Vapor Decomposition Research Articles

Density functional theory of vapor to liquid heterogeneous nucleation: Lennard–Jones fluid on solid substrate

Density functional theory has been applied to investigate the vapor to liquid heterogeneous nucleation on a flat solid surface, by invoking a model free energy density functional along with an exponential density model. The effects of supersaturation of the vapor and the strength of the solid-fluid interaction on the nucleation barrier have been investigated for Lennard–Jones fluid with 12–6 fluid–fluid and 9–3 solid–fluid interaction model. The spinodal decomposition of vapor has been observed at higher supersaturation or at higher strength of the solid–fluid interaction. The shape, density profile and the free energy of formation of droplets of any arbitrary size have been obtained in this work.

Oxygen Reduction Activity of Vapor-Grown Platinum Nanotubes

Supportless platinum nanotubes are synthesized by the decomposition of a platinum acetylacetonate vapor within anodic alumina templates at 210 {degree sign}C. As synthesized, the nanotubes are nanoparticulate aggregates composed of Pt crystallites approximately 3 nm in diameter and with a range of lengths from 1 μm to 20 μm. Annealing treatments result in crystallite growth and morphological evolution of the tubular nanostructures. The oxygen reduction activity of the PtNTs was investigated using the rotating disc electrode method at room temperature. PtNTs annealed at 500 {degree sign}C exhibited a specific activity of 2084 μA/cm2Pt at 0.9 V, a value approaching that of polycrystalline Pt. The electrochemical surface area of the annealed structures was found to be quite low, from 5-10 m2/g, resulting in moderate overall mass activity of up to 177 mA/mgPt.

Thermal behavior of a series of monomeric Ni(II) complexes with β-iminoketones

We presented a series of nickel(II) complexes with iminoketones Ni[R′C(O)CHC(NH)R″]2, where R′, R″=CH3, CF3, C(CH3)3, that could serve as MOCVD precursors for depositing Ni-containing films. By TGA in a helium flow, all the reported compounds show evaporation in a single smooth step with 100% mass loss up to temperature of 210 and 260°C for fluorinated and non-fluorinated ligands, respectively. Saturated vapor pressure of the compounds was measured by flow method, it was revealed that complexes with the fluorinated ligands have close volatility increased in comparison with non-fluorinated ones. Thermodynamic parameters of evaporation ΔHT0 and ΔST0 were determined. Mass spectrometric study of the thermal decomposition of the compounds vapor under conditions of low-pressure CVD showed that thermolysis starts within the temperature range of 270–310°C depending on the ligand.

Comparative Measurements and their Compliance with Standards of Total Mercury Analysis in Soil by Cold Vapour and Thermal Decomposition, Amalgamation and Atomic Absorption Spectrometry

Two methods to measure mercury concentration in soil are compared, and their compliance with international standards is determined: cold vapour atomic absorption spectrometry and thermal decomposition, amalgamation and atomic absorption spectrophotometry. The detection limit, quantification limit and uncertainty of these two analytical methods were evaluated and compared. The results indicated that thermal decomposition, amalgamation and atomic absorption spectrophotometry had a lower quantification limit and uncertainty than cold vapour atomic absorption spectrometry (quantification limit, 0.27 vs. 0.63 mg kg−1; expanded uncertainty, 9.30 % vs. 10.8 %, respectively). Thermal decomposition, amalgamation and atomic absorption spectrophotometry allowed the determination of the base values for the concentration of mercury in soil recommended by international standards, achieving a lower detection limit than cold vapour atomic absorption spectrometry under the study conditions. In addition, thermal decomposition, amalgamation and atomic absorption spectrophotometry represent a more environmentally friendly alternative for mercury determination because this method uses fewer reagents and therefore generates less waste.

Oxygen Reduction Activity of Vapor-Grown Platinum Nanotubes

Supportless platinum nanotubes (PtNTs) were synthesized by the decomposition of platinum acetylacetonate vapor within anodic alumina templates at 210°C. As synthesized, the nanotubes are nanoparticulate aggregates composed of Pt crystallites approximately 3 nm in diameter and with a range of lengths from 1 μm to 20 μm. Annealing treatments result in crystallite growth and morphological evolution of the tubular nanostructures including the development of nanoscale porosity. In rotating disk electrode measurements carried out in 0.1 M HClO4, porous PtNTs annealed at 500°C exhibited a specific activity for oxygen reduction of 2390 ± 423 μA/cm2Pt at 0.9 V, comparable to bulk polycrystalline Pt. The electrochemical surface area of the annealed structures was a relatively low 10 m2/g, resulting in a moderate overall mass activity of 240 ± 41 mA/mgPt.

Characteristics of Carbon Nanospheres Prepared from Locally Deoiled Asphalt

Iraqi deoil asphalt as a source of carbon is used to prepare the carbon nanospheres (CNS) by chemical vapor deposition (CVD) method. Asphalt after further chemical treatment to remove aromatic oil and impurities was crushed, weighted and evaporated under inert atmosphere using argon. The vapor/argon mixture was allowed to pass through high temperature zone 900°C in quartz tube over CO/Al2O3catalyst material. The carbon precipitated from the decomposition of asphalt vapor was collected and identified using atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffractometer (XRD), BET surface area technique and atomic force microscope. A sphere shape of carbon (94%) with nanosize and diameter less than 100 nm with surface area of 360 m2/g has been obtained.

Experiment and Modeling of Water Vapour Decomposition on ZrNi5 Alloy

Experiment and Modeling of Water Vapour Decomposition on ZrNi5 Alloy

Heat Conduction Characteristics of Vertically Aligned Single-Walled Carbon Nanotubes Measured by Raman Spectroscopy

In this work, the film thermal conductivity and the film-substrate interfacial thermal contact resistance of vertically-aligned single-walled carbon nanotube (VA-SWNT) films were measured with a proposed method utilizing temperature dependence of Raman spectrum. The proposed method harnesses the excitation laser power of the Raman spectroscopy to heat the VA-SWNT films synthesized on a silicon substrate by alcohol catalytic chemical vapor decomposition (ACCVD) method, and measures film temperature from the Raman spectrum. A relationship between the input laser heat and the measured temperature is modeled with a detailed heat conduction equation, and its numerical solutions were compared with the experimentally measured results to extract the film thermal conductivity and the film-substrate interfacial thermal contact resistance. The method found the thermal conductivity of the VA-SWNT film to be around 2 Wm-1K-1 and the film-substrate interfacial thermal contact resistance to be around 2×10-6 m2KW-1. The obtained film thermal conductivity corresponds to the thermal conductivity equivalent of an individual SWNT of several tens of Wm-1K-1. This value was more than an order of magnitude smaller than the values reported on individual SWNTs.

Decomposition of Odorous Toluene Vapor by Peroxide Ions

Decomposition of Odorous Toluene Vapor by Peroxide Ions

Synthesis of Al2O3 thin films using laser assisted spray pyrolysis (LASP)

The present study reports the development of a laser assisted ultrasonic spray pyrolysis technique and synthesis of dense optical alumina films using the same. In this technique ultrasonically generated aerosols of aluminum acetylacetonate dissolved in ethanol and a laser beam (Nd:YAG, CW, 1064nm) were fed coaxially and concurrently through a quartz tube on to a hot substrate mounted on an X–Y raster stage. At the laser focused spot the precursor underwent solvent evaporation and solute sublimation followed by precursor vapor decomposition giving rise to oxide coating, the substrate is rastered to get large surface area coating. The surface morphology revealed coalescence of particles with increase in laser power. The observed particle sizes were 17nm for films synthesized without laser and 18, 21 and 25nm for films made with laser at 25, 38 and 50W, respectively. Refractive index of the films synthesized increased from 1.56 to 1.62 as the laser power increased from 0 to 50W. The stoichiometry of films was studied using XPS and the increase in interfacial layer thickness with laser power was observed from dynamic SIMS depth profiling and ellipsometry.

High-Yield Synthesis of Cubic and Hexagonal Boron Nitride Nanoparticles by Laser Chemical Vapor Decomposition of Borazine

We report a new method for the synthesis of boron nitride nanostructures (nBN) using laser chemical vapor decomposition (LCVD). Borazine was used as precursor and excited with two simultaneous radiations, the fundamental and second YAG laser harmonics. If only one of the two radiations is employed, no reaction takes place. Abundant BN powder is obtained after one hour of laser radiation. The BN yield obtained with the LCVD technique is about 83% by weight. The BN material was characterized using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. They all indicate that the BN powder consists of a mixture of hexagonal and cubic BN nanostructures. No other BN phases or stoichiometries were found. The size of the resulting BN nanostructures is in the range of 20–100 nm and their B : N composition is 1 : 1. A simplified mechanism involving laser-excited states followed by photoinduced removal of hydrogen is proposed to understand the synthesis of BN nanopowder by LCVD of borazine.

Fabrication and Characterization of Highly Crystalline and Stable Phase-Pure Rutile Nanowires

A homogeneous thin layer of TiO2 has been successfully coated on the surface of multiwalled carbon nanotubes (MWCNTs), which were produced by catalytic chemical vapor decomposition method, via an in situ sol-gel method. The obtained MWCNT-TiO2 composite materials were heat treated in air at high temperatures, attempting to produce highly crystalline pure rutile nanowires. Through comprehensive characterization obtained by scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray (EDX), and X-ray powder diffraction (XRD), the effect of heat treatment on crystallization and phase transformation was discussed, and the effect of absence of MWCNTs on the morphology of pure rutile nanowires was analyzed. Both anatase and rutile phases exist after heat treatment in 700 degrees C while only rutile phase exists after heat treatment in 800 degrees C. The crystal size of rutile is formed to be significantly larger than that of anatase, and the hollow tubular structure is found to be destroyed which resulted in nanowire structure.

회전식 화학증착 장치 내부의 유동해석을 통한 최적 유량 평가

A numerical investigation is conducted to search for the optimal flow rate for a rotating-disk chemical vapor decomposition reactor operating at a high temperature and a low pressure. The flow of a gas mixture supplied into the reactor is modeled by a laminar flow of an ideal gas obeying the kinetic theory. The axisymmetric two-dimensional flow in the reactor is simulated by employing a CFD package FLUENT. With operating pressure and temperature fixed, numerical computations are performed by varying rotation rate and flow rate. Examination of the structures of flow and thermal fields leads to a flow regime diagram illustrating that there are a stable plug-like flow regime and a few unfavorable flow regimes induced by mass unbalance or buoyancy. The criterion for sustaining a plug-like flow regime is discussed based on a theoretical scaling argument. Interpretation of the flow regime map suggests that a favorable flow is attainable with a minimum flow rate at the smallest rotation rate guaranteeing the dominance of rotation effects over buoyancy.

Direct growth of graphene films on TEM nickel grids using benzene as precursor

We report a direct synthesis of single-layer, bi-layer, and multi-layer graphene films on a nickel grid surface by chemical vapor decomposition of liquid precursor benzene. The direct route, by avoiding several wet chemical steps and accompanying mechanical stresses and contamination common to all presently reported graphene transfer to microscopy grid method, enables providing pristine microstructure information for as-prepared graphene films. A liquid precursor based growth route opens a new door to tailor the electronic properties of graphene by doping heteroatoms using various organic liquids containing the dopant atoms.

Role of Hydrocarbon Radicals CHx (x=1, 2, 3) in Graphene Growth: A Theoretical Perspective

Many outstanding properties of graphene are blocked by the existence of structural defects. Herein, we propose an important healing mechanism for the growth of graphene, which is produced via plasma-enhanced chemical vapor decomposition (PECVD), that is, the healing of graphene with single vacancies by decomposed CH(4) (hydrocarbon radical CH(x), x=1, 2, 3). The healing processes undergo three evolutionary steps: 1) the chemisorption of the hydrocarbon radicals, 2) the incorporation of the C atom of the hydrocarbon radicals into the defective graphene, accompanied by the adsorption of the leaving H atom on the graphene surface, 3) the removal of the adsorbed H atom and H(2) molecule to generate the perfect graphene. The overall healing processes are barrierless, with a huge released heat of 530.79, 290.67, and 159.04 kcal mol(-1), respectively, indicative of the easy healing of graphene with single vacancies by hydrocarbon radicals. Therefore, the good performance of the PECVD method for the generation of graphene might be ascribed to the dual role of the CH(x) (x=1, 2, 3) species, acting both as carbon source and as defect healer.

Fabrication of nanostructured clay–carbon nanotube hybrid nanofiller by chemical vapour deposition

Growth of multiwalled carbon nanotube (CNT) assemblies by chemical vapour decomposition (CVD) technique was achieved through decomposition of acetylene using iron impregnated montmorillonite (MM) catalysts. Various amounts of iron loaded montmorillonite catalysts were prepared by wet impregnation method and calcined at 450°C. The catalysts were subjected to X-ray diffraction (XRD) and surface area analyses. Acetylene decomposition at a feed ratio of N2:H2:C2H2=1:1:0.18 was conducted in the presence of iron impregnated montmorillonite catalysts in the CVD reactor for the growth of CNT structures. The role of Fe-activated clay catalyst on the formation of CNT structures has been systematically examined at various temperatures and correlated with the morphological features of CNTs. Catalyst assisted acetylene decomposition results the formation of different carbon nanostructures such as nanotubes, nanofibres and nanoflakes. These clay–CNT products were characterised for their morphological, thermal, qualitative and quantitative analyses. The morphological variations of CNT assemblies reveal Fe-montmorillonite catalysts have high selectivity at given reaction conditions. Thermogravimetric and Raman spectral analyses prove that the CNTs contain a good crystallanity and less structural defects.

Reason for Ionic Liquids to be Combustible

Abstract Recently, ionic liquids were verified to be combustible instead of nonflammable; the contrary was thought to be true due their extremely low vapor pressure. Flash point is one of the most important variables used to characterize the fire and explosion hazards of liquids. Because of extremely low vapor pressure and decomposition at elevated temperatures, the reason for ionic liquids to be combustible should be different from that of traditionally defined liquids. The flash point of ionic liquids in relation to their decomposition was investigated in this study by the estimation of vapor pressure and by use of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and flash point analyzer apparatus. The ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]), 1-hexyl-3-methylimidazolium chloride ([C6mim][Cl]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]), were selected as test examples. Results revealed that the flammability of ionic liquids was mainly attributed to the decomposition of the ionic liquids generating flammable substances instead of themselves vaporizing, as do traditionally defined combustible/flammable liquids.

Relationship between flash point of ionic liquids and their thermal decomposition

Recently, ionic liquids were verified to be combustible instead of nonflammable; the contrary was thought to be true due their extremely low vapor pressure. Flash point is one of the most important variables used to characterize the fire and explosion hazards of liquids. Because of extremely low vapor pressure and decomposition at elevated temperatures, the reason for ionic liquids to be combustible should be different from that of traditionally defined liquids. The flash point of ionic liquids in relation to their decomposition was investigated in this study by the estimation of vapor pressure and by use of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and flash point analyzer apparatus. The ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]), 1-hexyl-3-methylimidazolium chloride ([C6mim][Cl]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]), were selected as test examples. Results revealed that the flammability of ionic liquids was mainly attributed to the decomposition of the ionic liquids generating flammable substances instead of themselves vaporizing, as do traditionally defined combustible/flammable liquids. Lyon's method, applied by Fox et al. to estimate the flash point of ionic liquids from the TGA decomposition temperature, was assessed using our experimental data and the data from the published literature and resulted in substantial overestimation of the flash-point values of ionic liquids, which underestimates the fire and explosion hazards of ionic liquids. This deviation is attributed to flash-point values of ionic liquids located in the second temperature range of the TGA tracing, rather than in the third analogue, as predicted by Lyon's method.

Synthesis of multiwalled carbon nanotubes from bamboo charcoal and the roles of minerals on their growth

Abstract Multiwalled carbon nanotubes (MWCNTs) were synthesized from bamboo charcoals by chemical vapor deposition in the presence of ethanol vapor. Fresh bamboo culms were first heat treated at 1000–1500 °C to form charcoals. The elemental composition and structure of mineral phases in the bamboo charcoal treated at different temperatures were analyzed. The results showed that Mg 2 SiO 4 and particularly calcium silicate were responsible for the nucleation and growth of MWCNTs at 1200–1400 °C. Transmission electron microscope and energy dispersive X-ray spectrometer observations indicated that the tips of nanotubes synthesized at 1200–1400 °C consist mainly of calcium silicate. Such silicate tips acted as effective catalysts for nanotubes. The growth of MWCNTs followed the vapor–liquid–solid model including an initial decomposition of ethanol vapor into carbon, dissolution of carbon inside molten silicate and final nucleation of nanotubes.

Growth of nitrogen-doped carbon nanotubes and fibers over a gold-on-alumina catalyst

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by chemical vapor decomposition of a N,C-precursor over a supported Au catalyst. Large quantities of carbon nanotubes with a compartmentalized structure containing ca. 5 at.% N were produced over a 1.5% Au/δ-Al 2O 3 catalyst with a mean diameter of Au particles equal to 2.8 nm under continuous flow conditions at 800 °С and 1 bar of the reaction gas mixture containing pyridine (Py) vapor (5 vol.%), Н 2 (10–20 vol.%) and Ar (balance). The majority of the N-CNTs obtained after 10 min have outer diameters (ODs) of 13–45 nm and closed tips without any encapsulated gold particles of the catalyst which indicates the “base-growth” mechanism of N-CNT formation. Carbon deposits synthesized for 30–135 min contain carbon fibers with OD values up to several micrometers, formed by self-assembling of N-CNTs, and individual N-CNTs. X-ray photoelectron spectra provide evidence for various chemical states of nitrogen (pyridinic, “quaternary” (graphitic) and pyrrolic nitrogen) in the N-CNTs, and these are discussed.