JP3409902B2 - PTCR element - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a PTCR element.

[0002]

2. Description of the Related Art PTCR characteristics, that is, the Positive Temperature Coefficient of Resistance
At present, BaTiO ₃ -based ceramics, PbTiO ₃ —TiO ₂ -based ceramics, (V, Cr) ₂ O ₃ ceramics, carbon-polymer composite materials, etc. are known as materials exhibiting vity).

The expression of these PTCR characteristics is expressed by BaTi.
For O ₃ -based ceramics and PbTiO ₃ —TiO ₂ -based ceramics, ferroelectric-paraelectric phase transformation (V,
It is believed that for Cr) ₂ O ₃ ceramics it is due to the metal-insulator transition and for carbon-polymer composites it is due to the thermal expansion of the polymer.

[0004]

OBJECT OF THE INVENTION It is an object of the present invention to provide a completely new PTCR element based on an expression mechanism different from the conventional one.

[0005]

Structure of the Invention By the way, as shown in the resistivity temperature characteristics of main metals (see FIG. 1) of the Practical Metal Handbook (published by Nikkan Kogyo Shimbun, October 30, 1937), some of the metals are For example, there are some materials such as Pb, Sn, In, etc., in which the specific resistance thereof rapidly increases when transitioning from solid to liquid at the melting point.

However, in order to apply this phenomenon to a PTCR element, it is difficult to put the metal into practical use because it uses the liquid phase state.

The present invention was made by paying attention to the above matters, and comprises the following inventions (1) to (8). (1) A metal or alloy exhibiting PTCR characteristics is dispersed between the main phases of the metal compound along with the phase transition between the solid phase and the liquid phase, and the specific resistance of the main phase is higher than the specific resistance of the metal or alloy. A PTCR element characterized by being set. (2) The PTCR element according to (1) above, wherein the metal or alloy has a melting point of 1100 ° C. or lower. (3) The metal is Pb, Sn, In, Cs, Al, A
g or Cd, and the alloy is a Pb-Sn alloy, Ag
The PTCR element according to (1) or (2) above, which is a -Pb alloy or a Cd-Pb alloy. (4) The PTCR element according to any one of (1) to (3) above, wherein the compound is one or more of an oxide, a nitride, a silicide, a carbide, a boride and a sulfide. (5) The PTCR element according to (4) above, wherein the oxide is an oxide containing at least one of titanium, zinc, tin, indium, iron, barium, strontium, nickel, manganese, and lead. (6) The PTCR element according to any one of (1) to (5), wherein the electrical resistance of the main phase is 10 ³ Ωm or less. (7) The PTCR element according to (6), wherein the electrical resistance of the main phase is on the order of 10 ^-1 Ωm or more. (8) Content of the metal or alloy is 5 to 50 vol%
The PTCR element according to any one of (1) to (7) above.

[0008]

[0009]

In the present invention, the phenomenon in which the resistivity of a metal or alloy rapidly changes due to the transition between the solid phase and the liquid phase is used to contain the metal or alloy in the main phase which is a compound. The metal or alloy is made to be able to be supported even when it melts into a liquid phase state, whereby a PTCR element based on a completely new expression mechanism of PTCR characteristics can be obtained.

The PTCR element of the present invention is a conventional P
Like the TCR element, it can be used as a self-heating heater such as a thermistor, and the temperature at which the PTCR characteristic is obtained can be selected by selecting the metal itself or designing an alloy with a controlled melting point. Sensors and the like for sensing can be freely obtained.

[0011]

Specific Structure The specific structure of the present invention will be described in detail below.

The PTCR element of the present invention is one in which a metal or an alloy exhibiting PTCR characteristics is dispersed between the main phases which are metal compounds, with the phase transition between the solid phase and the liquid phase.

The above-mentioned compound as the main phase may be any one or more of oxides, nitrides, silicides, carbides, borides and sulfides. As the oxide, titanium,
Oxides containing one or more of zinc, tin, indium, iron, barium, strontium, nickel, manganese and lead, such as titanium oxide (TiO ₂ ), zinc oxide (Zn oxide).
O), tin oxide (SnO ₂ ), indium oxide (In ₂
O ₃ ), iron oxide and its compounds (for example, ferrite), barium titanate (BaTiO ₃ ) and strontium titanate (SrTiO ₃ ), lead titanate (Pb).
TiO ₃ ), etc. are preferably contained, and the nitride may be TiN, TaN, or the like.

As the silicide, carbide, boride or sulfide, MoSi ₂ , WSi ₂ , SiC or B _{4 can be used.}
C, TiB ₂ , CrB ₂ , CdS, Cu ₂ S can be used.

The specific resistance of the main phase is low to some extent, specifically 10 ³ Ωm or less,
It is set higher than the metal or alloy dispersed in the main phase. Specifically, it is preferably 1 × 10 ³ Ωm or less. The lower limit is 1 × 10 ⁻¹ Ωm, more preferably 1 × 10 ⁰ Ω.
m, particularly 1 × 10 ¹ Ωm is preferable. Main phase resistivity is 1
The reason why it is preferably on the order of 0 ³ Ωm or less is that a certain degree of specific resistance is required for use as a heating element or a sensor. Therefore, it is desirable to add an additive to the above oxides or the like in order to reduce the specific resistance. Examples of the additive include Nb, Ta and Sb when the main phase is TiO ₂ , and Al and G when ZnO is the main phase.
It is preferable to select a and In. At this time, the addition amount is
The amount is 0.001 to 10.0 mol%. This is because if it is less than 0.001, the formation of a semiconductor is insufficient and the specific resistance does not sufficiently decrease, and if it exceeds 10.0, the specific resistance increases again.

As the above-mentioned additives, Nb, T
In addition to a, Sb, Al, Ga, and In, V, W, Y, rare earths, Sb, and B can be used depending on the type of oxide of the main phase. The resistivity of the main phase may be measured by preparing a sintered body of the main phase material alone under the same conditions as the actual element.

As described above, the specific resistance of the main phase is set higher than that of the metal or alloy dispersed in the main phase, so that most of the electric current does not flow in the metal or alloy but flows in the main phase. This is because the PTCR characteristic is not exhibited.

The melting point of the main phase is selected to be at least the melting point of the above-mentioned metal or alloy, specifically about 1100 ° C. or higher. This is because if the main phase melts together with the metal, it will no longer function as an element.

The main phase is usually 0.1 μm to 1 m.
It has a grain size of m and can be observed with a scanning electron microscope or the like.

The metal or alloy that can be used in the present invention is a metal or alloy that exhibits PTCR characteristics with the phase transition between the solid phase and the liquid phase. The melting point of such metals is
A material having a melting point lower than that of the main phase is selected. Specifically, it is preferably 1100 ° C. or lower, particularly 800 ° C. or lower. The lower limit of the melting point of this metal or the like is preferably about -50 ° C.

This is because sensing at low temperature is also possible.

The metals mentioned above include Pb, Sn,
It is desirable to use In, Cs, Al, Ag, Cd or the like. Further, as an alloy, Pb with an Sn content of 30 to 90 wt% is used.
It is desirable to use -Sn alloy, Ag-Pb alloy having a Pb content of 10 to 90 wt% or Cd-Pb alloy having a Pb content of 5 to 95 wt%. Other alloys that can be used include Pb-In, Pb-Mn, Pb-Al, and Cd-S.
n, etc.

Incidentally, according to the above-mentioned practical metal handbook, Pb
Then, in the vicinity of the melting point of 327 ° C., the specific resistance rises to 3.7 × 10 ⁻⁵ Ωcm (3.7 × 10 ⁻³ Ω).
m) was about three times 9.5 × 10 ^-5 Ωcm
(9.5 × 10 ⁻³ Ωm), and in Sn, the specific resistance rises near 232 ° C., which is the melting point of Sn.
What was 2.6 × 10 ⁻⁵ Ωcm (2.6 × 10 ⁻³ Ωm) increased to 4.7 × 10 ⁻⁵ Ωcm (4.7 × 10 ⁻³ Ωm).

Depending on the type of metal, it is 10 like Cs.
There are a wide variety of materials, such as those exhibiting a specific resistance rising at a relatively low temperature near 0 ° C. to those having a specific resistance rising at a relatively high temperature near a melting point of 1083 ° C. such as Cu, and moreover, Pb-Sn The melting point can be changed by changing the content ratio of components such as alloys, and the metal or alloy can be freely selected according to the purpose of use.

The above metal or alloy is preferably dispersed in the main phase in the form of metal particles or alloy particles,
The average particle size is preferably about 0.01 to 100 μm. However, the metal particles or the alloy particles may exist in a state of being separated from each other in a particle state, or in a state of being in contact with each other or a state of being fused.

The content of the above metal or alloy is 5 to 50.
It is desirable to be within the range of vol%. This is because if the content is too small, the PTCR characteristics will not be exhibited, and if it is too large, the shape of the sample cannot be retained.

A solid-phase reaction method is generally used for manufacturing the PTCR element of the present invention.

In the production, first, the raw material powder for the main phase and the raw material powder for the metal or alloy are prepared. As the raw material powder for the main phase, it is desirable to prepare a powder of the compound having the composition of the main phase. In the firing of the PTCR element of the present invention, it is necessary to prevent the metal or alloy from being oxidized in order to maintain desired specific resistance and PTCR characteristics, and it is usually performed in a non-oxidizing atmosphere such as Ar gas. Thereby, in the firing step, formation of oxides and the like can be suppressed to a minimum.

The average particle size of the raw material powder for the main phase is from 0.1 to 0.1
10 μm, the average particle size of the metal or alloy raw material powder is
A material having a thickness of about 0.1 to 100 μm is selected.

Mixing is performed using such raw materials. Although the mixing method is not particularly limited, for example, wet mixing with a ball mill or the like together with ethanol, water, hexane or the like is preferable,
Manual mixing may be performed. Next, the mixed material is dried and compression-molded into a predetermined shape. The molding pressure at this time is 100 kg
/ Cm ^{2 to 2} t / cm ² .

Then, for example, in Ar gas, the temperature raising rate is about 50 to 500 ° C./h and the temperature lowering rate is 50 to 500 ° C./h.
The sintering is performed at about 800 to 1400 ° C. for about 30 minutes to 4 hours to obtain a sintered body.

The above desirable firing conditions vary depending on the composition of the material used and the like. Generally, if the temperature is too low or the time is too short, the density of the sintered body is insufficient and the firing is porous, The metal etc. in the bound body will be oxidized later. On the other hand, if the firing temperature is too high or the firing time is too long, the specific resistance at room temperature increases. this is,
It is considered that this is mainly because a part of metal or the like is evaporated.

When firing the PTCR element of the present invention, air may be used as the firing atmosphere as long as it is possible to prevent the oxidation of metals and the like.

It should be noted that it is desirable to add the above-mentioned components for reducing the specific resistance of the main phase to the above-mentioned main phase. Even if such a component is added to the material powder in advance. Alternatively, it may be performed in the material mixing step before the element firing step.

Further, instead of simply mixing the raw material powder of the main phase and the powder of metal or the like, the raw material powder of the main phase, for example, ceramic powder is coated with metal or the like by vapor deposition, sputtering or the like and fired. You may obtain a sintered compact.

The PTCR element of the present invention is used as, for example, a self-controlled heating element, a color television degaussing element, a motor starting element, an overcurrent limiting element, a sensor at a specific temperature, a switching element used at a specific temperature, and the like. It

[0037]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 Raw material powder was used for the main phase and had an average particle size of 1 to ₂ μm TiO _2.
Powder, Pb with an average particle size of 5 to 10 μm for the metal phase
Powder having a melting point of 327 ° C. was used. In addition, TiO ₂
Nb was added in order to accelerate the decrease in the specific resistance. This addition of Nb was performed so that the molar ratio would be (Ti _0.99 Nb _0.01 ). Further, Nb was added in the form of Nb ₂ O ₅ powder, and the average particle size was 1 to 2 μm. These were mixed by the above method, and the resulting mixture powder was mixed with about 10
It was formed into a cylindrical shape of mmφ × 5 mm. This molded body is 1200
The composition x (Pb)-
A sintered body of (100-x) (Ti _0.99 Nb _0.01 ) O ₂ was obtained.

X (Pb)-(100- of the above sintered body
x) (Ti _0.99 Nb _0.01 ) O ₂ was used, and x was changed to 20 and 30 mol% (Pb is about 20 and about 30 vol%) to obtain Samples 1 and 2. From the SEM photograph of the cut surface of Sample 1 in FIG. 5, the dispersed state of Pb (black portion) in the main phase (white portion) was confirmed.

Then, the PTCR characteristics of the obtained sintered body were
It was measured by the following specific resistance temperature characteristic measuring method.

<Specific Resistance Temperature Characteristic Measurement Method> The specific resistance temperature characteristic of the sintered body was measured by using the DC two-terminal method. First, I
An n-Ga electrode was applied on the surface of the sintered body to obtain ohmic contact. Furthermore, the sample was sandwiched with a stainless steel plate to prevent oxidation and evaporation of the electrode due to temperature rise. The measurement was performed by raising and lowering the temperature of the sintered body sample in the air and recording the change in the current value flowing through the sample. The temperature raising rate was 5 ° C./min and the temperature was raised to 350 ° C., and the temperature lowering was the furnace cooling rate. Constant voltage power supply / monitor (Advantest; TR
-6143), an electric field of 5 mV / cm 2 was applied to the sample, the current value was measured, and the specific resistance (ρ) was calculated by the following formula.

[Specific Resistance (ρ) Calculation Formula] ρ = (E / I) × (S / h) where E: Applied voltage I: Current flowing through sample S: Cross-sectional area of sample h: Thickness of sample or more The specific resistance (ρ) at each temperature calculated by was plotted, and the specific resistance temperature characteristic curve of the sintered body having each composition ratio as shown in FIG. 2 was obtained.

As can be seen from FIG. 2, in Samples 1 and 2, the rise of the specific resistance is observed near 327 ° C., which is the melting point of Pb. Particularly, in the 30Pb-based sample 2, the specific resistance sharply rises from about 4.5 × 10 ⁻⁴ Ωm to about 7 × 10 ⁻⁴ Ωm. If this rise of the specific resistance is used, the PTCR used for a sensor at a specific temperature, etc.
The element can be constructed.

Example 2 Next, using the material having the composition of Sample 2, the firing temperature was set to 117.
Samples 3 and 4 were obtained in the same manner as in the above example except that the temperature was changed to 5 ° C and 1225 ° C.

With respect to these samples as well, the specific resistance temperature characteristics were measured in the same manner as in the above example, and the specific resistance temperature characteristic curves shown in FIG. 3 were obtained.

As can be seen from FIG. 3, the firing temperature is 1
In Samples 3 and 4 having a temperature of 175 ° C. or higher, a good rising of the specific resistance is observed near 327 ° C., which is the melting point of Pb, as in Sample 2.

Although the room temperature resistivity of the sample tended to decrease as the firing temperature increased from 1175 ° C., this was due to the reduction of the resistivity due to the action of Nb of TiO _{2 as} the main phase. Is considered to be. When the firing temperature was higher than the predetermined temperature, the room temperature resistivity tended to decrease again. This was due to the increase in the overall resistivity due to the evaporation of Pb rather than the decrease in the resistivity of TiO _2. Is considered to be. Therefore, in designing a PTCR element using the above materials, it is necessary to sufficiently consider the firing conditions.

Example 3 Next, Zn was used instead of Ti, Al was used as an additive for controlling the specific resistance, and the final composition was 20 Pb-80.
(Zn _0.99 Al _0.01 ) O, that is, Pb is about 20 vol%
A molded product was obtained in the same manner as in Example 1 except that the above was adopted. This was fired in an Ar atmosphere at 1050 ° C. for 2 hours to obtain a sintered body of Sample 5.

The specific resistance of the sintered body of Sample 5 was measured to obtain a specific resistance temperature characteristic curve as shown in FIG.
As described above, even if the material of the main phase was changed, as long as Pb was used as the metal, the rise of the specific resistance was observed near 327 ° C., which is the melting point of Pb, and it was found that it can be used as a PTCR element. The main phases (Ti _0.99 Nb _0.01 ) O ₂ and (Zn _0.99 A) of Examples 1 and 3 were used.
With respect to the sintered body of l _0.01 ) 0 as well, the specific resistance at room temperature was measured in the same manner as above, and was 1 × 10 ⁻¹ Ωm to ¹ ×.
It was within the range of 10 ³ Ωm.

In addition to the above, as a metal or the like, a rise in specific resistance is observed at the melting point, that is, a metal other than Pb which exhibits a PTCR characteristic at the phase transition between the solid phase and the liquid phase, for example, Sn,
Even if In, Cs, Al, Ag or Cd or Pb-Sn alloy, Ag-Pb alloy or Cd-Pb alloy was used, the same tendency as in the above-mentioned examples was observed, and it was found that it can be used as a PTCR element. .

Further, as the main phase for supporting a metal or the like, only the oxide is used in the above-mentioned examples, but if the oxide has the same electrical characteristics as those of the oxides in the above-mentioned examples, other oxides are used. The same tendency is observed when the compounds of, i.e., nitrides, silicides, carbides, borides or sulfides are used, and PT
It was found to be used as a CR element.

As described above, the present invention can provide a PTCR element based on a completely new expression mechanism which has never been obtained.

[Brief description of drawings]

FIG. 1 is a graph showing a specific resistance temperature characteristic of a typical metal.

FIG. 2 is a graph showing the specific resistance temperature characteristic of the sample of Example 1.

FIG. 3 is a graph showing the specific resistance temperature characteristic of the sample of Example 2.

FIG. 4 is a graph showing the specific resistance temperature characteristic of the sample of Example 3;

FIG. 5 is a photograph as a substitute for a drawing, which is an SEM photograph of a cross section of Sample 1 of the example of the present invention.

Continuation of the front page (72) Inventor Honma Kibun 1-7-7 Minami Yagiyama, Taihaku-ku, Sendai-shi, Miyagi (72) Inventor Matsudai Dai 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Masatada Yodogawa 1-13-1 Nihonbashi, Chuo-ku, Tokyo, TDK Corporation (56) References JP 62-214601 (JP, A) JP 51-150662 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (10)

(57) [Claims] Between a plurality of main phase consisting of 1. A metal compound, the solid phase - metal or alloy showing a PTCR characteristic with the phase transition between liquid phase Yes dispersed, the main phase, the metal or A melting point above the melting point of the alloy,
With a resistivity higher than that of the metal or alloy.
A PTCR element , which is rain and is formed by a sintering method . Wherein is a melting point of the main phase is 1100 ° C. or higher, PTCR element according to claim 1 melting point of the metal or alloy Ru der 1100 ° C. or less. 3. The PTCR element according to claim 1, wherein the resistivity of the main phase is on the order of 10 ³ Ωm or less. 4. The PTCR element according to claim 3, wherein the resistivity of the main phase is on the order of 10 ⁻¹ Ωm or more. 5. The PTCR element according to claim 1, wherein the compound is one or more of oxides, nitrides, silicides, carbides, borides and sulfides. 6. The oxide is titanium, zinc, tin, indium, iron, barium, strontium, nickel,
The PTCR element according to claim 5, which is an oxide containing at least one of manganese and lead. 7. The oxide is an oxide containing titanium.
Sometimes one or more selected from Nb, Ta and Sb
Is added as an additive, the PTC according to claim 6.
R element. 8. The oxide is an oxide containing zinc.
At least one selected from Al, Ga and In is
The PTCR element according to claim 6, which is added as an additive.
Child. 9. The metal is Pb, Sn, In, Cs, A.
9. The PTCR element according to claim 1, wherein the PTCR element is 1, Ag, or Cd, and the alloy is a Pb-Sn alloy, an Ag-Pb alloy, or a Cd-Pb alloy. 10. The content of the metal or alloy is 5 to 5
It is 0 vol%, The PTCR element in any one of Claim 1 to 9.