Background and Aim: Biocompatibility in some respects depends on the corrosion behavior of dental alloys. The purpose of this study was to investigate the effect of SURFACE PASSIVATION of a cobalt chromium alloy on corrosion behavior. Materials and methods: In this experimental study, 20 samples of Flexicast dental alloy were prepared according to ADA97 standard and after casting, the samples were polished to the mirror SURFACE. Electrolytic PASSIVATION was employed by immersion of one first series of samples in Na2SO4 solution for 24 hours at room temperature. The second series of specimens was not passivated. SURFACE morphology and chemical composition before and after PASSIVATION studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to investigate the corrosion behavior in saline solution. Corrosion test was conducted for 4 weeks and SURFACE of specimens were monitored each week. The chemical composition results were analyzed by Kruskal-Wallis and Mann-Whitney tests using SPSS17 software. Results: The passivated specimens exhibited higher corrosion resistance while pitting corrosion was detected in all specimens. Kruskal-Wallis test showed a significant difference between the two groups of passivated and non-passivated samples. The Mann-Whitney test showed that the cobalt, chromium and oxygen ions were significantly different between the two groups (P <. 05). Conclusion: The rate of corrosion and formation of pits were significantly reduced by SURFACE PASSIVATION.

In this research, the electronic and optical properties of the (001) SURFACE of SbNSr3 with SbSr and NSr2 terminations and SURFACE PASSIVATION impact on electronic properties were investigated. The calculations were done within density functional theory and using pseudo-potential method. HSE hybrid functional was used for exchange correlation potential. The SURFACE calculations were performed taking into account tetragonal supercell, periodic boundary conditions, sufficient vacuum and minimum force on atoms. Results of the electronic calculations show that despite the semiconducting nature of the SbNSr3 bulk, the electron states were observed near the Fermi level. The active SURFACE bonding was saturated through adsorbing hydrogen atoms on the SURFACE. Due to this, the electron states were removed and opened the band gap in both terminations. The calculated band gap of the SbSr and NSr2 terminations were calculated 0.808 and 1.029 eV, respectively. The optical properties of the SbNSr3 SURFACE were investigated without and with the SURFACE PASSIVATION. The results showed that in both terminations, the SURFACE PASSIVATION which causes the elimination of SURFACE electron states, leads to an increase in the optical gap. The calculated optical gap in both bare and passivated SURFACEs for the polarized incident light in the direction perpendicular to the SURFACE was obtained greater than in the direction parallel to the SURFACE. The optical gap of the SbSr termination was calculated to be less than that of the NSr2 termination in agreement with the results of the electronic calculations. It was also observed that the static dielectric constant at both terminations decreases with SURFACE PASSIVATION and the static dielectric constant in the z-direction is less than in the x- direction.

L-Arginine-passivated Nd3+ and Li+ co-doped CdS quantum dots (QDs) were synthesized by chemical precipitation method. Ultraviolet–visible absorption spectra of prepared QDs show absorption in the range of 477–450 nm indicating huge blue shift in energy band gap as compared to the bulk CdS due to quantum confinement effect. The optical band gap is found increasing from 2.44 to 2.97 eV as the doping concentration increased from 1 to 5 wt%. Photoluminescence spectra showed that codoped CdS QDs are highly luminescent and emit multiple intense violet (362, 371, 385, 395 nm) and blue (422, 445, 456 and 465 nm) coloured peaks with increasing intensity with co-dopant concentration. Fourier transform infrared study confirmed the interaction between CdS nanoparticles andL-arginine ligands. The structural and morphologicalstudy revealed the formation of orthorhombic crystal structure. The size of CdS QDs, as analysed by X-ray diffraction and high-resolution transmission electron microscopy, is found reducing with co-dopant concentration.The energy dispersive X-ray analysis shows no impurities present except dopants indicating high purity of the prepared samples. Based on the results, we proposed that this material is a new class of luminescent material suitable for optoelectronics devices’ application, especially in light emitting devices, electroluminescent devices and display devices.

The principal available methods for the preparation of high quality CdSe quantum dots (QDs) are based on organic ligands such as tri-n-octylphosphine oxide (TOPO) which lead to non-water soluble nanocrystal QDs. As most biological interactions take place in aqueous media, much effort has been made on preparation of water soluble QDs. In this report, the water soluble CdSe QDs were prepared via a ligand exchange process between organic soluble CdSe-TOPO quantum dots and poly (acrylic acid). The poly (acrylic acid) (PAA) can attach onto the SURFACE of CdSe-TOPO quantum dots in a ligand exchange process to make water-soluble CdSe-PAA complexes. In spite of CdSe-TOPO QDs, the resultant CdSe-PAA QDs are soluble in polar solvents such as methanol or water. Optical properties of CdSe-PAA QDs in several solvents showed that the emission intensity of QDs was mainly decreased in protic solvents such as methanol or water. The TEM images of dots in different solvents were examined and some aggregation of dots was found in protic solvents. In comparison with PAA, the addition of PDMAEMA to the solution of CdSe-TOPO QDs in THF increased the emission intensity of QDs. Furthermore, we found that the entitled ligand exchange process was fast and conjugation process completed at short time intervals. The UV-irradiation of the CdSe-PAA conjugate in water showed that the emission was amplified by increasing the irradiation time.

This work presents an investigation on the chalcopyrite leaching under different conditions, and studies the surficial characteristics of chalcopyrite using Scanning Electron Microscope (SEM) to determine the composition of the PASSIVATION layer on the SURFACE of chalcopyrite. The study of chalcopyrite dissolution was carried out in H2SO4 solution systems at pH of 1.2, with a chalcopyrite concentrate 5% in the redox potential of 460 mV at 90°C. The tests were meant to study the leaching of chalcopyrite in ferric sulfate solution to extract copper by adding pyrite, silver and silver coated pyrite. Using these approaches, the achieved recoveries were different. The results showed that in presence of pyrite, an elemental sulfur layer formed around chalcopyrite particles which hindered the complete dissolution of copper in chalcopyrite. No commercial process has been so far developed using silver as a catalyst to recover copper from chalcopyrite due to precipitation of argentojarosite which forms during the leaching process and limits the availability of silver ion as a catalyst. But, silver and pyrite assemblage to form silver coated pyrite caused an increase in dissolution. However, in presence of the pyrite coated silver, the leaching rate was very fast, and complete copper extraction was achieved within 10 hours.

Background and Aims: When composite resin polymerizes, shrinkage stresses tend to produce gaps at the tooth/ restoration interfaces. SURFACE sealants may reduce or avoid problems related to the marginal interface. The aim of this study was to evaluate the effect of two different SURFACE sealants (Fortify and Optiguard) on the microleakage of class V resin composite restorations.Materials and Methods: Twenty three sound noncarious molars were collected. Totally, 45 Class V cavities with the occlusal margins in enamel and cervical margins in cementum were prepared in both buccal and lingual SURFACEs. The specimens were randomly assigned in three groups (15 cavities in each group) and then restored with a resin composite. After the finishing and polishing procedures, the restorations in each group were covered with a specific SURFACE sealant, except for the control samples, which were not sealed. After placing restorations, the specimens were thermocycled and then immersed in a 50% silver nitrate solution (tracer agent) for four hours, sectioned longitudinally and analyzed for leakage using a stereomicroscope in a blind manner. The marginal microleakage was evaluated at the occlusal and cervical interfaces and compared among the three groups using the Kruskall-Wallis and the Mann-Whitney U tests.Results: Microleakage was found in all groups at both occlusal and cervical margins. Significantly greater leakage was observed at the cervical margins compared to the enamel margins of the material groups (P=0.005).There was no statistically significant difference among the groups at occlusal margins (P=0.66). In the cervical region, Fortify showed improved results and statistically presented the lowest degree of microleakage (P=0.003).Conclusion: The used sealant materials presented different rates of effectiveness and Fortify decreased marginal microleakage significantly.

Density functional theory and Time-dependent density functional theory (TDDFT) -based calculations were performed on SURFACE-passivated Silicon nanocrystals (SPSNs) of different sizes. The SURFACE PASSIVATION was achieved using H, F and Cl atoms. Various properties of the resulting optimized structures SinHn, Sin Hn-1F and SinHn-1Cl (n=20, 24, 26 and 28) like binding Energy, dipole moment, HOMO–LUMO gap, vibrational IR spectra and absorption wavelengths were determined. SURFACE PASSIVATION studies reveal that all the SPSNs are insulators...