• 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.

• Journal of Powder Materials
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• v.16 no.1
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• pp.9-15
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• 2009

Amorphization and crystallization behaviors of $Ti_{50}Cu_{50}Ni_{20}Al_{10}$ powders during high-energy ball milling and subsequent heat treatment were studied. Full amorphization obtained after milling for 30 h was confirmed by X-ray diffraction and transmission electron microscope. The morphology of powders prepared using different milling times was observed by field-emission scanning electron microscope. The powders developed a fine, layered, homogeneous structure with prolonged milling. The crystallization behavior showed that the glass transition, $T_g$, onset crystallization, $T_x$, and super cooled liquid range ${\Delta}T=T_x-T_g$ were 691,771 and 80 K, respectively. The isothermal transformation kinetics was analyzed by the John-Mehn-Avrami equation. The Avrami exponent was close to 2.5, which corresponds to the transformation process with a diffusion-controlled type at nearly constant nucleation rate. The activation energy of crystallization for the alloy in the isothermal annealing process calculated using an Arrhenius plot was 345 kJ/mol.

• Nuclear Engineering and Technology
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• v.24 no.1
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• pp.40-51
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• 1992

One of the important irradiation performance characteristics of the silicide dispersion fuel element in research reactors is the diameteral increase resulting from fuel swelling. This paper, will attempt to develop a physical model for the fuel swelling, DFSWELL, by analyzing the basic irradiation behaviours and some experimental evidences. From the experimental evidences, it was shown that the volume changes in irradiated U$_3$Si-Al were strongly dependent on temperature and fission rate. The quantitative-amount of swelling for silicide fuel is estimated by considering temperature, fission rate, solid fission product build-up and gas bubble behavior. The swelling for the silicide fuel is comprised of three major components : i ) a volume change due to the formation of an interfacial layer between the fuel particle and matrix. ii ) a volume change due to the accumulation of gas bubble nucleation iii ) a volume change due to the accumulation of solid fission products The DFSWELL model which takes into account the above three major physical components predicts well the absolute magnitude of silicide fuel swelling in accordance with the power histories in comparison with the experimental data.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.4
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• pp.153-157
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• 2011

We have investigated the effect of inductively coupled plasma (ICP) treatment on the early growth stage of heteroepitaxial Ge layers grown on Si(100) substrates using low pressure chemical vapor deposition (LPCVD), The Si(100) substrates were treated by ICP process with various source and bias powers, followed by the Ge deposition, The ICP treatment led to the enhancement in the coalescence of Ge islands, The growth rate of Ge on Si(100) with ICP surface treatment is about 5 times higher than that without ICP surface treatment. A missing dimer caused by the ICP surface treatment can act as a nucleation site for Ge adatoms, which could be responsible for the improvement in growth behavior of Ge on Si(100) substrates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1388-1398
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• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.735-739
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• 1999

In this study we investigated stress development and shrinkage of thickness for a single $PbTiO_3$(PT) layer prepared by sol-gel processing. Changes of microhardness for multideposited PT layers with temperatures are also monitored to understand the densification of thin films. Single PT layer shrank rapidly from room temperature to$ 220^{\circ}C$ yielding 83% of total shrinkage observed up to $500^{\circ}C$. A tensile stress of ~75MPa developed in an as-spun layer, and increased steadily beyond $130^{\circ}C$ until it reaches the maximum value of 147MPa at $250^{\circ}C$. The significant decrease of tensile stress in the film beyond $370^{\circ}C$ indicates that thermal expansion mismatch between the film and the substrate dominates the stress behavior in this temperature range. Microhardness of the multideposited coatings also increased rapidly above $300^{\circ}C$ regardless of the pyrolysis temperatures used. Large amount of perovskite phase formed in multideposited coatings after $550^{\circ}C$ may be due partly to enhanced homogeneous nucleation in the thicker coating.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.673-680
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• 2000

The effect of excess PbO(0, 1, 2, 4, and 8 mol%) on grain growth and densification of (65)Pb(Mg1/3Nb2/3)O3-(35)PbTiO3 [mol%] ceramics has been investigaetd. With increasing the amount of excess PbO and sintering time, densities of sintered samples decreased gradually. The samples containing less than 1 mol% of PbO showed normal grain growth behavior, however abnormal grain growth was observed to occur in the samples with more than 2 mol% of PbO. In the samples with more than 2 mol% of PbO, the number of abnormal grains decreased and thus the average grain size became smaller with increasing the amount of excess PbO. These results demonstrated that the abnormal grain growth started to occur when a critical amount of excess PbO was added to a (65)Pb(Mg1/3Nb2/3)O3-(35)PbTiO3 sample. Since PMN-PT grains in a liquid matrix were angular, the observed abnormal grain growth was explained to proceed through the two dimensional nucleation process.

• Journal of the Korean Magnetics Society
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• v.21 no.6
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• pp.193-197
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• 2011

The thickness dependence of the magnetic switching volumes in electrodeposited CoPt films was investigated from the magnetization reversal and the magnetic interaction behavior. As the sample thickness is increased, the field difference between the wall pinning field ($H_{DW}$) and the nucleation field ($H_N$) as well as the absolute value of ${\Delta}$area are increased. Therefore, the decrement tendency of the switching diameter with increasing sample thickness can be well explained by the domain wall motion controlled by the domain wall pinning and the strength of dipolar interaction.

• Metals and materials international
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• v.24 no.6
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• pp.1394-1402
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• 2018

This study investigates the mechanism of MnS precipitation on $Al_2O_3-SiO_2$ inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized $Al_2O_3-SiO_2$ inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the $Al_2O_3$-rich regions of the $Al_2O_3-SiO_2$ inclusions; this can be explained by the high lattice disregistry between MnS and $Al_2O_3$.

• Korean Journal of Metals and Materials
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• v.46 no.9
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• pp.593-603
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• 2008

In this study, effects of alloying elements on the sticking occurring during hot rolling of five kinds of ferritic STS430J1L stainless steels were investigated by analyzing high-temperature hardness and oxidation behavior of the rolled steels. Hot-rolling simulation tests were conducted by a high-temperature wear tester which could simulate actual hot rolling. The simulation test results revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation. Since the hardness continuously decreased as the test temperature increased, whereas the formation of Fe-Cr oxides in the rolled steel surface region increased, the sticking of five stainless steels was evaluated by considering both the high-temperature hardness and oxidation effects. The addition of Zr, Cu, or Si had a beneficial effect on the sticking resistance, while the Ni addition did not show any difference in the sticking. Particularly in the case of the Si addition, Si oxides formed first in the initial stage of high-temperature oxidation, worked as initiation sites for Fe-Cr oxides, accelerated the formation of Fe-Cr oxides, and thus raised the sticking resistance by about 10 times in comparison with the steel without Si content.