Pressure Field Assisted Polycondensation Nonaqueous Precipitation Synthesis of Mullite Whiskers and Their Application as Epoxy Resin Reinforcement

Mullite whiskers were novelty prepared via pressure field assisted polycondensation nonaqueous precipitation method. The precipitate phase transition in heating process, phase compositions and microstructure of samples calcined at different temperatures, effect of pressure field on precursors polycondensation and AlF3 amount on sample morphology, the structure and the growth mechanism of whiskers were investigated. The results indicate that pressure field caused by kettle treatment promotes the polycondensation reaction between AlF3 and tetraethyl orthosilicate (TEOS), the excess aluminum fluoride coordinates with the precipitate skeleton of the =Al–O–Si≡, which brings about the low mullitization temperature (900 °C). The sample prepared with the optimal amount of aluminum fluoride (1.3 of the theoretical amount) calcined at 1100 °C presents high yield and aspect ratio (>15, 100 nm in diameter) of mullite whiskers. Growth of whiskers prepared via pressure field assisted polycondensation nonaqueous precipitation method is attributed to a vapor-solid (VS) mechanism with the inducement of screw. These mullite whiskers with the structure of multi-needle whiskers connected in the same center can be distributed evenly in epoxy resin, which greatly improves the mechanical properties of epoxy resin.

Ultra-long SiC nanowires synthesized by a simple method

Ultra-long SiC nanowires synthesized by alumina-assisted growth of the vapor–solid (VS) mechanism.

Effect of CVD Synthesis Parameters on the Growth of Catalyst-Free ZnO NRs

The main development of ZnO nanorods (NRs) is focused on the gold catalyst and heteroepitaxial approach.However, the presence of Au may generate undesired deep level traps in the ZnO bandgap, which could be very harmful to the performance of transistors. The objective of this study is to synthesize ZnO NRs via homoepitaxial growth without using foreign catalyst by Chemical Vapour Deposition (CVD) technique. The growth of catalyst-free ZnO NWs at different CVD synthesis parameters such as amount of Zn powder, substrate location and synthesis duration on the catalyst-free ZnO NRs were studied systematically. The effect of these parameters on the size and areal density of ZnO NRs provided a better understanding on the growth mechanism of NRs via the Vapour-Solid (VS) mechanism.

Growth and Morphology of β-Si3N4 Nano-Belts by Carbothermal Reduction Nitridation of Used Silica Refractory Brick

Silicon nitride (β-Si3N4) nano-belts had been synthesized by used silica bricks and carbon powder as raw materials through carbothermal reduction nitridation. The morphology and microstructure of β-Si3N4 nano-belts were characterized by scanning electron microscopy (SEM/HRSEM), energy disperse spectrum (EDS) and X-ray diffraction (XRD). Results showed that the well-crystallized β-Si3N4 nano-beltes were grown with thinness of 50-150nm and width of 3-5μm. The relatively purer β-Si3N4 were prone to be thin films with thinness of 150nm, while the as-grown SiCN (impurityβ-Si3N4with C elements) were presented as nanorods with cross section length of 150*150nm. Orientation growth mechanism by grain dislocation and vapor-solid (VS) mechanism were both involved in the growth of nanostructures of β-Si3N4 nano-beltes and SiCN nanorods.

Synthesis and Growth Mechanism of Catalyst-Free ZnO Nanowires Using Chemical Vapour Deposition

Zinc oxides nanowires (ZnO NWs) were successfully synthesized on bare silicon substrates using Chemical vapour deposition (CVD) method without foreign catalyst. The ZnO NWs had good crystal quality as they exhibited a strong UV emission (373 nm) corresponding to the free exciton emission and a weak green arising from defect-related emission in PL measurement. Measurement of low temperature photoluminescence spectra show a peak of free exciton and defect bound excitons. The growth of these catalyst-free ZnO NWs was governed by Vapour-Solid (VS) mechanism.

Synthesis of Fiber-Like SiС by Carbothermal Reduction of Used Silica Bricks

Fiber-like SiC had been synthesized using used silica bricks and carbon powder as raw materials by carbothermal reduction. A new kind of beaded SiC also had been found in the specimen. The result showed that well-crystallized β-SiC fibers began to appear at 1550 °C with excessive of 100 wt% content of carbon. While at 1600 °C for 6 h with excessive of 100 wt% content of carbon, the as-synthesized SiC fibers were grown with some beads in the fiber strings. The beaded SiC consisted of strings with diameters of less than 0.5 μm (or even 0.1μm) and periodic beads with diameters of 0.5-1.0 μm. Vapor-solid (VS) mechanism and vapor-liquid-solid (VLS) mechanism were also discussed in the synthesizing process of fiber-like SiC. This kind of fiber-like SiC may used as reinforce materials in ceramic composites, the fracture toughness of brittle ceramics can be effectively improved via the incorporation of strong SiC fibers into the matrix due to crack deflection, bridging and fiber pull-out. Moreover, these toughening mechanisms do not diminish as temperature increases.

Growth Mechanism of Au-Catalyzed Zno Nanowires: VLS or VS-VLS?

A systematic study was carried out to study the effect of process parameters on the growth of Au-catalyzed ZnO nanowires (NWs). Growth of Au-catalyzed ZnO NWs could be mainly occurred at the tip or at the base of NWs. This study provided useful information in determining the process window for the tip-growth Au-catalyzed ZnO NWs. Besides, a generic growth mechanism, i.e. a combination of Vapor-Liquid-Solid and Vapor-Solid (VLS and VS) mechanism is proposed to explain the tip-growth and base-growth Au-catalyzed ZnO NWs.