ZnO Varistor Ceramic with Dopant System for Low-Temperature Sintering
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Solution Overview
Problem
Existing ZnO ceramic varistors face challenges in increasing specific varistor voltage while limiting grain growth and reducing inactive secondary phases, which affects their performance and miniaturization.
Innovation Solution
A ceramic material comprising ZnO with specific additives and dopants, such as Bi, Sb, Y, Co, Cr, Mn, and Ni, and Al, B, Si, Ba, and Y, is used to limit grain growth and reduce secondary phases, allowing for higher specific varistor voltage and lower sintering temperatures, enabling efficient production of varistors with improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a large amount of additives is used to enable sintering at low temperatures (850-900°C), then the sintering temperature is reduced, but grain growth of ZnO grains cannot be limited and inactive secondary phases (especially B2O3) occur more frequently
Solution Approach 1:
The patent changes the chemical composition parameters by introducing a specific dopant system (Al, B, Si, Ba in controlled ratios) that modifies the sintering behavior of ZnO. This allows achieving dense ceramics at lower temperatures (900-1000°C) while maintaining fine grain structure, resolving the contradiction between low-temperature sintering and grain size control
Solution Approach 2:
The patent creates a composite additive system combining multiple elements (Bi, Sb, Co, Cr, Mn, Ni as main additives plus Al, B, Si, Ba as dopants) that work synergistically. This composite approach enables simultaneous achievement of low sintering temperature, fine grain size control, and reduced secondary phases by distributing different functions across multiple components
2Reliability
If the size of ZnO grains is reduced to increase the number of series-connected grain boundaries, then the specific varistor voltage increases, but grain growth during sintering becomes more difficult to control
Solution Approach 1:
The patent introduces dopant elements (Al, B, Si, Ba) that act as intermediaries or grain boundary pinning agents. These elements segregate at grain boundaries and inhibit grain growth during sintering, allowing maintenance of fine grain sizes (0.5-2.0 μm) necessary for high specific varistor voltage while ensuring uniform grain structure throughout the ceramic body
3Use of energy by stationary object
If more additives are used to achieve lower sintering temperatures, then energy expenditure is reduced, but the occurrence of inactive secondary phases increases
Solution Approach 1:
The patent optimizes the concentration parameters of additives and dopants within specific ranges (e.g., Al2O3: 0.1-5.0 wt%, BaO: 0.1-3.0 wt%, B2O3: 0.01-1.0 wt%). This precise parameter control ensures sufficient liquid phase formation for low-temperature sintering while preventing excessive secondary phase formation that would degrade varistor performance
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 approach results in varistors with a specific varistor voltage of 1000 V/mm, reduced energy expenditure, and enhanced environmental sustainability by lowering sintering temperatures, while maintaining high varistor properties like power loss and nonlinearity.
Implementation Method 1
a ceramic material containing ZnO as main constituent and additionally at least one additive and at least one dopant... limit the grain growth of the ZnO grains during the sintering
Data Source
AI summary
In an embodiment a ceramic material includes ZnO as main constituent, Y as a first additive, second additives including at least one compound containing a metal element, wherein the metal element is selected from the group consisting of Bi, Cr, Co, Mn, Ni and Sb, Si4+ as a first dopant and second dopants having at least one compound containing a metal cation from Al3+, B3+, or Ba2+, wherein a corresponds to a molar proportion of Bi calculated as Bi2O3, b corresponds to a molar proportion of Y calculated as Y2O3, c corresponds to a molar proportion of Al calculated as Al2O3, d corresponds to a molar proportion of Ba calculated as BaO, e corresponds to a molar proportion of B calculated as B2O3, f corresponds to a molar proportion of Si calculated as SiO2, g corresponds to a molar proportion of Ni calculated as NiO, h corresponds to a molar proportion of Co calculated as Co3O4, i corresponds to a molar proportion of Cr calculated as Cr2O3, j corresponds to a molar proportion of Sb calculated as Sb2O3, and k corresponds to a molar proportion of Mn calculated as Mn3O4.