Trivalent Chromium Formate Bath for Anion Accumulation Control
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Solution Overview
Problem
Trivalent chromium-based deposition methods for functional chromium layers face issues with anion accumulation, leading to limited bath lifetime, precipitation, and inefficient operation, unlike hexavalent chromium methods, which can operate endlessly without anion accumulation.
Innovation Solution
A method using an aqueous deposition bath with trivalent chromium ions and formate ions, where solid trivalent chromium formate is dissolved in a separate partial volume and added back to maintain target concentrations, preventing anion accumulation and allowing for longer operation without membrane use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If trivalent chromium sources (chromium (III) sulfate or chromium (III) chloride) are used to replenish consumed chromium, then chromium deposition can be maintained, but inorganic counter anions (sulfate or chloride) accumulate in the deposition bath
Solution Approach 1:
The invention changes the chemical parameter of the chromium source from traditional sulfate or chloride salts to chromium formate. This parameter change transforms the anion type from accumulating inorganic anions to volatile formate ions that decompose during electrolysis, thereby preventing anion accumulation while maintaining chromium ion replenishment
Solution Approach 2:
The invention converts the potential harm of formate ion accumulation into a benefit by utilizing the volatile nature of formate. The formate ions decompose during electrolysis to produce carbon dioxide gas and hydrogen gas, which escape from the system, thus converting what could be an accumulation problem into a self-cleaning mechanism that prevents anion buildup
2Object-generated harmful factors
If membranes are used to restrict anion accumulation, then anion buildup can be prevented, but membranes are expensive and quickly decompose under high current densities
Solution Approach 1:
The invention extracts and removes the problematic component (accumulating inorganic anions) from the system by replacing them with formate ions that do not accumulate. This eliminates the need for membranes or other separation devices, simplifying the system while achieving the same goal of preventing anion buildup
Solution Approach 2:
The deposition bath becomes self-regulating through the use of chromium formate. The formate ions naturally decompose during electrolysis to release gases that escape, automatically preventing anion accumulation without requiring external membranes or intervention systems
3Object-generated harmful factors
If volatile anions (formate, acetate, propionates, etc.) are used, then anion accumulation can be avoided, but their solubility is too low and they do not harmonize well with complexing agents
Solution Approach 1:
The invention optimizes the specific parameter of solubility by selecting formate over other volatile anions like acetate or propionate. Chromium formate provides sufficient solubility to maintain effective chromium ion concentrations while still offering the benefit of volatile anion decomposition, representing an optimized parameter choice within the volatile anion class
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
This approach extends the operational time of the deposition bath, maintains high wear resistance and hardness of the chromium layers, and prevents anion accumulation, similar to hexavalent chromium methods, while being economically optimal and environmentally friendly.
Implementation Method 1
immersing the at least one substrate in the aqueous deposition bath and applying an electrical current such that the chromium or chromium alloy layer is deposited on the substrate
Implementation Method 2
a method for depositing a chromium or chromium alloy layer on at least one substrate
Implementation Method 3
adding dissolved trivalent chromium formate to the aqueous deposition bath such that trivalent chromium ions are present in a higher concentration than before step (d)
Data Source
AI summary
A method for depositing a chromium or chromium alloy layer on at least one substrate, the method comprising the steps(a) providing an aqueous deposition bath with a pH in the range from 4.1 to 6.9, the bath comprisingtrivalent chromium ions,formate ions, andoptionally sulfate ions,(b) providing the at least one substrate and at least one anode,(c) immersing the at least one substrate in the aqueous deposition bath and applying an electrical current such that the chromium or chromium alloy layer is deposited on the substrate, the substrate being the cathode,wherein, if during or after step (c) the trivalent chromium ions have a concentration below a target concentration of trivalent chromium ions, then(d) adding dissolved trivalent chromium formate to the aqueous deposition bath such that trivalent chromium ions are present in a higher concentration than before step (d),with the proviso thatsolid trivalent chromium formate is dissolved in a separated partial volume taken from the aqueous deposition bath to obtain said dissolved trivalent chromium formate for step (d).