In order to improve the magnetocaloric effects (MCEs), the partial substitution of Ce for La in the La(Fe/sub 0.86/Si/sub 0.14/)/sub 13/ has been examined. The MCEs in the La/sub 0.7/Ce/sub ...0.3/(F/sub 0.86/Si/sub 0.14/)/sub 13/ are much larger than those in the La(Fe/sub 0.86/Si/sub 0.14/)/sub 13/. The hysteresis loss due to the itinerant-electron metamagnetic transition of the La/sub 0.7/Ce/sub 0.3/(Fe/sub 0.86/Si/sub 0.14/)/sub 13/ is smaller than that of La(Fe/sub 0.88/Si/sub 0.12/)/sub 13/, though their MCEs are almost the same. Similar results are obtained in the case of z<0.3. Accordingly, La/sub 1-z/Ce/sub z/(Fe/sub 0.86/Si/sub 0.14/)/sub 13/ compounds are useful for high-performance magnetic refrigerants.
The adiabatic temperature change Δ
T
ad due to a change of the external magnetic field (the magnetocaloric effect) for a perovskite-type La
0.6Ca
0.4MnO
3 sample has been measured directly and ...indirectly (from the entropy change) and the results are compared. From the indirect method, involving magnetic and calorimetric measurements, a maximum temperature change of approximately 0.54
K can be expected with a field change of 0.7
T. Considering experimental errors, this is in fairly good agreement with the direct temperature measurement, where a maximum temperature change of about 0.5
K was observed with a corresponding change of the applied field. The experimental results are in accordance with theoretical estimates obtained from a mean field theory.
We measured the magnetization (M) and heat capacity (C p ) in the perovskite ferroelectric BaTiO 3 wherein 40 % Ba site is replaced by magnetic Eu 2+ (4f 7 , S = 7/2) ions. The temperature dependence ...of M and C p suggest that Ba 0.6 Eu 0.4 TiO 3 - is paramagnetic at and above 2.5 K. Isothermal magnetization and heat capacity data were used to estimate isothermal magnetic entropy change (ΔT ad ) and adiabatic temperature change. It is found that this magneto-ferroelectric compound exhibits and adiabatic temperature change. It is found that this magneto-ferroelectric compound exhibits 16.2 K as the field is changed from 0 T to 7 T, which suggests that this compound could be a potential candidate for cryogenic magnetic cooling.
Bulk nanocrystalline gadolinium metals have been consolidated from gadolinium nanoparticles using spark plasma sintering. Transmission electron microscopy observation shows that SPS technique can ...effectively restrain the grain growth in bulk Gd metals. The adiabatic temperature changes of the as-consolidated and coarse-grained gadolinium metals were measured directly using a homemade magnetocaloric effect (MCE) measuring apparatus with a magnetic-field change of 1.5 T. With the decrease of Gd grains from micrometre to nanometre range, the adiabatic temperature change drops surprisingly from 3.5 to 1.1 K, and their resultant adiabatic temperature change uniformly peaks at 298, 296 and 288 K, respectively, corresponding to the magnetic transition temperature of the three samples. The Curie temperature T
C
of the nanocrystalline Gd shifts by more than 10 K below that of coarse-grained Gd sample. However, the value of adiabatic temperature change of the as-consolidated sample at low temperature exhibits a more constant tendency compared with the coarse-grained sample. On the other hand, nanostructures do not change the magnetic transition and still preserve the second-order magnetic transition in the bulk nanocrystalline Gd metals. All results indicate the remarkable influence of the nanostructure on the MCEs of Gd due to the finite size effect.
A four-function principle was proposed for the optimization design of green high performance massive concrete (GHPMC) based on the theory of value engineering and the adiabatic temperature change ...control. A set of concrete formulas were designed according to the orthogonal experiment. The experimental results were analyzed by applying the variance analysis method to find out the effects of influential factors and determine the optimum mixture formula. In addition, the four-function principle was successfully applied to optimize the mixture formula in field massive concrete engineering. The practical results show the adiabatic temperature change of massive concrete could be efficiently controlled, and the excellent durability, good workability and high compressive strength could be achieved.PUBLICATION ABSTRACT
Single phase perovskite-type La
0.75Sr
x
Ca
0.25−
x
MnO
3 powder and ceramic were prepared by the sol–gel technique. The large magnetocaloric effects near room temperature in this type of materials ...were measured by a sensitive calorimetric system. The results indicated that the maximum adiabatic temperature changes of La
0.75Sr
0.075Ca
0.175MnO
3 and La
0.75Sr
0.1Ca
0.15MnO
3 produced by a magnetic field change of 1.4 Tesla are 0.78 K and 0.49 K, respectively.
Multiyear observations from the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) ...satellite are used to determine the daytime variations of ozone and atomic oxygen in the upper mesosphere. Both O3 and O vary during the daylight hours in response to tidal variations in temperature and winds. Ozone around 85 km responds most strongly to the very large O variations and its variations are in phase with those of O and T. At 97 km, where the O variations are weaker, ozone responds more strongly to the temperature and its variations are out of phase with those of O and T.
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•A phase-field model presented that provides martensitic transformation bands in CuAlBe SMA.•Reverse transformation indices an elastocaloric effect (eCE) of at least −10 K.•The ...elastocaloric effects has a good coefficient of performance (COP) of 9.04.•Higher loading rate or applied stress induce higher eCE up to a certain limit.•Functional fatigue decreases the eCE from −11.32 K to −11.04 K and COP from 9.04 to 8.03.
The reversible stress-induced phase transformation in shape memory alloys (SMAs) is a dissipative process during which heat is absorbed or released. The inherent temperature variations inside the material has an elastocaloric effect (eCE) with appealing applications in solid-state cooling technology such as compact and efficient on-board refrigeration system for eletronic devices. In this manuscript, we conduct the first study of eCE of CuAlBe SMAs utilizing phase-field modeling. For an applied stress of 500 MPa, the results for polycrystalline Cu-Al11-2Be (at. %) show a minimum adiabatic unloading temperature change of −10 K over a pseudoelastic window of 40 K. In the absence of plastic deformation, the material demonstrates good reproducibility of the eCE over a few loading–unloading cycles. The presence of plastic deformation is found to cause functional fatigue that deteriorates the cooling capacity; however, the coefficient of performance only decreases from 9.04 to 8.03, which is still a very good value. These results place CuAlBe as a frontrunner SMA for solid-state cooling compared to the expensive NiTi.
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