A. S. Biris

Self-Cleaning Transparent Dust Shields for Protecting Solar Panels and Other Devices

The development of transparent flexible dust shields using both single- and three-phase electrodynamic shields is reported here for possible application on Mars and Earth to minimize obscuration of solar panels from the deposition of dust. The electrodynamic screens (EDS) are made of transparent plastic sheets, such as polyethylene terephthalate (PET) for its UV radiation resistance, and a set of parallel conducting electrodes made of transparent indium tin oxide (ITO) embedded under a thin transparent film. The basic principle of EDS operation, a simplified mathematical model of particle trajectories, the experimental setup used for testing the screens, and their dust removal efficiencies (DRE) are described. Results of our measurements on dust removal efficiency of EDS as a function of the particle size and electrostatic charge distributions of Mars simulant dust are reported. The results show that the EDS technology has a strong potential for protecting solar panels against dust hazards with DRE higher than 80% for dust. The power requirements will be approximately 10 watts per square meter of the panels when cleaning is needed.

Particle Size and Charge Distribution Analysis of Pharmaceutical Aerosols Generated by Inhalers

Aerosol particles generated by inhalers for respiratory drug delivery acquire electrostatic charge during the dispersion process. The electrostatic charge distribution of the particles can affect the efficiency of drug delivery by influencing both the transport and deposition of inhaled particles in the human lung. To analyze the electrostatic charge acquired by the aerosol particles, two sets of metered-dose inhaler (MDI) and dry powder inhaler (DPI) devices were investigated. Both the particle size and charge distributions were measured simultaneously by using an electrical single-particle aerodynamic relaxation time (E-SPART) analyzer. The analyzer was calibrated with particles of known size, which were generated by a vibrating orifice aerosol generator (TSI Inc.) and charge using the Faraday cup method. The charge distributions of the pharmaceutical aerosols from both the DPI and MDI devices were bipolar in nature. Although the net charge-to-mass ratio was less than 0.2 μC/g, the individual particles were charged with a relatively high charge: −2 to + 2 μC/g. The count mean aerodynamic diameter of the aerosols generated from these devices was 3–5 μm.

Electrostatic Effects on Dispersion, Transport, and Deposition of Fine Pharmaceutical Powders: Development of an Experimental Method for Quantitative Analysis

Currently, there is no standard method for testing the electrostatic properties of pharmaceutical powders. The objective of this study was to develop a method of characterizing the dispersion, charging, and transport properties of fine powder flowing through tubes of different materials. Powders of known composition and size distribution were dispersed pneumatically and transported through a short section of tubing containing spiral baffle inserts of the same material to simulate powder flow in long sections of horizontal and vertical tubes with bends. The test powder was dispersed using ring jet suction and passed through the baffled tube to a sampling chamber, from which the powder cloud was sampled for particle size and electrostatic charge distribution measurement using an Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) analyzer. Experimental data on the tribocharging and transport properties of different powders are presented along with an explanation of the charging mechanisms. Analyses of particle size and electrostatic charge distributions in real time and on a single particle basis using the E-SPART analyzer coupled with surface structure analyses with XPS and UPS showed that: (1) most powders are charged bipolarly with relatively high charge-to-mass ratio (Q/M) values that would have a strong effect on transport and deposition of powders; and (2) surface structures, particularly adsorbates, influence the work function and tribocharging of powder. Different methods, including plasma treatment, with minimal changes or contamination of the bulk properties of the powders are also suggested. pharmaceutical powders tribocharging dispersion work function charge distributions charge decay plasma treatment

Growth of nanoscale carbon structures and their corresponding hydrogen uptake properties

Carbon nanostructures have been synthesized using the chemical vapor deposition technique (CVD) on different catalysts, using ethylene, acetylene, or methane as the hydrocarbons. Morphological characterizations obtained using a scanning electron microscope (SEM) showed that the reaction products are carbon nanofibers (CNF) with an outer diameter that depends on the reaction conditions and nature of the reactants. Hydrogen uptake measurements, performed volumetrically in a Sievert-type installation, showed the quantity of desorbed hydrogen (for pressure intervals ranging from 1 to 100 bars) depends on the synthesis conditions and the treatment preceding the hydrogen absorption process. For carbon nanotubes that were preparedaccording to literature guidelines and obtained from ethylene on a Ni:Cu catalyst, the amounts of absorbed hydrogen were less than 1% by weight. carbon nanostructures chemical vapor deposition hydrogen absorption SEM

Hydrogen Storage in Carbon-Based Nanostructured Materials

Carbon nanostructures represent a revolution in science and hold the potential for a large range of applications because of their interesting electrical, mechanical, and optical properties. Multiwall carbon nanotubes and carbon nanofibers of herringbone formation were grown by chemical vapor deposition on different catalysts from a number of hydrocarbon sources. After the total or particle removal of the catalyst system, the carbon nanostructures were analyzed for hydrogen uptake. Six samples of nanofibers grown on a Pd-based catalyst system (with a surface area of 425–455 m2/g) were controlled oxidized in air, such that they had different ratios of Pd/C varying from 0.05 to 0.9 mole ratio. The hydrogen uptake experiments were performed volumetrically in a Sievert-type installation and showed that the quantity of desorbed hydrogen (for pressure intervals ranging from 1 to 100 bars) by the carbon nanostructures free of any metal catalyst particles was between 0.04 and 0.33% by weight. For the samples of nanofibers that contained Pd in various Pd/C ratios, palladium revealed catalytic properties and supplied atomic hydrogen at the Pd/C interface by dissociating the H2 molecules. The results show a direct correlation between the Pd/C ratio and the quantity of hydrogen absorbed by these samples. A saturation value of about 1.5 wt.% was reached for a high ratio of about 1:1 of Pd/C. The multiwall carbon nanotubes grown on a Fe:Co:CaCO3 catalytic system and purified by acid cleaning and air oxidation showed a hydrogen uptake value of 0.1 to 0.2 wt.%.

Phosphate Glassy Network Depolymerization Induced by CaO Doping

The structure of xCaO·(100 −x)P2O5 glass system with 25 ≤ x ≤ 40 mol.% was investigated by means of Raman and infrared spectroscopy. The characteristic bands due to the stretching and bending vibrations were identified and analyzed by the increase of CaO content. The structural changes induced by the CaO presence in phosphatic matrix were determined and discussed in terms of the network depolymerization process and distortion of the PO4 tetrahedra.

Effect of ambient relative humidity on charge decay properties of polymer powder and on the occurrence of back corona in powder coating

Back corona on a highly resistive polymer powder layer deposited via the electrostatic powder coating process using corona guns has a strong influence on the texture of the cured powder film often evidenced by orange peel, micro-dents and pinholes. The surface resistivity of the sprayed polymer powder governs the charge decay process, and therefore the onset of back corona as the thickness of the powder layer increases. The polymer powders generally used in powder coating are highly insulative, with surface resistivity often greater than 10/sup 11/ /spl Omega//. Surface resistivity can be altered by the adsorption of moisture on the surfaces of the powder particles. By changing the relative humidity (RH) of the ambient air during the powder spraying process, it was observed that the surface resistivity could be varied by orders of magnitude. For example, the surface resistivity for an acrylic powder decreased from 1.77/spl times/10/sup 15/ /spl Omega// at 25% RH to 5.7/spl times/10/sup 13/ /spl Omega// at 70% RH. The effects of variation of REI on the texture of the powder surface layer and on the cured film are presented for an acrylic polymer powder. The film texture was characterized by microstructural surface analysis using an optical scanning instrument. Methods for decreasing surface resistivity by using hygroscopic surfactants or by plasma treatment are briefly discussed.

Effect of electrical resistivity on the adhesion and thickness of electrostatically deposited powder layers

Control of the charge decay process in an electrostatically-deposited powder layer has an important role in two areas: (1) adhesion of powder to a substrate, and (2) intensity of back corona in the deposited powder layer. If a powder is highly resistive, with resistivity greater than 10/sup 13/ /spl Omega/m, the accumulation of charge on the deposited powder layer often causes back corona, which limits further deposition of powder. However, if the powder has low resistivity, less than 10/sup 10/ /spl Omega/m, the charge decay is rapid enough that back corona does not set in and limit the deposition efficiency. However, at such low resistivity, the adhesion is so weak that the powder may not remain attached to the substrate. The role of resistivity in adhesion of powder to conducting and nonconducting substrates and the management of back corona to allow sufficient film build was studied using powders of different resistivities. Our research shows that charge-to-mass ratio (Q/M) and resistivity must both be taken into account for obtaining the desired film thickness with the necessary adhesion.

Portable Free-Fall Electrostatic Separator for Beneficiation of Charged Particulate Materials

A portable free-fall electrostatic separator capable of analyzing gram quantities of charged powders is presented. Unlike a Faraday pail, in which only the net average charge-to-mass (Q/M) ratio of the particles sampled by the instrument is measured, an electrostatic separator is capable of separately measuring the charge-to-mass ratios of positively and negatively charged sampled powders. Thus, with an electrostatic separator it is possible to measure the mass fractions of powders that are charged with different polarities and the respective charge-to-mass ratios, along with the mass fraction of particles that are uncharged or charged below a threshold level. We describe a method of measuring the total charge of the collected particles in real time by incorporating an electrometer to integrate the current flowing through the collecting electrode to the high voltage power supply. In this manner, both the total charge and total mass of powder deposited on the two electrodes are measured in near real time, providing information on charge-to-mass ratio of the aerosol cloud sampled. Such real time measurements are often needed to analyze the electrostatic charging properties of small quantities of dispersed powder, particularly in such applications where the charge characteristics are of high importance.

Effects of Powder Velocity and Contact Materials on Tribocharging of Polymer Powders for Powder Coating Applications

Electrostatic powder deposition using corona charging is widely used in a plethora of industrial applications. Disadvantages of this technique are back corona onset and the Faraday penetration limitation. Another method to charge powders is to use tribochargers. Tribocharging depends upon the work function difference between the contacting materials and generates bipolarly charged particles. In this study, acrylic and epoxy powders were fluidized and charged by passing through stainless steel, copper, aluminum, and polycarbonate static mixers, respectively. The particle velocity and powder flow rate were varied to determine their effect on the net charge-to-mass ratio (Q/M) acquired by the powders. The Q/M increased rapidly with velocities between 1.5 to 2.5 m/s and stabilized for higher velocities but decreased with increasing powder flow rate at a constant velocity. The net positive or negative charge on each powder was determined to be dependant on the charger material. The use of an aluminum charger (net negative charge) in combination with a PTFE finger nozzle (net positive charge) resulted in a net powder Q/M of − 0.05 μC/g. The generation of an ion-free powder cloud with high bipolar charge but overall charge density of almost zero is anticipated to provide a better coverage of recessed areas.