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Crystals, Volume 12, Issue 5 (May 2022) – 184 articles

Cover Story (view full-size image): Organic ultraviolet (UV) phototransistors are promising for diverse applications. However, wide-bandgap organic semiconductors (OSCs) with intense UV absorption tend to exhibit a large contact resistance (Rc) because of energy level mismatching with metal electrodes. Herein, we discovered that a molecular dopant of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was more efficient than a transition metal oxide dopant of MoO3 in doping a wide-bandgap OSC, although the former showed a smaller electron affinity (EA). By efficient contact doping, a low Rc of 889 Ω·cm and a high mobility of 13.89 cm2V−1s−1 were achieved. As a result, UV-sensitive phototransistors showed high photosensitivity and responsivity. View this paper
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Article
Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys
Crystals 2022, 12(5), 750; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050750 - 23 May 2022
Viewed by 476
Abstract
Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using [...] Read more.
Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using the Eagar-Tsai model and correlated cooling rates with characteristic microstructures, revealing that a cooling rate on the order of 104 K/s could lead to maximized fully eutectic microstructure morphology. Due to rapid solidification, the Si composition in the LSR eutectic was measured at 18.2 wt.%, higher than the equilibrium eutectic composition of 12.6 wt.%Si. Compared to Al-20Si, Ce addition had no significant effect on the volume fraction of the fully eutectic structure but refined Si fibers to approximately 30 nm in diameter. Sr addition did not further refine the diameter of eutectic Si fibers compared to Al-20Si but increased the volume fraction of the fully eutectic microstructure morphology. The refinement ratio (φ) of the Si fiber diameter from the bottom of the melt pool to the surface for the three alloys was similar, at around 28%. The established correlation between the cooling rate and the size and morphology of the microstructure within the melt pool will enable tailoring of the microstructure in laser-processed as well as deposited alloys for high strength and plasticity. Full article
(This article belongs to the Special Issue Structure and Properties of Nanocrystalline Metallic Materials)
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Article
Microstructural Characterization of the Corrosion Product Deposit in the Flow-Accelerated Region in High-Temperature Water
Crystals 2022, 12(5), 749; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050749 - 23 May 2022
Viewed by 372
Abstract
The clogging behavior of the micro-orifice under a flow accelerated condition was investigated after 500 h of immersion in high-temperature water. The results indicated the residual area of the micro-orifice was reduced to one-third of its original size after 500 h of immersion [...] Read more.
The clogging behavior of the micro-orifice under a flow accelerated condition was investigated after 500 h of immersion in high-temperature water. The results indicated the residual area of the micro-orifice was reduced to one-third of its original size after 500 h of immersion due to the deposition of corrosion products. In this process, the clogging behavior of micro-orifice can be divided into three stages: the stable deposition stage, the quick recovery stage, and the dynamic equilibrium stage. The corrosion products were porous and consisted of many deposited particles. The process of particle deposition and removal was carried out simultaneously. Full article
(This article belongs to the Special Issue Corrosion Resistant Alloy)
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Article
Effect of Laser Surface Structuring on Surface Wettability and Tribological Performance of Bulk Metallic Glass
Crystals 2022, 12(5), 748; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050748 - 23 May 2022
Viewed by 397
Abstract
Bulk metallic glasses (BMGs) have been extremely popular in recent decades, owing to their superior properties. However, how to improve the surface functions and durability of BMGs has always been a key engineering issue. In this work, a facile laser-based surface structuring technique [...] Read more.
Bulk metallic glasses (BMGs) have been extremely popular in recent decades, owing to their superior properties. However, how to improve the surface functions and durability of BMGs has always been a key engineering issue. In this work, a facile laser-based surface structuring technique was developed for modulation and control of the surface functionalities of Zr-based BMG. For this technique, a laser beam was first irradiated on the surface to create periodic surface structure, followed by heat treatment to control surface chemistry. Through experimental analyses, it was clearly shown that laser surface structuring turned the BMG surface superhydrophilic, and subsequent heat treatment turned the surface superhydrophobic. We confirmed that the combination of laser-induced periodic surface structure and modified surface chemistry contributed to the wettability transition. The laser-heat-treated surface also exhibited improved antifriction performance with the help of lubrication medium. This work provides a feasible method for surface modification of BMG, suggesting applications in the areas of medicine, biology and microelectronics. Full article
(This article belongs to the Special Issue Laser-Based Texturing Technique for Metallic Surface Engineering)
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Editorial
Additive Manufacturing: Materials, Processing, Characterization and Applications
Crystals 2022, 12(5), 747; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050747 - 23 May 2022
Viewed by 398
Abstract
The current Special Issue collected 19 original articles reporting the results of theoretical and experimental studies that provide new insights into this fascinating new generation manufacturing process, additive manufacturing (AM) [...] Full article
Article
Improved Optoelectronic Characteristics of Ga-In co-Doped ZnO UV Photodetectors by Asymmetric Metal Contact Structure
Crystals 2022, 12(5), 746; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050746 - 23 May 2022
Viewed by 357
Abstract
Transparent Ga and In co-doped ZnO (ZnO:Ga-In) semiconductor thin films were deposited on Corning glass substrates by the sol-gel spin-coating process. The ZnO:Ga-In thin films were used as the sensing layer of metal–semiconductor–metal (MSM)-type ultraviolet (UV) photodetectors (PDs). In this study, the optoelectronic [...] Read more.
Transparent Ga and In co-doped ZnO (ZnO:Ga-In) semiconductor thin films were deposited on Corning glass substrates by the sol-gel spin-coating process. The ZnO:Ga-In thin films were used as the sensing layer of metal–semiconductor–metal (MSM)-type ultraviolet (UV) photodetectors (PDs). In this study, the optoelectronic characteristics of ZnO:Ga-In MSM PDs with symmetrical interdigital electrodes (Al–Al) and asymmetrical interdigital electrodes (Al–Au) were compared. The as-prepared ZnO:Ga-In thin films were polycrystalline, and they had a single-phase hexagonal wurtzite structure and high transparency (~88.4%) in the visible region. The MSM-PDs with asymmetric electrodes had significantly reduced dark current (9.6 × 10−5 A at 5 V) according to the current-voltage (I-V) characteristics and higher photoresponse properties than those of the MSM-PDs with symmetric electrodes, according to the current-time (I-t) characteristics. In addition, the Al–Au devices were self-powered without an applied bias voltage. The photocurrent was 6.0 × 10−5 A; the sensitivity and responsivity were 0.25 and 0.03 mA/W, respectively, under UV illumination. Full article
(This article belongs to the Special Issue Optoelectronics and Photonics in Crystals)
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Article
Effects of n-Al2O3 and μ-TiCN on Microstructure and Mechanical Properties of Al2O3 Composite Ceramics Manufactured by Material Extrusion and Photo-Polymerization Combined Process
Crystals 2022, 12(5), 745; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050745 - 23 May 2022
Viewed by 561
Abstract
Alumina (Al2O3) composite ceramics with different composition ratio and particle-size distribution were fabricated by the material extrusion and photo-polymerization combined process (MEX-PPM) based on additive-manufacturing (AM) technology in our previous work. These particles were nanosized Al2O3 [...] Read more.
Alumina (Al2O3) composite ceramics with different composition ratio and particle-size distribution were fabricated by the material extrusion and photo-polymerization combined process (MEX-PPM) based on additive-manufacturing (AM) technology in our previous work. These particles were nanosized Al2O3 (n-Al2O3), micron-sized TiCN (μ-TiCN) and Al2O3. Effects of n-Al2O3 and μ-TiCN on Al2O3 composite ceramics were investigated by characterizing the volume density, EDS spectrum, mechanical properties and microstructure of the prepared samples. It was found that n-Al2O3 had a significant effect on the hardness of Al2O3 composite ceramics, μ-TiCN, with excellent performance in density, flexural strength and fracture toughness. The Al2O3 composite ceramics with optimum contents of 10 wt % n-Al2O3 and 30 wt % μ-TiCN showed good microstructure and mechanical properties. Their porosity and volume density were at 4.073% and 4.177 g/cm3, respectively. Their hardness, flexural strength and fracture toughness were at 16.592 GPa, 592.875 MPa and 6.308 MPa/mm2. The flexural strength of the ceramics was significantly higher than that of Al2O3 ceramics prepared by SLA in document (178.84 ± 17.66 MPa), which had great potential in high-pressure strength structure. Full article
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Review
ZnO under Pressure: From Nanoparticles to Single Crystals
Crystals 2022, 12(5), 744; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050744 - 23 May 2022
Viewed by 618
Abstract
In the present review, new approaches for the stabilization of metastable phases of zinc oxide and the growth of ZnO single crystals under high pressures and high temperatures are considered. The problems of the stabilization of the cubic modification of ZnO as well [...] Read more.
In the present review, new approaches for the stabilization of metastable phases of zinc oxide and the growth of ZnO single crystals under high pressures and high temperatures are considered. The problems of the stabilization of the cubic modification of ZnO as well as solid solutions on its basis are discussed. A thermodynamic approach to the description of zinc oxide melting at high pressures is described which opens up new possibilities for the growth of both undoped and doped (for example, with elements of group V) single crystals of zinc oxide. The possibilities of using high pressure to vary phase and elemental composition in order to create ZnO-based materials are demonstrated. Full article
(This article belongs to the Special Issue Crystalline Phases under Extreme Conditions)
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Article
Statistical Analysis of the Distribution of the Schmid Factor in As-Built and Annealed Parts Produced by Laser Powder Bed Fusion
Crystals 2022, 12(5), 743; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050743 - 23 May 2022
Viewed by 455
Abstract
This study documents a systematic analysis of the global Schmid factor for different deformation mechanisms in α′/α and β-grains in different forms of direct metal laser sintered (DMLS) Ti6Al4V(ELI) based on EBSD data. A novelty of this study is the use of these [...] Read more.
This study documents a systematic analysis of the global Schmid factor for different deformation mechanisms in α′/α and β-grains in different forms of direct metal laser sintered (DMLS) Ti6Al4V(ELI) based on EBSD data. A novelty of this study is the use of these data to calculate the values of the Schmid factor and the subsequent determination of their distribution and frequency, which, when compared to the slip systems of crystal structures, helps in determining the favourable slip systems in play. Both retained β-grains and reconstructed prior β-grains were considered in this analysis. The reconstruction of the prior β-grains was executed using the Automatic Reconstruction of Parent Grain for EBSD data (ARPGE) program. The distribution of the global Schmid factor for these Ti6Al4V phases was calculated using the MATLAB-based MTEX toolbox program. This analysis of deformation modes in the α′/α-phase was based on a uniaxial load state acting on the x, y, and z axes, while only the load along the build direction (x-direction) was considered in the analysis of deformation mechanisms in the β-phase of the alloy. The results of this study showed that the DMLS build direction influenced the distribution of the global Schmid factor for the basal slip system of α′/α-grains in as-built specimens and those samples that were heat treated below the α→β transformation temperature. Full article
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Article
Controlled Synthesis and Photoresponsive Properties of Spiropyran End-Functionalized Poly(vinyl ether)s
Crystals 2022, 12(5), 742; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050742 - 22 May 2022
Viewed by 434
Abstract
Due to the need to develop smart materials for a variety of applications such as catalysts and drug delivery, the development of photoresponsive polymers is receiving increasing attention. In particular, the photoisomerization of spiropyran (SP), unlike many other photoresponsive compounds, has attracted attention [...] Read more.
Due to the need to develop smart materials for a variety of applications such as catalysts and drug delivery, the development of photoresponsive polymers is receiving increasing attention. In particular, the photoisomerization of spiropyran (SP), unlike many other photoresponsive compounds, has attracted attention because it dramatically changes not only the molecular structure but also the polarity of the molecule. However, in most cases where SP is used as a photoresponsive functional group, SP is introduced in the side chain of the polymer, and few cases have been reported in which SP is introduced at the end of the polymer chain. Therefore, we designed a new amphipathic poly(vinyl ether) with an SP moiety at the end of the polymer chain. First, an initiator having an SP moiety was synthesized and used for living cationic polymerization to synthesize a poly(vinyl ether) bearing an SP moiety at the end of the polymer chain. Furthermore, we investigated the photoresponsive properties of the obtained polymers, we found that self-assembly of the amphiphilic polymers could be controlled by photoirradiation. Full article
(This article belongs to the Special Issue Feature Papers in Macromolecular Crystals)
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Article
Co (II) Complexes Based on the Bis-Pyrazol-S-Triazine Pincer Ligand: Synthesis, X-ray Structure Studies, and Cytotoxic Evaluation
Crystals 2022, 12(5), 741; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050741 - 20 May 2022
Viewed by 383
Abstract
Four pincer-type Co (II) complexes of the 2,4-bis (3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine ligand (L) were evaluated for their cytotoxic activities against lung and breast cancer cell lines using cell viability assay. The X-ray single crystal structure of [Co(L)(H2O)2 [...] Read more.
Four pincer-type Co (II) complexes of the 2,4-bis (3,5-dimethyl-1H-pyrazol-1-yl)-6-methoxy-1,3,5-triazine ligand (L) were evaluated for their cytotoxic activities against lung and breast cancer cell lines using cell viability assay. The X-ray single crystal structure of [Co(L)(H2O)2Br]Br (1) confirmed the pincer coordination behavior of the ligand L as an N-tridentate chelate. The hexa-coordination environment of Co (II) is completed by one bromide ion completing the equatorial plane of the octahedral structure and two trans water molecules at the axial positions. It crystallized in the monoclinic crystal system and P21/m space group with crystal parameters of a = 11.3170(10) Å, b = 7.4613(7) Å, c = 12.6917(12) Å and β = 95.927(3)°. Based on Hirshfeld analysis, the most dominant contacts are H…H (48.8%), Br…H (17.6%), H…C (11.2%) and O…H (10.1%), where the Br…H interactions are the most significant. The cytotoxic evaluation of the studied systems indicated that complex [Co(L)(NO3)2] (4) has the highest activity against lung (A-549) and breast (MCF-7) cell lines. In contrast, complex [Co(L)(H2O)3](ClO4)2.H2O(3) has the lowest cytotoxic activity against both cell lines. Full article
(This article belongs to the Special Issue New Trends in Crystals at Saudi Arabia (Volume II))
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Article
Characteristics of a 2-2 Piezoelectric Composite Transducer Made by Magnetic Force Assembly
Crystals 2022, 12(5), 740; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050740 - 20 May 2022
Viewed by 354
Abstract
A wider operational bandwidth, a higher electromechanical coupling factor, and lower acoustic impedance are important requirements for ultrasound transducers for use across many applications. Conventional 2-2 piezoelectric composite transducers have been widely researched because of their wider bandwidth and higher sensitivity over their [...] Read more.
A wider operational bandwidth, a higher electromechanical coupling factor, and lower acoustic impedance are important requirements for ultrasound transducers for use across many applications. Conventional 2-2 piezoelectric composite transducers have been widely researched because of their wider bandwidth and higher sensitivity over their piezoelectric ceramic counterparts. In this paper, the fabrication of a novel 2-2 piezoelectric composite using magnetic force assembly is proposed to explore the potential of the transducer and to minimize mode coupling effect compared to 1–3 composites. To determine the desired transducer performance, such as the electromechanical coupling factor, the operational bandwidth, and the acoustic impedance, the design of a 2-2 composite should be considered using the mode-coupling theory and an effective medium model. The experimental results indicate that the electromechanical coupling factor and the −6 dB fractional bandwidth of the composite achieve values of 0.58 and 65.2%, respectively, which are comparable to those of traditional 1-3 piezoceramic/epoxy composites. Full article
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Review
High-Pressure Polymorphism in Hydrogen-Bonded Crystals: A Concise Review
Crystals 2022, 12(5), 739; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050739 - 20 May 2022
Viewed by 457
Abstract
High-pressure polymorphism is a developing interdisciplinary field. Pressure up to 20 GPa is a powerful thermodynamic parameter for the study and fabrication of hydrogen-bonded polymorphic systems. This review describes how pressure can be used to explore polymorphism and surveys the reports on examples [...] Read more.
High-pressure polymorphism is a developing interdisciplinary field. Pressure up to 20 GPa is a powerful thermodynamic parameter for the study and fabrication of hydrogen-bonded polymorphic systems. This review describes how pressure can be used to explore polymorphism and surveys the reports on examples of compounds that our group has studied at high pressures. Such studies have provided insight into the nature of structure–property relationships, which will enable crystal engineering to design crystals with desired architectures through hydrogen-bonded networks. Experimental methods are also briefly surveyed, along with two methods that have proven to be very helpful in the analysis of high-pressure polymorphs, namely, the ab initio pseudopotential plane–wave density functional method and using Hirshfeld surfaces to construct a graphical overview of intermolecular interactions. Full article
(This article belongs to the Special Issue Polymorphism in Crystals)
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Article
High-Performance Piezoelectric Characteristics of Sm Substituted Pb(Ni,Nb)O3-Pb(Zr,Ti)O3-Pb(Mg,W)O3 System Ceramics for Ultrasonic Transducer Application
Crystals 2022, 12(5), 738; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050738 - 20 May 2022
Viewed by 400
Abstract
In this paper, in order to develop composition ceramics for an acoustic emission sensor application for nondestructive testing, Pb(Ni,Nb2/3)O3-Pb(Zr,Ti)O3-Pb(Mg,W)O3 [PNN-PZT-PMW] system ceramics were manufactured by conventional mixed oxide method using Li2CO3 and CaCO [...] Read more.
In this paper, in order to develop composition ceramics for an acoustic emission sensor application for nondestructive testing, Pb(Ni,Nb2/3)O3-Pb(Zr,Ti)O3-Pb(Mg,W)O3 [PNN-PZT-PMW] system ceramics were manufactured by conventional mixed oxide method using Li2CO3 and CaCO3 as sintering aids. Their microstructural, dielectric and piezoelectric properties were also investigated. At x = 0.0075 Sm, the substituted specimen sintered at 980 (°C), and high values of piezoelectric properties appeared: the dielectric constant (εr) of 2824, piezoelectric coefficient d33 of 630 [pC/N], planar electromechanical coupling factor kp of 0.665, piezoelectric voltage constant g33 of 25.2 [mV.m/N], and high Curie temperature (Tc) = 270 (°C), respectively. These values were applicable for devices such as acoustic emission sensor and ultrasonic transducer. Full article
(This article belongs to the Special Issue Piezoelectric Sensors Application)
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Article
The Crystal Structure of 2-Amino-4-(2,3-Dichlorophenyl)-6-Methoxy-4H-Benzo[h]chromene-3-Carbonitrile: Antitumor and Tyrosine Kinase Receptor Inhibition Mechanism Studies
Crystals 2022, 12(5), 737; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050737 - 20 May 2022
Viewed by 356
Abstract
The target compound, 2-amino-4-(2,3-dichlorophenyl)-6-methoxy-4H-benzo[h]chromene -3-carbonitrile (4), was synthesized via the reaction of 4-methoxynaphthalen-1-ol (1), 2,3-dichlorobenzaldehyde (2), and malononitrile (3) in an ethanolic piperidine solution under microwave irradiation. The synthesized β-enaminonitrile derivative (4) was characterized by [...] Read more.
The target compound, 2-amino-4-(2,3-dichlorophenyl)-6-methoxy-4H-benzo[h]chromene -3-carbonitrile (4), was synthesized via the reaction of 4-methoxynaphthalen-1-ol (1), 2,3-dichlorobenzaldehyde (2), and malononitrile (3) in an ethanolic piperidine solution under microwave irradiation. The synthesized β-enaminonitrile derivative (4) was characterized by spectral data and X-ray diffraction. The in vitro anti-proliferative profile was conducted against five cancer cell lines and was assessed for compound 4, which revealed strong and selective cytotoxic potency. This derivative showed promising inhibition efficacy against the EGFR and VEGFR-2 kinases in comparison to Sorafenib as a reference inhibitor. Lastly, the docking analysis into the EGFR and VEGFR-2 active sites was performed to clarify our biological findings. Full article
(This article belongs to the Special Issue Novel Nanomaterials for Catalytic and Biological Applications)
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Article
Surface Shape Evolution of Optical Elements during Continuous Polishing of Fused Quartz
Crystals 2022, 12(5), 736; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050736 - 20 May 2022
Viewed by 472
Abstract
Continuous polishing is the first choice for machining optical elements with a large aperture. The lubrication in the continuous polishing is an important factor affecting the surface quality of the optical elements. In this study, the lubrication system between the optic element and [...] Read more.
Continuous polishing is the first choice for machining optical elements with a large aperture. The lubrication in the continuous polishing is an important factor affecting the surface quality of the optical elements. In this study, the lubrication system between the optic element and polishing lap was analyzed firstly and then was verified by the measurement experiment of the friction coefficient. In addition, the numerical simulation model of the mixture lubrication was established. The polishing pressure distribution and material removal distribution can be obtained by the model. The influences of the rotating speed, optical element load, and surface roughness of the polishing lap on polishing pressure were also analyzed. Finally, the influence rules of the lubrication on the surface shape of optical elements were revealed by the polishing experiments. Full article
(This article belongs to the Special Issue Processing Technology of Brittle Crystal Materials)
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Article
Intermetallic Compounds Formation during 316L Stainless Steel Reaction with Al-Zn-Si Coating Alloy
Crystals 2022, 12(5), 735; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050735 - 20 May 2022
Viewed by 416
Abstract
Steel products are coated with Aluminum (Al) and Zinc (Zn) alloys to improve their corrosion properties. Bulk steel products are coated in batches; however, steel sheets are coated by a continuous hot-dip galvanizing process. Steel sheets are guided into and out of the [...] Read more.
Steel products are coated with Aluminum (Al) and Zinc (Zn) alloys to improve their corrosion properties. Bulk steel products are coated in batches; however, steel sheets are coated by a continuous hot-dip galvanizing process. Steel sheets are guided into and out of the molten Al-Zn-Si (AZ) bath with the help of stainless-steel rolls, known as guiding, and sink rolls. These rolls are subjected to excessive surface corrosion with molten AZ bath and, hence, are replaced frequently. The surface deterioration of the immersed rolls has been a long-standing issue in the galvanizing industry. In this study, 316L stainless-steel (SS) rods are immersed in the AZ alloy at 600 °C. The immersion time varied from 1 day to 7 days under the static melt conditions in the iron (Fe)-saturated AZ bath. Microstructural analysis of the immersed SS samples revealed two distinct intermetallic compound (IMC) layers forming between the SS substrate and AZ alloy. The IMC layer 1 (AL-1) formed between the SS substrate and IMC layer 2 (AL-2), growing in thickness from 68 µm to 120 µm within 5 days of immersion. The AL-2, which formed between AL-1 and AZ alloy after 24 h of immersion, then grew in thickness up to 150 µm with an uneven trend. The AL-1 is composed of Fe2Al5 and that of AL-2 is composed of FeAl3 that were predicted by the FactSage thermodynamic analysis. Crack development between AL-1 and AL-2 layers, and disintegration of AL-2 into the AZ bath, are key findings of this study. A drastic hardness increase was observed because the IMC layers produce a hard and brittle sink roll surface. Full article
(This article belongs to the Special Issue Frontiers of Intermetallic Compounds)
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Article
Facile Two-Step Deposition of Calcium Oxalate Film on Dolomite to Improve Acid Rain Resistance
Crystals 2022, 12(5), 734; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050734 - 20 May 2022
Viewed by 363
Abstract
The deposition of a calcium oxalate layer on dolomite demonstrates potential application in stone culture heritage conservation. However, due to insufficient coverage and the presence of cracks, the film’s usefulness is restricted. In this investigation, we used a simple two-step procedure to create [...] Read more.
The deposition of a calcium oxalate layer on dolomite demonstrates potential application in stone culture heritage conservation. However, due to insufficient coverage and the presence of cracks, the film’s usefulness is restricted. In this investigation, we used a simple two-step procedure to create a cohesive and uncracked film. The findings show that the protective layer provides better coverage of the dolomite surface without causing cracks and significantly improves acid resistance. Furthermore, after the simple two-step treatment, the color and adhesive strength of dolomite substrates remained nearly unchanged. Full article
(This article belongs to the Special Issue Corrosion, Coatings and Crystals)
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Article
Evaluation of the Characteristics of Cholesteric Liquid Crystal Diffuser Element Applied in Multi-Focal Display Architectures
Crystals 2022, 12(5), 733; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050733 - 20 May 2022
Viewed by 391
Abstract
Solid-state multi-focal and volumetric technologies highlight the future of 3D-display development. One of the most convenient implementations of multi-focal 3D displays are stacks of transparent liquid crystal displays. In this work, the core element is dissected—a switching optical diffuser element based on cholesteric [...] Read more.
Solid-state multi-focal and volumetric technologies highlight the future of 3D-display development. One of the most convenient implementations of multi-focal 3D displays are stacks of transparent liquid crystal displays. In this work, the core element is dissected—a switching optical diffuser element based on cholesteric liquid crystals, playing the role of a transparent display. In the present study, high-speed synchronized optical spectroscopy is used. We analyzed the kinetic and electro-optical characteristics of the diffuser element, the operation of which is based on the switching between diffuse and transparent states of this element. The underlying aim of this study was to investigate ways to improve some of these characteristics. It has been found that the transient peak in the optical transmission during field-off state, which is reducing the intensity of the light scattered by the diffuser element, is likely not associated to the assumed formation of the transient planar state. As the origin of this peak, we suggest a transient state possessing uniform lying helix structure, formed due the material flow taking place in the cell during relaxation of the liquid crystal. The role of the contacting surface’s pre-tilt angle in the switching process of the liquid crystal diffuser was established. Full article
(This article belongs to the Special Issue Optical Field Modulation Based on Liquid Crystals and Beyond)
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Article
Bending and Wave Propagation Analysis of Magneto-Electro-Elastic Functionally Graded Porous Microbeams
Crystals 2022, 12(5), 732; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050732 - 19 May 2022
Viewed by 390
Abstract
In this paper, a microstructure-dependent magneto-electro-elastic functionally graded porous (MEEFGP) beam model is proposed using a variational approach. To account for the microstructure effect, the extended modified couple stress theory is incorporated in the new model. In addition, the porosity variation of the [...] Read more.
In this paper, a microstructure-dependent magneto-electro-elastic functionally graded porous (MEEFGP) beam model is proposed using a variational approach. To account for the microstructure effect, the extended modified couple stress theory is incorporated in the new model. In addition, the porosity variation of the two-phase beam model through the thickness direction is also considered. The new developed model is verified in terms of its correctness with a FEM model. Based on the equations of motion and boundary conditions derived by Hamilton’s principle, the static bending and wave propagation behaviors of the new model are analytically determined. The results prove the existence of the microstructure effect and the magneto-electro-elastic multi-field coupling effect. There are significant differences between the new model and the classical model at the microscale. Moreover, the porosity also has an important influence on the mechanical properties of the new model. The results predicted by the new model can provide the theoretical basis for the design of microscale acoustic wave devices and micro-electro-mechanical systems. Full article
(This article belongs to the Special Issue Advances in Thin Structures and Materials Modelling)
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Article
Effect of Forced Melt Flow on Al–Si Eutectic-Alloy Microstructures
Crystals 2022, 12(5), 731; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050731 - 19 May 2022
Viewed by 389
Abstract
Al–Si eutectic alloys are industrially important; they play a significant role in the casting-manufacturing of most materials. The properties of the materials are governed by their microstructure, which can be tuned by adjusting the solidification process parameters. Herein, the effect of forced melt [...] Read more.
Al–Si eutectic alloys are industrially important; they play a significant role in the casting-manufacturing of most materials. The properties of the materials are governed by their microstructure, which can be tuned by adjusting the solidification process parameters. Herein, the effect of forced melt flow on the microstructure of an Al–Si eutectic alloy during unidirectional solidification was investigated experimentally. Al–12.6-wt%-Si alloy samples were solidified in a vertical Bridgman-type furnace equipped with a rotating magnetic inductor to induce flow in the melt. The samples were subjected to different magnetic induction conditions during the solidification experiments. The diameter of the samples was 8 mm, and their length was 120 mm. The eutectic alloy samples were solidified unidirectionally at a growth rate of v ≈ 0.1 mm/s and a temperature gradient of G ≈ 6 K/mm. The inter-lamellar distances (λ), lengths, and orientation angles of the Si lamellae were investigated using new measurement methods. The experimental results reveal that applying the rotating magnetic field (RMF) during the solidification has a distinct effect on the microstructure of Al–Si eutectic alloys. Indeed, the RMF refines the eutectic structure, reduces the interlamellar distances, and increases the diversity of the Si lamella angle’s orientations. However, the successive stirring process has a negligible effect on the lengths and angles of Si lamellae. Full article
(This article belongs to the Special Issue Microstructure Characterization and Design of Alloys)
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Article
In Situ Measurement Method Based on Edge Detection and Superpixel for Crystallization Imaging at High-Solid Concentrations
Crystals 2022, 12(5), 730; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050730 - 19 May 2022
Viewed by 325
Abstract
To facilitate measuring crystal sizes during batch crystallization at high-solid concentrations by using an invasive imaging system, an in situ imaging measurement strategy based on edge detection and superpixel is proposed for the ambiguous boundary problem of large amounts of crystals. Firstly, an [...] Read more.
To facilitate measuring crystal sizes during batch crystallization at high-solid concentrations by using an invasive imaging system, an in situ imaging measurement strategy based on edge detection and superpixel is proposed for the ambiguous boundary problem of large amounts of crystals. Firstly, an image filtering is employed to cope with image degradation caused by noise disturbance and suspension turbulence in the crystallizer. Subsequently, an image segmentation method is developed by utilizing improved edge detection and superpixel, which can be easily performed for crystal extraction. Accordingly, crystal size measurement can be developed for evaluation of the crystal size distribution. The experiment results on α-form L-glutamic acid present the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Artificial Crystals)
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Article
Study of PDMS Microchannels for Liquid Crystalline Optofluidic Devices in Waveguiding Photonic Systems
Crystals 2022, 12(5), 729; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050729 - 19 May 2022
Cited by 1 | Viewed by 368
Abstract
Microchannels in LC:PDMS structures must be of good quality and suitable geometry to achieve the desired orientation of the liquid crystalline molecules inside. When applying a casting technique, with the molds obtained even by the most accurate method, i.e., photolithography, it is still [...] Read more.
Microchannels in LC:PDMS structures must be of good quality and suitable geometry to achieve the desired orientation of the liquid crystalline molecules inside. When applying a casting technique, with the molds obtained even by the most accurate method, i.e., photolithography, it is still crucial to inspect the cross-section of the structure and the surface roughness of the PDMS material. This paper presents a study of PDMS microchannels using a Scanning Electron Microscope (SEM) to make such a characterization as accurate as possible. By comparing images of the samples taken using standard polarized light microscopy and SEM, it is likely to understand the mechanism of the liquid crystal molecular orientation occurring in the samples. The results obtained in this work may be used for numerical simulations and further development of LC:PDMS structures. Full article
(This article belongs to the Special Issue Optical and Molecular Aspects of Liquid Crystals)
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Article
Crystal Growth and Characterization of ZrSiS-Type Topological Dirac Semimetals
Crystals 2022, 12(5), 728; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050728 - 19 May 2022
Viewed by 342
Abstract
WHM materials (W = Zr/Hf, H = Si/Ge/Sn, M = S/Se/Te) represent a large family of topological semimetals, which have attracted intensive interest since they are considered to be good candidates for studying various topological states. Here, we report the crystal growth, characterization, [...] Read more.
WHM materials (W = Zr/Hf, H = Si/Ge/Sn, M = S/Se/Te) represent a large family of topological semimetals, which have attracted intensive interest since they are considered to be good candidates for studying various topological states. Here, we report the crystal growth, characterization, and electronic properties of HfSiS, ZrGeS, and ZrGeSe. All samples were prepared by a chemical vapor transport method with I2 as a transport agent, and the growth conditions were optimized. X-ray diffraction (XRD) measurements showed that the as-grown crystals crystallized in a PbFCl-type layered structure. They all showed metallic behavior from temperature-dependent resistivity measurements and the carrier densities were estimated to be in the order of 1021 cm−3. A large magnetoresistance of up to 1200% and an obvious Shubnikov–de Hass (SdH) oscillation were observed for HfSiS. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Mechanisms of Selected Anionic Dye Removal by Clinoptilolite
Crystals 2022, 12(5), 727; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050727 - 19 May 2022
Viewed by 346
Abstract
The extensive use of color dyes in modern society has resulted in serious concerns of water contamination. Many organic dyes bear charges; thus, materials of opposite charges have been tested for sorptive removal. However, the results from several studies also showed that anionic [...] Read more.
The extensive use of color dyes in modern society has resulted in serious concerns of water contamination. Many organic dyes bear charges; thus, materials of opposite charges have been tested for sorptive removal. However, the results from several studies also showed that anionic dyes methyl orange (MO) and alizarin red S (ARS) could be removed from water using minerals of negative charges, but the mechanisms were not addressed. In this study, negatively charged clinoptilolite was tested for its removal of anionic dyes MO and ARS from water under different physico-chemical conditions and to investigate the mechanism of Mo and ARS removal. The sorption capacities were 166 and 92 mmol/kg for MO and ARS, respectively, confirming the uptake of anionic dyes on negatively charged framework silicates. The influence of solution pH and ionic strength on MO removal was minimal, indicating the strong affinity of anionic dyes for clinoptilolite in comparison to other inorganic species. It was speculated that the N in the dimethyl group may bear a partial positive charge, which may have a net electrostatic attraction to the negatively charged mineral surfaces for MO sorption. For ARS, sorption may involve hydrogen bonding formation between the dye and the clinoptilolite. Moreover, under the experimental conditions, the MO molecules form dimers in solution via dimeric π-π interactions. Thus, the sorption of the dimers or aggregation of the MO monomers and dimers on clinoptilolite surface was attributed to additional MO removal, as suggested by molecular dynamic simulations. The speculation was supported by FTIR analyses and molecular dynamic simulations. As such, negatively charged Earth materials may be used as sorbents for the removal of certain anionic dyes via sorption, a new perspective for the innovative use of Earth materials. Full article
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Article
A Novel Nanostructured Mullite Feedstock for Environmental Barrier Coatings via Atmosphere Plasma Spraying
Crystals 2022, 12(5), 726; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050726 - 19 May 2022
Viewed by 322
Abstract
A novel strategy is proposed to design an exclusive nanostructured mullite spherical feedstock for environmental barrier coatings (EBCs) via atmosphere plasma spraying (APS). The nanostructured mullite spherical feedstocks are successfully obtained by the procedure of spray drying, solid-phase sintering and flame spheroidization. The [...] Read more.
A novel strategy is proposed to design an exclusive nanostructured mullite spherical feedstock for environmental barrier coatings (EBCs) via atmosphere plasma spraying (APS). The nanostructured mullite spherical feedstocks are successfully obtained by the procedure of spray drying, solid-phase sintering and flame spheroidization. The crystal grain size of nano-mullite increases with annealing temperature. When the temperature is as high as 1500 °C, the reaction of Al2O3 and SiO2 can be fully completed. The average size is 52 nm for the grain of mullite in feedstocks sintered at 1500 °C, which can be reduced from 52 nm to 48 nm by flame spheroidization treatment as well. Meanwhile, the nanostructured spherical feedstocks show high density and good flowability, which is suitable for APS. The mullite coatings is successfully prepared on a SiC substrate by APS, in which both the nanoscale crystals and nanostructures are perfectly kept as designed. Furthermore, there is no crack appeared in the nanostructured mullite coatings. Thus, the nanostructured mullite feedstock is one of promising candidates for the high performance EBCs. Full article
(This article belongs to the Special Issue Electronic Ceramic Materials)
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Article
Surface Quality Experimental Study on Rotary Ultrasonic Machining of Honeycomb Composites with a Circular Knife Cutting Tool
Crystals 2022, 12(5), 725; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050725 - 19 May 2022
Viewed by 376
Abstract
Honeycomb composites (HCs) are diversely employed in aerospace, national defense and other fields owing to their remarkable spatial geometry and excellent mechanical properties. Their complex hexagonal cell structure and heterogeneous material properties cause major problems when implementing high-quality processing. Surface defects generated by [...] Read more.
Honeycomb composites (HCs) are diversely employed in aerospace, national defense and other fields owing to their remarkable spatial geometry and excellent mechanical properties. Their complex hexagonal cell structure and heterogeneous material properties cause major problems when implementing high-quality processing. Surface defects generated by processing will reduce the capability and service lifespan of the honeycomb sandwich structure. Therefore, the high quality of HCs is a topic of close attention for researchers. In this paper, the consequences of different cutting parameters of rotary ultrasonic machining (RUM) on surface quality with an ultrasonic circular knife (UCK) were studied through multiple groups of single-factor and orthogonal experiments with two-factors/four-levels and one-factor/three-levels. The single factor experiment was used to explain the effect that the degree of cutting parameters has on surface quality, and the orthogonal experiments were applied to explain the interaction between the processing parameters and the influence law of each factor on surface quality. Therefore, the reasonable cutting parameters of HCs were determined through experimental results to provide guidance for the realization of the precise and efficient machining of HCs. This study can provide a basis for the subsequent comprehensive consideration of various factors to achieve high-quality machining of HCs. Full article
(This article belongs to the Special Issue Processing Technology of Brittle Crystal Materials)
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Article
Grain-Size-Induced Collapse of Variable Range Hopping and Promotion of Ferromagnetism in Manganite La0.5Ca0.5MnO3
Crystals 2022, 12(5), 724; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050724 - 19 May 2022
Viewed by 392
Abstract
Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) [...] Read more.
Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) phase, where conducting electrons localize and create a long range order giving rise to insulator-like behavior. One of the major open questions in manganites is the exact origin of this insulating behavior. Here we report a dc resistivity and magnetization study on manganite La1xCaxMnO3 ceramic samples with different grain size, at the very boundary between CO/AFM insulating and FM metallic phases x=0.5. Clear signatures of variable range hopping (VRH) are discerned in resistivity, implying the disorder-induced (Anderson) localization of conducting electrons. A significant increase of disorder associated with the reduction in grain size, however, pushes the system in the opposite direction from the Anderson localization scenario, resulting in a drastic decrease of resistivity, collapse of the VRH, suppression of the CO/AFM phase and growth of an FM contribution. These contradictory results are interpreted within the standard core-shell model and recent theories of Anderson localization of interacting particles. Full article
(This article belongs to the Special Issue New Spin on Metal-Insulator Transitions)
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Article
NAi/Li Antisite Defects in the Li1.2Ni0.2Mn0.6O2 Li-Rich Layered Oxide: A DFT Study
Crystals 2022, 12(5), 723; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050723 - 19 May 2022
Viewed by 606
Abstract
Li-rich layered oxide (LRLO) materials are promising positive-electrode materials for Li-ion batteries. Antisite defects, especially nickel and lithium ions, occur spontaneously in many LRLOs, but their impact on the functional properties in batteries is controversial. Here, we illustrate the analysis of the formation [...] Read more.
Li-rich layered oxide (LRLO) materials are promising positive-electrode materials for Li-ion batteries. Antisite defects, especially nickel and lithium ions, occur spontaneously in many LRLOs, but their impact on the functional properties in batteries is controversial. Here, we illustrate the analysis of the formation of Li/Ni antisite defects in the layered lattice of the Co-free LRLO Li1.2Mn0.6Ni0.2O2 compound through a combination of density functional theory calculations performed on fully disordered supercells and a thermodynamic model. Our goal was to evaluate the concentration of antisite defects in the trigonal lattice as a function of temperature and shed light on the native disorder in LRLO and how synthesis protocols can promote the antisite defect formation. Full article
(This article belongs to the Special Issue Feature Papers in Crystal Engineering in 2022)
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Article
The Atomic Layer Etching Technique with Surface Treatment Function for InAlN/GaN Heterostructure
Crystals 2022, 12(5), 722; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050722 - 19 May 2022
Viewed by 423
Abstract
This paper studied an atomic layer etching (ALE) technique with a surface treatment function for InAlN/GaN heterostructures with AlN spacer layers. Various parameters were attempted, and 30 s O2 + 15 W BCl3 was chosen as the optimal recipe. The optimal [...] Read more.
This paper studied an atomic layer etching (ALE) technique with a surface treatment function for InAlN/GaN heterostructures with AlN spacer layers. Various parameters were attempted, and 30 s O2 + 15 W BCl3 was chosen as the optimal recipe. The optimal ALE approach exhibited satisfactory etching results, with regard to the etch-stop effect, compared with other techniques. The atomic force microscopy (AFM) results showed an etching per cycle (EPC) value of 0.15 nm/cycle, with a 0.996 fit coefficient and root mean square (RMS) surface roughness of around 0.61 nm (0.71 nm for as-grown sample), which was the lowest in comparison with digital etching (0.69 nm), Cl2/BCl3 continuous etching (0.91 nm) and BCl3 continuous etching (0.89 nm). X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy measurements (STEM/EDS) verified the indium clustered phenomena at the bottom apex of V-pit defects in the epi structure of InAlN/GaN high electron mobility transistors (HEMTs) for the first time, in addition to the surface morphology optimization for the ALE under-etching technique used in this work. The resistor hall effect (Hall) and AFM measurements demonstrated that after 4 or 5 ALE cycles, the two-dimensional electron gas (2-DEG) density and RMS roughness were improved by 15% and 11.4%, respectively, while the sheet resistance (Rsh) was reduced by 6.7%, suggesting a good surface treatment function. These findings were important for realizing high-performance InAlN/GaN HEMTs. Full article
(This article belongs to the Special Issue Semiconductor Nanocrystals)
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Article
Low Forward Voltage III-Nitride Red Micro-Light-Emitting Diodes on a Strain Relaxed Template with an InGaN Decomposition Layer
Crystals 2022, 12(5), 721; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050721 - 19 May 2022
Viewed by 501
Abstract
In this study, III-nitride red micro-light-emitting diodes (µLEDs) with ultralow forward voltage are demonstrated on a strain relaxed template. The forward voltage ranges between 2.00 V and 2.05 V at 20 A/cm2 for device dimensions from 5 × 5 to 100 × [...] Read more.
In this study, III-nitride red micro-light-emitting diodes (µLEDs) with ultralow forward voltage are demonstrated on a strain relaxed template. The forward voltage ranges between 2.00 V and 2.05 V at 20 A/cm2 for device dimensions from 5 × 5 to 100 × 100 µm2. The µLEDs emit at 692 nm at 5 A/cm2 and 637 nm at 100 A/cm2, corresponding to a blueshift of 55 nm due to the screening of the internal electric field in the quantum wells. The maximum external quantum efficiency and wall-plug efficiency of µLEDs are 0.31% and 0.21%, respectively. This suggests that efficient III-nitride red µLEDs can be realized with further material optimizations. Full article
(This article belongs to the Special Issue GaN-Based Materials and Devices)
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