JP2015067495A - Conductive silicon carbide sintered body - Google Patents
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 80
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 78
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 81
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 33
- 239000000919 ceramic Substances 0.000 claims abstract description 13
- 239000002019 doping agent Substances 0.000 claims abstract description 11
- 238000007254 oxidation reaction Methods 0.000 abstract description 50
- 230000003647 oxidation Effects 0.000 abstract description 45
- 239000012071 phase Substances 0.000 description 88
- 238000000034 method Methods 0.000 description 21
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 19
- 229910001873 dinitrogen Inorganic materials 0.000 description 15
- 238000010304 firing Methods 0.000 description 15
- 230000001590 oxidative effect Effects 0.000 description 14
- 238000012360 testing method Methods 0.000 description 14
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 11
- 239000010410 layer Substances 0.000 description 11
- 239000001301 oxygen Substances 0.000 description 11
- 229910052760 oxygen Inorganic materials 0.000 description 11
- 239000000523 sample Substances 0.000 description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 10
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 10
- 229910052799 carbon Inorganic materials 0.000 description 10
- 229910052710 silicon Inorganic materials 0.000 description 10
- 239000010703 silicon Substances 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
- 235000012239 silicon dioxide Nutrition 0.000 description 8
- 239000000377 silicon dioxide Substances 0.000 description 8
- 229910052581 Si3N4 Inorganic materials 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 7
- 238000004519 manufacturing process Methods 0.000 description 7
- 239000002245 particle Substances 0.000 description 7
- 239000002994 raw material Substances 0.000 description 7
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 238000013507 mapping Methods 0.000 description 5
- 238000004458 analytical method Methods 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 229910052786 argon Inorganic materials 0.000 description 3
- 239000003575 carbonaceous material Substances 0.000 description 3
- 239000001307 helium Substances 0.000 description 3
- 229910052734 helium Inorganic materials 0.000 description 3
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007812 deficiency Effects 0.000 description 2
- 238000005470 impregnation Methods 0.000 description 2
- 239000012212 insulator Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000002250 progressing effect Effects 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000003610 charcoal Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000000921 elemental analysis Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000003574 free electron Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 238000003703 image analysis method Methods 0.000 description 1
- 229910052740 iodine Inorganic materials 0.000 description 1
- 238000007733 ion plating Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 150000002506 iron compounds Chemical class 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000005268 plasma chemical vapour deposition Methods 0.000 description 1
- 229910021426 porous silicon Inorganic materials 0.000 description 1
- 239000011241 protective layer Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 238000005211 surface analysis Methods 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- 239000012808 vapor phase Substances 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Abstract
Description
本発明は、導電性炭化珪素質焼結体に関するものである。 The present invention relates to a conductive silicon carbide based sintered body.
炭化珪素は、熱伝導率が高いことに加えて熱膨張率が小さいことから耐熱衝撃性に優れるため、高温下で使用されるフィルタ、触媒担体、熱交換体などの基体として適している。また、高純度の炭化珪素は電気抵抗が高く絶縁体に近いが、導電性が付与された炭化珪素質セラミックスは、通電により発熱させる自己発熱型の構造体として使用することが可能である。本出願人は過去に、炭化珪素に、炭化珪素を反応生成させる珪素源及び炭素源を加えた混合原料を、成形し焼成することにより、導電性が高められた炭化珪素質セラミックス焼結体を製造する方法を提案している（例えば、特許文献１参照）。 Since silicon carbide has a high thermal conductivity and a low coefficient of thermal expansion, it has excellent thermal shock resistance and is therefore suitable as a substrate for filters, catalyst carriers, heat exchangers and the like used at high temperatures. Further, high-purity silicon carbide has high electrical resistance and is close to an insulator, but silicon carbide-based ceramics imparted with conductivity can be used as a self-heating structure that generates heat when energized. In the past, the present applicant has obtained a silicon carbide ceramic sintered body having improved conductivity by molding and firing a mixed raw material obtained by adding a silicon source and a carbon source for reacting silicon carbide to silicon carbide. A manufacturing method is proposed (for example, see Patent Document 1).
炭化珪素は、酸素の存在下で高温に加熱されると、酸化してしまうという問題がある。炭化珪素の酸化により生成した二酸化珪素の皮膜で炭化珪素の表面が被覆されると、それ以上の酸化がある程度は抑制されると言われているが、それでは酸化の抑制としては不十分であるのが実情である。本出願人が過去に詳細に検討しているように、導電性炭化珪素質セラミックスの表面に二酸化珪素が生成すると、比抵抗値が変化する（例えば、特許文献２参照）。酸化によって焼結体の表面に形成される二酸化珪素の相は電気抵抗が高いため、酸化の進行に伴って、炭化珪素質セラミックス焼結体の比抵抗値が増大する。 Silicon carbide has a problem that it is oxidized when heated to a high temperature in the presence of oxygen. It is said that if the surface of silicon carbide is coated with a silicon dioxide film produced by the oxidation of silicon carbide, further oxidation will be suppressed to some extent, but that is not enough to suppress oxidation. Is the actual situation. As the present applicant has studied in detail in the past, when silicon dioxide is generated on the surface of the conductive silicon carbide ceramic, the specific resistance value changes (for example, see Patent Document 2). Since the phase of silicon dioxide formed on the surface of the sintered body by oxidation has high electrical resistance, the specific resistance value of the silicon carbide based ceramic sintered body increases with the progress of oxidation.
そこで、高温下での使用を継続しても、比抵抗値が一定に保持される導電性炭化珪素質セラミックスに対する要請があった。比抵抗値を変化させないために採るべき手段として、まずは、炭化珪素の酸化を抑制することを想到し得る。耐酸化性の炭化珪素焼結体を製造する方法として、鉄化合物の溶液を多孔質の炭化珪素焼結体に含浸させ、空気中で加熱する技術が提案されている（特許文献３参照）。これは、ＦｅＯとＳｉＯ２との共存下では、高温領域で石英の多形であるトリジマイト又はクリストバライトの溶液が生成することを利用し、炭化珪素焼結体の表面にクリストバライトの結晶を析出させることにより、酸化を防止する保護層としようとするものである。しかしながら、この技術では、含浸工程が必要であるため、工程が複雑となり手間がかかるという問題があった。また、含浸によって鉄が添加されるため、比抵抗値の制御が困難となるおそれがあった。 Therefore, there has been a demand for conductive silicon carbide ceramics that maintain a specific resistance value constant even if the use at a high temperature is continued. As a measure to be taken in order not to change the specific resistance value, it can be conceived first to suppress the oxidation of silicon carbide. As a method for producing an oxidation-resistant silicon carbide sintered body, a technique has been proposed in which a porous silicon carbide sintered body is impregnated with a solution of an iron compound and heated in air (see Patent Document 3). This is because, under the coexistence of FeO and SiO 2 , the crystal polycrystal form of tridymite or cristobalite is produced in a high temperature region, and cristobalite crystals are deposited on the surface of the silicon carbide sintered body. Thus, it is intended to be a protective layer for preventing oxidation. However, since this technique requires an impregnation process, there is a problem that the process becomes complicated and time-consuming. In addition, since iron is added by impregnation, it may be difficult to control the specific resistance value.
一方、炭化珪素などの基材の表面に、Ｃ−Ｘ結合（ＸはＦ，Ｃｌ，Ｉから選択された１種または２種以上）を有する炭素系皮膜を形成することにより、耐酸化性を高める技術が提案されている（特許文献４参照）。これは、プラズマＣＶＤ法やイオンプレーティング法等により、基材の表面に炭素系皮膜を形成しておき、この炭素系皮膜に化学気相法によってＣ−Ｘ結合を導入するというものである。しかしながら、この技術では、炭素系皮膜の形成工程、Ｃ−Ｘ結合を導入する工程が必要であり、工程が複雑で手間がかかることに加え、プラズマ発生装置など、通常の焼成工程には用いられない特殊な装置を必要とするという問題があった。また、有害なハロゲンガスを使用するため、安全面が考慮された環境を整えるための設備をも必要とするものであった。 On the other hand, by forming a carbon-based film having a C—X bond (X is one or more selected from F, Cl, I) on the surface of a substrate such as silicon carbide, oxidation resistance is improved. A technique for enhancing the content has been proposed (see Patent Document 4). This is a method in which a carbon-based film is formed on the surface of a base material by a plasma CVD method, an ion plating method, or the like, and C—X bonds are introduced into this carbon-based film by a chemical vapor phase method. However, this technique requires a carbon-based film forming process and a process for introducing C—X bonds, which are complicated and time-consuming, and are used in ordinary firing processes such as plasma generators. There was a problem of requiring no special equipment. In addition, since a harmful halogen gas is used, equipment for preparing an environment in consideration of safety is also required.
そこで、本発明は、上記の実情に鑑み、簡易に製造することが可能で、酸化による比抵抗値の変化が抑制された導電性炭化珪素質焼結体の提供を、課題とするものである。 Therefore, in view of the above circumstances, an object of the present invention is to provide a conductive silicon carbide sintered body that can be easily manufactured and in which a change in specific resistance value due to oxidation is suppressed. .
上記の課題を解決するため、本発明にかかる導電性炭化珪素質焼結体は、「ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体であり、少なくとも最外層に、前記導電性相における窒素の平均濃度より窒素の平均濃度が低い炭化珪素の相である高抵抗相が形成されている」ものである。 In order to solve the above problems, the conductive silicon carbide sintered body according to the present invention is “a sintered body of silicon carbide ceramics containing a conductive phase that is a phase of silicon carbide containing nitrogen as a dopant, At least the outermost layer is formed with a high resistance phase that is a silicon carbide phase having an average nitrogen concentration lower than the average nitrogen concentration in the conductive phase.
本発明の導電性炭化珪素質焼結体は、焼結体の少なくとも最外層に高抵抗相を有するものであれば、最外層ではない部分に導電性相より窒素の平均濃度が低い相を有していても構わない。また、導電性相も単相である必要はなく、例えば、窒素の濃度の異なる複数の導電性相を有していてもよい。なお、複数の導電性相を有する場合、「導電性相における窒素の平均濃度」は、複数の導電性相を総合して平均した窒素の濃度を指すものとする。 If the conductive silicon carbide sintered body of the present invention has a high resistance phase in at least the outermost layer of the sintered body, it has a phase having a lower average concentration of nitrogen than the conductive phase in a portion that is not the outermost layer. It does not matter. Also, the conductive phase need not be a single phase, and for example, it may have a plurality of conductive phases with different concentrations of nitrogen. In the case of having a plurality of conductive phases, the “average concentration of nitrogen in the conductive phase” refers to the concentration of nitrogen obtained by averaging the plurality of conductive phases.
高純度の炭化珪素は絶縁体に近いが、ドーパントとして窒素を含むことによりｎ型半導体となる。このような炭化珪素の焼結体を酸素が存在する雰囲気で高温で使用すると、炭化珪素の酸化により焼結体の表面に二酸化珪素の相が生成する。二酸化珪素の相は電気抵抗が高いため、酸化の進行に伴い焼結体全体の比抵抗値が増大してしまう。これに対し、本発明の導電性炭化珪素質焼結体は、少なくとも最外層に、ドーパントとして窒素を含む炭化珪素の相である導電性相より窒素の平均濃度が低い炭化珪素の相を有している。この相は、窒素の濃度が低いことにより自由電子の数が少なく、導電性相より電気抵抗が高いため、本発明では「高抵抗相」と称している。このように、元々電気抵抗が高い相は、焼結体全体の電気伝導性に対する寄与度が小さい。 High-purity silicon carbide is close to an insulator, but becomes an n-type semiconductor by containing nitrogen as a dopant. When such a silicon carbide sintered body is used at a high temperature in the presence of oxygen, a silicon dioxide phase is generated on the surface of the sintered body due to oxidation of silicon carbide. Since the phase of silicon dioxide has a high electric resistance, the specific resistance value of the entire sintered body increases with the progress of oxidation. On the other hand, the conductive silicon carbide based sintered body of the present invention has a silicon carbide phase having an average nitrogen concentration lower than that of a conductive phase that is a silicon carbide phase containing nitrogen as a dopant in at least the outermost layer. ing. This phase is referred to as a “high resistance phase” in the present invention because the number of free electrons is small due to the low concentration of nitrogen and the electric resistance is higher than that of the conductive phase. Thus, the phase with an originally high electrical resistance has a small contribution to the electrical conductivity of the entire sintered body.
焼結体の最外層に高抵抗相が形成されている本構成の焼結体では、酸素が存在する雰囲気で高温で使用されたときに、酸化されるのは高抵抗相である。元々焼結体全体の電気伝導性に対する寄与度が小さい高抵抗相が酸化された場合は、焼結体全体の電気伝導性に対する寄与度が大きい相、すなわち電気伝導性が高い相が酸化された場合に比べ、焼結体全体の電気伝導性に及ぼす影響は小さい。加えて、焼結体の最外層に高抵抗相が存在することにより、電気伝導性への寄与度の高い導電性相まで、酸化反応が及びにくい。従って、本構成の導電性炭化珪素質焼結体は、酸素の存在する雰囲気で高温で継続して使用されても、比抵抗値が変化しにくい。加えて、本構成の導電性炭化珪素質焼結体は、詳細は後述するように、導電性相を含む炭化珪素質セラミックスの焼結体を、実質的に窒素ガスを含まない非酸化性雰囲気で加熱するのみで、簡易に製造することが可能である。 In the sintered body of this configuration in which the high resistance phase is formed in the outermost layer of the sintered body, the high resistance phase is oxidized when used at a high temperature in an atmosphere in which oxygen exists. When the high resistance phase, which originally contributed little to the electrical conductivity of the entire sintered body, was oxidized, the phase with a large contribution to the electrical conductivity of the entire sintered body, that is, the phase with high electrical conductivity was oxidized. Compared to the case, the influence on the electrical conductivity of the entire sintered body is small. In addition, the presence of the high resistance phase in the outermost layer of the sintered body makes it difficult for the oxidation reaction to reach the conductive phase having a high contribution to electrical conductivity. Therefore, even if the conductive silicon carbide sintered body of this configuration is continuously used at a high temperature in an atmosphere in which oxygen is present, the specific resistance value hardly changes. In addition, the conductive silicon carbide-based sintered body of this configuration is a non-oxidizing atmosphere substantially free of nitrogen gas, as will be described in detail later. It is possible to manufacture simply by heating with.
本発明にかかる導電性炭化珪素質焼結体は、上記構成に加え、「前記高抵抗相は、少なくとも１６０ｎｍの厚さを有する」ものとすることができる。 In addition to the above configuration, the conductive silicon carbide sintered body according to the present invention may be “the high resistance phase has a thickness of at least 160 nm”.
後述のように、高抵抗相の厚さが少なくとも１６０ｎｍ以上であれば、炭化珪素の酸化が比抵抗値に及ぼす影響を低減して、酸化による比抵抗値の変化を抑制する作用が十分に発揮されることが確認された。なお、高抵抗相が厚ければ厚いほど、酸化による比抵抗値の変化を抑制する作用は大きくなると考えられるが、高抵抗相が厚くなれば、その分だけ導電性相が薄くなり比抵抗値が上昇する。そのため、後述のように、高抵抗相の厚さは２μｍ以下とすれば実用的である。 As will be described later, when the thickness of the high resistance phase is at least 160 nm or more, the effect of the oxidation of silicon carbide on the specific resistance value is reduced, and the effect of suppressing the change in the specific resistance value due to oxidation is sufficiently exerted. It was confirmed that It is thought that the thicker the high resistance phase, the greater the effect of suppressing the change in specific resistance value due to oxidation, but the thicker the high resistance phase, the thinner the conductive phase and the specific resistance value. Rises. Therefore, as described later, it is practical if the thickness of the high resistance phase is 2 μm or less.
以上のように、本発明の効果として、簡易に製造することが可能で、酸化による比抵抗値の変化が抑制された導電性炭化珪素質焼結体を、提供することができる。 As described above, as an effect of the present invention, it is possible to provide a conductive silicon carbide sintered body that can be easily manufactured and in which a change in specific resistance value due to oxidation is suppressed.
以下、本発明の一実施形態である導電性炭化珪素質焼結体、及び、その製造方法について説明する。本実施形態の導電性炭化珪素質焼結体は、ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体であり、少なくとも最外層に、導電性相における窒素の平均濃度より窒素の平均濃度が低い炭化珪素の相である高抵抗相が形成されているものである。 Hereinafter, the conductive silicon carbide sintered body and the manufacturing method thereof according to an embodiment of the present invention will be described. The conductive silicon carbide sintered body of the present embodiment is a sintered body of silicon carbide ceramics including a conductive phase that is a phase of silicon carbide containing nitrogen as a dopant, and at least the outermost layer has a conductive phase in the conductive phase. A high resistance phase, which is a silicon carbide phase having an average nitrogen concentration lower than the average nitrogen concentration, is formed.
このような導電性炭化珪素質焼結体は、ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体を、実質的に窒素ガスを含まない非酸化性雰囲気で加熱し、焼結体の最外層に導電性相における窒素の平均濃度より窒素の平均濃度が低い炭化珪素の相である高抵抗相を形成する高抵抗相形成工程、を具備する製造方法により製造することができる。 Such a conductive silicon carbide-based sintered body is a non-oxidizing material that is substantially free of nitrogen gas and is a silicon carbide-based ceramic sintered body containing a conductive phase that is a silicon carbide phase containing nitrogen as a dopant. A high resistance phase forming step of heating in an atmosphere and forming a high resistance phase, which is a silicon carbide phase having an average nitrogen concentration lower than the average nitrogen concentration in the conductive phase, in the outermost layer of the sintered body Can be manufactured.
本発明者らは、ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体を、実質的に窒素ガスを含まない非酸化性雰囲気で加熱することにより、一旦はドープされた窒素が焼結体から排出され、焼結体の表面側に窒素の濃度が低い炭化珪素の相が形成されることを見出した。この高抵抗相形成工程は、通常の焼成設備で行うことができ、特殊な設備や工程を要しないため、本製造方法は非常に簡易である。ここで、実質的に窒素ガスを含まない非酸化性雰囲気は、アルゴンやヘリウム等の希ガス雰囲気とすることができる。この場合、雰囲気中の窒素ガスの濃度は理想的にはゼロであるが、窒素ガスの濃度は５０００ｐｐｍ未満であれば許容され、より好ましくは５００ｐｐｍ未満である。或いは、実質的に窒素ガスを含まない非酸化性雰囲気は、真空雰囲気とすることもできる。 The present inventors heated a sintered body of a silicon carbide based ceramic containing a conductive phase that is a phase of silicon carbide containing nitrogen as a dopant in a non-oxidizing atmosphere substantially containing no nitrogen gas, It has been found that once doped nitrogen is discharged from the sintered body, a silicon carbide phase having a low nitrogen concentration is formed on the surface side of the sintered body. This high resistance phase forming step can be performed with ordinary firing equipment, and does not require special equipment or steps, so that this production method is very simple. Here, the non-oxidizing atmosphere substantially free of nitrogen gas can be a rare gas atmosphere such as argon or helium. In this case, the concentration of nitrogen gas in the atmosphere is ideally zero, but the nitrogen gas concentration is acceptable if it is less than 5000 ppm, more preferably less than 500 ppm. Alternatively, the non-oxidizing atmosphere substantially free of nitrogen gas can be a vacuum atmosphere.
ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体は、炭化珪素粉末を成形する成形工程と、該成形工程で得られた成形体を、窒素ガスを含む非酸化性雰囲気で焼成する焼成工程と、を具備する製造方法によって製造することができる。ここで、成形工程は、ハニカム構造の成形体を成形する工程とすることができる。また、焼成工程における窒素ガスを含む非酸化性雰囲気は、窒素ガス１００％雰囲気、アルゴンやヘリウム等の希ガスと窒素ガスとの混合雰囲気とすることができる。 A sintered body of a silicon carbide based ceramic containing a conductive phase which is a silicon carbide phase containing nitrogen as a dopant includes a forming step of forming silicon carbide powder, and a formed body obtained by the forming step using nitrogen gas. And a firing step of firing in a non-oxidizing atmosphere. Here, the forming step can be a step of forming a formed body having a honeycomb structure. The non-oxidizing atmosphere containing nitrogen gas in the firing step can be a nitrogen gas 100% atmosphere or a mixed atmosphere of a rare gas such as argon or helium and nitrogen gas.
また、ドーパントとして窒素を含む炭化珪素の相である導電性相を含む炭化珪素質セラミックスの焼結体は、炭化珪素を生成する珪素源及び炭素源からなる炭化珪素生成原料、及び、炭化珪素を含む混合原料を成形する成形工程と、該成形工程で得られた成形体を、窒素ガスを含む非酸化性雰囲気で焼成する焼成工程と、を具備する製造方法によって製造することができる。この製造方法では、焼成工程において珪素源と炭素源とを反応させ、炭化珪素を生成させつつ焼結させ（反応焼結）、この反応焼結を、窒素を含む非酸化性雰囲気で行う。これにより、焼成雰囲気に含まれる窒素が主に反応生成する炭化珪素にドープされ、導電性相が形成される。 Further, a sintered body of a silicon carbide based ceramic containing a conductive phase which is a phase of silicon carbide containing nitrogen as a dopant includes a silicon carbide producing raw material comprising a silicon source for producing silicon carbide and a carbon source, and silicon carbide. It can be manufactured by a manufacturing method comprising a forming step of forming a mixed raw material containing, and a firing step of firing the molded body obtained in the forming step in a non-oxidizing atmosphere containing nitrogen gas. In this manufacturing method, a silicon source and a carbon source are reacted in the firing step to sinter while generating silicon carbide (reactive sintering), and the reactive sintering is performed in a non-oxidizing atmosphere containing nitrogen. Thereby, nitrogen contained in the firing atmosphere is doped into silicon carbide that is mainly produced by reaction, and a conductive phase is formed.
なお、上記の混合原料は、非導電性の粒子を含んでいても良い。ここで、「非導電性」は、比抵抗値が１０００Ωｃｍ以上の場合を指している。 In addition, said mixed raw material may contain the nonelectroconductive particle. Here, “non-conductive” refers to the case where the specific resistance value is 1000 Ωcm or more.
「珪素源」としては、窒化珪素や珪素（単体）を使用可能である。「炭素源」としては、黒鉛、石炭、コークス、木炭、カーボンブラックなどの炭素質物質を使用可能である。化学量論的には珪素及び炭素のモル比（Ｓｉ／Ｃ）が１のときに過不足なく炭化珪素が生成するが、Ｓｉ／Ｃが０．８〜１．２であれば、珪素及び炭素の過剰分または不足分が少なく、望ましい。 As the “silicon source”, silicon nitride or silicon (simple substance) can be used. As the “carbon source”, carbonaceous materials such as graphite, coal, coke, charcoal, and carbon black can be used. Stoichiometrically, silicon carbide is generated without excess or deficiency when the molar ratio of silicon and carbon (Si / C) is 1, but if Si / C is 0.8 to 1.2, silicon and carbon It is desirable that there is little excess or deficiency.
珪素源として窒化珪素を使用した場合は、炭化珪素の反応生成に伴い窒化珪素の分解により発生した窒素も、反応生成する炭化珪素にドープされるため、導電性相の窒素の濃度を大きなものとし、導電性相の電気伝導性をより高めることができる。これにより、焼結体の少なくとも最外層に高抵抗相を形成することにより、焼結体において電気伝導性に寄与できる体積が減少しても、焼結体全体としての比抵抗値が増大するおそれを低減することができる。 When silicon nitride is used as the silicon source, the nitrogen generated by the decomposition of silicon nitride accompanying the reaction generation of silicon carbide is also doped into the silicon carbide generated by the reaction, so the concentration of nitrogen in the conductive phase is increased. The electrical conductivity of the conductive phase can be further increased. As a result, by forming a high resistance phase in at least the outermost layer of the sintered body, the specific resistance value of the entire sintered body may increase even if the volume that can contribute to electrical conductivity in the sintered body decreases. Can be reduced.
或いは、珪素源として窒化珪素を使用した場合は、窒化珪素の分解により発生する窒素のみをドーパントとし、焼成工程における雰囲気は窒素ガスを含まない非酸化性雰囲気とすることができる。窒素ガスを含まない非酸化性雰囲気は、アルゴンやヘリウム等の希ガス雰囲気、真空雰囲気とすることができる。 Alternatively, when silicon nitride is used as the silicon source, only nitrogen generated by decomposition of silicon nitride can be used as a dopant, and the atmosphere in the firing step can be a non-oxidizing atmosphere that does not contain nitrogen gas. The non-oxidizing atmosphere containing no nitrogen gas can be a rare gas atmosphere such as argon or helium, or a vacuum atmosphere.
＜実施例１＞
炭化珪素８７質量％、窒化珪素１０質量％、炭素質物質３質量％を含む混合原料を使用し、上記の成形工程、焼成工程、及び高抵抗相形成工程を経て、実施例１の試料を作製した。
<Example 1>
Using a mixed raw material containing 87% by mass of silicon carbide, 10% by mass of silicon nitride, and 3% by mass of carbonaceous material, the sample of Example 1 was prepared through the above-described forming process, firing process, and high resistance phase forming process. did.
実施例１、及び、焼成工程までは実施例１と同様に行い高抵抗相形成工程のみを行わなかった比較例１について、空気雰囲気で１０００℃の温度で加熱する酸化試験を行い、所定の時間間隔で、質量増加率（％）、及び、比抵抗変化率（％）を測定した。ここで、質量増加率（％）は、酸化試験に供する前の初期質量からの質量増加分の初期質量に対する割合である。また、比抵抗変化率（％）は、酸化試験に供する前の初期の比抵抗値を１００％とした値である。なお、比抵抗値（体積抵抗率）は、試料から４．５ｍｍ×４．５ｍｍ×４０ｍｍの試験片を切り出し、電圧端子間距離を１０ｍｍとし、ＪＩＳ Ｒ１６５０−２に則り、四端子法で測定した。 For Example 1 and Comparative Example 1, which was performed in the same manner as Example 1 up to the firing step and did not perform only the high resistance phase forming step, an oxidation test was performed by heating at a temperature of 1000 ° C. in an air atmosphere for a predetermined time. The mass increase rate (%) and the specific resistance change rate (%) were measured at intervals. Here, the mass increase rate (%) is a ratio with respect to the initial mass of the mass increase from the initial mass before being subjected to the oxidation test. The specific resistance change rate (%) is a value obtained by setting the initial specific resistance value before being subjected to the oxidation test to 100%. The specific resistance value (volume resistivity) was measured by a four-terminal method in accordance with JIS R1650-2 by cutting a 4.5 mm × 4.5 mm × 40 mm test piece from the sample and setting the distance between the voltage terminals to 10 mm. .
実施例１及び比較例１について、質量増加率（％）の測定結果を図１（ａ）に、比抵抗変化率（％）の測定結果を図１（ｂ）に示す。図１（ａ）から明らかなように、実施例１及び比較例１の何れも、時間の経過に伴い質量が増加している。これにより、空気雰囲気での加熱によって、炭化珪素から二酸化珪素が生成する酸化反応が時間の経過に伴って進行していることが分かる。 About Example 1 and Comparative Example 1, the measurement result of mass increase rate (%) is shown in FIG. 1 (a), and the measurement result of specific resistance change rate (%) is shown in FIG. 1 (b). As is clear from FIG. 1A, in both Example 1 and Comparative Example 1, the mass increases with the passage of time. Thereby, it turns out that the oxidation reaction which silicon dioxide produces | generates from silicon carbide is progressing with progress of time by the heating in an air atmosphere.
一方、図１（ｂ）から、比較例１では時間の経過に伴い比抵抗値が上昇し続けているのに対し、実施例１では１６時間まではわずかに比抵抗値が上昇しているものの、それ以降はほとんど比抵抗値が上昇していないことが分かる。つまり、高抵抗相を有する実施例１では、酸化反応が進行しているにも関らず、比抵抗値の上昇が抑制されている。このことから、電気伝導性への寄与度の小さい高抵抗相が最外層に形成されている実施例１では、この高抵抗相が酸化されることにより、炭化珪素の酸化が比抵抗値に及ぼす影響が低減されており、酸化による比抵抗値の変化が抑制されていると考えられた。なお、酸化試験に供する前の初期の比抵抗値は、実施例１が１５８Ωｃｍ、比較例１が０．４６Ωｃｍであった。 On the other hand, from FIG. 1B, in Comparative Example 1, the specific resistance value continues to increase with the passage of time, whereas in Example 1, the specific resistance value slightly increased up to 16 hours. After that, it can be seen that the specific resistance value hardly increases. That is, in Example 1 having a high resistance phase, an increase in specific resistance value is suppressed despite the progress of the oxidation reaction. From this, in Example 1 in which the high resistance phase having a small contribution to electrical conductivity is formed in the outermost layer, the oxidation of silicon carbide affects the specific resistance value by oxidizing the high resistance phase. The influence was reduced, and it was thought that the change in specific resistance value due to oxidation was suppressed. The initial specific resistance value before the oxidation test was 158 Ωcm in Example 1 and 0.46 Ωcm in Comparative Example 1.
この酸化試験における酸化時間の異なる試料、及び、酸化試験に供する前の試料について、走査型電子顕微鏡で観察を行うと共に、電子プローブマイクロアナライザ（日本電子製、ＪＸＡ８５３０Ｆ）を用いて元素分析（面分析）を行った。酸素を分析対象としたマッピング像を観察した結果、酸化試験に供する前の試料では酸素の存在は殆ど確認されなかったが、酸化試験を行った試料では、粒子の周縁に沿って酸素が分布している様子が観察された。そして、酸化時間の増加に伴い、酸素が分布している相の厚さが大きくなっていることが確認された。 Samples with different oxidation times in this oxidation test and samples before being subjected to the oxidation test are observed with a scanning electron microscope, and elemental analysis (surface analysis) using an electronic probe microanalyzer (JXA 8530F, manufactured by JEOL Ltd.) ) As a result of observing the mapping image with oxygen as the object of analysis, the presence of oxygen was hardly confirmed in the sample before being subjected to the oxidation test, but in the sample subjected to the oxidation test, oxygen was distributed along the periphery of the particle. Was observed. And it was confirmed that the thickness of the phase in which oxygen is distributed increases as the oxidation time increases.
図２に、酸化時間が１１２時間の試料について、酸素を分析対象として面分析したマッピング像（図２（ａ））、及び、同視野の反射電子像（図２（ｂ））を示す。マッピング像では、分析対象の元素が多く存在する部分ほど輝度が高く白っぽく見え、反射電子像では重い元素は明るく軽い元素は暗く観察される。マッピング像から計測したところ、粒子表面で酸素が分布している相の厚さは平均１６０ｎｍであり、この厚さの二酸化珪素の相が粒子表面に形成されていることが分かった。 FIG. 2 shows a mapping image (FIG. 2 (a)) obtained by plane analysis using oxygen as an analysis target and a reflected electron image (FIG. 2 (b)) having the same field of view for a sample having an oxidation time of 112 hours. In the mapping image, the portion with more elements to be analyzed looks brighter and brighter, and in the reflected electron image, heavier elements are observed brighter and lighter elements are observed darker. When measured from the mapping image, it was found that the average thickness of the phase in which oxygen was distributed on the particle surface was 160 nm, and a silicon dioxide phase having this thickness was formed on the particle surface.
上述したように、酸化時間が１１２時間の試料は、酸化反応がかなり進行しているにも関らず、比抵抗値の上昇が抑制されていた。このことから、実施例１の試料では、少なくとも１６０ｎｍ以上の厚さの高抵抗相が形成されており、この高抵抗相内で酸化が進行することにより、焼結体における比抵抗値の変化が抑制されていると考えられた。つまり、少なくとも１６０ｎｍ以上の厚さの高抵抗相が粒子表面に存在すれば、炭化珪素の酸化が比抵抗値に及ぼす影響を低減して、酸化による比抵抗値の変化を抑制する作用を発揮できると考えられた。 As described above, in the sample having an oxidation time of 112 hours, the increase in the specific resistance value was suppressed although the oxidation reaction proceeded considerably. From this, in the sample of Example 1, a high-resistance phase having a thickness of at least 160 nm or more is formed, and oxidation proceeds in the high-resistance phase, so that the specific resistance value in the sintered body changes. It was thought to be suppressed. That is, if a high resistance phase having a thickness of at least 160 nm is present on the particle surface, the effect of oxidation of silicon carbide on the specific resistance value can be reduced, and the effect of suppressing changes in the specific resistance value due to oxidation can be exhibited. It was considered.
なお、高抵抗相が厚ければ厚いほど、酸化による比抵抗値の変化を抑制する作用は大きくなると考えられるが、高抵抗相が厚くなれば、その分だけ導電性相が薄くなり比抵抗値が上昇する。そのため、比抵抗値の変化を抑制する作用を高めるために、高抵抗相を過度に厚くすることは現実的ではない。導電性炭化珪素質焼結体の実用性を考慮すると、高抵抗相の厚さは、高抵抗相を形成する前の導電性相の厚さの１／２以下とすることが望ましい。ここで、酸化試験に供していない実施例１の試料について、画像解析法で粒子径（直径）を測定し、その結果と混合原料中の炭化珪素の粒子径を対比した結果、約４μｍの厚さの導電性相が形成されていると考えられた。従って、高抵抗相の厚さは、その１／２以下である２μｍ以下とすることが望ましい。 It is thought that the thicker the high resistance phase, the greater the effect of suppressing the change in specific resistance value due to oxidation, but the thicker the high resistance phase, the thinner the conductive phase and the specific resistance value. Rises. Therefore, it is not realistic to make the high resistance phase excessively thick in order to enhance the effect of suppressing the change in the specific resistance value. Considering the practicality of the conductive silicon carbide sintered body, it is desirable that the thickness of the high resistance phase is ½ or less of the thickness of the conductive phase before forming the high resistance phase. Here, the particle diameter (diameter) of the sample of Example 1 not subjected to the oxidation test was measured by an image analysis method, and the result was compared with the particle diameter of silicon carbide in the mixed raw material. As a result, the thickness was about 4 μm. It was thought that a conductive phase was formed. Therefore, the thickness of the high resistance phase is desirably 2 μm or less, which is 1/2 or less of that.
＜実施例２＞
炭化珪素５８質量％、窒化珪素３３質量％、炭素質物質９質量％を含む混合原料を使用し、上記の成形工程、焼成工程、及び高抵抗相形成工程を経て、実施例２の試料を作製した。
<Example 2>
Using a mixed raw material containing 58% by mass of silicon carbide, 33% by mass of silicon nitride, and 9% by mass of carbonaceous material, the sample of Example 2 was prepared through the above-described forming process, firing process, and high resistance phase forming process. did.
実施例２、及び、焼成工程までは実施例２と同様に行い高抵抗相形成工程のみを行わなかった比較例２について、上記と同様に、空気雰囲気で１０００℃の温度で加熱する酸化試験を行い、所定の時間間隔で、質量増加率（％）、及び、比抵抗変化率（％）を測定した。質量増加率（％）の測定結果を図３（ａ）に、比抵抗変化率（％）の測定結果を図３（ｂ）に示す。 For Example 2 and Comparative Example 2 which was performed in the same manner as in Example 2 up to the firing step but did not perform only the high resistance phase forming step, an oxidation test was performed in the same manner as described above to heat at 1000 ° C. in an air atmosphere. The mass increase rate (%) and the specific resistance change rate (%) were measured at predetermined time intervals. The measurement result of mass increase rate (%) is shown in FIG. 3A, and the measurement result of specific resistance change rate (%) is shown in FIG. 3B.
図３（ａ）から明らかなように、実施例２及び比較例２の何れも、時間の経過に伴い質量が増加しており、空気雰囲気での加熱によって、炭化珪素から二酸化珪素が生成する酸化反応が時間の経過に伴って進行していることが分かる。 As is clear from FIG. 3 (a), both Example 2 and Comparative Example 2 have increased in mass over time, and oxidation in which silicon dioxide is generated from silicon carbide by heating in an air atmosphere. It can be seen that the reaction is progressing with time.
一方、図３（ｂ）から、比較例２では時間の経過に伴い、比抵抗値が上昇し続けているのに対し、実施例２では比抵抗値がほとんど変化していないことが分かる。つまり、高抵抗相を有する実施例２では、酸化反応が進行しているにも関らず、比抵抗値がほとんど変化していない。このことから、電気伝導性への寄与度の小さい高抵抗相が最外層に形成されている実施例２では、この高抵抗相が酸化されることにより、炭化珪素の酸化が比抵抗値に及ぼす影響が低減されており、酸化による比抵抗値の変化が抑制されていると考えられた。なお、酸化試験に供する前の初期の比抵抗値は、実施例２が５８２Ωｃｍ、比較例２が０．６０Ωｃｍであった。 On the other hand, it can be seen from FIG. 3B that the specific resistance value continues to increase with the passage of time in Comparative Example 2, whereas the specific resistance value hardly changes in Example 2. That is, in Example 2 having a high resistance phase, the specific resistance value hardly changes despite the progress of the oxidation reaction. Therefore, in Example 2 in which the high resistance phase having a small contribution to electrical conductivity is formed in the outermost layer, the oxidation of silicon carbide affects the specific resistance value by oxidizing the high resistance phase. The influence was reduced, and it was thought that the change in specific resistance value due to oxidation was suppressed. The initial specific resistance value before the oxidation test was 582 Ωcm in Example 2 and 0.60 Ωcm in Comparative Example 2.
以上のように、焼成工程の後に、実質的に窒素ガスを含まない非酸化性雰囲気で加熱する工程を付加するのみの簡易な工程で、酸化による比抵抗値の変化が抑制された導電性炭化珪素質焼結体を製造することができる。 As described above, the conductive carbonization in which the specific resistance value change due to the oxidation is suppressed by a simple process of adding a process of heating in a non-oxidizing atmosphere substantially not containing nitrogen gas after the baking process. A silicon-based sintered body can be manufactured.
以上、本発明について好適な実施形態を挙げて説明したが、本発明は上記の実施形態に限定されるものではなく、以下に示すように、本発明の要旨を逸脱しない範囲において、種々の改良及び設計の変更が可能である。 The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements can be made without departing from the scope of the present invention as described below. And design changes are possible.
例えば、導電性相を含むマトリクス中に非導電性の相を散在させることにより、焼結体の比抵抗値を調整することができる。 For example, the specific resistance value of the sintered body can be adjusted by interspersing a non-conductive phase in a matrix containing a conductive phase.
Claims (2)
少なくとも最外層に、前記導電性相における窒素の平均濃度より窒素の濃度が低い炭化珪素の相である高抵抗相が形成されている
ことを特徴とする導電性炭化珪素質焼結体。 It is a sintered body of silicon carbide based ceramics containing a conductive phase which is a phase of silicon carbide containing nitrogen as a dopant,
A conductive silicon carbide based sintered body characterized in that at least the outermost layer is formed with a high resistance phase which is a silicon carbide phase having a nitrogen concentration lower than the average concentration of nitrogen in the conductive phase.
ことを特徴とする請求項１に記載の導電性炭化珪素質焼結体。 The conductive silicon carbide based sintered body according to claim 1, wherein the high resistance phase has a thickness of at least 160 nm.
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| JPH0692736A (en) * | 1992-09-14 | 1994-04-05 | Tokai Carbon Co Ltd | Method for controlling electric resistance of silicon carbide sintered compact |
| JPH07230875A (en) * | 1994-02-18 | 1995-08-29 | Tokyo Tekko Co Ltd | Silicon carbide ceramic heater and manufacture of silicon carbide ceramic base body |
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| JPH0692736A (en) * | 1992-09-14 | 1994-04-05 | Tokai Carbon Co Ltd | Method for controlling electric resistance of silicon carbide sintered compact |
| JPH07230875A (en) * | 1994-02-18 | 1995-08-29 | Tokyo Tekko Co Ltd | Silicon carbide ceramic heater and manufacture of silicon carbide ceramic base body |
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