Effect of surfactant and heat treatment on morphology,surface area and crystallinity in hydroxyapatite nanocrystals

Hydroxyapatite (HA) powders were synthesized by the wet precipitation method, with and without surfactant, under identical processing parameters. These powders were then heat treated at 900 °C for 3 h in air. The detailed characterization of the powders was done by using SEM, dynamic light scattering, nitrogen adsorption, XRD, Raman spectroscopy, and FTIR techniques. The HA phase, identified by well defined PO₄^3? and OH^? ion peaks in Raman and FTIR spectra, was observed in all the powder samples. The addition of surfactant changed the morphology of the particles from spherical to needle/rod-like structure and increased the surface area up to three times (from 33 to 96 m²/g). Also, suppression in the evolution of β-TCP phase was observed along with decrease in the crystal size and crystallinity of the powder due to the addition of surfactant. Synthesized nano-HA crystals were found to have diameters and lengths in the range 10–25 nm and 75–150 nm, respectively. The heat treatment changed the architecture of the particles, increased the crystallinity and reduced the surface area to ≈7 m²/g. However, the relative increase in crystallinity was much higher for the powder synthesized with surfactant. The ratio of the average crystallite size to the crystallinity degree was about 0.53±0.07 for all the powders. The particle size distribution was bimodal and coarser for the powder synthesized without surfactant. The pore size analysis showed transformation of a predominantly mesoporous structure into a meso- plus macroporous one on heat treatment. The intensity of OH^? group peak in Raman spectra was found to be highly sensitive to the crystalline state of the HA powder and may be used to assess crystallinity.     

Passivity and passivity breakdown of a zinc electrode in aerated neutral sodium nitrate solutions

The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO₃⁻ concentration and temperature, but increases with increasing potential scan rate. Addition of SO₄²⁻ ions to the nitrate solution accelerates pitting corrosion, while addition of WO₄²⁻ and MoO₄²⁻ ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO₃⁻ concentration, temperature and applied anodic current density. Addition of SO₄²⁻ ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO₄²⁻ or MoO₄²⁻ ions.     

Low‐velocity impact of nanocomposite and polymer plates

Nanocomposites are more widely studied today because of higher stiffness, decreased permeability, thermal stability, and many other properties superior to those of regular polymers. However, manufacturers are concerned about implementing nanocomposites because of their lower impact properties with respect to the base polymer. This study focused on low‐velocity impact tests of a thermoplastic olefin by itself and with 5 wt % nanoclay. The impact tests were conducted at ?40, 23.9, and 65.6°C until the polymer and nanocomposite plates experienced complete striker penetration. The force–time and force–deflection responses obtained from the impact testing provided a means of comparing the impact performances of the two materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2309–2315, 2005     

Potency of Different Carbon Sources in Reduction of Microsilica to Synthesize SiC from Mechanically Activated Powder Mixtures

In the present study, the influences of three different types of carbon (carbon black, graphite, and petroleum coke) on SiC synthesis via mechanical activation and sintering were evaluated. In this regard, the phase components, morphology, and the formation mechanism were investigated. SiC nanoparticles were detected to be formed after 4 h of milling and sintering at 1450°C, regardless of the sources of carbon. The carbon types exert their effects on the morphology of the as‐synthesized particles, where carbon black leads to form rod‐like SiC particles and the other two carbon types result in semi‐spherical SiC particles. This is due to the dominant mechanism in the mentioned process. The rod‐like particles obtained from the carbon black‐containing powder were synthesized via the VSL mechanism, whereas the solid‐state reactions occurred to form the SiC particles in the graphite‐ or petroleum coke‐containing samples. In the VSL mechanism, any increase in the milling time leads to facilitate the SiC formation due to entrance of Fe debris, whereas in the other samples (graphite or petroleum coke) the procedure is reversed.     

Gate All Around Dopingless Nanotube TFET Biosensor with Si0.5Ge0.5 – Based Source

Silicon - Through this paper, we discuss how Tunnel Field Effect Transistors can be utilized for the detection of biomaterials hence acting as a biosensor. The device proposed is a 3-D Doping less...     

Conjugate heat transfer of laminar mixed convection of a nanofluid through an inclined tube with circumferentially non-uniform heating

Laminar mixed convection of a nanofluid consisting of water and Al₂O₃ in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector). Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen.     

Statistical assessment of starch removal from starchy wastewater using membrane technology

The present work deals with application of 2^5-2 fractional factorial design (FFD) to evaluate the operating parameters on starch separation from synthetic starchy wastewater using a hydrophilic polyethersulfone membrane with 0.65 μm pore size in a plate and frame handmade membrane module. The analysis of variance (ANOVA) combined with F-test was also used to recognize non-significant terms. The performance of the filtration process was evaluated by calculating the COD removal percentage (rejection factor) and permeate flux. In this experiment, five input parameters were surveyed, including trans membrane pressure (TMP), flow and temperature of feed, pH and concentration of wastewater. In this experiment, real wastewater was not used but synthetic starchy wastewater was prepared using starch. Two models were obtained from experimental data, capable of predicting COD removal percentage and permeate flux in different conditions. The predicted values obtained from the regression models were close to the actual ones. For the reduction of fouling, cleaning in place (CIP) method was used.     

Direct Growth and Photoluminescence of SiO<Subscript>x</Subscript> Nanowires and Aligned Nanocakes by Simple Carbothermal Evaporation

The growth of SiO_x nanowires and nanocakes on an Au-coated n-type-Silicon (100) substrate was achieved via carbothermal evaporation. The effects of the Au layer thickness and the rapid heating rate on the morphology of obtained SiO_x nanowires were investigated. A broad emission band from 290 to 600 nm was observed in the photoluminescence (PL) spectrum of these nanowires. There are four PL peaks: one blue emission peak 485 nm (2.56 eV) two green bands centered at 502 nm (2.47 eV) and 524 nm (2.37 eV) for nanocakes and one ultraviolet emission peak at 350 nm (3.54 eV) and a hemisphere curve over the bluish green area taken for SiO_x nanowires. These emissions may be related to the various oxygen defects and twofold coordinated silicon lone pair centers.     

Extraction conditions for removal of oxidized sulfur compounds in gas oil

An experimental study was conducted to investigate the extraction of oxidized sulfur compounds from gas oil. Solvents used for this purpose included acetone, acetonitrile, methanol and propanol. The effect of solvent concentration, solvent to gas oil ratio, temperature, time and number of stages was studied. To select the best solvent and conditions for extraction, two criteria were considered: high desulfurization and more hydrocarbon recovery. Results showed that extraction time and temperature have no significant effect. Methanol for low ability of extraction of oxidized sulfur compounds and propanol for low hydrocarbon recovery were excluded from further experiments. After the tests, the optimum conditions for extraction were determined to be 85% acetone, solvent/feed ratio of 1, two stages extraction in ambient temperature and enough time for mixing. In this condition 85% of sulfur compounds of gas oil containing 1,670 ppmw S were separated and 95% of gas oil was recovered.