The influence of ablation products on the ablation resistance of C/C-SiC composites and the growth mechanism of SiO_2 nanowires

Ablation under oxyacetylene torch with heat flux of 4186.8（10%kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration（CVI） combined with liquid silicon infiltration（LSI） process.The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC.The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process.Bulk quantities of SiO2 nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation.The growth mechanism of the SiO_2 nanowires was interpreted with a developed vapor-liquid-solid（VLS） driven by the temperature gradient.

CdS/SiO_2 nanowire arrays and CdS nanobelt synthesized by thermal evaporation

CdS/SiO2 nanowire arrays and CdS nanobelts were synthesized by thermal evaporation of CdS and CdO mixture powders, with highly selective etching occurring on the silicon substrate surfaces. Study of the growth mechanism of CdS/SiO2 nanowire arrays and the growth process of CdS nanobelts showed that the growth of CdS dendrites plays an important role in the formation of CdS/SiO2 nanowire arrays, and that the mechanism of CdS/SiO2 nanowire arrays growth was in good agreement with “self-assembling nanoelectrochemistry”. In the thermal evaporation process, an interaction between Si from silicon substrate and Cd took place.

In situ Formed Fan-Shaped Nanowires in Biomorphic SiO2：A Multidimensional Composite of Hierarchical Porous Material and Organic Pollutant Adsorption Behavior

Fan-shaped SiO2 nanowires modified SiO2@C composites with a bio-inspired hierarchical porous structure and a high accessible surface area were prepared by in situ molten salt template method.The combination of biogenic hierarchical porous structure and one-dimensional nanostructure with similar features was successfully obtained by one-pot heat treatment in the presence of rice husk SiO2 with SiO2 acting as precursor and ZnCl2 acting as molten salt and growth template.A large amount of fan-shaped SiO2 nanowires with numerous tiny branches sprouting from the central nanowires were grown in the inter-porous epidermis and on the surface of rice husk SiO2 for temperatures up to 1200 ℃.The in situ ZnCl2 molten salt template base-growth mechanism is responsible for the initial formation of SiO2/ZnCl2 co-melting nanowires and the subsequent growth of fan-shaped SiO2 nanowires.The as-prepared samples have been successfully employed as organic absorbers with high efficiency in the field of wastewater treatment.

SiC nanowires with thickness-controlled SiO2 shells： Fabrication, mechanism, reaction kinetics and photoluminescence properties

SiC nanowires with thickness-controlled SiO2 shells have been obtained by a simple and efficient method, namely treatment of SiC/SiO2 core-shell nanowires in NaOH solution. The products were characterized by transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HRTEM）, X-ray diffraction （XRD）, Raman spectroscopy, infrared （IR） spectroscopy, and photoluminescence spectroscopy. The thickness of the SiO2 shell can be effectively controlled by selecting the appropriate processing time, and pure SiC nanowires were also obtained by alkaline cleaning in 1 mol-L-1 NaOH solution for 40 min at 70 ~C. A mechanism for the removal of the SiO2 shells has been proposed, and a two-phase reaction kinetic equation was derived to explain the rate of the removal of the SiO2 shells. The validity of this equation was verified by experiment. This work not only describes an effective experimental method for achieving SiC nanowires with thickness-controlled SiO2 coatings but also provides a fundamental theoretical equation with a certain level of generality. In addition, photoluminescence （PL） measurement results showed that the SiC nanowires sheathed with an optimum SiO2 thickness （3.03 nm） have better photoluminescence properties than either the bare SiC nanowires or SiC nanowires with thicker coatings of SiO2.

Electrochemical preparation of silicon nanowires from porous Ni/SiO2 blocks in molten CaCl2

Silicon nanowires(SiNWs)with diameter distributions ranging from 80 to 350 nm were prepared by electrochemical reduction of Ni/SiO2 in molten CaCl2.The effect of the content of nickel additives on the morphology of produced silicon was investigated.Large quantities of SiNWs are obtained by the electrochemical reduction of Ni/SiO2 blocks with SiO2 to Ni molar ratio of 20 and 10.Nickel additives repress the growth of irregular branches and promote longitudinal growth of SiNWs.Wire morphologies and surfaces are influenced by the electrolysis temperature.SiNWs become thicker with the increase of the electrolysis temperature.The optimum temperature to prepare single crystal SiNWs with high aspect ratio and extraordinary surface quality seems to be 1173 K.The amorphous layer of the silicon nanowire is thinner compared to the SiNWs obtained from the pure SiO2 pellets.The produced SiNWs show a photoluminescence emission peak at about 758 nm at room temperature.This work demonstrates the potentiality for the electrochemical reduction process to obtain large quantities of SiNWs with high quality.

Growth of SiO_2 nanowires on different substrates using Au as a catalyst

SiO2 nanowires were prepared on a SiO2/Si（111） or Si substrate using Au as a catalyst. The products were characterized using scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）. SEM shows that large amounts of SiO2 nanowires with a diameter of 20-150 nm and length of several nanometers were formed on the entire surface of the substrate. XPS analysis indicates that the nanowires have the composition of Si and O in an atomic ratio of about 1 ： 2, and their composition approximates that of SiO2. The formation of the SiO2 nanowires was controlled by the vapor-liquid-solid mechanism. It is found that the annealing time affects the morphology of the products. Finally, the effect of the substrates on the growth of SiO2 nanowires was discussed. The Si source of the SiO2 nanowires comes from the substrate or Si powder for different substrates.

A novel chemical route to SiO_2 nanowires

A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO2nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during nanowire formation, is discussed.

Synthesis of β-SiC/SiO_2 core-shell nanowires with the assistance of cerium oxide

The β-SiC/SiO2 core-shell nanowires with the 'stem-and-node' structure were synthesized in the presence of cerium oxide by the carbothermal reduction of the starch-SiO2 hybrids gel.The samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM) and energy-dispersed X-ray(EDX).The results showed that the nanowires consisted of a 20-35 nm diameter crystalline β-SiC core wrapped with a 2-5 n...

Vanadium oxide assisted synthesis of networked silicon oxide nanowires and their growth dependence

Networked silicon oxide nanowires have been synthesized by VO2-assisted chemical vapor deposition at 1000 ~C on silicon substrate without supplying any gaseous or liquid Si source. Systematic study on the nanowire growth has indicated that morphology and composition of the final products are sensitive to the catalyst components, reaction atmosphere and temperature. Compared to Au and V02 as catalysts individually, co-catalysts of Au and V02 play a critical role in the formation of networked Si02 nanowires. Transmission electron microscopy （TEM） and scanning electron microscopy （SEM） observations indicate that the silicon oxide nanowires have smooth surfaces with uniform diameters of 30-100 rim, and their lengths reach several hundred micrometers. X-ray photoelectron spectroscopy （XPS） results reveal the atomic ratio of silicon to oxygen is about 1：2. Growth dependence of the networked nanowires on hydrogen and temperature is also discussed. Vapor-liquid-solid （VLS） process is proposed for the growth mechanism of the networked nanowires. It is also found that the growth mechanism of SiO2 nanowires by increasing the temperature up to 1200 ℃ changes to vapor-solid （VS） processes since wire-like structures can be formed without any catalyst or H2 gas introduced into the system.