JPH11288778A - Resistive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistive element usable at a high temperature, capable of quickly raising the temperature to an ignition temperature without providing a control circuit, and resistant to the repeated temperature rise and fall and the oxidation at high temperature by adding pentatungsten trisilicide to tungsten at a specified ratio and formly an electric conductive layer (heating layer) by using a uniforming dispersed mixture. SOLUTION: As a conductor layer, a material having a high melting point, a low expansion coefficient and a low electric resistance is used, and as such a material, a mixture of tungsten and pentatungsten trisilicide with a weight ratio of (48:62) to (76:24). According to this, it can be suppressed to an ignorable degree that tungsten is silicified in the boundary with a sialon base material in baking or current-carrying heating to form unpreferably tungsten disilicide. Consequently, this element is usable 50000 times or more in a cycle test of repeating the current-carrying for 15 seconds and the stopping thereof for 15 seconds at 1,400 deg.C or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel resistance element, and more particularly, to a method of rapidly increasing a temperature of 1100.degree. C. or more within about 3 seconds without providing a control circuit using a computer or the like. The present invention relates to a resistance element which has excellent durability, such as withstanding repeated temperature and oxidation at high temperature, is used for ignition of gaseous fuel or liquid fuel, and can be used as a thermistor capable of withstanding high temperature of 1200 ° C. or more. .

[0002]

2. Description of the Related Art Conventionally, an energized resistance element using ceramics is generally used for igniting a gaseous fuel such as natural gas, propane gas, or kerosene or a liquid fuel. At least 1000 ° C. within 3 seconds
A rapid increase in temperature to at least 12
In order to withstand a high temperature of 00 ° C. or more, it is required to have excellent thermal shock resistance and oxidation resistance.

In order to meet such a demand, a conventional ceramic resistor element is usually manufactured by burying a heating element such as tungsten in an insulator such as silicon nitride (Si ₃ N ₄ ) and firing the same. Was.

However, in this case, since silicon nitride is difficult to sinter, a rare earth element or the like is used as a sintering aid.
About 5% by weight is added to the sintered body.
In a temperature range of 1400 ° C. or more, oxidation resistance is inevitably reduced. Therefore, when the permissible endurance temperature is low, the time to reach the ignition temperature of 1100 ° C. becomes longer, so that the use temperature is suppressed to about 1300 ° C.
In the case where the heating rate is sacrificed or rapid heating is required, it is necessary to provide a control circuit using a computer or the like which increases costs.

[0005]

Under such circumstances, the present invention can be used at a temperature of 1500 ° C. or higher, and can be used within about 3 seconds without providing a control circuit.
To provide a low-cost current-carrying resistive element with good ignition performance, made of ceramics that can rapidly raise the temperature to ℃ or more and withstands repeated temperature rises and withstands oxidation at high temperatures. It was made for the purpose of.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a resistance element having excellent performance. As a result, tungsten, which is an internal heating element, loses one of its properties during firing or current generation. The portion is silicified in layers at the boundary between the tungsten and the silicon nitride base material to form tungsten disilicide, which has a coefficient of thermal expansion of 6.7 to
About 7.9 × 10 ⁻⁶ / ° C. and silicon nitride (3.2
× 10 ^-6 / ° C. approximately) and tungsten (4.3 × 10 ^-6 /
(About ° C), which is a point of destruction in the on-off cycle test and focuses on the phenomenon that the element is destroyed in a short number of cycles. Tungsten has a thermal expansion coefficient smaller than that of tungsten disilicide. By adding tungsten oxide (5.0 to 6.0 × 10 ⁻⁶ / ° C.) at a predetermined ratio and using a uniformly dispersed mixture to form a heating element layer (conductor layer), destruction can be prevented. They have found that they can be prevented, and have completed the present invention based on this finding.

That is, the present invention provides a laminated structure sintered body comprising an insulator material substrate layer and a conductor layer having a high melting point, a low coefficient of thermal expansion, and a low electric resistance provided thereon or embedded therein. In the resistive element consisting of:
Weight ratio of tungsten to pentatungsten trisilicide 4
An object of the present invention is to provide a resistive element characterized by being formed from a mixture of 8:52 to 76:24.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A resistance element according to the present invention comprises a sintered body having a laminated structure of an insulator material substrate layer and a conductor layer provided thereon or embedded therein. The insulating material substrate layer can be appropriately selected from known materials used in conventional rapid temperature heating elements, and can be appropriately selected and used. In particular, sialon containing silicon nitride and aluminum oxide is used as a main component, In some cases,
Those composed of a composition containing silicon oxide and a rare earth element oxide are suitable. It is known that when silicon oxide (Si ₃ N ₄ ), which is a main component in the sialon, is oxidized, a pure SiO ₂ protective film is formed on the surface, and oxidation resistance is imparted. However, since silicon nitride is difficult to sinter, densification by sintering alone is not achieved.

Therefore, in the present invention, in order to promote the densification of the silicon nitride sintered body, the silicon nitride 1
Aluminum oxide (Al ₂ O ₃ ) 4 to 10 per 100 moles
An insulating material made of a composition containing sialon as a main component is preferably used by adding about moles and firing. Here, sialon has a composition corresponding to Si _6-z Al _z O _z N _8-z and basically has a crystal structure of Si ₃ N ₄ ,
It is a substituted solid solution in which a part of Si is replaced by Al and a part of N is replaced by O. If the amount of aluminum is less than 4 moles in terms of aluminum oxide, the resulting insulator material will not be sufficiently densified. If it exceeds 10 moles, the oxidation resistance of the insulator material will decrease.

In the present invention, in order to improve the oxidation resistance of the obtained insulator material, silicon oxide (SiO ₂ ) may be added together with the aluminum oxide in an amount of about 1 to 12 mol per 100 mol of silicon nitride. They can be blended in proportions. If the amount of silicon oxide is less than 1 mol, the effect of improving oxidation resistance may not be sufficiently exhibited. If the amount exceeds 12 mol, the PTC characteristic (Positive T) in which the resistance value increases with increasing temperature in a low temperature part.
NTC characteristics (Negative Temperatur) in which the resistance value decreases with increasing temperature in a high-temperature portion, although the temperature coefficient indicates an environmental coefficient.
re-coefficient) appears and tends to exhibit unstable resistance-temperature characteristics. For use as a heater, PTC characteristics free from thermal runaway are preferred. When the SiO ₂ content is 12 mol or less, the PTC characteristics are generally exhibited.

Further, in the present invention, in order to improve sinterability and further increase the density, if necessary, a rare earth element oxide may be added together with the aluminum oxide to form a silicon nitride 10.
0.3 mol or less per 0 mol, preferably 0.001 to
It can be blended at a ratio of 0.3 mol. If the compounding amount of the rare earth element oxide is less than 0.001 mol, the effect of compounding the rare earth element oxide is not sufficiently exhibited, and if it exceeds 0.3 mol, the oxidation resistance of the obtained insulator material is significantly reduced. Here, examples of the rare earth element oxide include oxides such as yttrium, samarium, lanthanum, cerium, and neodymium. Among these, yttrium oxide, lanthanum oxide, and cerium oxide are preferable. . These rare earth element oxides may be used alone or in combination of two or more.

Meanwhile, as the conductor layer in the resistance element of the present invention, high melting point, the material having a low thermal expansion coefficient and low electrical resistivity is used, in particular melting point 2000 ° C. or higher, the thermal expansion coefficient of 6.0 × 10 ^-6 / ° C or lower and an electric resistance of 10 ⁻⁵ Ω · cm or lower are suitable.

In the present invention, a mixture of tungsten and pentatungsten trisilicide in a weight ratio of 48:52 to 76:24 is used as such a material. By blending tungsten trisilicide with tungsten at such a ratio, tungsten is silicified in a layer at the boundary with the sialon base material during firing or heat generation, and undesirable tungsten disilicide is formed. Is negligible. If the amount of pentatungsten trisilicide is less than the above range, the effects of the present invention will not be sufficiently exhibited, and if it is more than the above range, the thermal expansion coefficient will be too large, and desired characteristics will not be obtained.

Next, there is no particular limitation on the method of manufacturing the resistance element of the present invention, and a method conventionally used in the manufacture of ceramic heating elements can be used.
For example, first, a required amount of silicon nitride (α-Si ₃ N ₄ or β-Si ₃ N ₄ ) powder having an average particle size of about 0.1 to 1.5 μm, aluminum oxide powder, and silicon oxide powder optionally used Or a rare earth element oxide powder is wet-mixed with a suitable solvent and, if necessary, using a known binder or dispersant by a ball mill or the like to prepare a slurry. Next, it is formed into a desired shape by a doctor blade method, a press molding method, an extrusion molding method, or the like.

Next, a predetermined pattern is printed on the surface of the molded body thus obtained using a conductive paste containing tungsten and pentatungsten trisilicide at a predetermined ratio, and the resultant is laminated or laminated. After being wound and formed into a desired shape, the formed product is fired. The firing method is not particularly limited, and known methods such as a hot press firing method, a normal pressure firing method, a nitrogen gas pressure firing method, and a hot isostatic pressure (H
IP) firing method or the like is used. The firing temperature is generally selected to be 1900 ° C. or lower, preferably 1700 to 1900 ° C. This firing is advantageously performed in a non-oxidizing atmosphere such as a nitrogen gas atmosphere.
Next, the sintered body thus obtained is subjected to surface grinding and cutting, and an electrode for connecting to an external power supply is attached to the conductive layer, whereby a desired resistance element is obtained.

[0016]

According to the resistance element of the present invention, by using a mixture of a specific ratio of tungsten and pentatungsten trisilicide for the conductor layer, the layered silicide of tungsten during firing or energizing heat generation can be reduced. As a result, it can be used more than 50,000 times in a cycle test in which current is supplied at a temperature of 1400 ° C. or more for 15 seconds and stop is repeated for 15 seconds. The resistance element of the present invention is suitably used for igniting a gaseous fuel such as natural gas, propane gas, and kerosene or a liquid fuel. Further, the resistance element of the present invention can be used also as a thermistor.
Suitable for use at high temperatures of 0 ° C. or higher.

[0017]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Al ₂ O ₃ powder per 100 mol of α-Si ₃ N ₄ powder
A slurry was prepared by adding 86 mol, 10 mol of SiO ₂ powder, an appropriate amount of an acrylic binder and ethanol and toluene, and mixing with a ball mill. Next, the slurry was formed into a sheet by a doctor blade method, and then dried to prepare a sheet having a thickness of 500 μm, which was cut into a square having a side of 60 mm.

Next, a conductor paste in which the ratio of tungsten to pentatungsten trisilicide was changed as shown in Table 1 was printed on the above-mentioned sheet, and four unprinted sheets were placed above and below the printed sheet. The layers were laminated so as to have a total of nine layers, thereby producing a laminate.

The laminate was hot-pressed at 1750 ° C. for 1 hour under a pressure of 250 kg / cm ² in a nitrogen gas atmosphere at 1 atm to obtain a laminated structure sintered body. next,
This laminated structure sintered body is cut with a diamond grindstone, and then a tungsten-nickel electrode is baked on the exposed portion of the conductor layer on the cut surface, and then nickel plating is performed. The electrode terminals were provided by welding to prepare a resistance element. The following evaluation was performed on this resistance element.

(1) On-off cycle test A cycle test in which a predetermined voltage is applied, the temperature is raised to 1500 ° C. by energizing in air for 15 seconds, and the temperature is lowered to around room temperature by stopping for 15 seconds. Was done. The number of times at which the resistance value increased by 10% from the initial resistance value (one count in both processes of raising and lowering the temperature) was examined. The number of samples was 20, and the average was used as the number of times. Table 1 shows the results. In addition, 50,000 times or more is regarded as a pass.

(2) Continuous energizing test When a predetermined voltage is applied and continuous energizing is performed so that the resistance element is maintained at 1500 ° C., the time required for the resistance value to change by 10% from the initial value is determined. Examined. The number of samples was 20, and the average value was adopted. Table 1 shows the results. In addition, 1000 hours or more is considered as a pass.

[0023]

[Table 1]

Claims (2)

[Claims] 1. A resistance element comprising a laminated structure sintered body of an insulator material substrate layer and a conductor layer having a high melting point, a low coefficient of thermal expansion, and a low electric resistance provided thereon or embedded therein. In the above, the conductor layer may have a weight ratio of tungsten to pentatungsten trisilicide of from 48:52 to 7
6: A resistive element characterized by being formed from a mixture of 24. 2. The method according to claim 1, wherein the insulating material substrate layer comprises silicon nitride 100
2. The resistance element according to claim 1, comprising a sialon containing a rare earth element in an amount of 0.3 mol or less in terms of oxide per mol.