Materials最新文献

Waste concrete is a large amount of solid waste produced in the process of urban construction and renewal in China. Its resource utilization is of great significance for saving mineral resources and improving urban environmental quality. The present study was designed to investigate the effects of mechanical grinding time on the particle size distribution and activity of recycled waste concrete powder (RWCP). Combined with unconfined compressive strength, slump, electric flux and chloride ion penetration resistance tests, the effects of RWCP on the mechanical properties, working performance and impermeability of concrete were analyzed, and the phase and microstructure of concrete containing RWCP were analyzed by XRD and SEM. The results showed that the RWCP is mainly composed of quartz, gismondine, C₂S, cancrinite and portlandite. The optimum activity of RWCP obtained by ball milling for 45 min was 44.41%. RWCP can improve the fluidity of concrete and shorten the initial setting time of concrete. When the blast furnace slag in the concrete was replaced by the RWCP, the early strength and impermeability of the concrete decreased. When RWCP replaced blast furnace slag by 69.1%, the UCS of the concrete at 1, 3, 7, and 14 d decreased from 9.56, 22.1, 34.1, and 41.2 MPa to 5.9, 14.5, 22.7, and 33.2 MPa, respectively. While RWCP replaced fly ash, the normal strength of concrete increased with the increase in fly ash replacement amount. When RWCP completely replaced FA in concrete, the 28-day strength of the concrete increased from 45.2 MPa to 50.8 MPa. The impermeability results showed that the appropriate substitution of RWCP for fly ash was beneficial to increase the impermeability of concrete while excessive substitution reduced. Based on these results, the RWCP has the potential for large-scale application in the preparation of concrete.

Iron-based superconductors have strong potential for magnet applications through their very high upper critical field, low anisotropy and manufacturability through the powder-in-tube (PIT) route. The engineering critical current density (J_e) is a key parameter for measuring the maximum current density that superconducting materials can withstand in practical applications. It serves as a bridge between theoretical research and practical applications of superconductors and has great significance in promoting the development and application of superconducting technology. In this study, Ag sheathed Ba_0.6K_0.4Fe₂As₂ (Ba-122) iron-based superconducting tapes were prepared by using the process of drawing, flat rolling and heat treatment by hot pressing (HP). For the first time, the filling factor of the tapes increased to about 40%, leading to a reduction in the volume fraction of Ag, consequently lowering the overall cost. The optimal parameters for achieving high transport J_e were obtained by comparing the effects of different HP pressures on the properties and micro-morphology of the tapes. The prepared mono-filament tapes are capable of carrying the transport J_e of 4.1 × 10⁴ A/cm² (I_c = 350 A) at 4.2 K, 10 T, marking the highest J_e reported for Ba-122 wires and tapes to date. Our results show that high transport J_e can be obtained in Ba-122 superconducting tapes, and iron-based superconductors have a promising future in practical applications.

Among many iron-based superconductors, isovalently substituted BaFe₂(As_1-xP_x)₂ displays, for x ≈ 0.3, apart from the quite usual Second Magnetization Peak (SMP) in the field dependence of the critical current density, an unusual peak effect in the temperature dependence of the critical current density in the constant field, which is related to the rhombic-to-square (RST) structural transition of the Bragg vortex glass (BVG). By using multi-harmonic AC susceptibility investigations in three different cooling regimes-field cooling, zero-field cooling, and field cooling with measurements during warming up-we have discovered the existence of a temperature region in which there is a pronounced magnetic memory effect, which we attributed to the direction of the structural transition. The observed huge differences in the third harmonic susceptibility at low and high AC frequencies indicates the difference in the time-scale of the structural transition in comparison with the timescale of the vortex excitations. Our findings show that the RST influence on the vortex dynamics goes beyond the previously observed influence on the onset of the SMP.

Wire-based additive manufacturing (AM) is at the forefront of complex metal fabrication because of its scalability for large components, potential for high deposition rates, and ease of use. A common goal of wire directed energy deposition (DED) is preserving a stable process throughout deposition. If too little energy is put into the deposition, the wire will stub into the substrate and begin oscillating, creating turbulence within the meltpool. If too much energy exists, the wire will overheat, causing surface tension to take over and create liquid drips as opposed to a solid bead. This paper proposes a computer vision technique to work as both a state detection and event detection system for wire stability. The model utilizes intensity variations along with frame-to-frame difference calculations to determine process stability. Because the proposed model does not rely on machine learning techniques, it is possible for an individual to interpret and adjust as they see fit. The first part of this paper describes creation and implementation of the model. The model's capability was then evaluated using a 1D laser power experiment, which generated a wide range of stability states across varying powers. The model's accuracy was evaluated through 3D geometry data gathered from the experimentally deposited beads. The model proved to be both capable and accurate and has potential to be used as a real-time control system with future work.

Pulsed current has proven to be a promising alternative to direct current in electrochemical deposition, offering numerous advantages regarding deposit quality and properties. Concerning the electrodeposition of metal alloys, the role of pulsed current techniques may vary depending on the specific metals involved. We studied an innovative tin-ruthenium electroplating bath used as an anti-corrosive layer for decorative applications. The bath represents a more environmentally and economically viable alternative to nickel and palladium formulations. The samples obtained using both direct and pulsed currents were analyzed using various techniques to observe any differences in thickness, color, composition, and morphology of the deposits depending on the pulsed current waveform used for deposition.

Electrospun nanofibrous mats, consisting of chitosan (CS) and polyvinylpyrrolidone (PVP), were constructed with the addition of graphene oxide (GO) for enhancement of delivery of the 5-Fluorouracil (5-Fu) chemotherapy drug. Upon studying the range of GO concentrations in CS/PVP, the concentration of 0.2% w/v GO was chosen for inclusion in the drug delivery model. SEM showed bead-free, homogenous fibres within this construct. This construct also proved to be non-toxic to CaCo-2 cells over 24 and 48 h exposure. The construction of a drug delivery vehicle whereby 5-Fu was loaded with and without GO in various concentrations showed several interesting findings. The presence of CS/PVP was revealed through XPS, FTIR and Raman spectroscopies. FTIR was also imperative for the analysis of 5-Fu while Raman exclusively highlighted the presence of GO in the samples. In particular, a detailed analysis of the IR spectra recorded using two FTIR spectrometers, several options for determining the concentration of 5-Fu in composite fibre systems CS/PVP/5-Fu and GO/CS/PVP/5-Fu were demonstrated. By analysis of Raman spectra in the region of D and G bands, a linear dependence of ratios of integrated intensities of A_D and A_G on the intensity of host polymer band at 1425 cm^-1 vs. GO content was found. Both methods, therefore, can be used for monitoring of GO content and 5-Fu release in studied complex systems. After incorporating the chemotherapy drug 5-Fu into the constructs, cell viability studies were also performed. This study demonstrated that GO/CS/PVP/5-Fu constructs have potential in chemotherapy drug delivery systems.

Nowadays, with the development of electromobility, the requirements not only for the mechanical properties but also for the thermal conductivity of castings are increasing. This paper investigates the influence of casting and heat treatment technology on the thermal diffusivity and thermal conductivity of an AlSi10MnMg alloy. The thermal diffusivity was monitored as a function of temperature in the range of 50-300 °C for the material cast by high-pressure die casting (HPDC) and also by gravity sand casting (GSC) and gravity die casting (GDC). This study also investigated the effect of the T5 heat treatment temperature (artificial ageing without prior solution treatment-HT200, HT300, and HT400) on the thermal conductivity of the material cast by different technologies. Experiments confirmed that the thermal diffusivity or thermal conductivity of the alloy depends on the casting technology. The slower the cooling rate of the casting, the higher the thermal conductivity value. For the alloy in the as-cast condition, the thermal conductivity at 50 °C is in the range of about 125 to 138 [W·m^-1·K^-1]. Regardless of the casting method, the thermal conductivity tends to increase with temperature (50-300 °C). Furthermore, a positive effect of heat treatment without prior solution treatment (HT200, HT300, and HT400) on the thermal conductivity was demonstrated. Regardless of the casting method of the samples, the thermal conductivity also increases with increasing heat treatment temperature. The results further showed that when artificial ageing is performed in industrial practice on castings to increase mechanical properties in the temperature range of 160-230 °C, this heat treatment has a positive effect on thermal conductivity.

The rapid progress of urbanization and industrialization has led to the accumulation of large amounts of metal ions in the environment. These metal ions are adsorbed onto the negatively charged surfaces of clay particles, altering the total surface charge, double-layer thickness, and chemical bonds between the particles, which in turn affects the interactions between them. This causes changes in the microstructure, such as particle rearrangement and pore morphology adjustments, ultimately altering the mechanical behavior of the soil and reducing its stability. This study explores the effects of four common metal ions, including monovalent alkali metal ions (Na⁺, K⁺) and divalent heavy metal ions (Pb²⁺, Zn²⁺), with a focus on how ion valence and concentration impact the soil's microstructure and mechanical properties. Microstructural tests show that metal ion incorporation reduces particle size, increases clay content, and transforms the structure from layered to honeycomb-like. Small pores decrease while large pores dominate, reducing the specific surface area and pore volume, while the average pore size increases. Although cation exchange capacity decreases, cation adsorption density per unit surface area increases. Monovalent ions primarily disperse the soil structure, while divalent ions induce coagulation. Macro-mechanical tests reveal that metal ion contamination reduces porosity under loading, with compressibility rises as the ion concentration increases. Soils contaminated with alkali metal ions shows higher compression coefficients at all loads, while heavy metal ions cause higher compression under lower loads. Shear strength, the internal friction angle, and cohesion in metal-ion-contaminated clay decrease compared to uncontaminated field-state clay, with greater declines at higher ion concentrations. The Micropore Morphology Index and hydro-pore structural parameter effectively characterize both micro- and macrostructural properties, establishing a quantitative relationship between HPSP and the engineering properties of metal-ion-contaminated clay.

Magnesium-based materials are an interesting solution in terms of medical applications. Alloys that are hard to obtain via standard means may be manufactured via mechanical alloying (MA), which allows the production of materials with complex a chemical composition and non-equilibrium structures. This work aimed to investigate materials obtained by the MA process for 5, 8, 13, and 20 h in terms of their phase composition and changes during heating. The results of thermal XRD analysis were in the temperature range between 25 and 360 °C, which revealed MgZn₂, PrZn₁₁, Ca₂Mg₅Zn₁₃, and Ca phases as well as α-Mg and α-Zn solid solution. The structural analysis features the powder morphology of the analyzed samples, showing cold-welding and fracturing processes leading to their homogenization, which is supported by the EDS results. The base Mg-Zn-Ca alloy was modified by different additions, but a thorough analysis of the influence of praseodymium on its thermal properties has not yet been performed. We chose to focus on Pr addition because it belongs to low-toxicity rare earth metals, which is an essential feature of biomaterials. Also, the Ca₂Mg₅Zn₁₃ phase is not fully known, as there are no crystallographic data (hkl). Therefore, the investigation is important and scientifically justified.

Femtosecond laser two-photon polymerization (TPP) technology, known for its high precision and its ability to fabricate arbitrary 3D structures, has been widely applied in the production of various micro/nano optical devices, achieving significant advancements, particularly in the field of photonic wire bonding (PWB) for optical interconnects. Currently, research on optimizing both the optical loss and production reliability of polymeric photonic wires is still in its early stages. One of the key challenges is that inadequate metrology methods cannot meet the demand for multiphysical measurements in practical scenarios. This study utilizes novel in situ scanning electron microscopy (SEM) to monitor the working PWBs fabricated by TPP technology at the microscale. Optical and mechanical measurements are made simultaneously to evaluate the production qualities and to study the multiphysical coupling effects of PWBs. The results reveal that photonic wires with larger local curvature radii are more prone to plastic failure, while those with smaller local curvature radii recover elastically. Furthermore, larger cross-sectional dimensions contribute dominantly to the improved mechanical robustness. The optical-loss deterioration of the elastically deformed photonic wire is only temporary, and can be fully recovered when the load is removed. After further optimization based on the results of multiphysical metrology, the PWBs fabricated in this work achieve a minimum insertion loss of 0.6 dB. In this study, the multiphysical analysis of PWBs carried out by in situ SEM metrology offers a novel perspective for optimizing the design and performance of microscale polymeric waveguides, which could potentially promote the mass production reliability of TPP technology in the field of chip-level optical interconnection.