Vapor Decomposition Research Articles

Effect of water vapor and low-temperature decomposition on the structure and electrophysical properties of nonstoichiometric compound Ba2YCu3O7 − δ

The effect of water vapor and decomposition into phases with different oxygen contents on the structure and electrophysical properties of the nonstoichiometric compound Ba2YCu3O7 − δ has been studied. Both these factors were shown to lead to the formation of structural defects that can be pinning centers and improve the current-carrying capacity of materials. At the same time, the reaction with water leads to a deterioration of superconducting properties of grain boundaries. The optimum electrophysical properties of Ba2YCu3O7 − δ can be reached by choosing appropriate heat-treatment conditions, namely, the temperature and time of annealing and the water-vapor content in the annealing atmosphere. The phase diagram of the Ba2YCu3O6-Ba2YCu3O7 system below 400°C is refined.

Silver and gold modified plasmonic TiO 2 hybrid films for photocatalytic decomposition of ethanol under visible light

Plasmonic noble metal nanoparticles (NPs) (silver and gold) are able to sensitise photocatalysts in visible light by modifying the TiO 2 surface with 0.5 wt% loading. These plasmonic catalysts were supported by optically transparent zirconium dioxide and layer silicate. The hybrid catalyst films (with ∼10 μm thickness) were prepared by sputtering the aquatic suspension of the catalyst/support suspension on glass slides and irradiated the films by visible light ( λ ≥ 435 nm). The photocatalytic efficiency was studied on decomposition of ethanol vapour, and the residual concentration of ethanol was monitored. The intermediates during illumination were analysed by GC–MS. Modifications with silver and gold lead to a change in the optical properties due to the plasmonic light absorption on TiO 2. The supporting binding materials are almost transparent in UV–vis wavelength range, thus Ag- and Au-modified TiO 2 can be excited by the incoming light without much loss of the photon energy. Furthermore, the layered silicate promoted the photocatalytic process by its high adsorption capacity. Due to these two phenomena, a synergistic effect was found on the photocatalytic activity of the nanocomposite hybrid films.

Carbonyl materials: Preparation, properties, and application

The synthesis of powders, films, and coatings obtained by CVD during thermal decomposition of metal carbonyl vapors is considered. The conditions for obtaining them, as well as their main properties and fields of application, are shown.

Production of single-walled carbon nanotubes from methane over Co-Mo/MgO nanocatalyst: A comparative study of fixed and fluidized bed reactors

In this study, the performances of fixed and fluidized bed reactors in the production of single-walled carbon nanotubes (SWNTs) have been investigated. In both reactors, single-walled carbon nanotubes were grown by catalytic chemical vapor decomposition (CCVD) of methane over Co-Mo/MgO nanocatalyst under two different operating conditions. The synthesized samples were characterized by TEM, TGA and Raman spectroscopy. It is found that the performance of a fluidized bed in the synthesis of carbon nanotubes is much better than that of a fixed bed. The quality of carbon nanotubes obtained from the fluidized bed was significantly higher than that from the fixed bed and the former one with the I D /I G ratio of 0.11 while the latter one with the I D/ I G ratio of 0.71. Also, the yield of SWNTs in the fluidized bed was 92 wt%, while it was 78 wt% in the fixed bed. These advantages of fluidized bed reactors for the synthesis of carbon nanotubes can be attributed to more available space for the growth of carbon nanotubes and more uniform temperature and concentration profiles.

Growth of single-walled carbon nanotubes with controlled diameters and lengths by an aerosol method

On the basis of combined study of the transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and ultraviolet–visible–near infrared absorption spectroscopy, the properties of the single-walled carbon nanotubes (SWCNTs), synthesized by aerosol (floating catalyst) chemical vapor deposition method by ferrocene vapor decomposition in the presence of carbon monoxide, are studied in details. The results show that increasing the temperature gives rise to the formation of high quality and large diameter SWCNTs. By monitoring the water-cooled probe position, both the bundle length and the diameter of the SWCNTs are effectively tuned due to the variation of the residence time and temperature profile in the reactor. An introduction of a small amount of CO 2 suppresses the growth of small diameter nanotubes and enlarges the mean diameter of SWCNT samples. The mean diameter of SWCNTs could be easily altered in a broad range from 1.1 to 1.9 nm during growth, which is essential for the SWCNT applications in optical and electronic devices.

A very promising piezoelectric property of [formula omitted] thin films. I: Monoclinic–trigonal phase transition

Ceramic thin films of tantalum oxide of a new trigonal structure ( a=12.713(7) Å, α = 28.201 ( 0 ) ° , space-group R3) were produced by thermal treatments of amorphous deposits on (001)Si wafers, either by electrostatic spray deposition or by injection metal-organic chemical vapor decomposition. This trigonal phase comes from the transformation of a monoclinic phase 11L- or 25L- Ta 2 O 5 . The transformation is reversible under oxygen atmosphere and, from results of TEM investigations, occurs mainly via atomic motions along the z unique axis of the monoclinic structure parallel to the polar three-fold axis of the trigonal structure. The non-centrosymmetry and direction of polar axis of the trigonal phase, identified by high resolution TEM imaging, indicate a possibility of very high electric dipole moments linked to a strong piezoelectricity. From results of XPS analyses of both monoclinic and trigonal structures, the binding energies remain similar to those of Ta 2 O 5 . As the formation of the trigonal structure gives rise to an important volume expansion, stresses induced in ceramic thin films are likely influencing both properties of birefringence and piezoelectricity which are presented in a separated article (part II). It is mentioned that the formation of trigonal phase does not occur in bulk Ta 2 O 5 samples, for which an incommensurate phase transition has been observed in a previous work.

Investigation of thermal properties of the volatile carbonyl compounds of rhenium Re2(CO)10 and Re(CO)3(C5H5)

The present work deals with the investigation of the thermal properties of two volatile rhenium compounds Re2(CO)10 and Re(CO)3(C5H5). The thermal behaviour of Re(CO)3(C5H5) in the condensed phase is studied by means of thermogravimetry and differential scanning calorimetry. Thermal decomposition of the vapour of Re2(CO)10 and Re(CO)3(C5H5) is studied in vacuum and in the presence of hydrogen and water vapour by means of insitu high-temperature mass spectrometry. The routes of vapour decomposition on a heated surface are proposed. Using Knudsen’s effusion method with mass spectrometric registration of the composition of the gas phase, and the flow method, temperature dependences of saturated vapour pressure were measured; thermodynamic parameters of the sublimation of complexes were calculated. For Re2(CO)10 we specified the data on the saturated vapour pressure using two independent methods within the temperature range below the phase transformations of the compound and the start of decomposition of complex vapour: ΔHTaver∘=(95.5±2.3)kJ·mol−1, ΔSTaver∘=(188.3±7.0)J·mol−1·K−1 (effusion method), ΔHTaver∘=(93.6±1.7)kJ·mol−1, ΔSTaver∘=(187.5±5.0)J·mol−1·K−1 (flow method). For Re(CO)3(C5H5) the thermodynamic characteristics were determined for the first time: ΔHTaver∘=(85.2±1.0)kJ·mol−1, ΔSTaver∘=(173.6±2.7)J·mol−1·K−1 (flow method).

Non-Enzymatic Amperometric Glucose Biosensor from Zinc Oxide Nanoparticles Decorated Multi-Walled Carbon Nanotubes

The present work describes the development of novel ZnO dispersed multi-walled carbon nanotubes (MWNT) based non-enzymatic glucose biosensor with 1 M NaOH solution as the supporting electrolyte. For a comparison, the same material has been used for the fabrication of enzymatic biosensor and studied its electrochemical activity with phosphate buffer solution as the electrolyte. MWNT have been synthesized by catalytic chemical vapor decomposition (CCVD) and a simple sol-gel method was used for decorating crystalline ZnO nanoparticles on MWNT. Cyclic voltammetry and chronoamperometry were used to study and optimize the electrochemical performance of the resulting enzymatic and non-enzymatic ZnO/MWNT biosensors. The non enzymatic Nafion/ZnO/MWNT/GC electrode shows linearity in the range 700 nM to 31 mM with the detection limit of 500 nM. Similarly enzymatic biosensor fabricated using Nafion/GOD/ZnO/MWNT on glassy carbon electrode (GCE) shows a linearity from 1 microM to 22 mM. This excellent performance of non enzymatic Nafion/ZnO/MWNT/GC is due to high surface area, good electron transfer rate of ZnO/MWNT and the high electrochemical catalytic activity of ZnO in NaOH solution.

The effect of carbon precursors (methane, benzene and camphor) on the quality of carbon nanotubes synthesised by the chemical vapour decomposition

The effect of carbon precursors on carbon nanotube (CNT) formation was studied. The catalyst used was Fe 3O 4/MgO without prior reduction by hydrogen. Methane, benzene and camphor were used to produce CNTs at 600, 700, 800, 900 and 1000 °C. The results show that the types of carbon precursors greatly affect the quality of CNTs produced. The CNTs obtained from the decomposition of methane had the lowest intensity of D band to G band ratio ( I D/ I G) compared to the I D/ I G ratios of CNTs produced using benzene and camphor at 900 and 1000 °C, respectively. This low I D/ I G ratio is due to the difference in the molecule structures between methane, benzene and camphor, which resulted in different CNT growth mechanism. Raman analysis showed that single-walled carbon nanotubes of high quality were formed at 900 °C using methane as carbon precursor.

Preparation and surface functionalization of MWCNTs: study of the composite materials produced by the interaction with an iron phthalocyanine complex

Carbon nanotubes [CNTs] were synthesized by the catalytic vapor decomposition method. Thereafter, they were functionalized in order to incorporate the oxygen groups (OCNT) and subsequently the amine groups (ACNT). All three CNTs (the as-synthesized and functionalized) underwent reaction with an iron organometallic complex (FePcS), iron(III) phthalocyanine-4,4",4",4""-tetrasulfonic acid, in order to study the nature of the interaction between this complex and the CNTs and the potential formation of nanocomposite materials. Transmission electronic microscopy, N2 adsorption at 77 K, thermogravimetric analysis, temperature-programmed desorption, and X-ray photoelectron spectroscopy were the characterization techniques employed to confirm the successful functionalization of CNTs as well as the type of interaction existing with the FePcS. All results obtained led to the same conclusion: There were no specific chemical interactions between CNTs and the fixed FePcS.

Controlled Synthesis of Single-Walled Carbon Nanotubes in an Aerosol Reactor

The growth mechanism and influence of synthesis parameters on the properties of single-walled carbon nanotubes (SWNTs) produced by ferrocene vapor decomposition in a carbon monoxide atmosphere have been investigated in detail by a combined study of Raman and UV−vis−NIR absorption spectroscopy and transmission electron microscopy (TEM). CO2 plays an essential role in selective etching of small diameter nanotubes and the purification of SWNTs. This etching effect is beneficial to narrow the diameter distribution and to control the average diameter of SWNTs. Increasing the synthesis temperature results in the formation of larger catalyst particles due to a higher agglomeration rate, thereby forming larger diameter nanotubes. Decreasing the CO flow rate, and thus lengthening the agglomeration time, also provides the possibility to enlarge the diameter of SWNTs. Therefore, by varying the growth parameters, the mean diameter of SWNTs can be effectively changed from 1.2 to 1.8 nm to satisfy the needs of various applications.

Topography and nanomechanical properties of Pd-C films

Abstract Atomic force microscopy (AFM) topographical studies and results of nanoindentation experiment for several palladium-carbon films (Pd-C film) deposited on various substrates and with varying palladium content are presented. Pd-C films were prepared by a physical vapor decomposition (PVD) process and next were modified by a chemical vapor decomposition (CVD) method to obtain carbonaceous porous structure with dispersed palladium nanograins and a variation in roughness. The dependence of film topography on the kind of substrate such as Al2O3, Mo polycrystalline foil and fused silica was studied by AFM. Nanomechanical properties such as hardness and the reduced indentation modulus were determined by nanoindentation. A comparison of these values for films with different Pd content deposited on various substrates is presented.

A novel Ca3(PO4)2–CaCO3 support mixture for the CVD synthesis of roughened MWCNT-carbon fibres

Multiwalled carbon nanotubes (MWCNTs) with unusual rough surfaces (including pits) have been synthesised by the chemical vapour decomposition process of acetylene using a novel Ca3(PO4)2–CaCO3 support mixture. An Fe–Co bimetallic mixture (50 : 50, w/w) was impregnated (5 wt% loading) onto either Ca3(PO4)2 to give <1% MWCNTs or CaCO3 to give high yields of MWCNTs with smooth surfaces. Mixtures of Ca3(PO4)2–CaCO3 (0/100–100/0) yielded tubes with very rough surfaces (t = 30 min, 1 h) and the CNT yield increased with respect to the amount of CaCO3 in the support mixture. The inner walls of the CNTs possessed a regular orientation of crystalline graphite sheets (3–5 nm), while the outer surface of the CNTs had a thick, rough, compact layer (∼30 nm) of carbon with a random orientation of graphite sheets. These induced extremely rough surfaces of the CNTs could serve as ‘docking stations’ that can harbour a variety of metal catalyst particles for industrially important applications.

Aerosol characterization and lung deposition of synthesized TiO2 nanoparticles for murine inhalation studies

This study presents a novel exposure protocol for synthesized nanoparticles (NPs). NPs were synthesized in gas phase by thermal decomposition of metal alkoxide vapors in a laminar flow reactor. The exposure protocol was used to estimate the deposition fraction of titanium dioxide (TiO2) NPs to mice lung. The experiments were conducted at aerosol mass concentrations of 0.8, 7.2, 10.0, and 28.5 mg m−3. The means of aerosol geometric mobility diameter and aerodynamic diameter were 80 and 124 nm, and the geometric standard deviations were 1.8 and 1.7, respectively. The effective density of the particles was approximately from 1.5 to 1.7 g cm−3. Particle concentration varied from 4 × 105 cm−3 at mass concentrations of 0.8 mg m−3 to 12 × 106 cm−3 at 28.5 mg m−3. Particle phase structures were 74% of anatase and 26% of brookite with respective crystallite sized of 41 and 6 nm. The brookite crystallites were approximately 100 times the size of the anatase crystallites. The TiO2 particles were porous and highly agglomerated, with a mean primary particle size of 21 nm. The specific surface area of TiO2 powder was 61 m2 g−1. We defined mice respiratory minute volume (RMV) value during exposure to TiO2 aerosol. Both TiO2 particulate matter and gaseous by-products affected respiratory parameters. The RMV values were used to quantify the deposition fraction of TiO2 matter by using two different methods. According to individual samples, the deposition fraction was 8% on an average, and when defined from aerosol mass concentration series, it was 7%. These results show that the exposure protocol can be used to study toxicological effects of synthesized NPs.

Correlation between the characteristics of multi-wall carbon nanotubes and the structure of the metal oxides used as catalytic precursors for their production

Well defined La–Ni–O oxide structures are prepared by a sol–gel like method and treated at three different temperatures in order to modify their phases and degree of crystallinity, close to that of LaNiO 3 perovskite. It is observed that depending on the temperature of the treatment, three crystalline structures (LaNiO 3, La 2Ni 2O 5 and La 4Ni 3O 10) are obtained, some of them containing an additional NiO phase. All these structures, characterized by X-ray diffraction and scanning and transmission electron microscopy before reduction, are used for the synthesis of multi-wall carbon nanotubes (MWCNTs) by the catalytic decomposition of methane. The reducibility of each phase under hydrogen is studied by programmed thermo reduction. After reduction and chemical vapor decomposition, inner and outer diameters of the MWCNTs are analyzed. It is found that these characteristics are strongly correlated to the structure of the oxides formed as catalytic precursors.

Structural parameters of carbon nanotubes obtained by the chemical vapor decomposition of ethylene onto nickel nanoparticles deposited on basic supports

The structural parameters of carbon nanotubes (CNT) obtained on different catalysts were studied. Depending on the support and method of catalyst preparation, the formation of cylindrical multi-wall, spiral CNT and nanofibers with different mean diameters and diameter distribution is possible. Nitrogen adsorption occurs mainly on the outer surface of the CNT.

Influence of the chemical activation of carbon nanofibers on their use as catalyst support

Three nickel catalysts supported on carbon nanofibers (CNFs) have been prepared by deposition–precipitation (ca. 3%, w/w). The CNFs were prepared by catalytic chemical vapour decomposition of ethylene over a Ni/SiO 2 catalyst, and chemically activated with RbOH (CNF RbOH) and KOH (CNF KOH). The materials were characterized by transmission electron microscopy (TEM), N 2 adsorption–desorption, temperature-programmed oxidation, X-ray diffraction (XRD), acid–base titrations and temperature-programmed decomposition in helium. KOH was the most effective activating agent, developing carbon porosity, decreasing the crystalline character and increasing surface acidity to a higher extent. After nickel introduction, the catalysts were characterized by temperature-programmed reduction, XRD, TEM, N 2 adsorption–desorption and acid–base titrations. Surface-area weighted mean Ni particle diameters (post reduction at 400 °C) followed the sequence: Ni/CNF KOH (4.9 nm) < Ni/CNF RbOH (8.6 nm) < Ni/CNF (25.5 nm), where a further activation of the support led to smaller/better dispersed nickel particles. The surface acidity of the catalysts followed the sequence: Ni/CNF RbOH < Ni/CNF < Ni/CNF KOH. The gas phase hydrogenation of butyronitrile was used as a surface characterization test, where bigger nickel particles consistently developed higher catalytic activity. Selectivity, however, was not sensitive to metal particle size, but increased towards condensation products with increasing catalyst acidity.

Investigation on capacity fading of LiFePO4 in aqueous electrolyte

The capacity loss rate of LiFePO4 in aqueous electrolyte was found to be much faster than it in organic electrolyte. The cycling stability in aqueous electrolyte with various dissolved oxygen content and pH value was extensively studied by cyclic voltammetry. It was found that both high OH− and dissolve O2 content can accelerate the cycling fading of LiFePO4. It has been proved that the capacity fading of LiFePO4 is due to not only chemical instability but also electrochemical instability. Mössbauer spectroscopy demonstrated that the Fe(III)-containing species was formed in the active materials arisen from the irreversible side reaction. The carbon-coated LiFePO4 prepared by chemical vapor decomposition method shows significantly improvement in cycling stability. The carbon coating technology provides an effective approach to enhance cycling performance in aqueous electrolyte as well as proof of proposed fading mechanism.

Pre-exponential factor of the hopping conductivity in disordered carbon films

The conductivity of carbon films grown by polymethylphenylsiloxane vapor decomposition in stimulated dc discharge plasma was studied. It is found that the Mott hopping conductivity \( \sigma \left( T \right) = \sigma _0 \left( T \right)\exp \left\{ { - \frac{{T_0 }} {T}^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} } \right\} \) is characteristic of the samples under study in the temperature range of 80–400 K in the electric field E to 5 · 104 V/cm. An analysis of the pre-exponential factor σ 0(T) = σ 00(T 0)T α allowed the conclusion that the hopping transport is most adequately described in the model with the exponential energy dependence of the density of localized states for which α = −1/2 and the universal relation ln σ 00 −T 0 1/4 0 is valid, which is satisfied in the range where the parameter σ 00 varies by eight orders of magnitude.

Theoretical Investigation of the Interaction between Carbon Monoxide and Carbon Nanotubes with Single‐Vacancy Defects

Density functional theory calculations are used to study the healing process of a defective CNT (i.e. (8,0) CNT) by CO molecules. The healing undergoes three evolutionary steps: 1) the chemisorption of the first CO molecule, 2) the incorporation of the C atom of CO into the CNT, accompanied by the adsorption of the leaving O atom on the CNT surface, 3) the removal of the adsorbed O atom from the CNT surface by a second CO molecule to form CO(2) and the perfect CNT. Overall, adsorption of the first CO reveals a barrier of 2.99 kcal mol(-1) and is strongly exothermal by 109.11 kcal mol(-1), while adsorption of a second CO has an intrinsic barrier of 32.37 kcal mol(-1)and is exothermal by 62.34 kcal mol(-1). In light of the unique conditions of CNT synthesis, that is, high temperatures in a closed container, the healing of the defective CNT could be effective in the presence of CO molecules. Therefore, we propose that among the available CNT synthesis procedures, the good performance of chemical vapor decomposition of CO on metal nanoparticles might be ascribed to the dual role of CO, that is, CO acts both as a carbon source and a defect healer. The present results are expected to help a deeper understanding of CNT growth.