bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigations of Perforated CFRP Z-Cross-Section Profiles, under Axial Compression
Authors: Falkowicz Katarzyna
Published: October 2022

Thin-walled elements, thanks to their good properties, are increasingly used in structural applications, especially in the aircraft and building industries. These kinds of structures are often perforated for reducing weight and to ease servicing and maintenance operations, e.g., in aircraft wing ribs. These perforations cause a redistribution of stresses in the element which may change the ultimate strength of the structure and their elastic stiffness. The buckling behaviour of structural members with perforations is significantly influenced by the size, location, shape and number of perforations. Therefore, it is necessary to investigate the influence of these kinds of cut-out parameters on thin-walled structure buckling and postbuckling behaviour. This study investigated numerically the buckling and postbuckling behaviour of thin-walled perforated composite profiles with a Z-cross-section subjected to compression load. Numerical calculations were performed using the finite element method in the ABAQUS® program. The study investigated the effect of localisation and geometric parameters of cut-outs on the buckling load, postbuckling equilibrium path and failure load. Moreover, the perforated profiles were compared with a profile without cut-outs, which were experimentally tested in previous research. Results showed that the perforated profiles with a Z-cross-section do not lose their stability in the post-critical range. What is more, a well-chosen arrangement of the holes may prevent the mechanical properties from deteriorating.
Ultra-Fast Thermal Shock Evaluation of Ti2AlC Ceramic
Authors: Ding Wei , Hu Baotong , Fu Shuai , Wan Detian , Bao Yiwang , Feng Qingguo , Grasso Salvatore , Hu Chunfeng
Published: October 2022

In this work, the rapid thermal shock behavior of Ti2AlC ceramics was studied using induction heating. The present evaluation method possesses the merits of very rapid heating within tens of seconds and fast quenching in water of less than 0.1 s, removing the shortcomings of traditional thermal shock. For comparison, the samples were also quenched in the air to investigate the thermal shock mechanisms. The results showed that the abnormal shock occurred in the samples when quenching in water, ascribed to the formed oxide layer on the surface of Ti2AlC ceramic inhibited the water penetration into the substrate. The quenched Ti2AlC samples still had a high residual flexural strength above 167 MPa up to 1150 °C, exhibiting promising applications in the high-temperature fields.
State-of-the-Art Review on Engineering Uses of Calcium Phosphate Compounds: An Eco-Friendly Approach for Soil Improvement
Authors: Avramenko Maksym , Nakashima Kazunori , Kawasaki Satoru
Published: October 2022

Greenhouse gas emissions are a critical problem nowadays. The cement manufacturing sector alone accounts for 8% of all human-generated emissions, and as the world’s population grows and globalization intensifies, this sector will require significantly more resources. In order to fulfill the need of geomaterials for construction and to reduce carbon dioxide emissions into the atmosphere, conventional approaches to soil reinforcement need to be reconsidered. Calcium phosphate compounds (CPCs) are new materials that have only recently found their place in the soil reinforcement field. Its eco-friendly, non-toxic, reaction pathway is highly dependent on the pH of the medium and the concentration of components inside the solution. CPCs has advantages over the two most common environmental methods of soil reinforcement, microbial-induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP); with CPCs, the ammonium problem can be neutralized and thus allowed to be applied in the field. In this review paper, the advantages and disadvantages of the engineering uses of CPCs for soil improvement have been discussed. Additionally, the process of how CPCs perform has been studied and an analysis of existing studies related to soil reinforcement by CPC implementation was conducted.
Application of Nanofluids in Improving the Performance of Double-Pipe Heat Exchangers—A Critical Review
Authors: Louis Stephan Pierre , Ushak Svetlana , Milian Yanio , Nemś Magdalena , Nemś Artur
Published: October 2022

Nanofluids can be employed as one of the two fluids needed to improve heat exchanger performance due to their improved thermal and rheological properties. In this review, the impact of nanoparticles on nanofluid properties is discussed by analyzing factors such as the concentration, size, and shape of nanoparticles. Nanofluid thermophysical properties and flow rate directly influence the heat transfer coefficient and pressure drop. High thermal conductivity nanoparticles improve the heat transfer coefficient; in particular, metallic oxide (such as MgO, TiO2, and ZnO) nanoparticles show greater enhancement of this property by up to 30% compared to the base fluid. Nanoparticle size and shape are other factors to consider as well, e.g., a significant difference in thermal conductivity enhancement from 6.41% to 9.73% could be achieved by decreasing the Al2O3 nanoparticle size from 90 to 10 nm, affecting nanofluid viscosity and density. In addition, equations to determine the heat transfer rate and the pressure drop in a double-pipe heat exchanger are presented. It was established that the main factor that directly influences the heat transfer coefficient is the nanofluid thermal conductivity, and nanofluid viscosity affects the pressure drop.
Simulation Analysis of Delamination Damage for the Thick-Walled Composite-Overwrapped Pressure Vessels
Authors: Fang Houcheng , Wang Di
Published: October 2022

In order to verify the delamination damage occurring in thick-walled composite-overwrapped pressure vessels, firstly, for composite delamination damage, a composite laminate model was established. Model I and model II delamination failure processes of composite structures were simulated and verified based on a tiebreak contact algorithm for different mesh sizes, respectively, and the approximate equivalent results were achieved by correcting the inter-ply strength. Then, for in-plane damage to composite materials, the elastic–plastic process was verified by selecting a progressive damage model, with quasistatic nonlinear tensile shear of sample specimens as an example. Further, under the purpose of generality and simplicity, the location of the first occurrence of delamination failure was simulated and analyzed with the tiebreak contact algorithm and a reasonable mesh size, using quasistatic loading of a thick composite-overwrapped pressure vessel cylindrical section as an example. The results showed that delamination occurred at approximately the center, which is in general agreement with the experimentally observed phenomenon. On this basis, the locations of the first significant delamination phenomena in composite-overwrapped vessels under three different ratios of plus or minus 45-degree layup angles were predicted. Finally, the differences in structural strength between the single laying methods and the combined laying method were compared. The results showed that the ratio of 50% had a higher modulus value than a pure 0° ply, but too large a ratio was detrimental to the improvement of structural properties.
PbS and PbO Thin Films via E-Beam Evaporation: Morphology, Structure, and Electrical Properties
Authors: Akhtar Saad , Saeed Nimra , Hanif Muhammad Bilal , Zia-ur-Rehman  , Dogar Salahuddin , Mahmood Waqar , Mosiałek Michał , Napruszewska Bogna Daria , Ashraf Muhammad , Motola Martin , Khan Abdul Faheem
Published: October 2022

Thin films of lead sulfide (PbS) are being extensively used for the fabrication of optoelectronic devices for commercial and military applications. In the present work, PbS films were fabricated onto a soda lime glass substrate by using an electron beam (e-beam) evaporation technique at a substrate temperature of 300 °C. Samples were annealed in an open atmosphere at a temperature range of 200–450 °C for 2 h. The deposited films were characterized for structural, optical, and electrical properties. Structural properties of PbS have been studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and Rutherford backscattering spectrometry (RBS). The results of XRD showed that the PbS thin film was crystalline in nature at room temperature with cubic crystal structure (galena) and preferential (111) and orientation (022). The morphology of the thin films was studied by FESEM, which also showed uniform and continuous deposition without any peel-off and patches. EDS analysis was performed to confirm the presence of lead and sulfur in as-deposited and annealed films. The thickness of the PbS film was found to be 172 nm, which is slightly greater than the intended thickness of 150 nm, determined by RBS. Ultraviolet-Visible-Near-Infrared (UV-Vis-NIR) spectroscopy revealed the maximum transmittance of ~25% for as-deposited films, with an increase of 74% in annealed films. The band gap of PbS was found in the range of 2.12–2.78 eV for as-deposited and annealed films. Hall measurement confirmed the carriers are p-type in nature. Carrier concentration, mobility of the carriers, conductivity, and sheet resistance are directly determined by Hall-effect measurement. The as-deposited sample showed a conductivity of 5.45 × 10−4 S/m, which gradually reduced to 1.21 × 10−5 S/m due to the composite nature of films (lead sulfide along with lead oxide). Furthermore, the present work also reflects the control of properties by controlling the amount of PbO present in the PbS films which are suitable for various applications (such as IR sensors).
Iodide Removal by Resorcinol-Formaldehyde Carbon Aerogels
Authors: Domán Andrea , Battalgazy Bekassyl , Dobos Gábor , Kiss Gábor , Tauanov Zhandos , László Krisztina , Zorpas Antonis A. , Inglezakis Vassilis J.
Published: October 2022

The adsorption technique is widely used in water purification, and its efficiency can be significantly improved by target-specific adsorbent design. Research on iodine and its ion removal from water has attracted a great deal of interest due to increased concentrations in the environment and acute toxic effects, e.g., in human thyroid cells. In this work, the iodide removal performance of two high-surface-area resorcinol–formaldehyde-based carbon aerogels was studied under acidic conditions. The BET surface area was 790 m2/g (RF_ac) and 375 m2/g (RMF-GO), with a corresponding micropore ratio of 36 and 26%, respectively. Both aerogels showed outstanding adsorption capacity, exceeding the reported performance of other carbons and Ag-doped materials. Owing to its basic nature, the RMF-GO carbon aerogel showed higher I− capacity, up to 97 mg/g, than the acidic RF_ac, which reached a capacity of 82 mg/g. The surface chemistry of the aerogels also played a distinct role in the removal. In terms of kinetics, RF_ac removed 60% of the iodide ions and RMF-GO 30% within 8 h. The removal kinetics was of the first order, with a half-life of 1.94 and 1.70 h, respectively.
ZnAl-SO4 Layered Double Hydroxide and Allophane for Cr(VI), Cu(II) and Fe(III) Adsorption in Wastewater: Structure Comparison and Synergistic Effects
Authors: Cardinale Anna Maria , Carbone Cristina , Fortunato Marco , Fabiano Bruno , Reverberi Andrea Pietro
Published: October 2022

Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO4 LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO4 LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.
Enhancement of Magnetic and Dielectric Properties of Ni0.25Cu0.25Zn0.50Fe2O4 Magnetic Nanoparticles through Non-Thermal Microwave Plasma Treatment for High-Frequency and Energy Storage Applications
Authors: Munir Muhammad Adnan , Naz Muhammad Yasin , Shukrullah Shazia , Ansar Muhammad Tamoor , Farooq Muhammad Umar , Irfan Muhammad , Mursal Salim Nasar Faraj , Legutko Stanislaw , Petrů Jana , Pagáč Marek
Published: October 2022

Spinel ferrites are widely investigated for their widespread applications in high-frequency and energy storage devices. This work focuses on enhancing the magnetic and dielectric properties of Ni0.25Cu0.25Zn0.50 ferrite series through non-thermal microwave plasma exposure under low-pressure conditions. A series of Ni0.25Cu0.25Zn0.50 ferrites was produced using a facile sol–gel auto-ignition approach. The post-synthesis plasma treatment was given in a low-pressure chamber by sustaining oxygen plasma with a microwave source. The structural formation of control and plasma-modified ferrites was investigated through X-ray diffraction analysis, which confirmed the formation of the fcc cubical structure of all samples. The plasma treatment did not affect crystallize size but significantly altered the surface porosity. The surface porosity increased after plasma treatment and average crystallite size was measured as about ~49.13 nm. Morphological studies confirmed changes in surface morphology and reduction in particle size on plasma exposure. The saturation magnetization of plasma-exposed ferrites was roughly 65% higher than the control. The saturation magnetization, remnant magnetization, and coercivity of plasma-exposed ferrites were calculated as 74.46 emu/g, 26.35 emu/g, and 1040 Oe, respectively. Dielectric characteristics revealed a better response of plasma-exposed ferrites to electromagnetic waves than control. These findings suggest that the plasma-exposed ferrites are good candidates for constructing high-frequency devices.
Rheological Characterization and Accumulation Tests for Strong Thixotropic Engineering Slurry
Authors: Yuan Kekuo , Lu Yating , Li Wanlu , Yu Hongdan , Gao Shan
Published: October 2022

Underground void subsidence hazards, especially mine goaf, have now become one of the major social problems affecting the well-being of civilians and development in China. The objective of this study was to propose a kind of strong thixotropic engineering slurry and filling treatment for use in underground void subsidence hazards. The optimal agent ratio for thixotropic cement slurry/mortar was obtained by indoor tests, where the rheological agent is 7.5% compared to the weight of cement, the water–solid ratio is in the range of 0.7~0.8, and the aeolian sand ratio can be 0~1.5 times that of cement. The rheological properties of slurry and mortar were tested using a Brookfield RST-SST rheometer. The results show that aeolian sand can be used as thixotropic cement mortar for a backfilling treatment for underground voids (mine goaf). The static yield stress increases non-linearly compared to existing thixotropic models. The stress decays sharply with shearing (the shear rate is more or less 10 s−1) and then the stress increases with the increase in shear rate (the shear rate is more than 10 s−1). The increase in the stress of the slurry is greater than in the mortar. A natural logarithmic function between yield stress and rest time (only 1 parameter), an exponential function with two parts for stress–shear rate (a rheology model, with only 3 parameters), and an exponential function for the accumulation law (only 2 parameters) were proposed in turn.
Design of an Intermediate Die for the Multi-Pass Shape Drawing Process
Authors: Kim Jeong-Hun , Park Jeong-Hyun , Lee Kwang-Seok , Ko Dae-Cheol , Lee Kyung-Hun
Published: October 2022

The multi-pass shape drawing process is mainly used in metal forming processes to manufacture long components with constant arbitrary cross-sectional shapes along their lengths. The cross-roller guide is a typical component that is manufactured by a multi-pass shape drawing process. The cross-roller guide is mostly used in optical measurement equipment where high-precision movement is required. Therefore, the dimensional accuracy of the cross-roller guide is very important since it can influence precision linear motion. However, the unfilled defects can occur in a case where the product has a complex cross-sectional shape. In this study, a new design method for an intermediate die is suggested by using an equal-radial-velocity variation method in order to reduce the unfilled defects. The proposed design method can reduce the unfilled defects by minimizing the radial velocity variation in the deformation zone of the drawing die. The intermediate die was designed by geometrical information of the final product without prior finite element (FE) analysis. The suggested method was applied to design the multi-pass shape drawing process for manufacturing the cross-roller guide. FE analysis was performed to validate the effectiveness of the proposed method in comparison to the conventional design method that uses equipotential lines in the multi-pass shape drawing process. Finally, a shape drawing experiment was performed to compare the target shape and the FE analysis with the experimental data.
Sequential Smoothing Treatment of Glass Workpieces Cut by Abrasive Water Jet
Authors: Sutowska Marzena , Łukianowicz Czesław , Szada-Borzyszkowska Monika
Published: October 2022

A centrifugal disc and vibratory finishing machines were applied to improve the surface texture of soda-lime workpieces cut by an abrasive water jet. This innovative method was denoted as sequential smoothing treatment. An experimental study of the effect of the smoothing process conditions on the surface roughness, surface texture and micro roughness of the surface of glass workpieces was conducted. The analysis of the results obtained from experimental research made it possible to determine the optimum conditions for the smoothing process of glass workpieces after abrasive water jet cutting process. The proper selection of the finishing machine, machining media (abrasive chips) and compounds (liquids and powders) made it possible to reduce the surface roughness of areas located in the lower part of the cutting zone from Sa = 4.81 μm to Sa = 1.9 μm. The experimental results obtained confirmed the validity of using finishing machines to improve the surface quality of the soda-lime glass components. An important problem that requires further research is the increase in productivity and the reduction in machining time.
High Hardness and Wear Resistance in AlCrFeNiV High-Entropy Alloy Induced by Dual-Phase Body-Centered Cubic Coupling Effects
Authors: Feng Cong , Wang Xueliang , Yang Li , Guo Yongli , Wang Yaping
Published: October 2022

High-entropy alloys (HEAs) with high hardness are promising materials for advanced industrial manufacturing. In this study, the AlCrFeNiV HEA was designed and successfully prepared using a plasma instantaneous process. The hardness test showed that AlCrFeNiV had a high hardness of 1076 ± 15 HV, which was much higher than those reported in the literature. The microstructure of AlCrFeNiV was composed of two different types of body-centered cubic (BCC) structures, BCC1 (Al, Cr, Fe, and Ni) and BCC2 (enriched V and Cr). A mixture of different BCC systems produced solution strengthening, which was responsible for the superior hardness. Moreover, the reciprocating sliding wear behavior of HEA against Al2O3 balls under dry and lubricated conditions at ambient temperature was investigated. The wear rates of AlCrFeNiV against Al2O3 under dry wear and lubrication were 17.2 × 10−5 mm3 N−1·m−1 and 12.4 × 10−5 mm3N−1·m−1, respectively, which were of the same order of magnitude as the wear rates of BCC HEAs. Regardless of the dry wear or wear with lubrication, the wear mechanism of the HEA was abrasive and delamination wear.
Microstructure and Electrochemical Characterization of Ti-Sn Binary Alloys for Dental Applications
Authors: Hwang Moon-Jin , Song Ho-Jun , Park Yeong-Joon
Published: October 2022

This work investigated the microstructure and corrosion behaviors of Ti-Sn alloys with x wt% Sn (x = 5, 10, 15, and 20) for dental applications. The microstructures of commercially pure titanium (cp-Ti) and Ti-Sn alloys were characterized by X-ray diffractometry, optical microscopy, and transmission electron microscopy. The Vickers hardness of the Ti-Sn alloys was compared to that of cp-Ti. The corrosion behaviors of Ti-Sn alloys were tested in 0.9% NaCl solution at 37 °C using open circuit potential, potentiodynamic polarization, AC impedance, and galvanic corrosion tests. Ti-Sn alloys had a hexagonal close-packed structure and their microstructures were transformed from the equiaxed structure with irregular grain boundaries to the martensitic structure as the content of Sn in Ti-Sn alloys increased by over 15 wt%. Among the sample groups, Ti-15Sn and Ti-20Sn alloys exhibited better Vickers hardness values. Ti-Sn alloys had better corrosion resistance than cp-Ti. Ti-15Sn, which showed narrow martensitic bands, exhibited the highest corrosion resistance properties in AC impedance measurements due to its higher resistance and better capacitive parameters. Among the tested groups, the galvanic coupling of Ti-15Sn with cp-Ti showed higher corrosion potentials and lower current densities, which indicates that there was higher corrosion resistance.
Investigations of the Microstructure and Mechanical Properties of 17-4 PH ss Printed Using a MarkForged Metal X
Authors: Akessa Adugna D. , Tucho Wakshum M. , Lemu Hirpa G. , Grønsund Jørgen
Published: October 2022

The Markforged Metal X (MfMX) printing machine (Markforged Inc., Massachusetts, USA) is one of the latest introduced additive manufacturing (AM) devices. It is getting popular because of its safety, simplicity, and ability to utilize various types of powders/filaments for printing. Despite this, only a few papers have so far reported the various properties and performances of the components fabricated by the MfMX printer. In this study, the microstructure and mechanical properties of MfMX-fabricated 17-4 stainless steel (ss) in the as-printed and heat-treated conditions were investigated. XRD and microscopy analyses revealed a dominant martensitic microstructure with some retained austenite phase. The microstructure is generally characterized by patterned voids that were unfilled due to a lack of fusion between the adjacent filaments. Disregarding these defects (voids), the porosity of the dense region was less than 4%. Depending on the heat treatment conditions, the hardness and tensile strength were enhanced by 17–28% and 21–27%, respectively. However, the tensile strength analyzed in this work was low compared with some previous reports for L-PBF-fabricated 17-4 ss. In contrast, the hardness of the as-printed (331 ± 28 HV) and heat-treated samples under the H900 condition (417 ± 29 HV) were comparable with (and even better than) some reports in the literature, despite the low material density. The results generally indicated that the Markforged printer is a promising technology when the printing processes are fully developed and optimized.
The Effect of Smoking and Brushing on the Color Stability and Stainability of Different CAD/CAM Restorative Materials
Authors: Schelkopf Stuart , Dini Caroline , Beline Thamara , Wee Alvin G. , Barão Valentim A. R. , Sukotjo Cortino , Yuan Judy Chia-Chun
Published: October 2022

This study aimed to investigate and compare the color stability and stainability of computer-aided design/computer-aided manufacturing (CAD/CAM) restorative materials in their glazed (G) and polished (P) state when exposed to cigarette smoke, as well as after brushing. Three CAD/CAM restorative materials were investigated: lithium disilicate CAD (LD), zirconia (Zr), and Telio PMMA CAD (PMMA), according to their surface finishing and assignment to cigarette smoking exposure or soaking in the saliva (control) group. The color change (∆E) was calculated before and after the intervention performed for all specimens, using the L*a*b values to quantitatively assess the shade differences. Statistical analysis was performed using one-way repeated measures ANOVA and Bonferroni multiple comparison analysis (α = 0.05). The surface finishing did not influence the materials’ stainability. Color change was noted after smoking, LD and Zr-G and Zr-P had a comparable color change (p > 0.05), while PMMA presented lower ∆E values (p < 0.05). After brushing, all specimens had a significant color change that was high for LD-G and LD-P, and Zr-G, compared with Zr-P and PMMA (p < 0.05). In conclusion, the exposure to cigarette smoke showed that LD, Zr, and PMMA are all susceptible to staining, but brushing decreases surface staining.
Effect of Bi and Ca on the Solidification Parameters of Sr-Modified Al-S-Cu (Mg) Alloys
Authors: El-Hadad Shimaa , Samuel Agnes M. , Samuel Fawzy H. , Doty Herbert W. , Songmene Victor
Published: October 2022

The effect of tramp elements, mainly Bi and Ca, on the thermal characteristics of Sr-modified Al–Si–Cu and Al–Si–Cu–Mg alloys has been investigated using thermal analysis, X-ray radiography, and field emission scanning electron microscopy (FESEM) techniques. The high affinity of Bi to interact with Sr results in an increase in the Al-Si eutectic temperature, and hence an increase in the size of eutectic silicon particles. In contrast, the Ca–Sr interaction seems to have no significant effect on the alloy thermal behavior. The effect of these interactions on porosity formation has been discussed. Hot zones may be formed in thin cavities, in particular, near the bottom of the mold, leading to formation of unexpected coarse porosity, mostly shrinkage type. The study also highlights the significance of other parameters on porosity formation, such as no melt degassing, SrO, Al2O3 (strings or bifilms), as well as the presence of iron-based intermetallics.
Optical Properties and Light-Induced Charge Transfer in Selected Aromatic C60 Fullerene Derivatives and in Their Bulk Heterojunctions with Poly(3-Hexylthiophene)
Authors: Krajewski Maciej , Piotrowski Piotr , Mech Wojciech , Korona Krzysztof P. , Wojtkiewicz Jacek , Pilch Marek , Kaim Andrzej , Drabińska Aneta , Kamińska Maria
Published: October 2022

Fullerene derivatives offer great scope for modification of the basic molecule, often called a buckyball. In recent years, they have been the subject of numerous studies, in particular in terms of their applications, including in solar cells. Here, the properties of four recently synthesized fullerene C60 derivatives were examined regarding their optical properties and the efficiency of the charge transfer process, both in fullerene derivatives themselves and in their heterojunctions with poly (3-hexylthiophene). Optical absorption, electron spin resonance (ESR), and time-resolved photoluminescence (TRPL) techniques were applied to study the synthesized molecules. It was shown that the absorption processes in fullerene derivatives are dominated by absorption of the fullerene cage and do not significantly depend on the type of the derivative. It was also found by ESR and TRPL studies that asymmetrical, dipole-like derivatives exhibit stronger light-induced charge transfer properties than their symmetrical counterparts. The observed inhomogeneous broadening of the ESR lines indicated a large disorder of all polymer–fullerene derivative blends. The density functional theory was applied to explain the results of the optical absorption experiments.
Novel Alumina Matrix Composites Reinforced with MAX Phases—Microstructure Analysis and Mechanical Properties
Authors: Petrus Mateusz , Wozniak Jaroslaw , Cygan Tomasz , Pawlak Wojciech , Olszyna Andrzej
Published: October 2022

This article describes the manufacturing of alumina composites with the addition of titanium aluminum carbide Ti3AlC2, known as MAX phases. The composites were obtained by the powder metallurgy technique with three types of mill (horizontal mill, attritor mill, and planetary mill), and were consolidated with the use of the Spark Plasma Sintering method at 1400 °C, with dwelling time 10 min. The influence of the Ti3AlC2 MAX phase addition on the microstructure and mechanical properties of the obtained composites was analyzed. The structure of the MAX phase after the sintering process was also investigated. The chemical composition and phase composition analysis showed that the Ti3AlC2 addition preserved its structure after the sintering process. The increase in fracture toughness for all series of composites has been noted (over 20% compared to reference samples). Detailed stereological analysis of the obtained microstructures also could determine the influence of the applied mill on the homogeneity of the final microstructure and the properties of obtained composites.
Influence of Oxygen Plasma on the Growth and Stability of Epitaxial NiCo2O4 Ultrathin Films on Various Substrates
Authors: Ruwisch Kevin , Alexander Andreas , Pollenske Tobias , Küpper Karsten , Wollschläger Joachim
Published: October 2022

In this work, we investigated the influence of oxygen plasma on the growth of nickel cobaltite (NiCo2O4) thin films compared to growth in a molecular oxygen atmosphere. The films were grown on MgO(001), MgAl2O4(001) and SrTiO3(001) substrates by oxygen plasma (atmosphere of activated oxygen)-assisted and reactive molecular beam epitaxy (molecular oxygen atmosphere). Soft X-ray photoelectron spectroscopy showed that only the use of oxygen plasma led to a spectrum characteristic of (NiCo2O4). Low energy electron diffraction measurements were conducted to obtain information on the structure of the film surfaces. The results proved the formation of a spinel surface structure for films grown with oxygen plasma, while the formation of a rock salt structure was observed for growth with molecular oxygen. To determine the film thickness, X-ray reflectivity measurements were performed. If oxygen plasma were used to grow (NiCo2O4) films, this would result in lower film thicknesses compared to growth using molecular oxygen although the cation flux was kept constant during deposition. Additional X-ray diffraction experiments delivered structural information about the bulk structure of the film. All films had a rock salt bulk structure after exposure to ambient conditions. Angle-resolved hard X-ray photoelectron spectroscopy revealed a homogeneous depth distribution of cations of the grown film, but no typical (NiCo2O4) spectrum anymore. Thus, on the one hand, (NiCo2O4) films with a spinel structure prepared using activated oxygen were not stable under ambient conditions. The structure of these films was transformed into NiCo oxide with a rock salt structure. On the other hand, it was not possible to form (NiCo2O4) films using molecular oxygen. These films had a rock salt structure that was stable under ambient conditions.
Effect of Cold-Rolling Reduction on Recrystallization Microstructure, Texture and Corrosion Properties of the X2CrNi12 Ferritic Stainless Steel
Authors: Li Rui , Fu Binguo , Wang Yufeng , Li Jingkun , Dong Tianshun , Li Guolu , Zhang Guixian , Liu Jinhai
Published: October 2022

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111} orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111}<110> was strengthened and the α-fibers, particularly the {112}<110> component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance.
Relation between Ga Vacancies, Photoluminescence, and Growth Conditions of MOVPE-Prepared GaN Layers
Authors: Hospodková Alice , Čížek Jakub , Hájek František , Hubáček Tomáš , Pangrác Jiří , Dominec Filip , Kuldová Karla , Batysta Jan , Liedke Maciej O. , Hirschmann Eric , Butterling Maik , Wagner Andreas
Published: October 2022

A set of GaN layers prepared by metalorganic vapor phase epitaxy under different technological conditions (growth temperature carrier gas type and Ga precursor) were investigated using variable energy positron annihilation spectroscopy (VEPAS) to find a link between technological conditions, GaN layer properties, and the concentration of gallium vacancies (VGa). Different correlations between technological parameters and VGa concentration were observed for layers grown from triethyl gallium (TEGa) and trimethyl gallium (TMGa) precursors. In case of TEGa, the formation of VGa was significantly influenced by the type of reactor atmosphere (N2 or H2), while no similar behaviour was observed for growth from TMGa. VGa formation was suppressed with increasing temperature for growth from TEGa. On the contrary, enhancement of VGa concentration was observed for growth from TMGa, with cluster formation for the highest temperature of 1100 °C. From the correlation of photoluminescence results with VGa concentration determined by VEPAS, it can be concluded that yellow band luminescence in GaN is likely not connected with VGa; additionally, increased VGa concentration enhances excitonic luminescence. The probable explanation is that VGa prevent the formation of some other highly efficient nonradiative defects. Possible types of such defects are suggested.
Novel Osteogenic and Easily Handled Endodontic Calcium Silicate Cement Using Pluronic F127 Hydrogel
Authors: Ryu Jeong-Hyun , Roh Jiyeon , Mangal Utkarsh , Kim Kwang-Mahn , Choi Sung-Hwan , Kwon Jae-Sung
Published: October 2022

Calcium silicate cement (CSC) is widely used as an endodontic material in clinical applications such as direct pulp capping, pulpotomy, or root canal. CSC has good biocompatibility, sealing properties, and the ability to enhance hard tissue regeneration. However, the disadvantage of CSC is the difficulty in handling when placing it into endodontic tissue due to the long setting time. Several attempts have been made to improve handling of CSC; however, these methods were limited by osteogenic properties. To overcome such a disadvantage, this study investigated the use of Pluronic F127 (F127) for the development easy-to-handle novel endodontic CSCs with osteogenic properties. In this case, different concentrations of F127 (5%, 10%, 20%, 30%, and 40%) were implemented to generate CSC specimens H5, H10, H20, H30, and H40, respectively. Calcium ion was continuously released for 28 days. In addition, each group resulted in apatite formation for 28 days corresponding to calcium ion release. The concentration of F127 showed opposite relationships with water solubility and compressive strength. The H20 group showed a high level of osteogenic activity compared to other groups at 14 days. Mineralization of the H20 group was higher than that of the other groups. This study indicates that the novel F127-based hydrogel with CSC can potentially be used as endodontic filler.
A Decision-Making Algorithm for Concrete-Filled Steel Tubular Arch Bridge Maintenance Based on Structural Health Monitoring
Authors: Gui Chengzhong , Lin Weiwei , Huang Zuwei , Xin Guangtao , Xiao Jun , Yang Liuxin
Published: October 2022

This study focuses on establishing a novel heuristic algorithm for life-cycle performance evaluation. Special attention is given to decision-making algorithms for concrete-filled steel tubular (CFST) arch bridge maintenance. The main procedure is developed, including the ultimate loading-capacity modeling of CFST members, multi-parameter selection, ultimate thresholds presetting based on the finite element method, data processing, crucial parameters determination among sub-parameters, multi-parameter regression, ultimate state prediction, and system maintenance decision-making suggestions based on the multi-parameter performance evaluation. A degenerated ultimate loading-capacity model of CFST members is adopted in the finite element analysis and multi-parameter performance assessment. The multi-source heterogeneous data processing and temperature-effect elimination are performed for the data processing. The key sub-parameters were determined by the Principal Component Analysis method and the Entropy-weight method. The polynomial mathematical model is used in the multi-parameter regression, and the ±95% confidence bounds were verified. The system maintenance decision-making model combines the relative monitoring state, the relative ultimate state by the numerical analysis, and the relative residual life of degenerated members. The optimal system maintenance decision-making suggestions for the bridge maintenance system can be identified, including the most unfavorable maintenance time and parameter index. A case study on a CFST truss-arch bridge is conducted to the proposed algorithms. The obtained results demonstrated that the crack width deserves special attention in concrete bridge maintenance. Additionally, these technologies have enormous potential for the life-cycle performance assessment of the structural health monitoring system for existing concrete bridge structures.
High Concentration Crystalline Silk Fibroin Solution for Silk-Based Materials
Authors: Yao Danyu , Wang Ting , Zhang Xiaoli , Wang Yuqing
Published: October 2022

As a functional biomaterial, silk fibroin has been widely used in drug release, cell encapsulation and tissue regeneration. To meet the requirements of these applications, the properties of silk fibroin-based materials should be finely tunable. Many useful properties of biomaterials emerge from the collective interactions among ordered and disordered domains. Thus, increasing subtle control of silk hierarchical structures is required. As a characteristic of ordered silk fibroin, crystalline silk fibroin (CSF) is an important part of silk fibroin-based biomaterials, but the preparation of CSF solution, especially high concentration CSF solution, remains a challenge. Here, a solution composed of β-sheet-rich silk fibroin is reported. These CSF were obtained by the sonication of silk fibroin hydrogel, destroying the hydrogel network, and turning silk fibroin hydrogels into CSF solution. These β-sheet-rich CSF solutions were stable enough for several days or even weeks. In addition, they were typically ordered crystalline domains, which could be mixed with disordered domains and fabricated into porous scaffolds, films, hydrogels and other silk fibroin-based scaffolds with different properties.
{332}<113> and {112}<111> Twin Variant Activation during Cold-Rolling of a Ti-Nb-Zr-Ta-Sn-Fe Alloy
Authors: Dan Alexandru , Cojocaru Elisabeta Mirela , Raducanu Doina , Nocivin Anna , Cinca Ion , Cojocaru Vasile Danut
Published: October 2022

Deformation twinning is a phenomenon that causes local shear strain concentrations, with the material either experiencing elongation (and thus a tensile stress) or contraction (compressive stress) along the stress directions. Thus, in order to gauge the performance of the alloy better, it is imperative to predict the activation of twinning systems successfully. The present study investigates the effects of deformation by cold-rolling on the {332}<113> and {112}<111> twin variant activation in a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy. The Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) alloy was synthesized in a cold crucible induction levitation furnace, under an argon-controlled atmosphere, using high-purity elemental components. The TNZTSF alloy was cold-deformed by rolling, in one single step, with a total deformation degree (thickness reduction) of ε ≈ 1% (CR 1), ε ≈ 3% (CR 3), and ε ≈ 15% (CR 15). The microstructural investigations were carried out with the SEM-EBSD technique in order to determine the grain morphology, grain-size distribution, crystallographic orientation, accumulated strain-stress fields and Schmid Factor (SF) analysis, all necessary to identify the active twin variants. The EBSD data were processed using an MTEX Toolbox ver. 5.7.0 software package. The results indicated that the TNZTSF alloy’s initial microstructure consists of a homogeneous β-Ti single phase that exhibits equiaxed polyhedral grains and an average grain-size close to 71 μm. It was shown that even starting with a 1% total deformation degree, the microstructure shows the presence of the {332}<113> twinning ((233)[3¯11] active twin variant; Schmit factor SF = −0.487); at a 3% total deformation degree, one can notice the presence of primary and secondary twin variants within the same grain belonging to the same {332}<113> twinning system ((323¯)[13¯1¯] primary twin variant—SF = −0.460; (233¯)[3¯11¯] secondary twin variant—SF = −0.451), while, at a 15% total deformation degree, besides the {332}<113> twinning system, one can notice the activation of the {112}<111> twinning system ((11¯2)[1¯11] active twin variant—SF = −0.440). This study shows the {332}<113> and {112}<111> twinning variant activation during cold-deformation by rolling in the case of a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt.%) (TNZTSF) alloy.
Seagrass Leaves: An Alternative Resource for the Production of Insulation Materials
Authors: Kuqo Aldi , Mai Carsten
Published: October 2022

Seagrass wracks, the remains of dead leaves accumulated on seashores, are important ecosystems and beneficial for the marine environment. Their presence on the touristic beaches, however, is a problem for the tourism industry due to the lack of aesthetics and safety reasons. At the present time, seagrass leaves are landfilled, although this is not considered an ecological waste management practice. Among other proposed practices for more sustainable and environmentally friendly management, such as composting and biogas or energy generation, in this study we aim to use seagrass leaves for the production of insulation materials. Insulation boards from two types of seagrass leaves (Posidonia oceanica and Zostera marina) at densities varying from 80 to 200 kg m−3 were prepared and their physical and mechanical properties were examined and compared to those of wood fiber insulation boards. The thermal conductivity of seagrass-based insulation boards varied from 0.042 to 0.050 W m−1 K−1, which was up to 12% lower compared to the latter. The cone calorimetry analysis revealed that seagrass-based insulation boards are more fire resistant than those from wood fibers, as they release very low amounts of heat during combustion and do not ignite when exposed to a single flame (Bunsen burner). A simplified cost analysis showed that insulation boards made from seagrass leaves can be up to 30% cheaper compared to those made from wood fibers. After their end of life, seagrass leaves can again be considered a valuable resource and be further utilized by adopting other management strategies.
Influence of Sulfates on Formation of Ettringite during Early C3A Hydration
Authors: Yang Yong , Zhang Qianqian , Shu Xin , Wang Xiumei , Ran Qianping
Published: October 2022

The hydration of C3A-gypsum systems was studied in the presence of various types of sulfates such as gypsum, hemihydrate and Na2SO4 in the first hour. The BET method combined with a DSC analysis enabled us to quantitatively characterize the amount of precipitated ettringite and its specific surface area along the hydration. It was found that sulfates not only affected the formation rate of ettringite, but also had a significant impact on the morphology of ettringite. For all the C3A-gypsum systems, a large part of the ettringite precipitated within the first 20 min and the specific surface area of the hydrated sample strongly increased within the first 5 min, whereas the specific surface area of ettringite gradually decreased along the C3A hydration reaction. Incorporating a small amount of Na2SO4 in the C3A-gypsum system could greatly promote the formation rate of ettringite in the first 20 min, and significantly decrease the specific surface area of ettringite. As hemihydrate was added to the C3A-gypsum system, two processes of ettringite precipitation and gypsum precipitation occurred. The nucleation and growth process of ettringite and gypsum resulted in the complex changes in the specific surface area of the hydrated sample, which first increased at the very beginning, then decreased and, finally, increased.
Optimizing Ultrasonic Welding Parameters for Multilayer Lap Joints of PEEK and Carbon Fibers by Neural Network Simulation
Authors: Panin Sergey V. , Stepanov Dmitry Yu. , Byakov Anton V.
Published: October 2022

The aim of this study is to substantiate the use machine learning methods to optimize a combination of ultrasonic welding (USW) parameters for manufacturing of multilayer lap joints consisting of two outer PEEK layers, a middle prepreg of unidirectional carbon fibers (CFs), and two energy directors (EDs) between them. As a result, a mathematical problem associated with determining the optimal combination of technological parameters was formulated for the formation of USW joints possessing improved functional properties. In addition, a methodology was proposed to analyze the mechanical properties of USW joints based on neural network simulation (NNS). Experiments were performed, and threshold values of the optimality conditions for the USW parameters were chosen. Accordingly, NNS was carried out to determine the parameter ranges, showing that the developed optimality condition was insufficient and required correction, taking into account other significant structural characteristics of the formed USW joints. The NNS study enabled specification of an extra area of USW parameters that were not previously considered optimal when designing the experiment. The NNS-predicted USW mode (P = 1.5 atm, t = 800 ms, and τ = 1500 ms) ensured formation of a lap joint with the required mechanical and structural properties (σUTS = 80.5 MPa, ε = 4.2 mm, A = 273 N·m, and Δh = 0.30 mm).