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>

Shape-controlled synthesis of titanium microparticles using calciothermic reduction concept

Nersisyan, Hayk,Kwon, Suk Cheol,Ri, Vladislav,Lee, Young Jun,Yoo, Bung Uk,Lee, Jong Hyeon Elsevier 2018 Journal of solid state chemistry Vol.267 No.-

<P><B>Abstract</B></P> <P>This paper reports the preparation of Ti microparticles that are angular and spherical in shape through the combustion of a TiO<SUB>2</SUB> + αCa (where α is moles of Ca) exothermic mixture in an inert atmosphere. The relationship between the combustion parameters and the properties of the resultant Ti particles is discussed with consideration of the effect of Ca concentration. Using excess amounts of Ca in the experiment was effective in modifying the shape of the particles from angular to spherical. The Ti powder was found to be well-dispersed and the diameter of individual particles ranged from 5 µm to 50 µm. Based on the combustion parameters, the activation energy for the redox reaction was calculated as ∼ 138 kJ/mol. This paper discusses the chemistry of the reduction process and highlights the effects of combustion temperature and the amount of liquid calcium on the characteristics of the Ti particles.</P> <P><B>Graphical abstract</B></P> <P>The combustion process in TiO<SUB>2</SUB> + Ca mixture developed a maximum temperature of about 1820 °C and resulted in Ti spherical particles.</P> <P>[DISPLAY OMISSION]</P>

Zr fine powder synthesized from a ZrO₂–Mg-additives system and its burning stability when printed in thin layers

Nersisyan, Hayk,Yoo, Bung Uk,Kwon, Suk Cheol,Kim, Dae Young,Han, Seul Ki,Choi, Jeong Hun,Lee, Jong Hyeon Elsevier Science Inc 2017 Combustion and Flame Vol.183 No.-

<P><B>Abstract</B></P> <P>In this study, we examined the effect of potassium perchlorate (KClO<SUB>4</SUB>) and magnesium hydroxide (Mg(OH)<SUB>2</SUB>) additives on the combustion behavior of a ZrO<SUB>2</SUB> +2Mg mixture to produce a fine powder of zirconium metal. The results of thermodynamic analysis and experiments imply that nearly 0.04mol of KClO<SUB>4</SUB> is needed to initiate a combustion reaction in the ZrO<SUB>2</SUB> +2Mg system. As the amount of KClO<SUB>4</SUB> increases from 0.04 to 0.1mol, the combustion temperature increases from 1250 to 1850°C. This results in formation of fine zirconium powder with a typical particle size of less than 5µm, and with 1.4–2.2wt% residual oxygen. Subsequent reduction of particle size to 100–500nm, and oxygen content to <1.0wt% was achieved by adding Mg(OH)<SUB>2</SUB>. The as-prepared Zr powder was mixed with nitrocellulose and printed onto 10–100µm thin-layers to study their burning stability. The wave propagation in a thin layer was on the order of 0.35–30cm/s, which is suitable for applications requiring localized power generation.</P>

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>

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>

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>

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>

Melt-assisted solid flame synthesis approach to amorphous boron nanoparticles

Nersisyan, Hayk H.,Joo, Sin Hyong,Yoo, Bung Uk,Cho, Young Hee,Kim, Hong Moule,Lee, Jong-Hyeon Elsevier 2015 Combustion and Flame Vol.162 No.9

<P><B>Abstract</B></P> <P>A melt-assisted solid flame synthesis approach was applied to synthesize boron nanoparticles in argon gas and air atmospheres. For this purpose, we investigated the characteristics of a thermally induced combustion wave in B<SUB>2</SUB>O<SUB>3</SUB> + <I>α</I>Mg mixtures (<I>α</I> =1.0–1.5mol) in argon and air atmospheres. Utilizing stoichiometrically insufficient amounts of magnesium ensured that a large portion of molten B<SUB>2</SUB>O<SUB>3</SUB> remained in the sample, which reduced the combustion parameters and favored the formation of boron nanoparticles. Under these conditions the combustion temperature and burning velocity were controlled in the range of 1300–1580°C and 0.065–0.18cm/s, respectively, and boron nanoparticles in a ∼20–200nm size range were obtained. The characteristics of boron nanoparticles (morphology, purity, specific surface area, oxidation activity, etc.) were analyzed and a reaction pathway leading to boron nanoparticles synthesis was proposed.</P>

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>