Metol as Corrosion Inhibitor for zinc

The inhibition behavior of metol (N-methyl-p-aminophenol sulphate) on zinc in different corrosive solutions at room temperature was investigated by various techniques such as weight loss, polarization and linear polarization methods. The percentage inhibition efficiencies were evaluated at different concentrations of the inhibitors. The corrosion rate, inhibition efficiency and surface coverage were dependent on metol concentration. The electrochemical data indicated a basic modification of zinc surface resulting in a decrease in the corrosion rate. Corrosion inhibition was explained by considering an interaction between metal surface and the inhibitor. SEM images and FT-IR profiles confirmed the formation of passive film on the metal surface.     

Effect of Retrogression and Re-Aging on Tensile Mechanical Properties in Transverse Direction of Extruded Rods from Aluminum Alloy AA7049

Metal Science and Heat Treatment - The effect retrogression and re-aging (RRA treatment) on the tensile properties in the transverse direction of extruded rods from aluminum alloy AA7049 is...     

EVALUATION OF RHEOLOGICAL PROPERTIES OF MEDIUM FOR AFM PROCESS

Abrasive Flow Machining (AFM) is a new non-traditional machining process used to deburr, radius, polish, and remove recast layer of components used in a wide range of applications. Material removal in AFM takes place by flowing medium (i.e. carrier/or putty mixed with abrasive particles), across the surface to be machined. The medium is the key element in the process because of its ability to precisely abrade the selected areas along its flow path. From the literature review, it is found that there is a need to study how to evaluate rheological properties of the medium in general, and viscosity in particular. Viscosity of the medium has significant effects on the AFM process performance.

In the present work, effects of concentration and mesh size of abrasive particles, and temperature of medium on the medium viscosity have been studied. To determine the viscosity of the abrasive medium, a viscometer has been designed and fabricated based on the principle of capillary viscometry. Experiments have been conducted at different abrasive concentrations and mesh sizes, and medium temperatures. It is observed from the experiments that the viscosity of the medium increases with the abrasive concentration and decreases with the abrasive mesh size and medium temperature. Theoretical values obtained from mathematical model, and experimental results are compared. The results of viscosity are correlated with the process performance parameters, i.e. material removal and surface roughness. It is observed that there is an increase in material removal and decrease in surface roughness value as viscosity of the medium increases.     

EXACT ANALYSIS OF UNSTEADY CONVECTIVE DIFFUSION IN A SIMPLIFIED CROSS MODEL FLUID

The article presents the effect of non-Newtonian viscosity on the longitudinal dispersion of tracer molecules released in an incompressible viscous non-Newtonian fluid (known as the simplified Cross model fluid) under the action of a constant pressure gradient. The Gill and Sankarasubramanian model is used to solve the unsteady convection diffusion equation for all time periods. An exact expression is obtained for the longitudinal convection coefficient K ₁(η?), which shows the effect of the non-Newtonian parameter η? on the centerline coefficient. It is seen that the value of the K ₁(η?) for η? > 1 is always smaller than the corresponding value for a Newtonian fluid. Also, the longitudinal dispersion coefficient of the solute K ₂(τ, η?) is determined exactly. The results show that the K ₂(τ, η?) asymptotically reaches a stationary state after a certain time. The effect of the η? on the most dominant dispersion coefficient is clearly depicted. Finally, the axial distribution of the average concentration θ _m of the solute over the channel cross section is determined at a fixed instant after the solute injection for several values of the η?. The results for “pure convection” are also reported     

Flow of Newtonian fluid in non-uniform tubes with variable wall permeability with application to flow in renal tubules

Summary The hydrodynamical aspects of flow through proximal renal tubule have been investigated. Assuming renal fluid as Newtonian fluid, flow through diverging/converging tubes with variable wall permeability has been considered. Solutions have been obtained for approximate Navier-Stokes equations with boundary conditions which include a dynamic condition, i.e., leakage flux at the wall depends on variable wall permeability and transboundary pressure drop. Numerical solutions, using fourth order Runge-Kutta method, and approximate analytic solutions, using perturbation method, have been obtained. A comparison of the numerical solution with approximate analytic solution, shows a good agreement (difference less than 4%) between the two solutions for small values of ||, a tube non-uniformity parameter. The velocity profiles at different positions along the axis, the axial distribution of wall shear stress, flow rate and leakage flux have been obtained. For a given value of wall permeability, in diverging (converging) tubes the fractional reabsorption FR is more (less) than its corresponding value in uniform tubes. Further, FR increases (decreases) as the wall permeability increases (decreases) as a linear function of axial distance. The results for flow with constant/variable permeability through uniform tubes and for flow through diverging/converging tubes with constant permeability can be obtained as special cases of this analysis. It is shown that by considering the divergent tube model with linear increase of wall permeability along the axis, an improvement of about 20% in total reabsorption can be achieved over the uniform tube model with constant wall permeability. It is concluded that the approach of using a dynamic boundary condition for leakage flux at the wall has an advantage over the method of prescribing the leakage flux at the wall for this physical problem. Using a set of data, relevant to a physiological situation, implications of the results on glomerular tubular balance have been briefly discussed.     

Solute transfer in fluid flow in permeable tubes with application to flow in glomerular capillaries

Summary A mathematical model for solute transfer in an ultrafiltering glomerular capillary has been proposed. The solute transfer, by diffusion and convection, within and across the tube wall has been considered. Effects due to the presence of red cells are neglected and the blood is assumed to be Newtonian fluid with constant viscosity. The rate of fluid movement at the wall is assumed to be proportional to the difference between the net hydrostatic and osmotic forces — Starling's law. The velocity and concentration profiles, at different positions along the axis, the axial distribution of hydrostatic and osmotic pressures and the total solute clearance have been obtained. It is found that the osmotic pressure has relatively greater influence on capillary mass transfer than the hydrostatic pressure. Radial concentration gradients of considerable order have been observed, particularly near the entrance portion of the tube. The radial concentration gradient increases with ultrafiltration parameter and decreases, as the diffusion coefficient increases. The influence of transmittance coefficient (solute wall permeability coefficient) is found to be predominant at higher ultrafiltration rates (higher concentration difference across the membrane). The generalized nature of the present model has been illustrated by obtaining some of the existing results as the particular cases of this model. Using relevant data, the physiological implications of some of the obtained results have been briefly discussed.     

Enhanced photocatalytic,electrochemical and antimicrobial activities of α-Mn2V2O7 nanopebbles

Journal of Materials Science: Materials in Electronics - Manganese(II) divanadate nanopebbles (α-Mn2V2O7) were prepared by a simple solution combustion method and calcinated at...     

EFFECT OF INTERPHASE MASS TRANSFER ON UNSTEADY CONVECTIVE DIFFUSION IN A SIMPLIFIED CROSS MODEL FLUID

This article examines the influence of heterogeneous chemical reaction on the exchange coefficient, convective coefficient, and diffusive coefficient arising in the study of dispersion in a simplified Cross model fluid flow. The exchange coefficient emanates exclusively from the incorporation of the catalytic wall reaction. The convective and diffusive coefficients are also influenced by the wall reaction. The results show that the dispersion coefficient asymptotically reaches a stationary state after a critical time. This critical time decreases as the absorption at the walls increases. The problem finds application in biomechanics such as transport across a semipermeable membrane, in industries releasing waste into the environment, in crude oil conveyance, and in chromatography.     

Process and properties of electroless Ni–Cu–P–ZrO2 nanocomposite coatings

Electroless Ni–Cu–P–ZrO₂ composite coating was successfully obtained on low carbon steel matrix by electroless plating technique. Coatings with different compositions were obtained by varying copper as ternary metal and nano sized zirconium oxide particles so as to obtain elevated corrosion resistant Ni–P coating. Microstructure, crystal structure and composition of deposits were analyzed by SEM, EDX and XRD techniques. The corrosion behavior of the deposits was studied by anodic polarization, Tafel plots and electrochemical impedance spectroscopy (EIS) in 3.5% sodium chloride solution. The ZrO₂ incorporated Ni–P coating showed higher corrosion resistance than plain Ni–P. The introduction of copper metal into Ni–P–ZrO₂ enhanced the protection ability against corrosion. The influence of copper metal and nanoparticles on microhardness of coatings was evaluated.     

Fracture toughness of cast aluminium alloys

An investigation was carried out to evaluate the fracture toughness of cast aluminium alloys of different microstructural complexity, brought about by alloy constitution and cooling rate of castings. In all cases the three-point bend specimens, which had a thickness of 15 mm, did not provide valid plane — strain stress intensity factor values. The fracture susceptibility at a given stress level reckoned in terms of the conditional plane strain stress intensity factor (K _Q) was found to be lowest in aluminium-4.5% copper alloy castings and the susceptibility increased with increase in microstructural complexity. Casting cooling rate in these castings is likely to affect the damage potential of a given defect at yield stress to a greater extent than the fracture susceptibility at a given stress.