Thermal Emf Research Articles

Modern trends in the application of thermoelectric method in non-destructive testing (review)

The article provides an overview of the main directions of using the thermoelectric testing method in various spheres of the national economy. The thermoelectric method is most widely used in industry. There are publications on the application of the thermoelectric method for quality monitoring of turning and friction stir welding. It is shown that the thermoelectric method makes it possible to increase the reliability of testing and, based on testing data, ensure optimal modes of the technological process of metalworking and welding. A number of articles are devoted to the application of the thermoelectric method to plastic deformation testing, the dependence of thermal EMF on the degree of plastic deformation is revealed. Recently, publications have appeared on the application of the thermoelectric method to testing the thermal resistance of the design “housing of a power semiconductor device-thermal interface-cooling radiator”. This design is very widespread in electronic equipment. In addition, there are articles on the use of the thermoelectric method to testing the transient resistance of contacts in the power supply network. It is shown that with an increase in contact resistance, the value of thermal EMF increases proportionally, which can be used to prevent emergencies in the power supply network. The thermoelectric method has also been successfully applied to diagnose the degree of titanium flooding. The dependence of the thermal EMF value on the degree of hydrogenation has been revealed. The use of the thermoelectric method is not limited to the field of industrial production. The thermoelectric method is successfully used in medicine for the undetectable detection of nucleic acid sequences, for the temperature diagnosis of human teeth, as well as for the diagnosis of inflammatory processes in the human body.

Thermal properties of Cu2S binary copper sulfides

Copper chalcogenides have a complex electronic structure due to the interaction of hybridized s- and p-states of chalcogen forming a valence band with 3d states of copper, which greatly complicates the interpretation of temperature dependences of kinetic parameters having a nonmonotonic character. Cu2S copper sulfide is an effective thermoelectric material, so it is interesting to study its kinetic parameters of solid solutions that it forms with alkali metals. The nonstoichiometry of chalcogenides can be easily controlled electrochemically, therefore, the task of selecting the optimal composition according to the cationic sublattice is quite feasible. The paper presents experimental studies of the properties of Cu2S binary copper sulfide. Copper chalcogenides have a complex electronic structure due to the interaction of hybridized s- and p-states of chalcogen forming a valence band with 3d states of copper, which greatly complicates the interpretation of temperature dependences of kinetic parameters having a nonmonotonic character. For the Cu2S sample, rather low values of the electron thermal EMF coefficient of the sample from 0.05 mV/K to 0.25 mV/K were found, which are more typical for metals than for semiconductors. The thermal conductivity of the Cu2S sample is quite low, it rises to 0.3 W/m*K at a phase transition of about 380 K and does not fall below 0.2 W/m*K. Thus, the nonstoichiometry of chalcogenides can be easily controlled electrochemically, therefore, the task of selecting the optimal composition according to the cationic sublattice is quite feasible. In addition, to improve the thermoelectric properties of Cu2S, it can be achieved by alloying alkali metals into a binary copper sulfide matrix.

Investigation of thermoelectric properties of nanocrystalline copper chalcogenides

Modern research efforts are aimed at developing fuel cells characterized by high efficiency, low cost and environmental friendliness, which largely depend on the properties of the corresponding catalyst materials ― the most important components of the fuel cell. Catalysts based on metal chalcogenides, predominantly S based, have activity in accelerating the oxygen reduction reaction comparable to the activity of Pt in H2SO4. The work uses the technique of compacting powder materials and obtained volumetric samples. Nanodisperse powder fractions with an average particle size of (50–100) nm were obtained. The values of the thermo-emf coefficient (about 0.08 mV/K) were obtained for the studied alloy with low defects in the cation sublattice of the Сu2S0.5Te0.5 type. It was found that a decrease in grain size leads to a significant decrease in electronic conductivity for all studied samples. The paper presents the results of a study of the thermoelectric properties of the Cu2S0.5Te0.5 triple alloy. For the studied composition, a decrease in thermal conductivity by (25‒30)% and a slight increase in the thermal emf coefficient compared with large–crystal samples were obtained. Low thermal conductivity was found in the range (0.3–1.1) W m-1 K-1 with a conductivity above 1000 ohms-1cm-1. For the studied sample Cu2S0.5Te0.5 ― thermoelectric efficiency (ZT = 0.25) at 400 °C, which allows us to hope for the possibility of improving the characteristics of samples of this composition to acceptable values for practical thermoelectric devices by selecting the optimal alloying.

Thermal and thermoelectric properties of zinc oxide ceramics alloyed with metals

The paper studies the thermal, electrical and thermoelectric properties of ZnO–MexOy ceramics with 1 ≤ x, y ≤ 3, where Me = Al, Co, Fe, Ni, Ti. The samples were made on the basis of ceramic sintering technology of powder mixtures of two or more oxides in an open atmosphere with variations in temperature and duration of annealing. Structural and phase studies of ceramics indicate that the addition of powders of MexOy alloying agents to ZnO powder with a wurtzite structure after the synthesis process leads to the release of secondary phases such as Znx(Me)yO4 spinels and a 4-fold increase in the porosity of the resulting ceramics. Studies of thermal conductivity at room temperature indicate the predominance of the lattice contribution. The decrease in thermal conductivity during doping is due to an increase in phonon scattering due to the influence of the following factors: (1) the size factor when replacing zinc ions in the ZnO (wurtzite) crystal lattice with metal ions from the added MexOy oxides; (2) the formation of defects – point, grain boundaries (microstructure grinding); (3) increase in porosity (decrease in density); and (4) formation of additional phase particles (such as spinels Znx(Mе)yO4). The effect of these factors in the substitution of zinc ions with metals (Co, Al, Ti, Ni, Fe) leads to an increase in the thermoelectric Q-factor of ZT by 4 orders of magnitude (due to a decrease in electrical resistivity and thermal conductivity with a relatively small decrease in the coefficient of thermal EMF). The reason for the decrease in electrical resistance is the more uniform redistribution of alloying metal ions in the wurtzite lattice, resulting in an increase in the number of donor centers, formed with an increase in the duration of annealing.

Efficiency of nanostructured wear-resistant coatings in high-speed turning of titanium alloys

The paper presents the results of experimental studies of tribological properties of innovative composite nanostructured wear-resistant coatings during high-speed turning of heat-resistant and heat-resistant steels and alloys, as well as temperature and force conditions, contact processes in the cutting zone based on the use of equipment and equipment for control and registration of electrophysical parameters that accompany the process of blade cutting (thermal EMF and electrical conductivity of the "tool-workepiece" contact, temperature and cutting force components, and cutting tool wear resistance).

Investigation of the effect of thermal emf in carbon fibers

The article presents the result of a study of the occurrence of the thermoelectric effect in contact "modified carbon fiber - the original carbon fiber". The description of the method of modification of carbon fiber by pulsed current is given. The supposed physical process of this phenomenon is shown. The possibility of implementing this effect in rocket and space technology is being considered.

Electric Power Sources Based on the Seebeck Effect of Manganese Sulfides with Rare Earth Substitution

The thermoelectric properties of compounds with variable valence Mn1-ХReХS (0 ≤ X ≤ 0.2) in the temperature range of (80 – 1100) K are studied. The maxima on the temperature dependences of the Seebeck coefficient (thermal EMF) for all substitution concentrations and the change of the sign of the Seebeck coefficient from positive to negative with an increase in the substitution concentration in Mn1-XYbXS are determined. A model of impurity donor 4f-states is proposed and a satisfactory agreement with the data on the thermal EMF is obtained.

The temperature dependence of the electrical characteristics of natural pyrite FeS-=SUB=-2-=/SUB=- with the p-type conductivity in the temperature range of 295-635 K

The results of the investigation of samples of natural hole-type pyrite FeS2 are presented. The regularities of variations in their electrical properties with increasing temperature in the mode of uniform heating to 635 K are established. The results obtained are analyzed in terms of the dependence of the charge carriers diffusion intensity on temperature and material characteristics. Keywords: pyrite, non-uniform doping distribution, temperature dependence of conductivity, thermal EMF, diffusion and drift currents.

Development of technology for high-strength thermoelectrics with a diameter of up to 35 mm based on Bi-=SUB=-2-=/SUB=-Te-=SUB=-3-=/SUB=- polycrystals by hot extrusion

Hot extrusion of thermoelectric materials of large diameters is associated with the problem of preserving the deformation texture in them both in length and in cross-section. The paper shows for the first time the technology of obtaining polycrystals based on Bi2Te3 n- and p-type conductivity with a diameter of up to 35 mm, by hot extrusion. Detailed studies of the structural properties have been carried out. The mechanical properties (strength) of the crystals were measured. The thermoelectric properties of polycrystals of various diameters (the coefficient of thermal EMF α, electrical conductivity sigma and figure of merit Z by the Harman method) were measured. It is shown at the optimal technology polycrystals based on Bi2Te3 n- and p-type conductivity with a diameter of 35 mm were produced, which are comparable in thermoelectric and mechanical properties with polycrystals of traditional diameter (25 and 30 mm), which are currently commercially produced. Keywords: thermoelectricity, Bi2Te3, extrusion, thermoelectric properties, mechanical properties.

Положения экстремумов зонного спектра носителей заряда в тонких пленках висмута

Many studies report an increase in charge carrier concentration in thin bismuth films as their thickness decreases at low temperatures. These results are obtained on the basis of data on resistivity, magnetoresistance, Hall coefficient, and thermal EMF measured in these films. The calculation is most often carried out within the framework of the two-band approximation assuming the quadraticity of the dispersion law of electrons and holes. Using these approximations, it is possible to estimate the change in the position of energy extremes relative to the chemical potential in these films based on concentration values of charge carriers. This article presents all these calculations and analyses the extrema movement of the charge carrier band spectrum in bismuth films with a change in their thickness.

Allowed Spatial Transitions and Cancellation of the Richardson-Langmuir Ban

The ancient emission formulas of Langmuir and Richardson entered the calculations of subtle effects in semiconductor devices as basic ones. But, in the physics of semiconductor devices, these models have long played a purely decorative role, since they can describe in the most rough approximation only individual sections of the I – V characteristic. But it is precisely the fact that these formulas are basic when describing the barrier current-voltage characteristics (CVC) and prevented the consideration and use of thermoelectric effects in materials on a nano-scale. Thus, as these basic emission models actually imposed a ban on the MEASURABILITY of local thermoelectric effects, the existence of which has already been proven both phenomenologically and experimentally. The quantum transition technique is based on classical models. But it can also be used to correct these classic formulas. The calculation of the spatial transition of electrons over the potential barrier, taking into account the polarity of the kinetic energy, gives currents that are significantly higher than the currents of Langmuir and Richardson, including in the initial section of the I – V characteristic. Moreover, ballistic currents are concentrated at energy levels close to the threshold. This effect of condensation of electrons flowing down the barrier transforms the "anomalous" Seebeck coefficients into normal EASURABLE Local Thermal EMF, including in p-n junctions.

Features of temperature measurement of short thermal pulses

Short thermal impulses are typical for the explosions, glowing combustion products, which are accompanied by high pressure and destructive force. The most suitable thermocouples for measuring temperature values of a high-speed thermal process are thermocouples with known dynamic characteristics, which record the value of the output EMF during the temperature change transient process. Hourly dependence of the input temperature is calculated by converting from the operator to hourly form or from the hourly dependence through the inverted convolution of the output signal with the pulse transient characteristic by numerical methods.
 Restoration of the values of temperature acting on them is done by EMF measured values processing using the well-known dynamic characteristics of thermocouples, which are suggested to be pre-determined in the form of magnitude and phase frequency response, by heating the thermocouple with a sinusoidal electric current of the appropriate frequency. To be able to implement the method of determining the characteristics of thermocouple dynamics, a model of the processes that occur in the thermocouple when electric current is passing through it is presented. The use of sinusoidal electric current to heat up the thermocouple leads to the appearance of a DC component and a component with second harmonic in the output of EMF. On the basis of the proposed model, the algorithm of obtaining the magnitude and phase frequency response of the thermocouple by means of determining the ratio of the amplitudes of the EMF variable of the thermocouple in the form of a composition at the double frequency of the input current to the amplitude of the second harmonic of the input current, obtained by means of elevation to the square of output EMF instantaneous values by the calculating method, is developed.
 The methodology was developed, a research system was created, and experimental samples of the fast thermocouples were made. The obtained dynamic characteristics allow, by applying the inverse function, to adequately measure the current temperature of thermal impulses using the data of the output thermal EMF of thermocouples.
 
 Keywords: measurement; temperature; thermal pulse; thermocouple; dynamic characteristics; Nyquist plot.

ADAPTATION OF THE METHOD OF CONTROLLING CUTTING MODES TO INDUSTRIAL CONDITIONS

Variants of devices with the possibility of using the test pass method in industrial conditions for automatic determination of cutting modes by measuring the mutual properties of the tool - material contact pair through the value of the thermal EMF that occurs during machining are considered.

Температурные зависимости коэффициента термоэдс, удельного сопротивления и теплопроводности электронного и дырочного пирита FeS-=SUB=-2-=/SUB=- в интервале 293-400 K

Abstract The temperature dependences of the thermal EMF, the specific electrical conductivity, and the specific thermal conductivity of samples of natural pyrite FeS2, with electronic and hole-type conductivity, are studied in the temperature range of 293−400 K. The data obtained are in good agreement with the results of previous studies of the electrical properties of this mineral, established in the course of geophysical studies. Based on the results of the performed measurements, as well as taking into account the known data on the temperature behavior of the thermo-EMF and the specific electrical conductivity of pyrite in the range of 300−700 K, estimates of its thermoelectric efficiency are mad

Investigation of the Chemical Interaction in the Sb2Te3–InSe System and the Properties of the Obtained Phases

The interaction in the Sb2Te3–InSe system was studied and the T–x phase diagram was constructed by integrated methods of physicochemical analysis (differential thermal, X-ray powder diffraction, and microstructural analyses) and also by microhardness and density measurements. It was found that the Sb2Se3–InSe system is a quasi-binary section of the ternary reciprocal system Sb,In||Se,Te. In the Sb2Te3–InSe system, compounds InSb2SeTe3 and In3Sb2Se3Te3 form, which incongruently melt at 525 and 600°C, respectively. It was found that the regions of solid solutions based on Sb2Te3 and InSe extend to 3 and 2 mol %, respectively. The compounds Sb2Se3 and InSe form a eutectic with the coordinates 20 mol % InSe and 510°C. The temperature dependences of the electrical conductivity and thermal emf of the solid solutions (Sb2Te3)1 – x(InSe)x (x = 0.01, 0.02, and 0.03).

Differential Thermal EMF of Carbon Zigzag-Type Nanotubes in an External Electric Field

The thermoelectric characteristics of carbon nanotubes are studied theoretically. The behavior of the differential thermal EMF of single-layer carbon zigzag-type nanotubes is studied in an external longitudinal dc electric field. The dynamics of the electron subsystem of the nanotubes is described using the Boltzman kinetic equation in terms of the quasi-classical approximation of relaxation times. The analytic relationship has been obtained for the differential thermoelectric coefficient and its nonlinear dependence on the field strength has been revealed.

Effect of Pulsed Photon Treatment on Electrophysical and Thermophysical Properties of n-Type Solid Solution Based on Bi2Te3–Bi2Se3: I. Electrophysical Properties

The effect of the pulsed photon treatment exerted on the electrical conductivity, the thermal EMF, and the power factor of n-type solid solution Bi2Te3–Bi2Se3 has been studied. The samples have been obtained by means of powder metallurgy in two stages consisting in the synthesis and hot pressing in an argon atmosphere. It has been found that the pulsed photon treatment in an argon atmosphere of samples synthesized by means of powder metallurgy leads to the surface layer recrystallization and to the changes in the phase composition owing to selenium sublimation. As a result of this, the concentration of free charge carriers in the material decreases, the thermal EMF exhibits an increase, and the electrical conductivity decreases. Depending on the pulse intensity, the mobility of free charge carriers can either decrease or increase. This makes it possible to choose a mode of pulsed photonic processing wherein the relative increase in the thermal EMF exceeds the decrease in the electrical conductivity of the material, as a result of which the power factor of the material exhibits a 2.6% increase.

Hydrogen as an Alkaline Metal. Electron Transport Phenomena

The pairwise effective interionic interaction, the electrical conductivity and thermal EMF coefficients, and the temperature coefficient of resistivity of liquid metallic hydrogen have been calculated in a wide range of densities and temperatures. This range includes both the values achieved in the experiment and those that exist in the central regions of the giant planets. The perturbation theory in the electron–proton interaction potential is used for this. The electrical resistivity is calculated up to the third-order terms of the perturbation theory. Their role proved to be significant. For the ionic subsystem, a hard-sphere model was used. The packing density is considered one of the adjustable parameters of the theory. It is obtained as a function of density and temperature from the analysis of the effective proton–proton interaction. Its adjustment was carried out at the point of transition of hydrogen to the metallic state. Due to the lack of relevant data for metallic hydrogen, the packing density was taken in the same way as for other alkali metals: lithium, sodium, and potassium at their melting point, obtained from neutron scattering experiments.

The influence of organic binders and their decomposition products on the microstructure and thermoelectric properties of conductive materials based on si3n4 with transitional metal carbides additives

The object of research is the formation of the functional zone of a multicomponent ceramic composite based on refractory anoxic compounds. One of the most problematic points is the determination of influence of the type of binder on the formation of the functional zone of the device.During the study, the industrial powders of silicon nitride β – Si3N4 of the Baku Powder Metallurgy Plant (Azerbaijan) and hafnium and zirconium carbides of the Donetsk Chemical Reagents Plant (Ukraine) were used. The homogenization and grinding of the charge was carried out in a planetary mill of the Fritsch type (drum and Si3N4 balls) for 40 min. in ethyl alcohol. The concentration of the inclusion phase conductor in the composite thermoelectrodes was 5–40 %. The carboxymethyl cellulose compound in combination with a plasticizer, glycerol or rubber, was used as a binder for this method. Samples were made in the form of plates 100×7×6 mm. The investigated samples of nitro silicon composite materials were obtained by hot pressing of the prepared ceramic tapes using the induction method of heating the mold.It has been found that in case of the rubber-containing samples with a resistive HfC additive, the weight loss increases in proportion to the HfC concentration up to the additive concentration of 27 %, while the further HfC concentration increase causes the decline of weight loss. When using cellulose gum as a binder, the weight loss decreases by about 1.3–1.6 times; the regularities of weight loss changes depending on the HfC concentration remain the same. It has been shown that the modulus of thermal electromotive force was higher in case of fine composites than in case of coarse ones for all concentrations. The maximum thermal emf value reached 120 μV/deg in the subthreshold zone of the additive concentration. In the suprathreshold zone the maximum thermal emf value reached 60 μV/deg for the fine-grained composite and 30 μV/deg for the coarse-grained one. It has been proved that composites without a binder differ not by the typical course of dependency between the additive concentration and the resistivity, while the thermal emf of these composites equals zero with accuracy up to experimental error.

Effect of Anisotropy of Elastic Energy on the Electron–Phonon Drag and Temperature Dependences of Thermal EMF in Potassium Crystals at Low Temperatures

The effect of anisotropy of elastic energy on electron–phonon drag and thermoelectric phenomena in potassium crystals is studied. The temperature dependences of the thermal conductivity, thermal emf, and contributions to them from phonons of different polarizations are calculated. The calculation results are matched to the experimental data by varying the electron–phonon interaction constant for quasi-transverse phonons. It is established that the contribution of slow quasi-transverse phonons to the drag thermal emf of bulk potassium crystals is by an order of magnitude greater than the contribution of quasi-longitudinal phonons. The maximum values of the drag thermal emf in perfect potassium crystals are determined. It is shown that they do not depend on the electron–phonon interaction constants, but are determined by the second-order elastic moduli and the electron density.