Crystals

4717 KiB

Open AccessArticle

by Radovan Černý, Vincent Favre-Nicolin, Jan Rohlíček and Michal Hušák

Crystals 2017, 7(10), 322; https://doi.org/10.3390/cryst7100322 - 24 Oct 2017

Cited by 9 | Viewed by 11092

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 [...] Read more.

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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11185 KiB

Open AccessReview

Review of Nanoindentation Size Effect: Experiments and Atomistic Simulation

by George Z. Voyiadjis and Mohammadreza Yaghoobi

Crystals 2017, 7(10), 321; https://doi.org/10.3390/cryst7100321 - 23 Oct 2017

Cited by 111 | Viewed by 11494

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 [...] Read more.

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)

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Open AccessArticle

Formation Mechanism of CaCO₃ Spherulites in the Myostracum Layer of Limpet Shells

by Shitao Wu, Chang-Yang Chiang and Wuzong Zhou

Crystals 2017, 7(10), 319; https://doi.org/10.3390/cryst7100319 - 23 Oct 2017

Cited by 20 | Viewed by 8150

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 [...] Read more.

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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3134 KiB

Open AccessArticle

Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of [(µ₂-dppm)₂Cu₂(η²-BH₄)₂] Dichloromethane Solvate

by Natalia V. Belkova, Igor E. Golub, Evgenii I. Gutsul, Konstantin A. Lyssenko, Alexander S. Peregudov, Viktor D. Makhaev, Oleg A. Filippov, Lina M. Epstein, Andrea Rossin, Maurizio Peruzzini and Elena S. Shubina

Crystals 2017, 7(10), 318; https://doi.org/10.3390/cryst7100318 - 20 Oct 2017

Cited by 12 | Viewed by 9332

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)₂Cu₂(η₂-BH₄)₂], and crystallizes [...] Read more.

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)₂Cu₂(η₂-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

by Xiwei Zhang, Di Wu and Huijuan Geng

Crystals 2017, 7(10), 307; https://doi.org/10.3390/cryst7100307 - 20 Oct 2017

Cited by 29 | Viewed by 7306

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 [...] Read more.

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

(This article belongs to the Special Issue III-V and II-VI Compound Semiconductor Nanorods: Growth, Properties and Applications)

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3156 KiB

Open AccessArticle

Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

by Ana Cuesta, Jesus D. Zea-Garcia, Diana Londono-Zuluaga, Angeles G. De la Torre, Isabel Santacruz, Oriol Vallcorba and Miguel A.G. Aranda

Crystals 2017, 7(10), 317; https://doi.org/10.3390/cryst7100317 - 18 Oct 2017

Cited by 20 | Viewed by 5790

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 [...] Read more.

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

(This article belongs to the Special Issue Advances in Synchrotron Radiation Applications for Crystal Structure Studies)

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1827 KiB

Open AccessArticle

Phase Transformation and Hydrogen Storage Properties of an La_7.0Mg_75.5Ni_17.5 Hydrogen Storage Alloy

by Lin Hu, Rui-hua Nan, Jian-ping Li, Ling Gao and Yu-jing Wang

Crystals 2017, 7(10), 316; https://doi.org/10.3390/cryst7100316 - 18 Oct 2017

Cited by 5 | Viewed by 4461

Abstract

X-ray diffraction showed that an La_7.0Mg_75.5Ni_17.5 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 [...] Read more.

X-ray diffraction showed that an La_7.0Mg_75.5Ni_17.5 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, La_7.0Mg_75.5Ni_17.5 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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1542 KiB

Open AccessArticle

Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions

by Ronald W. Armstrong

Crystals 2017, 7(10), 315; https://doi.org/10.3390/cryst7100315 - 18 Oct 2017

Cited by 13 | Viewed by 4611

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 [...] Read more.

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

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Open AccessArticle

Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors

by Shi-Jun Ge, Zhi-Xiong Shen, Peng Chen, Xiao Liang, Xin-Ke Wang, Wei Hu, Yan Zhang and Yan-Qing Lu

Crystals 2017, 7(10), 314; https://doi.org/10.3390/cryst7100314 - 18 Oct 2017

Cited by 23 | Viewed by 7094

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

by Bor-Chau Juang, Baolai Liang, Dingkun Ren, David L. Prout, Arion F. Chatziioannou and Diana L. Huffaker

Crystals 2017, 7(10), 313; https://doi.org/10.3390/cryst7100313 - 18 Oct 2017

Cited by 7 | Viewed by 5703

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 [...] Read more.

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

(This article belongs to the Special Issue Current and Future Directions in Crystal Growth by Molecular Beam Epitaxy (MBE))

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Open AccessArticle

Preparation of Potassium Dichromate Crystals from the Chromite Concentrate by Microwave Assisted Leaching

by Hua Liu, Shenghui Guo, Jinhui Peng, Duan Yu, Libo Zhang and Linqing Dai

Crystals 2017, 7(10), 312; https://doi.org/10.3390/cryst7100312 - 18 Oct 2017

Cited by 6 | Viewed by 7486

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 [...] Read more.

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

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8566 KiB

Open AccessArticle

Breathing 3D Frameworks with T-Shaped Connecting Ligand Exhibiting Solvent Induction, Metal Ions Effect and Luminescent Properties

by Yong-Cong Ou, Ying-Yi Song, Hui-Ming Du, Meng-Meng Hao and Jian-Zhong Wu

Crystals 2017, 7(10), 311; https://doi.org/10.3390/cryst7100311 - 17 Oct 2017

Cited by 2 | Viewed by 4749

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 [...] Read more.

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 1–3 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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948 KiB

Open AccessReview

Recent Insights into the Crystallization Process; Protein Crystal Nucleation and Growth Peculiarities; Processes in the Presence of Electric Fields

by Christo N. Nanev

Crystals 2017, 7(10), 310; https://doi.org/10.3390/cryst7100310 - 15 Oct 2017

Cited by 21 | Viewed by 8353

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 [...] Read more.

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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4027 KiB

Open AccessReview

Challenges of Handling, Processing, and Studying Liquid and Supercooled Materials at Temperatures above 3000 K with Electrostatic Levitation

by Takehiko Ishikawa and Paul-François Paradis

Crystals 2017, 7(10), 309; https://doi.org/10.3390/cryst7100309 - 15 Oct 2017

Cited by 11 | Viewed by 5316

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 [...] Read more.

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

by Zary Adabavazeh, Weng-Sing Hwang and Amir R. A. Dezfoli

Crystals 2017, 7(10), 308; https://doi.org/10.3390/cryst7100308 - 15 Oct 2017

Cited by 8 | Viewed by 5445

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 [...] Read more.

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 Crystal Engineering)

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16311 KiB

Open AccessReview

Progress in Indentation Study of Materials via Both Experimental and Numerical Methods

by Mao Liu, Jhe-yu Lin, Cheng Lu, Kiet Anh Tieu, Kun Zhou and Toshihiko Koseki

Crystals 2017, 7(10), 258; https://doi.org/10.3390/cryst7100258 - 13 Oct 2017

Cited by 35 | Viewed by 10726

Abstract

Indentation as a method to characterize materials has a history of more than 117 years. However, to date, it is still the most popular way to measure the mechanical properties of various materials at microscale and nanoscale. This review summarizes the background and [...] Read more.

Indentation as a method to characterize materials has a history of more than 117 years. However, to date, it is still the most popular way to measure the mechanical properties of various materials at microscale and nanoscale. This review summarizes the background and the basic principle of processing by indentation. It is demonstrated that indentation is an effective and efficient method to identify mechanical properties, such as hardness, Young’s modulus, etc., of materials at smaller scale, when the traditional tensile tests could not be applied. The review also describes indentation process via both experimental tests and numerical modelling in recent studies. Full article

(This article belongs to the Special Issue Crystal Indentation Hardness)

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Open AccessTechnical Note

Time-Varying Characteristics of Granite Microstructures after Cyclic Dynamic Disturbance Using Nuclear Magnetic Resonance

by Chuanju Liu, Hongwei Deng, Yuan Wang, Yun Lin and Huatao Zhao

Crystals 2017, 7(10), 306; https://doi.org/10.3390/cryst7100306 - 12 Oct 2017

Cited by 32 | Viewed by 4991

Abstract

To investigate the variation in the characteristics of rock microstructure after cyclic dynamic disturbances, a split Hopkinson pressure bar (SHPB) was used to carry out cyclic dynamic impact tests on granite, and the P-wave velocity was used as the characteristic parameter representing the [...] Read more.

To investigate the variation in the characteristics of rock microstructure after cyclic dynamic disturbances, a split Hopkinson pressure bar (SHPB) was used to carry out cyclic dynamic impact tests on granite, and the P-wave velocity was used as the characteristic parameter representing the microstructural change. Using the nuclear magnetic resonance (NMR) technique, the porosity and the T2 distribution of rock samples were obtained. The results show that, after the cyclic dynamic disturbance, the P-wave velocity within the rock specimen decreases but rebounds with time. At the elastic phase, when the axial loading increases, the P-wave velocity declines. The T2 limit is shortened, and the cyclic dynamic disturbance process promotes the formation of small pores and decreases the size and quantity of large pores. After the cyclic dynamic disturbance, the porosity of the rock samples was reduced. Full article

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Open AccessCommunication

Synthesis, Crystal Structure and Catalytic Activity of a Novel Ba(II) Complex with Pyridine-2-Carboxaldehyde-2-Phenylacetic Acid Hydrazone Ligand

by Li-Hua Wang, Xi-Shi Tai, Li-Li Liu and Peng-Fei Li

Crystals 2017, 7(10), 305; https://doi.org/10.3390/cryst7100305 - 9 Oct 2017

Cited by 4 | Viewed by 4137

Abstract

A novel Ba(II) complex, [BaL₂Cl₂] (1) (L = pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone), has been synthesized using BaCl₂, pyridine-2-carboxaldehyde and 2-phenylacetohydrazide as raw materials. The structure of 1 has been determined by elemental analysis and X-ray single-crystal diffraction technique. [...] Read more.

A novel Ba(II) complex, [BaL₂Cl₂] (1) (L = pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone), has been synthesized using BaCl₂, pyridine-2-carboxaldehyde and 2-phenylacetohydrazide as raw materials. The structure of 1 has been determined by elemental analysis and X-ray single-crystal diffraction technique. X-ray structural analysis showed that the Ba(II) complex (1) crystallizes in monoclinic, space group P2₁/c with cell parameters: a = 12.464(3) Å, b = 13.531(3) Å, c = 8.8035(18) Å, β = 95.06(3)°. In 1, the Ba(II) atom is eight-coordinated in a distorted doubly-capped octahedral geometry through four N atoms and two O atoms from two different pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone ligands and two Cl⁻. The complex (1) forms a 3D network structure by the interaction of intermolecular N-H···Cl hydrogen bonds and π···π stacking of neighboring pyridine rings and benzene rings. The optimum conditions for the benzyl alcohol oxidation reaction using the Ba(II) complex as catalyst was investigated. Full article

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Open AccessArticle

Methods for Calculating Empires in Quasicrystals

by Fang Fang, Dugan Hammock and Klee Irwin

Crystals 2017, 7(10), 304; https://doi.org/10.3390/cryst7100304 - 9 Oct 2017

Cited by 9 | Viewed by 12661

Abstract

This paper reviews the empire problem for quasiperiodic tilings and the existing methods for generating the empires of the vertex configurations in quasicrystals, while introducing a new and more efficient method based on the cut-and-project technique. Using Penrose tiling as an example, this [...] Read more.

This paper reviews the empire problem for quasiperiodic tilings and the existing methods for generating the empires of the vertex configurations in quasicrystals, while introducing a new and more efficient method based on the cut-and-project technique. Using Penrose tiling as an example, this method finds the forced tiles with the restrictions in the high dimensional lattice (the mother lattice) that can be cut-and-projected into the lower dimensional quasicrystal. We compare our method to the two existing methods, namely one method that uses the algorithm of the Fibonacci chain to force the Ammann bars in order to find the forced tiles of an empire and the method that follows the work of N.G. de Bruijn on constructing a Penrose tiling as the dual to a pentagrid. This new method is not only conceptually simple and clear, but it also allows us to calculate the empires of the vertex configurations in a defected quasicrystal by reversing the configuration of the quasicrystal to its higher dimensional lattice, where we then apply the restrictions. These advantages may provide a key guiding principle for phason dynamics and an important tool for self error-correction in quasicrystal growth. Full article

(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)

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1947 KiB

Open AccessArticle

Synthesis and Crystal Structure of a New Hydrated Benzimidazolium Salt Containing Spiro Structure

by Wulan Zeng and Jinhe Jiang

Crystals 2017, 7(10), 303; https://doi.org/10.3390/cryst7100303 - 9 Oct 2017

Cited by 10 | Viewed by 4416

Abstract

A new hydrated benzimidazolium salt containing spiro structure was obtained when benzimidazole is added to ethyl alcohol of 1,5-dioxaspiro[5.5]undecane-2,4-dione and trimethoxymethane. The title compound (C₁₉H₂₁O₈) (C₇H₇N₂) (0.5H₂O) was characterized [...] Read more.

A new hydrated benzimidazolium salt containing spiro structure was obtained when benzimidazole is added to ethyl alcohol of 1,5-dioxaspiro[5.5]undecane-2,4-dione and trimethoxymethane. The title compound (C₁₉H₂₁O₈) (C₇H₇N₂) (0.5H₂O) was characterized by elemental analysis, IR, UV-Vis, and single-crystal X-ray diffraction. The result shows that it belongs to the triclinic system, space group P-1, with a = 11.017(2) Å, b = 11.424(2) Å, c = 11.650(2) Å, α = 70.60(3)°, β = 71.00(3)°, γ = 67.64(3)°, Mr = 505.51, V = 1245.2(5) Å, Z = 2, Dc = 1.348 g/cm³, F(000) = 534, μ(MoKa) = 0.102 mm⁻¹. There exist two types of hydrogen bonds in the crystal. (C₁₉H₂₁O₈)⁻ anions and (C₇H₇N₂)⁺ cations are linked by N–H···O hydrogen bonds, while (C₁₉H₂₁O₈)⁻ anions and free water are linked by O–H···O hydrogen bonds. All of the above hydrogen bonds form a one-dimensional (1D)-chained structure. The 1D chains further links the molecule into a three-dimensional (3D)-layered structure. Full article

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1391 KiB

Open AccessFeature PaperArticle

Modulating Nucleation by Kosmotropes and Chaotropes: Testing the Waters

by Ashit Rao, Denis Gebauer and Helmut Cölfen

Crystals 2017, 7(10), 302; https://doi.org/10.3390/cryst7100302 - 6 Oct 2017

Cited by 6 | Viewed by 6848

Abstract

Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With [...] Read more.

Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With certain small molecules affecting the hydration and conformational stability of co-solutes, this study systematically explores the effects of these chaotropes and kosmotropes as well as certain sugar enantiomers on the early stages of calcium carbonate formation. These small molecules appear to modulate mineral nucleation in a class-dependent manner. The observed effects are finite in comparison to the established, strong interactions between charged polymers and intermediate mineral forms. Thus, perturbations to hydration dynamics of ion clusters by co-solute species can affect nucleation phenomena in a discernable manner. Full article

(This article belongs to the Special Issue Biological and Biogenic Crystallization)

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Graphical abstract

2670 KiB

Open AccessReview

The Orbital Angular Momentum Modes Supporting Fibers Based on the Photonic Crystal Fiber Structure

by Hu Zhang, Xiaoguang Zhang, Hui Li, Yifan Deng, Lixia Xi, Xianfeng Tang and Wenbo Zhang

Crystals 2017, 7(10), 286; https://doi.org/10.3390/cryst7100286 - 6 Oct 2017

Cited by 54 | Viewed by 7254

Abstract

The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system. [...] Read more.

The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system. This paper reviews the recent progresses in photonic crystal fiber (PCF) supporting OAM modes, and summarizes why a PCF structure can be used to support stable OAM transmission modes. The emphasis is on the circular PCFs, which possess many excellent features of transmission performance, such as good-quality OAM modes, enough separation of the effective indices, low confinement loss, flat dispersion, a large effective area, and a low nonlinear coefficient. We also compare the transmission properties between the circular PCF and the ring core fiber, as well as the properties between the OAM EDFA based on circular PCF and the OAM EDFA based on the ring core fiber. At last, the challenges and prospects of OAM fibers based on the PCF structure are also discussed. Full article

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5160 KiB

Open AccessArticle

Impact of Annealing Temperature on the Physical Properties of the Lanthanum Deficiency Manganites

by Skini Ridha, Dhahri Essebti and El Kebir Hlil

Crystals 2017, 7(10), 301; https://doi.org/10.3390/cryst7100301 - 5 Oct 2017

Cited by 6 | Viewed by 4100

Abstract

The lanthanum deficiency manganites La_0.₈_-_x□_xCa_0.2MnO₃ (x = 0, 0.1 and 0.2), where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K). [...] Read more.

The lanthanum deficiency manganites La_0.₈_-_x□_xCa_0.2MnO₃ (x = 0, 0.1 and 0.2), where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K). The structural, magnetic, and magnetocaloric properties of these compounds were studied as a function of annealing temperature. It was noted that the annealing temperature did not affect the crystal structure of our samples (orthorhombic structure with Pnma space group). Nevertheless, a change in the variation of the unit cell volume V, the average bond length d_Mn–O, and the average bond angles θ_Mn–O–Mn were observed. Magnetization versus temperature study has shown that all samples exhibited a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with increasing temperature. However, it can be clearly seen that the annealing at 973 K induced an increase of the magnetization. In addition, the magnetocaloric effect (MCE) as well as the relative cooling power (RCP) were estimated. As an important result, the values of MCE and RCP in our Lanthanum-deficiency manganites are reported to be near to those found in gadolinium, considered as magnetocaloric reference material. Full article

(This article belongs to the Special Issue Crystal Structure of Magnetic Materials)

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3219 KiB

Open AccessReview

Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

by Kai Ding, Vitaliy Avrutin, Ümit Özgür and Hadis Morkoç

Crystals 2017, 7(10), 300; https://doi.org/10.3390/cryst7100300 - 4 Oct 2017

Cited by 44 | Viewed by 8402

Abstract

We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current [...] Read more.

We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD) and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice- and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p- and n-type conductivity of high Al-molar fraction AlGaN are reviewed. Full article

(This article belongs to the Special Issue Advances in GaN Crystals and Their Applications)

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288 KiB

Open AccessReview

An Overview on Magnetic Field and Electric Field Interactions with Ice Crystallisation; Application in the Case of Frozen Food

by Piyush Kumar Jha, Epameinondas Xanthakis, Vanessa Jury and Alain Le-Bail

Crystals 2017, 7(10), 299; https://doi.org/10.3390/cryst7100299 - 4 Oct 2017

Cited by 83 | Viewed by 14859

Abstract

Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however, [...] Read more.

Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however, this is still under debate in the literature. Static electric field (SEF) has a significant effect on crystallisation; this has been evidenced experimentally and confirmed by the theory. Oscillating magnetic field induces an oscillating electric field and is also expected to interact with water crystallisation. Oscillating electromagnetic fields interact with water, perturb and even disrupt hydrogen bonds, which in turn are thought to increase the degree of supercooling and to generate numerous fine ice crystals. Based on the literature, it seems that the frequency has an influence on the above-mentioned phenomena. This review article summarizes the fundamentals of freezing under magnetic, electric and electromagnetic fields, as well as their applicability and potentials within the food industry. Full article

(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)

8448 KiB

Open AccessReview

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

by Mongur Hossain, Zhaoyang Zhao, Wen Wen, Xinsheng Wang, Juanxia Wu and Liming Xie

Crystals 2017, 7(10), 298; https://doi.org/10.3390/cryst7100298 - 3 Oct 2017

Cited by 50 | Viewed by 21467

Abstract

Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers [...] Read more.

Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers of single unit cell thickness. Although bulk CDW materials have been studied for decades, recent developments in nanoscale characterization and device fabrication have opened up new opportunities allowing applications such as oscillators, electrodes in supercapacitors, energy storage and conversion, sensors and spinelectronic devices. In this review, we first outline the synthesis techniques of 2D CDW materials including mechanical exfoliation, liquid exfoliation, chemical vapor transport (CVT), chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and electrochemical exfoliation. Then, the characterization procedure of the 2D CDW materials such as temperature-dependent Raman spectroscopy, temperature-dependent resistivity, magnetic susceptibility and scanning tunneling microscopy (STM) are reviewed. Finally, applications of 2D CDW materials are reviewed. Full article

(This article belongs to the Special Issue Two-Dimensional Materials beyond Graphene and their Van der Waals Heterostructures)

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2509 KiB

Open AccessArticle

Synthesis, Crystal Structure and Water Vapor Adsorption Properties of a Porous Supramolecular Architecture

by Rui Qiao, Zi-You Zhang and Mei-An Zhu

Crystals 2017, 7(10), 297; https://doi.org/10.3390/cryst7100297 - 2 Oct 2017

Cited by 1 | Viewed by 4461

Abstract

A new complex, [Cu₄(HL)₄(H₂O)₁₄] (1, H₃L·HCl = 5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride), has been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and powder X-ray diffraction (PXRD). The result of [...] Read more.

A new complex, [Cu₄(HL)₄(H₂O)₁₄] (1, H₃L·HCl = 5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride), has been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and powder X-ray diffraction (PXRD). The result of the X-ray diffraction analysis reveals that the complex crystallizes in monoclinic, space group C2/c and three unique Cu(II) atoms that are connected by partially deprotonated HL²⁻ anion to form a cyclic structure. The rich hydrogen bonding and π-π non-covalent packing interactions extend cyclic units into a three-dimensional (3D) supramolecular polymer. Moreover, the thermogravimetric (TG) analysis and water vapor adsorption property of 1 were also discussed. Full article

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1415 KiB

Open AccessCommunication

Over-Production, Crystallization, and Preliminary X-ray Crystallographic Analysis of a Coiled-Coil Region in Human Pericentrin

by Min Ye Kim, Jeong Kuk Park, Yeowon Sim, Doheum Kim, Jeong Yeon Sim and SangYoun Park

Crystals 2017, 7(10), 296; https://doi.org/10.3390/cryst7100296 - 2 Oct 2017

Viewed by 4902

Abstract

The genes encoding three coiled-coil regions in human pericentrin were gene synthesized with Escherichia coli codon-optimization, and the proteins were successfully over-produced in large quantities using E. coli expression. After verifying that the purified proteins were mostly composed of α-helices, one of the [...] Read more.

The genes encoding three coiled-coil regions in human pericentrin were gene synthesized with Escherichia coli codon-optimization, and the proteins were successfully over-produced in large quantities using E. coli expression. After verifying that the purified proteins were mostly composed of α-helices, one of the proteins was crystallized using polyethylene glycol 8000 as crystallizing agent. X-ray diffraction data were collected to 3.8 Å resolution under cryo-condition using synchrotron X-ray. The crystal belonged to space group C2 with unit cell parameters a = 324.9 Å, b = 35.7 Å, c = 79.5 Å, and β = 101.6˚. According to Matthews’ coefficient, the asymmetric unit may contain up to 12 subunits of the monomeric protein, with a crystal volume per protein mass (V_M) of 1.96 Å³ Da⁻¹ and a 37.3% solvent content. Full article

(This article belongs to the Special Issue Biological and Biogenic Crystallization)

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2442 KiB

Open AccessArticle

Formation of Cellular Structure on Metastable Solidification of Undercooled Eutectic CoSi-62 at. %

by Sangho Jeon and Douglas M. Matson

Crystals 2017, 7(10), 295; https://doi.org/10.3390/cryst7100295 - 30 Sep 2017

Cited by 4 | Viewed by 4743

Abstract

The relationship between emissivity, delay time, and surface growth for metastable solidification of CoSi-62 at. % eutectic alloys is reported from undercooling experiments conducted using electrostatic levitation. A fraction of the undercooled melt is first solidified to CoSi₂ with subsequent nucleation in [...] Read more.

The relationship between emissivity, delay time, and surface growth for metastable solidification of CoSi-62 at. % eutectic alloys is reported from undercooling experiments conducted using electrostatic levitation. A fraction of the undercooled melt is first solidified to CoSi₂ with subsequent nucleation in the mushy-zone of CoSi after an observed delay time. During this double recalescence event, the temperature of the secondary recalescence exceeds the liquidus, indicating that the spectral emissivity has changed. This emissivity change increases with longer delay times during solidification and is linked to the growth of cellular structure on the sample surface. Density measurements showed that the cellular structure begins to grow rapidly at a certain time during metastable solidification. This phenomenon is likely associated with the constitutional undercooling of the remaining melt. Full article

(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)

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18121 KiB

Open AccessArticle

The Effect of Ultrasound on the Crystallisation of Paracetamol in the Presence of Structurally Similar Impurities

by Thai T. H. Nguyen, Azeem Khan, Layla M. Bruce, Clarissa Forbes, Richard L. O’Leary and Chris J. Price

Crystals 2017, 7(10), 294; https://doi.org/10.3390/cryst7100294 - 30 Sep 2017

Cited by 21 | Viewed by 11680

Abstract

Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused [...] Read more.

Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused Beam Reflectance Measurement (FBRM), crystal habit, filtration rate and impurity content in the crystal product by Liquid Chromatography-Mass Spectroscopy (LC-MS)) were investigated in bulk suspension crystallisation experiments with and without the use of ultrasound. The results demonstrate that ultrasonic intervention has a significant effect on both crystallisation and product crystal properties. It increases the nucleation rate resulting in smaller particles and a narrower Particle Size Distribution (PSD), the yield has been shown to be increase as has the product purity. The effect of ultrasound is to reduce the level acetanilide impurity incorporated during growth from a 2 mol% solution of the selected impurity from 0.85 mol% to 0.35 mol% and likewise ultrasound reduces the uptake of metacetamol from 1.88 mol% to 1.52 mol%. Full article

(This article belongs to the Special Issue Advances in Ultrasound Stimulated Crystallization)

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