Microstructure and magnetocaloric properties of non-stoichiometric La1.5Fe12.2-xCo0.8Six alloys

In this work, we have investigated the influence of annealing temperature and Si content on the microstructure and magnetocaloric properties of non-stoichiometric La1.5Fe12.2-xCo0.8Six (x = 1.0, 1.1, 1.2, 1.4) alloys. A high content of La( Fe, Co, Si) 13 phase (similar to 80 vol.%) can be achieved after annealing at 1000 degrees C for 24 h. The morphology of the 1: 13 phase evolves from facet to granule accompanying the aggregation of the alpha-Fe particles. The Curie temperature increases with increasing annealing temperature and decreases with the increase of nominal Si content. In addition, large entropy change values of 8.4 J/kg K and 8.0 J/kg K at 2 T are obtained for La1.5Fe11.1Co0.8Si1.1 and La1.5Fe11.1Co0.8Si1.2, respectively. The large entropy change, tunable transition temperature and short-time annealing make the currently studied non-stoichiometric La-Fe-Co-Si a promising magnetic cooling material. (C) 2017 Elsevier B.V. All rights reserved

Impact of interface structure on functionality in hot-pressed La-Fe-Si/Fe magnetocaloric composites

Although the design of composite materials has been proposed as an effective way to improve the mechanical properties and thermal conductivity for magnetocaloric refrigerants, the interface between the constituent phases has not yet been optimized. In the present work, the La-Fe-Si/Fe composites with superior interface conditions have been fabricated by hot pressing. Due to the limited solubility of the Fe element in the La-Fe-Si phase, the introduction of the reinforcing phase (i.e. the Fe phase) only brings out thin diffusion layers that still remain NaZn13 structure. The reinforcing phase with high ductility tends to flow during hot pressing and hence fills in the pores in the composite, leading to a compact structure which is studied by 3D high resolution X-ray tomography and electron probe micro-analyzer. According to the transmission electron microscope analyses, a part of the La-Fe-Si and the Fe phases show a preferred orientation relationship. As a result, the reduced phonon scattering as well as the cohesive bonding at the interfaces favors the thermal conductivity and mechanical stability of the La-Fe-Si/Fe composites. The value of thermal conductivity reaches 7.5 W/m K and compression strength is about 300 MPa in the La0.7Ce0.3Fe11.45Mn0.15Si1.4/13.5%Fe composites. Besides, an isothermal entropy change as large as 15 J/kg K under a magnetic field change of 2 T has been obtained in these magnetocaloric composites, which is comparatively promising for magnetic refrigeration applications. Of particular interest is the integrity of the composite after hydrogenation due to the outstanding mechanical properties of La-Fe-Si/Fe composites. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Enhanced thermal conductivity in off-stoichiometric La-(Fe,Co)-Si magnetocaloric alloys

A dual-phase structure consisting of the NaZn13-type (1: 13) matrix and a secondary (Fe, Co)-Si phase is designed in Fe-rich La-(Fe, Co)-Si compounds. As the extra-Fe doping altered Co content of the 1: 13 phase, the magnetic entropy change keeps to be a relatively large magnitude of 6.7-7.7 J/kgK in 265-290K for 2 T field change. In addition, mechanical properties were apparently improved by second-phase strengthening. The primary significance in this work is that the composition modification in matrix phase brings about a drastic increase in the thermal conductivity, which can be ascribed to the weakening effect of phonon point-defect-scattering. On the basis of Neilsen two-phase system model, the electrical conductivity of dispersed (Fe, Co)-Si phase plays very limited contribution to the enhanced thermal transport properties in composites. Our results demonstrate that the combined merits of high thermal conductivity, improved mechanical properties, large magnetic entropy change, and tunable transition temperature can be simultaneously realized in Fe-rich La-(Fe, Co)-Si composite materials. (C) 2015 AIP Publishing LLC

The influence of Ce on microstructure, phase formation and magnetocaloric properties in off-stoichiometric La2-xCex Fe11Si2 alloys

The influence of Ce on microstructure, phase formation and magnetocaloric properties in off-stoichiometric La2-xCex Fe11Si2 alloy

The influence of Ce on microstructure, phase formation and magnetocaloric properties in off-stoichiometric La2-xCex Fe11Si2 alloys

Microstructure and magnetocaloric properties have been investigated in a series of off-stoichiometric La2-xCexFe11Si2 (x = 0.2-1.2) magnetic refrigeration alloys. A complex multi-phase structure containing (La,Ce)(1)(Fe,Si)(13), La5Si3, (La,Ce)(2)(Fe,Si)(17), La1Fe1Si1\ and alpha-Fe phases was observed for Ce-doping alloys. Entropy change can be enhanced by the substitution of Ce for La, but higher Ce content (x > 0.8) leads to the decrease of magnetocaloric effect owing to the formation of (La,Ce)(2)(Fe,Si)(17) precipitates. The optimized composition of La1.2Ce0.8Fe11Si2 alloy exhibits a maximum entropy change of 21.8 J/kgK in 2 T, and a large volume change of 1.6% on the strong magnetoelastic coupled transition

LaFe11.6Si1.4Hy/Sn magnetocaloric composites by hot pressing

We report on the microstructure, mechanical properties, magnetocaloric effect and thermal transfer performance of LaFe11.6Si1.4Hy/Sn composites prepared by hot pressing. The liquid Sn forms a homogenous continuous matrix but does not react with LaFe11.6Si1.4Hy grains during compacting. By controlling pressing temperature, a set of composites combined high entropy change values of 10-13 J/kg K at 2 T with high thermal conductivity of about 7 W/mK has been obtained in a magnetostructural transition range of 1-17 degrees C. (C) 2016 Elsevier Ltd. All rights reserved

The influence of Ce on microstructure, phase formation and magnetocaloric properties in off-stoichiometric La2-xCex Fe11Si2 alloys

Microstructure and magnetocaloric properties have been investigated in a series of off-stoichiometric La2-xCexFe11Si2 (x = 0.2-1.2) magnetic refrigeration alloys. A complex multi-phase structure containing (La,Ce)(1)(Fe,Si)(13), La5Si3, (La,Ce)(2)(Fe,Si)(17), La1Fe1Si1\ and alpha-Fe phases was observed for Ce-doping alloys. Entropy change can be enhanced by the substitution of Ce for La, but higher Ce content (x > 0.8) leads to the decrease of magnetocaloric effect owing to the formation of (La,Ce)(2)(Fe,Si)(17) precipitates. The optimized composition of La1.2Ce0.8Fe11Si2 alloy exhibits a maximum entropy change of 21.8 J/kgK in 2 T, and a large volume change of 1.6% on the strong magnetoelastic coupled transition

Microstructure and Magnetocaloric Properties of LaFe11.8-xCoxSi1.2 Strip-Cast Flakes

Flake-like LaFe11.8-xCoxSi1.2 alloys were successfully prepared in kilogram quantities by a strip-casting technique. It is found that a large amount of NaZn13-type La(Fe,Co,Si)(13) phase (above 95 vol.%) can form in LaFe11Co0.8Si1.2 strip-cast flakes annealed at 1323 K for 24 h. The resulting alloy exhibits a maximum entropy change of 8.4 J/kg K and negligible magnetic hysteresis under a field change of 0-2 T. In addition, the Curie temperature can be accurately tuned by adjusting the concentration ratio of the Fe/Co. Our results indicate that the strip casting is an effective way to produce high-performance La(Fe,Co,Si)(13) materials for room-temperature magnetic cooling

Microfluidic Preconcentration Chip with Self-Assembled Chemical Modified Surface for Trace Carbonyl Compounds Detection

Carbonyl compounds in water sources are typical characteristic pollutants, which are important indicators in the health risk assessment of water quality. Commonly used analytical chemistry methods face issues such as complex operations, low sensitivity, and long analysis times. Here, we report a silicon microfluidic device based on click chemical surface modification that was engineered to achieve rapid, convenient and efficient capture of trace level carbonyl compounds in liquid solvent. The micro pillar arrays of the chip and microfluidic channels were designed under the basis of finite element (FEM) analysis and fabricated by the microelectromechanical systems (MEMS) technique. The surface of the micropillars was sputtered with precious metal silver and functionalized with the organic substance amino-oxy dodecane thiol (ADT) by self-assembly for capturing trace carbonyl compounds. The detection of ppb level fluorescent carbonyl compounds demonstrates that the strategy proposed in this work shows great potential for rapid water quality testing and for other samples with trace carbonyl compounds

High-performance solid-state cooling materials: Balancing magnetocaloric and non-magnetic properties in dual phase La-Fe-Si

La(Fe,Si)(13)H-based materials are considered to be one of the most promising room-temperature magnetic refrigerants. The intrinsic brittleness and relatively low thermal conductivity in La-Fe-Si-H alloys, however, have severely hindered its preparation, shaping and application. To solve this long-standing problem, in this work we propose a novel approach to fabricate stable La-Fe-Si-H blocks and plates by adding extra alpha-Fe as a reinforcing phase to enhance mechanical integrity. Much better bending strength compared to that in the stoichiometric composition has been observed in our dual phase La-Fe-Si-H magnetic refrigerants. Such novel Fe-rich plates can be exposed to 10(5) magnetic field cycles without losing mechanical integrity. In addition, a large and reproducible Delta T-ad of 5.4 K in 1.93 T and a thermal conductivity of 6 W/mK at room temperature have been obtained. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved