Pre-surface Layer Research Articles

The Theoretical Description for the Perylaldehyde Aldoxyme Anodic Electrochemical Determination, Assisted by the Novel Squaraine Dye Composite with Copper(ii) Sulfide Nanoparticles

In this work the perillaldehyde aldoxime electrochemical determination on an anode, modified by squaraine dye composite with copper sulfide nanoparticles is analyzed. The electroanalytical process involves the formation of trivalent copper species, capable to oxidize the analyte by two parallel mechanisms. The correspondent mathematical model, correspondent to both of them, has been developed and analyzed by means of linear stability theory and bifurcation analysis. The model analysis clearly shows that the composite of a squaraine dye in organic phase and bivalent copper sulfide in the inorganic phase may be an efficient electrode modifier for perillaldehyde aldoxime electrochemical determination on an anode. The electroanalytical process will be mostly kinetically-controlled with the possibility of the transfer to diffusion-controlled mode. On the other hand, both oscillatory and monotonic instabilities may be realized in the electroanalytical process, and their probability will depend on the direction of the electroanalytical scenario in the concrete conditions, due to the possibility of the formation of ionic compounds in the pre-surface layer. DOI: http://dx.doi.org/10.17807/orbital.v13i5.1501

MULTILAYER COMPOSITE PLASMA COATINGS ON SCREEN PROTECTION ELEMENTS BASED ON ZIRCONIUM DIOXIDE

The paper contains results of investigations pertaining to an influence of plasma jet parameters (current, spraying distance, consumption of plasma formation gas (nitrogen)), fractional composition of initial powder and degree of cooling with compressed air on anti-meteoric coating characteristics. Optimum modes (arc current 600 A; spray distance of 110 mm; consumption of plasma formation gas (nitrogen) – 50 l/min; fractional composition of zirconium dioxide powder <50 μm; compressed air consumption for cooling – 1 m3/min; p = 4 bar) make it possible to obtain anti-meteoric coatings based on zirconium dioxide with material utilization rate of 62 %, total ceramic layer porosity of 6 %. After exposure of compression plasma flows on a coating in the nitrogen atmosphere a cubic modification of zirconium oxide is considered as the main phase being present in the coating. The lattice parameter of cubic zirconium oxide modification is equal to 0.5174 nm. Taking into consideration usage of nitrogen as plasma formation substance its interaction with zirconium coating atoms occurs and zirconium nitride (ZrN) is formed with a cubic crystal lattice (lattice parameter 0.4580 nm). Melting of pre-surface layer takes place and a depth of the melted layer is about 8 μm according to the results of a scanning electron microscopy. Pre-surface layer being crystallized after exposure to compression plasma flows is characterized by a homogeneous distribution of ele-ments and absence of pores formed in the process of coating formation. The coating structure is represented by a set of lar- ge (5–7 μm) and small (1–2 μm) zirconium oxide particles sintered against each other. Melting of coating surface layer and speed crystallization occur after the impact of compression plasma flows on the formed coating. Cracking of the surface layer arises due to origination of internal mechanical stresses in the crystallized part. While using a scanning electron microscopy a detailed analysis of the surface structure has permitted to reveal a formation of a cellular structure with an average cell size of less than 1 μm in the crystallized portion and formation of the cells can be caused by speed crystallization of the melted layer.

Modeling of carbon penetration into silicon structure under the action of pulsed high-intensity ion beam

Abstract The action of high-intensity beam of carbon ions on a silicon sample is studied by means of a numerical modelling revealing formation of the in-depth carbon concentration profile in crystal lattice of silicon. We investigated three ways of the profile forming: short-pulsed ion implantation, recoil atoms mechanism and thermal diffusion of the carbon atoms adsorbed on the silicon surface. The latter is the result of high temperature gradient associated with the action of pulsed high-intensity ion beam. It is argued that the diffusion process plays the major role in forming of the concentration profile in the pre-surface layer of a silicon sample.

Thermal stability of silicon photovoltaic structures produced using compression plasma flows

Thermal stability investigations of photovoltaic structures synthesized by the compression-plasma-flow treatment of doped silicon are performed. The samples are annealed in an atmosphere of nitrogen, in air or in vacuum in a temperature range of 100–900°C for 30 min or 3 h. The photovoltaic effect does not change after annealing at temperatures up to 600–700°C. It decreases 1.3–1.7 times after thermal annealing at a temperature of 900°C. The structure-phase changes of silicon treated with compression plasma flows are studied using X-ray diffraction and scanning electron microscopy methods. It is established that a recrystallized pre-surface layer with a thickness of 10–20 μm and modified (but not melted) layer with a thickness of up to 50–60 μm localized below the recrystallized layer are formed.

Oxidation and surface segregation of chromium in Fe–Cr alloys studied by Mössbauer and X-ray photoelectron spectroscopy

The room temperature 57Fe Mössbauer and XPS spectra were measured for polycrystalline iron-based Fe–Cr alloys. The spectra were collected using three techniques: the transmission Mössbauer spectroscopy (TMS), the conversion electron Mössbauer spectroscopy (CEMS) and the X-ray photoelectron spectroscopy (XPS). The combination of these experimental techniques allows to determine changes in Cr concentration and the presence of oxygen in bulk, in the 300nm pre-surface layer and on the surface of the studied alloys.

Structural and phase changes in iron-on-silicon treated by compression plasma flows

Studies of structural and phase composition changes in pre-surface layers of iron-on-silicon treated by compression plasma flows (CPFs) (power density absorbed by the target varied from 0.6 to 1.4 GWt/m 2, pulse duration – 100 μs) are carried out by X-ray diffraction and scanning electron microscopy. The formation of tetragonal iron disilicide α-FeSi 2, silicon dendrite formation (average tip radius ∼0.2 μm, primary spacing increases with power density of the flow from 0.6 to 2 μm) are revealed. Radiation heat losses are established to be dominant at high power densities.

Development and evaluation of multilayer air filter media

Three types of multilayer air filter media were developed and evaluated. Two other existing filters were also used for comparison of filter performance. The pressure drop, the collection efficiency, and the dust-holding capacity of the tested filters were measured, and the internal structure of the filter media was analyzed by using a scanning electron microscope. The multilayer filters tested in this study are composed of pre-surface layer, surface layer, and substrate layer. Among those layers, the surface layer is mainly responsible for particle collection. As a test result, it was found that the thickness of a surface layer has the greatest effect on filtration performance of a multilayer air filter. Additionally, filtration velocity and electrostatic forces should be considered together as important parameters for multilayer air filter design.

Pitting of the rolling bodies contact surface

A calculational model for investigation of the fracture processes and durability of the surface contact zones of rolling bodies has been proposed within the framework of the fatigue fracture mechanics concepts. Unidirection rolling in conditions of dry friction and boundary lubrication has been investigated. The model basis is the algorithm step-by-step construction of the crack growth paths developed with application of singular integral equations of two-dimensional problem of the elasticity theory for bodies with curvilinear cracks and local fracture criteria for a complex stress-strain state. The paths calculation algorithm also takes into account redistribution of stresses, caused both by crack growth and mutual motion of contacting bodies. In the case of rolling with lubrication, that can fill the crack, its action is modeled by stresses, additionally distributed on the crack faces. Propagation paths of edge cracks have been constructed. The dependence of path form on friction coefficient between contacting bodies, the length and orientation of the initial crack, and in the presence of lubrication, on the intensity of its pressure on the crack faces, has been investigated. In calculations the generalized mode I fracture criterion ( σ θ -criterion) has been used. An attempt has been made to explain the mechanism of development of such crack-like defect as pitting and ‘squat’, often met during rolling contact fatigue. As an example, the residual durability of the ShH-15 bearing steel presurface layer under boundary lubrication has been estimated.

EXAFS study of the Fex/ZrO2 composite nanomaterials obtained by sol-gel synthesis.

The local Zr and Fe arrangements in the nanocomposite system Fe(x)/ZrO2 (x=0-0.2) obtained by sol-gel method were studied by EXAFS. The phase composition was found to vary significantly on iron loading. For the samples calcined at 500 or 600 degrees C, at x< or =0.01, the formed ZrO2 is a mixture of monoclinic and tetragonal structures. Only tetragonal structure is revealed at x > or = 0.05 with the exception of Fe0.2/ZrO2, calcined at 500 degrees C, where new non-typically short Zr-Zr distances (3.29, 3.43A) were observed. At low iron loading (less than one monolayer) Fe3+ ions were found to localize within the pre-surface layers of ZrO2 nanoparticles showing property of isolated ions. For greater Fe loading, iron exhibits either two-dimensional layer structure or two-phase system.

Critical current in NbTi wires irradiated by neutrons at 20 K

In the present paper the results of experimental investigations of NbTi superconducting wires are given with two different treatments: cold-deformed (CD), intermediate thermal treatment (ITT) and also NbTi multiwire of factory treatment. The influence of neutron irradiation on the critical current I c dependence on magnetic field was studied in the cryochannel of nuclear reactor. Integral neutron fluence of 3 × 10 18 cm −2 in one core wires increases I c for CD samples, but doesn't change for ITT samples. Integral neutron fluence of 1.6 × 10 18 cm −2 leads to substantial I c-degradation for multiwire, its value undergoes twofold reduction, that is due to the decrease of the working cross-section of the optimized superconducting buses at the expense of its presurface layer `spoiling' as a result of enrichment by foreign atoms from the matrix of stabilizer.

Direct hadron production in ultrarelativistic heavy-ion collisions

Hadrons emitted by the pre-surface layer of a quark-gluon plasma (QGP) before the phase transition into a hadronic gas are considered as possible sources of direct information about QGP. It is shown that if QGP is created in ultrarelativistic heavy-ion collisions, then these hadrons strongly contribute at soft p t at SpS energy and dominate up to an order of magnitude at LHC energy.

Microfracture of metals during high-temperature creep

1. A change from creep at moderate temperatures to high-temperature creep is accompanied by equalization of the defect density Δρ/ρ in the volume and in surface layers of polycrystalline metals resulting from microdiscontinuities. In this case Δρ/ρ varies with the applied stress, while the character of accumulation of defects in the process of creep changes. 2. The characteristics of high-temperature creep of polycrystalline materials are evidently due to a considerable extent to the activation of healing of microcracks in presurface layers at elevated temperatures.

Adsorption and dissolution of gases during the milling of solids

1. BET methods and measurement of H2 chemisorption have been combined to determine the rate of new surface formation in the milling of quartz, corundum, silicon, germanium dioxide, molybdenum disulfide, and boron nitride. The second of these two methods can be used to determine the rate of new surface formation in the latter stages of the milling process where the BET method is no longer applicable because of particle aggregation. The work required for the formation of unit new surface area has been estimated. 2. Adsorptional methods have been used to detect and study the disorganization of the pre-surface layer structure and the effect of this factor, first on the dissolution of argon during solid body milling (silicon, quartz, GeO2) and then on the low-temperature sintering of materials such as MoS2.

Flashover in a vacuum

It is shown that vacuum flashover is due to one or another process alternatively: (a) a thermal breakdown in the thin pre-surface layer of dielectric and (b) a streamer discharge in the desorbed gas cloud. The thermal flashover is observed in dielectrics with ρ v ≤ 10 11 -10 12 Ω cm under dc voltage. The desorption flashover exists under impulse voltage (and under dc voltage in insulators with ρ v > 10 13 Ω cm). Quantitative models are proposed to describe both the flashover mechanisms. The calculations are in good agreement with experimental data.

Change in composition of surface layer of palladium-rhodium alloys during catalytic reaction

1. A substantial enrichment of the presurface layer in rhodium of palladium alloys, containing 5 and 10% Rh, after cyclohexane was dehydrogenated on them, was detected by the x-ray photoelectronic spectroscopy (XPES) method. 2. Enrichment of the surface of the foil in rhodium is accompanied by an increase in the dehydrogenation rate of cyclohexane to benzene.

Surface state and induced conductivity of anthracene

1. Acceptor impurities on the surface of anthracene and in the presurface layer lead to the formation of regions with a high concentration of holes. 2. When an electrochemical reaction, which injects holes into anthracene, proceeds at the phase boundary, the existence of regions on the surface with a high concentration of holes leads to a pitting character of the corrosion, which indicates its autocatalytic character. 3. In the case where anthracene, excited by the pulses of low-energy electrons, exhibits a nonequilibrium conductivity, the existence of regions with a high concentration of holes is manifested in the appearance of the slow component of the hole conductivity and an increase in the efficiency of generating current carriers in the surface layer.