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.

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>

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.

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>

Combustion-mediated synthesis of hollow carbon nanospheres for high-performance cathode material in lithium-sulfur battery

Nersisyan, Hayk H.,Joo, Sin Hyong,Yoo, Bung Uk,Kim, Dae Young,Lee, Tae Hyuk,Eom, Ji-Yong,Kim, Chunjoong,Lee, Kap Ho,Lee, Jong-Hyeon Elsevier 2016 Carbon Vol.103 No.-

<P>Hollow carbon nanospheres as potential cathode materials for lithium-sulfur (Li-S) batteries were successfully synthesized using a metathesis reaction between sodium azide and halogen polymer. The reaction was driven by thermal heat from the exothermic recombination of Na+ and Cl- (or F-) ions into NaCl (or NaF) salts. The result was an increase of the overall system temperature up to 1320-1750 degrees C followed by the simultaneous formation of sodium halide-carbon coreeshell nanoparticles. Therefore, hollow carbon nanospheres with diameter and shell thickness of similar to 50-500 nm and similar to 10-50 nm, respectively, were produced after water washing of the reaction product. The composite cathode materials for Li-S batteries were manufactured by infiltrating sulfur into the hollow core of nanospheres. The electrochemical cycling showed discharge capacity of similar to 700 mAh g(-1) (after 100 cycles) at 0.5 degrees C current rate which is more than similar to 2.4 times larger than that for the sulfur/carbon black composites prepared by the same technique. The enhancement of battery performance was attributed to the well-organized and unique 3D structure of hollow carbon, enabling better utilization of sulfur. (C) 2016 Elsevier Ltd. All rights reserved.</P>

The growth of AlN dendritic crystals with uniform morphology by an aluminum microdroplet localization approach

Nersisyan, Hayk H.,Lee, Seong Hun,Yoo, Bung Uk,Lee, Jong Hyeon Elsevier 2018 Combustion and Flame Vol.196 No.-

<P><B>Abstract</B></P> <P>We developed an attractive combustion approach for synthesizing uniformly shaped AlN dendritic crystals by combustion of Al + 0.1AlF<SUB>3</SUB> <SUB> </SUB>+ <I>k</I>Al<SUB>2</SUB>O<SUB>3</SUB> powder mixtures in a nitrogen atmosphere. The combustion temperature measured for various <I>k</I> values was between 1650 and 1750 °C and the micro-droplets of Al formed in the beginning stages of the process were enveloped by the solid layers of Al<SUB>2</SUB>O<SUB>3</SUB>, and the subsequent multipoint nucleation and crystallization produced morphologically and size uniform dendritic crystals. We proposed a theoretical model for calculating the thickness and the number of Al<SUB>2</SUB>O<SUB>3</SUB> layers around of Al microdroplets at known concentration of Al<SUB>2</SUB>O<SUB>3</SUB>. Depending on the concentration of Al<SUB>2</SUB>O<SUB>3</SUB>, these structures were simple stars with six points and stellar dendrites with multiple petals.</P>

Single-step combustion process for the synthesis of 1-D, 2-D, and 3-D hierarchically grown AlN structures

Nersisyan, Hayk H.,Lee, Seong Hun,Choi, Jeong Hun,Yoo, Bung Uk,Lee, Jong Hyeon Elsevier 2017 Combustion and Flame Vol.185 No.-

<P><B>Abstract</B></P> <P>In this study, a single-step combustion process for the synthesis 1-D, 2-D, and 3-D micro and nanostructures of AlN was developed. The structures were grown by combustion of Al+<I>k</I>AlF<SUB>3</SUB> (or ZnF<SUB>2</SUB>)+<I>m</I>NH<SUB>4</SUB>Cl reaction mixture under 4.0 MPa nitrogen atmosphere. Based on experimental data, the growth conditions, morphology, and composition, optical, and thermal properties of AlN micro and nanostructures were determined. The formation of structures was associated with the combustion temperature, liquid and gas-phase reactions, and the type of additives used in the experiments. The new insight, we gleaned from this study may help in the selective growth of AlN micro and nanostructures of different morphology, enhancing their functionality.</P>

NaF-assisted combustion synthesis of MoSi₂ 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>

Highly Crystalline Rod-Shaped Zn₂SiO₄:Mn²⁺Phosphor Particles Prepared in Frontal Exothermic Waves

Nersisyan, H. H.,Won, H. I.,Youn, J. W.,Won, C. W. The Electrochemical Society 2012 Journal of the Electrochemical Society Vol.159 No.4

Experimental Growth of New 6-fold Symmetry Patterned Microcrystals of AlN: Equilibrium Structures and Growth Mechanism

Nersisyan, Hayk H.,Kim, DaeYoung,Yoo, BungUk,Kang, Woojong,Han, Byungchan,Lee, JongHyeon The American Chemical Society 2016 CRYSTAL GROWTH AND DESIGN Vol.16 No.9

<P>For the first time, we experimentally detected the formation of 6 fold symmetry patterned microcrystals of AIN (aluminum nitride), such as simple prisms, stellar and sectored plates, and stellar and fernlike stellar dendrites. These crystals were formed during combustion of a solid mixture of Al + kAIF(3) (k = 0.05-0.1 mol) under a nitrogen atmosphere (P-N2 = 2.5 MPa). The combustion temperature recorded with a thermocouple was in the 1700-1900 degrees C range. We examined the physical mechanisms governing the formation of AIN crystals, and we treated this problem as a case study of the dynamics of crystal growth from the liquid phase. Particular attention was given to the basic theoretical understanding of the subject, utilizing first-principles density functional theory calculations. The Wulff construction method was applied to identify equilibrium structures of nano and microscale AIN crystals. Energy minimization arguments were used to show that certain crystal planes of AIN are more probable than others, giving the crystal 6-fold symmetry. The integrated experiments and computations form the basis for our proposal of the underlying mechanisms for nucleation and growth of the AIN crystals.</P>