Selective Bismuth Removal from Copper Alloy Surfaces
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for preventing the elution of bismuth (Bi) from copper alloys are inadequate, as they either fail to effectively remove Bi or lead to increased costs due to the difficulty in reusing materials, and leadless copper alloys with Bi are challenging to process and recycle, especially when containing silicon, which deteriorates mechanical properties.
Innovation Solution
A method involving the use of nitric acid with a concentration of 4 to 20 mass % to selectively dissolve Bi from the surface of copper alloys, followed by shot-blasting to remove corrosive products and voids, thereby preventing Bi elution and enhancing the mechanical properties of the alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Bi is contained in copper alloy to improve cuttability, then machinability is improved, but Bi elution occurs which fails to satisfy lixiviation standards
Solution Approach 1:
The patent removes Bi from the water-contacting surface of copper alloy through selective dissolution using nitric acid treatment. This extraction eliminates the harmful Bi elution while preserving Bi in the bulk material to maintain cuttability benefits.
Solution Approach 2:
The patent creates a Bi-free zone at the water-contacting surface while maintaining Bi content in the interior material. This local modification ensures low Bi elution at the surface while preserving the overall machinability properties of the alloy.
2Quantity of substance
If nitric acid concentration is increased to remove Bi, then Bi removal effect is enhanced, but copper matrix dissolution increases
Solution Approach 1:
The patent optimizes nitric acid concentration to 5-20% to achieve selective Bi dissolution while minimizing copper matrix loss. This parameter optimization balances Bi removal efficiency with material preservation.
Solution Approach 2:
The patent references data from sand casting studies (Patent Document 3) and adapts the nitric acid treatment parameters for different copper alloy forms, applying the principle of transferring knowledge from one material form to another while adjusting for specific conditions.
3Object-affected harmful factors
If lead content is tightened to suppress lead elution, then lead safety is improved, but returned materials become difficult to reuse resulting in increased costs
Solution Approach 1:
The patent removes Bi from the surface through selective dissolution, creating a Bi-free zone that satisfies lixiviation standards while preserving the bulk material composition for efficient recycling and reuse.
Solution Approach 2:
The patent enables recovery and reuse of copper alloy materials by removing only the harmful surface Bi layer through controlled nitric acid treatment, allowing returned materials to be reused without contamination concerns.
4Object-affected harmful factors
If Bi is removed from surface to prevent elution, then lixiviation standards are satisfied, but surface segregation and Bi exposure complications arise
Solution Approach 1:
The patent applies nitric acid treatment before final surface finishing operations to pre-remove Bi from the surface, preventing Bi exposure complications during subsequent manufacturing steps.
Solution Approach 2:
The patent replaces mechanical grinding methods with chemical dissolution using nitric acid to remove Bi from the surface, achieving more uniform Bi removal without the surface segregation issues associated with mechanical methods.
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
Effectively prevents Bi elution from copper alloy surfaces, improves mechanical properties, and allows for the safe reuse of materials, meeting stringent lixiviation standards while maintaining the alloys' durability and machinability.
Implementation Method 1
treating the surface of the copper alloy with nitric acid having a concentration of 4 to 20 mass % to suppress the dissolution of a matrix comprising Cu, Zn and Sn and preferentially dissolve the Bi
Implementation Method 2
subjecting the surface of the copper alloy to shot-blasting to remove corrosive products including oxides produced from the nitric acid and impart gloss to the surface
Data Source
AI summary
Provided is a method for preventing the elution of Bi from copper alloy, in which the elution of Bi is prevented in leadless copper-alloy plumbing equipment and the like containing a trace of lead and a predetermined amount of Bi. The present invention relates to a method for preventing the elution of Bi from copper alloy in which at least Bi present on the surface of copper alloy containing Bi is selectively removed by preferentially dissolving Bi in a 4 to 20 mass % concentration of nitric acid while suppressing Cu dissolution. Furthermore, elution of Pb is suppressed using a 10-20 mass % concentration of nitric acid. In this case, by removing at least Bi present on the surface of copper alloy containing Bi using nitric acid and then treating the surface of the copper alloy by shot-blasting corrosive products, such as oxides, produced from the nitric acid are removed, and gloss is imparted to the surface.