Acid mine drainage presents an important threat to cementitious structures. This study is aimed at investigating the effect of cellulose nanocrystals (CNCs) on the acid resistance of cementitious composites. CNCs were added to mortar mixtures as additives at cement volume ratios of 0.2vol%, 0.4vol%, 1.0vol%, and 1.5vol%. After 28 d of standard curing, the samples were immersed in a sulfuric acid with a pH value of 2 for 75 d. The unconfined compressive strength (UCS) test, the density, water absorption, void volume test, and thermogravimetric analysis were carried out to investigate the properties of CNC mixtures before sulfuric acid immersion. It was found that the addition of CNC reduced the volume of permeable voids and increased the hydration degree and mechanical strength of the samples. Changes in mass and length were monitored during immersion to evaluate the acid resistance of mixtures. The mixture with 0.4vol% CNC showed a reduced mass change and length change indicating its improved acid resistance.

In this work, sodium dicyanamide (SD) was used as a leaching reagent for gold recovery, and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated. A gold recovery of 34.8% was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t. In the presence of a certain amount of potassium ferrocyanide (PF) in the SD solution, the gold recovery was found to increase from 34.8% to 57.08%. Using the quartz crystal microbalance with dissipation (QCM-D) technique, the leaching kinetics of SD with and without PF were studied. The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm^–2·min^–1 when the SD concentration was increased from 0 to 0.17 mol/L, and increased from 39.99 to 272.62 ng·cm^–2·min^–1 when 0.1 mol/L of PF was used in combination with SD. The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry, which indicated that Au and (N(CN)₂)^– in the SD solution formed a series of metal complex ions, [AuNa_x(N(CN)₂)_x+2]^– (x = 1, 2, 3, or 4).

Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed were comprehensively investigated. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate ([A336][Cyanex272]) could selectively extract W over Mo at an initial pH value of 5.5; the best separation factor β_W/Mo of 25.61 was obtained for a solution with low metal concentrations (WO₃: 2.49 g/L, Mo: 1.04 g/L). The [A336][Cyanex272] system performed effectively for solutions of different W/Mo molar ratios and different metal ion concentrations in the feed. The chemical reaction between [A336][Cyanex272] and W followed the ion association mechanism, which was further proved by the Fourier-transform infrared (FTIR) spectra of loaded [A336][Cyanex272] and the free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped using a 0.20 mol/L sodium hydroxide solution. Finally, the selective extractions of W and Mo from two synthetic solutions of different high metal concentrations were obtained; the separation factor β_W/Mo reached 23.24 and 17.59 for the first and second solutions, respectively. The results suggest the feasibility of [A336][Cyanex272] as an extractant for the separation of tungsten and molybdenum.

Composite electrodes prepared by cation exchange resins and activated carbon (AC) were used to adsorb V(IV) in capacitive deionization (CDI). The electrode made of middle resin size (D860/AC M) had the largest specific surface area and mesoporous content than two other composite electrodes. Electrochemical analysis showed that D860/AC M presents higher specific capacitance and electrical double layer capacitor than the others, and significantly lower internal diffusion impedance. Thus, D860/AC M exhibits the highest adsorption capacity and rate of V(IV) among three electrodes. The intra-particle diffusion model fits well in the initial adsorption stage, while the liquid film diffusion model is more suitable for fitting at the later stage. The pseudo-second-order kinetic model is suited for the entire adsorption process. The adsorption of V(IV) on the composite electrode follows that of the Freundlich isotherm. Thermodynamic analysis indicates that the adsorption of V(IV) is an exothermic process with entropy reduction, and the electric field force plays a dominant role in the CDI process. This work aims to improve our understanding of the ion adsorption behaviors and mechanisms on the composite electrodes in CDI.

In order to study the effect of continuous casting process parameters on the shape of slab solidification end under non-uniform cooling, a solidification model of a continuous-cast slab with non-uniform cooling condition was established with ProCAST software. The model was verified by the results of nail shooting tests and the infrared temperature measurement equipment. Four characteristic parameters were defined to evaluate the uniformity of the shape of slab solidification end. The results showed that the nonuniformity at the beginning and end of solidification, the solidification end length, and the solidification unevenness increased with the rise of casting speed. For each 10°C increase of superheat, the solidification unevenness increased by about 0.022. However, the effect of superheat on the solidification end length can be ignored. The secondary cooling strength showed minimal effect on the nonuniformity at the beginning and end of solidification. With the increase in secondary cooling intensity, the solidification end length decreased, but the solidification unevenness increased. In addition, the central segregation of the slab produced with and without the mechanical soft reduction (MSR) process was investigated. The transverse flow of molten steel with low solid fraction influenced the central segregation morphology under MSR.

Hot compression tests were performed on AISI 321 austenitic stainless steel in the deformation temperature range of 800–1200°C and constant strain rates of 0.001, 0.01, 0.1, and 1 s⁻¹. Hot flow curves were used to determine the strain hardening exponent and the strain rate sensitivity exponent, and to construct the processing maps. Variations of the strain hardening exponent with strain were used to predict the microstructural evolutions during the hot deformation. Four variations were distinguished reflecting the different microstructural changes. Based on the analysis of the strain hardening exponent versus strain curves, the microstructural evolutions were dynamic recovery, single and multiple peak dynamic recrystallization, and interactions between dynamic recrystallization and precipitation. The strain rate sensitivity variations at an applied strain of 0.8 and strain rate of 0.1 s⁻¹ were compared with the microstructural evolutions. The results demonstrate the existence of a reliable correlation between the strain rate sensitivity values and evolved microstructures. Additionally, the power dissipation map at the applied strain of 0.8 was compared with the resultant microstructures at predetermined deformation conditions. The microstructural evolutions strongly correlated to the power dissipation ratio, and dynamic recrystallization occurred completely at lower power dissipation ratios.

An explosion-welded technology was induced to manufacture the GH3535/316H bimetallic plates to provide a more cost-effective structural material for ultrahigh temperature, molten salt thermal storage systems. The microstructure of the bonding interfaces were extensively investigated by scanning electron microscopy, energy dispersive spectrometry, and an electron probe microanalyzer. The bonding interface possessed a periodic, wavy morphology and was adorned by peninsula- or island-like transition zones. At higher magnification, a matrix recrystallization region, fine grain region, columnar grain region, equiaxed grain region, and shrinkage porosity were observed in the transition zones and surrounding area. Electron backscattered diffraction demonstrated that the strain in the recrystallization region of the GH3535 matrix and transition zone was less than the substrate. Strain concentration occurred at the interface and the solidification defects in the transition zone. The dislocation substructure in 316H near the interface was characterized by electron channeling contrast imaging. A dislocation network was formed in the grains of 316H. The microhardness decreased as the distance from the welding interface increased and the lowest hardness was inside the transition zone.

The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated. In the present work, the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored. Specifically, the thermal conductivity (λ) of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations. The interface between the (100) plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al₄C₃ phases. By contrast, the interface between the (111) plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling. The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles. The λ of the diamond/Al composites decreased abruptly over the initial 20 cycles, increased afterward, and then decreased monotonously once more with increasing number of thermal cycles. Decreases in the λ of the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch, rather than interfacial debonding, may be the main factors influencing the decrease in λ of the diamond/Al composites, especially in the initial stages of thermal cycling.

Reaction-bonded B₄C–SiC composites are highly promising materials for numerous advanced technological applications. However, their microstructure evolution mechanism remains unclear. Herein, B₄C–SiC composites were fabricated through the Si-melt infiltration process. The influences of the sintering time and the B₄C content on the mechanical properties, microstructure, and phase evolution were investigated. X-ray diffraction results showed the presence of SiC, boron silicon, boron silicon carbide, and boron carbide. Scanning electron microscopy results showed that with the increase in the boron carbide content, the Si content decreased and the unreacted B₄C amount increased when the sintering temperature reached 1650°C and the sintering time reached 1 h. The unreacted B₄C diminished with increasing sintering time and temperature when B₄C content was lower than 35wt%. Further microstructure analysis showed a transition area between B₄C and Si, with the C content marginally higher than in the Si area. This indicates that after the silicon infiltration, the diffusion mechanism was the primary sintering mechanism of the composites. As the diffusion process progressed, the hardness increased. The maximum values of the Vickers hardness, flexural strength, and fracture toughness of the reaction-bonded B₄C–SiC ceramic composite with 12wt% B₄C content sintered at 1600°C for 0.5 h were about HV 2400, 330 MPa, and 5.2 MPa·m^0.5, respectively.

Ti₃AlC₂-reinforced Ag-based composites, which are used as sliding current collectors, electrical contacts, and electrode materials, exhibit remarkable performances. However, the interfacial reactions between Ag and Ti₃AlC₂ significantly degrade the electrical and thermal properties of these composites. To diminish these interfacial reactions, we fabricated carbon-coated Ti₃AlC₂ particles (C@Ti₃AlC₂) as reinforcement and prepared Ag–10wt%C@Ti₃AlC₂ composites with carbon-layer thicknesses ranging from 50–200 nm. Compared with the uncoated Ag–Ti₃AlC₂ composite, Ag–C@Ti₃AlC₂ was found to have a better distribution of Ti₃AlC₂ particles. With increases in the carbon-layer thickness, the Vickers hardness value and relative density of Ag–C@Ti₃AlC₂ gradually decreases. With a carbon-layer thickness of 150 nm, we obtained the lowest resistivity of Ag–C@Ti₃AlC₂ of 29.4 135.5×10⁻⁹ Ω·m, which is half that of Ag–Ti₃AlC₂ (66.7 × 10⁻⁹ Ω·m). The thermal conductivity of Ag–C@Ti₃AlC₂ reached a maximum value of 135.5 W·m⁻¹·K⁻¹ with a 200-nm carbon coating (~1.8 times that of Ag–Ti₃AlC₂). These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti₃AlC₂ composites.

Selective laser melting (SLM) technology plays an important role in the preparation of porous titanium (Ti) implants with complex structures and precise sizes. Unfortunately, the processing characteristics of this technology, which include rapid melting and solidification, lead to products with high residual stress. Herein, an in situ method was developed to restrain the residual stress and improve the mechanical strength of porous Ti alloys during laser additive manufacturing. In brief, porous Ti6Al4V was prepared by an SLM three-dimensional (3D) printer equipped with a double laser system that could rescan each layer immediately after solidification of the molten powder, thus reducing the temperature gradient and avoiding rapid melting and cooling. Results indicated that double scanning can provide stronger bonding conditions for the honeycomb structure and improve the yield strength and elastic modulus of the alloy. Rescanning with an energy density of 75% resulted in 33.5%–38.0% reductions in residual stress. The porosities of double-scanned specimens were 2%–4% lower than those of single-scanned specimens, and the differences noted increased with increasing sheet thickness. The rescanning laser power should be reduced during the preparation of porous Ti with thick cell walls to ensure dimensional accuracy.

3Y-TZP/3wt% Al₂O₃ powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12wt% showed the best processability, but had diminished mechanical properties (such as fracture toughness and bending strength). The ceramic with a BN content of 9wt% showed better processability than those with 3wt% and 6wt% BN. However, the fracture toughness was affected by the addition of 9wt% BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In contrast, the ceramics with a BN content of 3wt% or 6wt% fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.

Cobalt (Co)-modified brownmillerite KBiFe₂O₅ (KBFO; [KBiFe_2(1−x)Co_2xO₅ (x = 0, 0.05)]) polycrystalline is synthesized following the solid-state reaction route. Rietveld refinement of X-ray diffraction data confirmed the phase purity of KBFO and KBiFe_1.9Co_0.1O₅ (KBFCO). The optical bandgap energy (E_g) of KBFO decreased from 1.59 to 1.51 eV because of Co substitution. The decrease in bandgap can be attributed to the tilting of the Fe–O tetrahedral structure of KBFCO. The observed room-temperature Raman peaks of KBFCO shifted by 3 cm⁻¹ toward a lower wavenumber than that of KBFO. The shift in Raman active modes can be attributed to the change in the bond angles and bond lengths of the Fe–O tetrahedral structure and modification in response to oxygen deficiency in KBFO because of Co doping. Compared with that of KBFO, the frequency-dependent dielectric constant and dielectric loss of KBFCO decrease at room temperature, which is a consequence of the reduction in oxygen migration and modification in response to vibrational modes present in the sample.

Wood-based panels containing urea-formaldehyde resin result in the long-term release of formaldehyde and threaten human health. In this study, inorganic aluminosilicate coatings prepared by combining metakaolin, silica fume, NaOH, and H₂O were applied to the surfaces of wood-based panels to obstruct formaldehyde release. The Si/Al, Na/Al, and H₂O/Na₂O molar ratios of the coatings were regulated to investigate their effects on the structure and formaldehyde-resistant barrier properties of coatings. Results showed that the cracks in the coatings gradually disappeared and the formaldehyde resistance rates of the barrier increased as the Si/Al molar ratio was increased from 1.6 to 2.2. This value also increased as the Na/Al molar ratio was increased from 0.9 to 1.2 because of the improvement of the degree of polymerization. As the H₂O/Na₂O molar ratio was increased from 12 to 15, the thickness of the dry film decreased gradually and led to the reduction in the formaldehyde resistance rate. When the Si/Al, Na/Al, and H₂O/Na₂O molar ratios were 2.2, 1.2, and 12, respectively, the inorganic aluminosilicate coating showed good performance as a formaldehyde-resistant barrier and its formaldehyde resistance rate could reach up to 83.2%.