SiC Ceramic Joining with Fe3O4 Oxide Buffer
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Solution Overview
Problem
The joining of ceramic members containing Si, such as SiC, often results in a high reactivity between the metal joining material and Si, leading to the formation of a reaction layer that degrades mechanical and electrical joining properties, especially when exposed to high temperatures.
Innovation Solution
A joined body is created using a ceramic member with Si and a second member, joined by an electrically conductive oxide containing a Fe3O4 phase, which suppresses the formation of a reaction layer at the joining interface, enhancing reliability and maintaining mechanical and electrical properties under high-temperature conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal joining material is used to join a ceramic containing Si, then the joining strength is improved, but a reaction layer is formed between the metal and Si that degrades the joining properties
Solution Approach 1:
An oxide layer containing Fe3O4 is introduced as an intermediary between the metal joining material and the Si-containing ceramic. This oxide layer acts as a buffer that reduces the direct reactivity between metal and Si, preventing harmful reaction layer formation while still enabling effective joining. The oxide layer mediates the interaction between the two materials, allowing the joining process to proceed without the adverse chemical reactions that would otherwise occur.
Solution Approach 2:
The joining structure employs a composite approach by combining metal joining material with an oxide layer containing Fe3O4. This composite structure leverages the strengths of both materials: the metal provides joining strength while the oxide layer provides chemical compatibility with Si-containing ceramics. The composite material system resolves the contradiction by distributing functions across different material components.
2Ease of manufacture
If a reaction layer is formed at the joining interface, then the joining process is simplified, but the mechanical and electrical joining properties are degraded especially at high temperatures
Solution Approach 1:
The invention changes the chemical composition parameters of the joining interface by introducing an oxide layer with specific Fe3O4 content. This parameter change transforms the chemical environment at the joining interface, reducing reactivity between metal and Si while maintaining joining effectiveness. The controlled oxide composition allows the process to remain simple while achieving superior joining properties that are stable at high temperatures.
3Temperature
If the joined body is exposed to high temperature in air, then the operational temperature range is extended, but the reaction layer grows and degrades the joining properties
Solution Approach 1:
The oxide layer containing Fe3O4 is applied beforehand as a protective cushion between the metal joining material and the Si-containing ceramic. This pre-formed protective layer prevents direct contact and reaction between the metal and Si during high-temperature exposure. The cushioning effect is maintained throughout the service life of the joint, allowing the assembly to operate at elevated temperatures without degradation of joining properties.
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 use of an electrically conductive oxide with a Fe3O4 phase effectively reduces the reactivity with Si, improving the reliability and durability of the joined body by preventing the growth of a reaction layer, thus maintaining strong mechanical and electrical connections even at elevated temperatures.
Implementation Method 1
a Fe3O4 phase has a low reactivity with a member containing Si
Implementation Method 2
a joining portion which includes an electrically conductive oxide containing a Fe3O4 phase
Data Source
AI summary
A joined body 20 includes a first member 21 which is a ceramic containing Si, a second member 22, and a joining portion 30 which is formed of an electrically conductive oxide containing a Fe3O4 phase and which joins the first member 21 and the second member 22. In the joined body 20, no reaction layer is preferably formed at a joining interface between the electrically conductive oxide and the first member 21. The joining portion 30 is preferably formed to have a multilayer structure in which from the first matter 21 to the second member 22, a first layer containing a first oxide of a transition metal, a second layer containing an electrically conductive oxide of a transition metal having a low valence as compared to that of the first oxide, and a mixed layer containing a transition metal and an oxide thereof are formed.