Magnetocaloric effect: From materials research to refrigeration devices

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1222&context=ameslab_manuscripts

Current progress and future challenges in rare-earth-free permanent magnets

Composition dependence of structure, physical and mechanical properties of FeCoNi(MnAl)x high entropy alloys

Photocatalytic overall water splitting by Z-scheme g-C3N4/BiFeO3 heterojunction

Microstructure and magnetic properties of Mn–Al–C alloy powders prepared by ball milling

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn55Al45 based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal e crystal structure. Phase transformations between the e and the L10 (τ) phase are of interest. The e → τ transformation occurred at ~500 °C and the reversed τ → e transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L10 τ-phase and improved the hard magnetic properties. The Curie temperature T
 C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T
 C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially JS. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the e phase or the L10 hard magnetic τ phase.

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C, B, and rare earth elements

A series of the amorphous Gd75-55Al25-5Fe0–40 alloy ribbons were prepared by melt spinning. The structure, magnetic properties and magnetocaloric effect (MCE) of these alloys were investigated. The prepared samples have shown the characteristics of a second-order phase transition with zero hysteresis loss and the T
 c can be tuned by changing the Fe contents. For the different compositions, the magnetic entropy change (−ΔS
 m) for a field change of 0–5 T reached a maximum value of 7.14 J kg−1 K−1 in the Gd70Al20Fe10 alloy near its Curie temperature (T
 c) of 149 K. The non-linear composition dependence of (−ΔS
 m) could be caused by the competitions between Fe-Fe, Fe-Gd and Gd-Gd interactions. The refrigeration capacity (RC) values of these alloys are about 532–780 J/kg under a magnetic field change of 0–5 T. The results indicate that amorphous GdFeAl alloys can be considered as ideal candidates for a magnetic refrigerant in the temperature range of 104–222 K.

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

Facile synthesis of BiFeO3 nanoparticles by modified microwave-assisted hydrothermal method as visible light driven photocatalysts

The magnetic properties and magnetocaloric effects of amorphous and crystalline Gd55Co35Ni10 ribbons are investigated. A main phase with a Ho12Co7-type monoclinic structure (space group P21/c) and a minor phase with a Ho4Co3-type hexagonal structure (space group P63/m) are obtained for crystalline ribbon after annealing. The amorphous ribbons order ferromagnetically and undergo a second-order transition at 192 K. For crystalline Gd55Co35Ni10 ribbons, two magnetic phase transitions occur at 158 and 214 K, respectively. The peak value of −ΔSM under a field change of 0–5 T is 6.5 J/kg K at 192 K for amorphous Gd55Co35Ni10 ribbons. A relatively large magnetic entropy change (∼5.0 J/kg K) under a field change of 0–5 T for the crystalline Gd55Co35Ni10 ribbons is obtained in the temperature interval range of 154–214 K. The large platform of magnetic entropy change and the negligible thermal/magnetic hysteresis loss mean the crystalline Gd55Co35Ni10 compound can satisfy the requirement of the Ericsson-type refrigerator working in the temperature range from 154 K to 214 K.

Magnetic properties and magnetocaloric effects in amorphous and crystalline Gd 55 Co 35 Ni 10 ribbons

The invention belongs to the technical field of metal surface treatment and discloses chemical polishing liquid used for metal and a polishing technology. The polishing liquid includes 60 g/L-90 g/L of nitrate, 60 g/L-90 g/L of hydrochloric acid, 120 ml/L-180 ml/L of medium-strong acid, 20 g/L-50 g/L of a viscosity modifier, 1 g/L-10 g/L of a corrosion inhibitor, 2 g/L-6 g/L of a brightening agent and water. The polishing technology includes the steps that a metal workpiece is subjected to degreasing and activating pretreatment, the obtained metal workpiece is placed in the polishing liquid to be soaked for 2.5 min-4 min at the temperature ranging from 60 DEG C to 100 DEG C for being polished, after polishing is completed, the metal workpiece is subjected to neutralization aftertreatment, and therefore a flat and smooth metal surface can be obtained. The chemical polishing liquid is safe, environment-friendly, high in polishing efficiency, low in cost and suitable for industrial application.

Zhigang Zheng

Papers

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C, B, and rare earth elements

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

Facile synthesis of BiFeO3 nanoparticles by modified microwave-assisted hydrothermal method as visible light driven photocatalysts

Magnetic properties and magnetocaloric effects in amorphous and crystalline Gd 55 Co 35 Ni 10 ribbons

Chemical polishing liquid used for metal and polishing technology