Noble-Metal Paste Adhesion and Oxidation Resistance
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Solution Overview
Problem
Existing screen-printing pastes for producing electrical conductor arrangements, particularly for resistive particle sensors, face issues with insufficient substrate adhesion at high temperatures, leading to low durability and oxidative degradation of platinum electrodes.
Innovation Solution
A screen-printing paste composition containing 5 to 15 wt.% metal oxides based on noble metals like platinum or palladium, with a specific formulation of SiO2, Al2O3, and BaO, and the absence of boron oxides, combined with organic binders and solvents, applied onto a ceramic substrate and baked at high temperatures to form a stable and conductive electrode structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If platinum-ceramic mixture is used to reduce platinum content and improve adhesion, then cost is reduced and adhesion is improved, but electrode structure becomes porous leading to increased oxidation at high temperatures
Solution Approach 1:
The patent uses a composite material consisting of platinum particles embedded in a glass matrix formed from metal oxides (SiO2, Al2O3, BaO). This composite structure provides both good adhesion to the ceramic substrate and a dense, non-porous configuration that protects the platinum from oxidation at high temperatures, resolving the contradiction between adhesion improvement and oxidation resistance.
Solution Approach 2:
The patent changes the compositional parameters by limiting metal oxide content to 5-15 wt% and specifically excluding boron oxides, which would otherwise act as platinum poisons. This parameter optimization ensures the glass matrix forms a protective barrier against oxidation while maintaining adhesion, solving the contradiction between improved adhesion and reduced oxidation.
2Object-affected harmful factors
If glass content is increased to reduce porosity and prevent oxidation, then oxidation resistance improves, but adhesion to ceramic substrate deteriorates
Solution Approach 1:
The patent optimizes the glass content parameter to 5-15 wt% metal oxides, which is sufficient to form a protective matrix that prevents oxidation but low enough to maintain good adhesion to the ceramic substrate. This parameter control resolves the contradiction between oxidation protection and adhesion.
Solution Approach 2:
The specific composite formulation with platinum particles in a glass matrix formed from SiO2, Al2O3, and BaO creates a material that achieves both objectives: the glass provides oxidation protection while the optimized composition ensures adequate adhesion, resolving the contradiction between these two requirements.
3Reliability
If boron-containing glass is used to improve adhesion, then adhesion improves, but platinum stability deteriorates due to boron acting as a platinum poison
Solution Approach 1:
The patent extracts and eliminates boron oxides from the glass composition, removing the harmful component that acts as a platinum poison. This extraction maintains adhesion through the glass matrix while eliminating the destabilizing effect of boron on platinum, resolving the contradiction between adhesion and platinum stability.
Solution Approach 2:
The patent uses a composite material system based on SiO2, Al2O3, and BaO that provides adhesion without containing boron, thus maintaining both adhesion and platinum stability simultaneously.
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 solution enhances the adhesion and stability of noble-metal electrodes on ceramic substrates, maintaining conductivity and preventing oxidation at high temperatures, resulting in improved durability and consistent electrical resistance.
Implementation Method 1
the glass has a fusion temperature of 1000° C... subsequent heating of the mixture to a temperature above the fusion temperature of the glass precursors
Implementation Method 2
improve the adhesion of the electrodes on a substrate... enhances the adhesion and stability of noble-metal electrodes on ceramic substrates
Implementation Method 3
pores and intermediate spaces inside the electrodes can be minimized, and thus an oxidative attack on the platinum is made considerably more difficult... preventing oxidation at high temperatures
Implementation Method 4
The electrodes can be produced using a screen-printing method, wherein a mixture of the materials, from which the electrodes are formed, is applied onto a ceramic substrate
Implementation Method 5
The electrodes are then produced due to subsequent heating of the mixture to a temperature above the fusion temperature of the glass precursors
Implementation Method 6
the glass has a fusion temperature of 1000° C... heating of the mixture to a temperature above the fusion temperature of the glass precursors
Data Source
AI summary
The present invention relates to a screen-printing paste composition for producing an electrical conductor arrangement, which screen-printing paste composition comprises particulate noble metal, comprising platinum and palladium, metal oxides, and organic binders and/or solvents, the proportion of the metal oxides in the screen-printing paste composition being 5 to 15 wt. %, based on the total amount of platinum and metal oxides. Suitable screen-printing paste compositions can be processed to form composite products by means of application to a substrate, subsequent drying and baking, which composite products can be used, for example, in particle sensors or heating devices. The particle sensors and heating devices thus produced are characterized by improved adhesion to the substrate at high temperatures and by conductivity, and demonstrated very good reproducibility of the electrical resistance in different production batches.