Search

To solve the problem of carbon emission and high energy consumption of traditional binder, the coal-bearing metakaolin (CMK) geopolymer was used to stabilize sludge. The unconfined compressive strength (UCS) test was conducted to determine the proportion of alkali activator firstly. On this basis, the effects of alkali-precursor ratio, precursor content, NaOH molarity, curing time, curing temperature and slag content on the mechanical properties of stabilized sludge were investigated. Finally, the SEM and XRD tests were conducted to analyse the microstructure of stabilized sludge. The results showed that the UCS of stabilized sludge first increased and then decreased with increasing Na2SiO3:NaOH ratio and the rational proportion of alkali activator of geopolymer was Na2SiO3:NaOH=75:25. The UCS increased as the alkali-precursor ratio, precursor content and NaOH molarity increased. As the curing time, curing temperature and slag content increased, the UCS of stabilized sludge improved more obviously. The microstructural analysis showed that no new minerals were formed in geopolymer stabilized sludge. With the increase of alkali-precursor ratio, precursor content, NaOH molarity, curing time, curing temperature and slag content, the amount of amorphous N-A-S-H and C-(A)-S-H gels increased, which made the soil structure denser through bonding and filling effects, thus increasing the strength of stabilized sludge.

The microstructural, textural, and hardness evolution of a cold-rolled high-purity Ti sheet (50 pct reduction in thickness) during isochronal annealing at 350 °C to 550 °C was investigated by jointly using electron backscatter diffraction, electron channel contrast imaging, X-ray diffraction, and hardness test, with a dedicated correlation analysis between them performed. Results show that recrystallization nucleation starts at 400 °C with prior grain boundaries as preferential sites while fully recrystallized structures were obtained after annealing at 550 °C for 1 hours. During the primary recrystallization, contrary to earlier reports, considerable textural changes occur: the prior bimodal basal texture characteristic is essentially replaced by a ring-like basal texture. Such a textural change is attributed to the orientation-gradient-related subgrain coalescence mechanism that dominates the recrystallization nucleation of the high-purity Ti sheet. Specimen hardness always decreases with increasing the annealing temperature (from 234.3 ± 5.8 to 135.9 ± 2.9 HV), which is closely related to continuous variations of grain sizes and dislocation densities (mainly stored in low-angle boundaries). Quantitative analyses reveal that both grain sizes and dislocation densities have mild effects on the hardness change when annealed below 450 °C. However, the decrease in dislocation density leads to more significant softening than grain coarsening when the annealing temperature exceeds 450 °C. [ABSTRACT FROM AUTHOR]

Mg MB26/Al 7075 bimetal composite mandrels with different number of mandrels (one, three, and five) were successfully prapared by coating extrusion method. The effects of different number of mandrels on the microstructure and the interface quality were studied. The mechanical properties of Mg/Al composites with different mandrels were analyzed and compared. The results show that under the condition of extrusion temperature of 320 °C and extrusion ratio of 25, Mg/Al composite with different bimetals are produced. The grain refinement and homogenization degree of the five-core's core and edge are better than the three-core's, that is, the influence of the interface surface area of the multi-core structure on the grain refinement and uniformity are more obvious than the mechanical factor of the complete axial symmetry. As the number of mandrels increases, the thickness of the interlace layer decreases slightly, especially, the decrease in the thickness of the near-magnesium layer is more obvious. The yield strength varies little and has a slight increase trend. [ABSTRACT FROM AUTHOR]

Solutions of a novel zwitterionic gemini surfactant, 1,2-bis[ N-ethyl- N-(sodium 2-hydroxyl-3-sulfopropyl)-dodecyl-ammonium] ethane betaine (DBA), in presence of sodium salicylate (NaSal) can form wormlike micelles and thereby show a viscoelasticity. At low molar ratio of NaSal/DBA, R ≤ 0.3, the systems behaved like a Newton fluid. However, as the R increased, the systems exhibited shear-thinning behavior. The zero-shear viscosity η increased dramatically with increasing R and peaked with R = 0.8 at a value of 18.8 Pa s. This was attributed to the formation of long wormlike micelles (1.6 ∼ 2.9 μm) and network structure confirmed by scanning electron microscopy. Further increase in R beyond 0.8 resulted in a slight decrease in η, which may be caused by the branched micelles formed at high salt concentration. In addition, the tested systems showed a Maxwellian behavior at lower frequencies, but deviated from the Maxwellian mode at higher frequencies. [ABSTRACT FROM AUTHOR]

Thermoelectric BiTe alloy nanopowders with different morphologies were synthesized by hydrothermal processes with different surfactants. The nanopowders were hot-pressed into pellets, and their thermoelectric properties were investigated. The results show that the morphologies of the nanopowders have remarkable effects on the thermoelectric properties of the hot-pressed bulk pellets. A suitable microstructure of the bulk pellet prepared from flower-like nanosheets was found, having a lower electrical resistivity, larger Seebeck coefficient, and lower thermal conductivity, resulting in a high figure of merit ZT ≈ 1.16. The effects of the nanopowders with different morphologies on the microstructure and thermoelectric properties of hot-pressed bulk pellets are discussed. [ABSTRACT FROM AUTHOR]

Ca2.7Bi0.3Co4O9 samples have been sintered in temperature range of 1183–1243 K by conventional solid-state reaction method. XRD and SEM investigations show that c-axis-oriented structure could be formed in these samples and Lotgering factors increase with the increase of sintering temperature when it is below 1223 K, from 52% for the sample sintered at 1183 K to 86% for the sample sintered at 1223 K. Due to decomposition of Ca2.7Bi0.3Co4O9, however, the c-axis-oriented structure was destroyed in the sample sintered at 1243 K although Ca2.7Bi0.3Co4 O9 phase could be recovered at the cooling stage. The size of grains in all samples increases with the increase of sintering temperature, but the relative densities are almost kept unchanged for the samples sintered at the temperature higher than 1183 K. Due to the highly textured structure, the transport properties of the sample sintered at 1223 K are anisotropic and its ZT values in the ab plane are obviously larger than those along the c-axis. [ABSTRACT FROM AUTHOR]

Grafting polyphenols and glycosylation are effective means to enhance the wettability and emulsifying properties of natural protein particles. A stable pickering emulsion (PE) with antioxidant properties was prepared using β-Lactoglobulin-Rosmarinic acid-Pectin (β-LG-RA-PC) conjugates as stabilizers in this study. When PC and β-LG-RA with the same mass were covalently combined, the solid protein-based particles exhibited ideal wettability (84.2 ± 0.3°), emulsification performance, and molecular flexibility. PEs with an oil content of 66.7% were successfully prepared using a 10 mg/mL concentration of the complex. The intrinsic reasons for the stabilization of the PE were explored through interfacial tension (from 16.02 mN/m to 12.18 mN/m), adsorption kinetics, interfacial expansion viscoelastic modulus (the tangent of the phase angle was 0.22), microstructure, and rheological properties, revealing that the dense, ideally viscoelastic interface layer formed was the main factor. The electrostatic repulsion between droplets, and the formation of a robust spatial network structure, facilitated PEs' stability. These studies confirmed the possibility of implementing protein-based particles to yield food-grade PE. [Display omitted] • The grafting rate for the same mass of β-Lactoglobulin-Rosmarinic acid (β-LG-RA) conjugate and pectin (PC) reached 39.07%. • Pickering emulsions (PEs) prepared with β-LG-RA-PC (8–12 mg/mL) exhibited a solid-like structure. • The viscoelastic interface and accumulated network structure increased the stability of PEs. • The addition of RA and PC could make the three-phase contact angle of β-LG-RA-PC nanoparticles close to 90°. [ABSTRACT FROM AUTHOR]

Abstract: Silica hollow microspheres with a single hole in the shell have been prepared by the precipitation-phase separation method. The synthesis was performed by mixing a tetrahydrofuran (THF)–ethanol solution of poly(styrene-co-methyl methacrylate) (P(St-co-MMA)) and tetraethyl orthosilicate (TEOS) with water, adding ammonia to catalyze the hydrolysis of TEOS and finally removing P(St-co-MMA) by calcination. The effects of the THF-to-ethanol volume ratio, the P(St-co-MMA)-to-TEOS mass ratio, the organic solvent-to-water volume ratio, and the amount of ammonia on the final morphology, size and hole size of the microspheres have been investigated. Generally, the morphology of the microspheres ranged from single-hole to bowl-like, depending on the P(St-co-MMA)-to-TEOS mass ratio; the size of the microspheres decreased with increasing THF-to-ethanol volume ratio; and the size of the holes increased with decreasing THF-to-ethanol volume ratio and decreasing organic solvent-to-water volume ratio. The formation process of single-hole silica/P(St-co-MMA) composite microspheres was monitored with transmission electron microscopy (TEM). The TEOS and P(St-co-MMA) microphases separated from each other to form a hemispherical structure, which transformed to a single-hole structure after ammonia was added. A plausible mechanism for the formation of the single-hole hollow microspheres is proposed. [Copyright &y& Elsevier]

Abstract: SiC particulate-reinforced Al composites were prepared by powder metallurgy (PM) method and conventional atmospheric sintering. Scanning electron microscope (SEM), X-ray diffraction (XRD) techniques were used to characterize the sintered composites. The effect of temperature on the density, hardness, strength, and microstructure of composites was investigated. Detailed failure behavior was analyzed. It was found that the segregation of SiC appeared at higher temperature. The highest micro-hardness of 80MPa occurred at 700°C. The strength tended to increase with the increasing temperature due to the formation of Al2Cu. Both ductile and brittle fracture features were observed. [Copyright &y& Elsevier]

9310 carburized steel experiences significant wear and spalling problems when operating under high friction and heavy loads, which severely restricts its applications in the aviation industry. Therefore, it holds great significance to further enhance the surface mechanical properties of 9310 carburized steel through suitable surface strengthening technologies. The Electropulsing-Assisted Ultrasonic Surface Rolling Process (EP-USRP) has been successfully applied to carburized 9310 steel, yielding significant improvements in surface quality, hardness, friction and wear properties, and microstructure. Systematic investigations were conducted under varying EP-USRP parameters. Regarding the electric pulse parameters, it is observed that with the increase in output voltage, surface properties such as surface roughness and surface hardness tend to first optimize and then deteriorate. After applying EP-USRP with optimal parameters, the surface roughness of carburized 9310 steel was reduced to Ra 0.154 μm, a mere 5 % of its initial value. The surface hardness experienced a substantial increase, reaching 909.2 HV, representing a notable improvement of 29.9 % compared to the original sample, with a corresponding hardening depth of 1400 μm. Moreover, the wear amount of carburized 9310 steel witnessed a remarkable reduction to 11.8 % of its initial value, accompanied by a decrease in the coefficient of friction to 43.0 %. The enhancement of carburized 9310 steel through EP-USRP is attributed to two key mechanisms: deformation hardening induced by severe plastic deformation and microstructure strengthening resulting from strain-induced martensitic transformation. Among them, the severe plastic deformation mechanism is dominant, Through these mechanisms, the proportion of small-angle boundaries in carburized 9310 steel strengthened by EP-USRP increased. Additionally, the grain size of the surface layer decreased, and the content of retained austenite in the surface layer decreased, collectively contributing to significant improvements in surface properties, as well as friction and wear performance. • Proposing a novel technology for surface strengthening of 9310 carburized steel • The introduction of electropulsing offers further enhancement based on the USRP • Surface hardness increased 29.9 %, and roughness reduced 95 % under optimal parameters • At ideal conditions, wear amount and friction coefficient decreased 88.2 % and 57.0 %. [ABSTRACT FROM AUTHOR]

Abstract: The novel filled skutterudite materials have attracted much interest in recent years and experimental studies have revealed that electrical properties (electrical conductivity and Seebeck coefficient) in these materials are dominated by their electronic structure while the effective suppression of thermal conductivity is mainly determined by their lattice dynamics. To clarify the relationship between microstructure and properties in further, we report a systematic study of electronic structures and lattice dynamics of CoSb3 in this paper using linearized augmented plane waves based on the density functional theory of first principles. By calculating band structure and partial density of states (PDOS), effects of electronic structures of CoSb3 on electrical properties were investigated. Based on the calculated results of phonon dispersions and phonon density of states of CoSb3, lattice dynamics of CoSb3 (heat capacity, Debye temperature, mean free path and lattice thermal conductivity) are discussed in detail. The calculated results are excellently consistent with other work and experimental data. [Copyright &y& Elsevier]

Ca2.7Bi0.3Co4O9 samples have been sintered in temperature range of 1183–1243 K by conventional solid-state reaction method. XRD and SEM investigations show that c-axis-oriented structure could be formed in these samples and Lotgering factors increase with the increase of sintering temperature when it is below 1223 K, from 52% for the sample sintered at 1183 K to 86% for the sample sintered at 1223 K. Due to decomposition of Ca2.7Bi0.3Co4O9, however, the c-axis-oriented structure was destroyed in the sample sintered at 1243 K although Ca2.7Bi0.3Co4 O9 phase could be recovered at the cooling stage. The size of grains in all samples increases with the increase of sintering temperature, but the relative densities are almost kept unchanged for the samples sintered at the temperature higher than 1183 K. Due to the highly textured structure, the transport properties of the sample sintered at 1223 K are anisotropic and its ZT values in the ab plane are obviously larger than those along the c-axis. [ABSTRACT FROM AUTHOR]

Abstract: Double-layer glass-ceramic/ceramic tiles made from bauxite tailings and red mud were prepared using a single firing powder processing route. The influence of the preparation method used for the green bodies on the microstructure and mechanical properties of the final products was investigated. The macroscopic appearance, microstructure, and mechanical properties indicated that the production of double-layer glass-ceramic/ceramic tiles may be an attractive method for recycling industrial waste into building materials. [Copyright &y& Elsevier]

A NiCo coating was successfully prepared on the Inconel 718 substrate by pulsed laser cladding. The characteristics and performance of the coating, including microstructure, phase constitution, hardness, friction coefficient, wear volume, wear morphology, and residual stress, were investigated by multiple characterization methods. The hardness of the coating is 427.82 HV, 21.1% higher than that of the Inconel 718 substrate. The coating also shows a higher resistance to wear than the substrate. In addition, the coating's surface residual stress is compressive stress, which prevents crack generation and improves fatigue strength. • NiCo alloy coating was successfully prepared on Inconel 718 substrate by laser cladding. • Phase constitution, microstructure, and properties of NiCo coating were studied. • Essential reason of the properties difference between the substrate and the coating was discussed. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ternary compound additives, MnO2–TiO2–CAS (CaO–Al2O3–SiO2 glass) and MgO–Y2O3–SiO2 on the densification and microstructure of alumina have been investigated, using simplex design and regression analysis. The results show that the enhanced densifications can be achieved by co-doping due to the combined effects of compound additives. With the addition of MnO2, TiO2, and CAS fixed at 0.6wt% of the total weight of the ceramic and in the proportion of 2:3:1, the sample sintered at 1550°C for 1h reaches about 97% of theoretical density. Approximately 98% of theoretical density can be obtained for the sample incorporating the MgO–Y2O3–SiO2 additives, when the addition of MgO, Y2O3, and SiO2 was fixed at 6wt% of total weight of the ceramic and in the proportion of 1:3:2. The influence of proportions of MnO2, TiO2, and CAS as well as MgO, Y2O3, and SiO2 on the anisotropic and abnormal grain growth, and grain size are also discussed. [Copyright &y& Elsevier]

Abstract: Sintering behavior and crystallization of glass–ceramic using bauxite tailings as one constituent were investigated. Different heat-treatment schedules were used to study their sintering effect on the glass powder-coated tiles. The results show that different heat-treatment schedule will result different crystal shape of the glass–ceramic. It was found that applying a two-stage heat-treatment schedule, first sintered at the crystallization temperature and then sintered at a higher temperature can make the glass–ceramic-coating layer bond strongly with the tile body. [Copyright &y& Elsevier]

The microstructure and mechanical properties of Al2O3–5wt.% MgB2 composites were studied by scanning electron microscopy (SEM) and Vickers hardness measurements. The experiments show that MgO whiskers can grow at temperatures as low as 950 °C. When sintered at 1450 °C, due to the strong vaporization of Mg, MgO and MgAl2O4 appear around Al2O3 grains. The microstructure of the Al2O3–5wt.% MgB2 differs remarkably from Al2O3 sintered at the same temperature. The fracture toughness of the Al2O3–5% MgB2 composite is 4.0 MPa m1/2 which is slightly higher than for pure Al2O3 ceramics. [Copyright &y& Elsevier]

A hot-rolled Ti–6Al–4V (Ti-64) sheet was surface-treated by pulsed laser at two different powers (100 and 200 W), with microstructural features and hardness before and after the laser surface treatment (LST) systematically investigated. Results show that after the LST at both powers there are two modification zones with distinct microstructural characteristics: melted zone (MZ) near the laser beam center, completely composed of fine martensitic plates with dense {10–11} nanotwins inside them; heat-affected zone (HAZ) far away from the laser beam center, comprised of mixed structures of short-rod β particles, martensitic plates and untransformed bulk α grains. Hardness measurements reveal that the hardness of the Ti-64 sheet can be markedly increased (especially in the MZ) after the LST. In-depth analyses suggest that the hardness increase in the MZ can be ascribed to combined contributions from grain refinement, presence of nanotwins and solid solution of alloying elements, while only the structural refinement by fine plate structures contributes to hardening in the HAZ. Comparisons between both the LSTed specimens reveal that increasing the laser power from 100 W to 200 W can effectively enlarge the laser-modified zones (both the MZ and the HAZ) and simultaneously refine plate structures, leading to further hardness increase. Image 1 • Two modification zones (MZ and HAZ) are identified in Ti–6Al–4V LSTed at 100 and 200 W. • MZ is composed of fine martensitic plates with dense {10–11} nanotwins inside them. • HAZ is comprised of β particles, martensitic plates and untransformed bulk α grains. • Hardness increase in MZ results from grain refinement, nanotwins and solid solution. • Increasing power can enlarge laser-modified zones and simultaneously refine plate structures. [ABSTRACT FROM AUTHOR]