• Journal of the Korean institute of surface engineering
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• v.46 no.2
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• pp.68-74
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• 2013

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of $1{\mu}m$ thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, $2{\mu}m$ thick nanocrystalline diamond (NCD) films were deposited at $600^{\circ}C$ over the metal layers in a 2.45 GHz microwave plasma CVD system. The cross-sectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and $4{\mu}m$ with a fixed $2{\mu}m$ thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.116-119
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• 2010

Adsorption structures of the self-assembled thin films of $\alpha$-cyano-4-hydroxycinnamic acid (CHCA) anchoring on $TiO_2$ surfaces have been studied by using temperature-dependent diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy. From the presence of the strong $\nu(COO^-)$ band at ~1390 $cm^{-1}$ along with the disappearance of the OH bands in the carboxylic acid group in the DRIFT spectra at room temperature, CHCA appeared to adsorb onto $TiO_2$ surfaces as a carboxylate form. The absence of the out-of-plane benzene ring modes of CHCA in the DRIFT spectra suggests a rather vertical orientation of CHCA on $TiO_2$. Above ~220$ ^{\circ}C$, CHCA seemed to start to thermally degrade on $TiO_2$ surfaces referring from the disappearance of most vibrational modes in the DRIFT spectra, whereas the $\nu$(C ≡ N) bands were found to remain relatively conspicuous as the temperature increased even up to ~460$^{\circ}C$.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.112-125
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• 2021

The new emerging "High entropy materials" attract the attention of the scientific society because of their simpler structure and spectacular applications in many fields. A novel nanocrystalline high entropy (Be,Mg,Ca,Sr,Zn,Ni)3O4 oxide has been successfully synthesized through mechanochemical treatment followed by sintering and air quenching. The present research work focuses on the possibility of single-phase formation in the aforementioned high entropy oxide despite the great difference in the atomic sizes of reactant alkaline earth and 3d transition metal oxides. Structural properties of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide were explored by confirmation of its single-phase Fd-3m spinel structure by x-ray diffraction (XRD). Further, nanocrystalline nature and morphology were analyzed by scanning electron microscopy (SEM). Among thermal properties, thermogravimetric analysis (TGA) revealed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is thermally stable up to a temperature of 1200℃. Whereas phase evolution in (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide before and after sintering was analyzed through differential scanning calorimetry (DSC). Electrochemical studies of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide consists of a comparison of thermodynamic and kinetic parameters of water and hydrazine hydrate oxidation. Values of activation energy for water oxidation (9.31 kJ mol-1) and hydrazine hydrate oxidation (13.93 kJ mol-1) reveal that (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is catalytically more active towards water oxidation as compared to that of hydrazine hydrate oxidation. Electrochemical impedance spectroscopy is also performed to get insight into the kinetics of both types of reactions.

• Journal of Powder Materials
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• v.10 no.6
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• pp.390-394
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• 2003

Ultra fine titanium carbide particles were synthesized by novel metallic thermo-reduction process. The vaporized TiC1$_4$+$CCl_4$ gases were reacted with liquid magnesium and the fine titanium carbide particles were then produced by combining the released titanium and carbon atoms. The vacuum treatment was followed to remove the residual phases of MgC1$_2$ and excess Mg. The stoichiometry, microstructure, fixed and carbon contents and lattice parameter were investigated in titanium carbide powders produced in various reaction parameters.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.336-339
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• 2006

Magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as pain size (or particle size), internal strain and crystal structure. Thus, studies on the synthesis of nanostructured materials with controlled microstructure are necessary fur a significant improvement in magnetic properties. In the present work, nanostructured Fe-Co alloy powders with a grain size of 50 nm were successfully fabricated from the powder mixtures of (99.9% purity) $FeCl_2$ and $CoCl_2$ by chemical solution mixing and hydrogen reduction.

• Transactions of the Korean hydrogen and new energy society
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• v.8 no.1
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• pp.43-47
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• 1997

A new type of anode materials in form of nanocrystalline composite powders has been developed that offers the potential for dramatically improved discharge capacity and initial activation rate. The composites are synthesized by ball milling of two components - a major component (basic component) having high hydrogen capacity and a minor component (surface activator) with good electrocatalytic activity. The capacity increase observed by ball milling with surface activator. The ball-milled composite materials are easier to activate than the non ball-milled basic component.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.103.2-103.2
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• 2017

Nanocrystalline HfN coatings were prepared by reactively sputtering Hf metal target with N2 gas using a magnetron sputtering system operated in DC and ABPP (asymmetric bipolar pulsed plasma) condition with various duties and frequencies. The effects of duty and frequency, ranging from 75 to 100 % and 5 to 50 kHz, on the coating microstructure, crystallographic and mechanical properties were systematically investigated with FE-SEM, AFM, XRD and nanoindentation. The results show that pulsed plasma has a significant influence on coating microstructure and mechanical properties of HfN coatings. Coating microstructure evolves from the columnar structure to a highly dense one as duty decreases. Average grain size and nano hardness of HfN coatings were also investigated with various pulsed conditions.

• Journal of Powder Materials
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• v.2 no.3
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• pp.231-237
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• 1995

The powder mixtures of Al, Ti and Cr were mechanically alloyed to obtain nanocrystalline powders of $Ti_{25}Cr_8Al_{67}$ composition. Both FCC phase and undissolved metal chromium formed by MA. During the annealing of the MA powders, the phase transition from FCC to ordered $Ll_2$ started at ~$300^{\circ}C$ and was completed below $600^{\circ}C$. As a result of the high-temperature compressive test for the MA powder compacts, the stress-strain curves showed serrated yielding behavior at 400 and $600^{\circ}C$, and softening phenomenon below the strain rate of $5{\times}10^{-3}s^{-1}$ at $800^{\circ}C$. The compressive yield strength as a function of test temperatures showed the nature of the positive-temperature dependence which has the peak temperature around $600^{\circ}C$.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.83-89
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• 2004

SiC nanotubes were synthesized by SLS growth mechanism using various metal catalysts. Synthesized nanotubes had mean diameters of 20~50 nm and several $\mu\textrm{m}$ length. The kind of catalysts affected microstructures of SiC nanotubes by different diffusion routes. These differences are attributed to catalysts' physical properties and relative activities to the graphite substrate. Fe acted as a good catalyst of SLS growth mechanism. But in case of Ni, SiC nanotubes grew slowly. Optical property was measured by photoluminescence measurement. Relatively broad peak was obtained and mean peak positioned at about 430 nm. This result was the same as other nanocrystalline SiC materials, but was different from the results of bulk SiC probably due to quantum confinement effect and defect in the grown SiC nanotube.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.429-434
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• 2001

Ti-Cu-N nanocomposite films deposited by arc ion plating and magnetron sputter hybrid system with various copper contents. The microstructure and mechanical properties of Ti-Cu-N superhard nanocomposite films depend on the Cu concentration. In X-ray diffraction (XRD) analysis, intensity of TiN (111) and TiN (220) peak decreased and peak broadness increased with increasing the copper contents and Cu peak was not detected. The grain size of films decreased with increasing at%Cu and Transmission Electron Microscopy (TEM) analysis also showed that Ti-Cu-N film containing 1.5at%Cu was composed of very fine (<10nm) nanocrystalline grains. The maximum hardness of Ti-Cu-N (1.5at%Cu) film reached to 45GPa and friction coefficient was measured 0.3.