Modifications of the binder phase (γ) of cemented carbides have the potential to increase the hardness and wear resistance of the whole material. Partially, coherent precipitations with L12 structure (γ’) promise these improved properties without sacrificing tensile strength or toughness. γ’ is a metastable phase in the Al–Co–W ternary system in the form of Co3(Al,W) which is stabilized by the substitution of cobalt with nickel. Superalloys of the composition Co–(30Ni)–9Al–7 W with different carbon contents were prepared by inductive melting, and the resulting microstructures were analysed using SEM–EDS, XRD and Vickers hardness. Cemented carbides with γ/γ’ binder microstructure were prepared via DTA, and the phase equilibria in the composite material were investigated experimentally and in silico. It was shown that nickel stabilizes the γ’ phase in superalloys as well as in cemented carbides. Carbon leads to the formation of an additional phase with E21 structure (κ). DTA measurements of cemented carbides with different aluminium–cobalt–nickel mixtures as binder gave an overview of the compositional influence. Enthalpies of formation for compounds with L12 and E21 structure were calculated using ab initio methods and compared to experimental results.
Graphical AbstractCold welding technique at room temperature is the preferred option in nano-assembly and nano-jointing. In this study, the cold welding behavior and mechanical strength of Cu50Zr50 metallic glass nanowires (MGNWs) in head-to-head contact are investigated by molecular dynamics simulation based on the embedded atom method potential. Effects of welding velocity, operating temperature, and size of nanowires are discussed with the consideration of stress, shear strain, atomic deformation processes, and weld quality. Our simulation results demonstrate that a desirable weld quality can be obtained at room temperature. With an increase in welding velocity, the shear deformation zones of the welded MGNWs increase, leading to a decrease in mechanical strength. However, the effect of temperature on the weld quality is not pronounced. Besides, the elongation ability of the welded MGNWs increases with increasing diameters of nanowires. Smaller diameter results in better weld quality due to the size effect of metallic glass. For a pair of MGNWs with different diameters, the necking and fracture of the welded MGNWs occur in the regions of the nanowire with a relatively smaller diameter. This study carries major implications for the fabrication and structural assembly of metallic glass-based nanomaterials.
Graphical AbstractOrganic/inorganic thermoelectric composites have played an important role in the development of new, green, and renewable energy sources with potential applications in efficient thermal management, flexible electronics, and bioelectronics. Electrochemical syntheses, including electropolymerization, electrochemical deposition, electrochemical doping, electrochemical post-processing, etc., require no addition of surfactants or oxidants, the products of which are easy to separate and purify, providing clean, efficient, and facile routes for the preparation of organic thermoelectric materials and their composites. In this review, the preparation, properties, and applications of organic/inorganic thermoelectric composites from electrochemical synthesis were reviewed in detail, offering a perspective on the recent advances in the field.
Graphical abstractSilver nanowires find use in a myriad of applications, including communication systems, sensors, medical devices and electrical equipment. Temperature-dependent electrical and thermal properties of chemically derived silver nanowires are rarely explored. In the present work, seed-mediated synthesis of silver nanowires has been carried out, and their electrical and thermal conductivity at 300 K is found to be 1.848?×?107 S/m and 64.8 W/mK, respectively. A screen-printable ink of silver nanowires is formulated and printed on low-cost and widely used substrates like paper and cotton fabrics. Flexible printed electrodes could be made possible with uniform printed structures obtained in cotton fabric and paper substrate. The printed pattern exhibited sheet resistance of 0.7 Ω/sq. Screen-printed silver nanowires on paper show shielding efficiency of 99.9% in X band, which promotes them as excellent candidates in fabricating lightweight electronic devices by a one-step printing process.
Graphical abstractPolyimide aerogels are promising for diverse applications owing to their nanoporous structure and superior performance in thermal insulation, dielectric protection, etc. However, the severe shrinkage they usually suffer has long been a threat, and can pose great challenges to their shape-stable preparation and reliable applications. It is very important to clarify the effects of various factors on the shrinkage of PI aerogels and the effective strategies available for shrinkage reduction. These are also the focuses of the present review, to provide guidance for preparing PI aerogels with greatly reduced shrinkage, and thereby improved shape stability and use reliability. Since the shrinkage of PI aerogels is quite a complex issue, further studies on PI aerogels against shrinkage deserve continuous attention.
Graphical abstractThe caloric effects under combined applications of magnetic field and hydrostatic pressure to a MnCoSi meta-magnet were investigated. Under a magnetic field change of 0–5 T, the maximum magnetic entropy change was enhanced by 35.7% when a 3.2kbar hydrostatic pressure was applied, and the cooling temperature span was extended by 60 K when a hydrostatic pressure of 9.7 kbar was applied. The coupled caloric entropy change, which originates from the coupling between the magnetism and volume, was calculated and accounted for the enhanced entropy change of MnCoSi. The present work facilitates the use of MnCoSi as a solid-state refrigerant and also enriches the investigation of the multicaloric effect under multiple external fields.
Graphical abstractSilica aerogel composites reinforced with different aramid fibres have been synthesized and compared considering their potential use in thermal protection systems of Space devices. These composites were prepared from tetraethoxysilane and vinyltrimethoxysilane and the network was strengthened with aramid fibres. The results showed that the physical and chemical properties of the fibres were relevant, leading to composites with different properties/performance. In general, the obtained values for bulk density were low, down to 150 kg m?3. Very good thermal properties were achieved, reaching thermal conductivities bellow 30 mW m?1 K?1, and thermal stability up to 550 °C in all cases. Short length fibres produce stiffer composites with lower thermal conductivities, while among longer fibres, meta-aramid-containing fibres lead to nanocomposites with best insulation performance. Standard tests for Space materials qualification, as thermal cycling and outgassing, were conducted to assess the compliance with Space conditions, confirming the suitability of these aerogel composites for this application.
Graphical abstractVaristors are technologically important for their large energy handling capabilities and highly nonlinear electrical behavior when voltages above a characteristic switch field are applied. It is generally accepted that the prototypical ZnO–Bi2O3 varistor system forms electrostatic Schottky barriers at grain boundaries in response to residual Bi and other dopants left at grain surfaces during Bi2O3 segregation. While barrier heights can be modulated with formulation and defect chemistry, mechanisms by which dopant locations, defect compensation, and local phases determine varistor behavior are not completely understood. Bulk studies are challenging due to random grain boundary formation and difficulties studying individual boundaries. To circumvent these challenges in the ZnO–Bi2O3 varistor system, we use as-deposited and post-heat-treated thin film ZnO–Bi2O3 prototypes to simulate bulk varistor grain boundary phase formation and investigate resulting defect chemistry. Characterizing interactions between Bi2O3 films deposited on thin film and single-crystal ZnO by XRD and TEM-EDS revealed primarily Zn-out diffusion, resulting in two (Bi2O3)1?x(ZnO)x, or BZO, phases. Using these results, we present a saturated front model correlating changes in Bi2O3 thickness to phase evolution. We subsequently explore the influence of MnO doping leading to substantial changes in phase evolution for post-heat-treated (Mn:ZnO)–Bi2O3 stacks. Dopant-controlled Bi2O3 phase formations yield a 12?×?difference, on average, between nonlinear coefficients for γ*- and β*-BZO.
Graphical AbstractThree-dimensional (3-D) printing, also known as additive manufacturing, refers to a method used to generate a physical object by joining materials in a layer-by-layer process from a three-dimensional virtual model. 3-D printing technology has been traditionally employed in rapid prototyping, engineering, and industrial design. More recently, new applications continue to emerge; this is because of its exceptional advantage and flexibility over the traditional manufacturing process. Unlike other conventional manufacturing methods, which are fundamentally subtractive, 3-D printing is additive and, therefore, produces less waste. This review comprehensively summarises the application of additive manufacturing technologies in chemistry, chemical synthesis, and catalysis with particular attention to the production of general laboratory hardware, analytical facilities, reaction devices, and catalytically active substances. It also focuses on new and upcoming applications such as digital chemical synthesis, automation, and robotics in a synthetic environment. While discussing the contribution of this research area in the last decade, the current, future, and economic opportunities of additive manufacturing in chemical research and material development were fully covered.
Graphical abstractHere, we report a multiferroic relaxor material 0.41Bi(Ni1/2Zr1/2)O3–0.59PbTiO3, which exhibits a large piezoelectric coefficient (d33, 391 pC/N), high remnant polarization (Pr, 52.3 μC/cm2) and a high electrical freezing temperature (Tf, 498 K). The electric-field-induced transition from a cubic-like phase to a tetragonal phase was confirmed by the XRD patterns and first-cycle bipolar electrostrain loop. The magnetization and magnetic field relationship changes from nonlinear to linear when cooled from 300 to 2 K. The unusual trend in magnetic behavior could be interpreted as the transitions between the super short-range orderings. Furthermore, the maximum value of magnetization shows a 14% decrease at 300 K after electrical poling.
Graphical abstractHybrid organic–inorganic nanocomposites are great candidates for display and illumination systems due to improved optoelectronic properties and photostability. This work endeavours towards the scientific study of the influence of defect-induced zinc oxide nanoparticles (ZnO) on the optical characteristics of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). ZnO nanoparticles consist of many vacancies which facilitate light emission across the visible region. The green defective emission occurring due to the presence of oxygen vacancies in ZnO was used to re-excite MEH-PPV and hence, improve the luminescence quantum efficiency. The photostability of the nanocomposite was enhanced through charge transfer (prevents the formation of superoxides) and energy transfer (reduces the non-radiative decay) mechanisms.
Graphical abstractWe review the literature describing the use of interleaves to increase interlaminar fracture toughness in fibre-reinforced polymer composites and hence to improve damage tolerance. From an analysis of data provided in the literature from the use of microfibre and nanofibre interleaves, we show that the performance of these widely researched systems is clearly differentiated when plotted against the mean coverage of the interleaf. Using a simple analysis, we suggest that this can be attributed to the influence of their porous architectures on the infusion of resin. We show also that the superior toughening performance of microfibre interleaves is only weakly influenced by the choice of fibre. We find also that the inclusion of carbon nanotubes within interleaves to deliver multifunctional composites can be optimised by using a hybrid system with microfibres.
Graphical abstractQuenching from sintering temperature enhances the depolarization temperature (Td) in Na1/2Bi1/2TiO3-based ceramics without significant deterioration of piezoelectric properties (d33). In this work, quenching effects in an ergodic relaxor 0.97(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–0.03AgNbO3 (NBT–6BT–3AN) were investigated based on structure, ferroelectric, and dielectric properties. The ergodicity to nonergodicity transition was obtained by quenching NBT–6BT–3AN above 1000 °C. The temperature stability of the quenching-induced nonergodicity was examined by annealing the quenched sample at 300 °C and 600 °C. The effect of oxygen vacancy on ergodicity to nonergodicity transition was investigated by comparing ferroelectric and electrostrain responses of the quenched and nitrogen-atmosphere-annealed samples. The influence of quenching on the structure including the average crystal structure, phase fraction and lattice distortion and the local structure including bond lengths and ordering of ions was analyzed. The ergodicity to nonergodicity transition upon quenching is ascribed to the contribution of the off-centered Bi3+ ions and ordered local structure.
Graphical abstractThe friction stir welded joint of wrought ZM21 alloy was divided into five parts, and their localized creep behavior was studied via the impression method. The tests were carried out in the stress range of 300–450 MPa (σimp/G ≈ 0.02–0.03) and in the temperature range of 448–523 K. Optical and SEM micrographs and EDS taken before and after the impression tests were used to study the microstructure of various zones of the FS welded joint. Power law was found to satisfactorily relate the stress and strain rates. The steady-state impression velocity was found to vary significantly between the advancing and retreating sides of TMAZ and HAZ. For TMAZ, the creep exponent on the AS was 4.8, and on the RS, it was 7.8. The activation energy on the AS was ~?133 kJ/mol, and on the RS, it was ~?101 kJ/mol. Similarly, for HAZ, the creep exponent on the AS was found to be 5.5 and on the RS, it was 4.9. The activation energy on the AS was ~?86 kJ/mol and on the RS, it was ~?232 kJ/mol. The cross-over of steady-state impression velocity of different zones indicates that the weak zone was temperature and stress dependent. Within the stresses and temperatures studied, the weld zone's creep resistance (i.e., lower minimum impression velocity) was found to be better than the base material. As it is with most magnesium alloys, dislocation climb was found to be the operative mechanism in the FS weldments of ZM21 alloy. The rate-controlling mechanism remains to be identified because the wide variation in n and Q values suggests that different creep mechanisms are in operation in different zones.
Graphical abstractThe effect of thermal pretreatment on the porous structure and adsorption properties of asphalt-based carbons activated with potassium hydroxide was investigated by FTIR, Raman spectroscopy, TEM, N2 and CO2 adsorption. Two series of the activated carbons were prepared by a one-stage method using KOH as the activating agent and a two-stage method including pretreatment of asphalt at 450 °C. A cross-effect of the KOH/asphalt ratio and pretreatment conditions on the characteristics of the porous structure of the activated carbons was revealed. The pretreatment of asphalt before activation is demonstrated to be a necessary stage for the effective control of the carbon porous structure by variation the KOH/asphalt ratio from 2 to 4. The porous carbon derived from petroleum asphalt exhibited the high CO2 adsorption capacity of 3.8 mmol/g at 25 °C and 1 atm and good selectivity for CO2 over N2, indicating possible applications in CO2 capture technology.
Graphical abstractIn this critical note, the thermal stability behavior of ultra-fine grained (UFG) and nano-structured (NS) metals and alloys produced through severe plastic deformation (SPD) techniques is reviewed. For this case, the common engineering metals with body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) crystal structures such as aluminum, copper, nickel, magnesium, steel, titanium, and their relating alloys were assessed. Microstructural evolution in these severely deformed materials following post-processing annealing treatment was investigated for various times and temperatures below the recrystallization point. The microstructure development reported in the literature was studied in terms of the stable grain structures correlated with different levels of plastic straining. The stacking fault energy (SFE) is noted to be a key issue which has a critical influence in predicting the coalescence or coarsening behavior of ultra-fine and nanoscale grains after SPD treatment by controlling the cross-slip phenomenon for screw dislocations.
Graphical AbstractProton conductivity, morphology, phase composition and mechanical properties of (1-x)CsH2PO4-xp(VDF/HFP) (x?=?0.05–0.25, weight ratio) polymer electrolytes were investigated for the first time. The chemical interaction of the organic matrix and acid salt was not observed and crystal structure of CsH2PO4 was preserved. A method for the synthesis of thin membranes with uniform distribution of the components was proposed. Thin flexible membranes with uniform distribution of sub-micrometer CsH2PO4 particles in the polymer membranes and improved hydrolytic stability were obtained firstly by using a bead mill. The mechanical strength of the hybrid polymer compounds was determined using the Vickers microhardness measurements. Proton conductivity in the (1-x)CsH2PO4-xp(VDF/HFP) electrolytes decreases monotonically with x increase due to the «conductor–insulator» percolation. Nevertheless, the values of proton conductivity remain sufficiently high, and along with small thickness, flexibility, improved mechanical and hydrophobic properties, it makes polymer electrolytes based on CsH2PO4 promising for membranes of medium-temperature fuel cells.
Graphical abstractDeveloping high dielectric performance of polymer nanocomposites is still a long-standing issue to simultaneously inherit the high dielectric constant of nanofillers and maintain the high breakdown strength of polymer matrix. In the current study, a tri-layered nanocomposite film is fabricated by a simple and effective solution-casting and dip-coating method, where graphene oxide nanosheets (GONSs) were modified by insulating SiO2 layer (SiO2@GONSs) and polyvinylidene fluoride (PVDF)/SiO2@GONS nanocomposite inner layer was sandwiched by polycarbonate (PC) layers. The surface modification could minimize the local electric field concentration and block conductive path. Furthermore, the sandwich or tri-layered structure inhibited the relaxation and migration of space charge or impurity ions and suppressed the charge injection, thus achieving enhanced breakdown strength and discharged energy efficiency. As a result, the as-prepared tri-layered nanocomposite film exhibited a dielectric constant of 5.2 and a low dielectric loss (tanδ) of 0.013 at 1 kHz, and breakdown strength of 219 MV m?1, which was significantly higher than single-layered nanocomposite films and its counterpart without SiO2 modification. The corresponding discharged energy density was 1.20 J cm?3 with an excellent efficiency of 86.2% at 200 MV m?1. More interestingly, the insulating SiO2 modification layer and PC outer layers could also effectively restrict the relaxation or migration of impurity ions at a high temperature of 120 °C, endowing excellent high-temperature dielectric performance to the as-prepared tri-layered nanocomposite film. The combination of surface modification and sandwich structure opens up an avenue to fabricate GONS-based dielectric nanocomposites with low dielectric loss, high breakdown strength, high efficiency and high temperature tolerance.
Graphical abstractIn view of the disadvantages of concentration polarization and trade-off effects in the application of membrane in desalination field, oxide-nano graphene oxide/polyamide (O-NGO/PA) loose intermediate layer and PA ultra-thin dense layer were introduced to fabricate PA/O-NGO/polyphenylene sulfide composite membrane with sandwich structure via multi-step interfacial polymerization (MS-IP) method. The selective permeation mechanism of ultrathin layer produced by different aqueous monomers (PIP and MPD) was studied, the effect of its physicochemical structure on the relief of concentration polarization phenomenon and the breakthrough of trade-off effect was analyzed. The ultra-thin and dense PA layer mainly played the role of interception and shortened the water molecular penetration path. In the retention test of metal salt solution, compared with the rough surface, it was found that the smooth surface was more conducive to the diffusion of intercepted metal ions into the feed solution, thus alleviating the concentration polarization phenomenon.
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