RU2259335C2 - Blend for thermistor-destined semiconductor ceramic material and a method for preparing material therefrom - Google Patents

Abstract

FIELD: electronic engineering.

SUBSTANCE: invention relates to manufacture of heating thermistors with positive resistance coefficient. Blend contains, wt %: CaTiO₃ 1.06-8,88; PbO 7.78-25.67, TiO₂ 2.43-9.03, SiO₂ 0.54-0.71, YCl₃·6H₂O 0.69-0.98, MnSO₄·5H₂O 10.07-0.13, and BaTiO₃ - the rest. Method comprises preliminary preparation of barium titanate via calcination of barium titanyl oxalate at 1130-1180°C, preliminary preparation of calcium titanate via calcination of calcium carbonate/titanium dioxide mixture at 1000-1080°C, preliminary mixing and dry grinding of barium and calcium titanates, lead oxide, titanium dioxide, and silicon dioxide on vibration or ball mill provided with zirconium dioxide-based milling bodies to achieve particle size below 1,2 μm, after which blend components are blended in ammonium carbonate or bicarbonate aqueous solution inside ball mill using polymeric milling bodies. Thus obtained blend is then dehydrated, dried, and molded to form blanks.

EFFECT: improved performance characteristics and reliability of thermistors and reduced power and material consumption on manufacture thereof.

2 cl, 1 tbl, 3 ex

Description

The invention relates to the field of electronic engineering, namely to compositions and methods for producing semiconductor ceramic materials for heating thermistors with a positive temperature coefficient of resistance (posistors).

A known composition of ceramic material for the manufacture of thermistors containing barium titanate, strontium titanate, lead titanate, manganese, copper, silicon dioxide, one or more elements from a number of rare earth elements: niobium, antimony, bismuth, tungsten, thorium (1).

There is also a known method of manufacturing a mixture of semiconductor ceramic material, including wet mixing the mixture in a ball mill, dehydration, drying, calcining the mixture at a temperature of 1100-1150 ° C, crushing, fine grinding and mixing cake with an organic binder, granulating, pressing products of a given shape (1 )

The disadvantages of this ceramic material and its production method are: the need for double firing and grinding of the mixture and material after high-temperature synthesis, which increases production costs; lack of reproducibility of properties due to the introduction of additives of rare-earth elements and other additives that provide semiconductor properties in the form of oxides, which are difficult to evenly distribute throughout the charge by mixing in ball and other mills. The introduction of an addition of strontium titanate in posistor materials with a high switching temperature requires an increase in the content of lead titanate, since strontium titanate reduces the Curie temperature of barium titanate. A high content of lead titanate and an increased firing temperature complicate the firing of products due to the high volatility of lead oxide, which negatively affects the achievement of the required switching temperature of the finished thermistors.

Closest to the claimed is the composition of the charge material for thermistors with a high switching temperature, containing barium titanate, lead titanate, calcium titanate, silicon dioxide, manganese dioxide, aluminum oxide and rare earth elements (2).

This composition of the charge has several disadvantages: increased manufacturing costs due to two-stage grinding and firing; the dispersion of properties due to the uneven distribution of oxides of rare-earth elements and manganese over the volume of the charge; partial volatilization of lead oxide during preliminary and final firing.

The closest in technical essence to the invention is a method of preparing a mixture of ceramic material for thermistors, based on the use of finished cakes of barium titanate, calcium titanate, lead titanate, obtained by calcining the corresponding barium titanyl oxalates at a temperature of 800-900 ° C. The synthesized specs are mixed in a ball mill in an aqueous medium with rare-earth oxides, manganese, silicon dioxide, aluminum oxide, followed by dehydration, drying, and the formation of preforms (3).

The disadvantage of this method is the very low temperature for the synthesis of barium titanate, which does not provide the required microstructure of posistor ceramics, as well as the resistance of barium titanate to leaching of barium oxide when grinding in an aqueous medium. The use of pre-synthesized lead titanate cake does not provide the required level of electrophysical properties of thermistors and their repeatability due to increased losses of lead oxide during firing.

The problem to be solved is the development of the composition of the charge of a semiconductor ceramic material and the method for its production in order to increase technical characteristics, yield and reduce the cost of manufacturing thermistors by increasing the uniformity of the charge, reducing the loss of lead oxide during firing, and improving the microstructure of ceramics.

The problem is solved in that the mixture of semiconductor ceramic material for thermistors, including barium titanate, calcium titanate, silicon dioxide, additionally contains lead oxide, titanium dioxide, and yttrium trichloride hexahydrate and manganese sulfate pentahydrate are included in the following ratio of components, wt.%:

CaTiO ₃ 1.06 ÷ 8.88 Pbo 7.78 ÷ 25.67 TiO ₂ 2.43 ÷ 9.03 SiO ₂ 0.54 ÷ 0.71 YCl ₃ · 6H ₂ O 0.69 ÷ 0.98 MnSO ₄ · 5H ₂ O 10.07 ÷ 0.13 BaTiO ₃ rest

And in the method for producing a mixture, including preliminary preparation of barium titanate by calcining barium titanyl oxalate, preliminary preparation of calcium titanate, mixing of the components of the mixture in an aqueous solution of ammonium carbonate or bicarbonate in a ball mill with grinding balls of polymer material, subsequent dehydration, drying, forming blanks, technical result provided that the barium titanyl oxalate is calcined at a temperature of 1130 ÷ 1180 ° C, calcium titanate is obtained by calcining a mixture of coal acid calcium and titanium dioxide at a temperature of 1000 ÷ 1080 ° C, while mixing the components in an aqueous medium is preceded by preliminary mixing and dry grinding of barium titanates, calcium, lead oxide, titanium dioxide and silicon dioxide in a vibration or ball mill with grinding media based on dioxide zirconium to a particle size of less than 1.2 microns.

The possibility of carrying out the invention is confirmed by the following information relating to the composition and method of preparation of the mixture of ceramic material, the results of experimental verification and the achieved technical effect.

Preliminarily, BaTiO ₃ barium titanate sintered by calcining barium titanyl oxalate BaTiO (C ₂ O ₄ ) ₂ · 4Н ₂ O at a temperature of 1130 ÷ 1180 C and calcium titanate sintered by calcining a CaCO ₃ + TiO ₃ mixture at a temperature of 1000 ÷ 1080 ° С. The specs BaTiO ₃ and CaTiO ₃ , lead oxide PbO, titanium dioxide TiO ₂ and silicon dioxide SiO ₂ are mixed and ground by a dry method in a vibratory mill with caprolon lining and grinding bodies made of zirconia with increased wear resistance. The grinding is carried out to an average particle size of 0.5-1.2 microns. YCl ₃ · H ₂ O, MnSO ₄ · 5H ₂ O are added to the resulting mixture and stirring is carried out for 8-20 hours in a caprolon-coated ball mill with caprolone grinding balls in an aqueous medium containing ammonium carbonate or bicarbonate. When mixing the components of the ceramic mixture, the material, grinding media, and aqueous medium are loaded in the ratio 1: (1.7 ÷ 2.4): (0.6 ÷ 1). The resulting suspension of the charge is dehydrated by filtration and dried at a temperature of 120 ÷ 160 ° C to a residual moisture content of not more than 0.5%, mixed with a binder based on an aqueous solution of polyvinyl alcohol, granulated by rubbing through a nylon mesh with a mesh size of 300 ÷ 400 μm and pressed disc or rectangular blanks with a specific pressure of 1000 ÷ 1500 kg / cm ² . The obtained preforms are fired at a temperature of 1280 ÷ 1300 ° C. Silicon dioxide may be introduced at the mixing stage in an aqueous medium.

Specific examples of the mixture illustrating the invention are its following optimal compositions, wt.%:

Composition 1 Composition 2 Composition 3 BaTiO ₃ 79.26 75.00 62.77 CaTiO ₃ 8.88 4.49 1.06 Pbo 7.78 14.23 25.67 TiO ₂ 2.43 4.61 9.03 SiO ₂ 0.54 0.67 0.71 YCl ₃ · 6H ₂ O 0.98 0.88 0.69 MnSO ₄ · 5H ₂ O 0.13 0.12 0,07

The properties of the ceramic material and the characteristics of the products based on the proposed composition of the mixture and the method of its manufacture are confirmed by the results of experimental verification, the data of which are shown in table 1.

Table 1. The investigated parameters The studied compositions and methods for producing a mixture of ceramic material Declare Famous Composition 1 Composition 2 Composition 3 Composition according to US patent 5815063 The method according to US patent 5219811 Resistivity, ohm · cm 600 1030 9100 9500 19000 Switching Temperature ° С 145 175 240 165 230 Electrical strength, V / mm 355 350 370 290 290 Temperature coefficient of resistance,% · K ^-1 24 21 12.5 16 14 Firing temperature, ° C 1300 1290 1280 1350 1350 Holding time at maximum firing temperature, min. fifteen fifteen 10 60 60 Yield,% 85 82 80 67 65 Energy intensity of 1 kg of charge, kW · h 2,3 2,3 2,3 4,5 3.4

As can be seen from table 1, the inventive mixture and a method of manufacturing a ceramic material from it provides, in comparison with the prototypes, higher values of electric strength, more optimal values of the temperature coefficient of resistance (at a relatively low switching temperature higher, at an elevated - lower), lower sintering temperature by 50-60 ° С, reduction of the exposure time at the maximum temperature by 4-6 times, reduction of the energy intensity of the process by 1.5-2 times, increase in yield by 13-17%.

The optimality of the proposed composition of the mixture is confirmed by the fact that the output of CaTiO ₃ and MnSO ₄ · 5Н ₂ О beyond the lower limit of the claimed area leads to a decrease in electrical strength and a positive temperature coefficient of resistance (PTKS), and an increase leads to an increase in resistivity and a decrease in yield for this parameter. The output of the SiO ₂ content beyond the lower limit contributes to the deterioration of the reproducibility of electrical characteristics, increase the resistivity and reduce yield. When the SiO ₂ content exceeds the upper limit, a decrease in PTC and electronic strength is observed. A decrease or increase in the concentration of YCl ₃ · 6H ₂ O compared with the claimed limits leads to different increases in resistivity and lower yield. The output of PbO content beyond the lower limit of the patented area while maintaining the optimal ratio of PbO and TiO ₃ leads to a decrease in the switching temperature (heating temperature), and going beyond the upper limit leads to an increase in resistivity and lower dielectric strength.

The practical application of the material and method allows to increase the operational properties and reliability of thermistors while reducing energy and material costs for their manufacture.

Sources of information

1. US patent No. 4483933, IPC H 01 With 7/10, 1984.

2. US patent No. 5815063, IPC H 01 C 7/10, 1998, prototype.

3. US Patent No. 5219811, IPC C 04 B 35/46, 1993, prototype.

Claims (2)

1. The mixture of semiconductor ceramic material for thermistors, including barium titanate, calcium titanate, silicon dioxide, characterized in that it additionally contains lead oxide, titanium dioxide, and yttrium trichloride hexahydrate and manganese pentahydrate are included in the following ratio components, wt.%: CaTiO ₃ 1.06-8.88 Pbo 7.78-25.67 TiO ₂ 2.43-9.03 SiO ₂ 0.54-0.71 YC1 ₃ · 6H ₂ O 0.69-0.98 MnSO ₄ · 5H ₂ O 10.07-0.13 BaTiO ₃ Rest 2. The method of producing a semiconductor ceramic material for thermistors from a charge according to claim 1, which consists in preliminary preparation of barium titanate by calcining barium titanyl oxalate, preliminary preparation of calcium titanate by calcining a mixture of calcium carbonate and titanium dioxide, mixing the components of the mixture in an aqueous solution of ammonium carbonate or ammonium bicarbonate in ball mill grinding balls of polymer material, subsequent dehydration, drying, forming blanks, characterized in that the calcination barium taniloxalate is produced at a temperature of 1130-1180 ° C, calcium titanate is obtained by calcining the mixture at a temperature of 1000-1080 ° C, and pre-mixing and dry grinding of barium, calcium, lead oxide, titanium dioxide and silicon dioxide precede mixing of components in an aqueous medium in a vibration or ball mill, grinding media based on zirconium to a particle size of less than 1.2 microns, while silicon dioxide can be introduced at the stage of mixing in an aqueous medium.