Vertical section phase diagrams of La−Fe−B ternary system

The vertical sections of the La−Fe−B system were investigated using electron probe microanalysis and differential thermal analysis.Based on the microstructures and phase compositions of the as-cast and equilibrium alloys,together with their heat flow−temperature curves,phase diagrams for three vertical sections were drawn:La_(x)Fe_(82)B_(y)(x+y=18),La_(x)Fe_(70)B_(y)(x+y=30)and La_(x)Fe_(53)B_(y)(x+y=47),where x and y represent mass fraction of La and B,respectively,%.Additionally,according to the phase diagrams,the compound La2Fe14B was identified as a stable phase at high temperatures.It was found to be stable between 926.2 and 792.6℃;at low temperatures,however,it decomposed into α-La,α-Fe and LaFe_(4)B_(4),according to the reaction La_(2)Fe_(14)B→α-Fe+α-La+LaFe_(4)B_(4).

Realizing remarkable sodium storage performance of a Sn-based anode material with an oxide-alloy intergrowth structure

As a promising anode for sodium-ion batteries(SIBs),the performance of SnO_(2) is still limited by inferior electronic conductivity and large volume change.To address this issue,herein,the intergrowth structured SnO_(2)/CoSn_(2)@C nanocomposite has been fabricated by a two-step process combining hydrothermal synthesis with carbon coating.

Structure and electrochemical properties of La_(1-x)Mg_(x)Ni_(2.8)Co_(0.4)Mn_(0.1)Al_(0.2)(x=0.25,0.30,0.33)hydrogen storage alloys

La_(1-x)Mg_(x)Ni_(2.8)Co_(0.4)Mn_(0.1)Al_(0.2)(x=0.25,0.30,0.33)alloys were prepared by induction melting followed by annealing treatments(1,073 K)for 10 h.The structure and electrochemical properties of La_(1-x)Mg_(x)Ni_(2.8)Co_(0.4)Mn_(0.1)Al_(0.2)(x=0.25,0.30,0.33)hydrogen storage alloys were investigated by X-ray powder diffraction(XRD)and electrochemical measurement methods.XRD results reveal that all the alloys mainly consist of LaNi5 phase and La2 Ni7 phase.The electrochemical experiments demonstrate that the substitution of Mg for La can increase the maximum discharge capacity and improve the high-rate dischargeability of the alloy electrodes.The high-rate dischargeability of alloy electrodes increases from 39.4%to63.1%with x increasing from 0.25 to 0.33 at discharge current density of 1,500 mA·g^(-1).However,the addition of Mg reduces the cycling stability of the electrodes.Furthermore,the results obtained from the electrochemical impedance spectroscopy and linear polarization measurements show that the hydriding kinetics on the hydrogen storage alloys are controlled by charge-transfer step.

Experimental study of phase equilibria on Co-Fe-rich side of Co-Al-Fe system

Despite various studies on Co-Al-Fe ternary system, its phase equilibria are still in doubt. Phase equilibria, magnetic transition and bcc_A2/bcc_B2 order-disorder transformation at the Co-Fe-rich side of the Co-Al-Fe alloys were carefully investigated by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calo-rimetry. The equilibrium phases and their compositions were determined by 18 alloy samples annealed at 900, 1000, 1100 and 1200℃ for 528, 336, 168 and 96h, respectively, followed by quenching. However, by adopting the above traditional method, bcc_A2 and fcc_A1 phases are difficult to be distinguished through XRD analysis at room temperature due to the martensitic transformation of fcc_A1 phase during quenching. For this reason, high-temperature insitu XRD technique was utilized to correctly establish the phase relationships among bcc_A2, bcc_B2 and fcc_A1 phases. The phase transformation between bcc_A2 and B2 phases was determined to be second order instead of first order at temperatures higher than 900℃. The equilibrium phases and compositions were further confirmed by fabricating 16 diffusion couples together with EPMA. Meanwhile, using three-dimensional differential scanning calorimetry method, bcc_A2/B2 and ferro-/paramagnetic transi-tions were determined with high accuracy.