JPH11121203A - Manufacture of current-limiting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance long-term reliability by performing stabilizing process, wherein the metal-insulator transition through temperature rising and temperature reduction is repeated beforehand, in the manufacturing method of a current- limiting element using a V2 O3 -based PTC resistor. SOLUTION: In the manufacturing method of a current-limiting element, which comprises vanadium-based ceramics (V1-x Ax )2 O3 [A is at least one kind of element selected from among Al, Cr, Sc or rare-earth element, and 0.001<=x<=0.30] and uses the PTC resistor of a sintered body having positive resistance temperature characteristics, stabilizing process is performed, wherein metal-insulator transition is repeated by temperature rising and falling. Then, as a stabilizing process, the heating cycle wherein the temperature is increased by at least 30 deg.C or more than the temperature, at which the maximum value (ρu max) of the resistivity in temperature rising appears, and the temperature is decreased by 30 deg.C lower than the temperature, at which the maximum value (ρd max) of the resistivity in temperature reduction appears, is repeated. Thus, a PTC resistor, wherein the fluctuations of the PTC characteristics are suppressed can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Vanadium oxide based [(V_1-XA_X)_TwoO _Three , A
Is aluminum, chromium, scandium or lantano
At least one element selected from the group consisting of PTC resistors]
(Hereinafter V_TwoO_ThreeCurrent limiter using PTC resistor)
Of the current limiting element, which has excellent long-term reliability
It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, the capacity of a low-voltage distribution system has been increased, and the overcurrent flowing when a load is short-circuited has also been increased. As a result, the breaker is also required to have a higher breaking capacity. In response to such technical trends, for example, V ₂ O _{3 is} used as an overcurrent protection element for large current and large power.
The use of a current limiting element using a system PTC resistor is expected.

[0003] V ₂ O ₃ -based PTC resistors are 100 to 200
The property of transition from metal to insulator at ℃ (MI transition)
Although the specific resistance is as small as 10 ⁻³ Ω · cm near room temperature, it gradually increases from room temperature to 100 to 150 ° C., and rapidly increases by about two digits near 150 ° C. (this rapidly increasing temperature). Is referred to as a transition temperature), 150 to 200 ° C.
Has a PTC characteristic of peaking at.
At higher temperatures, the resistivity drops again. In addition, this characteristic has a hysteresis in which the peak temperature decreases by about 50 ° C. when the temperature is lowered compared to when the temperature is raised.

[0004] V ₂ O ₃ -based PTC having such properties
By utilizing the fact that the temperature of the resistor increases due to Joule heat when the overcurrent flows and the resistance value increases, the overcurrent can be limited by the increase in resistance. Therefore, an electrode is joined to this to use as a current limiting element. The PTC phenomenon of the V ₂ O ₃ -based PTC resistor is such that the specific resistance increases rapidly due to a change in the band structure at the time of transition. And with the change of the band structure, while the c-axis is contracted 0.6%, since the a-axis to expand 1.0%, the thermal expansion coefficient of the V ₂ O ₃ based PTC resistor, M- This is a non-linear change indicating a negative expansion during the I transition.

[0005]

Incidentally, since the PTC resistor is a sintered body, there is residual stress in the crystal grain boundaries immediately after sintering, and this residual stress has a great effect on the change in characteristics at the time of transition. ing. FIG. 2 shows a sintered PTC resistor,
FIG. 3 is a diagram showing a change in resistance in transition with a single crystal having the same additive amount x. It can be seen that the transition temperature of the sintered PTC resistor is lower than that of the single crystal and the PTC magnification is higher. In addition, the single crystal was cut out from the crystal obtained by solidifying the melt.

[0006] In the sintered PTC resistor, micro-cracks proceed to the crystal grain boundaries due to the contraction and expansion of the c-axis and the a-axis during the above-mentioned transition during the repetition of the transition caused by the electric heating. A phenomenon occurs in which the residual stress is relaxed and approaches the value of the single crystal. That is, the characteristics change greatly (the transition temperature increases and the PTC magnification decreases) as compared to immediately after sintering.

[0007] This decrease in the PTC magnification is mainly due to the decrease in the resistance on the high temperature side. Therefore, even if the overcurrent can be cut off at the initial stage, the coordination with the circuit breaker is lost after several repetitions. There is a problem that it becomes impossible to shut off. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method of manufacturing a current-limiting element having stable characteristics and excellent long-term reliability.

[0008]

[MEANS FOR SOLVING THE PROBLEMS]
Akira is a vanadium-based ceramic (V_1-XA_X)_TwoO _Three 
[A is aluminum, chromium, scandium or run
At least one element selected from the group consisting of
01 ≦ x ≦ 0.30] and has a positive resistance temperature characteristic.
For manufacturing a current limiting element using a sintered PTC resistor
, The metal-insulator transition is repeated
It is assumed that a stabilization process is performed.

FIG. 1 is a diagram showing a change in the PTC magnification at the time of repeated transfer. As described above, in the current limiting element using the V ₂ O ₃ -based PTC resistor, when the transition is repeated, a large change is observed at the initial stage, and the current gradually decreases. Therefore, a PTC resistor in which the fluctuation of the PTC characteristics is suppressed can be obtained by performing the temperature stabilization processing of the temperature rise / fall in advance. This is because the residual stress at the crystal grain boundaries, which is a cause of PTC characteristic fluctuation, is gradually released. As shown in FIG. 1, since the PTC magnification considerably decreases at the beginning of the repetition of the transition, the addition amount x of the element A is set to a slightly higher amount in anticipation of the decrease, and the PTC magnification is increased. (Approximately 100 times) It is preferable to prepare an element. However, if the addition amount x is too large, the transition temperature becomes low and it becomes unsuitable for practical use. Therefore, the larger the addition amount x, the better.

[0010] In particular, the stabilization treatment is at least three times lower than the temperature at which the maximum value (ρ _u max) of the resistivity at the time of temperature rise appears.
The maximum value of resistivity when the temperature rises by 0 ° C or more (ρ _d max)
It is assumed that a thermal cycle of lowering the temperature to 30 ° C. or lower from the temperature at which the temperature occurs appears. This is to allow the transition to proceed completely, so that the characteristics are stabilized.

Further, it is preferable that the heat cycle is performed 10 times or more. By doing so, for example, the change in PTC magnification is 1%
Very stable characteristics can be obtained as described below.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described based on examples. [Embodiment] FIG. 3 is a sectional view of a current limiting device according to an embodiment of the present invention. In FIG. 3, 1 is a PTC resistor,
The dimensions are, for example, φ12 × 20 mm. φ15 × 5mm
And an active metal brazing with a current limiting element element 1 using an Ag-Cu eutectic solder 3. 2 may be a copper (Cu) electrode.

The manufacture of this current limiting element is performed in the following procedure. (1) V ₂ O ₅ or V ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O
₃ The composition after firing is (V _0.996 Cr _0.004 ) ₂ O
_A mixture of ₃ + Fe of 5 wt% is mixed and pulverized for 12 hours by a wet ball mill. (2) The above-mentioned powder was put into a mold and pressed, and the formed body was fired at 1550 ° C. for 1 hour in a hydrogen stream to obtain a PTC.
The resistor 1 is obtained. (3) The Mo electrode 2 is brazed to the PTC resistor 1 through the Ag-Cu eutectic brazing foil 3 by heat treatment at 750 ° C. for 5 minutes in a vacuum to form a current limiting element. (4) As a stabilization treatment, a temperature cycle of 200 ° C. → 0 ° C. was performed 10 times, and a metal-insulator transition was repeatedly performed. For example, the transition temperature (ρ _max ) at the time of temperature rise is 15
In the case of this element having a transition temperature of 0 ° C. and a temperature drop of 100 ° C., 1
A temperature cycle of 80 ° C. or more →→ 70 ° C. or less is effective as a stabilization process. As shown in FIG. 1, when the number of repetitions is 3 to 5 or more, the change rate tends to be saturated. However, 10 or more times are desirable for complete stabilization.

In order to obtain a PTC magnification of several tens of times, it is sufficient to set the additive amount x of Cr to 0.0035. On the other hand, in the current limiting element of this embodiment, the additive amount x of Cr is set to 0.1. As 004, the initial PTC magnification was increased so that a PTC magnification of several tens of times could be secured even after the stabilization processing. Table 1 shows the rate of change of the PTC characteristic (PTC magnification) of the current limiting element A manufactured in this manner and the conventional current limiting element B which has not been subjected to the stabilization process, in a 500 A repetitive energizing test.

[0015]

[Table 1] As is clear from Table 1, a large change in the PTC magnification was observed in the conventional current limiting element B, whereas almost no PTC was found in the current limiting element A according to the present invention even when the repetitive current test was performed.
It was confirmed that there was no change in the TC magnification and stable characteristics were obtained.

[0016]

As described above, according to the present invention,
In a method of manufacturing a current-limiting element using a V ₂ O ₃ -based PTC resistor, a stabilization process in which a metal-insulator transition is repeatedly performed by raising and lowering the temperature in advance to minimize fluctuations in PTC characteristics and long-term reliability Can be obtained as a current limiting element having a significantly improved current limiting element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in PTC magnification when transition of a (V _0.996 Cr _0.004 ) ₂ O ₃ PTC resistor (sintered body) is repeated.

FIG. 2 (V _0.996 Cr _0.004 ) of a sintered body and a single crystal
Comparison chart of PTC characteristics of ₂ O ₃ PTC resistor

FIG. 3 is a sectional view of a current limiting element.

[Explanation of symbols]

 1 PTC resistor 2 Mo electrode 3 Ag-Cu eutectic solder

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Kunihara 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd.

Claims (3)

[Claims] _1. A vanadium oxide-based ceramic (V1 _- XA)
_X ) ₂ O ₃ [A is at least one element selected from the group consisting of aluminum, chromium, scandium and lanthanoids, and is comprised of 0.001 ≦ x ≦ 0.30] and has a positive resistance temperature characteristic. A method of manufacturing a current limiting element using a PTC resistor, characterized in that a stabilization process of repeating a metal-insulator transition by raising and lowering the temperature is performed. 2. The stabilization treatment is to raise the temperature by at least 30 ° C. from the temperature at which the maximum value of the resistivity (ρ _u max) appears at the time of temperature rise, and the maximum value of the resistivity (ρ _d max) at the time of temperature decrease. 2. The method for manufacturing a current limiting element according to claim 1, wherein the thermal cycle is repeated in which the temperature is lowered to 30 ° C. or less from the temperature at which the temperature appears. 3. The method for manufacturing a current limiting element according to claim 2, wherein the thermal cycle is performed 10 times or more.