Wide Temperature Span Research Articles

Enhancement of Refrigeration Capacity and Table-Like Magnetocaloric Effect in LaFe 10.7Co 0.8Si 1.5/ La 0.6Pr 0.4Fe 10.7Co 0.8Si 1.5 Composite

In this work, we have investigated the magnetocaloric effect (MCE) in a two-phase composite system (LaFeCoSi) 1−x/(LaPrFeCoSi) x based on LaFe 10.7 Co 0.8Si 1.5 and La 0.6Pr 0.4Fe 10.7Co 0.8Si 1.5 with Curie temperature values 275 and 295 K, respectively. The temperature dependence of the isothermal magnetic entropy change, ΔS(T), has been calculated for the biphasic system with 0<x<1. The optimum MCE properties, i.e., a ΔS(T) curve with table-like shape, has been found in the temperature interval of 271–287 K for the composite with x = 0.45 at 5 T. The |ΔSM| of the composite come close to a constant value of 9.78 J/(kg K) in a field change of 0–5 T in a wide temperature span over 16 K resulting in large refrigerant capacity value of ∼534.45 J/kg. This composite can be used as the working material in the Ericsson cycle magnetic regenerative refrigerator. Our findings constitute a good starting point to stimulate the search for new composites with enhanced MCE properties near room temperature.

Electrical conductivity of quasi-binary (LiCl-KCl)eut. - CdCl2 melts

The electrical conductivity of (LiCl-KCl)eut. - CdCl2 quasi-binary melts was measured over entire concentrations range and in a wide temperature span. The liquidus line of the system was plotted based on conductivity data. The equivalent conductivity and its activation energy were calculated. The results were interpreted in terms of coexistence and mutual influence of the complexes formed by the Li+ and Cd2+ cations.

Successive magnetic transitions and magnetocaloric effect in Dy3Al2 compound

Magnetic properties and magnetocaloric effect (MCE) of intermetallic Dy3Al2 compound have been investigated systematically. Two successive magnetic transitions, a paramagnetic–ferromagnetic transition at TC = 94 K followed by a spin reorientation around TSR = 69 K, are observed with the variation of temperature. Large permanent magnetic properties at low temperatures, i.e., the coercivity Hci and maximum energy product (BH)max at 5 K are 26.0 kOe and 58.5 MGOe, respectively, suggest Dy3Al2 compound as attractive candidate for low-temperature permanent magnets. For a magnetic field change of 50 kOe, two successive magnetic entropy change (ΔSM) peaks of 5.2 and 12.1 J/kg K are observed around TSR and TC, respectively. These two ΔSM peaks overlap partly, and thus giving rise to a high refrigerant capacity (RC = 360 J/kg at 50 kOe) over a wide temperature span. The universal curve of successive ΔSM peaks is constructed by using a phenomenological procedure. It is found that not only the curves under different magnetic field changes but also the curves around different transitions collapse onto the nearly same universal curve. Our result suggests that the phenomenological construction of universal curve is applicable in materials with successive second-order phase transitions.

Magnetic frustration and magnetocaloric effect in AlFe2−xMnxB2 (x = 0–0.5) ribbons

The crystal structure and magnetic properties of AlFe2−xMnxB2 (x = 0–0.5) compounds were investigated. With increasing Mn content, the magnetic properties of these compounds evolve gradually and the lattice parameters change continuously: Curie temperature (Tc) decreases from 312 K (x = 0) to 220 K (x = 0.5) and a new phase transition from the ferromagnetic state (FM) to spin-glass state (SPG) appears upon cooling. The lattice shrinks in the ab plane while it expands in the c direction. The formation of re-entrant SPG around 50 K was studied via temperature dependent ac and dc magnetization as well as the initial magnetization curves in 5 K. The reason for this glass state is the triangular configuration of magnetic atoms and the antiferromagnetic interactions introduced by Mn substitutions. The Curie transition leads to a conventional magnetocaloric effect (MCE). The Mn doping leads to a decrease in the MCE near room temperature, but there is a plane in entropy change (ΔS) for the x = 0.1 compound under low field which makes these compounds good candidates to produce composites used for magnetic refrigeration application in a wide temperature span.

A semi-empirical correlation for the thermal conductivity of frost

The present work is aimed at advancing an improved correlation for the thermal conductivity of frost. The analysis was conducted based on the weighted geometric mean of the thermal resistances of moist air and ice crystals, thus setting the theoretical background for a dimensionless model for the thermal conductivity as a function of the porosity of the frosted medium. Experimental data obtained elsewhere for a wide wall surface temperature span (from −30 °C to −4 °C) were employed to fit the model, coming up with a semi-empirical correlation for the thermal conductivity of frost valid for porosities ranging from 0.5 to 0.95. Comparisons of the proposed correlation with the experimental data showed that it is able to predict 81% of the data points (153 out of 188) within the 15% thresholds. Comparisons with other correlations available in the open literature are also reported.

Large magnetic entropy change and relative cooling power in the rare earth intermetallic HoCo0.25Ni1.75 compound

Magnetic and magnetocaloric properties of cubic Laves phase rare earth intermetallic HoCo0.25Ni1.75 compound have been investigated. Magnetization measurements show that HoCo0.25Ni1.75 orders ferromagnetically at 22K (TC). The magnetization vs field (M–μ0H) isotherm at 2K shows negligible hysteresis. The isothermal magnetic entropy change (ΔSm) is calculated from the measured M–µ0H data near TC. The maximum value of ΔSm, ΔSmmax, is about −18.9J/kg-K at TC for a field change of 5T with a refrigerant capacity of 572J/kg. The material exhibits large ΔSmmax of −9.4J/kg-K even for a low field change of 2T. Universal master curve is constructed by rescaling ΔSm vs T curves for various fields to confirm the second order nature of the magnetic transition at TC. Large ΔSmmax value, wide temperature span of cooling and high relative cooling power make HoCo0.25Ni1.75 a potential magnetic refrigerant for low temperature applications such as hydrogen liquefaction.

Magnetic phase transitions and large magnetic entropy change with a wide temperature span in HoZn

CsCl-type HoZn undergoes two successive magnetic phase transitions: (i) paramagnetic to ferromagnetic (FM) at TC∼72K and (ii) a spin reorientation (SR) at TSR∼26K. Magnetization and modified Arrott plots indicate that HoZn undergoes a second-order magnetic phase transition around TC. The obtained critical exponents have some small deviations from the mean-field theory, indicating a short range or a local magnetic interaction which is properly related to the coexistence of FM and SR transitions at low temperature. Two successive magnetic transitions in HoZn induce one broad pronounced peak together with a shoulder in the temperature dependence of the magnetic entropy change −ΔSM(T) curves, resulting in a wide temperature range with a large relative cooling power (RCP). For a field change of 0–7T, the maximum value of −ΔSM is 15.2J/kgK around TC with a large RCP value of 1124J/kg. The large reversible magnetocaloric effect (MCE) and RC indicate that HoZn is a good candidate for active magnetic refrigeration.

Table-like magnetocaloric effect of Fe88−xNdxCr8B4 composite materials

The narrow working temperature range due to the sharp magnetic entropy change |ΔSM| peak and large thermal or magnetic hysteresis restricts the practical application of magnetocaloric materials. In this work, the table-like magnetocaloric effect (MCE) was obtained in the multilayer composite of Fe88−xNdxCr8B4 alloys with various Nd substitutions for Fe (x=5, 8, 10, 12, and 15), which were prepared by arc-melting followed by melt-spinning. The substation of Nd was found to enhance the glass-forming ability. For the alloys with Nd substitution from 5 at% to 15 at%, the Curie temperature (TC) ranged from 322K to 350K and the peak value of |ΔSM| remained almost constant, 3.4–3.5J/(kgK) under an applied field of 0–5T. The composite with various Nd contents was prepared by stocking the ribbons layer by layer. The |ΔSM| of the composite approached a nearly constant value of ∼3.2J/(kgK) in a field change of 0–5T in a wide temperature span over 40K, resulting in large refrigerant capacity value of >408J/kg. This |ΔSM| value was much larger than the previous reported Fe-based amorphous composite Fe78−xCexSi4Nb5B12Cu1. This composite can be used as the working material in the Ericsson-cycle magnetic regenerative refrigerator around room temperature.

High-temperature solvothermal synthesis and magnetic properties of nearly monodisperse CdCr2S4 nanocrystals

Magnetic spinel CdCr2S4 nanocrystals have been synthesized using a high-temperature solvothermal method, which exhibit a large reversible magnetic entropy change over a wide temperature span.

Achieving table-like magnetocaloric effect and large refrigerant capacity around room temperature in Fe78−xCexSi4Nb5B12Cu1 (x=0–10) composite materials

Fully amorphous Fe78−xCexSi4Nb5B12Cu1 (x=0, 1, 3, 5 and 10) alloy ribbons were prepared by melt-spinning. With partial substitution of Ce for Fe, the Curie temperature could be tuned in a large temperature range from 465 to 281K and the maximum magnetic entropy change (−ΔSM) for a field change from 0 to 5T decreased from 3.25 to 2.18J/kgK. Two types of composite materials with varied Ce contents were obtained by assembling the ribbons layer by layer or mixing the powders with various Ce contents. A table-like magnetocaloric effect (MCE) was observed in these composites. The −ΔSM of the composites approach a nearly constant value of ~2.0J/kgK for a field change of 0–5T in a wide temperature span over 80K, resulting in large refrigerant capacity values, >370J/kg. These composites can be used as the working material in an active magnetic regenerative refrigerator around room temperature.

Large magnetocaloric effect with a wide working temperature span in the R2CoGa3 (R = Gd, Dy, and Ho) compounds

We investigate magnetic properties and magnetocaloric effects of R2CoGa3 (R = Gd, Dy, and Ho) compounds. It is found that all the compounds are ferromagnetic with the Curie temperatures of TC = 50, 17, and 10 K for R = Gd, Dy, and Ho, respectively. The R2CoGa3 have large magnetic entropy change (ΔS) that arise from the second-order ferromagnetic-to-paramagnetic phase transition. The maximum values of ΔS are found to be −12.6, −10.8, and −13.8 J/kg K with corresponding refrigerant capacity values of 382, 252, and 287 J/kg for a magnetic field change of 0–50 kOe, respectively. The large ΔS values with little or no hysteresis losses as well as wide working temperature spans imply that the R2CoGa3 compounds may serve as promising candidates for magnetic refrigeration.

AMR (Active Magnetic Regenerative) refrigeration for low temperature

This paper reviews AMR (Active Magnetic Regenerative) refrigeration technology for low temperature applications that is a novel cooling method to expand the temperature span of magnetic refrigerator. The key component of the AMR system is a porous magnetic regenerator which allows a heat transfer medium (typically helium gas) to flow through it and therefore obviate intermittently operating an external heat switch. The AMR system alternatingly heats and cools the heat transfer medium by convection when the magneto-caloric effect is created under varying magnetic field. AMR may extend the temperature span for wider range than ADR (Adiabatic Demagnetization Refrigerator) at higher temperatures above 10K because magneto-caloric effects are typically concentrated in a small temperature range in usual magnetic refrigerants. The regenerative concept theoretically enables each magnetic refrigerant to experience a pseudo-Carnot magnetic refrigeration cycle in a wide temperature span if it is properly designed, although adequate thermodynamic matching of strongly temperature-dependent MCE (magneto-caloric effect) of the regenerator material and the heat capacity of fluid flow is often tricky due to inherent characteristics of magnetic materials. This paper covers historical developments, fundamental concepts, key components, applications, and recent research trends of AMR refrigerators for liquid helium or liquid hydrogen temperatures.

Temperature dependence of photosynthesis and thylakoid lipid composition in the red snow algaChlamydomonascf.nivalis(Chlorophyceae)

Here, we report an effect of short acclimation to a wide span of temperatures on photosynthetic electron transfer, lipid and fatty acid composition in the snow alga Chlamydomonas cf. nivalis. The growth and oxygen evolution capacity were low at 2 °C yet progressively enhanced at 10 °C and were significantly higher at temperatures from 5 to 15 °C in comparison with the mesophilic control Chlamydomonas reinhardtii. In search of the molecular mechanisms responsible for the adaptation of photosynthesis to low temperatures, we have found unprecedented high rates of QA to QB electron transfer. The thermodynamics of the process revealed the existence of an increased structural flexibility that we explain with the amino acid changes in the D1 protein combined with the physico-chemical characteristics of the thylakoid membrane composed of > 80% negatively charged phosphatidylglycerol.

Wide temperature span of entropy change in first-order metamagnetic MnCo1−xFexSi

The crystal structure and magnetic properties of MnCoxFe1−xSi (x = 0–0.5) compounds were investigated. With increasing Fe content, the unit cell changes anisotropically and the magnetic property evolves gradually: Curie temperature decreases continuously, the first-order metamagnetic transition from a low-temperature helical antiferromagnetic (AFM) state to a high-temperature ferromagnetic state disappears gradually and then a spin-glass-like state and another AFM state emerge in the low-temperature region. The Curie transition leads to a moderate conventional entropy change. The metamagnetic transition not only yields a larger negative magnetocaloric effect at lower applied fields than in MnCoSi but also produces a very large temperature span (103 K for Δμ0H = 5 T) of ΔS(T), which results in a large refrigerant capacity. These phenomena were explained in terms of crystal structure change and magnetoelastic coupling mechanism. Because of the large isothermal entropy change, the wide working temperature span and the low cost, MnCo1−xFexSi compounds are promising candidates for near room-temperature magnetic refrigeration applications.

Coexistence of large magnetoresistance and magnetocaloric effect in monovalent doped manganite La0.5Ca0.4Li0.1MnO3

An investigation of the structural, transport, magnetic and magnetocaloric properties of polycrystalline La0.5Ca0.4Li0.1MnO3 is presented. A metal–insulatortransition occurs at 162K and shifts to higher temperatures under applied magnetic fields. It shows a large negative magnetoresisance (MR) effect (40% at 3T field) in a wide temperature range of 200K. Magnetic measurements and Arrott plot analysis reveal that the system undergoes a second order paramagnetic–ferromagnetic (PM–FM) phase transition at TC=250K. A large magnetocaloric effect (MCE) occurs in vicinity of the phase transition. The magnetic entropy change |ΔSM|max attains 4.16J/(kgK) under field change ∆H=3T and 2.11J/(kgK) under ∆H=1T. It possesses a large relative cooling power (RCP= 140J/kg) and a relatively wide temperature span (δTFWHM=34K) for ∆H=3T. By using the equation ΔSM(T,H)=−α∫0H[∂(lnρ)/∂T]HdH, we examine the relationship between the magnetic entropy change and the resistivity in the system and find a poor satisfiability of the relationship between them. This can be understood by the significant magnetoresistance originating from the electron tunneling between the FM domains.

Magnetic properties and magnetocaloric effect in the HoNi1−xCuxIn (x=0, 0.1, 0.3, 0.4) intermetallic compounds

The magnetic properties and magnetocaloric effect (MCE) in HoNi1−xCuxIn (x=0, 0.1, 0.3, 0.4) compounds have been investigated. With the substitution of Cu for Ni, the Ho magnetic moment will cant from the c-axis, and form a complicated magnetic structure. These compounds exhibit two successive magnetic transitions with the increase in temperature. The large reversible magnetocaloric effects have been observed in HoNi1−xCuxIn compounds around Tord, with no thermal and magnetic hysteresis loss. The large reversible isothermal magnetic entropy change (−ΔSM) is 20.2J/kgK and the refrigeration capacity (RC) reaches 356.7J/kg for field changes of 5T for HoNi0.7Cu0.3In. Especially, the value of −ΔSM (12.5J/kgK) and the large RC (132J/kg) are observed for field changes of 2T for HoNi0.9Cu0.1In. Additionally, the values of RC are improved to 149J/K for the field changes of 2T due to a wide temperature span for the mix of HoNi0.9Cu0.1In and HoNi0.7Cu0.3In compounds with the mass ratio of 1:1. These compounds with excellent MCE are expected to have effective applications in magnetic refrigeration around 20K.

High-temperature laser absorption diagnostics for CH2O and CH3CHO and their application to shock tube kinetic studies

Laser absorption diagnostic methods were developed for the quantitative measurement of formaldehyde (CH2O) and acetaldehyde (CH3CHO) at high temperatures in shock tube kinetic studies. Investigation of the high-temperature CH2O spectrum has shown that the optimal wavelength for CH2O detection using commercially available lasers is near 2896cm−1. By exploiting the structural difference between the absorption spectra of CH2O and that of broadband interfering species, a two-color (2895.92cm−1 and 2895.60cm−1) interference-free detection scheme for CH2O sensing in a combustion environment was developed. A third color (32601.10cm−1) has also been added to develop a UV/IR detection scheme for combined CH3CHO/CH2O measurements. To implement these schemes, aldehyde cross-sections at all three colors were measured behind reflected shock waves over a wide span of temperatures (600–1800K) and pressures (0.8–3.6atm), with an uncertainty of ±5%, and the diagnostic schemes were validated using two controlled experiments with well-established chemistry. Applications of these diagnostics were also demonstrated in shock tube pyrolysis experiments of 1,3,5-trioxane, CH2O and CH3CHO. The unimolecular decomposition rate of 1,3,5-trioxane was determined over 869–1037K at an average pressure of 2.1atm: kI=3.58×1012 exp (−18,590K/T)s−1, with an overall uncertainty of less than 20%.

Magnetic Phase Transitions and Magnetocaloric Properties of Gd&lt;sub&gt;5&lt;/sub&gt;Si&lt;sub&gt;0.4&lt;/sub&gt;In&lt;sub&gt;3.6&lt;/sub&gt; Compound

The magnetic phase transitions and magnetocaloric properties of Gd5Si0.4In3.6 compound have been investigated. Magnetothermal measurements performed at different conditions reveal that the sample undergoes two magnetic phase transitions. One is a second-order transition from paramagnetic to ferromagnetic state at about 197 K, the other is a first-order transition when the temperature is reduced to 75 K. The magnetocaloric effect around Curie temperature (TC) was calculated in terms of isothermal magnetic entropy change by using Maxwells equation,which remains over a quite wide temperature span of 70 K between the temperature region from160 to 240 K, and thus makes this material attractive for magnetic refrigerator applications.

The magnetocaloric effect of the Gd-based amorphous composite with Gd nanocrystals

The Gd-based amorphous/nanocrystal composite is prepared by controlling the cooling rate and the element ratio. The X-ray diffraction, differential scanning calorimeter and atomic force microscope/magnetic force microscope are used to confirm the composite microstructures from different perspectives. The magnetic test shows the great enhancement of magnetocaloric effect in the metallic glassy composite. The large magnetic refrigerant capacity (RC) up to 103 J. kg-1 is more than double the RC values of the Gd-based bulk metallic glass and pure Gd. The full width at half maximum of the magnetic entropy change (Sm) peak almost spreads over the whole low-temperature range, which is five times wider than that of the pure Gd. The maximum Sm approaches a nearly constant value in a wide temperature span (over 80 K). The super paramagnetic nanoclusters of the composite increase the magnetic refrigerant capacity greatly. In combination with the low magnetic hysteresis and large resistance, the metallic glass composite may be a potential candidate for the ideal Ericsson-cycle magnetic refrigeration.

Cold Adaptation of Tropomyosin

The conformational stability of unphosphorylated and phosphorylated α,α-striated tropomyosins from rabbit and shark (95% identical sequences) has been investigated. Three additional core positions are occupied by atypical amino acids in the protein from shark: Thr179(d), Ser190(a), and Ser211(a). These changes are thought to have further destabilized most, if not all, of the carboxyl-terminal half of the molecule. Heat-induced unfolding of shark tropomyosin (2 mg/mL, 0.1 M salt, pH 7) as monitored by far-UV circular dichroism is biphasic [T(m1) ∼ 33 °C (main), and T(m2) ∼ 54 °C] and takes place over a wider temperature span than that of the mammalian protein. The relationship between ellipticity (and excess heat) and temperature is insensitive to the presence in either tropomyosin of covalently bound phosphate. At ∼10 mg/mL, the minor endotherm of shark tropomyosin is shifted to ∼60 °C and T(m2) - T(m1) is increased to 25 °C; otherwise, the results of calorimetry are in agreement with those of circular dichroism. Analyses of cyanogen bromide fragments by far-UV circular dichroism and intact protein by near-UV circular dichroism (T(m) ∼ 32 °C) show that the most stable sizable portion of shark tropomyosin is located within the amino-terminal half of the molecule. These findings illuminate those regions in tropomyosin where flexibility is critical and show that substitutions predicted to be unfavorable in one temperature regime are desirable in another.