JPH0487285A - Insulator for spark plug - Google Patents

Abstract

PURPOSE:To prevent an accidental fire while in use by adding a specific quantity for the equivalent oxide in a sintered body of an alkaline earth metal compound to a nitride ceramic raw material, molding it, then baking it in the fixed nonoxidizing atmosphere to form the grain boundary phase. CONSTITUTION:One or two or more kinds of compounds selected from a group of alkaline earth metal oxide, chloride, hydroxide, fluoride, carbide, sulfate, carbonate, nitrate, acetate, and phosphate 0.5-15wt.% for the equivalent oxide in a sintered body are added to a nitride ceramic raw material, it is molded, then it is baked in the nonoxidizing atmosphere at 1600-1950 deg.C to form the grain boundary phase. The grain boundary phase has a high electric resistance value, and a sintered insulating insulator maintains high insulation resistance at a high temperature. No spark energy flows inside the insulator, and an accidental fire caused by it is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an insulator for a spark plug for an internal combustion engine.

[Prior Art] Japanese Patent Publication No. 55-46634 describes a technique using aluminum nitride for the insulator of a spark plug.

[Problems to be Solved by the Invention] However, such a spark plug has a drawback in that the insulation resistance of the aluminum nitride decreases due to heat, spark energy flows inside the insulator, and it is easy to misfire.

An object of the present invention is to provide an insulator for a spark plug that is less likely to cause a misfire during use.

[Means for Solving the Problems] In order to achieve the above problems, the present invention employs the following configuration.

(1) Nitride-based ceramic raw materials include alkaline earth metal oxides, chlorides, hydroxides, fluorides, carbides, sulfates,
One or more compounds selected from the group consisting of carbonates, nitrates, acetates, and phosphates are added in an amount of 0.5 to 15% by weight in terms of oxides in the sintered body, and this is then shaped.
A grain boundary phase was formed by firing in a non-oxidizing atmosphere at 1600-1950°C.

(2) Further, boron nitride is supported on the outer periphery of the molded article and the firing is performed.

[Function and Effect of the Invention] (Regarding Claim 1) (Function) During firing of the molded product, the alkaline earth metal compound decomposes into each oxide, forming a grain boundary phase and forming a nitride ceramic. Contributes to sintering of raw materials.

Since this grain boundary phase has a high electrical resistance value, the sintered insulator maintains high insulation resistance even at high temperatures.

When the amount of the compound is less than 0.5% by weight in terms of oxide in the sintered body, the insulation resistance of the sintered body becomes extremely low, making it unsuitable for use as an insulator for a spark plug. Also, 15
If the weight percentage is exceeded, the compound becomes excessive, and when the compound decomposes and foams, it leaves harmful pinholes in the sintered body.

The molded body is fired in a non-oxidizing atmosphere at 1600-1950°C.

(Effects) The insulator can maintain high insulation resistance even at high temperatures during use, and spark energy does not flow inside the insulator, preventing misfires caused by this.

(Regarding claim 2) Since boron nitride is supported on the outer periphery of the molded product and fired, it is possible to prevent the decomposition of the nitride-based ceramic, as well as to prevent the migration and decomposition and disappearance of the compound and to leave the grain boundary phase. be able to. Therefore, the insulation resistance of the insulator at high temperatures can be further improved.

[Example] Next, an example of the present invention will be described based on each person and each figure.

The compounds include calcium fluoride (CaFz), calcium carbonate (CaCOi), strontium carbonate (SrCO
3), barium carbonate (BaCOl), barium fluoride (B
aFi) and are used in the weight percent (however, CaO equivalent amount) shown in Table 1, and are used in the form of -juvenile or a mixture of two types.

The nitride-based ceramic raw material is aluminum nitride (1!N) powder having an average particle size of 1.5 μm and an oxygen concentration of 1.0% by weight, having the weight percentages shown in Table 1.

The method for manufacturing the test piece will be described below.

(1) The aluminum nitride powder and the compound are mixed at the mixing ratio shown in Table 1 and mixed well in ethanol.

(2) Spray-dry the obtained slurry and spray approximately 1t/
Pressure-molded into a disk shape with a diameter of 50 mm and a thickness of 3 mm using a pressure of 100 mm, and then oxidized and calcined (500°C for 2 hours).
do.

(3) This was fired at normal pressure in a nitrogen gas atmosphere under the firing conditions shown in Table 2, and polished to a diameter of 40 mm and a thickness of 1.0 mm.
Disk-shaped test pieces A and B (Samples Null to 13)
Make it.

Note that for sample interval 10.12, particles having a particle size of less than 5 μm were embedded in 80% by weight boron nitride (BN) powder and fired. Also, regarding sample 11kL11.13,
A slurry made by mixing boron nitride with ethanol is applied and fired.

Next, the insulation resistance (700℃) of these test pieces
We will describe the measurement of

In Table 1, Samples 1 to 13 are invented products, and Samples 14 to 24 are comparative products that are outside the scope of the claims.

As shown in FIG. 2, brass electrodes 100 (contact surface 6R) and 200 are placed between each of the test pieces, and the test pieces are heated to 700°C with a heater 300.
00■ The insulation resistance was measured using a DC digital resistance meter 400, and the results are shown in Table 2.

Next, the effects of the embodiment will be described.

(a) Calcium, strontium, and barium compounds decompose during firing to become their respective oxides, and contribute to the sintering of aluminum nitride while forming grain boundary layers 12 between crystal grains 11 of aluminum nitride. For example, if the oxide is C
If aO, the grain boundary layer 12 is Ca AtJrxo re
, CaAl407, CaA1204, etc., and AfJ203.

These grain boundary layers 12 have extremely high insulation resistance even at high temperatures, so the insulation resistance (700° C.) of test pieces A and B of samples 11Q1 to 13 is extremely high. Incidentally, if this insulation resistance is 50 MΩ or more, misfire will not occur.

(a) Sample clay 10 that was fired with boron nitride supported
As shown in FIG. 1, test piece B of ~13 can prevent escape of component 13, which becomes the grain boundary layer 12, due to the boron nitride coating 21, and the insulation resistance (700°C) of test piece B is extremely high. .

(1) Manufacture a spark plug insulator using the same material as test pieces A and B, and seal the center electrode in the shaft hole of this insulator together with the resistor and terminal electrode using a known method of glass sealing. When this was assembled into a metal shell equipped with mounting screws, it was found that a spark plug with a wide range and no misfires could be obtained.

The present invention includes the following embodiments in addition to the above embodiments.

81 In this specification, nitride-based ceramic ink raw material number,
In addition to nitride raw materials such as aluminum nitride, it also includes oxynitride raw materials such as aluminum oxynitride (Aj!ON) and Sialon raw materials.

b. Calcium (Ca), strontium (Sr), and barium (Ba) are suitable for the alkaline earth metal.

(Margin below) Table 1 (The weight percent of the auxiliary agent is expressed in CaO equivalent) Table 2

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating the formation of a grain boundary phase by enlarging the cross section of a test piece in an example, and FIG. 2 is an explanatory diagram of an apparatus for measuring the insulation resistance of the test piece. In the diagram A, B...Test piece (spark plug insulator)

Claims (1)

[Claims] 1) A nitride-based ceramic raw material containing alkaline earth metal oxides, chlorides, hydroxides, fluorides, carbides, sulfates, carbonates, nitrates, acetates, and phosphates. One or more compounds selected from the group are added in an amount of 0.5 to 15% by weight in terms of oxide in the sintered body, which is shaped and then fired in a non-oxidizing atmosphere at 1600 to 1950°C. A spark plug insulator with a grain boundary phase. 2) The insulator for a spark plug according to claim 1, wherein the firing is carried out with boron nitride supported on the outer periphery of the molded product.