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Choi, Pyuck-Pa,Povstugar, Ivan The Korean Powder Metallurgy Institute 2012 한국분말재료학회지 (KPMI) Vol.19 No.1
The present paper gives an overview about the Atom Probe Tomography technique and its application to powder materials. The preparation of needle-shaped Atom Probe specimens from a single powder particle using focused-ion-beam milling is described. Selected experimental data on mechanically alloyed (and sintered) powder materials are presented, giving insight into the atomic-scale elemental redistribution occurring under powder metallurgical processing.
Oxidation behavior of AlN/CrN multilayered hard coatings
Tytko Darius,Choi Pyuck-Pa,Raabe Dierk 나노기술연구협의회 2017 Nano Convergence Vol.4 No.15
We report on the oxidation behavior of AlN/CrN multilayers at 900 °C, deposited by radio frequency magnetron sputtering. It is shown that oxidation in this system is controlled by diffusion of Cr towards the surface and formation of Cr2O3. Cr diffusion is found to mainly occur along grain boundaries. Thus, coherent cubic AlN/CrN multilayer regions with coarse columnar grain structures are found to be oxidation resistant, whereas regions decomposed into hexagonal AlN/cubic CrN are prone to oxidation.
Kim, Se-Ho,Choi, Pyuck-Pa The Royal Society of Chemistry 2017 Dalton Transactions Vol.46 No.44
<▼1><P>Congo red adsorption tests reveal that the highest adsorption capacity (1735 mg g<SUP>−1</SUP>) is achieved for amorphous iron nanoparticles synthesized under ambient conditions.</P></▼1><▼2><P>We report on the Congo red dye removal properties of body centred cubic and amorphous iron nanoparticles, synthesized by a facile borohydride reduction method under ambient conditions. We have analyzed the adsorption of Congo red as a function of dye concentration, time, and temperature and measured a Congo red adsorption capacity of 1735 mg g<SUP>−1</SUP> for the amorphous iron nanoparticles. To our knowledge, this is the highest value reported so far for Congo red adsorption. The acquired data have been evaluated applying various models for adsorption kinetics and thermodynamic studies. The isotherm models as well as acquired Fourier transform infrared spectra suggest that both chemi- and physisorption occur for Congo red adsorption on iron nanoparticles, where chemisorption appears to be dominant. The kinetics of adsorption of Congo red on both bcc-structured and amorphous iron follow a pseudo-second order equation and are characterized by high initial adsorption rates. Diffusion studies indicate that adsorption occurs in two stages, namely film diffusion followed by intraparticle diffusion. Our studies show that amorphous iron nanoparticles are highly promising for dye adsorption and wastewater treatment applications.</P></▼2>
Amorphous phase separation in an Fe-based bulk metallic glass
Guo, Wei,Choi, Pyuck-Pa,Seol, Jae-Bok Elsevier 2017 Materials letters Vol.190 No.-
<P><B>Abstract</B></P> <P>Although lanthanide elements play a critical role in increasing the glass forming ability and mechanical property alternation of Fe based bulk metallic glass (Fe-BMG), the atomic scale configuration of lanthanide in Fe-BMG remained unexplored. Here we have studied atomic configuration in the amorphous state of as-cast 4mm FeCoCrMoCBY bulk metallic glass sheet and its mechanical properties by nanoindentation, transmission electron microscopy, and atom probe tomography. The current results showed that yttrium rich clusters are enriched with carbon atoms in the amorphous state, and the three dimensional densities of these clusters can influence the hardness at the localized region. The finding of Y-C rich clusters also suggests that the amorphous phase separation can precede the devitrification process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 4mm thick FeCoCrMoCBY bulk metallic glass sheet was successfully synthesized. </LI> <LI> Atomic scale characterization of amorphous phase separation preceding crystallization. </LI> <LI> Yttrium-carbon enriched nanoclusters was observed in amorphous state. </LI> <LI> The nanohardness increased with increasing spatial density of yttrium-carbon clusters. </LI> <LI> Propose new clues how yttrium increased the glass forming ability of Fe-bulk metallic glass. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Peng, Zirong,Choi, Pyuck-Pa,Gault, Baptiste,Raabe, Dierk Cambridge University Press 2017 Microscopy and Microanalysis Vol.23 No.2
<B>Abstract</B><P>Cemented tungsten carbide has been analyzed using laser-pulsed atom probe tomography (APT). The influence of experimental parameters, including laser pulse energy, pulse repetition rate, and specimen base temperature, on the acquired data were evaluated from different aspects, such as mass spectrum, chemical composition, noise-to-signal ratio, and multiple events. Within all the applied analysis conditions, only 1 MHz pulse repetition rate led to a strong detector saturation effect, resulting in a largely biased chemical composition. A comparative study of the laser energy settings showed that an ~12 times higher energy was required for the less focused green laser of the LEAP<SUP>TM</SUP> 3000X HR system to achieve a similar evaporation field as the finer spot ultraviolet laser of the LEAP<SUP>TM</SUP> 5000 XS system.</P>
Kinetic and Thermodynamic Features of Combustion of Superfine Aluminum Powders in Air
Kwon, Young-Soon,Park, Pyuck-Pa,Kim, Ji-Soon,Gromov, Alexander,Rhee, Chang-Kyu The Korean Powder Metallurgy Institute 2004 한국분말재료학회지 (KPMI) Vol.11 No.4
An experimental study on the combustion of superfine aluminum powders (average particle diameter, a$_{s}$: ∼0.1 ${\mu}{\textrm}{m}$) in air is reported. The formation of aluminum nitride during the combustion of aluminum in air and the influence of the combustion scenario on the structures and compositions of the final products are in the focus of this study. The experiments were conducted in an air (pressure: 1 atm). Superfine aluminum powders were produced by the wire electrical explosion method. Such superfine aluminum powder is stable in air but once ignited it can burn in a self-sustaining way due to its low bulk: density (∼0.1 g/㎤) and a low thermal conductivity. During combustion, the temperature and radiation were measured and the actual burning process was recorded by a video camera. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and chemical analysis were performed on the both initial powders and final products. It was found that the powders, ignited by local heating, burned in a two-stage self-propagating regime. The products of the first stage consisted of unreacted aluminum (-70 mass %) and amorphous oxides with traces of AlN. After the second stage the AlN content exceeded 50 mass % and the residual Al content decreased to ∼10 mass %. A qualitative discussion is given on the kinetic limitation for AlN oxidation due to rapid condensation and encapsulation of gaseous AlN.N.
On the detection of multiple events in atom probe tomography
Peng, Zirong,Vurpillot, Francois,Choi, Pyuck-Pa,Li, Yujiao,Raabe, Dierk,Gault, Baptiste Elsevier 2018 Ultramicroscopy Vol.189 No.-
<P><B>Abstract</B></P> <P>In atom probe tomography (APT), multiple events can arise as a consequence of e.g. correlated field evaporation and molecular ion dissociation. They represent challenging cases for single-particle detectors and can cause compositional as well as spatial inaccuracies. Here, two state-of-the-art atom probe microscopes (Cameca LEAP 5000 XS and 5000 XR) were used to investigate cemented tungsten carbide, which exhibits high amounts of multiple events. By advanced data analysis methods, the natural character of the multiple events, as well as the performance of the APT detectors, are assessed. Accordingly, possible signal loss mechanisms are discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Delay line detectors in atom probe tomography exhibit dead time and dead zone. </LI> <LI> For both Cameca LEAP 5000 XS and 5000 XR instruments, the dead time is about 3 ns. </LI> <LI> The dead zone evolves with the propagation of signals on the delay lines. </LI> <LI> The dead time and dead zone can cause signal loss during multiple events detection. </LI> <LI> The compositional and spatial accuracies can be strongly deteriorated. </LI> </UL> </P>
Cu-Based Nanocomposite Produced by a Non-equilibrium Method
Kwon, Young-Soon,Kim, Ji-Soon,Choi, Pyuck-Pa,Song, Jun-Ho,Dudina, Dina 한국공업화학회 2005 Journal of Industrial and Engineering Chemistry Vol.11 No.1
A nanocomposite Cu-TiB₂ powder was synthesized in situ by means of self-propagating high-temperature synthesis (SHS) using high-energy ball-milled Ti-B-Cu elemental mixtures as powder precursors. The effect of the preliminary mechanical treatment on the SHS reaction was studied. The size of the TiB₂ particles produced by SHS decreased upon increasing the duration of the preliminary mechanical treatment. Subsequent mechanical treatment of the SHS products led to a reduction of the sizes of the TiB₂ particles down to 30~50 nm. The microstructural evolution of the synthesized powder compacts during sintering was investigated. During spark plasma sintering, a fine-grained skeleton of TiB₂ with well-connected particles was formed. This interpenetrating phase composite of Cu-TiB₂ is produced by the simultaneous action of pressure, temperature, and electrical current. The TiB₂ nanoparticles distributed in the copper matrix agglomerate to form a fine-grained skeleton. Upon conventional sintering, the nanoparticles show a surprising behavior: at low temperatures, fiber-like structures are formed while higher temperatures caused faceted crystals to be observed.