The resistance of NTC thermistor is decreased with the increase of temperature, it's widely used in the fields of temperature measurement, temperature control, temperature compensation, and inrush current suppression.
At present, in the temperature range of -60℃ to 300℃, most of the NTC thermistor materials in practice and research have selected Mn-Co-Ni-Cu-Fe spinel-type transitional metal oxides., usually using the spinel structure material bases on MnO. But the high resistivity of the MnO material is not suitable for NTC thermistor resistive materials, the current practice is to improve its conductivity by doping other metal elements. Nickel is one of the most widely used elements, at present most of the spinel structure of the NTC materials have been added nickel, because Ni ions are not easily converted to high or low valence ions, its main role is to enter the B-position to form an inverse or half-inverse spinel-type crystal structure, prompting the formation of carriers. This kind of NTC material mainly includes Ni-Mn-o, Fe-Ni-Mn-o, Zn-Ni-Mn-o, Co-Ni-Mn-o, and Cu-Ni-Mn-o, etc..
However, the addition of nickel element has the following disadvantages:
(1) Nickel is a expensive element relatively, through the doping of nickel to improve the electrical properties of the NTC material, which would make the cost of material higher;
(2) When nickel is applied to certain devices in contact with the human body (such as bioengineering materials devices, medical equipment, etc.), some people will be allergic, so the use of nickel-containing products would be controlled more and more stringently in the world, in some industries the application of nickel-containing products would be even prohibit.
In order to overcome the shortcomings of the existing technology, a low cost and widely used NTC thermistor material and its preparation method is provided. The NTC Thermistor obtained by this method, its B-value range is 3000-5500k, resistivity is 100-60000Ω·CM at 25℃, resistance drift is 0.1-3%. The operations are as follows:
(1) In accordance with the structural formula CuZnMnO, wherein the 0.1≤x≤0.9, 0.8≤y≤1, weigh and take the materials which is including CU, Zn, MN to mixed respectively, add dispersant and abrasive material into the mixed material, grinding and mixing;
(2) Drying the ground mix powder, control drying temperature at 70-120℃;
(3) Calcining the dried powder, control calcined temperature at 600-900℃, calcined time is1-12 hours;
(4) In the calcined powder after the addition of s for granulation, to obtain a good fluidity of the powder; Add binder into the calcined powder for the granulation, to get the better fluid powder particle;
(5) Pressure molding the powder particle obtained from step (4), control molding pressure at 200~300 Mpa;
(6) Sintering the molded billet from room temperature to 1000-1200℃ sintering, control the heating rate at 1-20℃/min, thermal insulation sintering 2-24 hours, then cool the furnace to room temperature, get the NTC thermistor material.
As described in step (1), the materials included Cu, Zn, MN elements are selected from the Oxides, Carbonate, acetate or Oxalates which are including Cu, Zn, MN elements.
As described in step (1), the dispersant comprises Ethyl Alcohol Absolute, Deionized Water, Acetone or 2-Butanone, the grinding material comprises Agate Ball, Zirconium Dioxide Ball or Aluminium Oxide Ball; the quality ratio of raw material and dispersant is 1:1-4, the quality ratio of raw material and grinding material is 1:3-5, The ball-milling time is 0.5-10 hours, the speed of ball-milling machine is 50-200 rpm/min.
As described in step (4), the binder comprises Polyvinyl Alcohol, Polyvinyl Butyral or Carboxymethyl Cellulose, the quality ratio of binder and calcined powder is 1-5:99-95.
Compared with the existing technology, this method has the following advantages:
(1) The NTC thermistor material provided by this method does not need to be doped with relatively expensive elements, such as nickel to improve its conductivity, but has good electrical properties, which reduces the production cost of the material greatly;
(2) The NTC thermistor material provided by this method can be applied in the industry of biological engineering materials devices, medical equipment, such as the prohibition and other nickel-containing products, product applications are wide;
(3) The process of the NTC thermistor material provided by this method is simple, the repeatability is good, the electronic device produced by this material has good stability and high precision.