Multilayer Varistor Inner Electrodes With Nickel Oxide Barrier
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing multilayer varistors face challenges in maintaining the integrity of silver electrodes due to oxidation by bismuth(III) oxide during sintering, which is exacerbated at higher temperatures, leading to electrode thinning or disappearance, and alternative approaches using pure nickel electrodes require protective atmospheres, limiting commercial viability.
Innovation Solution
A method involving a metal paste with a controlled nickel content (0-25% by mass) is applied to silver electrodes, allowing sintering in an oxygen-rich atmosphere, where nickel diffuses and forms a protective nickel oxide phase, preventing silver oxidation and enabling effective grain growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If sintering temperature is increased to enable effective grain growth and varistor-active ceramic formation, then ceramic properties are improved, but silver electrode oxidation is intensified leading to electrode thinning or disappearance
Solution Approach 1:
Nickel is introduced as an intermediary substance that forms nickel oxide during sintering. This nickel oxide acts as a protective barrier between the silver electrode and the bismuth oxide-containing ceramic, preventing direct contact and oxidation reactions. The nickel oxide layer mediates the interaction between the electrode and ceramic, allowing high-temperature sintering without electrode degradation.
Solution Approach 2:
The invention converts the harmful oxidation reaction into a beneficial protective mechanism. By adding nickel, the bismuth oxide that would otherwise attack and oxidize the silver electrode is redirected to oxidize the nickel instead, forming a protective nickel oxide layer. This transforms the harmful oxidative environment into a beneficial protective barrier formation process.
2Reliability
If silver content in electrode paste is increased to maintain electrode integrity, then electrode stability is improved, but manufacturing cost increases due to precious metal content
Solution Approach 1:
Nickel serves as a sacrificial intermediary that protects the silver from oxidation. The nickel oxide layer formed during sintering acts as a barrier, allowing reduced silver content in the electrode paste while maintaining electrode integrity through the protective nickel oxide barrier rather than relying solely on high silver content.
Solution Approach 2:
The invention changes the chemical composition parameters of the electrode paste by introducing nickel at controlled concentrations (0.1-10 wt%). This compositional parameter change enables the formation of a protective nickel oxide layer that compensates for reduced silver content, maintaining electrode stability while reducing precious metal usage.
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
This process maintains electrode integrity, reduces silver consumption, and enhances electrical properties by forming a nickel oxide barrier, allowing higher sintering temperatures without damaging silver, thus improving varistor performance and reducing material costs.
Implementation Method 1
During sintering, nickel is preferentially diffused into transition layers of the forming ceramic layers and oxidized there.
Implementation Method 2
nickel is preferentially diffused into transition layers of the forming ceramic layers and oxidized there. In this way, transition layers are formed adjacent to the inner electrode, in which a nickel oxide phase is formed.
Implementation Method 3
The nickel oxide phase can, for example, take the form of several cristallites or a continuous crystalline film.
Implementation Method 4
In a further step, the green films are sintered with the applied metal paste in a joint process step, whereby the green films are converted into ceramic layers and the metal paste is converted into an inner electrode.
Data Source
AI summary
SummaryThe present invention relates to a method of manufacturing a multilayer varistor (1) comprising the steps of:Preparing a metal paste (103) comprising silver and nickel, wherein the mass fraction of nickel in the metals of the metal paste (103) is at most 25%,Applying of the metal paste (103) to a ceramic green film (102),Applying of a further ceramic green film (102) to the metal paste (103) to produce a sandwich-like structure and Sintering of the green films (102) with the applied metal paste (103), whereby the green films (102) are converted into ceramic layers (2) and the metal paste (103) is converted into an inner electrode (3).