Palladium Sensing Element Thermal Stability
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Solution Overview
Problem
Existing gas sensors, particularly those used in automotive exhaust systems, face challenges due to high costs associated with platinum (Pt) materials and non-ideal behavior under non-equilibrium conditions, leading to broadened voltage transitions and dependence on mass transport processes, adsorption, and chemical reactions.
Innovation Solution
A sensing element comprising a palladium (Pd) or Pd alloy electrically conductive element, which is thermally stable at high temperatures, formed by sintering non-spherically shaped Pd particles with an organic vehicle, offering a cost-effective alternative to platinum and improved thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If platinum (Pt) materials are used in sensing elements, then thermal stability and electrical conductivity are improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive platinum materials with cheaper palladium-based materials for electrically conductive elements and heaters. This substitution maintains functional performance while significantly reducing manufacturing costs, making the sensor more economically viable for mass production and widespread application.
Solution Approach 2:
The patent employs composite material structures including palladium-aluminum oxide composites and palladium-rhodium alloys. These composite materials combine the beneficial properties of different substances to achieve both cost-effectiveness and the required thermal stability and electrical conductivity, resolving the contradiction between material cost and performance.
2Reliability
If zirconia-based electrolyte materials are used, then ionic conductivity is improved, but sensor behavior becomes non-ideal under non-equilibrium conditions
Solution Approach 1:
The patent modifies the electrolyte material composition by using alumina-stabilized alumina instead of traditional zirconia-based materials. This parameter change in material composition alters the electrochemical properties to achieve more ideal sensor behavior under non-equilibrium conditions while maintaining sufficient ionic conductivity for sensor operation.
3Ease of manufacture
If spherical Pd particles are used, then ease of manufacture is improved, but thermal stability at high temperatures deteriorates
Solution Approach 1:
The patent specifies the use of non-spherical palladium particles with aspect ratios between 2:1 and 10:1. This asymmetric particle shape provides better thermal stability at high firing temperatures (above 1400°C) compared to spherical particles, while still allowing for practical manufacturing through screen printing and other conventional deposition techniques.
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 Pd-based sensing elements provide thermal stability comparable to platinum at high temperatures, reducing manufacturing costs and improving sensor performance by maintaining sharp EMF transitions at stoichiometric air-to-fuel ratios, thus enhancing the accuracy of gas composition monitoring.
Implementation Method 1
heating the precursor material to a temperature of greater than or equal to about 1450° C. for a sufficient period of time to sinter the precursor material and form the sensing element
Implementation Method 2
an electromotive force (EMF) is developed between the electrodes according to the Nernst equation
Data Source
AI summary
Disclosed herein is a method of making a sensing element comprising forming an electrically conductive element, wherein the sensing element comprises a metal selected from the group consisting of Pd and alloys and combinations comprising Pd; and wherein the electrically conductive element is thermally stable at temperatures as high as 1,200° C.