Aluminum Tripolyphosphate|13939-25-8

Aluminum Tripolyphosphate|13939-25-8

Aluminum tripolyphosphate is an important non-toxic, anti-corrosive pigment that is increasingly replacing traditional anti-rust pigments containing heavy metals like lead and chromium.

Basic Information

Chemical Name: Aluminum Tripolyphosphate

Synonyms: ATP, Aluminum triphosphate

Chemical Formula: AlH₂P₃O₁₀·2H₂O (The most common commercial form, a dihydrated acid salt)

CAS Number: 13939-25-8

Molecular Weight: 317.94 (for AlH₂P₃O₁₀·2H₂O)

Key Properties

1. Physical Properties:

Typically a white or off-white fine powder, odorless and tasteless.

Slightly soluble in water (undergoes slow hydrolysis). Soluble in strong acids (e.g., hydrochloric acid) and strong bases.

Good thermal stability, with a high decomposition temperature (begins to dehydrate and decompose above approximately 550°C).

2. Chemical Properties:

Corrosion Inhibition Mechanism (Core Function):

Passivation/Film Formation: Phosphate ions can react with metal surfaces (especially iron and steel) to form a dense, adherent passivation film (mainly consisting of FePO₄, AlPO₄), isolating the metal from corrosive media.

Inhibitor Ion Release:The tripolyphosphate ion (P₃O₁₀⁵⁻) has strong chelating ability. It can form stable complexes with metal ions (e.g., Fe²⁺), suppressing anodic reactions and preventing rust propagation.

Self-Healing Property:If the coating is scratched or locally damaged, aluminum tripolyphosphate can re-dissolve and migrate to the exposed metal surface to form a new protective film, exhibiting a "self-healing" function.

Non-toxic,free of heavy metal ions like lead, chromium, or cadmium. Environmentally safe.

Primary Applications

Its applications are almost entirely based on its excellent anti-corrosion and rust-inhibiting properties.

1. Paint & Coatings Industry (Primary Use):

Anti-Corrosion Primers:Widely used in various solvent-based and water-based industrial anti-rust primers and coatings for steel structures, ships, bridges, automobiles, machinery, containers, etc.

Topcoats: Can be used in eco-friendly topcoat systems.

Compatibility: Compatible with various resin systems such as epoxy, alkyd, acrylic, polyurethane, and chlorinated rubber.

2. Other Fields:

Plastics & Rubber: Used as a functional filler to improve flame retardancy and corrosion resistance.

Ceramics & Glass: Used as a fluxing agent and opacifier.

Flame Retardants: Can serve as an inorganic flame-retardant additive due to its phosphorus content.

Metal Treatment: Used in formulating chromium-free metal pre-treatment and passivation solutions.

Product Advantages (vs. Traditional Anti-Corrosion Pigments)

Environmental Friendliness:Non-toxic, heavy metal-free, compliant with stringent environmental regulations (e.g., RoHS, REACH).

High Efficiency: Strong rust-inhibiting performance, typically used at relatively low loading levels. Can partially or fully replace red lead, zinc chromate, zinc phosphate, etc.

Broad Applicability: Provides good corrosion protection for various metals (steel, galvanized steel, aluminum, etc.).

Good Synergy: Often used in combination with other pigments/fillers like zinc oxide or silicates, resulting in a synergistic effect that significantly enhances anti-corrosion performance.

Safety & Storage

Safety: Considered low-toxicity or non-toxic. May cause mild irritation to skin and eyes (primarily due to physical irritation from dust). Use with standard precautions like dust masks and goggles is still recommended.

Environmental Impact: Environmentally benign due to its low solubility and absence of heavy metals.

Storage: Store in a dry, cool, well-ventilated area. Protect from moisture and package damage. Keep away from strong acids and bases.

Considerations in Coating Formulations

Optimum Loading: Typically 5% - 20% of the total paint formulation, depending on the resin system, performance requirements, and synergy with other components (determined experimentally).

pH Influence: Its effectiveness is influenced by the pH of the coating system. It is generally recommended to adjust the system to a neutral or slightly alkaline pH to ensure stable release of its inhibitory ions.

Dispersion: As a powder, it requires adequate dispersion during production to ensure optimal performance.

Summary: Aluminum tripolyphosphate is a high-performance, environmentally friendly "green" anti-corrosion pigment.It provides long-lasting protection through a triple mechanism of film formation, chelation, and self-healing. It has become an indispensable component in modern industrial coatings, especially in water-based and eco-friendly systems. With increasing global environmental regulations, its market demand and application prospects remain very strong.

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