Wide Temperature Span Research Articles

Successive magnetic transitions with large refrigerant capacity in arc-melted Mn[formula omitted]Fe[formula omitted]Sn2 ([formula omitted] = 0.3, 0.7) alloys

This work investigates the magneto-caloric effect and critical behavior in Mn3−xFexSn2 (x = 0.3, 0.7) alloys synthesized by arc melting method. The alloys show two successive second order magnetic phase transitions at TC1≈ 254 K (261 K) and TC2≈ 205 K (185 K), respectively for x = 0.3 (0.7). The modified Arrot plot study around paramagnetic–ferromagnetic transition at TC1 reveals the critical exponent, β = 0.397 (0.378) with long-range of magnetic interactions for x = 0.3 (0.7). Importantly, the magneto-caloric study for x = 0.3 (0.7) gives large refrigerant capacity (RC) of 330 (250) J/kg at 5 T applied magnetic field. The large RC value and two successive magnetic transitions makes these earth abundant-based Mn3−xFexSn2 alloys highly promising for magnetic refrigeration in a wide temperature span.

Reduction of thermal hysteresis and improvement of magnetocaloric properties in ball milled Mn0.98CoGe

The Mn0.98CoGe compound can be as alternative refrigerants due to its low cost and large magentocaloric effect near room temperature. However, the narrow work temperature range and the large thermal hysteresis restrict its application. In this work, we investigate the influence of ball milling (BM) time on the thermal hysteresis and magnetocaloric properties of Mn0.98CoGe compound. Results show that the thermal hysteresis of Mn0.98CoGe reduced markedly after BM 5 h, and disappeared completely after BM 12 h. Furthermore, the magnetic entropy change (ΔSM) over a wider temperature span are observed, which leads to the relative cooling power (RCP) of BM-12 h sample as high as those typical refrigerants.

Achieving excellent superelasticity and extraordinary elastocaloric effect in a directionally solidified Co-V-Ga alloy

We demonstrate excellent superelasticity and giant elastocaloric effect in a directionally solidified Co50.7V33.3Ga16 alloy. Owing to the formation of [001]A preferentially oriented columnar grains, the as-grown alloy displays nearly perfect superelastic behaviors with fully reversible compressive strain of up to 5.4%, narrow stress hysteresis of about 40 MPa and a wide operating temperature window from 258 to 373 K. Simultaneously, a giant adiabatic temperature change ΔTad of -18.7 K is obtained on removing a uniaxial stress of 400 MPa at room temperature, which is in good agreement with the theoretical values based on Maxwell relation (-19.0 K) and calorimetric measurements (-19.9 K). A large |ΔTad| of greater than 12.5 K is obtained over a wide temperature span of at least 115 K. Moreover, both superelasticity and elastocaloric effect remain good functional stability without any evident degradation for 100 cycles.

Electrocaloric Effect in Sn‐ and Y‐Codoped BaTiO3 Ceramics

BaSnxTi1–xO3 + 0.5 mol% Y ceramics (x = 0.06, 0.08, 0.11, and 0.13) are synthesized using citrate combustion technique and the electrocaloric effect (ECE) is investigated. Dense microstructures with fine grain are observed as increasing Sn contents. The dielectric results reveal that TO–T (tetragonal‐to‐orthorhombic phase) shifts toward higher temperature, whereas TC (cubic‐to‐tetragonal phase) shifts toward lower temperature as increasing Sn, and TO–T merges with TC at x = 0.11. An improving EC temperature change accompanying with large electrocaloric efficiency (ΔT/ΔE) of 0.28 × 10−6 K mV−1 over a wide temperature span is obtained at x = 0.11 under electric field of 50 kV cm−1. The enhanced ECE is mainly attributed to the multiphase coexistence. The dielectric properties and the grain boundary resistance are enhanced by optimizing Sn doping contents.

The multiple magnetic transitions and magnetic entropy change of RGa compounds

<p indent=0mm>Magnetic refrigerant materials working at middle and low temperature range have drawn much attention because they can be used for gas liquefaction such as oxygen, nitrogen, hydrogen and helium. It is continuous goal for researchers to explore and obtain magnetic refrigerant materials with large magnetic entropy change, wide refrigerant temperature span, high refrigeration capacity and large adiabatic temperature change. RGa family is a kind of rare earth based intermetallic compounds with abundant magnetic transitions. This paper reviews the results of low-temperature order-order magnetic transition, high-temperature order-disorder magnetic transition and magnetic entropy change for PrGa, NdGa, SmGa, GdGa, TbGa, DyGa, HoGa, ErGa, TmGa and Er₁₋_{<italic>x</italic>}Gd_{<italic>x</italic>}Ga compounds. The low-temperature order-order magnetic transition includes spin reorientation transition, ferromagnetic to modulated antiferromagnetic transition and cone-ferromagnetic to cone-ferromagnetic transition. There are several peaks on the magnetic entropy change curves which provide ideas for designing magnetic refrigerant materials with large temperature span. The characteristics of magnetic transitions and magnetic entropy change for RGa compounds are analyzed, the dependency relationship together with related physical mechanism are expounded and the possible research interests in the future are discussed.

Reversible colossal barocaloric effects near room temperature in 1-X-adamantane (X=Cl, Br) plastic crystals

Plastic crystals undergo phase transitions with unusually large volume and entropy changes related to strong molecular orientational disordering. These features have led to a resurgent interest in these materials because recently they have shown great potential in solid-state cooling applications driven by pressure. Here we demonstrate that two plastic crystals derived from adamantane -1-Br-adamantane and 1-Cl-adamantane- undergo colossal reversible barocaloric effects under moderate pressure changes in a wide temperature span near room temperature thanks to a relatively small hysteresis and very high sensitivity of the transition temperature to pressure. In particular, 1-Cl-adamantane displays an optimal operational temperature range covering from ~40 K below and up to room temperature, and under a pressure change of 1 kbar this compound outperforms any other barocaloric material known so far. Our work gives strong support to plastic crystals as best candidates for barocaloric cooling. We also provide insight into the physical origin of the entropy changes through the analysis of the disorder on the involved phases.

Assessment of the Overall Efficiency in WPT Stations for Electric Vehicles

The on-site assessment of the efficiency of a charging station is not a trivial process and is a topic of discussion for professionals. The efficiency of electric Vehicle Supply Equipment (EVSE), is an important parameter for both the user and the EVSE operator. This paper deals with a particular type of EVSE, using static wireless power transfer (WPT). This paper proposes a clear method to account for the parameters which can affect the correct determination of efficiency, such as in particular the accuracy of the meters and the effect of temperature. This work proposes a method to define the accuracy of the power and efficiency on-site assessment, and is aimed at clarifying that despite distorted waveforms at the charging stations, it is possible to reach a good accuracy in a wide temperature span (expanded uncertainty &lt;0.5% between 5 °C and 40 °C). Analysis initiated from the measurement conditions and the actual waveforms recorded at two WPT EVSEs with differently rated power. This paper paves the way for the possibility of verifying class 0.5 m on-site, desirable for this type of application. The paper also clarifies that despite the evident presence of voltage and current ripple at the batteries, the weight of the ripple power on the total power is nevertheless lower than 0.1%. Finally, the paper highlights how, for the correct measurement of the ripple, it would be advisable to calibrate the instrumentation in DC and in AC, at a frequency double that of the working frequency of the EVSE coils.

In-plane low thermal expansion of NiTi via controlled cross rolling

Shape memory alloy (SMA) sheets processed via unidirectional rolling (UniR) exhibit macroscopic low thermal expansion (TE) over a wide temperature span but only along a certain direction. Here, we use controlled cross rolling (CroR) to achieve in-plane low coefficients of TE (CTEs) of polycrystalline NiTi sheets. It is shown that the in-plane CTEs of a CroRed NiTi sheet with the three-step rolling path (RD-15%, TD-10% and RD-5%) can be reduced close to zero within a very narrow range (-2.7 × 10−6 K−1 to +3.0 × 10−6 K−1) over a large temperature span of 223 K. The obtained in-plane CTEs are an order of magnitude smaller than those of UniRed NiTi sheets and are comparable to that of commercial FeNi Invar alloy (+2.0 × 10−6 K−1). The physical origin of such in-plane low TE is explored through in situ neutron diffraction from 2.3 K to 300 K and a rule-of-mixture theoretical model. It is found that in the CroRed nanostructured NiTi, the in-plane positive TEs of textured B2 and B19’ aggregates are compensated by the in-plane negative TE caused by the continuous formation (vanishing) of {102}〈UVW〉 fiber-textured B19’ variants in cooling (heating), thereby leading to the overall in-plane low TE. Such compensation mechanism in CroR can also be used to achieve in-plane low TE of other SMAs.

It’s not about the mass

Electrocaloric cooling devices traditionally comprise sub-millimetre-thick ceramic working bodies surrounded by relatively massive apparatus. Now, cooling devices that are each based on a thin polymer layer have been stacked to yield a composite lightweight device that pumps heat across a wide temperature span.

Improved work hardening of a medium carbon-TRIP steel by partial decomposition of retained austenite

In this study, the microstructure and mechanical properties of the 0.56 wt % C transformation-induced plasticity (TRIP) steel are investigated by conducting tensile tests at a wide span of deformation temperatures (25–400 °C) and strain rates (0.001–1 s−1). The target is to explore the stability of retained austenite (RA) at various temperatures and strain rates, and the influence of the RA stability on the TRIP effect. Tensile strength decreases with the increasing deformation temperature at a constant strain rate. When temperature changes from 200 °C to 300 °C, tensile strength increases from 1154 ± 10 MPa to 1227 ± 10 MPa. Interestingly, at 300 °C the total elongation at a strain rate of 0.01s−1 can reach 90%, which is twice than that at 25 °C. Moreover, the deformation induced precipitation of carbides reduces the stability of RA, promoting the martensitic transformation. This process counteracts the suppressed TRIP effect with the increase of temperatures. The newly formed precipitates effectively increase work hardening. Thus the TRIP effect and precipitation strengthening jointly lead to excellent mechanical properties of the steel at 300 °C. After deformation, the volume fraction of RA increases with the increasing strain rate at constant temperatures, suggesting that the increasing strain rate suppresses the transformation from RA to martensite.

Enhanced electrocaloric effect in compositional driven potassium sodium niobate-based relaxor ferroelectrics

Abstract

Magnetocaloric properties and unconventional critical behavior in (Gd,Tb)6(Fe,Mn)Bi2 intermetallics

The magnetic and magnetocaloric properties of the intermetallic family (Gd,Tb)6(Fe,Mn)Bi2 have been studied from 2 K to temperatures above the respective Curie temperatures TC. The substitution of Gd by Tb (Gd6FeBi2, Gd3Tb3FeBi2, Tb6FeBi2) tunes TC in the range 350-250 K and favors the apparition of a metamagnetic transition at very low temperature (below 10 K) from a complex magnetic state to a ferromagnetic one, as well as a spin reorientation transition below Tm = 72 K. As a consequence, an important inverse magnetocaloric effect (IMCE) appears below 20 K and an interesting direct magnetocaloric effect (DMCE) appears over a wide temperature span between TC and Tm with maxima at those temperatures. The partial substitution of Fe by Mn in Tb6Fe0.5Mn0.5Bi2 shifts these effects upwards in temperature while expanding the region of the direct magnetocaloric effect between 70 and 400 K. The combination of adjoint IMCE and DMCE as well as the wide span of the latter shows that tuning this family allows to locate the magnetocaloric effect in different regions of interest. The critical behavior of the PM-FM transitions has been studied obtaining the critical exponents α, β, γ, δ and checking that the respective magnetocaloric effects also scale with the critical parameters n and δ. The transition in Gd6FeBi2 belongs to the Heisenberg universality class with deviations due to magnetocrystalline anisotropies; the critical exponents for Gd3Tb3FeBi2 (in agreement with the Mean Field model) suggest the presence of long range order magnetic interactions, while Tb6FeBi2 and Tb6Fe0.5Mn0.5Bi2 present an unconventional critical behavior aligned with long range order interactions.

The realization of insulator-metal transition in a p-type metastable ZnSb by dual-phase nanostructure

Insulator-metal transition (IMT) in a metastable phase of ZnSb-based films has been explored systematically. It is found that the reduction of thickness contributes to the precipitation of metastable structure and induces a wide controllable temperature span for the presence of metastable ZnSb phase, resulting in thickness dependent IMT of p-type ZnSb film during annealing process. The metastable structure can be obtained without any void generation after erbium-filling by the formation of crystalline/crystalline dual-phase nanostructure, which can improve the electrical transport and trigger IMT behavior with the temperature of 430 °C, providing a strategy for realizing multi-level data storage.

Regulation of phase transition and magnetocaloric effect by ferroelectric domains in FeRh/PMN-PT heterojunctions

The narrow temperature span, ΔTspan, of first-order magnetocaloric materials is a serious problem that limits the application as refrigerants. Here we report tunable phase transition and magnetocaloric effect controlled by ferroelectric (FE) domains in FeRh films grown on (001)- and (011)-cut PMN-PT substrates. Adjacent two-step phase transition, and hence significantly broadened ΔTspan, has been achieved in FeRh films by utilizing the multi-domain structure of PMN-PT substrates. The results of aberration corrected (ac)-STEM, EELS and EDX analysis revealed that a 3~4 nm buffer layer with AB2O4-type spinel structure is naturally formed at the interface, which largely reduces the lattice mismatch between FeRh and PMN-PT and plays a key role for the successful growth of epitaxial (oriented) FeRh film on either (001)- or (011)-oriented PMN-PT. The switched FE domains by electric field govern the phase transition of FeRh films. As a result, regulated entropy change and refrigeration capacity in a wide temperature span have been achieved. On this basis, a feasible magnetic refrigeration cycle facilitated by electric field is designed. The present study provides an experimental basis for expanding the refrigeration temperature span by ferroelectric domain engineering, which is significant for promoting refrigeration application of first-order magnetocaloric materials particularly in micro-devices.

In-situ DRIFTs study on different exposed facets of VOx-MnOx/CeO2 catalysts for low-temperature NH3-SCR

In order to achieve the low-temperature (200–250°C) NH3-SCR, highly dispersed VOx-MnOx/CeO2 catalysts with different exposed facets were produced. The NH3-SCR performance results indicate that the NO conversion over VOx-MnOx/CeO2-R with preferentially exposed {110} facets can achieve NO conversion >95% over a wide temperature span of 220–330°C. From the in-situ DRIFTs, gaseous NH3 and NO are favorable to be absorbed on the surface of the VOx-MnOx/CeO2-R catalyst with preferentially exposed {110} facets, which improves the efficiency of NO conversion. The mechanism study via in-situ DRIFTs demonstrates that the well dispersed vanadium species on CeO2{110} absorb NH3 to generate NH3(L) and NH+ 4(B) species, which in turn become highly reactive toward bridging nitrate and bidentate nitrate species to form N2 and H2O according to the Langmuir-Hinshelwood mechanism.

Effect of Dy substitution in the giant magnetocaloric properties of HoB2

ABSTRACT Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB2. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho1-x Dy x B2 alloys (x = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature (T C) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |ΔS M| and adiabatic temperature change ΔT ad showed a gradual decrease. On the other hand, due to the presence of successive transitions in these alloys, the peak height of the above magnetocaloric properties tends to be kept in a wide temperature range, leading to a relatively robust figure of merit in a wide temperature span. These alloys could be interesting candidates for magnetic refrigeration in the temperature range of 10–60 K.

Reversible barocaloric effects over a large temperature span in fullerite C60

Giant reversible barocaloric effects at low pressures in a wide temperature span near room temperature in C60 for solid-state cooling.

Increasing working temperature span in Ni-Mn-Sn-Co alloys via introducing pores

Enhanced magnetic refrigeration performance via introducing pores in a ferromagnetic shape memory Ni-Mn-Sn-Co alloy was demonstrated. The Ni40.7Mn42.9Sn10.4Co6.0 foam, with a porosity of 56% created by replication casting technique, exhibited reduced thermal hysteresis because of the high specific surface area. A maximum magnetic entropy change (ΔSM) 4.7 J/kg·K with a very wide working temperature span (ΔTFWHM) 40 K under 5.0 T were found in the annealed foam. Furthermore, the foam showed a small hysteresis loss (AHL) 17.4 J/kg under 5.0 T. As a result, refrigeration capacity (RC) 155 J/kg and relative cooling power (RCP) 188 J/kg were produced.

Magnetocaloric properties, magnetic interactions and critical behavior in Ho6(Fe,Mn)Bi2 intermetallics

Four polycrystaline Fe2P-type Ho6(Fe,Mn)Bi2 intermetallic compounds (space group P6‾2m, No. 189, hP9) have been studied using magnetic techniques in order to explore their ability as magnetocaloric materials, and study the critical behavior of the paramagnetic (PM) to ferromagnetic (FM) transitions to obtain a deeper understanding of the range of the magnetic interactions. The obtained critical exponents β, γ and δ for the four compounds studied (Ho6MnBi2, Ho6FeBi2, Ho6(Mn0.5Fe0.5)Bi2, Ho6(Mn0.75Fe0.25)Bi2) point to long-range order interactions, as they are close to those of the Mean Field Universality class. All of the compounds show relevant magnetocaloric properties over a very broad temperature range, limited by the PM-FM transition and a spin-reorientation one, well separated in all cases. They present very high values of the refrigerant capacities (from 520 J/kg to 709 J/kg at 5 T), good magnetic entropy changes (from 3.4 to 5.7 J/(kgK) at 5 T), and a flat and wide temperature span for the working temperature range (nearly 200 K for Ho6MnBi2, 80 K for Ho6FeBi2 at 5T). The change in properties with composition proves that the magnetocaloric properties can be tuned in Fe2P-type compounds to accommodate different refrigeration applications. Finally, the magnetocaloric scaling laws have been successfully tested and universal curves for the magnetic entropy change have also been obtained in the PM-FM transition region.

ПРОВЕРКА ИЗНОСОСТОЙКИХ И ПРИРАБАТЫВАЕМЫХ ПОКРЫТИЙ

It is provided results of works on creation and operational development (improvement) of the unit on the incision, for check of various systems of coverings (wearproof, abradable, etc.), compressor or turbine. It is stated the problems concerning the creation of unit and criteria which must be considered in improvement and unit modernization. Some calculations were made for definition the unit’s operating modes, which should provide the possibility to model to (simulate) the operation of turbine and compressor covering, on various types of engines both modern and future. The unit should provide a wide temperature span and speeds of incision etc., the design of unit details should be technological and provide the possibility to put on the shovel and prorate simulator various systems of coverings. The offered coverings test method will allow to reduce expenses on the check of again developed coverings, and also to reduce terms on the check of again developed coverings. The technical project demands have not been provided during the initial tests of the unit (after designing and manufacturing). For the purpose of maintenance of the technical project, demands took on the tasks of the unit’s modernization. In our opinion, it was necessary to reduce weight and resistance to air medium of the blade to satisfy the requirements. It was able to reduce weight by means of «dovetail», instead of a bolt joint, and also application of turbine airfoil similar in shape to a real blade. According to the results of the spent analysis was accepted the solution to apply the blades of the compressor of real engines, made of various materials EP 718 ID and VT 8 as simulators of blades, for check of turbine coverings, the simulator heat sink nickel alloys will be designed. The improvement works of the available disk simulator were carried out for applying the new simulators of blades. For this purpose, the technology for producing dovetail-type locks was completed by milling. It was completed the improvement of the disk simulator by milling of dovetail-type grooves.