Alaa A. Elmoursi

Modeling of corona characteristics in a wire-duct precipitator using the charge simulation technique

The charge simulation technique has been adapted to model the electrostatic and the corona characteristics in clean air of a duct-type electrostatic precipitator. The study involves the evaluation of the electric potential, electric field, and charge density in the interelectrode space as a function of corona current. The results show good agreement with published experimental data. The method developed can be applied to other geometries in the presence of space charge. The commonly used assumption that the space charge affects the magnitude but not the direction of the electric field is shown to be inadequate for large values of corona current. Also, the effect of using different values for the mobility of negative ions is presented.

Diamond-like carbon coating for aluminum 390 alloy — automotive applications

In an attempt to increase the wear resistance of automotive powertrain components, General Motors Research and Development Center initiated a study to determine the potential of surface modification as a means of improving the tribological properties of highly eutectic aluminum alloys, and to investigate feasibility of their mass production. In particular, plasma immersion ion implantation technique was employed to develop diamond-like hydrocarbon coating of aluminum 390 alloy and the coatings performance was verified both in a bench and, in an engine dynamometer test.

Simulation of space charge in unbounded geometries

In corona ion devices the electric field distribution is highly dependent on the form of the electrostatic space-charge distribution. In many instances these devices also have essentially unbounded geometries. A numerical technique is presented based on the combined method of charge simulation and the method of characteristics to evaluate fields in such geometries. The numerical procedure utilizes a nonrigid grid structure which, after convergence to a self-consistent solution, is a map of the field lines and equipotential contours. The numerical procedure is applied to a rod-to-plane geometry, and the simulation results show good agreement with experimental data. >

The Analysis of Corona Quenching in Cylindrical Precipitators Using Charge Simulation

The well-known technique of charge simulation has been adapted to model the electrical characteristic of cylindrical electrostatic precipitators. The study involved the evaluation of the electric field, voltage, and charge density distributions in the presence of mild corona quenching. The problem has been treated differently than the classic solution of Pauthenier by modifying the assumptions used for solving Poissons equation. A comparative study of the classical and modified solutions is performed. The results of the charge simulation model show good agreement with the suggested modified solution of Poissons equation.

Laplacian fields of bell-type electrostatic painting systems

A Laplacian model (i.e excluding the space charge effect) for a bell-type electrostatic painting system has been developed using the charge-simulation technique. The study involved the evaluation of the electric field in the space between the bell and the paint target as well as at their surfaces. An investigation was also conducted to determine the variations that occur to the electrical parameters when: (1) the bell-to-target spacing is changed; and (2) the size of the target is varied. Finally, results are reported for incorporating the charge-simulation model in a routine that predicts the paint-droplet trajectories from the bell to the target. The results of the developed model predict that the field-dependent droplet charging mechanisms, which are required to ensure strong electrical forces on the droplets, will be insensitive to the size of the workpiece and the spacing between the bell and the target. However, the magnitude of the fields at the workpiece, which account for the enhanced deposition in electrostatic painting, are shown to be highly dependent on these parameters. >

Thermal properties of kinetic spray Al-SiC metal-matrix composite

Kinetic spray deposition provides a new means for producing composite materials with tailored physical properties. We report on measurements of the thermal conductivity and thermal-expansion coefficient for several compositional variations of kinetically sprayed Al-SiC metal-matrix composites. As a result of the deposition process, inclusion of SiC particles saturates in the 30-40% volume fraction range.

Electrical characterization of bell-type electrostatic painting systems

A numerical model that determines the electrical characteristics of a bell-type electrostatic painting system is presented. The model is capable of handling the complex geometries of practical sprayers and accounts for the space-charge effect of charged paint droplets. The influence of aerodynamic forces in tracing droplet trajectories is considered. As a test of the simulation approach, the restricted case of a sprayer emitting ions, rather than charged paint droplets, was modeled. The simulation results were compared to experimental data and showed good agreement. For the more general case, maps of equipotential contours and the paint droplet trajectories were generated for a bell-type sprayer. It was found that the space charge tends to increase the deposition field, although not as strongly as increased bell potential or decreased bell-to-target spacing. However, the space charge also caused the spray pattern to expand, which can increase overspraying.<<ETX>>

Characterization of surface modified α-iron by nitrogen plasma immersion ion implantation: a microstructural study

Abstract This paper discusses the morphology of pure iron surfaces modified by nitrogen plasma immersion ion implantation and compares them to similar surfaces treated with conventional plasma nitriding. Analysis of the samples was performed with glancing angle X-ray diffraction and traditional Bragg–Brentano geometry X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and depth profiling using X-ray photoelectron spectroscopy in combination with sputtering. The structures formed both by thermal nitriding and plasma ion implantation correlate very well with the Fe–N phase diagram, as the surface temperature and nitrogen concentration are decisive factors in developing specific crystalline phases. Only at lower temperatures, where chemical absorption and thermal diffusion effects are strongly limited, does the distribution of implanted nitrogen become substantially of the non-equilibrium type, and can almost be freely tailored. At low temperatures, however, the nitrided layer becomes extremely shallow (defined almost solely by the ballistic ion model), thereby limiting the applicability of this technology for iron-based materials. Hence, unless specific ferrous alloy materials are chosen which promote nitride formation and diffusion, e.g. chromium and iron-chromium alloys, the niche for nitrogen plasma ion implantation into ferrous materials seems to be limited to those cases where surface nitriding is desired, but where exposure of the workpiece to high temperature is forbidden.

Surface enhancement by shallow carbon implantation for improved adhesion of diamond-like coatings

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamond-like carbon (DLC) coating. A plasma immersion ion implantation based procedure is described which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. This proposed implantation procedure employs a low target bias of only 10–12 kV, a pulse repetition rate of around 5 kHz, and a duty cycle of 25%. The resultant shallow implantation profile, followed by an argon sputter cleaning, is continued until a saturated carbon matrix is brought to the surface providing an excellent interface for subsequent growth of DLC. At a carbon retained dose above 1018 atoms/cm2, the DLC adhesion exceeds the coating’s cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 150 MPa to separate an epoxy coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chro...

Improved adhesion of diamondlike coatings using shallow carbon implantation

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides an excellent interface for subsequent growth of DLC. At a carbon retained dose above 10 18 atoms/cm 2 the DLC adhesion exceeds the coatings cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 140 MPa to separate an epoxy-coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to substantially exceed performance of DLC coatings produced by any other method.