Phosphates & Corrosion Inhibitors
Zinc Phosphate
CAS 7779-90-0 — Corrosion-Inhibiting Pigment & Pretreatment
Zinc phosphate is the preferred non-toxic corrosion-inhibiting pigment for industrial primers and a key metal pretreatment chemical for steel and zinc surfaces. Texas-Chem supplies zinc phosphate in bulk drums and super sacks.
CAS Number
7779-90-0
Formula
Zn₃(PO₄)₂
Density
3.9 g/cm³
Pack Sizes
Bags · Super Sacks · Drums
Structure
Zn₃(PO₄)₂ — Zinc Phosphate — CAS 7779-90-0
Safety & Regulatory
- NFPA Health
- 2 — Moderate hazard
- NFPA Flammability
- 0 — Non-flammable
- NFPA Reactivity
- 0 — Stable
- OSHA PEL (dust)
- 5 mg/m³ (as Zn)
- DOT Hazard Class
- Not regulated
- Skin/Eye
- Irritant — wear gloves and safety glasses
Grades & Packaging
Available Grades
Pack Sizes
Also Known As
Physical & Chemical Properties
| CAS Number | 7779-90-0 |
| Molecular Formula | Zn₃(PO₄)₂ |
| Molecular Weight | 386.11 g/mol |
| Appearance | White to off-white powder |
| Solubility in Water | Practically insoluble (0.018 g/L) |
| pH (saturated solution) | 6.5–7.5 |
| Oil Absorption | 15–25 g/100 g (pigment grade) |
| Particle Size | 1–10 microns (pigment grade) |
| Density | 3.9 g/cm³ |
| Refractive Index | 1.595 |
| Corrosion Inhibition | Excellent — anodic inhibitor |
| Toxicity | Low — preferred over lead/chromate |
Industrial Applications
Corrosion-Inhibiting Primers
Zinc phosphate is the primary corrosion-inhibiting pigment in industrial primers for steel structures, bridges, pipelines, and oilfield equipment. It replaces toxic lead and chromate pigments while providing excellent corrosion protection.
Metal Pretreatment
Zinc phosphate conversion coating is applied to steel and zinc surfaces before painting to improve adhesion and corrosion resistance in automotive and industrial applications. The coating provides a crystalline phosphate layer that bonds to both the metal and the paint.
Cooling Water Treatment
Zinc phosphate is used as a corrosion inhibitor in cooling water systems, forming a protective film on metal surfaces. Often used in combination with polyphosphate or molybdate inhibitors.
Oilfield Coatings
Used in corrosion-inhibiting primers for oilfield equipment, pipelines, and offshore structures in the Gulf of Mexico and Permian Basin. Provides long-term corrosion protection in harsh environments.
Marine Coatings
Zinc phosphate primers are used in marine coatings for ship hulls, offshore platforms, and port structures where long-term corrosion protection in saltwater environments is required.
Architectural Coatings
Used in architectural primers for steel windows, doors, and structural steel in commercial and industrial buildings where corrosion protection is required.
Why Source Zinc Phosphate from Texas-Chem
- Industrial grade zinc phosphate in stock — drums and super sacks
- Consistent quality with CoA on every lot
- Same-week delivery across Texas; nationwide LTL
- Technical support for coating, pretreatment, and water treatment applications
- One rep from first call to final delivery
Zinc Phosphate — Frequently Asked Questions
What is the difference between zinc phosphate and zinc chromate as corrosion inhibitors?▾
Zinc phosphate provides excellent corrosion inhibition through an anodic inhibition mechanism, forming a protective zinc phosphate film on steel surfaces. Zinc chromate provides similar or better corrosion protection but is classified as a carcinogen (hexavalent chromium) and is heavily restricted under REACH and EPA regulations. Zinc phosphate is the preferred non-toxic replacement for zinc chromate in industrial primers.
How does zinc phosphate pretreatment work?▾
Zinc phosphate conversion coating is applied by immersing or spraying steel parts with a zinc phosphate solution (typically 1–3% concentration at 40–70 °C). The phosphate reacts with the steel surface to form a crystalline zinc iron phosphate layer (hopeite/phosphophyllite). This layer improves paint adhesion and provides a barrier against corrosion. The process requires degreasing, pickling, and rinsing steps before and after phosphating.
What is the typical loading of zinc phosphate in an industrial primer?▾
Zinc phosphate is typically used at 10–25% by weight in the dry film of industrial primers. Higher loadings provide better corrosion protection but may reduce mechanical properties. The optimal loading depends on the primer formulation, binder system, and target corrosion protection level.
Is zinc phosphate suitable for food contact applications?▾
Zinc phosphate is not approved for direct food contact applications. It is used in industrial coatings and pretreatment applications where food contact is not a concern. For food plant equipment, consult the coating manufacturer for food-contact approved primer systems.