Sharif Digital Repository

Formation of machinable glass-ceramic in the system MgO-SiO 2-Al2O3-K2O-B2O 3-F with and without addition of MgF2 has been investigated. Crystallization of glass sample was done by controlled thermal heat treatment at nucleation and crystallization temperatures. The results showed that MgF2 in high concentration had a synergistic effect and enhanced the formation of interlockedmica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235-405 kJ/mol, while the crystallization activation energies of samples with addition of MgF2 were changed in the range of 548-752 kJ/mol  

In this study, polypropylene/carbon nanotube nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. In this system, magnesium ethoxide and multiwall carbon nanotubes (MWCNTs) are jointly used as catalyst supports. SEM images reveal the distribution and quite good dispersion of MWCNTs throughout the polypropylene (PP) matrix. The thermal properties of the samples were examined using DSC and TGA tests. The results show that the crystallization temperature of the nanocomposites significantly increases while the melting point is not markedly affected. In addition, the thermal stability is improved. The melt rheological properties of PP/MWCNT... 

We present the preparation of polypropylene (PP)/fumed silica (FS) nanocomposites via in situ polymerization in this article. The approach includes preparation and utilization of a bisupported Ziegler-Natta catalytic system in which magnesium ethoxide and FS are used as conjugate supports of the catalyst. Catalyst preparation and polymerization processes are carried out in the slurry phase and under argon atmosphere. Scanning electron microscopy images show a good dispersion of the FS throughout the PP matrix. Results from differential scanning calorimetry reveal that the crystallization temperature of prepared nanocomposites increases by increasing FS loading. Also, crystal content of... 

Formation of transparent glass-ceramic in the system MgO-SiO 2-Al 2O 3-K 2O-B 2O 3-F with and without addition of LiF and NaF has been investigated. Crystallization of glass-sample was conducted by controlled thermal heat-treatment, at determined nucleation and crystallization temperatures. In this regard, the effects of addition of LiF and NaF were investigated on the crystallization behavior and transparency of the samples. Low transmission (less than 80% at 600. nm) was observed in the basic composition (K).The addition of NaF and LiF caused more intense phase separation in the system. The results indicated that the glass-ceramic can remain transparent if fine grains with nano size are... 

Decreasing particle size results in larger increase of external surface area and shorter diffusion path, both reducing mass and heat transfer resistances in catalysis and sorption. A rapid high-temperature hydrothermal synthesis method was developed to synthesize uniform nanoparticles of SAPO-34 zeolite with high crystallinity. To investigate the effects of temperature and synthesis time on purity and crystallinity of the final products, the crystallization temperature was increased from 468 to 673 K while the synthesis time was decreased from 24 h to 45 min. The products were characterized by XRD and SEM techniques. It was found that high temperature and short synthesis time reduce the... 

NiTiHf thin films with varying hafnium contents up to 28.7at% were fabricated using simultaneous sputter deposition from separate Ni, Ti, and Hf targets onto unheated substrates. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; and post deposition annealing was performed at 550°C, slightly above their crystallization temperatures. The crystallization temperature of the films varied as a function of Hf concentration, and was as high as 520°C at a Hf content of 28.7at%. 2μm thick crystallized films with I0at% or greater Hf were martensitic at room temperature. DSC analysis demonstrated that above 10at%Hf additions... 

SiO2-CaO-MgO glass and glass-ceramic powder doped with Nd 3+ were synthesized with sol-gel method. Tetraethylorthosilicate (TEOS), Ca(NO3)2·4H2O, Mg(NO 3)2·6H2O, Nd(NO3) 3·6H2O, ethanol, distilled water, and HNO 3 were used as starting materials. The synthesized powder's properties were examined with simultaneous thermal analysis (STA), X-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM) analysis. The STA curves showed that the softening point and crystallization temperatures were shifted to higher temperatures with increasing dopant content. Regarding XRD patterns of glass samples, Nd was found to act as an intermediate oxide in glass matrix. The XRD... 

Ultrahigh-molecular-weight polyethylene (UHMWPE)/fumed silica nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Nanocomposites with different nanoparticle weight fractions were produced in order to investigate the effect of fumed silica on thermal and mechanical properties of UHMWPE/fumed silica nanocomposites. The viscosity average molecular weight (M) of all samples including pure UHMWPE as the reference sample and nanocomposites were measured. Scanning electron microscope (SEM) images showed the homogenous dispersion of nanoparticles throughout the UHMWPE matrix while no nanoparticle cluster has been formed. Crystallization... 

MFI-type zeolite was successfully synthesized by hydrothermal crystallization of clear synthesis mixtures. A statistical experimental design method (the Taguchi method with an L8 orthogonal array) was implemented to optimize the experimental conditions for the preparation of MFI nanocrystals with respect to particle size and distribution as the desirable properties. In the Taguchi experimental design, crystallization temperature, water content, template/silica molar ratio, aluminum content, as well as the presence of alkaline cations were chosen as significant parameters affecting the properties. It was shown that water and aluminum content of the synthesis solution were the most important... 

Molecular dynamics simulations are employed to investigate material properties of nanocrystalline aluminum and nanocrystalline Al/Ni multilayers at low temperature. For this purpose, both single crystal and nanocrystalline multilayers with different grain sizes and grain morphology are used as the substrate. The results of the simulations show that hardness and elastic modulus decrease with refinement of grain size in nanocrystalline aluminum and refinement of grain size and layer thickness in nanocrystalline Al/Ni multilayers, regardless of grain morphology. Furthermore, the angle between two adjacent grains, which is directly connected to the grain boundary thickness, has a great influence... 

Low silicon content SAPO-34 was successfully synthesized using the conventional hydrothermal crystallization in the static condition. Effects of different synthesis conditions including crystallization temperature and the silicon source were investigated through X-ray diffraction patterns. It was concluded that the silicon source had a significant effect on silicon incorporation into the alumino-phosphate building blocks in the course of crystallization. Using precipitated silica instead of silica sol resulted in the formation of impurities of alumino-phosphates phases whose crystalline structures collapse at the high temperature of calcination. For the low silicon SAPO-34 synthesis, the... 

In this paper, preparation of polyethylene/clay nanocomposites (PECNC) by in situ Ziegler-Natta catalyst polymerization was investigated. A Ziegler-Natta catalyst was first supported on montmorillonite (MMT) type clay and subsequently used for polymerizing ethylene. Clay and clay supported catalyst were characterized by Fourier transmission infrared and ICP method. X-ray diffraction (XRD) and transmission electron microscopy results show that silicate layers of the mineral clay in prepared nanocomposites were intercalated and exfoliated in the polymeric matrix. Differential scanning calorimetry results show that the prepared nanocomposites have higher crystallization temperature than pure... 

In this research, ultrahigh-molecular-weight polyethylene (UHMWPE)/multiwalled carbon nanotube (MWCNT) nanocomposites with different nanotube concentrations (0.5, 1.5, 2.5, and 3.5 wt %) were prepared via in situ polymerization with a novel, bisupported Ziegler-Natta catalytic system. Magnesium ethoxide [Mg(OEt) 2] and surface-functionalized MWCNTs were used as the support of the catalyst. Titanium tetrachloride (TiCl 4) accompanied by triethylaluminum constituted the Ziegler-Natta catalytic system. Preparation of the catalyst and the polymerization were carried out in the slurry phase under an argon atmosphere. Support of the catalyst on the MWCNTs was investigated with Fourier transform... 

In this research, polypropylene (PP) nanocomposite films were prepared by melt intercalation method and their properties have been evaluated. To facilitate the formation of either intercalated or exfoliated nanocomposites, ethylene vinyl acetate copolymer (EVA) was used as a compatibiliser. Morphology of composites was determined by X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM analyses confirmed that increasing of EVA content leads to achievement of intercalated nanocomposites. Furthermore, differential scanning calorimetry (DSC) measurement indicated a decrease in crystallinity, melting point and crystallization temperature. Also, permeability tests showed... 

A new bi-supported Ziegler–Natta catalyst was prepared successfully by supporting TiCl4 on the carbon black (CB) and magnesium dichloride. Then, this catalyst was used to prepare ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites via in situ polymerization. The effects of difference molar ratios of triisobutylaluminum as activator to TiCl4, polymerization temperature, pressure of monomer and polymerization time on productivity of the catalyst were studied. The maximum activity was obtained at [Al]/[Ti] = 121:1. Increasing monomer pressure raised catalyst activity. Increasing temperature to 60 °C increased the polymerization yield; however, the higher temperature decreased the... 

Several SAPO-34 samples with different Si/Al ratio (0.05-0.5) of synthesis gel were prepared hydrothermally at crystallization temperature of 190-215 °C. The products were characterized by XRD, SEM/EDX, NH3-TPD, FT-IR and nitrogen adsorption techniques. EDX data showed a deviation of elemental composition of products with respect to the Al, Si, and P from that of the gel mixture, but the increasing trend of Si/Al ratio of the products was confirmed. According to XRD and SEM results, crystallinity of samples increased with Si/Al ratio up to the low to medium range of ca. 0.13. However, a reduction in the crystallinity was observed with further increase of the silicon content of the synthesis... 

The comparative study of Active Screen Plasma Nitriding (ASPN) treatment of two Finemet-type alloys with the compositions of Fe73.5Si 13.5B9Nb3Cu1 and Fe 77Si11B9Nb2.4Cu0.6 was investigated in different temperatures ranging from 410°C to 56°C. Differential Scanning Calorimetry (DSC), X-Ray Diffractometery (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), electrical resistivity, microhardness measurements and magnetic characterization by a Vibrating Sample Magnetometer (VSM) were utilized to characterize the treated samples. The comparison of the DSC data for the alloys suggested that the smaller amount of Nb as a growth inhibitor shifted the crystallization... 

This paper is devoted to investigation of morphological and physical-mechanical properties of polyethylene (PE)/clay nanocomposites prepared via in situ polymerization method using bi-supported Ziegler-Natta catalyst. Bentonite type clay and MgCl2 (ethoxide type) were used as the support of TiCl4. Catalyst support and polymerization process have been done in slurry phase using Triisobutylaluminum as the co-catalyst. The microstructure of the nanocomposites was examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD and TEM indicated that almost fully exfoliated PE/clay nanocomposites were produced successfully using this method. According to permeability...