JPH0612693B2 - Ceramic heater and method of manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ceramic heater for a glow plug mounted on a diesel engine and a method for manufacturing the same.

"Prior Art" A ceramic heater generally used conventionally is a heating resistor having an arbitrary shape such as a comb tooth shape or a spiral shape in an alumina or silicon nitride ceramic sintered body and having an arbitrary length and width. There is known a ceramic heater which is provided with a lead terminal and is attached with a lead terminal so that electricity is supplied from the lead terminal. (Japanese Patent Application Laid-Open No. 57-67296) Among these ceramic heaters, a silicon nitride material and a non-oxide ceramic such as sialon are damaged by thermal shock even when repeatedly used at a high temperature such as a glow plug for a diesel engine. It is evaluated as having stable high temperature characteristics.

However, in the conventional non-oxide ceramic material, trace impurities are mixed due to wear of a pot mill or the like used when mixing and pulverizing raw material powders. If a pot mill or ball made of iron or stainless steel is used, those metal impurities are mixed, but it is extremely difficult to control the amount mixed, and wear particles from the pot mill or ball are evenly distributed in the raw material particles. It is not possible to disperse or coat, so it is not possible to obtain the expected uniform properties.

Further, in the case of producing a silicon nitride sintered body, the present applicant has made Fe, Cr, Ni, Co, W, Ti, Ta, Mo, Nb, etc. in order to prevent a decrease in strength of the degreased body caused by removal of the molding binder. We have developed a method for coating a silicon nitride material with the above metal element (Japanese Patent Application No. 61-206892).

This method specifically coats the metal component in the form of a thin film in the range of 10 rpm to 2000 rpm and can be employed in either mechanochemical reaction or chemical reaction.

[Problems to be Solved by the Invention] When powders containing no transition metal element are used as the silicon nitride material powders in the above conventional technique, (1) the strength after calcination and degreasing is low and the workability is poor.

(2) When used for a ceramic heater The adhesion strength between the heating element after sintering and the ceramic is low, and a wire breakage occurs at the electrode extraction portion.

(3) The resistance change rate due to firing is relatively large.

In contrast to the above, in the case of using an iron or stainless steel pot mill and mixing in metal elements by abrasion,
Although the problems of (1) and (2) are solved, there is a problem that the rate of change in resistance due to firing is extremely large, which inevitably causes large variations, which reduces the yield of non-defective products. It is difficult to control.

"Means for solving the problem" A heating element made of a high melting point metal or its alloy and a non-oxide ceramic sintered body such as silicon nitride or sialon mixed with 0.06 to 1.5% by weight of a transition metal. The adding means is achieved by adding and mixing an organic metal salt solution of a transition metal into the non-oxide ceramic raw material powder, shaping the mixture, and firing.

"Function" In addition to adding metal oxides such as Al ₂ O ₃ , Y ₂ O ₃ and MgO which are sintering aids to non-oxide ceramics such as silicon nitride and sialon, organic solvents such as ethyl alcohol and trichloroethane are added. A soluble organic metal salt (transition metal) of 0.06 to 1.5% by weight in terms of metal element is added and mixed to dissolve and dilute the organic metal salt in the solvent, and the surface of the ceramic raw material particles is uniformly coated with the metal. It is possible to control the addition amount of the metal salt easily,
Further, the mixed and pulverized ceramic sludge is then subjected to spray drying, reduced pressure drying or the like to remove the solvent content to obtain a dry powder.

When a heating element made of a high melting point metal is embedded in the ceramic powder obtained in this way and fired by the pot press method, 1) the resistance change is caused because the excessive chemical reaction between the heating element and the ceramic during firing is suppressed. The rate is extremely small, and as a result, the variation in resistance value is minimized, and the yield is improved.

2) Since the adhesion between the refractory metal and the ceramic is improved,
The bonding strength between the ceramic and the metal at the electrode extraction portion is increased, and the reliability as a heater is improved.

3) Since the green strength after degreasing is improved, handling in the manufacturing process and raw processing become easier.

[Examples] Examples will be described below.

Example 1 920 g of Si ₃ N ₄ having an average particle size of 0.5 μm and Y having an average particle size of 1.2 μm
₂ O ₃ 40 g, Al ₂ O ₃ 40 g with an average particle size of 0.3 μm, 800 cc of ethyl alcohol was added, and Fe methoxide was converted to 0% (no addition) 0.06%, 0.2%, 0.5%, and 1.5% in terms of Fe. Then, the mixture was added, mixed for 16 hours in alumina ball stone and alumina trommel, and dried in hot water. For comparison, Fe
Without adding methoxide, the mixture was mixed for 16 hours using an iron pot and an iron ball, and dried by boiling to prepare a powder. This powder contains 0.56% Fe from the iron pot and balls due to wear and contamination. Using the obtained powder mixture as a support,
A heating element made of an alloy of W90 wt% / Re10 wt% was embedded in this, press molding, degreasing and H. A P firing test was performed.

The test conditions are as follows.

Press molding 600kg / cm ² Degreasing 400 ℃ × 1Hr (50 ℃ / Hr heating, N ₂ atmosphere) Hot press (HP) firing 1850 ℃ × 30 minutes Pressure 200kg / cm ^{2 If} the test result is displayed, It is as shown in Table 1.

As can be seen from this table, according to the present invention, remarkable effects such as improvement in strength after degreasing, reduction in variation in firing resistance change rate, and improvement in lead adhesion strength were recognized.

The addition amount of Fe is 0.06 to 1.50%, preferably 0.06 to 0.
It can be seen that the range is 2%.

(Note) As shown in FIG. 1, the lead adhesion strength is such that a heater 4 is prepared by embedding a high melting point metal heating element 1 and a high melting point metal lead 2 in a ceramic 3 and forming a Ni wire on the exposed end of the lead 2. 5 was L-shaped, was brazed with silver 6, and was measured by pulling a Ni wire.

Example 2 7200 g of Si ₃ N ₄ having an average particle size of 0.5 μm and an average particle size of 1.2 μm
Trichloroethane 11 was added to 320 g of Y ₂ O ₃ and 480 g of Al ₂ O ₃ having an average particle size of 0.3 μm, and 16 g of an organic salt of iron in terms of Fe and 30 g of a dispersant were added, and an alumina ball was used. The mixture was mixed with an attritor for 5 hours and spray dried.

Here, as the organic Fe salt, Fe butoxide 0.2%, iron propionate 0.2%, and Fe 0% and Fe 0.56% for comparison.
(Mixed from wear material) was prepared.

The press-degreasing-firing was performed under the same conditions as in Example 1 to investigate the characteristics. The results are shown in Table 2.

As a result, it was found that the expected effect was obtained regardless of the type of organic salt containing Fe.

Example 3 In place of using Fe methoxide of Example 1, Ni methoxide, Cr methoxide, and Co methoxide were used at 0.2% in terms of metal element, except for compounding and pressing-degreasing-H. The test conditions for P firing were the same as in Example 1 except that a sample was prepared and tested.

The results are shown in Table 3.

According to the above table, the resistance change rate is considerably high in the material with Cr added, but the variation is suppressed. Good results were obtained for both materials containing Ni and Co.

And so on.

[Brief description of drawings]

FIG. 1 is a simplified explanatory diagram of a lead adhesion strength measuring method. 1 ... Refractory metal heating element, 2 ... Refractory metal lead, 3
…… Ceramic, 4 …… Ceramic heater, 5 …… Ni wire, 6 …… With silver braze

Claims (2)

[Claims] 1. A ceramic heater in which a heating element made of a high melting point metal such as W or Mo or an alloy thereof is embedded in a non-oxide ceramic sintered body such as silicon nitride or sialon. 0.06 to 1.
A ceramic heater containing 5% by weight. 2. A ceramic characterized by adding and mixing an organic metal salt solution of a transition metal to a ceramic raw material powder for embedding a heating element made of a high melting point metal such as W or Mo or an alloy thereof, and shaping and firing. Heater manufacturing method.