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681.
Microstructure of Ordinary Portland Cement paste subjected to early age carbonation curing was studied to examine the effect of early carbonation on performance of paste at different ages. The study was intended to understand the mechanism of concrete carbonation at early age through the microstructure development of its cement paste. Early carbonation was carried out after 18-hour initial controlled air curing. The microstructure characterized by XRD, TGA, 29Si NMR and SEM was correlated to strength gain, CO2 uptake and pH change. It was found that early carbonation could accelerate early strength while allowing subsequent hydration. The short term carbonation created a microstructure with more strength-contributing solids than conventional hydration. Calcium hydroxide was converted to calcium carbonates, and calcium–silicate–hydrate became intermingled with carbonates, generating an amorphous calcium–silicate–hydrocarbonate binding phase. Carbonation modified C–S–H retained its original gel structure. The re-hydration procedure applied after carbonation was essential in increasing late strength and durability. 相似文献
682.
Zahra Moridi Mahdieh Vahid Mottaghitalab Negin Piri Akbar Khodaparast Haghi 《Korean Journal of Chemical Engineering》2012,29(1):111-119
The current study focuses on the electrospinning of chitosan (CHT)/multi walled carbon nanotubes (MWNTs) composite nanofiber
using a highly stable dispersion. The acetic acid (1–100%) and trifluoroacetic acid/dichloromethane (TFA/DCM 70: 30) was tested
as solvent, and the TFA/DCM (70 : 30) is most preferred for fiber formation process with acceptable electrospinnability. Moreover,
a new protocol was used to establish proper technique for preparation of electrospinning solution. FT-IR spectroscopy utilized
to infer the extent of interaction between CHT polymer chain and MWNT filaments. A quite simple technique was employed to
show the stability of electrospinning solution before nanofiber formation process. Scanning electronic microscope (SEM) was
employed to show the influence of spinning parameters on surface morphology of electrospun fiber. Under optimized condition,
homogeneous and beadfree CHT/MWNTs nanofibers and known physical characteristics were prepared. The formation of conducting
nanofibers based on CHT nanocomposites can be considered as a significant improvement in electrospinning of CHT/CNT dispersion.
The direct outcome of the current study includes the homogeneous CHT/MWNTs nanofibers with an average diameter of 275 nm and
a conductivity of 9×10−5 S/cm. These results are extremely important for further investigation regarding biomedical applications. 相似文献
683.
Omid Sadeghi Mostafa M. Amini Mona Feiz Bakhsh Bazargani Azadeh Mehrani Amineh Aghabali Maryam Adineh Vahid Amani Kheirollah Mehrani 《Journal of Inorganic and Organometallic Polymers and Materials》2012,22(2):530-535
Magnetic nanoparticles, Fe3O4, have been prepared and functionalized by (N-(3-(triethoxysilyl)propyl)isonicotinamide) and characterized by infrared spectroscopy, thermal analysis (TGA/DTA), X-ray
powder diffraction, scanning electron microscopy, elemental analysis and BET surface area measurement. The functionalized
Fe3O4 nanoparticles were used as a support to anchor metalloporphyrin. Application of immobilized metalloporphyrin as a heterogeneous
catalyst in the oxidation of cyclohexene was explored. Effect of various parameters such as solvent and temperature on immobilization
process and also various parameters (solvent, time, oxidant and axial group effect) on oxidation of cyclohexene has been investigated.
The result showed that the immobilized metalloporphyrin on functionalized magnetic nanoparticles is an efficient and reusable
catalyst for oxidation of cyclohexene. 相似文献
684.
Mahmood Payehghadr Vahid Safarifard Maryam Ramazani Ali Morsali 《Journal of Inorganic and Organometallic Polymers and Materials》2012,22(2):543-548
A one-dimensional Cd(II) coordination polymer containing 2-pyridinecarboxylate (2-pyc−) and iodide anions [Cd(μ-2-pyc)(μ-I)]
n
(1), is synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis and X-ray crystallography. The
single-crystal X-ray data show that the coordination number for the Cd2+ ion is five. The thermal stability of 1 was studied by thermogravimetry and differential thermal analyzes. Cd(II)O nanoparticles were prepared by direct calcination
of 1 at different temperatures. The Cd(II)O nanoparticles were characterized by X-ray powder diffraction and scanning electron
microscopy. The results show that the morphology of the Cd(II)O nanoparticles is dependent upon the thermolysis temperature. 相似文献
685.
Khezrollah Khezri Vahid Haddadi-Asl Hossein Roghani-Mamaqani Mehdi Salami-Kalajahi 《Journal of Polymer Research》2012,19(5):9868
Encapsulation of organomodified montmorillonite within poly (methyl methacrylate) via in situ atom transfer radical polymerization
with simultaneous reverse and normal initiation system (SR&NI ATRP) was successfully performed. Miniemulsion polymerization
technique has been employed for its abundant advantages to encapsulate inorganic materials. Successful SR&NI ATRP was carried
out using 4,4′-dinonyl-2,2′-bipyridine (dNbPy) as a hydrophobic ligand and cetyltrimethylammonium bromide (CTAB) as an effective
cationic surfactant at high temperatures. Homogeneous distribution of droplets and particles with sizes in the range of around
170 nm was evaluated by dynamic light scattering (DLS) analysis. Final monomer conversion and molecular weight were determined
by gravimetry and size exclusion chromatography (SEC) respectively. By increasing nanoclay content, conversion and molecular
weight of nanocomposites decreased. Meanwhile, an increase in PDI values was also observed. X-ray diffraction (XRD) analysis
results display organoclay layers disordered and delaminated in the polymer matrix. Thermal stability improvement of all the
nanocomposites in comparison with the neat polymer was revealed by thermogravimetric analysis (TGA). Homogeneous distribution
of spherical particles with sizes in the range of 170 nm was demonstrated by scanning electron microscopy (SEM) images. These
results are complied with the DLS results. Transmission electron microscopy (TEM) image display a dispersion of partially
exfoliated clay stacks in the matrix of PMNM 2. 相似文献
686.
Leila Ahmadian-Alam Vahid Haddadi-Asl Hossein Roghani-Mamaqani Leila Hatami Mehdi Salami-Kalajahi 《Journal of Polymer Research》2012,19(1):9773-12
Atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) was employed to synthesize
well-defined poly (styrene-co-butyl acrylate)/clay nanocomposites. Dodecyltrimethylammonium bromide (DDTMAB) and Vinylbenzyltrimethylammonium
chloride (VBTMAC) surfactants were used as clay modifier. The classical surfactant is used to expand the interlayer gallery
of montmorillonite; however, double bond of reactive modifier participates in chain propagation process and forms clay-attached
polymer chains. Subsequently synthesis of attached and free poly (styrene-co-butyl acrylate) chains and their composition
was confirmed by Fourier-transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR). Narrow distribution of nanocomposites molecular weight was confirmed by gel permeation chromatography (GPC). Partially
exfoliated clay layers in the copolymer matrix were revealed by X-ray diffraction (XRD) and transmission electron microscopy
(TEM). Thermal properties of the nanocomposites were evaluated by differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA). Thermal decomposition of the nanocomposites was hindered in the presence of nanoclay. Dynamic mechanical thermal
analysis (DMTA) results show that addition of nanoclay was also resulted in enhanced storage modulus (E′) in comparison with
the neat copolymer. Lower glass transition temperature of nanocomposites was displayed by DSC. 相似文献
687.
Liquid–liquid extraction process with the recommended low interfacial tension chemical system of butanol–succinic acid–water was performed in a two impinging-jets contacting device (TIJCD), working continuously with opposed impinging jets. A range of extraction efficiency of 58–96% was achieved under different conditions. Overall volumetric mass transfer coefficient and specific power input criteria clearly indicate the great performance capability of TIJCD. An increase in nozzle diameter and/or jets force results an efficiency enhancement, while increase in inter-nozzle distance leads the efficiency diminish. The overall volumetric mass transfer coefficient was satisfactorily correlated in the form of ordinary and dimensionless correlations. 相似文献
688.
Khezrollah Khezri Vahid Haddadi‐Asl Hossein Roghani‐Mamaqani Mehdi Salami‐Kalajahi 《应用聚合物科学杂志》2012,124(3):2278-2286
Poly(styrene‐co‐methyl methacrylate) nanocomposites were synthesized using reverse atom transfer radical polymerization (RATRP) in miniemulsion. Cetyltrimethylammonium bromide (CTAB) as a cationic surfactant applicable at higher temperatures was used for miniemulsion stabilization. Successful RATRP was carried out by using 4,4′‐dinonyl‐2,2′‐bipyridine (dNbPy) as ligand. Monodispersed droplets and particles with sizes in the range of 200 nm were revealed by dynamic light scattering (DLS). Conversion and molecular weight study was carried out using gravimetry and size exclusion chromatography (SEC) respectively. By adding clay content, a decrease in the conversion and molecular weight and an increase in the PDI value of the nanocomposites are observed. Thermal stability of the nanocomposites in comparison with the neat copolymer is revealed by thermogravimetric analysis (TGA). Increased Tg values by adding clay content was also obtained using differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) images of the nanoconposite with 1 wt % of nanoclay loading, display monodispersed spherical particles with sizes in the range of ~ 200 nm. SEM findings are more compiled with dynamic light scattering (DLS) results. Well‐dispersed exfoliated clay layers in the polymer matrix of the nanocomposite with 1 wt % nanoclay loading is confirmed by transmission electron microscopy (TEM) images and X‐ray diffraction (XRD) data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
689.
Mehdi Salami‐Kalajahi Vahid Haddadi‐Asl Farid Behboodi‐Sadabad Saeid Rahimi‐Razin Hossein Roghani‐Mamaqani 《Polymer Composites》2012,33(2):215-224
A number of batch polymerizations were performed to study the effect of multi‐walled carbon nanotubes (MWCNTs) on the properties of PMMA/MWCNTs nanocomposites. To improve the dispersion of nanotubes in PMMA matrix, MWCNTs were functionalized with methacrylate groups via a four‐step modification process and the modified nanoparticles were used to synthesize the nanocomposites. The prepared samples were characterized by Raman spectroscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, gel permeation chromatography, UV–visible, and TEM techniques. According to the results, modified nanotubes improved thermal and mechanical properties better than the pristine MWCNTs. The main improvement in the mechanical and thermophysical properties was achieved for the nanocomposite containing 0.5 wt% of MWCNTs. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers 相似文献
690.
Vahid Garousi 《Software Testing, Verification and Reliability》2011,21(2):101-124
In a previous article, a stress testing methodology was reported to detect network traffic‐related Real‐Time (RT) faults in distributed RT systems based on the design UML model of a System Under Test (SUT). The stress methodology, referred to as Test LOcation‐driven Stress Testing (TLOST), aimed at increasing the chances of RT failures (violations in RT constraints) associated with a given stress test location (an network or a node under test). As demonstrated and experimented in this article, although TLOST is useful in stress testing different test locations (nodes and network, it does not guarantee to target (test) all RT constraints in an SUT. This is because the durations of message sequences bounded by some RT constraints might never be exercised (covered) by TLOST. A complementary stress test methodology is proposed in this article, which guarantees to target (cover) all RT constraints in an SUT and detect their potential RT faults (if any). Using a case study, this article shows that the new complementary methodology is capable of targeting the RT faults not detected by the previous test methodology. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献