HX AP-18 Aluminum zinc tripolyphosphate
of elevated zinc content?
Technical Information
What Is HX AP-18 Aluminum Zinc Tripolyphosphate
HX AP-18 is a zinc-enhanced aluminum tripolyphosphate anti-corrosion pigment featuring an orderly elevated active zinc content designed for maximum substrate passivation in waterborne systems. The tripolyphosphate structure — with its characteristic P-O-P chain — provides a larger reservoir of inhibitive phosphate ions compared to orthophosphate grades. Combined with the elevated zinc content, AP-18 forms a dense, durable passivation film on metal substrates that performs exceptionally well in waterborne epoxy coatings, where the synergy between the alkaline curing agent and the pigment’s active surface creates superior early water resistance. Not recommended for automotive applications.
Key Features
- Elevated Active Zinc Content — Higher Zn ion availability than standard tripolyphosphate grades, producing a denser passivation film with improved water resistance
- Tripolyphosphate Chain Structure — P-O-P backbone provides sustained phosphate release compared to orthophosphate’s rapid initial burst
- Waterborne Epoxy Optimized — Validated performance in waterborne epoxy systems; synergizes with amine curing agents for enhanced early water resistance
- Moderate Oil Absorption (20-35 g/100g) — Balanced binder demand suitable for both primer and direct-to-metal applications
- Wide pH Compatibility (6.5-9.5) — Works across mildly acidic to alkaline coating environments
- Cost-Effective Industrial Grade — Optimized performance for decorative and industrial paints without the premium of automotive-grade pigments
Recommended Applications
| Application | Suitability |
|---|---|
| Industrial Paints | ✅ Recommended |
| Decorative Water Base Paints | ✅ Recommended |
| Decorative Solvent Base Paints | ✅ Recommended |
| Decorative Universal Stainers | ✅ Recommended |
| Powder Coatings | ✅ Recommended |
| Automotive OEM | ❌ Not Recommended |
| Automotive Refinish | ❌ Not Recommended |
✅ Recommended | ⚪ Suitable | ❌ Not Recommended
Technical Data
| Physical Form | White powder |
| Oil Absorption | 20-35 g/100g |
| Water Soluble Matter | < 1.5% |
| pH Value | 6.5-9.5 |
| Sieve Residue (45 μm) | < 1.0% |
| Primary Particle Size D50 | 1.0-6.0 μm |
Packaging
25 kg/bag. Custom packaging available upon request.
Frequently Asked Questions
How does tripolyphosphate differ from orthophosphate for corrosion inhibition?
Tripolyphosphates (like AP-18) have a P-O-P-O-P chain structure containing three phosphate units linked together, compared to orthophosphates (like AP-13) which have a single PO₄ unit. The chain structure acts as a sustained-release reservoir — as the coating ages and moisture penetrates, the P-O-P bonds gradually hydrolyze, releasing fresh phosphate ions over an extended period. Orthophosphates release all available phosphate quickly. This makes tripolyphosphates better suited for long-service-life architectural and industrial maintenance coatings, while orthophosphates excel in applications requiring rapid initial protection like automotive primers.
Why is AP-18 not recommended for automotive applications?
Automotive OEM and refinish coatings demand Class A surface finishes with zero visible particles at film thicknesses as low as 15-20 μm. AP-18’s particle size distribution (D50: 1.0-6.0 μm with a broader range than AP-13 or AP-17) and moderate oil absorption (20-35) can produce slight surface texture under these extreme thin-film conditions. For automotive applications, we recommend AP-13 (narrow distribution orthophosphate) or AP-16/AP-17 (ultra-fine premium grades).
What is the advantage of elevated zinc content?
Higher active zinc content means more Zn²⁺ ions available at the coating-metal interface to form zinc-phosphate-hydroxide passivation complexes. These complexes are particularly effective at blocking the cathodic half-reaction of corrosion (oxygen reduction), which is the rate-limiting step in most atmospheric corrosion scenarios. The practical result is better performance in salt spray (ASTM B117) and humidity resistance testing compared to standard zinc phosphate grades at equivalent loading levels.
Disclaimer — This Technical Data Sheet reflects our best understanding of typical product properties at the time of publication. Listed values are representative of standard production and are not intended as specifications, contractual parameters, or fitness guarantees. Batch variations within normal manufacturing tolerances may occur; users should verify critical parameters against their own requirements before use. Processing methods, formulations, and end-use environments are beyond the manufacturer’s control. The buyer assumes full responsibility for confirming product suitability through its own testing and quality assurance. No intellectual property license is granted or implied. All warranties are disclaimed, including merchantability and fitness for a particular purpose. The manufacturer is not liable for incidental, consequential, or special damages. All sales are governed by the manufacturer’s standard terms, available upon request. This product may contain particles below 0.1 μm.