Materials最新文献

The last decade was dominated by a serious problem that now affects all the planet's natural ecosystems: the increasing growth of plastics and microplastics that are difficult to dispose of. One strategy to mitigate this problem is to close the life cycle of one of them-polyethylene terephthalate (PET)-by reusing it within the most common building materials, such as mortars and concretes. The reuse of PET waste as aggregates also allows us to limit the CO₂ emissions released during the production of natural aggregates. This paper analyzes the outcomes of many studies carried out on the characteristics of cementitious mixtures reinforced with waste PET material. Many researchers have demonstrated how PET used as reinforcement of mortars and concretes can produce an increase in the mechanical strengths of the corresponding cementitious mixtures without PET. The tensile strength of this resin is higher than that of concrete; so, by combining the two materials it is possible to obtain a mixture with an overall higher tensile strength, resulting in increased flexural strength and reduced cracking. Using an effective size of PET fibers, it is possible to achieve an increase in the ductility and toughness of the cementitious mixture. Several studies reveal that PET reinforcement reduces the density with a consequent decrease in weight and structural loads, while the workability increases using spherical and smoother PET aggregates.

In this study, wettability was employed to evaluate the effect of alkali activation by NaOH on different fly ash (FA) particle sizes. The results indicated that the surface wettability of FA particles with 13.8 μm increased from 0.025 g²/s to 0.034 g²/s after activation by the NaOH solution, which is suitable for silane modification and electroless plating. X-ray photoelectron spectroscopy (XPS) was used to analyze whether three kinds of silane coupling agents coated on FA surfaces could detect the chemical bonds between silane coupling agents coated on the FA surface and silver layers by shortening the plating time. The XPS results demonstrated that N-Ag coordination bonds can be detected by reducing silver plating time to 2 min for Ag-plated FA modified by N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792). However, there were no chemical bonds detected for Ag-plated FA modified by γ-(2,3-epoxypropoxy)propytrimethoxysilane (KH560) and methyltrimethoxysilane (MTMS), even when the satellite peak of Ag disappeared after plating for 80 s. The SEM showed that Ag particles agglomerated on FA surfaces, and even a bare surface was found after modification by KH560 and MTMS, which further proved no chemical bonds between silver layers and the silane coupling agents.

This study evaluated the effects of adding waste PET fibers on the mechanical properties and chloride ion penetration of latex-modified ultra-rapid hardening cement concrete used for emergency road pavement repairs. The primary experimental variable was the content of waste PET fibers. The mechanical properties of the concrete were evaluated through compressive strength, flexural strength, and splitting tensile strength tests. Its durability was evaluated through chloride ion penetration, surface resistivity, and abrasion resistance tests. The experimental results were compared with the quality standards for emergency repair concrete set by the Korea Expressway Corporation. As a result, this study has enhanced the strength and resistance to chloride ions of latex-modified concrete by incorporating waste PET fibers. In the mixture with 3.84 kg/m³ of waste PET fibers, the compressive strength was 29.9 MPa at 4 h and 42.5 MPa at 28 curing days. The flexural strength was 6.0 MPa at 4 curing hours and 7.0 MPa at 28 days, and the splitting tensile strength was 4.5 MPa at 28 days of curing. The chloride ion permeability amount and abrasion depth were 1081C and 0.82 mm, respectively. The mixture with 3.84 kg/m³ of waste PET fibers has superior compressive strength, flexural strength, splitting tensile strength, chloride ion penetration, and surface resistivity compared to the mixture with 7.68 kg/m³. This result means that the waste PET fibers caused poor dispersion and fiber-balling within the concrete, leading to loose internal void structures when incorporated at 3.84 kg/m³. However, the abrasion resistance test showed better results for the mixture with 7.68 kg/m³ of waste PET fibers than the 3.84 kg/m³ mixture. Therefore, the test results indicated that 3.84 kg/m³ of waste PET fibers is the most effective for latex-modified concrete used in emergency road pavement repairs.

In this paper, the texture evolution of the Ni-5%W alloy baseband with different strain variables (ε_vM = 3.9, 4.9, and 5.1) during rolling and annealing was studied using the electron back scattering diffraction (EBSD) technique. The results indicate that after high-temperature annealing at 1150 °C, all three strain levels of the alloy substrates can achieve a strong cubic texture, with a content exceeding 99% (<10°). However, the texture evolution trajectory is significantly influenced by the strain level. When the content of cubic texture in the alloy substrates under strain levels of 3.9 and 5.1 is the same, significant temperature differences exist. Additionally, the different strain levels result in varying nucleation rates and growth rates of cubic texture in the Ni-5%W alloy substrates. The study reveals that in the alloy substrates under strain levels of 3.9 and 4.9, recrystallized cubic grain nuclei grow within a layered structure, resulting in larger grain sizes and lower nucleation rates. In contrast, in the alloy substrates under a strain level of 5.1, recrystallized cubic grain nuclei form from small equiaxed grains, leading to higher nucleation rates but smaller grain sizes, competing with random orientations. In the later stages of nucleation, recrystallized grains in the alloy substrates under a strain level of 5.1 exhibit a significant size advantage, rapidly growing by engulfing randomly oriented grains. Compared to the alloy substrates with lower strain levels, the recrystallized cubic grains in the alloy substrates under a strain level of 5.1 have higher nucleation rates and faster growth rates.

The cement industry is of great importance in terms of raw materials consumed, energy consumed, and greenhouse gases emitted. Grinding aids (GA) are used to reduce energy consumption and costs, as well as to reduce the amount of CO₂ released into the environment. In this study, the effect of GA-polycarboxylate ether-based water-reducing admixture (PCE) compatibility on some fresh, rheological and hardened state properties of cementitious systems was investigated. In order to investigate the rheological properties and thixotropic behavior of the mixtures, a total of 51 cement paste mixtures were prepared, containing 4 different types (molasses, MEG, DEA and ethanol) and ratios (0.025, 0.05, 0.75 and 0.1) of GAs and 2 different ratios (0.08% and 0.16%) of PCE in addition to the control mixture. In addition, the effect of the used GAs on the grinding efficiency and compressive strength value was investigated. Additionally, the predictability of the type of GA, dosage and cure time using the Taguchi method was investigated. It was determined that the highest grinding performance was obtained in mixtures containing MEG. It was determined that in cement paste mixtures containing GAs, the dynamic yield stress and viscosity values generally decrease with the increase in PCE usage rate up to a certain value, and these values may increase if the PCE usage increases further. It was determined that such behavior is not present in cement paste mixtures containing GAs and that the structural build-up value of the mixtures generally increases with the increase in the PCE admixture usage rate. It was determined that the use of GAs had a positive effect on 28-day compressive strength.

Residual stresses and anisotropic structures characterize laser powder bed fusion (L-PBF) products due to rapid thermal changes during fabrication, potentially leading to microcracking and lower strength. Post-heat treatments are crucial for enhancing mechanical properties. Numerous dental technology laboratories worldwide are adopting the new technologies but must invest considerable time and resources to refine them for specific requirements. Our research can assist researchers in identifying thermal processes that enhance the mechanical properties of dental Co-Cr alloys. In this study, high cooling rates (quenching) and annealing after quenching were evaluated for L-PBF Co-Cr dental alloys. Cast samples (standard manufacturing method) were tested as a second reference material. Tensile strength, Vickers hardness, microstructure characterization, and phase identification were performed. Significant differences were found among the L-PBF groups and the cast samples. The lowest tensile strength (707 MPa) and hardness (345 HV) were observed for cast Starbond COS. The highest mechanical properties (1389 MPa, 535 HV) were observed for the samples subjected to the water quenching and reheating methods. XRD analysis revealed that the face-centered cubic (FCC) and hexagonal close-packed (HCP) phases are influenced by the composition and heat treatment. Annealing after quenching improved the microstructure homogeneity and increased the HCP content. L-PBF techniques yielded superior mechanical properties compared to traditional casting methods, offering efficiency and precision. Future research should focus on fatigue properties.

Dense lithium hydride (LiH) is widely used in neutron shielding applications for thermonuclear reactors and space systems due to its unique properties. However, traditional sintering methods often lead to cracking in LiH products. This study investigates the densification sintering of LiH using microwave technology. A multiphysics model was established based on the measured dielectric properties of LiH at different temperatures, allowing for a detailed analysis of the electromagnetic and thermal field distributions during the microwave heating of cylindrical LiH samples. The results indicate that the electric field distribution within the LiH is relatively uniform, with resistive losses concentrated primarily in the LiH region of the microwave cavity. LiH rapidly absorbs microwave energy, reaching the sintering temperature of 520 °C in just 415 s. Additionally, the temperature difference between the low- and high-temperature regions during the sintering process remains below 5 °C, demonstrating excellent uniform heating characteristics. The microwave sintering process enhances interface migration within the LiH samples, resulting in dense metallurgical bonding between grains. In summary, this research provides valuable insights and theoretical support for the rapid densification of LiH materials, highlighting the potential of microwave technology in improving material properties.

It has recently been found that magnesium potassium phosphate cement (MKPC) paste coating applied on the surface of steel reinforcement can effectively retard the onset of corrosion and suppress corrosion reactions. However, the fast-setting nature of MKPC-which is a merit in repair-can be problematic in a practical engineering process of coating the steel reinforcement with MKPC paste. To address this problem, boric acid (H₃BO₃) was added as a retarder in an MKPC formulation to prolong the setting time. This work investigated the impact of boric acid (at 5% by weight of MgO) on the anti-corrosion performance of MKPC paste coating through a series of electrochemical (EC) tests. The results showed that the anti-corrosion performance of MKPC paste coating for a mild steel bar could be interfered with by the presence of boric acid. In the same testing situation (immersed in 3.5 wt.% NaCl corrosion solution), the polarization resistance and corrosion current density of the group including boric acid were inferior and exceeded the corrosion thresholds prior to the control group without boric acid. Meanwhile, the time constant phase in the frequency range from 1 Hz to 10 kHz was rarely observed, implying that the presence of boric acid probably impaired the formation of the passivation layer. This decrease in anti-corrosion performance of MKPC paste coating could be related to the larger volume fraction of pores in the range from 0.1 to 10 µm that are formed during the initial stage of coating formation.

The emerging paradigm of personalised bone repair embodies a transformative triad comprising bio-inspired design, digital fabrication, and the exploration of innovative materials. The increasing average age of the population, alongside the rising incidence of fractures associated with age-related conditions such as osteoporosis, necessitates the development of customised, efficient, and minimally invasive treatment modalities as alternatives to conventional methods (e.g., autografts, allografts, Ilizarov distraction, and bone fixators) typically employed to promote bone regeneration. A promising innovative technique involves the use of cellularised scaffolds incorporating mesenchymal stem cells (MSCs). The selection of materials-ranging from metals and ceramics to synthetic or natural bio-derived polymers-combined with a design inspired by natural sources (including bone, corals, algae, shells, silk, and plants) facilitates the replication of geometries, architectures, porosities, biodegradation capabilities, and mechanical properties conducive to physiological bone regeneration. To mimic internal structures and geometries for construct customisation, scaffolds can be designed using Computer-aided Design (CAD) and fabricated via 3D-printing techniques. This approach not only enables precise control over external shapes and internal architectures but also accommodates the use of diverse materials that improve biological performance and provide economic advantages. Finally, advanced numerical models are employed to simulate, analyse, and optimise the complex processes involved in personalised bone regeneration, with computational predictions validated against experimental data and in vivo studies to ascertain the model's ability to predict the recovery of bone shape and function.

One of the key trends affecting the future of the construction industry is the issue of ecology; therefore, current activities in construction aim to reduce the use of raw materials, which is made possible by including recycled materials in composites, among other methods. This article describes the results of tests conducted using four types of epoxy composites, i.e., composites modified with waste rubber (WR), composites modified with waste polyethylene (PE) agglomerate, glycolysate obtained using polyethylene terephthalate (PET) waste, and control unmodified mortars (CUM). Selected properties of the mortars were monitored during their maturation under laboratory conditions, as well as after post-curing at elevated temperatures in the range of 60 °C-180 °C. With the increase in the reheating temperature, an increase in the flexural strength of all types of mortars was noted, with the highest more than twofold stronger than the unmodified composites. The compressive strength increased up to a temperature of 140 °C, and then decreased slightly. The highest value of 139.8 MPa was obtained using PET mortars. Post-curing also led to a slight loss of mass of all samples in the range of 0 to 0.06%. Statistical methods were employed, which made it possible to determine the post-curing temperature and composite composition for which the determined properties are simultaneously the most beneficial, especially for the prefabricated elements.