Farhat Samir - Academia.edu (original) (raw)

Papers by Farhat Samir

One-dimensional transport models of moderate-pressure H2 and H2/CH4 plasmas obtained in a diamond... more One-dimensional transport models of moderate-pressure H2 and H2/CH4 plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H2 plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H2/CH4 discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ionization kinetics of the plasma. Three major ions are generally obtained in H2/CH4 plasmas: C2H2, C2H3, and C2H5. The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the substrate surface. Finally the use of this transport model along with the surface chemistry model of Goodwin(1) enabled us to estimate the diamond growth rate for several discharge conditions.

Subject Index of Volume 29

Thermodynamic Criteria for Heat-Exchanger Networks Design

Diamond growth chemistry in a microwave PECVD reactor

Temperatures and Hydrogen Atom Concentrations in a Microwave Plasma Used for Diamond Deposition

Design of a substrate holder to surface temperature control in a microwave plasma reactor for CVD diamond films

Single wall carbon nanotubes synthesis by plasma arc-parameters of plasma

Heat of Adsorption of Hydrogen in Nanoporous Materials

Energy storage performance of metal allyl acetoacetate complex

Chemical Kinetics-Role of the plasma composition at the surface on diamond growth

of the plasma density at moderate pressures for a J. Thermophys

Non-Maxwellian effect on species and energy transport in moderate pressure H2 plasmas

Surface and Coatings Technology, 1997

An investigation of the electron kinetics, and species and energy transport in moderate pressure ... more An investigation of the electron kinetics, and species and energy transport in moderate pressure H2 plasmas is presented. The two-term expansion of the electron Boltzmann equation is solved for determining the electron energy distribution function (EEDF), which is used to estimate the rates of chemical reactions and of energy transfer between electrons and heavy species. These rates are then used in a one-dimensional transport model, which enables estimation of species concentrations and plasma temperatures. Results show that, in the considered plasmas, the electron-heavy species reaction rates depend mainly on the average electron energy. The assumption of a Maxwellian EEDF leads to a strong overestimation of the ionization degree (which is approximately equal to the electron mole fraction) and to the underestimation of H-atom density and average electron energy. The predicted gas and vibration temperature are only slightly affected by such an assumption.

Determining electron temperature and density in a hydrogen microwave plasma

Journal of Thermophysics and Heat Transfer, 1996

ABSTRACT A three-temperature thermo-chemical model is developed for analyzing the chemical compos... more ABSTRACT A three-temperature thermo-chemical model is developed for analyzing the chemical composition and energy states of a hydrogen microwave plasma used for studying diamond deposition. The chemical and energy exchange rate coefficients are determined from cross section data, assuming Maxwellian velocity distributions for electrons. The model is reduced to a zero-dimensional problem to solve for the electron temperature and ion mole fraction, using measured vibrational and rotational temperatures. The calculations indicate that the electron temperature may be determined to within a few percent error even though the uncertainty in dissociation fraction is many times larger.

Journal of Nanoscience and Nanotechnology, 2004

Single-walled carbon nanotubes (SWCNTs) were discovered by Iijima and Ichihashi 1 and Bethune et ... more Single-walled carbon nanotubes (SWCNTs) were discovered by Iijima and Ichihashi 1 and Bethune et al. 2 in the soot of an arc process similar to the classical Krätschmer-Huffman 4 apparatus, used originally to produce fullerenes. By modifying the discharge conditions and anode composition, various products were obtained, e.g., multi-walled carbon nanotubes (MWCNTs) 4 when a pure graphite anode is used, and SWCNTs 1, 2, 5 when iron or cobalt catalysts were co-evaporated with graphite. Arc synthesis was improved by Journet et al. 6 by the use of suitable operating conditions and a mixture of nickel and yttrium as a catalyst. In addition to the arc 1, 2, 5, 6 process, several laboratoryscale methods have been proposed to produce SWCNTs including condensation of laser 7, 8 vaporized carbon in the presence of catalysts, decomposition of hydrocarbons on supported, 9-12 entrained, 13-6 or fluidized bed catalysts, 17 and decomposition of carbon monoxide on supported catalysts. 9, 18 More recently, Smalley' et al. 19 and Bradley 20 proposed a technique involving high-pressure decomposition of carbon monoxide (HiPco) on gas-phase metallo-organic iron pentacarbonyl Fe(CO) 5 .

Performance of Carbon Arc-Discharge Nanotubes to Hydrogen Energy Storage

Journal of Nanoscience and Nanotechnology, 2007

Adsorption properties of gram-scale samples of different kind of arc discharge nanotubes were stu... more Adsorption properties of gram-scale samples of different kind of arc discharge nanotubes were studied, namely: (A) raw collaret collected on the cathode, (B) raw soots collected on the lateral reactor wall, (C) thermally treated soot, and (D) thermally then chemically treated soot. The morphology, structure, and composition of these materials were characterized by SEM, TEM, TGA, and BET. In addition, hydrogen adsorption isotherms were recorded experimentally for A, B, and D samples over the pressure range of 0 to 55 bar at ambient temperature. Our experiments indicated a maximum-yet weak-hydrogen storage at room temperature of approximately 0.13 H2 wt% for the purified product (D).

Effect of temperature on carbon nanotube diameter and bundle arrangement: Microscopic and macroscopic analysis

Journal of Applied Physics, 2004

Journal de Physique III, 1996

Diamond and Related Materials, 1994

The quality and the growth rate of diamond films produced in a microwave bell jar plasma reactor ... more The quality and the growth rate of diamond films produced in a microwave bell jar plasma reactor are strong functions of the plasma characteristics at the plasma-surface interface (temperatures, species concentrations). These local parameters are shown to be functions of the plasma operating conditions (dissociation in volume) and of the boundary conditions at the surface. Spectroscopic measurements of some plasma parameters based on coherent anti-Stokes Raman and optical emission spectroscopy are presented: the deposition results are correlated with these measurements. A zero-dimensional chemical kinetics model is developed for studying the influences of the gas temperature and the electron temperature on the production of atomic hydrogen.

Optimal control of batch distillation via nonlinear programming

Chemical Engineering and Processing: Process Intensification, 1991

ABSTRACT