Raymond F. Baddour

Surface modification of low density polyethylene in a fluorine gas plasma

Abstract Low density polyethylene was fluorinated in a glow discharge generated from a dilute mixture of fluorine in helium. The effects of pressure, flow rate, power and time of treatment have been examined. The fluorinated polymers were characterized using e.s.c.a. to identify the species present in the surface layer and to estimate the depth of fluorination. For typical plasma treatment of polyethylene films the fluorination depth was about 40 A; a competition of ablation and ion-assisted etching processes with chemical reaction was observed. The depth of fluorination was increased to values above 60 A by carrying out the reaction within a metal screen. The presence of the screen also reduced the reaction rate by about a factor of two. Other features of the treated polyethylene were determined by contact angle measurements, surface infra-red spectroscopy, solvent sorption and differential scanning calorimetry. Some early results of treatment of polyethylene powders in a fluidized bed reactor are also presented.

Modification of carbon surfaces in cold plasmas

Various forms of carbon, including carbon black, carbon fibre and pyrolytic graphite, have been surface-modified in a cold-plasma reactor. Plasma fluorination of the carbon surfaces was performed using variable flow rates, treatment times, and types of gas. The plasma-modified carbon surfaces were characterized using electron spectroscopy (ESCA), contact angle measurements, and scanning electron microscopy (SEM). The surface chemical structure of the plasma-fluorinated carbon blacks appeared to be similar to that of commercial Fluorographite. Nitrogen-containing groups were introduced into the surfaces of carbon blacks and carbon fibres by exposure to glow discharges in mixtures of ammonia and N2-H2. The surface concentration of functional groups containing nitrogen decreased with time. Several mechanisms for this degradation have been proposed. Plasma-modified carbon blacks and carbon fibres have potential for improving the properties of composites by achieving appropriate levels of adhesion between filler and matrix through physical compatibility and/or chemical bonding.

Steady-state simulation of an ammonia synthesis converter

Abstract A simple one-dimensional model of a T.V.A. ammonia synthesis converter approximates closely the ammonia production rate and the catalyst bed temperature profile of an industrial reactor. Using this simulation, the effects of space velocity, feed gas ammonia and inert contents, reactor heat conductance, and catalyst activity upon reactor stability, ammonia production rate, and catalyst bed temperature profile have been determined.

Kinetics of polymer surface fluorination: Elemental and plasma-enhanced reactions

Abstract E.s.c.a. spectra of surface fluorinated polyethylene, poly(vinyl fluoride), and poly(vinylidene fluoride) are reported. Two reaction environments were used in this study: exposure to elemental fluorine and immersion in a glow discharge plasma. The systematic variation of fluorine composition in the polymer phase is shown to have a dramatic effect on the kinetics of the elemental reaction and little effect in the plasma reaction.

Simultaneous measurement of oxygen diffusion coefficients and solubilities in electrolyte solutions with a polarographic oxygen electrode

Abstract The objective of this paper is to present a reliable yet convenient method of measuring simultaneously oxygen diffusion coefficients and solubilities in aqueous electrolyte solutions with a membrane-covered oxygen electrode. Measurements have been conducted in solutions of sodium chloride, potassium chloride, sodium sulfate, and magnesium sulfate over wide ranges of salt concentrations. The experimental results on oxygen diffusion coefficients and solubilities in test electrolyte solutions show an excellent accord with the literature data.

A Mechanisms and Kinetics Study of Polymeric Thin-Film Deposition in Glow Discharge

Abstract Polymeric thin-film deposition in a capacitively coupled rf glow discharge of styrene has been investigated. A kinetic scheme for the polymerization was proposed in which initiation of monomers by electron impact was followed by propagation and termination as in conventional polymerization, the initiation rate constant being a function of electron temperature alone. Four mechanism models were examined, depending on where each reaction step takes place: in the gas phase or on the substrate. Free-radical polymerization was assumed. Experiments were carried out at pressures ranging from 0.25 to 1.05 Torr and at voltages and currents that yielded cold and stable discharges. Substrate temperature was controlled. Deposition rate was determined by weighing. A regression program was used in addition to experimental tests in which substrate temperature was varied. The best approximation to the plasma polymer deposition process was found to be the following model: monomers are activated in the gas phase by...

Transient behaviour of an ammonia synthesis reactor

Abstract The dynamic behaviour of a widely used type of ammonia synthesis reactor (The Tennessee Valley Authority Reactor) is simulated on a digital computer. The mathematical model, which retains the major processes of transport and accumulation of enthalpy and matter, is solved by a series of finite difference analogs which proved to be highly efficient. The transient behaviour of the reactor is interpreted physically, and frequency responses and simplified transfer functions are proposed for operation within the linear range.

Effective diffusivity of oxygen in microbial pellets

In a typical submerged aerobic fermentation with microbial pellets, the effective diffusivity of oxygen in the pellets is probably the most important, yet most difficult transport property to characterize experimentally. Its values directly indicate the efficiency or deficiency of oxygen to individual cells, and thus the biological activity of the microorganisms. In the past, it was not possible to assess reliably the effective diffusivity of oxygen in pellets due to several reasons. Firstly, most oxygen electrodes available were coarse, and hence not suitable for in situ measurements. Secondly, there was a lack of methods rigorous enough to characterize the structure of the microbial pellets. A state-of-the-art review of the literature relating to the feature subject is presented. Emphasis is laid upon development and evolution of the means for quantitative characterization of the effective diffusivity of oxygen in microbial pellets.

Gas solubility in glassy polymers—a correlation with excess enthalpy

Abstract Solubility coefficients for CO 2 , Ar and CH 4 in polystyrene (PS) films with glass transition temperatures ( T g ) of 52 to 107°C were measured in a pressure-decay sorption apparatus at 1 atm over a temperature range of 20 to 90°C. The gas solubility at 30°C increased as the T g of the PS increased; the heat of solution was largest for the PS with the highest T g . This observed dependence of gas solubility on T g was analysed in terms of enthalpy-temperature relationships for glassy polymers. The solubilities for PS samples with different glass transition temperatures converged when comparisons were made on the basis of states of equal enthalpy instead of the temperature of measurement.