Influence of the duty cycle on structural and mechanical properties of oxide layers on Al-1050 by a plasma electrolytic oxidation process

Oxide layers were prepared on Al-1050 substrates by an environmentally friendly plasma electrolytic oxidation process using an alkaline solution of Na₂SiO₃ (8 g/L) and NaOH (3 g/L) as the electrolyte. The effects of three different duty cycles (20%, 40%, and 60%) on the structure and hardness of the oxides were investigated. XRD analysis revealed that the oxides were mainly composed of α-Al₂O₃, γ-Al₂O₃, and mullite. The proportion of each phase depended on various electrical parameters, such as the duty cycle and frequency. The morphology, thickness, and the elemental distribution of the oxides were examined by scanning electron microscopy and energy dispersive spectroscopy. The thicknesses of the oxides were found to vary from 20 μm to more than 60 μm for various duty cycles, when identical treatment durations were used. The oxidation treatment also resulted in good adhesion between the oxide layer and the substrate. SEM images indicated that the oxide layers formed at the 60% duty cycle exhibited relatively coarser surfaces with larger pore sizes and sintering particles, and slower growth rates than did those formed at the 20% duty cycle, under identical treatment durations. The oxides prepared at the 20% duty cycle showed smooth surfaces. The oxides layers were found to improve the micro-hardness of Al-1050. In particular, the oxide layers formed at the 40% duty cycle exhibited relatively better micro-hardness owing to their compact microstructures.     

A study on the behaviors and stresses of O-ring under uniform squeeze rates and internal pressure by transparent type photoelastic experiment

The behaviors and stresses of an O-ring under uniform squeeze rates and internal pressure change with real time. Therefore, the behaviors and stresses of O-rings under uniform squeeze rates and internal pressures should be studied with real time. To achieve this, a loading device for a transparent type photoelastic experiment, through which various internal pressures and uniform squeeze rates are applied, was developed. The validity of the loading device in analyzing the behaviors and stresses of the O-ring under uniform squeeze rates and internal pressures with real time was verified. It was observed that the filling phenomenon of the O-ring into the space between the lower and front side occurred after forcing out continued for a duration of time. The study also indicated that maximum shear stress would be more effective as a fracture parameter than the maximum normal stress fracture criterion for an O-ring made from rubber.     

The effect of top and bottom lids on natural convection inside a vertical cylinder

Natural convection experiments inside a vertical cylindrical cavity were performed for Rayleigh numbers of 1.08 × 10¹⁰–2.11 × 10¹³ and for four different geometrical arrangements: both-open (pipe-shape), bottom-closed (cup-shape), top-closed (cap), and both-closed (cavity) cylinders. A copper electroplating system was employed for the measurements of heat transfer rates using analogy concept. The lids used to close top or bottom were adiabatic; i.e. inactive surfaces in the electrodeposition experiments. The bottom-closed cavity showed the highest heat transfer rates and then followed both-closed, both-open, top-closed ones in both laminar and turbulent flows. The results were in satisfactory agreements with the existing correlations developed for similar geometrical configurations and the empirical correlations were derived. The numerical simulations were carried out using the FLUENT 6.2 to explain the measured results. The analysis of the streamline and the local Nusselt number gave explanations for the observation.     

Influence of helical tube dimensions on open channel natural convection heat transfer

Natural convection heat transfer of a helical tube was investigated experimentally for varying tube diameter, length, height, pitch, radius, and number of turns, in order to determine an appropriate characteristic length to describe the phenomenon. Mass-transfer rates of a CuSO₄–H₂SO₄ electroplating system were measured by replacing the heat transfer system according to the analogy concept. When the pitch-to-diameter ratio was larger than 5 and the pitch-to-radius ratio was smaller than 2.3, the heat transfer rates were very close to those of a horizontal cylinder, and decreased with the diameter of the tube while remaining unaffected by the total length and height. The natural convection heat transfer of the Nth turn of a helical tube was measured for varying pitch-to-diameter ratio and number of turns, and the results were formulated as an empirical correlation.     

A study on the flow characteristics of butterfly valve with baffles

Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically...     

Determination of the interface energy level alignment of a doped organic hetero-junction using capacitance–voltage measurements

A simple method based on capacitance–voltage (C–V) measurements is reported to determine the interface energy level alignment at the junction of 15 mol% Cs₂CO₃ doped 4,7-diphenyl-1,10-phenanthroline (BPhen) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) fabricated under high vacuum. The junction properties, such as the depletion layer thickness, built-in potentials and vacuum level shift were calculated with simple Mott–Schottky and Poisson’s equations with the boundary condition of a continuous electric flux density using the information from the C–V data. The interface energy level alignment determined by this method is well matched with the one determined using the in situ ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) experiments performed under ultra-high vacuum. This method can be applied to other semiconductor junctions such as the organic p–n homojunctions and heterojunctions with known energy levels, as long as the metal/semiconductor contact is Ohmic without referring to the photoemission spectroscopies. Moreover, the energy level alignment determined by the C–V measurement gives a more realistic result since the films for the measurements are formed under high vacuum which is a normal device fabrication environment rather than under ultra high vacuum.     

Transport of small cuttings in solid-liquid flow with inclined slim hole annulus

During drilling, the precipitation velocity of cuttings within an annulus depends on the density, configuration, and size of the cuttings, and on the density, viscosity, and rheological characteristics of the drilling fluid. In directional drilling in particular, it is difficult to adjust and control the cuttings. In contrast to vertical drilling, it is very important to evaluate the flow characteristics of a drilling flow field. However, research on the transfer features of cuttings is inadequate. In this study, in order to identify transfer features of cuttings, an experiment was performed under wide-ranging conditions by constructing a slim hole annulus (44 mm×30 mm) device. In this experiment, the friction coefficient, pressure loss, particle transport ratio, and particle volume fraction were measured. These quantities were influenced by particle concentration within the flow, pipe rotation, flow volume, and inclination of the annulus. In addition, a mathematical formula for volumetric concentration was deduced and compared to the test results and behavior of cuttings under the other drilling condition was made to be predicted. Therefore, this study can provide meaningful data for vertical and horizontal drilling, and for directional drilling.     

Effects of Al2O3 on the properties and densification of 8YSZ after pulsed current activated sintering

Dense 8YSZ was subjected to pulsed current activated sintering (PCAS) within 1 min of 8YSZ nanopowder preparation using a co-precipitation method. Sintering was accomplished by combining a pulsed current and mechanical pressure. Highly dense 8YSZ with a relative density of up to 99% was produced under simultaneous application of a pressure of 80 MPa and the pulsed current. The effects of the addition of Al₂O₃ on the sintering behavior, mechanical properties, and ionic conductivities of 8YSZ were investigated.     

Robust size control of bovine serum albumin (BSA) nanoparticles by intermittent addition of a desolvating agent and the particle formation mechanism

In polymeric nanoparticle preparation, despite similar conditions, large fluctuations in particle size distributions are usually observed. Herein, we demonstrate that the intermittent addition of a desolvating agent can improve reproducibility in the preparation of polymeric bovine serum albumin (BSA) nanoparticles. Using this modification, BSA nanoparticles of controlled size can be manufactured with narrow particle size distributions. In our study, ethanol as a desolvating agent was added intermittently to 1% BSA solutions at different pHs with stirring at 700 rpm. The effect of the preparation parameters on size and optical density of the fabricated nanoparticles were studied. The average particles sizes of BSA nanoparticles prepared at pH values of 6, 7 and 9 were approximately 100, 200 and 300 nm, respectively. As ethanol addition increased, desolvation of BSA molecules resulted in formation of loose-structured particles with pH-dependent size. Beyond that, only particle density increased, but size remained unchanged with further addition of ethanol. Consistently uniform particle size distribution was achieved by adding ethanol intermittently.