Temperature-induced DSC Study Of The Heterogeneous Phase Transition Behavior Of Metal Ruthenium

Cerium exhibits a variety of allotropicity due to its unique electron structure,its crystal structure exhibits a complex transformation with changing of temperature,pressure and chemical composition.In this paper,two kinds of cerium samples with different microstructure were obtained by vacuum induction melting and vacuum arc melting method.The phase transition behavior in the range of 100 to 600 K was studied by DSC,and the resistance method of phase transition behavior was studied preliminarily.The microstructure of Ce obtained by two methods was studied by optical metallography,SEM and XRD.The results show that the grain of the Ce produced by vacuum induction is coarse and uneven,the average grain size is about 50 ?m,and there is substructure in the grain.The sample prepared by arc melting is uniform and fine,and the average grain size is about 10 ?m.The XRD results show that the two samples are the same,the single phase of fcc structure.The phase transition temperature and phase transition heat of two kinds of Ce were obtained by differential scanning calorimeter(DSC).From the continuous cooling from room temperature to 100 K,??? transition occur at 128 K.From 100 K continuous heating to room temperature,the two transition in samples of ??? and ??? happened at 127 K and 170 K respectively,and two phase transition heat is related to samples,the sample of vacuum induction melting are 0.4,0.82 kJ/mol,and the sample of vacuum arc melting are 0.27 kJ/mol and 0.82 kJ/mol.The results show that if the samples after low temperature treatment,the highest temperature of the sample heated to effects transition behavior during heating from room temperature to the highest temperature.If the samples heat to 500 K after cooling treatment,there is an abnormal endothermic transition in temperature rise.Transition temperature is from 358 to 330 K,and the heat of transition is 0.19 kJ/mol.If the samples heat from room temperature to 600 K,there is an exothermic phase transition,the phase transition temperature is 518.2 K,the phase transition heat is 0.07 kJ/mol,and no phase transition occurs during the cooling process.This study also explores the method of resistance change research in Ce phase transition behavior of the continuous heating and continuous cooling process.In the 300?500 K range,the resistance curve is completely coincided,so that the phase composition is consistent in this process.In the cooling process,the ???,??? and ??? phase transition began at 250 K,100-110 K and 50 K,respectively.In the process of heating,th ???+? phase transition begins at 220 K,and ends at 260 K.The heat of transition is related to the variation of the phase content of samples.And the hysteresis temperature of ??? is 110?160 K.Finally,the change of resistivity with temperature is calculated.