Printable NTC Ink Composition for Thermistor Manufacturing
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Solution Overview
Problem
Existing methods for manufacturing negative temperature coefficient (NTC) ceramics are inflexible, costly, and unsuitable for small batch production due to the need for complex mould design and sintering processes, which can lead to phase separation and instability in thermistors.
Innovation Solution
A printable NTC ink composition is developed by mixing ceramic precursor materials of manganese and nickel oxides, heated between 800° C and 1000° C in oxygen to form a spinel phase and nickel oxide phase, avoiding sintering and macro phase separation, allowing for the creation of NTC products in various geometries without complex shaping steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sintering methods are used to manufacture NTC ceramics, then dense homogeneous ceramic with single phase structure can be obtained, but the process is slow, costly, and inflexible to design changes
Solution Approach 1:
The invention divides the traditional sintering process into two distinct stages: (1) low-temperature calcination at 800-1000°C to form spinel phase and nickel oxide phase without complete sintering, and (2) subsequent printing/deposition of the calcined particles to form the final product shape. This segmentation allows each stage to be optimized independently, achieving phase homogeneity in the calcination stage while enabling design flexibility in the printing stage.
Solution Approach 2:
The invention performs preliminary calcination of the ceramic precursor mixture at 800-1000°C before the final shaping process. This preliminary action pre-forms the spinel phase and nickel oxide phase, ensuring phase homogeneity is achieved before the product is printed or deposited into its final shape, thereby eliminating the need for high-temperature sintering later.
2Reliability
If high temperature sintering is used to form single phase ceramic, then desired NTC properties are achieved, but phase separation and instability occur at temperatures above 1000°C
Solution Approach 1:
The invention changes the temperature parameter from traditional high-temperature sintering (>1200°C) to low-temperature calcination (800-1000°C). This parameter change is sufficient to form the desired spinel phase and nickel oxide phase while avoiding the phase separation and instability that occurs at temperatures above 1000°C during conventional sintering.
Solution Approach 2:
The invention utilizes controlled phase transitions during calcination at 800-1000°C to form the spinel phase (Mn-Ni-O) and nickel oxide phase from precursor materials. By controlling the phase transition at this specific temperature range, the invention achieves the desired crystalline structure without reaching temperatures that cause destabilizing phase separation.
3Shape
If complex mould design and sintering processes are used, then predefined shape NTC products can be obtained, but the process becomes costly and inflexible
Solution Approach 1:
The invention replaces the traditional mechanical sintering process in moulds with a printing/deposition process. The calcined particles are printed or deposited directly into the final shape using printing technology, eliminating the need for complex mould design, uniaxial pressing, and subsequent machining operations.
Solution Approach 2:
The invention inverts the traditional manufacturing sequence by first forming the ceramic particles with desired phase composition through low-temperature calcination, and then using printing technology to create the final product shape. This is the reverse of the traditional approach where shape is formed first by pressing in moulds, then sintered at high temperature.
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 improved long-term stability and reduced electrical resistance drift in thermistors, with the high nickel oxide content incorporated at the mesoscale mitigating mechanical stability issues under thermal loads.
Implementation Method 1
heating the mixture of ceramic precursor materials at a temperature between 800° C. and 1000° C. in the presence oxygen to form the printable NTC material comprising the particles that include a spinel phase and a nickel oxide phase
Implementation Method 2
At these temperatures these materials are observed to crystallize into a single spinel crystal structure that yields the desired NTC properties
Data Source
AI summary
The present disclosure relates to a negative temperature coefficient product comprising an electrically conductive percolation network of printable NTC material as particles in a cross-linked dielectric polymer matrix and to a method of manufacturing thereof. The particles comprising a spinel phase, preferably a C-spinel phase, having a general formula M3O4 comprising at least a first metal MI that is manganese and second metal MII that is nickel. In addition the particles include a nickel oxide phase. The printable NTC material can be dispersed in a printable NTC ink comprising a dispersant, from which the NTC product, e.g. a thermistor, can be formed, e.g., after drying of the dispersant. During processing the ink is kept at a temperature below 300° C. Optionally, the spinel phase comprises a further metal MIII. The weight fraction of nickel oxide with respect to the overall mass of the printable NTC material is preferably in a range between one and twenty weight percent.