Deposition Of Carbide Research Articles

On the change of preferential growth orientation in chemical vapor deposition of titanium carbide by aromatic hydrocarbon precursors

Thin films of titanium carbide grown by chemical vapor deposition exhibit a strong preferential (111) growth direction if aromatic hydrocarbons, such as benzene, are used as a carbon precursor. If aliphatic hydrocarbons such as methane are used, growth on the (100) surface is preferred. In this study, quantum chemical computations are used to study the adsorption of benzene and methane on the (100) and (111) surfaces to provide an explanation for the changed growth behavior. The adsorption energy of benzene is found to be approximately twice as high on the (111) surface as compared to the (100) surface, and adsorption studies further suggest that benzene chemisorbs on the (111) surface, while it physisorbs on the (100) surface. The studies reveal no significant differences in adsorption energy or behavior for methane on the two surfaces. The authors propose that the higher benzene adsorption energy and different adsorption behavior on the (111) surface are the explanations for the preferential growth orientation.

Thermodynamic Analysis and Growth of Zirconium Carbide by Chemical Vapor Deposition

Abstract Equilibrium calculations were used to optimize conditions for the chemical vapor deposition of zirconium carbide from zirconium halide + CxHy+H2+Ar system. The results show the CVD-ZrC phase diagram is divided into ZrC+C, ZrC and ZrC+Zr zones by C, Zr generating lines. For the same mole of ZrCl4 reactant, it needs higher concentration of CH4 to generate single ZrC phase than that of C3H6. Using these calculations as a guide, single-phase cubic zirconium carbide coatings were deposited onto graphite substrate.

PH localization: a case study during electrophoretic deposition of ternary MAX phase carbide-Ti<sub>3</sub>SiC<sub>2</sub>

The pH localization phenomenon during electrophoretic deposition (EPD) of the MAX phase-Titanium silicon carbide (Ti3SiC2), from suspension in aqueous and mixed (water-ethanol) solvent was experimentally verified in presence of a cationic dispersant, polyethyleneimine (PEI). The local pHs at the electrodes were dependent on solid loadings of the suspensions; pH localization was pronounced at lower solid loading. Higher solid loading resulted in thicker deposits, shielding the electrode surface and hindering direct interaction of the electrode with the particles, thereby suppressing the change in local pH. Comparison of local pH at cathode during EPD from aqueous and mixed solvent revealed a delay in the attainment of isoelectric point (IEP) at the vicinity of electrode and slower deposition rate for mixed solvent. A necessity of concurrence between the IEP of the material and the local pH at the deposition electrode for a given system was established for the formation of good deposits.

Scaling of Thermal Positioning in Microscale and Nanoscale Bridge Structures

Heat transfer in a thermally positioned doubly clamped bridge is simulated to obtain a universal scaling for the behavior of microscale and nanoscale bridge structures over a range of dimensions, materials, ambient heat transfer conditions, and heat loads. The simulations use both free molecular and continuum models to define the heat transfer coefficient, h. Two systems are compared: one doubly clamped beam with a length of 100 μm, a width of 10 μm, and a thickness of 3 μm, and a second beam with a length of 10 μm, a width of 1 μm, and a thickness of 300 nm, in the air at a pressure from 0.01 Pa to 2 MPa. The simulations are performed for three materials: crystalline silicon, silicon carbide, and chemical vapor deposition (CVD) diamond. The numerical results show that the displacement and the response of thermally positioned nanoscale devices are strongly influenced by ambient cooling. The displacement depends on the material properties, the geometry of the beam, and the heat transfer coefficient. These results can be collapsed into a single dimensionless center displacement, δ* = δk/q″αl2, which depends on the Biot number and the system geometry. The center displacement of the system increases significantly as the bridge length increases, while these variations are negligible when the bridge width and thickness change. In the free molecular model, the center displacement varies significantly with the pressure at high Biot numbers, while it does not depend on cooling gas pressure in the continuum case. The significant variation of center displacement starts at Biot number of 0.1, which occurs at gas pressure of 27 kPa in nanoscale. As the Biot number increases, the dimensionless displacement decreases. The continuum-level effects are scaled with the statistical mechanics effects. Comparison of the dimensionless displacement with the thermal vibration in the system shows that CVD diamond systems may have displacements that are at the level of the thermal noise, while silicon carbide systems will have a higher displacement ratios.

Transient stages during the chemical vapour deposition of silicon carbide from CH3SiCl3/H2: impact on the physicochemical and interfacial properties of the coatings

Transient chemical vapour deposition experiments were produced from MTS/H2 mixtures by varying the deposition temperature or the gas flow rates (QMTS or QH2) versus time. The gas phase, deposition rates and properties of the transient coating (φTr) were investigated and adhesion assessments of SiC/φTr/SiC bilayers were performed by scratch testing. Transient stages resulting from a decrease of QMTS or temperature lead to silicon co-deposition, but do not affect interfacial properties. Transient stages resulting from a decrease of QH2 eventually lead to carbon co-deposition. Thick and continuous carbon interlayers lead to a poor adhesion whereas thin and discontinuous layers do not.

Deposition of TiC film on titanium for abrasion resistant implant material by ion-enhanced triode plasma CVD

Deposition of titanium carbide (TiC) layer on titanium (Ti) surface has been demonstrated by an ion-enhanced triode plasma chemical vapor deposition (CVD) method using a TiCl4+CH4+H2 gas mixture. Physical and mechanical properties of the deposited TiC film on Ti were investigated to examine its potential application as an abrasion resistant implant material. X-ray diffraction (XRD) showed that the specimen was consisted of TiC and Ti. Carbide layer of about 6μm thickness was observed on the cross section of the specimen by scanning electron microscopy (SEM). The Vickers hardness of surface carbide was more than 2000, which confirmed its high abrasion resistance.

Modular deposition chamber forin situX-ray experiments during RF and DC magnetron sputtering

A new sputtering system for in situ X-ray experiments during DC and RF magnetron sputtering is described. The outstanding features of the system are the modular design of the vacuum chamber, the adjustable deposition angle, the option for plasma diagnostics, and the UHV sample transfer in order to access complementary surface analysis methods. First in situ diffraction and reflectivity measurements during RF and DC deposition of vanadium carbide demonstrate the performance of the set-up.

C3H8-SiCl4-H2시스템에서 FactSage를 이용한 압력-조성-온도 3차원 상평형도의 응용

In order to deposit a homogeneous and uniform β-SiC films by chemical vapor deposition, we constructed the phase-diagram of β-SiC over graphite and silicon via computational thermodynamic calculation considering pressure(P), temperature(T) and gas composition(C) as variables in C 3 H 8 -SiCl 4 -H 2 system. During the calculation, the ratio of Cl/Si and C/Si is maintained to be 4 and 1, respectively, and H/Si ratio is varied from 2.67 to 15,000. The P-T-C diagram showed very steep phase boundary between SiC+C and SiC region perpendicular to H/Si axis and also showed SiC+Si region with very large H/Si value of ~6700. The diagram can be applied not only to the prediction of the deposited phase composition but to compositional variation due to the temperature distribution in the reactor. The P-T-C diagram could provide the better understanding of chemical vapor deposition of silicon carbide.

Investigation of iron oxide reduction by ethanol as a potential route to produce hydrogen

In this work, a novel way to indirectly store and produce H2 from ethanol was investigated using a two-step process based on the reduction of iron oxide followed by oxidation with H2O. The reduction of different iron oxides, i.e., Fe2O3, Fe3O4 and FeOOH, with ethanol to produce Feo was investigated. TPRe (Temperature Programmed Reactions) and Mössbauer and XRD analyses showed that ethanol reduces Fe2O3 sequentially to Fe3O4 at 350–500°C, to Fe3O4/FeO at 500–600°C and finally to Feo at 700°C. The formed Feo can then be oxidized by H2O to produce H2 and Fe3O4, as shown by Mössbauer and XRD analyses. Cyclic experiments showed that iron could be consecutively reduced/oxidized at least 5 times without any significant decrease in H2 production after the second cycle. However, reactions of Fe2O3 with ethanol at higher temperatures, i.e., 800 and 900°C, led to the formation of iron carbide and significant carbon deposition. XPS, SEM, TEM, Raman and TG showed 24–28wt% carbon content, particularly on the surface as nanofibers and as amorphous and graphitic carbon.

Mo2C/SBA-15 Modified by Ni for the Dry Reforming of Methane

A Ni/Mo2C/SBA-15 catalyst was prepared for carbon dioxide reforming of methane to produce synthesis gas. The catalysts modified by nickel were prepared from ammonium heptamolybdate that was supported with SBA-15 and were carburized in a flow of 20.0 vol% CH4/H2 gas mixture. The catalyst was characterized by N2 adsorption, X-ray diffraction, and scanning electron microscopy analysis. The activity and stability of the catalysts for dry reforming of methane was tested at 1073 K, atmospheric pressure, gaseous hourly space velocity of 8,000 ml3 h−1 g−1, and a CH4/CO2 molar ratio of 1. The Ni/Mo2C/SBA-15 catalyst exhibited a better catalytic and anti-coking performance due to smaller metal particles, higher metal dispersion, and better ordered pore distribution compared with Mo2C catalysts. The surface carbon of nickel migrated to molybdenum carbide, which prevented the oxidation of molybdenum carbide and coke deposition.

Reaction Mechanism for the Thermal Decomposition of BCl3/CH4/H2 Gas Mixtures

This paper presents an ab initio study of the B/C/Cl/H gas phase mechanism, featuring 10 addition-elimination reactions involving BH(i)Cl(j) (i + j ≤ 3) species and a first description of the chemical interaction between the carbon-containing and boron-containing subsystems through the three reactions BCl(3) + CH(4) ⇌ BCl(2)CH(3) + HCl, BHCl(2) + CH(4) ⇌ BCl(2)CH(3) + H(2), and BCl(2) + CH(4) ⇌ BHCl(2) + CH(3). A reaction mechanism is then proposed and used to perform some illustrative equilibrium and kinetic calculations in the context of chemical vapor deposition (CVD) of boron carbide. Our results show that the new addition-elimination reaction paths play a crucial role by lowering considerably the activation barrier with respect to previous theoretical evaluations; they also confirm that BCl(2)CH(3) is an important species in the mechanism.

Multiscale Analysis of Silicon Carbide-Chemical Vapor Deposition Process

A kinetic study, which was performed by using multi-scale (a macro and a micro-scale) analysis, is presented in order to determine the reaction mechanism of the chemical vapor deposition (CVD) of silicon carbide (SiC) from CH3SiCl3 (MTS)/H2 gaseous mixture. The multi-scale analysis provides two well-defined reaction fields, corresponding to the flat substrates placed in a hot wall reactor and micro trenches on the substrate surface, with centimeter and submicron characteristic length scales, respectively. The microcavity method is a micro-scale analysis used to study the relative contributions of gas-phase and surface reactions to the SiC growth, and to determine the sticking probability of growth species in CVD reaction systems. From the macro-scale analysis, activation energy of the growth rate was estimated to be 43.0 kcal/mol at the up-stream part and the sticking probability was estimated to be 9.5 x 10(-7) at 1273 K and 6.8 x 10(-6) at 1373 K. On the other hand, we examined a sticking probability (eta) and the reaction mechanism by using the microcavity method. From the micro-scale analysis, we found that at least two growth species, a stable intermediate 1 (eta 1, = 1.3 x 10(-3) at 1273 K and 4.5 x 10(-3) at 1373 K) and a highly active intermediate 2 (eta 2 = 2.0 x 10(-1) at 1273 K and 5.4 x 10(-1) at 1373 K), are formed as byproducts of the gas-phase reaction. Activation energy of the sticking probability was 43.9 kcal/mol in the case of the intermediate 1 and 34.5 kcal/mol in the case of the intermediate 2. We could also confirm that the source precursor, MTS, was not the film growth species. Another analytical model based on Monte Carlo simulations correlates the film profile in the microcavity to the sticking probability of the deposition species. The combination of these two analysis techniques presents an overall picture of the reaction scheme.

Thermodynamic analysis and phase equilibria in the Ni-Cr-C system

In thermodynamic simulation of the phaseequi� libria in the threecomponent Ni-Cr-C system, we need to know the properties of the material formed in the twocomponent Ni-Cr, Ni-C, and Cr-C sys� tems. These systems were analyzed in (1-3). The agreement of the calculated and experimental coordi� nates of the invariant equilibria has been established. Systems with nickel are characterized by the forma� tion of substitutional and interstitial solid solutions. In the reaction of chromium and carbon, carbides of dif� ferent composition and structural type may be formed: Cr 23C6, Cr7C3, and Cr3C2 (4). In this system, there are two eutectic and two peritectic transformations, lead� ing to the deposition of various refractory chromium carbides from the melt. The Ni-Cr-C system was investigated in detail in (5). In this system, a threecomponent liquid solution is formed as well as ternary interstitial solid solutions of bcc structure (ferrite) and fcc structure (austenite). The reaction of the solution components leads to the formation of chromium and nickel carbides of compo� sition M 7 C 3 , M 23 C 6 , and Cr 3 C 2 , where M = Cr, Ni are components of the metallic sublattice.

Correlation of acoustic, physicochemical, and mechanical properties of coatings obtained using electron-beam welding deposition of chromium carbide on low-carbon steel

Multifunctional coatings have been developed using the method of nonvacuum electron-beam welding deposition of chromium carbide powder on low-carbon steel. The correlation dependences of the ultrasonic velocity, the thickness of coatings, the content of chromium in the coatings, and the loss of mass under exposure to corrosive media on the mechanical properties are constructed using the bend tests. It was shown that the observed correlation relations are mainly determined by two factors, i.e., the presence of a substitute doping agent of chromium in a solid solution and the character of a dislocation structure, which forms inside of the grain.

Study of hybrid PVD–PECVD process of Ti sputtering in argon and acetylene

Hybrid PVD–PECVD process of target sputtering in hydrocarbon containing atmosphere combines aspects of both conventional reactive magnetron sputtering (PVD) and plasma enhanced chemical vapour deposition (PECVD). Such process is being typically used for deposition of metal carbides embedded in hydrogenated carbon matrix. Compared to the conventional co-sputtering of metal and carbon targets, in the hybrid deposition process the source of the carbon is dissociated hydrocarbon vapour in plasma. The aim of this paper is to study the extent of similarities or differences between this hybrid process and the conventional reactive magnetron sputtering. We have chosen the sputtering of titanium target in acetylene containing atmosphere as a representative of the hybrid processes. We focused on experimental measurements of the hybrid PVD–PECVD process behaviour, the time necessary for the process to achieve steady-state conditions and basic modelling of the process.

Study on Alumina-Supported Cobalt–Nickel Oxide Catalyst for Synthesis of Acetonitrile from Ethanol

A new alumina-supported cobalt–nickel oxide catalyst for the synthesis of acetonitrile from ethanol and ammonia was prepared by coprecipitation-kneading method. The parameters influencing the reaction were studied thoroughly and an optimized process, which is running the reaction at 380 °C under atmospheric pressure while keeping the ammonia/alcohol molar ratio of 5 and GHSV of 1,163 h−1, was obtained. Under the optimized conditions the catalyst reached its best performance when being on stream for 40 h, at which the yield of acetonitrile was 92.6%. Then the selectivity to acetonitrile decreased gradually but the yield of acetonitrile always remained higher than 81% within 720 h. The samples of the fresh and used catalyst were characterized by XRD, XPS, TEM, EDX and N2 adsorption–desorption analysis. The results revealed that carbon deposition and formation of metal carbides from the active species in the catalytic runs led to the deterioration of the catalyst. A new Co–Ni/γ-Al2O3 catalyst for the amination of ethanol to acetonitrile was studied in a continuous fixed-bed reactor and the reaction parameters were optimized. The mechanisms for the formation of acetonitrile and butyronitrile were discussed. The reasons leading to the deterioration of the catalyst were investigated through the characterization of the fresh, used and regenerated samples of the catalyst by means of XRD, XPS, TEM and N2 adsorption–desorption techniques.

Experimental investigation of chemical looping hydrogen generation using iron oxides in a batch fluidized bed

Chemical looping hydrogen generation (CLHG) is a promising technology for the combustion of gas or solid fuels with hydrogen production and inherent separation of CO 2. In this paper, experiments on CLHG using iron oxides as oxygen carrier and CO as fuel were carried out in a batch fluidized bed. The effects of reduction time, operation temperature, particle sizes and addition of CO 2 in the reduction gases on hydrogen production were investigated. At 900 °C, the hydrogen concentration on a nitrogen-free base reached 99.3% in the steam oxidation phase. The key process for the redox of hematite for hydrogen generation was the reduction of hematite to wüstite or metallic iron. Iron carbide and carbon deposit occurred in the reduction phase, which released a little amount of CO and CO 2 in hydrogen production phase, while little CO or CO 2 were detected in the air oxidation phase. Longer reduction time favored deeper reduction of the oxygen carrier and increased hydrogen production. When the reduction time decreased from 40 to 20 min, the hydrogen concentration peak lowered from 17.72% to 10.68%. High temperature improved reduction reactivity and elevated hydrogen production. The average hydrogen concentrations were 6.15%, 6.22%, 6.28% and 7.50% for the redox temperatures of 800, 850, 900 and 950 °C, respectively. Particles in smaller sizes with higher BET surface areas and better fluidizability had higher hydrogen production. The rise of the CO 2 partial pressure in the reduction gases decreased hydrogen production. The peak of hydrogen concentration dropped from 12.10% to 3.30% when the inlet CO 2 partial pressure increased from 0% to 45.5%.

Pulsed ion beam-assisted carburizing of titanium in methane discharge

The carburizing of titanium (Ti) is accomplished by utilizing energetic ion pulses of a 1.5 kJ Mather type dense plasma focus (DPF) device operated in methane discharge. X-ray diffraction (XRD) analysis confirms the deposition of polycrystalline titanium carbide (TiC). The samples carburized at lower axial and angular positions show an improved texture for a typical (200)TiC plane. The Williamson–Hall method is employed to estimate average crystallite size and microstrains in the carburized Ti surface. Crystallite size is found to vary from ∼ 50 to 100 nm, depending on the deposition parameters. Microstrains vary with the sample position and hence ion flux, and are converted from tensile to compressive by increasing the flux. The carburizing of Ti is confirmed by two major doublets extending from 300 to 390 cm−1 and from 560 to 620 cm−1 corresponding to acoustic and optical active modes in Raman spectra, respectively. Analyses by scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) have provided qualitative and quantitative profiles of the carburized surface. The Vickers microhardness of Ti is significantly improved after carburizing.

Multiscale simulation for epitaxial silicon carbide growth by chlorides route

A multiscale–multi-hierarchy approach, based on a succession of simplified models, was used to describe the deposition and the film morphology evolution during the epitaxial silicon carbide deposition in an industrial hot wall reactor. The attention was focused on the system involving chlorinated species because of its superior performances with respect the traditional silane/hydrocarbons process. The evolution of the crystalline structure (i.e., from poly to single) and of the surface roughness can be understood by simply comparing two characteristic times, like those inherent the surface diffusion and the matter supply to the surface. Two other characteristic times were introduced to describe through a kinetic Monte Carlo model the line defects formation.

Growth Process of Polyaniline Thin Films Formed by Hot Wire CVD

AbstractWe explore the use of hot‐wire (HW) CVD as an alternative, solvent‐free technique to produce compact films similar to conventional polyaniline. Film deposition and molecular bonding are studied as functions of Ta filament temperature, aniline pressure, and substrate temperature to allow an insight into the film growth mechanism, which is postulated to depend largely on reactions of aniline with H and C atoms generated at the hot wire. The process gas, aniline, is found to cause rapid formation of tantalum carbide and carbon deposits on the hot Ta surface. The accompanying change in film quality as the filament ages is studied.