zinc dihydrogen phosphate has a defined composition and controllable purity, and can be used as an analytical reagent for zinc and phosphate and a laboratory preservative to ensure accurate detection (acid corrosion prevention is required during handling).

8. Fine Chemical Industry for Production of Zinc Compounds and Raw Materials for Chemical Synthesis

Areas of application: Inorganic syntheses and speciality chemicals

Corresponding products:Raw materials for the preparation of zinc oxide, zinc carbonate, zinc phosphate, the synthesis of zinc salts, intermediates of inorganic zinc compounds, catalyst precursors, etc.

Why it works for this purpose:Zinc dihydrogen phosphate dissolves in water to give zinc ions and phosphate groups, which can be used as a source of zinc to make various zinc compounds by neutralisation, precipitation and metathesis reactions. It is an important raw material in inorganic chemistry of zinc.

In summary： zinc dihydrogen phosphate (CAS 13598-37-3) is an acidic phosphate used as a “metal coating for rust prevention.” It has eight applications through the use of its acidic salts' solubility and film-forming chemistry and zinc source chemistry: steel phosphating agents, electroplating industry anti-corrosion treatment, anti-corrosion coatings and rust-preventive components, white colourants for ceramics, glass clarifying agents, additives for plastic packaging materials, analytical reagents and laboratory applications, and raw materials for chemical synthesis and zinc compound preparation. Steel phosphating and electroplating corrosion prevention are the largest consumption fields among them. Note: Zinc dihydrogen phosphate is highly corrosive in solution due to high level of free acid and hygroscopic nature. Handling must be kept away from acid mist and corrosion. The use of plastic food packaging shall comply with the migration limits specified in GB 9685.corrosion prevention are the core areas with the largest consumption. Note: Zinc dihydrogen phosphate contains a high level of free acid, its solution is highly corrosive, and it is hygroscopic. Handling must be protected against acid mist and corrosion. Applications in plastic food packaging must comply with the migration limits specified in GB 9685.