Steve Trigwell

Effects of surface properties on the tribocharging characteristics of polymer powder as applied to industrial processes

Experiments performed on different powders of different size distributions tribocharged with stainless steel beads, showed the charge acquired by the powder can be correlated with the actual work function difference between the powder and stainless steel and particle size. The charge acquired increased with particle size, but the charge distribution was generally bi-polar. Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) were performed on a selection of materials, and showed the work function increased with surface contamination and oxidation, and the difference narrowed for metals and polymers. Such a small difference in work function may contribute to bi-polar charging, suggesting for tribocharging, minimization of oxidation and contamination and relative humidity control are needed.

Effects of surface treatment on the surface chemistry of NiTi alloy for biomedical applications

Alloys of NiTi have gained popularity in biomedical applications; however, Ni is known to cause toxic and allergic reactions in the body, and concerns have been expressed regarding the materials biocompatibility. In this study, coupons of equiatomic NiTi were prepared by four methods, namely, mechanically polishing to a mirror finish, electropolishing, chemical etching and argon plasma etching, to produce various levels of roughness, and then examined by atomic force microscopy (AFM), XPS and AES. The resulting surface chemistry depended upon the method of preparation and was found not to be a function of surface roughness. The mechanically polished samples, although having the smoothest surface, showed the highest level of Ni in the near-surface region. The other preparation methods produced surfaces that were predominantly TiO2, with the electropolished surfaces showing the next smoothest surface and the least Ni in the near-surface region. The correlation between method of preparation, surface roughness and surface chemistry may be important in the preparation of NiTi for biomedical applications.

Precombustion Cleaning of Coal By Triboelectric Separation of Minerals

In one method of electrostatic beneficiation, pulverized coal is tribocharged by contact with electrically grounded copper. Coal maceral and mineral particles charge with positive and negative polarities, respectively. The charged particles are passed through a separator consisting of two plate electrodes, across which a high voltage is applied, and the positively charged coal particles are separated from the negatively charged mineral particles. The efficiency of separation is dependent upon coal bulk and surface composition, and fineness of grind. Analyses of total sulfur and ash content of the charge-separated particles were used to evaluate beneficiation success of the Illinois No. 6 and Pittsburgh No. 8 coals studied. Two-stage beneficiation demonstrated improved separation. Exposing coal powders to chemical vapors of SO 2 , NH 3 , or acetone prior to beneficiation did not enhance beneficiation.

Carbon-covered magnetic nanomaterials and their application for the thermolysis of cancer cells

Three types of graphitic shelled-magnetic core (Fe, Fe/Co, and Co) nanoparticles (named as C-Fe, C-Fe/Co, and C-Co NPs) were synthesized by radio frequency-catalytic chemical vapor deposition (RF-cCVD). X-ray diffraction and X-ray photoelectron spectroscopy analysis revealed that the cores inside the carbon shells of these NPs were preserved in their metallic states. Fluorescence microscopy images indicated effective penetrations of the NPs through the cellular membranes of cultured cancer HeLa cells, both inside the cytoplasm and the nucleus. Low RF radiation of 350 kHz induced localized heating of the magnetic NPs, which triggered cell death. Apoptosis inducement was found to be dependent on the RF irradiation time and NP concentration. It was showed that the Fe-C NPs had a much higher ability of killing the cancer cells (over 99%) compared with the other types of NPs (C-Co or C-Fe/Co), even at a very low concentration of 0.83 μg/mL. The localized heating of NPs inside the cancer cells comes from the hysteresis heating and resistive heating through eddy currents generated under the RF radiation. The RF thermal ablation properties of the magnetic NPs were correlated with the analysis provided by a superconducting quantum interference device (SQUID).

Enhancement of the photoelectrochemical conversion efficiency of nanotubular TiO2 photoanodes using nitrogen plasma assisted surface modification.

A synergistic combination of nanostructure synthesis and plasma surface modification was used to enhance the photoelectrochemical activity of titania (TiO(2)) anodes. Titania nanotubular photoanodes were synthesized by electrochemical anodization of Ti thin foils. Nitrogen plasma was used to dope N at the surface of the photoanodes while removing chemisorbed species. X-ray photoelectron spectroscopy analysis showed an increase in the surface concentration of nitrogen. The photocurrent density of plasma treated samples was approximately 80% higher than that of the control. The open circuit potential of the plasma treated samples was more negative compared to that of the control, implying a favorable energetics for water splitting. This increase in photoactivity could be ascribed to: (1) increased absorption of visible light due to bandgap reduction, (2) minimization of charge carrier traps, (3) optimal oxygen vacancies, and (4) increased surface area for enhanced optical absorption and improved charge carrier generation.

Controlled growth of self-organized hexagonal arrays of metallic nanorods using template-assisted glancing angle deposition for superhydrophobic applications.

The fabrication of controlled, self-organized, highly ordered tungsten and aluminum nanorods was accomplished via the aluminum lattice template-assisted glancing angle sputtering technique. The typical growth mechanism of traditional glancing angle deposition technique was biased by self-organized aluminum lattice seeds resulting in superior quality nanorods in terms of size control, distribution, and long range order. The morphology, size, and distribution of the nanorods were highly controlled by the characteristics of the template seeds indicating the ability to obtain metallic nanorods with tunable distributions and morphologies that can be grown to suit a particular application. Water wettability of hexagonally arranged tungsten and aluminum nanorods was studied after modifying their surface with 5 nm of Teflon AF 2400, as an example, to exhibit the significance of such a controlled growth of metallic nanorods. This facile and scalable approach to generate nano seeds to guide GLAD, with nano seeds fabricated by anodic oxidization of aluminum followed by chemical etching, for the growth of highly ordered nanorods could have significant impact in a wide range of applications such as anti-icing coating, sensors, super capacitors, and solar cells.

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

Effect of ambient relative humidity and surface modification on the charge decay properties of polymer powders in powder coating

Back corona on a powder layer deposited via the electrostatic powder-coating process using corona guns has a strong influence on the corrosion resistance and appearance of cured powder films. The presence of the back corona is often evidenced by orange peel, micro-dents, and pinholes on the film surface. The surface resistivity of the sprayed powder governs the charge decay process and, hence, the onset of back corona. The polymer powders used in powder coating are highly resistive, with surface resistivity often greater than 10/sup 15/ /spl Omega///spl square/. Surface resistivity can be altered by the adsorption of moisture on the surfaces of the powder particles. The objectives of this research were: (1) investigate the effect of decreasing surface resistivity on the appearance of the powder-coated film and (2) enhance hydrophilic properties of polymer powder by plasma treatment. By changing the relative humidity (RH) of powder during the spraying process, it was observed that the surface resistivity could be lowered by orders of magnitude. For example, the surface resistivity for an acrylic powder decreased from 2.96/spl times/10/sup 13/ /spl Omega///spl square/ at 25% RH to 9.6/spl times/10/sup 11/ /spl Omega///spl square/ at 70% RH. The plasma treatment of this powder further improved its charge decay properties. The effects of variation of RH on the appearance of powder-coated panels surface layer are presented for an acrylic polymer powder. The film texture has been characterized by microstructural surface analysis using an optical scanning instrument. Methods of plasma and corona treatments of the powder for increasing moisture adsorption on the surface and decreasing surface resistivity are discussed along with analysis of surface morphology using the atomic force microscope.

The Use of Tribocharging in the Electrostatic Beneficiation of Lunar Simulant

The use of tribocharging as a potential method to provide sufficient charge to several different lunar simulants for electrostatic beneficiation was investigated. The objective was to determine whether specific minerals of interest (e.g., ilmenite) that are present in lunar regolith could be enriched in concentration by beneficiation that would therefore allow for more efficient extraction for in situ resource utilization use. The production of oxygen, water, and other resources on the Moon from raw materials is vital for future missions to the Moon. Successful separation of ilmenite was achieved for a prepared simulant (KSC-1), which is a mixture of pure commercially supplied pyroxene, olivine, feldspar, and ilmenite, in a 4 : 4 : 1 : 1 ratio, showing proof of concept when tribocharged against three different charging materials, namely, Al, Cu, and PTFE. Separation by chemical composition was also observed for existing lunar simulants JSC-1 and JSC-1A; however, the interpretation of the separation was difficult due to the complex mineralogy of the simulants compared to the simple prepared mixture.

Multifunctional Coatings With Carbon Nanotubes for Electrostatic Charge Mitigation and With Controllable Surface Properties

Electrostatic charge dissipation presents a major problem for applications ranging from electronics to space exploration. A novel method to control both the bulk and the surface electrical conductivity of polymeric films is presented. By dispersing small amounts of multiwall carbon nanotubes (CNTs) in the polymeric material, the electrical bulk resistivity decreased by seven orders of magnitude. Also, nanolayers of single and multiwall CNTs were electrosprayed on the surface of the polymeric films, and the surface resistivity was monitored as a function of nanotube loading. The films with CNT-modified surfaces were found to have the highest charge dissipation rates with decay times in seconds.