In situ synthesis,mechanical and cyclic oxidation properties of Ti3AlC2/Al2O3 composites

ABSTRACT

Ti₃AlC₂/Al₂O₃ composite materials were successfully fabricated from TiO₂/TiC/Ti/Al powders by the in situ reactive hot pressed technique. The microstructure, mechanical and oxidation properties of the composites were investigated in the paper. Vickers hardness increased with the Al₂O₃ content. The relative density of Ti₃AlC₂/Al₂O₃ composites exhibits a declining tendency with Al₂O₃ content especially exceeds 10 vol.?%. The Ti₃AlC₂/Al₂O₃ composites show excellent electrical conductivity. The flexural strength and fracture toughness of Ti₃AlC₂/10 vol. % Al₂O₃ are 461 ± 20?MPa and 6.2?±?0.2?MPa m^1/2, respectively. The cyclic oxidation behaviour of resistance of Ti₃AlC₂/10 vol. % Al₂O₃ composites at 800–1000°C generally obeys a parabolic law. The oxide scale of sample consists of a mass of α-Al₂O₃ and TiO₂, forming a dense and adhesive protect layer. The result indicates that the Al₂O₃ can greatly improve the oxidation resistance of Ti₃AlC₂.     

Hydrothermal synthesis of 3D hollow porous Fe3O4 microspheres towards catalytic removal of organic pollutants

Three-dimensional hollow porous superparamagnetic Fe₃O₄ microspheres were synthesized via a facile hydrothermal process. A series of characterizations done with X-ray diffraction, Brunauer-Emmett-Teller method, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy indicated that the production of Fe₃O₄ microspheres possessed good monodispersity, uniform size distribution, hollow and porous structural characters, and strong superparamagnetic behavior. The obtained Fe₃O₄ microspheres have a diameter of ca. 300 nm, which is composed of many interconnected nanoparticles with a size of ca. 20 nm. The saturation magnetization is 80.6 emu·g^-1. The as-prepared products had promising applications as novel catalysts to remove organic pollutants (methylene blue) from wastewater in the presence of H₂O₂ and ultrasound irradiation.     

Hydrothermal epitaxy and resultant properties of EuTiO3 films on SrTiO3(001) substrate

We report a novel epitaxial growth of EuTiO₃ films on SrTiO₃(001) substrate by hydrothermal method. The morphological, structural, chemical, and magnetic properties of these epitaxial EuTiO₃ films were examined by scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffractometry, X-ray photoelectron spectroscopy, and superconducting quantum interference device magnetometry, respectively. As-grown EuTiO₃ films with a perovskite structure were found to show an out-of-plane lattice shrinkage and room-temperature ferromagnetism, possibly resulting from an existence of Eu³⁺. Postannealing at 1,000°C could reduce the amount of Eu³⁺, relax the out-of-plane lattice shrinkage, and impact the magnetic properties of the films.

PACS

81.10.Aj; 81.15.-z; 61.05.-a     

In situ preparation of SiC/Si3N4-NW composite powders by combustion synthesis

Large-scale composite powders containing silicon carbide (SiC) particles and silicon nitride nanowires (Si₃N₄-NWs) were synthesized in situ by combustion synthesis (CS). In this process, a mixture of silicon, carbon black, polytetrafluoroethylene (PTFE) and a small amount of iron powders was used as the precursor. The products were characterized by XRD, SEM, EDS and TEM. The particles are equiaxed with diameters in the micron range, and the in situ formed nanowires are straight with uniform diameters of 20-350 nm and lengths of tens of microns. The Si₃N₄-NWs are characterized to be α-phase single crystals grown along the [1 0 1] or [1 0 0] direction. VLS and SLGS processes are proposed as the growth mechanisms of the nanowires. The as-synthesized powders have great potential for use in the preparation of high-performance SiC/Si₃N₄-NW composites.     

Self-Assembled 3D Flower-Like Hierarchical β-Ni(OH)2 Hollow Architectures and their In Situ Thermal Conversion to NiO

Three-dimensional (3D) flower-like hierarchical β-Ni(OH)₂ hollow architectures were synthesized by a facile hydrothermal route. The as-obtained products were well characterized by XRD, SEM, TEM (HRTEM), SAED, and DSC-TGA. It was shown that the 3D flower-like hierarchical β-Ni(OH)₂ hollow architectures with a diameter of several micrometers are assembled from nanosheets with a thickness of 10–20 nm and a width of 0.5–2.5 μm. A rational mechanism of formation was proposed on the basis of a range of contrasting experiments. 3D flower-like hierarchical NiO hollow architectures with porous structure were obtained after thermal decomposition at appropriate temperatures. UV–Vis spectra reveal that the band gap of the as-synthesized NiO samples was about 3.57 eV, exhibiting obviously red shift compared with the bulk counterpart.     

Characterization of photovoltaics with In2S3 nanoflakes/p-Si heterojunction

We demonstrate that heterojunction photovoltaics based on hydrothermal-grown In₂S₃ on p-Si were fabricated and characterized in the paper. An n-type In₂S₃ nanoflake-based film with unique ''cross-linked network’ structure was grown on the prepared p-type silicon substrate. It was found that the bandgap energy of such In₂S₃ film is 2.5 eV by optical absorption spectra. This unique nanostructure significantly enhances the surface area of the In₂S₃ films, leading to obtain lower reflectance spectra as the thickness of In₂S₃ film was increased. Additionally, such a nanostructure resulted in a closer spacing between the cross-linked In₂S₃ nanostructures and formed more direct conduction paths for electron transportation. Thus, the short-circuit current density (Jsc) was effectively improved by using a suitable thickness of In₂S₃. The power conversion efficiency (PCE, η) of the AZO/In₂S₃/textured p-Si heterojunction solar cell with 100-nm-thick In₂S₃ film was 2.39%.     

In situ vibration enhanced pressure slip casting of submicrometer alumina powders

This paper presents a novel method for improvement of particle packing in consolidation of submicrometer alumina powders by pressure slip casting. In this method, filtration cell is subjected to a mechanical vibration field with constant frequency of 50 Hz and vibration amplitudes ranging from 0 (no vibration) to 2 mm. Filtration rate, thickness and green density of the fabricated samples were measured to investigate the influence of vibration on filtration characteristics. It was revealed that employment of vibration can significantly increase filtration rate. Furthermore, there is an optimum vibration amplitude which results in the structure with the highest packing density. This value is shifted to higher vibration amplitudes as more concentrated alumina slurries is used. As the available formulation based on Darcy's law could not predict the results of the present investigation, a “Correction Factor” was utilized in order to increase the accuracy of the prediction in the presence of a vibration field.     

In situ growth of CuInS2 nanocrystals on nanoporous TiO2 film for constructing inorganic/organic heterojunction solar cells

Inorganic/organic heterojunction solar cells (HSCs) have attracted increasing attention as a cost-effective alternative to conventional solar cells. This work presents an HSC by in situ growth of CuInS₂(CIS) layer as the photoabsorption material on nanoporous TiO₂ film with the use of poly(3-hexylthiophene) (P3HT) as hole-transport material. The in situ growth of CIS nanocrystals has been realized by solvothermally treating nanoporous TiO₂ film in ethanol solution containing InCl₃ · 4H₂O, CuSO₄ · 5H₂O, and thioacetamide with a constant concentration ratio of 1:1:2. InCl₃ concentration plays a significant role in controlling the surface morphology of CIS layer. When InCl₃ concentration is 0.1 M, there is a layer of CIS flower-shaped superstructures on TiO₂ film, and CIS superstructures are in fact composed of ultrathin nanoplates as ‘petals’ with plenty of nanopores. In addition, the nanopores of TiO₂ film are filled by CIS nanocrystals, as confirmed using scanning electron microscopy image and by energy dispersive spectroscopy line scan analysis. Subsequently, HSC with a structure of FTO/TiO₂/CIS/P3HT/PEDOT:PSS/Au has been fabricated, and it yields a power conversion efficiency of 1.4%. Further improvement of the efficiency can be expected by the optimization of the morphology and thickness of CIS layer and the device structure.     

Hydrothermal synthesis of Li(Ni1/3Co1/3Mn1/3)O2 for lithium rechargeable batteries

Ultrafine powders of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials for lithium-ion secondary batteries were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/(Ni + Co + Mn) was studied. The products were investigated by XRD, TEM and EDS. The final products were found to be well crystallized Li(Ni_1/3Co_1/3Mn_1/3)O₂ with an average particle size of about 10 nm.     

A novel 3D network coordination polymer consisting of paddlewheel Co3 clusters connected by PO4 and 4-pyridinecarboxylate

The synthesis, structural characterization and preliminary magnetic studies of a novel coordination polymer with paddlewheel Co₃ clusters are reported firstly. In the polymer, Co₃ clusters are covalently linked through PO₄ tetrahedra and 4-pyridinecarboxylate (4-pya) ligands into interpenetrated three-dimensional network.     

Side-by-Side In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanotubes: Synthesis and Optical Properties

A simple and mild wet-chemical approach was developed for the synthesis of one-dimensional (1D) In(OH)₃ nanostructures. By calcining the 1D In(OH)₃ nanocrystals in air at 250 °C, 1D In₂O₃ nanocrystals with the same morphology were obtained. TEM results show that both 1D In(OH)₃ and 1D In₂O₃ are composed of uniform nanotube bundles. SAED and XRD patterns indicate that 1D In(OH)₃ and 1D In₂O₃ nanostructures are single crystalline and possess the same bcc crystalline structure as the bulk In(OH)₃ and In₂O₃, respectively. TGA/DTA analyses of the precursor In(OH)₃ and the final product In₂O₃ confirm the existence of CTAB molecules, and its content is about 6%. The optical absorption band edge of 1D In₂O₃ exhibits an evident blueshift with respect to that of the commercial In₂O₃ powders, which is caused by the increasing energy gap resulted from decreasing the grain size. A relatively strong and broad purple-blue emission band centered at 440 nm was observed in the room temperature PL spectrum of 1D In₂O₃ nanotube bundles, which was mainly attributed to the existence of the oxygen vacancies.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

Study on the preferred orientations of nearly cubic PZT particles synthesized by hydrothermal methods using TiCl3 reagent

Various parameters such as gel composition, aging, organic additive, and heating method affected the preferred orientation of nearly cubic PZT particles that were prepared by hydrothermal methods using TiCl₃ as a Ti³⁺ source, at relatively low temperatures of 100-140 °C. The newly found synthetic conditions could be used to develop specially orientated PZT particles, which may be useful in growing oriented films, for example, by electrophoretic deposition.     

Efficient perovskite solar cells based on low-temperature solution-processed (CH3NH3)PbI3 perovskite/CuInS2 planar heterojunctions

In this work, the solution-processed CH₃NH₃PbI₃ perovskite/copper indium disulfide (CuInS₂) planar heterojunction solar cells with Al₂O₃ as a scaffold were fabricated at a temperature as low as 250°C for the first time, in which the indium tin oxide (ITO)-coated glass instead of the fluorine-doped tin oxide (FTO)-coated glass was used as the light-incidence electrode and the solution-processed CuInS₂ layer was prepared to replace the commonly used TiO₂ layer in previously reported perovskite-based solar cells. The influence of the thickness of the as-prepared CuInS₂ film on the performance of the ITO/CuInS₂(n)/Al₂O₃/(CH₃NH₃)PbI₃/Ag cells was investigated. The ITO/CuInS₂(2)/Al₂O₃/(CH₃NH₃)PbI₃/Ag cell showed the best performance and achieved power conversion efficiency up to 5.30%.     

The current image of single SnO2 nanobelt nanodevice studied by conductive atomic force microscopy

A single SnO₂ nanobelt was assembled on a pair of Au electrodes by electric-field assembly method. The electronic transport property of single SnO₂ nanobelt was studied by conductive atomic force microscopy (C-AFM). Back-to-back Schottky barrier-type junctions were created between AFM tip/SnO₂ nanobelt/Au electrode which can be concluded from the I-V curve. The current images of single SnO₂ nanobelt nanodevices were also studied by C-AFM techniques, which showed stripes patterns on the nanobelt surface. The current images of the nanobelt devices correlate the microscopy with separate transport properties measurement together.     

Electrochemical performance of CoSb3/MWNTs nanocomposite prepared by in situ solvothermal synthesis

In situ solvothermally synthesized composite (SSC) and mechanically blended composite (MBC) of nanosized CoSb₃ and multiwalled carbon nanotubes (MWNTs) were prepared and investigated as potential anode materials for Li-ion batteries. It was found that SSC exhibits an entanglement structure of nanosized CoSb₃ and MWNTs and shows significantly better cycling stability than MBC. The reversible capacity of SSC electrode reaches 312 mA h g⁻¹ at the first cycle and remains above 265 mA h g⁻¹ after 30 cycles.     

Synthesis, structure, and photovoltaic property of a nanocrystalline 2H perovskite-type novel sensitizer (CH3CH2NH3)PbI3

A new nanocrystalline sensitizer with the chemical formula (CH₃CH₂NH₃)PbI₃ is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a = 8.7419(2) Å, b = 8.14745(10) Å, and c = 30.3096(6) Å, which can be described as 2 H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6 eV versus vacuum and the optical bandgap of ca. 2.2 eV. A spin coating of the CH₃CH₂NH₃I and PbI₂ mixed solution on a TiO₂ film yields ca. 1.8-nm-diameter (CH₃CH₂NH₃)PbI₃ dots on the TiO₂ surface. The (CH₃CH₂NH₃)PbI₃-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5 G one sun (100 mW/cm²) illumination.     

In situ growth of TiC whiskers in Al2O3 matrix for ceramic machine tools

TiC whiskers have been synthesized via a carbothermal reduction technique in an α-Al₂O₃ matrix within a temperature range of 1380–1580 °C in an argon atmosphere. The raw materials consist of TiO₂, carbon, nickel and NaCl. Various mixing procedures and reaction temperatures were used. The yield of the whiskers is mainly dependent on the mixing procedures and the morphology of the synthesized composite powders is mainly dependent on the synthesis temperatures. The majority of the synthesized whiskers display an ideal aspect ratio of 10–30 with a diameter of 1–3 μm. No significant influence on the growth of the TiC whiskers by the present of the Al₂O₃ matrix powder can be noted.     

Fabrication of Porous TiO<Subscript>2</Subscript> Hollow Spheres and Their Application in Gas Sensing

In this work, porous TiO₂ hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH₄HCO₃ as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m²/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area.     

g-B3N3C: a novel two-dimensional graphite-like material

A novel crystalline structure of hybrid monolayer hexagonal boron nitride (BN) and graphene is predicted by means of the first-principles calculations. This material can be derived via boron or nitrogen atoms which are substituted by carbon atoms evenly in the graphitic BN with vacancies. The corresponding structure is constructed from a BN hexagonal ring linking an additional carbon atom. The unit cell is composed of seven atoms, three of which are boron atoms, three are nitrogen atoms, and one is a carbon atom. It shows a similar space structure as graphene, which is thus coined as g-B₃N₃C. Two stable topological types associated with the carbon bond formation, i.e., C-N or C-B bonds, are identified. Interestingly, distinct ground states of each type, depending on C-N or C-B bonds, and electronic bandgap as well as magnetic properties within this material have been studied systematically. Our work demonstrates a practical and efficient access to electronic properties of two-dimensional nanostructures, providing an approach to tackling open fundamental questions in bandgap-engineered devices and spintronics.