Surface Characterization and Corrosion Resistance of Boron Nitride Coated Titanium Dental Implants

Protection of Metals and Physical Chemistry of Surfaces - Surface modifications of dental implants are of vital importance to enhance osseointegration and improve their corrosion resistance. This...     

Morphologic characterization and fractal analysis of lapped and polished surfaces of quartz single crystals

Lapping and polishing are industrial processes sometimes used alternatively for surface finishing of hard and brittle materials. This article presents advanced image analysis of surfaces of quartz crystal blanks finished by lapping and polishing. Scanning electron micrographs were obtained from workpiece surfaces parallel to Y-, AT-, and Z-cut crystal planes treated with different normal stress and abrasive grit size, and stereometric and fractal/multifractal approaches were used to analyze the respective surfaces. Fractal dimensions and segmentation parameters were able to decode the effect of normal stress increasing on the surface roughness of lapped and polished samples. Moreover, the texture isotropy and the bifractal—hence agglomerated—nature of the surface patterns, suggest that both treatments dismiss the anisotropic signature of hardness and fracture toughness inherent to each crystal plane. This study provides promising results regarding the applicability of fractal analysis in the assessment of surfaces severely worn by the combined effect of brittle microcracking and plastic deformation mechanisms.     

Subcooled Flow Boiling Over Microstructured Plates In Rectangular Minichannels

Microstructures offer enhancements in boiling heat transfer by increasing bubble departure frequency, active nucleation site density, critical cavity size, and surface area. Integration of microstructures to surfaces alters significant surface parameters such as porosity of the microstructured plates, contact angle, and configuration of microstructures on the surface, which all affect boiling heat transfer. The goal of this study is to investigate boiling heat transfer on different microstructured plates and the effect of various microscale surface morphologies on boiling heat transfer. The microstructured surfaces were formed on aluminum alloy 2024 sheets with the use of a simple and environmentally friendly technique of random mechanical sanding (grits of #36, #60, #400, and #1,000). Distilled water was pumped using a micro gear pump to the rectangular minichannel test section at flow rates of 100, 180, and 290 ml/min, which correspond to mass fluxes of 5.46, 10.58, and 16.15 kg/m².s, respectively. It was observed that surfaces with low grit (grit #36) showed no considerable enhancement, whereas the use of higher grit counts considerably enhanced boiling heat transfer up to a critical grit count. The results were supported by the images from the performed visualization of flow boiling.     

Knowledge extraction for water gas shift reaction over noble metal catalysts from publications in the literature between 2002 and 2012

In this work, a database (containing 4360 experimental data points) on water gas shift reaction (WGS) over Pt and Au based catalysts was constructed using the data obtained from the published papers between the years 2002 and 2012. Then, the database was analyzed using three data mining tools to extract knowledge in three areas: Decision trees to determine the empirical rules and conditions that lead to high catalytic performance (high CO conversion); artificial neural networks (ANNs) to determine the relative importance of various catalyst preparation and operational variables and their effects on CO conversion; support vector machines (SVMs) to predict the outcome of unstudied experimental conditions. It was concluded that, all three models were quite successful and they complement each other to extract knowledge from the past published works and to deduce useful trends, rules and correlations, which are not easily comprehensible by the naked eyes.     

Calculation of a phase diagram for the ice II - V - VI transitions

In this study we calculate the P - T phase diagram of ice II - V - VI using a mean field model. Our calculated phase line equations are fitted to the experimental data from the literature. There is a very good agreement between our calculated and experimentally observed P - T phase diagram of ice II - V - VI.     

The influence of moisture content on the polymer structure of polyvinyl alcohol in dispersion barrier coatings and its effect on the mass transport of oxygen

This paper presents a study of the effect of moisture on the gas permeability of polyvinyl alcohol (PVOH) and PVOH–kaolin dispersion barrier coatings. The oxygen permeability was measured at different humidity levels, and the material properties were characterized under the same conditions: polymer crystallinity, kaolin concentration, and kaolin orientation were all evaluated. The experimental results revealed that the water plasticizes the PVOH material of the coatings, and the presence of kaolin filler is unable to affect such behavior significantly. The PVOH crystallinity was affected drastically by the humidity, as water melts polymer crystallites, which is a reversible process under removal of water. The permeability data were analyzed using a thermodynamic-based model able to account for the water effect on both the solubility of the gas and the diffusivity coefficients in the polymer and composite. The results showed good agreement between the model’s predictions and the experimental data in terms of the overall permeability of the material.     

FREE VIBRATIONS OF A CONICAL SHELL WITH TEMPERATURE-DEPENDENT MATERIAL PROPERTIES

This article presents an analysis of the free vibrations of a truncated conical thin shell subjected to thermal gradients. The governing equations of the shell are based on the Donnell-Mushtari theory of thin shells. Simply supported and clamped boundary conditions are considered at both ends of truncated conical shell. Temperature loading due to supersonic flow is assumed to vary along the meridian and across the thickness of the shell Hamilton's principle is used to derive the appropriate governing equations of a conical shell with temperature-dependent material properties. The shell material has a kind of inhomogeneity due to the varying temperature load and temperature dependency of material properties. The resulting differential equations are solved numerically using the collocation method. The results are compared with certain earlier results. The influence of temperature load on the vibration characteristics is examined for the conical shells with various geometrical properties.     

Characterization of Ni-W solid solution alloy powders and sintered compacts synthesized via mechanically activated hydrogen reduction of NiO-WO3 mixtures

Blended nickel oxide — tungsten oxide powders corresponding to the compositions of 70 wt% nickel — 30 wt% tungsten were mechanically alloyed (MA’d) for different durations such as 0 h, 6 h, 12 h and 24 h and reduced/alloyed at 550 °C for 1 h followed by 600 °C for 0.5 h under hydrogen (H₂) atmosphere. H₂ reduction of the MA’d fine oxide powders resulted in the fabrication of nanocrystalline Ni(W) solid solution alloy powders, whereas a mixture of Ni and WO₂ powders were obtained via hydrogen reduction of asblended oxide mixtures, which revealed the activation of the reduction process by MA. Obtained powders were sintered at 1300 °C for 1 h under H₂ and Ar gas flowing conditions. X-ray diffraction patterns taken from the sintered samples revealed the presence of the Ni(W) solid solution phase for all samples, whereas the presence of elemental W phase was observed in the sintered as-blended and reduced powders. The lowest relative density value of 92.04% and microhardness value of 1.27 GPa were measured for the sintered as-blended and reduced powders, which increased to between 97.62% and 98.72% and 2.19 GPa and 2.23 GPa, respectively, with the applied MA.     

Experimental investigation of thermal performance of solar air heater having different obstacles on absorber plates

This paper presents the results of an experimental investigation of the performance for a new flat plate solar air heater (SAH) with several obstacles (Type I, Type II, and Type III) and without obstacles (Type IV). The efficiencies, the heat gain factors and heat loss coefficients are determined for the collectors and comparisons were made among them. The experimental data along with the correlations obtained by linear regression are presented. The optimal value of efficiency was determined for the solar air heater with Type II absorbent plate in flow channel duct for all operating conditions and the collector supplied with obstacles appears significantly better than that without obstacles.