DD266670A1 - SINTER CERAMICS FOR HIGH-ACCURACY THERMISTORS - Google Patents

Abstract

The present invention relates to low-ratio oxide semiconductor-based precision thermistors, thereby achieving the formation of a uniform, dense low grain boundary resistance fabric at a relatively low sintering temperature. Such thermistors or hot conductors are suitable for a wide range of applications for measuring temperatures, temperature differences and temperature control, for. B. suitable in the Lichtleiternachrichtenuebertragung. Additions are intended to produce a uniformly dense structure of the sintered ceramic and to inhibit kinetically the precipitation processes which preferably take place in the intergrain region during cooling or under operating conditions. According to the invention, this is achieved by adding an amorphous phase consisting of a PbO / GeO 2 mixture and / or BaO / WO 3 mixture.

Description

Field of application of the invention

The invention relates to the production of thermistors based on suitable oxide semiconductors in combination with small additions, whereby the formation of a uniform, dense microstructure with low grain boundary resistance at a relatively low sifitertemperatur is achieved. Such thermistors or thermistors are for a wide application for the measurement of tempatures, temperature differences and temperature control z. For example, in the Oldtimer Messaging.

Characteristic of the known state of the art

Known technical solutions are based on semiconducting oxides of the transition elements and their combinations z, B. in spinels and perovskites.

This often reach Mchrphasensysteme, z. B. Cobalt Manganoxidsysteme (GB 1 226789, PL 48183) are used, which are modified by other components such as copper oxide, nickel oxide or lithium oxide (GB 1 992491, US 3 219480). On the basis of such multiphase systems, the nominal resistance H ₂₀ (electrical resistance of the thermistor at T = 20 "C) and the relevant for the sensitivity of the temperature measurement B-constant according to the relationship

R 11

_p (T) = J) ₀ exp γ = ^ 2o exp ( γ - - ^ j-)

be set to variable values by a corresponding reaction procedure in the sintering process, so that at a given offset, the production of a particular assortment of thermistors is possible. This procedure generally involves a considerable spread of the data of the individual specimens, and in particular from batch to batch the electrical parameters characterizing the thermistor assume different values depending on the structure structure of the ceramic obtained. As a rule, equilibrium states are not reached, which results in a lack of reproducibility and inadequate long-term stability. A sufficiently tightly tolerated assortment of thermistors therefore requires different forms of thermal and electrical aftertreatment as well as classifying and separating as separate working steps.

It has become known that thermistors are manufactured, for example, on the basis of the system of nickel oxide-manganese oxide (H. Walch, Siemens Zeitschrift 47 (1973) 65, Siemens-Datenbuch thermistor 1980/81), for the range of composition 0 <xi 1.275 results in a largely uniform phase in the form of nickel-manganese spinel N _x Mn ₃ ^ O ₄ with a between χ = 0.45 and χ = 1.275 only weakly compositionally dependent B constants, so that the desired relative insensitivity to variations in the composition The goal of the sintering process for the fabrication of thormistors is to ensure a uniform phase while largely avoiding pores in the structure of the sintered ceramic,

Due to the high lattice energy of the nickel-manganese spinel, the sintering temperatures required for this purpose increase due to the phase bending of NiO-Mn ₂ Oa-O ₂ (DG Wlckham, J. inorg., Nucl. C'hem., 26 (1964) 1369). permissible value of 1000 ^° C. Above this temperature, the aspired single-phase ceramic is not present since, in addition to the nickel-manganese spinel phase, NiO is increasingly present with the temperature in the sintered ceramic. For temperatures below 1100 ^° C., the sintering process produces ceramic bodies with a nonuniform structure, the considerable porosity of which is disadvantageous for a uniform sample surface. According to the proportion of the pore volume in the total volume present in each sample body, the electrical parameters of such thermistors have a more or less large fluctuation angle.

Another disadvantage is that the thermodynamic stability is given only above 740 ° C. Below this temperature, a mixture of Q-Mn ₂ O ₃ precipitates in the strongly disordered fractions in the mid grain area and in the considerable surface area (due to the relatively large pore volume) according to the phase diagram

-2- 26ΘΘ70

thermal parameters characterizing the thermal expeller are adversely affected in terms of their stability and reproducibility.

To reduce these fluctuations, various solutions have been described. Thus, by applying a passivation layer and subsequent artificial aging of the arrangement, a reduction of the spread and an increase in long-term stability are postulated (DD 12b 530). Another solution variant for improving the long-term stability is the construction of a system Überoinandorllegender, with respect to their electrical properties stable thin Schichton (DD 210779). Dom glelchon The aim of reducing production-related parameter tolerances is to provide solutions in which the geometrical dimensions of the thermistor are adjusted (Dc 2816003; DF 3029446).

Object of the invention

The object of the invention is to produce by suitable additives a uniform dense structure of the sintered ceramic and kinetically inhibit the preferably in Zwif chenkornberelch during cooling or under operating conditions Ausscheidungsprozosse to get highly accurate thermistors based on a highly reproducible structure ru. .

Explanation of the essence of the invention

The invention is based on the object, for the purposes of use as a thermistor powder suitable Oxldhalbloitern by small additions tiereich in the range of tenth of a few percent to a few percent of a low-melting oxide mixture, eg BaO / WCMA) or BaOZV ₂ O ₆ - (B) or PbO / GeOj mixtures (C) whose composition corresponds to 0.25 mol% or 0.35 mol% BaO and 62.5 mol% PbO ett a eutectic of the respective binary system, already at 1100 ⁰ C. and below into a high-density sintered ceramic with a largely uniform Gofugo to convert, the additives are largely amorphous in Zwischonkornöerelch. The boim cooling or at the operating temperature of the thermistors possible precipitations, as they are potentially possible in the case of Nlckel-manganese spinel below 740 ° C, are kinetically inhibited by these amorphous substance parts or are largely suppressed due to the greatly reduced inner surface. In addition to the substantial improvement of the reproducibility of the thermistor characterizing properties (specific conductivity and B-Konstanto) in addition a considerably greater stability with respect to the aging behavior is achieved at the same time.

Inventions are combined by additions. μηβη phase, consisting of a PbO / GeO ₂ mixture and / or Ba0 / WO ₃ mixture obtained a dense structure of increased uniformity. In a sintered ceramic based on the systems nickel oxide-manganese oxide, for example, the realization is carried out by by thermal decomposition of the mixture of Nlckelcarbonat / manganese carbonate at 600 ⁰ C obtained mixture ΝΙΟ / α-Μη ₂ Ο ₃ or the by theoretical decomposition of Nlckel Manganese oxalate mixed crystals in the air already at 35O ⁰ C obtained spinel NI _x MI ₃ ^ O ₁₁ corresponding to the composition 0 <xS 1.275 with an addition of about 1 mol%

(BaO) ₀ . ₂₅ (WO ₃ WA) or

V ₂ O ₆ Wb (B) resp

₀ ^ ₆ (Ge0 ₂ ) o, 376 (C)

is offset. The additives (A) and (C) are in this case in accordance with the invention, while the additive (B) is not covered by the invention. In this case, 1 mol% indicates the proportion of cations of (A), (B) or (C) relative to the three cations of the spinel. After dom mixing in an aqueous slurry, drying and pressing in the case of the additive (C) by sintering at a temperature = 1100 ⁰ C, a ceramic with greatly inhibited porosity, ie dense structure and increased uniformity obtained whose Thermistoreigonschafton by a greatly improved reproducibility and increased stability in terms of aging behavior is characterized. The addition (A) is compared to the pure nickel Manganoxldgemisch achieved a significant improvement, caused by the noninventive additive (B), however, a deterioration.

embodiment

In Table 1 are examples of the high-density sintered ceramic body according to the invention for high-precision thermistors under No. 4.6.1. and 6.2. indicated together with offsets, which do not have the Thermietoreigenschaftöri invention.

Table 1: Composition and properties of cylindrical sintered ceramic bodies with a diameter of 4.0 to 4.8 mm and a height of 1.6 to 2.0 mm

Kr. Composition

Ni, Mn ₃ . _x O ₄

g · cm ³ g · cm ³ 4:67 ) 4,76 f 4,64 J 4.69 ± 0.05 4,31 ") 4,15 {4,26 J 4.24 ± 0.06 4.04 - | 3.71 l 3,70 y 3.82 ± 0.15 3.56 \ 3.61 (· 3.55 y 3.57 ± 0.02 4,56) 4,25 ) 4,27 J 4.36 ± 0.13 4, 91 ") 4,80 f 4,72 y 4.81 ± 0.07 5,17 ") 5,19 I 5,18 J 5.18 ± 0.01 5.17 η 5.17 \ 5.15 5.16 ± 0.01

100

j) 20

Ωαη

J_

1,000

χ = 1.000 8 = 1.033 χ = 0.983

8 = 1.000 1 mol% additive (A)

χ = 1.000 1 mol% additive (B)

x = 1.000 1 mol% additive (C)

χ = 1.000 1 mol% additive (C)

88.6%

80.1%

72.2%

67.5%

82.4%

90.0%

97.9%

97.6%

6160 3090 6 776

6166 5023 5 093

5,702,669

6 501

7 345 4656 7482

7145 6699 6383

21677 28510 25335

2366 2399 2388

2163 2193 2153

± 1501

± 492

390 ± 458

6494 + 1226

742 ± 268

274 ± 2 331

2384 ± 12

2170 ± 16

3 852 3836 3 838

3974 3928 390D

3845 3859 3 850

3847 3822 3771

3838 3833 J 799,

4064 '

4068

4089

3836 3834 3834

3804 3806 3804

3842 ± 7

3 936 ± 22

3851 ± 5

3813 ± 29

3 823 ± 16

4074 ± 10

3835 ± 1

3805 ± 1

Claims (3)

1. sintered ceramic with dense structure of increased uniformity for high-precision thf rmistoren based on oxide semiconductors, characterized by additions of an amorphous phase consisting of a PbO / GeO ₂ mixture and / or BaO / WOA mixture, 2. sintered ceramic for high-precision thermistors according to claim 1, characterized in that it consists of the following components: 99 parts of a mixture of 3.3 to 42.5 mol% of NiO and 96.7 to 57.5 mol% Mn oxide and a portion of an additive consisting of 50 to 80mol% PbO and from 0 to 20 mol% GeO ₂ . 3. sintered ceramic for high-precision thermistors according to claim 1, characterized in that the additives are partially or completely replaced by a mixture consisting of 20 to 35mol% BaO j .d
80 to 65 mol% WO ₃ .