Spinel Thermal Spray Coating for Electrical Insulation
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Solution Overview
Problem
Existing insulating materials for metallic bodies, such as ceramics, face issues with thermal expansion mismatch, leading to mechanical stresses and degradation during thermal spraying processes, and materials like MgO decompose at high temperatures, limiting their suitability for thermal barrier coatings.
Innovation Solution
A thermal spray coating process that forms a spinel layer from non-spinel starting materials, such as MgO and Al2O3, which react during deposition to match the thermal expansion coefficient of the metallic substrate, using a core-shell structure with an outer insulating layer to prevent sublimation and evaporation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ceramic coatings are used for electrical insulation on metallic bodies, then electrical insulation is provided, but thermal expansion mismatch causes mechanical stresses and coating degradation
Solution Approach 1:
The patent changes the chemical composition parameters of the coating material by using spinel (MgAl2O4) instead of pure ceramic coatings. Spinel has a coefficient of thermal expansion (10-12 μm/m/K) that matches metallic substrates, eliminating thermal expansion mismatch while maintaining electrical insulation properties.
Solution Approach 2:
The patent employs composite material structure with spinel as the base material and optional additional oxides (Al2O3, SiO2, TiO2) to create a coating that combines the benefits of thermal expansion matching with enhanced electrical insulation and chemical resistance properties.
2Reliability
If MgO is used as coating material, then high electrical insulation and suitable thermal expansion are achieved, but MgO decomposes at high temperatures during thermal spraying
Solution Approach 1:
The patent combines MgO with Al2O3 to form spinel (MgAl2O4), which merges the advantages of both materials: MgO provides electrical insulation and appropriate thermal expansion, while Al2O3 contributes high-temperature stability and prevents MgO decomposition during thermal spraying processes.
Solution Approach 2:
Al2O3 acts as a stabilizing intermediary that prevents MgO decomposition at high temperatures. The spinel structure serves as a stable intermediate phase that maintains MgO's beneficial properties while protecting it from thermal decomposition during the coating application process.
3Reliability
If sintered ceramics with MgO and Al2O3 are used, then chemical and thermal resistance is improved, but MgO evaporates during thermal spraying
Solution Approach 1:
The patent performs preliminary chemical bonding by forming spinel structure where MgO and Al2O3 are chemically combined before the thermal spraying process. This pre-bonding prevents MgO evaporation during spraying, as the spinel structure maintains structural integrity at thermal spray temperatures.
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 process enables the creation of temperature-resistant, electrically insulating coatings with tunable thermal expansion, preventing cracking and delamination, and maintaining electrical insulation properties even at high temperatures.
Implementation Method 1
starting materials that do not comprise a spinel. In a preferred embodiment, the non-spinel starting materials are thermally deposited onto a substrate. In a preferred embodiment, the starting material is injected into a hot zone where it is heated and/or melted and is then propelled toward a surface for deposition thereon. The heating may be accomplished by any suitable method and equipment, e.g., with use of high temperature (such as a flame, fuel burning, or an electric arc). Without being bound by theory, it is believed that the non-spinel compounds react on the way to the surface, thereby forming a spinel in transit to the surface.
Implementation Method 2
the starting material is injected into a hot zone where it is heated and/or melted and is then propelled toward a surface for deposition thereon. The heating may be accomplished by any suitable method and equipment, e.g., with use of high temperature (such as a flame, fuel burning, or an electric arc).
Implementation Method 3
it is then propelled toward a surface for deposition thereon
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
Compositions and method for preparing thermally sprayed coatings are disclosed. The inventive compositions include at least one component that is electrically-insulating and/or non-subliming at thermal spray temperatures; and at least one component that has a high coefficient of thermal expansion. The invention also provides a compositions and methods for preparing a coating comprising a spinel, from materials that do not comprise a spinel; and also provides non-spinel materials used to prepare coatings comprising spinel. The invention includes coatings made from the materials and methods; and articles comprising the coatings.