Refrigerant Materials Research Articles

Data driven accelerated design of high-efficiency corrosion inhibitor for magnetic refrigeration materials

Water-based heat exchange fluid causes severe corrosion of magnetic refrigeration materials. Here we successfully predict a high-efficiency corrosion inhibitor for magnetic refrigeration by using machine learning trained on a small database. The inhibitor has a significant corrosion inhibition effect, e.g., the La(Fe, Si)13 alloy maintains perfect surface after 60 days of immersion, whereas Na2MoO4 and Na2HPO4 from an inhibitor form the protective film to prevent corrosion. In comparison with the traditional trial-and-error method, the machine learning method could reduce data collection by approximately 26 times, while the prediction accuracy can be improved by approximately 2–3 orders of magnitude.

Superelasticity and elastocaloric effect in a textured Ti-Nb-Zr-Ta alloy with narrow stress hysteresis

Recently, elastocaloric cooling has been authoritatively regarded as the most promising alternative for replacing conventional vapor compression technology, yet obstacles like structural/functional fatigue and high processing cost still exist, which boost the investigation of new elastocaloric materials. In this paper, we investigated the superelasticity (SE) as well as the elastocaloric effect (eCE) in a textured Ti-22 Nb-4Zr-2Ta alloy prepared by cold rolling of 97% in thickness and subsequent annealing at 973 K for 30 min. The strong texture is in favor of harmonizing the superelastic critical stress and enhancing transformation homogeneity. As a result, superelasticity with narrow stress hysteresis of ∼47 MPa at ambient temperature and outstanding homogeneous eCE has been confirmed elaborately through observing strain together with temperature distribution during a superelastic cycle. The standard deviations (Sdev) of the strain distribution during superelastic deformation was in the range of 0.17%− 0.37% accompanying with temperature change (ΔTadi) of ∼4.4 K and ∼3.9 K during loading and unloading processes, respectively. Moreover, the narrow superelastic hysteresis and homogenous transformation behavior allowed for a coefficient of performance (COP) value of 13.2 and little degradation after 240 elastocaloric cycles. As eCE homogeneity and SE hysteresis correlate closely with functional fatigue behavior, the present Ti-22 Nb-4Zr-2Ta alloy may act as potential working materials for stable solid-state refrigeration.

Cryogenic magnetocaloric effect in R2GeMoO8 (R = Gd and Dy) compounds

The cryogenic magnetocaloric effect has attracted great attention due to its application in cryogenic refrigeration technology, which is essential for space science and quantum computing. In this study, the magnetocaloric effect of Gd2GeMoO8 (GGMO) and Dy2GeMoO8 (DGMO), which were prepared by simple solid-state reactions, had been investigated. The XRD refinement analysis suggested that GGMO and DGMO crystallize in a tetragonal structure. A large magnetic entropy change (ΔSM) of −41.2 J kg−1 K−1 was observed at 1.8 K for GGMO under a magnetic field (ΔH) of 7 T. A moderate ΔSM of −14.1 J kg−1 K−1 was obtained at 4.5 K under a ΔH of 7 T in DGMO. The refrigeration capacity and relative cooling power reached 257.4 and 337.8 J kg−1 for GGMO and 133.3 and 143.7 J kg−1 for DGMO, respectively, under a ΔH of 0–7 T. Our results suggest that GGMO is a competitive cryogenic magnetic refrigeration material.

Effects of composition variation and hydrogenation on magnetocaloric properties of the (Gd1-xTbx)Ni (x = 0.1; 0.9) compounds

To identify promising magnetic refrigerant materials, we have studied the influence of composition variations and hydrogenation on the magnetocaloric effect (MCE) of the (Gd1-xTbx)Ni compounds. The end compositions of the series, Gd0.9Tb0.1Ni and Gd0.1Tb0.9Ni crystallize in orthorhombic CrB-type and monoclinic TbNi-type structures, respectively. Hydrogenation boosts the unit cell volume of (Gd,Tb)Ni by more than 20 % upon absorption of 4 at.H/f.u. Hydrogen absorption changes the structure type from TbNi to the CrB-type in Gd0.1Tb0.9Ni. Decrease of the Curie temperature in hydrides reaches ∼ 60 K. The magnetocaloric effect in (Gd,Tb)NiHy (y = 0 and 4) obtained by indirect method in the vicinity of TC revealed similar values of the maximum of specific isothermal entropy change -ΔST = 20.5 J kg−1 K−1 for Gd0.9Tb0.1Ni and its hydride Gd0.9Tb0.1NiH4 at μ0ΔH = 7 T. We show that the controlled synthesis of hydrides allows us to tailor the magnetocaloric effect in the multicomponent rare earth intermetallics and obtain materials with largely different TCs but with the same MCE values that are attractive for use in low-temperature magnetic cooling applications.

Tuning the temperature range of superelastic Ni-Ti alloys for elastocaloric cooling via thermal processing

Caloric cooling enlisting solid-state refrigerants is potentially a promising eco-friendly alternative to conventional cooling based on vapor compression. The most common refrigerant materials for elastocaloric cooling to date are Ni-Ti based superelastic shape memory alloys. Here, we have explored tuning the operation temperature range of Ni50.8Ti49.2 for elastocaloric cooling. In particular, we have studied the effect of thermal treatments (a.k.a. aging) on the transformation temperature, superelasticity, and elastocaloric effects of Ni50.8Ti49.2 shape memory alloy tubes. The isothermal compressive test revealed that the residual strain of thermally-treated Ni-Ti tubes at room temperature approaches zero as aging time is increased. Short-time aging treatment at 400 °C resulted in good superelasticity and elastocaloric cooling performance with a large tunable austenite finish (A f) temperature range of 24.7 °C, as determined from the A f temperature of the samples that were aged 5–120 min. The main reason of the property change is the formation of a different amount of Ni4Ti3 precipitates in the NiTi matrix. Our findings show that it is possible to tailor the A f temperature range for development of cascade elastocaloric cooling systems by thermally treating a starting single composition Ni-Ti alloy.

Large low-field reversible magnetocaloric effect in K3Gd(PO4)2 at sub-Kelvin temperature

We synthesized a potassium gadolinium phosphate K3Gd(PO4)2 with monoclinic structure (P21/m) by the high-temperature solid–state reaction method. Its lattice constants obtained by Rietveld refinements of XRD curve are a = 0.7411 nm, b = 0.5624 nm, and c = 0.9433 nm. Magnetic and magnetocaloric properties of K3Gd(PO4)2 were investigated in detail. The magnetic phase transition temperature of K3Gd(PO4)2 was determined by ultra-low temperature testing to be 0.58 K. K3Gd(PO4)2 exhibits large magnetic entropy changes (–ΔSM). The maximum –ΔSM are 20.2 and 29.4 J/(kg·K) in the magnetic field variation (ΔH) of 1 and 2 T, respectively, which are larger than that of the commercial Gd3Ga5O12 (GGG). The maximum adiabatic temperature change (ΔTad) reaches 5.91 K under a magnetic field change (ΔH) of 1 T. K3Gd(PO4)2 is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.

Substantially Enhanced Electrocaloric Effect in Ba(Zr0.2Ti0.8)O3 Lead-Free Ferroelectric Ceramics via Lattice Stress Engineering.

As an alternative to conventional vapor-compression refrigeration, cooling devices based on electrocaloric (EC) materials are environmentally friendly and highly efficient, which are promising in realizing solid-state cooling. Lead-free ferroelectric ceramics with competitive EC performance are urgently desirable for EC cooling devices. In the past few decades, constructing phase coexistence and high polarizability have been two crucial factors in optimizing the EC performance. Different from the external stress generated through heavy equipment and inner interface stress caused by complex interface structures, the internal lattice stress induced by ion substitution engineering is a relatively simple and efficient means to tune the phase structure and polarizability. In this work, we introduce low-radius Li+ into BaZr0.2Ti0.8O3 (BZT) to form a particular A-site substituted cell structure, leading to a change of the internal lattice stress. With the increase of lattice stress, the fraction of the rhombohedral phase in the rhombohedral-cubic (R-C) coexisting system and ferroelectricity are all pronouncedly enhanced for the Li2CO3-doped sample, resulting in the significant enhancement of saturated polarization (Ps) as well as EC performance [e.g., adiabatic temperature change (ΔT) and isothermal entropy change (ΔS)]. Under the same conditions (i.e., 333 K and 70 kV cm-1), the ΔT of 5.7 mol % Li2CO3-doped BZT is 1.37 K, which is larger than that of the pure BZT ceramics (0.61 K). Consequently, in cooperation with the great improvement of electric field breakdown strength (Eb) from 70 to 150 kV cm-1, 5.7 mol % Li2CO3-doped BZT achieved a large ΔT of 2.26 K at a temperature of 333 K, which is a competitive performance in the field of electrocaloric effect (ECE). This work provides a simple but effective approach to designing high-performance electrocaloric materials for next-generation refrigeration.

Synthesis, structure, morphology, magnetism, and magnetocaloric-effect studies of (La1−xPrx)0.7Sr0.3MnO3 nanocrystalline perovskites

Single-Phase (La1–xPrx)0.7Sr0.3MnO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) perovskites were synthesized by the sol–gel method followed by sintering at 700 °C for 5 h. Samples with x = 0.0–0.4 are found to crystallize into rhombohedral structure (R-3c space group) while the ones with x = 0.6–1.0 crystallize into orthorhombic structure (Pbnm space group). The average particle size of the samples was in the range of 21–44 nm. All samples exhibit a ferromagnetic to paramagnetic second-order magnetic phase transition at Curie temperature, which is found to decrease linearly with increasing the Pr concentration. The magnetic coercivity was found to be small (~ 10 Oe) for all the samples, at T < TC. The experimental effective paramagnetic moment (µeff) is found to increase with increasing x from 3.99 µB (x = 0.0) to 5.05 µB (x = 1.0). The magnitude of the maximum magnetic entropy change (−ΔSM)max. and the relative cooling power (RCP) for the samples having orthorhombic structure increases as x increases reaching a maximum value of 4.67 J/kg.K and 574 J/kg at ΔµoH = 9 T for x = 1.0. While the ones with the rhombohedral structure have the maximum values of (−ΔSM)max. and RCP of 4.63 J/kg.K and 472 J/kg at ΔµoH = 9 T are for x = 0.2. The large values of (−ΔSM)max. and RCP (at room temperature (RT)) and the wider temperature range of −ΔSM for the sample with x = 0.6 suggests that this compound may be considered as magnetic refrigerant material at RT, and the other compounds can be candidates in the vicinity of RT.

Strong Magnetocaloric Coupling in Oxyorthosilicate with Dense Gd3+ Spins.

Searching for working refrigerant materials is the key element in the design of magnetic cooling devices. Herein, we report on the thermodynamic and magnetocaloric parameters of an X1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements. An overall correlation strength of |J|S2 ≈ 3.4 K is derived via the mean-field estimate, with antiferromagnetic correlations between the ferromagnetically coupled Gd-Gd layers. The magnetic entropy change -ΔSm is quite impressive, reaches 0.40 J K-1 cm-3 (58.5 J K-1 kg-1) at T = 2.7 K, with the largest adiabatic temperature change Tad = 23.2 K for a field change of 8.9 T. At T = 20 K, the lattice entropy SL is small enough compared to the magnetic entropy Sm, Sm/SL = 21.3, which warrants its potential in 2 -20 K cryocoolers with both the Stirling and Carnot cycles. Though with relatively large exchange interactions, the layered A-type spin arrangement ultimately enhances the magnetocaloric coupling, raising the possibilities of designing magnetic refrigerants with a high ratio of cooling capacity to volume.

Magnetic Refrigerant Materials for Hydrogen Liquefaction by Active Magnetic Regenerative Refrigeration

Magnetic refrigerant materials are one of the key factors for governing the cooling performance of magnetic refrigeration systems. In particular, not only the physical properties such as magnetocaloric effects, but also the practical form of the magnetic material are of crucial importance to active magnetic regenerative refrigeration （AMRR）. In this JST-mirai project, the development of several types of magnetic materials that show the large magnetocaloric effects in the temperature range from 20 K to 80 K and fabrication of spherical particles of the materials were conducted. The magnetic properties and magnetocaloric effects between the mother-alloy and spherical particles were compared for HoAl2, ErCo2, and HoB2. Moreover, thermal property and electrical property as well as the shape and size of the materials are discussed from the perspective of their application to the AMRR system for hydrogen liquefaction.

Cover Picture: Materials and Corrosion. 3/2023

Cover: There are concerns about the acid of refrigerant oils (inside piping) and corrosion by the salts in seawater (outside piping) for industrial piping. Corrosion-resistant characteristics of various aluminum alloys were investigated by accelerated degradation tests with changing storage conditions, such as temperature and atmosphere. The results from immersion tests in a refrigerant and cyclic corrosion tests (intermittent cycles between salt mist and drying) proved that aluminum alloys can be used for refrigerant piping. More detailed information can be found in: Seiji Uchiyama, Satoshi Uemura, Koji Hiraoka, Yuji Kimura, Shiro Seki, Corrosion and degradation behavior of aluminum and copper refrigerant piping, Materials and Corrosion 2023, 74, 344.

Theoretical modeling and verification of storage time of cold box based on network method of radiation heat transfer

The storage time of cold box is an important subject. At present, the research method of the storage time is mainly an experiment, and the theoretical research is incomplete. Therefore, in this work, theoretical modeling combined with a network method of radiation heat transfer, the shape factor of heat conduction, and sensible heat of refrigerant were proposed to calculate the storage time of a cold box at various ambient temperatures and amounts of refrigerant. The experimental and simulation results were used to verify the theoretical modeling of the storage time. The influences of the sensible heat of refrigerant and radiation heat transfer in the cold box were analyzed. The stability of the theoretical modeling was studied via simulation of the different cold box and refrigerant materials. The results of the accuracy of the theoretical model confirmed that the maximum error between the theoretical and the experimental storage times is 8.45%, and the error between the theoretical and the simulation results is 7.51%, indicating that the sensible heat of refrigerant and radiation heat transfer have big impacts on the storage time. The stability of the theoretical model is confirmed under the different box and refrigerant materials, and different shapes of refrigerant. The storage time model has stability on different box materials and refrigerant materials. The theoretical model can be severed as a fundamentally guidance for the cold box production design.

Crystal electric field level scheme leading to giant magnetocaloric effect for hydrogen liquefaction

In recent years, magnetic refrigeration has attracted considerable attention for hydrogen liquefaction. Most materials used for magnetic refrigeration contain heavy rare earth ions with complex crystalline electric field energy splittings, whose effect on the magnetic entropy change ΔSM has not been systematically studied. In particular, the theoretical upper limits of ∣ΔSM∣ for general heavy earth cases are unknown. Here, we show that the crystalline electric field level schemes result in a large ΔSM for general heavy rare earth cases. We provide a specific example of the magnetic refrigeration material HoB2 using inelastic neutron scattering experiments combined with mean-field calculations with crystal field splitting and exchange interactions. The relationship between ΔSM and crystal field parameters presented in this study can be useful for developing compounds with a large ∣ΔSM∣ and advancing the design of magnetic refrigeration materials.

Large Refrigerant Capacity Induced by Table‐Like Magnetocaloric Effect in High‐Entropy Alloys TbDyHoEr

Rare‐earth‐based high‐entropy alloys (HEAs) with large magnetocaloric effect (MCE) have been recently recognized as good candidates for magnetic refrigeration. Herein, the complex magnetic transition, MCE, refrigerant capacity (RC), and magnetic‐phase diagram of single‐phase TbDyHoEr HEA are studied. It is showed in the results that due to complex magnetic transition and an ideal table‐like MCE, the RC of TbDyHoEr is significantly improved from 883.19 to 1049.22 J kg−1by melt‐spun treatment. In terms of RC value and hysteresis performance, the melt‐spun treatment significantly improves the application potential of TbDyHoEr HEA as a high‐efficient magnetic refrigeration material, and the ideal table‐like MCE in a large temperature range enables this material to meet the requirements of both cryogenic refrigeration and mesothermal refrigeration for an Ericsson cycle.

Dissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys

Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change Δst exists so far for Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition and temperature dependence of Δst. Our results reveal a substantial structural entropy change contribution of approximately 65 J(kgK)-1, which is compensated at lower temperatures by an increasingly negative entropy change associated with the magnetic subsystem. This leads to compensation temperatures Tcomp of 75 K and 300 K in Ni35Co15Mn50-yTiy and Ni33Co17Mn50-yTiy, respectively, below which the martensitic transformations are arrested. In addition, we simultaneously measured the responses of the magnetic, structural and electronic subsystems to the temperature- and field-induced martensitic transformation near Tcomp, showing an abnormal increase of hysteresis and consequently dissipation energy at cryogenic temperatures. Simultaneous measurements of magnetization and adiabatic temperature change ΔTad in pulsed magnetic fields reveal a change in sign of ΔTad and a substantial positive and irreversible ΔTad up to 15 K at 15 K as a consequence of increased dissipation losses and decreased heat capacity. Most importantly, this phenomenon is universal, it applies to any first-order material with non-negligible hysteresis and any stimulus, effectively limiting the utilization of their caloric effects for gas liquefaction at cryogenic temperatures.

Preparation and magnetocaloric performance of La(Fe,Co,Si)13 alloys with wide transition temperature range

NaZn13-type La(Fe,Si)13 alloys are one of the most promising magnetocaloric materials for room-temperature magnetic refrigeration. However, the narrow ferromagnetic-to-paramagnetic transition temperature range of La(Fe,Si)13 alloys severely limited their magnetic refrigeration application. Herein, a series of La1.4Fe11.8-xCoxSi1.2 (x = 0.88, 0.94, 0.98, 1.02, 1.06) alloys were designed and prepared by high-energy ball milling and annealing. It is discovered that all the samples are composed of La(Fe,Co,Si)13 main phase and a small amount of α-Fe phase. The Curie temperature of the ferromagnetic-to-paramagnetic transition was well adjusted to room temperature by optimizing the x. A maximum magnetic entropy change (-ΔSM) of 4.0 J kg−1 K−1 for the sample with x = 0.98 was obtained at a magnetic field of 2 T. Meanwhile, all the samples exhibit a significant increase in the half-height width of -ΔSM reaching approximately 35 K, increased by more than 41% compared with that of the reference sample prepared by arc melting. The broadened temperature range originates from the lattice distortion induced by the ball milling process. Our work indicates that La(Fe,Si)13 alloys with relatively large -ΔSM and wide transition temperature range can be simultaneously obtained around room temperature by optimizing the composition and the ball milling process.

Performance of refrigeration system using Al2O3, CuO and TiO2 nano-enhanced refrigerants: A review

Refrigeration is an ever-growing field where we are always looking for environmentally cleaner, more efficient and more usable ways to enhance and discover substances and materials for refrigeration. Nanoparticles are one way to achieve this goal of great energy savings and resulting emissions reductions. The refrigeration interaction becomes more proficient and protected as contrasted with the past in the environment. The key objective of this article is to review the performance of refrigeration systems with Al2O3, CuO and TiO2 nano-enhanced refrigerants. The Review revealed that when the TiO2 nanoparticle was introduced to the R134a refrigerant, the maximum enhancement in coefficient of performance is 18.75%. On the other hand, Al2O3/R134a offers a 27% reduction in power usage when compared to traditional fluids. Compared to R134a/CuO, the Al2O3/R134a nano-refrigerant offers energy savings that are more than five times greater and 80% more effective.

On the structural and magnetic properties of Al-rich high entropy alloys: a joint experimental-theoretical study

The present work investigates how the vanadium (V) content in a series of Al50V x (Cr0.33Mn0.33Co0.33)(50−x) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (T C) of the BCC phase in comparison with the B2 phase. We find that lower V content increases the B2 phase fraction, the saturation magnetization, and the Curie point, in line with the calculations. This trend is primarily connected with the preferential partition of V in the BCC phase, which however hinders the theoretically predicted antiferromagnetic B2 phase stabilizing effect of V. On the other hand, the chemistry-dependent properties of the ferromagnetic B2 phase suggest that a careful tuning of the composition and phase fractions can open the way towards promising high-entropy magnetic materials.

The effect of defect and substitution on barocaloric performance of neopentylglycol plastic crystals

Plastic crystal neopentylglycol (NPG, C5H12O2) has become an important candidate material in the future solid-state refrigeration field due to its huge colossal barocaloric effects near room temperature. However, NPG encounters significant shortcomings in practical cooling process that hinders its further application. Here, we systematically investigate the effect of defects and substituting a small amount of additional alien molecules on the barocaloric performance of NPG plastic crystals. It is found that low concentration of defects and substitution moderately affect the isothermal entropy, adiabatic temperature, and thermal hysteresis of NPG. Importantly, the substituted carbon nanotubes significantly enhance the thermal conductivity by more than one order of magnitude, arising from structural-modification enhanced acoustic phonons. Using dimensionless variable, we define the comprehensive cooling performance that represents the most promising working materials for barocaloric refrigeration. The present work provides important guidance on improving the barocaloric performance of NPG as prototypical plastic crystals for practical cooling applications.

Giant Negative Electrocaloric Effect over an Ultra-Wide Temperature Region in Relaxation Frozen State Ferroelectrics

A giant negative electrocaloric effect with the electrocaloric temperature change range from -27.3 to -9.8 K over an ultra-wide temperature region of 260 K (-180 to 80 °C) is obtained in a relaxation frozen state ferroelectric film of Bi5Ti3AlO15. A strategy is proposed to extend the temperature region of the electrocaloric effect by gradually slowing and locally freezing the relaxation dynamics. The slow and frozen nanodomains below freezing temperature Tf of ∼80 °C do not yield to the applied electric field but are noncolinear to the field, which results in an inverse configuration entropy change and negative electrocaloric effect over an ultra-wide temperature region in frozen relaxor state ferroelectric films. A semiphenomenological model based on modified Ginzburg-Landau-Devonshire theory is presented to reveal the evolution of the slowing and freezing of the nanodomains. The breakthroughs in the operating temperature region and cooling temperature change make relaxation frozen state ferroelectrics excellent electrocaloric refrigeration materials.