Virgin Surface Research Articles

Anisotropy of the crater function of the Cu surface under Ar bombardment

Using molecular-dynamics simulation we calculate the crater function – i.e., the surface height profile averaged over many ion impacts on a virgin surface – for the case of a single-crystalline surface. The special case of 500eV Ar impact into a Cu surface is considered, and 3 different surface orientations – (100), (110) and (111) – are calculated. We find that the crater function reflects the anisotropy of the surface. In particular, the crater rim follows the adatom angular emission distribution; its symmetry corresponds to the well-known angular distribution of sputtered atoms, the so-called Wehner spots. Erosive (sputtering) and relocative (adatom formation) contributions to the crater pit follow the energetics of the necessary bond breaks and are in a ratio of ∼1:2.5.

Analysis of total metals in waste molding and core sands from ferrous and non-ferrous foundries

Waste molding and core sands from the foundry industry are successfully being used around the world in geotechnical and soil-related applications. Although waste foundry sands (WFSs) are generally not hazardous in nature, relevant data is currently not available in Argentina. This study aimed to quantify metals in waste molding and core sands from foundries using a variety of metal–binder combinations. Metal concentrations in WFSs were compared to those in virgin silica sands (VSSs), surface soils and soil guidance levels. A total analysis for Ag, Al, Ba, Be, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sb, Te, Tl, V, and Zn was conducted on 96 WFSs and 14 VSSs collected from 17 small and medium-sized foundries. The majority of WFSs analyzed, regardless of metal cast and binder type, contained metal concentrations similar to those found in VSSs and native soils. In several cases where alkyd urethane binder was used, Co and Pb concentrations were elevated in the waste sands. Elevated Cr, Mo, Ni, and Tl concentrations associated with VSSs should not be an issue since these metals are bound within the silica sand matrix. Because of the naturally low metal concentrations found in most WFSs examined in this study, they should not be considered hazardous waste, thus making them available for encapsulated and unencapsulated beneficial use applications.

Analysis of Desorbed Gases from Oxygen-free Copper Stimulated by Irradiation with Single Pulsed Electron Beam

Desorbed gases from anode stimulated by electron irradiation are regarded as one of causes leading to vacuum breakdown. To understand the vacuum breakdown phenomena, it is important to analyze composition and quantity of electron stimulated desorption gases. Single pulsed electron beam irradiation method was developed for the detailed analysis of the desorbed gas characteristics. It is possible for this method to reduce the modification of surface condition due to electron beam irradiation and enables to measure the transition of gas desorption rate from the virgin surface state to a certain period. Using this method, we investigated the desorbed gases from oxygen-free copper electrode. It was found that electron irradiation caused H2 gas desorption from copper electrode and the conditioning of the gas desorption. Moreover, a large amount of H2 gas was desorbed when the first electron beam was irradiated. By using desorbed gases analysis method stimulated by irradiation with single pulsed electron beam, it is possible to observe change of gas desorption rate from virgin surface to a certain number of electron irradiated surface state. Analyzing desorbed gas from the sample in detail can evaluate the electrode material in vacuum.

Nanocomposite silicasurfactant microcapsules by evaporation induced self assembly: tuning the morphological buckling by modifying viscosity and surface charge

Nanocomposite microcapsules of silica and surfactants have been synthesized using evaporation induced self-assembly through spray drying. It was established using electron microscopy and small-angle neutron/X-ray scattering experiments that the viscosity of the virgin dispersion and surface charge of colloidal components play a significant role in the buckling of spray droplets during drying. Hollow spherical grains are realized at relatively low viscosity and higher surface charge while mushroom like grains manifest at higher viscosity and lower surface charge. In the intermediate conditions, deformed doughnut shaped microcapsules are obtained. Scattering experiments establish the presence of the organization of micelle like aggregates of surfactants in the dried grains and also corroborate with the observations from electron microscopy. A plausible mechanism regarding the chronological pathways of morphological transformation is illustrated. Computer simulation, based on buckling of an elastic shell using a surface evolver, has been attempted in order to corroborate the experimental results.

The tribological behaviour of different clearance MOM hip joints with lubricants of physiological viscosities

Clearance is one of the most influential parameters on the tribological performance of metal-on-metal (MOM) hip joints and its selection is a subject of considerable debate. The objective of this paper is to study the lubrication behaviour of different clearances for MOM hip joints within the range of human physiological and pathological fluid viscosities. The frictional torques developed by MOM hip joints with a 50 mm diameter were measured for both virgin surfaces and during a wear simulator test. Joints were manufactured with three different diametral clearances: 20, 100, and 200 microm. The fluid used for the friction measurements which contained different ratios of 25 percent newborn calf serum and carboxymethyl cellulose (CMC) with the obtained viscosities values ranging from 0.001 to 0.71 Pa s. The obtained results indicate that the frictional torque for the 20 microm clearance joint remains high over the whole range of the viscosity values. The frictional torque of the 100 microm clearance joint was low for the very low viscosity (0.001 Pa s) lubricant, but increased with increasing viscosity value. The frictional torque of the 200 microm clearance joint was high at very low viscosity levels, however, it reduced with increasing viscosity. It is concluded that a smaller clearance level can enhance the formation of an elastohydrodynamic lubrication (EHL) film, but this is at the cost of preventing fluid recovery between the bearing surfaces during the unloaded phase of walking. Larger clearance bearings allow a better recovery of lubricant during the unloaded phase, which is necessary for higher viscosity lubricants. The selection of the clearance value should therefore consider both the formation of the EHL film and the fluid recovery as a function of the physiological viscosity in order to get an optimal tribological performance for MOM hip joints. The application of either 25 per cent bovine serum or water in existing in vitro tribological study should also be revised to consider the relevance of clinic synovial fluid viscosities and to avoid possible misleading results.

Biocompatibility of polypropylene non-woven fabric membrane via UV-induced graft polymerization of 2-acrylamido-2-methylpropane sulfonic acid

This work described the graft polymerization of a sulfonic acid terminated monomer, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), onto the surface of polypropylene non-woven (NWF PP) membrane by O 2 plasma pretreatment and UV-induced photografting method. The chemical structure and composition of the modified surfaces were analyzed by FTIR-ATR and XPS, respectively. The wettability was investigated by water contact angle and equilibrium water adsorption. And the biocompatibility of the modified NWF PP membranes was evaluated by protein adsorption and platelet adhesion. It was found that the graft density increased with prolonging UV irradiation time and increasing AMPS concentration; the water contact angles of the membranes decreased from 124° to 26° with the increasing grafting density of poly(AMPS) from 0 to 884.2 μg cm −2, while the equilibrium water adsorption raised from 5 wt% to 75 wt%; the protein absorption was effectively suppressed with the introduction of poly(AMPS) even at the low grafting density (132.4 μg cm −2); the number of platelets adhering to the modified membrane was dramatically reduced when compared with that on its virgin surface. These results indicated that surface modification of NWF PP membrane with AMPS was a facile approach to construct biocompatible surface.

An investigation into the tribological behaviour of a work roll material at high temperature

Abstract The tribological behaviour of work roll materials is always a key issue during the hot rolling of metals where high pressure and high temperature are applied to the strip. In this paper, the oxidation behaviour of a high speed steel roll material is investigated by a Gleeble 3500 thermal–mechanical simulator at 700 °C for different oxidation periods in dry air as well as in a moist atmosphere. The surface characteristics after oxidation are characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The results indicate that the humid atmosphere has a significant effect on the surface morphology of the oxide scale. A simulation of the hot rolling process is also conducted on a mini rolling mill which is incorporated within the Gleeble 3500 simulator. Two types of roller surfaces are investigated, one is a virgin surface and the other a pre-oxidized surface with 7 μm thick oxide scale. The experimental results show that the two types of roller surface exhibit quite different tribological behaviour in terms of friction and surface roughness. The rolling force and friction of pre-oxidized rolls are higher than that of virgin surface rolls for different thickness reductions and temperatures.

Characterization and effect of biofouling on polyamide reverse osmosis and nanofiltration membrane surfaces

Biofouling is a major reason for flux decline in the performance of membrane-based water and wastewater treatment plants. Initial biochemical characterization of biofilm formation potential and biofouling on two commercially available membrane surfaces from FilmTec Corporation were investigated without filtration in laboratory rotating disc reactor systems. These surfaces were polyamide aromatic thin-film reverse osmosis (RO) (BW30) and semi-aromatic nanofiltration (NF270) membranes. Membrane swatches were fixed on removable coupons and exposed to water with indigenous microorganisms supplemented with 1.5 mg l−1 organic carbon under continuous flow. After biofilms formed, the membrane swatches were removed for analyses. Staining and epifluorescence microscopy revealed more cells on the RO than on the NF surface. Based on image analyses of 5-μm thick cryo-sections, the accumulation of hydrated biofoulants on the RO and NF surfaces exceeded 0.74 and 0.64 μm day−1, respectively. As determined by contact angle the biofoulants increased the hydrophobicity up to 30° for RO and 4° for NF surfaces. The initial difference between virgin RO and NO hydrophobicities was ∼5°, which increased up to 25° after biofoulant formation. The initial roughness of RO and NF virgin surfaces (75.3 nm and 8.2 nm, respectively) increased to 48 nm and 39 nm after fouling. A wide range of changes of the chemical element mass percentages on membrane surfaces was observed with X-ray photoelectron spectroscopy. The initial chemical signature on the NF surface was better restored after cleaning than the RO membrane. All the data suggest that the semi-aromatic NF surface was more biofilm resistant than the aromatic RO surface. The morphology of the biofilm and the location of active and dead cell zones could be related to the membrane surface properties and general biofouling accumulation was associated with changes in the surface chemistry of the membranes, suggesting the validity of the combination of these novel approaches for initial assessment of membrane performance.

Control of surface ripple amplitude in ion beam sputtered polycrystalline cobalt films

We have grown both polycrystalline and partially textured cobalt films by magnetron sputter deposition in the range of thickness (50–200nm). Kinetic roughening of the growing film leads to a controlled rms surface roughness values (1–6nm) increasing with the as-grown film thickness. Ion erosion of a low energy 1keV Ar+ beam at glancing incidence (80°) on the cobalt film changes the surface morphology to a ripple pattern of nanometric wavelength. The wavelength evolution at relatively low fluency is strongly dependent on the initial surface topography (a wavelength selection mechanism hereby confirmed in polycrystalline rough surfaces and based on the shadowing instability). At sufficiently large fluency, the ripple wavelength steadily increases on a coarsening regime and does not recall the virgin surface morphology. Remarkably, the use of a rough virgin surface makes the ripple amplitude in the final pattern can be controllably increased without affecting the ripple wavelength.

Role of Self-Assembled Monolayer of 1,2,3-Benzotriazole in Protecting Copper Artifacts Covered with Sulfide Film

Abstract Corrosion inhibition of the self-assembled monolayer (SAM) of 1,2,3-Benzotriazole (BTAH) on virgin and sulfide-covered (tarnished) copper surfaces was studied using impedance, scanning electron microscopy, and Raman spectroscopy. SAM on preexisting sulfide film develops a more improved protection than on the virgin surface. Addition of HS− ions and non-ionic surface active agents (NIS) in SAM-forming solution deteriorate its properties. Raman spectroscopy established formation of polymeric film by adsorption of triazolate ion rather than triazole molecule. A scheme is suggested for improved inhibition of SAM on tarnished copper. Studies indicate a predominant cathodic control of corrosion reaction by the SAM film.

Patterning of Polystyrene by Scanning Electrochemical Microscopy. Biological Applications to Cell Adhesion

Polystyrene surfaces may be patterned by Ag(II), NO(3)(•), and OH(•) electrogenerated at the tip of a scanning electrochemical microscope. These electrogenerated reagents lead to local surface oxidation of the polymer. The most efficient surface treatment is obtained with Ag(II). The patterns are evidenced by XPS and IR and also by the surface wettability contrast between the hydrophobic virgin surface and the hydrophilic pattern. Such Ag(II) treatment of a polystyrene Petri dish generates discriminative surfaces able to promote or disfavor the adhesion of proteins and also the adhesion and growth of adherent cells. The process is also successfully applied to a cyclo-olefin copolymer and should be suitable to pattern any hydrogenated polymer.

Steel surface modification by pulsed air arc treatment

Pulsed air arc treatment (PAAT) was used to modify the surface morphology and phase composition of 5010 and 01 steel. The arc produced local heating and eroded the steel surface forming craters, and the subsequent modification depended on the crater density. X-ray diffraction showed that the volume fraction of ferrite decreased while that of austenite increased with crater density. Cementite was practically absent in 5010 steel, while its volume fraction in O1 steel increased with crater density. PAAT increased the microhardness of the surfaces by 10–40% over that of the virgin surfaces. PAAT increased the lifetime of a lubricant film applied to the surface by more than an order of magnitude, by forming craters on the surface which retained the lubricant.

Fabrication of thick W coatings by atmospheric plasma spraying and their transient high heat loading performance

Both tungsten coatings with or without a W/Cu graded interlayer on an oxygen-free copper substrate were fabricated by atmospheric plasma spraying. High purity argon gas was used for cooling the substrate and preventing the coating from oxidation. The thickness of both coatings is ∼1 mm. XRD and EDS measurements of the coatings show that minimal oxidation occurred during the deposition process. Transient high heat load tests by electron beam with a pulse duration of 5 ms were performed on both coatings. The single pulse loading was applied on the virgin surfaces at several power densities (from 0.22 to 0.9 GW/m 2). Although the weight loss of the W/Cu FGM (functionally graded materials) based coating was slightly lower than that of the pure W coating, their transient high heat loading performances were quite similar.

In situ thermal treatment of UV-oxidized diamond hydrogenated surface

Surface properties of polycrystalline hydrogenated diamond produced by chemical vapour deposition upon oxidation under UV irradiation are studied. The diamond surfaces were cleaned in vacuum by thermal treatment. They were characterized estimating the electron affinity of the virgin surface by UV photoelectron spectroscopy and controlling the surface composition by X-ray photoelectron spectroscopy. The cleaned surfaces were then exposed to pure oxygen and UV radiation (deuterium lamp). Ozone induced surface oxidation was verified by XPS estimating the oxygen atomic concentration and the presence of specific chemical bonds. Surface oxidation was also verified analyzing the change in the diamond electron affinity. Oxygen was then removed in situ by a series of thermal treatments at increasing temperature. Already at ∼300 °C a remarkable reduction of the oxygen concentration occurs which persists increasing the annealing temperature. Contemporary, a progressive recovery of the initial electron affinity is also obtained. These effects are observed up to 970 °C, a temperature at which the electron affinity assumes a negative value. Specific chemical reactions are hypothesized to describe the oxidation process and to explain the electronic behaviour of the diamond surface.

10.1007/s11454-008-2010-5

The nanorelief of orienting surfaces in a nematic layer is studied experimentally. The initial inclination angle of the director and the phase retardation of light in the crystal are determined, and the director reorientation dynamics in the crystal under SB deformation in an electric field is analyzed. It is shown that a thin layer of amorphous hydrogenated carbon (a-C: H) deposited on a GeO monoxide layer with an anisotropic nanorelief produced by the inclined deposition method smoothens the surface topography without changing the surface structure. Modification of the structure and physicochemical properties of the GeO surface alters the conditions of the anisotropic-elastic interaction at the interface with the liquid crystal, as evidenced by an increase in the S-effect threshold and a decrease in the initial inclination of the director from 22° (on the GeO surface) to 0–6°. Strong influence of the surface nanostructure on the dynamics of the director reorientation in the electric field and on the phase modulation of light is experimentally demonstrated. It is shown that the phase retardation of light in the GeO layer covered by an a-C: H film is twice as large as in the layer of the same thickness with a virgin surface.

A cell migration device that maintains a defined surface with no cellular damage during wound edge generation

Studying the rate of cell migration provides insight into fundamental cell biology as well as a tool to assess the functionality of synthetic surfaces and soluble environments used in tissue engineering. The traditional tools used to study cell migration include the fence and wound healing assays. In this paper we describe the development of a microchannel based device for the study of cell migration on defined surfaces. We demonstrate that this device provides a superior tool, relative to the previously mentioned assays, for assessing the propagation rate of cell wave fronts. The significant advantage provided by this technology is the ability to maintain a virgin surface prior to the commencement of the cell migration assay. Here, the device is used to assess rates of mouse fibroblasts (NIH 3T3) and human osteosarcoma (SaOS2) cell migration on surfaces functionalized with various extracellular matrix proteins as a demonstration that confining cell migration within a microchannel produces consistent and robust data. The device design enables rapid and simplistic assessment of multiple repeats on a single chip, where surfaces have not been previously exposed to cells or cellular secretions.

Measurement of polyphenol–membrane interaction forces during the ultrafiltration of black tea liquor

This paper reports the use of atomic force microscopy (AFM) surface interaction measurements for a model polyphenol present in tea (theaflavin-3-gallate) with a regenerated cellulose ultrafiltration membrane. Differently treated membranes from throughout the fouling cleaning cycle were investigated. The adhesion of the foulant to the virgin and the fouled once/cleaned once (F1C1) membrane surface was stronger than that recorded for foulant–foulant interactions (1.87 and 1.72 N m −2, respectively, matching curves ranging between 0 and 5.5 N m −2 with a single shallow peak). Interestingly, NaOH cleaning of the virgin conditioned membrane reduced foulant–membrane adhesion compared to the virgin or F1C1 surface (0.96 N m −2) with a narrow spread of the adhesion (80% of measurements being within the range 0.5–0.99 N m −2). The uniform narrow distribution of attraction (approach) forces to the fouled and cleaned surfaces helps explain this due to uniformly charged foulant/hydroxyl ions adhering to these membrane surfaces, whereas the virgin membrane distribution was very wide demonstrating no charge modification of this surface. The present study has demonstrated how the AFM coated colloid probe technique can be used with multiple (200×) measurements across a surface to further aid understanding of the nature of fouling and cleaning mechanisms, particularly in protein/polyphenol systems.

Characterizing cavitation erosion particles by analysis of SEM images

Wear particles produced by vibratory cavitation erosion on stationary-aluminum Al-99.999 were analyzed using scanning electron microscope (SEM), forming a database for further analysis. The particle morphology features were first clarified based on the characteristic stages of the vibratory erosion rate-time pattern. Next, size, area, perimeter and shape factors (elongation and roundness) were determined for eroded particles, using image analysis software. In incubation period, the particles have distinctive characteristics which differed from that for the subsequent periods. These characteristics include the value of longitudinal ratio and roundness factor, limit size range and morphological features such as lamella shape, folding, curving with one of the particle surfaces as the virgin surface. In acceleration, steady-state and attenuation periods, the particles have a wide size range and larger thickness compared with that for the incubation period. The maximum particle size reached about 360 μm in acceleration and steady-state period. For all the cavitation erosion rate periods, the particles were out of sphericity and they have a roundness factor larger than 2. Detailed surface characteristics of the particles produced during cavitation erosion is significant and can open ways for monitoring the cavitation erosion progress.

Laser-Plasma X-ray Sources Using Ceramic Target

Ceramic plates (AlN and alumina) were used as targets for laser-plasma X-ray sources for the first time. The radiation intensity of soft X-ray spectra from Li-like ions (Al XI) for the AlN target was almost the same as that in the case of pure aluminum target. It was found that the ceramic target can be irradiated at the same place up to 70 times or more, delivering soft X-rays with nearly the same intensity as in the case when a virgin surface was irradiated. The profiles of the crater marks formed on the target surface after irradiations were measured three-dimensionally and their hollow volumes below the initial surface were evaluated. The ablated mass for the AlN or alumina target was less than 1/6 of that for a pure Al target.

Low Friction in CuO-Doped Yttria-Stabilized Tetragonal Zirconia Ceramics: A Complementary Macro- and Nanotribology Study

The tribological behavior of CuO-doped yttria-stabilized tetragonal zirconia (3Y-TZP) ceramics in the absence of additional lubricants was characterized by macroscale pin-on-disk measurements and nanoscale atomic force microscopy (AFM) for a broad range of velocities. The previously observed low shear strength interfacial layers generated in pin-on-disk tracks by Al2O3 ball counter surfaces on CuO-doped 3Y-TZP, as well as virgin surfaces, were probed quantitatively by AFM with Si3N4 tips as the counter surface. The observed trends in nanoscale coefficient of friction determined by AFM were found to be in agreement with data acquired using a pin-on-disk tribometer. The combined data support the notion that a layer of surface contaminations is removed during the initial sliding, and wear of high asperities occurs. Subsequently, an interfacial layer with low shear strength is generated during sliding. While these results do not provide an exhaustive explanation for the process of layer formation, they represent the first report of bridged nano- and macrotribological analysis of a compositionally heterogeneous low-friction, low-wear ceramic material and further confirm some of the key assumptions for the deterministic model reported previously by Pasaribu and Schipper.