JP2005317210A - Lanthanum chromite-based heating element having heating part and terminal part and its manufacturing method - Google Patents
Lanthanum chromite-based heating element having heating part and terminal part and its manufacturing method Download PDFInfo
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本発明は、耐久性に優れた発熱部と端子部を有するランタンクロマイト系発熱体およびその製造方法に関するものである。 The present invention relates to a lanthanum chromite heating element having a heat generating portion and a terminal portion excellent in durability and a method for manufacturing the same.
従来より使用されている炭化ケイ素発熱体は大気中で用いる場合には、炭化ケイ素の酸化、及び炭化ケイ素の熱伝導率が高いことから、１５００℃以上の温度領域での使用は不可能であり、１５００℃以下であっても発熱部の寸法を長尺化し、端子部の温度を低下させること及び発熱部の緻密性を高める必要があり、所望の温度とする有効加熱領域に対して発熱体が大型化し、ひいては電気炉が大型化してしまう問題がある。また、急速加熱冷却を繰り返すと酸化を促進させて短期で破断してしまうため寿命にも問題がある。このため、高温焼成や急速昇降温が必要な高機能性ガラス、半導体材料の合成や熱処理などに対応できない。 Conventionally used silicon carbide heating elements cannot be used in the temperature range of 1500 ° C. or higher because of the oxidation of silicon carbide and the high thermal conductivity of silicon carbide when used in the atmosphere. Even if the temperature is 1500 ° C. or lower, it is necessary to lengthen the size of the heat generating portion, to lower the temperature of the terminal portion, and to increase the density of the heat generating portion. However, there is a problem that the electric furnace becomes larger. In addition, repeated rapid heating and cooling promotes oxidation and breaks in a short time, so there is a problem in life. For this reason, it cannot respond to the synthesis | combination of a highly functional glass and a semiconductor material which require high temperature baking and rapid temperature raising / lowering, heat processing, etc.
ペロブスカイト型結晶構造を有するランタンクロマイト（ＬａＣｒＯ３）を主成分とし、必要に応じてＬａの一部をＣａ、Ｓｒなどで、Ｃｒの一部をＣｏ、Ｎｉ、Ａｌ、Ｍｇなどで置換固溶した組成を有する発熱体（以下単にランタンクロマイトという）は１５００℃以上の高温酸化雰囲気において優れた安定性と長寿命をもつセラミックス抵抗発熱体として広く利用されている。
しかし、ランタンクロマイトは難焼結材料であるため、緻密な焼結体が得られがたく、開放気孔を持った状態で使用されている。このような開放気孔を有する焼結体は気孔部分に対応して導通面積が減少するので、導電性が低下するのみならず、高温での使用時に開放気孔からのＣｒの蒸発が多くなり組成変動による特性の低下が起こる。
開放気孔の少ないランタンクロマイトを得るために焼結をより高温で行うことも試みられているが、この場合にはＣｒの蒸発量が増加して、所定の組成を有する焼結体が得られがたくなるばかりでなく、焼成コストが高くなり経済的でない。更に、特許文献１には様々な成分を焼結助剤として添加することにより緻密化が行われてることが記載されているが、焼結体の導電性が大幅に低下してしまうため問題がある。
The main component is lanthanum chromite (LaCrO 3 ) having a perovskite type crystal structure, and if necessary, a part of La is replaced with Ca, Sr, etc., and a part of Cr is replaced by solid solution with Co, Ni, Al, Mg, etc. A heating element having a composition (hereinafter simply referred to as lanthanum chromite) is widely used as a ceramic resistance heating element having excellent stability and long life in a high-temperature oxidizing atmosphere of 1500 ° C. or higher.
However, since lanthanum chromite is a difficult-to-sinter material, it is difficult to obtain a dense sintered body and is used in a state having open pores. Since the sintered body having such open pores has a reduced conductive area corresponding to the pore portion, not only the conductivity is lowered, but also the evaporation of Cr from the open pores increases at the time of use at a high temperature. Degradation of characteristics due to.
In order to obtain lanthanum chromite with fewer open pores, it has also been attempted to perform sintering at a higher temperature, but in this case, the amount of Cr evaporation increases, and a sintered body having a predetermined composition can be obtained. Not only does it make it difficult, but the baking cost is high and it is not economical. Furthermore, Patent Document 1 describes that densification is performed by adding various components as a sintering aid, but there is a problem because the conductivity of the sintered body is greatly reduced. is there.
特許文献２には、ランタンクロマイト発熱体の主成分であるＣｒ２Ｏ３が酸化雰囲気下の高温で蒸発することによる耐久性の劣化を、発熱体に中空部を設けその中空部分にＣｒ２Ｏ３、Ｃｒ２Ｏ３を含む酸化物の混合物又はＣｒ２Ｏ３を含む複合酸化物を充填することによって改善されることが記載されている。しかし、Ｃｒ２Ｏ３の蒸発自体は抑制されないことから、蒸発による炉内汚染および環境面においては問題があった。 Patent Document 2 describes deterioration in durability caused by evaporation of Cr 2 O 3, which is a main component of a lanthanum chromite heating element, at a high temperature in an oxidizing atmosphere. A hollow part is provided in the heating element, and Cr 2 O is provided in the hollow part. 3, Cr 2 mixture of O 3 oxide containing or composite oxide containing Cr 2 O 3 can be improved by filling are described. However, since the evaporation of Cr 2 O 3 itself is not suppressed, there are problems in terms of furnace contamination and environmental aspects due to evaporation.
全体が単一の組成からなる発熱体では、発熱部の電気抵抗を端子部の電気抵抗よりも大きくするために、発熱部の断面積を端子部の断面積よりも小さくする必要があり、成形体あるいは焼結体で加工が必要となるため製造工程にコストがかかる。また、端子部温度を十分に低くするには端子部の断面積を大きくする必要があり、端子部の寸法によって発熱体が大型化し、ひいては電気炉が大型化してしまい実用的でない。更に、発熱体の寿命を長くするには発熱部にかかる表面負荷密度をできるだけ小さくする必要があるが、発熱部の断面積を小さくすると表面負荷密度が高くなり、また、端子部の断面積を大きくすると電気炉に設置できる発熱体本数が発熱に直接寄与しない端子部の寸法によって制限されるために発熱部の全表面積が減少し表面負荷密度が高くなる。このような問題を解決するため、 In a heating element having a single composition as a whole, it is necessary to make the cross-sectional area of the heat generating portion smaller than the cross-sectional area of the terminal portion in order to make the electric resistance of the heat generating portion larger than the electric resistance of the terminal portion. The manufacturing process is costly because processing is required for the body or sintered body. Further, in order to sufficiently lower the terminal portion temperature, it is necessary to increase the cross-sectional area of the terminal portion, and the heating element increases in size due to the size of the terminal portion, and the electric furnace increases in size, which is not practical. Furthermore, in order to extend the life of the heating element, it is necessary to reduce the surface load density applied to the heating part as much as possible. However, if the sectional area of the heating part is reduced, the surface load density increases, and the sectional area of the terminal part increases. If it is increased, the number of heating elements that can be installed in the electric furnace is limited by the dimensions of the terminal portion that does not directly contribute to the heat generation, so the total surface area of the heat generating portion is reduced and the surface load density is increased. To solve these problems,
特許文献３には、ランタンクロマイト系発熱体としてランタンクロマイトのＬａイオンをＣａイオン又はＳｒイオンで１〜１０モル％置換させた固溶体組成を有する発熱部及びランタンクロマイトのＬａイオンをＣａイオン又はＳｒイオンで上記発熱部における置換率以上多くとも２０％以下置換させた固溶体組成を有する端子部からなることを特徴とするランタンクロマイト系発熱体が記載されている。しかし、発熱部と端子部の焼成収縮率に差があり焼成時に亀裂が発生しやすく、また、熱膨張係数が異なるため急速昇降温など厳しい条件下で使用される場合には割れが発生することがあった。それを防止するためには端子部と発熱部との間に端子部と発熱部の組成を混合した中間層を設ける必要があり、製造工程が複雑になりコスト高の要因となっているうえ、有効加熱領域に対して発熱体が大型化し、ひいては電気炉が大型化するという問題があった。 Patent Document 3 discloses a lanthanum chromite heating element having a solid solution composition in which La ions of lanthanum chromite are substituted with 1 to 10 mol% of Ca ions or Sr ions, and La ions of lanthanum chromite as Ca ions or Sr ions. The lanthanum chromite heating element is characterized by comprising a terminal portion having a solid solution composition substituted at a substitution rate of 20% or less in the heating portion. However, there is a difference in the firing shrinkage ratio between the heat generating part and the terminal part, and cracks are likely to occur during firing. Also, since the thermal expansion coefficient is different, cracks will occur when used under severe conditions such as rapid heating and cooling. was there. In order to prevent it, it is necessary to provide an intermediate layer in which the composition of the terminal part and the heat generating part are mixed between the terminal part and the heat generating part, which is a factor in increasing the manufacturing process and increasing the cost. There has been a problem that the heating element is increased in size relative to the effective heating region, and as a result, the electric furnace is increased in size.
また、特許文献４には、化学式Ｌａ１−ｘＡｘＣｒ１−ｙＡｌｙＯ３（式中ＡはＣａおよびＳｒの少なくとも一種を示し０．００５≦ｘ≦０．１２であり、０．０２≦ｙ≦０．５０である）で表されるペロブスカイト型結晶構造を有する焼結体について記載されているが、この焼結体は厚みの薄い肉薄形状でのみ良好な焼結性が得られるものであり、大型肉厚形状品などでは試料の表面付近と内部で均一に焼結せず密度差が生じたり、焼成時の収縮差のためにクラックや割れが発生するなどの問題があった。特に発熱部と端子部の組成が異なる発熱体の場合には、その影響がより大きく、焼結性が悪い場合は発熱部と端子部の中間層を傾斜組成にすることが不可能であり、発熱部と端子部の接合強度が低くなるため中間層で破損しやすく寿命が短くなるという問題があった。 Further, Patent Document 4, the chemical formula La 1-x A x Cr 1 -y Al y O 3 ( wherein A is 0.005 ≦ x ≦ 0.12 indicates at least one of Ca and Sr, 0. 02 ≦ y ≦ 0.50), a sintered body having a perovskite type crystal structure is described. However, this sintered body can obtain good sinterability only in a thin and thin shape. However, there are problems such as large thickness products that do not sinter uniformly near the surface of the sample and inside, resulting in density differences, and cracks and cracks due to shrinkage differences during firing. . In particular, in the case of a heating element having a different composition of the heat generating part and the terminal part, the effect is greater, and when the sinterability is poor, it is impossible to make the intermediate layer of the heat generating part and the terminal part have a gradient composition, Since the bonding strength between the heat generating portion and the terminal portion is low, there is a problem that the intermediate layer is easily damaged and the life is shortened.
本発明は、このような従来の問題点を解決し、高温まで急速加熱および高温からの急速冷却が可能でＣｒの蒸発量が少なく耐久性に優れた発熱部と端子部を有するランタンクロマイト系発熱体を提供することを目的とする。 The present invention solves such conventional problems, and can be rapidly heated to a high temperature and rapidly cooled from a high temperature, and has a heat generating portion and a terminal portion having a low Cr evaporation amount and excellent durability. The purpose is to provide a body.
本発明の前記目的は、発熱体の発熱部と端子部の導電率および導電率比を適切な範囲に設定し、ＬａＣｒＯ３を基本構造とするペロブスカイト型結晶構造を有する材料のＬａの一部をＳｒで、Ｃｒの一部をＡｌで置換すると共に、ある特定微量のＳｉＯ２を該焼結体中に均一に含有させること、発熱部と端子部組成の粉体粒度を制御することで発熱部と端子部の収縮率を同等にし、且つ焼結性を向上させＳｒイオンを端子部から発熱部へと拡散しやすくすることによって発熱部と端子部の中間層を傾斜組成とすることができ、発熱部と端子部の導電率および導電率比、更にかさ密度を一定の範囲となるように制御したランタンクロマイト系発熱体は、高温まで急速加熱および高温からの急速冷却が可能でＣｒの蒸発量が少なく極めて優れた耐久性を有するものとなることを見出し本発明を完成した。即ち、 The object of the present invention is to set the conductivity and conductivity ratio of the heat generating part and the terminal part of the heat generating element within an appropriate range, and to replace a part of La of the material having a perovskite crystal structure having LaCrO 3 as a basic structure. A part of Cr is replaced by Al with Sr, and a certain trace amount of SiO 2 is uniformly contained in the sintered body, and the particle size of the heat generating part and the terminal part composition is controlled to thereby generate the heat generating part. The intermediate layer of the heat generating part and the terminal part can be made into a gradient composition by making the shrinkage rate of the terminal part equal and improving the sinterability and facilitating diffusion of Sr ions from the terminal part to the heat generating part. The lanthanum chromite heating element, which controls the conductivity and conductivity ratio of the heat generating part and the terminal part, and also the bulk density within a certain range, can be rapidly heated to high temperature and rapidly cooled from high temperature, and the amount of Cr evaporated Very good with few The present invention has been completed found that comes to have a durability. That is,
本発明の第１は、発熱部と端子部を有するランタンクロマイト系発熱体において、化学式Ｌａ１−ｘＳｒｘＣｒ１−ｙＡｌｙＯ３（式中、０．００５≦ｘ≦０．１２であり、０．０２≦ｙ≦０．５０である）で表されるペロブスカイト型結晶構造を有し、発熱部および端子部の焼結体中に含有するＳｉＯ２の含有率が３００〜１０００ｐｐｍであり、発熱部および端子部の焼結体の大気中１０００℃における導電率が１〜３０Ｓ／ｃｍであり、発熱部の導電率Ｅ１と端子部の導電率Ｅ２の比率（Ｅ２／Ｅ１）が２〜２０であって、発熱部および端子部の焼結体かさ密度が６．０ｇ／ｃｍ３以上であり、発熱部と端子部の中間層が傾斜組成であることを特徴とする発熱部と端子部を有するランタンクロマイト系発熱体に関する。
本発明の第２は、化学式Ｌａ１−ｘＳｒｘＣｒ１−ｙＡｌｙＯ３（式中、０．００５≦ｘ≦０．１２であり、０．０２≦ｙ≦０．５０である）で表されるペロブスカイト型結晶構造を有し、合成粉末の粉砕、分散工程においてＳｉＯ２を、酸化物もしくは化合物の形態で、最終的な焼結体中における含有率が３００〜１０００ｐｐｍとなるように添加した平均粒子径が０．３〜２．０μｍの発熱部組成の粉末と平均粒子径が０．３〜２．０μｍの端子部組成の粉末を用いて所定形状に成形し、大気中１６００〜１９００℃で焼成することを特徴とする請求項１記載の発熱部と端子部を有するランタンクロマイト系発熱体の製造方法に関する。
A first aspect of the present invention is a lanthanum chromite-based heating element having a heating portion and a terminal portion, wherein a chemical formula La 1-x Sr x Cr 1-y Al y O 3 (where 0.005 ≦ x ≦ 0.12). Yes, and 0.02 ≦ y ≦ 0.50), and the content of SiO 2 contained in the sintered body of the heat generating portion and the terminal portion is 300 to 1000 ppm. The conductivity of the sintered body of the heat generating part and the terminal part at 1000 ° C. in the atmosphere is 1 to 30 S / cm, and the ratio of the electric conductivity E 1 of the heat generating part and the electric conductivity E 2 of the terminal part (E 2 / E 1 ) Is 2 to 20, the sintered body bulk density of the heat generating portion and the terminal portion is 6.0 g / cm 3 or more, and the intermediate layer of the heat generating portion and the terminal portion has a gradient composition. The present invention relates to a lanthanum chromite heating element having a portion and a terminal portion.
The second of the present invention has the formula La 1-x Sr x Cr 1 -y Al y O 3 ( wherein a 0.005 ≦ x ≦ 0.12, a 0.02 ≦ y ≦ 0.50) In the pulverization and dispersion process of the synthetic powder, SiO 2 is formed in the form of oxide or compound so that the content in the final sintered body is 300 to 1000 ppm. The heat generating part composition powder having an average particle diameter of 0.3 to 2.0 μm and the terminal part composition powder having an average particle diameter of 0.3 to 2.0 μm are molded into a predetermined shape, and 1600 in the atmosphere. The method for producing a lanthanum chromite heating element having a heating portion and a terminal portion according to claim 1, wherein the firing is performed at 1900 ° C.
化学式Ｌａ１−ｘＳｒｘＣｒ１−ｙＡｌｙＯ３（０．００５≦ｘ≦０．１２であり、０．０２≦ｙ≦０．５０である）で表されるペロブスカイト型結晶構造を有するランタンクロマイト系発熱体である点について、
本発明のランタンクロマイト系発熱体はＬａＣｒＯ３を基本構造とするペロブスカイト型構造を有する焼結体であり、Ｌａの一部をＳｒで置換固溶し、Ｃｒの一部をＡｌで置換固溶したものである。ＬａＣｒＯ３は焼結過程においてＣｒ分が揮発し、酸化クロムの蒸気圧が高くなって緻密化が阻害され、しかも陽イオンの拡散が極めて遅いために焼結性に劣るものであるが、Ｌａの一部をＳｒで置換固溶すると共に、Ｃｒの一部をＡｌで置換固溶することによって焼結性が大幅に改善され、Ｌａの一部をＳｒで置換固溶しただけの場合に比べると、同じＳｒの置換量であっても、焼結性が向上して非常に緻密な焼結体とすることができる。
また、ＡｌはＣｒと同じ３価の元素であり、従来のペロブスカイト型焼結体においてＣｒの一部を置換固溶していた２価の元素であるＣｏ又はＮｉと比べると、低酸素分圧下での体積膨張に与える影響が少なく、高温の大気中及び低酸素分圧下における安定性を長時間持続することができる。
Formula La 1-x Sr x Cr 1 -y Al y O 3 ( a 0.005 ≦ x ≦ 0.12, a 0.02 ≦ y ≦ 0.50) having a perovskite type crystal structure represented by About the point that it is a lanthanum chromite heating element,
The lanthanum chromite-based heating element of the present invention is a sintered body having a perovskite structure having a basic structure of LaCrO 3, in which a part of La is replaced with Sr and a part of Cr is replaced with Al. Is. LaCrO 3 is inferior in sinterability because the Cr content is volatilized in the sintering process, the vapor pressure of chromium oxide is increased and densification is inhibited, and the diffusion of cations is extremely slow. Sinterability is greatly improved by substituting partly with Sr and partly replacing Cr with Al. Compared to the case where only part of La is replaced with Sr. Even with the same substitution amount of Sr, the sinterability is improved and a very dense sintered body can be obtained.
Al is the same trivalent element as Cr. Compared with Co or Ni, which is a divalent element in which a part of Cr is substituted and dissolved in the conventional perovskite-type sintered body, Al is under a low oxygen partial pressure. It has little influence on volume expansion at high temperature, and can maintain the stability in a high temperature atmosphere and under a low oxygen partial pressure for a long time.
更に、本発明のランタンクロマイト系発熱体は、３価のＬａの一部を２価のＳｒで置換固溶することにより生じた正の電荷の不足分を、置換固溶量に比例してＣｒイオンが３価から４価へとなることにより電荷補償しており、その結果、優れた導電性を有する。
上記化学式の中のＳｒの置換固溶量のモル比であるｘ値は、０．００５≦ｘ≦０．１２であることが必要であり、０．０１≦ｘ≦０．１０であることがより好ましい。ｘ値が０．００５を下回ると、置換固溶量が少ないため焼結性および導電性の向上の効果がない。ｘ値が０．１２を越えた場合には、焼結性および導電性は向上するものの、４価のＣｒが優先的に蒸発するため、Ｃｒ成分の蒸発量が増加して、焼結体の寿命の低下を引き起こしやすい。このため、０．００５≦ｘ≦０．１２であることが必要である。
また、上記化学式の中のＡｌの置換固溶量のモル比であるｙ値は０．０２≦ｙ≦０．５０とし、好ましくは０．０５≦ｙ≦０．３０とする。ｙの値が小さすぎると焼結性改善の効果が小さく、ｙの値が大きくなりすぎると焼結性は向上するものの耐熱性及び導電性が低下し熱膨張係数も大きくなり過ぎるので好ましくない。
Furthermore, the lanthanum chromite heating element according to the present invention can reduce the shortage of positive charges generated by substituting and dissolving a portion of trivalent La with divalent Sr in proportion to the amount of substitutional solid solution. Charge compensation is performed by changing the ion from trivalent to tetravalent, and as a result, it has excellent conductivity.
The x value which is the molar ratio of the substitutional solid solution amount of Sr in the above chemical formula needs to be 0.005 ≦ x ≦ 0.12, and 0.01 ≦ x ≦ 0.10. More preferred. When the x value is less than 0.005, since the substitutional solid solution amount is small, there is no effect of improving the sinterability and conductivity. When the x value exceeds 0.12, the sinterability and conductivity are improved, but since tetravalent Cr evaporates preferentially, the amount of Cr component evaporated increases, It tends to cause a decrease in life. For this reason, it is necessary that 0.005 ≦ x ≦ 0.12.
The y value, which is the molar ratio of the substitutional solid solution amount of Al in the above chemical formula, is 0.02 ≦ y ≦ 0.50, preferably 0.05 ≦ y ≦ 0.30. If the value of y is too small, the effect of improving the sinterability is small, and if the value of y is too large, the sinterability is improved but the heat resistance and conductivity are lowered and the thermal expansion coefficient is too large, which is not preferable.
発熱部および端子部の焼結体中に含有するＳｉＯ２の含有率が３００〜１０００ｐｐｍであるである点について、
従来の技術においては、該耐熱導電性セラミックスの製造工程中において、Ａｌ成分やＳｉ成分が混入すると導電性及び耐熱性が低下するため、製造工程においてこれらの成分の混入を極力抑えることが必要とされていた。しかし、本発明者らが鋭意研究した結果、Ｌａの一部をＳｒで置換固溶した場合には、該焼結体に対してある特定微量の範囲のＳｉＯ２を焼結体中に均一に含有させることにより、導電性及び耐熱性を低下させることなく焼結性を向上させることが可能であることを見出した。これにより、Ｌａの一部をＳｒで置換固溶すると共に、Ｃｒの一部をＡｌで置換固溶しただけの場合に比べると、同じ置換量であっても焼結性がより向上して非常に緻密な焼結体を得ることができる。また、これによりＳｒイオンが端子部から発熱部へと拡散しやすくなるため、発熱部と端子部の接合強度を更に高めることができ、加熱冷却による劣化が少なく長寿命となる。また、Ｃｒ成分の分解蒸発量を小さくすることができ、６価のＣｒの発生量も極めて微量に抑制することが可能である。焼結体に含有するＳｉＯ２の含有率が３００ｐｐｍ未満ではＳｉ成分による焼結性の向上は見られず、ＳｉＯ２の含有量が１０００ｐｐｍを越える場合にはＳｉ成分の量が過多となり、焼結性は向上するものの、導電性及び耐熱性の低下が発生するため問題がある。このため、焼結体中に含有するＳｉＯ２の含有率が３００〜１０００ｐｐｍであることが必要であり、４００〜８００ｐｐｍであることがより好ましい。
About the point that the content rate of SiO 2 contained in the sintered body of the heat generating part and the terminal part is 300 to 1000 ppm,
In the conventional technology, when Al component or Si component is mixed in the manufacturing process of the heat-resistant conductive ceramics, the conductivity and heat resistance are lowered. Therefore, it is necessary to suppress the mixing of these components as much as possible in the manufacturing process. It had been. However, as a result of intensive studies by the present inventors, when a part of La is substituted and dissolved with Sr, a certain small amount of SiO 2 in the sintered body is uniformly distributed in the sintered body. It has been found that the inclusion makes it possible to improve the sinterability without lowering the conductivity and heat resistance. As a result, a part of La is solid-dissolved with Sr and a part of Cr is solid-dissolved with Al. A dense sintered body can be obtained. In addition, since Sr ions easily diffuse from the terminal portion to the heat generating portion, the bonding strength between the heat generating portion and the terminal portion can be further increased, and the deterioration due to heating and cooling is reduced and the life is prolonged. In addition, the amount of decomposition and evaporation of the Cr component can be reduced, and the amount of hexavalent Cr generated can be suppressed to a very small amount. When the content of SiO 2 contained in the sintered body is less than 300 ppm, the sinterability is not improved by the Si component. When the content of SiO 2 exceeds 1000 ppm, the amount of the Si component is excessive, and the sintering is performed. However, there is a problem because conductivity and heat resistance are reduced. Therefore, the content of SiO 2 contained in the sintered body is required to be 300～1000Ppm, more preferably 400～800Ppm.
発熱部および端子部の焼結体の大気中１０００℃における導電率が１〜３０Ｓ／ｃｍである点について、
本発明において、導電率は焼結体を３×４×４０ｍｍ角棒の形状に削りだし、白金電極および電圧測定用の白金リード線を端子間距離１８ｍｍとなるように約１３００℃で焼き付け、直流４端子法により大気中１０００℃で測定した値である。
導電率が１Ｓ／ｃｍ未満の場合には、導電率が不十分であり抵抗が高いために制御に必要な印加電圧値の範囲が大きくなり実用的ではない。導電率が３０Ｓ／ｃｍを上回る場合には、抵抗が小さすぎて大電流型となり、電極、リード線との接触抵抗やリード線等の配線抵抗を低く抑えないと局所的に発熱するため、取扱に細心注意を必要とするのみならず、大電流に対応させるべく電源装置の容量も大型化するため実用的ではない。このため、大気中１０００℃における導電率は１〜３０Ｓ／ｃｍの範囲にあることが必要であり、１．５〜２０Ｓ／ｃｍの範囲であることが好ましい。
About the point that the conductivity at 1000 ° C. in the atmosphere of the sintered body of the heat generating part and the terminal part is 1 to 30 S / cm,
In the present invention, the electrical conductivity is obtained by cutting the sintered body into a 3 × 4 × 40 mm square bar shape, baking the platinum electrode and the platinum lead wire for voltage measurement at about 1300 ° C. so that the distance between terminals is 18 mm, It is a value measured at 1000 ° C. in the atmosphere by the 4-terminal method.
When the electrical conductivity is less than 1 S / cm, the electrical conductivity is insufficient and the resistance is high, so that the range of the applied voltage value necessary for control becomes large, which is not practical. If the electrical conductivity exceeds 30 S / cm, the resistance is too small and a large current type is generated. If the contact resistance with the electrode and lead wire and the wiring resistance of the lead wire are not kept low, heat is generated locally. This is not practical because the capacity of the power supply device is increased to cope with a large current. For this reason, the electrical conductivity at 1000 ° C. in the atmosphere needs to be in the range of 1 to 30 S / cm, and preferably in the range of 1.5 to 20 S / cm.
発熱部の導電率Ｅ１と端子部の導電率Ｅ２との比率（Ｅ２／Ｅ１）が２〜２０である点について、
発熱部と端子部の導電率比が２以下の場合、発熱部の抵抗と端子部の抵抗の差が小さすぎて、端子部電極が抵抗発熱を起こすため短寿命となる。発熱部と端子部の導電率比が２０以上の場合、発熱部と端子部の抵抗差が大きくなりすぎるため、繰り返しの熱衝撃に対する耐久性に劣り発熱体が短寿命となり実用的でなくなる。このため、発熱部の導電率Ｅ１と端子部の導電率Ｅ２との比率（Ｅ２／Ｅ１）が２〜２０の範囲とすることが必要であり、２．５〜１０の範囲とすることがより好ましい。
The points ratio between the conductivity E 2 conductivity E 1 and the terminal portion of the heat generating portion (E 2 / E 1) is 2 to 20,
When the conductivity ratio between the heat generating part and the terminal part is 2 or less, the difference between the resistance of the heat generating part and the resistance of the terminal part is too small, and the terminal part electrode generates resistance heat, resulting in a short life. When the electrical conductivity ratio between the heat generating portion and the terminal portion is 20 or more, the resistance difference between the heat generating portion and the terminal portion becomes too large, so that the durability against repeated thermal shock is inferior and the heat generating element has a short life and becomes impractical. For this reason, the ratio (E 2 / E 1 ) between the conductivity E 1 of the heat generating part and the conductivity E 2 of the terminal part needs to be in the range of 2 to 20, More preferably.
発熱部および端子部の焼結体かさ密度が６．０ｇ／ｃｍ３以上である点について、
かさ密度が６．０ｇ／ｃｍ３未満では気孔の増加により機械的強度および導電率が低下し、また気孔を含めた焼結体の表面積が増加するために、高温の酸化雰囲気中でのＣｒ成分の蒸発量も増加するため、より高温で使用する場合や急速加熱冷却など過酷な条件で使用する場合には、Ｃｒの蒸発による寿命の低下や、熱応力による亀裂が生じたりするため実用上問題がある。従って、かさ密度が６．０ｇ／ｃｍ３以上であることが必要であり、６．２ｇ／ｃｍ３以上であることがより好ましい。
About the point that the sintered body bulk density of the heat generating part and the terminal part is 6.0 g / cm 3 or more,
When the bulk density is less than 6.0 g / cm 3 , the mechanical strength and electrical conductivity are reduced due to the increase in pores, and the surface area of the sintered body including the pores is increased. As the amount of evaporation increases, when used at higher temperatures or under harsh conditions such as rapid heating and cooling, there is a problem in practical use because the life of the Cr decreases and cracks occur due to thermal stress. There is. Accordingly, the bulk density needs to be 6.0 g / cm 3 or more, and more preferably 6.2 g / cm 3 or more.
発熱部と端子部の中間層が傾斜組成である点について、
従来のランタンクロマイト系発熱体では端子部と発熱部の熱膨張率が異なるため、加熱冷却により大きな熱応力が発生し耐熱衝撃性に劣り、発熱部と端子部の間に発熱体の温度勾配を緩和するため、また発熱部と端子部の収縮率および焼結性に差があり焼成時に亀裂が発生する可能性が大きかったため、発熱部と端子部の組成を混合した中間層を形成する必要があった。しかし、本発明者らが鋭意研究した結果、発熱部および端子部組成の粉体粒度を制御することで発熱部と端子部の収縮率を同等にし、且つ焼結性を向上させＳｒイオンを端子部から発熱部へと拡散しやすくすることによって、発熱部と端子部の反応性を高め中間層を傾斜組成にすることができ、発熱部と端子部の組成を混合した中間層を設けなくても発熱部と端子部を緻密で強固な接合状態にすることが可能であることを見出した。
尚、本発明における傾斜組成とは発熱部と端子部の中間層を段階的にＳｒ量を変化させた組成のことを示す。これにより、発熱部と端子部の組成を大きく変化させて端子部温度を低下することも可能となる。更に、発熱部と端子部の組成を混合した中間層の作製が必要なくなるため製造工程が簡略化され、コストも安くすることができる。発熱部と端子部の中間層が傾斜組成でない場合には、熱膨張差により大きな熱応力が発生し使用時に亀裂が生じるため、発熱部と端子部の中間層は傾斜組成であることが必要である。
About the intermediate layer of the heat generating part and the terminal part is a gradient composition,
In the conventional lanthanum chromite heating element, the thermal expansion coefficient of the terminal part and the heating part is different, so a large thermal stress is generated by heating and cooling, resulting in poor thermal shock resistance, and the temperature gradient of the heating element is increased between the heating part and the terminal part. It is necessary to form an intermediate layer in which the composition of the heat generating part and the terminal part are mixed because the shrinkage rate and sintering property of the heat generating part and the terminal part are different and the possibility of cracking during firing is large. there were. However, as a result of diligent research by the present inventors, by controlling the powder particle size of the heat generating part and the terminal part composition, the shrinkage rate of the heat generating part and the terminal part is made equal, the sinterability is improved, and the Sr ions are terminalized. By making it easy to diffuse from the heat generating part to the heat generating part, the reactivity of the heat generating part and the terminal part can be increased and the intermediate layer can be made into a gradient composition, and an intermediate layer in which the composition of the heat generating part and the terminal part is mixed is not provided. It has also been found that the heat generating portion and the terminal portion can be in a dense and strong bonded state.
The gradient composition in the present invention means a composition in which the Sr amount is changed stepwise in the intermediate layer of the heat generating portion and the terminal portion. As a result, the composition of the heat generating portion and the terminal portion can be greatly changed to lower the terminal portion temperature. Furthermore, since it is not necessary to prepare an intermediate layer in which the composition of the heat generating portion and the terminal portion is mixed, the manufacturing process is simplified and the cost can be reduced. If the intermediate layer between the heat generating part and the terminal part is not in a gradient composition, a large thermal stress is generated due to the difference in thermal expansion and cracks occur during use.Therefore, the intermediate layer between the heat generating part and the terminal part must have a gradient composition. is there.
更に、本発明は原料粉末を発熱部組成および端子部組成となるようにそれぞれ所定の割合で配合した粉末混合物を熱処理し、得られた合成粉末の粉砕、分散工程においてＳｉＯ２を、酸化物もしくは化合物の形態で、最終的な焼結体中におけるＳｉＯ２含有率が３００〜１０００ｐｐｍとなるように添加し、平均粒子径０．３〜２μｍ、比表面積３〜７ｍ２／ｇに粉砕し、得られた発熱部組成および端子部組成の粉末を所定形状に成形し、大気中１６００〜１９００℃で焼成することにより、優れた耐久性を有するランタンクロマイト系発熱体を提供することができる。焼結体に対してある特定微量の範囲のＳｉＯ２を焼結体中に均一に含有させることにより、導電性および耐熱性を低下させることなく焼結性を向上させることが可能であるため、焼結体中におけるＳｉＯ２含有率が３００〜１０００ｐｐｍとなるようにＳｉＯ２を均一に分散することが重要である。粉砕後の平均粒子径が２μｍより大きいと、粉末の活性度が低いため焼結性が悪くなり、発熱部と端子部の反応性が低下するため好ましくない。また、平均粒子径が０．３μｍより小さいと、焼結性は良いが焼結収縮による変形が大きく発熱部と端子部の中間層で亀裂が発生しやすくなるため好ましくない。
粉砕後の平均粒子径は０．５〜１．５μｍ、比表面積は３．５〜６．５ｍ２／ｇとすることがより好ましい。
更に、発熱部組成の平均粒子径Ｐ１と端子部組成の平均粒子径Ｐ２の比率（Ｐ２／Ｐ１）が０．５以下あるいは１．５以上の場合には発熱部と端子部の収縮率を同等とすることが困難となり、焼成時にクラックや割れが発生したり、発熱部と端子部の中間層を傾斜組成にすることが困難で、発熱部と端子部の接着強度が低くなり、中間層で破損しやすく寿命が短くなるため、発熱部組成の平均粒子径と端子部組成の平均粒子径の比率（Ｐ２／Ｐ１）が０．５〜１．５であることが好ましい。
発熱部および端子部組成の粉体粒度をこの範囲に制御することで発熱部と端子部の焼結性が良好で且つ収縮率を同等にすることができ、Ｓｒイオンを端子部から発熱部へと拡散しやすくすることによって反応性を高め、中間層を傾斜組成にすることが可能となり、発熱部と端子部は強固に接合される。焼成温度が１９００℃より高いと、結晶子径が大きく成長しすぎて強度の低下を招き、また、焼成中のＣｒ成分の蒸発が多いため、得られた焼結体の寿命が低下する。焼成温度が１６００℃より低いと焼結不足となり機械的特性などの低下を招くだけでなく、発熱部と端子部の反応性が悪くなり接合強度が低下するため好ましくない。焼成温度としては１６５０℃〜１８００℃がより好ましい。
Furthermore, the present invention is respectively so that the heating portion composition and the terminal unit composition of the raw material powder was heat treated powder mixture was blended in a predetermined ratio, ground synthetic powder obtained, the SiO 2 in the dispersion step, the oxide or In the form of a compound, it is added so that the SiO 2 content in the final sintered body is 300 to 1000 ppm, and is pulverized to an average particle diameter of 0.3 to 2 μm and a specific surface area of 3 to 7 m 2 / g. The obtained lanthanum chromite heating element having excellent durability can be provided by forming the powder of the heating part composition and the terminal part composition into a predetermined shape and firing the powder in the atmosphere at 1600 to 1900 ° C. Since it is possible to improve the sinterability without lowering the conductivity and heat resistance by uniformly containing a certain small amount of SiO 2 in the sintered body in the sintered body, It is important to uniformly disperse SiO 2 so that the SiO 2 content in the sintered body is 300 to 1000 ppm. When the average particle diameter after pulverization is larger than 2 μm, the activity of the powder is low, so that the sinterability is deteriorated, and the reactivity between the heat generating portion and the terminal portion is not preferable. On the other hand, if the average particle size is smaller than 0.3 μm, the sinterability is good, but deformation due to sintering shrinkage is large, and cracks are likely to occur in the intermediate layer between the heat generating portion and the terminal portion.
More preferably, the average particle size after pulverization is 0.5 to 1.5 μm and the specific surface area is 3.5 to 6.5 m 2 / g.
Moreover, the average of the heat generating portion composition particle diameter P 1 and an average particle size P 2 of the terminal portion composition ratio (P 2 / P 1) of the heating portion and the terminal portion in the case of 0.5 or less or 1.5 or more It becomes difficult to equalize the shrinkage rate, cracking or cracking occurs during firing, or it is difficult to make the intermediate layer between the heat generating part and the terminal part a gradient composition, and the adhesive strength between the heat generating part and the terminal part is lowered. In addition, since the intermediate layer is easily damaged and the life is shortened, it is preferable that the ratio (P 2 / P 1 ) of the average particle size of the heat generating portion composition to the average particle size of the terminal portion composition is 0.5 to 1.5. .
By controlling the powder particle size of the heat generating part and the terminal part within this range, the sinterability of the heat generating part and the terminal part is good and the shrinkage rate can be made equal, and Sr ions are transferred from the terminal part to the heat generating part. By making it easy to diffuse, it becomes possible to increase the reactivity and make the intermediate layer have a gradient composition, and the heat generating portion and the terminal portion are firmly bonded. When the firing temperature is higher than 1900 ° C., the crystallite size grows too much, leading to a decrease in strength, and the Cr component during the firing is largely evaporated, so that the life of the obtained sintered body is shortened. When the firing temperature is lower than 1600 ° C., not only sintering is insufficient and mechanical properties and the like are deteriorated, but also the reactivity between the heat generating portion and the terminal portion is deteriorated and the bonding strength is lowered. The firing temperature is more preferably 1650 ° C to 1800 ° C.
本発明のランタンクロマイト系発熱体は従来のランタンクロマイト系発熱体とは異なり、緻密質でＣｒの蒸発量が少なく、発熱部と端子部の中間層が傾斜組成で接合強度が高いため発熱部と端子部の中間層での亀裂発生が生じにくいことから急速加熱冷却が可能で長寿命である。また、従来のケラマックス発熱体はＣｒの蒸発が多いため、寿命改善のため内部にＣｒ成分を充填する必要があったが、本発明の発熱体の場合、Ｃｒの蒸発が少ないためＣｒ充填の必要がなく、発熱部と端子部の中間層が傾斜組成となっているため発熱部と端子部の組成を混合した中間層作製の必要もないため製造工程が簡略化され、コストダウンも可能となる。 Unlike the conventional lanthanum chromite heating element, the lanthanum chromite heating element of the present invention is dense and has a small amount of Cr evaporation, and the intermediate layer between the heating part and the terminal part has a gradient composition and high bonding strength. Since cracks are unlikely to occur in the intermediate layer of the terminal portion, rapid heating and cooling are possible and the service life is long. In addition, since the conventional Keramax heating element has a large amount of Cr evaporation, it was necessary to fill the inside with a Cr component in order to improve the life. However, in the case of the heating element according to the present invention, the Cr evaporation is small, so There is no need, and since the intermediate layer of the heat generating part and the terminal part has a gradient composition, there is no need to prepare an intermediate layer by mixing the composition of the heat generating part and the terminal part, so the manufacturing process is simplified and the cost can be reduced. Become.
本発明のランタンクロマイト系発熱体は、以下に示す方法で製造できる。
Ｌａ、Ｃｒ、Ｓｒ、Ａｌの各原料としては、酸化物、水酸化物、炭酸塩、硝酸塩、金属アルコキシドなどのセラミックス製造に通常使用される化合物を使用でき、各成分の純度が９９．５重量％以上、より好ましくは９９．９重量％以上の原料を用いることが適当である。Ｌａの一部をＳｒで置換し、特定微量の範囲のＳｉＯ２を焼結体中に含有させる場合には、焼結体中に不純物として含有するＣａＯ含有率が０．０５重量％を越えると急激に耐熱性が低下するため、最終的に焼結体に不純物として含有するＣａＯの含有率が０．０５重量％未満になるように、これら原料中におけるＣａＯの含有量ができるだけ少ないものを用いることが好ましい。
製造にあたっては、発熱部組成および端子部組成の粉末を得るために、まず、各原料を所定の割合に配合し、均一に混合、分散して粉末混合物を得る。原料粉末の粒度は１０μｍ以下程度とすることが好ましく、５μｍ以下とすることがより好ましい。混合・分散はポットミル、アトリッションミルなどを用いて行うことができ、原料粉末を湿式混合又は乾式混合すればよく、また、各元素を含む水溶液を混合してもよい。湿式混合の場合には、溶媒として水またはアルコール等の有機溶媒が使用できるが、水を使用する場合には、不純物、特に導電率および耐熱性を低下させるアルカリ成分をできるだけ少なくするためにイオン交換水、または蒸留水を使用することが望ましい。この際に各成分を均一に混合・分散させるため、湿式混合の場合はスラリーの粘度が１００〜１０００ｃｐ程度となるように、スラリーの濃度の調整を行い、公知の分散剤を適量添加してもよい。
The lanthanum chromite heating element of the present invention can be produced by the following method.
As raw materials for La, Cr, Sr, and Al, compounds that are usually used in the production of ceramics such as oxides, hydroxides, carbonates, nitrates, and metal alkoxides can be used, and the purity of each component is 99.5 wt. % Or more, more preferably 99.9% by weight or more of the raw material is used. When a part of La is replaced with Sr and a specific trace amount of SiO 2 is contained in the sintered body, the CaO content contained as an impurity in the sintered body exceeds 0.05% by weight. Since the heat resistance is drastically reduced, those having as little CaO content as possible in these raw materials are used so that the content of CaO contained as an impurity in the sintered body is finally less than 0.05% by weight. It is preferable.
In production, in order to obtain a powder having a heat generating portion composition and a terminal portion composition, first, the respective raw materials are blended in a predetermined ratio, and uniformly mixed and dispersed to obtain a powder mixture. The particle size of the raw material powder is preferably about 10 μm or less, and more preferably 5 μm or less. Mixing / dispersing can be performed using a pot mill, an attrition mill, or the like. The raw material powder may be wet-mixed or dry-mixed, or an aqueous solution containing each element may be mixed. In the case of wet mixing, water or an organic solvent such as alcohol can be used as a solvent. However, when water is used, ion exchange is performed in order to minimize impurities, particularly alkali components that reduce conductivity and heat resistance. It is desirable to use water or distilled water. In this case, in order to uniformly mix and disperse each component, in the case of wet mixing, the slurry concentration is adjusted so that the viscosity of the slurry is about 100 to 1000 cp, and an appropriate amount of a known dispersant may be added. Good.
湿式混合の場合は、上記で得られたスラリーを乾燥させるが、この時の乾燥温度は使用した溶媒の沸点によって適宜設定すればよく、混合・分散させた各原料粉末が分離しないように、できるだけ短時間で乾燥させるのがよい。
次いで、得られた粉末混合物を熱処理して、９０％以上がペロブスカイト型結晶構造となった合成粉末とする。合成が不十分のまま粉砕を行い、これを用いて成形、焼成する場合、或いは未合成のまま成形、焼成する場合には、成形体の焼成中に未合成成分の分解が生じたり、焼成収縮が大きくなるなどして焼結体中に多数の気孔を残したり、亀裂が生じるので好ましくない。合成温度は、通常８００〜１５００℃程度の範囲とすることが好ましく、９００〜１４００℃の範囲とすることがより好ましい。合成時間は合成温度とも関係するが、通常０．５〜１０時間程度である。合成雰囲気は大気中などの酸素含有雰囲気が好ましい。
次いで、得られた合成粉末をポットミル、アトリッションミルなどを用いて粉砕、分散する。ＳｉＯ２は、この工程において酸化物もしくは化合物の形態で最終的な焼結体における含有率が上記範囲となるように適量添加する。ＳｉＯ２はスラリー中に均一に分散させるため粒度が１０μｍ以下、より好ましくは５μｍ以下の粉末を用いるか、単体組成の粉末よりも均一分散が可能な化合物を用いてもよい。この工程は前記した混合処理と同様に、溶媒として水またはアルコール等の有機溶媒が使用できるが、水の存在下で行う場合には、焼結体に含有される不純物量をできるだけ少なくするためにイオン交換水、又は蒸留水を使用することが望ましい。この際に、原料粉末の混合、分散の場合と同様に公知の分散剤を適量添加しても良い。粉砕、分散後の合成粉末は、平均粒子径０．３〜２．０μｍ、比表面積３〜７ｍ２／ｇにする。発熱部組成および端子部組成共に平均粒子径０．３〜２．０μｍにする必要があり、また、発熱部組成の平均粒子径Ｐ１と端子部組成の平均粒子径Ｐ２の比率（Ｐ２／Ｐ１）が０．５〜１．５とすることが好ましい。
更に、上記の熱処理によるペロブスカイト型粉末の合成と、粉砕を数回繰り返して組成の均一化を図ることが望ましい。
次いで、所定の粒度に粉砕したスラリーに公知の成形助剤を適量添加し、スプレードライヤーで乾燥・造粒して成形用粉体とする。金型プレス、ＣＩＰ（冷間静水圧成形法）などのプレス成形では造粒した粉体の特性（形状、潰れ性、流動性など）が、成形体のかさ密度、密度ムラに影響を与え、その結果、焼結体のかさ密度や導電率などに大きな影響を与える。このため、成形用粉体としては、形状の中実球であって、流動性に優れ、低圧力でも潰れるものが好ましい。このような良質な造粒粉体は、添加するバインダーの種類と量及びスプレードライヤーの条件を適宜選択することによって得ることができる。一般的には、材料との相性がよいバインダーを用いて、適度に分散・凝集した顆粒の噴霧が可能な特性をもつスラリーを調整し、スラリー流量、アトマイザーディスクの回転速度、乾燥温度等の条件を適切な範囲に設定することにより良好な成形性をもつ造粒粉体の作製が可能である。
次いでこの粉体を用いてセラミックスの製造における常法に従って金型プレス、ＣＩＰ等のプレス成形により、所定の形状に成形する。
次いで得られた成形体を焼成する。焼成雰囲気は、常圧及び加圧いずれであってもよい。焼成温度は通常１６００℃〜１９００℃程度の範囲とし、好ましくは１６５０℃〜１８００℃程度の範囲とする。
In the case of wet mixing, the slurry obtained above is dried, but the drying temperature at this time may be appropriately set according to the boiling point of the solvent used, and as much as possible so that the mixed and dispersed raw material powders are not separated. It is better to dry in a short time.
Next, the obtained powder mixture is heat-treated to obtain a synthetic powder having a perovskite crystal structure of 90% or more. When the composition is pulverized with insufficient synthesis and molded and fired using this, or when molded and fired without being synthesized, decomposition of unsynthesized components may occur during firing of the molded body, or firing shrinkage. This is not preferable because a large number of pores are left in the sintered body due to an increase in the size of the sintered body or cracks occur. The synthesis temperature is usually preferably in the range of about 800 to 1500 ° C, and more preferably in the range of 900 to 1400 ° C. The synthesis time is related to the synthesis temperature, but is usually about 0.5 to 10 hours. The synthesis atmosphere is preferably an oxygen-containing atmosphere such as in the air.
Next, the obtained synthetic powder is pulverized and dispersed using a pot mill, an attrition mill or the like. In this step, SiO 2 is added in an appropriate amount so that the content in the final sintered body is in the above range in the form of an oxide or a compound. Since SiO 2 is uniformly dispersed in the slurry, a powder having a particle size of 10 μm or less, more preferably 5 μm or less may be used, or a compound that can be more uniformly dispersed than a powder having a single composition may be used. In this step, an organic solvent such as water or alcohol can be used as a solvent in the same manner as the mixing treatment described above. However, in the case of performing in the presence of water, in order to minimize the amount of impurities contained in the sintered body. It is desirable to use ion exchange water or distilled water. At this time, an appropriate amount of a known dispersant may be added as in the case of mixing and dispersing the raw material powder. The synthetic powder after pulverization and dispersion has an average particle size of 0.3 to 2.0 μm and a specific surface area of 3 to 7 m 2 / g. Must average particle diameter 0.3~2.0μm to the heat generating portion composition and the terminal unit composition co, The average particle size P 1 and the average ratio of particle size P 2 of the terminal portion composition of the heat generating portion composition (P 2 / P 1 ) is preferably 0.5 to 1.5.
Furthermore, it is desirable to make the composition uniform by repeating the synthesis and pulverization of the perovskite powder by the above heat treatment several times.
Next, an appropriate amount of a known molding aid is added to the slurry pulverized to a predetermined particle size, and dried and granulated with a spray dryer to obtain a molding powder. In press molding such as die press and CIP (cold isostatic pressing), the characteristics (shape, crushability, fluidity, etc.) of the granulated powder affect the bulk density and density unevenness of the molded product. As a result, the bulk density and conductivity of the sintered body are greatly affected. For this reason, the powder for molding is preferably a solid sphere having excellent fluidity and being crushed even at low pressure. Such a high quality granulated powder can be obtained by appropriately selecting the kind and amount of the binder to be added and the conditions of the spray dryer. In general, using a binder that is compatible with the material, adjust the slurry so that it can spray appropriately dispersed and agglomerated granules, and adjust the slurry flow rate, atomizer disk rotation speed, drying temperature, etc. It is possible to produce a granulated powder having a good moldability by setting to an appropriate range.
Next, this powder is molded into a predetermined shape by press molding such as a die press or CIP according to a conventional method in the production of ceramics.
Next, the obtained molded body is fired. The firing atmosphere may be normal pressure or pressurized. The firing temperature is usually in the range of about 1600 ° C to 1900 ° C, preferably in the range of about 1650 ° C to 1800 ° C.
本発明に係るランタンクロマイト系発熱体は、棒状発熱体、螺旋形状発熱体、Ｕ字形状発熱体等、各種形状および各種サイズの発熱体を作製することが可能であるが、例えば棒状発熱体の場合、発熱部の長さＬ１と端子部の長さＬ２の比率（Ｌ２／Ｌ１）は０．３〜２．０の範囲にすることが望ましく、長さの比率が０．３未満の場合、端子部が短すぎるため端子部の冷却が十分にできず高温となり、端子部電極の劣化が速くなるため短寿命となり好ましくない。長さの比率が２．０を越える場合には端子部が不必要に長くなり消費電力が増大することにより寿命が短くなるだけでなく、発熱体の有効発熱領域に対して発熱体が大型化するため好ましくない。このため発熱部の長さＬ１、端子部の長さＬ２の比率（Ｌ２／Ｌ１）を０．３〜２．０の範囲にすることが好ましく、０．５〜１．５の範囲にすることがより好ましい。
また、炉の構造によっては発熱部を螺旋形状にする方が好ましい場合があり、螺旋形状によって抵抗値を制御することが可能である。
The lanthanum chromite heating element according to the present invention can produce heating elements of various shapes and sizes such as a rod heating element, a spiral heating element, a U-shaped heating element, etc. In this case, the ratio (L 2 / L 1 ) between the length L 1 of the heat generating portion and the length L 2 of the terminal portion is preferably in the range of 0.3 to 2.0, and the length ratio is 0.3. If it is less than 1, the terminal portion is too short, the terminal portion cannot be sufficiently cooled, and the temperature becomes high, and the deterioration of the terminal portion electrode is accelerated. When the ratio of length exceeds 2.0, the terminal part becomes unnecessarily long and power consumption increases, which not only shortens the service life but also enlarges the heating element relative to the effective heating area of the heating element. Therefore, it is not preferable. The length L 1 of the heat generation unit, it is preferable that the ratio of the length L 2 of the terminal portion (L 2 / L 1) in the range of 0.3 to 2.0, 0.5 to 1.5 of A range is more preferable.
In addition, depending on the furnace structure, it may be preferable to form the heat generating portion in a spiral shape, and the resistance value can be controlled by the spiral shape.
本発明のランタンクロマイト系発熱体は緻密質で発熱部と端子部の結合強度が高いため高温における安定性、耐久性に優れ長寿命となるほか、急速昇降温などの過酷な条件下でも優れた耐久性を示す。また、Ｃｒ成分の蒸発量が少ないため環境汚染も少ないものである。 The lanthanum chromite heating element of the present invention is dense and has high bonding strength between the heat generating part and the terminal part, so it is excellent in stability and durability at high temperatures and has a long life, and is excellent in harsh conditions such as rapid heating and cooling. Shows durability. Further, since the evaporation amount of the Cr component is small, environmental pollution is also small.
本発明に係るランタンクロマイト系発熱体は、高温まで急速加熱及び高温からの急速冷却が可能で長寿命であるため、高温焼成や急速昇降温が必要な高機能性ガラス、半導体材料の合成や熱処理などに広く利用できる。また、従来のランタンクロマイト系発熱体よりもＣｒの蒸発量が少ないため環境にやさしく、緻密で強度が高いため、棒状発熱体ばかりでなく、螺旋形発熱体、Ｕ字形状発熱体等、各種形状および各種サイズの発熱体の作製が可能である。更に、発熱部と端子部の組成を混合した中間層を形成する必要がないため製造が容易で安価に作製が可能である。 The lanthanum chromite heating element according to the present invention is capable of rapid heating to a high temperature and rapid cooling from a high temperature and has a long life. Therefore, a high-functional glass that requires high-temperature firing and rapid heating and cooling, synthesis of semiconductor materials, and heat treatment It can be used widely. In addition, since it has less Cr evaporation than conventional lanthanum chromite heating elements, it is environmentally friendly, dense and strong, so it has various shapes such as a rod-shaped heating element, spiral heating element, U-shaped heating element, etc. It is also possible to produce heating elements of various sizes. Furthermore, since it is not necessary to form an intermediate layer in which the composition of the heat generating portion and the terminal portion is mixed, the manufacture is easy and can be made at low cost.
以下に実施例をあげて本発明を説明するが、本発明はこれにより何ら限定するものではない。 EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.
実施例および比較例
表１に示す発熱部組成および端子部組成の配合となるように、それぞれ原料粉末を秤量配合し、イオン交換水の存在下で９２％アルミナ製（ニッカトー製ＨＤ）ポットミル（内容積：２リットル）とφ１０ｍｍの９９．９％アルミナ製（ニッカトー製ＳＳＡ−９９９Ｗ）ボール（１リットル）を用いて、濃度５０％で２０時間湿式で混合、分散を行った後、スラリーを１０５℃にて乾燥し、大気中１３７０℃で５時間加熱して、９５％以上がペロブスカイト型構造に合成された粉末を得た。尚、原料粉末としては、純度９９．５％以上のＬａ２Ｏ３、Ｃｒ２Ｏ３、ＳｒＣＯ３及びＡｌ２Ｏ３を用いた。得られた合成粉末を９２％アルミナ製（ニッカトー製ＨＤ）ポットミル（内容積：２リットル）とφ１０ｍｍの９９．９％アルミナ製（ニッカトー製ＳＳＡ−９９９Ｗ）ボール（１リットル）を用いて、イオン交換水の存在下で合成粉末濃度５０％とし、ＳｉＯ２ゾルを焼結体中のＳｉＯ２含有率が表１に記載の量となるように添加した後、表１に示す平均粒子径となるよう湿式で粉砕分散した。本発明において、焼結体に対して、表１に記載のように特定微量の範囲のＳｉＯ２を焼結体中に均一に含有させることにより、導電性および耐熱性を低下させることなく焼結性を向上させることが可能であるため、ＳｉＯ２ゾルを均一に分散することが重要である。
また、発熱部と端子部の中間層を傾斜組成とし発熱部と端子部を緻密で強固な接合状態とするためには、発熱部と端子部の収縮率を同等にし、且つ焼結性が良好でＳｒイオンを端子部から発熱部へ拡散しやすくする必要があることから、発熱部組成の平均粒子径および端子部組成の平均粒子径を０．３〜２．０μｍにすることが必要であり、更に、発熱部組成の平均粒子径Ｐ１と端子部組成の平均粒子径Ｐ２の比率（Ｐ２／Ｐ１）が０．５〜１．５であることが好ましい。
Examples and Comparative Examples Each raw material powder was weighed and blended so as to have the composition of the exothermic part composition and the terminal part composition shown in Table 1, and 92% alumina (Nikkato HD) pot mill (contents) in the presence of ion-exchanged water. (Product: 2 liters) and φ10 mm 99.9% alumina (Nikkato SSA-999W) balls (1 liter) were mixed and dispersed in a wet condition at a concentration of 50% for 20 hours. And dried in the atmosphere at 1370 ° C. for 5 hours to obtain a powder in which 95% or more was synthesized in a perovskite structure. As the raw material powder, La 2 O 3 , Cr 2 O 3 , SrCO 3 and Al 2 O 3 having a purity of 99.5% or more were used. The synthetic powder obtained was ion-exchanged using a 92% alumina (Nikkato HD) pot mill (internal volume: 2 liters) and a 99.9% alumina (Nikkato SSA-999W) ball (1 liter) of φ10 mm. After adding a synthetic powder concentration of 50% in the presence of water and adding the SiO 2 sol so that the SiO 2 content in the sintered body is the amount shown in Table 1, the average particle diameter shown in Table 1 is obtained. It was pulverized and dispersed by wet. In the present invention, the sintered body is uniformly sintered with a specific trace amount of SiO 2 as shown in Table 1 without reducing the conductivity and heat resistance. Therefore, it is important to uniformly disperse the SiO 2 sol.
Also, in order to make the intermediate layer between the heat generating part and the terminal part into a gradient composition and to make the heat generating part and the terminal part a dense and strong joined state, the shrinkage rate of the heat generating part and the terminal part is made equal and the sinterability is good. Therefore, it is necessary to easily diffuse Sr ions from the terminal portion to the heat generating portion, so that the average particle size of the heat generating portion composition and the average particle size of the terminal portion composition must be 0.3 to 2.0 μm. further, it is preferable that the average particle size P 1 and the average ratio of particle size P 2 of the terminal portion composition of the heat generating portion composition (P 2 / P 1) is 0.5 to 1.5.
これに成形助剤としてアクリル樹脂を粉末重量に対して固形分で２重量％を加えた後、スプレードライヤーにより成形用顆粒粉体（顆粒平均粒径５０μｍ）に調整した。この顆粒粉体を成形圧力１ｔｏｎｆ／ｃｍ２でＣＩＰ成形し、６０×６０×５ｍｍの板状の成形体を得た後、大気中において、表１に記載の条件で焼成した。得られた焼結体を１５×１５×５ｍｍの大きさに切断し表面研磨を行った試料についてアルキメデス法によりかさ密度を測定した。また、該焼結体から別途３×４×４０ｍｍの大きさの角棒状に切断後、ダイヤモンド砥石により研削加工して表面を仕上げた試料について、端子間距離１８ｍｍとして直流４端子法により大気中１０００℃における導電率を測定した。また、別途化学分析を実施しＳｉＯ２の含有率を測定した。
発熱体の作製は所定の発熱体形状に対応するプレス型にまず端子部組成を有する顆粒粉体を入れ、次いで発熱部組成を有する顆粒粉体を入れ、最後に再び端子部組成を有する顆粒粉体を入れた後、成形圧力１ｔｏｎｆ／ｃｍ２でＣＩＰ成形した。成形後旋盤で外形加工を行い、大気中において、表１に記載の条件で焼成し、内径５ｍｍ、発熱部および端子部外径１０ｍｍの中空棒状の発熱体を作製した。その両端からそれぞれ１０ｍｍの部位に白金ペーストを塗布し、その上から太さ０．５ｍｍ、長さ２０ｃｍの白金線を２回巻き付け、さらにその上から白金ペーストを塗布し、１３００℃で焼き付けて、高温用電極及び金属リード線を形成した。これらの発熱体を純度９９．５％、相対密度９７％の中空状のアルミナセラミックス（以下外套管と呼ぶ）（外径２０ｍｍ×内径１５ｍｍ×長さ１３５ｍｍ）に挿入し、外側には断熱材として純度９８％、かさ密度１．４ｇ／ｃｍ３のアルミナ耐火断熱煉瓦を幅６０ｍｍ×高さ６０ｍｍ×長さ１７０ｍｍの大きさで、中央部に２０．５ｍｍの貫通孔を有する形状にして配置した。電極保護のため電極部は炉外に出し、発熱部中央に温度制御・計測用としてＰＲ２０−４０型熱電対をセットしＰＩＤ温度制御方式〔プロセス温度制御方式の一つで、Ｐ（比例）、Ｉ（積分）、Ｄ（微分）の３つの基本演算を用いて目標値と現在値の差を制御量（電力値）に変換する方式〕により、電圧をかけて室温より１時間あたり６００℃の昇温速度で、発熱部表面温度約１８５０℃まで昇温し、３０分間保持後室温まで昇温時と同速度で降温する操作を繰り返す。
最高温度を１８５０℃に設定し、３０分保持後発熱体表面温度および電気特性、即ち電流、電圧を測定し電力を算出した。
After adding 2% by weight of an acrylic resin as a molding aid to the powder in terms of solid content, it was adjusted to a granular powder for molding (average particle diameter of 50 μm) with a spray dryer. This granular powder was CIP-molded at a molding pressure of 1 tonf / cm 2 to obtain a plate-like molded body of 60 × 60 × 5 mm, and then fired in the air under the conditions shown in Table 1. The obtained sintered body was cut into a size of 15 × 15 × 5 mm and subjected to surface polishing, and the bulk density was measured by Archimedes method. In addition, a sample whose surface was finished by cutting the sintered body into a 3 × 4 × 40 mm square bar and then grinding with a diamond grindstone was used in the atmosphere by a direct current four-terminal method with a distance between terminals of 18 mm. The conductivity at ° C was measured. Separately, chemical analysis was performed to measure the content of SiO 2 .
The heating element is produced by first putting granule powder having a terminal part composition into a press mold corresponding to a predetermined heating element shape, then putting granule powder having a heating part composition, and finally having the terminal part composition again. After putting the body, CIP molding was performed at a molding pressure of 1 tonf / cm 2 . After forming, the outer shape was processed with a lathe and fired in the air under the conditions shown in Table 1 to produce a hollow rod-shaped heating element having an inner diameter of 5 mm, a heating portion, and a terminal portion outer diameter of 10 mm. A platinum paste is applied to each 10 mm portion from both ends, a platinum wire having a thickness of 0.5 mm and a length of 20 cm is wound twice from above, and further a platinum paste is applied from above and baked at 1300 ° C., High temperature electrodes and metal leads were formed. These heating elements are inserted into hollow alumina ceramics (hereinafter referred to as a mantle tube) having a purity of 99.5% and a relative density of 97% (outer diameter 20 mm × inner diameter 15 mm × length 135 mm), and on the outside as a heat insulating material An alumina refractory heat insulating brick having a purity of 98% and a bulk density of 1.4 g / cm 3 was arranged in a shape having a width of 60 mm × height of 60 mm × length of 170 mm and having a through hole of 20.5 mm in the center. In order to protect the electrode, the electrode part is taken out of the furnace, a PR20-40 type thermocouple is set in the center of the heat generating part for temperature control and measurement, and PID temperature control system [P (proportional), one of process temperature control systems, The method of converting the difference between the target value and the current value into a controlled variable (power value) using three basic operations of I (integration) and D (differentiation)] is 600 ° C. per hour from room temperature by applying a voltage. The operation of increasing the temperature of the surface of the heat generating portion to about 1850 ° C. at the rate of temperature increase, holding for 30 minutes, and then decreasing the temperature to the room temperature at the same rate as the temperature increase is repeated.
The maximum temperature was set at 1850 ° C., and after maintaining for 30 minutes, the surface temperature and electrical characteristics of the heating element, that is, current and voltage were measured to calculate electric power.
表１において、ランタンクロマイト系発熱体の発熱部および端子部の各焼結体の組成、粉砕粉体の平均粒子径、平均粒子径比およびＳｉＯ２含有率を示し、
表２において、焼成条件、発熱部および端子部の各焼結体の導電率、導電率比及びかさ密度を示し、
表３において、繰り返し通電試験を実施したときの、消費電力が最大となる保持温度到達時の電圧、電流、消費電力および発熱体が破損するまでのサイクル回数を示す。
また、図１に試料Ｎｏ．１（実施例）の発熱部から端子部のＥＤＸ線分析（エネルギー分散型Ｘ線分光法）結果を示す。
（１）は、発熱部と端子部の中間層のＳＥＭ（走査電子顕微鏡）写真である。
（２）は、ＥＤＸ線分析によるＳｒ（Ｌα１線）の強度を示す。
図２に試料Ｎｏ．１３（比較例）の発熱部から端子部のＥＤＸ線分析結果を示す。
（３）は、発熱部と端子部の中間層のＳＥＭ（走査電子顕微鏡）写真である。
（４）は、ＥＤＸ線分析によるＳｒ（Ｌα１線）の強度を示す。
以上のように本発明のランタンクロマイト系発熱体は高温まで急速加熱および高温からの急速冷却が可能で耐久性に優れることが明らかである。
In Table 1, the composition of each sintered body of the lanthanum chromite-based heating element and the sintered body of the terminal part, the average particle diameter of the pulverized powder, the average particle diameter ratio and the SiO 2 content are shown,
In Table 2, the firing conditions, the conductivity of each sintered body of the heat generating part and the terminal part, the conductivity ratio and the bulk density are shown,
Table 3 shows the voltage, current, power consumption, and the number of cycles until the heating element is damaged when the holding temperature reaches the maximum power consumption when the current application test is repeatedly performed.
In addition, in FIG. 1 shows the results of EDX ray analysis (energy dispersive X-ray spectroscopy) from the heat generating portion to the terminal portion of 1 (Example).
(1) is an SEM (scanning electron microscope) photograph of an intermediate layer between the heat generating portion and the terminal portion.
(2) shows the intensity of Sr (Lα1 line) by EDX ray analysis.
In FIG. 13 shows the result of EDX ray analysis from the heat generating portion to the terminal portion of 13 (Comparative Example).
(3) is an SEM (scanning electron microscope) photograph of the intermediate layer between the heat generating portion and the terminal portion.
(4) shows the intensity of Sr (Lα1 line) by EDX ray analysis.
As described above, it is clear that the lanthanum chromite heating element of the present invention can be rapidly heated to a high temperature and rapidly cooled from a high temperature and has excellent durability.
Claims (2)
Perovskite crystals represented by the chemical formula La 1-x Sr x Cr 1-y Al y O 3 (where 0.005 ≦ x ≦ 0.12 and 0.02 ≦ y ≦ 0.50). In the pulverization / dispersion step of the synthetic powder, the average particle size is 0 when SiO 2 is added in the form of oxide or compound so that the content in the final sintered body is 300 to 1000 ppm. 3. Molding into a predetermined shape using a powder having a heat generating part composition of 3 to 2.0 μm and a powder having a terminal part composition having an average particle diameter of 0.3 to 2.0 μm, and firing at 1600 to 1900 ° C. in the atmosphere. The method for producing a lanthanum chromite heating element having a heat generating portion and a terminal portion according to claim 1.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007285644A (en) * | 2006-04-19 | 2007-11-01 | Nitsukatoo:Kk | Electric furnace |
| CN117024129A (en) * | 2023-08-16 | 2023-11-10 | 内蒙古工业大学 | Preparation method of chromium-doped lanthanum disilicate ceramic |
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| JPS518221B1 (en) * | 1971-06-28 | 1976-03-15 | ||
| JPH0616471A (en) * | 1991-06-28 | 1994-01-25 | Nitsukatoo:Kk | Heat resistant conductive sintered body |
| JPH09196098A (en) * | 1996-01-17 | 1997-07-29 | Nitsukatoo:Kk | Heat resistant and conductive ceramics |
| JP2003314970A (en) * | 2002-04-17 | 2003-11-06 | Nitsukatoo:Kk | Tubular electric furnace |
| JP2004131350A (en) * | 2002-10-15 | 2004-04-30 | Nitsukatoo:Kk | Heat-resistant conductive ceramic |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPS518221B1 (en) * | 1971-06-28 | 1976-03-15 | ||
| JPH0616471A (en) * | 1991-06-28 | 1994-01-25 | Nitsukatoo:Kk | Heat resistant conductive sintered body |
| JPH09196098A (en) * | 1996-01-17 | 1997-07-29 | Nitsukatoo:Kk | Heat resistant and conductive ceramics |
| JP2003314970A (en) * | 2002-04-17 | 2003-11-06 | Nitsukatoo:Kk | Tubular electric furnace |
| JP2004131350A (en) * | 2002-10-15 | 2004-04-30 | Nitsukatoo:Kk | Heat-resistant conductive ceramic |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007285644A (en) * | 2006-04-19 | 2007-11-01 | Nitsukatoo:Kk | Electric furnace |
| CN117024129A (en) * | 2023-08-16 | 2023-11-10 | 内蒙古工业大学 | Preparation method of chromium-doped lanthanum disilicate ceramic |
| CN117024129B (en) * | 2023-08-16 | 2024-01-16 | 内蒙古工业大学 | Preparation method of chromium-doped lanthanum disilicate ceramic |
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