KR20060073018A - Manufacturing method of porous thermoelectric material - Google Patents
Manufacturing method of porous thermoelectric material Download PDFInfo
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- H—ELECTRICITY
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- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/80—Constructional details
- H10N10/85—Thermoelectric active materials
- H10N10/851—Thermoelectric active materials comprising inorganic compositions
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/80—Constructional details
- H10N10/85—Thermoelectric active materials
- H10N10/856—Thermoelectric active materials comprising organic compositions
Abstract
본 발명은 다공성 열전소자 제조방법에 관한 것으로서, 이는 순도 99%이상의 전해철분말 및 규소분말이 몰비로 1:2의 비율을 갖는 잉곳을 분쇄기로 조 분쇄한 후 그를 평균입도 1㎛이하의 미립이 되게 볼밀로 분쇄하고 이에 바인더로 폴리비닐알콜 1∼4wt%와 기공형성제로 녹말 1∼25Vol%을 첨가하여 혼합한 뒤 분무건조기를 건조하여 과립화시키고, 그 과립을 냉간정수압성형기를 이용하여 성형한 후 그 성형체를 분위기 제어가 가능한 소결로에서 산화분위기로 소결한 후 또, 환원분위기로 소결하고, 진공 중에서 어닐링하는 방법으로 보다 우수한 특성을 갖는 열전재료를 얻게 되었다.The present invention relates to a method for manufacturing a porous thermoelectric element, which is an electrolytic iron powder and a silicon powder having a purity of 99% or more and coarsely pulverize an ingot having a ratio of 1: 2 in a molar ratio by a grinder so that the average particle size is 1 탆 or less. After grinding with a ball mill, polyvinyl alcohol 1 ~ 4wt% as a binder and starch 1 ~ 25Vol% as a pore-forming agent are mixed, dried by spray drying, and granulating the granules by using a cold hydrostatic molding machine. The molded body was sintered in an oxidizing atmosphere in an sintering furnace capable of controlling the atmosphere, and then sintered in a reducing atmosphere and annealed in vacuo to obtain a thermoelectric material having better characteristics.
다공성 열전소자, 환원분위기, 어닐링, 녹말Porous thermoelectric element, reducing atmosphere, annealing, starch
Description
본 발명은 열전소자의 성형 및 소결공정시 기공 형성제로서 전분을 첨가하여 혼합한 뒤 분무 건조기를 이용하여 과립화하고, 상기의 과립들을 냉간 정수압 성형기를 이용하여 성형한 후, 상기 성형체를 분위기 제어가 가능한 소결로에서 산화분위기 및 환원분위기의 단계적 방법으로 소결하고, 진공중에서 어닐링하여 보다 우수한 특성을 갖는 다공성 열전소자를 제조하고자 하는 것이다. In the present invention, the starch is added as a pore forming agent during the molding and sintering process of the thermoelectric element, mixed and granulated using a spray dryer, and the granules are molded using a cold hydrostatic pressure molding machine, and then the molded body is controlled in an atmosphere. The sintering furnace can be sintered by a stepwise method of an oxidation atmosphere and a reducing atmosphere and annealed in vacuo to produce a porous thermoelectric device having better characteristics.
일반적으로 열전재료는 열을 전기로 또는 전기를 열로 직접 변환시키는 기능을 갖는 금속 또는 세라믹 재료로서, 쓰레기 소각에 의한 폐열, 터빈발전 폐열, 자동차 배기가스의 열, 도시가스의 연소 배열 및 산업폐열 등을 사용하여 열전발전 또는 열전냉각 등에의 응용이 주목을 받고 있다. In general, thermoelectric material is a metal or ceramic material having a function of directly converting heat into electricity or electricity directly into heat. Waste heat from incineration of waste, waste heat from turbine power generation, heat from automobile exhaust gas, combustion heat from city gas, industrial waste heat, etc. The use of thermoelectric power generation or thermoelectric cooling has attracted attention.
열전재료를 이용한 열전발전은 온도차만 부여하면 가동부분 없이 발전이 가능한 특성 이외에 구조가 간단하고 고장이 적어 유지관리가 유용하고, 소음이 없으며, 이용열원의 선택범위가 넓다. 또한 열전냉각은 고장이 적고 소음이 없으며 미소부분의 선택적 냉각이 가능하며, 열응답 감도가 높아 온도제어가 정밀하고, 압축 기나 냉매가 필요 없는 특징과 이점을 갖고 있다. Thermoelectric power generation using thermoelectric materials is possible to generate power without moving parts by simply giving a temperature difference, and the structure is simple and there are few failures, so maintenance is useful, there is no noise, and there is a wide range of heat sources to use. In addition, thermoelectric cooling has the features and advantages of low breakdown, no noise, selective cooling of minute parts, high temperature response, precise temperature control, and no need of compressor or refrigerant.
열전재료의 특성은 통상적으로 하기 [식1]로 표현되는 성능지수(Z)로 평가할 수 있다.The characteristics of the thermoelectric material can be generally evaluated by the performance index (Z) represented by the following [Formula 1].
[식1][Equation 1]
Z= α2σ/κZ = α 2 σ / κ
α : 제벡(Seebeck)계수α: Seebeck coefficient
σ : 전기전도도σ: electrical conductivity
κ : 열전도도κ: thermal conductivity
열전재료는 성능지수가 크면 클수록 발생되는 전위차가 커지므로 우수한 특성을 나타낸다. 따라서 상기 [식1]로부터 열전재료로서의 응용을 위해서는 제벡계수 및 전기전도도가 크고 열전도도가 작은 재료가 바람직하다. 여기서 제벡계수는 온도의 함수로 주어지는 재료 고유의 물성치로 형상과는 무관하지만, 전기전도도 및 열전도도는 재료의 형상 및 carrior 농도, 결정구조, 결합의 성질, 결합강도 등에 따라 최적화가 가능하다. The larger the performance index, the greater the potential difference, and thus, the thermoelectric material exhibits excellent characteristics. Therefore, for the application as a thermoelectric material from [Equation 1], a material having a high Seebeck coefficient and high electrical conductivity and low thermal conductivity is preferable. Here, the Seebeck coefficient is a material intrinsic property given as a function of temperature. The electrical conductivity and thermal conductivity can be optimized according to the shape, carrior concentration, crystal structure, bonding properties, and bonding strength of the material.
특히 분말소결체의 경우 무질서 구조의 결정입계가 존재하므로 장파장의 격자열진동은 입계에서, 그리고 단파장의 격자열진동은 결정내부의 미세한 strain에서 각각 산란되어 열전도율의 저하를 유도할 수 있다. 그러나 이 경우에는 carrior의 산란에 의한 전기전도도의 저하도 수반될 우려가 있으므로 정밀한 미세구조 제어 및 소결합성 기술의 필요성이 대두되고 있는 실정이다. Particularly, in the case of powder sintered bodies, since the grain boundaries of disordered structure exist, lattice thermal vibrations of long wavelengths are scattered at grain boundaries, and lattice thermal vibrations of short wavelengths can be induced to decrease thermal conductivity. However, in this case, there is a possibility that the electrical conductivity may be accompanied by the scattering of the carrior, and therefore, the necessity of precise microstructure control and non-bonding technology is emerging.
또한 통상적으로 세라믹 소결체의 열전도도를 낮추기 위한 방법으로 소결온도의 제어를 통해 소결밀도를 낮추는 방법이 있으나 동시에 전기전도도가 저하되거나 기계적 강도가 떨어져서 실제 상용 소자로서 적용하기에 어려운 문제가 발생하게 된다. In addition, there is a method for lowering the thermal conductivity of the ceramic sintered body as a method of lowering the sintered density through the control of the sintering temperature, but at the same time, the electrical conductivity is lowered or the mechanical strength is lowered, making it difficult to apply as a practical commercial device.
본 발명은 상기와 같은 문제점을 해결하기 위하여 발명한 것으로서 그 목적은 열전소자 제조시 기공형성제의 첨가에 의해 전기전도도가 저하되지 않으면서 열전도도가 낮은 열전소자의 제조가 가능하도록 함으로써 보다 우수한 성능의 다공성 열전소자를 제조하는 방법을 제공함에 있다. The present invention has been invented to solve the above problems, the object of which is to provide a better performance by allowing the manufacture of a low thermal conductivity thermoelectric element without the electrical conductivity is lowered by the addition of a pore-forming agent in the thermoelectric device manufacturing The present invention provides a method of manufacturing a porous thermoelectric device.
상기 목적을 달성하기 위한 본 발명의 열전소자 제조방법은 순도 99%이상의 전해철분말 및 규소분말이 몰비로 1:2의 비율을 갖는 잉곳을 분쇄기로 조 분쇄한 후 그를 평균입도 1㎛이하의 미립이 되게 볼밀로 분쇄하고 이에 바인더로 폴리비닐알콜 1∼4wt%와 기공형성제로 녹말 1∼25Vol%을 첨가하여 혼합한 뒤 분무건조기를 건조하여 과립화시키고, 그 과립을 냉간정수압성형기를 이용하여 성형한 후 그 성형체를 분위기 제어가 가능한 소결로에서 산화분위기로 소결한 후 또, 환원분위기로 소결하고, 진공 중에서 어닐링하는 것으로 이루어진다.In order to achieve the above object, the method of manufacturing a thermoelectric device according to the present invention comprises coarsely pulverizing an ingot having a ratio of 1: 2 in an electrolytic iron powder and a silicon powder having a purity of 99% or more, and then having a fine particle having an average particle size of 1 μm or less. Grind it into a ball mill, add 1 to 4 wt% of polyvinyl alcohol as a binder, and add 1 to 25 vol% of starch as a pore-forming agent, mix, dry the spray dryer and granulate, and shape the granules using a cold hydrostatic molding machine. Thereafter, the molded body is sintered in an oxidizing atmosphere in a sintering furnace capable of controlling the atmosphere, and then sintered in a reducing atmosphere and annealed in vacuo.
그리고, 상기 성형체를 소결로에서 산화분위기로 소결하는 조건은 산화분위기에서 1℃/min.의 속도로 승온하여 450∼550℃에서 1∼4시간동안 유지시켜 소결하 는 것이며, 상기 성형체를 소결로에서 환원분위기로 소결하는 조건은 Ar-H2를 이용하여 환원분위기에서 3℃/min의 속도로 승온하여 1100∼1200℃에서 1∼4시간동안 유지시켜 소결하는 것이며, 상기 소결된 성형체를 진공 중에서 어닐링하는 조건은 750∼850℃에서 5∼20시간 동안이다.In addition, the conditions for sintering the molded body in an oxidizing atmosphere in a sintering furnace are to sinter by raising the temperature at a rate of 1 ° C./min. The conditions for sintering in a reducing atmosphere at sintering are to sinter by heating at a rate of 3 ° C./min using Ar—H 2 at 1100 to 1200 ° C. for 1 to 4 hours. The annealing conditions are for 5 to 20 hours at 750 to 850 占 폚.
상기 본 발명에서 전해철 및 규소분말의 순도는 99% 이상인 것을 사용하는 것이 바람직하다. 그 이유는 순도가 99% 이하로 떨어지면 함유되어 있는 탄소나 실리카에 의해 입자성장을 과도하게 촉진시킬 뿐 아니라 소결이 과도하게 진행되어 열전소자의 제조에 어려움이 따른다.In the present invention, the purity of the electrolytic iron and silicon powder is preferably 99% or more. The reason is that when the purity falls below 99%, not only the grain growth is excessively promoted by the carbon or silica contained therein, but the sintering is excessively progressed, thus making it difficult to manufacture the thermoelectric element.
또, 상기 1차 소결은 소결로에서 산화분위기로 소결하는 것인데 그 조건은 산화분위기에서 1℃/min.의 속도로 승온하여 450∼550℃에서 1∼4시간동안 유지시켜 하는 것으로, 이는 바인더인 폴리비닐알콜과 기공형성제인 녹말을 제거하기 위한 것이다.In addition, the primary sintering is to sinter in an oxidizing atmosphere in a sintering furnace, and the conditions are to increase the temperature at a rate of 1 ℃ / min in the oxidizing atmosphere and to maintain for 1 to 4 hours at 450 ~ 550 ℃, which is a binder Polyvinyl alcohol and pore-forming starch to remove.
또한, 상기 2차소결은 환원성분위기에서 함이 바람직하고 소결온도는 1100∼1200℃로 함이 바람직한데 1100℃ 미만에서는 소결이 이루어지지 않아 강도가 약하며, 1200℃를 초과면 과도한 입자성장과 과도한 소결로 다공체를 얻기 어렵다. In addition, the secondary sintering is preferably in the reducing component crisis and the sintering temperature is preferably set to 1100 ~ 1200 ℃ but less than 1100 ℃ sintering is not strong strength, exceeding 1200 ℃ excessive grain growth and excessive sintering It is difficult to obtain a porous body.
상기 폴리비닐알골을 1∼4Wt%첨가하는 이유는 성형성을 좋게 하기 위한 것으로서 첨가량이 1중량% 미만이면 성형성 부족으로 성형체의 제조가 어렵고, 4중량%를 초과하면 성형체 분말 제조시 과량의 포리비닐알콜로 인해 분말이 딱딱해져 처리하는데 어려움이 있다. 가장 바람직하게는 1중량%이다. The reason for adding 1 to 4 Wt% of the polyvinyl algol is to improve moldability. If the amount is less than 1% by weight, it is difficult to manufacture the molded product due to lack of moldability. Vinyl alcohol hardens the powder, making it difficult to process. Most preferably 1% by weight.
상기 녹말을 1∼25Vol%첨가하는 이유는 기공성을 좋게 하기 위한 것으로서 첨가량이 1Vol% 미만이면 기공성 부족하고, 25Vol%를 초과하면 기공성를 좋으나 필요이상이 된다. 따라서, 녹말은 1∼25Vol%첨가함이 바람직하다. The reason for adding 1 to 25 vol% of the starch is to improve the porosity. If the amount is less than 1 Vol%, the porosity is insufficient, and if it exceeds 25 Vol%, the porosity is good but more than necessary. Therefore, it is preferable that starch adds 1-25 Vol%.
이하 실시예를 통하여 본 발명을 보다 상세하게 설명한다.Hereinafter, the present invention will be described in more detail with reference to the following examples.
(실시예)(Example)
본 발명의 다공성 열전소자를 제조하기 위하여 출발원료로서 상용의 FeSi2(Cerak)분말을 사용하여 볼밀로 24시간 분쇄하여 평균입도가 1㎛이하의 미분이 되도록 하였다. 상기 분말에 바인더로 폴리비닐알콜(PVA)를 1wt% 첨가하고, 기공형성제로서 상용의 녹말을 1~25Vol% 첨가한 범위를 갖도록 하기 표1의 비교예 1,2 내지 발명예 4의 조성을 설계하였다.In order to manufacture the porous thermoelectric device of the present invention, a commercially available FeSi 2 (Cerak) powder was used as a starting material, and pulverized with a ball mill for 24 hours to obtain a fine particle having an average particle size of 1 μm or less. 1 wt% of polyvinyl alcohol (PVA) was added to the powder as a binder, and the composition of Comparative Examples 1, 2 and 4 of Table 1 was designed to have a range in which 1 to 25 vol% of starch was added as a pore forming agent. It was.
상기 각각의 조성에 대하여 볼밀을 사용하여 에탄올 용매중에서 24시간 혼합한 후 분무건조기(Spray dryer)로 건조하여 과립화시켰다. 상기 분말은 먼저 유압프레스를 이용하여 단면적이 20㎜ x 40㎜의 성형몰드로 가압 성형한 후, 냉간정수압프레스(Cold Isostatic Press)에 의하여 2.0톤/㎠의 압력으로 성형하였다.For each of the above compositions, the mixture was mixed for 24 hours in an ethanol solvent using a ball mill and then granulated by drying with a spray dryer. The powder was first press-molded into a molding mold having a cross-sectional area of 20 mm x 40 mm by using a hydraulic press, and then molded at a pressure of 2.0 ton / cm 2 by a cold isostatic press.
상기 성형시편은 산화분위기의 소결로에서 1℃/min.의 속도로 승온하여 500℃에서 2시간 유지시켜 바인더 및 기공형성제를 제거한 후, Ar-H2를 이용하여 환원분위기에서 3℃/min의 속도로 승온하여 1150℃에서 3시간동안 유지시켜 소결을 행하였다. The molded specimen was heated at a rate of 1 ° C./min in an oxidizing atmosphere and maintained at 500 ° C. for 2 hours to remove the binder and the pore-forming agent, and then 3 ° C./min in a reducing atmosphere using Ar-H 2 . It heated up at the speed of and maintained at 1150 degreeC for 3 hours, and performed sintering.
상기 소결된 시편들은 반도체화를 위해 진공중에서 800℃에서 10시간 동안 어닐링 한 후, 크기가 4㎜ x 4㎜ x 20㎜가 되도록 절단하여 최종 특성평가용 시편으로 사용하였다. The sintered specimens were annealed at 800 ° C. for 10 hours in vacuum for semiconductorization, and then cut into 4 mm × 4 mm × 20 mm in size and used as final characterization specimens.
상기 비교예1,2 내지 발명예4에 대하여 소결성, 전기전도도, 열전도도도를 측정하여 그 결과를 하기 표1에 나타내었다. Sinterability, electrical conductivity, and thermal conductivity of the Comparative Examples 1, 2 to 4 were measured, and the results are shown in Table 1 below.
[표1] Table 1
상기 표1에서 알 수 있는 바와 같이 발명예1 내지 발명예4의 경우 소결성이 양호하고 전기전도도가 크게 저하되지 않으면서 열전도도가 1/2 정도로 낮아 우수한 열전특성을 나타내었다.As can be seen in Table 1, in the case of Inventive Examples 1 to 4, the sinterability is good and the thermal conductivity is about 1/2 lower without the electrical conductivity being greatly reduced, thereby showing excellent thermoelectric properties.
상기와 같은 본 발명의 열전소자의 제조방법은 기공형성제의 첨가에 의해 전기전도도가 저하되지 않으면서 열전도도가 낮은 열전소자의 제조가 가능하도록 함으로써 열전발전 및 열전냉각용 소자로서 실용성이 높은 효과가 있다. The method of manufacturing a thermoelectric device of the present invention as described above enables the production of a low thermal conductivity thermoelectric device without the electrical conductivity being lowered by the addition of a pore-forming agent, thereby making it highly practical as an element for thermoelectric power generation and thermoelectric cooling. There is.
Claims (4)
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