Removal Of Surface Layer Research Articles

津波を受けた水田土壌塩分の経時変化

A field test was conducted in a tsunami-affected paddy field in Natori city, Miyagi prefecture to understand temporal changes in soil salinity over the past 27 months and to collect information about the desalinization in the near future. Vertical profiles of the soil salinity and water content were obtained by TDR and four-electrode sensors installed down to a depth of 0.6m below the paddy soil surface near our micrometeorological station. Salt mass in the soil up to 200mm from the soil surface varied greatly due to eluviation of salt from the soil by rainfall and due to re-adsorption by the drying of the soil surface. Salt movement in the soil deeper than 200mm was, however, hardly observed for about one month to two years. Cl- concentration in the soil was reduced to below the allowable concentration of rice planting about 400 days after the tsunami attack by runoff from the paddy field due to rainfall. It is seen from the above results that the salt removal of saline soil surface layer of 200mm is effective for the desalinization.

Modification of surface pretreatment of white spot lesions to improve the safety and efficacy of resin infiltration.

ObjectiveA low-viscosity resin (infiltrant) was used to inhibit the progression of white spot lesions (WSLs) and resolve associated esthetic issues. An alternative pretreatment was explored to increase the pore volume of the surface layer of the WSLs. Also, the penetration effects of the infiltrant were evaluated for various pretreatments.MethodsSixty two artificial lesions were fabricated on bovine teeth. As a positive control, 15% HCl gel was applied for 120 seconds. Further, 37% H3PO4 gel was applied for 30 seconds using three methods. The samples were divided as follows: H3PO4 only group, H3PO4 sponge group, and H3PO4 brush group. The acid was gently rubbed with the applicators (i.e., a sponge or brush) throughout the application time. To compare the effects of resin infiltration, twenty paired halves of specimens were treated with an infiltrant (ICON®).ResultsThicknesses of the removed surface layers and infiltrated areas were evaluated by confocal laser scanning microscope. The positive control and the 37% H3PO4 brush group failed to show significant differences in the removed thickness (p > 0.05); however, the mean percentage of the infiltrated area was higher in the 37% H3PO4 brush group (84.13 ± 7.58%) than the positive control (63.51 ± 7.62%, p < 0.001). Scanning electron microscope observations indicate higher pore volumes for the 37% H3PO4 brush group than for the positive control.ConclusionsApplication of 37% H3PO4 with a brush for 30 seconds increased the pore volume of WSL surface layers and the percentage of infiltrated areas in comparison to the use of 15% HCl for 120 seconds.

Titanium-Mediated Tribo-Chemically Activated Cold Welding of Aluminum

The paper describes a new phenomenon of titanium-mediated cold welding of which was observed during development of titanium window for energetic electrons. During compression of two aluminum sheets with an intermediate titanium foil, the imposed tribological conditions developed at the mating interfaces of titanium/aluminum sheets activated a chemical reaction causing removal of alumina surface layer. Complete wear of titanium foil brought two virgin aluminum surfaces into intimate contact which resulted in their welding at room temperature. The phenomenon provides a new direction to facilitate cold welding between aluminum sheets.

Photocatalytic NO removal of concrete surface layers intermixed with TiO2

The combination of TiO2 with cementitious materials to develop functional photocatalytic products (PCP) has garnered considerable attention on a global scale. In practical application, a wide variety of admixtures will be introduced to the PCP. The present study evaluated the effects of a number of factors on the photocatalytic NO removal performance of the PCP. The results showed that the photocatalytic NO removal rate of concrete surface layers increased when glass cullets were used as a replacement of sand. Compared to samples with light green glass cullets, those concrete surface layers with transparent glass cullets displayed a slightly elevated NO removal ability. In addition, it was observed that the concrete surface layers prepared with white cement (WC) and ground granulated blastfurnace slag (GGBS) had a slightly higher photocatalytic NO removal compared with those prepared with WC and metakaolin (MK). Furthermore, adding different coloured pigments into the concrete surface layers significantly reduced the NO removal rate. It was also found that harsh abrasion exerted no obvious deterioration to the TiO2-intermixed concrete surface layers with respect to the photocatalytic NO removal.

Improving biogas production from wheat plant using alkaline pretreatment

Alkaline pretreatment of wheat plant (WP), including its grains and straw, was investigated under different conditions in order to enhance biomethane production at mesophilic temperature. Alkaline pretreatment was performed using 8% (w/v) NaOH solution at different temperatures (0, 25, 50, 75 and 100°C). The best improvement in the yield of methane production was achieved by pretreatment at 75°C for 60min, giving a methane yield of 404mlg−1VS. The highest glucose content was also obtained under this pretreatment. The cumulative methane yield for pretreated WP at 25, 50 and 75°C increased the methane yield around 47.5%, 40.8% and 54.5% higher than that of the untreated WP, respectively, while pretreatment at 0 and 100°C was not effective in improving the biogas production. Qualitative analysis of pretreated WP using Scanning Electron Microscopy and Fourier Transform Infrared showed the reduction of crystallinity as well as the removal of surface layers of lignin and hemicellulose.

Photoelectrochemical Transients for Chlorine/Hypochlorite Formation at “Roll-On” Nano-WO3 Film Electrodes

Commercial nano-WO3 (10–100 nm average particle size) is dispersed in n-hexanol and applied to tin-doped indium oxide (ITO) substrates in a simple “roll-on” process. As-deposited and annealed (500 °C) films are compared and shown to be photoactive for the formation of hypochlorite in neutral aqueous NaCl (e.g., seawater). Annealing at 500 °C in air improves photocurrents most likely due to improved interparticle charge transport (e.g., removal of hydration or n-hexanol surface layers). In phototransients (interpreted here in the limiting case of a weakly associated nanoparticle aggregate as opposed to the limiting case of a single-crystal semiconductor), evidence for the presence of both holes (as O(-I), fast moving) and electrons (as W(V), slow moving) is obtained in particular in as-deposited films. Bipotentiostat experiments reveal the presence of chlorine as a reaction intermediate close to the photoanode when immersed in 3 M NaCl. A “molecular conduit” effect with adsorbed Co(II/III) sepulchrate is observed to significantly enhance the photocurrents at as-deposited electrodes (but not at annealed electrodes).

Layer transfer by controlled spalling

In this communication, we present what may be the simplest method yet devised for removing surface layers from brittle substrates. The process is called controlled spalling technology (CST) and works by depositing a tensile stressor layer on the surface of a substrate, introducing a crack near the edge of the substrate, and mechanically guiding the crack as a single fracture front across the surface. The entire process is performed at room-temperature using only common laboratory equipment. We present here, for the first time, the specific process conditions required for controlled spalling of Ge 〈0 0 1〉 substrates using Ni as the stressor layer. We also illustrate the versatility of CST by removing completed CMOS circuits from a Si wafer and demonstrate functionality of the flexible circuits. Raman spectroscopy of spalled circuits with the Ni stressor intact indicates a residual compressive Si strain of 0.0029, in good agreement with the calculated value of 0.0022. Therefore, CST also permits new opportunities for strain engineering of nanoscale devices.

Studies on Biodegradation of normal concrete surfaces by fungus Fusarium sp.

The main objective of this study was to identify the potential of different concrete deteriorating acid producing microbes for removing surface layers of contaminated concrete structures. Studies were made using an acid producing fungus, Fusarium sp in a humidity chamber for one year and compared the degradation with the Thiobacillus sp. The growth of fungus as a black biofilm on the normal concrete surface in the humidity chamber was confirmed by culture techniques even after one year. Results of degradation parameters showed higher pH reduction, weight loss and thickness loss under Fusarium sp. biofilms. Epifluorescence micrographs clearly confirmed dense growth of filamentous Fusarium sp. Laser Raman spectroscopic and XRD analysis showed weakening of calcium silicate bands and presence of calcium oxalate bands confirming biodegradation. Thus by thinning of the concrete specimen by 2.27mm in one year the potential of this species for cleaning contaminated concrete surfaces is demonstrated.

Direct observations of the influence of solution composition on magnesite dissolution

In situ observations during atomic force microscopy experiments and ex situ observations after static and flow-through experiments were used to explore the effect of three different electrolytes on magnesite (MgCO3) dissolution at pH 2. The experiments showed that the magnesite dissolution rate varied in the order NO3->Cl->SO42- when these anions were present in solution. Under the experimental conditions magnesite dissolution occurred via the removal of successive single surface layers, where changes in magnesite reactivity in the presence of different electrolytes could be observed as variations in the cycle length for the removal of one unit cell layer. The cycles began with the formation of sporadically distributed etch pits followed by the nucleation of homogeneously distributed etch pits. Coalescence of the etch pits formed isolated sections of the remnant surface, which then dissolved away. The timing of sporadic and homogeneous etch pit nucleation was constant despite the presence of different anions. However, the cycles in surface roughness and etch pit spreading rates indicate that the different anions affect step retreat rates and hence dissolution rates. Differences in magnesite reactivity can be attributed to the direct interaction of sulphate with the magnesite surface and the indirect effects of chloride and nitrate on the magnesite surface hydration and hydration of the Mg2+ ion in solution. In all experiments during the dissolution process evidence for the precipitation of a new phase was observed, either directly as precipitates forming on the magnesite surface in the AFM and after the experiments, seen in SEM analysis, or as changes in the Mg outlet concentration during flow-through experiments. EDX and Raman spectroscopy were used to analyse the composition of the precipitate and although it could not be definitively identified, considering previous observations the precipitate is most likely a hydrated Mg-carbonate phase with a MgCO3·xH2O composition. Thus, the formation of a precipitate can facilitate further magnesite dissolution by increasing the undersaturation of the interfacial solution.

Mineralisation of Developmentally Hypomineralised Human Enamel in vitro

Molar-incisor hypomineralisation (MIH) is a problematic and costly condition. Caries remineralising agents are often recommended for MIH management despite the lack of evidence that these lesions have the capacity for increasing their mineral content. Following surface layer removal ± NaOCl pre-treatment and 14-day exposure to a CPP-ACFP solution at pH 5.5, MIH lesions were analysed using transverse microradiography and polarised light microscopy. Lesions were highly variable but treatment with the remineralising solution increased mineral content (1,828 ± 461 vol% min·µm, %R = 17.7 ± 5.7) and porosity decreased demonstrating the proof of concept that the mineral content of developmentally hypomineralised enamel can be improved after eruption.

Applied Pressure on Altering the Nano‐Crystallization Behavior of Al86Ni6Y4.5Co2La1.5 Metallic Glass Powder during Spark Plasma Sintering and Its Effect on Powder Consolidation

Metallic glass powder of the composition Al86Ni6Y4.5Co2La1.5 was consolidated into 10 mm diameter samples by spark plasma sintering (SPS) at different temperatures under an applied pressure of 200 MPa or 600 MPa. The heating rate and isothermal holding time were fixed at 40°C/min and 2 min, respectively. Fully dense bulk metallic glasses (BMGs) free of particle‐particle interface oxides and nano‐crystallization were fabricated under 600 MPa. In contrast, residual oxides were detected at particle‐particle interfaces (enriched in both Al and O) when fabricated under a pressure of 200 MPa, indicating the incomplete removal of the oxide surface layers during SPS at a low pressure. Transmission electron microscopy (TEM) revealed noticeable nano‐crystallization of face‐centered cubic (fcc) Al close to such interfaces. Applying a high pressure played a key role in facilitating the removal of the oxide surface layers and therefore full densification of the Al86Ni6Y4.5Co2La1.5 metallic glass powder without nano‐crystallization. It is proposed that applied high pressure, as an external force, assisted in the breakdown of surface oxide layers that enveloped the powder particles in the early stage of sintering. This, together with the electrical discharge during SPS, may have benefitted the viscous flow of metallic glasses during sintering.

Thermodynamic modeling and experimental tests of irradiated graphite molten salt decontamination

ABSTRACTMolten salt flameless oxidation of graphite is one of the prospective methods of irradiated graphite waste processing. Molten salts are capable to retain a considerable part of radionuclides, to neutralize acidic off gases, moreover spent salts could be vitrified on completion of the process. We have used thermodynamic modelling to assess the efficiency of molten salt oxidation of graphite. Equilibrium compositions of both the melt and the off gas were calculated depending on graphite content and temperature. The feasibility of decontaminating the irradiated graphite of its near-surface layers using complete molten salt oxidation was investigated in a series of laboratory experiments. As the molten salt medium used to oxidize irradiated graphite we have investigated lithium, potassium and sodium carbonates. Sodium sulphate, boron oxide, barium and potassium chromates were also used as oxidizers. Tests were carried out at 870–1270 К. The efficiency of decontamination of graphite blocks has been assessed based on the activity of 137Cs and 60Со in the samples before and after molten salt oxidation. Data obtained demonstrated the feasibility of decontamination by molten salt removal of near surface layers on irradiated graphite blocks. Decontamination rate and efficiency depend on oxidizers used and temperature of process.

Effects of Water Jet on Heat-Affected Concretes

The paper is dealing with the effects of flat high-speed water jet on concretes affected by high temperature. Research should help to correct use of water jet technology in repair works on concrete structures especially after wildfires in tunnels, underground garages, etc., which are exposed to enormous thermal stress. Four concrete mixtures were prepared for tests of interaction of water jet with concrete. The samples were exposed to 200°C and 600°C and for comparison one third of samples were left unaffected. It was found, that both lower traversing velocity (cutting speed) and higher water pressure led to removal of higher amount of concrete. Higher temperature loading caused decrease of concrete strength and thus easier removal of surface layers by water jet. Concrete mixtures with basalt aggregate demonstrate higher resistance against water jet penetration regardless thermal loading compared to mixture with standard granodiorite aggregate. Presence of polypropylene fibres has substantial influence on concrete strength properties, however only marginal impact on resistance against water jet penetration.

A photoelectron spectroscopy study of lava stones

In areas surrounding volcanoes, atmospheric agents remove surface layers from the emitted stones that go directly into the air and groundwater. The chemical composition of magmatic stones is currently studied using techniques that do not differentiate between bulk and surface composition. To the best of our knowledge there are no XPS investigations of magmatic stones. Therefore, in this study we report on the first surface chemical investigation of magmatic stones, and in particular of lapilli emitted by the Etna volcano (Sicily), using the X-ray photoelectron spectroscopy technique. Results show important differences between bulk and surface composition of major oxides. We found that Si, Fe, Ca and K segregate into the bulk, whereas Al, Na, P and Mn segregate on the surface. For example, the Mn surface concentration is 266.7% with respect to that observed in the bulk, and is due to the water soluble MnOOH species at the surface. The present study highlights the potentiality of the XPS technique in the investigation of the surface composition of magmatic materials.

Enhanced Lithiation of Doped 6H Silicon Carbide (0001) via High Temperature Vacuum Growth of Epitaxial Graphene

The electrochemical lithiation capacity of 6H silicon carbide (0001) is found to increase by over 1 order of magnitude following graphitization at 1350 °C in ultrahigh vacuum. Through several control experiments, this Li-ion capacity enhancement is correlated with SiC substrate doping and removal of the native oxide surface layer by thermal annealing, which renders both the bulk and surface electrically conductive. Characterization via multiple depth-resolved spectroscopies shows that lithium penetrates the activated SiC upon lithiation, the bulk lattice spacing does not appreciably change, and the surface structure remains largely intact. The electron energy-loss spectroscopy (EELS) extracted compositional ratio of Li to Si is approximately 1:1, which indicates an intrinsic bulk Li capacity in activated SiC of 670 mAh g–1. In addition, inelastic X-ray scattering spectra show changes in the Si chemical bonding configuration due to lithiation. X-ray scattering data show a decrease in the SiC Bragg peak intensity during lithiation, suggesting changes to the bulk crystallinity, whereas the emergence of a diffuse scattering feature suggests that lithiation is associated with the development of substrate defects. Overall, these results illustrate that the electrochemical capacity of a traditionally inert refractory material can be increased substantially via surface modification, thus suggesting a new strategy for improving the performance of next generation Li-ion battery electrodes.

In situ transmission electron microscopy study of dielectric breakdown of surface oxides during electric field-assisted sintering of nickel nanoparticles

The removal of ultra-thin oxide surface layers on nanometric nickel particles is investigated in the framework of electric field-induced dielectric breakdown. In situ transmission electron microscopy was used to directly apply electrical biasing to agglomerates of nanoparticles during simultaneous imaging of the contact area between two adjacent particles. The applied electrical field initiated dielectric breakdown of the surface layers through percolation of oxygen vacancies and the migration of oxygen away from the particle contact, which leads to the formation of metallic necks and their subsequent growth. The experimental results represent direct evidence for surface cleaning effects during electric field-assisted sintering.

Vegetation and Soil Development in Compost‐Amended Iron Oxide Precipitates at a 50‐Year‐Old Acid Mine Drainage Barrens

AbstractAcid mine drainage (AMD) barrens result from destruction of vegetation within AMD flow paths. When exposed to air, soluble iron in AMD undergoes oxidation and hydrolysis to form ferric iron (oxyhydr)oxides which accumulate on soil surfaces. A restoration experiment was conducted at a 50‐year‐old AMD barrens created by discharge from an abandoned underground coal mine. The objective was to determine whether vegetation could be established by altering rather than removing surface layers of acidic precipitates at a site representative of other mining‐degraded areas. Three zones in the barrens were identified based on moisture content, pH (2.7–3.3), and thickness of precipitates (0–35 cm). Our hypothesis was that application of the same reclamation method to all zones would fail to sustain &gt;70% vegetative cover in each zone after four growing seasons. The method consisted of applying 11 t/ha lime and 27 or 54 t/ha compost before rototilling (top 15 cm) and mulching with oat straw containing viable seeds for a nurse crop. Lime‐only plots were included for comparison, and all amended plots were sown with a mine reclamation seed mix. Oats, sown species, and indigenous species dominated cover in the first, second, and fourth growing seasons, respectively. In the fourth year following reclamation, compost‐amended plots had &gt;70% cover and improved soil properties in all three zones, providing evidence to reject our hypothesis. Vegetative restoration of AMD barrens did not require removal of highly acidic precipitates, since they could be transformed at low‐cost into a medium that supports indigenous plants.

Effects of Multiphase Flow on Internal CO2 Corrosion of Mild Steel Pipelines

The focus in this paper is on the effects of multiphase flow on CO2 corrosion of mild steel pipelines. The significance of mass transfer in turbulent flow is discussed first: (i) when an increased rate of mass transfer of corrosive species, such as H+ ions, to the steel surface leads to an acceleration of the cathodic reactions and a higher corrosion rate and (ii) when an increased mass-transfer rate of the corrosion product, ferrous ions (Fe2+), away from the steel surface makes it harder to form protective ferrous carbonate layers. The mechanical interaction of the flow with the pipe walls is discussed next, where the wall shear stress is often blamed for removal of protective surface layers, such as iron carbonate or inhibitor films. Using macroscopic as well as atomic scale measurements [atomic force microscopy (AFM)], it was found that it is very unlikely that truly protective surface layers can be removed by mechanical forces alone. The other multiphase flow effects on corrosion, such as the effect ...

Doping characterization for germanium-based microelectronics and photovoltaics using the differential Hall technique

In this coming decade, complementary metal-oxide-semiconductor microelectronic devices may undergo a major change with the implementation of germanium channels. Likewise, the performance of photovoltaic cells based on elemental semiconductors will continue to be optimized. Both technologies will rely on a detailed and thorough understanding of electrical properties, and here, precise doping characterization will play a key role. The differential Hall technique combines resistivity and Hall-effect measurements with successive surface layer removal, allowing one to measure independent carrier concentration and mobility depth profiles. In this Letter, we apply the technique for both microelectronic- and photovoltaic-relevant doping structures in germanium. Controllable and uniform layer removal is achieved with tailored depth resolution (&amp;lt;1–20 nm) for a range of doping structures (30–600 nm).

Kerf-Less Removal of Si, Ge, and III–V Layers by Controlled Spalling to Enable Low-Cost PV Technologies

Kerf-less removal of surface layers of photovoltaic materials including silicon, germanium, and III-Vs is demonstrated by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to be deposited on the surface of a brittle material, and the controlled removal of a continuous surface layer could be performed at a predetermined depth by manipulating the thickness and stress of the Ni layer. Because the entire process is at room temperature, this technique can be applied to kerf-free ingot dicing, removal of preformed p-n junctions or epitaxial layers, or even completed devices. We successfully demonstrate kerf-free ingot dicing, as well as the removal of III-V single-junction epitaxial layers from a Ge substrate. Solar cells formed on the spalled and transferred single-junction layers showed similar characteristics to nonspalled (bulk) cells, indicating that the quality of the epitaxial layers is not compromised as a result of spalling.