Granular Diamond Electrode Thermal Stress Management
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Solution Overview
Problem
Conventional diamond electrodes face challenges in achieving a balance between high conductivity and large surface area due to cracking or peeling issues caused by residual stress from differences in thermal expansion coefficients between diamond and metal bases during CVD processing, limiting their size and effectiveness in electrochemical processing.
Innovation Solution
The use of granular diamond electrodes with columnar or spherical bases made of Nb, Ti, or W, where the conductive diamond coating covers at least 30% of the surface, specifically designed to minimize cracking and peeling by controlling the base size and shape, allowing for high conductivity and large surface area without the drawbacks of conventional methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a plate-like metal base (Nb, Ti) is used to achieve greater surface area, then the surface area is improved, but crack or peeling of conductive diamond occurs due to residual stress from thermal expansion difference during CVD
Solution Approach 1:
The patent divides the large plate-like base into multiple smaller columnar bases arranged in an array. Each columnar base has a limited height (1-30 mm) that prevents excessive thermal stress accumulation, while the collective array of multiple bases provides the necessary large surface area for high productivity. This segmentation resolves the contradiction by distributing the thermal stress across multiple smaller units rather than concentrating it in one large base.
Solution Approach 2:
The patent changes the geometric parameters of the base from a single large plate-like structure to multiple smaller columnar structures with specific height constraints (1-30 mm). This parameter change limits the thermal expansion stress differential during CVD processing, preventing diamond cracking and peeling while maintaining adequate surface area through the multiplicity of columnar units.
2Reliability
If a base of silicon or SiC is used to reduce thermal expansion difference, then crack or peeling is suppressed, but high conductivity is not obtained
Solution Approach 1:
The patent applies different material properties to different parts of the electrode structure: the columnar bases are made of metal (Nb, Ti, W) to provide high conductivity and thermal conductivity, while the diamond coating is applied locally on the surface to provide electrochemical activity. This local differentiation allows the metal base to deliver high power conductivity without suffering from thermal expansion issues, as the diamond coating thickness is controlled to minimize stress concentration.
Solution Approach 2:
The patent creates a composite structure combining metal columnar bases (Nb, Ti, or W) with conductive diamond coating. This composite approach leverages the high conductivity of metal for power transmission while the diamond coating provides the necessary electrochemical surface area. The specific dimensional constraints on the columnar bases ensure that the composite structure maintains both high conductivity and resistance to thermal stress-induced cracking.
3Productivity
If the length of the round bar is increased to process larger solution volumes, then productivity is improved, but peeling of conductive diamond occurs due to residual stress
Solution Approach 1:
The patent segments the electrode into multiple columnar bases arranged in an array, where each columnar base has a limited height (1-30 mm) that prevents excessive thermal stress. The collective array of multiple columnar bases provides the necessary large surface area and solution processing capacity, resolving the contradiction between productivity and peeling resistance by distributing the functional requirements across multiple stress-limited units.
Solution Approach 2:
The patent transitions from a single long round bar structure to a two-dimensional array of multiple shorter columnar bases. This dimensional change allows the electrode to achieve large surface area and high productivity through the multiplicity of units rather than through the length of a single unit, thereby avoiding the thermal stress problems associated with long structures.
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 results in diamond electrodes with significantly improved durability and electrolysis performance, capable of processing larger volumes of solutions efficiently with reduced peeling and cracking, leading to longer electrode life and enhanced electrolysis efficiency.
Implementation Method 1
coating the surface of a base with conductive diamond, by CVD (Chemical Vapor Deposition) using carbon-containing gas such as methane as a main material
Implementation Method 2
residual stress attributed to a difference in coefficient of thermal expansion between the diamond and the metal during CVD
Data Source
AI summary
This invention provides a granular diamond(1) consisting of: a columnar base(2) formed by Nb, Ti or W and having a length(L) in a longitudinal direction of not more than 30 mm and a maximum length(R) in a direction perpendicular to the longitudinal direction of not more than 15 mm; and conductive diamond(3) coating not less than 30% of a surface of the base(2), or a granular diamond including: a spherical base formed by Nb, Ti or W and having a diameter of not more than 15mm, and conductive diamond coating not less than 50% of a surface of the base, and a diamond electrode having a great surface area and a high conductivity by using such many granular diamonds.