Kyoung Ran Han

Quantitative phase analysis in tetragonal-rich tetragonal/monoclinic two phase zirconia by Raman spectroscopy

Abstracts are not published in this journal

Study on sensing properties of tin oxide CO gas sensor with low power consumption

In this paper, the fabrication method of a new type of carbon monoxide gas sensor based on SnOx with low power consumption and its sensing characteristics have been reported. The electric conductance of this type of sensor evolves oscillation form regularly when the sensor is exposed to low level of CO gas. The oscillation amplitude is directly proportional to the concentration of CO gas over a wide range. The effects of relevant factors. such as. humidity, temperature and interference gases on the sensor properties were examined. The sensing oscillation response mechanism was also discussed.

New preparation method of low-temperature sinterable Pb(Mg1/3Nb2/3)O3 powder and its dielectric properties

A relaxor ferroelectric material, Pb(Mg1/3Nb2/3)O3(PMN) with perovskite phase was prepared by one-step calcination in the present study. The PMN powder with >99% perovskite phase was prepared successfully by adding an aqueous Mg(NO3)2 solution rather than MgO to the alcoholic slurry of PbO and Nb2O5, followed by calcination at 950°C for 2 h. The DSC and XRD analysis showed that the pathway in the one-step calcination was different from those of the known columbite or solution processes. The PMN powder sintered to 95.6% of the theoretical density at even 900°C for 2 h. Its room temperature dielectric constant showed 13800 at 1 kHz, the loss of dielectric constant of 0.05% and the specific resistivity of 2.4 × 1010 Ω·cm.

Development of SnO2 based semiconductor gas sensor with Fe2O3 for detection of combustible gas

Six kinds of SnO2 based semiconductor gas sensors have been fabricated and investigated in the aspects of gas sensitivity to and selectivity for combustible gases. It was found that Fe2O3 was a more effective additive than Pd or Pt. It showed high sensitivity to and high selectivity for H2, CH4, C4H10, and little cross-sensitivity to ethanol and smoke.

Electrochemical properties of Al doped Li (Ni1/3Co1/3Mn1/3 )O2

Al doped Li(Ni1/3Co1/3Mn1/3-xAlx)O2 (x=0.005, 0.01, 0.05) and Li(Ni1/3-x/2Co1/3Mn1/3-x/2Alx)O2 (x=0.01, 0.05) cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis and heat treatment. The substitution with Al reduced the content of Mn3+, promoted grain growth, and broadened the particle size distribution of synthesized powders. The initial discharge capacity of cells made with 0.5 mol% Al doped Li(Ni1/3Co1/3Mn1/3-0.005Al0.005)O2 powder was as high as that of the undoped (~180 mAhg-1, 3.04.5 V), and showed an excellent cycle stability. The improvement of the cycle stability was considered to be due to the decrease of Mn3+ in Li(Co1/3Ni1/3Mn1/3-xAlx)O2 by Al doping.

Surface Modification of Li (Co1/3Mn1/3Ni1/ 3)O2 Fine Powders Using Aqueous Al2O3 Sol

The surface of Li(Ni1/3Co1/3Mn1/3)O2 was modified with Al2O3 using aqueous alumina sol and the electrochemical properties of the coated oxide were measured and compared with both uncoated and Al-doped one. The alumina coated powder showed 185 mAh/g at first cycle, and 139 mAh/g after 50 cycles in the voltage range of 3.0~4.6 V at 1C rate. The initial discharge capacity of the coated powder was slightly lower than that of the alumina doped one, but the cycle stability of the coated was better than that of the doped.

Cu/GDC cermet anodes by sintering via surface modification with MgO sol

CuO/GDC composite powder with 50 wt% of CuO was prepared by surface modification of ~60 nm GDC powder with Cu precursors. Since copper oxide melts at lower temperature than GDC sintering temperature, fabrication procedure was modified by inducing infiltration of molten copper oxide via capillary force and then followed by heat treatment at ~1000. Surface modification was carried out with a MgO sol to suppress agglomeration of GDC. Such prepared Cu/GDC cermets showed uniform microstructure and excellent electronic conductivity of ~8500 S/cm for the Cu/GDC cermet and ~10200 S/cm for the modified one at 800.

Combinational Effects of Ni Precursors on Ni/YSZ Cermet Anode

NiO/YSZ composite powder with 70 wt% of NiO was prepared by surface modification of ~30 nm YSZ with Ni precursors. As Ni precursors, acidic nickel nitrate and basic nickel carbonate were employed. By varying the ratio of Ni precursors, substantially different particle sizes were obtained. Their Ni/YSZ cermets also showed substantially different microstructures and porosities. Effects of combination of Ni precursors on Ni/YSZ cermets were studied by using XRD, zetapotential, and SEM.

Microstructure and electrochemical properties of post heat-treated Li(Ni1/3Co1/3Mn1/3)O2 cathode materials for lithium ion battery

Li(Ni1/3Co1/3Mn1/3)O2 powders were synthesized by using an ultrasonic spray pyrolysis method, and then heat-treated at 900 or 1000°C for 20 h. The morphology of the as-synthesized powder was spherical. The post heat-treatment changed the particle size and morphology of the synthesized powders. Structural characteristics of the heat-treated powders were analyzed using XRD and SEM, and their electrochemical properties were compared. Higher first discharge capacity was obtained from the powder heat-treated at 1000°C, but its rough and rugged surface might cause a rapid decrease of the capacity retention.

Preparation of Cu/GDC Cermet Anode by Sintering via Surface Modification with MgO Sol

CuO/GDC composite powder with 50 wt% of CuO was prepared by surface modification of ~60 nm GDC powder with Cu precursors. Since copper oxide melts at lower temperature than GDC sintering temperature, fabrication procedure was modified by inducing infiltration of molten copper oxide via capillary force and then followed by heat treatment at ~1000 °C . Surface modification was carried out with a MgO sol to suppress agglomeration of GDC. Such prepared Cu/GDC cermets showed uniform microstructure and excellent electric conductivity of ~6000 S/cm for the Cu/GDC cermet and ~10000 S/cm for the modified one at 800°C.