JP3547154B2 - Ceramic heating element - Google Patents

Description

【００１１】
発熱線７は、線径０．２ｍｍのコイル状のタングステン線を略Ｕ字形に成形して成り、両端部がそれぞれタングステン製の電極取出し線８、９に接続されている。
一対の電極取出し線８、９は、セラミック焼結体６の後方側に平行的に埋設されている。一方の電極取出し線８は、後端部８ａがセラミック焼結体６の側面より露出して設けられ、その露出した後端部８ａがろう付けによって支持筒３の内面に接合されている。他方の電極取出し線９は、後端部９ａがセラミック焼結体６の後端側面より露出して設けられ、その露出した後端部９ａがろう付けによって金属キャップ５ａの内壁に接合されている。
【００１２】
次に、セラミック発熱体４の製造方法の一例を説明する。
ア）Ｓｉ_３ Ｎ_４ 、Ｙｂ_２ Ｏ_３ 、Ｙ_２ Ｏ_３ 、Ｅｒ_２ Ｏ_３ 、Ａｌ_２ Ｏ_３ 、およびＡｌＮの各粉末を上記の表１に示す割合で配合した後、ボールミルにてアルコール湿式混合を２０時間行った後、乾燥して混合粉末を得る。
イ）続いて、タングステン、モリブデン、レニウム等の高融点金属、もしくはこれらを主体とする合金、これら金属の炭化物、これら金属とセラミック焼結体材との混合物等より成る発熱線７（本実施例ではタングステン線）を所定の形状に成形し、前記ア）で得られた混合粉末中に埋設する。
ウ）続いて、その発熱線７が埋設された混合粉末を、非酸素雰囲気中でホットプレス焼成することにより、Ｎｏ．１〜１４のセラミック発熱体４を得る。なお、焼成条件は、焼成温度：１７００℃、保持時間：３０分、圧力：３００ｋｇ／ｃｍ^２ である。
【００１３】
次に、上記製造方法によって得られたセラミック発熱体４を以下の各試験方法によって評価し、その評価結果を下記の表２に示す。なお、耐酸化性の評価については、セラミック自体の特性を評価するために、発熱線７を埋設する上記イ）の工程を省略して行った。
▲１▼偏析部最大長
焼結体断面を鏡面研磨し、走査電子顕微鏡（ＳＥＭ：日本電子株式会社製）により観察し、偏析部最大長（μｍ）の測定を行った。
▲２▼気孔率
アルキメデス法により焼結体の気孔率を測定した。
▲３▼抗析強度
室温および１１００℃にてＪＩＳ−Ｒ１６０１およびＪＩＳ−Ｒ１６０４に従う４点曲げ試験を行い、抗析強度（ＭＰａ）を測定した。
▲４▼酸化増量
各試験品から、３×４×３５ｍｍの試験片を切り出し、次いで、大気中温度１０００℃の雰囲気中で、１００時間放置し、酸化した後、重量増加分（ｍｇ／ｃｍ^２ ）を測定することにより行った。
▲５▼通電性能
各試験品に試験用の電極を取付け、直流電流を印加して、飽和温度が１１００℃となるように電圧を制御し、１分間通電、１分間エアー吹き付けによる急冷の通電耐久テストを１００００回行って、抵抗の変化および抗析強度を測定した。
【００１４】
【表２】

【００１５】
上記表２に示すように、Ｎｏ．９、１０の試験品は、希土類元素中のＹｂ_２ Ｏ_３ の割合が低い（８０重量％より少ない）ため、焼結助剤の偏析部最大長が３μｍ以上となり、室温および１１００℃において抗析強度が低く、耐酸化性も低い。Ｎｏ．１１の試験品は、「Ａｌ_２ Ｏ_３ ＋ＡｌＮ」（Ａｌ量）が過剰（５重量％を越える）であるため、耐熱性が低下して高温強度、耐酸化性が低下し、さらには、通電性能（抵抗変化、通電後強度）も低下する。Ｎｏ．１２の試験品はＡｌ化合物の量が少なく（１重量％より少ない）、またＮｏ．１３の試験品はＹｂ_２ Ｏ_３ の量が少ない（５重量％より少ない）ことから、焼結助剤が不十分であるため十分緻密化せず、抗析強度、耐酸化性、さらには通電後強度が低下する。Ｎｏ．１４の試験品は、Ｙｂ_２ Ｏ_３ が過剰（１２重量％を越える）であるため、高温強度、耐酸化性が低下し、さらには、通電性能（抵抗変化、通電後強度）が低下する。
【００１６】
これに対して、Ａｌ化合物等をＡｌ換算で１〜５重量％、およびＹｂを酸化物換算で８０重量％以上含有した希土類元素化合物等を酸化物換算で５〜１２重量％含有したＮｏ．１〜８の各試験品（本発明の組成を満足するセラミック発熱体４）は、室温および１１００℃の抗析強度が極めて高く、１１００℃においても９００ＭＰａ以上の高抗析強度を示す。また、耐酸化性においても、１０００℃×１００時間で０．１ｍｇ／ｃｍ^２ 以下と非常に小さく、耐酸化性も優れている。さらには、通電性能においても抵抗変化は見られず、通電後強度も９００ＭＰａ以上と優れていることが確認された。
【００１７】
【発明の効果】
本発明のセラミック発熱体は、セラミック焼結体に含有されるＡｌ化合物等の含有量および希土類元素化合物等の含有量を特定するとともに、主として焼結助剤成分からなる偏析部の最大長さを３μｍとしたことにより、高強度で耐酸化性に優れ、且つ通電性能（抵抗変化、通電後強度）にも優れる。
【図面の簡単な説明】
【図１】本実施例に係るセラミック発熱体を用いたグロープラグの断面図である。
【符号の説明】
４ セラミック発熱体
６ セラミック焼結体
７ 発熱線[0001]
[Industrial applications]
The present invention relates to a ceramic heating element having a heating wire embedded in a ceramic sintered body, and is particularly suitable for use in a glow plug of a diesel engine.
[0002]
[Prior art]
BACKGROUND ART Conventionally, a ceramic heating element has been manufactured in which a heating wire made of tungsten is embedded in a sintered body of silicon nitride (which includes a sialon in addition to Si ₃ N ₄ ).
[0003]
[Problems to be solved by the invention]
However, when a conventional ceramic heating element is used as a heat source of a glow plug used in a diesel engine, sufficient strength and oxidation resistance are obtained in a temperature range from room temperature to about 1200 ° C. (particularly around 1100 ° C.). I can't get it.
When a conventional ceramic heating element is used as a heat source for a glow plug and a DC voltage is applied intermittently to the ceramic heating element, the ions of the grain boundary phase of the sintered body move to move the positive electrode to the positive electrode side. Structural degradation such as cracking occurs in the sintered body near the coil. For this reason, the strength of the sintered body is deteriorated, the resistance of the heating resistance wire is changed, or the wire is easily broken. As a result, the current-carrying performance is reduced.
The present invention has been made on the basis of the above circumstances, and has as its object to have excellent strength and oxidation resistance from room temperature to about 1200 ° C. (particularly around 1100 ° C.), and to have an energizing performance when a DC voltage is applied. It is an object of the present invention to provide a ceramic heating element capable of suppressing a decrease in the temperature.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a ceramic heating element in which a heating wire is embedded in a ceramic sintered body, wherein the ceramic sintered body includes Al or an Al compound as a sintering aid component, and a rare earth element. A sialon-based sintered body to which a compound is added, wherein the sialon-based sintered body contains 1 to 5% by weight of Al or an Al compound in terms of Al and 80% by weight or more of Yb in terms of an oxide. Alternatively, the technical means is that a rare earth element compound is contained in an amount of 5 to 12% by weight in terms of oxide, and the maximum length of the segregated portion mainly composed of the sintering aid component is 3 μm or less.
[0005]
[Action]
The ceramic heating element of the present invention having the above-described structure reduces the sinterable temperature by adding Al or an Al compound (hereinafter referred to as an Al compound or the like) as a sintering aid component of the ceramic sintered body. The effect occurs. Thus, if a dense sintered body can be obtained at a sintering temperature of 1700 ° C. or less, the growth of sialon particles is suppressed, and a high-strength sintered body can be obtained.
If the content of the Al compound or the like as a sintering aid component is less than 1% by weight in terms of Al, it cannot function sufficiently as a sintering aid, and a dense sintered body may be obtained. Can not. On the other hand, when the content exceeds 5% by weight, heat resistance, high-temperature strength, and oxidation resistance decrease, and the current-carrying performance (resistance change, strength after current-carrying) decreases. Therefore, the content of the Al compound and the like is set to 1 to 5% by weight in terms of Al.
[0006]
When the content of the rare earth element or the rare earth element compound (hereinafter referred to as the rare earth element compound, etc.) as the sintering agent component is less than 5% by weight, there is no effect as a sintering aid, and when it exceeds 12% by weight. In addition, the high-temperature strength and the oxidation resistance are reduced, and the energization performance (resistance change, strength after energization) is reduced. Therefore, the content of the rare earth element compound and the like is set to 5 to 12% by weight in terms of oxide. If the rare earth oxide other than Yb ₂ O ₃ contained in the rare earth element compound exceeds 20% by weight, the sintering temperature is reduced to 1700 ° C. or lower in order to improve the strength level. agents segregation _{[Si 3 N 4 / RE 2} O 3 (RE: rare earth element): melilite type compound, consisting of RE-Si-Al-ON compounds] generates the, acid at intermediate temperature range of 800 to 1000 ° C. A melilite type compound of Si ₃ N ₄ .RE ₂ O ₃ which degrades the chemical property is easily formed. Therefore, the rare earth element contains Yb in an amount of 80% by weight or more in terms of oxide.
[0007]
Further, when the maximum length of the segregated portion mainly composed of the sintering aid component exceeds 3 μm, the strength of the segregated portion is reduced due to the origin of the fracture, and the high-temperature strength is particularly affected. The segregated portion having a maximum length of more than 3 μm is formed when the above-mentioned rare earth oxide other than Yb ₂ O ₃ is used in an amount exceeding 20% by weight, or when the firing conditions are not suitable, for example, when the appropriate temperature It also occurs when firing at higher or lower temperatures. Therefore, the maximum length of the segregated portion composed of the sintering aid component is set to 3 μm or less.
The “segregated portion mainly composed of the sintering aid component” refers to a segregated portion composed of the compound of the sintering aid component and Si ₃ N ₄ even if it is a segregated portion composed only of the sintering aid component. It means that there may be.
[0008]
【Example】
Next, an embodiment using the ceramic heating element of the present invention as a heat source of a glow plug will be described with reference to FIG.
FIG. 1 is a sectional view of a glow plug.
The glow plug 1 according to the present embodiment has a mounting screw portion 2a formed on the outer periphery, and is fitted into a cylindrical mounting member 2 constituting an outer electrode, and a tip (lower end in FIG. 1) of the mounting metal member 2. A joined metal supporting tube 3, a ceramic heating element 4 supported at the center by the supporting tube 3 in a state where the tip side protrudes from the supporting tube 3, and a metal cap 5a having a U-shaped cross section are integrally formed. Then, a center shaft 5 disposed through the axis of the mounting bracket 2 in a state where the inner surface of the metal cap 5a is brazed to the rear end surface of the ceramic heating element 4, and connected to the rear end of the center shaft 5, It is composed of a terminal electrode 12 and the like held at the rear end of the mounting bracket 2 by a nut 11 via an insulator 10.
[0009]
The ceramic heating element 4 includes a silicon nitride ceramic sintered body 6, a heating wire 7 buried in the sintered body 6, and a pair of electrode lead wires 8 and 9, and a tip protruding from the support cylinder 3 has a It is exposed to a pre-combustion chamber (not shown) of the diesel engine.
The ceramic sintered body 6 is obtained by adding Yb ₂ O ₃ , Y ₂ O ₃ , Er ₂ O having an average particle diameter of 2 μm and a purity of 99.9% to Si ₃ N ₄ powder having an average particle diameter of 0.7 μm and an α ratio of 95%. _3, an average particle size 1μm of _Al 2 _{O 3,} in proportions showing each powder having an average particle size of 0.7μm of AlN in Table 1 below, No. Test items 1 to 14 were produced. The “Al amount” in the table is an amount (% by weight) of the amount of the Al compound in the sintering aid component in terms of Al.
[0010]
[Table 1]

[0011]
The heating wire 7 is formed by forming a coil-shaped tungsten wire having a wire diameter of 0.2 mm into a substantially U-shape, and both end portions are connected to tungsten electrode lead wires 8 and 9, respectively.
The pair of electrode lead wires 8 and 9 are buried in parallel behind the ceramic sintered body 6. One of the electrode lead wires 8 has a rear end 8a exposed from the side surface of the ceramic sintered body 6, and the exposed rear end 8a is joined to the inner surface of the support cylinder 3 by brazing. The other electrode lead wire 9 has a rear end portion 9a exposed from the rear end side surface of the ceramic sintered body 6, and the exposed rear end portion 9a is joined to the inner wall of the metal cap 5a by brazing. .
[0012]
Next, an example of a method for manufacturing the ceramic heating element 4 will be described.
A) After blending each powder of Si ₃ N ₄ , Yb ₂ O ₃ , Y ₂ O ₃ , Er ₂ O ₃ , Al ₂ O ₃ , and AlN at a ratio shown in Table 1 above, alcohol wet by a ball mill. After mixing for 20 hours, the mixture is dried to obtain a mixed powder.
B) Subsequently, a heating wire 7 made of a refractory metal such as tungsten, molybdenum, rhenium or the like, an alloy mainly composed of these, a carbide of these metals, a mixture of these metals and a sintered ceramic material, etc. Then, a tungsten wire) is formed into a predetermined shape and embedded in the mixed powder obtained in the above a).
C) Subsequently, the mixed powder in which the heat generating wires 7 are embedded is hot-pressed in a non-oxygen atmosphere to obtain No. 2 powder. 1 to 14 ceramic heating elements 4 are obtained. The firing conditions were as follows: firing temperature: 1700 ° C., holding time: 30 minutes, pressure: 300 kg / cm ² .
[0013]
Next, the ceramic heating element 4 obtained by the above manufacturing method was evaluated by the following test methods, and the evaluation results are shown in Table 2 below. The oxidation resistance was evaluated by omitting the step a) of embedding the heating wire 7 in order to evaluate the characteristics of the ceramic itself.
{Circle around (1)} Maximum length of segregation part The cross section of the sintered body was mirror-polished, observed with a scanning electron microscope (SEM: manufactured by JEOL Ltd.), and the maximum length of the segregation part (μm) was measured.
(2) Porosity The porosity of the sintered body was measured by the Archimedes method.
{Circle around (3)} Electrodeposition strength A four-point bending test according to JIS-R1601 and JIS-R1604 was performed at room temperature and 1100 ° C., and the anti-deposition strength (MPa) was measured.
{Circle around (4)} Oxidation weight increase A 3 × 4 × 35 mm test piece was cut out from each test product, then left in an atmosphere at a temperature of 1000 ° C. for 100 hours, oxidized, and then increased in weight (mg / cm ^2). ) Was measured.
(5) Conducting performance Attach test electrodes to each test product, apply DC current, control the voltage so that the saturation temperature becomes 1100 ° C, conduct for 1 minute, and endurance of rapid cooling by blowing air for 1 minute The test was performed 10,000 times to measure the change in resistance and the precipitation strength.
[0014]
[Table 2]

[0015]
As shown in Table 2 above, no. Since the proportion of Yb ₂ O ₃ in the rare earth element was low (less than 80% by weight), the maximum length of the segregation portion of the sintering aid was 3 μm or more in the test samples 9 and 10, and the anti-deposition at room temperature and 1100 ° C. Low strength and low oxidation resistance. No. In the test sample No. 11, since “Al ₂ O ₃ + AlN” (the amount of Al) was excessive (exceeding 5% by weight), the heat resistance was lowered, the high-temperature strength and the oxidation resistance were lowered, and furthermore, the current was not applied. The performance (resistance change, strength after energization) also decreases. No. Test specimen No. 12 had a low amount of Al compound (less than 1% by weight), and Test sample No. 13 has a small amount of Yb ₂ O ₃ (less than 5% by weight), and therefore does not sufficiently densify due to insufficient sintering aid, and has a high anti-deposition strength, oxidation resistance, and electric current. After strength decreases. No. In the test sample No. 14, since Yb ₂ O ₃ is excessive (exceeding 12% by weight), high-temperature strength and oxidation resistance are reduced, and furthermore, current carrying performance (resistance change, strength after current passing) is reduced.
[0016]
On the other hand, No. 1 containing 5 to 12% by weight of a rare earth element compound or the like containing an Al compound or the like in an amount of 1 to 5% by weight in terms of Al and Yb in an amount of 80% by weight or more in terms of oxide. Each of the test articles 1 to 8 (the ceramic heating element 4 satisfying the composition of the present invention) has extremely high anti-deposit strength at room temperature and 1100 ° C., and shows high anti-deposit strength of 900 MPa or more even at 1100 ° C. In addition, the oxidation resistance is very small, 0.1 mg / cm ² or less at 1000 ° C. for 100 hours, and the oxidation resistance is excellent. Furthermore, no change in resistance was observed in the current-carrying performance, and it was confirmed that the strength after current-carrying was excellent at 900 MPa or more.
[0017]
【The invention's effect】
The ceramic heating element of the present invention specifies the content of the Al compound and the like and the content of the rare earth element compound and the like contained in the ceramic sintered body, and sets the maximum length of the segregated portion mainly composed of the sintering aid component. By setting the thickness to 3 μm, high strength, excellent oxidation resistance, and excellent current-carrying performance (resistance change, strength after current-carrying) are obtained.
[Brief description of the drawings]
FIG. 1 is a sectional view of a glow plug using a ceramic heating element according to the present embodiment.
[Explanation of symbols]
4 Ceramic heating element 6 Ceramic sintered body 7 Heating wire

Claims (1)

In a ceramic heating element having a heating wire embedded in a ceramic sintered body,
The ceramic sintered body is a sialon-based sintered body to which Al or an Al compound as a sintering aid component and a rare earth element compound are added, and the sialon-based sintered body is obtained by converting Al or an Al compound into Al. A segregation part mainly containing the sintering aid component, while containing 5 to 12% by weight of a rare earth element or a rare earth element compound containing 1 to 5% by weight and Yb in an amount of 80% by weight or more in terms of oxide; Wherein the maximum length of the ceramic heating element is 3 μm or less.

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