Cobalt-Free Trivalent Chromium Conversion Coating for Zinc Alloy
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Solution Overview
Problem
The use of cobalt compounds in black trivalent chromium conversion coatings for zinc or zinc alloy plating is environmentally restricted due to their impact, and alternatives without cobalt fail to provide adequate corrosion resistance and scratch resistance, while also suffering from stability issues like turbidity and precipitation.
Innovation Solution
A treatment liquid for black trivalent chromium conversion coating using organic acids or organic acid salts, organic sulfur compounds, and nitrate ions, along with a trivalent chromium-containing water-soluble liquid for finishing treatment that includes transition metal compounds, but no cobalt, to achieve high-quality design, corrosion resistance, and scratch resistance, while maintaining stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt compounds are used in black trivalent chromium conversion coating, then corrosion resistance and scratch resistance are improved, but environmental compliance deteriorates
Solution Approach 1:
The invention extracts and removes cobalt compounds from the treatment liquid formulation. The patent specifically formulates a treatment liquid that achieves black appearance and adequate corrosion resistance through alternative components (trivalent chromium compounds, organic acids, oxidizing agents) without containing cobalt, thereby eliminating the environmental harm while maintaining protective functionality.
Solution Approach 2:
The invention changes the chemical composition parameters of the treatment liquid by substituting cobalt-containing compounds with cobalt-free alternatives. The patent specifies particular concentrations and combinations of trivalent chromium compounds, organic acids, and oxidizing agents to achieve the desired black appearance and corrosion resistance without cobalt, representing a parameter change in the formulation.
2Object-affected harmful factors
If cobalt-free alternatives are used in treatment liquid, then environmental compliance is improved, but corrosion resistance and scratch resistance deteriorate
Solution Approach 1:
The invention creates a composite treatment liquid system combining multiple components: trivalent chromium compounds, organic acids (such as oxalic acid, malonic acid, citric acid), oxidizing agents (such as hydrogen peroxide, sodium percarbonate), and optional additives. This composite formulation achieves synergistic effects that provide both black appearance and adequate corrosion resistance without cobalt, resolving the contradiction between environmental compliance and protective performance.
3Ease of manufacture
If treatment liquid contains multiple components without heating to form chelate, then processing simplicity is improved, but stability deteriorates due to turbidity and precipitation
Solution Approach 1:
The invention applies preliminary action by pre-forming chelate complexes between trivalent chromium compounds and organic acids through heating before use. The patent specifies heating the treatment liquid to 50-90°C for 30 minutes to 3 hours to form stable chelate products, which then remain stable during storage and application without requiring further heating, thus maintaining both simplicity and stability.
Solution Approach 2:
The invention changes the thermal parameter (temperature and time) during formulation to induce chelate formation. By controlling heating temperature (50-90°C) and duration (30 minutes to 3 hours), the patent transforms the chemical state of components into stable chelate complexes, preventing subsequent precipitation and turbidity while maintaining formulation simplicity.
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 solution provides excellent corrosion resistance and scratch resistance without cobalt, ensuring high stability and environmental considerations, with the use of organic acids, sulfur compounds, and transition metals, effectively replacing cobalt in the treatment process.
Implementation Method 1
a method for combining a thermal reaction product of a trivalent chromium compound and a chelating agent or an organic acid capable of forming a chelate
Implementation Method 2
contains a trivalent chromium compound, two or more organic acids or organic acid salts, or one or more organic sulfur compounds, and nitrate ions
Implementation Method 3
a trivalent chromium-containing water-soluble liquid for finishing treatment which contains one or more transition metal compounds
Data Source
AI summary
Provided are a treatment liquid for a black trivalent chromium conversion coating, and a trivalent chromium-containing water-soluble liquid for finishing treatment, achieving excellent corrosion resistance and scratch resistance without containing a cobalt compound, with high stability and adequate consideration for environmental issues; and a method for treating a metal substrate using the same. The treatment liquid for a black trivalent chromium conversion coating on the surface of a metal substrate contains a trivalent chromium compound, two or more organic acids or organic acid salts, or one or more organic sulfur compounds, and nitrate ions, and contains no cobalt compound.