Magnetocaloric Properties Of ?La,R??Fe,M,Si?₁₃?H,C?_x Their Powder Bonded Composite And Hot Press Alloys

Magnetic refrigeration technology shows promising features for further application, since it's an energy-conserving and environment-protective, non-toxic and steady technology. Recently, magnetic refrigerants for room temperature magnetic cooling has attracted much attention. Besides metal Gd, the alternative is the La(FexSi1-x)13 based alloys with NaZn13-type cubic structure. In this thesis, by introducing interstitial element H or C. bonding and hot-pressing technology, the magnetic cooling refrigerant were obtained, which shows broadened refrigeration range and enhanced mechanical properties. The structural, magnetocaloric and mechanical properties were studied using XRD. VSM. SEM and XHY-type technology.The mother alloys La0.9Ce0.1Fe11.7-xMnxSi1.3 with x= 0.21 and 0.25 were synthesized by high-frequency induction furnace, the obtained samples were hydrogenated and epoxy resin bonded, then, the final composites were achieved. Studies show that the Curie temperatures can be adjusted by varying Mn concentration; the bonded composites show broadened working temperature range and the maximum magnetic entropy change of 6.4 J/(kg·K) is larger than that of Gd, the maximum adiabatic temperature change is about 1.8 K. Due to the FWHM (full width at half maximum) broadening of the composites, the RCP(S) (relative cooling power) enhanced and the value is about 105 J/kg.The mother alloy La0.8Ce0.2Fe11.47Mn0.23Si1.3. which was synthesized by using high frequency induction furnace, was mechanically ground. The obtained powder were loaded into a O20 mm mould, then the final sample was achieved after being hot pressed at 750? and 30 MPa for 20 mins. Finally, the hot pressed sample was fully hydrogenated at certain condition. Structure and phase analysis shows that the hot pressed sample contains relatively large amount of a-Fe impurity phase and the porosity is about 24.83%. Magnetocaloric properties were investigated by employing VSM magnetometer:the Curie temperature slightly increased after hot pressing, and then, strongly increased to around room temperature after hydrogenation:the isothermal magnetic entropy change slightly decreases after hot pressing, the isothermal magnetic entropy change is about 9.49 J/(kg·K) and the RCP(S) is about 97.75 J/kg after hydrogenation. The maximum adiabatic temperature change was measured by using the home-made Model XHY magnetocaloric effect equipment and the value is about 2.4 K, the compressive stress-strain data were measured by employing dynamic mechanical analyzer, the maximum compressive strength is about 78.6 MPa.LaFe11.2Co0.7Si1.1Cx(x= 0,0.05,0.10,0.15 and 0.20) series alloys were synthesized by using high frequency induction furnace. The heat treatment effects on the structure and magnetocaloric properties were investigated. Studies show that:all samples crystallize in NaZn13-type cubic structure with a minor amount of a-Fe impurity phase; the longer the sintering duration, the less the amount of the impurity phase and the larger of the lattice parameter; the lattice parameter increases with increasing C content. Sample sintered for 144 hrs show a maximum isothermal magnetic entropy change of 6.56 J/(kg·K). While, with 72 hrs sintering, the maximum isothermal magnetic entropy change reduced to 97.4%. the RCP(S) is about 110.72 J/kg; as for the samples with 72 hrs sintering, when x= 0.2, the Curie temperature linearly increase with increasing C concentration, the rate is about 12 K per 1 at%; Sample with x-0.05 show maximum adiabatic temperature change, the value is about 6.39J/(kg·K), indicates that the sintering duration can be reduced by introducing interstitial element C.