Low wear metal sliding electrical contacts at high current density

Operation of a low wear (2 × 10^?5 mm³/(N-m)), low contact resistance copper sliding electrical contact was demonstrated. The wear rate of a lightly loaded copper–beryllium metal fiber sliding on a polished copper counterface was insensitive to (DC) current density values as great as 440 A/cm² (in a brush positive or anodic configuration). Low wear and relatively low friction (μ ～ 0.2 to 0.3) was achieved by operating the contact immersed in a liquid medium consisting of a hydrofluoroether with helium cover gas, inhibitingoxidationand providing cooling of the contact. Similar experiments performed in liquid mediums of ultrapure water and dilute (3%) hydrogen peroxide show an order of magnitude increase in wear rate and provide further insight on the role of electrochemically enhanced oxidation and the degraded contact resistance and tribological behavior of non-noble sliding electrical contacts in general. In contrast to high current density slidingin hydrofluoroether, an order of magnitude greater wear rate was observed for similar sliding conditionsin hydrogen peroxide or water without the aid of externally supplied electric potential. A conceptual model is proposed correlatingthe rate of brush wear to fatigue strength and electrochemically enhanced oxidation as a result of high current density transport through the contact. A mathematical expression was derived to calculate the approximate wear volume of a single fiber laterally contacting a slip-ring, based on direct measurement of the wear scar geometry.     

In-situ TEM on (de)hydrogenation of Pd at 0.5-4.5 bar hydrogen pressure and 20-400°C

We have developed a nanoreactor, sample holder and gas system for in-situ transmission electron microscopy (TEM) of hydrogen storage materials up to at least 4.5 bar. The MEMS-based nanoreactor has a microheater, two electron-transparent windows and a gas inlet and outlet. The holder contains various O-rings to have leak-tight connections with the nanoreactor. The system was tested with the (de)hydrogenation of Pd at pressures up to 4.5 bar. The Pd film consisted of islands being 15 nm thick and 50-500 nm wide. In electron diffraction mode we observed reproducibly a crystal lattice expansion and shrinkage owing to hydrogenation and dehydrogenation, respectively. In selected-area electron diffraction and bright/dark-field modes the (de)hydrogenation of individual Pd particles was followed. Some Pd islands are consistently hydrogenated faster than others. When thermally cycled, thermal hysteresis of about 10-16 °C between hydrogen absorption and desorption was observed for hydrogen pressures of 0.5-4.5 bar. Experiments at 0.8 bar and 3.2 bar showed that the (de)hydrogenation temperature is not affected by the electron beam. This result shows that this is a fast method to investigate hydrogen storage materials with information at the nanometer scale.     

The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part I: Mathematical modeling and numerical simulation

The existing models based on classical nucleation theory are not able to explain satisfactorily the nucleation phenomenon of microcellular foams in thermoplastics. Here, we extend the analysis of Kweeder (24), who developed a new model that considers the presence of microvoids, resulting from the thermal processing history of the polymer, as potential nucleation sites. The nucleation model “concentrates” on the stresses and thus void formations in the rubber particles. Since these are pre-existing microvoids, bubble nucleation depends on the survival of these voids to grow rather than the formation of a new phase as modeled by classical nucleation theory. The population of viable microvoids with a sufficiently large radius to survive and overcome surface and elastic forces has been modeled to yield the cell density. A log-normal distribution, which relates to the rubber particle size, has been used to model the distribution of microvoids in the polymer composite material. The model depends on various process parameters such as saturation pressure, foaming temperature, concentration of nucleating agents, solubility of the blowing agent in the polymer, and the modulus. High impact polystyrene (HIPS) was added to polystyrene to obtain polymers with different concentrations of rubber gel particles, the nucleating agent, and used here for this study.     

A non-contact method for detecting on-line industrial robot position errors using a microwave Doppler radar motion detector

To be useful, industrial robots must meet positioning accuracy requirements for their given applications. Off-line calibration generally improves robot positioning accuracy to levels needed for open-loop use in most industrial applications. Applications that require greater accuracy with respect to external assemblies generally turn to closed-loop control or passive compliance. However, industrial robot systems do not generally monitor in-process robot position to detect machine faults that can lead to product faults, scrap, machine damage, and additional costs. To achieve greater operational efficiencies, new non-invasive, non-contact methods for monitoring robot position are needed. The investigators developed a low-cost method for in-process industrial robot position monitoring using a Doppler motion detector and a statistical position error measure. The method detects position errors at robot repeatability levels.     

Analysis of lateral track buckling using new frame-type equations

In the past several decades, many lateral track buckling studies have been conducted in an effort to determine an allowable safe temperature increase for preventing the occurrence of buckling. The present analysis builds on some of these studies, but uses recently derived frame-type equations that more accurately represent the response of the rail-tie structure in the lateral plane. The presented analysis takes into account the effects of the torsional stiffness of the rail fasteners, the lateral bending stiffness of the cross-ties, and the track gauge to model more accurately the lateral response of the track panel to temperature increases. It determines effective ways to raise the allowable safe temperature increase, whether by increasing the axial and lateral resistances or by increasing the rotational stiffness of the fasteners. Also, the effect of lateral tie-stiffness on the safe temperature increase is examined.     

On the friction and wear performance of boric acid lubricant combinations in extended duration operations

Lubrication is critical for minimizing wear in mechanical systems that operate for extended time periods. Developing lubricants that can be used in engineering systems without replenishment – particularly those that are environmentally friendly – is very important for increasing the functional lifetime of mechanical components. In the present investigation, extended duration pin-on-disk experiments were carried out to determine the relative performance of a wide range of lubricant combinations in a commercial brake valve assembly. In the experiments, the lubricants were initially applied to the disk surface but were not replenished over a sliding distance of more than 6000 m. The experimental results revealed that the environmentally friendly lubricant boric acid was highly ineffective for reducing the wear in the surfaces tested. When combined with a commercial transmission fluid, however, the boric acid mixture proved to be highly effective in terms of both friction and wear performance. Based on the success of the combined lubricant experiments, the boric acid was then mixed with canola oil to form a completely natural lubricant combination. Based on further pin-on-disk experiments, this lubricant combination yielded the best wear performance of all the lubricants tested. The importance of these results, as related to the use of the natural lubricant combination in other engineering systems such as sheet metal stamping, was subsequently ascertained and discussed.     

Sorption Kinetics of 60Co with Termoxid 35 Composite Sorbent in the Presence of Humic Acids

Radiochemistry - The sorption kinetics of microamounts of Co(II) ions by the Termoxid 35 sorbent in a constant ionic strength chloride–acetate solution with and without the presence of...     

Structure and Thermodynamic Properties of the DyGaTi2O7 and EuGaTi2O7 Titanates

Inorganic Materials - The DyGaTi2O7 and EuGaTi2O7 titanates have been prepared by solid-state reactions in a starting mixture of Dy2O3 (Eu2O3), Ga2O3, and TiO2 via firing in air at temperatures of...     

An Antioxidant Enzyme Therapeutic for COVID-19

The COVID-19 pandemic has taken a significant toll on people worldwide, and there are currently no specific antivirus drugs or vaccines. Herein it is a therapeutic based on catalase, an antioxidant enzyme that can effectively breakdown hydrogen peroxide and minimize the downstream reactive oxygen species, which are excessively produced resulting from the infection and inflammatory process, is reported. Catalase assists to regulate production of cytokines, protect oxidative injury, and repress replication of SARS-CoV-2, as demonstrated in human leukocytes and alveolar epithelial cells, and rhesus macaques, without noticeable toxicity. Such a therapeutic can be readily manufactured at low cost as a potential treatment for COVID-19.     

Binary Codes Formed by Functions with Nontrivial Inertia Groups

Let K be a permutation group acting on binary vectors of length n and F _K be a code of length 2 ⁿ consisting of all binary functions with nontrivial inertia group in K. We obtain upper and lower bounds on the covering radii of F _K , where K are certain subgroups of the affine permutation group GA _n . We also obtain estimates for distances between F _K and almost all functions in n variables as n . We prove the existence of functions with the trivial inertia group in GA _n for all n 7. An upper bound for the asymmetry of a k-uniform hypergraph is obtained.