Gas-phase Chemical Deposition Research Articles

Modification of chemical vapor-phase deposition and coking resistance over HZSM-5 catalysts for toluene disproportionation

Abstract To achieve higher catalytic activity of toluene disproportionation and improve the p-xylene selectivity and stability of coking resistance on HZSM-5 catalysts, tetrabutyl titanate, ethyl orthosilicate and diethyl phosphite were used for chemical gas-phase deposition modification on HZSM-5 catalysts. The properties of acid sites on catalysts were characterized by infrared spectroscopy (IR) and temperature-programmed desorption of pyridine (TPD), respectively. The experimental results showed that the type of acid sites and density of weaker acid sites over HZSM-5 zeolites deposited by oxides containing Ti, Si and P in chemical vapor coating did not change while the density of stronger acid sites decreased, in which acid intensity on HZSM-5 zeolite deposited by oxides containing P enhanced obviously. Using HZSM-5 zeolites modified as catalysts of toluene disproportionation, HZSM-5 catalysts deposited by oxides containing Si and P can greatly improve both catalytic activity and coking resistance on catalysts.

Оценка коррозионных свойств вольфрамового покрытия контейнеров для РАО, нанесенного газофазным методом

The article summarizes the study exploring the anti-corrosion characteristics of tungsten coatings produced by chemical gas-phase deposition in a solution simulating the geochemical conditions at the Yeniseiskiy site. The study shows that a 30-micron-thick tungsten-based coating appears to be quite stable with an average corrosion rate of 1.4 microns/year. It also notes the high stability of tungsten coatings under microbial fouling conditions.

Calculating the penetration depth of reaction in chemical gas-phase deposition of boron nitride within porous bodies

The thermodynamic calculations conducted using the TERRA software package for the B–Cl–N–H system revealed that the inclusion of hydrogen into the B–Cl system significantly diminishes the thermodynamic stability of BCl3 with the possibility of boron formation in the condensed phase. On the other hand, the introduction of ammonia, which includes hydrogen, results in the synthesis of boron nitride across a broad temperature spectrum. The analysis of kinetic relationships uncovered three distinct regions in the boron nitride deposition process: K – kinetic region (up to 1400 K), D – diffusion region (above 1800 K) and T – transition region. The activation energy for the kinetic region was calculated as Ea = 134 kJ/mol. Within the temperature range of 1023–1123 K, linear dependences were observed. The computation of the penetration depth for the boron nitride deposition process assumed a gas mixture of boron trichloride, ammonia, and argon (BCl3 + NH3 + 30Ar). The results indicated that boron trichloride governs the extent of penetration. The depths of penetration for the chemical vapor infiltration boron nitride (CVI-BN) process, conducted at 0.1 kPa within the temperature range of 1100–1400 K, were determined for pore diameters of 1, 10, 30, 100, 200 and 300 µm. When porosimetry data for a specific preform is available, the acquired penetration depth relationships for the CVI-BN process under specific parameters and process temperatures facilitate the estimation of essential parameters for interphase formation using pyrolytic boron nitride.

Thermodynamic Study of a Volatile Complex of Magnesium Benzoyltrifluoroacetonate with N,N,N',N'-Tetramethylethylenediamine

To expand the library of volatile magnesium precursors certified for effective use in chemical gas-phase deposition of the corresponding oxide or fluoride layers, a thermodynamic study of the mixed ligand complex Mg(tmeda)(btfac)2 (tmeda is N,N,N',N'-tetramethylethylenediamine, btfac is benzoyl trifluoroacetonate) have been performed. The melting process has been studied using DSC (Tm = 459.4 ± 0.3 K,= 42.9 ± 0.4 kJ/mol); the sublimation process has been studied using the flow (transfer) method in the temperature range 407–447 K (= 163 ± 6 kJ/mol, ΔsublS427 = 293 ± 14 J/(mol K)). The substance passes into the gas phase with partial decomposition. Thermodynamic modeling of the composition of condensed phases formed from Mg(tmeda)(btfac)2 with the addition of H2 or O2 has been performed depending on the temperature (700–1300 K), total pressure (133–13 332 Pa), and the ratio of the reagent gas to the precursor (0–300). The data obtained can be used to determine the experimental parameters of the processes for obtaining functional layers. Comparison of the results with a similar trifluoroacetylacetonate complex made it possible to quantitatively reveal the effect of replacing the methyl group in the anionic ligand with a phenyl one.

Prospects of Application and Global Significance of Graphene

The review article is an excursus into the world publications describing the properties of graphene, methods of synthesis of it and variety of its application fields. The paper describes in detail the structure of graphene as well as the methods for its fabrication: micromechanical cleavage, chemical stratification, epitaxial growth, and chemical gas-phase deposition, including their advantages and disadvantages. In addition, the review contains information on the electronic, mechanical, optical, and chemical properties of graphene, which lend its uniqueness. Due to its unique properties, graphene and its modified quasi-two-dimensional structures are the objects of increased scientific interest in various fields of science, such as energy, electronics, optoelectronics, medicine, bioengineering, aerospace, aviation, ecology, materials engineering, etc. In order to expand the journal readership among the physicists, chemists, and materials scientists, who are not deep specialists in graphene science, the style of the present review is somewhere close to popular science one.

Thermodynamic Study of Iridium(I) Complexes as a Basis for Chemical Gas-Phase Deposition Technology

Thermodynamic Study of Iridium(I) Complexes as a Basis for Chemical Gas-Phase Deposition Technology

TSF-MOCVD – a novel technique for chemical vapour deposition on oxide thin films and layered heterostructures

A new principle for supplying volatile precursors to MOCVD gas-phase chemical deposition systems is proposed, based on a two-stage evaporation of an organic solution of precursors from a soaked cotton thread, which passes sequentially through the zones of evaporation of the solvent and precursors. The technological capabilities of TSF-MOCVD (Thread-Solution Feed MOCVD) are demonstrated based on examples of obtaining thin epitaxial films of СеО2, h-LuFeO3 and thin-film heterostructures β-Fe2O3/h-LuFeO3. The results of studying the obtained films by X-ray diffraction, energy dispersive X-rayanalysis, and high- and low-resolution transmission microscopy are presented. Using the TSF module, one can finely vary the crystallisation conditions, obtaining coatings of the required degree of crystallinity, as evidenced by the obtained dependences of the integral width of the h-LuFeO3 reflection on the film growth rate. Based on the TEM and XRD data, it was concluded that β-Fe2O3 grows epitaxially over the h-LuFeO3 layer. Thus, using TSF-MOCVD, one can flexibly change the composition of layered heterostructures and obtain highly crystalline epitaxial films with a clear interface in a continuous deposition process

Colloidal Nanostructures of Transition-Metal Dichalcogenides.

ConspectusLayered transition-metal dichalcogenides (TMDs) are intriguing two-dimensional (2D) compounds where metal and chalcogen atoms are covalently bonded in each monolayer, and the monolayers are held together by weak van der Waals forces. Distinct from graphene, which is chemically inert, layered TMDs exhibit a wide range of electronic, optical, catalytic, and magnetic properties dependent upon their compositions, crystal structures, and thicknesses, which make them fundamentally and technologically important. TMD nanostructures are traditionally synthesized using gas-phase chemical deposition methods, which are typically limited to small-scale samples of substrate-bound planar materials. Colloidal synthesis has emerged as an alternative synthesis approach to enable the scalable synthesis of free-standing TMDs. The judicious selection of precursors, solvents, and capping ligands together with the optimization of synthesis parameters such as concentrations and temperatures leads to the fabrication of colloidal TMD nanostructures exhibiting tunable properties. In addition, understanding the formation and transformation of TMD nanostructures in solution contributes to the discovery of important structure-function relationships, which may be extendable to other anisotropic systems.In this Account, we summarize recent progress in the colloidal synthesis, characterization, and applications of TMD nanostructures with tunable compositions, structures, and thicknesses. On the basis of the preparation of Mo- and W-based disulfide, diselenide, and ditelluride nanostructures, we discuss examples of phase engineering where various metastable TMD compounds can be directly accessed at low temperatures in solution. We also analyze the chemistry involved in broadly tuning the composition across the MoSe2-WSe2, WS2-WSe2, and MoTe2-WTe2 solid solutions as well as atomic-level microscopic characterization and the resulting composition-tunable properties. We then highlight how the high densities of defects in the colloidally synthesized TMD nanostructures enable unique catalytic properties, including their ability to facilitate the selective hydrogenation of substituted nitroarenes using molecular hydrogen. Finally, using this library of colloidal TMD nanostructures as substrates, we discuss the pathways by which noble metals deposit onto them in solution. We highlight the importance of the relative strengths of the interfacial metal-chalcogen bonds in determining the sizes and morphologies of the deposited noble metal components. These synthesis capabilities for colloidal TMD nanostructures, which have been generalized to a library of composition-tunable phases, enable new systematic studies of structure-property relationships and chemical reactivity in this important class of 2D materials.

ИНФОРМАЦИОННАЯ ПОДДЕРЖКА ПРИНЯТИЯ РЕШЕНИЙ ПРИ ПРОИЗВОДСТВЕ КАТАЛИЗАТОРА СИНТЕЗА УГЛЕРОДНЫХ НАНОТРУБОК

The aim of the study is to develop information systems for supporting and supporting decision-making in the production of a metal oxide catalyst that provides targeted synthesis of carbon nanotubes by gas-phase chemical deposition. To achieve the goal, the following tasks were solved: a new approach to the process of creating a catalyst for the thermal decomposition of unstable compounds for synthetic nanotubes was developed; experimental studies of the effect on the post-thermal treatment of the catalyst and its precursors by physical action (ultrasonic, electromagnetic and microwave fields, etc.), which were obtained the approximating characteristics of the synthesized models of carbon nanostructures on the parameters of the process of pre- and post-thermal treatment of the catalyst were used to create a recommendation module. On the basis of the results obtained, blocks of implementation and technologies were developed, used in the creation of a system for maintaining and supporting solutions for the production of a catalyst for synthetic nanotubes. The application of the developed system of maintenance and support of decisions makes it possible to form a catalyst that makes it possible to synthesize carbon nanotubes with specified characteristics. Also, the use of this information system in the production of a catalyst helps to expand the range of synthesized nanoproducts in the process of gas-phase chemical deposition without changing the composition of the catalyst.

Investigation of gas-phase processes for the preparation of fiber-reinforced organomorphic ceramic composites with a SiC-matrix

The isothermal process of gas-phase chemical deposition for the compaction of organomorphic carbon-fiber preforms with a SiC-matrix obtained by carbonization of compressed fibers of oxidized polyacrylonitrile has been investigated. Their feature is high (up to 70 %) and uniform pore size (reduced pore diameter from several micrometers to several tens of micrometers) porosity. The problem of optimizing the technological parameters of the process of obtaining ceramic-matrix composites (CMC) was solved by a combination of experimental research and numerical modeling. Experimental samples of CMC were obtained using a non-halogen precursor of methylsilane CH3SiH3, and their residual porosity was determined. For the numerical study of the gas-phase process of compaction of preforms, a 1D model was used. The simulation results were compared with experimental observations.

SYNTHESIS AND FUNCTIONALIZATION OF CARBON NANOTUBES FOR SUPERCAPACITOR ELECTRODES

Carbon nanotubes (CNTs) have been synthesized using catalysts of the Ni/Mg, Fe-Co/Al2O and Co-Mo/Al2O3-MgO composition with different component ratios by gas-phase chemical deposition. They differ in geometric parameters, the nature of the inclusion of metal oxide catalyst impurities, and morphological features. To form oxygen-containing functional groups on the surface, CNTS were oxidized with ozone-oxygen mixture (1 vol.% O3) at room temperature for 5 h. Initial and functionalized CNT samples were characterized by scanning and transmission electron microscopy, Raman and IR spectroscopy. It is shown that as a result of oxidation, the amorphous phase is removed from the material, and oxygen-containing groups-OH, >C=O and –O–C–O–are formed on the CNT surface. Also, during functionalization, there is a slight decrease in the specific surface area of the studied nanotube samples. The electrochemical behavior of initial and functionalized carbon nanotubes in an alkaline electrolyte was studied using cyclic voltammetry. It is shown that based on the analysis of CVA curves, CNTS can be divided into two groups-with the Faraday and non-Faraday character of the current electrode processes. The contribution of the non-Faraday component prevails when carbon nanotubes synthesized on Ni/Mg and Co-Mo/Al2O3-MgO catalysts are used as electrode materials. Oxidative functionalization of CNTs of this type is appropriate and contributes to the improvement and stabilization of capacitance properties during cycling. The positive influence of metal oxide catalyst admixtures on the properties of electrode materials was also noted. Therefore, ozone oxidation is a promising way to functionalize CNTs for their subsequent use as electrode materials for electrochemical capacitors.

INFLUENCE OF LIQUID-PHASE OXIDATIVE TREATMENTS ON STRUCTURE AND HYDROPHILITY OF CARBON NANOTUBES

Carbon nanotubes (CNTs) were synthesized by gas phase chemical deposition (CVD) using methane as a hydrocarbon reagent and using a catalyst of iron oxide deposited on fine aluminum oxide, as well as the same catalyst with the addition of molybdenum oxide deposited on fine magnesium oxide. The synthesized materials were treated with concentrated nitric acid (HNO3) or a mixture of concentrated nitric and sulfuric acids (HNO3 / H2SO4) in a volume ratio of 2: 1, at a temperature of 110-120 ° C for 1 h. Some of them were subjected to peroxide action (H2O2) before oxidative acid treatments for 1-2 h at a temperature of 100-110 ° C. Structural features, elemental compositions of synthesized CNTs were investigated before and after liquid-phase oxidative treatments by methods such as transmission electron microscopy, Raman spectroscopy, X-ray energy dispersive spectroscopy, X-ray phase analysis. In this work, the ability of CNTs that were undergone treatment in various oxidizing environments to form stable concentrated aqueous suspensions was studied. It was established that the initial defectity of the CNT molecules significantly affects the hydrophilic properties of oxidized CNT modifications. This causes their different ability to form concentrated, stable aqueous suspensions, predetermines the choice of combinations of oxidizing liquid-phase treatments that most contributing to this. It was revealed that HNO3 and HNO3 / H2SO4 mixture at the used temperature conditions of treatments and their duration do not have a strong destructive effect on the structure of CNT. The oxidative effect of these reagents on the molecules of this material is manifested mainly in defective places. The cleaning of the catalytic components of the synthesis from the catalytic components contributes to the more efficient purification of HNO3 / H2SO4 with the formation of stable aqueous suspensions from the molecules of this material, and this does not depend on the characteristics of the synthesis of the CNTs.

Heat conduction in a shell with gas-phase deposition of material on its surface

The development of additive technologies such as gas-phase deposition provides the possibility of applying various coatings with different properties. The study introduces a model of heat conduction which relies on the specific character of heat and mass transfer in chemical gas-phase deposition on a curvilinear surface with a linear change in the curvature over the shell thickness. A difference scheme was constructed with use the interpolation method, and the computational solution of the problem was found. The approximation and the stability of difference schemes were investigated, and examples of numerical calculations for various materials were given.

Thermal Stability of Ni3Al-Based Composite with Honeycomb Structure

By powder metallurgy, materials in the form of a single-phase alloy based on Ni3Al and the corresponding composite Ni3Al + W with honeycomb structure are produced. The structural unit of the composite is a round granule (mean size 25 μm) of nickel alloy surrounded by a continuous tungsten coating (thickness ~0.4 μm) applied by chemical gas-phase deposition. Compressive tests at room temperature show that the yield point of the composite Ni3Al + W at 20–1000°C exceeds that of the single-phase Ni3Al-based alloy (by a factor of as much as 1.7). However, at higher temperatures, the yield points of the alloy and composite are comparable. The unit yield point (standardized at a density of 7.8 g/cm3 for the alloy and 9.5 g/cm3 for the composite) behaves analogously. At 1300°C, the single-phase Ni3Al-based alloy exhibits solid–liquid behavior in compression. Creep tests with compression in vacuum at 1000–1200°C are conducted. By pair and parametric analysis of the creep processes according to Hollomon, regression equations for the creep rate, stress, and test temperature are obtained. The creep limit is calculated from the tolerances on the steady creep rate and its inverse. At all the test temperatures, the composite is characterized by lower creep rate (by a factor of seven) and higher creep limit (by a factor of 2.5) than for the nickel alloy on which it is based. The activation energy of creep is determined for the alloy and composite on the basis of an exponential relationship between the experimental quantities. The activation energy of creep for the nickel alloy is close to the activation energy of nickel self-diffusion in Ni3Al and materials based on it (230–310 kJ/mol). For the composite, it is close to the activation energy of tungsten self-diffusion (503 kJ/mol).

Применение ионно-лучевой обработки для предварительной активации поверхности многостенных углеродных нанотрубок при формировании композитов с оксидом олова методом химического газофазного осаждения

Применение ионно-лучевой обработки для предварительной активации поверхности многостенных углеродных нанотрубок при формировании композитов с оксидом олова методом химического газофазного осаждения

Hexanuclear Na(I) complex with 3,5-dimethyl-1H-pyrazole and its anion

The crystal structure of a hexanuclear Na(I) complex based on 3,5-dimethyl-1H-pyrazole (C5H8N2) and its anion is determined (space group P21/c, a = 12.2194(5) A, b = 24.1554(9) A, c = 11.3311(4) A, β = 109.942(1)°, V = 3143.99(8) A3, Z = 2). The crystal structure is formed by Na6(C5H8N2)4(C5H7N2)6 molecules. Thermogravimetric studies show that the compound exhibits volatility at elevated temperatures. The compound can be used in chemical gas-phase deposition processes.

Producing hardfacing composite materials for ecologically safe technologies

The application of hardfacing materials for producing high-strength coatings on components working in abrasive wear conditions is one of the important directions of research into increasing the service life of road construction, agricultural and other types of equipment. However, in producing this equipment, the ecological safety requirements are sometimes ignored and this results in negative effects on the environment and the health of personnel. This article describes the results of scientific and research investigations of the team of authors to develop a cladding powder by the method of chemical gas phase deposition of nickel tetracarbonyl on the surface of aluminium oxide particles and application of the powder for producing wear-resistant coatings. The powder materials are deposited in a closed cycle excluding contact of the personnel with toxic substances and emission of contaminants into the atmosphere, resulting in a safe process. Plasma coatings with the required physical–mechanical properties have been produced. This confirms the efficiency of the approaches used in this case and increases the service life of working sections of machines subjected to abrasive wear.

Synthesis of Carbon Nanostructures on Nickel Nanopowders Produced by the Method of Electric Explosion of Conductors

The authors present the results of experiments on the synthesis of carbon nanostructures by the method of thermal chemical gas-phase deposition with the use of nickel nanopowders produced by the method of electric explosion of conductors and utilized as the catalysts. To study the process of origination and growth of individual carbon nanostructures, the authors conducted experiments not only on nanopowders, but also on separated clusters. Experiments were conducted at different temperatures (200–700°C) and pressures (100–400 mbar) to determine optimum conditions and the lower temperature boundary for carbon-nanostructure synthesis. The experiments have shown that the lower boundary of synthesis for nanopowders is a temperature of 325°C. For the separated powders, as for the nanopowders, stable growth of carbon nanostructures was observed at 350°C, but at pressures lower than 300 mbar. Unlike the carbon nanostructures produced on nanopowders, carbon nanostructures on separated powders exhibit a strong dependence of their origination and growth on temperature and pressure. Results of the Raman spectroscopy and of the x-ray structural analysis have shown that carbon nanostructures grown at 325°C and 300 mbar have the highest purity.

Production of Amorphous and Nanocrystalline Silicon Films by the Hot-Wire Activation Method

Thin films of amorphous silicon with inclusions of a nanocrystalline silicon phase have been obtained by the method of gas-phase chemical deposition with hot-wire activation of the precursor. The influence of the gas pressure and of the hydrogen–monosilane ratio on the rate of growth and the degree of crystallinity of the deposited silicon has been investigated. Characteristic values of the synthesis parameters for obtaining silicon films of various degrees of crystallinity have been established.

Solvent-free thermoplastic-poly(dimethylsiloxane) bonding mediated by UV irradiation followed by gas-phase chemical deposition of an adhesion linker

Here, we introduce a solvent-free strategy for bonding various thermoplastic substrates with poly(dimethylsiloxane) (PDMS) using ultraviolet (UV) irradiation followed by the gas-phase chemical deposition of aminosilane on the UV-irradiated thermoplastic substrates. The thermoplastic substrates were first irradiated with UV for surface hydrophilic treatment and were then grafted with vacuum-evaporated aminosilane, where the alkoxysilane side reacted with the oxidized surface of the thermoplastic substrate. Next, the amine-terminated thermoplastic substrates were treated with corona discharge to oxidize the surface and were bonded with PDMS, which was also oxidized via corona discharge. The two substrates were then hermetically sealed and pressed under atmospheric pressure for 30 min at 60 °C. This process enabled the formation of a robust siloxane bond (Si–O–Si) between the thermoplastic substrate and PDMS under relatively mild conditions using an inexpensive and commercially available UV lamp and Tesla coil. Various thermoplastic substrates were examined for bonding with PDMS, including poly(methylmethacrylate) (PMMA), polycarbonate (PC), poly(ethyleneterephthalate) (PET) and polystyrene (PS). Surface characterizations were performed by measuring the contact angle and performing x-ray photoelectron spectroscopy analysis, and the bond strength was analyzed by conducting various mechanical force measurements such as pull, delamination, leak and burst tests. The average bond strengths for the PMMA–PDMS, PC–PDMS, PET–PDMS and PS–PDMS assemblies were measured at 823.6, 379.3, 291.2 and 229.0 kPa, respectively, confirming the highly reliable performance of the introduced bonding strategy.