Values Of Thermoelectric Power Research Articles

Non-destructive evaluation of aging in welded pipeline X60 and X65 by thermoelectric power means

In this investigation, the sensibility of the thermoelectric power (TEP) to the aging condition of API X60 and API X65 steel pipeline welded joints was evaluated. Specimens of both API welded joints were artificially aged at 300 °C for 3, 7, 9, 18, 30 and 45 h, the microstructural evolution was assessed via optical microscopy (OM) and scanning electron microscopy (SEM). Image analysis revealed no significant changes in the microstructure with respect to the aging time. Vickers micro-hardness evaluation showed that both welded joints reach a maximum hardness value after 3 h of artificial aging followed by a reduction in its value in the next aging conditions. TEP was measured using the hot tip technique applying different hot tip temperatures (55, 60, 65, 70 °C), where higher temperature values showed to increase the sensibility of the technique to detect microstructural changes that affect micro-hardness and where not possible to observe via OM and SEM. TEP and micro-hardness exhibit an opposite correlation, which was confirmed calculating the Pearson's correlation coefficient (r). The correlation coefficient decreases when higher hot tip temperatures where employed to measure TEP. The good correlation between TEP values and micro-hardness allows to use TEP measurement as a prediction tool of material micro-hardness.

Structural, spectroscopic, magnetic, and magneto-transport behavior of Ruddlesden-Popper Ca4Mn3-xWxO10 (x = 0, 0.05, 0.1) compounds

This report comprehensively investigates the crystal structure, magnetism, and transport properties of tungsten (W6+) substituted polycrystalline Ca4Mn3-xWxO10 (x = 0, 0.05, 0.1) compounds. The compounds were synthesized using the solid-state method and found to exhibit a single-phase orthorhombic structure confirmed by the Rietveld refinement. The substitution of (W6+) induces a change in the Mn octahedron and enhances the unit cell volume. The morphology indicates the crystalline nature of all the samples. The FTIR spectroscopic study revealed the position of the IR bands, which is highly sensitive to the oxidation state of Mn-ions. The shift to higher wavenumbers indicates reduced oxidation from Mn4+ to Mn3+ species. The appearance of the Mn4+ oxidation state in (x = 0) and the emergence of Mn3+ on W6+ substitution for (x = 0.05, 0.1) compounds are explored. The electrical resistivity plots revealed that compounds are semiconducting. The magnitude of resistivity decreases with W6+ substitution. The reported compounds exhibit a significant negative magneto-resistance towards lower temperatures. The compounds also demonstrate short-range ferromagnetic (FM) behavior attributed to the charge compensation effect's double exchange interaction (DE) connecting Mn4+ and Mn3+. The negative value of thermoelectric power (S) suggests the presence of charge carriers such as electrons, and the value ofSfirst increased and then decreased in doped samples. The conduction in the studied compound is attributed to small polaron hopping.

Galvanomagnetic and Thermoelectric Properties of Bismuth Films Doped with Tin

This paper presents the experimental study of the galvanomagnetic and thermoelectric properties of thin bismuth films doped with tin. The amount of tin is 0.06 at. % with the thickness ranged within 250-800 nm, and it is deposited on mica-muscovite substrates in vacuum up to 1·10-5 mm Hg. The galvanomagnetic and thermoelectric coefficients of all presented films are measured in the temperature range of 77-300 K in a magnetic field of up to 0.65 T. It is found that the classical size effect in the films occurs due to mobility of electrons being restricted by the thickness of the film. A characteristic maximum of temperature dependence of relative transverse magnetoresistance in the temperature range of 150-200 K is observed. A change in the sign of the Seebeck coefficient at the temperature of 175 K is found. It can be explained by the temperature change ratio of the electron and hole components contributions to galvanomagnetic and thermoelectric phenomena, and the contribution of holes at the L, T points of the Brillouin zone. The positive values of differential thermoelectric power in bismuth films doped with tin can become the basis for searching for the possibility of creating a p-branch of thermoelectric energy converters in the low-temperature area. The obtained results of measurements can be used for creation of a low-dimensional bismuth-based structures with a controlled hole concentration.

Thermoelectric Effects in Tunneling of Spin-Polarized Electrons in a Molecular Transistor

Thermal transmission in a molecular transistor with fully spin-polarized electrodes subjected to a temperature gradient is considered. The problem has been solved by using density matrix method in perturbation approach over small tunneling width. It has been found that due to the vibronic effects spintronic molecular transistor is characterized by negative differential thermoconductance. It has been demonstrated that in the dependence of thermopower $S$ on the detuning energy there is an increased number of points of change of the sign and magnitude of $S$ comparing with that of conventional molecular transistor. Optimal parameters, that provide the highest thermoelectric power at maximum efficiency $P_{me}$ for spintronic molecular transistor, have been found. The dependences of the figure of merit $ZT$ and $P_{me}$ on temperature and an external magnetic field have been calculated and the influence of Coulomb interaction on the thermolelectric properties has been studied. It has been revealed, that for non-zero Coulomb interaction more handy regime of thermoelectric device develops, characterized by continuous region of external magnetic fields, which provide high values of thermoelectric power.

Lattice Dynamics of Bi1.9Dy0.1Te3 Topological Insulator

In this report, we have investigated the Density functional theory (DFT) calculation, temperature-dependent thermoelectric power and Raman spectroscopy of Bi1.9Dy0.1Te3 topological insulator (TI). In this system, discrepancy due to the rare earth ion Dy initiates a Red-shift in Raman active modes in the Bi2Te3 TI. Here, the lattice thermal conductivity (κL) was evaluated in the Umklapp scattering limit using the temperature dependency of the vibrational phonon modes and was used to evaluate the Figure of merit (ZT) of the system. It has been demonstrated that the estimated Power factor and ZT is very large, confirming the efficiency of Bi1.9Dy0.1Te3 for better thermoelectric and electronic applications. Such immense thermoelectric power value of the corresponding system was further supported by the DFT calculation.

Temperature and Electron concentration dependent Thermoelectric Power in Wide Band Gap semiconductor GaN Nanowire

Abstract: Nanostructures have a significant promise as potential building blocks for the next generation thermoelectric devices. While the thermal transport properties of bulk materials have been intensely studied, the understanding of nanostructure thermoelectric properties and their interrelation is still incomplete. In the calculated temperature range, the thermoelectric power (TEP) was found to be linearly dependent on temperature, suggesting the degenerate nature of the GaN semiconductor nanowire similar to that of ZnO semiconductor nanowire. Observed negative values of TEP indicating that, majority charge carriers are electrons in GaN semiconductor. Linear dependence of TEP with temperature shows that TEP is only due to electron diffusion and not due to phonon-drag effect. Also observed the calculated TEP values are in good agreement with the experimental results in the overall temperature range 10 – 300 K. Keywords: Semiconductor nanowire, GaN, Mott relation, Thermoelectric power, wide band gap semiconductor

Electrical and Thermal Transport Properties of the β-Pyrochlore Oxide CsW2O6

We report the electrical resistivity, thermoelectric power, and thermal conductivity of single-crystalline and sintered samples of the 5d pyrochlore oxide CsW2O6. The electrical resistivity of the single crystal is 3 mΩ cm at 295 K and gradually increases with decreasing temperature above 215 K (Phase I). The thermoelectric power of the single-crystalline and sintered samples shows a constant value of approximately −60 µV K−1 in Phase I. These results reflect that the electron conduction by W 5d electrons in Phase I is incoherent and in the hopping regime, although a band gap does not open at the Fermi level. The thermal conductivity in Phase I of both samples is considerably low, which might be due to the rattling of Cs+ ions. In Phase II below 215 K, the electrical resistivity and the absolute value of thermoelectric power of both samples strongly increase with decreasing temperature, corresponding to a transition to a semiconducting state with a band gap open at the Fermi level, while the thermal conductivity in Phase II is smaller than that in Phase I.

Backup thermoelectric sources of electric energy

The article presents the rationale for the use of thermoelectric systems to provide backup power supply for actuators and automation systems for engineering systems of multistory buildings. The experiments were carried out using the developed stand, which modulated the parameters of the engineering systems of multi-storey buildings. The stand consists of a NEPS-100-220-0.03-UHL4 heating element and a CoolerMasterI30 cooler, the temperature on the sides of the thermoelectric module is controlled by a TPM-2 thermostat using a solid-state relay, the thermoelectric power value is recorded by an OVEN IMS device. F1, the electrical load is set by the resistance bridge. Temperature control of thermoelectric elements, hot and cold sides of a thermoelectric module, as well as sources of “heat” and “cold” is carried out by thermocouples, the data is recorded by the TPM138 meter-regulator. As a result of the work carried out, it was found that with the help of new technical solutions it is possible to increase the temperature on the heat exchange sides of thermoelectric modules and bring their technical parameters to the area of maximum efficiency. When organizing thermoelectric systems, it will be possible to provide backup power to the equipment used in heat points of multi-storey buildings.

Unraveling energy consumption by using low-cost and reevaluated thermoelectricThin Films

Energy is undoubtedly one of our most important demands whose consumption is constantly increasingand will continue to increase soon. One of the most important factors in attaining the required energy is to providehigh efficiency at a low cost with the help of new technological improvements by evaluating wastes. Energy demandcould be achieved for a relatively large thermoelectric power value by recycling the Peltier modules from waste onesand adjusting their properties with nanotechnology. For this aim, thermoelectric thin film modules were grown onsilicon (Si), glass, and Kapton substrates with thermal evaporation method by using two different BiTeSb/BiTeSealloy materials which are placed in industrial Peltiers as the p- and n-type semiconductor. The thin films structuraland morphological characterizations were investigated by X-ray diffraction (XRD) and scanning electron microscopy(SEM) experiments reveal fine surface with uniformly distributed continuous structure. Seebeck coefficiency (|S|) of thesubstantial modules were investigated by forming certain temperature gradients on them making serial connections usinga homemade measurement setup. |S|=143.86μV/K is obtained for the thermoelectric module on Si substrate and 44.96μV/K and 24.98μV/K are calculated for glass and Kapton, respectively.

A quantitative model and solution of reaction heat for microfluidic chips based on Kriging and NSGA-II

Microfluidic chips have been widely used in microfluidic calorimeters. The thermoelectric power can be obtained by measuring the laminar flow peak value of the reaction liquid. Due to heat dissipation and heat inhomogeneity, thermodynamic parameters can not accurately describe the thermal state and thermal properties. With the inlet velocity and velocity ratio in Y-channel as the two key parameters affecting the peak value of thermoelectric power, the reaction heat governing equation is established. The Kriging method is used to establish the reaction heat quantification model and Nondominated Sorting Genetic Algorithm (NSGA-II) is used in global optimization. Then, the Pareto solution set of optimal inlet velocity and optimal velocity ratio is obtained. Finally, the established reaction heat governing model was experimentally verified; The predicted values of the Kriging quantitative model were consistent with the experimental results; The three sets of Pareto solutions can accurately describe the thermal state and thermal properties.

Vapor grown carbon nanofiber based cotton fabrics with negative thermoelectric power

Vapor grown carbon nanofiber (CNF) based ink dispersions were used to dip-coat woven cotton fabrics with different constructional parameters, and their thermoelectric (TE) properties studied at room temperature. Unlike the positive thermoelectric power (TEP) observed in TE textile fabrics produced with similar carbon-based nanostructures, the CNF-based cotton fabrics showed negative TEP, caused by the compensated semimetal character of the CNFs and the highly graphitic nature of their outer layers, which hinders the p-type doping with oxygen groups onto them. A dependence of the electrical conductivity (σ) and TEP as a function of the woven cotton fabric was also observed. The cotton fabric with the largest linear density (tex) showed the best performance with negative TEP values around − 8 μV K−1, a power factor of 1.65 × 10−3 μW m−1 K−2, and a figure of merit of 1.14 × 10−6. Moreover, the possibility of a slight e− charge transfer or n-doping from the cellulose onto the most external CNF graphitic shells was also analysed by computer modelling. This study presents n-type carbon-based TE textile fabrics produced easily and without any functionalization processes to prevent the inherent doping with oxygen, which causes the typical p-type character found in most carbon-based TE materials.

Prediction of J-R curves and thermoelectric power evolution of cast austenitic stainless steels after very long-term aging (200,000 h) at temperatures below 350 °C

Cast austenitic stainless steels (CASS) are materials used to fabricate many important safety-related components in the primary circuits of light water reactors since the early 1970’s. The primary circuit, which transports heated water by nuclear reaction to steam generators, is subjected to in-service temperatures between 285 °C and 325 °C. Under these conditions, CASS undergo thermal aging which may significantly affect their mechanical properties and more especially their fracture toughness. From a metallurgical point of view, the changes in mechanical properties are attributable to several solid-state phase transformation processes including the spinodal decomposition of the ferritic phase and the precipitation of G phase. The kinetics of these phase transformations depends primarily on the time and temperature of aging, secondly on the chemical composition of the heat (chromium, molybdenum, silicon and nickel contents) and thirdly on the heat treatments performed during component manufacturing. The prediction of the long-term behavior of CASS is an important industrial issue for nuclear power plant operators. In the early 1980’s, Electricité De France (EDF) engaged an unparalleled laboratory aging program that is still in progress. Presently, some materials have been aged for more than 200,000 h at low temperatures. The results of this program allow the development of prediction models for Charpy-impact energies, J−R curves and thermoelectric power values much more precise than those proposed so far, based on aging at 400 °C and rarely exceeding 30,000 h. These prediction models are described in this paper.

Investigation of Thermoelectric Power of CuInGaTe2 Single Crystals

Thermoelectric power values of CuInGaTe2 (CIGT) single crystals were estimated without precedent for a wide temperature range. An authorial unique design dependent on Bridgman procedure for crystal growth from the melt has been utilized to prepare our sample. The single crystals show a p-type conductivity within the full range of temperature. Experimental examination has been made of the variety of electrical conductivity and thermoelectric power with CIGT single crystals. The holes and electrons effective masses, the mobilities of the electrons and holes, and the diffusion length of the majority and minority carriers were determined at room temperature. The electron and hole diffusion coefficients in CIGT single crystals are Dn = 7.938 m2/s and Dp = 7.365 m2/s, respectively. Additionally, the holes and electrons relaxation times were derived from the mobilities. These outcomes give us a complete and clear picture for the main physical parameters essential for the industrial applications.

Magnetocaloric and electrical transport properties of selenospinels A0.9Cu0.1Cr2Se4 (A = Cd and Zn)

Magnetization, electrical resistivity and Seebeck coefficient of ACr2Se4 (A = Cd and Zn) spinels with 10% Cu-substitution at A-site have been studied. While Cd0.9Cu0.1Cr2Se4 orders ferromagnetically at 129 K (TC), Zn0.9Cu0.1Cr2Se4 displays complex antiferromagnetic order at TN = 20 K. Magnetocaloric effect (MCE) in the vicinity of the magnetic transition has been estimated in terms of isothermal magnetic entropy change (ΔSm). The maximum values of ΔSm for Cd0.9Cu0.1Cr2Se4 and Zn0.9Cu0.1Cr2Se4 are about −4.2 J/kg K and −3.4 J/kg K respectively at 133 K and 48 K for a field change from 0 to 70 kOe. Electrical resistivity shows Mott variable range hopping behaviour below 50 K. Large positive thermoelectric power values are observed below 300 K in both Cd0.9Cu0.1Cr2Se4 and Zn0.9Cu0.1Cr2Se4.

Negative thermoelectric power of melt mixed vapor grown carbon nanofiber polypropylene composites

In this work, commercial vapor grown carbon nanofibers (CNF), produced by chemical vapor deposition (CVD), were melt extruded with polypropylene (PP) with the aim of analyzing their thermoelectric properties (i.e., electrical conductivity, thermoelectric power, power factor and figure of merit). Unexpectedly, all PP/CNF composites showed negative thermoelectric power (TEP) values instead of showing the typical positive TEP observed for this type of carbon-based polymer composites. These results can be attributed to the double layer structure surrounding the tubular core of the carbon nanofiber grown by the CVD method at 1100 °C, which may lead the intrinsically negative TEP contribution from the larger inner layer to counteract the positive TEP contribution from the smaller outer layer due to common oxygen doping. Overall, all composites showed negative TEP values around −8.5 μVK−1 and a maximum power factor of 1.75 × 10-3 μW m-1 K−2, corresponding to a figure of merit of 1.2 × 10-6 at room temperature. This study demonstrates that melt mixed polymer composites with large-diameter tubular carbon nanostructures and negative Seebeck coefficients can be directly produced with large-scale processing methods without requiring specific additives and/or deoxygenation treatments.

Beneficial effect of phase transition on kinetics of deintercalation/intercalation process in lithium\u2013manganese spinel

In this work, a detailed characterization of LixMn2O4 spinel oxides is shown to demonstrate the correlation between the anomalous thermoelectric properties of this cathode material and its crystal and electronic structure. The analysis of structural and transport in LixMn2O4 cathode materials obtained by solid-state reaction and sol–gel method allows formulating a conclusion that the performance of manganese spinel-based cathode depends on the occurrence of anomalous electron effects. The recorded maxima in absolute values of thermoelectric power correspond to high diffusivity of electrons at the Fermi level. A correlation between the occurrence of thermoelectric peaks and effectiveness of deintercalation/intercalation of lithium has been shown. The obtained results indicate a beneficial effect of phase transition on electrochemical properties of lithium–manganese spinel cathode material.

Transport properties of transition-metal doped BiS2-based superconductors

We performed the electrical resistivity and thermoelectric power measurements of the polycrystalline La0.8Ti0.2OBi(S1-xSex)2. The electrical resistivity of La0.8Ti0.2OBi(S0.7Se0.3)2 at room temperature dramatically decreases, and the temperature dependence shows metallic-like behavior. From the electrical resistivity, superconductivity was not observed in La0.8Ti0.2OBi(S1-xSex)2 above 2.8 K. The value of thermoelectric power S(300 K) of La0.8Ti0.2OBiSSe was about -65 μV/K, which is comparable to that of the polycrystalline LaOBiS2. The value of S(300 K) of La0.8Ti0.2OBiS2 was about -115 μV/K. These power factors are relatively smaller than that of the polycrystalline LaOBiSSe.

Study of the Precipitation Process in Aging Steel Pipeline Weldments by Thermoelectric Power Means

The microstructural changes due to the aging process in steel pipeline weldments as a function of the thermoelectric power (TEP) were studied. In general, the thermoelectric methods are based on the well-known Seebeck effect. The thermoelectric methods monitor the TEP via an electron flux induced by a temperature gradient in metallic materials, which is affected by the different types of defects that are present in the atomic lattice, such as atoms in the solid solution, precipitates and dislocations. In this present study, the relationship among the TEP data, hardness and the microstructure of steel pipeline weldments was investigated. In addition, the coarse and dendritic grain structure of the welding material is extremely and unpredictably anisotropic. Such microstructures are no longer direction-independent to the electron flux. Therefore, it has an opposite negative effect on the TEP and overlaps the precipitation effect due to the aging process. TEP and hardness measurements were obtained in each zone of the weldments. For each section of the weldment, the weld bead (WB), heat affected zone (HAZ) and base metal (BM) were found to correspond to particular values of TEP. The relationship between the TEP and the microstructure of a weldment of X60 and X65 micro-alloyed steel that was artificially aged was obtained using the conventional contact TEP technique (hot-tip) and scanning electron microscopy (SEM). It was found that thermoelectric power is very sensitive to the aging process in the two-studied steel pipeline weldments.

Influence of High Pressure Torsion on Thermoelastic and Thermoelectric Response of Pure Copper and Aluminum under Pulsed Laser Radiation

This work presents experimental studying the effect of processing by severe plastic deformation (SPD) on the thermoelastic and thermoelectric properties of pure aluminum and copper under pulsed laser radiation. The studies were carried out on technical aluminum AD1 (99.3%) and pure copper M1 (99.9%). High pressure torsion (HPT) was used for processing by SPD. After the HPT processing, the materials samples in the form of a plane disk were subjected to pulsed laser radiation focused on the disk center. Pulsed lasers with a wavelength of 1.06 micron and operating in the free laser oscillation mode with pulse duration of 100 microseconds or in the mode of a single pulse with duration of about 10 nanoseconds were used. The thermoelastic and thermoelectric responses of the materials were determined by measuring acoustic waves and the thermoelectric power. The disks with the initial coarse-grained material state were considered as a reference sample, and the disks of the materials after SPD processing were considered as a controlled object. The results demonstrated a very high sensitivity of the parameters of thermoelastic and thermoelectric response to structural changes in the materials. For example, the used HPT mode led to a reduction in the maximum thermoelectric power value for aluminum by 40% and for copper by 35%.

MAGNETIC AND TRANSPORT PROPERTIES OF STAINLESS STEELS AT LOW TEMPERATURE

Magnetic and transport properties of cold rolled SUS304 stainless steels were investigated via measurements of X-ray diffraction, magnetization, thermoelectric power (TEP), thermal conductivity and electrical resistivity from 300 K down to low temperatures. Saturation magnetizations at 300 K were 1.6, 37.5, 72.6 and 105.6 emu/g for rolled thickness reduction ratios of 0, 33, 50 and 75%, respectively. The thermoelectric power (TEP) values at 300 K were found to be -1.3, -0.4, 1.6 and 2.9 V/K for the reduction ratios of 0, 33, 50 and 75%, respectively. Least-squares fits of the experimental data predicted a saturation magnetization of 141 emu/g and a thermoelectric power of 4.3 V/K for SUS304 in the martensite phase at 300 K.