Gas Sensor Porous Layer NTC Thermal Conductivity
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Solution Overview
Problem
Conventional gas sensor elements with porous protective layers exhibit reduced water repellency and increased thermal shock when continuously exposed to water, due to a decrease in thermal conductivity with temperature, leading to decreased functionality.
Innovation Solution
A gas sensor element with a porous protective layer formed from an aggregate containing alumina and a silica coating material, where the weight concentration and porosity satisfy a specific relational expression, exhibiting Negative Temperature Coefficient (NTC) characteristics, thereby maintaining water repellency even at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous protective layer with PTC characteristics is used to achieve water repellency through Leidenfrost phenomenon, then water repellency is obtained at high temperatures, but water repellency is reduced when temperature decreases due to continuous water pouring
Solution Approach 1:
The patent changes the thermal conductivity parameter of the porous protective layer by selecting specific materials (alumina, silica, zirconia) and controlling their proportions, pore size distribution, and layer structure to achieve NTC characteristics where thermal conductivity increases as temperature decreases, reversing the conventional PTC behavior
Solution Approach 2:
The patent uses composite materials consisting of multiple ceramic components (alumina, silica, zirconia) with different thermal properties to create a porous protective layer with tailored NTC characteristics, combining the advantages of each material to achieve temperature-stable water repellency
2Device complexity
If the thermal conductivity of the porous protective layer decreases with temperature decrease (PTC characteristics), then the structure is simple and conventional, but thermal shock increases towards the gas sensor element due to insufficient vapor film formation
Solution Approach 1:
The patent changes the thermal conductivity-temperature relationship parameter by designing the porous protective layer with NTC characteristics, where thermal conductivity increases as temperature decreases, ensuring sufficient heat transfer to maintain vapor film formation and reduce thermal shock even under continuous water pouring conditions
Solution Approach 2:
The patent applies beforehand cushioning by designing the porous protective layer to proactively compensate for temperature decreases before they cause harmful thermal shock, using NTC characteristics to increase thermal conductivity in advance when temperature drops, ensuring continuous vapor film stability and protecting the gas sensor element from thermal shock
Data Source
AI summary
The present disclosure provides a gas sensor element comprising a porous protective layer with improved water repellency upon continuously water pouring, which is a gas sensor element comprising:a detection portion; anda porous protective layer formed around the detection portion, whereinthe porous protective layer is formed from an aggregate containing alumina and a coating material containing silica, andin the porous protective layer, the weight concentration x % by weight of the coating material with respect to the total weight of the aggregate and the coating material, and the porosity y %, satisfy the following formula (1):y≤0.0058x2−1.2666x+68 (1), andin the porous protective layer, the pore volume of pores having a pore diameter of 100 nm or less is 0.02 mL/g or less.