Phosphoric-Polyphosphonic Acid Passivation for Stable Zinc Coatings
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Solution Overview
Problem
Existing passivation compositions for zinc or zinc alloy coatings rely on toxic hexavalent chromium, peroxide, or persulphate compounds, leading to environmental pollution and high economic costs due to frequent replenishment, and often result in inferior corrosion resistance and stability issues.
Innovation Solution
An aqueous passivation composition comprising phosphoric acid, water-soluble polyphosphonic acid, divalent metal cations, and fluoroacids, free from hexavalent chromium, peroxide, and persulphate, forming a stable passivate film on zinc or zinc alloy coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hexavalent chromium is used in passivation compositions, then corrosion resistance is improved, but environmental pollution and toxicity increase
Solution Approach 1:
The patent removes hexavalent chromium from the passivation composition entirely, extracting the harmful substance while maintaining the passivation function through alternative chemicals (phosphoric acid, polyphosphonic acid, and metal cations). This resolves the contradiction by eliminating the toxic component while preserving corrosion resistance through a different chemical mechanism.
Solution Approach 2:
The patent changes the chemical parameters of the passivation composition by using trivalent chromium or chromium-free alternatives with different chemical mechanisms (phosphoric-polyphosphonic acid systems). This parameter change allows achieving corrosion protection without the harmful effects of hexavalent chromium.
2Reliability
If peroxide or persulphate compounds are used in passivation compositions, then passivation film formation is improved, but economic costs increase due to frequent replenishment
Solution Approach 1:
The patent removes peroxide and persulphate compounds from the composition, extracting the problematic oxidizing agents that cause high consumption rates. The passivation process is reformed to use air oxidation or alternative oxidizing mechanisms that do not require frequent replenishment of expensive chemicals.
Solution Approach 2:
The patent replaces expensive, rapidly consumed peroxide/persulphate compounds with cheaper, more stable oxidizing systems (such as air oxidation or nitrate-based systems) that have longer service life and lower replenishment costs, effectively using more economical substitutes.
3Reliability
If peroxide or persulphate compounds are used in passivation compositions, then passivation activity is improved, but stability decreases due to catalytic decomposition
Solution Approach 1:
The patent removes peroxide and persulphate compounds that are susceptible to catalytic decomposition, extracting the unstable components from the system. This eliminates the stability problem while maintaining passivation activity through alternative chemical pathways.
Solution Approach 2:
The patent replaces unstable peroxide/persulphate systems with more stable oxidizing agents (such as nitrate salts or air oxidation systems) that resist catalytic decomposition and provide consistent passivation performance over time.
4Object-affected harmful factors
If chromium (III) is used instead of hexavalent chromium, then toxicity is reduced, but passivation performance deteriorates
Solution Approach 1:
The patent changes the chemical mechanism from chromium-based oxidation to a phosphoric-polyphosphonic acid system with metal cations. This fundamental parameter change allows achieving effective passivation through a different chemical pathway that inherently provides both protection and desired aesthetic properties without chromium toxicity.
Solution Approach 2:
The patent uses a composite chemical system combining phosphoric acid, polyphosphonic acid, and divalent/trivalent metal cations to achieve passivation performance that compensates for the reduced effectiveness of chromium (III), creating a synergistic formulation that delivers both safety and performance.
5Stability of the object's composition
If passivation compositions are formulated without peroxide or persulphate, then stability is improved, but corrosion resistance may be compromised
Solution Approach 1:
The patent changes the chemical composition parameters by eliminating peroxide/persulphate and using alternative oxidizing mechanisms (air oxidation, nitrate salts) combined with phosphoric-polyphosphonic acid systems. This parameter change achieves both stability and effective corrosion resistance through a different chemical mechanism.
Solution Approach 2:
The patent creates a composite passivation system combining multiple components (phosphoric acid, polyphosphonic acid, metal cations, and alternative oxidizing agents) that work synergistically to provide both compositional stability and effective corrosion protection, compensating for the absence of peroxide/persulphate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition provides effective corrosion resistance and stability, reducing environmental impact and operational costs while maintaining high performance in neutral salt spray tests.
Implementation Method 1
aqueous, acidic passivation compositions comprising both phosphoric acid and at least one water-soluble polyphosphonic acid
Implementation Method 2
comprising (i) phosphoric acid; (ii) at least one water-soluble polyphosphonic acid... (iii) at least one divalent metal cation (M2+); and (iv) at least one water-soluble or water-dispersible fluoroacid
Data Source
AI summary
The present invention provides an aqueous passivation composition for the treatment of zinc or zinc alloy coatings, comprising:i) phosphoric acid;ii) at least one water-soluble polyphosphonic acid or a water-soluble salt thereof,iii) at least one divalent metal cation (M2+); and,iv) at least one water-soluble or water-dispersible fluoroacid or a salt thereof, wherein said fluoroacid is defined by the following general empirical formula (II):HpTqFrOs (II)wherein: each of q and r represents an integer from 1 to 10;each of p and s represents an integer from 0 to 10; and,T represents an element selected from the group consisting of Ti, Zr, Hf, Si, Sn, Al, Ge, and B.