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Materials, Volume 12, Issue 24 (December-2 2019) – 223 articles

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Cover Story (view full-size image) By systematic tuning of the components of the electrolyte, the performances of dye-sensitized solar [...] Read more.
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Open AccessArticle
Concrete Protective Layer Cracking Caused by Non-Uniform Corrosion of Reinforcements
Materials 2019, 12(24), 4245; https://doi.org/10.3390/ma12244245 - 17 Dec 2019
Viewed by 338
Abstract
The volume expansion of reinforcement corrosion products resulting from the corrosion of steel reinforcement embedded into concrete causes the concrete’s protective layer to crack or spall, reducing the durability of the concrete structure. Thus, it is necessary to analyze concrete cracking caused by [...] Read more.
The volume expansion of reinforcement corrosion products resulting from the corrosion of steel reinforcement embedded into concrete causes the concrete’s protective layer to crack or spall, reducing the durability of the concrete structure. Thus, it is necessary to analyze concrete cracking caused by reinforcement corrosion. This study focused on the occurrence of non-uniform reinforcement corrosion in a natural environment. The characteristics of the rust layer were used to deduce the unequal radial displacement distribution function of concrete around both angular and non-angular bars. Additionally, the relationship between the corrosion ratio and the radial displacement of the concrete around the bar was established quantitatively. Concrete cracking due to the non-uniform corrosion of reinforcements was simulated using steel bars embedded in concrete that were of uneven displacement because of rust expansion. The distribution of the principal tensile stress around the bar was examined. A formula for calculating the critical radial displacement at the point when cracking began was obtained and used to predict the corrosion ratio of the concrete cover. The determined analytical corrosion ratio agreed well with the test result. The effect factor analysis based on the finite element method indicated that increasing the concrete strength and concrete cover thickness delays concrete cracking and that the adjacent rebar causes the stress superposition phenomenon. Full article
(This article belongs to the Section Construction and Building Materials)
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Open AccessArticle
The Influence of a Polymer Powder on the Properties of a Cold-Recycled Mixture with Foamed Bitumen
Materials 2019, 12(24), 4244; https://doi.org/10.3390/ma12244244 - 17 Dec 2019
Viewed by 334
Abstract
The paper investigates the influence of redispersible polymer powder (RPP) on the physical and mechanical properties of a cold-recycled mixture with foamed bitumen (CRM-FB). Four types of RPP with a varied chemical base were used: VA-VeoVA, VA-VeoVa-Ac, EVA and VA/VV/E/Ac. The polymer powder-modified [...] Read more.
The paper investigates the influence of redispersible polymer powder (RPP) on the physical and mechanical properties of a cold-recycled mixture with foamed bitumen (CRM-FB). Four types of RPP with a varied chemical base were used: VA-VeoVA, VA-VeoVa-Ac, EVA and VA/VV/E/Ac. The polymer powder-modified cold recycled mixture with foamed bitumen, (P)CRM-FB, was composed of 45.8% reclaimed asphalt pavement (RAP), 45.8% natural aggregate (VA), 3.0% Portland cement CEM I 42,5R, 3.0% foamed bitumen 50/70 and 3.0% RPP, all dosed by weight. The reference mixture, (R)CRM-FB, served as a reference point for comparison. It was found that RPP improved the workability of the CRM-FB mixture. This results in a reduced number of compaction cycles and lower energy needed to obtain the air void content as in the reference mixture. In addition, the RPP modifier markedly increased the CRM-FB mixture cohesion (ITSDRY) and strength, by approximately 40–70%, depending on the RPP used. These findings are particularly important for CRM-FB mixtures designed for road bases. The present investigations confirmed the improvement of the CRM-FB mixture parameters after the modification with RPP, regardless of the powder type used. Full article
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Open AccessArticle
Strain Range Dependent Cyclic Hardening of 08Ch18N10T Stainless Steel—Experiments and Simulations
Materials 2019, 12(24), 4243; https://doi.org/10.3390/ma12244243 - 17 Dec 2019
Cited by 1 | Viewed by 319
Abstract
This paper describes and presents an experimental program of low-cycle fatigue tests of austenitic stainless steel 08Ch18N10T at room temperature. The low-cycle tests include uniaxial and torsional tests for various specimen geometries and for a vast range of strain amplitude. The experimental data [...] Read more.
This paper describes and presents an experimental program of low-cycle fatigue tests of austenitic stainless steel 08Ch18N10T at room temperature. The low-cycle tests include uniaxial and torsional tests for various specimen geometries and for a vast range of strain amplitude. The experimental data was used to validate the proposed cyclic plasticity model for predicting the strain-range dependent behavior of austenitic steels. The proposed model uses a virtual back-stress variable corresponding to a cyclically stable material under strain control. This internal variable is defined by means of a memory surface introduced in the stress space. The linear isotropic hardening rule is also superposed. A modification is presented that enables the cyclic hardening response of 08Ch18N10T to be simulated correctly under torsional loading conditions. A comparison is made between the real experimental results and the numerical simulation results, demonstrating the robustness of the proposed cyclic plasticity model. Full article
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Open AccessArticle
Food Waste Materials as Low-Cost Adsorbents for the Removal of Volatile Organic Compounds from Wastewater
Materials 2019, 12(24), 4242; https://doi.org/10.3390/ma12244242 - 17 Dec 2019
Viewed by 313
Abstract
The aim of this work was to study the potential of food waste materials (banana peel, potato peel, apple peel, lemon peel, coffee waste, decaf coffee waste, grape waste, and carob peel) as low-cost adsorbents for the removal of aliphatic and aromatic volatile [...] Read more.
The aim of this work was to study the potential of food waste materials (banana peel, potato peel, apple peel, lemon peel, coffee waste, decaf coffee waste, grape waste, and carob peel) as low-cost adsorbents for the removal of aliphatic and aromatic volatile organic compounds (VOCs) from wastewater. The ability of examined food waste materials to adsorb VOCs from synthetic multi-component standard solutions was evaluated and the examined food waste materials showed high removal efficiency. Performances of coffee waste, grape waste, and lemon peel were detailed by using Trichloroethylene and p-Xylene in mono-component standard solutions. The adsorption capacity of the three selected food wastes was determined by using linear Langmuir and Freundlich isotherm models. Two errors functions, average percentage error (APE) and the chi-square test (χ2), were used for isotherm optimization prediction. Freundlich isotherm well described the adsorption of VOCs on the considered materials. According to the obtained results, a multilayer, physical, and cooperative adsorption process was hypothesized, particularly evident when the VOCs’ concentrations are high. This was confirmed by the high adsorption efficiency percentages (E% > 80%) of VOCs from a real polluted matrix (urban solid waste leachate), containing high concentrations of total organic content. Full article
(This article belongs to the Special Issue Materials for Waste Water Treatment)
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Open AccessArticle
Micro–Macro Relationships in the Simulation of Wave Propagation Phenomenon Using the Discrete Element Method
Materials 2019, 12(24), 4241; https://doi.org/10.3390/ma12244241 - 17 Dec 2019
Viewed by 288
Abstract
The present work is aimed to investigate the capability of the discrete element method (DEM) to model properly wave propagation in solid materials, with special focus on the determination of elastic properties through wave velocities. Reference micro–macro relationships for elastic constitutive parameters have [...] Read more.
The present work is aimed to investigate the capability of the discrete element method (DEM) to model properly wave propagation in solid materials, with special focus on the determination of elastic properties through wave velocities. Reference micro–macro relationships for elastic constitutive parameters have been based on the kinematic hypothesis as well as obtained numerically by simulation of a quasistatic uniaxial compression test. The validity of these relationships in the dynamic analysis of the wave propagation has been checked. Propagation of the longitudinal and shear wave pulse in rectangular sample discretized with discs has been analysed. Wave propagation velocities obtained in the analysis have been used to determine elastic properties. Elastic properties obtained in the dynamic analysis have been compared with those determined by simulation of the quasistatic compression test. Full article
(This article belongs to the Special Issue Multi-scale Modeling of Materials and Structures)
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Open AccessArticle
Effect of Trace Zn Addition on Interfacial Evolution in Sn-10Bi/Cu Solder Joints during Aging Condition
Materials 2019, 12(24), 4240; https://doi.org/10.3390/ma12244240 - 17 Dec 2019
Viewed by 335
Abstract
Excessive growth of intermetallic compounds (IMCs) during service affects the reliability of solder joints, so how to suppress the growth of IMC thickness at the interface in solder joints becomes a widespread concern. In this work, the interfacial reaction between Sn-10Bi solder and [...] Read more.
Excessive growth of intermetallic compounds (IMCs) during service affects the reliability of solder joints, so how to suppress the growth of IMC thickness at the interface in solder joints becomes a widespread concern. In this work, the interfacial reaction between Sn-10Bi solder and Cu substrate after thermal aging was investigated. Moreover, to depress the IMC growth at the interface, trace amounts of Zn was added into the Sn-10Bi solder, and the interfacial reactions of Sn-10Bi-xZn solders (x = 0.2, 0.5) and Cu substrate after thermal aging were studied in this paper. Compounds such as Cu6(Sn, Zn)5 and Cu5Zn8 were formed at the interface after adding trace amounts of Zn. The addition of 0.2 and 0.5 wt% Zn significantly inhibited the thickness growth of IMCs and the formation of Cu3Sn IMC at the interface of Sn-10Bi-0.2Zn/Cu and Sn-10Bi-0.5Zn/Cu during thermal aging. Therefore, the addition of trace Zn had an obvious effect on the interfacial reaction of Sn-10Bi/Cu solder joint. Interestingly, the evolution of IMC thickness in Sn-10Bi-0.5Zn/Cu solder joints was completely different from that in Sn-10Bi or Sn-10Bi-0.2Zn solder joints, in which the spalling of IMCs occurred. In order to explore the mechanisms on the depressing effect from the addition of trace Zn, the activation energy Q in solder joints during aging was calculated. Full article
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Open AccessArticle
HPMC- and PLGA-Based Nanoparticles for the Mucoadhesive Delivery of Sitagliptin: Optimization and In Vivo Evaluation in Rats
Materials 2019, 12(24), 4239; https://doi.org/10.3390/ma12244239 - 17 Dec 2019
Viewed by 340
Abstract
Mucoadhesive nanoparticles represent a potential drug delivery strategy to enhance the therapeutic efficacy in oral therapy. This study assessed the prospective of developing HPMC- and PLGA-based nanoparticles using a nanospray drier as a mucoadhesive extended release drug delivery system for sitagliptin and evaluated [...] Read more.
Mucoadhesive nanoparticles represent a potential drug delivery strategy to enhance the therapeutic efficacy in oral therapy. This study assessed the prospective of developing HPMC- and PLGA-based nanoparticles using a nanospray drier as a mucoadhesive extended release drug delivery system for sitagliptin and evaluated their potential in an animal model. Nanoparticles were prepared using a Buchi® B-90 nanospray drier. Optimization of particle size was performed using response surface methodology by examining the influence of spray-drying process variables (inlet temperature, feed flow, and polymer concentration) on the particle size. The prepared nanoparticles were characterized for various physicochemical characteristics (yield, drug content, morphology, particle size, thermal, and crystallographic properties) and assessed for drug release, stability, and mucoadhesive efficacy by ex vivo and in vivo studies in rats. A linear model was suggested by the design of the experiments to be the best fit for the generated design and values. The yield was 77 ± 4%, and the drug content was 90.5 ± 3.5%. Prepared nanoparticles showed an average particle size of 448.8 nm, with a narrow particle size distribution, and were wrinkled. Thermal and crystallographic characteristics showed that the drug present in the nanoparticles is in amorphous dispersion. Nanoparticles exhibited a biphasic drug release with an initial rapid release (24.9 ± 2.7% at 30 min) and a prolonged release (98.9 ± 1.8% up to 12 h). The ex vivo mucoadhesive studies confirmed the adherence of nanoparticles in stomach mucosa for a long period. Histopathological assessment showed that the formulation is safe for oral drug delivery. Nanoparticles showed a significantly higher (p < 0.05) amount of sitagliptin retention in the GIT (gastrointestinal tract) as compared to control. The data observed in this study indicate that the prepared mucoadhesive nanoparticles can be an effective alternative delivery system for the oral therapy of sitagliptin. Full article
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Open AccessFeature PaperArticle
Visible-Light Activated Titania and Its Application to Photoelectrocatalytic Hydrogen Peroxide Production
Materials 2019, 12(24), 4238; https://doi.org/10.3390/ma12244238 - 17 Dec 2019
Viewed by 338
Abstract
Photoelectrochemical cells have been constructed with photoanodes based on mesoporous titania deposited on transparent electrodes and sensitized in the Visible by nanoparticulate CdS or CdS combined with CdSe. The cathode electrode was an air–breathing carbon cloth carrying nanoparticulate carbon. These cells functioned in [...] Read more.
Photoelectrochemical cells have been constructed with photoanodes based on mesoporous titania deposited on transparent electrodes and sensitized in the Visible by nanoparticulate CdS or CdS combined with CdSe. The cathode electrode was an air–breathing carbon cloth carrying nanoparticulate carbon. These cells functioned in the Photo Fuel Cell mode, i.e., without bias, simply by shining light on the photoanode. The cathode functionality was governed by a two-electron oxygen reduction, which led to formation of hydrogen peroxide. Thus, these devices were employed for photoelectrocatalytic hydrogen peroxide production. Two-compartment cells have been used, carrying different electrolytes in the photoanode and cathode compartments. Hydrogen peroxide production has been monitored by using various electrolytes in the cathode compartment. In the presence of NaHCO3, the Faradaic efficiency for hydrogen peroxide production exceeded 100% due to a catalytic effect induced by this electrolyte. Photocurrent has been generated by either a CdS/TiO2 or a CdSe/CdS/TiO2 combination, both functioning in the presence of sacrificial agents. Thus, in the first case ethanol was used as fuel, while in the second case a mixture of Na2S with Na2SO3 has been employed. Full article
(This article belongs to the Special Issue Advanced Photocatalytic Materials)
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Open AccessArticle
Feasibility of Utilizing Recycled Aggregate Concrete for Revetment Construction of the Lower Yellow River
Materials 2019, 12(24), 4237; https://doi.org/10.3390/ma12244237 - 17 Dec 2019
Viewed by 268
Abstract
To explore the feasibility of utilizing recycled aggregate concrete (RAC) in revetment construction of the lower Yellow River, a series of mix proportions with local recycled aggregates (RA) were designed to evaluate its mechanical properties and durability. The morphology and micro-hardness of the [...] Read more.
To explore the feasibility of utilizing recycled aggregate concrete (RAC) in revetment construction of the lower Yellow River, a series of mix proportions with local recycled aggregates (RA) were designed to evaluate its mechanical properties and durability. The morphology and micro-hardness of the interface transition zone (ITZ) were also characterized to explain the performance of RAC. Based on the compressive strength data of 13 groups of mixtures, which is larger than 30 MPa, and with the RA substitution rate not less than 50%, the RAC containing 50% recycled fine aggregate (RFA) (HDX50), 70% RFA (HDX70), and 50% recycled coarse aggregate (RCA) (HDC50) were selected. The experiment results suggest that the mechanical performance, frost resistance, and carbonation resistance of the selected RAC is generally poorer than that of natural aggregate concrete (NAC), but can meet the performance requirement of concrete for the revetment construction of the lower Yellow River. The comprehensive performance of these three mixtures ranks as: HDX50 > HDX70 > HDC50. When considering the RA substitution ratio as a priority, HDX70 would be the best choice and can be applied in the revetment engineering. A number of defects are observed on the surface of RA with old pastes attached. Furthermore, the ITZs formed around RA are loose and with low micro-hardness, which is deemed to be the dominating reasons leading to the weaker performance of RAC than that of NAC. Full article
(This article belongs to the Special Issue Recycled Concrete with Waste and By-products)
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Open AccessArticle
Study on In-Doped CdMgTe Crystals Grown by a Modified Vertical Bridgman Method Using the ACRT Technique
Materials 2019, 12(24), 4236; https://doi.org/10.3390/ma12244236 - 17 Dec 2019
Viewed by 312
Abstract
Cadmium–magnesium–telluride (CdMgTe) crystal was regarded as a potential semiconductor material. In this paper, an indium-doped Cd0.95Mg0.05Te ingot with 30 mm diameter and 120 mm length grown by a modified Bridgman method with excess Te condition was developed for room [...] Read more.
Cadmium–magnesium–telluride (CdMgTe) crystal was regarded as a potential semiconductor material. In this paper, an indium-doped Cd0.95Mg0.05Te ingot with 30 mm diameter and 120 mm length grown by a modified Bridgman method with excess Te condition was developed for room temperature gamma-ray detection. Characterizations revealed that the as-grown Cd0.95Mg0.05Te crystals had a cubic zinc-blende structure and additionally Te-rich second phase existed in the crystals. From the tip to tail of the ingot, the density of Te inclusions was about 103–105 cm−2. The crystals had a suitable band-gap range from 1.52–1.54 eV. Both infrared (IR) transmittance and resistivity were relatively low. Photoluminescence measurement indicated that the ingot had more defects. Fortunately, after annealing, IR transmittance and the resistivity were significantly enhanced due to the elimination of Te inclusions. CdMgTe crystal after annealing showed a good crystal quality. The energy resolutions of the detector for 241Am and 137Cs gamma-ray were 12.7% and 8.6%, respectively. The mobility-lifetime product for electron was 1.66 × 10−3 cm2/V. Thus, this material could be used for room temperature radiation detectors. Full article
(This article belongs to the Section Electronic Materials)
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Open AccessArticle
Application of a Dy3Co0.6Cu0.4Hx Addition for Controlling the Microstructure and Magnetic Properties of Sintered Nd-Fe-B Magnets
Materials 2019, 12(24), 4235; https://doi.org/10.3390/ma12244235 - 17 Dec 2019
Viewed by 290
Abstract
The focus of new technologies on the formation of inhomogeneous distributions of heavy rare-earth metals (REMs) in hard magnetic Nd–Fe–B materials is of scientific importance to increase their functional properties, along with preserving existing sources of heavy REMs. This paper focused on the [...] Read more.
The focus of new technologies on the formation of inhomogeneous distributions of heavy rare-earth metals (REMs) in hard magnetic Nd–Fe–B materials is of scientific importance to increase their functional properties, along with preserving existing sources of heavy REMs. This paper focused on the coercivity enhancement of Nd2Fe14B-based magnets by optimizing the microstructure, which includes the processes of grain boundary structuring via the application of a Dy3Co0.6Cu0.4Hx alloy added to the initial Nd–Fe–B-based powder mixtures in the course of their mechanical activation. We have studied the role of alloying elements in the formation of phase composition, microstructure, the fine structure of grains, and the hysteretic properties of hard magnetic Nd(R)2Fe14B-based materials. It was shown that the Dy introduction via the two-component blending process (the hydrogenated Dy3Co0.6Cu0.4 compound is added to a powder mixture) resulted in the formation of the core-shell structure of 2–14–1 phase grains. The efficient improvement of the coercivity of Nd(RE)–Fe–B magnets, with a slight sacrifice of remanence, was demonstrated. Full article
(This article belongs to the Special Issue Advanced Powder Metallurgy Technologies)
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Open AccessArticle
Structural Analysis of Calcium Phosphate-Based Submicrospheres with Internally-Crystallized Iron Oxide Nanoparticles Fabricated by a Laser-Assisted Precipitation Process
Materials 2019, 12(24), 4234; https://doi.org/10.3390/ma12244234 - 17 Dec 2019
Viewed by 270
Abstract
Calcium phosphate (CaP)-based submicrospheres containing magnetic iron oxide (IO) nanoparticles (IO–CaP submicrospheres) have potential for various biomedical applications. We recently achieved facile one-pot fabrication of IO–CaP submicrospheres using a laser-assisted precipitation process in which weak pulsed laser irradiation was applied to a labile [...] Read more.
Calcium phosphate (CaP)-based submicrospheres containing magnetic iron oxide (IO) nanoparticles (IO–CaP submicrospheres) have potential for various biomedical applications. We recently achieved facile one-pot fabrication of IO–CaP submicrospheres using a laser-assisted precipitation process in which weak pulsed laser irradiation was applied to a labile CaP reaction mixture supplemented with ferrous ions under adequate pH. In this study, we performed cross-sectional transmission electron microscopy (TEM) analysis of the resulting IO–CaP submicrospheres. The cross-sectional TEM analysis revealed that the IO–CaP submicrospheres were heterogeneous in their internal nanostructures and could be categorized into two types, namely types A and B. The type A submicrospheres contained single nano-sized IO nanoparticles homogeneously dispersed throughout the CaP-based matrix. The type B submicrospheres contained larger IO nanoparticles with an irregular or spherical shape, which were mostly a few tens of nanometers in size along with one or two submicron-sized domains. These findings provide new insight into the formation mechanism of IO–CaP submicrospheres in this fabrication technique as well as future applications of the resulting IO–CaP submicrospheres. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessFeature PaperArticle
The Effect of Hot Working on the Mechanical Properties of High Strength Biomedical Ti-Nb-Ta-Zr-O Alloy
Materials 2019, 12(24), 4233; https://doi.org/10.3390/ma12244233 - 17 Dec 2019
Viewed by 276
Abstract
Beta titanium alloy Ti-35Nb-6Ta-7Zr-0.7O (wt%) was developed as a material intended for the manufacturing of a stem of a hip joint replacement. This alloy contains only biocompatible elements and possesses a very high yield strength already in the cast condition (900 MPa). However, [...] Read more.
Beta titanium alloy Ti-35Nb-6Ta-7Zr-0.7O (wt%) was developed as a material intended for the manufacturing of a stem of a hip joint replacement. This alloy contains only biocompatible elements and possesses a very high yield strength already in the cast condition (900 MPa). However, the porosity, large grain size and chemical inhomogeneity reduce the fatigue performance below the limits required for utilization in the desired application. Two methods of hot working, die forging and hot rolling, were used for processing of this alloy. Microstructural evolution, tensile properties and fatigue performance of the hot worked material were investigated and compared to the cast material. Microstructural observations revealed that porosity is removed in all hot-worked conditions and the grain size is significantly reduced when the area reduction exceeds 70%. Static tensile properties were improved by both processing methods and ultimate tensile strength (UTS) of 1200 MPa was achieved. Fatigue results were more reproducible in the hot rolled material due to better microstructural homogeneity, but forging leads to an improved fatigue performance. Fatigue limit of 400 MPa was achieved in the die-forged condition after 70% of area reduction and in the hot rolled condition after 86% of area reduction. Full article
(This article belongs to the Special Issue Alloys for Biomedical Application)
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Open AccessArticle
Structural Characterisation and Chemical Stability of Commercial Fibrous Carbons in Molten Lithium Salts
Materials 2019, 12(24), 4232; https://doi.org/10.3390/ma12244232 - 17 Dec 2019
Viewed by 227
Abstract
The growing trend towards sustainable energy production, while intermittent, can meet all the criteria of energy demand through the use and development of high-performance thermal energy storage (TES). In this context, high-temperature hybrid TES systems, based upon the combination of fibrous carbon hosts [...] Read more.
The growing trend towards sustainable energy production, while intermittent, can meet all the criteria of energy demand through the use and development of high-performance thermal energy storage (TES). In this context, high-temperature hybrid TES systems, based upon the combination of fibrous carbon hosts and peritectic phase change materials (PCMs), are seen as promising solutions. One of the main conditions for the operational viability of hybrid TES is the chemical inertness between the components of the system. Thus, the chemical stability and compatibility of several commercial carbon felts (CFs) and molten lithium salts are discussed in the present study. Commercial CFs were characterised by elemental analysis, X-ray diffraction (XRD) and Raman spectroscopy before being tested in molten lithium salts: LiOH, LiBr, and the LiOH/LiBr peritectic mixture defined as our PCM of interest. The chemical stability was evaluated by gravimetry, gas adsorption and scanning electron microscopy (SEM). Among the studied CFs, the materials with the highest carbon purity and the most graphitic structure showed improved stability in contact with molten lithium salts, even under the most severe test conditions (750 °C). The application of the Arrhenius law allowed calculating the activation energy (in the range of 116 to 165 kJ mol−1), and estimating the potential stability of CFs at actual application temperatures. These results confirmed the applicability of CFs as porous hosts for stabilising peritectic PCMs based on molten lithium salts. Full article
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Open AccessArticle
Pozzolanic Activity of Zeolites: The Role of Si/Al Ratio
Materials 2019, 12(24), 4231; https://doi.org/10.3390/ma12244231 - 17 Dec 2019
Viewed by 271
Abstract
A great challenge of research is the utilization of natural or synthetic zeolites, in place of natural pozzolans, for manufacturing blended cements. The difficulties of interpretation of the pozzolanic behavior of natural zeolite-rich materials and the role played by their nature and composition [...] Read more.
A great challenge of research is the utilization of natural or synthetic zeolites, in place of natural pozzolans, for manufacturing blended cements. The difficulties of interpretation of the pozzolanic behavior of natural zeolite-rich materials and the role played by their nature and composition can be overcome by studying more simple systems, such as pure synthetic zeolites. This study aims at investigating the pozzolanic ability of isostructural zeolites with different framework compositions, such as three sodium zeolites of the faujasite (FAU) framework type: LSX, X, and Y. The pozzolanic activity has been estimated by thermogravimetry and X-ray diffraction analysis. The overall outcome of the investigation is that the zeolite structure affects its pozzolanic activity, as zeolites with similar framework densities exhibit distinct abilities to fix lime. Moreover, the framework composition is effective either from a kinetic point of view or on the total amount of fixed lime. Zeolite X appears to possess the best average features. Full article
(This article belongs to the Special Issue Zeolites: Synthesis, Properties and Applications)
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Open AccessArticle
Effects of Ce-Rich Mischmetal on Microstructure Evolution and Mechanical Properties of 5182 Aluminum Alloy
Materials 2019, 12(24), 4230; https://doi.org/10.3390/ma12244230 - 17 Dec 2019
Viewed by 266
Abstract
This paper addresses the effects of Ce-rich mischmetal on the microstructure evolution of a 5182 aluminum alloy during annealing and rolling processes. The Ce-rich mischmetal was added to an as-cast 5182 aluminum alloy in an induction furnace, and this was followed by homogenized [...] Read more.
This paper addresses the effects of Ce-rich mischmetal on the microstructure evolution of a 5182 aluminum alloy during annealing and rolling processes. The Ce-rich mischmetal was added to an as-cast 5182 aluminum alloy in an induction furnace, and this was followed by homogenized annealing at 450 °C for 24 h and a rolling operation. The microstructure evolution and mechanical properties’ analysis of the 5182 Al alloy were characterized. The results show that the Ce-rich mischmetal could modify the microstructure, refine the α-Al grains, break the network distribution of Mg2Si phases, and prevent Cr and Si atoms from diffusing into the Al6(Mn, Fe) phase in the as-cast 5182 Al alloys. Ce-rich mischmetal elements were also found to refine the Al6(Mn, Fe) phase after cold rolling. Then, the refined Al6(Mn, Fe) particles inhibited the growth of recrystallization grains to refine them from 10.01 to 7.18 μm after cold rolling. Consequently, the tensile strength of the cold-rolled 5182 Al alloy increased from 414.65 to 454.34 MPa through cell-size strengthening, dislocation density strengthening, and particle strengthening. The tensile strength of the recrystallization annealed 5182 Al alloy was increased from 322.16 to 342.73 MPa through grain refinement strengthening, and this alloy was more stable after the recrystallization annealing temperature. Full article
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Open AccessArticle
Effect of Different Aggregates on the Mechanical Damage Suffered by Geotextiles
Materials 2019, 12(24), 4229; https://doi.org/10.3390/ma12244229 - 17 Dec 2019
Viewed by 297
Abstract
The installation process of geosynthetics can be, in some applications, one of the most relevant degradation mechanisms of these construction materials, affecting their performance and useful lifetime. In this work, three nonwoven geotextiles with different masses per unit area were submitted to mechanical [...] Read more.
The installation process of geosynthetics can be, in some applications, one of the most relevant degradation mechanisms of these construction materials, affecting their performance and useful lifetime. In this work, three nonwoven geotextiles with different masses per unit area were submitted to mechanical damage under repeated loading tests with corundum and with different natural aggregates. The damage occurred in the geotextiles was evaluated by visual inspection and by monitoring changes in their short-term tensile and puncture behaviors (mechanical properties) and in their water permeability behavior normal to the plane (hydraulic property). The mechanical damage under repeated loading tests provoked relevant changes in the mechanical and hydraulic properties of the geotextiles. These changes depended on the mass per unit area of the geotextiles and on the characteristics of the aggregates. The results enabled the establishment of a correlation between the loss of mechanical strength and the variation of the water permeability normal to the plane of the geotextiles. Full article
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Open AccessArticle
The Influence of Microstructure on the Mechanical Properties and Fracture Behavior of Medium Mn Steels at Different Strain Rates
Materials 2019, 12(24), 4228; https://doi.org/10.3390/ma12244228 - 17 Dec 2019
Viewed by 255
Abstract
The primary task of automotive industry materials is to guarantee passengers’ safety during a car crash. To simulate a car crash, the influence of strain rates on mechanical properties and fracture behavior of medium Mn steels with different Si content (0Si without δ-ferrite [...] Read more.
The primary task of automotive industry materials is to guarantee passengers’ safety during a car crash. To simulate a car crash, the influence of strain rates on mechanical properties and fracture behavior of medium Mn steels with different Si content (0Si without δ-ferrite and 0.6Si with about 20% δ-ferrite) was conducted using the uniaxial tensile test. The results show that ultimate tensile strength is higher, whereas total elongation is lower in 0Si than in 0.6Si. As the strain rate increases, ultimate tensile strength and total elongation decrease in both 0Si and 0.6Si; nonetheless, total elongation of 0.6Si decreases faster. Meanwhile, the area reduction of 0.6Si increases as the strain rate increases. The microcrack′s number on a rolling direction (RD)-transverse direction (TD) surface is considerably increased; nonetheless, the microcrack′s size is restrained in 0.6Si compared with 0Si. Microcracks start at γ(α′)/α-ferrite interfaces in both 0Si and 0.6Si, whereas little nucleation sites have also been found at (γ(α′)+α-ferrite)/δ-ferrite boundaries in 0.6Si. Meanwhile, δ-ferrite reveals a higher capacity for microcrack arrest. As the strain rate decreases, increased lower crack growth results in fine and even dimples on fractographs with abundant second cracks on fractographs; meanwhile, the small microcrack′s number increases, while the large microcrack′s number decreases on an RD-TD surface. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Steels)
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Open AccessArticle
Microstructure Formation in Cast TiZrHfCoNiCu and CoNiCuAlGaIn High Entropy Shape Memory Alloys: A Comparison
Materials 2019, 12(24), 4227; https://doi.org/10.3390/ma12244227 - 16 Dec 2019
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Abstract
The present study is dedicated to the microstructure characterization of the as-cast high entropy intermetallics that undergo a martensitic transformation, which is associated with the shape memory effect. It is shown that the TiZrHfCoNiCu system exhibits strong dendritic liquation, which leads to the [...] Read more.
The present study is dedicated to the microstructure characterization of the as-cast high entropy intermetallics that undergo a martensitic transformation, which is associated with the shape memory effect. It is shown that the TiZrHfCoNiCu system exhibits strong dendritic liquation, which leads to the formation of martensite crystals inside the dendrites. In contrast, in the CoNiCuAlGaIn system the dendritic liquation allows the martensite crystals to form only in interdendritic regions. This phenomenon together with the peculiarities of chemical inhomogeneities formed upon crystallization of this novel multicomponent shape memory alloys systems will be analyzed and discussed. Full article
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Open AccessArticle
Improving the Tribological Performance of MAO Coatings by Using a Stable Sol Electrolyte Mixed with Cellulose Additive
Materials 2019, 12(24), 4226; https://doi.org/10.3390/ma12244226 - 16 Dec 2019
Viewed by 276
Abstract
In this study, micro-arc oxidation (MAO) of aluminum 6061 alloy was carried out within a silicate base electrolyte containing 0.75 g/L of cellulose, and the tribological properties of the coating were investigated. The as-prepared coating was detected by Fourier Transform Infrared Spectroscopy (FTIR), [...] Read more.
In this study, micro-arc oxidation (MAO) of aluminum 6061 alloy was carried out within a silicate base electrolyte containing 0.75 g/L of cellulose, and the tribological properties of the coating were investigated. The as-prepared coating was detected by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS), respectively. The results suggested that cellulose filled in the microcracks and micropores, or it existed by cross-linking with Al3+. In addition, it was found that the cellulose had little effect on the coating hardness. However, the thickness and roughness of the coating were improved with the increase in cellulose concentration. Moreover, the ball-on-disk test showed that the friction coefficient, weight loss and wear rate of the MAO coating decreased with the increase in cellulose concentration. Further, the performances of the coatings obtained in the same electrolyte, under different preserved storage periods, were compared, revealing that the cellulose was uniformly dispersed in the electrolyte and improved the tribological properties of the MAO coating within 30 days. Full article
(This article belongs to the Special Issue Metal Oxide Thin Film: Synthesis, Characterization and Application)
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Open AccessArticle
Correlation between Dental Vestibular–Palatal Inclination and Alveolar Bone Remodeling after Orthodontic Treatment: A CBCT Analysis
Materials 2019, 12(24), 4225; https://doi.org/10.3390/ma12244225 - 16 Dec 2019
Viewed by 279
Abstract
The aim of this study was to evaluate the correlation between dental vestibular–palatal inclination changes and the cortical bone remodeling after fixed orthodontic treatment using cone beam computed tomography (CBCT). Twenty-two patients with Angle Class I malocclusion, permanent dentition, and mild to moderate [...] Read more.
The aim of this study was to evaluate the correlation between dental vestibular–palatal inclination changes and the cortical bone remodeling after fixed orthodontic treatment using cone beam computed tomography (CBCT). Twenty-two patients with Angle Class I malocclusion, permanent dentition, and mild to moderate dental crowding were included in the present three-dimensional (3D) analysis. Bone dimensions were evaluated by CBCT scans obtained before and after orthodontic treatment, whereas the torque values were calculated by means of digital models using the 3D VistaDent software. A paired t-test was used to compare the changes between the pretreatment and post-treatment measurements. The correlations between variables were analyzed with linear regression analysis. A significant correlation between torque variations and bone thickness changes was observed for the apical buccal level of the anterior side (P < 0.05). Limited and not significant alveolar bone resorption for the apical thickness of anterior teeth occurred at ± 5 degrees of torque variation, while for tooth inclination exceeding +5 or −5 degrees, the bone remodeling was more evident. The present study demonstrated that anterior region was the most affected area by bone remodeling and that torque variation was highly related to apical bone thickness adaptation for maxillary and mandibular incisors and maxillary canines. Full article
(This article belongs to the Special Issue Digital Manufacturing in Dentistry)
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Open AccessArticle
In-depth Investigation of Hg2Br2 Crystal Growth and Evolution
Materials 2019, 12(24), 4224; https://doi.org/10.3390/ma12244224 - 16 Dec 2019
Viewed by 263
Abstract
Physical vapor transport (PVT) has frequently been adopted for the synthesis of mercurous bromide (Hg2Br2) single crystals for acousto-optic modulators. However, thus far, very few in-depth studies have been conducted that elucidate the growth process of the Hg2 [...] Read more.
Physical vapor transport (PVT) has frequently been adopted for the synthesis of mercurous bromide (Hg2Br2) single crystals for acousto-optic modulators. However, thus far, very few in-depth studies have been conducted that elucidate the growth process of the Hg2Br2 single crystal. This paper reports an in-depth investigation regarding the crystal growth and evolution behavior of the Hg2Br2 crystal with facet growth mode. Based on the experimental and simulation results, the temperature profile conditions concerning the seed generation and seed growth could be optimized. Next, the PVT-grown Hg2Br2 crystals (divided into single crystal and quasi-single crystal regions) were characterized using various analysis techniques. The single-crystal Hg2Br2 was found to possess a more uniform strain than that of the quasi-single crystal through a comparison of the X-ray diffraction data. Meanwhile, the binding energy states and electron backscatter diffraction images of the as-synthesized Hg2Br2 crystals were similar, regardless of the crystal type. Furthermore, Raman spectroscopy and transmission electron microscopy analyses provided information on the atomic vibration mode and atomic structures of the two kinds of samples. The synergistic combination of the simulation and experimental results used to verify the growth mechanism facilitates the synthesis of high-quality Hg2Br2 crystals for potential acousto-optic tunable filter device applications. Full article
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Open AccessArticle
Microstructure Evolution and Mechanical Properties of AZ80 Mg Alloy during Annular Channel Angular Extrusion Process and Heat Treatment
Materials 2019, 12(24), 4223; https://doi.org/10.3390/ma12244223 - 16 Dec 2019
Viewed by 259
Abstract
Microstructure evolution and mechanical properties of AZ80 Mg alloy during annular channel angular extrusion (350 °C) and heat treatment with varying parameters were investigated, respectively. The results showed that dynamic recrystallization of Mg grains was developed and the dendritic eutectic β-Mg17Al [...] Read more.
Microstructure evolution and mechanical properties of AZ80 Mg alloy during annular channel angular extrusion (350 °C) and heat treatment with varying parameters were investigated, respectively. The results showed that dynamic recrystallization of Mg grains was developed and the dendritic eutectic β-Mg17Al12 phases formed during the solidification were broken into small β-phase particles after hot extrusion. Moreover, a weak texture with two dominant peaks formed owing to the significant grain refinement and the enhanced activation of pyramidal <c + a> slip at relative high temperature. The tension tests showed that both the yield strength and ultimate tensile strength of the extruded alloy were dramatically improved owing to the joint strengthening effect of fine grain and β-phase particles as compared with the homogenized sample. The solution treatment achieved the good plasticity of the alloy resulting from the dissolution of β-phases and the development of more equiaxed grains, while the direct-aging process led to poor alloy elongation as a result of residual eutectic β-phases. After solution and aging treatment, simultaneous bonding strength and plasticity of the alloy were achieved, as a consequence of dissolution of coarse eutectic β-phases and heterogeneous precipitation of a large quantity of newly formed β-phases with both the morphologies of continuous and discontinuous precipitates. Full article
(This article belongs to the Special Issue Light-weight Metallic Materials)
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Open AccessArticle
The AC Soft Magnetic Properties of FeCoNixCuAl (1.0 ≤ x ≤ 1.75) High-Entropy Alloys
Materials 2019, 12(24), 4222; https://doi.org/10.3390/ma12244222 - 16 Dec 2019
Viewed by 274
Abstract
High-entropy alloys (HEAs) with soft magnetic properties are one of the new candidate soft magnetic materials which are usually used under an alternating current (AC) magnetic field. In this work, the AC soft magnetic properties are investigated for FeCoNixCuAl (1.0 ≤ [...] Read more.
High-entropy alloys (HEAs) with soft magnetic properties are one of the new candidate soft magnetic materials which are usually used under an alternating current (AC) magnetic field. In this work, the AC soft magnetic properties are investigated for FeCoNixCuAl (1.0 ≤ x ≤ 1.75) HEAs. The X-ray diffraction (XRD) and scanning electron microscope (SEM) show that the alloy consists of two phases, namely a face-centred cubic (FCC) phase and a body-centred cubic (BCC) phase. With increasing Ni content, the FCC phase content increased. Further research shows that the AC soft magnetic properties of these alloys are closely related to their phase constitution. Increasing the FCC phase content contributes to a decrease in the values of AC remanence (AC Br), AC coercivity (AC Hc) and AC total loss (Ps), while it is harmful to the AC maximum magnetic flux density (AC Bm). Ps can be divided into two parts: AC hysteresis loss (Ph) and eddy current loss (Pe). With increasing frequency f, the ratio of Ph/Ps decreases for all samples. When f ≤ 150 Hz, Ph/Ps > 70%, which means that Ph mainly contributes to Ps. When f ≥ 800 Hz, Ph/Ps < 40% (except for the x = 1.0 sample), which means that Pe mainly contributes to Ps. At the same frequency, the ratio of Ph/Ps decreases gradually with increasing FCC phase content. The values of Pe and Ph are mainly related to the electrical resistivity (ρ) and the AC Hc, respectively. This provides a direction to reduce Ps. Full article
(This article belongs to the Special Issue Magnetic Materials and Applications)
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Open AccessArticle
Functionalized rGO Interlayers Improve the Fill Factor and Current Density in PbS QDs-Based Solar Cells
Materials 2019, 12(24), 4221; https://doi.org/10.3390/ma12244221 - 16 Dec 2019
Viewed by 328
Abstract
Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in [...] Read more.
Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers. Full article
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Open AccessArticle
Low Temperature Characteristics of Hydrogen Storage Alloy LaMm-Ni4.1Al0.3Mn0.4Co0.45 for Ni-MH Batteries
Materials 2019, 12(24), 4220; https://doi.org/10.3390/ma12244220 - 16 Dec 2019
Viewed by 281
Abstract
Nickel hydride batteries (Ni-MH) are known of their good performance and high reliability at temperatures below 0 °C, which is significantly dependent on electrolyte composition. Here we present the low temperature characteristics of pristine AB5-type alloy, LaMm-Ni4.1Al0.3Mn0.4Co [...] Read more.
Nickel hydride batteries (Ni-MH) are known of their good performance and high reliability at temperatures below 0 °C, which is significantly dependent on electrolyte composition. Here we present the low temperature characteristics of pristine AB5-type alloy, LaMm-Ni4.1Al0.3Mn0.4Co0.45, determined in various alkali metal hydroxide solutions. We found that the combination of KOH with NaOH showed a significant effect of enhancement of low temperature performance of the electrode material and diffusion of hydrogen in the alloy. This 6M binary mixed NaOH/KOH electrolyte, comprising 4M KOH component and 2M NaOH component, made it possible to maintain 81.7% and 61.0% of maximum capacity at −20 °C and −30 °C, respectively, enhancing the hydrogen storage properties of the alloy after reheating to room temperature. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
Effect of Flow State of Pure Aluminum and A380 Alloy on Porosity of High Pressure Die Castings
Materials 2019, 12(24), 4219; https://doi.org/10.3390/ma12244219 - 16 Dec 2019
Viewed by 263
Abstract
Air entrapment defects prevent the heat treatment from improving the mechanical properties of die castings, which limits the die casting of high-performance components. The flow pattern of the filling process is complicated and experimental analysis is difficult in thin-walled complex die castings. In [...] Read more.
Air entrapment defects prevent the heat treatment from improving the mechanical properties of die castings, which limits the die casting of high-performance components. The flow pattern of the filling process is complicated and experimental analysis is difficult in thin-walled complex die castings. In this study, we constructed a shock absorption tower to observe in real-time the filling process of pure aluminum and A380 aluminum alloy at different fast injection speeds. The degree of breakup of pure aluminum was larger than that of A380 during the filling process, which caused the porosity of pure aluminum to be greater than that of the A380 at each observation position. Re-Oh diagrams explained the difference in porosity between the two metals. The porosity in different regions was closely related to the flow state of aluminum liquid. In addition to porosity measurements, we specifically analyzed the relationship between the porosity of the flowback zone, the final filling zone, and the near-tail zone of cylinder. At the same injection velocity, the porosity at flowback zone was greater than that at the final filling position, the porosity at final filling position was larger than that at the near-tail zone of cylinder, and the final filling position changed as the injection velocity changed. Full article
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Open AccessArticle
From Silver Nanoflakes to Silver Nanonets: An Effective Trade-Off between Conductivity and Stretchability of Flexible Electrodes
Materials 2019, 12(24), 4218; https://doi.org/10.3390/ma12244218 - 16 Dec 2019
Viewed by 247
Abstract
Flexible and stretchable conductive materials have received significant attention due to their numerous potential applications in flexible printed electronics. In this paper, we describe a new type of conductive filler for flexible electrodes—silver nanonets prepared through the “dissolution–recrystallization” solvothermal route from porous silver [...] Read more.
Flexible and stretchable conductive materials have received significant attention due to their numerous potential applications in flexible printed electronics. In this paper, we describe a new type of conductive filler for flexible electrodes—silver nanonets prepared through the “dissolution–recrystallization” solvothermal route from porous silver nanoflakes. These new silver fillers show characteristics of both nanoflakes and nanoparticles with propensity to form interpenetrating polymer–silver networks. This effectively minimizes trade-off between composite electrode conductivity and stretchability and enables fabrication of the flexible electrodes simultaneously exhibiting high conductivity and mechanical durability. For example, an electrode with uniform, networked silver structure from the flakiest silver particles showed the lowest increase of resistivity upon extension (3500%), compared to that of the electrode filled with less flaky (3D) particles (>50,000%). Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Investigation on the Thermal Conductivity of Mineral Oil-Based Alumina/Aluminum Nitride Nanofluids
Materials 2019, 12(24), 4217; https://doi.org/10.3390/ma12244217 - 16 Dec 2019
Viewed by 255
Abstract
Al2O3/AlN–mineral oil nanofluids were prepared by dispersing commercially available Al2O3 and AlN nanoparticles into mineral oil. SEM measurements showed that the average diameter of the Al2O3 and AlN nanoparticles was about 55 and [...] Read more.
Al2O3/AlN–mineral oil nanofluids were prepared by dispersing commercially available Al2O3 and AlN nanoparticles into mineral oil. SEM measurements showed that the average diameter of the Al2O3 and AlN nanoparticles was about 55 and 50 nm, respectively. The experiments showed that the thermal conductivity systematically improved as the Al2O3 and AlN nanoparticles were introduced into the mineral oil. The thermal conductivity of the mineral oil-based nanofluids increased by 18% with a 1% volume fraction of Al2O3 and increased by 7% with a 0.5% volume fraction of AlN. The experimental data were compared with the values that were predicted by four typical thermal conductivity models, and a large disparity was disclosed between the models and the experimental data. After considering the thermal dynamic factors in the Al2O3/AlN–mineral oil nanofluids, a universal model is proposed that agrees well with the variation of thermal conductivity of the nanofluids. Full article
(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)
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Open AccessArticle
Enhanced Positioning Algorithm Using a Single Image in an LCD-Camera System by Mesh Elements’ Recalculation and Angle Error Orientation
Materials 2019, 12(24), 4216; https://doi.org/10.3390/ma12244216 - 16 Dec 2019
Viewed by 262
Abstract
In this article, we present a method to position the tool in a micromachine system based on a camera-LCD screen positioning system that also provides information about angular deviations of the tool axis during its running. Both position and angular deviations are obtained [...] Read more.
In this article, we present a method to position the tool in a micromachine system based on a camera-LCD screen positioning system that also provides information about angular deviations of the tool axis during its running. Both position and angular deviations are obtained by reducing a matrix of LEDs in the image to a single rectangle in the conical perspective that is treated by a photogrammetry method. This method computes the coordinates and orientation of the camera with respect to the fixed screen coordinate system. The used image consists of 5 × 5 lit LEDs, which are analyzed by the algorithm to determine a rectangle with known dimensions. The coordinates of the vertices of the rectangle in space are obtained by an inverse perspective computation from the image. The method presents a good approximation of the central point of the rectangle and provides the inclination of the workpiece with respect to the LCD screen reference system of coordinates. A test of the method is designed with the assistance of a Coordinate Measurement Machine (CMM) to check the accuracy of the positioning method. The performed test delivers a good accuracy in the position measurement of the designed method. A high dispersion in the angular deviation is detected, although the orientation of the inclination is appropriate in almost every case. This is due to the small values of the angles that makes the trigonometric function approximations very erratic. This method is a good starting point for the compensation of angular deviation in vision based micromachine tools, which is the principal source of errors in these operations and represents the main volume in the cost of machine elements’ parts. Full article
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