JPH0816030B2 - Silicon Nitride-Titanium Nitride Composite Conductive Material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silicon nitride-titanium nitride-based composite conductive material, and more specifically, it can be manufactured by a pressureless firing method and has a positive temperature coefficient of resistance. And a silicon nitride-titanium nitride-based composite conductive material that can be used at high temperatures. Here, the pressureless firing method is a firing method excluding a hot pressing method, a hot isostatic pressing (HIP) method, etc., for example, a gas pressure firing method such as a normal pressure firing method or an atmosphere pressure firing method. Say.

The present composite conductive material can be used, for example, as a ceramic heater, especially a far infrared heater used for household heating, various kinds of drying, etc., and a ceramic heater for regenerating a diesel particulate filter used in exhaust gas.

[Prior Art] The following are known as conventional silicon nitride-titanium nitride-based composite conductive materials.

The first is 20 to 75% silicon nitride and titanium nitride.
There is known a composite conductive material having a composition containing 10% by weight or less of one kind or two or more kinds of aluminum oxide, oxides of rare earth metals and the like, by weight% (JP-A-58-9564).
Four). This material has high strength and is suitable for cutting tools.

Second, 30 to 70 parts by volume of silicon nitride, titanium nitride, etc. 30
There is known a composite conductive material obtained by mixing about 70 parts by volume, aluminum oxide or the like with 1 to 10 parts by weight of the above silicon nitride and sintering the mixture (JP-A-60-33265). This material has a positive temperature coefficient of resistance and high mechanical strength.

Thirdly, the heating element is composed of a sintered body containing silicon nitride and conductive ceramics such as titanium nitride as main components, and the ratio of the conductive ceramics when the whole is 100 mol%. Is known to be 10 to 80 mol% (Japanese Patent Laid-Open No. 60-
60983). This ceramic heater has a specific resistance that can be adjusted by aggregate sintering.

Fourthly, it is known that ceramics having insulating properties, for example, silicon nitride or the like is added with titanium nitride or the like so as to have conductivity to enable grinding and drilling with an electric discharge machine (“functional material”). February 1986 issue P71-74).

[Problems to be Solved by the Invention] It is shown that the above-mentioned first and second composite conductive materials of the related art are both hot-pressed products. The third composite conductive material is a sintered body produced by pressureless sintering, but the temperature coefficient of resistance is not mentioned. Further, although the firing method of the fourth conventional composite conductive material is unknown, the temperature coefficient of resistance is not mentioned.

From the above, there is no report that in the above-mentioned conventional composite conductive material, one having a positive temperature coefficient of resistance was obtained by the pressureless sintering, which is relatively simple and has a large degree of freedom in sample shape.

The present invention overcomes the above-mentioned problems, and a silicon nitride and titanium nitride material having a positive temperature coefficient of resistance and favorable characteristics as a heater is a pressureless firing method, which is simple and has a high degree of freedom in sample shape. It is an object to provide a ceramic composite conductive material that can be manufactured by a sintering method and can be used at high temperature.

[Means for Solving the Problems] In the silicon nitride-titanium nitride-based composite conductive material of the present invention, a mixture of silicon nitride and titanium nitride is 100 parts by weight, and the silicon nitride in the mixture is 50 to 74 parts by weight. Part, the titanium nitride is contained in an amount of 26 to 50 parts by weight, and one or more sintering aids selected from rare earth oxides, aluminum oxide, aluminum nitride, magnesium oxide, spinel and silicon dioxide are contained in an amount of 3 to 5 parts by weight.
1 to 20 parts by weight of 20 parts by weight and one or more additives selected from metals of Group VIA of the periodic table and oxides, silicides, and compounds of the metals that become silicides by firing. And a sintered body composed of parts.

As a result of detailed study of the silicon nitride-titanium nitride-based composite conductive material, the present inventor has revealed the following. As the sintering aid, rare earth oxide, alumina, spinel, and aluminum nitride were used.

One of them is to obtain a material having a positive temperature coefficient of resistance by hot pressing.

Second, resistance-temperature characteristics (hereinafter referred to as RT characteristics) are abnormal due to pressureless firing, and high temperature (400-800 ℃)
The temperature coefficient of resistance becomes negative.

Thirdly, the oxidation resistance is poor and it is difficult to use at a high temperature (800 to 1100 ° C) in both the hot pressing method and the pressureless baking method.

It is considered that the cause of the above-mentioned RT characteristic abnormality is the following two points. One of them is that the coefficient of thermal expansion of silicon nitride and titanium nitride is about 3 times larger than that of titanium nitride, so that a conductive path of titanium nitride different from that at low temperature occurs at high temperature, resulting in RT
The characteristic is abnormal (in this case, the temperature coefficient of resistance is not positive). Secondly, titanium nitride tends to aggregate during firing, and this aggregation further deteriorates the RT characteristic.

The rationale for reaching the above-mentioned idea is that, firstly, when a composite conductive material is produced using a material having a close thermal expansion coefficient, the RT characteristic is normal even if the dispersion of the conductive material is poor.
For example, it was confirmed that the composite materials of silicon nitride-tantalum nitride and alumina-titanium nitride all have normal RT characteristics. Secondly, titanium nitride does not easily agglomerate in the hot pressing method and titanium nitride agglomerates in the pressureless firing method.

From the above, in order to normalize the RT characteristics by the pressureless firing method, the titanium nitride particles should be dispersed well, but both silicon nitride and titanium nitride are relatively hard to sinter, so that they are relatively large in amount. It is not easy to avoid agglomeration of titanium nitride due to the liquid phase derived from this sintering auxiliary agent.

As a result of various earnest studies, the present inventor has added rare earth oxides, alumina, magnesia, spinel, etc., which are general sintering aids for silicon nitride, to silicon nitride and titanium nitride, and further added VIA group metals and the like. RT by adding additives
The inventors have found that the characteristics are normal and completed the present invention.

In the present composite conductive material, when the mixing ratio of silicon nitride and titanium nitride is 100 parts by weight and the titanium nitride is less than 26 parts by weight, the specific resistance rapidly increases and the reproducibility is poor, and when it exceeds 50 parts by weight. It is not preferable because it has poor oxidation resistance and is difficult to use at high temperatures.

As the sintering aid used in the present composite conductive material, one or more selected from rare earth oxides, aluminum oxide, aluminum nitride, magnesium oxide, spinel and silicon dioxide are used. The blending amount of these is 3 to 20 parts by weight. If the mixing ratio is less than 3 parts by weight, the sinterability of silicon nitride is not good, and the mixing amount is 20%.
If the amount is more than parts by weight, the high temperature strength decreases, which is not preferable.

As the additive used in the present composite conductive material, one or two or more selected from the group VIA metals, and oxides, silicides and compounds of the metals which become silicides by firing are used. Here, the VIA group metal means chromium (Cr), molybdenum (Mo), and tungsten (W). Of these, Mo is usually used. This is because Mo and W are more effective for dispersion of titanium nitride, and Cr and Mo are more effective for oxidation resistance. Further, as this additive, an oxidizing agent of Mo, for example, molybdenum oxide (referred to as MoO ₃ ) is usually used. This is because the titanium nitride is better dispersed when added in the form of oxide. Examples of the compound that becomes a silicide by firing include molybdic acid and ammonium molybdate. If the amount of these sintering aids is less than 1 part by weight, the RT characteristic becomes abnormal, and if the amount exceeds 20 parts by weight, the strength of the sintered body decreases, which is not preferable.

It should be noted that the blending amount of this additive tends to be small when the blending ratio of titanium nitride is larger than that of silicon nitride.
This is considered to be because the conductive path becomes more stable as the amount of titanium nitride added increases, as is clear from the percolation theory. Therefore, the following test examples (No. 3, 8, 10, 12)
In the case of the MoO ₃ blending ratio of 1.5 parts by weight, the current transient characteristics show anomalous.
When it is increased to 40 to 50 parts by weight or the like, it is considered that the current transient characteristics are normal even if the mixing ratio of MoO ₃ is 1 to 3 parts by weight. Further, in the present invention, metallic Mo can be used as an additive, and in this case, the molecular weight is smaller than that of MoO ₃ and is equivalent to Mo.
From the fact that 1.5 parts by weight of O ₃ corresponds to 1 part by weight of Mo,
It can be said that 1 part by weight is appropriate as the lower limit of this additive.

This composite conductive material has a resistivity of 10 ^-1 Ωcm at room temperature.
In the following, those having a positive temperature coefficient of resistance are preferable. The reason why the specific resistance at room temperature is limited in this way is that the reproducibility of the resistance is poor and the RT characteristic is likely to be abnormal when the specific resistance exceeds 10 ⁻¹ Ω · cm.

As the method for producing the composite conductive material, usually, after mixing a predetermined amount of raw materials in a predetermined mixing ratio, mixing with a ball mill or the like using water or alcohol as a medium, and further adding a small amount of an acrylic binder or the like. Mold into a predetermined shape.
After this is degreased, it is fired by a pressureless firing method or a hot pressing method in a nitrogen atmosphere at a temperature of about 1650 to 1850 ° C. If the firing temperature is less than 1650 ° C, the sintered body will not be densified, and
This is because when the temperature exceeds 1850 ° C., the decomposition of silicon nitride is so severe that the densification is hindered and the strength and oxidation resistance are reduced.

[Effects of the Invention] In the silicon nitride-titanium nitride-based composite conductive material of the present invention, the mixture of silicon nitride and titanium nitride is 100 parts by weight, and the silicon nitride in the mixture is 50 to 74 parts by weight. 26 to 50 parts by weight, 3 to 20 parts by weight of a general sintering aid of silicon nitride such as rare earth oxides, and 1 to 20 parts by weight of additives such as metals of Group VIA of the periodic table. And a sintered body composed of

That is, the present composite conductive material is a material in which a VIA group metal or the like is added in addition to general sintering aids of silicon nitride, titanium nitride, and silicon nitride, whereby the RT characteristic is normal or positive. It has a temperature resistance coefficient. Therefore, the present composite conductive material can be made into a material having a positive temperature coefficient of resistance not only by the hot pressing method but also by the pressureless firing method which has a large degree of freedom in the shape of the sample and is inexpensive. Since the material is a ceramic sintered body, it can be used at high temperatures.

Among these composite conductive materials, the one to which yttria, alumina and MoO ₃ are added is particularly excellent, the RT characteristic is normal, and the oxidation resistance is greatly improved, which is most suitable as a high temperature heater material or conductive material. ing.

The reason why the characteristics of the composite conductive material are improved by adding the additive such as the metal of Group VI A is that (1) titanium nitride can be prevented from agglomerating, and (2) at least molybdenum and the like are present as molybdenum silicide. Therefore, it is considered that this acts as a second conductive phase other than titanium nitride, and it is considered that the presence of this layer improves the oxidation resistance.

[Test Example] Hereinafter, the present invention will be described with reference to test examples.

Test Example 1 This test example examines whether or not MoO ₃ is added.

First of all, the raw materials prepared according to the component composition (No.1 to No.2) shown in Table 1 were used in an alumina ball mill in a poly pot.
Wet mixing was performed in an aqueous system for 15 hours. No. 2 does not contain MoO ₃ and shows a composition not included in the present invention. After adding 1.5% by weight of acrylic binder, vacuum Freeze-drying was performed.

After the mold press the dry powder at a pressure of 400 kgf / cm ^2, performing rubber press under a pressure of 2000kgf / cm ^2, 5 ×
It was molded into a 5 × 50 mm test piece shape.

This molded body was degreased in a nitrogen stream at 550 ° C. for 2 hours, placed in a silicon nitride setter, and fired at 1750 ° C. for 4 hours in an atmosphere of 9 atm of nitrogen to obtain a sintered body.

This sintered body is ground into the shape shown in FIGS. 4 and 5. Incidentally, FIG. 4 shows a plan view of this ground product, and FIG. 5 shows a front view thereof. Then, after electroless nickel plating was applied to the portion A shown in these figures, a silver paste was baked to form an electrode, which was used as a sample for measuring current-carrying characteristics.

The energization characteristics (RT characteristics, voltage (V) -current (I) characteristics) were measured as follows. That is, in the measurement of the RT characteristic, asbestos was sprinkled on the center of the ground product, a platinum wire was sprinkled on the asbestos, and then asbestos was sprinkled on the platinum wire. The platinum wire was heated by being energized, and the resistance value when the grinding object was heated was measured. The temperature was measured with a thermocouple. For the VI characteristic, the current value when a voltage was applied between the electrodes of the ground portion was read. The results are shown in FIGS. According to these figures, No. 1 included in the present invention had a positive temperature coefficient of resistance in the temperature range of room temperature to 1000 ° C., and the VI characteristic was also normal. No. 2 which was not tested had abnormal characteristics.

Test Example 2 In this test example, silicon nitride, titanium nitride, a sintering aid (Y ₂ O ₃ ,
Al ₂ O ₃ ) and MoO ₃ are properly investigated in respective blending ratios.

First, the raw materials prepared to have the component compositions (No. 3 to No. 28) shown in Table 2 were fired and treated in the same manner as in Test Example 1 to produce a sample having the same shape for measuring current-carrying characteristics.

The current-carrying characteristics were measured as follows. That is, a voltage was applied so that the exothermic temperature of the sample due to energization would be 1100-1250 ° C, and the transient characteristics of the current value were measured.

The evaluation was performed based on whether the transient characteristic of this current value shows normal attenuation. The normal RT characteristic means that the temperature resistance coefficient is always positive and has no inflection point from room temperature to exothermic temperature of 1200 ° C., and shows transient characteristics of current value as shown in FIG. . Abnormal RT characteristics mean that the RT characteristics have a negative or inflection point in a certain temperature range, and show transient characteristics of current values as shown in FIGS. 7 and 8.

No.3 to No.28 tests performed in this test example The transient characteristics of the specific resistance and current value of the test product are shown in Table 2 and FIGS. 6 to 8.

According to the above results, the mixture of silicon nitride and titanium nitride is 100 parts by weight, and the silicon nitride of the mixture is 63 parts by weight.
˜70 parts by weight, the titanium nitride content is 30 to 37 parts by weight, and the rare earth oxide and aluminum oxide sintering aid is 8.4 to 13 parts by weight.
By weight, the additive is 3 to 5.6 parts by weight (No.
(Except for 3, 8, 10, and 12), the current transient characteristics are normal. In addition, except for No. 9, the specific resistance is 84 × 10 ^{-3 to} 2.7 × 10 ^-3 Ωcm, which is 10 ^{-1 in} all cases.
It is smaller than Ω · cm.

Test Example 3 In this test example, the type of sintering aid (alumina (No. 29) or spinel (No. 30)) was examined.

The raw materials prepared according to the compositional composition (No. 29, No. 30) shown in Table 3 were used in an alumina ball mill in a poly pot.
Wet mixing was carried out in an aqueous system for an hour. After that, it was dried using a drum dryer.

A wax-based binder was added to this dry powder, and the mixture was kneaded and then extrusion-molded to obtain a pipe-shaped molded body having a size of 10 (outer diameter) × 7 (inner diameter) × 650 (length) mm. After degreasing this molded body in a nitrogen stream at 500 ° C. for 2 hours, it was placed in a silicon nitride setter and fired at 1750 ° C. for 4 hours in an atmosphere of 9 atm of nitrogen to obtain a sintered body.

After removing unnecessary matters by shot blasting on the outer surface of this sintered body, after electroless nickel plating was applied to the portion A in FIG. 9, a silver paste was baked to form an electrode, which was used as a sample for measuring electric current characteristics. did.

The output transient characteristics when AC 100 V was applied to this sample
It is shown in Figure 10. The material of No. 29 showed a normal attenuation of the output transient characteristics and a rapid rise of temperature, and showed favorable characteristics as a heater. That is, the results using yttria and alumina as the sintering aid (No. 29) are superior to those using yttria and spinel (MgAl ₂ O ₄ ) (No. 30).

Test Example 4 In this test example, the oxidation resistance of the sintered body was examined depending on the presence or absence of the MoO ₃ additive and the type of the sintering aid. No. 33 and 35 do not contain MoO ₃ .

Raw materials mixed in the composition No. 31 to No. 35 shown in Table 4 were obtained in the same process as in Test Example 1 to obtain a sintered body. This sintered body was ground into a 3.5 × 3.5 × 42 mm square rod shape, and then its oxidation resistance was examined at 800 ° C. in a still atmosphere. This oxidative test examined oxidative weight gain over time (up to about 610 hours). The results are shown in FIG.

In this test example, particularly yttria, alumina and MoO ₃ were used as sintering aids (No. 32, No. 34)
Is superior in oxidation resistance to other materials (No. 31, No. 33, No. 35) and is therefore extremely excellent as a high temperature heater material. It should be noted that yttrium and spinel are used as sintering aids without MoO ₃ , and the compounding ratio of silicon nitride is relatively small (N o.35) has particularly poor oxidation resistance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between resistance and temperature of a composite conductive material with and without molybdenum oxide. FIG. 2 is a graph showing the voltage-current characteristics of the composite conductive material containing molybdenum oxide. FIG. 3 is a graph showing voltage-current characteristics when molybdenum oxide is not contained. FIG. 4 is a plan view of the sintered body used in Example 1.
FIG. 5 is a front view of the sintered body shown in FIG. FIG. 6 is a graph showing the transient characteristics of current value of No. 6 composite conductive material in Test Example 2. FIG. 7 shows No. 3 in Test Example 2
It is a graph which shows the transient characteristic of the electric current value of (materials other than this invention product). FIG. 8 is a graph showing transient characteristics of the current value of No. 8 composite conductive material (not included in the present invention) in Test Example 2. FIG. 9 is a schematic explanatory diagram of a sintered body produced in Test Example 3. FIG. 10 is a graph showing the output transient characteristics of the composite conductive material (No. 29, 30) manufactured in Test Example 3. FIG. 11 is a graph showing the oxidation resistance of the composite conductive material produced in Test Example 4.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H05B 3/14 B 7512-3K C04B 35/58 102 K (72) Inventor Jun Niwa Kariya city 1-chome Showa-cho, Nippon Denso Co., Ltd. (72) Inventor Naoto Miwa 1-1-chome Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (56) Reference JP 62-140386 (JP, A) ) JP-A-62-78158 (JP, A) JP-A-60-33265 (JP, A) JP-A-60-60983 (JP, A)

Claims (4)

[Claims] 1. A mixture of silicon nitride and titanium is 100 parts by weight, and the mixture contains 50 to 74 parts by weight of silicon nitride.
26-50 parts by weight of the titanium nitride, a rare earth oxide, aluminum oxide, aluminum nitride,
3 to 20 parts by weight of one or more sintering aids selected from magnesium oxide, spinel and silicon dioxide, a metal of Group VIA of the periodic table, and oxides, silicides and 1 to 20 parts by weight of one or two or more additives selected from compounds that become silicides by firing,
A silicon nitride-titanium nitride-based composite conductive material, which is a sintered body made of. 2. A mixture of silicon nitride and titanium nitride is 100.
In the mixture, 63 to 70 parts by weight of the silicon nitride, 30 to 37 parts by weight of the titanium nitride, and 8 to 13 parts by weight of the sintering aid of rare earth oxide and aluminum oxide are included in the mixture. And the additive is 3 to 6 parts by weight.
Item 7. A silicon nitride-titanium nitride-based composite conductive material according to the item. 3. The silicon nitride-titanium nitride-based composite conductive material according to claim 1, which has a specific resistance at room temperature of 10 ⁻¹ Ω · cm or less and a positive temperature coefficient of resistance. 4. The metal of Group VI A of the Periodic Table is molybdenum (Mo).
The silicon nitride-titanium nitride based composite conductive material according to claim 1.