Chromium(III) Coating Bath Without Silanes
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Solution Overview
Problem
Conventional methods for producing corrosion-protective coating layers on metallic surfaces often require multi-stage processes, leading to wastewater contamination, inhomogeneous coatings, and reduced barrier effects, especially when using film-forming polymers, which are not suitable for all geometric shapes and can lead to corrosion issues due to salt formation and water crystallization.
Innovation Solution
A single-step method using a treatment solution containing chromium(III) ions, phosphate, and citrate, without silanes, which forms a homogeneous, flexible, and effective corrosion-protective coating layer that integrates passivation and sealing, reducing redissolution in aqueous media and avoiding the need for rinsing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-stage processes (passivation, rinsing, sealing) are used to achieve sufficient corrosion protection, then corrosion protection is improved, but process complexity and wastewater contamination increase
Solution Approach 1:
The patent combines passivation and sealing into a single integrated treatment step using one bath solution containing chromium(III) ions, phosphate, and citrate. This eliminates the need for separate rinsing and sealing steps, reducing process complexity while maintaining effective corrosion protection through the synergistic action of the combined components
2Reliability
If film-forming polymers are used in single-stage processes to achieve corrosion protection, then corrosion protection is improved, but coating homogeneity and barrier effect deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the treatment solution by using chromium(III) ions complexed with phosphate and citrate at controlled pH levels (2-6). This chemical parameter optimization enables single-stage passivation and sealing without film-forming polymers, producing homogeneous conversion layers with excellent barrier properties and consistent corrosion protection
3Stability of the object's composition
If low pH treatment solutions (pH < 3) are used to prevent chromium hydroxide precipitation, then chromium ion stability is improved, but surface over-activation and salt formation increase
Solution Approach 1:
The patent introduces phosphate and citrate as intermediary complexing agents that bind chromium(III) ions. These intermediaries prevent chromium hydroxide precipitation at higher pH values (2-6) by forming stable soluble complexes, thereby eliminating the need for extremely low pH conditions and preventing surface over-activation and harmful salt formation
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 protection, improved storage stability, and flexibility, preventing cracks and corrosion losses, while avoiding the use of toxic chromium(VI) ions and ensuring compatibility with friction additives, resulting in a durable and effective coating that maintains surface appearance under corrosive stress.
Implementation Method 1
the surface to be treated is brought into contact with a treatment solution... forms a homogeneous, flexible, and effective corrosion-protective coating layer
Implementation Method 2
Aqueous treatment solutions of chromium (III) ions and phosphate... and a citrate source
Data Source
Figure 1
AI summary
The invention relates to a treatment solution for a method for producing an anti-corrosion coating layer on a metal surface, wherein the surface to be treated is brought in contact with a treatment solution, which contains a chromium(III) ion source, a phosphate source, a zinc ion source, and a citrate source, wherein the amount-of-substance ratio of chromium(III) ions to zinc ions is 1 to at least 1.65 and the amount-of-substance ratio of chromium(III) ions to citrate is 1 to at least 1.4 and the treatment solution is substantially free of polymers that can be obtained by reacting one or more alkoxysilanes of the formula: R4-xSi(OR1)x, wherein the groups R are the same or different from each other and each represent a substituted or unsubstituted hydrocarbon group having 1 to 22 hydrocarbon atoms, x is equal to 1, 2, or 3, and R1 stands for a substituted or unsubstituted hydrocarbon group having 1 to 8 hydrocarbon atoms, and one or more alkoxides of the formula: Me(OR2)n, wherein Me stands for Ti, Zr, Hf, Al, Si and n stands for the oxidation number of Me and R2 represents a substituted or unsubstituted hydrocarbon group having 1 to 8 hydrocarbon atoms.