Chromium III Conversion Coating for Hexavalent Chromium Replacement
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Solution Overview
Problem
Hexavalent chromium compounds, used for improving corrosion resistance and paint adhesion on metal surfaces, pose toxicological and carcinogenic risks, necessitating the development of alternative coatings that are free from hexavalent chromium while maintaining performance.
Innovation Solution
Aqueous compositions containing high-purity chromium III salts, such as Cr2(GF6)3, where G is a Group IV-B element, are used in combination with polymers having carboxylic acid and hydroxyl groups, and are formulated to have low levels of alkali metal and halide ions, ensuring effective corrosion resistance and paint adhesion without the risks associated with hexavalent chromium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hexavalent chromium compounds are used as conversion coatings, then corrosion resistance and paint adhesion are improved, but toxicological and carcinogenic risks increase
Solution Approach 1:
The patent changes the chemical parameter of chromium from hexavalent (Cr(VI)) to trivalent (Cr(III)) state, thereby eliminating toxicological effects while maintaining corrosion resistance and paint adhesion properties through the use of chromium III salts in conversion coating compositions
Solution Approach 2:
The patent replaces expensive and hazardous hexavalent chromium compounds with safer, less toxic chromium III salts, achieving similar protective functions without the carcinogenic risks associated with Cr(VI) compounds
2Strength
If hexavalent chromium compounds are used as conversion coatings, then paint adhesion is improved, but health risks increase
Solution Approach 1:
The patent changes the oxidation state parameter of chromium from +6 to +3, eliminating carcinogenic risks while preserving paint adhesion through the use of chromium III salts combined with appropriate polymers and additives in the conversion coating formulation
3Reliability
If traditional conversion coating processes are used, then corrosion resistance is achieved, but environmental harm increases
Solution Approach 1:
The patent changes the chemical composition parameter from hexavalent chromium to chromium III salts, thereby reducing environmental harm and toxicological effects while maintaining effective corrosion resistance on metal surfaces through conversion coating formation
Solution Approach 2:
The patent converts the previously harmful hexavalent chromium chemistry into beneficial chromium III-based conversion coatings that provide corrosion protection without environmental harm, effectively turning a hazardous material system into a safe and effective alternative
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 chromium III salt compositions provide excellent corrosion resistance and paint adhesion on metal surfaces, reducing the risk of toxicological and carcinogenic hazards, and can be used without rinsing, thereby saving steps and reducing waste handling.
Implementation Method 1
The composition includes Cr2(GF6)3 in which G is a Group IV-B element... contacting the metal surface with an aqueous composition including dissolved Cr2(GF6)3
Implementation Method 2
adding hydrogen peroxide to a mixture including water and a chromium VI compound in the presence of at least one acid according to the formula H2GF6
Implementation Method 3
applying the above composition to the metal surface and subsequently drying the contacted metal surface
Data Source
AI summary
A composition for forming a protective coating on a metal surface includes water;Cr2(GF6)3 in which G is a Group IV-B element; andat least one polymer having a plurality of carboxylic acid groups and at least one polymer having a plurality of hydroxyl groups, and/or at least one polymer having a plurality of both carboxylic acid and hydroxyl groups;wherein the composition contains less than 500 ppm of alkali metal ions and less than 200 ppm of halide ions relative to chromium. A method of forming a protective coating on a metal surface includes contacting the metal surface with the composition.