Virgin Surface Research Articles

New aspects of solid-state welding in the aluminium accumulative roll bonding

The phenomena in solid-state welding (SSW) of metals during accumulative roll bonding (ARB) are analysed. The basic mechanism in SSW is described by the ‘film theory’, where superficial oxide layers/cover layers of metals fracture when submitted to elongations, the material on both sides of the sheets to be joined are extruded through these fractures and opposing virgin surfaces touch and weld. Present results reveal new aspects of these phenomena: the presence of ‘mountain ridges’ on delaminated surfaces after ARB, bonding regions along the rolling direction and the flattening of the geometric characteristics of delaminated surfaces as the number of ARB passes rises. A model is proposed for the development of the bonds along the rolling direction.

Effects of surfactant adsorption on the wettability and friction of biomimetic surfaces.

The properties of solid-liquid interfaces can be markedly altered by surfactant adsorption. Here, we use molecular dynamics (MD) simulations to study the adsorption of ionic surfactants at the interface between water and heterogeneous solid surfaces with randomly arranged hydrophilic and hydrophobic regions, which mimic the surface properties of human hair. We use the coarse-grained MARTINI model to describe both the hair surfaces and surfactant solutions. We consider negatively-charged virgin and bleached hair surface models with different grafting densities of neutral octadecyl and anionic sulfonate groups. The adsorption of cationic cetrimonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) surfactants from water are studied above the critical micelle concentration. The simulated adsorption isotherms suggest that cationic surfactants adsorb to the surfaces via a two-stage process, initially forming monolayers and then bilayers at high concentrations, which is consistent with previous experiments. Anionic surfactants weakly adsorb via hydrophobic interactions, forming only monolayers on both virgin and medium bleached hair surfaces. We also conduct non-equilibrium molecular dynamics simulations, which show that applying cationic surfactant solutions to bleached hair successfully restores the low friction seen with virgin hair. Friction is controlled by the combined surface coverage of the grafted lipids and the adsorbed CTAB molecules. Treated surfaces containing monolayers and bilayers both show similar friction, since the latter are easily removed by compression and shear. Further wetting MD simulations show that bleached hair treated with CTAB increases the hydrophobicity to similar levels seen for virgin hair. Treated surfaces containing CTAB monolayers with the tailgroups pointing predominantly away from the surface are more hydrophobic than bilayers due to the electrostatic interactions between water molecules and the exposed cationic headgroups.

Heat Transfer on Micro and Nanostructured Rough Surfaces Synthesized by Plasma

The review summarizes recent experimental results of studying heat transfer on rough surfaces synthesized by plasma. The plasma-surface interaction leads to the stochastic clustering of the surface roughness with a high specific area breaking the symmetry of the virgin surface of the initial crystalline materials. Such a surface is qualitatively different from the ordinary Brownian surface. The micro- and nanostructured surface consist of pores, craters, and nanofibers of size from tens of nanometers to tens of microns, which can provide new heat transfer properties related to a violation of the symmetry of the initial materials. In recent years, new results have been obtained in the study of heat transfer during phase change on plasma-modified surfaces in relation to energy, chemical, and cryogenic technologies. The objective of the review is to describe the specific structure of refractory metals after high-temperature plasma irradiation and the potential application of plasma processing of materials in order to create heat exchange surfaces that provide a significant intensification of two-phase heat transfer. Refractory metals with such a highly porous rough surface can be used as plasma-facing components for operation under extreme heat and plasma loads in thermonuclear and nuclear reactors, as catalysts for hydrogen production, as well as in biotechnology and biomedical applications.

Blue afterglow in Eu2+ doped CaAl2O4 by electron irradiation

1 mol% Eu2O3 – 99 mol% CaAl2O4 disc-shaped pellet sample was irradiated with a 5 keV electron beam on one of its surfaces to study the effects of electron bombardment on its structural, vibrational and photo-luminescence properties. X-ray diffraction studies found monoclinic phases of CaAl2O4 (major) and CaAl4O7 (minor) and the Raman spectra showed AlO bond vibrational bands in both the electron-irradiated and virgin (non-irradiated) sample surfaces. Electron irradiated surface has higher concentration of Eu2+ (strong blue light emission at 442 nm) than that of Eu3+ (weak red light emission at 616 nm) as compared to that in the virgin sample. Eu3+ reduce to Eu2+ with electron irradiation and this produces intense blue afterglow with a persistence time of ∼3 s, while the virgin surface exhibits orange-red light emission without afterglow effects.

Experimental investigations on two-sided upward flame spreading over thin flax fabric under the influence of restricted distance

Up to 2021, most previous work focused on upward flame spread over thin solid fuel completely attached to objects or with both sides freely exposed to the air, but did not take the restricted distance (distance between fuel and objects) effects into account. In this paper, the restricted distance effects on upward flame spread over thin solid fuels were investigated using 0.65 mm thick, 120 cm tall and 6.0 cm wide flax fabric sheets under various restricted distances of 1.0–3.5 cm. The essential parameters were monitored and analyzed simultaneously, including flame length, pyrolysis spread rate, surface temperature and ignition time. The main conclusions drawn are as follows: when the restricted distance is no more than 1.5 cm, the flame length on the unrestricted side is larger than that on the restricted side, whereas the variation exhibits the opposite trend when the restricted distance is beyond 1.5 cm. As the restricted distance increases from 1.0 to 3.5 cm, the flame length and flame spread rate first increase and then decrease, reaching a maximum value at 3.0 cm restricted distance, whereas the ignition time shows the opposite trend. The decrease rate of the surface temperature with the distance from the pyrolysis front first drops and then rises as the restricted distance increases, which qualitatively characterizes that the heat flux received by the virgin surface first increases and then decreases with restricted distance. The non-monotonic trends of heat flux received by the virgin surface and consequently the flame spread rate as a function of restricted distance are due to the combined restricted distance effects of the chimney effect, wall radiation and restricting oxygen supply. The results of this paper are not only helpful in better understanding the upward flame spread over a thin flax fabric under restricted distance, but also provide some basic data for fire prevention of thin solid fuels.

Contemporary Sterilization Protocols of Healing Abutments for Reusability: A Systematic Review.

Although healing abutments are designated for single use by most implant manufacturers, it is common practice for clinicians to reuse healing abutments. However, there is a lack of adequate references that describe detailed sterilization protocols for reuse of healing abutments. The purpose of this systematic review was to compile, organize, and describe the most common techniques for the sterilization of healing abutments and their efficiency in eliminating traces of microorganisms. An electronic search in 5 different databases was performed, including the National Library of Medicine (MEDLINE via PubMed), Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Google Scholar from January 2000 to December 2020. Search variables included were dental implant, healing abutment, contaminate, contamination, reuse, and sterilization. Studies reporting with a minimum sample size of 10 healing abutments (5 per group) published in the English language were evaluated. Risk of bias assessment was elaborated for included investigations. In total, 812 articles were identified, of which 8 were included in the analysis. Steam autoclave was the most widely used form of resterilization. Not a single protocol, however, was able to achieve 100% virgin surface of the healing abutments. Although reuse of dental implant healing abutments is a cost-effective measure in dental practice, thorough surface decontamination followed by resterilization is highly recommended before reuse. With consideration of cost and patient preference, results of this review would be useful in knowing various sterilization protocols for reusing healing abutments that could lead to more appropriate therapeutic decisions.

Mechanical Preparation Procedure for Characterizing by EBSD the Crystallographic Orientation in Surface Layers of Austenitic Stainless Steels Plasma Nitrided

Abstract This contribution reports on an experimental polishing procedure, that is comprised of early grinding in Al2O3 slurries and late polishing in colloidal silica, which is used for preparing the nitrided region of a plasma nitrided austenitic stainless steel, for crystallographic analysis via electron backscatter diffraction (EBSD). The suitability of the polished surfaces for conducting EBSD characterization was assessed through an analysis of both the surface roughness (appraised by atomic force microscopy) and the quality of the Kikuchi diffraction patterns. We observed that as-nitrided virgin surfaces were not suitable for EBSD characterization, due to intense surface roughening, which was induced by the nitriding process itself. At the subsurface region, exposed by on-top mechanical polishing, the flatter nature of the polished surfaces allowed the acquisition of EBSD patterns with enough quality for microtexture analysis. A resolution of 100 nm in the total removed layer was attainable via careful control of the polishing parameters. Close parallelism between the polished and original surfaces was verified.

Experimental Analysis of Limited Distance Effects on Self Induced Blow Off and Heat Transfer in Upward Flame Spread Over Thin Fabric Fuels

Most previous work concentrated on the one-sided upward flame spread under limited conditions. However, few investigations have studied the effects of limited distance between wall and fuel surface on two-sided upward flame spreading. In this paper, a series of upward flame spread experiments were conducted using 0.65 mm thick, 130 cm tall and 4.0 cm wide flax fabric sheets with various limited distance of 1.0 cm–3.5 cm. The flame shape, flame length, flame standoff distance, pyrolysis spread rate and surface temperature were measured and analyzed. An unexpected but interesting behavior of one-sided flame blow off was observed in upward flame spread. When limited distance is no more than 1.5 cm, the one-sided flame blow off behavior occurs on unlimited side, whereas this behavior occurs on limited side for 2.0 cm–3.5 cm limited distance. This result could be qualitatively explained by Damkohler number Da, which could be characterized by two parameters of induced flow velocity and heat flux received by virgin surface. Moreover, the maximum flame length, steady flame length, maximum spread rate and steady spread rate first increase and then decrease as the limited distance. This non-monotonicity trend is determined by heat flux profiles in the preheating zone, which is due to the combined limited distance effects of restricting oxygen supply, chimney effect and wall radiation. The surface temperature profile ahead of pyrolysis front is used to qualitatively describe the heat flux received by virgin surface. The results in this paper are essential for better understanding of self induced flame blow off mechanism and upward flame spread under limited distance conditions.

Determination of sp2 and sp3 phase fractions on the surface of diamond films from C1s, valence band X-ray photoelectron spectra and CKVV X-ray-excited Auger spectra

The practice of applying the methods for determining the relative contents of carbon atoms in sp2 and sp3 hybridization states from the profiles of C1s X-ray photoelectron and carbon KVV (CKVV) Auger spectra is analyzed. Difficulties in using C1s and CKVV spectra for determining the sp2/sp3 ratios are discussed. A method is proposed for evaluating the fractions of sp2 and sp3 phases based on the fitting of the valence band X-ray photoelectron spectra by superposition of valence band spectra of samples with carbon atoms in pure sp2 and sp3 states. Relative fractions of sp2 and sp3 phases on the virgin surfaces of two ultrananocrystalline diamond films, and on their surfaces subjected to friction, were determined using C1s spectra, CKVV Auger spectra, and valence band spectra. All three methods gave the results that are consistent for virgin film surfaces with accuracy of 2%, and for the surfaces of films subjected to friction, 15%. In contrast to the ultrananocrystalline films, three XPS-based methods applied to a microcrystalline diamond film yielded significantly different sp2/sp3 ratios. The reasons for this discrepancy are shown to lie in different analysis depths of these methods, and in different morphology of the film surfaces.

Effects of porosity and area density on upward flame spread characteristics over thin flax fabric

Few investigations have systematically addressed the porosity effects of upward flame spread over fabric fuels, although the porosity is a special property for fabric fuels. The present paper studies the porosity and area density effects on upward flame spreading using 160.0 cm tall and 8.0 cm wide flax fabric samples with various porosities and area densities. The flame shape, flame length, flame spread rate, ignition time, standoff distance and surface temperature distribution are obtained and analyzed. The major findings are summarized as follows: as the porosity increases and corresponding area density declines, the flame spread rate and flame length increase, whereas the ignition time decreases, which is because the oxygen can reach the fuel surface in the pyrolysis region more easily and, subsequently, the heat flux received by the virgin fuels increases. The two parameters of flame standoff distance and surface temperature in the preheating region can be applied to characterize the heat flux received by the virgin fuels. Generally, when the porosity increases and the corresponding area density decreases, the flame standoff distance and the surface temperature at the same distance from pyrolysis front increase, which reveals that the heat flux received by the virgin surface increases.

Describing and explaining the reaction of soils with phosphate using existing observations

AbstractSorption of phosphate by soils is an important determinant of fertiliser efficiency. Its extent and rate differ between soils. This paper considers both how these differences can be described and how they can be explained. Published data on the rate of reaction of soil with phosphate are assembled. There are 88 soil samples from five continents, as reported in six publications. In almost all cases, sorption (S) was related to solution concentration (c) and time (t) by: S = a cb1tb2 – qtb3. The term after the minus sign describes the rate of desorption; its value is affected by soil phosphate status. The “a” parameter reflects the amount of adsorbing surfaces present plus their affinity for phosphate. The b1 parameter, which describes the curvature of the sorption plots, reflects the composition of the adsorbing surfaces and their phosphate status. Large values are obtained for soils with a small range of electric potentials of their reacting surfaces and a low phosphate status, as is common for Australian virgin surface soils. The greatest influence on the b2 parameter, which describes the curvature of the plots against time, is the method of measurement. Large values were observed when soil and solution were shaken together and are probably an artefact caused by mutual abrasion of the soil particles. When this problem was avoided, large values of b2 were associated with very phosphate‐deficient soils; small values of b2 often occurred when b1 was also small, suggesting surfaces of varying potential were present. If the substances present included components such as kaolin, that might explain both the range in potentials and limited penetration.Highlights The effect of solution concentration (c) and time (t) on sorption (S) can be described by S = acb1tb2 – qtb3 and the other terms are parameters. Small values of the “curvature” term b1 are associated with large values for heterogeneity of the reacting surfaces. Mutual abrasion of the soil particles causes large values of rate parameter b2 when soil and solution are shaken. When this problem is avoided the value of b2 depends on the rate of penetration.

Analysis of lubricant performance in punching and blanking

Abstract Punching and blanking processes are characterized by severe tribological conditions due to the creation of virgin surfaces, which are highly prone to develop pick-up of workpiece material on the punch surface. Hazardous forming lubricants are, therefore, commonly used in punching and blanking processes for avoidance of wear induced process deviations such as diminished surface quality, reduced dimensional accuracy and reduced tool life. The present study characterizes the function and performance of lubricants used for punching and blanking operations for assessment of the tribological lubricant properties necessary for adaption of environmentally friendly lubricant alternatives. Analysis of the tribochemical properties of the studied lubricants indicate that an applicable temperature range and a high load bearing capacity are central lubricant properties necessary for ensuring sufficient lubricating ability for punching and blanking operations.

An experimental study on the micromechanical behavior of pumice

Pumice has a large potential to be used in structural and geotechnical engineering projects as a lightweight aggregate, and it is a material of unique characteristics. Gravel-sized pumice from Yunnan, China, was examined in the present study with a custom-built micromechanical apparatus investigating the properties of pairs of grains at their interfaces subjected to monotonic and cyclic tests under different saturation states. Based on interferometer measurements, the vesicular surface of the pumice was characterized to be very rough. From the interface micromechanical experiments, it was shown that the virgin surfaces appeared to be very soft under normal loading tests, during which micro-asperity breakage was caused. After preloading and preshearing, the normal load–displacement curves became much smoother and the Young’s moduli, which remained relatively low in magnitude compared with other geo-materials previously studied, could be quantified applying the Hertzian model. Large hysteretic loops were observed from cyclic normal load tests. Plastic displacements dominated the first normal loading cycle, while elastic displacements prevailed in the subsequent cycles. High values of the apparent coefficient of friction were observed from the monotonic shearing tests. A modification of the power value of the Mindlin and Deresiewicz model was necessary to be applied during the fitting of the experimental data so that theoretical and laboratory curves could match. It was shown that this power had a direct correlation with the coefficient of friction.

Prevention of lipid loss from hair by surface and internal modification

Surfactants during routine washing have a tremendous effect on lipid loss from hair. This study aims to understand the loss of lipids from hair upon contact with surfactants and develop a way to prevent the lipid loss. The change in lipid levels depends on the relative hydrophobicity of the lipid. We herein propose that the change in lipid levels can be protected by two modifications. In the case of fatty acids and cholesterol (group A), the concentration difference between virgin hair versus surface modified hair with highly charged polymer was 22 to 32% higher after washing with surfactants while the loss of squalene and wax esters (group B) in response to surfactants still occurred even after the surface modification. In the hair treated by internal modification with the carbodiimide reaction, 52.0 to 81.3% more lipids in group B were prevented than in the untreated hair. Finally, different types of lipids were successfully protected by surface and internal modifications from the surfactant treatment. This study will be the basis for understanding the mechanisms by which surfactants damage the lipid barrier of tissues including hair and for establishing strategies to defend the barrier.

Latex particle rejections from virgin and mixed charged surface polycarbonate track etched membranes

In this study, the impact of membrane surface characteristics on particle rejections was experimentally examined for virgin and surface modified polycarbonate track etched microporous membranes with different pore sizes. The membrane surface was modified by covalently binding tetraethylpentamine, resulting in changes in measured zeta potential. The zeta potential of the modified membranes was pH sensitive, indicating these membranes had mixed surface charges, with the tetraethylpentamine binding to only a fraction of the carboxylic acid groups on the original polycarbonate surface. There was no observable change in pore size with the surface modification. Rejections of 0.71 μm diameter negatively charged spherical red fluorescent latex particles were measured under conditions where the virgin membranes carry a strong negative charge and the surface modified membranes carry a net zero charge. Observed particle rejections from both types of membranes were two to three times larger than predictions based on steric particle-membrane interactions. These results are interpreted by considering particle adsorption to the membrane surface which is greater for the modified membranes than for the virgin membranes. This work demonstrates that mixed charged membrane surfaces show enhanced fouling, in contrast to previous studies which have shown reduced fouling for membranes with zwitterionic surfaces.

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl2(Si3Al)O10(OH)2] like important multi‐elemental layered substrate can be precisely tailored by ion bombardment. The detailed X‐ray photoelectron spectroscopic studies of a freshly cleaved as well as 12‐keV Ar+ and N+ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N+ or Ar+ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si3N4) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.

Resistance to corona discharge of HTV silicone rubber surface layers fluorinated at different temperatures

In order to investigate the effect of fluorination temperature on the resistance to corona discharge of HTV silicone rubber, HTV silicone rubber samples were fluorinated using a F2/N2 mixture at temperatures of 25, 55, and 85 °C for 30 min. The surface fluorinated and unfluorinated (virgin) samples were simultaneously exposed to corona discharge generated by a multi-needle-to-plate electrode system. ATR-IR analysis and SEM observation indicate that the virgin surface layer is severely oxidized and degraded by corona discharge. In contrast with this, the surface layer fluorinated at 85 °C does not show obvious changes in the chemistry, surface morphology and thickness after corona exposure. However, the corona exposure led to definite changes in both the chemistry and surface morphology of the surface layer fluorinated at 55 °C, and its corona-resistance property appears to be worse than the surface layer fluorinated at 25 °C. The abnormal effect of fluorination temperature on corona resistance is explained by unusual changes of surface physicochemical characteristics with fluorination temperature. Measurements of contact angle show a much higher water contact angle on the fluorinated surfaces than the virgin surface before corona exposure, an initial significant decrease in water contact angle for all the surfaces just after the end of the corona exposure, and the subsequent recovery of contact angle only for the exposed virgin surface. Measurements of surface potential reveal that the potential decay rate obviously increases for the virgin sample after corona exposure, while the decay rate decreases rather than increases for the fluorinated samples after the same exposure. There is no significant difference in surface properties between the fluorinated samples before or after corona exposure. This is considered to be due to the combined effect of compositional and structural changes and the fact that the surface properties are very sensitive to the top several molecular layers.

Multigenerational memory and adaptive adhesion in early bacterial biofilm communities

Using multigenerational, single-cell tracking we explore the earliest events of biofilm formation by Pseudomonas aeruginosa During initial stages of surface engagement (≤20 h), the surface cell population of this microbe comprises overwhelmingly cells that attach poorly (∼95% stay <30 s, well below the ∼1-h division time) with little increase in surface population. If we harvest cells previously exposed to a surface and direct them to a virgin surface, we find that these surface-exposed cells and their descendants attach strongly and then rapidly increase the surface cell population. This "adaptive," time-delayed adhesion requires determinants we showed previously are critical for surface sensing: type IV pili (TFP) and cAMP signaling via the Pil-Chp-TFP system. We show that these surface-adapted cells exhibit damped, coupled out-of-phase oscillations of intracellular cAMP levels and associated TFP activity that persist for multiple generations, whereas surface-naïve cells show uncorrelated cAMP and TFP activity. These correlated cAMP-TFP oscillations, which effectively impart intergenerational memory to cells in a lineage, can be understood in terms of a Turing stochastic model based on the Pil-Chp-TFP framework. Importantly, these cAMP-TFP oscillations create a state characterized by a suppression of TFP motility coordinated across entire lineages and lead to a drastic increase in the number of surface-associated cells with near-zero translational motion. The appearance of this surface-adapted state, which can serve to define the historical classification of "irreversibly attached" cells, correlates with family tree architectures that facilitate exponential increases in surface cell populations necessary for biofilm formation.

Surface Modification of Ti6Al4V Alloy by Pulsed Lasers: Microstructure and Hydrophobic Behavior

In many aerospace applications, it is important to produce hydro-repellent surfaces because water and ice accumulation could lead to malfunctioning of the part or component with a potential critical failure. In this study, it was investigated the texturing of a titanium alloy (Ti6Al4V) by applying a pulsed Nd:YAG laser, aimed at the surface characterization by microscopy, X-ray diffraction, roughness and nano-indentation tests as well as free fall drop test. The experimental procedure aimed to understand the influence of three variables: (N) the number of laser runs 1, 2, 5 and 10; (V) laser speeds of 25, 50 and 100 cm/s and (P) laser power of 5, 10 and 20 W on the microstructure and the hydrophobic behavior. The Vickers hardness and elastic modulus of laser processed surfaces were similar to the untreated surfaces. When the number of the laser runs (N) increased, a TiO phase amount increases as a result of increasing heat input. The measured roughnesses decreased with increasing P as a direct result of remelting. As the number of runs (N) increases the surface became more and more flat, consequently the overlapping runs induced polishing of the titanium surfaces. The mean roughness Ra attained 0.23 µm after 10 runs at V=100m/s and P=10W, compared to Ra=0.41 µm of the virgin surface. The water repellent conditions were N1V50P05, N1V100P05, N2V25P05, N2V50P05, N5V25P05, N5V50P05, N5V100P10 and N10V25P10. These conditions were associated with a homogeneous remelted layer, low power, partial superposition of the laser shots of 50% or 75%, and a surface finish slightly rougher than the original material.

Chemical sputtering of boronized and oxidized carbon surfaces irradiated by low-energy deuterium atoms

We use molecular dynamics to study the chemical sputtering of boronized and oxidized amorphous carbon surfaces by deuterium irradiation in the range of impact energies of 5–30 eV. We report the sputtering yield as well as mass, energy, and angular spectra of ejected atoms and molecules of both virgin and deuterium saturated BCO surfaces and compare them with our data for a deuterated BC surface and existing theoretical and experimental results for amorphous C:D surfaces. Boron significantly suppresses the erosion of carbon, while the presence of oxygen results in further suppression.