Aligning Forces on Wood Particles in an Electric Field

Electrostatic alignment affords a promising route to improved mechanical properties in anisotropic particleboards aimed at competition with sawn lumber in structural uses. A quartz-fiber torque balance was used to measure the aligning torque exerted on elongated wood particles by DC and AC fields over a range of wood moisture content, field intensity, and frequency. Approximate predicting equations relating aligning torque to relevant process parameters have been developed, which should aid the process designer. The dynamics of free-falling particles in an electric field favors small slender particles and high field intensity for best alignment. However, slender particles have long charge relaxation times and thus require high moisture content for effective alignment in a field of a given frequency

Material growth and characterization directed toward improving III-V heterojunction solar cells

In addition to the existing materials growth laboratory, the photolithographic facility and the device testing facility were completed. The majority of equipment for data acquisition, solar cell testing, materials growth and device characterization were received and are being put into operation. In the research part of the program, GaAs and GaA1As layers were grown reproducibly on GaAs substrates. These grown layers were characterized as to surface morphology, thickness and thickness uniformity. The liquid phase epitaxial growth process was used to fabricate p-n junctions in Ga(1-x)A1(x)As. Sequential deposition of two alloy layers was accomplished and detailed analysis of the effect of substrate quality and dopant on the GaA1As layer quality is presented. Finally, solar cell structures were formed by growing a thin p-GaA1As layer upon an epitaxial n-GaA1As layer. The energy gap corresponding to the long wavelength cutoff of the spectral response characteristic was 1.51-1.63 eV. Theoretical calculations of the spectral response were matched to the measured response

Material growth and characterization for solid state devices

Manganese was used as the dopant for p-type InGaAs layers grown on semi-insulating (Fe-doped) and n-type (Sn-doped) InP substrates. Optical, electrical (Hall) and SIMS measurements were used to characterize the layers. Mn-diffusion into the substrate (during the growth of In GaAs) was observed only when Fe-doped substrates were used. Quaternary layers of two compositions corresponding to wavelengths (energy gaps) of approximated 1.52 micrometers were successfully grown at a constant temperature of 640 C and InP was grown in the temperature range of 640 C to 655 C. A study of the effect of pulses on the growth velocity of InP indicated no significant change as long as the average applied current was kept constant. A system for depositing films of Al2O3 by the pyrolysis of aluminum isopropoxide was designed and built. Deposited layers on Si were characterized with an ellipsometer and exhibited indices of refraction between 1.582 and 1.622 for films on the order of 3000 A thick. Undoped and p-type (Mn-doped) InGaAs epitaxial layers were also grown on Fe-doped InP substrates through windows in sputtered SiO2 (3200 A thick) layers

Enhanced TiO2 Photocatalytic Processing of Organic Wastes for Green Space Exploration

The effect of transition metal co-catalysts on the photocatalytic properties of TiO2 was investigated. Ruthenium (Ru), palladium, platinum, copper, silver, and gold, were loaded onto TiO2 powders (anatase and mixed-phase P25) and screened for the decomposition of rhodamine B (RhB) under broad-band irradiation. The morphology and estimated chemical composition of photocatalysts were determined by scanning electron microscopy and energy dispersive spectroscopy, respectively. Brunhauer, Emmett and Teller (BET) analysis measured mass-specific surface area(s). X-ray diffraction analysis was performed to confirm the identity of titania phase(s) present. The BET surface area of anatase TiO2/Ru 1% (9.2 sq m/gm) was one of the highest measured of all photocatalysts prepared in our laboratory. Photolyses conducted under air-saturated and nitrogen-saturated conditions revealed photodegradation efficiencies of 85 and 2 percent, respectively, after 60 min compared to 58 percent with no catalyst. The cause of low photocatalytic activity under an inert atmosphere is discussed. TiO2/Ru 1% showed a superior photocatalytic activity relative to P25-TiO2 under broad-band irradiation. A potential deployment of photocatalytic technologies on a mission could be a reactor with modest enhancement in solar intensity brought about by a trough-style reactor, with reactants and catalyst flowing along the axis of the trough and therefore being illuminated for a controlled duration based on the flow rate

Lipid Vesicles as Model Membranes in Photocatalytic Disinfection Studies

The potential use of solar-powered photocatalytic disinfection water systems is an attractive concept and has generated much research over the last two decades. Photocatalytic inactivation of a wide range of water pathogens has shown promise to provide an effective alternative to traditional disinfection methods. However, in order for photocatalysis to be effectively used as a water disinfection process, its inactivation kinetics must be well established. Recent literature points to the peroxidation of phospholipid membranes as the main mechanism for photocatalytic inactivation of bacteria. To test the peroxidation hypothesis, researchers utilized free lipids, particularly lipids with the ethanolamine polar group which is dominant in the cell membrane of Escherichia coli. Although these experiments yielded useful information about byproducts, they did not provide information on the kinetics of lipid peroxidation in cells exposed to photocatalytic treatment. In this work, lipid vesicles were prepared with a mixture of natural E. coli phospholipids and appropriately sized to be comparable to real cells. The vesicles and E. coli cells were photocatalytically treated in a test tube batch reactor using TiO2 (Degussa P25) and UVA lamps. The rate of phospholipid membrane degradation was determined by measuring the production of malondialdehyde (MDA) and lipid hydroperoxide (LOOH), byproducts of lipid peroxidation. Thiobarbituric Acid Reactive Species (TBARS) and Ferrous Oxidation of Xylenol (FOX) assays were used to assess each byproduct respectively. The fatty acid content of E. coli cells was also modified by adding oleic (C18:1 n-9) and α-linolenic (C18:3 n-3) acids to the growth media. Byproduct formation and oxidation kinetics were compared for all experiments. The results show that the oxidation kinetics of lipid vesicles closely matched the oxidation of E. coli cells in photocatalytic systems proving that the vesicles are useful model systems to study the interaction of cell membranes with TiO2. However, differences in monosaturated fatty acids in E. coli did not appear to affect the overall disinfection kinetics. While these findings further validate membrane peroxidation as an important process in the mechanism of photocatalytic disinfection, they suggest that overall inactivation results from a far more complex collection of processes