Search Results (22)

Composite grids serve as reinforcement in concrete structures, offering alternatives to conventional steel reinforcement. These grids can be fabricated from various materials, including synthetic polymers, metals, and natural fibers. This study explores the use of composite grids as lateral confinement of self-compacting concrete (SCC) cylinders and examines their impact on the failure mode under axial compression. In the experiment, the types of grids and mesh shapes used were plastic grids of diamond mesh (PGD) and regular mesh (PGT), metallic grids of diamond mesh (MGD) and square mesh (MGS), vegetable grids of Alfa fiber mesh, 10 × 10 mm (VGAF-1) and 20 × 20 mm (VGAF-2), and vegetable grids of date palm fibers (VGDF). The binder of SCC mixtures incorporated 10% marble powder as a partial replacement for ordinary Portland cement (OPC). SCC mixtures were tested in the fresh state by measuring the slump flow diameter, V-funnel flow time, L-box blocking ratio, and segregation index. Cylinders with a diameter of 160 mm and a height of 320 mm were made to assess the mechanical properties of hardened SCC mixtures under axial compression. The results indicate that most of the confined cylinders exhibited an increase in ductility compared to unconfined cylinders. Grid types MGD and PGD provided the best performance, with ductility increases of 100.33% and 96.45%, respectively. VGAF-2 cylinders had greater compressive strength than cylinders with other grid types. The findings revealed that the type and mesh shape of the grids affects the failure mode of confined cylinders, but has minimal influence on their modulus of elasticity. This study highlights the potential of lateral grid confinement as a technique for rehabilitating, strengthening, and reinforcing weaker structural concrete elements, thereby improving their mechanical properties and extending the service life of building structures. Full article

Industrial and construction wastes make up about half of all world wastes. In order to reduce their negative impact on the environment, it is possible to use part of them for concrete production. Using experimental–statistical modeling techniques, the combined effect of brick powder, recycling sand, and alkaline activator on fresh and hardened properties of self-compacting concrete for the production of textile-reinforced concrete was investigated. Experimental data on flowability, passing ability, spreading speed, segregation resistance, air content, and density of fresh mixtures were obtained. The standard passing ability tests were modified using a textile mesh to maximize the approximation to the real conditions of textile concrete production. To determine the dynamics of concrete strength development, compression and flexural tests at the ages of 1, 3, 7, and 28 days and splitting tensile strength tests of 28 days were conducted. The preparation technology of the investigated modified mixtures depending on the composition is presented. The resulting mathematical models allow for the optimization of concrete compositions for partial replacement of slag cement with brick powder (up to 30%), and natural sand with recycled sand (up to 100%) with the addition of an alkaline activator in the range of 0.5–1% of the cement content. This allows us to obtain sustainable, alkali-activated high-strength self-compacting recycling concrete, which significantly reduces the negative impact on the environment and promotes the development of a circular economy in the construction industry. Full article

The development of self-compacting lightweight concretes is associated with solving two conflicting tasks: achieving a structure with both high flowability and homogeneity. This study aimed to identify the technological and rheological characteristics of the flow of concrete mixtures D1400…D1600 based on hollow microspheres in comparison with heavy fine-grained D2200 concrete and to establish their structural and physico-mechanical characteristics. The study of the concrete mixtures was carried out using the slump flow test and the rotational viscometry method. The physical and mechanical properties were studied using standard methods for determining average density and flexural and compressive strength. According to the results of the research conducted, differences in the flow behaviors of concrete mixtures on dense and hollow aggregates were found. Lightweight concretes on hollow microspheres exhibited better mobility than heavy concretes. It was shown that the self-compacting coefficients of the lightweight D1400...D1600 concrete mixtures were comparable with that of the heavy D2200 concrete. The rheological curves described by the Ostwald–de Waele equation showed a dilatant flow behavior of the D1400 concrete mixtures, regardless of the ratio of quartz powder to fractionated sand. For D1500 and D1600, the dilatant flow behavior changed to pseudoplastic, with a ratio of quartz powder to fractional sand of 25/75. The studied compositions of lightweight concrete can be described as homogeneous at any ratio of quartz powder to fractional sand. It was shown that concrete mixtures with a pronounced dilatant flow character had higher resistance to segregation. The value of the ratio of quartz powder to fractional sand had a statistically insignificant effect on the average density of the studied concretes. However, the flexural and compressive strengths varied significantly more in heavy concretes (up to 38%) than in lightweight concretes (up to 18%) when this factor was varied. The specific strength of lightweight and heavy concrete compositions with a ratio of quartz powder to fractional sand of 0/100 had close values in the range of 20.4...22.9 MPa, and increasing the share of quartz powder increased the difference between compositions of different densities. Full article

The influence of the charge treatment by ultrahigh dilution (UHD) technology on oxide single crystals grown by the Czochralski technique was studied for monoclinic MgMoO₄ crystals doped by 1 at. % of Nd³⁺ ions. The series of 10 Nd:MgMoO₄ crystals was grown from the charges that were subjected to UHD treatment, as well as from the charges treated with two types of control or with no special treatment at all. The grown crystals were studied by X-ray powder diffraction analysis, inductively coupled plasma atomic emission spectroscopy, mass-spectrometry, optical absorption, emission spectroscopy and luminescence kinetic analysis. We found that: (i) wetting of MgO + MoO₃ mixture by a water-ethanol solution before calcining leads to some enrichment of the mixture with MoO₃, whereas the wetting of the charge after the calcining leads to some enrichment of it with MgO; (ii) congruent melting composition of MgMoO₄ crystal is in the field of some MoO₃ excess; (iii) the solid-phase solubility of the excess MoO₃ in MgMoO₄ probably does not depend on temperature, whereas the solid-phase solubility of the excess MgO in MgMoO₄ crystal depends on temperature. We suggest that the corresponding solidus line passes through the range of retrograde solubility; (iv) the crystals grown within this range are characterized by the enhanced Nd³⁺ segregation coefficient between the crystal and the melt (approximately 0.006 versus 0.004); (v) unit cell parameters of MgMoO₄ crystal with the excess of MoO₃ are larger than those of the crystal of the stoichiometric composition and of the crystal with the excess of MgO; (vi) the shapes of the optical absorption and luminescence spectra of Nd:MgMoO₄ crystal do not depend on the charge treatment; (vii) luminescence decay kinetics are single-exponential for all the studied crystals, the luminescence decay time being different for the crystals grown from the charges that underwent different types of treatment; (viii) the luminescence intensity of Nd:MgMoO₄ crystal grown from the charge that underwent UHD treatment before calcining (solid-phase synthesis) is reduced by an order of magnitude in comparison with the other studied crystals. Full article

Ni-based composite coatings reinforced by high-entropy intermetallic compounds (HEICs) were prepared by detonation spraying (DS) on low alloy steel substrates. To this end, first (Ti-Nb)(V-Cr-Ni-Fe) and Al₃(TiZrNbCrHfTa) HEIC powders were fabricated by arc melting followed by ball milling. The as-milled HEIC powders were then employed as reinforcement particles to prepare Ni-7wt.% HEIC composite coatings. The average particle size of the (Ti-Nb)(V-Cr-Ni-Fe) and Al₃(TiZrNbCrHfTa) HEIC powders were 18 and 35 µm, respectively, while the average particle size of the Ni powder was 56 µm. (Ti-Nb)(V-Cr-Ni-Fe) exhibited a single hexagonal C14 Laves phase in spite of Ti and Nb segregations. The XRD pattern of Al₃(TiZrNbCrHfTa) indicated the presence of a tetragonal D0₂₂-type structure along with some minor CrTi and Cr₅Al₈ phases. The sprayed Ni-7wt.% FeNiCrV-TiNb and Ni-7wt.% Al₃(TiZrNbCrHfTa) composite coatings retained crystal structures of the powder mixtures, suggesting proper thermal stability for both powders. The coatings exhibited a dense microstructure consisting of a lamellar microstructure with low porosity and sound bonding with the substrate. The microhardness of Ni-7wt.% FeNiCrV-TiNb (450 HV) was higher than that of Al₃(TiZrNbCrHfTa) (338 HV), and it exhibited lower fluctuation than that of Ni-7wt.% Al₃(TiZrNbCrHfTa). DS is an effective method to fabricate metal matrix composites reinforced by HEICs with a low level of porosity. Full article

This study investigated the allowability of materials in the laser powder melting process, with a focus on powder mixing as a means of adjusting the material composition quickly and cost-effectively. By mixing different powders, a desired alloy can be created during additive processing without the need to produce new powder, which can be expensive. However, one of the main challenges in this process is the segregation of powders, which can lead to non-homogeneous alloys. To address this challenge, the study examined the use of a single component 316L mixed with 1% and 5% copper powder in the additive processing. The results showed that homogeneous components with a uniform and targeted copper content could be produced. However, the mechanical-technological properties of both alloys were lower than those of 316L in situ. To optimize and extend this study, further investigation could be conducted to improve the homogeneity of the powder mixture and to enhance the mechanical-technological properties of the alloys produced. This could involve exploring different alloy designs, optimizing the laser powder melting process parameters, and using advanced characterization techniques to gain a deeper understanding of the microstructure and properties of the alloys. By addressing these challenges, the laser powder melting process could become an even more promising method for producing customized alloys with tailored properties. Full article

Conglomerate formation, where enantiomers within a racemic mixture self-segregate upon crystallization, is an advantageous property for obtaining chirally pure crystals and allows large-scale chiral resolution. However, the prevalence of conglomerates is low and difficult to predict. In this report, we describe our attempts to engineer conglomerates from racemate-forming compounds by integrating them into a conglomerate-forming matrix. In this regard, we found that Ni(II) and Fe(II) form molecular alloys with Zn(II) in [M_xZn_(1−x)(bpy)₃](PF₆)₂ (where bpy = 2,2′-bipyridyl). Powder X-ray Diffraction (PXRD) and Energy-Dispersive X-ray spectroscopy (EDX) evidenced conglomerate crystallization with Ni(II) concentrations up to about 25%, while it was observed only for much lower concentrations of Fe(II). This can be attributed to the ability of [Ni(bpy)₃](PF₆)₂ to access a metastable conglomerate phase, while no such phase has been detected in [Fe(bpy)₃](PF₆)₂. Furthermore, the chiral phase appears to be favored in fast-growing precipitates, while the racemic phase is favored in slow re-crystallizations for both Ni(II) and Fe(II) molecular alloys. X-ray natural circular dichroism (XNCD) measurements on [Ni_0.13Zn_0.87(bpy)₃](PF₆)₂ demonstrate the chirality of the nickel molecules within the zinc molecular matrix. Full article

This paper focuses on the microstructure, phase composition, mechanical, tribological and corrosion properties of high-entropy alloys (HEAs) in the CoCrCuFeNi system depending on copper content, which was varied from 0 to 20 at. % with an increment of 5%. CoCrCuFeNi alloys were manufactured by powder metallurgy methods: mechanical alloying and hot pressing of element mixtures. The solubility limit of copper in CoCrFeNi solid solution was found to be 9 at. %. Segregation of irregularly shaped copper grains sized 1–30 μm is observed at concentrations above this solubility limit. As copper concentration increases, the phase composition of CoCrCuFeNi alloys changes from the single phase based on FCC1 solid solution (Cu = 0–5 at. %) to the dual-phase FCC1 + FCC2 alloy (Cu = 10–20 at. %), where FCC1 is the main phase and FCC2 is the secondary copper-rich phase. Tribological tests have shown that doping the CoCrFeNi alloy with copper increased wear resistance by 23% due to solid solution hardening. As copper content rises above 20%, the content of the secondary FCC2 phase increases, while wear resistance and alloy hardness decline. An analysis of wear tracks and wear products has shown that abrasion of CoCrCuFeNi alloys occurs via the abrasive-oxidative wear mechanism. The corrosion tests of CoCrCuFeNi HEAs in 3.5% NaCl solution had demonstrated that doping the alloy with copper at low concentrations (5–10%) leads to decreasing of corrosion resistance, possibly due to the formation of undesirable oxide Cu₂O along with protective Cr₂O₃. At high copper concentrations (15–20%) galvanic corrosion is suppressed due to coarsening of FCC2 grains and thus decreasing the specific contact surface area between the cathode (FCC2) and the anode (FCC1). Full article

Piezoelectric materials are a class of compounds that is gaining increasing interest in various applications such as energy harvesting. During the last decade, lead-free ZnSnO₃ perovskite ceramic has gained attention among the scientific community thanks to its unique symmetry-dependent and spontaneous polarization properties such as piezoelectricity and ferroelectricity. Nevertheless, only a few studies successfully prepared pure ZnSnO₃, while most seem to mislead the product for its hydroxide precursor (ZnSn(OH)₆) or a mixture of Zn₂SnO₄ and SnO₂. In our work, we investigated the conversion of ZnSn(OH)₆ at different temperatures (500, 600, 700, 750 and 800 °C) by X-ray powder diffraction analysis, and in-situ using synchrotron radiation up to 950 °C under ambient atmosphere and in a vacuum, to reproduce conventional reaction conditions. SEM and TEM have been used to understand the evolution of the particle shape and surface structure before and after the thermal treatments. Our results show the instability of the ZnSn(OH)₆ phase, which converts into an amorphous structure at low temperature. Above 750 °C, the material segregates into Zn₂SnO₄ and SnO₂, supporting the hypothesis that the thermal treatment of the hydroxide phase under typical conditions results in the formation of an oxide mixture rather than the phase pure ZnSnO₃. Full article

This study investigates the application of centrifugal force for the compaction of metal powder. Previous studies using the centrifugal force for manufacturing the green bodies were focused on fine powders with narrow particle size distribution or binary mixtures. This study explores the particle packing of multi-sized powder. Aluminum alloy powder with a particle size less than 100 µm and polymer binder were admixed and compacted in the centrifugal casting with ranging magnitudes of centripetal acceleration. Three different centrifugal forces were tested: 700, 1800, and 3700 G. The microstructure of the green bodies was then observed on the SEM micrographs. The obtained green bodies had high packing densities ranging from 62 to 69%. The packing density and median particle size increase at the positions further away from the center of rotation of the centrifuge with an increase of centrifugal force. The effect of centrifugal force on the segregation of particles was investigated through the quasi-binary segregation index. The segregation phenomena was not observed at 700 G, but clear particle segregation was found at higher centrifugal forces. The increase of the centrifugal force resulted in higher segregation with finer particles moving to the inner part of the spinning mold, with a significant change in the size of particles located closer to the center of rotation. Overall, the centrifugal process was found to produce highly compacted green bodies while yielding a segregation effect due to wide particle size distribution. Full article

Layered ternary Ti₂SnC carbides have attracted significant attention because of their advantage as a M2AX phase to bridge the gap between properties of metals and ceramics. In this study, Ti₂SnC materials were synthesized by two different methods—an unconventional low-energy ion facility (LEIF) based on Ar⁺ ion beam sputtering of the Ti, Sn, and C targets and sintering of a compressed mixture consisting of Ti, Sn, and C elemental powders up to 1250 °C. The Ti₂SnC nanocrystalline thin films obtained by LEIF were irradiated by Ar⁺ ions with an energy of 30 keV to the fluence of 1.10¹⁵ cm⁻² in order to examine their irradiation-induced resistivity. Quantitative structural analysis obtained by Cs-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed transition from ternary Ti₂SnC to binary Ti_0.98C carbide due to irradiation-induced β-Sn surface segregation. The nanoindentation of Ti₂SnC thin nanocrystalline films and Ti₂SnC polycrystalline powders shows that irradiation did not affect significantly their mechanical properties when concerning their hardness (H) and Young’s modulus (E). We highlighted the importance of the HAADF-STEM techniques to track atomic pathways clarifying the behavior of Sn atoms at the proximity of irradiation-induced nanoscale defects in Ti₂SnC thin films. Full article

The stability of nanostructured metal alloys is currently being extensively investigated, and several mathematical models have been developed to describe the thermodynamics of these systems. However, model capability in terms of thermal stability predictions strongly relies on grain boundary-related parameters that are difficult to measure or estimate accurately. To overcome this limitation, a novel theoretical approach is proposed and adopted in this work to identify W-based nanocrystalline alloys which are potentially able to show thermodynamic stability. A comparison between model outcomes and experimental findings is reported for two selected alloys, namely W-Ag and W-Al. Experimental results clearly highlight that W-Ag mixtures retain a segregated structure on relatively coarse length scales even after prolonged mechanical treatments. Moreover, annealing at moderate temperatures readily induces demixing of the constituent elements. In contrast, homogeneous nanostructured W-Al solid solutions are obtained by ball milling of elemental powders. These alloys show enhanced thermal stability with respect to pure W even at high homologous temperatures. Experimental evidences agree with model predictions for both the investigated systems. Full article

Oleic acid (OA)-modified Fe₃O₄ nanoparticles were successfully covered with polyanilines (PANIs) via inverse suspension polymerization in accordance with SEM and TEM micrographs. The obtained nanoparticles were able to develop into a ferrite (α-Fe) and α″-Fe₁₆N₂ mixture with a superparamagnetic property and high saturated magnetization (SM) of 245 emu g⁻¹ at 950 °C calcination under the protection of carbonization materials (calcined PANI) and other iron-compounds (α″-Fe₁₆N₂). The SM of the calcined iron-composites slightly decreases to 232 emu g⁻¹ after staying in the open air for 3 months. The calcined mixture composite can be ground into homogeneous powders without the segregation of the iron and carbon phases in the mortar without significantly losing magnetic activities. Full article

In this study, 5Y-PSZ-based ceramics with 15 mol.% of manganese oxide were obtained from PSZ + MnO₂ powders mixtures by pressing and direct firing. The resulting materials show a stable cubic fluorite structure with only minor traces of segregated manganese oxides and relative density from 90% to 98%. The linear thermal expansion coefficient is in the order of 10⁻⁵ K⁻¹ at 500 K and increases gradually with temperature, due to the onset of a contribution of chemical expansion, reaching about 13 × 10⁻⁶ K⁻¹ at 1100 K. These results are suitable for prospective applicability as buffer layers to minimize degradation and delamination of electrolyte/oxygen electrode interfaces in solid electrolyte cells. The electrical conductivity remains close to 1 S/m at 973 K and close to 7 S/m at 1273 K, suggesting mixed conductivity with a prospective contribution to electrode processes occurring at electrode/electrolyte interfaces. Guidelines for further improvement were also established by a detailed analysis of the impact of heating/cooling rate, firing temperature, and time on those properties, based on Taguchi planning. Full article

Segregation is a common problem in batch-based direct compression (BDC) processes, especially with low-dose tablet products, as is the preparation of a homogenous mixture. The scope of the current work was to explore if a continuous direct compression (CDC) process could serve as a solution for these challenges. Furthermore, the principle of a platform formulation was demonstrated for low dose tablets. The combination of filler excipients and the API in the formulation used was suitable for direct compression, but also prone to induce segregation in BDC process. The CDC process was found to be very promising; it was shown that tablets with the desired quality parameters could be manufactured successfully with both of the APIs studied. Powder analysis indicated that the APIs display some fundamental differences in their physical properties, which was also reflected in powder mixture properties and, hence, eventually in processing. However, process parameters, especially mixer impeller speed, were not found to have any significant influence on end product quality. The study suggests that a CDC process can be a viable solution to resolve the challenges described. Moreover, manufacturing by using a universal platform formulation seems to be a feasible way for producing low-dose tablets. Full article