Preparation And Magnetocaloric Effects Of Fe-based Amorphous Ribbons

Magnetic refrigeration is becoming increasingly attractive due to its high-efficiency,energy-conservation, and environment-friendliness compared with the traditional gascompression refrigeration, which can help reaching the goal of low carbon economyadvocated in the modern world and has broad application prospects. Magnetic refrigerationtechnology, using the magnetocaloric effect of materials, So far, magnetic refrigerationtechnology has very wide range of applications at low temperature. With the development oftechnology, magnetic refrigeration develops gradually to the high temperature. Magneticrefrigeration material is the key to the room temperature magnetic refrigeration technology.The amorphous alloys magnetic refrigeration materials are suitable for Ericsson refrigerationcycle because of large magnetic order transition temperature region and large refrigerantcapacity, and which recently become the competitive candidate materials for magneticrefrigeration. In this thesis, the preparation, magnetic properties and magnetocaloric effect ofFe-based amorphous alloys (Fe80-xMxB10Zr9Cu1) have been studied. The influence of dopingsome transition metal and adding a small amount of rare-earth elements on the structure,magnetic properties and magnetocaloric effect of Fe80-xMxB10Zr9Cu1amorphous alloys werestudied.Fe80-xMxB10Zr9Cu1(M=Ni, Ta) amorphous ribbons were prepared by melt-spinning; thelow content of Fe was benefit for the formation of the amorphous structure. The effects of Niand Ta doping on the crystallization temperature was small, the crystallization temperature ofthis series of alloys were considerably higher than the Curie temperature, which means thisseries of materials have a good thermal stability. These alloys were ferromagnetic under theCurie temperature, and above the Curie temperature they were paramagnetic, which meansthe ferromagnetic-paramagnetic transition was of second-order without thermal/magnetichysteresis. With the increase of Ni content, the Curie temperature rised and the maximumisothermal magnetic entropy change was decreased. Under an applied filed change from0to5T, the values of (-ΔSM) for Fe80-xNixB10Zr9Cu1(x=0,3,5,7) alloys were3.3,3.1,2.6and3.0J·kg-1·K-1, respectively. With the increase of Ta content, both the Curie temperature and the maximum isothermal magnetic entropy change were decreased. The TCwas in roomtemperature range, it was very suitable for magnetic refrigeration substance working in thevicinity of room temperature. Under an applied filed change from0to5T, the values of (-ΔSM)for Fe80-xTaxB10Zr9Cu1(x=0,3,5,7) alloys were3.3,2.8,2.1and2.0J·kg-1·K-1, respectively.Fe80-xMxB10Zr9Cu1(M=Ni, Ta) amorphous alloys showed that they had very largerefrigeration capacity (RC), the maximum value of RC for Fe73Ni7B10Zr9Cu1amorphousalloys was357J·kg-1, the refrigeration capacity was increased with the increase of Ni content,but the increase of Ta content reduced the value of RC.Adding the rare-earth element was possible to increase the magnetocaloric effect byenhancing the atomic magnetic moment of the alloy. The study of adding the heavy rare-earthelement Gd and light rare-earth element Pr in Fe75Ta5B10Zr9Cu1, which prepared bymelt-spinning method, the results showed that they had very large refrigerant capacity (RC)and good magnetocaloric effect. The crystallization temperature had no obvious change withthe increase of Gd and Pr content, which means that this series of materials had good thermalstability. Fe75-xTa5B10Zr9Cu1Rx（R=Gd、Pr）alloys were ferromagnetic under the Curietemperature, and above the Curie temperature they were paramagnetic, which means thealloys had the second-order transition without thermal/magnetic hysteresis. Adding a smallamount of Gd (2%) increased the magnetization, thus the Curie temperature was graduallyrise. But with further increasing Gd content (2%), the magnetization of the alloy decreasedsharply, the isothermal magnetic entropy change was also decreased at the same time. Underan applied field change from0to5T, the maximum values of (-ΔSM) were2.1,2.2and1.2J·kg-1·K-1for Fe75-xTa5B10Zr9Cu1Gdxamorphous ribbons with x=0,2and7, respectively.Moreover, adding a small amount of Gd increased the Curie temperature of the alloy slightly.As the Pr content continued to increase, the TCdecreased. When the Pr content was2%, themagnetization of the alloy increased slightly, but the magnetic entropy change had no obviouschange, which kept in2.1J·kg-1·K-1under an applied field change from0to5T. When the Prcontent increased up to7%, the magnetization and the magnetic entropy change were bothdecreased. The heavy rare-earth element Gd decreased the refrigeration capacity of alloys gradually,the values of (-ΔSM) were235,220and105J·kg-1for Fe75-xTa5B10Zr9Cu1Gdx(x=0,2,7),respectively, under an applied field change from0to5T. A small amount of Pr doping wasgreatly increased the refrigeration capacity of Fe75-xTa5B10Zr9Cu1Prxalloys, the value of RCincreased from235to282J·kg-1, but the refrigeration capacity decreased slightly with theincrease of Pr content.