JPH0244122B2 - KOONYOSAAMISUTA - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic thermistor with excellent stability at high temperatures. Thermistors are used as thermometers, temperature compensation circuits, liquid level gauges,
The thermistor of the present invention is widely used as a temperature detection element in flowmeters, non-contact temperature switches, etc., and is particularly suitable as a high-temperature element in afterburners, catalytic converters, thermal reactors, etc. for automobile exhaust gas purification. One of the problems with temperature sensing elements for high temperatures is deterioration due to heat. In particular, deterioration at temperatures above 900°C is difficult to avoid even with ceramic thermistors. The purpose of the present invention is to provide a long-life thermistor with little thermal deterioration over 900°C, and also to provide a thermistor with resistance value and thermistor constant (B An object of the present invention is to provide a thermistor that can appropriately set the constant ((u)CaO・(l) _TiO2・
(w) Cr ₂ O) ₁ Fe ₂ O _3y Al ₂ O _3x The present invention provides a ceramic thermistor consisting essentially of the composition represented by (w) Cr 2 O) 1 Fe 2 O 3y Al 2 O 3x, with the essential components being CaO, TiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ ,
Contains five components of Al ₂ O ₃ , and the molar ratio of CaO and Cr ₂ O ₃ is u (CaO) = 0.3 to 1.1, w when TiO ₂ is 1.
( _Cr2O3 )=0.9~ ₃ , ((u)CaO・_TiO2・
(w) Cr ₂ O ₃ ) y (Fe ₂ O ₃ ) = 0.01 to 1 mole
0.3, x(Al ₂ O ₃ )=0.01 to 0.3. The desirable characteristics of a thermistor that can be used in combination with a commercially available control circuit without any special changes and used at high temperatures are at least the following:
Resistance value (R900) at 900℃ is 0.3KΩ to 2.5KΩ, thermistor constant B
= 6000 to 16000 (K), and the thermal deterioration at 900 to 1000°C is as small as possible. A ceramic thermistor that satisfies these conditions is the thermistor of the present invention. When _{the amount of Fe 2 O 3} and Al ₂ O ₃ per 1 mole of TiO 2 is within the above composition range, the resistance value at 900℃ (R900)
is 0.35 to 1.0KΩ, and outside this range 2KΩ
increase to a certain extent. However, this resistance value itself can be said to be within a sufficiently usable range. What poses a practical problem is the rate of thermal deterioration. That is, Fe ₂ O ₃ and
Al ₂ O ₃ per mole of (CaO・TiO ₂・Cr ₂ O ₃ )
At levels below 0.15 mol, the resistance value tends to decrease when thermal history is applied, and the rate of change is Fe ₂ O ₃ ,
It increases with decreasing amount of Al ₂ O ₃ and exhibits a rate of change of more than 10% at levels below 0.01 mol.
At levels of 2.0 mol of Fe ₂ O ₃ and 0.15 mol of Al ₂ O ₃ or more, the resistance value increases when subjected to thermal history, and when it exceeds 0.3 mol, the rate of change in resistance value exceeds 10%, which is still a practical problem. occurs. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 As raw materials, purity (weight%) of 99%, 99.5%,
_TiO2 , _CaCO3 , with 99%, 99.5%, 99.9%
Using Cr ₂ O ₃ , Fe ₂ O ₃ , and Al ₂ O ₃ as raw materials, CaO:TiO ₂ :Cr ₂ O ₃ (molar ratio) = 1:1:1, and the moles of Fe ₂ O ₃ and Al ₂ O ₃ Various thermistors were manufactured with varying ratios and their characteristics were investigated. Above raw materials Al ₂ O ₃ , Fe ₂ O ₃ , CaO, TiO ₂ , Cr ₂ O ₃
are mixed in a predetermined raw material ratio, wet mixed in a ball mill, and dried at 1400°C.
This is then wet-milled using a ball mill for 60 min.
Make a slurry of the entire mesh. The slurry was dried and pulverized again to a 150 μm diameter. After drying, 2% by weight of stearic acid was mixed as a molding aid, and the mixture was filled into a mold and two 0.4 mmφ platinum wires were inserted to yield 1000 Kg/cm ^{2 .}
After press molding at a pressure of
Fired at 1400-1500℃, the above two 0.4mmφ platinum wires were placed in a 4mmφ×1.5mmt ceramic disk.
Thermistors of various compositions were manufactured by inserting and embedding them on the same plane in the thickness direction and parallel to each other with a spacing of 2 mm maintained along the center line in the radial direction with their ends exposed. These thermistors can be used at high temperatures (800~1200℃)
After holding for 200 hours and performing stabilization treatment,
Resistance value (R900) at ℃, rate of change in R900 after 500 hours of thermal history at 1000℃ (△R900), and resistance-temperature characteristics at 900℃ and 750℃ were measured in an electric furnace maintained in a neutral atmosphere. The results are shown in Table 1 and Figure 1.

[Table] Example 2 A thermistor was manufactured and tested in the same manner as in Example 1 while varying u and w. The results are shown in Table 2 and Figure 1.

【table】 [Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between resistance temperature change rate ΔR900 and time in an example of the present invention.
The code of each curve indicates the sample number.

Claims (1)

[Claims] 1 Formula ((u) CaO・TiO ₂・(w) Cr ₂ O ₃ ) ₁ Fe ₂ O _3y
It essentially consists of the composition represented by Al ₂ O _3x , in molar ratio u = 0.3 ~ 1.1, w = 0.9 ~ 3, y = 0.01
~0.3 and x=0.01-0.3.