Unoxidized Surface Research Articles

On mechanism of hydrogen generation at oxidation of activated aluminum in aqueous solutions

To clarify the mechanism of hydrogen generation upon aluminum oxidation by water, the behavior of the mechanical alloys {Al+20%Bi} and {Al+7%Ga+3%In} in various salt solutions has been studied. Analysis of the reaction rate and the overall hydrogen yield in the studied systems allows us to suggest that, unlike the oxidation of magnesium-based materials, the hydrogen generation by activated aluminum is not mainly controlled by electrochemical processes. Additives of activating metals, bismuth and gallium-indium alloys, primarily act as surfactants, making an unoxidized intergranular surface accessible to water according to the Rebinder effect.

Microstructure, mechanical property and bonding mechanism of SiC ceramic joint using a novel Y2Si2O7/Mullite glass-ceramic interlayer

Joining of SiC ceramics with a pre-oxidized or unoxidized surface and the subsequent mechanical properties have been studied using Y2O3–Al2O3–SiO2 glass bonding method, and the mechanism of interface bonding was revealed. The joining parameter of interest was temperature from 1400 °C to 1500 °C for a dwell time 10 min. The microstructure, compositions, and interfacial properties were characterized via electron microscopy and X-ray diffractometry. A multiphase glass-ceramic interlayer mainly consisting of Y2Si2O7 and mullite was formed in the joint, which possessed good thermal matching with the SiC substrate. Moreover, the softening temperature of glass-ceramic could exceed to 1200 °C. The joint obtained from the pre-oxidized SiC substrate exhibited a more reliable interface bonding than the unoxidized surface. A preferable shear strength of 48 MPa was achieved within 10 min at 1420 °C. The elemental diffusion at the interface and the chemical bonding between glass-ceramic and SiC contributed to a reliable SiC–SiC joint.

The utilization of BHA and SBX collector mixture for the flotation of moderately oxidized pyrrhotite

The benzohydroxamic acid (BHA) and sodium butyl xanthate (SBX) mixture was used as a collector for the flotation of moderately oxidized pyrrhotite (MOP) in this work. Microflotation results revealed that the flotation recovery of MOP was not very high with the addition of individual SBX or BHA collector, but significantly improved using a mixed collector of SBA/BHA, the maximum flotation recovery of could reach 88.55%. Zeta potential measurement revealed that the surface charges of MOP were negatively moved after the addition of mixed SBX/BHA compared to adding SBX or BHA alone, revealing a much stronger interaction between the collector mixture and MOP surface, leading to the improvement of MOP floatability. The FTIR spectra analysis revealed that the synergistic effect of SBX/BHA was attributed to the interaction between BHA and MOP, which could reduce the hydrophilic Fe(OH)3 on the pyrrhotite surface, allowing more adsorption of SBX onto the generated fresh unoxidized surfaces.

Autonomous Chemistry Enabling Environment-Adaptive Electrochemical Energy Storage Devices

Autonomous Chemistry Enabling Environment-Adaptive Electrochemical Energy Storage Devices

Оптические свойства и электронные характеристики празеодима и неодима в конденсированном состоянии

The optical properties of unoxidized surfaces of polycrystalline Pr and Nd films in the spectral range 0.4 - 2.6 μm are studied. Optical constants were measured by Beattie ellipsometric method. Dispersion dependences of the optical conductivity σ, the reflectivity R, imaginary and real parts of the dielectric constant ε1 and ε2, and the function of characteristic electron energy losses Im (ε) -1 were calculated using the obtained optical constants. The paper presents the optical properties of both films and liquid metals studied earlier. The electronic characteristics of praseodymium and neodymium in solid thin-film and liquid states are calculated using the results of measurements in the infrared region of the spectrum using the two-band conductivity model.

Reconsidering X-ray Photoelectron Spectroscopy Quantification of Substitution Levels of Monolayers on Unoxidized Silicon Surfaces

The covalent functionalization of unoxidized silicon surfaces is of interest for a wide range of applications and for fundamental studies linking surface functionalization and electronic properties...

Determination of the Optical Properties and Electrical Characteristics of Solid and Liquid Ytterbium with Ellipsometric Measurements

An ellipsometric method is used to study the optical properties of unoxidized surfaces of polycrystalline ytterbium film in the spectral range of 0.4–2.6 mm. The measured refractive indices and absorption coeffi cient of the film are used to calculate the dispersion dependences of the optical conductivity σ reflectivity R, the imaginary and real parts of the dielectric constant e1 and e2, and the characteristic electron energy loss functions Im(e–1). The infrared measurements are used in a two-band model for the conductivity to calculate the electronic characteristics of ytterbium in the solid and liquid states.

Формирование границ раздела полупроводник-сера-переходный металл

Выполнены термодинамические расчеты при стандартных условиях химических реакций, протекающих при сульфидной пассивации поверхности элементарных полупроводников (Si, Ge), нитридов галлия, индия, алюминия (GaN, InN, AlN). Осуществление сульфидной пассивации нитрида алюминия, кремния и германия термодинамически вероятнее для неокис-ленной поверхности полупроводников, контактирующей с газовой фазой, содержащей серу или сероводород. Существует термодинамическая вероятность сульфидирования окисленной поверхности германия из газовой фазы. Сульфидирование нитридов галлия и индия самопроизвольно возможно из водных растворов сульфидов щелочных металлов. Сравнение кристаллохимических параметров атомов (ковалентные и атомные радиусы), типов симметрии возможных фазовых соединений на границах раздела полупроводник-сульфид-металл и полупроводник-оксид-металл показало, что для сульфидированной поверхности полупроводника имеется большее структурное соответствие, чем для окисленной поверхности полупроводника, контактирующего с переходным металлом. При замещении атомов кислорода на атомы серы в приграничном слое между переходным металлом и полупроводником наблюдается меньший скачок в величинах электроотрицательностей элементов, образующих границу раздела фаз. Формирование с помощью сульфидной пассивации поверхности полупроводника более совершенной и стабильной (по химическим и физическим свойствам) границы раздела фаз способствует созданию выпрямляющих контактов металл-полупроводник с улучшенными электрофизическими параметрами.DOI 10.14258/izvasu(2018)4-02

A margin missed: The effect of surface oxidation on CHF enhancement in IVR accident scenarios

In severe accident mitigation approaches that aim to achieve In-Vessel Retention (IVR) the decay heat is removed from the corium by conduction through the Reactor Pressure Vessel (RPV) wall, and by flow boiling on the outer surface of the RPV. The boiling Critical Heat Flux (CHF) limit must not be exceeded to prevent RPV failure. Previous studies for prediction of CHF in IVR were predominantly based on data for stainless-steel heaters and de-ionized (DI) water coolant. However, the RPV is made of low-carbon steel, and its surface has an oxide layer that results from pre-service heat treatment as well as oxidation during service; this oxide layer renders the surface much more hydrophilic and rough with respect to an un-oxidized stainless-steel surface, which can have a significant influence on boiling heat transfer. In this study, test heaters were fabricated from low-carbon steel (grade 18MnD5), pre-oxidized in a controlled, high-temperature, humid-air environment, reproducing the prototypical surface oxides present on the outer surface of the RPV. The heaters were then tested in a flow boiling loop using the IVR water chemistry, i.e., DI water with addition of boric acid and sodium tetra-borate. CHF was measured in the range of pressures (100–440 kPa), mass fluxes (180–2450 kg/m2 s), inclination angles (30–90°) and equilibrium qualities (from −0.020 to +0.034) encompassing the IVR conditions. Up to 70% enhancement in CHF values was observed for pre-oxidized, low-carbon steel heaters in comparison to the stainless-steel control heaters. The effect of water chemistry on the CHF was found to be marginal. An empirical correlation fitting the CHF data for pre-oxidized, low-carbon steel surfaces with IVR water chemistry is also presented.

Effect of Al* generated in situ in hydriding on the dehydriding properties of Mg-Al alloys prepared by hydriding combustion synthesis and mechanical milling

In this work, the effects of Al* generated in situ in hydriding on the dehydriding of Mg-Al alloys prepared by Hydriding Combustion Synthesis (HCS) and Mechanical Milling (MM) were studied. Thermal analysis showed that the peak dehydriding temperature of MgH2 was reduced by 25 °C (or 11 °C) when 20 at% Al was added in HCS (or MM) process, even though, the same dehydriding reaction of 17MgH2 + 12Al*/Al → Al12Mg17 + 17H2 was observed. Isothermal dehydriding at 300 °C for 3 h demonstrated that it took 81 min for HCS+MM-MgH2 to desorb 50% of hydrogen, while only 24 min was required for HCS+MM-Mg80Al*20. The apparent activation energy for dehydriding of MgH2 was reduced from 144.3 ± 7.19 kJ/mol for HCS+MM-MgH2 to 118.8 ± 6.73 kJ/mol for HCS+MM-Mg90Al*10. The scanning electron microscopy/energy dispersive spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the Al* in situ generated from the hydriding of Al12Mg17 in HCS would significantly decrease dehydriding temperature and improve dehydriding kinetics of the MgH2-Al composites because of a uniform distribution, the shortening reaction diffusion length, providing unoxidized surfaces to react with MgH2 and the high chemical activity of Al*.

Predicting the degree of surface oxidation on fine coals by measuring the oxygen transfer rate in coal suspensions

Coal surface oxidation plays a dominant role in differential coal flotation and the utilization of coal products. However, a robust and reliable tool to determine coal surface oxidation in coal preparation plants is not currently available. In this study, a novel technique was developed to determine the degree of coal surface oxidation by measuring the adsorption rate of oxygen on coal surfaces after understanding the nature of oxygen transfer in water and oxygen adsorption on oxidized and un-oxidized coal surfaces. In this study, coal samples with different extents of surface oxidation were prepared and the degree of coal surface oxidation was quantified by X-ray photoelectron spectroscopy (XPS) as the percentage of oxidized carbon. Oxygen was purged into the coal suspension at a constant flow rate and the change of dissolved oxygen (DO) concentration was monitored. It was found that the DO concentration increased with oxygen purging time and the rate of increase was dependent on the degree of coal surface oxidation. A faster increase in DO concentration was observed for more oxidized coals, which is related to a slower adsorption of oxygen on oxidized coal surfaces and, therefore, more dissolved oxygen remained in the suspension. The kinetics of the change of DO concentration was calculated using the oxygen transfer equation, based on which the rate of oxygen adsorption on coal surfaces was obtained. A linear relationship was found between the oxygen adsorption rate and the degree of coal surface oxidation. This technique may be implemented in coal preparation plants as a daily tool to closely monitor the coal oxidation status due to its simplicity and accuracy.

Tribological behavior of O2 and CF4 plasma post-treated diamond-like carbon films under dry air and in a high relative humidity environment

In this article, the results obtained from a study of the plasma post-treatment of diamond-like carbon (DLC) films using O2 and CF4 plasma are reported. The friction and wear behaviors of the films in dry air and a high relative humidity environment were characterized using ball-on-disk friction testing and an optical microscope. The results indicated that both O2 and CF4 plasma post-treatments of DLC films had strong influences on the friction coefficient measured under dry air, which were compared with the result of the as-deposited DLC film. This effect was due to the passivation of free σ-carbon bonds with hydroxyl (OH) and fluorinated (F) groups on the unoxidized surfaces of the DLC films. Furthermore, the O2 plasma post-treated DLC films exhibited the lowest specific wear rates both in dry air and at high relative humidity, as evidenced by their small wear scars. Therefore, O2 plasma post-treatment can be considered beneficial for improving tribological performance.

Determination of thermodynamic characteristics of metal surfaces under selective wetting conditions

Surface free energy and its components for the oxidized and unoxidized metallic surfaces are determined under selective wetting conditions using test liquids and neutral hydrocarbons. A well-distinguished oleophily of the surfaces under study due to their molecular nature is established. A preliminary thermal oxidation surface does not significantly affect the surface characteristics.

Dielectric properties of nanocomposite (Cu)x(SiO2)(100−x) produced by ion-beam sputtering

It has been established that in the nanocomposite Cux(SiO2)(100−x) with the metallic phase content x = 27.27 at.% the following phenomena occur: hopping conductivity, additional polarity and coilless-like inductance. Coilless-like inductance phenomenon consists in the occurrence of positive values of phase shift in the high frequency area. Activation energy of the dielectric relaxation time for copper nanoparticles of unoxidized surface is of approx. 0.0003 eV, whereas surface oxidation causes a potential barrier occurrence and activation energy increase up to approx. 0.3360 eV. Comparative analysis of results obtained for the Cux(SiO2)(100−x) material and the measurements results obtained for the nanocomposites (FeCoZr)x(Al2O3)(100−x), (FeCoZr)x(CaF2)(100−x) and (FeCoZr)x(PZT)(100−x), which containing nanoparticles of ferromagnetic alloy, has been performed. It has shown that the type of magnetic properties of metallic phase, which is ferromagnetic ones for FeCoZr and diamagnetic ones for Cu, does not affect capacitive and inductive phenomena of the nanocomposites. The phenomena are related only to the nanogranular structure of the materials and the hopping mechanism of the charge transport between the metallic phase nanoparticles.

Effect of surface oxidation on interfacial water structure at a pyrite (100) surface as studied by molecular dynamics simulation

In the first part of this paper, a SEM and contact angle study of a pyrite (100) surface is reported describing the relationship between surface oxidation and the hydrophilic surface state. In addition to these experimental results, the following simulated surface states were examined using molecular dynamics simulation (MDS): a fresh unoxidized (100) surface; polysulfide at the (100) surface; and elemental sulfur at the (100) surface. Crystal structures for the polysulfide and elemental sulfur at the (100) surface were simulated using density functional theory (DFT) quantum chemical calculations. The well known oxidation mechanism which involves formation of a metal deficient layer was also described with DFT. Our MDS results of the behavior of interfacial water at the fresh and oxidized pyrite (100) surfaces without/with the presence of ferric hydroxide include simulated contact angles, number density distribution for water, water dipole orientation, water residence time, and hydrogen-bonding considerations. The significance of the formation of ferric hydroxide islands in accounting for the corresponding hydrophilic surface state is revealed not only from experimental contact angle measurements but also from simulated contact angle measurements using MDS. The hydrophilic surface state developed at oxidized pyrite surfaces has been described by MDS, on which basis the surface state is explained, based on interfacial water structure.

Morphology, chemical composition, and electrical characteristics of hybrid (Ni-C) nanocomposite structures grown on the van der Waals GaSe(0001) surface

The morphology and chemical composition of metal (Ni), carbon, and composite (Ni-C) nanostructures grown on oxidized and unoxidized (0001) surfaces of a layered GaSe crystal by electron beam vacuum evaporation of the material from a liquid ion source in an electric field have been investigated using atomic force microscopy and X-ray photoelectron spectroscopy. It has been demonstrated that this technology makes it possible to grow nanostructures with different morphologies depending on the growth mode and substrate surface state. Dense homogeneous arrays of nickel nanoparticles (Ni@C) (with geometrical sizes of ∼1–15 nm and a lateral density of higher than 1010 cm−2) encapsulated into carbon shells, as well as carbon layers (with a thickness of the order of several nanometers), are grown on the unoxidized van der Waals GaSe(0001) surface, whereas Ni-C composite nanostructures are grown on the oxidized surface. The formation of oxide nanostructures on the van der Waals surface and their chemical composition have been examined. Vertical hybrid Au/Ni/(Ni-C)/n-Ga2O3(Ni@C)/p-GaSe structures grown on the GaSe(0001) surface contain Ni@C nanoparticles embedded in the wide-band-gap n-Ga2O3 oxide. The current-voltage characteristics of these structures at temperatures close to T = 300 K exhibit specific features of the Coulomb blockade effect.

Fabrication of p-type porous silicon nanowire with oxidized silicon substrate through one-step MACE

In this paper, the simple pre-oxidization process is firstly used to treat the starting silicon wafer, and then MPSiNWs are successfully fabricated from the moderately doped wafer by one-step MACE technology in HF/AgNO3 system. The PL spectrum of MPSiNWs obtained from the oxidized silicon wafers show a large blue-shift, which can be attributed to the deep Q. C. effect induced by numerous mesoporous structures. The effects of HF and AgNO3 concentration on formation of SiNWs were carefully investigated. The results indicate that the higher HF concentration is favorable to the growth of SiNWs, and the density of SiNWs is significantly reduced when Ag+ ions concentrations are too high. The deposition behaviors of Ag+ ions on oxidized and unoxidized silicon surface were studied. According to the experimental results, a model was proposed to explain the formation mechanism of porous SiNWs by etching the oxidized starting silicon.

Studies on the Bioceramic Coating on Titamium Substrate Including Silicon and Calcium by Micro-Arc Oxidation and Osteoblast’s Adhesion and Proliferation on the Coating

This study used micro-arc oxidation technology for pure titanium alloy surface modification, which 400μm titanium beads were sintered into porous titanium in vacuum conditions, and produced silicon and calcium coatings. Scanning electron microscope(SEM), X-ray diffraction (XRD) and Energy dispersion spectrometer(EDS) were employed to investigate the surface morphology and phase composition of the coatings. The results are listed as follows: the main component of porous titanium MAO coating is anatase TiO2,and the coating introduced silicon and calcium element successfully. The proliferation ability of osteoblasts on the oxidized and unoxidized surface was determined by CCK-8 method, The results indicated that both the proliferation and adhesion ability of osteoblast on the oxidized surface were better than the unoxidized surface.

Graphene-Passivated Nickel as an Oxidation-Resistant Electrode for Spintronics

We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin devices. GPFE are shown to act as spin-polarized oxidation-resistant electrodes. The direct coating of nickel with few layer graphene through a readily scalable chemical vapor deposition (CVD) process allows the preservation of an unoxidized nickel surface upon air exposure. Fabrication and measurement of complete reference tunneling spin valve structures demonstrate that the GPFE is maintained as a spin polarizer and also that the presence of the graphene coating leads to a specific sign reversal of the magneto-resistance. Hence, this work highlights a novel oxidation-resistant spin source which further unlocks low cost wet chemistry processes for spintronics devices.

Void-Free Cuprous Oxide Tube Prepared by Thermal Oxidation on Outside of Copper Tube

A new setup in an oxidation system was proposed to remove voids from cuprous oxide during the oxidation of copper. The key is the formation of a single cuprous oxide layer. To form the layer on the outside surface of a copper tube, argon gas was introduced into the tube. In the cuprous oxide wall oxidized at 920–950 °C in air for 8 h, no voids were found. The diameter of the tube indicated that the voids were swept out from the inner unoxidized surface. This knowledge contributes to the development of the growth of high-quality cuprous oxide crystals.