ترموالکتریک و کاربردهای آن Thermoelectrics

Thermoelectrics: a review of present and potential applications

ترمو الکتریک: مروری بر پتانسیل کاربردهای کنونی 

ABSTRACT

Thermoelectric devices are solid state devices. They are reliable energy converters and have no noise or vibration as there are no mechanical moving parts. They have small size and are light in weight. As refrigerators, they are friendly to the environment as CFC gas or any other refrigerant gas is not used. Due to these advantages, the thermoelectric devices have found a large range of applications. In this paper, basic knowledge of the thermoelectric devices and an overview of these applications are given. The prospects of the applications of the thermoelectric devices are also discussed.

 

بهبود خصوصیات ترموالکتریکی هگزابورید‌های قلیایی خاکی

Improvement of thermoelectric properties of

alkaline-earth hexaborides

بهبود خصوصیات ترموالکتریکی هگزابورید‌های قلیایی خاکی

ABSTRACT

Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10W/mK even at 1073K, which is relatively high among TE materials. Alloys of CaB6 and SrB6 were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB6 and SrB6 single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca0.5Sr0.5B6, indicating that alloying is effective in improving the performance.

 

محلول جامد هگزابورید قلیایی خاکی و خواص ترموالکتریک دما بالای آن ها

ssureHigh-pre densified solid solutions of alkaline earth

hexaborides (Ca/Sr,Ca/Ba,Sr/Ba) 

and their high-temperature thermoelectric properties

محلول جامد هگزابورید قلیایی خاکی (Ca/Sr, Ca/Ba, Sr/Ba)

متراکم شده تحت فشار بالا و خواص ترموالکتریک دما بالای آن ها

ABSTRACT

Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1−xB6, CaxBa1−xB6, SrxBa1−xB6 (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

 

خصوصیات ترموالکتریکی بهبود یافته در ساماریم بورید

Enhanced thermoelectric properties of samarium boride

خصوصیات ترموالکتریکی بهبود یافته در ساماریم بورید

ABSTRACT

SmB62 single crystals were successfully grown by the floating zone (FZ) method. The high-temperature thermoelectric properties were investigated, together with magnetic properties and specific heat at low-temperature. The electrical resistivity, ρ, shows variable-range-hopping (VRH) behavior with significantly lower values than other rare-earth RB62 (RB66) compounds. An effective magnetic moment, μeff, of 0.42 μB/Sm was estimated, which if straightforwardly taken indicates a mixed valency for SmB62 with Sm2+:Sm3+ = 1:1, which is the first ever indicated for RB66-type compounds. Localization length of the VRH at the Fermi level, ξ, was estimated to be 3.33 Å indicating that carriers in SmB62 are much less localized than in YB66 which has 0.56 Å. The thermoelectric behavior of SmB62 is striking, with ρ reduced by two orders of magnitude while maintaining large Seebeck coefficients, and as a result the power factor is ∼30 times higher than other rare-earth phases. Overall the figure of merit ZT amounts to ∼0.13 at 1050 K, with an extrapolated value of ∼0.4 at 1500 K, an expected working temperature for topping cycles in thermal power plants; that gives a ∼40 times enhancement for Sm. Since there are few thermoelectric materials applicable for very-high temperature applications, this discovery gives new interest in the samarium higher borides.

 

افزودن کاربید بور پراکنده شده به مواد ترموالکتریک برپایه تلوراید بیسموت

Spark Plasma Sintered bismuth telluride-based thermoelectric

materials incorporating dispersed boron carbide

افزودن کاربید بور پراکنده شده به مواد ترموالکتریک برپایه تلوراید بیسموت

سینتر شده به روش پلاسمای جرقه ای

ABSTRACT

The mechanical properties of bismuth telluride based thermoelectric materials have received much less attention in the literature than their thermoelectric properties. Polycrystalline p-type Bi0.5Sb1.5Te3 materials were produced from powder using spark plasma sintering (SPS). The effects of nano-B4C addition on the thermoelectric performance, Vickers hardness and fracture toughness were measured. Addition of 0.2 vol% B4C was found to have little effect on zT but increased hardness by approximately 27% when compared to polycrystalline material without B4C. The KIC fracture toughness of these compositions was measured as 0.80 MPa m1/2 by Single-Edge V-Notched Beam (SEVNB). The machinability of polycrystalline materials produced by SPS was significantly better than commercially available directionally solidified materials because the latter is limited by cleavage along the crystallographic plane parallel to the direction of solidification.

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چکیده

خواص مکانیکی مواد ترموالکتریک برپایه تلوراید بیسموت، خیلی کمتر از خواص ترموالکتریکی آنها مورد توجه قرار گرفته است. ماده Bi0.5Sb1.5Te3 نوع p پلی کریستال، به روش سینتر پلاسمای جرقه ای (SPS) از پودر تولید شد. اثر افزودن نانوذرات B4C روی عملکرد ترموالکتریکی، سختی ویکرز و چقرمگی شکست اندازه گیری گردید. مشخص شد که افزودن 2/0%  B4C اثر اندکی روی zT دارد، اما در مقایسه با ماده پلی کریستالی بدون B4C، تقریباً 27% افزایش سختی دارد. چقرمگی شکست KIC این ترکیبات به وسیله "آزمایش تیر با شیار V شکل لبه ای " (SEVNB) به صورت Mpa m1/2 80/0 اندازه گیری شد. قابلیت ماشین کاری مواد پلی کریستالی تولید شده به روش SPS، به طور قابل توجهی بهتر از مواد با انجماد جهت دار رایج تجاری است، چرا که ماشین کاری مواد با انجماد جهت دار، با کلیواژ در طول صفحه کریستالوگرافی موازی با جهت انجماد، محدود می گردد.

فرایند زینترینگ انفعالی و خواص ترموالکتریک کاربیدهای غنی از بور

Reactive sintering process and thermoelectric properties of

boron rich boron carbides

فرایند زینترینگ انفعالی و خواص ترموالکتریک کاربیدهای غنی از بور

ABSTRACT

Dense boron rich boron carbides were reactive sintered by hot pressing at 2050 °C using elementary boronsingle bondcarbon compositions with carbon contents of 9.1, 11.1, 13.3 and 18.8 at.%. The following material characteristics are presented: relative density, SEM images, EDX, X-ray diffraction and corresponding lattice parameters, Seebeck coefficient, electrical conductivity and thermoelectric power factor. Significant grain growth has been obtained with increasing boron content. A deeper understanding of the boron and carbon reaction and the overall sintering process is gained by thermal and chemical analysis in combination with X-ray diffraction. Additionally a thermal experiment with boron and carbon layers illustrates the solid state diffusion behaviour. The found results of boron carbide properties of this paper correspond with results by other authors. The aim is to correlate technological aspects of sintering procedure with material properties. This should help to improve the thermoelectric efficiency of boron carbide based materials.

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