Oxide Buildup Research Articles

Effects of Process Conditions on the Fluidised Cathode Electrochemical Reduction of Tungsten Oxide in Molten LiCl-KCl Eutectic

The electrochemical reduction of metal oxides is important in the production of refractory metals. Conventional electroreduction routes have limitations related to oxide build-up near the surface of solid precursors, as well as operative electrolyte access to the inner parts of the precursors. The fluidised cathode process offers a promising substitute. The process is demonstrated on a WO3 and LiCl-KCl model system. Cyclicvoltammetry and chronoamperometry were used to investigate the process. Process conditions such as fluidisation rate and concentration of particles in the melt, and their effects, are investigated.

Enhanced Adhesion of Nanoporous Metal Layers on Modified Glassy Carbon Surfaces

The development of efficient catalysts, mostly involving Pt is very important in modern fuel cells. Pt is highly efficient at catalyzing fuel cell reactions as oxygen reduction and organic fuel oxidation. The high cost of Pt calls for limited use of the material. To this end, many approaches use nanoparticles. However, capping agents and material loss reduce efficiency of such nanoparticles. It has been suggested that electrochemical deposition of thin film catalytic materials can greatly increase the efficiency of fabrication, while also introducing a new level of control to the amount of deposited active catalyst. Recently, a successful development of protocol for fabrication of NPG has been established based electrodeposition of an ultrathin, continuous film of single-phase alloy followed by a selective electrochemical dissolution (de-alloying) intended for the less-noble component removal. If the deposited alloy is Au(1-x)Agx the newly introduced protocol serve for the synthesis of NPG of thickness that could be as low as 20 nm.Platinized NPG thin films fabricated on Au substrate have proven to be an efficient and yet low Pt-loading catalyst. However, when processed on low-cost substrates like glassy carbon (GC); the electrodeposited catalyst precursor grows in large isolated and poorly adhering clusters that are associated with considerable material loss upon long-term catalytic performance tests. Some oxidative avenues like thermal treatment, electrochemical treatment and plasma treatment have been explored for improving the adhesion of metals to GC surfaces. These are associated with opening of pores and substantial improvement of the wettability of GC surfaces. In particular, the thermal and electrochemical oxidation approaches are key treatment options for adhesion improvement. These treatments can be precisely monitored vis-à-vis oxide buildup and respectively oxide layer thickness rendering the treatment process readily controllable.In view of our group’s long-term interest in the development of nanoporous metal layers on C-based substrates (like GC) for ultimate support of high-efficiency catalysts, the presented research will assess the applicability of oxidative routines in the NPG supported catalyst production. An in-depth look will be taken at continuity and adhesion of the NPG thin films fabricated on thermally or electrochemically oxidized GC surface. The research will primarily focus on (i) the charge accumulation with time during the oxidation of GC surface, vis-à-vis the thickness of the resulting oxide layer. Also, a point of interest will be the metal/alloy deposition efficiency as a function of the oxide layer thickness; (ii) the resultant morphology and the continuity of NPG thin films on GC substrate; (iii) comparison of NPG thin films on accordingly oxidized GC surfaces (i) as a function on the oxidation routine and (ii) to the untreated GC in terms of layer quality and adhesion; (iv) the specific composition of the oxidized layers depending upon the employed oxidation routine. More specifically, the growth of the oxidized layer on GC will be monitored by chronoamperometry in the course of electrochemical oxidation. The fabrication of NPG thin film on oxidized layers will be followed with a special attention on the deposition efficiency in stripping configuration. The resultant morphology and continuity of the fabricated catalyst supportwill be derived by SEM as shown by preliminary results in the attached Figure where NPG is fabricated on untreated (left) and oxidized 1 μm in depth (right) GC electrode. The adhesion of the NPG thin films on GC substratewill be tested by mechanical agitation via Rotating Disk Electrode. The comparison of the electrochemically oxidized GC and untreated GC will be measured by Pb-UPD, and (independently) by stripping experiments before and after rotation. The comparative results will be analyzed in detail and critically discussed. Figure

In situ low-cost and adaptable braze tool evaluation system with vision analysis

In this study, a low-cost, flexible process monitoring system for focussed arc tungsten inert gas welder tool electrodes is presented. The system is capable of acquiring and processing geometric data that are used to define acceptance criteria. This system is used to characterise tool wear phenomena in repetitive brazing runs ensuring that the tool is operating within its process window. It was found, using this apparatus, that a build-up of zinc oxide, originating from the zinc-coated steel, on the braze tool prohibits arcing and delivery of a good quality joint. The vision system can identify build-up of this layer before failure of ignition. Measurements showed that after 990 s of continuous arcing, the zinc oxide build-up would cause system malfunction. The vision system gave a warning of zinc build-up at 577 s.

Novel fluidised cathode approach for the electrochemical reduction of tungsten oxide in molten LiCl–KCl eutectic

The electrochemical reduction of metal oxides is an important step in refractory metal production and in the pyroprocessing of spent nuclear materials. The FFC Cambridge process has revolutionised molten salt electrolysis; however, it has quite a low efficiency and has diffusion and oxide build-up issues. The fluidised cathode approach eliminates some of these issues. To illustrate the process, the electroreduction of tungsten oxide particles from a LiCl–KCl eutectic is demonstrated. Cyclic voltammetric measurements were taken and show the main reduction peak for WO3 to W to be at −2.135V (vs. Ag/Ag+) at an operating temperature of 450°C. Chronoamperometry shows an increase in current associated with an increasing current collector size and the spalling of deposited W from the surface. SEM and EDS analyses of the product reveal the deposit to be pure W.

Kinetics and Active Surfaces for CO Oxidation on Pt-Group Metals Under Oxygen Rich Conditions

This mini review summaries recent works on identifying the active surfaces for CO oxidation on Pd, Pt, and Rh under oxygen rich conditions. A significantly high reaction rate for CO oxidation under oxygen rich conditions has been observed. Results using in situ characterization methods of ambient scanning tunneling microscope, surface X-ray diffraction, ambient pressure X-ray photoemission spectroscopy, X-ray absorption spectroscopy, and infrared reflection adsorption spectroscopy (IRAS), were included. Most X-ray related methods reveal that the achievements of the high reaction rates for CO oxidation on Pd, Pt, and Rh under oxygen rich conditions are accompanied with the appearance of oxides on the surface, leading to that the oxide phase is considered to be the active surface. In contrast, recent in situ IRAS results conclude that a chemisorbed oxygen covered metallic surface is the active surface. Kinetic data support that the reaction on the metallic surfaces can reach the high rate, e.g. a mass-transfer limit turnover frequency, without the necessity of the presence of oxide. Therefore, we point out that the appearance of oxides on Pt-group metals during CO oxidation is possibly due to the transfer-limit of CO gas, resulting in exposing the catalyst surface to an ambient atmosphere much richer in oxygen and thus building-up the oxide. Moreover, photons in X-ray related experiments may aid to overcome the formation barrier of oxide on a chemisorbed oxygen covered metallic surface. The formation of oxide is also affected by the mass-transfer properties of the in situ reaction cells. If the amount of incoming CO molecules under the mass-transfer limit of CO is high enough, the build-up of oxide may be precluded being consumed by reacting with CO.

Biomolecular Gradients via Semiconductor Gradients: Characterization of Amino Acid Adsorption to InxGa1–xN Surfaces

The band gap of indium gallium nitride can be tuned by varying the compositional ratio of indium to gallium, spanning the entire visible region and extending into the near-infrared and near-ultraviolet. This tunability allows for device optimization specific to different applications, including as a biosensor or platform for studying biological interactions. However, these rely on chemically dependent interactions between the device surface and the biostructures of interest. This study presents a material gradient of changing In:Ga composition and the subsequent evaluation of amino acid adsorption to this surface. Arginine is adsorbed to the surface in conditions both above and below the isoelectric point, providing insight to the role of electrostatic interactions in interface formation. These electrostatics are the driving force of the observed adsorption behaviors, with protonated amino acid demonstrating increased adsorption as a function of native surface oxide buildup. We thus present a gradient inorganic substrate featuring varying affinity for amino acid adhesion, which can be applied in generating gradient architectures for biosensors and studying cellular behaviors without application of specialized patterning processes.

Host-Mycobacterium avium subsp. paratuberculosis interactome reveals a novel iron assimilation mechanism linked to nitric oxide stress during early infection.

BackgroundThe initial interaction between host cell and pathogen sets the stage for the ensuing infection and ultimately determine the course of disease. However, there is limited knowledge of the transcripts utilized by host and pathogen and how they may impact one another during this critical step. The purpose of this study was to create a host-Mycobacterium avium subsp. paratuberculosis (MAP) interactome for early infection in an epithelium-macrophage co-culture system using RNA-seq.ResultsEstablishment of the host-MAP interactome revealed a novel iron assimilation system for carboxymycobactin. Iron assimilation is linked to nitric oxide synthase-2 production by the host and subsequent nitric oxide buildup. Iron limitation as well as nitric oxide is a prompt for MAP to enter into an iron sequestration program. This new iron sequestration program provides an explanation for mycobactin independence in some MAP strains grown in vitro as well as during infection within the host cell. Utilization of such a pathway is likely to aid MAP establishment and long-term survival within the host.ConclusionsThe host-MAP interactome identified a number of metabolic, DNA repair and virulence genes worthy for consideration as novel drug targets as well as future pathogenesis studies. Reported interactome data may also be utilized to conduct focused, hypothesis-driven research. Co-culture of uninfected bovine epithelial cells (MAC-T) and primary bovine macrophages creates a tolerant genotype as demonstrated by downregulation of inflammatory pathways. This co-culture system may serve as a model to investigate other bovine enteric pathogens.

New approaches to the study of sepsis

Models of sepsis have been instructive in understanding the sequence of events in animals and, to an extent, in humans with sepsis. Events developing early in sepsis suggest that a hyperinflammatory state exists, accompanied by a buildup of oxidants in tissues reflective of a redox imbalance. Development of immunosuppression and degraded innate and adaptive immune responses are well-established complications of sepsis. In addition, there is robust activation of the complement system, which contributes to the harmful effects of sepsis. These events appear to be associated with development of multiorgan failure. The relevance of animal models of sepsis to human sepsis and the failure of human clinical trials are discussed, together with suggestions as to how clinical trial design might be improved.

Effect of humidity, temperature and railhead contamination on the performance of friction modifiers: Pin-on-disk study

Commercially available friction modifiers are used in many different countries that have widely different atmospheric conditions. These variations in atmospheric conditions lead to varying levels of railhead oxidation and debris build-up. Friction modifiers can be applied to the rail without any prior cleaning of the rail and this can lead to varying friction modifier/iron oxide ratios potentially affecting the performance of the friction modifier. This paper reports the results of an investigation that was performed to determine the effects of varying atmospheric and oxide conditions on the performance of friction modifiers. A pin-on-disk test rig with an attached environmental chamber was used for the study. Results show that relative humidity has a pronounced effect on the way in which the friction modifier affects friction levels, and also the amount of time it remains on the disk. This also depends on the concentration of oxide in the friction modifier. Glow discharge optical emission spectroscopy analysis was also carried out to assess the effect of the friction modifier and atmospheric conditions on the chemical composition of the surface of the disk. Results show that the depth of surface modification is vastly different depending on the conditions and level of railhead debris.

A Strategy to Produce Single and Double Layer Graphene Sheets

We report an easy and scaleable approach to produce single and double layer graphene (Gr)-sheet from re-exfoliation of expanded graphite (EG) with large area. Transmission and scanning electron microscopic observations show that the Gr-sheets have an area of ~ (12 x 10) μm2. Raman spectroscopy has confirmed the presence of single and double layer Gr-sheet with I2D/IG ratio as ~ 1.7. Scanning probe microscopy studies reveals that on re-exfoliation of EG, thickness of Gr-layer decreases from 6-7 nm to 0.8-1.1 nm. This infers that re-exfoliation overcomes the problem of insufficient oxidation or inadequate pressure buildup during heat treatment.

Contributions of regional and intercontinental transport to surface ozone in the Tokyo area

Abstract. Japan lies downwind of the Asian continent and for much of the year air quality is directly influenced by emissions of ozone precursors over these heavily-populated and rapidly-industrializing regions. This study examines the extent to which oxidant transport from regional and distant anthropogenic sources influences air quality in Japan in springtime, when these contributions are largest. We find that European and North American contributions to surface ozone over Japan in spring are persistent, averaging 3.5±1.1 ppb and 2.8±0.5 ppb respectively, and are greatest in cold continental outflow conditions following the passage of cold fronts. Contributions from China are larger, 4.0±2.8 ppb, and more variable, as expected for a closer source region, and are generally highest near cold fronts preceding the influence of more distant sources. The stratosphere provides a varying but ever-present background of ozone of about 11.2±2.5 ppb during spring. Local sources over Japan and Korea have a relatively small impact on mean ozone, 2.4±7.6 ppb, but this masks a strong diurnal signal, and local sources clearly dominate during episodes of high daytime ozone. By examining the meteorological mechanisms that favour transport from different source regions, we demonstrate that while maximum foreign influence generally does not occur at the same time as the greatest buildup of oxidants from local sources, it retains a significant influence under these conditions. It is thus clear that while meteorological boundaries provide some protection from foreign influence during oxidant outbreaks in Tokyo, these distant sources still make a substantial contribution to exceedance of the Japanese ozone air quality standard in springtime.

Oxygen control systems and impurity purification in LBE: Learning from DEMETRA project

Operating a system using Lead–Bismuth Eutectic (LBE) requires a control of the dissolved oxygen concentration to avoid corrosion of structural materials and oxide build-up in the coolant. Reliable devices are therefore needed to monitor and adjust the oxygen concentration and to remove impurities during operation. In this article, we describe the learning gained from experiments run in the framework of the DEMETRA project (IP-EUROTRANS 6th FP contract) on the oxygen supply in LBE and on impurity filtration and management in different European facilities. An oxygen control device should supply oxygen in LBE at sufficient rate to compensate loss by surface oxidation, otherwise local dissolution of oxide layers might lead to the loss of steel protection against dissolution. Oxygen can be supplied by gas phase H 2O or O 2, or by solid phase, PbO dissolution. Each of these systems has substantial advantages and drawbacks. Considerations are given on devices for large scale facilities. The management of impurities (lead oxides and corrosion products) is also a crucial issue as their presence in the liquid phase or in the aerosols is likely to impair the facility, instrumentation and mechanical devices. To avoid impurity build-up on the long-term, purification of LBE is required to keep the impurity inventory low by trapping oxide and metallic impurities in specific filter units. On the basis of impurities characterisation and experimental results gained through filtration tests in different loops, this paper gives a description of the state-of-art knowledge of LBE purification with different filter media. It is now understood that the nature and behaviour of impurities formed in LBE will change according to the operating modes as well as the method to propose to remove impurities. This experience can be used to validate the basis filtration process, define the operating procedures and evaluate perspectives for the design of purification units for long-term application in lead-alloys liquid metal coolant systems.

Effect of Mn on the Formation of Oxide Buildups Upon HVOF-Sprayed MCrAlY-Ceramic-Type Cermet Coatings

Thermal spray coatings have been widely used on hearth rolls in a continuous annealing line to improve steel sheet quality and to prolong the roll service life. One of the common defects formed on a working hearth roll is the oxide buildup. HVOF-sprayed CoCrAlY-CrB2-Y2O3 coating was used in this study to duplicate buildups by reacting with Fe and Mn oxides. The reaction was performed in a furnace at 900 °C with inert gases flowing through. After reacting for 8 days, large Mn-rich buildups were formed on the coating while the buildups without Mn were very small. Mn was shown to enhance the formation of buildups. Buildups from a hearth roll were also examined and compared with the laboratory ones.

Multi-mechanism crack closure simulations in various steels

A multi-mechanism modeling of fatigue crack growth is presented in this paper. The model accounts for the combined effect of plasticity-induced crack closure, oxide-induced crack closure and embrittlement effects near the crack tip. The development of oxide debris behind the crack tip causing oxide-induced crack closure is relevant at low stress intensity factor ranges, in the near-threshold regime. The oxide build-up is empirically modeled to account for fretting oxidation. Embrittlement is assumed to be the result of hydrogen diffusion in the near crack-tip region. Several parametric studies are performed to understand the computing limits of the model. Fatigue crack growth simulations are performed for various steels, and fatigue crack growth rates are determined. The model calculations are shown to match experimental data from literature.

Spatial Distribution of Incrustations around a Water Well after 38 Years of Use

The spatial distribution of iron incrustations around an abandoned water well after 38 years of use was studied by analyzing the iron content of soil samples from 12 core borings. Three of these were performed inside the gravel pack, the rest at different distances in the adjacent aquifer. Incrustations had preferentially accumulated at the bottom of the screen coinciding with a zone of higher aquifer permeability. As expected, all cores from the annulus show buildup of iron oxides but the ones outside also showed elevated iron content up to 4 m away from the screen. Such distant incrustations are very difficult to remove, by mechanical or chemical methods. The common procedure of removing tubing and annulus material to install a new well at the same location could therefore give the replacement well a hydraulic disadvantage as the incrustations in the aquifer remain in place.

Forced flotation of inclusions in tundish

With increased usage of steel for critical applications, the demand for cleaner steel has increased. Existing technologies have been improved and new technologies are being introduced all along the process route to minimise the size and quantity of inclusions. In continuous casting, the function of tundish has changed from its early role as a liquid steel buffer to a multifunctional vessel, dominating quality adjustments, specifically inclusion flotation. To meet stringent cleanliness requirements, a methodology of forced flotation of inclusions by controlled bubbling of inert gas in tundish was developed and investigated. Location of the bubbling arrangement was optimised using the flow profile generated by water modelling experiments. Optimum gas flowrates were calculated mathematically and further adjusted with a series of experiments. Extensive plant scale trials were used to optimise the process parameters and bring the technology to practice. There was a 33–70% reduction in inclusions of size greater than 50 μm and a 13–36% reduction in inclusions 25–50 μm. Inclusion removal reduced at higher casting speeds. Under steady state conditions, efficiency of inclusion flotation was found to be a function of casting speed. Additionally, a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life.

A model considering the ionizing radiation effects in MOS structure

Based on the physical process of holes trapped in oxide and interface trap buildup induced by proton, a unified physics-based model of oxide-trapped charge and interface trap charge in MOSFET after ionizing radiation exposure as a function of radiation dose is proposed. This model predicts that the oxide-trapped charge density and interface trap charge density induced by radiation rays would be linear in dose at low dose levelss, and would deviate from linear relationship and tend to saturation at moderate to high dose levels. The change of these two kinds of charge induced by ionizing radiation as a function of radiation dose can be well described by the expressions proposed in this model. At last, the correlation between these two kinds of charge is discussed and a linear dependence is suggested at low dose level. This model gives insights into the trap generation in gate oxide induced by radiation, and provides a more accurate predictive model for radiation damage in MOS devices operated in space ionizing radiation environment.

Practice Advisory for the Prevention and Management of Operating Room Fires

Practice Advisory for the Prevention and Management of Operating Room Fires: An Updated Report by the American Society of Anesthesiologists Task Force on Operating Room Fires Jeffrey Apfelbaum;Robert Caplan;Steven Barker;Richard Connis;Charles Cowles;Jan Ehrenwerth;David Nickinovich;Donna Pritchard;David Roberson;Robert Caplan;Steven Barker;Richard Connis;Charles Cowles;Albert de Richemond;Jan Ehrenwerth;David Nickinovich;Donna Pritchard;David Roberson;Gerald Wolf; Anesthesiology

High-Temperature Oxidation of Fe- Si Alloys in the Temperature Range 900-1250°C

Exposure of metals and alloys to high temperatures leads to the formation of oxide scales, with a large impact on surface quality. The most important features of the oxide layer are its thickness, composition, structure, adherence and coherence. Temperature, time, gas atmosphere and chemical composition determine the growth of oxide layers. In this paper, the characteristics of the high temperature oxidation properties of Fe-Si alloys are discussed in terms of oxide growth mechanism, kinetics and phase morphology. The oxidation kinetics of different Fe-Si alloy steels in air, its scale structure and composition were investigated over the temperature range 900-1250°C. Oxidation experiments were performed in air, to analyse the oxidation process. Experiments were carried out in an electric furnace at temperatures ranging from 900 to 1250°C, for times between 16 and 7200s. Thus treated specimens were characterised by metallography and their scale thickness was measured by optical microscopy. Scale morphology was studied and scale composition confirmed by EDS (Energy Dispersive Spectroscopy) and EBSD (Electron Backscattered Diffraction) analysis. Results show that high temperature oxidation of Si- alloys presents the classic three layered oxide scale. On the grain boundaries in the scale, iron-silicate was found. Observations show a Sienrichment at the scale –metal interface. This enrichment is present in the form a mixed wustite-iron silicate (fayalite) phase, FeO-Fe2SiO4. A very rapid build-up of oxide occurs when a liquid phase, due to the wustite-fayalite eutectic, is present in the surface of the steel.

Seasonal and diel variation of atmospheric mercury concentrations in the Reno (Nevada, USA) airshed

This paper describes total gaseous mercury (TGM) concentrations measured in Reno, Nevada from 2002 to 2005. The 3-year mean and median air Hg concentrations were 2.3 and 2.1 ng m −3, respectively. Mercury concentrations exhibited seasonality, with the highest concentrations in winter, and the lowest in summer and fall. A well-defined diel pattern in TGM concentration was observed, with maximum daily concentrations observed in the morning and minimum in the afternoon. A gradual increase of TGM concentration was observed in the evening and over night. The early morning increase in TGM was likely due to activation of local surface emission sources by rising solar irradiance and air temperature. The subsequent decline and afternoon minimum in TGM were likely related to increased vertical mixing and the buildup of atmospheric oxidants during the day resulting in increased conversion to oxidized species that are quickly deposited, coupled with weakening of the surface emissions processes. The described diel pattern was seasonally modulated with the greatest amplitude in variation of TGM concentrations occurring in the summer. It is suggested based on the comparison of diel TGM pattern with other gaseous pollutants that natural source surface emissions are a dominant source of TGM in the study area.