Improvement of PEEM images from thick inhomogeneous antiwear films using a thin Pt coating

Antiwear films formed from zinc dialkyl-dithiophosphate, in base oil, are known to create inhomogeneous agglomeration of patches on metallic surfaces up to 400 nm thick. It has been found that these patches (termed antiwear pads) are also non-conducting. These two features create difficulties in analyzing data obtained using X-ray photoelectron emission microscopy (X-PEEM). Topography and near-surface charging dominate images obtained using X-PEEM techniques, which can alter electron trajectories and lower signal-to-noise counts. It has been found that the application of a thin continuous platinum coating provides sufficient neutralization to eliminate the positive charge-buildup and improve signal-to-noise. This improves data analysis even with the thickest pads. Examples of charging alleviation and improved signal-to-noise ratios (obtained in the P L-edge spectroscopy) are shown. Furthermore, data analysis of the spectromicroscopy stacks show improved fitting and better polyphosphate distribution mapping for the films.     

Nanometer Scale Chemomechanical Characterization of Antiwear Films

We report the first nanometer scale chemical and mechanical (chemomechanical) characterization of selected features of a tribologically derived zinc dialkyl-dithiophosphate (ZDDP) antiwear film. AFM permits identification of the features responsible for preventing wear. These features are identified by nearby microscale fiducial marks, and their mechanical properties are determined by imaging nanoindentation. The same features are then studied by X-ray photoelectron emission microscopy (X-PEEM), which provides both elemental and chemical information at 200 nm spatial resolution. The mechanical properties are then determined for the same features, which are formed of a polyphosphate glass. This information provides new insights into the mechanisms by which ZDDP antiwears films are effective at inhibiting asperity contact between two metal surfaces     

Operational characteristics of laboratory scale alumina reduction cells with wettable cathodes

The operational characteristics of a laboratory-scale alumina reduction cell incorporating a wettable cathode were evaluated by electrolyses in a 10 wt% alumina/cryolite melt at 975° C. It was shown that as the anode—cathode distance (a.c.d.) decreased, the mass transfer rate increased and the current efficiency decreased. The contribution to cell resistance from the anode bubble-layer at small a.c.d.'s was found to be significant. The ohmically corrected cell voltage decreased with decreasing a.c.d., increasing anode immersion and increasing anode rotation rate, indicating a substantial influence of mass-transfer on cell operation. Digital analysis of cell voltage and resistance data was used to characterize bubble behaviour over a range of operating conditions. The frequency spectra varied over the course of a run due to the cessation of the regular formation and detachment of large bubbles. Bubble behaviour was strongly dependent on anode geometry, current density and anode rotation rate, tending towards smaller bubbles at high angles of inclination, low current density and high rotation rate.     

The electrodeposition of gallium from synthetic Bayer-process liquors

Gallium was electrodeposited from a synthetic Bayer solution comprising 4.5m NaOH/0.2m Na₂CO₃/0.3m NaCl/1.7m Al(OH)₃. Hydrogen evolution occurred in parallel with gallium deposition, the latter process being in part controlled by mass transfer and in part by the electron transfer step. Combined coulometric and voltammetric measurements allowed estimation of a diffusion coefficient for Ga (III) of 3.6×10^–6 cm² sec^–1 at 40° C. The coulombic efficiency for gallium deposition was a function of current density, deposition time, electrode rotation rate, temperature and gallium concentration. Values of up to 11% were obtained on a copper electrode from a solution containing 3.2×10^–3 m Ga (III). Heavy-metal impurities, such as iron and vanadium, usually found in these liquors, promote the hydrogen evolution reaction, completely inhibiting gallium production if present above certain critical concentrations.     

Impairment of Coronary Arteriolar Endothelium-Dependent Dilation after Multi-Walled Carbon Nanotube Inhalation: A Time-Course Study

Engineered nanomaterials have been developed for widespread applications due to many highly unique and desirable characteristics. The purpose of this study was to assess pulmonary inflammation and subepicardial arteriolar reactivity in response to multi-walled carbon nanotube (MWCNT) inhalation and evaluate the time course of vascular alterations. Rats were exposed to MWCNT aerosols producing pulmonary deposition. Pulmonary inflammation via bronchoalveolar lavage and MWCNT translocation from the lungs to systemic organs was evident 24 h post-inhalation. Coronary arterioles were evaluated 24–168 h post-exposure to determine microvascular response to changes in transmural pressure, endothelium-dependent and -independent reactivity. Myogenic responsiveness, vascular smooth muscle reactivity to nitric oxide, and α-adrenergic responses all remained intact. However, a severe impact on endothelium-dependent dilation was observed within 24 h after MWCNT inhalation, a condition which improved, but did not fully return to control after 168 h. In conclusion, results indicate that MWCNT inhalation not only leads to pulmonary inflammation and cytotoxicity at low lung burdens, but also a low level of particle translocation to systemic organs. MWCNT inhalation also leads to impairments of endothelium-dependent dilation in the coronary microcirculation within 24 h, a condition which does not fully dissipate within 168 h. The innovations within the field of nanotechnology, while exciting and novel, can only reach their full potential if toxicity is first properly assessed.     

Visualization and Genetic Algorithms in Minimax Theory for Nonlinear Functionals

In this paper, evolution and visualization of the existence of saddle points of nonlinear functionals or multi-variable functions in finite dimensional spaces are presented. New algorithms are developed based on the mountain pass lemma and link thery in nonlinear analysis. Further more, a simple comparison of the steepest descent algorithm and the genetic algorithm is given. The process of the saddle point finding is visualised in an inteactive graphical interface.     

Promotion of lung adenocarcinoma following inhalation exposure to multi-walled carbon nanotubes

Background

Engineered carbon nanotubes are currently used in many consumer and industrial products such as paints, sunscreens, cosmetics, toiletries, electronic processes and industrial lubricants. Carbon nanotubes are among the more widely used nanoparticles and come in two major commercial forms, single-walled carbon nanotubes (SWCNT) and the more rigid, multi-walled carbon nanotubes (MWCNT). The low density and small size of these particles makes respiratory exposures likely. Many of the potential health hazards have not been investigated, including their potential for carcinogenicity. We, therefore, utilized a two stage initiation/promotion protocol to determine whether inhaled MWCNT act as a complete carcinogen and/or promote the growth of cells with existing DNA damage. Six week old, male, B6C3F1 mice received a single intraperitoneal (ip) injection of either the initiator methylcholanthrene(MCA, 10 μg/g BW, i.p.), or vehicle (corn oil). One week after i.p. injections, mice were exposed by inhalation to MWCNT (5 mg/m³, 5 hours/day, 5 days/week) or filtered air (controls) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for lung tumor formation.

Results

Twenty-three percent of the filtered air controls, 26.5% of the MWCNT-exposed, and 51.9% of the MCA-exposed mice, had lung bronchiolo-alveolar adenomas and lung adenocarcinomas. The average number of tumors per mouse was 0.25, 0.81 and 0.38 respectively. By contrast, 90.5% of the mice which received MCA followed by MWCNT had bronchiolo-alveolar adenomas and adenocarcinomas with an average of 2.9 tumors per mouse 17months after exposure. Indeed, 62% of the mice exposed to MCA followed by MWCNT had bronchiolo-alveolar adenocarcinomas compared to 13% of the mice that received filtered air, 22% of the MCA-exposed, or 14% of the MWCNT-exposed. Mice with early morbidity resulting in euthanasia had the highest rate of metastatic disease. Three mice exposed to both MCA and MWCNT that were euthanized early had lung adenocarcinoma with evidence of metastasis (5.5%). Five mice (9%) exposed to MCA and MWCNT and 1 (1.6%) exposed to MCA developed serosal tumors morphologically consistent with sarcomatous mesotheliomas, whereas mice administered MWCNT or air alone did not develop similar neoplasms.

Conclusions

These data demonstrate that some MWCNT exposures promote the growth and neoplastic progression of initiated lung cells in B6C3F1 mice. In this study, the mouse MWCNT lung burden of 31.2 μg/mouse approximates feasible human occupational exposures. Therefore, the results of this study indicate that caution should be used to limit human exposures to MWCNT.     

Identification of optimum conditions for zinc electrowinning in high-purity synthetic electrolytes

The optimum conditions for zinc electrowinning in synthetic acidic zinc sulphate electrolytes (0.8 M ZnSO₄+1.07 M H₂SO₄) were determined using response surface statistical analysis. The coulombic efficiency (QE) was optimized with respect to temperature (T), current density (J) and electrode rotation rate (n). For an electrolyte prepared from AR zinc sulphate and Aristar sulphuric acid, containing trace lead and nickel, QE reached a maximum of 98.8% on a zinc substrate under the following conditions:T=50°C,J=500 A m^–2,n=35s^–1. For a very-high-purity electrolyte, prepared by dissolution of 99.9999% zinc in Aristar sulphuric acid, a maximum QE of 98.4% was predicted and obtained at:T61°C,J890 A m^–2,n38s^–1. Using a statistical response surface model calculated during the optimization process, QE contours giving an overall view of electrolyte performance were constructed. The QE responses were determined principally byT andJ, with significant interaction betweenn andJ orT andJ, depending on the impurity composition of the electrolyte. The model was also used to predict the QE response of the above electrolytes under conditions similar to industrial practice.