Effect of Y2O3 on the crystallization kinetics of TiO2 nucleated LAS glass for the production of nanocrystalline transparent glass ceramics

Crystallization kinetics of metastable β-quartz solid solution as a desirable phase for the production of transparent lithium aluminosilicate (LAS) glass ceramics was investigated in the presence of Y₂O₃. Accordingly, differential thermal analysis scans were performed thoroughly to study the mechanism of crystallization kinetics. The aim of this investigation is to discover the complicated mechanism of crystallization process in the presence of co-additives and accordingly find a way for increasing the transparency of glass ceramics. It is shown that the bulk (3D) growth is intensively increased by the enhancement of Y₂O₃. Then again, reducing nucleation and increasing growth mechanisms were recognized for the LAS system in the presence of Y₂O₃. Results of the investigation illustrate that when co-additives are added to glasses, it is necessary to nucleate the optical component separately before the growth process.     

Evaluating the Impacts of Virtual Organization Absorption on the Quality of Urban Private Constructions; the System Dynamics Approach

Quality compliance checking of urban private constructions in Iran follows a fragmented pattern. By considering this fragmentation along with the inherent complexities of the quality compliance checking, it becomes urgent to look closer at this mechanism to find a way for making improvements. Since there is no determination to change the existing mechanism, this study discusses the use of virtual organizations as a strategy to enhance the level of quality. To this end, according to the intended approach for developing virtual organizations, this study identifies the capabilities of this type of systems in the first step. Then, this research evaluates the impacts of virtual organization absorption on the quality of urban private constructions. In this evaluation, the paper applies the system dynamics approach as the modeling tool due to its ability to address complexities and feedback structures. The resulted dynamic model needs initial values and requires functions to be able to run the simulation. In this case, the Delphi Technique is used to extract the functions and the values. After importing the resulted values and functions into the model, the focus group is used for the validation. The result of this analysis represents the positive impacts of the virtual organization absorption in the quality compliance checking mechanism. Fifty-percent improvement in the quality level of urban private constructions after a twenty-year period is one of the results, which could be considered as an indicator of virtual organization impacts.

     

Production of ultra-transparent glass-ceramics via controlled crystallization of nanocrystals in the glassy matrix of LAST

Microstructural variation in glass-ceramics encompasses the range from nanocrystalline transparent materials to microcrystalline tough materials. In this investigation, the crystallization process was controlled for the development of ultra transparent Li₂O-Al₂O₃-SiO₂ glass-ceramics containing TiO₂ as a nucleating agent (LAST). Results of UV-Vis absorption spectra were compared with the expected theoretical values calculated by the Rayleigh scattering method for the determination of ultra transparency. Results of the investigation illustrate that the control of crystallization increases the range of ultra transparency by the reduction of crystal size and their uniformity in the glassy matrix. Last but not the least, the optimized samples are ultra transparent approximately in the whole light wavelengths.     

Fabrication,microstructure, and optical properties of nanocrystalline transparent LAST glass ceramics containing CeO2

In the present research, the effect of CeO2 dopant on the fabrication of transparent lithium aluminosilicate titanate （LAST） glass ceramics was investigated. Nanocrystallineβ-quartz solid solution （s.s.） was observed to be the main phase crystallized in this system. Com-parable refractive indices of the glassy matrix andβ-quartz s.s., as well as the incorporation of very fine grains size were determined as the main reasons for retaining the transparency of the glass ceramics. CeO2 was introduced as a suitable optical agent, playing a role as a network modifier in the glass ceramics, because it does not accelerate the growth process and retards the extended growth of crystals. Optical investi-gations indicate that the Fermi energy level, direct and indirect band gaps, and Urbach energy decrease with increasing nanocrystal content in the glassy matrix of specimens, which can be related to the expansion of conduction band, the enhancement of ionic bonds in the crystal lat-tice, and the enhancement of structural arrangement degree, respectively.     

Effect of CNTs and nano ZnO on physical and mechanical properties of polyaniline composites applicable in energy devices

Polyaniline was synthesized chemically in an acidic medium in the presence of Ammonium Peroxydisulphate (APS) as an oxidizing agent. PANI(Polyaniline) nanocomposites were prepared in the presence of various amount of carbon nanotube and zinc oxide (from 1 to 5 wt%) by solution casting method. The free-standing film of polyaniline and its nanocomposites were obtained by vaporization of solvent content. The composition, morphology and structure of the polymer and the nanocomposites were characterized by Fourier transform infrared spectroscopy FT-IR spectra, scanning electron microscopy (SEM) image and XRD pattern. In addition, thermal stability was studied by TGA analysis, electrical conductivity was measured by four-point probe technique and mechanical properties were studied by tensile strength test. The characteristic FTIR peaks of PANI were found to shift to lower wave number in nanocomposites due to the formation of H-bonding. XRD results revealed that the crystallinity of PANI was more noticeable after addition of nano-ZnO, while the intensity of the peaks increased by the addition of ZnO nanoparticles. Furthermore, TGA results showed that the decomposition of the nanocomposite was less than that of pure polyaniline which confirms the successful fabrication of products. Young''s modulus and strength at break point were increased in the case of the nanocomposite, in addition, the electrical conductivity of the PANI/ZnO nanocomposite film was found to be smaller than that of the PANI film while CNTs increase the conductivity of polyaniline.