Solvent-particles interactions during composite particles formation by pulsed laser melting of α-Fe2O3.

This work thoroughly investigates chemical solvent-particles interactions during the formation of composite particles by pulsed laser melting of α-Fe2O3. Two solvents, with different dielectric constants, such as ethyl acetate (εr = 6) and ethanol (εr = 24.6), were examined in terms of their effect on the morphology, size, and phase composition of iron oxide composites. We calculated the laser fluence curves using the heating-melting-evaporation approach to identify the critical particle size that undergoes the phase changes first. We assessed the temperature of the particles irradiated with 390 mJ/pulse.cm2 in both solvents, including the heat dissipation between the particles and the liquid. The phase diagram of the Fe-O-C-H system was calculated to determine the temperature-pressure relationship of the system in equilibrium. We also employed an in situ GC-MS analysis to identify the volatile products during irradiation. Based on our experimental results, we concluded that the final diameter of the composites increases from 400 to 600 nm, along with the decreasing dielectric constant of the solvent, which is related to the different polarization of the organic liquid and the degree of particle agglomeration. The reduction of hematite in ethanol proceeded much faster, ending up with Fe/FeCx, while in ethyl acetate, it ended up with Fe3O4. Among all the particles, those with a diameter of 200 nm have the highest temperature and undergo the phase transition first. The temperature of a 200 nm composite particle in ethanol is slightly lower than in ethyl acetate, i.e. 1870 K as compared to 1902 K. Phase equilibrium diagrams proved the existence of Fe, FeO, and Fe3O4 as the preferred phases at about 1900 K. Our research provides a new insight into the process of submicron particle formation during pulsed laser irradiation and allows proposing a mechanism for the growth of particles of different size and phase composition depending on the solvent.

Effect of surface modification by nitrogen ion implantation on the electrochemical and cellular behaviors of super-elastic NiTi shape memory alloy.

The aim of this investigation was to enhance the biological behavior of NiTi shape memory alloy while preserving its super-elastic behavior in order to facilitate its compatibility for application in human body. The surfaces of NiTi samples were bombarded by three different nitrogen doses. Small-angle X-ray diffraction was employed for evaluating the generated phases on the bombarded surfaces. The electrochemical behaviors of the bare and surface-modified NiTi samples were studied in simulated body fluid (SBF) using electrochemical impedance and potentio-dynamic polarization tests. Ni ion release during a 2-month period of service in the SBF environment was evaluated using atomic absorption spectrometry. The cellular behavior of nitrogen-modified samples was studied using fibroblast cells. Furthermore, the effect of surface modification on super-elasticity was investigated by tensile test. The results showed the improvement of both corrosion and biological behaviors of the modified NiTi samples. However, no significant change in the super-elasticity was observed. Samples modified at 1.4E18 ion cm(-2) showed the highest corrosion resistance and the lowest Ni ion release.

Electrochemical and cellular behavior of ultrafine-grained titanium in vitro.

The electrochemical and cellular behavior of commercially pure titanium (CP-Ti) with both ultrafine-grained (UFG) and coarse-grained (CG) microstructure was evaluated in this study. Equal channel angular pressing was used to produce the UFG structure titanium. Polarization and electrochemical impedance tests were carried out in a simulated body fluid (SBF) at 37°C. Cellular behaviors of samples were assessed using fibroblast cells. Results of the investigations illustrate the improvement of both corrosion and biological behavior of UFG CP-Ti in comparison with the CG counterpart.

Optical properties and structural evaluation of Li2O-Al2O3-SiO2-TiO2 glassy semiconductor containing passive agent CeO2.

In the present work, the effect of CeO(2) as the passive agent on glassy structure of Li(2)O-Al(2)O(3)-SiO(2)-TiO(2) (LAST) material for production of a new amorphous semiconductor has been investigated. Optical properties and vibrational spectroscopy of the samples have been studied using UV-Vis and FTIR absorption spectra, respectively. Accordingly, structural variations of 0-1.5% CeO(2):LAST glasses were evaluated by calculation of density, molar volume, Urbach band tailing, direct and indirect optical band gaps, Fermi energy level and metallization criterion. Eventually for the analysis of the variation of energy level in presence of passive agent CeO(2), Licciardello's model for glassy semiconductors was utilized. Results of the investigation illustrates that while Ce(3+) ions could be regarded as the color agents due to spin allowed f-f transition, Ce(4+) ions might have a destructive influence on negative-U centers (color centers) of the glass and hence, reduce the recombination centers in the band gap of the glass.

Optical band gap and spectroscopic study of lithium alumino silicate glass containing Y3+ ions.

The effect of different amounts of Y2O3 dopant on lithium alumino silicate (LAS) glass has been studied in this work. Glasses having 14.8Li2O-20Al2O3-65.2SiO2 (wt%) composition accompanied with Y2O3 dopant were prepared by normal melting process. In order to calculate the absorption coefficient of samples, transmittance and reflectance spectra of polished samples were measured in the room temperature. Optical properties i.e. Fermi energy level, direct and indirect optical band gaps and Urbach energy were calculated using functionality of extinction coefficient from Fermi-Dirac distribution function, Tauc's plot and the exponential part of absorption coefficient diagram, respectively. It has been clarified that variation in mentioned optical parameters is associated with the changes in physical properties of samples i.e. density or molar mass. On the other hand, increasing of Y3+ ions in the glassy microstructure of samples provides a semiconducting character to LAS glass by reducing the direct and indirect optical band gaps of glass samples from 1.97 to 1.67 and 3.46 to 2.1 (eV), respectively. These changes could be attributed to the role of Y3+ ions as the network former in the track of SiO4 tetrahedrals.

Which agents cause reactive airways dysfunction syndrome (RADS)? A systematic review.

AIM: To identify those agents reported as being associated with reactive airways dysfunction syndrome (RADS). METHODS: A systematic review was undertaken. Abstracts were screened and those selected reviewed against pre-determined diagnostic criteria for RADS. RESULTS: Significant information gaps were identified for all measures of interest. In some articles, even the causative agent was not reported. The most commonly reported agents were chlorine (nine subjects), toluene di-isocyanate (TDI) (n = 6) and oxides of nitrogen (n = 5). Most exposures occurred in the workplace (n = 51) and affected men (60%). Dyspnoea (71%) and cough (65%) were the commonest symptoms. Median symptom duration was 13 months (interquartile range = 6.5-43.5) for RADS. CONCLUSIONS: Although the most commonly reported agent associated with RADS was chlorine, the main finding of a general lack of adequate information on exposure, investigation and outcome suggests that to better explore RADS a more structured approach to gathering information is required. A minimum data set for reporting RADS cases is proposed.