PTC SEMICONDUCTOR CERAMIC COMPOSITION, METHOD FOR PRODUCING THE SEMICONDUCTOR CERAMIC AND HEATING DEVICE AND USE

Abstract

A semiconductor ceramic composition may include, as a main component, a BaTiO.sub.3-based compound according to the formula [Ba.sub.bCa.sub.cSr.sub.sPb.sub.pR.sub.x][Ti.sub.tA.sub.aMn.sub.m]O.sub.3+z. R may represent at least one element selected from a group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. A may represent at least one element selected from a group consisting of V, Nb, and Ta. The variables b, c, s, p, x, t, a, m, and z may be defined as: b=1cspx; 0<c+s+p<0.51; 0.490<b<0.999; 0.0<c<0.5; 0.0<s<0.5; 0.05<p<0.5; 0.001<x<0.01; 1.0001<(t+a+m)<1.011575; 0.9889<t<1.000375; 0.00010<a<0.0012; 0.0001<m<0.01; and 0.0001<z<0.01.

Claims

1. A semiconductor ceramic composition, comprising, as a main component, a BaTiO.sub.3-based compound according to the formula [Ba.sub.bCa.sub.cSr.sub.sPb.sub.pR.sub.x][Ti.sub.tA.sub.aMn.sub.m]O.sub.3+z, wherein: R represents at least one element selected from a group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb; A represents at least one element selected from a group consisting of V, Nb, and Ta; and the variables b, c, s, p, x, t, a, m, and z are defined as follows: $b=1-c-s-p-x;$ $0<c+s+p<0.51;$ $0.49<b<0.999;$ $0.<c<0.5;$ $0.<s<0.5;$ $0.05<p<0.5;$ $0.001<x<0.01;$ $1.0001<\left(t+a+m\right)<1.011575;$ $0.9889<t<1.000375;$ $0.0001<a<0\text{.0012};$ $0.0001<m<0.01;$ $\mathrm{and}$ $0.0001<z<0.01.$

2. The semiconductor ceramic composition according to claim 1, further comprising silicon dioxide.

3. The semiconductor ceramic composition according to claim 1, wherein R represents at least one element selected from a group consisting of Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er.

4. The semiconductor ceramic composition according to claim 1, wherein A represents the element Nb.

5. The semiconductor ceramic composition according to claim 1, wherein the variables t, a, and m assume values as follows: $0.9985<t<1.000075;$ $0.0002<a<0.0006;$ $\mathrm{and}$ $0.0003<m<0.001.$

6. The semiconductor ceramic composition according to claim 1, wherein the variables b, c, s, p, x, t, a, m assume values as follows: $b=0.627;$ $c=0.12;$ $s=0.03;$ $p=0.22;$ $x=0.003;$ $t=0.999625;$ $a=0.0003;$ $\mathrm{and}$ $m=\_0.00065.$

7. A semiconductor ceramic, comprising a sintered body having the semiconductor ceramic composition according to claim 1.

8. A method for producing a semiconductor ceramic with a sintered body having the semiconductor ceramic composition according to claim 1, the method comprising: weighing-in of raw materials; mixed grinding; drying and pre-granulation; calcining; fine grinding; spray granulating; pressing; and debinding and sintering.

9. A PTC thermistor, comprising: a sintered body having the semiconductor ceramic composition according to claim 1; and a plurality of electrodes disposed on a surface of the sintered body.

10. A use of a semiconductor ceramic having the semiconductor ceramic composition according to claim 1 in at least one of a high-voltage heating application, a switching element, a measuring element, and a temperature control element.

11. The semiconductor ceramic composition according to claim 1, further comprising impurities that account for 0.5 wt.-% or less of a total mass of the semiconductor ceramic composition.

12. The semiconductor ceramic composition according to claim 1, further comprising at least one sintering aid.

13. The semiconductor ceramic composition according to claim 2, wherein the silicon dioxide accounts for approximately 0.01 wt.-% to 5 wt.-% of a total mass of the semiconductor ceramic composition.

14. The semiconductor ceramic composition according to claim 13, wherein the silicon dioxide accounts for approximately 0.1 wt.-% to 1 wt.-% of the total mass of the semiconductor ceramic composition.

15. The semiconductor ceramic composition according to claim 3, wherein R represents at least one of the element Y and the element La.

16. The semiconductor ceramic composition according to claim 15, wherein R represents the element Y.

17. The semiconductor ceramic composition according to claim 5, wherein A represents the element Nb.

18. The semiconductor ceramic composition according to claim 17, wherein R represents at least one of the element Y and the element La.

19. The semiconductor ceramic composition according to claim 6, wherein: R represents the element Y; and A represents the element Nb.

20. The semiconductor ceramic composition according to claim 19, further comprising silicon dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 is a schematic general illustration of the voltage-current characteristic curve of a PTC component.

[0074] FIG. 2 is a schematic illustration of an example of a semiconductor ceramic with metallization on two opposing sides.

[0075] FIG. 3 is a schematic illustration of the inventive method for the production of a semiconductor ceramic.

[0076] FIG. 4 is a schematic illustration of a high-voltage air heater.

[0077] FIG. 5 shows a typical curve of the specific electrical resistance p with the temperature T for the PTC ceramic according to the invention.

DETAILED DESCRIPTION

[0078] FIG. 1 shows a schematic illustration of a typical voltage-current characteristic curve of a PCT component. Here, U.sub.R represents the nominal voltage, for example 350 V or 800 V, for which the PCT ceramic is designed. U.sub.max is the maximum voltage that is present when the battery is fully charged. I.sub.re represents the corresponding maximum current that flows when U.sub.max is present. U.sub.BD represents the punch-through voltage.

[0079] FIG. 2 a) shows an example of a PTC semiconductor ceramic having a sintered body 201 according to a semiconductor ceramic composition proposed in the present application. The semiconductor ceramic 201 is in this case coated on two opposing [sic: sides] with a metal layer 202, which can be used for electrical contacting. As can be seen from FIG. 1 b) and FIG. 1 c), it is conceivable that this is a cylindrical arrangement (tablet), and it is also conceivable that the arrangement is designed in a box-shaped manner (cuboid). In this context, it should be noted that a metal layer is also present on the two opposing sides in FIG. 2c, wherein one side is not shown in the perspective illustration. A cuboid shape is advantageously used.

[0080] FIG. 3 first shows in method step a) a weighing-in of raw materials 300. It is conceivable that all weighed-in starting materials are combined in the subsequent step b). Alternatively, however, it is conceivable that, for example, the doped elements and/or SiO.sub.2 are not added until step e). A mixed grinding 301 takes place in step b). Then, a drying and pre-granulation 302 takes place in step c). In step d), a calcining 303 of the previously obtained granulate takes place. This is followed in step e) by a fine grinding 304. In the event that not all weighed-in starting materials have already been added in step b), the remaining starting materials are now added in step e). After the fine grinding 304, particle sizes d.sub.90 of approx. <10 m and d.sub.50 of approx. <3 m are preferably present, preferably a d.sub.50 of approx. <2 m. Particle sizes d.sub.50 of 1 m are particularly preferred. This is followed by the spray granulation 305 in step f). This preferably leads to a granulate moisture of approx. <15% and to granulate sizes (d.sub.50) of approx. less than 100 m. In step g), a pressing 306 then takes place, followed by a debinding and sintering 307 in step h).

[0081] For all method steps a) to h), unless otherwise described, the foregoing applies in connection with the method steps.

[0082] In a further step, it is optionally conceivable for the obtained and cooled sintered body to be polished to the shape required for the desired application, 308. Furthermore, a metallization 309 can optionally occur after polishing, i.e. metal layers that enable electrical contacting are applied on two opposing sides of the sintered body.

[0083] FIG. 4 schematically shows the design of a high-voltage air heater. Here, a PTC heating element 403 is contacted by an Al contact film 400. These two elements are in turn insulated by an Al.sub.2O.sub.3 insulation 401 and are located in an Al tube 402 in the form of a cemented PTC heating element 405 with contacting and insulation. Six such modules are in turn electrically connected to one another 406 and can be installed in a housing 407. Together with a control unit and a terminal, the element 408 results. The latter is in turn equipped with a cover for the control unit and results in the ready-to-use electrical PTC heater 409.

[0084] FIG. 5 shows a typical curve of the specific electrical resistance p at the temperature ((T) curve) of the PTC ceramic according to the invention. The geometry of the PTC ceramic has been calculated. Here, a strong increase in the specific resistance can be seen in the range of the phase conversion as described above.

[0085] In the following, the invention is described in detail by means of an example, without the scope of the invention being limited thereto:

Materials Used:

BaCO.sub.3, CaCO.sub.3, SrCO.sub.3, Nb.sub.2O.sub.5, Y.sub.2O.sub.3, PbO.sub.2, TiO.sub.2, Mn(CH.sub.3COO).sub.2, SiO.sub.2

Inventive Example IE1

[0086] A semiconductor ceramic having the following semiconductor ceramic composition is produced.

[Ba.sub.bCa.sub.cSr.sub.sPb.sub.pR.sub.x][Ti.sub.tA.sub.aMn.sub.m]O.sub.3+z.

[0087] where

[0088] R: Y

[0089] A Nb

[0090] b: 0.627

[0091] c: 0.12

[0092] s: 0.03

[0093] p: 0.22

[0094] x: 0.003

[0095] t: 0.999625

[0096] a: 0.0003

[0097] m: 0.00065

[0098] z: 0.00065

[0099] and 0.3 wt.-% SiO.sub.2.

Implementation:

[0100] First, the starting materials BaCO.sub.3, CaCO.sub.3, SrCO.sub.3, Nb.sub.2O.sub.5, Y.sub.2O.sub.3, PbO.sub.2, TiO.sub.2 were weighed in. A mixed grinding was then carried out in a suspension of deionized water for 4 h in a planetary ball mill (200 rpm; grinding balls: ZrO2, 2 mm). Then, the powder was pestled and sieved, dried in a drying cabinet at a temperature of 120 C. for 14 h, and calcined for 2 h at 1000 C.

[0101] Then, Mn(CH.sub.3COO).sub.2 was added. In addition, SiO.sub.2 was added with a share of 0.3 wt. % in relation to the total composition. This mixture was then fine-ground in a planetary ball mill (duration: 6 h; 200 rotations/min, grinding balls: ZrO.sub.2, 2 mm). Unlike mixed grinding, in this case grinding was carried out in a suspension with isopropanol. Furthermore, a binder (PVB) was also added to the suspension during the fine grinding. The subsequent spray drying was carried out at a gas inlet temperature of 170 C. and a gas outlet temperature of 85 C. After spray granulation, the d.sub.90 of the granulate was 74 m and the bulk density was 1.28 g/cm.sup.3.

[0102] The granules obtained were pressed by uniaxial pressing to green densities of approx. 3.4 g/cm.sup.3. The sintering was performed at T=1300 C. and a hold time of 1 h using sintering aids consisting of zirconium oxide.

[0103] The sintered skin of the obtained blanks was then polished away and purified using deionized water and isopropanol. For contacting, one layer of Al paste (thickness: approx. 10 m) was applied to the respective end faces of the polished sintered bodies. This was dried at a temperature of 150 C. for 15 min and then baked in at a temperature of 720 C. and a hold time of 15 min.

[0104] The parts contacted with Al were then electrically measured, i.e. a -T curve of the parts was measured (see FIG. 5).