Silicon Nitride Glow Plug Base with Chromium Silicide
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Solution Overview
Problem
Ceramic glow plugs face issues with thermal stress-induced cracks and corrosion due to differences in thermal expansion coefficients between the heating element and the base, as well as exposure to engine oil components, which can lead to oxidation and degradation of the heating element.
Innovation Solution
A ceramic heater design incorporating a heating element made from silicides, nitrides, and carbides of molybdenum and tungsten, embedded in a silicon nitride base with specific additions of rare earth elements, chromium silicides, and aluminum nitride to control thermal expansion and corrosion resistance, including a surface layer with controlled aluminum content and porosity to prevent calcium component adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If materials with larger thermal expansion coefficient (such as metal carbides) are incorporated into the base material, then the thermal expansion coefficient of the base is increased to match the heating element, but the base becomes more susceptible to corrosion by calcium components in engine oil
Solution Approach 1:
The base is formulated as a composite material containing silicon nitride (50-90 wt%), aluminum oxide (5-40 wt%), and aluminum nitride (1-20 wt%). This composite structure combines the high thermal expansion coefficient of silicon nitride with the corrosion resistance of aluminum oxide and aluminum nitride, achieving both thermal expansion matching and corrosion protection simultaneously
Solution Approach 2:
The invention changes the chemical composition parameters of the base material by specifying precise weight percentage ranges of silicon nitride, aluminum oxide, and aluminum nitride. This parameter optimization allows the base to achieve the desired thermal expansion coefficient (3.0-5.0×10^-6/K) while maintaining corrosion resistance through the protective aluminum-containing phases
2Reliability
If the heating element is exposed to engine oil and combustion gases, then the heating element can perform its function, but oxidation and corrosion occur leading to degradation
Solution Approach 1:
The base material acts as an intermediary protective layer between the heating element and the corrosive environment (engine oil and combustion gases). The aluminum oxide and aluminum nitride in the base form a protective barrier that prevents direct contact between corrosive substances and the heating element, extending service life while maintaining heating function
Solution Approach 2:
The invention converts the potentially harmful interaction between the heating element and corrosive environment into a beneficial protective mechanism. The base material is designed to interact with corrosive substances first, forming protective alumina and aluminum nitride layers that actually protect the heating element from damage
3Productivity
If repeated heating and cooling cycles are applied, then the glow plug can operate the diesel engine, but thermal stress causes cracks in the base
Solution Approach 1:
The base material is specifically designed with a thermal expansion coefficient (3.0-5.0×10^-6/K) that closely matches the heating element material. This thermal expansion matching minimizes differential thermal stress during heating and cooling cycles, preventing crack formation and maintaining structural integrity during repeated engine starting operations
Solution Approach 2:
The composite structure of silicon nitride, aluminum oxide, and aluminum nitride creates a material with optimized mechanical properties including high strength and crack resistance. The interlocking grain structure and phase distribution in this composite material enhance toughness and resistance to thermal shock
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 design enhances high-temperature durability, prevents thermal stress-induced cracks, and provides excellent corrosion resistance, ensuring reliable operation in diesel engine environments.
Implementation Method 1
a heater including a heating element inside it that heats when electrified
Implementation Method 2
the material for the heating element is apt to have a larger thermal expansion coefficient than the material for the base. When the difference between the thermal expansion coefficient of the former and that of the latter is large, the thermal shrinkage of the former is greatly different from that of the latter during, for example, a cooling process from a heated state to a cooled state
Data Source
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AI summary
Disclosed is a ceramic heater capable of preventing failures due to the thermal stress, such as cracks, and corrosion by a calcium component. The ceramic heater has a heating element including at least one substance selected from silicides, nitrides and carbides of molybdenum and silicides, nitrides and carbides of tungsten as a main component, and a base mainly containing silicon nitride in which the heating element is embedded, wherein the base includes: a rare earth element component in an amount from 4 to 25% by mass in terms of an oxide thereof; a silicide of chromium in an amount from 1 to 8% by mass in terms of chromium silicide; and an aluminum component in an amount from 0.02 to 1.0% by mass in terms of aluminum nitride.