Presence Of Surface Coatings Research Articles

Transport and retention of silver nanoparticles in soil: Effects of input concentration, particle size and surface coating

Soils are considered as a major sink for engineered nanoparticles (ENPs) because of their inevitable release to the subsurface environment during production, transportation, use and disposal processes. In this context, the transport and retention of silver nanoparticles (AgNPs) with different input particle concentration, particle size, and surface coating were investigated in clay loam using water-saturated column experiments. Our results showed that the mobility of AgNPs in the soil was considerably low, and >73.9% of total injected AgNPs (except for no coating condition) was retained in columns. This is primarily due to the high specific surface area and favorable retention sites in soil. Increased transport of AgNPs occurred at higher input concentration and smaller particle size. The presence of surface coatings (i.e., polyvinylpyrrolidone (PVP) and citrate) further promoted the transport and reduced the retention of AgNPs in soil, which is likely due to their effective blocking of the solid-phase sites that are originally available for AgNPs retention. Although the shape of retention profiles (RPs) of AgNPs was either hyperexponential or nonmonotonic that is different from the colloid filtration theory prediction, the 1-species (consider both time- and depth-dependent retention) and/or 2-species (account for the release of reversibly deposited AgNPs) model successfully described the transport behaviors of AgNPs in soil columns under all the investigated conditions. This study proves the applicability of mathematical model in predicting the fate and transport of ENPs in real soils, and our findings presented herein are significant to ultimately develop management strategies for reducing the potential risks of groundwater contamination due to ENPs entering the environment.

Limiter observations during W7-X first plasmas

During the first operational phase (referred to as OP1.1) of the new Wendelstein 7-X (W7-X) stellarator, five poloidal graphite limiters were mounted on the inboard side of the vacuum vessel, one in each of the five toroidal modules which form the W7-X vacuum vessel. Each limiter consisted of nine specially shaped graphite tiles, designed to conform to the last closed field line geometry in the bean-shaped section of the standard OP1.1 magnetic field configuration (Sunn Pedersen et al 2015 Nucl. Fusion 55 126001). We observed the limiters with multiple infrared and visible camera systems, as well as filtered photomultipliers. Power loads are calculated from infrared (IR) temperature measurements using THEODOR, and heating patterns (dual stripes) compare well with field line mapping and EMC3-EIRENE predictions. While the poloidal symmetry of the heat loads was excellent, the toroidal heating pattern showed up to a factor of 2× variation, with peak heat loads on Limiter 1. The total power intercepted by the limiters was up to ~60% of the input ECRH heating power. Calorimetry using bulk tile heating (measured via post-shot IR thermography) on Limiter 3 showed a difference between short high power discharges, and longer lower power ones, with regards to the fraction of energy deposited on the limiters. Finally, fast heating transients, with frequency >1 kHz were detected, and their visibility was enhanced by the presence of surface coatings which developed on the limiters by the end of the campaign.

Wall slip phenomena in talc-filled polypropylene compounds

Slip velocities of unfilled and talc-filled polypropylene (PP) compounds, detectable at the die wall during pressure driven shear flow, have been determined using capillary rheometry. The presence of low molar mass, polar additives is responsible for the detection of wall slip in unmodified PP. Slip velocity increases with shear stress, beyond the critical onset condition. Increasing talc concentration in the PP compounds reduces slip velocity systematically, according to the talc volume fraction, whilst talc particle morphology appears to modify the wall slip behaviour to a greater extent than particle size. In comparison to PP-talc composites based on untreated filler, the presence of surface coatings tends to increase wall slip velocity, at any given shear stress, when the coating concentration exceeds monolayer level. These observations are explained in terms of a mechanism for wall slip in a low cohesive strength interphase, rich in low molar mass amide species, close to the flow boundary. This behaviour has also been modelled using a power law, to define wall slip parameters as a function of shear stress and talc concentration that can be used to enhance process simulation. It is demonstrated that the onset and magnitude of wall slip may be controllable by compound formulation and process conditions, creating exploitation potential to enhance process control and product properties of particle-modified PP composites.

The characterization of nanostructured CVD Ni powders using transmission electron microscopy

Studies of Ni powders using a state-of-the-art transmission electron microscope with a field-emission electron source show that this instrument can be an invaluable tool for studying the morphology and character of nanostructured Ni powder manufactured by a commercial nickel carbonyl vapor deposition process. This study has revealed the presence of surface coatings, including NiO and turbostratic graphite on some powders, which can degrade the electrical conductivity of the powder. Due to the high curvature of hexagonal carbon (graphene) planes, and subsequent high density of defects, the turbostratic graphitic nanocarbon may exhibit new properties.

Bond and slip of coated reinforcement in concrete

Concrete beams reinforced with black, epoxy coated or galvanized steel were tested to failure in flexure and the slip of the reinforcement was monitored. While there was clear evidence of the influence of bar deformations on the bond capacity of beams reinforced with smooth compared to ribbed black steel bars, the majority of the work concentrated on comparing the load-slip behaviour of ribbed bars as affected by the presence of surface coatings. The ultimate capacity in flexure of beams reinforced with ribbed galvanized or epoxy coated bars was not statistically different to that of black steel reinforced beams. The results from load-slip measurements were indicative of the variation in bond for the different bar coatings. It was found that loads at a slip of 0.05 mm were generally too close to the ultimate load and accordingly lower slip values in the serviceability range, i.e. 0.01 and 0.02 mm, were adopted for the analysis. From this it was found that the mean critical load at these slip values for the ribbed galvanized bars was not statistically different to the black steel. On the other hand, the load at slip for the epoxy coated ribbed bars was significantly lower, by about 20%, than that for both the black and galvanized steel bars. Overall, the results of this work indicated that there was no significant loss in bond with the use of galvanized bars, though a significant reduction was observed with epoxy coated bars.

Capillary moisture flow and the origin of cavernous weathering in dolerites of Bull Pass, Antarctica

Flow of water through joint blocks that exhibit cavernous weathering was modeled for the Ferrar dolerite in Bull Pass, Antarctica. A peculiar moisture regime allows an analytical solution under steady-state, saturated conditions. The presence of surface coatings on the top surface of the blocks causes the matric potential gradient within the blocks to be horizontal near the surface, deflecting the flow of migrating water toward the uncoated sides during evaporation. Because weathering of the rock interior is proportional to the moisture flux, the extent of rock weathering will be similar along similar contours of the matric potential gradient. As granular disintegration occurs, it will also follow the lines of equipotennal, and cavernous weathering will result if those lines are concave.

Optical and Other Properties Changes of M-50 Bearing Steel Surfaces for Different Lubricants and Additives Prior to Scuffing

An ester lubricant base oil containing one or more standard additives to protect against wear, corrosion, and oxidation was used in an experimental ball/plate elastohydrodynamic contact under load and speed conditions such as to induce scuffing failure in short times. Both the ball and the plate were of identically treated M-50 steel. After various periods of operating time, the wear track on the plate was examined (a) with an interference microscope of ± 30 A depth resolution and (b) sometimes also with a scanning ellipsometer, and (c) a scanning Auger spectrometer. The optically deduced surface profiles varied with wavelength, indicating the presence of surface coatings, which were confirmed by the other instrumentations. As scuffing was approached, a thin (∼40 A) oxide layer and a carbide layer formed in the wear track, in particular, when tricresylphosphate antiwear additive was present in the lubricant. The rates of the formation of these layers and their reactivity toward dilute alcoholic HCl depend...

SEM and microprobe analyses of enamel-metal-fluoride interactions.

SEM and microprobe analysis of enamel, pre-treated with polyvalent metals followed by APF application, showed the presence of surface coatings, but very little penetration of fluoride or metal into the subsurface enamel. However, in vitro caries-like lesion formation in the pre-treated enamel was retarded to a greater extent than in APF-only treated enamel.

Studies on the surface coat of Paramecium aurelia. II. Relationship to the immobilization antigen.

Correlations between the presence of surface coat and immobilization antigen of Paramecium tetraurelia were studied. Supravital, partial removal of the surface coat resulted in accelerated response of monobacterially and axenically grown cells to the homologous antiserum. Ciliates pretreated with trypsin or pronase (0.5 mg/ml for 45 min at 0-4 degrees C) were immobilized approximately twice as fast as untreated control cells. The probable localization of at least part, of the immobilization antigen within the surface coat of P. tetraurelia is discussed.

Calibration of Photographic Emulsions for Low Energy Electrons

Measurements are reported for the dependence on energy of photographic darkening due to electrons of energies between 4.4 and 45 kev. For Ilford B-2 plates, in the linear density exposure region, the results can be expressed by the empirical formula D/Q/A=KEx. D is the photometric density, Q/A the exposure in electrons/mm2, E the energy in electron-volts; K and x are constants with the values (0.30±0.03)×10−12 and 1.45±0.05, respectively. The relationship for two other emulsions tested is complicated by the presence of surface coatings on the emulsions. Reproducibility of results is discussed. Results are given on density fluctuations due to granularity of Ilford and x-ray emulsions. The limit of sensitivity, using the L. and N. recording microphotometer with scanning beam 1.0 by 1.3 mm, is estimated at 450 electrons/mm2 of 40 kev energy for the x-ray emulsion and 680 electrons/mm2 for the Ilford plates. The latter is limited by photometric sensitivity.