JP3240130B2 - Thermistor material and thermistor element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermistor material and a thermistor element which are effective when applied to a thermistor element having a negative resistance temperature characteristic for a high temperature.

As <Prior Art> carbide sintered boron, in JP-A-62-153166, the B ₄ C as a main component, 1 to 15 wt% of SiC as by-products,
_{ZrB 2, TiB 2, TiC,} B 4 C composite sintered body containing 4～50Wt% at least one member selected from TiN and Ti (CN) is disclosed.

JP-A-63-234763 discloses Ti, Nb, V, Z
A boron carbide sintered body containing 0.5 to 30% by weight of at least one selected from r, Mo, Ta, Hf, W or Si and 0.5 to 5% by weight of carbon and having a density of 85% or more of the theoretical density is disclosed. ing.

 These sintered bodies are used as structural materials.

<Problems to be Solved by the Invention> The present inventors have obtained an idea that the thermistor characteristics can be exhibited by selecting the composition of these boron carbide sintered bodies.

The object of the present invention is a wide temperature range, for example, from room temperature to 1000 ° C.
It is an object of the present invention to provide a thermistor material which has stability even when used at a temperature of 3 ° C. and is easily sealed with glass, and a thermistor element having excellent characteristics by applying this material.

<Means for Solving the Problems> Such an object is achieved by the present invention of the following (1) and (2).

(1) A sintered body using boron carbide as a conductive path forming substance, comprising titanium carbide and / or boride, or titanium carbide and / or boride and silicon carbide, and aluminum oxide, carbide and boron. Titanium carbide and / or boride is added to boron carbide in an amount of 0.1 to 2 wt% in terms of titanium element, and silicon carbide is added to boron carbide in an amount of 0 to silicon carbide in terms of silicon element.
A thermistor material obtained by adding at least 1% by weight of aluminum oxide, carbide and boride to boron carbide in an amount of 0 or less than 1% by weight in terms of aluminum element and adding to boron carbide.

(2) A thermistor element having a thermistor chip formed from the thermistor material of (1).

<Operation> The thermistor material of the present invention has a low B constant.

 Then, a constant B constant is obtained over a wide temperature range.

Therefore, a thermistor element that can be used in a wide temperature range, for example, from room temperature to 1000 ° C. can be realized.

In addition, such a thermistor material is realized only when a predetermined amount of titanium carbide and / or boride is added to boron carbide and sintered.

Such a sintered body composition is included in the composition range disclosed in the above-mentioned publication, but since the publication is focused on the use as a structural material, it is within the composition range of the present invention. No relevant information is shown.

<Specific Configuration of the Invention> Hereinafter, the specific configuration of the present invention will be described in detail.

The thermistor material of the present invention comprises a sintered body containing boron carbide as a conductive path forming substance and further containing titanium carbide and / or boride.

The inclusion of titanium carbide and / or boride provides a constant B constant over a wide temperature range, for example, from room temperature to 1000 ° C.

The boron carbide in the sintered body is represented by the chemical formula B ₄ C, and its composition may be slightly different in stoichiometry.

The average grain size of boron carbide is usually 0.1 to 1
It is in the range of 5 μm.

The titanium in the sintered body is added as titanium carbide and / or titanium boride, but part of titanium carbide may be changed to titanium boride or the like by sintering,
Part of the titanium boride may be changed to titanium carbide or the like.

Titanium carbide and titanium boride are each represented by the chemical formula Ti
Although represented by C and TiB ₂ , the composition may be slightly different in stoichiometry.

The average grain size of the titanium carbide and titanium boride is usually in the range of 0.1 to 10 μm.

The boron carbide exhibits a thermistor characteristic by forming a conductive path, and has stable and good thermistor characteristics over a wide range of room temperature to 1000 ° C. by addition of titanium carbide or titanium boride.

The composition in the following description is represented by the weight percentage obtained by chemically analyzing the sintered body.

The content of the titanium compound such as titanium carbide and titanium boride with respect to boron carbide is 0.1 to 2% by weight, particularly preferably 0.5 to 1% by weight in terms of element.

If the content exceeds 2% by weight, a constant B constant cannot be obtained in a wide temperature range, for example, from room temperature to 1000 ° C.

If the amount is too small, a wide temperature range, for example, from room temperature to
Stable thermistor characteristics cannot be obtained at 1000 ° C.

The thermistor material of the present invention further includes silicon carbide (Si
Preferably, C) is contained.

Silicon carbide is added as a sintering aid, and a part thereof may be changed to silicon boride (SiB ₂ ) by sintering. These may be stoichiometrically deviated in their composition to some extent.

The average grain size of silicon carbide and silicon boride is usually in the range of 0.1 to 10 μm.

The content of silicon compounds such as silicon carbide and silicon boride with respect to boron carbide is 1 wt% in terms of silicon element.
It is preferably less than 0.1, especially 0.1 to 0.5.

The thermistor material of the present invention preferably contains aluminum carbide (Al ₄ C ₃ ) and / or boride (AlB ₂ ) instead of or in addition to silicon carbide.

Aluminum carbide (Al ₄ C ₃ ) Aluminum boride (AlB
₂ ) is added as a sintering aid, and part of aluminum carbide may be changed to aluminum boride or the like and part of aluminum boride may be changed to aluminum carbide or the like by sintering. These may be stoichiometrically deviated in their composition to some extent.

The average grain diameter of aluminum carbide, aluminum boride and the like is usually in the range of 0.1 to 10 μm.

Further, the content of aluminum compounds such as aluminum carbide and aluminum boride with respect to boron carbide is preferably less than 1 wt%, particularly preferably 0.1 to 0.5 in terms of aluminum element.

Their presence can be confirmed with an analytical electron microscope, and their contents may be measured by quantitative analysis using an X-ray diffraction method.

In the thermistor material, B, Ti, Si, Al
, Etc., may be contained.

This is because firing in an N ₂ atmosphere may include BN, TiN, Si ₃ N ₄ , AlN, and the like.

The above-mentioned subcomponent may be contained as a simple metal, a compound, or a composite of these.

The sum of these subcomponents is calculated as elemental
It is preferably at most 1 wt%. Note that TiN, Si ₃ N ₄ and AlN are preferably within the above-mentioned ranges.

When these subcomponents in the sintered body are contained as compounds, their compositions may be stoichiometrically slightly different in composition.

The average grain size of the subcomponent is usually in the range of 1 to 5 μm in the case of a simple metal, and is usually in the range of 0.1 to 5 μm in the case of a compound.

 Next, a method for producing the thermistor material of the present invention will be described.

Predetermined amounts of a raw material powder of boron carbide and a titanium carbide powder and / or a titanium boride powder are prepared, and a solvent such as ethanol or acetone is added thereto and wet-mixed by a ball mill or the like.

As a raw material powder of boron carbide (B ₄ C), a powder having an average particle diameter of 0.5 to 10 μm and a purity of 97 wt% or more is generally used.

As the raw material powder of boron carbide, besides boron carbide powder, a raw material powder of carbon and a raw material powder of boron may be used, or these may be used in combination.

As the powder of titanium carbide (TiC) or titanium boride (TiB ₂ ), powder having an average particle diameter of 0.5 to 5 μm and a purity of 98% or more is generally used.

In the present invention, titanium carbide and / or titanium boride is added to boron carbide in an amount of 2% by weight or less, more preferably 0.1 to 2% by weight, particularly preferably 0.5 to 1% by weight in terms of titanium element.

Then, it is preferable to further add silicon carbide (SiC) as a sintering aid.

The addition amount of silicon carbide is preferably less than 1 wt%, more preferably 0.1 to 0.5 wt%, in terms of silicon element, based on boron carbide.

When the above range is exceeded, the resistance value of the thermistor material tends to change with time.

 However, when the amount is too small, sintering is difficult.

In addition to silicon carbide, or in addition to silicon carbide, aluminum carbide (Al ₄ C ₃ ), aluminum boride (AlB ₂ ), and aluminum oxide (Al ₂ O ₃ )
It is preferable to add one or more of ₃ ).

The amount of addition is based on aluminum element conversion with respect to boron carbide.
It is preferably less than 1 wt%, more preferably 0.1 wt% or more and less than 1 wt%, particularly preferably 0.1 to 0.5 wt%.

When the above range is exceeded, the resistance value of the thermistor material tends to change with time.

 However, when the amount is too small, sintering is difficult.

The aluminum oxide is changed to aluminum carbide, aluminum boride, or the like by sintering, but a part of the aluminum oxide may remain in the form of aluminum oxide.

The amount of the solvent is about 100 to 120% by weight of the powder. If necessary, a dispersant or the like may be further added.

Thereafter, the above mixture is pressure-formed at room temperature, and is subjected to a normal pressure sintering method, a hot press (HP) sintering method, a hot isostatic pressure (HIP) method or the like in an oxygen atmosphere or a non-oxidizing atmosphere. The compact is sintered and allowed to cool to obtain a thermistor material.

The pressure at the time of pressure molding is about 500 to 2000 kg / cm ² .

The non-oxidizing atmosphere at the time of sintering may be an inert gas such as N ₂ , Ar, He, H, CO, various hydrocarbons, etc., or a mixed atmosphere thereof, or may be various things such as vacuum. .

In the case of the normal pressure sintering method, the atmospheric pressure is sufficient, and the sintering temperature is 1600 to
2200 ° C, especially 1800-2100 ° C, more preferably 1950-2050
Effective at ° C.

When the temperature is lower than 1600 ° C., the powder is not sufficiently densified even after sintering for a long time. When the temperature is higher than 2200 ° C., the surface of the sintered body becomes porous due to sublimation or the like.

 The sintering time is usually 0.5 to 20 hours.

In the case of the HP sintering method, the pressing pressure is 150 to 250 kg / cm ² , and the sintering temperature is 1500 to 2100 ° C, particularly 1600 to 2050 ° C, and more preferably 1900 to 2000 ° C.

If the temperature is lower than 1500 ° C, a dense sintered body cannot be obtained,
If the temperature is higher than 2100 ° C., abnormal grain growth occurs, and the grain size becomes non-uniform.

 The sintering time is generally between 1 and 30 hours.

In the case of the HIP sintering method, a green compact of the raw material powder is pre-sintered in an oxygen atmosphere or a non-oxidizing atmosphere (for example, in a vacuum to 1200 ° C., and thereafter preferably in an Ar atmosphere),
Next, the pre-sintered body is sintered in a HIP furnace. The pre-sintering temperature is preferably 1600 to 1800 ° C., and the time is preferably 1 to 50 hours.

The sintering temperature in the HIP method is 1500 to 1900 ° C., the sintering time is 1 to 50 hours, the pressure is 1000 to 1500 kg / cm ² , and the sintering may be performed in an oxygen atmosphere or an inert atmosphere such as Ar.

In this case, at room temperature, oxygen gas, Ar gas, etc. should be 300 ~ 400kg / c
Pressurize to m ² and then apply pressure by heating as described above.

The thermistor material thus produced has a resistivity ρ
It is 10 ³ to 10 ⁶ Ω · cm at 25 ° C., and the thermistor constant B is almost constant from room temperature to 1000 ° C. The value of the thermistor constant B is also 1000-2000K at 25-500 ° C.

Further, there is almost no positional variation in the resistance value or the resistivity.

In addition, there is almost no change in resistance even when used or stored in a temperature range of 25 to 1000 ° C.

The thermistor material produced as described above is applied to the thermistor element of the present invention as a thermistor chip.

As the thermistor element of the present invention, a so-called glass-sealed thermistor element is particularly preferred.

In such a glass-sealed thermistor element 1, for example, as shown in FIG. 1, a pair of electrode layers 33 and 35 are formed on a thermistor chip 11, and a lead body 4 is formed on the electrode layers 33 and 35.
3, 45 are connected, and this is sealed with glass 5.

Alternatively, two lead bodies may be connected to each of the pair of electrode layers 33 and 35 to form a four-terminal structure.

In the case of a thermistor element having a four-terminal structure, the resistance of the thermistor chip can be accurately measured excluding the resistance of the lead body, so that a wide temperature range can be measured. In particular, it is effective at a high temperature where the resistance value is low.

There is no particular limitation on the dimensions of the thermistor chip.
The length is about 0.5 to 1.0 mm, the width is about 0.5 to 1.0 mm, and the thickness is about 0.5 to 1.0 mm.

Various thermistor elements are described in detail in JP-A-64-64202.

<Example> Hereinafter, the present invention will be described in detail with reference to specific examples of the present invention.

Example 1 Preparation and Measurement of Sample of the Present Invention The following starting materials were weighed at the ratios shown in Table 1, and wet-mixed with acetone in a ball mill for 20 hours. The average particle size is a value measured by observation with an electron microscope.

・ B ₄ C (purity 98 wt% or more) Average particle size: 2 μm ・ TiC (Purity 98 wt% or more) Average particle size: 2 μm ・ TiB ₂ (Purity 98 wt% or more) Average particle size: 3 μm ・ SiC (Purity 98 wt%) %) Average particle size: 1 μm, ・ Al ₄ C ₃ (purity 98 wt% or more) Average particle size: 2 μm, ・ NbC (purity 98 wt% or more) Average particle size: 3 μm The mixed slurry was dried and granulated and filled in a graphite mold having an inner diameter of 77 mm.

This was subjected to hot press sintering at a press pressure of 200 to 300 kg / cm ² in an Ar atmosphere.

The firing conditions were a firing temperature of about 1980 ° C. and a holding time of about 2 hours. After cooling, a sintered body of 50 × 50 × 0.5 mm was obtained.

Observation of the obtained sintered body by transmission electron microscopy and X-ray fluorescence diffraction revealed that TiC, NbC, SiC, and a part of Al ₄ C _{3 changed to} TiB ₂ , NbB ₂ , SiB ₂ , AlB ₂ etc. And part of TiB ₂ is Ti
It had changed to C etc.

A 3.5 μm thick Ni-B electrode layer was formed on both surfaces of the obtained composite sintered body by electroless plating to form a wafer.

The obtained wafer was cut into a square having a side of 0.75 × 0.75 × 0.5 mm with a diamond blade using an outer peripheral slicing machine to obtain a thermistor chip.

A Kovar lead wire having a diameter of 0.3 mm and a length of 65 mm is connected to each of the two electrode layers of the thermistor chip.
They were connected one by one by a parallel gap welding method (four-terminal structure).

Next, it was inserted into a borosilicate glass having a diameter of 2.5 mm and a length of 4 mm, and sealed at 850 ° C. in an Ar gas atmosphere. This was subjected to an aging treatment to produce a thermistor element sample as shown in FIG.

Then, the thermistor characteristics of the chip were measured, and a temperature range ΔT in which the thermistor constant B was in a range of ± 10% was obtained.

Further, the resistivity ρ at 25 ° C. and the thermistor constant B at 25 to 500 ° C. were determined.

In addition, for these, the initial and 500 ℃ 500
The change in resistance after storage for 0 hours was measured.

The evaluation was calculated as (ΔR / ₀ ) × 100 (%), where ΔR is the change in resistance and _R0 is the initial resistance.

 The results are as shown in Table 2.

From the results shown in Table 2, the effect of the present invention is clear.

In addition, using the sample No. 2 to No. 5 of the present invention, a lead body,
When a thermistor element was manufactured by changing the sealing glass, ΔT was about 25 to 1000 ° C.

<Effect of the Invention> The thermistor material of the present invention has a low B constant, and a constant B constant can be obtained in a wide temperature range, for example, from room temperature to 1000 ° C.

And, because boron carbide occupies most of the sintered body,
The positional variation of the resistance value distribution generated in the sintered wafer is extremely small.

When such a thermistor material is applied to a glass-sealed thermistor element, a thermistor element having a wide applicable temperature range and uniform electric resistance can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the thermistor element of the present invention. DESCRIPTION OF SYMBOLS 1 ... Thermistor element 5 ... Glass 11 ... Thermistor chip 33, 35 ... Electrode layer 43, 45 ... Lead body

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-153166 (JP, A) JP-A-64-64202 (JP, A)

Claims (2)

(57) [Claims] 1. A sintered body using boron carbide as a conductive path forming substance, comprising titanium carbide and / or boride, or titanium carbide and / or boride and silicon carbide and aluminum oxide and carbide. And one or more borides, and adding a carbide and / or boride of titanium to boron carbide in an amount of 0.1 to 2 wt% in terms of titanium element, and adding silicon carbide and 0 in terms of boron element in terms of boron carbide. A thermistor material obtained by adding less than 1 wt% of aluminum oxide, carbide and boride and adding 0 to less than 1 wt% of boron carbide in terms of aluminum element. 2. A thermistor element having a thermistor chip formed from the thermistor material according to claim 1.