High-Purity Electrolytic Copper Refining via PEG Molecular Weight Control
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Solution Overview
Problem
High-purity electrolytic copper produced using large cathodes is prone to brittleness and peeling during electrolysis, leading to reduced productivity and quality, especially when using polyethylene glycol (PEG) additives with higher molecular weights, which increases tensile stress and causes the copper to warp and peel off from the cathode.
Innovation Solution
Control the molecular weight of PEG and current density during electrolysis to maintain a concentration of additives in the electrolyte at 20 ppm or more, with specific ranges for different molecular weights of PEG (1000 to 2000) to ensure the copper is not brittle and resists peeling, using a copper nitrate solution and stainless steel cathodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PEG with higher molecular weight is used to improve rigidity, then brittleness is reduced, but tensile stress increases causing the copper to warp and peel off from the cathode
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight of PEG within 1000-2000 and maintaining additive concentration at 20 ppm or more. This optimization balances the rigidity improvement from higher molecular weight PEG while preventing excessive tensile stress that would cause peeling. The specific parameter ranges were determined through systematic experimentation to achieve the optimal trade-off between brittleness reduction and peeling resistance.
Solution Approach 2:
The patent implements dynamics by adjusting current density based on PEG molecular weight and maintaining appropriate additive concentrations. The current density is controlled within specific ranges (1.2-2.2 A/dm2 for PEG 1000, 0.8-1.7 A/dm2 for PEG 1500, 0.4-1.2 A/dm2 for PEG 2000) to dynamically balance deposition rate, rigidity development, and stress accumulation. This dynamic control prevents peeling while ensuring sufficient rigidity for large cathode applications.
2Productivity
If current density is increased to improve productivity, then output increases, but the copper becomes more prone to peeling and warping
Solution Approach 1:
The patent applies parameter changes by establishing specific current density ranges correlated with PEG molecular weight. For PEG 1000, current density is 1.2-2.2 A/dm2; for PEG 1500, it is 0.8-1.7 A/dm2; for PEG 2000, it is 0.4-1.2 A/dm2. These parameter optimizations enable high productivity through increased current density while simultaneously preventing peeling and warping by maintaining stress within acceptable limits.
Solution Approach 2:
The patent implements feedback control by monitoring and adjusting current density based on the observed effects of PEG molecular weight and additive concentration. The current density is tuned to achieve optimal deposition rates while observing the mechanical properties of the deposited copper. This feedback mechanism ensures that productivity improvements do not compromise peeling resistance, particularly for large cathode applications.
3Productivity
If large area cathodes are used to improve productivity, then output increases, but the deposited copper becomes brittle and peels off
Solution Approach 1:
The patent applies parameter changes by optimizing PEG molecular weight (1000-2000) and concentration (20 ppm or more) specifically for large area cathodes. These parameter adjustments ensure that even with large cathode areas, the deposited copper maintains sufficient ductility and does not become brittle. The controlled parameters produce a uniform deposit with appropriate mechanical properties across the entire cathode surface.
Solution Approach 2:
The patent implements preliminary action by pre-establishing the optimal PEG concentration and molecular weight before beginning electrolysis with large cathodes. The additive concentration is maintained at 20 ppm or more from the outset, and the appropriate current density range is selected based on the PEG molecular weight. This preliminary preparation ensures that the deposited copper will have the necessary ductility and adhesion properties before the deposition process begins, preventing brittleness and peeling in large area applications.
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 method achieves high-purity electrolytic copper with sulfur content below 0.01 ppm, maintaining rigidity and resistance to peeling, thereby improving productivity and quality without extensive facility costs, even with large cathodes.
Implementation Method 1
performing electrolysis by using an electrolyte which includes a copper nitrate solution
Implementation Method 2
a mixture of polyethylene glycol and polyvinyl alcohol at a content of 20 ppm or more as an additive
Data Source
AI summary
This electrolytic refining method of high-purity electrolytic copper includes: performing electrolysis by using an electrolyte which includes a copper nitrate solution, a cathode made of stainless steel, and an anode made of copper so as to deposit high-purity electrolytic copper on the cathode.(a) The electrolyte includes a mixture of polyethylene glycol and polyvinyl alcohol at a content of 20 ppm or more as an additive.(b) When a molecular weight of the polyethylene glycol is given as Z and a current density during the electrolysis is given as X (A/dm2), the electrolysis is performed under conditions that fulfill the following relational expressions,1000≦Z≦20001.2−(Z−1000)×0.0008≦X≦2.2−(Z−1000)×0.001.