JP2000286042A - Resistance element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resistance element capable of being used for a long period under a high-temperature environment of 1,000 deg.C or higher (preferably 1,400 deg.C or higher), and having a small variation of a resistance value and excellent in durability, even if temperature increase from a room temperature to 1,000 deg.C or higher (preferably 1,400 deg.C or higher) and temperature reduction in the reverse direction are repeated. SOLUTION: In this resistance element 20 having a resistance element body 22 composed of ceramics containing zircon as a main component, and an inner conductor 14 embedded inside the resistance element body 22, the inner conductor 14 has a melting point of 1,700 deg.C or higher, a thermal expansion coefficient in the range from a room temperature to 800 deg.C of 4×10-6/ deg.C-6×10-6/ deg.C, and a resistivity of 10-5 Ωcm or less. The inner conductor 14 preferably contains one or more electric conductors selected from, for example, tungsten(W), tungsten carbide(WC, W2C), molybdenum(Mo) and chromium(Cr).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be used for a long period of time in a high temperature environment of 1000 ° C. or more, and even if the temperature is repeatedly increased and decreased from room temperature to a high temperature of 1000 ° C. or more or vice versa. Also, the present invention relates to a resistance element which has little fluctuation in resistance and has excellent durability.

[0002]

2. Description of the Related Art Conventionally, a current-carrying type ignition resistance element using ceramics has been generally used for igniting gaseous fuel or liquid fuel such as natural gas, propane gas, and kerosene. This kind of ignition resistance element takes 10 to 2 seconds.
In order to withstand a rapid temperature rise of at least 00 ° C. and a high temperature of about 1550 ° C. in air, it is required to have excellent thermal shock resistance and oxidation resistance.

Further, a resistance element for a high-temperature thermistor that instantaneously measures a high temperature of 1000 ° C. or more is required to have excellent thermal shock resistance and oxidation resistance. In order to meet such demands, high-strength silicon nitride having a small coefficient of thermal expansion is used as a ceramic body of a conventional ceramic resistance element. In a ceramic resistance element, an internal conductor used as a heating resistor must be embedded in the ceramic body. Since such an internal conductor needs to be fired together with the silicon nitride ceramics, it is necessary to have a melting point of 1800 ° C. or more. Examples of such a conductor include tungsten (W), tungsten carbide (WC, W ₂ C), molybdenum (Mo), and chromium (Cr).

However, the coefficient of thermal expansion of silicon nitride ceramics is 3 × 10 ⁻⁶ / 0 to 100 ° C.
° C and W as an internal conductor used as a resistor
Has a thermal expansion coefficient of 4.4 × 10 ⁻⁶ / ° C. The coefficient of thermal expansion of Mo is 5 × 10 ⁻⁶ / ° C.,
That of WC is 5.3 × 10 ⁻⁶ / ° C., and W ₂ C
Is between 4 and 5.3 × 10 ⁻⁶ / ° C. Thus, the thermal expansion coefficient of the internal conductor used as a resistor is
At present, they are larger than silicon nitride ceramics and do not match.

In order to reduce the difference in the coefficient of thermal expansion,
A method has been proposed in which an insulating component having a small coefficient of thermal expansion, such as silicon nitride or boron nitride, is added to the internal conductor (JP-A-7-239123). In order to increase the coefficient of thermal expansion of the ceramic body, Mo having a large coefficient of thermal expansion is used.
A method of adding Si ₂ has been proposed (Japanese Unexamined Patent Publication No.
251862).

However, if the amount of the insulating component added to the internal conductor is increased in order to reduce the difference in the coefficient of thermal expansion even a little, there is a disadvantage that the resistance value of the internal conductor increases. Furthermore, even if the same component as that of the ceramic body is added to the internal conductor, the thermal expansion coefficients of the internal conductor and the ceramic body are not equal.

Further, MoSi _{2 is} contained in the ceramic body.
The addition of large substance of such a thermal expansion coefficient of, MoSi ₂
Is a conductor, and if the addition amount is too large, the insulating property of the ceramic body is impaired, so the addition amount is limited.

For the above reasons, it is difficult to equalize the coefficients of thermal expansion of both the internal conductor and the ceramic body even if a substance that approximates the coefficient of thermal expansion is added to both.
Further, since silicon nitride ceramics use a rare earth oxide as a sintering aid, there is also a problem that oxidation resistance is reduced at a temperature of 1400 ° C. or more in air, which makes it difficult to use.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has been made at a temperature of 1000 ° C. or more (preferably 1 ° C.).
It can be used for a long period of time under a high temperature environment of 400 ° C. or more, and even when the temperature is repeatedly increased and decreased from room temperature to 1000 ° C. or more (preferably 1400 ° C. or more) or vice versa. It is an object of the present invention to provide a resistance element having a small value variation and excellent durability.

[0010]

Means for Solving the Problems The present inventors have selected ceramics containing zircon as a main component as a resistance element main body, and have specified conductors such as tungsten, tungsten carbide, molybdenum and chromium as internal conductors. By selecting, it is possible to actually use the device for a long period of time in a high temperature environment of 1000 ° C. or more (preferably 1400 ° C. or more), and further, from room temperature to 1000 ° C. or more (preferably 1400 ° C. or more) It has been found that even if the temperature is repeatedly increased or decreased, a resistance element having a small variation in resistance value and excellent in durability can be obtained, and the present invention has been completed.

That is, a resistance element according to the present invention is a resistance element having a resistance element main body made of ceramics containing zircon as a main component, and an internal conductor embedded inside the resistance element main body. The internal conductor has a melting point of 1700 ° C. or more, and is room temperature to 800 ° C.
Has a coefficient of thermal expansion of 4 × 10 ⁻⁶ / ° C. to ⁶ × 10
^-6 / ° is C, the specific resistance is 10 ^- wherein the at ⁵ Omega · cm or less. In the present invention, the ceramic containing zircon as a main component means that the ceramic may contain some impurities other than zircon (preferably about 10% by weight or less, more preferably about 2% by weight or less). .

The inner conductor is not particularly limited, but may be tungsten (W), tungsten carbide (WC, W
₂ C), molybdenum (Mo), preferably includes one or more conductors to be selected from among chromium (Cr).

[0013]

The zircon is represented by ZrSiO ₄ and ZrO _4
2 and SiO ₂ . The coefficient of thermal expansion of zircon is 5 × 10 ⁻⁶ / ° at room temperature to 800 ° C.
C, tungsten carbide (WC, W ₂ C),
Very close to the expansion coefficients of molybdenum (Mo) and chromium (Cr). Further, since zircon is an oxide, it does not oxidize further and has excellent oxidation resistance. For this reason, the resistance element according to the present invention has a temperature of 1000 ° C.
It can be used for a long period of time in a high temperature environment (preferably 1400 ° C. or more) and at room temperature to 100 ° C.
Even if the temperature is repeatedly raised and lowered at a high temperature of 0 ° C. or higher (preferably 1400 ° C. or higher), the resistance value does not change much.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments shown in the drawings. FIG. 1 is a perspective view of a resistance element according to one embodiment of the present invention, and FIG. 2 is a perspective view showing a manufacturing process of the resistance element shown in FIG.

[0015] As shown in resistive element Figure 1, the resistance element 20 of the present embodiment, for example, is used as a heating element or hot thermistor (temperature sensor), it has a resistance element body 22, internal to the resistance element body 22 A predetermined pattern of internal conductors 14 (see FIG. 2) is formed. A pair of extraction electrode portions 1 of the internal conductor 14 formed in a predetermined pattern inside the resistance element body 22
As shown in FIG. 1, 4 a are formed on two rear side surfaces of the element body 22, respectively, and are joined to the external terminal electrodes 24.

In the present embodiment, the resistance element body 22 is made of ceramic made of zircon (ceramic containing zircon as a main component), and the inner conductor 14 is made of 170 ceramics.
Has 0 ° C or higher melting point, room temperature thermal expansion coefficient at to 800 ° C is ^{4 × 10 -6 / ° C~6 ×} 10 -6 / ° C, the specific resistance is not more than ^{10 -5 Ω} · cm It is composed of a certain conductor. Examples of such a conductor include one or more conductors selected from tungsten, tungsten carbide (WC, W ₂ C), molybdenum (Mo), and chromium (Cr).

In the present embodiment, the material of the external terminal electrode 24 is not particularly limited, and is composed of nickel, tungsten, molybdenum, gold, silver, copper, a combination of the above, and the like.

Manufacturing Method of Resistive Element To manufacture the resistive element 20 shown in FIG. 1, first, as shown in FIG. 2, the internal conductor 14 is formed on the surface in a predetermined repetitive pattern by a screen printing method or the like. A green sheet 12 and a green sheet 16 on which no internal conductor 14 is formed are prepared.

In the present embodiment, the green sheets 12 and 16 are obtained by adding an aqueous solution containing an organic binder or an organic solvent-based solution to zircon raw material powder, forming a slurry, forming a sheet, and drying the resulting sheet. As the zircon raw material powder, a mixed powder of a silica powder and a zirconium oxide powder in a predetermined molar ratio is used. The particle size of the zircon raw material powder is not particularly limited, but is generally 0.1
About 1.5 μm. The binder added to the zircon raw material powder is not particularly limited, and examples thereof include polyvinyl alcohol and acrylic resin. Examples of the method for forming a sheet include a doctor blade method and an extrusion method.

The thickness of the green sheets 12 and 16 is
Although not particularly limited, it is generally 50 to 1500 μm. The thickness of the inner conductor 14 formed on the surface of the green sheet 12 by screen printing or the like is not particularly limited, but is preferably 5 to 50 μm, more preferably 15 μm.
２５25 μm.

As a conductive paste for forming the internal conductor 14, an organic binder, a solvent, a plasticizer, and the like are added to a raw material powder that becomes tungsten carbide after firing and / or a molybdenum raw material powder and / or a chromium raw material powder. A paste is used. The particle size of these raw material powders is not particularly limited, but is preferably set to 0.1.
It is about 5 to 8 μm, more preferably about 1 to 5 μm.

As shown in FIG. 2, a single or a plurality of green sheets 16 are laminated on the upper and lower surfaces of the green sheet 12 on which the pattern of the internal conductors 14 is formed to form the laminate unit 10. Disconnect each time.

The compact cut for each element is placed in a binder removal furnace before being mounted in a normal pressure firing furnace, and subjected to a binder removal treatment. The heating temperature at the time of the binder removal processing varies depending on the type of the binder to be removed from the binder and the like, but is generally 400 to 1000 ° C.
The time for the binder removal treatment varies depending on the size of the molded body, the heating temperature, and the like, but is generally several hours to several tens of hours.

Thereafter, the molded body block after the binder removal treatment is set and fired in, for example, a normal-pressure firing furnace.

The firing is preferably performed in an inert gas atmosphere or a reducing atmosphere to prevent oxidation of the conductor. The inert gas is not particularly limited, but is preferably a nitrogen gas. The firing temperature is not particularly limited, but is preferably 1300 to produce zircon ceramics.
To 1800 ° C, particularly preferably 1500 to 1700 °
C.

By such firing, the resistance element body 22
Is obtained.

The extraction electrode portions 14a of the internal conductor 14 are exposed on the two rear sides of the resistance element body 22. afterwards,
A brazing material is applied to these extraction electrode portions 14a, and external terminal electrodes 24 are attached and joined. As joining means,
Although not particularly limited, for example, a vacuum baking method is used. Vacuum baking, for example, 1.3 × 10 ^{- 2}
800 to 980 in a vacuum of about 1.3 × 10 ⁻³ Pa
It is performed under a temperature condition of ° C. Although there is no particular limitation on the brazing material, for example, a silver brazing material is used. The silver brazing material preferably contains an active metal such as titanium or zirconium. The addition of the active metal to the brazing material is intended to ensure sufficient adhesive strength to both the zircon ceramic as an insulating material and the internal conductor as a resistance material. If the strength is not sufficient, and if it exceeds 5% by weight, the flexibility of the brazing material tends to decrease.

Other Embodiments The present invention is not limited to the above-described embodiments, but can be variously modified within the scope of the present invention. For example, in the above-described embodiment, a multilayer resistive element has been exemplified as the resistive element. However, the specific structure of the resistive element according to the present invention is not particularly limited. It may be a resistance element. In the above-described embodiment, the normal pressure firing method is employed as the firing method. However, in the present invention, the firing method is not particularly limited, and a known method, a nitrogen gas pressure firing method, or the like may be used. . Further, in the present invention, the material and shape of the external terminal electrode 24 are not particularly limited.

[0029]

EXAMPLES Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

Example 1 A slurry was prepared with zircon raw material powder having an average particle diameter of 0.7 μm (silicon oxide powder and zirconium oxide powder at a predetermined molar ratio) using an acrylic binder, toluene and ethanol, and the thickness was adjusted to 1 mm by a doctor blade method. Green sheets 12 and 16 for ceramics were produced.

The inner conductor 1 is provided on the surface of the green sheet 12.
The pattern No. 4 was formed by screen printing. Internal guidance
As a conductive paste for printing the body 14, after firing
To W ₂Tungsten carbide and tan at a predetermined molar ratio to become C
Raw material powder containing gustene, ethyl cellulose, α-
A paste made by adding terpineol was used.
The thickness of the conductive pattern was 25 μm.

On the upper and lower surfaces of the green sheet 12 on which the pattern of the internal electrode 14 is printed, two green sheets 14 on which no pattern of the internal electrode 14 is printed are laminated so that the total number of the green sheets 14 is five. The laminate unit 10 was cut into each element. Next, in a nitrogen atmosphere,
The binder was removed at 00 ° C. Thereafter, the cutting element was set in a normal-pressure firing furnace and fired in a nitrogen atmosphere (nitrogen + hydrogen + steam atmosphere) at 1700 ° C. and 250 kg / cm ² . After firing, a resistor element body 22 made of zircon shown in FIG. 1 was obtained. The internal conductor 14 is built in the resistance element main body 22, and a silver electrode containing an active metal is applied to an exposed electrode portion which is an exposed portion thereof, and the applied portion is covered with a nickel external terminal electrode 24. , In vacuum, 92
The resistive element 20 was manufactured by baking at 0 ° C.

Each of the 50 obtained devices was placed in air for 15 days.
Under an environment of 50 ° C., the resistance value between the terminal electrodes 24 was measured before and after the lapse of 5000 hours, and the increase in the resistance value after the lapse of 5000 hours was examined. Table 1 shows the results.
As shown in Table 1, the resistance increase rate was 2%.

[0034]

[Table 1]

Further, by applying a current for 15 seconds between the 50 external electrode terminals 24 and 24 for each of the obtained devices, the temperature of the tip of the device main body is raised to 1500 ° C., and the device is stopped for 15 seconds. A cycle test in which cooling to near was repeated was performed. The number of times at which the resistance value increased by 10% from the initial resistance value (one cycle of temperature rise / fall is regarded as one count) was examined. The initial resistance value is 1 at the first energization.
The resistance value at 500 ° C. was used. The number of samples was 50, and the number of times employed an average value. Table 2 shows the results. In addition, 50,000 times or more are considered as pass. As shown in Table 2, the number of cycles in Example 1 was 1,000,000 times.

[0036]

[Table 2]

Example 2 The procedure of Example 1 was repeated, except that a raw material powder containing a predetermined molar ratio of carbon and tungsten, which became WC after firing, was used as a conductive paste for printing the inner conductor 14.
The resistance element 20 was manufactured.

For each of the 50 obtained devices, the amount of increase in the resistance value after lapse of 5000 hours was examined in the same manner as in Example 1. Table 1 shows the results. As shown in Table 1, the rate of increase in resistance was 1%. The number of cycles was examined in the same manner as in Example 1. Table 2 shows the results. As shown in Table 2, the number of cycles was 1.2 million times.

Example 3 As a conductive paste for printing the inner conductor 14, C was used.
A resistance element 20 was produced in the same manner as in Example 1 except that the raw material powder containing r was used. For each of the 50 obtained devices, the amount of increase in the resistance value after lapse of 5000 hours was examined in the same manner as in Example 1. Table 1 shows the results. As shown in Table 1, the rate of increase in resistance was 5%. Example 1
In the same manner as in the above, the number of cycles was examined. Table 2 shows the results. As shown in Table 2, the number of cycles was 800,000.

Example 4 As a conductive paste for printing the inner conductor 14, M
A resistance element 20 was produced in the same manner as in Example 1 except that a raw material powder containing o was used. For each of the 50 obtained devices, the amount of increase in the resistance value after lapse of 5000 hours was examined in the same manner as in Example 1. Table 1 shows the results. As shown in Table 1, the rate of increase in resistance was 1%. Example 1
In the same manner as in the above, the number of cycles was examined. Table 2 shows the results. As shown in Table 2, the number of cycles was 1.3 million.

COMPARATIVE EXAMPLE 1 Instead of the zircon raw material powder, a silicon oxynitrite raw material powder (mixed powder composed of a silica powder and a silicon nitride powder in a predetermined molar ratio) was used, and the inner conductor 1 was used.
4 as a conductive paste for printing Mo after firing.
A resistance element 20 was produced in the same manner as in Example 1 except that the raw material powder to be Si ₂ was used. For each of the 50 obtained devices, the amount of increase in the resistance value after lapse of 5000 hours was examined in the same manner as in Example 1. Table 1 shows the results. As shown in Table 1, the resistance increase rate was infinite. Also,
The number of cycles was examined in the same manner as in Example 1. Table 2 shows the results. As shown in Table 2, the number of cycles was 70
It was 00 times.

COMPARATIVE EXAMPLE 2 Instead of the zircon raw material powder, a mixed powder obtained by adding yttrium oxide and aluminum oxide to the silicon nitride powder in an amount of 2% by weight each was used, and firing was performed as a conductive paste for printing the inner conductor 14. A resistance element 20 was manufactured in the same manner as in Example 1, except that a raw material powder containing a predetermined molar ratio of carbon and tungsten to become WC later was used.

For each of the 50 obtained devices, the amount of increase in the resistance value after lapse of 5000 hours was examined in the same manner as in Example 1. Table 1 shows the results. As shown in Table 1, the resistance increase rate was infinite. In addition, oxidation of the device was also confirmed. The number of cycles was examined in the same manner as in Example 1. Table 2 shows the results. As shown in Table 2, the number of cycles was 32,000.

As shown in Evaluation Tables 1 and 2, the resistance elements according to Examples 1 to 4 are different from the resistance elements according to Comparative Examples 1 and 2 by 1
It was confirmed that long-term use was possible in a high-temperature environment of 550 ° C., and furthermore, even if the temperature was repeatedly increased and decreased from room temperature to 1500 ° C. or vice versa, it was confirmed that the resistance value fluctuated little.

[0045]

As described above, according to the present invention, 1000 ° C. or higher (preferably 1400 ° C. or higher)
Can be used for a long period of time in a high-temperature environment, and at room temperature to 1000 ° C or higher (preferably 1400 ° C
Even if the temperature is repeatedly increased and decreased by the above-mentioned temperature or vice versa, it is possible to realize a resistance element having a small resistance value variation and excellent durability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a resistance element according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a manufacturing process of the resistance element shown in FIG.

[Explanation of symbols]

 12, 16 ... Green sheet 14 ... Internal conductor 14a ... Extraction electrode part 20 ... Resistor 22 ... Resistor element main body 24 ... External terminal electrode

Claims (2)

[Claims] 1. A resistance element comprising: a resistance element main body made of ceramics containing zircon as a main component; and an internal conductor embedded inside the resistance element main body, wherein the internal conductor is 1700 ° It has a melting point of at least C and a thermal expansion coefficient of 4 × 10 ⁻⁶ / ° C. from room temperature to 800 ° C.
An ~6 × ^{10 -6} / ° C, a specific resistance of 10 ^{- 5} Ω · c
m or less. 2. The method according to claim 1, wherein the inner conductor is selected from the group consisting of tungsten, tungsten carbide, molybdenum, and chromium.
The resistance element according to claim 1, comprising the above conductor.