Papers by Author: Jie Zhao

Abstract: Multi-elements doped LaCoO₃-based mixed conductors La_0.7Sr_0.1Ca_0.1Co_0.8Fe_0.2O_2.9 (LSCCF-112) and La_0.7Sr_0.2Ca_0.1Co_0.7Fe_0.3O_2.85 (LSCCF-213) were synthesized by conventional solid state reaction (CSSR). The forming process, microstructure and crystal structure of the prepared samples were analyzed by TG/DTA, SEM and XRD. The mixed conductivities of the samples were measured using DC four-terminal method in 150-950 °C. Thermal expansion coefficients (TEC) of the samples were tested in 20-950°C. LSCCF-112 and LSCCF-213 exhibit pure perovskite phase and porous structure after sintered at 1200 °C. The average TECs of LSCCF-112 and LSCCF-213 are 18.17×10^-6 K^-1 and 17.52×10^-6 K^-1 respectively. The mixed conductivity of the samples shows semiconducting behavior up to 700-750°C and then decreases as the temperature is further raised. At intermediate temperature (IT), the conductivity values of the samples are both much higher than 100 S/cm.

Abstract: CaS:Eu²⁺ phosphors were prepared by two steps method at a relatively low temperature (1050°C) using NH₄Cl as a flux. The influences of NH₄Cl flux concentrations on the crystal structure, morphology and photoluminescent properties of CaS:Eu²⁺ phosphors were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL), respectively. XRD analysis shows that when the raw materials added with the NH₄Cl flux, the crystal structure was not changed .The SEM images indicate that increase of the NH₄Cl flux enlarged the grain size of the phosphor particles. The luminescence intensity of CaS:Eu²⁺ was enhanced with adding NH₄Cl flux and up to the maximum emission intensity when the addition of NH₄Cl flux is 1wt%.

Abstract: Sr, Ca and Fe doped cathode materials Ln_0.7Sr_0.2Ca_0.1Co_0.7Fe_0.3O_2.85 (LnSCCF, Ln=La, Pr and Nd; abbreviated as L-72173, P-72173 and N-72173) were synthesized by microwave sintering (MWS) techniques. The formation process, phase structure and composition were characterized using TG/DTA, XRD and EDS. The thermal expansion behavior of the samples was analyzed in the range of 20-950 °C by thermal dilatometer. The electrical conductivity of the samples was measured with DC four-terminal method from 25 to 900 °C. The X-ray diffraction shows that the samples exhibit a single phase with rhombohedral or cubic perovskite structure after sintered at 1200 °C for 20 min. The electrical conductivity of the samples increases with temperature up to a maximum, and then decreases gradually at higher temperature owing to the creation of oxygen vacancies. The small polaron hopping is regarded as the conducting mechanism (T 550 °C). L-72173 has higher mixed conductivity ( >300 S·cm^-1) in 550-800 °C. The average TECs of L-72173, P-72173 and N-72173 are 1.389× 10^-5 K^-1, 1.417 × 10^-5 K^-1 and 1.416 × 10^-5 K^-1 in the range of 25-800 °C, respectively. They are thermally matched to the GDC better than the YSZ and SDC.

Abstract: Continuous cooling transformation (CCT) curves of deformed austenite (A) of Nb-Ti microalloying high strength steel were measured using Gleeble-3800 thermo-mechanical simulator, and corresponding transformation and structure were analyzed, and the effects of cooling rate on the tested steels mechanical property were studied. The resultes showed that the Ar₃ transformation point decreased with increasing cooling rate after hot-rolling. The morphology of ferrite (F) grains changed from polygonal to lath, and the pearlite (P) colonies became more fine with increasing cooling rate. The quantity of ferrite and pearlite decreased, and the quantity of bainite (B) and martensite (M) increased. Then the hardness of Nb-Ti micro-alloyed steel is increased along with the increasing cooling rate, which may owing to the reasons that the hardness of ferrite and pearlite is far smaller than that of bainite and martensite, and the grain refinement causes the hardness increasing.

Abstract: In order to accelerate the commercialization of SOFCs technology, the key is the development of high performance cathode materials operated at intermediate temperature. Sr and Cu doped rare earth oxide La_1-xSr_xFe_1-yCu_.yO_3-δ (x=0.1, 0.3 ; y=0.1, 0.2, denoted as LSFCu-11, LSFCu-31 and LSFCu-32 ) were synthesized by solid state reaction method (SSR). The formation process, phase structure and microstructure of the synthesized samples were characterized using TG/DSC, XRD and SEM. The thermal expansion coefficients (TEC) of the samples were analyzed by thermal dilatometry. The electrical conductivities of the samples were measured with DC four-terminal method from 25 to 950 °C. The results indicate that the samples exhibit a single phase with orthorhombic and hexagonal perovskite structure after sintered at 1200 °C for 4h. The electrical conductivity of the samples increases with temperature up to a maximum value, and then decreases gradually. The small polaron hopping is regarded as the conducting mechanism for synthesized samples at T 550 °C. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. LSFCu-32 has higher mixed conductivity (> 100 S·cm^-1) at intermediate temperature and can meet the demand of cathode material for IT-SOFC. In addition, the average TECs of LSFCu-11, LSFCu-31 and LSFCu-32 are 1.22 × 10^-6 K^-1 , 1.30 × 10^-6 K^-1 and 1.34 × 10^-6 K^-1 respectively.

Abstract: The transformation behavior of Nb-V micro-alloyed low carbon steel during continuous cooling was studied through thermomechanical simulator and metallographic analysis. The results show that the dynamic CCT diagrams shift to the left and upper compared with the static ones, the begin temperature of γ→α transition is gradually lower with the increase of cooling rate. The high temperature deformation decreases Ferrite transition zone. When the cooling rate is lower, the deformation improves Bainite transition; when the cooling rate is higher, the deformation inhibition Bainite transition.

Abstract: Silicon/carbon anode materials of different proportions for lithium ion battery were prepared by high energy ball milling. The composites were characterized using X-ray diffraction (XRD), and scanning electron microscope (SEM). The electrochemical performance of the composites was tested by means of galvanostatic testing system. The results indicated that the initial reversible capacity reached to 2162 mAh•g^-1, which was much larger than the theoretical capacity of carbon negative materials at the ratio of 6:4 (Si: C). The capacity maintained to 1042 mAh•g^-1 after 50 cycles. High capacity and good cycle property of the Si/C composites revealed that they were potential to take the place of the traditional carbon anode materials.

Abstract: To achieve reasonable rolling technology of the novel Nb-V composite microalloyed steel, the continuous cooling transformation (CCT) curve was established by thermal simulation experiment. Microstructure and microhardness at different cooling rates were characterized using an optical microscope (OM) and microhardness tester. The results indicate that the critical quenching speed of Nb-V microalloyed steel is about 23 °C/s. The start and finishing temperatures of phase transformation decreased with the rise of cooling rate. Widmannstatten (W) structure appears at lower cooling rate interval. Microstructure transfers into martensite (M) and bainite (B) with obviously refined grains in higher cooling rate interval. Microhardness improves with the increase of cooling rates. Microhardness value is greatly improved to 298.6 HV at the cooling rate of 11 °C/s, which could be related to the formation of lower bainite during phase transformation process. When the cooling rate is above 29 °C/s, microhardness values remain unchanged basically. This illustrates that the microstructure of Nb-V microalloyed steel consists of martensite and lower bainite.

Abstract: Through study on the regulation of tensile strength and reduction of area after artificial aging and natural aging for SWRH82B wire rod, indicate that the tensile strength of wire rod unchanged through artificial aging or natural aging treatment while the reduction of area changes significantly the reduction of area is effected by aging temperature and aging time. Reduce the residual stress in the wire rod and lattice distortion is the main reason for reduction of area improving the composite brittle inclusions in the wire rod are not good for the rod plastic recovery.

Abstract: Through the thermal simulation test of the Nb-Ti micro-alloyed steel austenite cooling process and microstructure observation & microhardness test, the tests indicate cooling rates have effect on the phase transition and microstructure of tested steel, the critical quenching speed of Nb-Ti micro-alloyed steel is about 23°C/s with very good hardenability. With the increasing of the cooling rate, the beginning and ending temperature of phase transformation decrease and the ferrite structure content was decreased at room temperature. It’s easy to happen Bainite transformation at the beginning, and make the M block or flake M fine, which is to increase the strength and toughness of the steel.