Recrystallization of Cold Spray-Fabricated CP Titanium Structures

Cold gas dynamic spray (cold spray) is a promising rapid deposition technology in which particles deposit at supersonic velocities. The effect of isothermal annealing on recrystallization and mechanical properties of commercial purity (CP) titanium structures that were directly fabricated through cold spray deposition is studied. The optimized cold spray parameters led to a dense cold spray structure. Results show that annealing improves ductility of the cold-sprayed CP titanium structure. The mechanism for softening is the nucleation and growth of equiaxed grains, which include an ultrafine grain structure. A physical-based model for recrystallization of the cold spray CP titanium is proposed. The results show that recrystallization does not eliminate preferred orientation inherited from the cold spray material.     

Synthesis, Characterization, and Optimization of Co2SnO4 Nanoparticles via Co-precipitation Method

Nano-structured pure Co₂SnO₄ powders have been synthesized using the co-precipitation method in the presence of oleic acid (OA) as a capping agent. The Taguchi L₄ statistical design was used to investigate the effect of the main parameters (i.e., OA concentration, calcination time, and calcination temperature) on Co₂SnO₄ formation, crystallite size, and morphology. Co₂SnO₄ particles were characterized by powder x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy, scanning electron microscopy (SEM), Fourier transform of infrared spectroscopy (FT-IR), dynamic light scattering (DLS), and Brunauer-Emmett-Teller (BET) surface area measurements. The formation of small and well-crystalline particles, on the order of 41.12-90.60 nm in crystal size, has been determined from XRD patterns and confirmed by SEM and DLS. The specific surface area was measured by a BET method to be 25.43 m²/g. The particle size of the product was observed by DLS to be in the range of 40-105 nm. The results indicated that calcination temperature has the most significant effect on the produced cobalt stannate crystal size.     

Seasonal Influence on Vapor-and Particle-Phase Polycyclic Aromatic Hydrocarbon Concentrations in School Communities Located in Southern California

Ambient concentrations of 15 vapor-and particle-phase (PM _2.5 ) polycyclic aromatic hydrocarbons (PAHs), listed by the US EPA as priority pollutants, were measured between July 2002 and November 2003 in six Southern California communities participating in a multi-year chronic respiratory health study of schoolchildren. The communities were geographically distributed over two hundred kilometers, extending from Long Beach in coastal Los Angeles, to high mountain areas to the north and west of the Los Angeles basin, and south into Eastern San Diego County. Seasonal and spatial variation in the atmospheric concentrations of PAHs is of interest because this class of compounds includes potent mutagens, carcinogens, and species capable of generating reactive oxygen species (ROS) that may lead to oxidative stress. Naphthalene accounted for 95% of the total PAH mass; annual averages ranged from 89 to 142 ng m ^{? 3} . Benzo[ghi]perylene (BGP) and the pro-carcinogen benzo[a]pyrene (BAP), present almost exclusively in the particle-phase, ranged respectively from 38 to 231 pg m ^?3 and 75 and 111 pg m ^{? 3} , with the highest values observed in Long Beach, a community with a high volume of seaport-related activities, and Lancaster, a commuter dormitory community. A considerable increase in the particle-phase PAH concentration, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM _2.5 averaged 5.7, reaching 54 at Long Beach. The presented data underscore the importance of seasonal variations on atmospheric PAH concentrations. These observations are relevant to future interpretation and analysis of community-scale human health effects research.     

Novel functionalized monomers based on kojic acid: snythesis,characterization, polymerization and evalution of antimicrobial activity

Two novel acrylate monomers, [5-(benzyloxy)-4-oxo-4H-pyran-2-yl]methyl acrylate and {1-[(5-(benzyloxy)-4-oxo-4H-pyran-2-yl)methyl]-1,2,3-triazol-4-yl}methyl acrylate were synthesized by the reaction of 5-benzyloxy-2-(hydroxymethyl)-4H-pyran-4-one and 5-(benzyloxy)-2-{[4-(hydroxymethyl)-1,2,3-triazol-1-yl]methyl}-4H-pyran-4-one with acryloyl chloride in the presence of triethylamine, respectively. These monomers were polymerized using 2,2^′-azobisisobutyronitrile (AIBN) as the initiator in N,N-dimethylformamide:14-dioxane (10:1) solution. The thermal behavior of the polymers was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The synthesized compounds were evaluated for their antibacterial and antifungal activites aganist bacteria and fungi using the disk diffusion method. The results indicated that some of these compounds demonstrated moderate to good antibacterial and antifungal activities.