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Crystals, Volume 7, Issue 10 (October 2017)

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Cover Story (view full-size image) Quasicrystal dynamics and growth are guided by the non-local empires—tiles forced by certain local [...] Read more.
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Open AccessArticle FOX, Current State and Possibilities
Crystals 2017, 7(10), 322; https://doi.org/10.3390/cryst7100322
Received: 15 August 2017 / Revised: 25 September 2017 / Accepted: 13 October 2017 / Published: 24 October 2017
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Abstract
FOX (Free Objects for Xtallography) is a computer program for solving crystal structures of all types of compounds using the powder data (but also the single crystal data) measured using X-ray, neutron and electron diffraction. It works in direct space using the reversed
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FOX (Free Objects for Xtallography) is a computer program for solving crystal structures of all types of compounds using the powder data (but also the single crystal data) measured using X-ray, neutron and electron diffraction. It works in direct space using the reversed Monte Carlo algorithm of global optimization. Since its release fifteen years ago, it has developed into a powerful tool, simplifying the powder pattern analysis starting from the background determination, indexing and space group selection over the structure modelling using various pre-programmed structural fragments up to the validation of the proposed structural model. Full article
(This article belongs to the Special Issue Structural Analysis of Crystalline Materials from Powders)
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Open AccessReview Review of Nanoindentation Size Effect: Experiments and Atomistic Simulation
Crystals 2017, 7(10), 321; https://doi.org/10.3390/cryst7100321
Received: 26 September 2017 / Revised: 17 October 2017 / Accepted: 20 October 2017 / Published: 23 October 2017
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Abstract
Nanoindentation is a well-stablished experiment to study the mechanical properties of materials at the small length scales of micro and nano. Unlike the conventional indentation experiments, the nanoindentation response of the material depends on the corresponding length scales, such as indentation depth, which
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Nanoindentation is a well-stablished experiment to study the mechanical properties of materials at the small length scales of micro and nano. Unlike the conventional indentation experiments, the nanoindentation response of the material depends on the corresponding length scales, such as indentation depth, which is commonly termed the size effect. In the current work, first, the conventional experimental observations and theoretical models of the size effect during nanoindentation are reviewed in the case of crystalline metals, which are the focus of the current work. Next, the recent advancements in the visualization of the dislocation structure during the nanoindentation experiment is discussed, and the observed underlying mechanisms of the size effect are addressed. Finally, the recent computer simulations using molecular dynamics are reviewed as a powerful tool to investigate the nanoindentation experiment and its governing mechanisms of the size effect. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness) Printed Edition available
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Open AccessArticle Formation Mechanism of CaCO3 Spherulites in the Myostracum Layer of Limpet Shells
Crystals 2017, 7(10), 319; https://doi.org/10.3390/cryst7100319
Received: 14 August 2017 / Revised: 16 October 2017 / Accepted: 16 October 2017 / Published: 23 October 2017
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Abstract
CaCO3 spherulites were found in the myostracum layer of common limpet shells collected from East Sands, St Andrews, Scotland. Their microstructures were revealed by using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray microanalysis. The formation
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CaCO3 spherulites were found in the myostracum layer of common limpet shells collected from East Sands, St Andrews, Scotland. Their microstructures were revealed by using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray microanalysis. The formation mechanisms of these spherulites and their morphology evolution were postulated. It was proposed that spherical particles of an inorganic and biological composite formed first. In the centre of each spherical particle a double-layer disk of vaterite crystal sandwiching a biological sheet developed. The disk crystal supplies a relatively strong mirror symmetric dipole field, guiding the orientations of the nanocrystallites and the arrangement of mesorods and, therefore, determining the final morphology of the spherulite. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of [(µ2-dppm)2Cu22-BH4)2] Dichloromethane Solvate
Crystals 2017, 7(10), 318; https://doi.org/10.3390/cryst7100318
Received: 18 September 2017 / Revised: 13 October 2017 / Accepted: 17 October 2017 / Published: 20 October 2017
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Abstract
Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu22-BH4)2], and crystallizes
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Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu22-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. The rare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. Full article
(This article belongs to the Special Issue Crystal Structures of Boron Compounds)
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Open AccessReview Heterojunctions Based on II-VI Compound Semiconductor One-Dimensional Nanostructures and Their Optoelectronic Applications
Crystals 2017, 7(10), 307; https://doi.org/10.3390/cryst7100307
Received: 1 August 2017 / Revised: 29 September 2017 / Accepted: 10 October 2017 / Published: 20 October 2017
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Abstract
Wide band gap II-VI semiconductor nanostructures have been extensively studied according to their great potentials for optoelectronic applications, while heterojunctions are fundamental elements for modern electronic and optoelectronic devices. Subsequently, a great deal of achievements in construction and optoelectronic applications of heterojunctions based
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Wide band gap II-VI semiconductor nanostructures have been extensively studied according to their great potentials for optoelectronic applications, while heterojunctions are fundamental elements for modern electronic and optoelectronic devices. Subsequently, a great deal of achievements in construction and optoelectronic applications of heterojunctions based on II-VI compound semiconductor one-dimensional nanostructures have been obtained in the past decade. Herein, we present a review of a series of progress in this field. First, construction strategies towards different types of heterojunctions are reviewed, including core-shell heterojunctions, one-dimensional axial heterojunctions, crossed nanowires heterojunctions, and one-dimensional nanostructure/thin film or Si substrate heterojunctions. Secondly, optoelectronic applications of these constructed heterojunctions, such as photodetectors, solar cells, light emitting diodes, junction field effect transistors, etc., are discussed briefly. This review shows that heterojunctions based on II-VI compound semiconductor 1-D nanostructures have great potential for future optoelectronic applications. Full article
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Open AccessArticle Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements
Crystals 2017, 7(10), 317; https://doi.org/10.3390/cryst7100317
Received: 22 September 2017 / Revised: 12 October 2017 / Accepted: 17 October 2017 / Published: 18 October 2017
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Abstract
The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement
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The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement pastes. Here, we use the synchrotron pair distribution function (PDF) chiefly to characterize the local atomic order of the nanocrystalline phases, gels, in cement pastes. We have used a multi r-range analysis approach, where the ~4–7 nm r-range allows determining the crystalline phase contents; the ~1–2.5 nm r-range is used to characterize the atomic ordering in the nanocrystalline component; and the ~0.2–1.0 nm r-range gives insights about additional amorphous components. Specifically, we have prepared four alite pastes with variable water contents, and the analyses showed that a defective tobermorite, Ca11Si9O28(OH)2.8.5H2O, gave the best fit. Furthermore, the PDF analyses suggest that the calcium silicate hydrate gel is composed of this tobermorite and amorphous calcium hydroxide. Finally, this approach has been used to study alternative cements. The hydration of monocalcium aluminate and ye’elimite pastes yield aluminum hydroxide gels. PDF analyses show that these gels are constituted of nanocrystalline gibbsite, and the particle size can be as small as 2.5 nm. Full article
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Open AccessArticle Phase Transformation and Hydrogen Storage Properties of an La7.0Mg75.5Ni17.5 Hydrogen Storage Alloy
Crystals 2017, 7(10), 316; https://doi.org/10.3390/cryst7100316
Received: 25 September 2017 / Revised: 9 October 2017 / Accepted: 16 October 2017 / Published: 18 October 2017
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Abstract
X-ray diffraction showed that an La7.0Mg75.5Ni17.5 alloy prepared via inductive melting was composed of an La2Mg17 phase, an LaMg2Ni phase, and an Mg2Ni phase. After the first hydrogen absorption/desorption process, the
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X-ray diffraction showed that an La7.0Mg75.5Ni17.5 alloy prepared via inductive melting was composed of an La2Mg17 phase, an LaMg2Ni phase, and an Mg2Ni phase. After the first hydrogen absorption/desorption process, the phases of the alloy turned into an La–H phase, an Mg phase, and an Mg2Ni phase. The enthalpy and entropy derived from the van’t Hoff equation for hydriding were −42.30 kJ·mol−1 and −69.76 J·K−1·mol−1, respectively. The hydride formed in the absorption step was less stable than MgH2 (−74.50 kJ·mol−1 and −132.3 J·K−1·mol−1) and Mg2NiH4 (−64.50 kJ·mol−1 and −123.1 J·K−1·mol−1). Differential thermal analysis showed that the initial hydrogen desorption temperature of its hydride was 531 K. Compared to Mg and Mg2Ni, La7.0Mg75.5Ni17.5 is a promising hydrogen storage material that demonstrates fast adsorption/desorption kinetics as a result of the formation of an La–H compound and the synergetic effect of multiphase. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions
Crystals 2017, 7(10), 315; https://doi.org/10.3390/cryst7100315
Received: 22 September 2017 / Revised: 14 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
The mechanical strengths of nano-scale individual crystal or nanopolycrystalline metals, and other dimensionally-related materials are increased by an order of magnitude or more as compared to those values measured at conventional crystal or polycrystal grain dimensions. An explanation for the result is attributed
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The mechanical strengths of nano-scale individual crystal or nanopolycrystalline metals, and other dimensionally-related materials are increased by an order of magnitude or more as compared to those values measured at conventional crystal or polycrystal grain dimensions. An explanation for the result is attributed to the constraint provided at the surface of the crystals or, more importantly, at interfacial boundaries within or between crystals. The effect is most often described in terms either of two size dependencies: an inverse dependence on crystal size because of single dislocation behavior or, within a polycrystalline material, in terms of a reciprocal square root of grain size dependence, designated as a Hall-Petch relationship for the researchers first pointing to the effect for steel and who provided an enduring dislocation pile-up interpretation for the relationship. The current report provides an updated description of such strength properties for iron and steel materials, and describes applications of the relationship to a wider range of materials, including non-ferrous metals, nano-twinned, polyphase, and composite materials. At limiting small nm grain sizes, there is a generally minor strength reversal that is accompanied by an additional order-of-magnitude elevation of an increased strength dependence on deformation rate, thus giving an important emphasis to the strain rate sensitivity property of materials at nano-scale dimensions. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors
Crystals 2017, 7(10), 314; https://doi.org/10.3390/cryst7100314
Received: 20 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
Liquid crystal (LC) is a promising candidate for terahertz (THz) devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual
[...] Read more.
Liquid crystal (LC) is a promising candidate for terahertz (THz) devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual component. Thus, a separating process is indispensable. Here, we introduce a gradient blazed phase, and propose a THz LC forked polarization grating that can simultaneously generate and separate pure THz vortices with opposite circular polarization. The specific LC gradient-rotation directors are implemented by a photoalignment technique. The generated THz vortex beams are characterized with a THz imaging system, verifying features of polarization controllability. This work may pave a practical road towards generating, separating and polarizing THz vortex beams, and may prompt applications in THz communications, sensing and imaging. Full article
(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment)
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Open AccessArticle Optical Characterization of AlAsSb Digital Alloy and Random Alloy on GaSb
Crystals 2017, 7(10), 313; https://doi.org/10.3390/cryst7100313
Received: 9 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been
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III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study. Full article
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Open AccessArticle Preparation of Potassium Dichromate Crystals from the Chromite Concentrate by Microwave Assisted Leaching
Crystals 2017, 7(10), 312; https://doi.org/10.3390/cryst7100312
Received: 28 August 2017 / Revised: 10 October 2017 / Accepted: 11 October 2017 / Published: 18 October 2017
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Abstract
In the present investigation, the oxidizing roasting process of chromite with sodium carbonate to prepare potassium dichromate crystals was studied in the microwave field with air, by heating the chromite and sodium carbonate. The chromite and sodium carbonate heated separately at 1000 °C
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In the present investigation, the oxidizing roasting process of chromite with sodium carbonate to prepare potassium dichromate crystals was studied in the microwave field with air, by heating the chromite and sodium carbonate. The chromite and sodium carbonate heated separately at 1000 °C in the microwave oven (frequency: 2.45 GHz; power 1.5 kW) in order to study the microwave absorption properties. The dielectric constant and dielectric loss factor of the chromite and sodium carbonate examined. Then, chromite with sodium carbonate taken in (1:2) ratio and heated at 750 °C. Thus obtained samples were characterized using various techniques includes Powder-XRD (XRD), Scanning Electron Microscopy (SEM), and X-ray fluorescence (XRF). The XRD pattern reveals the existence of Fe3O4, Fe2O3, NaAlO2, and Na2CrO4. The iron and aluminum were leached out as Fe2O3 and Al(OH)3 respectively. The resulting sample treated with the KCl to prepare potassium dichromate crystals. Finally, potassium dichromate crystals formed. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Breathing 3D Frameworks with T-Shaped Connecting Ligand Exhibiting Solvent Induction, Metal Ions Effect and Luminescent Properties
Crystals 2017, 7(10), 311; https://doi.org/10.3390/cryst7100311
Received: 18 August 2017 / Revised: 6 October 2017 / Accepted: 13 October 2017 / Published: 17 October 2017
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Abstract
To study the structural effects in three-dimensional porous coordination polymers, three novel flexible porous coordination polymers—[Cd2(bpdc)2](DMF)3(H2O) (1) and [M(bpdc)](DMF)(H2O) (M = Cd (2), Zn (3))—have been synthesized
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To study the structural effects in three-dimensional porous coordination polymers, three novel flexible porous coordination polymers—[Cd2(bpdc)2](DMF)3(H2O) (1) and [M(bpdc)](DMF)(H2O) (M = Cd (2), Zn (3))—have been synthesized under solvothermal conditions with d10 block metal ions and T-shaped connecting ligand. Complexes 13 crystallize in different space groups, but they display the same ant network. The first two complexes can transform into each other via the alteration of guest, whereas complex 3 shows no structural change. The structural details reveal that the size of metal ions might be responsible for the transformation of porous frameworks. Furthermore, luminescent properties have been explored, and a guest-dependent shift of emission peaks was observed, suggesting potential application of the complexes as a probe. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessReview Recent Insights into the Crystallization Process; Protein Crystal Nucleation and Growth Peculiarities; Processes in the Presence of Electric Fields
Crystals 2017, 7(10), 310; https://doi.org/10.3390/cryst7100310
Received: 22 September 2017 / Revised: 11 October 2017 / Accepted: 12 October 2017 / Published: 15 October 2017
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Abstract
Three-dimensional protein molecule structures are essential for acquiring a deeper insight of the human genome, and for developing novel protein-based pharmaceuticals. X-ray diffraction studies of such structures require well-diffracting protein crystals. A set of external physical factors may promote and direct protein crystallization
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Three-dimensional protein molecule structures are essential for acquiring a deeper insight of the human genome, and for developing novel protein-based pharmaceuticals. X-ray diffraction studies of such structures require well-diffracting protein crystals. A set of external physical factors may promote and direct protein crystallization so that crystals obtained are useful for X-ray studies. Application of electric fields aids control over protein crystal size and diffraction quality. Protein crystal nucleation and growth in the presence of electric fields are reviewed. A notion of mesoscopic level of impact on the protein crystallization exercised by an electric field is also considered. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessReview Challenges of Handling, Processing, and Studying Liquid and Supercooled Materials at Temperatures above 3000 K with Electrostatic Levitation
Crystals 2017, 7(10), 309; https://doi.org/10.3390/cryst7100309
Received: 13 July 2017 / Revised: 13 September 2017 / Accepted: 12 October 2017 / Published: 15 October 2017
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Abstract
Over the last 20 years, great progress has been made in techniques for electrostatic levitation, with innovations such as containerless thermophysical property measurements and combination of levitators with synchrotron radiation source and neutron beams, to name but a few. This review focuses on
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Over the last 20 years, great progress has been made in techniques for electrostatic levitation, with innovations such as containerless thermophysical property measurements and combination of levitators with synchrotron radiation source and neutron beams, to name but a few. This review focuses on the technological developments necessary for handling materials whose melting temperatures are above 3000 K. Although the original electrostatic levitator designed by Rhim et al. allowed the handling, processing, and study of most metals with melting points below 2500 K, several issues appeared, in addition to the risk of contamination, when metals such as Os, Re, and W were processed. This paper describes the procedures and the innovations that made successful levitation and the study of refractory metals at extreme temperatures (>3000 K) possible; namely, sample handling, electrode design (shape and material), levitation initiation, laser heating configuration, and UV range imaging. Typical results are also presented, putting emphasis on the measurements of density, surface tension, and viscosity of refractory materials in their liquid and supercooled phases. The data obtained are exemplified by tungsten, which has the highest melting temperature among metals (and is second only to carbon in the periodic table), rhenium and osmium. The remaining technical difficulties such as temperature measurement and evaporation are discussed. Full article
(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)
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Open AccessArticle Pinning Effect of Cerium Inclusions during Austenite Grains Growth in SS400 Steel at 1300 °C: A Combined Phase Field and Experimental Study
Crystals 2017, 7(10), 308; https://doi.org/10.3390/cryst7100308
Received: 12 September 2017 / Revised: 10 October 2017 / Accepted: 11 October 2017 / Published: 15 October 2017
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Abstract
The pinning effect of cerium inclusions in the austenite grain growth of SS400 steel at 1300 °C is investigated by using a semi-empirical-simulation. Firstly, steel samples containing cerium inclusions are prepared; then the properties of inclusions are determined using SEM. In situ observation
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The pinning effect of cerium inclusions in the austenite grain growth of SS400 steel at 1300 °C is investigated by using a semi-empirical-simulation. Firstly, steel samples containing cerium inclusions are prepared; then the properties of inclusions are determined using SEM. In situ observation of austenite grain growth is performed by LSCM, to determine the fitting parameters of the model such as the grain mobility and the pinning parameter. These parameters are directly inserted into our phase field simulation. The time-dependent Ginzburg-Landau (TDGL) equation is implemented in our phase field model, where the effects of inclusion and grain boundary interaction are inserted as a potential term in the local free energy. The results proved that the optimal size of austenite grains can be achieved by changing the volume fraction of inclusions. In fact, by increasing the volume fraction of inclusions from 0 to 0.1, the austenite grain growth can be decreased where the boundary mobility reduces from 2.3×10−12 m4/Js to 1.0×10−12 m4/Js. The results also demonstrated that increasing the temperature can provide more energy for grain to overcome the inclusions’ pinning force. Moreover, it was shown that the classical Zener model, R c = 0.45 r p f i 1 , describes the pinning effect of cerium inclusions. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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