Multifunctional carbon nanotube coatings used as strain sensors for composite tanks

The modern strain sensors currently used in monitoring the structural properties of such tank structures suffer from a number of limitations, including a low level of sensitivity and detection. In this work, we present a novel method of structural monitoring utilizing a thin film of carbon nanotubes carefully deposited on carbon fiber composites. The nanotube film and raw material were first characterized via microscopy and spectroscopy techniques. Bowing of the tank wall was simulated by applying a three-point bend load test, which was found to strongly affect the electrical resistance of the carbon nanotube film. These measurements were very reproducible, as the film resistance returned to its original value each time that the load was slowly released. We believe that these highly sensitive carbon nanotube films are potential candidates as replacements for the current health-monitoring sensors.     

The Royal College examinations: preparation and practice

Membership examinations are complex and difficult. Important practical issues must be considered at an early stage, and you can improve upon your chance of success by addressing your learning style, revision strategy and examination technique.     

Measurement of Surface Topography,Packing Density,and Surface Charge Distribution of an Electrostatically Deposited Powder Layer by Image Analysis of Fluorescent Latex Spheres

A novel method of nonintrusive measurement of surface profile, packing density, and surface charge distributions of a powder layer deposited on a substrate is reported. The method employs the deposition of electrostatically charged monodispersed fluorescent latex spheres (FLS), approximately 2 m in diameter, on the surface of: (1) the substrate before deposition, (2) the powder layer after deposition, and (3) the film formed by curing the powder layer. The surface topography in all cases was mapped using an epi-fluorescent microscope with a vertical resolution of - 2 m in the z axis and - 10 m in the x and y axes. An area of 1 cm 2 1 cm is scanned in 1 mm segments, providing approximately 100 data points per cm 2 for the surface topography. For each measurement of surface topography, the substrate was positioned on the microscope stage in a manner such that the reference points (x, y, and z) remained the same for all measurements of the substrate. The surface profiles, with respect to the same reference points, were plotted using Origin 6.0 software for 3D presentation of the topography. The method was also applied to map the surface charge density distribution of electrostatically charged surfaces. The FLS imaging method provides a new tool for examination of surface profiles, packing density, and charge distribution of powder layers on a microscopic scale not provided by optical or atomic force/electrostatic force microscopy (AFM/EFM). While AFM and EFM are very effective in providing similar information with nanometer resolution, they cannot be directly applied on a larger macroscopic scale to study powder layers and for a larger surface area (up to 1 cm 2 or greater) involving deposited particles in the range of 1-50 m in diameter. For AFM, the range in the z-axis is limited to - 3 m and the x-y scan area is limited to 100 m 2 100 m. The FLS method has a much wider range but it is operated manually; an automated scanning process is required for rapid measurement. A comparison of the FLS and EFM techniques as they apply to analyzing charge distribution on coal surfaces is presented.     

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.     

Measurement of Surface Topography, Packing Density, and Surface Charge Distribution of an Electrostatically Deposited Powder Layer by Image Analysis of Fluorescent Latex Spheres

A novel method of nonintrusive measurement of surface profile, packing density, and surface charge distributions of a powder layer deposited on a substrate is reported. The method employs the deposition of electrostatically charged monodispersed fluorescent latex spheres (FLS), approximately 2 µm in diameter, on the surface of: (1) the substrate before deposition, (2) the powder layer after deposition, and (3) the film formed by curing the powder layer. The surface topography in all cases was mapped using an epi-fluorescent microscope with a vertical resolution of ±2 µm in the z axis and ±10 µm in the x and y axes. An area of 1 cm ×1 cm is scanned in 1 mm segments, providing approximately 100 data points per cm 2 for the surface topography. For each measurement of surface topography, the substrate was positioned on the microscope stage in a manner such that the reference points (x, y, and z) remained the same for all measurements of the substrate. The surface profiles, with respect to the same reference points, were plotted using Origin 6.0 software for 3D presentation of the topography. The method was also applied to map the surface charge density distribution of electrostatically charged surfaces. The FLS imaging method provides a new tool for examination of surface profiles, packing density, and charge distribution of powder layers on a microscopic scale not provided by optical or atomic force/electrostatic force microscopy (AFM/EFM). While AFM and EFM are very effective in providing similar information with nanometer resolution, they cannot be directly applied on a larger macroscopic scale to study powder layers and for a larger surface area (up to 1 cm 2 or greater) involving deposited particles in the range of 1-50 µm in diameter. For AFM, the range in the z-axis is limited to ±3 µm and the x-y scan area is limited to 100 µm ×100 µm. The FLS method has a much wider range but it is operated manually; an automated scanning process is required for rapid measurement. A comparison of the FLS and EFM techniques as they apply to analyzing charge distribution on coal surfaces is presented.     

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 (SS) beads showed the charge acquired by the powder could be correlated with the actual work function difference between the powder and SS. Ultraviolet and X-ray photoelectron spectroscopy were performed on various materials involved, 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 bipolar charging. Experiment data showed that while charge acquired increased with particle size, the charge distribution was generally bipolar. Both surface analysis and charge distribution studies suggest that for tribocharging, minimization of oxidation and surface contamination are needed. It also appears that the relative humidity must also be controlled to obtain reliable tribocharging. Semiempirical molecular modeling calculations of the work function of several polymers showed good agreement with experiment. Surface plasma treatment is presented as a viable method for modifying the work function.     

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.     

Cobalt nanoparticles coated with graphitic shells as localized radio frequency absorbers for cancer therapy

Graphitic carbon-coated ferromagnetic cobalt nanoparticles (C-Co-NPs) with diameters of around 7?nm and cubic crystalline structures were synthesized by catalytic chemical vapor deposition. X-ray diffraction and x-ray photoelectron spectroscopy analysis indicated that the cobalt nanoparticles inside the carbon shells were preserved in the metallic state. Fluorescence microscopy images and Raman spectroscopy revealed effective penetrations of the C-Co-NPs through the cellular plasma membrane of the cultured HeLa cells, both inside the cytoplasm and in the nucleus. Low radio frequency (RF) radiation of 350 kHz induced localized heat into the metallic nanoparticles, which triggered the killing of the cells, a process that was found to be dependent on the RF application time and nanoparticle concentration. When compared to carbon nanostructures such as single-wall carbon nanotubes, these coated magnetic cobalt nanoparticles demonstrated higher specificity for RF absorption and heating. DNA gel electrophoresis assays of the HeLa cells after the RF treatment showed a strong broadening of the DNA fragmentation spectrum, which further proved the intense localized thermally induced damages such as DNA and nucleus membrane disintegration, under RF exposure in the presence of C-Co-NPs. The data presented in this report indicate a great potential of this new process for in vivo tumor thermal ablation, bacteria killing, and various other biomedical applications.     

Analysis of effluent gases during the CCVD growth of multi-wall carbon nanotubes from acetylene

Catalytic chemical vapor deposition was used to grow multi-walled carbon nanotubes on a Fe:Co:CaCO₃ catalyst from acetylene. The influent and effluent gases were analyzed by gas chromatography and mass spectrometry at different time intervals during the nanotubes growth process in order to better understand and optimize the overall reaction. A large number of byproducts were identified and it was found that the number and the level for some of the carbon byproducts significantly increased over time. The CaCO₃ catalytic support thermally decomposed into CaO and CO₂ resulting in a mixture of two catalysts for growing the nanotubes, which were found to have outer diameters belonging to two main groups 8-35 nm and 40-60 nm, respectively.     

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.