Magneticaloric Effect And Phase Structure Of La(Fe, Si)₁₃ And (Nd_1-xCe_x)₂Fe₁₇ Compounds

Magnetocaloric effect had been discovered since 1881,People had been thinking of Magnetic refrigerant as higher efficiency,environmental friendship technology.Therefore people had been paying attention to it.Investigation and application of Low temperature magnetic refrigerant is better maturity past 80 years'development. But magnetic refrigerant technology at room temperature is not perfect at many aspects,Magnetic refrigeration material is one of it.Last years,Scholar investigated a lot of magnetic refrigeration material in the world,Such as La1-xBaxMnO3 with perovskite-like structure,Gd5(SixGe1-x)4 alloys,a series of Mn alloys,La(FeM)13 compounds,2:17 series compounds,thulium and rare earth compound,etc.But as far as making magnetic refrigeration at room temperature go into market.Materials offer lower magnetocaloric effect or Curie temperature of materials is not about room temperature,etc.In this thesis,magnetic refrigerants,especially room temperature magnetic refrigerants are comprehendsively reviewed. It is primary to investigate magnetocaloric effect for different produce method on LaFe11.9-xCoxSi1.1B0.25(X=0.7,0.8) alloys,Gd-Si-Ge-Fe .and Nd-Ce-Fe alloys.Investigated result shows:Different produce method on magnetocaloric effects of LaFe11.9-xCoxSi1.1B0.25 ,Investigated result shows:Under the same heat treatment condition,By XRD analysis show:Theα-Fe phase of as-cast samples is less than melt spun LaFe11.9-xCoxSi1.1B0.25 sample.By scanning electron microscopy analysis show:The as-cast samples have more NaZn13 than melt spinning.By magnetic measurement analysis shows:The magnetocaloric effect of as-cast simples is superior to melt spun. The Curie temperature Tc shifts to high value with the amount of Co added in the alloys and the measured adiabatic temperature change ,magnetic entropy change decreases.Under the sample conditions,The magnetocaloric effect decreases with wheel speed increased.This shows:The magnetocaloric effect decreases with cooling speed increased.Furthermore,The measured adiabatic temperature of powder metallurgy decreases with milling times increasing.The adiabatic temperature change of annealed samples is inferior to non-annealed.But the magnetocaloric effect of powder metallurgy is inferior to as-cast. By XRD analysis shows:α-Fe phase(impurity phase) of LaFe11.2Co0.7Si1.1B0.25 alloys firstly decreased ,then it increased with annealing time extended.By SEM analysis show:The as-cast LaFe11.2Co0.7Si1.1B0.25 alloys mostly consisted of Fe rich phase and La rich phase. The major phase La:(Fe,Co,Si) close with 1:13 after annealed for 6h.That is to say NaZn13.By magnetic measurements are as follows :The adiabatic temperature change fistly increases,then it decreases with increasing anneal times.When it annealed for 72h,The Curie temperature increases by 10℃.People pay attention to 2:17 compounds due to low cost,no poison gas,tunable Curie temperature, large magnetocaloric effects.This chapter are as follows:Theα-Fe phase of (Nd1-xCex)Fe17 decrease after annealed,consequently the magnetocaloric effect increase.Simultaneously,Theα-Fe phase,Fe2Y phase,Fe7Nd phase decrease with Nd increasing.The Curie temperature is proportional to x.Furthermore,By magnetic measurements are as follows:The magnetocaloric effects of Gd-Si-Ge alloys are sensitive to purity.The Curie temperature of Gd-Si-Ge alloys increase with Fe increasing.The magnetocaloric effect of Gd-Si-Ge alloys are not increasing after annealed.