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      • Fabrication of tunable carbon micro- and nanotubes using reed as bio-template

        Nersisyan, H.H.,Lee, T.H.,Lee, K.H.,Maeng, D.Y.,Lee, J.H. North-Holland 2013 Materials letters Vol.107 No.-

        Reed bristles (Andropogon virginicus) were used as precursors and bio-templates for tubular carbon synthesis. The carbonization of the bristles was performed at 1200<SUP>o</SUP>C in a double crucible system using charcoal as a reducing agent. Following carbonization, carbon microtubes with outer and inner diameters of 4-8 and 3-7μm, respectively, were obtained. Moreover, the seeds of reeds demonstrated catalytic activity that led to the formation of multiwalled carbon nanotubes with outer diameters of 10-15nm. The BET specific surface area of CMTs prepared at 1200<SUP>o</SUP>C calculated using the adsorption data was 145m<SUP>2</SUP>/g. The corresponding pore size evaluated using the HK plot was 0.5-1.5nm.

      • SCIESCOPUS

        Control and Theoretical Modeling of the Growth Process of AlN Six-fold and Multifold Armed Dendritic Crystals

        Nersisyan, Hayk H.,Kim, Wan Bae,Lee, Seong Hun,Yoo, Bung Uk,Choi, Hyuk,Kim, Hyun You,Lee, Jong Hyeon The American Chemical Society 2019 CRYSTAL GROWTH AND DESIGN Vol.19 No.6

        <P>Through a combinatorial approach involving theory and experiments, this study investigated the mechanism of the dendritic growth of AlN microcrystals during the combustion of Al + 0.1AlF<SUB>3</SUB> + <I>k</I>Al<SUB>2</SUB>O<SUB>3</SUB> powder mixtures under nitrogen-rich conditions. The experimentally observed morphology of the dendritic AlN crystals is characterized by the six-fold branches that developed outward within an equatorial plane and secondary dendrites that grew above and below the equatorial plane. The physical mechanisms that lead to the shape-controlled synthesis of AlN dendritic crystals were studied through experimental analysis and theoretical investigation including density functional theory (DFT) calculation and phase-field (PF) crystal growth modeling. Based on the DFT-calculated surface energy values, an energy minimization argument was used to construct the AlN nucleus. PF crystal growth modeling provides the details of the sequential crystallization process of the dendritic AlN crystals. The results of this study provide a complete understanding of the shape-controlled growth of AlN crystals, which aids the rational growth design of AlN and other relevant compounds.</P><P>A combinatorial approach involving combustion−nitridation experiments and computational modeling based on density functional theory (DFT) and phase-field (PF) crystal growth modeling provides the details of AlN six-fold and multifold armed dendritic crystals formation in a limited space.</P> [FIG OMISSION]</BR>

      • Hierarchically porous carbon nanosheets derived from alkali metal carbonates and their capacitance in alkaline electrolytes

        Nersisyan, Hayk H.,Lee, Seong Hun,Choi, Jeong Hun,Yoo, Bung Uk,Suh, Hoyoung,Kim, Jin-Gyu,Lee, Jong-Hyeon Elsevier 2018 Materials chemistry and physics Vol.207 No.-

        <P><B>Abstract</B></P> <P>With the assistance of alkali metal carbonate M<SUB>2</SUB>CO<SUB>3</SUB> (M is Na and K) as a carbon source and silicon as a displacement agent, an exothermic and self-sustaining reaction to produce two-dimensional (2-D) hierarchically porous carbon nanosheets (denoted as HP-CNSs) was achieved. The combustion reaction developed a temperature in the range of 1100–1400 °C and resulted in a two-phase product consisting of HP-CNSs and alkali metal silicate (M<SUB>2</SUB>O⋅<I>n</I>SiO<SUB>2</SUB>). After dissolving the M<SUB>2</SUB>O⋅<I>n</I>SiO<SUB>2</SUB> in distilled water, a black carbon powder was formed. Despite the simple synthesis process, the HP-CNSs had a BET surface area of about 178.6–860 m<SUP>2</SUP>g<SUP>−1</SUP> and a pore diameter in the range 0.5–150 nm. HP-CNSs based capacitors showed a specific capacity of about 85–240 Fg<SUP>−1</SUP> and good cyclic performance for over 1000 cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The combustion process in M<SUB>2</SUB>CO<SUB>3</SUB> (Me is Na and K) + Si system was investigated. </LI> <LI> The formation of hierarchically porous carbon nanosheets was observed in the temperature range of 1000–1400 °C. </LI> <LI> Carbon nanosheets exhibited 178.6–860 m<SUP>2</SUP> g<SUP>−1</SUP> surface area and 0.09–1.94 cm<SUP>3</SUP> g<SUP>−1</SUP> pore volume. </LI> <LI> The maximum capacitance of carbon was 240 F g<SUP>−1</SUP> under the scan rate of 10 mV s<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • Combustion synthesis of zero-, one-, two- and three-dimensional nanostructures: Current trends and future perspectives

        Nersisyan, Hayk H.,Lee, Jong Hyeon,Ding, Jin-Rui,Kim, Kyo-Seon,Manukyan, Khachatur V.,Mukasyan, Alexander S. Elsevier 2017 Progress in energy and combustion science Vol.63 No.-

        <P><B>Abstract</B></P> <P>The combustion phenomenon is characterized by rapid self-sustaining reactions, which can occur in the solid, liquid, or gas phase. Specific types of these reactions are used to produce valuable materials by different combustion synthesis (CS) routes. In this article, all three CS approaches, i.e. solid-phase, solution, and gas-phase flame, are reviewed to demonstrate their attractiveness for fabrication of zero-, one-, two-, and three-dimensional nanostructures of a large variety of inorganic compounds. The review involves five sections. First, a brief classification of combustion synthesis methods is given along with the scope of the article. Second, the state of art in the field of solid-phase combustion synthesis is described. Special attention is paid to the relationships between combustion parameters and structure/properties of the produced nanomaterials. The third and fourth sections describe details for controlling material structures through solution combustion synthesis and gas-phase flame synthesis, respectively. A variety of properties (e.g., thermal, electronic, electrochemical, and catalytic) associated with different types of CS nanoscale materials are discussed. The conclusion focuses on the most promising directions for future research in the field of advanced nanomaterial combustion synthesis.</P>

      • NaF-assisted combustion synthesis of MoSi<sub>2</sub> nanoparticles and their densification behavior

        Nersisyan, Hayk H.,Lee, Tae Hyuk,Ri, Vladislav,Lee, Jong Hyeon,Suh, Hoyoung,Kim, Jin-Gyu,Son, Hyeon Taek,Kim, Yong-Ho Elsevier 2017 The Journal of physics and chemistry of solids Vol.102 No.-

        <P><B>Abstract</B></P> <P>The exothermic reduction of oxides mixture (MoO<SUB>3</SUB>+2SiO<SUB>2</SUB>) by magnesium in NaF melt enables the synthesis of nanocrystalline MoSi<SUB>2</SUB> powders in near-quantitative yields. The combustion wave with temperature of about 1000–1200°C was recorded in highly diluted by NaF starting mixtures. The by-products of combustion reaction (NaF and MgO) were subsequently removed by leaching with acid and washing with water. The as-prepared MoSi<SUB>2</SUB> nanopowder composed of spherical and dendritic shape particles was consolidated using the spark plasma sintering method at 1200–1500°C and 50MPa for 10min. The result was dense compacts (98.6% theoretical density) possessing submicron grains and exhibiting hardness of 8.74–12.92GPa.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • SCISCIESCOPUS

        Two-step process of regeneration of acid(s) from ZrF<sub>4</sub> containing spent pickle liquor and recovery of zirconium metal

        Nersisyan, Hayk,Han, Seul Ki,Choi, Jeong Hun,Lee, Young-Jun,Yoo, Bung Uk,Ri, Vladislav E.,Lee, Jong Hyeon Elsevier 2017 JOURNAL OF NUCLEAR MATERIALS Vol.486 No.-

        <P><B>Abstract</B></P> <P>In this paper we describe a progressive two-step process that allows zirconium fluoride (ZrF<SUB>4</SUB>) contained in spent baths for etched zirconium alloys to be effectively recycled on a pilot scale and produce a high purity regenerated pickling acid. In the first step, a spent pickling liquor is treated by a BaF<SUB>2</SUB> suspension to produce water insoluble Ba<SUB>2</SUB>ZrF<SUB>8</SUB>. After filtration of Ba<SUB>2</SUB>ZrF<SUB>8</SUB> more than 99.9 wt % purity pickling acid is regenerated. The precipitation mechanism of Ba<SUB>2</SUB>ZrF<SUB>8</SUB> is discussed and the role of BaF<SUB>2</SUB> particles size on the precipitation process is demonstrated. In the second step the as-precipitated Ba<SUB>2</SUB>ZrF<SUB>8</SUB> is mixed with Mg and Cu metal powders and heat-treated at 1200 °C (or above) to produce CuZr alloy ingot. The characteristics of the ingot are discussed in regard to Cu concentration and the heating temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two-step process for recycling ZrF<SUB>4</SUB> containing pickling acid on a pilot scale is developed. </LI> <LI> Water insoluble Ba<SUB>2</SUB>ZrF<SUB>8</SUB> is precipitated by mixing spent pickling liquor with BaF<SUB>2</SUB>. </LI> <LI> The recycled pickling acid demonstrates more than 99.9 wt % purity. </LI> <LI> The processing of Ba<SUB>2</SUB>ZrF<SUB>8</SUB> with Cu and Mg metals at 1200 °C yielded CuZr alloy. </LI> <LI> The recovery depth of Zr was more than 95 wt%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • SCISCIESCOPUS

        Gas-phase supported rapid manufacturing of Ti-6Al-4V alloy spherical particles for 3D printing

        Nersisyan, Hayk H.,Yoo, Bung Uk,Kim, Young Min,Son, Hyeon Taek,Lee, Ki Yong,Lee, Jong Hyeon Elsevier 2016 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.304 No.-

        <P><B>Abstract</B></P> <P>In this study, a combustion process for a TiO<SUB>2</SUB> +0.12Al+(2.5+6<I>k</I>)Mg+0.021V<SUB>2</SUB>O<SUB>5</SUB> + <I>k</I>MgCl<SUB>2</SUB>·6H<SUB>2</SUB>O mixture was studied to fabricate Ti-6Al-4V alloy spherical particles. From the temperature-time profiles, the average value of the synthesis temperature was estimated to be 1650±20°C. Based on FESEM observations, spherical shape particles were obtained when 0.05–0.1mol MgCl<SUB>2</SUB>·6H<SUB>2</SUB>O was added to the initial reaction mixture. Therefore, spherical alloy particles were achieved by consecutive processes of cooling and acid purification of the burned down sample. According to laser particle size analysis, the average diameter of the spheres was between 5 and 25μm. A selective laser melting process was applied to build dense Ti-6Al-4V alloy samples. The tensile properties and the microhardness were evaluated and compared to those characteristics of a reference sample prepared from commercial Ti-6Al-4V alloy spherical powder.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ti-6Al-4V alloy spherical particles 5–25μm in diameter were fabricated by combustion technique. </LI> <LI> The spherical shape of particles was achieved by MgCl<SUB>2</SUB>·6H<SUB>2</SUB>O component added to the mixture. </LI> <LI> The concentration of MgCl<SUB>2</SUB>·6H<SUB>2</SUB>O in the reaction mixture was 0.05–0.1mol range. </LI> <LI> Ti-6Al-4V alloy particles were processed by SLM technique to produce 3D printed parts. </LI> <LI> 3D printed parts demonstrated high microhardness and yield strength. </LI> </UL> </P>

      • SCISCIESCOPUS
      • A thermochemical pathway for controlled synthesis of AlN nanoparticles in non-isothermal conditions

        Nersisyan, H.H.,Yoo, B.U.,Lee, K.H.,Lee, J.H. Elsevier 2015 Thermochimica acta Vol.604 No.-

        The synthesis of AlN nanoparticles in non-isothermal high-temperature conditions was developed. The process involved Al<SUB>2</SUB>O<SUB>3</SUB>-Mg-NH<SUB>4</SUB>Cl mixtures preparation and combustion in nitrogen atmosphere. Temperature profiles in the combustion waves were recorded by thermocouples, and the values of combustion temperature and wave velocity were determined from the recorded profiles. The existence of two independed combustion regimes with maximum temperatures of about 850<SUP>o</SUP>C and 1400-1600<SUP>o</SUP>C were revealed based on concentrations of NH<SUB>4</SUB>Cl. AlN nanocrystals were obtained and investigated by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller surface area. AlN nanocrystals prepared under non-isothermal combustion process were comprised well distributed multi-faceted particles with an average size of 50-200nm. The chemical reactions in the combustion wave were discussed and a possible thermochemical pathway for the synthesis of AlN nanoparticles was proposed.

      • SCISCIESCOPUS

        Thermally induced formation of 2D hexagonal BN nanoplates with tunable characteristics

        Nersisyan, Hayk,Lee, Tae-Hyuk,Lee, Kap-Ho,Jeong, Seong-Uk,Kang, Kyung-Soo,Bae, Ki-Kwang,Lee, Jong-Hyeon Elsevier 2015 Journal of solid state chemistry Vol.225 No.-

        <P><B>Abstract</B></P> <P>We have investigated a thermally induced combustion route for preparing 2D hexagonal BN nanoplates from B<SUB>2</SUB>O<SUB>3</SUB>+(3+0.5<I>k</I>)Mg+<I>k</I>NH<SUB>4</SUB>Cl solid system, for <I>k</I>=1–4 interval. Temperature–time profiles recorded by thermocouples indicated the existence of two sequential exothermic processes in the combustion wave leading to the BN nanoplates formation. The resulting BN nanoplates were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy, PL spectrometry, and Brunauer–Emmett–Teller surface area analysis. It was found that B<SUB>2</SUB>O<SUB>3</SUB> was converted into BN completely (by XRD) at 1450–1930°C within tens of seconds in a single-step synthesis process. The BN prepared at a <I>k</I>=1–4 interval comprised well-shaped nanoplates with an average edge length ranging from 50nm to several micrometer and thickness from 5 to 100nm. The specific surface area of BN nanoplates was 13.7g/m<SUP>2</SUP> for <I>k</I>=2 and 28.4m<SUP>2</SUP>/g for <I>k</I>=4.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermally induced combustion route was developed for synthesizing BN nanoplates from B<SUB>2</SUB>O<SUB>3</SUB>. </LI> <LI> Mg was used as reductive agent and NH<SUB>4</SUB>Cl as an effective nitrogen source. </LI> <LI> Temperature–time profiles and the combustion parameters were recorded and discussed. </LI> <LI> BN with an average edge length from 50nm to several micrometer and thickness from 5 to 100nm were prepared. </LI> <LI> Our study clarifies the formation mechanism of BN in the combustion wave. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>2D hexagonal BN nanoplates with an average edge length ranging from 50nm to several micrometer and thickness from 5 to 100nm were prepared by combustion of B<SUB>2</SUB>O<SUB>3</SUB>+(3+0.5<I>k</I>)Mg+<I>k</I>NH<SUB>4</SUB>Cl solid mixture in nitrogen atmosphere.</P> <P>[DISPLAY OMISSION]</P>

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