JPH0121110B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a high temperature thermistor that can be used in a high temperature range of 400 to 1100°C. (Prior art) In general, an NTC thermistor whose resistance value has a negative temperature coefficient
There is a relationship between the specific resistance of the thermostor and the temperature: ρ=ρ ₀ exp B (1/T−1/T ₀ ). Here, ρ, ρ ₀ are temperature T,
The specific resistance value at T ₀ (k)k), B is a constant called the B constant or thermistor constant, and lnρ is 1/
This value represents the slope of a straight line when plotted against T. When trying to measure temperature from changes in the resistance value of a thermistor, as can be seen from the above equation, the larger the B constant, the greater the rate of change in resistance value with respect to temperature change at a certain temperature. Can be detected. In addition, in the above formula, the value of 1/T decreases rapidly as the value of T increases, that is, as the temperature increases,
In order to accurately detect temperature particularly in a high temperature range, it is necessary to select a material with a large B constant for the thermistor. As such a thermistor, JP-A-Sho
No. 48-61984 is proposed. This is a zinc oxide sintered body containing predetermined amounts of antimony oxide and cobalt oxide, and its B constant is about 7,000. However, on the other hand, there is also the problem that a large B constant means that the design usable temperature range becomes narrower than one with a small B constant. Therefore, in actual use, it is necessary to select a thermistor with an appropriate resistance value and B constant depending on the purpose and application. Conventionally, high-temperature thermistors with a spinel crystal structure have been made using Mg(Al, Cr, Fe) ₂ O ₄ , Co
Mixed compositions of (Al, Cr, Fe) ₂ O ₄ , Co (Al, Cr) ₂ O ₄ and LaCrO ₃ are known, but these have a small B constant for use in high temperature ranges. , or even if the B constant was large to some extent, the resistance value was also significantly large and could not be said to be practically satisfactory. (Problem to be solved by the invention) A thermistor with various resistance values and B constants depending on the actual purpose and application in a spinel solid solution of the composition (Co _x Mg _1-x ) Al ₂ O ₄ . It's about getting. That is, by changing the ratio of Co and Mg, aluminum was mixed with antimony in a (Co, Mg) Al ₂ O ₄ solid solution that exhibited various resistivity values while maintaining a large B constant value. By replacing it with , it is intended to obtain a thermistor in which the specific resistance value is further reduced and the value of the B constant can be varied within a relatively large range of values. (Means for solving the problem) The present invention provides (C _x Mg _1-x ) Al ₂ O ₄ (however, 0.1≦
x≦0.95), aluminum is mixed with Sb ₂ O ₃ in the spinel solid solution.
This is a high-temperature thermistor characterized in that antimony is substituted with 5 to 90 mol% of antimony. MgAl ₂ O ₄ generally has a resistance of 10 ⁷ to 10 ⁸ Ω at 1000°C
CoAl ₂ O ₄ has a high resistivity of 10 ² Ω
It has a low resistivity of about cm. Therefore, (C _x
Mg _1-x ) The specific resistance of Al ₂ O ₄ can be changed sequentially from the specific resistance value of MgAl ₂ O ₄ to the specific resistance value of CoAl ₂ O ₄ by changing the value of x from 0 to 1. It can be decreased. Moreover, the value of the B constant in that case shows almost no change at 20,000 or more, specifically around 22,000. However, in order to provide a practical thermistor for various purposes and uses, it is necessary to be able to easily change not only the specific resistance value but also the B constant according to requirements. As a result of research to meet this demand, the inventors discovered that this object could be achieved by replacing aluminum in the solid solution with antimony, thereby completing the present invention. First, the inventor studied the change in resistivity in a spinel-type solid solution (C _x Mg _1-x ) Al ₂ O ₄ and found that the value of x was 0.1 to
We confirmed that it can be implemented within the range of 0.95. When the value of x is less than 0.1, there is almost no effect, that is, the change in the B constant due to the substitution of antimony does not appear sufficiently. Moreover, if the value of x exceeds 0.95, warpage or distortion will occur in the sintered body, which is not preferable. In order to obtain a good sintered body and to be able to arbitrarily change the B constant by antimony substitution, the value of x in the chemical formula of the solid solution above should be 0.1.
A range of ~0.95 is good. In addition, in order to change the B constant, aluminum in the spinel type solid solution must be converted to Sb ₂ O ₃ by 5 to 90
It has been found that it is sufficient to substitute with mol % of antimony. When Sb ₂ O ₃ is less than 5 mol %, the B constant hardly decreases. Moreover, if Sb ₂ O ₃ exceeds 90 mol %, it is inappropriate because it will melt during the calcination stage. Further explanation will be given below with reference to Examples. Example 1 A sintered body was obtained by blending reagent powders of Al(OH) ₃ , Mg(OH) ₂ , CoO, and Sb ₂ O ₃ in the proportions shown in Table 1. The manufacturing method is to dry mix the above reagent powder in an alumina automatic mortar for 1 hour, then wet mix for 2 hours using ethanol as a dispersion medium, and finally dry mix for 1 hour, then put it in an alumina crucible and mix at a temperature of 1200 to 1400℃ for 4 hours. Calcined for an hour. This calcined powder was dry-pulverized for 2 hours in an automatic alumina mortar, and mixed with an aqueous solution of 6% by weight polyvinyl alcohol as a binder at a ratio of 0.05 ml per 1 g of powder. The mixture was press-molded into a disk shape with a diameter of 10 mm and a thickness of 2 mm at a pressure of 1 ton/cm ² and fired in an electric furnace at a temperature of 1450 to 1600° C. for 2 hours to produce a sintered body. Next, platinum electrodes were baked on both surfaces of this sintered body. The resistivity-temperature characteristics of the element thus obtained were measured in a temperature range of 200 to 1100°C using a DC stabilized power supply and an electrometer. The results are shown in Figure 1. In addition, in the formulation shown in Table 1, Mg
(OH) ₂ and Al(OH) ₃ are shown as values converted to MgO and Al ₂ O ₃ , respectively, and the total amount of CoO and MgO is 100 mol%, and the total amount of Al ₂ O ₃ and Sb ₂ O ₃ is 100 mol%, and
The ratio of the sum of MgO and CoO to the sum of Al ₂ O ₃ and Sb ₂ O ₃ was set to 1:1.

[Table] Table 2 also shows the 1000°C, 700°C,
The values of each specific resistance and B constant at 500°C are shown.

[Table] From Figure 1 and Table 2, by replacing aluminum in (Co _x Mg _1-x ) Al ₂ O ₄ with antimony, B
The constant can be varied from 22,000 to nearly half that value, 11,500 (see A to F). Moreover, the rate of decrease tends to increase as the amount of Sb ₂ O ₃ increases. Also, the specific resistance is 1000℃, 700
It can be seen that the temperature decreases both at ℃ and 500℃. Furthermore, from C, G, and H in Table 1, as the proportion (x) of CoO increases, the effect of lowering the resistivity and lowering the B constant due to Sb ₂ O ₃ will decrease even if Sb ₂ O ₃ is the same at 20 mol%. It can be seen that the CoO ratio (x) is larger compared to that without increasing it. Example 2 Al(OH) ₃ , Mg(OH) ₂ , CoO without using Sb ₂ O ₃
(C _x
A Mg _1-x ) Al ₂ O ₄ based sintered body was obtained. However, the value of x was varied as shown in Table 3. The obtained sintered body was made into an element in the same manner as in Example 1, and its resistivity-temperature characteristics were measured in the temperature range of 200 to 1100°C. The results are shown in Figure 2. In addition, this element's 1000℃,
Table 3 shows each specific resistance value and B constant at 700°C.

[Table] As is clear from Figure 2 and Table 3, as the value of x increases, that is, even if Co is increased and Mg is decreased, the specific resistance increases at both 1000℃ and 700℃. However, the B constant is over 20000, especially when x
Above 0.1, there is almost no change. (Effects of the Invention) As explained above, _the thermistor of _the present invention _combines Co _and
By changing the ratio of Mg and the ratio of Al to Sb, it is possible to easily obtain thermistors with various resistivity and B constant values. The thermistor thus obtained can be highly sensitive and practical.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the resistivity-temperature characteristics of the thermistor according to the present invention. Figure 2 is (Co _x Mg _1-x )
Specific resistance when changing x of Al ₂ O ₄ based sintered body -
Diagram showing temperature characteristics.

Claims (1)

[Claims] 1 (Co _x Mg _1-x ) Al ₂ O ₄ (0.1≦x≦0.95)
In a spinel solid solution with _a composition _of
A high-temperature thermistor characterized by replacing ~90 mol% of antimony.