Small Thermal Hysteresis Research Articles

Effect of Fe Composition and Heat Treatment Temperature on the Transformation Temperature of R-Phase of Ti-Ni-Fe Alloy

R-phase transformations in TiNi shape memory alloys (Nitinol) have various applications because of their small thermal hysteresis and low fatigue resistance. Adding a third element such as Fe or Al is one of the useful ways to induce R-phase transformation. Controlling the R-phase transformation temperature is crucial for industrial and bio-field applications. However, the effects of adding Fe have rarely been reported. In this study, the effects of Fe addition and heat treatment temperature on the R-phase transformation temperature of TiNiFe shape memory alloys were systematically investigated. Results showed that increasing Fe composition decreases the R-phase and martensitic transformation temperatures of 19K/1at%Fe and 51 K/1at%Fe, respectively. Additionally, in the Ti–49Ni–1Fe alloy, rather than a martensite transformation, the R phase transformation temperature was constant irrespective of heat treatment temperature and increasing number of thermal cycles. This means that the R-phase transformation temperature is not affected by dislocation density resulting from the heat cycling or cold working processes. This allows practical applications of R-phase transformation to be easily realized. Furthermore, this means that the R-phase transformation temperature is only affected by the Ni content of the matrix.

Effect of temperature and magnetic field induced hysteresis on reversibility of magnetocaloric effect and its minimization by optimizing the geometrical compatibility condition in Mn–Ni–Fe–Si alloy

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (|ΔSMmax|) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (RCeffe) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases.

The effect of Hf on the microstructure, transformation temperature, and the shape memory properties of Zr–Cu-based high-entropy shape memory alloys

The microstructures, phase transformation temperatures, and shape memory properties of Hf-modified Zr50−xHfxCu25Ni7.5Co17.5 and Zr50−xHfxCu25Ni10Co15 high-entropy shape memory alloys (SMAs) were investigated. Hf additions can alter the valence electron concentration, strengthen the alloy matrix, and introduce more secondary phase particles, which significantly influence the properties of the alloys. The results reveal that high austenitic transformation temperature (over 600 K) with very small thermal hysteresis (70–80 K) can be achieved by tailoring the Hf contents, and the best shape memory recovery strain (up to 2.44%) compared with other Zr–Cu-based SMAs could be obtained in Zr42Hf8Cu25Ni10Co15 alloy. This study demonstrated that high-performance Zr–Cu-based high-entropy SMAs can be realized by incorporating Hf additions.

Pd2 MnGa Metamagnetic Shape Memory Alloy with Small Energy Loss.

Metamagnetic shape memory alloys (MMSMAs) are attractive functional materials owing to their unique properties such as magnetostrain, magnetoresistance, and the magnetocaloric effect caused by magnetic-field-induced transitions. However, the energy loss during the martensitic transformation, that is, the dissipation energy, Edis , is sometimes large for these alloys, which limits their applications. In this paper, a new Pd2 MnGa Heusler-type MMSMA with an extremely small Edis and hysteresis is reported. The microstructures, crystal structures, magnetic properties, martensitic transformations, and magnetic-field-induced strain of aged Pd2 MnGa alloys are investigated. A martensitic transformation from L21 to 10M structures is seen at 127.4K with a small thermal hysteresis of 1.3K. The reverse martensitic transformation is induced by applying a magnetic field with a small Edis (=0.3Jmol-1 only) and a small magnetic-field hysteresis (=7kOe) at 120K. The low values of Edis and the hysteresis may be attributed to good lattice compatibility in the martensitic transformation. A large magnetic-field-induced strain of 0.26% is recorded, indicating the proposed MMSMA's potential as an actuator. The Pd2 MnGa alloy with low values of Edis and hysteresis may enable new possibilities for high-efficiencyMMSMAs.

A micro graphene high temperature sensor with a single Si3N4 protective layer

Temperature sensors are widely used in industrial production, national defense and military fields. The traditional temperature sensors normally operate in a limited temperature range no more than 200 °C, which cannot be used for extreme high temperature detections. In this paper, a thermal protection method for the sensing graphene membrane is proposed and a graphene high temperature sensor has been fabricated and investigated. By growing a single silicon nitride (Si3N4) protective layer on top of graphene, our design not only solves the problem that graphene is easily oxidized at high temperature, but also prevents graphene from being polluted by impurities, which would lead to the degradation of graphene performance. We further explore the protective effect of Si3N4 layer with different thicknesses on the performance of the sensor. It has been found that the 400 nm Si3N4 protective layer gives the best protective capability. The sensor exhibits a positive temperature coefficient (PTC) from 50 to 600 °C and a maximal temperature coefficient of resistance (TCR) value of 0.29% °C−1 at 150 °C is achieved. It has been demonstrated that our graphene high temperature sensor with protective layer structure maintains good stability not only at high temperature up to 600 °C, but also over a long-period of time under room temperature. In short, the high temperature sensor possesses a wide temperature measurement range with micro dimensions, a relatively high TCR and a smaller thermal hysteresis. The thermal protection approach proposed in this paper provides a new idea for the fabrication of high temperature pressure sensor, which is expected to be applied in aerospace engines and oil wells, etc.

Enhanced magnetocaloric properties and reduced annealing time of off-stoichiometric La1.2Fe11.6Si1.4B0.75 melt-spun ribbons

The off-stoichiometric La1.2Fe11.6Si1.4B0.75 alloys with different solidification rate were prepared by the arc-melting and melt-spinning methods, and the microstructure, magnetic and magnetocaloric properties of the annealed samples were investigated. It is found that the extra La and refined microstructure (induced by rapid cooling technique) shortened the annealing time to 30 min at 1273 K. The B atoms partially dissolved in lattice interstice of 1:13 phase and brings about the lattice expansion, which improves the TC and enhances the MCE of the La1.2Fe11.6Si1.4B0.75 alloy. The high cooling rate contributes to the depression of thermal and magnetic hysteresis. In the annealed La1.2Fe11.6Si1.4B0.75 ribbon with wheel speed of 10 m/s, the mass fraction of 1:13 phase is 86.8 wt%, and a large maximum magnetic entropy change of 20.2 J·kg−1K−1 with small thermal and magnetic hysteresis can be obtained at 193 K under field change of 2 T.

Oligonucleotides as Inhibitors of Ice Recrystallization.

Oligonucleotides of adenine (A20), guanine (G20), cytosine (C20), thymine (T20), cytosine-guanine ((CG)20), and adenine-thymine ((AT)20) were investigated as model compounds for ice recrystallization inhibition (IRI). Dehydroxy uracil (dU20), U20, and T20 were also compared to investigate the effect of minute changes in the hydrophobicity of the oligonucleotides on the IRI activity. Among the oligonucleotides considered in this study, T20 exhibited the best performance for IRI. In addition, the degree of polymerization of oligothymines varied over 5, 10, 20, 30, 50, and 100, and T20 was found to be the most effective for IRI. The IRI mechanism was investigated by comparing U20 and T20, which exhibited the lowest and highest IRI activity, respectively, among the oligonucleotides for their dynamic ice-shaping, thermal hysteresis, and ice nucleation inhibition. Little or no dynamic ice-shaping activity and small thermal hysteresis were observed for both nucleotides. All of the findings suggest that not the ice-polymer adhesion but the hydrophobic interactions of T20 in the interface layer might interfere with the water deposition on the ice crystal surfaces and contribute to the IRI activity of the T20 oligonucleotide.

An enhanced thin-film resistance temperature detector and its application for catalyst layer surface temperature measurement inside PEMFC

Temperature detection is of vital significance for the thermal management of proton exchange membrane fuel cells (PEMFCs). In this work, a robust Au thin-film resistance temperature detector (RTD) was fabricated based on the micro-electro-mechanical system (MEMS) to achieve temperature monitoring inside PEMFC. Low-temperature heat treatment was carried out to promote the performance of RTD, and was confirmed to help achieve good linearity and small thermal hysteresis. Combined with X-ray diffusion (XRD) Rietveld refinement and morphology analysis, particularly the lattice strain and dislocation calculation, low-temperature heat treatment is supposed to help eliminate lattice defects and residual strains in the film. Subsequently, this prepared RTD was applied to measure cathode catalyst layer (CCL) temperature inside PEMFC under different relative humidity (RH) and current loads. The results show that current loads are positively related to temperature variation. The higher the current, the more Joule and irreversible heat are generated. The RH of anode and cathode has a more complex impact on temperature evolution, depending on the water concentration in the electrode sites, which is not only affected by RH, but also by the oxygen reduction reaction (ORR). Too high water contents in the electrode area would bring about flooding, while too low would result in membrane drying, so both of them cause different levels of ohmic and mass transport loss, hence inducing temperature variations. This work is supposed to benefit the research of RTD enhancement and thermal state inside PEMFC.

Colossal Barocaloric Effect in Carboranes as a Performance Tradeoff

AbstractThe discovery of colossal barocaloric effects in organic plastic crystals has significantly advanced the development of solid‐state refrigerant techniques. Adapting to the real application, a tradeoff of various barocaloric performances has to be achieved. Here, it is reported a novel plastic crystal system, that is, carboranes (C2B10H12), including three positional isomers: ortho‐carborane, meta‐carborane, and para‐carborane, which are characterized by C2v, C2v, D5d point groups, respectively. They all undergo an orthorhombic‐to‐tetragonal phase transition around room temperature. Compared to the previously reported organic plastic crystals, this system exhibits a combination of large pressure‐normalized entropy changes, the high‐pressure sensitivity of the transition temperature, small thermal hysteresis, and so forth. Their barocaloric performances are positional‐isomerism dependent, and the best performances are obtained in para‐carborane with maximum entropy changes of about 106.2 J kg−1 K−1 achieved under pressure changes below 30 MPa. This study not only suggests that carboranes would be a considerably promising working material for barocaloric refrigeration at room temperature but also indicates that delicate tuning of molecular isomerism is an effective strategy to enhance barocaloric performances.

Spin-up conversion, exchange-interactions, and tailored magnetic properties in core-shell La2NiMnO6 of small crystallites

La2NiMnO6—a ferromagnetic (FM) insulator offers tunable charge carriers and spins useful to devise its multiple properties and applications. In this view, we studied a core-shell La2NiMnO6 (2–3 nm shell on 65 – 80 nm core) of a Ni2+/Ni3+(d7) to Mn4+/Mn3+ (d4) spin-up conversion— revived a new FM phase-2, raising a spin-density σ s = 0.7 s a− 1 over the Ni2+/Mn4+ species (phase-1), σ s = 0.5 s a− 1, i.e. 2.12 μB /f.u. larger spin moment. HRTEM images studied with x-ray diffraction characterizing core-shell structure that plays a crucial role in tuning the high spin FM phase-2 of profound properties. Below 110 K, the dc magnetization and ac magnetic susceptibility χ(ω, T) reveal a metastable magnetic behavior on an antiferromagnetic canting of a spin-glass nature. The results follow a Vogel–Fulcher type relaxation with a relaxation time τ 0 ∼ 10−13 s, confirming a spin-glass freezing behavior. Uniquely, FM field of phase-1 controls magnetics of phase 2 of a coupled magnet, modulating joint features with small thermal magnetic hysteresis on heating-cooling cycles.

Low-field reversible magnetocaloric effect in Co-dopedMn-Cr-Sb alloys

The magnetic phase transition and magnetocaloric effect in the Mn1.89− x Cr0.11Co x Sb ( x =0, 0.04, 0.06) alloys were studied in this work. Results show that the alloys undergo the first-order magneto-elastic phase transition from ferrimagnetic phase to antiferromagnetic phase on cooling, with very narrow thermal hysteresis, i.e., 3–4 K. Co doping cannot only enhance the transformation temperatures of magneto-elastic phase transition, but also avoid the formation of unfavorable MnSb phase. Direct measurements on the adiabatic temperature change ∆ T ad are employed to evaluate the magnetocaloric properties for the studied alloys. Under the field change of 1.5 T, the maximum ∆ T ad up to −1.4 K and the reversible ∆ T ad of −1.2 K can be achieved in the Mn1.85Cr0.11Co0.04Sb alloy. The combination of very small thermal hysteresis and large low-field reversible magnetocaloric effect makes the present alloys very attractive for the potential applications in magnetic refrigeration.

Observation of table-like magnetocaloric effect and large refrigerant capacity in Nd6Fe13Pd1–xCux compounds

The table-like magnetocaloric effect is significant for the magnetic refrigeration applications above 20 K based on the Ericsson cycle. Herein, we prepared a series of Nd6Fe13Pd1–xCux (x = 0.05, 0.1, 0.15) compounds by the arc-melting method. These compounds show the single crystalline phase in the tetragonal Nd6Fe13Si-type structure with the space group I4/mcm. A magnetic phase transition from ferromagnetism to antiferromagnetism and a metamagnetic transition from the antiferromagnetic state to the ferromagnetic state are observed in each of the compounds. The compounds exhibit table-like magnetocaloric effects with large refrigerant capacities. A constant ΔSM in a temperature span of 40 K in the Nd6Fe13Pd0.85Cu0.15 compound are observed. For a field change of 0–5 T, the peak values of –ΔSM for the Nd6Fe13Pd0.95Cu0.05, Nd6Fe13Pd0.90Cu0.10, and Nd6Fe13Pd0.85Cu0.15 compounds are estimated to be 4.8, 4.6 and 4.4 J/(kg·K) with corresponding refrigerant capacity values of 323, 331 and 316 J/kg, respectively. The obtained table-like magnetocaloric effects with large refrigerant capacities as well as fairly small thermal and magnetic hysteresis deem these series of compounds good candidates for single-phase magnetic refrigeration based on the Ericsson cycle.

Fully Controllable Structural Phase Transition in Thermomechanical Molecular Crystals with a Very Small Thermal Hysteresis

The construction of a practical crystalline molecular machine faces two challenges: to realize a collective molecular movement, and to amplify this movement into a precisely controlled mechanical response in real time and space. Thermosalient single crystals display cooperative molecular movements that are converted to strong macroscopic mechanical responses or shape deformations during temperature-induced structural phase transitions. However, these collective molecular movements are hard to control once initiated, and often feature thermal hystereses that are larger than 10°C, which greatly hamper their practical applications. Here, it is demonstrated that the phase boundaries of the thermomechanical molecular crystal based on a fluorenone derivative 4-DBpFO can be used to finely control its structural phase transition. When this phase transition is triggered at two opposite crystal faces, it is accompanied by two parallel phase boundaries that can be temperature controlled to move forward, backward, or to halt, benefitting from the stored elastic energy between the parallel boundaries. Moreover, the thermal hysteresis is greatly decreased to 2-3°C, which allows for circular heating/cooling cycles that can produce a continuous work output.

Microstructure and magnetocaloric properties in melt-spun and high-pressure hydrogenated La0.5Pr0.5Fe11.4Si1.6 ribbons* *Project supported by the National Natural Science Foundation of China (Grant No. 51771197), the Fund from the Chinese Academy of Sciences (Grant No. KJZD-EW-M05), and the Liaoning Revitalization Talents Program, China (Grant No. XLYC1807122).

The effects of wheel speeds and high-pressure hydrogen treatment on phase evolution, microstructure, and magnetocaloric properties in La0.5Pr0.5Fe11.4Si1.6 melt-spun ribbons are studied in this work. The results reveal that the increase of wheel speed is beneficial to the formation of cubic NaZn13-type phase and the grain refinement. The optimized wheel speed for microstructural and magnetocaloric properties is 30 m/s. The largest entropy change of 18.1 J/kg⋅K at 190 K under a magnetic field change of 0 T–5 T is obtained in La0.5Pr0.5Fe11.4Si1.6 ribbons melt-spun at 30 m/s. After a high-pressure hydrogen treatment of 50 MPa, the Curie temperature of the ribbons prepared at 30 m/s is adjusted to about 314 K and the large –ΔS M of 17.9 J/kg⋅K under a magnetic field change of 0 T–5 T is achieved at room temperature with almost none hysteresis loss. The small thermal and magnetic hysteresis and the large –ΔS M make the La0.5Pr0.5Fe11.4Si1.6 hydride ribbons appropriate for magnetic refrigerant applications around room temperature.

Pt thin-film resistance temperature detector on flexible Hastelloy tapes

Platinum (Pt) thin-film resistance temperature detector was fabricated on the flexible Hastelloy tapes using magnetron sputtering and MEMS processes. NiCrAlY buffer layer and AlON/Al2O3 insulating layer were deposited on the tapes for stress release and electrical insulation. Post annealing was applied to improve the stability of the sensors. The performance of the sensor was calibrated with temperature up to 550 °C. Compared with the sensor on the alumina ceramic substrate, the sensor on Hastelloy tapes have much smaller thermal hysteresis, higher linearity and excellent stability. Moreover, this flexible sensor can be easily integrated with the metallic components by the welding and the maximum curvature of the sensor is 2 cm−1. This Pt thin-film temperature sensor has great potential in the surface temperature measurement of hot components in harsh environment.

Effects of Nanodomains on Local and Long-Range Phase Transitions in Perovskite-Type Eu0.8Ca0.2TiO3-δ.

The determination of reversible phase transitions in the perovskite-type thermoelectric oxide Eu0.8Ca0.2TiO3–δ is fundamental, since structural changes largely affect the thermal and electrical transport properties. The phase transitions were characterized by heat capacity measurements, Rietveld refinements, and pair distribution function (PDF) analysis of the diffraction data to achieve information on the phase transition temperatures and order as well as structural changes on the local level and the long range. On the long-range scale, Eu0.8Ca0.2TiO3–δ showed a phase transition sequence during heating from cubic at 100 < T < 592 K to tetragonal and finally back to cubic at T > 846 K. The phase transition at T = 592 K (diffraction)/606 K (thermal analysis) was reversible with a very small thermal hysteresis of about 2 K. The local structure at 100 K was composed of a complex nanodomain arrangement of Amm2- and Pbnm-like local structures with different coherence lengths. Since in Eu0.8Ca0.2TiO3–δ the amount of Pbnm domains was too small to percolate, the competition of ferroelectrically distorted octahedra (Amm2 as in BaTiO3) and rigid, tilted octahedra (Pbnm as in CaTiO3) resulted in a cubic long-range structure at low temperatures.

Improved crystallographic compatibility and magnetocaloric reversibility in Pt substituted Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy

We present here the improved crystallographic/geometric compatibility and magnetocaloric reversibility by measurement of magnetic entropy change using different protocols in 10% Pt substituted Ni2Mn1.4In0.6 magnetic shape memory alloy. The substitution of Pt reduces the thermal hysteresis about 50% to the Ni2Mn1.4In0.6. The origin of the reduced thermal hysteresis is investigated by the crystallographic compatibility of the austenite and martensite phases. The calculated middle eigenvalue of the transformation matrix turned out to be 0.9982, which is very close to 1 (deviation is only 0.18%) suggests for the crystallographic compatibility between the austenite and martensite phases in Ni1.9Pt0.1Mn1.4In0.6. A very small thermal hysteresis and crystallographic compatibility between two phases in this alloy system indicate a stress-free transition layer (i.e. perfect habit plane) between the austenite and martensite phase, which is expected to give reversible martensite phase transition and therefore reversible magnetocaloric effect (MCE) as well. The calculated value of the isothermal entropy change (ΔSiso) using the magnetization curve under three different measurement protocols (i.e. isothermal, loop, and isofield measurement protocol) is found to be nearly same indicating a reversible MCE in the present alloy system. Our work provides a path to design new magnetic shape memory Heusler alloys for magnetic refrigeration and also suggest that any of the above measurement protocol can be used for the calculation of ΔSiso for materials satisfying geometrical compatibility condition.

The Effect of Quenching Methods on Transformation Characteristics and Microstructure of an NiTiCu Shape Memory Alloy

Shape memory alloys are used in diverse fields. It is Ni–Ti alloys that are predominantly used for applications capitalizing on the functional properties of shape memory and superelastic effect. These properties are influenced by factors, such as alloy composition, alloying addition, thermal and mechanical treatment, etc. In any application, the transformation temperatures of the alloy/device are very critical. Moreover, the stability of transformation temperatures and a smaller hysteresis are preferred. Ni–Ti alloys have their own limitations, such as low transformation temperatures and lack of ductility. In order to overcome these limitations, researchers have used ternary additions, such as Zr, Hf, Cu, Pd and Au. The use of copper is practicable because of its lower cost as compared to Ti and Ni. Substitution of Cu for Ni up to ~ 25% in an equiatomic NiTi alloy causes it to exhibit SME. The transformation temperatures of NiTiCu exhibit less sensitivity to composition and a smaller thermal hysteresis. In this work, therefore, the effect of methods of quenching on transformation temperatures and microstructure of an Ni–Ti–4Cu (at.%) alloy has been explored. The material was cast using vacuum induction melting. It was solutionized at 950 °C for 2 h and cooled using different methods/quenchants: liquid nitrogen, water at room temperature, air, annealing (furnace cooling). The samples quenched by different techniques were characterized by XRD, DSC, OM, SEM and hardness test. The results indicated that the martensite plate size varied in samples quenched using different quenchants even though the morphology was the same in all specimens. In addition, the transformation temperatures and hardness values of the alloy specimens varied as the intensity of quenching varied. The results are presented and discussed in detail in the paper.

Multi-step hydration/dehydration mechanisms of rhombohedral Y2(SO4)3: a candidate material for low-temperature thermochemical heat storage.

To evaluate rhombohedral Y2(SO4)3 as a new potential material for low-temperature thermochemical energy storage, its thermal behavior, phase changes, and hydration/dehydration reaction mechanisms are investigated. Rhombohedral Y2(SO4)3 exhibits reversible hydration/dehydration below 130 °C with relatively small thermal hysteresis (less than 50 °C). The reactions proceed via two reaction steps in approximately 0.02 atm of water vapor pressure, i.e. “high-temperature reaction” at 80–130 °C and “low-temperature reaction” at 30–100 °C. The high-temperature reaction proceeds by water insertion into the rhombohedral Y2(SO4)3 host structure to form rhombohedral Y2(SO4)3·xH2O (x = ∼1). For the low-temperature reaction, rhombohedral Y2(SO4)3·xH2O accommodates additional water molecules (x > 1) and is eventually hydrated to Y2(SO4)3·8H2O (monoclinic) with changes in the host structure. At a water vapor pressure above 0.08 atm, intermediate Y2(SO4)3·3H2O appears. A phase stability diagram of the hydrates is constructed and the potential usage of Y2(SO4)3 for thermal energy upgrades is assessed. The high-temperature reaction may act similarly to an existing candidate, CaSO4·0.5H2O, in terms of reaction temperature and water vapor pressure. Additionally, the hydration of rhombohedral Y2(SO4)3·xH2O to Y2(SO4)3·3H2O should exhibit a larger heat storage capacity. With respect to the reaction kinetics, the initial dehydration of Y2(SO4)3·8H2O to rhombohedral Y2(SO4)3 introduces a microstructure with pores on the micron order, which might enhance the reaction rate.

Magnetic Properties and Magnetocaloric Effect of Binary Compound NdPd

The crystal structure, magnetic and magnetocaloric properties of the binary NdPd compound were investigated by X-ray diffraction and the physical property measurement system in detail. The NdPd compound with a CrB structure exhibits a second-order magnetic phase transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 15.5 K. For a magnetic field change of 0–5 T, the peak value of magnetic entropy change (− ΔSM) is evaluated to be 12.2 J/kg K, and the corresponding refrigerant capacity (RC) reaches its maximal value of 94 J/kg. The relatively small thermal hysteresis and magnetic hysteresis with the considerable magnetocaloric effect indicate that NdPd is an anticipated material for the low-temperature magnetic refrigeration.