JP4064277B2 - Ceramic heater - Google Patents

Description

【００２７】
上記で得られたセラミックヒータ本体１〜１１についての熱膨張係数、粒界強度及び絶縁抵抗値を測定した。その結果を以下の表１に示す。ここで、ヒータ部材の熱膨張係数（ｐｐｍ／℃）は下記の式により算出することができる。
熱膨張係数（ｐｐｍ／℃）＝−{（１０００℃における標準試料長さ−１０００℃における測定試料長さ）／〔３０℃における測定試料長さ×（１０００℃−３０℃）〕}+８．４５×１０^−６
なお、上記式において、「１０００℃における標準試料長さ」は、標準試料として１０００℃における熱膨張係数が８．４５×１０^−６／℃であるアルミナを使用した場合のこのアルミナの１０００℃における長さを意味する。尚、この標準試料の３０℃における長さは、測定試料の３０℃における長さと等しい長さであるとする。また、発熱体の熱膨張係数は上記の式より算出すると、４．６ｐｐｍ／℃である。また、界面強度（ＭＰａ）は、ＪＩＳ Ｒ １６０１に準じて界面部の３点曲げ強度を測定して求めた。なお、表１において、Ｎｏ．２〜５が本発明範囲の実施例であり、その他の＊で示したのがＮｏ．１、６、７比較例である。
【００２８】
これによると、Ｎｏ．６は熱膨張係数が、３．４ｐｐｍ／℃となり、他の実施例と比較すると、発熱体との熱膨張係数の差が大きくなる。また、Ｎｏ．１、７は界面強度が３７６ＭＰａ、３２３ＭＰａと他の実施例よりも強度が弱い。よって、Ｎｏ．２〜５の実施例のようにＣｒとＷとからなる化合物を粒径が３μｍ未満で５〜１０ｖｏｌ％とすることで、ヒータ部材の熱膨張係数を向上させ、ヒータ部材と発熱体との熱膨張係数の差を少なくし、且つＣｒ成分がヒータ部材と発熱体の界面に凝集することを抑制することができる。
【００２９】
さらに、本発明の実施例である、Ｎｏ．２〜５、８〜１１について絶縁抵抗値を測定した。絶縁抵抗値は、上記焼結体を３ｍｍ×４ｍｍ×１７ｍｍの形状の試験片に加工し、測定装置として東亜電波工業株式会社製超絶縁計「ＳＭ−８２０５」を用いて、室温にてこの試験片の両端をワニ口クリップ端子により挟み、１０００Ｖの電圧を１分間チャージした後、抵抗値を測定した。その結果を表１に示す。また、実施例のＳｉＣの平均粒径について表１に示す。
【００３０】
さらに、Ｎｏ．８は、ＳｉＣの含有量が１．０８ｖｏｌ％と少ないため、絶縁性が７×１０^３Ωと少ない。Ｎｏ．９は、ＳｉＣの平均粒径が０．０５と小さいため、７×１０^３Ωと少ない。Ｎｏ．１０は、ＳｉＣの平均粒径が１．２０と大きいため、１０×１０^３Ωと少ない。Ｎｏ．１１は、ＳｉＣの含有量が４．８２ｖｏｌ％と多いため、絶縁性が９×１０^３Ωと少ない。よって、ＳｉＣの平均粒径０．１〜１．０μｍであって且つ１．５〜４ｖｏｌ％含有することで、ヒータ部材の絶縁性も良好に保つことができることが判る。
【図面の簡単な説明】
【図１】本発明の実施形態１を示すグロープラグ１の縦断面図である。
【図２】図１の要部を示す縦断面図である。
【図３】グロープラグ１のセラミックヒータ２の製造工程の説明図である。
【図４】図３に続く、グロープラグ１の製造工程の説明図である。
【符号の説明】
１・・・グロープラグ、２・・・セラミックヒータ本体、２１・・・ヒータ部材、２２・・・発熱体、２３、２４・・・リード端子、３・・・外筒、３１・・・突出部、４・・・主体金具、５・・・中軸、６・・・セラミックリング、７・・・ガラス充填層、８・・・絶縁ブッシュ、９・・・端子金具、１００・・・リング部材、２００・・・複合成形体、２１１、２１２・・・分割成形体、２２０・・・発熱部粉末成形体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic heater, and more particularly to a ceramic glow plug used for a diesel engine or the like, and a ceramic heater used for sensor heating or fan heater heating.
[0002]
[Prior art]
A conventional ceramic heater used for starting a diesel engine or early activation of various sensors has a structure in which a heating element made of conductive ceramic is embedded in a heater member. In particular, when high-temperature performance of 1200 ° C. or higher is required, a heating element mainly composed of Mo, W silicide, nitride, or carbide is embedded in a heater member made of silicon nitride ceramic having excellent corrosion resistance at high temperatures. A ceramic heater is used.
[0003]
In such a ceramic heater, the difference between the thermal expansion coefficient of the heater member and the thermal expansion coefficient of the heating element is large, and stress due to heat is applied to the ceramic heater during use. As a result, a crack or the like is generated in the heater member, and in some cases, the heater member may be broken. Therefore, in the conventional ceramic heater, various studies have been made in order to bring the coefficient of thermal expansion of the heater member closer to that of the heating element. For example, a heater member made of nitride ceramic contains at least 1 vol% and less than 5 vol% of metal carbide, silicide, nitride, boride having a larger thermal expansion coefficient than the heater member. Yes. (See Patent Document 1)
[0004]
[Patent Document 1]
JP 10-25162 (2nd page)
[0005]
[Problems to be solved by the invention]
However, in the ceramic heater disclosed in Patent Document 1, the content of the above-described metal carbide, silicide, nitride, and boride in the heater member is limited in order to ensure the insulation of the heater member. Therefore, the difference in coefficient of thermal expansion between the heater member and the heating element cannot be made sufficiently small.
[0006]
The present invention has been made in view of these problems, and an object of the present invention is to provide a ceramic heater that reduces a difference in thermal expansion coefficient between a heater member and a heating element and suppresses cracking and breakage of the heater member. To do.
[0007]
[Means for Solving the Invention]
The ceramic heater of the present invention is a ceramic heater in which a heating element having Mo or W silicide, nitride, or carbide as a main component is embedded in a heater member.
The heater member includes silicon nitride as a main component, a rare earth element, a Cr compound, a compound having a particle size of less than 3 μm and 5 to 10 vol% Cr and W, and 0.4 to 1.1 vol% W. It is characterized by containing the compound of these.
[0008]
As a result of investigations by the present inventors, it has been clarified that further high thermal expansion of the heater member can be achieved by dispersing a Cr compound having a predetermined particle diameter in the heater member. In addition, although Cr compound is contained also in the conventional ceramic heater, high thermal expansion is attained by containing a larger amount than the conventional content. However, if the heater member simply contains a large amount of Cr compound, the Cr component of the heater member aggregates in the vicinity of the boundary between the heater member and the heating element, and there is a problem that causes a decrease in strength such as breakage of the heating element. It was. Therefore, as a result of further investigation by the inventors, instead of containing a large amount of the compound of Cr, by containing a predetermined amount of the compound of Cr and W while containing a predetermined amount of the compound of Cr, It has been found that the Cr component of the heater member can be prevented from aggregating near the boundary. That is, by containing a predetermined amount of a compound consisting of Cr and W in the heater member, the coefficient of thermal expansion of the heater member can be improved, the difference in coefficient of thermal expansion between the heater member and the heating element can be reduced, and the Cr component is the heater. The strength reduction of the heating element can be suppressed without aggregating near the boundary between the member and the heating element.
[0009]
In addition, content of the compound which consists of Cr and W shall be 5-10 vol%. When the content of the compound consisting of Cr and W is less than 5 vol%, the effects as described above cannot be obtained. On the other hand, when the content of the compound composed of Cr and W exceeds 10 vol%, the Cr component in the heater member increases, the Cr component aggregates near the boundary between the heater member and the heating element, and the heating element strength decreases. To do. Moreover, the insulation resistance value of the heater member obtained will fall.
[0010]
The average particle size of the compound composed of Cr and W is 3 μm or less. When the average particle size of the compound composed of Cr and W exceeds 3 μm, the compound composed of Cr and W whose particle size is larger than the particle size of the silicon nitride ceramic increases in the heater member, and the strength of the heater member decreases. This is not preferable.
[0011]
And a heater member is good to contain the compound of 0.4-1.1 vol% W. By containing the W compound, it is possible to suppress the Cr compound contained in the heater member from aggregating at the interface between the heater member and the heating element. In addition, when it is less than 0.4 vol, the above effects cannot be obtained, and when it exceeds 1.1 vol, the difference in thermal expansion coefficient between the heater member and the heating element becomes large, and the heater member is cracked or broken. Can not be suppressed.
[0012]
Further, in the ceramic heater, the compound composed of Cr and W is preferably a solid solution of Cr silicide and W silicide.
[0013]
Since Cr silicide (CrSi2) has a large thermal expansion coefficient, high thermal expansion can be achieved without adding a large amount. Therefore, W component also becomes silicide accordingly. That is, if the compound composed of Cr and W is a solid solution of Cr silicide and W silicide, high thermal expansion can be achieved without adding a large amount of the compound composed of Cr and W.
[0014]
Furthermore, it is good to contain silicon carbide with an average particle diameter of 0.1-1.0 micrometer by 1.5-4 vol%. By containing silicon carbide in the heater member, grain growth of silicon nitride particles can be suppressed. Thereby, the specific surface area of the silicon nitride particles as an insulator is increased, and it is possible to suppress the formation of a conductive path by conductive particles of Cr and W. Therefore, the insulation of the heater member can be maintained. When the average particle size of silicon carbide is less than 0.1 μm, the above effect cannot be obtained. Moreover, when the average particle diameter of silicon carbide exceeds 1.0 μm, the grain growth of silicon nitride cannot be suppressed, and the insulation resistance value of the heater member decreases.
[0015]
Furthermore, when the silicon carbide content is less than 1.5 vol%, the grain growth of silicon nitride particles cannot be suppressed, and the above effect cannot be obtained. On the other hand, when the content of silicon carbide exceeds 4 vol%, the insulation resistance value of the heater member decreases due to the conductivity of silicon carbide itself.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 shows the internal structure of a glow plug 1 which is an example of the heater of the present invention. FIG. 2 is an enlarged view of the main part. The glow plug 1 includes a ceramic heater body 2, an outer cylinder 3 that holds the ceramic heater body 2, a metal shell 4 that holds the outer cylinder 3, and a middle shaft 5 that is disposed on the rear end side of the ceramic heater body 2.
[0017]
In the ceramic heater body 2, a heating element 22 is embedded on the front end side of the heater member 21 having a rod shape, and a pair of lead terminals 23 and 24 that energize the heating element 22 are exposed on the outer peripheral surface of the rear end portion of the heater member 21. Is formed. The heating element 22 is made of a mixture of tungsten carbide (WC) and molybdenum disilicide (MoSi2) conductive ceramic and insulating ceramic, and has a U-shape. The heater member 21 is composed mainly of silicon nitride, a rare earth element such as Yb ₂ O ₃ , a Cr compound such as Cr ₂ O ₃ , and Cr and W having a particle diameter of less than 3 μm and 5 to 10 vol%. And a compound containing Thereby, the thermal expansion coefficient of the heater member 21 is improved, the difference in thermal expansion coefficient between the heater member 21 and the lead terminals 23 and 24 or the heating element 22 is reduced, and the Cr component is between the heater member 21 and the heating element 22. Suppresses aggregation at the interface. Furthermore, it is preferable to contain 0.4 to 1.1 vol% of the W compound. Thereby, it can suppress that Cr component of the further heater member 22 aggregates in the interface of the heater member 21 and the heat generating body 22. FIG. Further, the compound composed of Cr and W is preferably a solid solution of Cr silicide and W silicide. Thereby, the high thermal expansion of the heater member 21 can be achieved without containing a large amount of a compound composed of Cr and W. Furthermore, it is good to contain 1.5-4 vol% of silicon carbide with an average particle diameter of 0.1-1.0 micrometer. Thereby, the insulation of the heater member 22 can be maintained. The lead terminals 23 and 24 are made of a mixture of conductive ceramics and insulating ceramics having different electrical resistivity from the heating element 22.
[0018]
The outer cylinder 3 is a stainless steel cylindrical member such as SUS630 or SUS430, and is held inside itself with the front end side and rear end side of the ceramic heater body 2 protruding. And the front end surface of the metal shell 4 made of S40C and the rear end surface of the outer cylinder 3 are joined, and the rear end side of the outer cylinder 3 is fitted to the metal shell 4. Further, the outer cylinder 3 and one lead terminal 24 are mechanically and electrically connected.
[0019]
A screw portion 41 for fixing the glow plug 1 to an engine block (not shown) is formed on the outer peripheral surface of the metal shell 4, and a middle shaft 5 is attached to the rear end side.
[0020]
Next, the middle shaft 5 is disposed in an insulated state from the metal shell 4, a ceramic ring 6 is disposed between the outer peripheral surface of the rear end side of the middle shaft 5 and the inner peripheral surface of the metal shell 4, and glass is disposed on the rear end side. The filling layer 7 is fixed. A ring-side engagement portion 61 is formed on the outer peripheral surface of the ceramic ring 6 in the form of a large diameter portion, and the metal fitting formed in the shape of a circumferential step near the rear end of the inner peripheral surface of the metal shell 4. By engaging with the side engaging portion 42, the tip end side is prevented from coming off. Moreover, the outer peripheral surface part which contacts the glass filling layer 7 of the center shaft 5 is provided with irregularities by knurling or the like. Further, the rear end portion of the middle shaft 5 extends rearward of the metal shell 4, and a terminal metal fitting 9 is fitted into the extended portion via an insulating bush 8. The terminal fitting 9 is fixed in a conductive state to the outer peripheral surface of the middle shaft 5 by a caulking portion 91 in the circumferential direction.
[0021]
On the other hand, the rear end side outer peripheral surface of the ceramic heater body 2 is made of stainless steel such as SUS630 or SUS430 that is electrically connected to the lead terminal 23 (lead terminal 23 different from the lead terminal 24 electrically connected to the outer cylinder 3). The ring member 100 is attached so as to cover the lead terminal 23. The ring member 100 is attached by brazing, binding, welding or the like. The middle shaft 5 and the ring member 100 are electrically connected by a metal lead 110 having one end welded to the ring member 100 and the other end welded to the middle shaft 5.
[0022]
Hereinafter, a method for manufacturing the glow plug 1 will be described. First, as shown in FIG. 3, a heating element powder molded body 220 in which the heating element 22 and the lead terminals 23 and 24 are integrated is formed by injection molding. Moreover, the division | segmentation molded bodies 211 and 212 as a main body molded object formed in the upper-lower separate body are prepared by carrying out the die press molding of the raw material powder for forming the ceramic main body 21 previously. In these divided molded bodies 211 and 212, concave portions having a shape corresponding to the heating element powder molded body 220 are formed on the mating surfaces thereof, and the heating element powder molded body 220 is accommodated therein to form the divided preforms as described above. As shown in FIG. 3 (b), a composite molded body 200 in which these are integrated is produced by fitting on the mating surfaces and further pressing and compressing.
[0023]
The composite molded body 200 thus obtained is subjected to a binder removal process, and then fired at 1700 ° C. or higher, for example, around about 1800 ° C. by hot pressing or the like to obtain a fired body, and further, the outer peripheral surface is polished into a cylindrical shape. The main body 2 is obtained. Then, as shown in FIG. 4, the ring member 100 is attached by press fitting or the like so as to be electrically connected to the pair of lead terminals 23. Similarly, the outer cylinder 3 is attached to the ceramic heater body 2 by press-fitting or the like so as to be electrically connected to the pair of lead terminals 24.
[0024]
Then, one end of the metal lead 110 is welded to the ring member 100 by resistance welding or the like. Thereafter, the other end of the metal lead 100 is welded to the distal end side of the middle shaft 5 by resistance welding or the like. When the metal shell 4 and necessary parts are assembled by a known method, the glow plug 1 shown in FIG. 1 is completed.
[0025]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples and comparative examples.
Silicon nitride powder having an average particle size of 0.7 μm, Cr compound powder such as Yb ₂ O _{3 having} an average particle size of 1.0 μm and Cr ₂ O ₃ .CrSi ₂ having an average particle size of 1.0 μm as the rare earth oxide, A silicon carbide powder having a diameter of 1.0 μm and α or β as a crystal structure, a powder of silicon dioxide, and a W compound powder such as WSi _{2 having} an average particle diameter of 1.0 μm are blended in the composition shown in Table 1, and this is mixed with silicon nitride. Wet mixing was performed in ethanol for 40 hours using a manufactured cobblestone, and then dried in a hot water bath. Thereafter, the powder of the heater member obtained in this way is pressure-molded to prepare a divided molded body as a main body molded body formed separately in upper and lower parts. Then, a heating element composed of WC.Si3N4 as a main component and a rare earth oxide as an auxiliary agent is accommodated in the divided molded body, and simultaneously fired by hot pressing in a nitrogen atmosphere at 1800 ° C. and 25 MPa for 1 hour, 20 mm The bar-shaped members 1-9 of x40mmx40mm were obtained. And this rod-shaped member No. 1-9 are processed into a shape of 3 mm × 4 mm × 40 mm, and the ceramic heater body No. 1 is processed. 1 to 11 were obtained.
[0026]
[Table 1]

[0027]
The thermal expansion coefficient, grain boundary strength, and insulation resistance value of the ceramic heater bodies 1 to 11 obtained above were measured. The results are shown in Table 1 below. Here, the thermal expansion coefficient (ppm / ° C.) of the heater member can be calculated by the following equation.
Thermal expansion coefficient (ppm / ° C.) = − {(Standard sample length at 1000 ° C.−measured sample length at 1000 ° C.) / [Measured sample length at 30 ° C. × (1000 ° C.−30 ° C.)]} + 8. 45 × 10 ⁻⁶
In the above formula, “standard sample length at 1000 ° C.” means that when alumina having a thermal expansion coefficient of 8.45 × 10 ⁻⁶ / ° C. at 1000 ° C. is used as a standard sample, this alumina at 1000 ° C. It means length. It is assumed that the length of the standard sample at 30 ° C. is equal to the length of the measurement sample at 30 ° C. Further, the thermal expansion coefficient of the heating element is 4.6 ppm / ° C. when calculated from the above formula. The interface strength (MPa) was determined by measuring the three-point bending strength at the interface according to JIS R 1601. In Table 1, no. Nos. 2 to 5 are examples of the scope of the present invention. 1, 6, and 7 are comparative examples.
[0028]
According to this, no. No. 6 has a coefficient of thermal expansion of 3.4 ppm / ° C., and the difference in coefficient of thermal expansion from that of the heating element is larger than in other examples. No. Nos. 1 and 7 have interfacial strengths of 376 MPa and 323 MPa, which are weaker than other examples. Therefore, no. The thermal expansion coefficient of the heater member is improved by making the compound composed of Cr and W 5 to 10 vol% with a particle size of less than 3 μm as in the examples 2 to 5, and the heat of the heater member and the heating element It is possible to reduce the difference in expansion coefficient and to suppress the Cr component from aggregating at the interface between the heater member and the heating element.
[0029]
Furthermore, No. 1, which is an example of the present invention. The insulation resistance values were measured for 2 to 5 and 8 to 11. Insulation resistance value was determined by processing the above sintered body into a test piece having a shape of 3 mm × 4 mm × 17 mm and using a super insulation meter “SM-8205” manufactured by Toa Denpa Kogyo Co., Ltd. as a measuring device. Both ends of the piece were sandwiched between alligator clip terminals and charged with a voltage of 1000 V for 1 minute, and then the resistance value was measured. The results are shown in Table 1. Moreover, it shows in Table 1 about the average particle diameter of SiC of an Example.
[0030]
Furthermore, no. No. 8 has a low SiC content of 1.08 vol%, and therefore has a low insulating property of 7 × 10 ³ Ω. No. No. 9 is as small as 7 × 10 ³ Ω because the average particle size of SiC is as small as 0.05. No. No. 10 is as small as 10 × 10 ³ Ω because the average particle size of SiC is as large as 1.20. No. No. 11 has a high SiC content of 4.82 vol%, and therefore has a low insulating property of 9 × 10 ³ Ω. Therefore, it can be seen that the insulating property of the heater member can be kept good by containing SiC with an average particle size of 0.1 to 1.0 μm and containing 1.5 to 4 vol%.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a glow plug 1 showing a first embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing a main part of FIG.
FIG. 3 is an explanatory diagram of a manufacturing process of the ceramic heater 2 of the glow plug 1;
4 is an explanatory diagram of a manufacturing process of the glow plug 1 subsequent to FIG. 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glow plug, 2 ... Ceramic heater main body, 21 ... Heater member, 22 ... Heat generating body, 23, 24 ... Lead terminal, 3 ... Outer cylinder, 31 ... Projection 4, 4 ... metal shell, 5 ... middle shaft, 6 ... ceramic ring, 7 ... glass-filled layer, 8 ... insulating bush, 9 ... terminal fitting, 100 ... ring member , 200... Composite molded body, 211, 212... Split molded body, 220.

Claims (4)

In a ceramic heater in which a heating element having Mo or W silicide, nitride or carbide as a main component is embedded in a heater member,
The heater member contains silicon nitride as a main component, and contains a rare earth element, a Cr compound, and a compound composed of Cr and W having a particle diameter of less than 3 μm and 5 to 10 vol%. . The ceramic heater according to claim 1, wherein the heater member contains 0.4 to 1.1 vol% of a W compound. 3. The ceramic heater according to claim 1, wherein the compound composed of Cr and W is a solid solution of a silicide of Cr and a silicide of W. 4. 4. The ceramic heater according to claim 1, comprising 1.5 to 4 vol% of silicon carbide particles having an average particle diameter of 0.1 to 1.0 μm.

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