【０００１】
【発明の属する技術分野】本発明は熱電変換素子に関する。より詳しくは粉末の焼結接合を利用して製造するｐ型およびｎ型材料一体型の熱電変換素子に関する。
【０００２】
【従来の技術】熱電変換素子はｐ型およびｎ型熱電材料の一端を接合した構造をしており、素子の両端部に温度差を与えると起電力が生じ、回路で結ぶと電流が流れる。このように熱電変換素子は熱を直接電気に変換することが出来る。
【０００３】熱電変換素子においてｐ型およびｎ型熱電材料の接合には、一般に金属電極板を介して半田付けやロウ付けなどが行われているが、高温での接合耐久性が低い欠点があった。そのためｐ型およびｎ型熱電材料粉末成形体を焼結接合した熱電変換素子も開発されている。
【０００４】また難焼結性の熱電材料では、ｐ型およびｎ型熱電材料粉末を黒鉛等の型内に積層充填し、ホットプレスあるいは放電焼結することにより積層焼結体を作製した後、一部接合部を残してｐ型およびｎ型材料境界部を切り離す切れ込み加工を行い電気的に絶縁した熱電変換素子が開発されている。
【０００５】さらに（０００４）において切れ込み加工の代わりに絶縁層としてセラミックス粉末やセラミックスシートをｐ型およびｎ型材料粉末層の間に挟んでホットプレスあるいは放電焼結することにより製作する熱電変換素子も開発されている。
【０００６】
【発明が解決しようとする課題】（０００５）に記載の熱電変換素子では、ホットプレスあるいは放電焼結に際し、加圧力を粉末に均一にかける、鋭い角は応力が集中し型が割れやすいので避けるなどの必要があり、焼結型は円柱形状が望ましい。そのため円柱状焼結体を焼結し、素子はこれを切断、研削加工して製造していた。しかしこれらの熱電材料は硬くまた脆いためこれらの加工が難しく、加工に伴い欠けや割れなどが生じやすい問題点があった。また、これらの加工には長時間を必要とし、高コストであるなどの問題点もあった。
【０００７】
【課題を解決するための手段】本発明の熱電変換素子は、素子の形状を円筒形にし、円筒の内と外で温度差をつけ、発電する方式をとる。そのため円筒形の焼結体がそのまま熱電変換素子となるので、焼結後、（０００４）および（０００６）に記載の切断等の加工を必要としない。
【０００８】（請求項１）に記載のｐ型およびｎ型材料一体型の円筒型多層熱電変換素子の横断面図を図１に、上から見た図を図２に示す。本発明の円筒型多層熱電変換素子は図中番号３の大きな外径と中心穴を持つ中心穴付き円形セラミックス繊維シートおよび番号４の小さな外径と中心穴を持つ中心穴付き円形セラミックス繊維シートの２種類のセラミックス繊維シートをｐ型熱電材料粉末層とｎ型熱電材料粉末層の間に交互に挿入する形で黒鉛等の円筒形の型内に複数積層充填した後、黒鉛等の上下パンチにより加圧しながら、ホットプレスあるいは放電焼結することにより製造する。番号３および４のセラミックス繊維シートは積層焼結後、充分な電気絶縁性を持つものでなければならない。番号１のｐ型熱電材料層と番号２のｎ型熱電材料層は、焼結により円筒の外側と内側で数ｍｍの厚みで直接に接合する。円筒素子の頭部と底部にはニッケル板などにより番号６の電極をもうけることが望ましく、また番号７のリード線を繋ぎやすいよう突起等をもうける工夫も必要となる。
【０００９】（請求項２）に記載の円筒型多層熱電変換素子は、水冷却により発電性能の向上が図れるＳｉが７０〜１００原子％、Ｇｅが０〜３０原子％、Ｂが０〜１原子％およびＰが０〜１原子％の化学組成を持つＳｉＧｅ系熱電材料を用い、ステンレス鋼等の水冷パイプを素子の中心穴に通して、円筒内側を低温部とし、円筒の外周側を高温部とした発電用素子である。
【００１０】
【発明の実施の形態】実施例を挙げ、実施の形態を説明する。ｐ型熱電材料の原料粉末としてＢを０．３原子％添加した平均粒径約３０μｍのガスアトマイズＳｉ粉末、ｎ型熱電材料の原料粉末としてＰを０．３原子％添加した同様の粉末を１層につき６ｇ用い、また厚さ２ｍｍのセラミックス繊維シートから外径３４ｍｍ、内径１６ｍｍと外径３０ｍｍ、内径１２ｍｍの大小２種類の中心穴付き円形セラミックス繊維シートを切り出し、絶縁層とした。これらを順にｐ、ｎ、大セ、小セと略して記すると、ｐ／小セ／ｎ／大セ／ｐ／小セ／ｎ／大セ／ｐ／小セ／ｎの順番に計６層の熱電材料原料粉末を円筒形黒鉛型の中に積層した。
【００１１】焼結は放電プラズマ焼結機を用い、黒鉛パンチで２５ＭＰａの圧力で加圧しながら１２７０℃まで昇温して行った。焼結した円筒素子の頭部と底部には突起をつけて、これにリード線を繋げた。また外径９ｍｍのステンレス鋼の水冷パイプを素子の中心穴に通して、素子とステンレス鋼パイプとの間にはセラミックウールを詰めて電気絶縁した。
【００１２】このようにして作製した円筒型多層熱電変換素子についてガスバーナーによる加熱実験を行った結果、加熱と冷却の繰り返しに伴う素子の割れ等の異状は観察されなかった。また加熱時には相当量の電力が得られることを電圧、電流測定にて確認した。
【００１３】
【発明の効果】本発明のｐ型およびｎ型材料一体型の円筒型多層熱電変換素子では、ホットプレスあるいは放電焼結後の切れ込み加工や切断加工なしで直接、素子となるので、製造工程が短縮され、また加工に伴う欠けや割れがなくなり、製品歩留まりが大きく向上する。そのため製造コストは大幅に低減され、安価な熱電変換素子として提供される。
【図面の簡単な説明】
【図１】ｐ型およびｎ型材料一体型の円筒型多層熱電変換素子の横断面の概略図である。
【図２】ｐ型およびｎ型材料一体型の円筒型多層熱電変換素子を上から見た概略図である。
【符号の説明】
１ ｐ型熱電材料
２ ｎ型熱電材料
３ 大きな中心穴と外径を持つ中心穴付き円形セラミックス繊維シート
４ 小さな中心穴と外径を持つ中心穴付き円形セラミックス繊維シート
５ 絶縁層
６ 電極
７ リード線
８ 水冷パイプ
９ 冷却水[0001]
[0001] The present invention relates to a thermoelectric conversion element. More specifically, the present invention relates to a thermoelectric conversion element integrated with p-type and n-type materials manufactured by using powder sintering.
[0002]
2. Description of the Related Art A thermoelectric conversion element has a structure in which one end of a p-type and n-type thermoelectric material is joined. When a temperature difference is applied to both ends of the element, an electromotive force is generated, and when connected in a circuit, a current flows. As described above, the thermoelectric conversion element can directly convert heat into electricity.
[0003] In the thermoelectric conversion element, the p-type and n-type thermoelectric materials are generally joined by soldering or brazing via a metal electrode plate, but have a drawback that the joining durability at high temperatures is low. Was. Therefore, thermoelectric conversion elements in which p-type and n-type thermoelectric material powder compacts are sintered and bonded have been developed.
[0004] In the case of a thermoelectric material which is difficult to sinter, p-type and n-type thermoelectric material powders are laminated and filled in a mold such as graphite, and hot-pressed or discharge-sintered to produce a laminated sintered body. 2. Description of the Related Art Thermoelectric conversion elements that have been cut and cut to separate a boundary between p-type and n-type materials and are electrically insulated while leaving a part of the junction have been developed.
Further, in (0004), there is also provided a thermoelectric conversion element manufactured by hot pressing or electric discharge sintering a ceramic powder or a ceramic sheet as an insulating layer between p-type and n-type material powder layers instead of cutting. Is being developed.
[0006]
In the thermoelectric conversion element described in (0005), during hot pressing or electric discharge sintering, a pressing force is uniformly applied to the powder. Sharp corners are concentrated because stress is concentrated and the mold is liable to be broken. It is necessary that the sintered mold has a cylindrical shape. Therefore, a columnar sintered body was sintered, and the element was cut and ground to produce the element. However, these thermoelectric materials are hard and brittle, so that their processing is difficult, and there has been a problem that chipping, cracking, and the like are apt to occur with the processing. In addition, there is a problem that these processes require a long time and are expensive.
[0007]
Means for Solving the Problems The thermoelectric conversion element of the present invention employs a method in which the element is formed into a cylindrical shape, and a temperature difference is generated between the inside and the outside of the cylinder to generate power. Therefore, since the cylindrical sintered body becomes the thermoelectric conversion element as it is, there is no need to perform processing such as cutting described in (0004) and (0006) after sintering.
FIG. 1 is a cross-sectional view of a cylindrical multilayer thermoelectric conversion element integrated with a p-type and n-type material according to claim 1, and FIG. 2 is a top view thereof. The cylindrical multilayer thermoelectric conversion element of the present invention is composed of a circular ceramic fiber sheet with a central hole having a large outer diameter and a central hole of No. 3 and a circular ceramic fiber sheet with a central hole having a small outer diameter and a central hole of No. 4 in the figure. Two types of ceramic fiber sheets are alternately inserted between a p-type thermoelectric material powder layer and an n-type thermoelectric material powder layer, and are filled in a plurality of layers in a cylindrical mold such as graphite. It is manufactured by hot pressing or electric discharge sintering while applying pressure. The ceramic fiber sheets of Nos. 3 and 4 must have sufficient electrical insulation after lamination and sintering. The p-type thermoelectric material layer of No. 1 and the n-type thermoelectric material layer of No. 2 are directly joined with a thickness of several mm on the outside and inside of the cylinder by sintering. It is desirable to provide the electrode No. 6 with a nickel plate or the like on the head and bottom of the cylindrical element, and it is also necessary to provide a projection or the like so that the lead wire No. 7 can be easily connected.
In the cylindrical multilayer thermoelectric conversion element according to the present invention, 70 to 100 atomic% of Si, 0 to 30 atomic% of Ge, and 0 to 1 atomic of B can improve power generation performance by water cooling. % And P are chemical elements having a chemical composition of 0 to 1 atomic%, and a water-cooled pipe such as stainless steel is passed through the center hole of the element to make the inside of the cylinder a low temperature part and the outside of the cylinder a high temperature part. This is a power generating element.
[0010]
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments will be described with reference to examples. One layer of a gas atomized Si powder having an average particle diameter of about 30 μm to which B is added as a raw material powder of a p-type thermoelectric material and about 0.3 μm of P as a raw material powder of an n-type thermoelectric material In addition, two types of large and small circular ceramic fiber sheets having a center hole having an outer diameter of 34 mm, an inner diameter of 16 mm, an outer diameter of 30 mm, and an inner diameter of 12 mm were cut out from a ceramic fiber sheet having a thickness of 2 mm. These are abbreviated as p, n, large size, and small size in this order, and a total of 6 layers in the order of p / small size / n / large size / p / small size / n / large size / p / small size / n The thermoelectric material raw material powder was laminated in a cylindrical graphite mold.
The sintering was performed by using a discharge plasma sintering machine and increasing the temperature to 1270 ° C. while applying a pressure of 25 MPa with a graphite punch. The head and the bottom of the sintered cylindrical element were provided with protrusions to which lead wires were connected. A stainless steel water-cooled pipe having an outer diameter of 9 mm was passed through the center hole of the element, and ceramic wool was filled between the element and the stainless steel pipe for electrical insulation.
As a result of conducting a heating experiment using a gas burner on the cylindrical multilayer thermoelectric conversion element manufactured as described above, no abnormality such as cracking of the element due to repeated heating and cooling was observed. Further, it was confirmed by voltage and current measurement that a considerable amount of electric power was obtained during heating.
[0013]
According to the present invention, the cylindrical multi-layer thermoelectric conversion element integrated with p-type and n-type materials is directly formed into an element without cutting or cutting after hot pressing or electric discharge sintering. It is shortened, chipping and cracking due to processing are eliminated, and the product yield is greatly improved. Therefore, the manufacturing cost is significantly reduced, and the thermoelectric conversion element is provided as an inexpensive thermoelectric conversion element.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a cylindrical multilayer thermoelectric conversion element integrated with p-type and n-type materials.
FIG. 2 is a schematic view of a cylindrical multilayer thermoelectric conversion element integrated with p-type and n-type materials as viewed from above.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 p-type thermoelectric material 2 n-type thermoelectric material 3 circular ceramic fiber sheet with large center hole and center hole with outer diameter 4 circular ceramic fiber sheet with center hole with small center hole and outer diameter 5 insulating layer 6 electrode 7 lead wire 8 Water cooling pipe 9 Cooling water
