Crystals, Volume 10, Issue 10 (October 2020) – 104 articles

(E)-1-(1H-Benzo[d]imidazol-2-yl)-3-(dimethylamino)prop-2-en-1-one 2 was synthesized by one-pot synthesis protocol of 2-acetyl benzo[d]imidazole with dimethylformamide dimethylacetal (DMF-DMA) in xylene at 140 °C for 8 h. Reaction of enaminone derivative 1 with acetylacetone in the presence of AcOH/NH₄OAc under reflux afforded the cyclized pyridino-benzo[d]imidazole derivative 3. The latter compound was converted into the corresponding β-enaminone 4 with DMF-DMA. The single crystal X-ray diffraction technique eventually confirmed the assigned chemical structure of the N-alkyl-β-enaminone 2 and pyridino-benzo[d]imidazole derivative 3. N-alkyl-β-enaminone 2 crystallized in the monoclinic space group P2₁/n with unit cell parameters of a = 9.8953(3) Å, b = 5.7545(2) Å, c = 21.7891(7) Å, and β =100.627(2)°, and with one molecule per asymmetric unit. On the other hand, compound 3 crystallized in the orthorhombic crystal system and space group P2₁2₁2₁ with unit cell parameters of a = 6.82950(10) Å, b = 8.00540(10) Å, c = 22.4779(2) Å, and also with one molecule per asymmetric unit. Based on Hirshfeld analysis, the H...H (51.3%), O...H (10.0%), N...H (10.3%), and C...H (27.6%) contacts in 2 and the H...H (46.8%), O...H (9.9%), N...H (13.0%), and C...H (21.6%) in addition to the C…C (6.7%) interactions in 3 are the most important towards crystal stability via molecular packing. The main difference is the presence of π–π interaction among the molecular units of 3 but not in 2. The calculated ¹H and ¹³C NMR chemical shifts showed good agreements with experimental data. Electronic properties and reactivity parameters of both compounds are also calculated and compared. Full article

The synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al layered double hydroxides (LDHs) was investigated with a one-step wet mechanochemical route. The research aims to expand on the mechanochemical synthesis of LDH using a mill designed for wet grinding application. A 10% slurry of solids was added to a Netzsch LME 1 horizontal bead mill and milled for 1 h at 2000 rpm. Milling conditions were selected according to machine limitations and as an initial exploratory starting point. Precursor materials selected consisted of a mixture of oxides, hydroxides and basic carbonates. Samples obtained were divided such that half was filtered and dried at 60 °C for 12 h. The remaining half of the samples were further subjected to ageing at 80 °C for 24 h as a possible second step to the synthesis procedure. Synthesis conditions, such as selected precursor materials and the M^II:M^III ratio, were adapted from existing mechanochemical methods. LDH synthesis prior to ageing was successful with precursor materials observably present within each sample. No Cu-Al LDH was clearly identifiable. Ageing of samples resulted in an increase in the conversion of raw materials to LDH product. The research offers a promising ‘green’ method for LDH synthesis without the production of environmentally harmful salt effluent. The synthesis technique warrants further exploration with potential for future commercial up-scaling. Full article

Calcium phosphate nanoparticles (CaP NPs) are an efficient class of nanomaterials mainly used for biomedical applications but also very promising in other sectors such as cosmetics, catalysis, water remediation, and agriculture. Unfortunately, as in the case of other nanomaterials, their wide application is hindered by the difficulty to control size, morphology, purity and degree of particle aggregation in the translation from laboratory to industrial scale production that is usually carried out in batch or semi-batch systems. In this regard, the use of continuous flow synthesis can help to solve this problem, providing more homogenous reaction conditions and highly reproducible synthesis. In this paper, we have studied with a design of experiment approach the precipitation of citrate functionalized CaP NPs aided by sonication using a continuous flow wet chemical precipitation, and the effect of some of the most relevant process factors (i.e., reactant flow rate, sonication amplitude, and maturation time) on the physico-chemical properties of the NPs were evaluated. From the statistical data analysis, we have found that CaP NP dimensions are influenced by the reactor flow rate, while the crystalline domain dimensions and product purity are influenced by the maturation process. This work provides a deeper understanding of the relationships between reaction process factors and CaP NP properties, and is a relevant contribution for the scale-up production of CaP NPs for nanomedical or other applications. Full article

Although several methods exist for the synthesis of circularly polarized luminescent (CPL) materials, the methods are extremely complex and tedious. In recent years, the chiral host-achiral luminescent guest method and the achiral host-achiral luminescent guest method have been employed to fabricate CPL materials; however, the main disadvantage of the latter is the small luminescence dissymmetry factor (g_lum) that limits the practical applications of the method. Therefore, this study reports on the enhancement of g_lum in a nano-segregated phase system, generated by the phase separation between helical nanofilaments (HNFs; originating from an achiral bent-core molecule) and a liquid-crystalline (LC) smectic A (SmA) phase (originating from an achiral rod-like mesogen). The observed g_lum value in the nano-segregated phase between the HNFs and LC SmA phase was larger than that in the nano-segregated phase between the HNFs and LC nematic (N) phase. The enhancement of the g_lum value was attributed to the order parameter (S) of the dye molecules in the SmA phase being larger than that in the N phase. Therefore, we concluded that the S value of the fluorescent dye molecules, doped into the embedded LC phase between the HNFs, strongly influenced the g_lum value. Full article

The gel of zeolite NaY has potential as a precursor of other zeolites. The particular interest in this work is to convert the gel of NaY to NaP2. We found that the pure phase NaP2 can be produced simply by the conventional hydrothermal (CH) method at 150 °C for 24 h. This NaP2 sample, named CH150, has an average particle size of 10.3 µm and an Si/Al ratio of 1.82. In the case of single crystallization via microwave-assisted hydrothermal (MH) method, various parameters were studied, including the crystallization temperature (90, 150, 175 °C) and time (15, 30, 45, 60 min). The samples were analyzed by X-ray diffraction and scanning electron microscopy. However, mixed phases of P1 and P2 or ANA were obtained from all samples. Another attempt was made by a double crystallization via MH method as followed: at 90 °C for 1 h, quickly cooled down to room temperature in the microwave chamber and aged for 23 h, and finally at 150 °C for 1 h. The sample, named MH90A150, has an average crystal size of 16.45 µm and an Si/Al ratio of 1.85. The high Al content of NaP2 in both samples (CH150 and MH90A150) could lead to interesting applications. Full article

Magnetic properties of the high-pressure stabilized perovskite BiFe_1-ySc_yO₃ phases (0.1 ≤ y ≤ 0.9) have been studied by means of magnetization measurements and neutron diffraction. The metastable perovskites of this series undergo irreversible polymorphic transformations upon annealing, the phenomenon referred to as conversion polymorphism. It has been found that the solid solutions with y ≥ 0.70 exhibit no long-range magnetic ordering regardless of their polymorph modification, while those with y ≤ 0.60 are all antiferromagnets. Depending on the scandium content, temperature and structural distortions, three types of the antiferromagnetic orderings, involving collinear, canted and cycloidal spin arrangements, have been revealed in the phases obtained via conversion polymorphism and the corresponding magnetic phase diagram has been suggested. Full article

Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. The silicalite-1 membrane became (h0l)-orientation with increasing membrane thickness, possibly because the orientation was attributable to “evolutionally selection”. The (h0l)-oriented silicalite-1 membrane showed high p-xylene separation performance for a xylene isomer mixture (o-/m-/p-xylene = 0.4/0.4/0.4 kPa). The p-xylene permeance through the membrane was 6.52 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ with separation factors α_p/o, α_p/m of more than 100 at 373 K. As a result of microscopic analysis, it was suggested that a very thin part in the vicinity of surface played as effective separation layer and could contribute to high permeation performance. Full article

Foam concrete (FC) serves as an efficient construction material that combines well thermal insulation and structural properties. The studies of material characteristics, including the mechanical, physical, rheological, and functional properties of lightweight concrete, have been conducted rigorously. However, a lack of knowledge on the design efficiency of reinforced FC (RFC) was found in current research trends, compared to reinforced lightweight aggregate concrete. Therefore, this paper presents a review of the performance and adaption in structures for RFC. According to the code specifications, the feasibility investigation was preliminarily determined in structural use through the summary for the mechanical properties of FC of FC’s mechanical properties. For reinforced concrete design, a direct method of reduction factors is introduced to design lightweight aggregate concrete, which is also suggested to be adapted into a lightweight FC design. It was found that flexural shear behavior is a more complex theoretical analysis than flexure. However, a reduction factor of 0.75 was recommended for shear, torsion, and compression; meanwhile, 0.6 for flexural members. Serviceability limit states design should be applied, as the crack was found predominant in RFC design. The deflection controls were recommended as 0.7 by previous research. Research on RFC’s compression members, such as a column or load load-bearing wall, were rarely found. Thus, further study for validating a safe design of RFC applications in construction industries today is highly imperative. Full article

For an in-depth characterization of catalytic materials and their properties, spectroscopic in-situ (operando) investigations are indispensable. With the rapid development of advanced commercial spectroscopic equipment, it is possible to combine complementary methods in a single system. This allows for simultaneously gaining insights into surface and bulk properties of functional oxides, such as defect chemistry, catalytic characteristics, electronic structure, etc., enabling a direct correlation of structure and reactivity of catalyst materials, thus facilitating effective catalyst development. Here, we present a novel sample-stage, which was specifically developed to pave the way to a lab–based combination of near ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy with simultaneous catalytic operando measurements. This setup is designed to probe different (model) systems under conditions close to real heterogeneous catalysis, with a focus on solid oxide electrochemical cells. In a proof of concept experiment using an electrochemical model cell with the doped perovskite Nd_0.6Ca_0.4Fe_0.9Co_0.1O_3-δ as working electrode, the precise control of the surface chemistry that is possible with this setup is demonstrated. The exsolution behavior of the material was studied, showing that at a lower temperature (500 °C) with lower reducing potential of the gas phase, only cobalt was exsolved, forming metallic particles on the surface of the perovskite-type oxide. Only when the temperature was increased to 600 °C and a cathodic potential was applied (−250 mV) Fe also started to be released from the perovskite lattice. Full article

This article reports the production and characterization of a hybrid concrete based on the alkaline activation of a fly ash (FA) of Colombian origin, which was added with 10% Portland cement (OPC) in order to promote the compressive strength development at room temperature. The alkali-activated hybrid cement FA/OPC 90/10 was classified as a low heat reaction cement (type LH), according to American Society of Testing Materials, ASTM C1157; the compressive strength was of 31.56 MPa and of 22.68 MPa (28 days) at the levels of paste and standard mortar, respectively, with an initial setting time of 93.3 min. From this binder, a hybrid concrete was produced and classified as a structural type, with a compressive strength of 23.16 MPa and a flexural modulus of rupture of 5.32 MPa, at 28 days of curing. The global warming potential index (GWP 100), based on life cycle analysis, was 35% lower than the reference concrete based on 100% OPC. Finally, its use was validated in the manufacture of a solid block-type construction element, which reached a compressive strength of 21.9 MPa at 28 days, exceeding by 40.6% the minimum strength value established by the Colombia Technical Standard, NTC 4026 (13 MPa) to be classified as high class structural blocks. Full article

This Special Issue on “Microstructural and Mechanical Characterization of Alloys” features eight papers that cover the recent developments in alloys (engineering materials), methods of improvement of strength and cyclic properties of alloys, the stability of microstructure, the possible application of new (or improved) alloys, and the use of treatment for alloy improvement. Full article

Crystal plasticity simulations help to understand the local deformation behavior of multi-phase materials based on the microstructural attributes. The results of such simulations are mainly dependent on the Representative Volume Element (RVE) size and composition. The effect of RVE thickness on the changing global and local stress and strain is analyzed in this work for a test case of dual-phase steels in order to identify the minimal RVE thickness for obtaining consistent results. $100\times 100\times 100$ voxel representative volume elements are constructed by varying grain size and random orientation distribution in DREAM-3D. The constructed RVEs are sliced in depth up to 1, 5, 10, 15, 20, 25, 30, 40, and 50 layers to construct different geometries with increasing thickness. Crystal plasticity model parameters for ferrite and martensite are taken from already published data and assigned to respective phases. Although the global stress/strain behavior of different RVEs is similar (<5% divergence), the local stress/strain partitioning in RVEs with varying thickness and grain size shows a considerable variation when statistically compared. It is concluded that two-dimensional (2D) RVEs can be used for crystal plasticity simulations when global deformation behavior is of interest. Whereas, it is necessary to consider three-dimensional (3D) RVEs, which have a specific thickness and number of grains for determining stabilized and more accurate local deformation behavior. This estimation will help researchers in optimizing the computation time for accurate mesoscale simulations. Full article

Iron-chromium-aluminum (FeCrAl) alloys are used in automobile exhaust gas purifying systems and nuclear reactors due to its superior high-temperature oxidation and excellent corrosion resistance. Single-phase FeCrAl alloys with a body centered cubic structure plastically deform through dislocation slips at room temperature. Here, we investigated the orientation dependence of mechanical responses of FeCrAl alloy through testing single-crystal and bi-crystal micropillars in a scanning electron microscopy at room temperature. Single-crystal micropillars were fabricated with specific orientations which favor the activity of single slip system or two slip systems or multiple slip systems. The strain hardening rate and flow strength increase with increasing the number of activated slip system in micropillars. Bi-crystal micropillars with respect to the continuity of slip systems across grain boundary were fabricated to study the effect of grain boundary on slip transmission. The high geometrical compatibility factor corresponds to a high flow strength and strain hardening rate. Experimental results provide insight into understanding mechanical response of FeCrAl alloy and developing the mechanisms-based constitutive laws for FeCrAl polycrystalline aggregates. Full article

The one-dimensional extended Hubbard model with lattice dimerization and alternated site potentials is analyzed using the renormalization group method. The coupling of electrons to structural degrees of freedom such as the anion lattice and acoustic phonons is investigated to obtain the possible instabilities against the formation of lattice superstructures. Applications of the theory to anionic and spin-Peierls instabilities in the Fabre and Bechgaard salts series of organic conductors and ordered alloys are presented and discussed. Full article

The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC. Full article

A bismuth subbromide, Bi₆Br₇, was synthesized in the form of single crystals using the reaction between Bi and Hg₂Br₂ in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, a = 15.4996(6) Å, b = 23.6435(7) Å, c = 9.0231(2) Å, Z = 8, R₁ = 0.041, wR_all = 0.087). Based on the diffraction data, the structure description was revised as containing Bi₉⁵⁺ cluster polycations and ¹_∞[Bi₃Br₁₄⁵⁻] ladder-like anions. DFT calculations of band structure showed the compound to be a narrow-gap semiconductor with a band gap of ca. 1.3 eV, with the nature of the compound as ionic salt confirmed by charge density analysis. Direct-space bonding analysis based on the ELF topology and QTAIM partitioning, performed for all known homoatomic bismuth polycations, as well as isoelectronic main-group metal ions, shows patterns of localized pairwise and three-center bonding forming the frameworks of the clusters. In addition to obtaining new data, the use of highly augmented basis sets allowed us to revise and amend several previously made conclusions regarding bonding in such species. Full article

Paratellurite, also known as α-tellurium dioxide, is a ceramic that is primarily employed for its interesting optical properties. However, this material’s crystal structure belongs to the 422 symmetry class that allows a unique piezoelectric behavior to manifest itself: deformation in pure face-shear. This means that crystal symmetry necessitates the piezoelectric tensor to have only a single non-zero coefficient, d₁₂₃ = d₁₄: such unique behavior has the potential to enable novel gyroscopic sensors and high-precision torsional microelectromechanical systems (MEMS) actuators, as pure face-shear can be used to induce pure torsion. Although α-TeO₂ is one of the few known materials belonging to this symmetry class, considerable uncertainty in its single piezoelectric coefficient exists, with the few reported literature values ranging from 6.13 to 14.58 pC/N; this large uncertainty results from the difficulty in using conventional piezoelectric characterization techniques on paratellurite, limiting measurements to indirect methods. The novel applications that would be enabled by the adoption of this extraordinary material are frustrated by this lack of confidence in the literature. We therefore leverage, for the first time, a first-principles analytical physical model with electrochemical impedance spectroscopy (EIS) to determine, directly, the lone piezoelectric coefficient d₁₂₃ = d₁₄ = 7.92 pC/N. Full article

Among different approaches to designing metasurfaces, surface sheet impedance is proving to be a straightforward path for many applications. Recent publications have proposed several methods for optimizing this design approach, enabling rapid metasurface development. Upon finding the requirements using the sheet impedance approach, design continues with the selection of unit cell geometry. This choice is usually based on approximate expressions that have been published throughout the years. We review the approximate expressions for metasurface unit cell design, with consideration of their applicability to certain applications, namely polarization-dependent beam-shaping metasurfaces. We evaluate the accuracy of the approximate expressions against simulation results from a full-wave electromagnetic solver, and propose an optimization approach to correct the proposed design for the observed error. The applicability of different unit cell types is discussed, especially considering the limitations of technological processes typically used in metasurface production. A prototype was developed to verify the validity of this design approach. Full article

Thermally induced deterioration processes were studied in cold worked (up to 60% deformation) SAF 2507 type super-duplex stainless steel (SDSS) by differential thermal analysis (DTA). DTA results revealed two transformations. Parent and inherited phases of these transformations were examined by other methods too, such as micro-hardness tests, optical metallography and X-ray diffraction (XRD). Finally, these transformations were identified as the formation of α’- and σ-phases. Formation of strain-induced martensite (SIM) and recrystallization were not experienced until 1000 °C, despite high degree of cold working. Activation energies of the σ-phase precipitation and α’-phase formation were determined from the Kissinger plot, through DTA measurements—they are 275 and 220 kJ/mol, respectively—in good agreement with the values found in the literature. Full article

We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La₃Ta_0.5Ga_5.5O₁₄ (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and metals at high temperatures. To formulate this method, the thermal stresses of order-type langasite crystals, in which each cation site is occupied by one element only, were calculated and compared to each other. Our results suggest that the largest cation site affects the thermal stress. We attempted to replace La³⁺ in LTG by a larger ion and considered Sr²⁺. Single crystals of strontium-substituted LTG (Sr-LTG) were grown using the Czochralski method. The thermal stress along the crystallographic c-axis decreased but that perpendicular to the c-axis increased by strontium substitution into the LTG crystal. The anisotropic thermal stress was reduced effectively. The Sr-LTG single crystal is a superior candidate material for pressure sensors usable at high temperatures. Full article

A series of photopolymers based on ethylene glycol phenyl ethyl arylate (EGPEA) monomers and poly(methyl methacrylate) (PMMA) matrix with varying initiator concentrations and sample thicknesses have been synthesized and their optical performance characterized in this study. The advantages of lowering the initiator concentration, including a rather short initiation time within a few seconds; a sharp rising optical response; and a stable saturated diffraction efficiency are demonstrated. The variation in the diffraction efficiency and response time with the exposure energy under various sample thickness and initiator concentrations is examined; a diffraction efficiency as high as 80% and a relatively short response time of 12–39 s are attainable. The dependence of the normalized optical parameter “sensitivity” on the exposure time is depicted, and the peak value of S ranges vastly from about 0.2 to 1.2 × 10⁴ cm/J within a period of 15 s or so, with a maximum value of nearly 1.2 × 10⁴. Favorable evidence of low initiator concentration can further be found when the dependence of the saturated diffraction efficiency with the exposure energy is examined. The data from this study using a low initiator concentration cover a range of exposure energy from 100 to 800 mJ/cm² and a saturated diffraction efficiency from about 15% to 80%. The successful image reconstruction of 6-membered-ring metal nuts on a hologram based on this EGPEA/PMMA photopolymer system using a reflective holographic recording setup is demonstrated to verify its applicability to holographic storage. Full article

Dislocation-based functionalities in inorganic ceramics and semiconductors are drawing increasing attention, contrasting the conventional belief that the majority of ceramic materials are brittle at room temperature. Understanding the dislocation behavior in ceramics and advanced semiconducting materials is therefore critical for the mechanical reliability of such materials and devices designed for harvesting the dislocation-based functionalities. Here we compare the mechanical testing between indentation at nano-/microscale and bulk uniaxial deformation at macroscale and highlight the dislocation plasticity in single crystal SrTiO₃, a model perovskite. The similarities and differences as well as the advantages and limitations of both testing protocols are discussed based on the experimental outcome of the crystal plasticity, with a focus on the pre-existing defect population being probed with different volumes across the length scales (“size effect”). We expect this work to pave the road for studying dislocation-based plasticity in various advanced functional ceramics and semiconductors. Full article

Herein, the synthesis and antimicrobial activities of [Mn(^MorphBPT)(H₂O)₂NO₃]NO₃; (1) and [Mn(^PipBPT)(H₂O)₂NO₃]NO₃; (2) complexes of the pincer-type tridentate ligands ^MorphBPT; 4-(4,6-di(1H-pyrazol-1-yl)-1,3,5-triazin-2-yl)morpholine and ^PipBPT; 2-(piperidin-1-yl)-4,6-di(1H-pyrazol-1-yl)-1,3,5-triazine are presented. Both complexes have slightly distorted octahedral coordination geometry. Their molecular packing depends on O–H···O, C–H···O hydrogen bonds and anion–π stacking contacts. Hirshfeld analysis was used to quantify the different contacts. Both complexes exhibited better anti-fungal activity than the standard Fluconazole and comparable antibacterial activity to Gentamycin against Staphylococcus aureus and Escherichia coli microbes. Moreover, complexes 1 and 2 are biologically more active than the free ligands against these microbes. Full article

The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl₃(H₂O) and [4MiH]MnCl₃(H₂O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl₃(H₂O)]_n⁻ edge-sharing octahedral chains. The structures are compared to the previously reported isomeric analogue [2MiH]MnCl₃(H₂O) ([2MiH] = 2-methylimidazolium), and three closely related compounds. The variations in packing of the inorganic chains are shown to be influenced by hydrogen bonding abilities of the imidazolium or related moieties. Both new compounds show intense red luminescence at ambient temperature under UV irradiation. Full article

A FeCoNi(B_0.5Si_0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution appears after 50 h of milling. The grain size was 10 nm after 150 h of milling. Microstructure parameters were calculated by the Rietveld fitting of the X-ray Diffraction patterns. Magnetic characterizations of milled and annealed powders at 650 °C for 1 h were investigated. The heat treatment improves the magnetic properties of the milled powders by enhancing the saturation magnetization value from 94.31 to 127.30 emu/g and decreasing the coercivity from 49.07 to 29.57 Oe. The cohabitation of the FCC phase with the equilibrium crystalline phases observed after annealing is responsible of this magnetic softening. The as-milled powder was also consolidated by spark plasma sintering at 750 and 1000 °C. The obtained specimen consolidated at 750 °C improved the coercivity to 25.06 Oe and exhibited a compressive strength of 1062 Mpa and Vickers hardness of 518 ± 14 HV, with a load of 2 kN. The nanoindentation technique with the Berkovich indentor gave hardness and indentation elastic modulus of 6.3 ± 0.3 Gpa (~640 HV) and 111 ± 4 Gpa for samples consolidated by SPS at 750 °C. Full article

To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test of the HFRC shaft lining structure with four factors and three levels was carried out, and the mechanical characteristics of the shaft lining structure were obtained. The results show that under a uniform surface load, the maximum hoop stress position of the HFRC shaft lining presents a transition trend from the inside surface to the outside surface; the hoop strain of shaft lining concrete is always a compressive strain, and the inside surface is greater than the outside surface. The empirical formula for the ultimate capacity of this new type of shaft lining structure was obtained by fitting. Compared with the model test results, the maximum relative error of the calculated value is only 6.69%, which provides a certain reference value for designing this kind of shaft lining structure. Full article

The purpose of this study was to clarify the influence of alumina air-abrasion on flexural and bond strengths of CAD/CAM composites. The flexural strength (FS) of two brands of commercial CAD/CAM composites was investigated by the three-point bending test using two specimen designs: the single-bar according to the ISO standard and the bonded-double-bar fabricated by bonding two bars with a resin cement. The bond strength between the composites and the resin cement was measured by a conventional shear bond strength (SBS) test. The FS of single-bar specimens was significantly decreased by the air-abrasion. For the FS of the bonded-double-bar specimen, on the other hand, there was no significant difference between the specimens with/without air-abrasion. The SBS for the composites was significantly increased by air-abrasion. The results suggest that alumina air-abrasion improves the SBS of the composites while weakening its FS. Contrarily, the FS of the air-abraded composite did not decrease when the composites were bonded with the resin cement. Full article

The effect of reverse straining on the microstructure, texture, and hardness of the pure Al during the single cycle of the simple shear extrusion (SSE) process is investigated. Electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are used for microstructural evaluations. Due to the nature of the SSE process, the direction of the shear is reversed in the second half channel. As a result, the mean misorientation angle, dislocation density, and hardness decrease. The grain size increases to some extent in the exit of the channel compared with that in the middle. The structural evolution during the single pass of SSE is described in terms of the dislocation cancelling, “untangling” of the cell walls and disintegration of the “forward” cell structure due to the reverse straining in the second half channel. Some simple shear components replace the first texture component in the middle of the channel. At the exit of the channel, the primary texture components appear somewhat confirming the strain reversal effect in the second half channel. Full article