JPH04233187A - Ceramic heater and its manufacture - Google Patents

Abstract

PURPOSE:To improve durability and acid resistance by so constituting it as to provide a ceramic heating body, which contains a specified amount or more of zirconium nitride inside specified ceramics. CONSTITUTION:A ceramic heating body 2, which contains zirconium nitride by 10% or more inside with BETA-thyaron ceramics 1 as a matrix built in. Hereby, the differences of shrinkage factor and thermal expansion coefficient during sintering between the heating body 2 and the matrix 1 are small, so it is hard to cause wire breaking of the heating body, and also since the acid resistance of the matrix is strong, acid resistance becomes high. Furthermore, the coupling between the heating body and the matrix becomes firm and the durability can be elevated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic heater used as a preheating plug for a diesel engine or a spark plug for a fan heater, and a method for manufacturing the same.

0002

2. Description of the Related Art In recent years, ceramic heaters have been widely used in spark plugs such as those mentioned above because of their rapid startability and high heat resistance. Conventional heaters of this type have a heating element made of a high melting point metal such as tungsten or molybdenum embedded in a sintered body of silicon nitride ceramics or sialon ceramics. In addition, the method for manufacturing these heaters involves adding a heating element of a high melting point metal such as tungsten or molybdenum to a molded body of silicon nitride ceramics or sialon ceramics, and then firing the molded body.

0003

[Problems to be Solved by the Invention] Since such conventional ceramic heaters use metal for the heating element, the contraction rate of the heating element is different from that of the base ceramic during sintering, so delamination is likely to occur. , and the strength was also weak. Additionally, because the thermal expansion coefficients of the base ceramic and the heating element are significantly different, wires are likely to break during repeated operations, posing a problem with durability.

The object of the present invention is to solve these problems and provide a ceramic heater that has high durability and excellent productivity.

[0005]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention proposes a ceramic heater having a ceramic heating element containing 10 wt % or more of zirconium nitride inside Sialon ceramics. Furthermore, a ceramic heater is provided in which a mixture of aluminum nitride and zirconium oxide, which becomes a heating element after firing, is applied to a molded body of Sialon ceramics, and then a molded body of Sialon ceramics is layered on top of the mixture, and then fired. This paper proposes a manufacturing method.

[0006]

[Operation] According to this configuration, since the heating element is made of ceramics, there is no large difference in shrinkage rate during sintering with the ceramic matrix, and the thermal expansion coefficients are similar, so even if the heating element is operated repeatedly, it will not break. It becomes difficult. Further, by providing a heating element containing zirconium nitride in sialon ceramics having strong oxidation resistance, oxidation resistance is improved. Furthermore, according to the manufacturing method of the present invention,
Since the heating element is formed by the reaction between aluminum nitride and zirconium oxide and is simultaneously sintered with the sialon ceramic matrix, the bond between the heating element and the sialon ceramic matrix becomes strong, resulting in a highly durable ceramic heater. This means that you can do it.

[0007]

[Embodiment] An embodiment of the present invention will be described below. First, polyvinyl butyral as a binder, dibutyl phthalate as a plasticizer, and isopropyl alcohol as a solvent were added to a mixture of β-Sialon (Si4Al2O2N6) powder and yttrium oxide powder added in an amount of 5 wt%, and the mixture was thoroughly kneaded in a ball mill. The slurry thus obtained was molded to a thickness of 0.2 mm using a doctor plate method. Next, after laminating a predetermined number of sheets of this molded body, it is cut into 10
A molded body of x50 x 2 mm was obtained. On this molded body, a mixed powder of aluminum nitride and zirconium oxide in a molar ratio of 3:1 was added, and polyvinyl butyral was added as a binder.
Dibutyl phthalate was added as a plasticizer and isopropyl alcohol was added as a solvent, and the mixture was thoroughly kneaded in a ball mill to form a paste, which was then printed in the shape of a predetermined heating element. After this paste was dried, a β-sialon formed body produced in the same manner as the former was stacked. This was sintered at 2000° C. for 2 hours in a nitrogen atmosphere.

The structure of the sintered body thus obtained was composed of a matrix of β-sialon ceramics 1 and a heating element 2, as shown in FIG. The heating element 2, that is, the portion that was a mixture of aluminum nitride and zirconium oxide before firing, was found to be a composite sintered body of zirconium nitride and aluminum oxynitride according to the effect of X-ray diffraction analysis. Then, 0.1μmTi-1.0μmMn-1.0μm was deposited on both ends of the sintered body obtained as described above.
A Cu electrode was formed, annealed at 800° C. in a ring atmosphere, and then 1 μm Ni plating was applied to form the electrode 3.

When this heater was connected to a 12V DC power source and energized, it showed a temperature rise curve as shown in FIG. As shown in Fig. 2, the heater of the present invention uses β-sialon ceramics with good thermal conductivity as the base material, so it can rapidly heat up to 900°C in about 3 seconds. The temperature is constant at 1100° C., indicating that current control of the heater temperature is possible.

FIG. 3 shows the temperature change at the center of the heater when the heater is continuously energized in air. Figure 3
According to the above, it can be seen that there is almost no deterioration even after 1000 hours have passed since the start of energization. Furthermore, when zirconium nitride is oxidized, it becomes zirconium oxide, which causes a volume expansion of about 27%, which causes destruction of the heater, but in the present invention, as shown in Figure 3, no deterioration of the heater is observed. First, the zirconium nitride in the heating element was completely protected.

Next, Table 1 below shows a comparison with a conventional ceramic heater. The measurement results here are for the number of samples: 1
I saw it with 0 pieces.

0012

[Table 1]

Sample No. in the above (Table 1). Sample No. 1 is a conventional example having the same structure as the present invention except that tungsten was used for the heating element. 4 is a comparative example as described later. In addition, the bending strength in (Table 1) is span 30
It was measured by the three-point bending method. Furthermore, the number of non-defective products after 1000 cycles is the ratio of the number of non-defective products after 1000 cycles, where one cycle is 10 minutes of energization and 10 minutes of no current. As can be seen from this (Table 1), in conventional tungsten heating elements, the β
- The bending strength is low due to poor bonding with the SiAlON ceramics, whereas the products of the present invention (Samples No. 2 and 3) have high bending strength because the bonding between the heating element and the base β-SiAlON ceramics is good. It shows.

[0014] In addition, in conventional products using tungsten for the heating element, the coefficient of thermal expansion between the heating element and the matrix β-SiAlON ceramics is significantly different, resulting in defective products (broken wires) after 1000 cycles of life test. However, in the case of the present invention, since there is no difference in the coefficient of thermal expansion between the two, no defective products (broken wires) occur, and it can be seen that the product has excellent durability. Furthermore, as can be seen from Table 1, when the amount of zirconium nitride (ZrN) in the heating element becomes less than 10 wt%, Sample No. 4, the conductivity of the heating element is lost. This is because the only conductive material in the heating element is zirconium nitride. Further, since aluminum nitride and zirconium oxide react at a molar ratio of 3:1, when aluminum nitride and zirconium oxide are blended at a molar ratio of 3:1, the amount of zirconium nitride in the heating element is maximized.

In the above example, 5w of yttrium oxide was added to β-sialon as the sialon ceramic.
Although sialon with t% added was used, the effectiveness of the present invention remains unchanged even if Sialon of other composition, with or without addition of other sintering aids is used. Needless to say.

Furthermore, as the ceramic containing 10 wt % or more of zirconium nitride, other than the aluminum nitride shown in the above embodiment, a ceramic such as silicon nitride may be used. The upper limit of zirconium nitride contained in ceramics is determined by considering sinterability, and in the case of aluminum nitride, it is 50wt.
It will be about %. Note that the mixture of aluminum nitride and zirconium oxide becomes an oxide or oxynitride of zirconium nitride and aluminum after firing, depending on the amount of aluminum nitride contained.

[0017]

As described above, according to the present invention, 10% by weight of zirconium nitride is contained inside Sialon ceramics.
Since the heating element is made of ceramic, the difference in shrinkage rate during sintering between the sialon ceramic base and the heating element is small. It has good bonding properties with Sialon ceramics and has strong strength. In addition, since the difference in thermal expansion coefficient between the heating element and the base Sialon ceramic is small, the wire does not break even after repeated operations, resulting in significantly improved durability. Furthermore, by making the heating element containing zirconium nitride, which has weak oxidation resistance, exist in the sialon ceramic, which has strong oxidation resistance, the heating element is protected, and a ceramic heater with strong oxidation resistance can be obtained. On the other hand, by applying a mixture of aluminum nitride and zirconium oxide onto a molded body of Sialon ceramics, stacking the molded body of Sialon ceramics on top of it, and then sintering it, the formation of the heating element is prevented from forming with aluminum nitride during firing. This is done by generating an oxide or oxynitride of zirconium nitride and aluminum through the reaction of zirconium oxide, so ceramics containing zirconium nitride, which is difficult to sinter, can be easily obtained, and bonding with the base sialon ceramics is possible. It also becomes more solid, resulting in significantly improved durability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a ceramic heater according to an embodiment of the present invention.

[Fig. 2] A diagram showing the current conduction characteristics of the ceramic heater of the present invention.

[Fig. 3] Diagram showing continuous energization characteristics of the ceramic heater of the present invention

[Explanation of symbols]

1 β-sialon ceramics 2 Heating element 3 Electrode

Claims (2)

[Claims] 1. A ceramic heater comprising a ceramic heating element containing 10 wt % or more of zirconium chloride inside a sialon ceramic. 2. A mixture of zirconium oxide and aluminum chamber oxide, which will become a heating element after firing, is applied to the molded body of Sialon ceramics, and then the molded body of Sialon ceramics is placed on top of the mixture, and then fired. A method of manufacturing a ceramic heater.