Wide Range Of Low Temperatures Research Articles

Hierarchical Low-Temperature n-Type Bi2Te3 with High Thermoelectric Performances.

The high performance of a multistage thermoelectric cooler (multi-TEC) used in a wide low-temperature range depends on the optimized thermoelectric (TE) performance of materials during the corresponding working temperature range for each stage. Despite decades of research on the commercial TE materials of Bi2Te3, the main research is still focused on temperatures above 300 K, lacking suitable hierarchical low-temperature n-Bi2Te3 for multistage TEC. In this work, we systematically investigated the influence of doping concentration and matrix material compositions on the TE performance of n-Bi2Te3 below room temperature by the high-energy ball milling and hot deformation. Consequently, two hierarchical n-Bi2Te3 materials with excellent mechanical properties working below 248 and around 298 K, respectively, have been screened out. The Bi2Te2.7Se0.3 + 0.03 wt % TeI4 can be adopted in a low-temperature range that exhibits the high average figure of merit (zTave) of 0.61 within 173-248 K. Meanwhile, the Bi2Te2.7Se0.3 + 0.05 wt % TeI4 sample displays a competitive zTave of 0.85 within 248-298 K, which can be applied above 248 K. The research of hierarchical TE materials provides valuable insights into the high-performance design of multistage TE cooling devices.

Non-linear temperature dependences of pseudoelastic stress and stress hysteresis of a nanocrystalline Ni47Ti50Fe3 alloy

This paper reports a study on non-linear temperature dependences of the critical pseudoelastic stress and stress hysteresis for stress-induced martensitic transformation deformation of a nanocrystallined Ni47Ti50Fe3 alloy. Such non-linear temperature dependences were found over a wide low temperature range from -196 °C to 20 °C and they defy the predictions of the Clausius-Clapeyron law for the transformation. The pseudoelastic behaviour exhibited two unusual characteristics, including a progressively decreasing dσ/dT slope and a rapidly widening stress hysteresis with decreasing the temperature. In-situ X-ray diffraction analysis indicated that the starting microstructure of the alloy for pseudoelastic deformation was a mixture of the B2 and a crystallographically suppressed R phase (denoted R*) within -8 °C to -196 °C. The volume fraction, the rhombohedral lattice distortion and the internal atomic shuffle of the suppressed R phase increased upon cooling. These continued evolutions of the crystal structure of the R* phase and the microstructure of the alloy upon cooling are ascribed to be responsible for the abnormal non-linear temperature dependences of the pseudoelastic stresses and the widening of the stress hysteresis.

Creation of a heterogeneous grain structure is a condition for increasing the low-temperature ductility of nanocrystalline hcp metals

The paper considers the influence of a heterogeneous (bimodal) grain structure on the ductility characteristics of commercial purity titanium in a wide range of low temperatures (4.2–395 K) as a strategy for optimizing mechanical properties within the framework of the “strength–plasticity” ratio. Using titanium as an example, the physical mechanism for increasing the low-temperature ductility of hcp nanocrystalline metals with a heterogeneous grain size distribution is explained by a combination of several processes: an increase in the activity of intragrain dislocation slip, dynamic grain growth under tensile stresses, and activation of nanotwinning in submicron-sized grains.

Essential Features of Gliding Arc Plasma for High-Performance Hydrocarbon Selective Catalytic Reduction of NOxat Low Temperatures

The high removal efficiency of NOx from diesel engine exhaust gas at low temperatures remains challenging due to the poor activity of catalysts under this condition. This work investigated the effectiveness of gliding arc plasma in the NOx removal over the Ag/γ-Al2O3 catalyst with n-heptane as a reducing agent source for NOx reduction. The plasma conjugated with the catalyst was performed like an injection method, i.e., a small part flow (1/26) that consisted of n-heptane was reformed to H2 and oxygenated hydrocarbons (OHCs) by gliding arc plasma before mixing it with the gas containing NOx. Then, the overall gas was passed through the catalyst stage at various temperatures from 127 to 253 °C. The experimental data revealed that NOx removal efficiency significantly increased with plasma treatment. The enhancement by plasma treatment increased with temperature from 127 to 226 °C, but the enhancement reduced at a temperature of 253 °C. The result came from formation of H2 and OHCs in the treated plasma gas, which reactivated NOx removal over the catalyst at low temperatures. Moreover, the enhanced NOx removal efficiency in a wide low-temperature range is obtained due to considerable hydrogen formation by the gliding arc plasma. To sum up, the highest NOx removal efficiency was 68.5% under a temperature of 226 °C and specific energy input of 34.6 J/L, while it was 20.3% for the catalyst alone; in other words, the removal efficiency increased by 48.1% with using plasma under these conditions. Owing to its low energy consumption, high-throughput gas treatment, and effectiveness at low temperatures, the technology is promising in practical applications for refining diesel exhaust gases.

Liquid crystal mixtures with the chiral benzoate dopant

ABSTRACT The results of studies conducted by means complementary methods: differential scanning calorimetry, transmitted light intensity measurements, polarized optical microscopy and electrooptical methods of two new liquid crystal mixtures are presented. The investigated mixtures consist of achiral thiosobenzoates, 7OS5 and 8OS5, and a chiral addition of benzoate, MHOBCO6. In all mixtures there is a wide low temperature range of the existence of the ferroelectric SmC* phase.

Structural and Magnetic Properties of (1-x)Ba5PrTi3V7O30-xBiFeO3

Bismuth Ferrite (BiFeO3) is a single phase Fe- based multiferroic having Perovskite structure. It shows both ferroelectric and ferromagnetism simultaneously in the single material. But the magnetic order is very low due to complex antiferromagnetic order yielding small remnant magnetization. However, Magnetic property could be improved if BiFeO3 mixed with Ba5PrTi3V7O30 having TB-structure. Solid Solution (1-x)Ba5PrTi3V7O30-xBiFeO3 is prepared by using Solid State Reaction technique for different values of x. Pellets are calcined at 750  then sintered at 800 . Basic Crystal qualities and formation of single phase compound is confirmed by the XRD (X-Ray Diffractogram). The crystal structure is more or less constant i.e. Orthorhombic.  However, further increase in x changes the crystal structure. For x= 0.7 the system is Rhombohedral in structure. Grain morphology is being analysed by Scanning Electron Microscope (SEM: JOEL-IT300).Surface morphology shows that average grain size range from around 0.75 µm to 2.10 µm. Average grain size is maximum for x = 0.3 and minimum for x=0 (i.e. pure ferroelectric material). Magnetic measurement is done at a wide low temperature range (10-350K) by Physical Property Measurement System (PPMS: Quantum Design, San Diego, USA) Vibrating Sample Magnetometer (VSM). Hysteresis (M-H) loops are measured at room temperature (300K).It shows that the magnetization changes when the value of x changes. Remanence is maximum for x=0.3 and Coercivity is maximum for x=0.7. The material could be suitable to fabricate non volatile magnetic storage memory device.

Structural and Magnetic Properties of (1-x)Ba5PrTi3V7O30-xBiFeO3

Bismuth Ferrite (BiFeO3) is a single phase Fe- based multiferroic having Perovskite structure. It shows both ferroelectric and ferromagnetism simultaneously in the single material. But the magnetic order is very low due to complex antiferromagnetic order yielding small remnant magnetization. However, Magnetic property could be improved if BiFeO3 mixed with Ba5PrTi3V7O30 having TB-structure. Solid Solution (1-x)Ba5PrTi3V7O30-xBiFeO3 is prepared by using Solid State Reaction technique for different values of x. Pellets are calcined at 750 then sintered at 800 . Basic Crystal qualities and formation of single phase compound is confirmed by the XRD (X-Ray Diffractogram). The crystal structure is more or less constant i.e. Orthorhombic. However, further increase in x changes the crystal structure. For x= 0.7 the system is Rhombohedral in structure. Grain morphology is being analysed by Scanning Electron Microscope (SEM: JOEL-IT300).Surface morphology shows that average grain size range from around 0.75 µm to 2.10 µm. Average grain size is maximum for x = 0.3 and minimum for x=0 (i.e. pure ferroelectric material). Magnetic measurement is done at a wide low temperature range (10-350K) by Physical Property Measurement System (PPMS: Quantum Design, San Diego, USA) Vibrating Sample Magnetometer (VSM). Hysteresis (M-H) loops are measured at room temperature (300K).It shows that the magnetization changes when the value of x changes. Remanence is maximum for x=0.3 and Coercivity is maximum for x=0.7. The material could be suitable to fabricate non volatile magnetic storage memory device.

Design of efficient noble metal single-atom and cluster catalysts toward low-temperature preferential oxidation of CO in H2

The preferential oxidation of CO in H2 is attractive for the removal of trace amounts of CO to meet the requirement of proton-exchange membrane fuel cells (PEMFCs) application. The key is to design highly effective catalysts that work well in a wide range of low temperatures. Here, the recent progress in Au and Pt group metal catalysts for the PROX reaction is summarized, covering those with single-atom and cluster dispersed metal species with remarkable performance. Firstly, the progress of some representative catalysts is overviewed, with an emphasis on the strategies for improving low-temperature activity, selectivity, and stability. Then, special attention is focused on the key parameters affecting performance in the PROX reaction. Moreover, the reaction mechanisms in terms of adsorption and activation of reactants are discussed. Finally, the challenges and opportunities are offered for guiding the design of advanced noble metal catalysts toward the PROX process.

Evaluation of the effect of heat treatment on the structure parameters and cold resistance of metals produced by additive electric arc growth

In this work, we studied the influence of the type and mode of heat treatment on the structure and parameters of cold resistance of 09Mn2Si and 07Cr25Ni13 steels obtained by additive electric arc growth. It is shown that, under optimal printing conditions, a relatively uniform and fine-grained material structure is observed in 09Mn2Si steel, while a dendritic structure is observed in the 07Cr25Ni13 alloy. Heat treatment of the investigated alloys leads to a more uniform distribution of structural components in metals, and in steel 07Cr25Ni13 the dendrites are destroyed, which leads to a decrease in the anisotropy of material properties. Also, heat treatment leads to a significant reduction in internal residual stresses in the material. The results of the study of impact strength in a wide range of low temperatures show that in the initial state after surfacing, the investigated alloys have a significant anisotropy of impact strength (up to 8 and 25% for alloy 09Mn2Si and 07Cr25Ni13, respectively). Heat treatment significantly reduces the anisotropy of the properties of the studied alloys and increases the values ​​of impact strength. So for steel 09Mn2Si after heat treatment, an increase in impact strength by more than 1.5 times is observed over the entire temperature range. The studies carried out made it possible to identify the temperature range of the ductile-brittle transition and the impact strength of 09Mn2Si and 07Cr25Ni13 alloys, which is of great practical importance in the manufacture of parts and structural elements of the Northern version.

Study of the fatigue strength of steel 09G2S obtained by 3D printing based electric arc welding in a wide range of low temperatures

In this work, we consider the issues of obtaining workpieces from cold-resistant steel 09Mn2Si by a promising method of 3D-printing by electric arc surfacing (electric arc additive growing). The task of assessing the mechanical properties of the obtained material and understanding the process of its destruction is urgent. The assessment of the fatigue strength of the obtained material after deposition and after subsequent heat treatment (HT) (normalization) in a wide range of low temperatures is carried out. A fractographic analysis of fatigue fractures of 9Mn2Si steel using scanning electron microscopy was also carried out. Ultimately, this makes it possible to assess the reliability of parts manufactured by 3D-printing arc welding. In the course of the work, the mechanical properties were obtained and the analysis of the curves of low-cycle fatigue of the samples after 3D-printing and after further HT in the temperature range of -60 ... 20 °C was carried out. Metallographic studies have been carried out and structural changes have been established in the process of fatigue loading at different operating time of the sample. A relationship was established between the value of the maximum cycle stress and the operating time corresponding to the onset of the onset of the main crack and the moment of fracture of the sample for steel 9Mn2Si steel. The dependence of the average growth rate of the main crack on the applied stress during fatigue tests is obtained.

A sample holder for simultaneous neutron and dielectric spectroscopy – dielectric tests with glycerol, glycerol-water, water and phosphoric acid

We report on dielectric test measurements of a rectangular flat sample holder which serves as capacitor and which is aimed for simultaneous neutron and dielectric (n-DE) spectroscopy of acidic liquid samples. We describe technical details of the sample holder assembly and the dielectric and neutron equipment as well as the sample preparation procedure of the air sensitive acidic samples. The sample holder was characterised off-line from the neutron spectrometer by dielectric spectroscopy, but using the standard IN16B cryofurnace with a dielectric sample stick with 4-wire connection and a Novocontrol equipment, previously setup by a collaborative effort between ILL and Roskilde University. Temperature-dependent dielectric scans on standard samples (glycerol, glycerol-water, and Milli-Q water) were measured in the frequency range between 0.27 Hz and 1 MHz. Step-like temperature changes allowed to probe the temperature equilibrium conditions and continuous temperature changes were made to mimic typical IN16B backscattering neutron fixed window scans. Both type of scans were carried out in cooling and in heating. The standard samples show that our dielectric setup with flat sample holder is well suited for simultaneous n-DE-experiments. On the other hand, the dielectric scan on phosphoric acid reveals the limitations of our setup in case of high sample conductivities, but also shows that the DC-conductivity can still be accessed in a sufficiently wide low temperature range where the onset of conductivity can be simultaneously probed with the change in proton dynamics as seen by neutron spectroscopy.

Scrutinization of non‒saturation behaviour of reverse current‒voltage characteristics in Ni/SiO2/p-Si/Al diodes

The present work is an endeavour to investigate non‒saturation behaviour of reverse current in Ni/SiO 2 / p -Si/Al over a wide low temperature range of 70–300 K at step of 10 K using well accepted models i.e., Poole-Frenkel emission, Schottky emission and Fowler‒Nordheim tunneling mechanisms. The results of the study revealed that Schottky emission has the dominance over Poole-Frenkel emission in the temperature range of 200–300 K with the trap state activation energy of 0.17 eV. In the remaining temperature range trap assisted tunnelling and involvement of other mechanisms were suggested. Further, the Fowler‒Nordheim tunneling mechanism was found to be effective above reverse bias of 0.5 V over the entire temperature range of 70–300 K. Thus, variation of barrier height with temperature was examined using Fowler‒Nordheim tunneling model and it was found to increase from 0.17 eV to 0.28 eV as temperature varied from 300 to 70 K. The increase in barrier height with decrease in temperature corroborates the decrease in reverse current with temperature. • Reverse current in Ni/SiO 2 /p-Si/Al MIS diodes was analyzed using various models. • Possible current conduction mechanism is predicted for the diode using various employed mechanisms. • Schottky emission process found to be dominating others mechanisms in the temperature range of 200–300 K at low bias range. • Whereas, Fowler-Nordheim tunneling was found to be effective in the bias range between 0.5 and 2.0 V. • The variation of barrier height with temperature was also examined using FNT.

Ductile-to-brittle transition in fracture behaviors of common solder alloys over a temperature range down to −150 °C

Detailed comprehensive comparison of temperature variations of ductility over common solders forms the sound basis of designing reliable solder joints that operate across a wide range of low temperatures, but the cryogenic fracture mechanism needs further investigation. Here, we investigate fracture behaviors of typical solders at different temperatures from −150 to 20 °C. Using standardized Charpy impact tests and fractography, we discover that all Pb-free Sn-based solders (Sn, Sn0.7Cu and SAC305) make abrupt transitions from ductile to brittle with decreasing temperature. Instead, Pb-containing solders (Sn37Pb and Sn36Pb2Ag) gradually change their fracture mode across the broad temperature range; and furthermore, a Pb-based solder (Pb10Sn) undergoes ductile deformation even at −150 °C. Sn exhibits deformation twinning below the DBTT and the cryogenic intergranular fracture is due to the strain incompatibility. Intermetallics in Sn matrix facilitate the transgranular cleavage fracture and the cleavage plane is {211}. Pb-rich phase can block cleavage crack propagation to prevent brittle failure. Estimated toughness together with presented cryogenic fracture mechanisms would be useful to inspire the design of robust joints that survive cryogenic temperatures.

Study of the low cycle fatigue of 12Cr18Ni10Ti steel based on fractal analysis and artificial intelligence approaches

The evolution of the structure and assessment of the age limit of steel 12Cr18Ni10Ti upon fatigue loading is considered using neural network modeling and approaches of fractal analysis of the microstructure. An algorithm for processing images of the microstructures has been developed to improve their quality. An indicator of the fractal dimension of the image is used as a quantitative indicator for assessing the evolution of the microstructure of the surface metal layer. A quantitative assessment of the structures at different stress amplitudes is carried out in a wide range of low temperatures using the fractal dimension index. Correlation of the fractal dimension index with the run of the sample material is shown. The appearance of the main crack was observed in the range of 0.7 - 0.8 from the number of cycles to failure, after which the crack growth rate increased. At a lower temperature, the main crack is formed later, but further loading results in a higher crack growth rate. Formation of the secondary phases in austenitic steel at a lower temperature occurred at earlier stages than that at a temperature of t = +20°C, which led to hardening of the material. An artificial neural network (ANN) has been developed and trained for assessing structural changes in metal proceeding from the fractal dimensionality of the microstructure images at different stages of fatigue loading. The developed neural network made it possible to estimate with a sufficiently high accuracy the number of cycles before damage of the sample and the residual life of the material. Thus, the developed ANN can be used to assess the current state of the material in a wide range of low temperatures.

Thermal Properties of Biological Tissue Gel-Phantoms in a Wide Low-Temperature Range

Thermal Properties of Biological Tissue Gel-Phantoms in a Wide Low-Temperature Range

Experimental Assessment of a Multi-Variable Control Strategy of a Micro-Cogeneration Solar-ORC Plant for Domestic Application

Suitability to off-design operation, applicability to combined thermal and electrical generation in a wide range of low temperatures and pressures and compliance with safety and environmental limitations qualify small-scale Organic Rankine Cycle plants as a viable option for combined heat and power generation in the residential sector. As the plants scale down, the electric and thermal output maximization has to account for issues, spanning from high pump power absorption, compared to the electric output of the plant, to intrinsically low plant permeability induced by the expander, to the intermittent availability of thermal power, affected by the heat demand for domestic hot water (DHW) production. The present paper accounts for a flat-plate solar thermal collector array, bottomed by an ORC unit featuring a sliding vane expander and pump and flat-plate heat exchangers. A high-temperature buffer vessel stores artificially heated water – electric heaters, simulating the solar collector - and feeds either the hot water line for domestic use or the ORC evaporator, depending on the instantaneous demand (i.e., domestic hot water or electric power), the temperature conditions inside the tank and the stored mass availability. A low-temperature receiver acts like the heat sink of the ORC unit and harvests the residual thermal power, downstream the expander: a dedicated control, modelled to properly modulate the mass addition/subtraction to this storage unit allows to restore the operating points of the cycle and to limit the incidence of off-design operation, via real-time adjustment of the cycle operating parameters. Indeed, the possibility of continuous ORC generation depends on (i) the nature of the demand and (ii) the amount of hot water withdrawn from the high-temperature buffer vessel. The time-to-temperature for the mass stored inside the buffer affects the amount of ORC unit activations and eventually the maximum attainable generation of electric energy. The plant energy performance is experimentally assessed, and various characteristic operating points are mapped, based on test runs carried out on a real-scale ORC pilot unit.

Thermal Properties of Human Soft Tissue and Its Equivalents in a Wide Low-Temperature Range

Thermal Properties of Human Soft Tissue and Its Equivalents in a Wide Low-Temperature Range

RESEARCH OF THE RELATIONSHIP OF THE RATE OF ULTRASOUND IN METALS WITH THEIR IMPACT VISCOSITY AND HARDNESS UNDER THE CONDITIONS OF REDUCED TEMPERATURES

The paper presents the results of the study of the relationship between the velocity of propagation of longitudinal waves in a metal with the values ​​of impact toughness and hardness in a wide range of low temperatures. It’s been found that with a decrease of temperature, an increase of hardness, a decrease of impact toughness and an increase of the velocity of propagation of a longitudinal wave in the studied metals are observed, and the velocity of propagation of a longitudinal wave has a close correlation with the characteristics under consideration. An increase of the speed of sound with decreasing temperature, in our opinion, is explained by an increase of the thermal conductivity of metals. Thus, by the values ​​of the speed of sound propagation in metals, it is possible to predict the level of its impact toughness, as well as hardness at low temperatures, and, consequently, the tendency to brittle fracture of structures.

Study of the Features of Damage Accumulation in Steel 12Cr18Ni10Ti at Low Temperatures Using Non-Destructive Testing Methods

The paper considers the features of damage accumulation during fatigue loading of 12Cr18Ni10Ti steel, in particular at low temperatures. The character of changes in the magnetic and acoustic characteristics, as well as the index of the fractal dimension of microstructures during the accumulation of damage to the metal structure, is studied. The correlation of the considered indicators is shown, which indicates the possibility of using indicators such as the acoustic parameter, magnetic characteristics (Hc/Br ratio, as well as the coercive force Hc) and the fractal dimension of the metal microstructure to assess structural damage, such as in laboratory conditions, and during the operation of individual parts and structural elements in a wide range of low temperatures. The use of the considered indicators in the complex will significantly increase the accuracy of forecasting metal damage and its residual life.

Model of fragile destruction of metal constructions at reduced temperatures

The paper presents the results of studies of metals with different types of crystalline structure in a wide range of low temperatures. Based on the data obtained, a model of brittle fracture of metals at low temperatures is proposed. The relationship between the lattice parameter of metals and the temperature of a viscous-brittle transition is established. A quantum-mechanical simulation of the effect of temperature on the lattice parameter has been carried out. It is shown that a decrease in the lattice parameter is observed with decreasing temperature.