Search results for "surface layer"
showing 10 items of 72 documents
Formation of Layers of Diverse Stoichiometric and Phase Composition in Lithium Tantalate Crystals at Treatment by Vapour Transport Equilibration
2012
Layers from tens to hundreds of microns thick of a different phase composition and stoichiometry are shown to form in lithium tantalate crystals subjected to treatment by vapor transport equilibration in lithium vapour. The 500 microns thick stoichiometric (Li/Ta ≈ 1) layers have ten times lower values of the coercive field compared with congruent lithium tantalate. As electrical measurements suggest, a new polar structure of phase transition at ∼120°C is possibly formed within a thin (30 μm) surface layer of the lithium tantalate sample after vapour transport equilibration treatment.
Initial Surface Film on Magnesium Metal. A Characterization by X-ray Photoelectron Spectroscopy (XPS) and Photocurrent Spectroscopy (PCS)
2007
Abstract A detailed investigation of the initial film grown on mechanically polished Mg electrodes has been carried out by ex situ X-ray Photoelectron Spectroscopy (XPS) and in situ Photocurrent Spectroscopy (PCS), allowing to reach a detailed picture of the passive layer structure. The XPS data show that the films formed soon after mechanical treatment and immersion in aqueous electrolyte have a bilayer structure, consisting of an ultra-thin MgO inner layer (∼2.5 nm) and a Mg(OH) 2 external layer. The thickness of the Mg(OH) 2 layer is a function of immersion time and solution temperature. After mechanical treatment and immersion in aqueous solution at room temperature, the MgO/Mg(OH) 2 la…
In situ characterization of passive films on al-ti alloy by photocurrent and impedance spectroscopy
1998
Abstract The anodic behaviour of an Al-Ti alloy (Ti-48Al-1V, atomic %) was investigated in different aqueous electrolytes. In all cases the alloy was passive owing to the growth of a barrier-like oxide film according to the high field mechanism. The study of the growth curves suggests partial dissolution of the film during the formation process in acidic solution. The kinetic parameters for film formation have been estimated in neutral solutions and the dielectric constant of the passive layer was roughly estimated. The in-situ characterization of the passive film revealed a n-type behaviour only for very low thicknesses, whilst thicker films showed insulator-like characteristics. The analy…
Study of passive films on stainless steels by photocurrent measurements
1990
Abstract Passive films formed on three different stainless steels have been studied by means of photocurrent spectroscopy. Differences in the photoelectrochemical behaviour have been attributed to the influence of the nickel content of the alloys and to the formation of different oxide phases.
A photocurrent spectroscopic investigation of passive films on chromium
1990
Abstract Photoelectrochemical experiments have been carried out in order to identify the passive layers grown on chromium metal in different conditions. Changes in the values of the band gap of the films have been related to changes of composition, due to the different water content of the films.
Drop Shapes and Axis Ratio Distributions: Comparison between 2D Video Disdrometer and Wind-Tunnel Measurements
2009
Abstract Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of dat…
Surface processing of TlBr single crystals used for radiation detectors
2009
Abstract The processing method for obtaining the high-quality surfaces of TlBr single crystals, providing removal of a mechanically destroyed surface layer by chemical etching, is developed. The crystals grown from the melt of purified materials by the Bridgman–Stockbarger method were used for the experiments. The Vickers microhardness as a structure-sensitive technique was used in a study of the crystal quality and properties of the plastically deformed surface layer created by cutting. It was shown that even under highly accurate conditions of cutting, the depth of the work-hardened surface layer with a high density of dislocations, vacancies and other structural defects exceeds 20 μm. Th…
Structural transformations in amorphous selenium as studied by the differential thermal analysis and exoelectron emission technique
2007
The parameters (temperature, activation energy) of the surface and volume glass transition (retrification process) in amorphous selenium produced by rapid quenching of the liquid phase have been determined using the EEE and DTA techniques. EEE is a surface effect connected with structural transformations in the surface layer whereas the DTA measurements give the information about the transformations occurring in the volume of the sample. It has been found that the surface retrification of selenium occurs with activation energy smaller than the volume retrification, both observed in the first heating run. The value of activation energy for the volume retrification measured in the second DTA …
Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization
2014
Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5 μm. An additional mesoporous titania top layer following the contour of the macropores, of 100-200 nm thickness and with a pore diameter of 10nm, was formed by using the evaporation-induced self-assembly (EISA) method with titanium (IV) tetraethoxide as the precursor. A coherent laminar titania surface layer was thus obtained, creating a hierarchical macro- and mesoporous surface that was characterized by high-resolution electron microscopy. The interfacial bonding between the surface layers and the titanium matrix was characterized by the scratch test that con…
Testing an adapted beerkan infiltration run for a hydrologically relevant soil hydraulic characterization
2020
Abstract Literature raises doubts about the usability of infiltrometer methods to characterize soils in a hydrological perspective since these methods often yield excessively high infiltration rates or saturated soil hydraulic conductivity, Ks, values. For a loam (AR) and a silty-clay (RO) soil, beerkan infiltration runs were adapted in the perspective to obtain usable soil data to predict rainfall partition into infiltration and rainfall excess. In particular, the initially nearly dry soil was sampled with different water volumes (15 or 30) and heights of water application (low, L, 0.03 m, and high, H, 1.5 m), and the BEST-steady algorithm was applied to determine sorptivity, S, and Ks. Th…