Coated Filament Mercury-Free CVD via Misaligned Electrodes
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Solution Overview
Problem
Existing methods for producing coated filaments using chemical vapor deposition result in mercury contamination due to physical contact and vaporization, posing health hazards and affecting the filament's properties.
Innovation Solution
A filament coating apparatus and method that eliminates mercury contamination by using a vertical deposition chamber with misaligned capillary tubes for direct electrical contact, preventing gas escape, and using innocuous gases for sealing, allowing for mercury-free coating deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid metal electrodes (mercury, mercury/indium, mercury/cadmium, gallium/indium) are used to provide gas seal and electrical contact, then electrical contact and gas sealing are achieved, but mercury or other metal contamination occurs on the filament and coating
Solution Approach 1:
The patent removes the liquid metal electrode system entirely from the deposition chamber. Instead of using mercury or other liquid metals to provide both gas sealing and electrical contact, the invention uses a solid electrode system with a gas-tight seal that eliminates contamination while maintaining electrical contact functionality.
Solution Approach 2:
The patent introduces an intermediary gas sealing mechanism between the electrode and the filament. A gas-tight seal system using inert gas pressure differential acts as an intermediary to prevent contamination while allowing the filament to pass through the electrode structure for electrical contact.
2Reliability
If liquid metal electrodes are used to provide gas seal, then gas sealing is achieved, but gas may escape through the electrode-filament contact area
Solution Approach 1:
The patent uses pneumatic pressure differential to achieve gas sealing. By maintaining a positive pressure differential across the gas-tight seal using inert gas, the system prevents gas leakage through the electrode-filament contact area without requiring liquid metal seals.
3Productivity
If mercury electrodes are used for coating deposition, then coating can be deposited, but mercury vapour is produced and adheres to the filament and coating
Solution Approach 1:
The patent uses an inert gas atmosphere (such as argon or nitrogen) within the deposition chamber to prevent mercury vaporization and contamination. The inert environment prevents reactions between the coating materials and mercury vapour, eliminating the harmful effects while allowing coating deposition to proceed normally.
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 effectively prevents mercury contamination, ensuring a cleaner coated filament and reducing health hazards while maintaining excellent electrical contact and coating quality.
Implementation Method 1
the filament is heated by the passage of an electrical current
Implementation Method 2
the gas or gases deposit a coating on the hot filament
Data Source
AI summary
A coating is formed by chemical vapor deposition an electrically heated filament which is passed through an end plate into a deposition chamber and leaves the deposition chamber through a similar end plate. The filament slides through an entrance passage into the deposition chamber. The entrance passage is formed from misaligned portions which press the filament into direct electrical contact with their walls. A tube communicates with a chamber between the ends of the passage and acts as a sealing means to prevent gas escaping from the deposition chamber through the entrance passage. The end plate operates in exactly the same manner. As no mercury or a low-melting point eutectic alloy is used, no contaminants associated therewith are produced and the resultant coated filament is free of such contaminants.