• Computers and Concrete
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• v.8 no.6
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• pp.647-675
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• 2011

Our ability to predict hydration behavior is becoming increasingly relevant to the concrete community as modelers begin to link material performance to the dynamics of material properties and chemistry. At early ages, the properties of concrete are changing rapidly due to chemical transformations that affect mechanical, thermal and transport responses of the composite. At later ages, the resulting, nano-, micro-, meso- and macroscopic structure generated by hydration will control the life-cycle performance of the material in the field. Ultimately, creep, shrinkage, chemical and physical durability, and all manner of mechanical response are linked to hydration. As a way to enable the modeling community to better understand hydration, a review of hydration models is presented offering insights into their mathematical origins and relationships one-to-the-other. The quest for a universal model begins in the 1920's and continues to the present, and is marked by a number of critical milestones. Unfortunately, the origins and physical interpretation of many of the most commonly used models have been lost in their overuse and the trail of citations that vaguely lead to the original manuscripts. To help restore some organization, models were sorted into four categories based primarily on their mathematical and theoretical basis: (1) mass continuity-based, (2) nucleation-based, (3) particle ensembles, and (4) complex multi-physical and simulation environments. This review provides a concise catalogue of models and in most cases enough detail to derive their mathematical form. Furthermore, classes of models are unified by linking them to their theoretical origins, thereby making their derivations and physical interpretations more transparent. Models are also used to fit experimental data so that their characteristics and ability to predict hydration calorimetry curves can be compared. A sort of evolutionary tree showing the progression of models is given along with some insights into the nature of future work yet needed to develop the next generation of cement hydration models.

• Steel and Composite Structures
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• v.28 no.5
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• pp.589-606
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• 2018

The previous studies reflected the significant effect of neutral-axis position and coupling of in-plane and out-of-plane displacements on behavior of functionally graded (FG) nanobeams. In thin FG beam, this coupling can be eliminated by a proper choice of the reference axis. In shear deformable FG nanobeam, not only this coupling can't be eliminated but also the position of neutral-axis is dependent on through-thickness distribution of shear strain. For the first time, in this paper it is avoided to guess a shear strain shape function and the exact shape function and consequently the exact position of neutral axis for arbitrary gradation of higher order nanobeam are obtained. This paper presents new methodology based on differential transform and collocation methods to solve coupled partial differential equations of motion without any simplifications. Using exact position of neutral axis and higher order beam kinematics as well as satisfying equilibrium equations and traction-free conditions without shear correction factor requirement yields to better results in comparison to the previously published results in literature. The classical rule of mixture and Mori-Tanaka homogenization scheme are considered. The Eringen's nonlocal continuum theory is applied to capture the small scale effects. For the first time, the dependency of exact position of neutral axis on length to thickness ratio is investigated. The effects of small scale, length to thickness ratio, Poisson's ratio, inhomogeneity of materials and various end conditions on vibration and buckling of local and nonlocal FG beams are investigated. Moreover, the effect of axial load on natural frequencies of the first modes is examined. After degeneration of the governing equations, the exact new formulas for homogeneous nanobeams are computed.

• Journal of Powder Materials
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• v.12 no.4 s.51
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• pp.279-283
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• 2005

In this study, the ZnS composite powders for host material in phosphor was synthesized in situ by mechanical alloying. As the mechanical alloying time increases, particle size of ZnS decreases. ZnS powders of $1.85\;\mu{m}$ in a mean size was fabricated by mechanical alloying for 10h. The crystal structures of ZnS powders were investigated by X-ray diffraction and the photo-luminescence properties was evaluated with the optical spectra analyzer. The steady state condition of mechanically alloyed ZnS was obtained as a mean particle size of $2\;\mu{m}$ in 5h milling. The sphalerite and wurtize structures coexist in the ZnS mechanically alloyed for 5h. The ZnS powder mechanically alloyed for 10h grows to the sphalerite structure. And the strong emission peaks of ZnS are observed at 480 nm wave length at the powders of mechanically alloyed for 10h, but the sphalerite and wurtize structures in ZnS coexist and emission peaks are not appeared at the powders of mechanically alloyed for 10h.

• Elastomers and Composites
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• v.46 no.2
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• pp.112-117
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• 2011

Recently, high growth potential of barrier materials industry including high performance packing materials was expected with increasing the national income and well-being culture. As high barrier materials, polymer nanocomposites have considerable attractions due to their excellent physical properties compared to conventional composite materials. In general, polymer nanocomposites were consisted of polymer matrix and inorganic fillers, such as layered silicate, carbon nanotubes, and metal- or inorganic nanoparticles. Among these materials, layered silicate which was called as the clay was usually used as nano-fillers because of naturally abundant and most economical and structural properties. Clay-reinforced polymer nanocomposites have various advantages, such as high strength, flammability, gas barrier property, abrasion resistance, and low shrinkage and used for automotive and packing materials. Therefore, in this paper, we focused on the need of gas barrier materials and materials-related technologies.

• Korean Journal of Materials Research
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• v.20 no.9
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• pp.472-477
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• 2010

$Al_2O_3$ has received wide attention with established use as a catalyst and growing application in structural or functional ceramic materials. On the other hand, the boehmite (AlO(OH)) obtained by sol-gel process has exhibited a decrease in surface area during phase transformation due to a decline in surface active site at high temperature. In this work, $Al_2O_3$-CuO/ZnO (ACZ) and $Al_2O_3$-CuO/CeO (ACC) composite materials were synthesized with aluminum isopropoxide, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate or zinc (II) nitrate hexahydrate. Moreover, the Span 80 as the template block copolymer was added to the ACZ/ACC composition to make nano size particles and to keep increasing the surface area. The ACZ/ACC synthesized powders were characterized by Thermogravimetry-Differential Thermal analysis (TG/DTA), X-ray Diffractometer (XRD), Field-Emmision Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller (BET) surface analysis and thermal electrical conductivity (ZEM-2:M8/L). An enhancement of surface area with the addition to Span 80 surfactant was observed in the ACZ powders from 105 $m^2$/g to 142 $m^2$/g, and the ACC powders from 103 $m^2$/g to 140 $m^2$/g, respectively.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.64-69
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• 2009

In the present study the effect of cooling rate during solidification on the microstructural characteristics of Al-xAg (x = 31, 33, 35 at.%) in-situ binary eutectic composites has been investigated. To provide a wide range of cooling rate three different casting techniques, i.e. conventional casting, injection casting, and melt spinning have been used. The observed microstructure is very much dependent on the cooling rate. The fcc ${\alpha}$-Al and hcp $Ag_2Al$ phases exhibits an orientation of (111)Al//(0001)$Ag_2Al$, [1-10]Al//[11- 20]$Ag_2Al$. The microstructure of the melt-spun samples contains Widmanstatten structure resulting from solid-state transformation and nano scale two-phase structure resulting from solid-state phase separation. The microstructure of injection-cast samples contains eutectic structure and solid state phase-separated structure. On the other hand, conventional-cast samples exhibit a microstructure consisted of plate-type eutectic structure.

• Composites Research
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• v.32 no.6
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• pp.388-394
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• 2019

Inherited the excellent electrical and mechanical properties based on the low dimensional structure of graphene, three-dimensional graphene nanostructures have gathered great attention as electrochemical energy storage electrodes owing to their high porosity and large specific surface area. Also, having the catecholamine structure, dopamine has been regarded as a multifunctional material to possess high affinity to various organic/inorganic materials and to modify a hydrophobic surface to a hydrophilic one. In this work, through coating dopamine on the three-dimensional graphene nanostructure, we tried to increase the specific capacitance by enhancing the wettability with electrolyte and to improve the mechanical compressive property by strengthening the nano-architecture. As a result, the dopamine-coated nanostructure exhibited significant improvement on the specific capacitance (51.5% increase) and compressive stress (59.6% increase).

• Molecular & Cellular Toxicology
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• v.5 no.2
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• pp.172-178
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• 2009

Nanoparticles are small-scale substances (<100 nm) with unique properties, complex exposure and health risk implications. Aluminum oxide ($Al_2O_3$) nanoparticles (NP) have been widely used as abrasives, wear-resistant coatings on propeller shafts of ships, to increase the specific impulse per weight of composite propellants used in solid rocket fuel and as drug delivery systems to increase solubility. However, recent studies have shown that nano-sized aluminum (10 nm in diameter) can generate adverse effects, such as pulmonary response. The cytotoxicity and genotoxicity of $Al_2O_3$ NP were investigated using the dye exclusion assay, the comet assay, and the mouse lymphoma thymidine kinase (tk$^{+/-}$) gene mutation assay (MLA). IC$_{20}$ values of $Al_2O_3$ NP in BEAS-2B cells were determined the concentration of 273.44 $\mu$g/mL and 390.63 $\mu$g/mL with and without S-9. However IC$_{20}$ values of $Al_2O_3$ NP were found nontoxic in L5178Y cells both of with and without S-9 fraction. In the comet assay, L5178Y cells and BEAS-2B cells were treated with $Al_2O_3$ NP which significantly increased 2-fold tail moment with and without S-9. Also, the mutant frequencies in the $Al_2O_3$ NP treated L5178Y cells were increased compared to the vehicle controls with S-9. The results of this study indicate that $Al_2O_3$ NP can cause primary DNA damage and cytotoxicity but not mutagenicity in cultured mammalian cells.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.91-96
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• 2013

The present paper focuses on the fabrication of materials with higher thermal conductivity. Nanofluid is a novel transfer prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. The purpose of this study is making the nano-size particle. The experiment of MWCNT and $Al_2O_3$ was carried out using a planetary ball mill at several rotation speeds: 200 ~ 400 rpm. The results were examined using scanning electron microscope(SEM). In the case of the MWCNT, it could be more grinding into the small particle in the dry condition and it confirm in the case of the $Al_2O_3$ to be more grinding into the small particle contrary to the MWCNT in the wet condition. In the mixture grinding result of MWCNT and $Al_2O_3$, the dry condition showed the good result in low rotation speed than the wet condition.

• Journal of Magnetics
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• v.20 no.4
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• pp.353-359
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• 2015

Dielectric properties of $xBaTiO_3-(1-x)CoFe_2O_4$ composite materials have been investigated. Dielectric properties of $BaTiO_3$, $CoFe_2O_4$ and $0.5BaTiO_3-0.5CoFe_2O_4$ samples show frequency dependence, which is classified as relaxor behavior with different relaxing degree. The relaxor behaviors were described using the modified Curier-Weiss and Vogel-Fulcher laws. Among three above samples, the $BaTiO_3$ sample has highest relaxing degree. Photoluminescence spectral indicated defects, which might in turn control relaxing degree.