Fabrication of black-colored CuO–Al2O3–ZrO2 ceramics via heterogeneous nucleation method

We have reported the fabrication of black-colored CuO–Al₂O₃–ZrO₂ ceramics via a heterogeneous nucleation method. The as-prepared ZrO₂ ceramics exhibit a deep and genuine black color with a uniform color distribution. PEG2000 has been used as the dispersants for the preparation of ZrO₂ nanopowder solutions. Then Cu and Al hydrates have been introduced into the solutions with tailored pH values for the fabricated coated ZrO₂ powders, to induce the heterogeneous nucleation of the colorants within ZrO₂ matrixes. CuO and Al₂O₃ transformed from Cu and Al hydrates act as the black colorant and colorant stabilizer, respectively, which make the fabrication of black ZrO₂ at a relatively low sintering temperature of 1200 °C. The fabricated black-colored ZrO₂ ceramics are characterized by scanning electron microscopy, X-ray diffraction and optical reflectance spectrum. It can be believed that current work could present a facile and cost-saving method for fabrication of black-colored ZrO₂ ceramics without using any toxic chromophore elements.     

Fabrication and properties of ultra highly porous silicon carbide by the gelation–freezing method

Silicon carbide (SiC) with ultra high porosity and unidirectionally oriented micrometer-sized cylindrical pores was prepared using a novel gelation–freezing (GF) method. Gelatin, water and silicon carbide powder were mixed and cooled at 7 °C. The obtained gels were frozen from ?10 to ?70 °C, dried using a vacuum freeze drier, degreased at 600 °C and then sintered at 1800 °C for 2 h. The gels could be easily formed into various shapes, such as cylinders, large pipes and honeycombs using molds. Scanning electron microscopy (SEM) observations of the sintered bodies showed a microstructure composed of ordered micrometer-sized cylindrical cells with unidirectional orientation. The cell size ranging from 34 to 147 μm could be modulated by changing the freezing temperatures. The numbers of cells for the samples frozen at ?10 and ?70 °C were 47 and 900 cells/mm², respectively, as determined from cross-sections of the sintered bodies. The resulting porous SiC with a total porosity of 86%, exhibited air permeability from 2.3 × 10^?11 to 1.0 × 10^?10 m², which was the same as the calculated ideal permeability, and high compressive strength of 16.6 MPa. The porosity, number of cells, air permeability and strength of the present porous SiC were significantly higher than that reported for other porous SiC ceramics.     

Direct and facile synthesis of Li–Sr–Zn ferrites via low temperature solution combustion route

Li–Sr–Zn nanoferrites i.e. Li_0.25Sr_0.5–xZn_xFe_2.25O₄, where ‘x’ varies from 0–0.5, have been synthesized using a low temperature solution combustion method which proves to be an efficient and economical technique for synthesizing these type of nanoferrites. The as-synthesized nanoferrites have cubic spinel structure as characterized by X-ray powder diffraction. Powder XRD and TEM (Transmission Electron Microscopy) characterization also evidence that the crystallite and particle size are in close agreement to each other. Mössbauer spectroscopy studies demonstrate that there is a gradual transition from ferrimagnetic to superparamagnetic character, which is also supported by the saturation magnetization and coercivity values. At room temperature, the nanoferrites were found to be superparamagnetic with negligible coercivities approaching towards zero while saturation magnetization values were found to be in the range 6.87–30.10 emu g⁻¹. The frequency dependent dielectric constant and loss values are in accordance with Koop׳s model. These nanoferrites show great potential in high density recordings, magnetic nanodevices and biomagnetic applications.     

Fabrication and characterization of anorthite–mullite–corundum porous ceramics from construction waste

In this work, anorthite–mullite–corundum porous ceramics were prepared from construction waste and Al₂O₃ powders by adding AlF₃ and MoO₃ as mineralizer and crystallization catalyst, respectively. The effects of the sintering temperature and time on open porosity, mechanical properties, pore size distribution, microstructure, and phase composition were characterized in detail. The results showed that the formation of the mullite whiskers and the properties of the anorthite–mullite–corundum porous ceramics depended more on the sintering temperature than the holding time. By co-adding 12 wt% AlF₃ and 4 wt% MoO₃, mullite whiskers were successfully obtained at sintering temperatures upon 1350 °C for 1 h. Furthermore, the resultant specimens exhibited excellent properties, including open porosity of 66.1±0.7%, biaxial flexural strength of 23.8±0.9 MPa, and average pore size of 1.32 µm (the corresponding cumulative volume percent was 37.29%).     

Fabrication and characterization of multiwalled carbon nanotube–loaded interconnected porous nanocomposite scaffolds

Novel nanocomposite porous scaffolds based on poly(?-caprolactone) (PCL) and multiwalled carbon nanotubes (MWCNTs) were manufactured by a compression-molding/polymer-leaching approach utilizing cryomilling for homogeneous dispersion of nanotubes and blending of polymers. Addition of MWCNTs to PCL and PCL/polyglycolide (PGA) blends resulted in significant changes to scaffold morphology compared to control samples despite persistent interconnected porosity. Several structures exhibiting rough and nanotextured surfaces were observed. Mean pore sizes were in the range of ～3–5?µm. The nanocomposites presented good mechanical and water uptake properties. The results of this research provide significant insight into a strategy for producing nanocomposite scaffolds with interconnected porosity.     

Influence of quinone grafting via Friedel–Crafts reaction on carbon porous structure and supercapacitor performance

High specific surface area carbon has been modified with para-benzoquinone (p-BQ) via Friedel–Crafts reaction catalyzed by Iron(III) chloride followed by oxidation, in order to explore alternative strategies for obtaining high energy density supercapacitor materials by the combination of the double layer capacitance of carbons with the redox pseudocapacitance of the organic redox couple added on the carbon surface.Suitable structural and physicochemical characterization proved the formation of covalent bonds between carbon and p-BQ, and the electrochemical characterization showed a significant increase in gravimetric capacitance values after the addition of p-BQ which is maintained even after many cycles.This gravimetric capacitance increase was not only due to the redox reactions of p-BQ, but also to an increased double layer capacitance after p-BQ modification even when the BET surface area decreases after modification. A correlation with the pore structure of carbons showed that the increased double layer capacitance can be attributed to a better matching of carbon pore size with the size of electrolyte ions after p-BQ addition. Thus, this new addition strategy opens the way for the development of carbon-based materials for supercapacitors with higher energy densities coming from both increased pseudocapacitive reactions and increased double layer capacitance.     

Fabrication of mullite-bonded porous SiC ceramics via a sol–gel assisted in situ reaction bonding

In the present work, mullite-bonded porous SiC ceramics were fabricated using reaction bonding techniques. The morphologies, phase composition, open porosity, pore size distribution and mechanical strength of porous ceramics were examined as a function of alumina sources (calcined nano-sized alumina powder and alumina sol prepared from hydrolysis of aluminum isopropoxide) and contents. It was found that the addition of alumina in powder form effectively enhanced the strength and decreased the porosity. In contrast, when alumina was added in sol form, a reverse effect was observed. Moreover, it was revealed that when a portion of calcined alumina was replaced by alumina sol, the mechanical properties improved significantly (more than 30%) as well as porosity compared to the traditional method. Pore size distribution analysis showed that the dispersion of nanosize alumina powder and SiC micro-particles in alumina sol is strongly improved compared to mixing in ethanol.     

Effect of activation temperature on the surface copper particles and catalytic properties of Cu–Ni–Mg–Al oxides from hydrotalcite-like precursors

The Cu–Ni–Mg–Al oxides catalysts for furfural hydrogenation were prepared from the hydrotalcite-like precursors, and the effect of activation temperature on the Cu⁰ particles and catalytic properties of the catalyst was thoroughly investigated. The catalyst activated by H₂ at 300 °C was found to exhibit the best catalytic activity, due to the presence of the smallest Cu⁰ particles with a high dispersion. Moreover, the bigger Cu⁰ particles were active for furfuralcohol hydrogenolysis to 2-methylfuran in the liquid-phase (ethanolic solution), and the hydrogenation of the furan ring of furfuralcohol and 2-methylfuran on Cu⁰ particles was easily achieved in the vapour-phase.     

Coil-coated Zn–Mg and Zn–Al–Mg: Effect of climatic parameters on the corrosion at cut edges

We studied the effect of temperature, wet/dry cycling, pH, and the type and concentration of the corrosion activator on cut edge corrosion of painted Zn–15Mg and Zn–1.5Al–1.5Mg coated steel. In most accelerated tests, paint delamination and red rust formation were reduced compared to hot dip galvanised steel (HDG), and Zn–15Mg outperformed Zn–1.5Al–1.5Mg; however, Zn–1.5Al–1.5Mg showed better results when exposed outdoors. The alloyed materials were particularly resistant when HDG was prone to elevated corrosion, i.e. under permanent wetness, at higher temperatures, with high chloride loadings and in the presence of sulphate. Oxygen reduction on steel cut edges was inhibited by the alloying elements.     

Construction of Zn–Co–Ni–Se nanosheet arrays on nickel foam for hybrid supercapacitors

The polymetallic selenides exhibit rich redox reactions and high conductivity, making them promising electroactive materials for hybrid supercapacitors (HSCs). Herein, a two-step hydrothermal strategy was developed to grow ternary metal selenides (Zn–Co–Ni–Se) nanosheet arrays on Ni foam (NF) for HSCs. The Zn–Co–Ni–Se nanosheets uniformly covered on NF are favorable to boosting the energy storage activity because they can afford abundant pores, which is beneficial to increase the contact areas and promote ion transport. The binder-free feature can further improve the rate and cyclic performance. As an innovative binder-free electrode, the Zn–Co–Ni–Se NA@NF can deliver 2.5 C cm^–2 at 3.1 mA cm^–2. Strikingly, the Zn–Co–Ni–Se NA@NF//AC HSC can afford 0.13 mWh cm^–2 at 1.27 mW cm^–2. The capacity retention of Zn–Co–Ni–Se NA@NF//AC HSC is 92.9% after 5000 cycles at 6.4 mA cm^–2. A Zn–Co–Ni–Se NA@NF//AC HSC device could successfully drive a small fan for about 150 s, displaying the bright application prospect of Zn–Co–Ni–Se@NF. Therefore, the present work demonstrates that Zn–Co–Ni–Se NA@NF is an excellent electroactive material for HSCs.     

Electrochemical behaviour of Al, Al–Sn, Al–Zn and Al–Zn–Sn alloys in chloride solutions containing indium ions

The electrochemical behaviour of pure aluminium and three of its alloys were investigated in 0.6m NaCl in the presence and absence of In3+ ions. The study comprised polarization and potentiostatic current–time measurements complemented by SEM–EDAX investigation. In 0.6m NaCl the corrosion resistance of the alloys decreases in the following order: Al < Al–Sn < Al–ZnAl–Zn–Sn. The addition of In3+ ions to the test electrolyte revealed activation of pure Al which increases with increase of In3+ concentration. Similar results were obtained for the binary Al–Zn and the ternary Al–Zn–Sn alloys, while Al–Zn alloy displayed a higher activation effect with In3+. It is also concluded that the existence of Zn either as an alloying element or present as a cation in the electrolyte leads to an enhanced activity of aluminium in presence of In3+ ions. Deactivation is observed in the case of Al–Sn alloy on addition of In3+ because tin retards the diffusion pathway of In to the bulk alloy, in addition to the presence of iron as an impurity in the alloy.     

Effect of microstructural evolution on wettability and tribological behavior of TiO2 nanotubular arrays coated on Ti–6Al–4V

Self-organized TiO₂ nanotubular arrays were fabricated by electrochemical anodization of Ti–6Al–4V plates in an NH₄F/H₃PO₄ electrolyte. The effect of microstructural evolutions on the wettability and tribological behavior of the TiO₂ nanotubes was investigated. Based on the XRD profiles of the fabricated material, the characteristic TiO₂ peaks were not recognized after anodization; however, highly crystalline TiO₂ (anatase and rutile) was formed due to crystallization during annealing at 500 °C for 1.5 h. The nanotube arrays were converted entirely to rutile at 700 °C. From a microstructure point of view, a highly ordered nanotube structure was achieved when the specimen was annealed at 500 °C, with a length of 0.72 μm and a pore diameter of 72 nm. Further increasing the annealing temperature to 700 °C resulted in the complete collapse of the tubular structure. The results indicate that the improved wettability of the anodized specimens was due to the combination of the effects of both the surface oxide layer and the increased surface roughness achieved after anodization. Moreover, the wear resistance and wettability of the sample annealed 500 °C were improved due to the high hardness (435 HV) and low coefficient of friction (0.133–168) of the highly crystalline structure of the TiO₂ nanotubes.     

The protective properties of epoxy coating electrodeposited on Zn–Mn alloy substrate

The epoxy coating was cataphoretically deposited on steel and steel modified by electroplated Zn–Mn alloy of different chemical contents. The samples were immersed in 0.5 mol dm⁻³ NaCl solution for 60 days. The electrochemical impedance spectroscopy (EIS) analysis showed that the values of pore resistance for epoxy coating on steel and Zn–Mn alloy with 16 at.% Mn were two orders of magnitude higher, while the capacitance values were two orders of magnitude lower than those for the epoxy coating on Zn–Mn alloy substrates with 5 and 8 at.% Mn. It was assumed that the main reason for such a difference was metallic substrate dissolution during cataphoretic deposition, due to high pH (12.9). This assumption was supported by energy dispersive X-ray spectrometry (EDS) measurements showing that the amount of released Zn in epoxy coatings decreased as Mn percent in the Zn–Mn alloys increased. In addition, Zn–Mn alloy coatings on steel, as well as bare steel, were immersed in 0.1 mol dm⁻³ NaOH solution, pH 12.9, simulating conditions during cataphoretic deposition, and polarization resistance measurement in this solution indicated that Mn inclusions in Zn–Mn alloy substrate prevent Zn dissolution in alkaline medium.     

Influence of iron addition on the microstructure and the electrochemical corrosion of Al–Zn–Mg alloys

The effect of Fe addition on the microstructural properties and the corrosion resistance of Al–Zn–Mg alloys submitted to different heat treatments (cast, annealed and aged), has been studied in chloride solutions using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), cyclic polarization (CP) and open circuit potential (o.c.p.) measurements. The presence of 0.3% Fe in the alloy limited the growth of the MgZn₂ precipitates, both in the annealed and in the quenched specimens. No effect of Cr on the grain size in the presence of Fe was found because of the accumulation of Cr in the Fe-rich particles. Fe in the Al–Zn–Mg alloys also made them more susceptible to pitting. Pitting occurred mainly near the Fe-rich particles both, under o.c.p. conditions in O₂-saturated solutions and during the CP.     

Fabrication of core–shell microspheres using alginate and chitosan–polycaprolactone for controlled release of vascular endothelial growth factor

Alginate microspheres loaded with vascular endothelial growth factor (VEGF) were prepared via an emulsification method using calcium chloride as a crosslinker. The microspheres with encapsulation efficiency of about 80% were coated by chitosan–polycaprolactone (CH–PCL) with various PCL percentages changing from around 15 to 42 wt.% to fabricate core–shell alginate/CH–PCL microspheres with an average size of around 40 μm. It was found that the CH–PCL coating layer on the core–shell microspheres could have a sandwich-like structure. The PCL content in the CH–PCLs and the concentration of CH–PCL solutions in preparing the microsphere functioned as two key factors to regulate the release profiles of the microspheres. Some selected alginate/CH–PCL microspheres were further crosslinked using genipin as a crosslinker, and the amount of genipin was found to be another impactful factor to mediate the release patterns of the microspheres. In vitro release measurements revealed that VEGF-release from these core–shell microspheres was controlled either by Fickian diffusion or non-Fickian transport that involves both diffusion and swelling. Some optimized core–shell microspheres were capable of maintaining sustained VEGF-release in an approximately linear manner over a period of time longer than 4 weeks and did not involve a significant initial burst.     

Influence of alloying elements and microstructure on aluminium sacrificial anode performance: case of Al–Zn

The electrochemical behaviour of Al–x%Zn alloys (1 wt% x 80 wt% ) was studied in 0.5 m sodium chloride solution. The experiments focused on the influence of casting conditions on sacrificial anode performance. The influence of casting conditions, solidification structure, polarization behaviour and attack morphology on the anode efficiency and operating potential was analysed. For alloys with low Zn content (1–5 wt%), the interdendritic zones or grain boundaries were the initial sites of attack and self corrosion was the principal cause of efficiency loss. Particularly, for Zn contents below 3 wt% the operating potential was strongly affected by the solidification macrostructure. Casting conditions that produced better alloying element distribution (chill structures) promoted higher anode efficiency. For Zn content higher than 5 wt% the operating potential and the anode efficiency were defined by the / phases area relationship.     

Fabrication and properties of thermal insulating material using hollow glass microspheres bonded by aluminum–chrome–phosphate and tetraethyl orthosilicate

Thermal insulation material made by hollow glass microspheres (HGM) with different content of aluminum–chrome–phosphate solution (ACP) and tetraethyl orthosilicate (TEOS) as binders was formed, dried and sintered at 250 °C, 450 °C or 650 °C for 2 h. Properties such as density, compressive strength, thermal conductivity and microstructure of the specimens were determined. It is found that TEOS improved the distribution of ACP and increased the compressive strength of the specimens. HGM bonded by appropriate amount of ACP and TEOS achieved preferable value of density, compressive strength and thermal conductivity which were significant for thermal insulation materials. The compressive strength of specimens sintered at 450 °C and 650 °C was higher than that of the specimens sintered at 250 °C.     

Fabrication and characterization of hybrid coating on Mg–Zn–Ca Mg alloy for enhanced corrosion and degradation resistance as medical implant

Magnesium (Mg)-based alloys have appealing properties as promising implants for medical applications. However, their clinical applications are hindered due to the rapid corrosion and degradation rate in the physiological environment. In this investigation, we reported a novel interfacial engineering approach for the fabrication of polymer/ceramic hybrid coating on Mg–Zn–Ca Mg alloy. Firstly, hydroxyapatite (HA) coating was fabricated on the Mg–Zn–Ca sample followed by an alkali treatment that was performed in 1 M NaOH solution at 60 °C. Finally, polycaprolactone (PCL) coating was synthesized using a dip-coating approach on the top of the HA-coated Mg–Zn–Ca specimen. Microhardness test and adhesion test revealed that PCL/HA hybrid coating significantly improved mechanical properties and enhanced biointerface property between the substrate and coating. The immersion tests showed that the hybrid coating considerably slowed down the degradation in the simulated body fluid (SBF) solution. In addition, in vitro electrochemical investigations confirmed that PCL/HA coating significantly improved corrosion resistance and greatly reduced corrosion rate by about 10 times compared to HA coating and about 900 times to untreated Mg–Zn–Ca sample. Moreover, cytotoxicity assessment exhibited PCL/HA hybrid coating enhanced biocompatibility and bioactivity due to adopting a suitable interfacial engineering approach.     

Hydrodeoxygenation of p-cresol on unsupported Ni–W–Mo–S catalysts prepared by one step hydrothermal method

Unsupported Ni–Mo–W sulfide catalysts were prepared by one step hydrothermal method using ammonium heptamolybdate and thiocarbamide in water, and characterized by X-ray diffraction (XRD), nitrogen physisorption and transmission electron microscopy (TEM). The effect of W/Mo molar ratio on the catalytic performance was studied using the HDO of p-cresol as a probe. The results showed that the Ni–Mo–W–S catalyst with an appropriate W/Mo molar ratio possesses the short slab length of MoS₂ or WS₂ structure and many active sites, leading to the high HDO activity and HYD selectivity.     

All-cellulose films with excellent strength and toughness via a facile approach of dissolution–regeneration

This study describes a green method for preparing all-cellulose nanocomposites through a dissolution and regeneration process. Cotton linter pulp was dissolved in 7 wt % NaOH/12 wt % urea aqueous solution precooled to −12°C. Self-assembly of cellulose molecules into nanostructured cellulose fiber is achieved by using water addition and controlling the temperature to regenerate cellulose. By changing the microenvironment of the cellulose solution, the morphology of the nanostructured cellulose fibers and the mechanical properties of the regenerated cellulose films can be tuned. Then, a series of regenerated cellulose films have been prepared and characterized from various aspects. Compared with other all-cellulose films in the literature, the regenerated all-cellulose nanocomposite films prepared in this work exhibited good optical transparency, thermal stability, and excellent tensile strength (up to 135 MPa) when the regeneration temperature was adjusted to 50°C. This work provided a green and promising approach to prepare high-performance and environmentally friendly all-cellulose nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46925.