Modeling effects of gas adsorption and removal on friction during sliding along diamond-like carbon films

In this paper, the physical and tribochemical processes that occur in a sliding contact between two diamond-like-carbon (DLC)-coated counterparts are discussed. The applicability of some of the most cited of the adsorption kinetics equations for modeling the gas adsorption process when environment molecules form bonds to the surface are examined. The process modeling is also discussed when part of the adsorbate is removed due to rubbing the surface by a slider. A direct connection between a kind of molecular friction and gradual wear is established. The models are compared with some recent experimental results. The present computer simulations of the adsorption and mechanical desorption of oxygen help to explain how microscopic processes, such as the breaking and forming of interatomic bonds, may affect macroscopic phenomena such as friction. In particular, it is shown that the initial roughness of the DLC surface may have a considerable influence on the probability of breaking bonds during mechanical removal of adsorbate and on the process of the gradual tribochemical wear of DLC films.     

Novel application of nanocrystalline nickel electrodeposit: Making good diamond tools easily, efficiently and economically

Electrodeposition has been identified as a feasible and economical technique for nanomaterials application. This article details an improved approach to producing better diamond tools at lower cost and with higher productivity. Pulse-electroformed nanocrystalline nickel was used as the new matrix. The pulse parameters were determined after examination of the microstructure, grain size, hardness and tensile strength of the deposits obtained at different average current densities (J_m) with constant pulse-on time and pulse-off time. It is shown that, with J_m ranging from 1 Adm^− 2 to 14 Adm^− 2, the grain size decreases sharply from 180 nm to about 10 nm while the hardness and tensile strength significantly increase at first and then reach their peaks respectively, although the strength fails to stay long. Current density J_m that produced the highest hardness and strength of deposit (with grain size of 20 nm) was chosen for new diamond tools that exhibited 20.2% longer service life than their usual Ni-Co counterparts. Therefore, nanocrystalline electrodeposits are expected to be an upgrading substitute for conventional polycrystalline matrix.     

A variational approach to multi-phase motion of gas, liquid and solid based on the level set method

We propose a simple and robust numerical algorithm to deal with multi-phase motion of gas, liquid and solid based on the level set method [S. Osher, J.A. Sethian, Front propagating with curvature-dependent speed: Algorithms based on Hamilton-Jacobi formulation, J. Comput. Phys. 79 (1988) 12; M. Sussman, P. Smereka, S. Osher, A level set approach for capturing solution to incompressible two-phase flow, J. Comput. Phys. 114 (1994) 146; J.A. Sethian, Level Set Methods and Fast Marching Methods, Cambridge University Press, 1999; S. Osher, R. Fedkiw, Level Set Methods and Dynamics Implicit Surface, Applied Mathematical Sciences, vol. 153, Springer, 2003]. In Eulerian framework, to simulate interaction between a moving solid object and an interfacial flow, we need to define at least two functions (level set functions) to distinguish three materials. In such simulations, in general two functions overlap and/or disagree due to numerical errors such as numerical diffusion. In this paper, we resolved the problem using the idea of the active contour model [M. Kass, A. Witkin, D. Terzopoulos, Snakes: active contour models, International Journal of Computer Vision 1 (1988) 321; V. Caselles, R. Kimmel, G. Sapiro, Geodesic active contours, International Journal of Computer Vision 22 (1997) 61; G. Sapiro, Geometric Partial Differential Equations and Image Analysis, Cambridge University Press, 2001; R. Kimmel, Numerical Geometry of Images: Theory, Algorithms, and Applications, Springer-Verlag, 2003] introduced in the field of image processing.     

P-stability, Trigonometric-fitting and the numerical solution of the radial Schrödinger equation

In this paper we will study the importance of the properties of P-stability and Trigonometric-fitting for the numerical integration of the one-dimensional Schrödinger equation. This will be done via the error analysis and the application of the studied methods to the numerical solution of the radial Schrödinger equation.     

On the security of a chaotic encryption scheme: problems with computerized chaos in finite computing precision

Zhou et al. have proposed a chaotic encryption scheme, which is based on a kind of computerized piecewise linear chaotic map (PWLCM) realized in finite computing precision. In this paper, we point out that Zhou's encryption scheme is not secure enough from strict cryptographic viewpoint. The reason lies in the dynamical degradation of the computerized piecewise linear chaotic map employed by Zhou et al. The dynamical degradation of the computerized chaos induces many weak keys to cause large information leaking of the plaintext. In addition, we also discuss three simple countermeasures to enhance the security of Zhou's cryptosystem, but none of them can essentially enhance the security.     

Proton beam writing and electroplating for the fabrication of high aspect ratio Au microstructures

We present an approach to fabricate tall high aspect ratio Au microstructures by means of proton beam direct writing. Combining proton beam direct writing and electroplating, we successfully produced gold structures with sub-micrometer lateral dimensions, structure heights in excess of 11 μm, and aspect ratios over 28. Sidewall quality of the Au structures was improved by lowering the process temperature to 20 °C when developing PMMA patterns with GG developer. The application of such structures as X-ray masks for deep X-ray lithography with synchrotron radiation was demonstrated.     

External-beam PIXE characterization of volcanic material used in ancient Roman mortars

Volcanic deposits from two volcanic districts, Monti Sabatini (MSVD) and Colli Albani (CAVD), NW and SE of Rome, were analyzed using the particle-induced X-ray emission (PIXE) technique, in order to obtain chemical fingerprints that can be used for provenance studies of filler materials in ancient Roman mortars. The rock samples were mounted on an X-Y stage enabling scanning over the sample surface and irradiated in air with a collimated 3 MeV proton beam. The samples were either analyzed by scanning the beam over a polished surface or they were crushed, ground and homogenized prior to the irradiation. However, scanning over polished sample surfaces avoiding heterogeneities gave quite similar results as scanning over pellet surfaces, especially for the minor and trace elements. This study shows that the deposits of MSVD and CAVD can be distinguished from each other. Several elements or elemental ratios can be used to characterize the districts. Even the individual volcanic deposits of CAVD can be identified.     

Effect of surfactant on the bath stability and electrodeposition of Sn-Ag-Cu films

A methanesulphonic acid based bath for the co-deposition of Sn-Ag-Cu films is developed. The bath contains thiourea as chelating agent, while iso-octyl phenoxy polyethoxy ethanol (OPPE) is added as a non-ionic surfactant. Studies show that OPPE plays a major role in improving the bath stability from few hours up to 1 week. However, there is no evidence of any strong chelation between any metal ion and OPPE. There is a slight modification in the reduction potentials of individual ions after addition of OPPE, which is attributed to some weak bonding through the lone-pair electrons of this molecule. Bath investigations confirm that thiourea forms chelates with electropositive Ag⁺ and Cu²⁺ ions and alters their deposition potentials. Consequently, the deposition of three elements takes place at a single potential of − 0.541 V. The proposed bath is capable of depositing Sn-Ag-Cu films having near eutectic composition that remains consistent even with increase in current density beyond 5 mA cm^− 2. This is attributed to the three metals reaching their limiting current density. The deposited films have compact microstructure with grain size in the range 6-8 μm and thickness in the range 20-100 μm. The studies show that OPPE brings about refinement in film microstructure.     

High level nuclear waste glass corrosion in synthetic clay pore solution and retention of actinides in secondary phases

The corrosion of the simulated high level waste glass GP WAK1 in synthetic clay pore solution was studied in batch-type experiments at 323 and 363 K with special focus on the effect of high carbonate concentration in solution. The corrosion rate after 130 days was <10⁻⁴ g m⁻² d⁻¹ - no significant effect of the carbonate was identified. During glass corrosion, crystalline secondary phases (powellite, barite, calcite, anhydrite and clay-like Mg(Ca,Fe)-silicates) were formed. To obtain a molecular level picture of radionuclide speciation within the alteration layer, spectroscopic methods have been applied including grazing incidence X-ray absorption spectroscopy (XAS) to study the structural changes in the coordination of uranyl upon alteration layer formation. The number of equatorial oxygen atoms increases from 4 in the bulk glass to 5 in the alteration layer. Furthermore, reduced coordination symmetry was found. Hectorite, a frequently observed secondary clay mineral within the glass alteration layer, was synthesized in the presence of trivalent f-elements (e.g. Eu) and structurally characterized using time-resolved laser fluorescence spectroscopy. Structural incorporation into the octahedral layer is indicated.     

Electrodeposition of nickel-molybdenum alloys from ammonium citrate baths containing intermediate valence molybdenum compounds

Electrodeposition of a Ni-Mo alloy under different electrolysis conditions, such as pH and temperature from ammonium citrate baths containing intermediate-valence molybdenum compounds is studied. The effect of differing molybdenum compounds (oxidation degrees of +6, +5, and +3) on the alloy formation makes possible controlling the alloy composition and the current efficiency, by varying the concentration ratio of molybdenum in different states of the oxidation. The prospects for the formation of deposits of adequate quality (compact, with no edge effects) with the current efficiency of nearly 80% are demonstrated. Original Russian Text ? M.P. Pavlov, N.V. Morozova, V.N. Kudryavtsev, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 503–509.