Spherical Hard Particles Research Articles

유한요소해석에 의한 DLC 코팅면의 마멸기구에 대한 연구

Various heat treatment and surface coating methods have been applied to machine parts. Nowadays, diamond-like carbon (DLC) coatings are widely used because of their excellent tribological characteristics. Despite the numerous studies on DLC-coated engineering surfaces, the exact wear mechanisms related to the coating thickness and elastic modulus have not been fully examined. In this study, a sliding contact problem between a small spherical hard particle and a DLC-coated steel surface is analyzed using a nonlinear finite element code, MARC. The maximum principal stress distributions and deformed surfaces are compared for different coating thicknesses and Young's modulus values. Plastically deformed surface shapes such as a groove and torus indicate that the most dominant wear mechanism for a DLC-coated surface is abrasive wear. Fatigue wear can also play a role in a case where the coating thickness is relatively large and the elastic modulus is high.

PHASE--FIELD METHOD SIMULATION OF THE EFFECT OF HARD PARTICLES WITH DIFFERENT SHAPES ON TWO--PHASE GRAIN GROWTH

The effects of hard particles with different shapes, volume fractions and sizes on two- phase grain growth have been systematically investigated by phase-field method. The results showed that most of the spherical hard particles located at the intersection of tricrystal boundary, while flaky hard particles distributed along the grain boundary. Particles of different shapes have not obvious effect on the α phase grain growth, and the effect of hard particles with different shapes on the β phase grain growth depends on the number of particles. The flaky particles have stronger pinning effect on the β phase grain growth than the spherical particles when hard particles reach enough number. The pinning effect of the hard particles is enhanced when the volume fraction increased or the size of hard particles reduced. The greater the volume fraction or the smaller the size of hard particles is, the smaller the grains'size is.

Determination of electrokinetic and hydrodynamic parameters of proteins by modeling their electrophoretic mobilities through the electrically charged spherical soft particle

This work explores the possibility of using the electrically charged "spherical soft particle" (SSP) to model the electrophoretic mobility of proteins in the low charge regime. The general framework concerning the electrophoretic mobility of the SSP already presented in the literature is analyzed and discussed here in particular for polyampholyte-polypeptide chains. In this regard, this theory is applied to BSA for different protocol pH values. The physicochemical conditions required to model proteins as SSP from their experimentally determined electrophoretic mobilities are established. In particular, the protein charge regulation phenomenon and the SSP particle core are included to study BSA having isoelectric point pI ≈ 5.71, within a wide range of bulk pH values. The results of this case study are compared with previous ones concerning the spherical porous particle and the spherical hard particle with occluded water. A discussion of chain conformations in the SSP polyampholyte layer is presented through estimations of the packing and friction fractal dimensions.

Electrodeposition of bright nickel coating under perturbation of hard particles

Bright nickel was produced by a new electroforming technique with spherical hard particles filling between the electrodes. The related theories and the structure of the bright deposit were studied. It was found that the hard particles could increase the brightness of nickel deposits by perturbing the process of crystal nucleation and polishing the cathode surface during electrodepositing. A mathematical model about brightening effects of hard particles was constructed. A sound smooth nickel deposit, which was nearly mirror-bright, was electroformed by the presented technique. The analyses of transmission electron microscope (TEM) and X-ray diffraction (XRD) showed that the grain size was less than 80 nm and the deposit revealed a (2 0 0) preferential orientation.

Electrophoresis of soft particles: Analytic approximations

An approximate analytic expression is derived for the electrophoretic mobility of a weakly charged spherical soft particle (i.e., a hard particle covered with a weakly charged polyelectrolyte layer) on the basis of the general mobility expression for soft particles (Ohshima, H., J. Colloid Interface Sci. 2000, 228, 190-193). The obtained mobility expression, which reproduces various approximate results so far derived and gives some new mobility formulas, covers all types of weakly charged soft particles with arbitrary values of the thickness of polymer layer, the radius of the particle core, the electrophoretic softness, and the Debye length, including spherical polyelectrolytes with no particle core as well as spherical hard particles with no polyelectrolyte layer.

Lyapunov spectra of billiards with cylindrical scatterers: Comparison with many-particle systems

The dynamics of a system consisting of many spherical hard particles can be described as a single point particle moving in a high-dimensional space with fixed hypercylindrical scatterers with specific orientations and positions. In this paper, the similarities in the Lyapunov exponents are investigated between systems of many particles and high-dimensional billiards. The billiards contain cylindrical scatterers which have isotropically distributed orientations and homogeneously distributed positions. The dynamics of the isotropic billiards are calculated using a Monte Carlo simulation, and a reorthogonalization process is used to find the Lyapunov exponents. The results are compared to numerical results for systems of many hard particles as well as the analytical results for the high-dimensional Lorentz gas. The smallest three-quarters of the positive exponents behave more like the exponents of hard-disk systems than the exponents of the Lorentz gas. This similarity shows that the hard-disk systems may be approximated by a spatially homogeneous and isotropic system of scatterers for a calculation of the smaller Lyapunov exponents, apart from the exponent associated with localization. The method of the partial stretching factor is used to calculate these exponents analytically, with results that compare well with simulation results of hard disks and hard spheres.

Direct observation of the enhancement of noncooperative protein self-assembly by macromolecular crowding: indefinite linear self-association of bacterial cell division protein FtsZ.

Recent measurements of sedimentation equilibrium and sedimentation velocity have shown that the bacterial cell division protein FtsZ self-associates to form indefinitely long rod-like linear aggregates in the presence of GDP and Mg(2+). In the present study, the newly developed technique of non-ideal tracer sedimentation equilibrium was used to measure the effect of high concentrations-up to 150 g/liter-of each of two inert "crowder" proteins, cyanmethemoglobin or BSA, on the thermodynamic activity and state of association of dilute FtsZ under conditions inhibiting (-Mg(2+)) and promoting (+Mg(2+)) FtsZ self-association. Analysis of equilibrium gradients of both FtsZ and crowder proteins indicates that, under the conditions of the present experiment, FtsZ interacts with each of the two crowder proteins essentially entirely via steric repulsion, which may be accounted for quantitatively by a simple model in which hemoglobin, albumin, and monomeric FtsZ are modeled as effective spherical hard particles, and each oligomeric species of FtsZ is modeled as an effective hard spherocylinder. The functional dependence of the sedimentation of FtsZ on the concentrations of FtsZ and either crowder indicates that, in the presence of high concentrations of crowder, both the weight-average degree of FtsZ self-association and the range of FtsZ oligomer sizes present in significant abundance are increased substantially.

Dynamic Electrophoretic Mobility of a Soft Particle

A theory of the dynamic electrophoretic mobility of a spherical soft particle (that is, a polyelectrolyte-coated spherical particle) in an oscillating electric field is presented. In the absence of the polyelectrolyte layer a spherical soft particle becomes a spherical hard particle, while in the absence of the particle core it tends to a spherical polyelectrolyte. The present theory thus covers two extreme cases, that is, dynamic electrophoresis of hard particles and that of spherical polyelectrolytes. Simple analytic mobility expressions are derived. It is shown how the dynamic electrophoretic mobility of a soft particle depends on the volume charge density distributed in the polyelectrolyte layer, on the frictional coefficient characterizing the frictional forces exerted by the polymer segments on the liquid flow in the polyelectrolyte layer, on the particle size, and on the frequency of the applied oscillating electric field.

Electrophoretic Mobility of Soft Particles in Concentrated Suspensions

A general theory is developed for the electrophoretic mobility of spherical soft particles (i.e., spherical hard colloidal particles of radius a coated with a layer of polyelectrolytes of thickness d) in concentrated suspensions in an electrolyte solution as a function of the particle volume fraction φ on the basis of Kuwabara's cell model. In the limit d→0, the mobility expression obtained tends to that for spherical hard particles in concentrated suspensions, whereas in the limit a→0, it becomes that for spherical polyelectrolytes (charged porous spheres with no particle core). Simple approximate analytic mobility expressions are derived for the case where relaxation effect is negligible. It is found that in practical cases, the φ dependence of the mobility is negligible for d⪡a, whereas for d⪢a, the mobility strongly decreases with increasing φ.

Electrophoretic Mobility of Soft Particles

A general expression is derived for the electrophoretic mobility of a soft particle, i.e., a spherical hard colloidal particle of radius a coated with a layer of polyelectrolytes of thickness d in an electrolyte solution, In the limit of d → 0, the mobility expression tends to that for a spherical hard particle (Ohshima et al., J. Chem. Soc. Faraday Trans.2 79, 1613 (1983)), whereas in the limit of a → ∞, it tends to that for a plate-like soft particle derived previously (J. Colloid Interface Sci.130, 281 (1989)). Also in the limit of a → 0 and low potentials, the obtained mobility expression tends to a mobility formula for a spherical polyelectrolyte (a charged porous sphere with no particle core) derived by Hermans and Fujita (K. Ned. Akad. Wet. Proc. Ser. B58, 182 (1955)). A simple approximate analytic mobility expression is presented.