• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.427-431
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• 2015

In this study, vanadium dioxide ($VO_2$) powder well known as a thermochromic material was prepared from $V_2O_5$ powder and oxalic acid dihydrate by hydrothermal and calcination process at various conditions. The chemical bonding and crystal structures in addition to thermal property of samples were determined using FE-SEM, XRD, XPS, and DSC. Also, spectroscopic and thermochromic properties of film samples were analyzed by UV-Vis-NIR spectroscopy after the thin film was prepared from the sol dispersed with the size of below 50 nm by the ball-milling of powder sample. With increasing the calcination temperature, the phase transition temperature of samples increased from $40^{\circ}C$ to $70^{\circ}C$ due to the increase of particle size.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.690-695
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• 2003

Soft-solution route employing PVA(Polyvinyl Alcohol) as a polymeric carrier in a mixed metal cation solution was used for synthesis of single-phase nickel aluminate (NiA1$_2$O$_4$) powders. The PVA ensured the homogeneous distribution of metal ions in the solution and it resulted in the decrease of crystallization temperature. The synthesized powders prepared by PVA addition were soft and ball-milled easily. The ball-milled powders of about 300 nm in size were fully densified to density of 4.35 g/㎤ at 1600$^{\circ}C$ for 1 h. The Vickers hardness, flexural strength, fracture toughness and thermal expansion coefficient of the sintered nickel aluminate were 14.2 ㎬, 304 ㎫, 4.8 ㎫$.$m$\^$1/2/ and 9.8${\times}$10$\^$-6//$^{\circ}C$, respectively.

• Journal of Powder Materials
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• v.28 no.6
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• pp.462-469
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• 2021

Tin/graphite composites are prepared as anode materials for Li-ion batteries using a dry ball-milling process. The main experimental variables in this work are the ball milling time (0-8 h) and composition ratio (tin:graphite=5:95, 15:85, and 30:70 w/w) of graphite and tin powder. For comparison, a tin/graphite composite is prepared using wet ball milling. The morphology and structure of the different tin/graphite composites are investigated using X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, and scanning and transmission electron microscopy. The electrochemical properties of the samples are also examined. The optimal dry ball milling time for the uniform mixing of graphite and tin is 6 h in a graphite-30wt.%Sn sample. The electrode prepared from the composite that is dry-ball-milled for 6 h exhibits the best cycle performance (discharge capacity after 50^th cycle: 308 mAh/g and capacity retention: 46%). The discharge capacity after the 50^th cycle is approximately 112 mAh/g, higher than that when the electrode is composed of only graphite (196 mAh/g after 50^th cycle). This result indicates that it is possible to manufacture a tin/graphite composite anode material that can effectively buffer the volume change that occurs during cycling, even using a simple dry ball-milling process.

• Korean Journal of Materials Research
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• v.4 no.6
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• pp.681-686
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• 1994

Microwave Detector Using $YBa_{2}Cu_{3}O_{7-x}$, Grain Boundary Junction $YBa_{2}Cu_{3}O_{7-x}$ superconductor thin films were deposited on $LaAIO_{3}$ (100) single crystal substrates using a metal organic chemical vapor deposition (MOCVD) method. These films showed the critical temperature of about 9OK and critical current density of over $10^5/A \textrm{cm}^2$at 77K. These films showed granular structure with 0.5~1.5$\mu \textrm{m}$ grains. Bridge-type junctions, 6$\mu \textrm{m}$ in width and 6pm in length, were fabricated using the photolithography and the Ar ion milling techniques. Current-voltage (I-V) characteristics of these junctions with the microwave irradiation at 77K were studied. The critical current densities decreased as the irradiated microwave power increased. When microwaves were irradiated on the bridge at 77K. the I-V charateristics showed constant voltage stcp(Shapiro steps) at $\Delta$=nho/2e.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.86-91
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• 1999

We have fabricated high-$\textrm{T}_c$ superconducting $\textrm{YBa}_{2}\textrm{Cu}_{3}\textrm{O}_{7-x}$(YBCO) grain boundary junctions at a step-edge on (001) $\textrm{SrTiO}_3$(STO) substrates. A diamond-like carbon (DLC) film grown by plasma enhanced chemical vapor deposition were used as an ion milling mask to make steps on the STO (100) single crystal and was removed by an oxygen reactive ion etch process. The c-axis oriented YBCO and TO thin films were deposited epitaxially on the STO substrate with a step-edge by pulsed laser deposition. The grain boundary junctions were formed at the top and the bottom of the step. The junctions worked at temperatures above 77 K, and had I\ulcornerR\ulcorner products of 7.5mV at 16K and 0.3 mV at 77K, respectively. The I-V characteristics of these junctions showed the shape of the two noisy resistively shunted junction model.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.191-198
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• 2018

SnSb alloy powders with excess Sn or Sb are fabricated by the high energy ball-milling of pure Sn and Sb powders with different Sn/Sb molar ratios, and then their material properties and lithium electrochemical performances are investigated. It is revealed by X-ray diffraction that SnSb alloys are successfully synthesized, and the powder size is decreased via ball-milling. Charge-discharge test using a coin-cell shows that the best result, in terms of the cyclability and the capacity after 50 cycles, comes from the electrode composed of Sn : Sb = 4 : 6, i.e. the capacity of $580mAh\;g^{-1}$ after 50 cycles. When the electrode is composed of Sn : Sb = 3 : 7, however, the capacity is noticeably decreased by the restrained Sn reaction with Li-ion. The pure SnSb alloy powders (Sn : Sb = 5 : 5) results in the second best performance. In the case of Sn-rich SnSb alloys, the initial capacity is relatively high, but the capacity is quickly fading after 20 cycles.

• Applied Chemistry for Engineering
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• v.26 no.5
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• pp.543-548
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• 2015

Si/C/CNF composites as anode materials for lithium-ion batteries were examined to improve the capacity and cycle performance. Si/C/CNF composites were prepared by the fabrication process including the synthesis and magnesiothermic reduction of SBA-15 to obtain Si/MgO by ball milling and the carbonization of phenol resin with CNF and HCl etching. Prepared Si/C/CNF composites were then analysed by BET, XRD, FE-SEM and TGA. Among SBA-15 samples synthesized at reaction temperatures between 50 and $70^{\circ}C$, the SBA-15 at $60^{\circ}C$ showed the largest specific surface area. Also the electrochemical performances of Si/C/CNF composites as an anode electrode were investigated by constant current charge/discharge test, cyclic voltammetry and impedance tests in the electrolyte of LiPF6 dissolved in mixed organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%). The coin cell using Si/C/CNF composites (Si : CNF = 97 : 3 in weight) showed better capacity (1,947 mAh/g) than that of other composition coin cells. The capacity retention ratio decreased from 84% (Si : CNF = 97 : 3 in weight) to 77% (Si : CNF = 89 : 11 in weight). It was found that the Si/C/CNF composite electrode shows an improved cycling performance and electric conductivity.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.294-299
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• 2001

Effects of the surface fluorination on the electrochemical charge-discharge properties of $Mg_2$Ni electrode in Ni-MH batteries fabricated by mechanical alloying were investigated. After 20h ball milling, Mg and Ni powder formed nanocrystalline $Mg_2$Ni. Discharge capacity of this alloy increased greatly at first one cycle, but due to the formation of Mg(OH)$_2$ passive layer, it showed a rapid degradation in alkaline solution within 10cyc1es. In case of 6N KOH +xN KF electrolyte (x = 0.5, 1, 2), a continuous and stable fluorinated layer formed by adding excess F$^{[-10]}$ ion, increased durability of $Mg_2$Ni electrode greatly and high rate discharge capability(90-100mAh/g). 2N KF addition led to the highest durability of all tested here. The reason of the improvement is due to thin MgF$_2$, which can prevent the $Mg_2$Ni electrode from forming Mg(OH)$_2$layer that is the main cause of degradation.