Metal Paste for Gas Sensor Electrodes with Porous Structure
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Solution Overview
Problem
Conventional metal pastes used for forming sensor electrodes in gas sensors are inadequate in terms of electrode activity due to their dense structure, which hinders the formation of a sufficient three-phase interface necessary for effective gas sensing, while attempting to achieve porosity and low resistance simultaneously proves challenging.
Innovation Solution
A metal paste configuration is developed, incorporating conductive particles like Pt or Pt alloys, ceramic powders such as zirconia, inorganic oxide particles to suppress sintering, and insoluble particles to create a porous structure, with specific mass and particle diameter ratios to ensure both conductivity and porosity, facilitating the formation of a three-phase interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dense electrode structure is used, then low resistance is achieved, but electrode activity is insufficient due to inadequate three-phase interface formation
Solution Approach 1:
The patent applies porous materials by incorporating porous formers (such as organic polymers or inorganic particles) into the metal paste composition. During sintering, these porous formers decompose or volatilize, creating a porous structure in the electrode. This porous structure increases the specific surface area and facilitates the formation of three-phase interfaces (gas-electrode-electrolyte), thereby improving electrode activity while maintaining adequate conductivity through the metallic network.
Solution Approach 2:
The patent uses composite materials by combining conductive metal particles (Pt, Pd, or their alloys) with ceramic particles (such as Al2O3, ZrO2) and porous formers in specific ratios. This composite structure allows the metal phase to provide electrical conductivity while the ceramic and porous former phases create the porous architecture necessary for gas diffusion and three-phase interface formation, resolving the contradiction between conductivity and activity.
2Reliability
If porosity is increased to improve electrode activity, then three-phase interface formation is enhanced, but resistance increases
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratios of metal particles, ceramic particles, and porous formers, as well as controlling sintering parameters (temperature, time, atmosphere). By adjusting these parameters, the electrode achieves an optimal balance between porosity (for activity) and metal particle connectivity (for conductivity). The metal content and particle size distribution are specifically tuned to maintain low resistance while accommodating the porous structure.
3Strength
If ceramic powder is added to improve adhesion and moldability, then substrate bonding is enhanced, but resistance value increases
Solution Approach 1:
The patent applies local quality by creating regions with different compositions and properties within the electrode. The metal particles form a continuous conductive network in certain regions to ensure low resistance, while ceramic particles are distributed in other regions to provide adhesion to the substrate and structural support. This spatial differentiation allows the electrode to simultaneously achieve good adhesion, low resistance, and high activity.
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 resulting electrode exhibits improved activity and conductivity with a low resistance value, effectively supporting gas sensing applications by maintaining a fine dispersion of conductive particles and ceramic powders within a porous structure.
Implementation Method 1
an inorganic oxide particle including alumina... to suppress sintering of the conductive particle and the ceramic powder
Implementation Method 2
applying and calcining the metal paste on a green sheet forming a ceramic substrate
Data Source
AI summary
To be provided is a metal paste from which an electrode having high electrode activity as a sensor electrode of various gas sensors can be produced. The present invention is a metal paste for forming a gas sensor electrode obtained by dispersing a conductive particle including Pt or a Pt alloy and a ceramic powder including zirconia or stabilized zirconia, or any of zirconia and stabilized zirconia and one or more oxides of La, Ce, Pr, Nd, Sm, and Hf in a solvent, the metal paste further including an inorganic oxide particle containing alumina and an insoluble particle that is insoluble in the solvent, in which 0.5 or more to 3.0 mass % or less of the inorganic oxide particle and 1.0 to 5.0 mass % of the insoluble particle are dispersed based on the mass of the solid content of the conductive particle, the ceramic powder, the inorganic oxide particle, and the insoluble particle.