Microstructure and Corrosion Properties of CP-Ti Processed by Laser Powder Bed Fusion under Similar Energy Densities

In this work, two types of CP Ti cubes with similar volumetric energy densities (VED) but different process parameters were produced using laser powder bed fusion (LPBF) method. The corrosion behavior of the fabricated specimens was investigated by conducting electrochemical impedance spectroscopy (EIS) and polarization experiments in simulated body fluid (SBF) solution at 37 °C. The results indicated that the microstructure and porosities, which are of great importance for biomedical applications, can be controlled by changing the process parameters even under constant energy densities. The sample produced with a lower laser power (E1) was featured with a higher level of porosity and thinner alpha laths, as compared with the sample fabricated with a higher laser power (E2). Moreover, results obtained from the bioactivity tests revealed that the sample produced with a higher laser power conferred a slight improvement in the bioactivity due to the higher amount of porosity. Lower laser power and hence higher porosity level promoted the formation of bone-like apatite on the surface of the printed specimens. The potentiodynamic polarization tests revealed inferior corrosion resistance for the fabricated sample with higher porosity. Moreover, the EIS results after different immersion times indicated that a stable oxide film was formed on the surface of samples for all immersion times. After 1 and 3 days of immersion, superior passivation behavior was observed for the sample fabricated with lower laser power. However, very similar impedance and phase values were observed for all the samples after 14 days of immersion.     

Development and field evaluation of an online monitor for near-continuous measurement of iron,manganese, and chromium in coarse airborne particulate matter (PM)

A novel air sampling monitor was developed for near-continuous (i.e., 2-h time resolution) measurement of iron (Fe), manganese (Mn), and chromium (Cr) concentrations in ambient coarse particulate matter (PM) (i.e., PM_10–2.5). The developed monitor consists of two modules: (1) the coarse PM collection module, utilizing two virtual impactors (VIs) connected to a modified BioSampler to collect ambient coarse PM into aqueous slurry samples; (2) the metal concentration measurement module, which quantifies the light absorption of colored complexes formed through the reactions between the soluble and solubilized target metals and pertinent analytical reagents in the collected slurries using a micro volume flow cell (MVFC) coupled with UV/VIS spectrophotometry. The developed monitor was deployed in the field for continuous ambient PM collection and measurements from January to April 2016 to evaluate its performance and reliability. Overall, the developed monitor could achieve accurate and reliable measurements of the trace metals Fe, Mn, and Cr over long sampling periods, based on the agreement between the metal concentrations measured via this online monitor and off-line parallel measurements obtained using filter samplers. Based on our results, it can be concluded that the developed monitor is a promising technology for near-continuous measurements of metal concentrations in ambient coarse PM. Moreover, this monitor can be readily configured to measure the speciation (i.e., water-soluble portion as well as specific oxidation states) of these metal species. These unique abilities are essential tools in investigations of sources and atmospheric processes influencing the concentrations of these redox-active metals in coarse PM.

Copyright © 2016 American Association for Aerosol Research     

Constitutive modeling of isotropic hyperelastic materials using proposed phenomenological models in terms of strain invariants

Rubber‐like materials deform largely and nonlinearly under loading and preserve their initial configuration after removal of the load. These materials are usually modeled as being homogeneous, isotropic, and incompressible elastic solids that are supported by experimental data. In this article, a general form for the strain energy density of these materials is assumed as the sum of two independent functions of the first and second strain invariants. Applying the essential requirements on the form of the strain energy density, the mathematical form of these functions is obtained as polynomial, logarithmic, and exponential. Then a general form is derived for the strain energy density of compressible materials and its effectiveness is evaluated for hydrostatic compression and uniaxial tension tests. The determination of material parameters and the evaluation of effectiveness of models are done based on the correlation between the values of the strain energy density (rather than the stresses) cast from the theory and the test data. Comparison of the theoretical predictions with the experimental data indicates that the represented models can achieve a satisfactory agreement with the behavior of different materials. POLYM. ENG. SCI., 56:299–308, 2016. © 2015 Society of Plastics Engineers     

Adsorption and photocatalytic degradation of organic dyes onto crystalline and amorphous hydroxyapatite: Optimization,kinetic and isotherm studies

We evaluated the adsorptive/photodegradation properties of hydroxyapatite. Hydroxyapatite was synthesized by two different precipitation methods and examined for the removal of two kinds of textile dye. The physicochemical properties of the products were characterized using Fourier transform infrared, X-ray diffraction, inductively coupled plasma atomic emission spectroscopy and scanning electron microscopy. The effects of different parameters, including hydroxyapatite synthesis method and removal process type, pH, reaction time, temperature and amount of hydroxyapatite, were investigated and optimized by Taguchi design. The kinetics of adsorption and isotherm studies showed that the pseudo-second-order model and the Freundlich isotherm were the best choices to describe the adsorptive behavior of hydroxyapatite. Photocatalytic degradation of dye followed Langmuir-Hinshelwood mechanism, illustrated a pseudo-first-order kinetic model with the adsorption equilibrium constant and kinetic rate constant of surface reaction equal to 0.011 (l mg^-1) and 1.3 (mg l ^-1 min^-1), respectively.     

A simple accurate model for prediction of physical properties of petroleum fractions

We utilized genetic programming approach for generation of a new model for prediction of critical properties and acentric factor of petroleum fractions. Usually for estimation of critical properties, molecular weight, specific gravity and boiling point are needed, while in this work in order to present an applicable model, just the boiling point and specific gravity have been used as the model parameters. Our results showed that using new correlations, critical temperature, pressure, volume and acentric of petroleum fractions can be correlated within 0.07, 0.65, 0.45 and 0.79 percent average absolute relative deviation. respectively.     

Biosorption of anionic dyes from aqueous solutions using a novel magnetic nanocomposite adsorbent based on rice husk ash

This study investigated the potential use of an agricultural waste, rice husk ash, for the removal of methyl orange. The adsorbent was prepared via a simple one-pot synthesis of magnetic iron oxide nanoparticles (MIONs). The prepared magnetic nanocomposites were characterized using Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and vibrating sample magnetometer techniques. Bach adsorption experiments were carried out to evaluate the effects of initial dye concentration, pH and contact time as well as MION content on adsorption capacity. The mechanism of dye adsorption was well fitted to a pseudo-second-order kinetic model. Moreover, the equilibrium data fitted well with the Langmuir isotherm model.     

Comparative assessment of growth supporting potential of different alginic acid salts

This study compares the cell survival of HeLa, osteoblasts (MG 63), and human umbilical cord stem cells (hUMSCs) in three different salts of alginic acid including sodium, potassium, and triethanolamine. While the treatment of the cells with wide range of concentrations of potassium and triethanolamine alginate did not adversely affect the cell growth, higher concentrations of sodium alginate inhibited cell growth on all the cell types tested. Furthermore, the cells encapsulated in potassium alginate beads showed enhanced cell survival compared to the growth in other salts. Our results indicated that potassium alginate can be used with wide varieties of cell types.     

The 2016 Thermal Spray Roadmap

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.     

The influence of Si as reactive bonding agent in the electrophoretic coatings of HA–Si–MWCNTs on NiTi alloys

In this study, different composite coatings with 20 wt.% silicon and 1 wt.% multi-walled carbon nanotubes of hydroxyapatite were developed on NiTi substrate using a combination of electrophoretic deposition and reactive bonding during the sintering. Silicon was used as reactive bonding agent. During electrophoretic deposition, the constant voltage of 30 V was applied for 60 s. After deposition, samples were dried and then sintered at 850 °C for 1 h in a vacuum furnace. SEM, XRD and EDX were used to characterize the microstructure, phase and elemental identification of coatings, respectively. The SEM images of the coatings reveal a uniform and compact structure for HA–Si and HA–Si–MWCNTs. The presence of silicon as a reactive bonding agent as well as formation of new phases such as SiO₂, CaSiO₃ and Ca₃SiO₅ during the sintering process results in compact coatings and consumes produced phases from HA decomposition. Formation of the mentioned phases was confirmed using XRD analysis. The EDX elemental maps show a homogeneous distribution of silicon all over the composite coatings. Also, the bonding strength of HA–Si–MWCNTs coating is found to be 27.47 ± 1 MPa.