NTC Thermistor Ceramic Voltage Resistance via Plate Crystal Phase
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Solution Overview
Problem
Existing NTC thermistor ceramics have insufficient voltage resistance due to inhomogeneous material dispersion and variations in ceramic grain diameters, leading to local low-resistance regions that can melt under inrush current, causing thermal issues and reduced voltage resistance.
Innovation Solution
Incorporating a second phase with plate crystals having higher electrical resistance than the matrix phase, specifically with higher manganese content, to moderate electrical field concentration and prevent thermal melting and cracking, thereby enhancing voltage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermistor ceramic compositions are used, then the basic NTC function is achieved, but the voltage resistance is insufficient due to inhomogeneous material dispersion and local low-resistance regions
Solution Approach 1:
The patent applies composite materials by combining a spinel phase matrix with a hausmannite phase dispersed throughout. The hausmannite phase (Mn3O4) forms as distinct particles within the spinel matrix, creating a two-phase composite structure. This composite approach allows the hausmannite phase to act as high-resistance barriers that interrupt current paths, thereby improving voltage resistance while the spinel matrix maintains the overall NTC functionality.
Solution Approach 2:
The patent implements local quality by creating regions with different electrical resistance characteristics. The hausmannite phase particles are distributed throughout the spinel matrix, creating local high-resistance zones. These localized high-resistance regions prevent the formation of continuous low-resistance paths through the ceramic, thereby improving overall voltage resistance without compromising the bulk NTC properties.
2Ease of manufacture
If inhomogeneous material dispersion occurs, then manufacturing is simpler, but local low-resistance regions form that can melt under inrush current
Solution Approach 1:
The composite structure of spinel matrix with dispersed hausmannite particles creates inherent thermal stability. The hausmannite phase, being a stable Mn3O4 structure, acts as thermal anchors that prevent runaway heating in local regions. Even if material dispersion is not perfectly homogeneous, the presence of these stable high-resistance particles throughout the matrix prevents the formation of continuous thermal failure paths.
3Productivity
If ceramic grain diameter varies, then processing is easier, but electrical field concentration increases leading to fractures
Solution Approach 1:
The patent applies local quality by introducing hausmannite phase particles at grain boundaries and within grains. These particles create localized stress relief zones and electrical field distribution uniformity. Even when ceramic grain diameters vary, the hausmannite particles act as distributed anchors that prevent stress concentration and electrical field runaway, thereby improving fracture resistance without requiring narrow grain size distribution.
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 effectively increases the voltage resistance of NTC thermistors by dispersing a high-resistance phase within the matrix, reducing electrical field concentration and improving hardness and toughness, thus preventing fractures and maintaining high voltage resistance under inrush current conditions.
Implementation Method 1
the second phase includes plate crystals and has an electrical resistance higher than that of the first phase
Implementation Method 2
NTC thermistor ceramics and in particular to NTC thermistor ceramics suitable for use in a NTC thermistor
Data Source
AI summary
A NTC thermistor ceramic having higher voltage resistance and a NTC thermistor are provided. The NTC thermistor ceramic either contains manganese and nickel, the manganese/nickel content ratio being is 87/13 to 96/4, or the manganese/cobalt content ratio being is 60/40 or more and 90/10 or less. The NTC thermistor ceramic includes a first phase, which is a matrix, and a second phase composed of plate crystals dispersed in the first phase, the second phase has an electrical resistance higher than that of the first phase and a higher manganese content than the first phase, and the first phase has a spinel structure. A NTC thermistor includes a ceramic element body composed of the NTC thermistor ceramic having the above-described features, internal electrode layers formed inside the ceramic element body, and external electrode layers disposed on two side faces of the ceramic element body.