Search

The wettability and reactivity between molten aluminum (Al) and carbon nanotubes (CNTs) are a key issue in the preparation of CNTs-reinforced Al-matrix composites using a solidification route. In this work, we measured the wettability of randomly aligned multi-walled carbon nanotubes (buckypaper) by molten Al at 973–1173 K in a high vacuum using a modified sessile-drop method and examined their interactions using a droplet-sucking technique. The wettability between Al and CNTs is even worse than that of the Al/graphite system. The contact angles are basically larger than 140° and show only a sluggish decrease with time during isothermal dwelling. The chemical stability of CNTs in contact with Al is closely related to their structural integrity. The CNTs with good crystallinity and structural integrity have relatively high chemical stability and exhibit only a weak interfacial reaction with Al at 973 K. However, the stability of structural defective parts is much lower. They are readily eroded by molten Al, leading to the fragmentation of the CNTs. These CNT fragments having an open tubular structure are then rapidly dissolved in molten Al along the axial and radial directions. Simultaneously, a large amount of Al4C3 is formed at the interfaces.

The wettability of TiC by Al alloys plays a key role in the preparation of TiC-reinforced Al matrix composites. Despite some prior work has been reported on this issue, few studies concern the influence of Si. In this work, the effects of Si concentration (0, 7Si, 12Si in wt%) and temperature on the wettability in the Al/TiC system were investigated by a dispensed sessile drop method at 1073–1173 K in a high vacuum. The initial contact angles were 103°–105°, almost independent of temperature, while the final contact angles decreased with increasing temperature. Formation of an Al4C3 phase and adsorption of the displaced [Ti] at the solid–liquid interface were two primary driving forces for the wetting improvement. On the other hand, an increase in the Si concentration greatly weakened the stability of TiC in Al melt, promoted the formation of Al4C3, and thus led to the faster spreading of the liquid in the early wetting stage. However, as the interfacial reaction progressed, the displaced [Ti] was bound by the Si in the Al melt due to their strong chemical affinity, thus weakening the adsorption effect of [Ti] for the wetting. As a consequence, the final apparent wettability of the Al–Si/TiC system was even worse than that of the Al/TiC system, and this situation was more prominent with increasing Si content.

To develop good rate capability and good cycle stability electrode, hierarchical porous coral-like ZnO/ZnCo2O4/Co3O4 coating was fabricated on a novel 3D straight-through layered copper current collector with one-step solution combustion method and used as self-supporting anode for lithium-ion batteries (LIBs). The coral-like ZnO/ZnCo2O4/Co3O4 coating facilitated the full penetration of the electrolyte and increased the activation rate of the active material. Also, the novel 3D copper current collector has an increased surface area compared to a traditional foam metal, providing an optimal structure for balancing the volume-change tolerance and the energy density of the porous electrode. In addition, the highly oriented structure favors the effective transport of electrons and Li ions within the 3D electrode. As a consequence, high reversible capacity of 1428 mAh g−1 at a current density of 200 mA g−1 after 100 cycles and excellent rate capability of 682 mAh g−1 at 1000 mA g−1 were achieved. This study provides a facile and scalable path toward high-performance self-supporting electrodes for LIBs and demonstrates that the volume density of self-supporting electrodes can be enhanced by increasing surface area of the 3D structured current collector.

Directionally aligned prismatic and lamellar porous alumina scaffolds with a high strength-to-density ratio were fabricated from submicron Al2O3 powders and a tiny quantity of nanoscale TiO2 sintering aids by freeze casting using TBA and water as solvents. Both freezing temperature (− 10 °C, − 50 °C, − 90 °C) and sintering temperature (1300 °C, 1350 °C, 1400 °C) were varied to adjust pore parameters while a low solid loading (15 vol%) was maintained to ensure high porosity. This paper describes and compares the microstructures, porosity, pore size, wall thickness and compressive behavior of the scaffolds with two typical pore morphologies (lamella and honeycomb), which help to identify their scope of application and to unveil the relationship between pore morphology and mechanical property to optimize the material performance. The failure modes of these two types of scaffolds under compression were simulated. The TBA-based 1 wt% TiO2-containing alumina scaffolds with dense ceramic walls that were freeze-cast at − 90 °C and sintered at 1400 °C exhibited a compressive strength of 160 MPa with a porosity of 59%, indicating lightweight and high-strength characteristics.

We developed a facile and low-cost approach to prepare lightweight and high-strength magnesium–matrix composites with a nacre-inspired laminated structure. First, lamellar Mg2B2O5 whisker (Mg2B2O5w) scaffolds with initial solid loadings of 10, 15 and 20 vol% were prepared by ice templating. The wettability between a molten AZ91D alloy and the Mg2B2O5w scaffold was greatly improved by the incorporation of nano-SiO2 sol in the aqueous slurry, making the preparation of nacre-mimetic AZ91D/Mg2B2O5w composite by way of pressureless infiltration feasible. The SiO2 content in the Mg2B2O5w scaffold has a significant effect on the processing and the microstructure and properties of the composites. The optimum SiO2 content was about 6–8 wt% of the total ceramic loading. A lower SiO2 content resulted in incomplete infiltration, while a higher content led to the formation of a large quantity of Mg2Si in the composite. The flexural strength of the composites seemed independent of the initial ceramic loading (10–20 vol%), whereas the compressive strength and elastic modulus increased considerably and the crack-growth fracture toughness decreased with increasing ceramic content. The mechanism for such variations was addressed.

Using 3 wt% TiO2 nanopowders as sintering aid, we prepared porous lamellar Al2O3–ZrO2 composites with an initial solid loading of 30 vol% and the Al2O3/ZrO2 weight ratios of 1:9, 3:7, 5:5, 7:3, and 9:1 by freeze casting. The viscosity of water-based slurries decreased with increasing Al2O3 content while the porosity and the wavelength of the lamellae in the sintered scaffolds showed first an increase and then decrease with maximum values appearing at Al2O3:ZrO2 = 5:5. A relatively large amount of tetragonal (t) ZrO2 transformed to monoclinic (m) ZrO2 with the increase in the Al2O3 content and sintering temperature, thus reducing stress-induced phase transformation effect during loading. The compressive strength of the sintered scaffolds depended on sintering temperature, porosity, and the phase composition in the composites. A maximum value of 105 ± 10 MPa was achieved in the scaffolds with a composition of Al2O3:ZrO2 = 3:7 after sintering at 1450 °C for 2 h.

Annealing-induced structural transition from amorphous to nanocrystalline states is believed to have a significant effect on the wettability of metallic glass alloys. In this study, an amorphous Ni80P20 alloy was pre-annealed at various temperatures to yield different structures and then wetted by a eutectic Sn–Bi solder at 473 K in a high vacuum using a dispensed sessile drop method. The results show that the structural relaxation and primary crystallization in the amorphous substrates greatly deteriorate the wettability while large-scale eutectic crystallization and the growth of nanocrystallites after high-temperature annealing improve it primarily due to the formation of a precursor film ahead of triple line. Moreover, the amorphous Ni–P substrates are more reactive with the molten Sn–Bi solder than the crystallized ones. The interfacial reaction yields Ni3Sn4 and a P-rich crystalline layer consisting mainly of Ni3P and Ni2SnP intermetallics. The presence of this layer dramatically retards the subsequent growth of the Ni3Sn4 phase.

The wetting of (100), (110), and (111) MgO single crystals by molten Mg was studied in a flowing Ar atmosphere at 1073 K using an improved sessile drop method. The results show that the contact angle and work of adhesion are mildly dependent on MgO substrate orientation. However, the work of separation calculated by density functional theory shows a sequence of (100)

Wetting of poly- and mono-crystalline MgO substrates by molten La was investigated at 1323 K in a high vacuum using a modified sessile drop method. The wettability seems to depend mildly on the substrate orientation but strongly on the surface roughness. The initial contact angles on the smooth (100), (110), and (111) surfaces are 63° ± 1°, 69° ± 1°, and 69° ± 1°, respectively, while on the rough polycrystalline surfaces they are much larger (104° ± 3°). The wetting behavior is dictated by the disruption of the oxide film covering the La surface, the extent of the interfacial reaction and the evolution of the reaction product. A thick layer of La2O3 phase formed at the interface and then enwrapped the liquid surface, leading to the recession and warping of the triple line and finally the deterioration in the wettability. On the other hand, magnesium was displaced by the reaction and its evaporation provided additional impetus for the movement of the triple line. Due to different reaction intensities, the wetting behavior of La on the different orientations of the MgO surfaces also showed some discrepancies.

The wetting of (0001) α-alumina single crystals by Mg–Al alloys over a wide composition range at 1073 K was investigated using an improved sessile drop method in a flowing argon atmosphere. The initial contact angles are between 103° and 84°, almost linearly decreasing with increasing nominal Mg concentration, suggesting that the addition of Mg to Al improves the initial wettability. According to the evolution of contact angle and contact diameter, representative stages were identified to characterize the complex wetting behavior in the presence of evaporation. The wetting kinetics was dependent on the nominal Mg concentration in the alloy. Two patterns of “stick–slip” behavior were observed in the wetting process and interpreted by combining the effects of interfacial reaction and evaporation of magnesium. In addition, the dependence of the interfacial reaction on the Mg–Al alloy concentration was thermodynamically analyzed. The dominant reaction product at 1073 K should be MgO when x Mg > 9 mol%, while MgAl2O4 when x Mg

Three novel low-band gap phenylenevinylene copolymers (P1, P2, and P3), containing dihexylthienylbenzothiadiazole (DTBT) and triphenylamine (TPA) or tetraphenylbenzidine (TPD) were synthesized via the Wittig–Horner reaction. The effects of TPA and TPD on the thermal, optical, electrochemical and photovoltaic properties were investigated. The UV–Vis spectrum of P3, which contains TPD in the polymer backbone, exhibits a broader and stronger absorption in the film than those of P1 and P2. The bulk heterojunction solar cells were fabricated with the as-synthesized polymers as the donors and [6,6]-phenyl-C61-butyric acid methyl ester as the acceptor in a 1:4 weight ratio. The device based on P3 exhibits the maximum power conversion efficiency of 1.11 % under simulated AM 1.5 G solar irradiation (100 mW/cm2).

Low-cost quasi-solid-state dye-sensitized solar cells (DSSCs) are designed and fabricated by using a metal-free organic dye and a mesoporous carbon aerogel instead of expensive ruthenium-based sensitizers and Pt electrode. The electrospun TiO2 nanorods are added into a polyvinylidene fluoride (PVDF) solution to form a 3D network nanocomposite gel electrolyte. The presence of TiO2 nanorods in the gel electrolyte obviously increases the ionic conductivity and decreases charge-transfer resistance of the DSSC. The effects of the gel electrolyte and the carbon aerogel counter electrode on electrochemical and photovoltaic properties have been investigated in detail. Particularly, an optimized DSSC with a nanocomposite gel electrolyte and a carbon aerogel counter electrode affords a power conversion efficiency (PCE) of 6.20% at a light intensity of 100 mW cm−2.

The TiC–TiB2/Al composites were fabricated by self-propagating high-temperature synthesis (SHS) from Al–Ti–B4C compacts. The addition of Al to the Ti–B4C reactants facilitates the ignition occurrence, lowers the reaction exothermicity, and modifies the resultant microstructure. The maximum combustion temperature and combustion wave velocity decrease with the increase in the Al amount. The B4C particle size exerts a significant effect on the combustion wave velocity and the extent of the reaction, while that of Ti has only a limited influence. The reaction products are primarily dependent on the B4C particle size and the Al content in the reactants. Desired products consisting of only the TiC, TiB2, and Al phases could be obtained by a cooperative control of the B4C particle size and the Al content.

Steel matrix composites locally reinforced by in situ TiC and TiB2 particulates were successfully fabricated using self-propagating high-temperature synthesis (SHS) in a Fe–Ti–B4C–C system during casting. The locally reinforced steel matrix composites consist of three distinct regions: (i) a TiC and TiB2 particulate-reinforced region, (ii) a transition region, and (iii) a steel matrix region. The TiC and TiB2 particulates in the locally reinforced regions display a relatively uniform distribution, and their sizes decrease with the increase in Fe content from 10 wt.% to 40 wt.%. The wear resistance of the locally reinforced region of the steel matrix composites is much higher than that of the unreinforced steel matrix.

Reactive wetting of hexagonal BN by molten Al at 1073–1273 K was studied using an improved sessile drop method. The temperature and substrate surface roughness have a remarkable effect on the wetting behavior. Reasons for the large discrepancy in the final contact angles reported in the literature were addressed.

The wetting behaviors of $$\hbox{R}(01\bar{1}2)$$ single crystalline and polycrystalline $$\alpha\hbox{-}\hbox{Al}_{2}\hbox{O}_{3}$$ substrates by Al–Si alloys were studied over wide composition and temperature ranges. The wettability is quite good for all compositions of the alloys. The effect of temperature is moderate while that of the composition is significant. The dependence of the wettability on the alloy composition displays a “valley” profile with the minimum value appearing in the range of 60–70at.%Si. The wetting improvement by the addition of Al to Si mainly results from the decrease in the solid–liquid interfacial free energy by the Al segregation at the interface, while that by the addition of Si to Al results from the decrease in the surface tension of the liquid by the Si segregation.