JPH04129189A - Ceramic heater - Google Patents

Abstract

PURPOSE:To prolong a lifetime of ceramic heater by composing a surface layer out of composite ceramics including the ceramics of two kinds or more and making a coefficient of thermal expansion of the composite ceramics a larger value than that of insulating ceramics. CONSTITUTION:To make a heater formed body, a heater electrifying circuit consisting of a heating part 4 and a conductive part 5 is printed on a green sheet 2 for an insulating base material. A layer of composite ceramics 1 consisting of silicon carbide and zirconium boride is formed on the whole surface or in part of both upper and lower surfaces of the formed body. At this time, the ceramics 1 is made to have a coefficient of thermal expansion slightly larger than that of the insulating ceramics green sheet material 2. The formation of the ceramics 1 layer consisting of the silicon carbide and zirconium boride on the surface of the heater formed body raises heat resistance temperature of the heater.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention improves oxidation resistance and high-temperature strength, can withstand rapid heating and cooling, and maintains the temperature of the electrode part even when the heat-generating part reaches a high temperature. This invention relates to a ceramic heater that suppresses rise as much as possible.

[Conventional technology]

The conventional ceramic heater is disclosed in Japanese Patent Application Laid-open No. 57-1]-48.
As described in Publication No. 8, the surface layer near the heat generating part is made of the same insulating ceramic as the inside, and no consideration has been given to controlling the coefficient of thermal expansion between the main constituent materials. Furthermore, there is no example in which the material composition of the heat generating part at the tip and the conductive part other than the total heat part is changed.

[Problem to be solved by the invention]

The above conventional technology does not take into consideration placing a material with high high temperature strength near the surface of the heater or controlling the coefficient of thermal expansion of the main constituent materials, so it is not used at high temperatures or is heated or cooled rapidly. There was a problem that the product would be damaged and its lifespan would be shortened. In addition, since the composition of the heat generating part and the conductive part are the same, the temperature of the conductive part increases significantly, and if heating and cooling are repeated,
There have been problems in that cracks occur in the vicinity of the electrodes, and the resistance at the joints between the electrodes and the lead wires increases, causing the lead wires to break due to oxidation or heat generation.

An object of the present invention is to provide a ceramic heater that has both high high-temperature strength and thermal shock resistance that can withstand rapid heating and cooling, and has a long life.

[Means to solve the problem]

The above problem is solved by a ceramic heater in which a heat generating part and a conductive part made of a conductive material are built into an insulating ceramic, in which a surface layer adjacent to the insulating ceramic is
This is achieved by constructing a composite ceramic containing two or more types of ceramics, and making the coefficient of thermal expansion of the composite ceramic larger than the coefficient of thermal expansion of the insulating ceramic.

The above object is also achieved by the ceramic heater according to claim 1, wherein the electrical resistivity of the conductive material constituting the conductive part is smaller than the electrical resistivity of the conductive material constituting the heat generating part.

The above problem also arises when the conductive material is IVa in the periodic table.
The present invention is also achieved by the ceramic heater according to claim 1 or 2, which comprises one or more compounds among borides, carbides, silicides, and nitrides of group VIa elements.

The above issues are also the same. The conductive material is silicon carbide.

One or more compounds of silicon nitride, aluminum nitride, aluminum oxide, zirconium oxide and one of borides, carbides, silicides, and nitrides of elements of group IVa, Va, or VIa in the periodic table This can also be achieved by the ceramic heater according to any one of claims 1 to 3, which comprises the above-mentioned compounds.

The above object is also achieved by the ceramic heater according to claim 1 or 2, wherein the conductive material is made of a heat-resistant metal such as tungsten, molybdenum, tantalum, or the like.

The above object is also achieved by the ceramic heater according to claim 1 or 2, wherein the insulating ceramic is made of one or more compounds among silicon nitride, sialon, aluminum nitride, boron nitride, aluminum oxide, and zirconium oxide. be done.

The above issues also arise when composite ceramics contain silicon carbide,
One or more compounds of silicon nitride, aluminum nitride, aluminum oxide, zirconium oxide and one of borides, carbides, silicides, and nitrides of elements of group IVa, Va, or VIa in the periodic table This can also be achieved by the ceramic heater according to claim 1 or 2, which comprises the above-mentioned compounds.

The above object is also achieved by the ceramic heater according to any one of claims 1 to 7, wherein compressive stress is applied to the insulating ceramic.

The above-mentioned object is further achieved by the ceramic heater according to any one of claims 1 to 8, characterized in that the current-carrying circuit such as the heat-generating portion and the conductive portion is formed by a printing method.

[Effect]

Borides and carbides of IVa, Va, and VIa group elements;
Nitride and silicide have a high melting point and excellent heat resistance, but have a rather large coefficient of thermal expansion and poor oxidation resistance.

By mixing and sintering silicon carbide, silicon nitride, sialon, zirconium oxide, etc., which do not easily react with these compounds, have a small coefficient of thermal expansion, high strength at high temperatures, and excellent oxidation resistance and thermal shock resistance. The fact that composite ceramics with high high temperature strength, oxidation resistance, and thermal shock resistance can be obtained is shown in the literature of Jimbo et al. (Advan-
ced CeraIIlic Materials, v
ol, 1. Nn4. Oct, 1986.341-345
An example can be found on page ).

The coefficient of thermal expansion of the composite ceramic can be controlled by changing the mixing amount of the borides, carbides, nitrides, and silicides of the IVa, Va, and VIa group elements.

A boride of the above IVa, Va, and VIa group elements.

Carbides, nitrides, and silicides are also low-resistance materials with extremely good conductivity, so the mixed powder of the above composite ceramics is made into a paste, and aluminum nitride, boron nitride, silicon nitride, sialon, aluminum oxide, zirconium oxide, etc. Alternatively, a heat generating and conductive circuit is printed using the paste on the surface of a green sheet made of insulating ceramics, and the #@marginal green sheet is laminated thereon, or the insulating ceramic powder is laminated thereon. It may be laminated. At this time, by arranging composite ceramics having a coefficient of thermal expansion slightly larger than that of the insulating ceramic green sheet material on the upper and lower surfaces of the heater, a sintered body is formed by sintering the insulating green sheet and the composite ceramic at the same time. Compressive stress acts on the insulating ceramic inside after sintering.

Furthermore, by configuring the conductive part with a material that has a lower resistivity than the heat generating part, even if the heat generating part at the tip reaches a high temperature, the amount of heat generated in the conductive part is minimized and the temperature rise near the electrode part is reduced. Ru.

The composite ceramic surface is electrically insulated from the internal heat-generating and conductive parts via insulating ceramics, so even if carbon or other soot adheres to the surface while the heater is in use, it will not generate heat or conduct electricity. The circuit will not be shorted.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

<Example 1> For 90 weight percent of aluminum nitride powder with an average particle size of 3 to 4 μm, in order to improve high-temperature insulation, an average particle size of about 2 μm was used.
10 weight percent of micron boron nitride powder was added. To 100% by weight of this mixed powder, 6% by weight of polyvinyl butyral was added, and trichlorethylene was further added to prepare a slurry. This slurry was cast by a doctor blade method to produce a green sheet for an insulating base material having a thickness of 1.2 square meters, and a disc-shaped sheet 2 having a diameter of 170 m was cut from it.

55% by volume of silicon carbide powder with an average particle size of about 3 μm, and 45% by volume of tantalum boride powder, also with an average particle size of 0.5 to 0.7 μm.
Volume percent of powder mixed with an average particle size of 0.5 μm
A conductive paste for a heat generating part was prepared by adding 2% by weight of aluminum oxide to silicon carbide, and further adding appropriate amounts of ethyl cellulose and terpineol. Similarly, instead of tantalum boride, the average particle size is 3 to 5μ.
A conductive paste for the conductive part was prepared by adding 36 volume percent of zirconium boride of m to 64 volume percent of silicon carbide. As can be seen from FIG. 6, the resistivity of the material of the paste component for the conductive part is about one order of magnitude lower than that of the material of the paste component for the heat generating part.

Using these conductive pastes and screen meshes, as shown in FIG.
A heater energizing circuit consisting of a .mu.m conductive section 5 was printed. At the ends of the printed circuit, electrodes 3 are cut from a conductive green sheet of 68 volume percent silicon carbide and 32 volume percent zirconium boride, prepared similarly to the aluminum nitride green sheet.
was placed. Furthermore, the green sheet for the insulating base material or a mixed powder of aluminum nitride and boron nitride having the same composition ratio was laminated and pressed on top of the green sheet to produce a heater molded body. At this time, as shown in FIGS. 1, 3, and 4A, a composite ceramic 1 consisting of 68 volume percent silicon carbide and 32 volume percent zirconium boride is applied to the entire or part of the upper and lower surfaces of the molded body. A layer was formed. This is because, as shown in FIG. 7, the coefficients of thermal expansion of this composite ceramic and aluminum nitride are almost equal.

This molded body was charged into a hot press equipment and heated to 2,100°C at 60°C under a pressure of 300 kg/d in a vacuum.
It was held for a minute and was sintered densely. The amount of raw material powder was adjusted so that the sintered body had a diameter of 170 m and a thickness of about 3 mm. From this sintered body, as shown in FIGS.
A heater approximately 3 mm thick was cut out. Figure 4B shows the fourth
The arrangement of the electrodes 3 is shown by removing the portion indicated by line BB' in Figure A.

FIG. 5 shows the temperature distribution along the center line 7 of the surface when this heater is energized and the vicinity of the tip (the side far from the electrode 3) is heated to about 1,100°C. The material of the conductive part 5 is changed to a low resistivity material different from that of the heat generating part 4, and the surface temperature near the electrode part is increased from about 500°C to about 100°C by about 1
It has fallen to 75. Note that this heater has a tip temperature of 1
, resistance continues to increase with temperature up to around 250℃,
When this temperature is exceeded, the resistance begins to decrease and thermal runaway occurs.

The temperature near the tip of this heater (the hottest part) is 1°200°C.
When heated (approximately 1,000 times), 10
Eight of the books were sound, but cracks occurred in two.

On the other hand, in a heater made of aluminum nitride, a heat generating part, and a conductive part without forming a layer of composite ceramics 1 on the surface,
When the vicinity of the tip was heated to about 1,000'C two to three times, cracks occurred in the aluminum nitride insulating layer of the heat generating part, and the tip broke.

From this, it has become clear that forming a layer of composite ceramics made of silicon carbide and zirconium boride on the surface improves the heat resistance temperature of the heater.Compared to aluminum nitride, the thermal expansion coefficient is approximately ri0
When silicon carbide, which is small in size, was laminated on the surface, countless cracks occurred in the aluminum nitride, which is an insulating material.
If a material with a small coefficient of thermal expansion is placed on the surface of the heater, a healthy sintered body cannot be produced.

<Example 2> In order to make the coefficient of thermal expansion of the composite ceramic of the surface layer larger than that of aluminum nitride, which is an insulating material, as shown in Fig. 6, zirconium boride was mixed in the composite ceramic of the surface layer. The amount was increased from 32 to 36 volume percent. Additionally, to ensure that the resistance continues to increase up to higher temperatures, the amount of tantalum boride in the heat generating paste was increased from 45 to 7 volume percent. Otherwise, a heater was manufactured in the same manner as in Example 1, and the temperature was 1°4.
No cracking occurred even after repeated heating to around 00°C. This is because the coefficient of thermal expansion of composite ceramics is larger than that of aluminum nitride, so compressive stress acts on the aluminum nitride of the sintered body, making it difficult to damage the aluminum nitride even when the temperature rises rapidly. As a result, the heat resistance of the heater is improved. Note that when the surface temperature of the tip heating part is 1,400°C, the temperature near the electrode part is about 300°C, which is about 115°C at the tip.
The resistance continued to increase up to 400°C, and thermal runaway did not occur.

<Example 3> 6 weight percent of polyvinyl butyral was added to aluminum nitride powder having an average particle size of about 3 μm, and trichlorethylene was further added to prepare a slurry. This slurry was cast by a doctor blade method to produce a 1.2 mm thick green sheet for an insulating base material, and a disc-shaped sheet with a diameter of 170 mm was cut from it.

For 100% by weight of a powder mixed with 40% by volume of silicon carbide powder with an average particle size of about 3 μm and 60% by volume of titanium carbide powder with an average particle size of 4 to 6 μm,
Similarly, a conductive paste for a heat generating part was prepared by adding approximately 1 weight percent of 0.5 μm aluminum nitride powder and appropriate amounts of ethyl cellulose and butyl calpitol. Similarly, a conductive paste for a conductive part was prepared by adding 60 volume percent of tungsten carbide powder with an average particle size of 3 to 5 μm instead of titanium carbide to 40 volume percent of silicon carbide powder.

Using these conductive pastes and screen meshes, as shown in FIG.
A heater energizing circuit consisting of a .mu.m conductive section 5 was printed. At the ends of the printed circuit, conductive green sheet electrodes 3 made of 60 volume percent silicon carbide and 40 volume percent tungsten carbide, prepared in the same way as for the aluminum nitride green sheets, were placed.

Furthermore, the aluminum nitride powder for the insulating base material was laminated and pressed on top of the aluminum nitride powder to produce a molded body of a heater. At this time, in the same manner as in Example 1, a composite ceramic consisting of 64 volume percent silicon carbide and 36 volume percent zirconium boride was laminated on the entire or part of the bottom and surface of the molded body.

This molded body was charged into a hot press apparatus, and a heater was produced in the same manner as in Example 1.

Even when this heater was repeatedly heated to around 1,350° C., no cracking or thermal runaway occurred, and it was sound.

<Example 4> A slurry was prepared by adding 6 weight percent of polyvinyl butyral to aluminum nitride powder having an average particle size of about 3 μm, and further adding trichlorethylene. A green sheet for an insulating base material having a thickness of 1.2 mm was prepared by casting this slurry by a doctor blade method, and a disc-shaped sheet having a diameter of 170 am was cut from the green sheet.

9 weight percent of yttrium oxide (y2o3) and 4 weight percent of oxide were added to 100 parts by weight of a powder that was a mixture of 40 volume percent of silicon nitride powder with an average particle size of about 0.7 μm and 60 volume percent of titanium nitride powder with an average particle size of 2 μm. A conductive paste for a heat generating part was prepared by adding aluminum and appropriate amounts of ethyl cellulose and terpineol. Similarly, 50 volume percent of tantalum nitride with an average particle size of about 3 μm was added instead of titanium nitride to 50 volume percent of silicon nitride powder with an average particle size of about 0.7 μm to prepare a conductive paste for conductive parts. Created. The material of the paste component for the conductive part has a resistivity of about 1 order compared to the material of the paste component for the heat generating part.

Using these conductive pastes and screen mesh, as shown in FIG.
A heater energization circuit consisting of a .mu.m conductive section 5 was printed. At the ends of the printed circuit were placed electrodes 3 cut from a conductive green sheet made of 50 volume percent silicon nitride and 50 volume percent titanium nitride, prepared in the same way as for the aluminum nitride green sheets. . And on top of that, said! ! 1! ! Green sheets for m-based substrates or aluminum nitride powder laminated/
A heater molded body was produced by pressing. At this time, as shown in FIGS. 1, 3, and 4A, a composite ceramic layer consisting of 50 volume percent titanium nitride was formed on all or part of the upper and lower surfaces of the compact.

The thermal expansion coefficient of this composite ceramic is larger than that of aluminum nitride.

This molded body was charged into a hot press device, and after being evacuated at room temperature, it was heated to 1,75
It was kept at 0° C. for 60 minutes and sintered densely. A heater having a width of about 8I, a length of about 80 nn+, and a thickness of about 3I as shown in FIGS. 1, 3, and 4A was cut out of this sintered body.

Even when this heater was repeatedly heated to around 1,300°C, no damage occurred.

<Example 5> A slurry was prepared by adding 10 weight percent of polyvinyl butyral to aluminum oxide powder having an average particle size of 1 μm, and further adding trichlorethylene. This slurry was casted using the doctor blade method to a thickness of 1.2m. ! A green sheet for the edged substrate was prepared, and a disc-shaped sheet with a diameter of 170 mm was cut from it.

To 100 parts by weight of a mixed powder of 40 volume percent aluminum oxide powder with an average particle size of about 2 μm and 60 volume percent tantalum boride powder with an average particle size of 3 μm, 1 weight percent aluminum oxide was added, and appropriate amounts of ethyl cellulose and terpineol were added. A conductive paste for the heat generating part was prepared. Similarly, a conductive paste for a conductive part was prepared by adding 50 volume percent of zirconium boride powder having an average particle size of 3 to 5 μm instead of tantalum boride.

Using these conductive pastes and screen meshes, as shown in FIG.
A heater energizing circuit consisting of a .mu.m conductive section 5 was printed. The width of the conductive part may be larger than the width of the heat generating part. At the ends of the printed circuit, electrodes 3 cut out from a conductive green sheet made of 50 volume percent aluminum oxide and 50 volume percent zirconium boride, prepared in the same manner as in the case of the aluminum oxide green sheet, are placed. Ta. Furthermore, the green sheet for the insulating base material or the aluminum oxide powder was laminated and pressed on top of the green sheet to produce a molded body of the heater. A composite ceramic consisting of aluminum oxide and 10 volume percent magnesium oxide was laminated onto this compact.

This molded body was charged into a hot press apparatus and maintained at 1,750° C. for 60 minutes in a vacuum without applying pressure to be densely sintered. From this sintered body, as shown in FIGS. 1, 3, and 4A, a diameter of about 8 mm and a length of about 8 C) m+,
A heater with a thickness of about 3 sides was cut out.

This heater did not break even when repeatedly heated to around 1,200°C.

<Example 6> To silicon nitride powder with an average particle size of 1 μm, 9% by weight of yttrium oxide (Y2O2) and 4% by weight of aluminum oxide were added as sintering aids, and further 5% by weight of aluminum oxide was added.
A 10% PVA (polyvinyl alcohol) solution was added and mixed using a sieve machine. When this mixed powder was formed into a disk shape, a heat generating/conductive circuit made of tungsten or molybdenum metal wires (or strip plates) was embedded inside the disk. At this time, the width and thickness of the conductive circuit were made larger than those of the heat generating circuit, and the electrical resistance of the conductive circuit was reduced to reduce the amount of heat generated.

A molded body or powder of a composite ceramic consisting of silicon nitride and 30% by volume titanium nitride was laminated on the upper and lower surfaces of this molded body. The coefficient of thermal expansion of this composite ceramic is larger than that of silicon nitride, and compressive stress is applied to the silicon nitride inside the sintered body and the heat generating/conductive circuit of tungsten or molybdenum embedded therein. Because of this effect, this heater did not break even when heated rapidly and for a long time at 1,300°C or higher.

In this heater, the molded body is charged into a hot press device, and a pressure of 300 kg/a& is applied in 1 atm of nitrogen.
, and was held at 750°C for 60 minutes to be densely sintered.

〔Effect of the invention〕

According to the present invention, since the surface layer is made of ceramic which has a larger coefficient of thermal expansion than the internal insulating material and has excellent heat resistance and oxidation resistance, the heater is less likely to be damaged even during rapid heating. It maintains high strength up to high temperatures, exhibits better oxidation resistance, and has a longer lifespan than other heaters.

Further, according to the present invention, since a material having an electrical resistivity lower than that of the heat generating member is used for the conductive circuit, the temperature near the electrode at the other end is lower than the temperature at the tip of the heater.
The temperature can be kept significantly lower than in the past, which has the effect of preventing deterioration of the electrode section and lead wire connection section.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a ceramic heater according to an embodiment of the present invention, Fig. 2 is a perspective view showing a cross section taken along the line AA' in Fig. 1, and Figs. FIG. 5 is a graph showing an example of temperature distribution on the surface of the ceramic heater shown in FIG. 1. FIG. A graph showing an example of the relationship between mixing ratios, and FIG. 7 is a graph showing an example of the coefficient of thermal expansion of each constituent material. DESCRIPTION OF SYMBOLS 1... Composite ceramics, 2... Insulating ceramics, 3... Electrode, 4... Heat generating part, 5... Conductive part.

Claims (1)

[Claims] 1. A ceramic heater in which a heat generating part and a conductive part made of a conductive material are built into an insulating ceramic, wherein the surface layer adjacent to the insulating ceramic is a composite containing two or more types of ceramics. A ceramic heater made of ceramic, characterized in that the composite ceramic has a coefficient of thermal expansion larger than that of the insulating ceramic. 2. The ceramic heater according to claim 1, wherein the electrical resistivity of the conductive material constituting the conductive part is lower than the electrical resistivity of the conductive material constituting the heat generating part. 3. The conductive material is IVa, Va, or V in the periodic table.
The ceramic heater according to claim 1 or 2, comprising one or more compounds among borides, carbides, silicides, and nitrides of Group Ia elements. 4. The conductive material is one or more compounds among silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide, and IVa, Va, or V in the periodic table.
The ceramic heater according to any one of claims 1 to 3, characterized in that the ceramic heater is made of one or more compounds among borides, carbides, silicides, and nitrides of Group Ia elements. 5. The ceramic heater according to claim 1 or 2, wherein the conductive material is made of a heat-resistant metal such as tungsten, molybdenum, tantalum, or the like. 6. Insulating ceramics include silicon nitride, sialon,
The ceramic heater according to claim 1 or 2, comprising one or more compounds selected from aluminum nitride, boron nitride, aluminum oxide, and zirconium oxide. 7. The composite ceramic is made of one or more compounds among silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide, and borides, carbides, and silicides of group IVa, Va, or VIa elements in the periodic table. The ceramic heater according to claim 1 or 2, comprising: and one or more compounds among nitrides. 8. The ceramic heater according to any one of claims 1 to 7, wherein compressive stress is applied to the insulating ceramic. 9. The ceramic heater according to any one of claims 1 to 8, wherein the current-carrying circuit consisting of the heat generating part and the conductive part is formed by a printing method.