Fabrication in-situ SiC nanowires/SiC matrix composite by chemical vapour infiltration process
ABSTRACT A SiC nanowires-reinforced SiC matrix composite was fabricated using chemical vapour infiltration (CVI) process. SiC nanowires with thin carbon coating were grown directly in a fibrous preform prior to the CVI matrix densification. The nanowires consist of single crystal β phase SiC and uniform carbon shell coating of ∼5 nm, with diameters of several tens to 100 nm. The volume fraction of the nanowires in the fabricated composite is ∼5%. Contributions of the nanowires to the mechanical properties of the composite are expected.
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ABSTRACT: Template-free, single crystalline novel hydroxyapatite (HAp) nanorings with an inner diameter of 70 nm were grown by a combined high gravity and hydrothermal approach. Nanodisks were suggested to be formed by oriented aggregation and Ostwald ripening of mostly calcium pyrophosphate nanospheres prepared initially by the high gravity method with a stepwise increase of flow rate of phosphate solution. The prolonged hydrothermal treatment of nanodisks appeared to induce the nanoring formation via acid penetration along the dislocations in HAp nanodisks. The presence of edge dislocations in the central region of nanodisks was confirmed by high resolution transmission electron microscopy. The mechanical evaluation of high molecular weight polyethylene (HMWPE) composite with various shaped HAp nanocrystals and in vitro cellular analysis of HAp nanocrystals revealed that mechanical and bioactive performances improved with an increase of the specific surface area of HAp nanocrystals. The enhanced mechanical performance of HMWPE/ HAp nanoring composite and the excellent cell viability for HAp nanorings are attributed to the superior interface bonding and cell activity, respectively, both of which are enhanced by the high specific surface area.Crystal Growth & Design 05/2012; 12:3565-3574. · 4.56 Impact Factor
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ABSTRACT: Silicon carbide whiskers have been synthesized by using reactive graphite as a template. Natural graphite flake was firstly activated using chemical oxidation and thermal oxidation methods. After that, the reactive graphite sources were mixed with silicon powder and heated in the coke bed at 1200 and 1400 °C. The structural evolution of graphite and morphologies of SiC whiskers were studied with the aids of XRD, SEM, TEM and EDS techniques. The results showed that natural graphite flake can be activated into reactive graphite such as oxidized graphite and expanded graphite with much more defects using thermal and chemical oxidation methods. The expanded graphite with a great deal of defects has higher reactivity than natural graphite flake and oxidized graphite and accelerates the formation of long and thick SiC whiskers. It is proposed that the vapor–solid mechanism is predominant for the growth of β-SiC whiskers in this system. During heating-up, Si or SiO vapors meet with the activated carbon atoms on graphite substrate to form SiC nucleus. Then these vapors continually deposit on the SiC nucleus following the SiC whiskers which grow along the 〈111〉 direction.Ceramics International 01/2014; 40(1):1481–1488. · 2.09 Impact Factor
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ABSTRACT: A novel and simple sol–gel route has been used for the fabrication of composite structure composed of carbon fibers and silicon carbide nanowires embedded in dense silicon carbide matrix. The carbonaceous silica sol was impregnated in the carbon fiber preform at atmospheric pressure. The sol impregnated carbon preform was cured and heat treated to convert into silicon carbide. The analysis by X-ray diffraction, scanning electron microscopy, X-ray tomography, and transmission electron microscopy indicates that the impregnated carbonaceous silica gel converts to β-silicon carbide with dense and wire morphology. Different morphological silicon carbide was uniformly distributed inside carbon fiber preform and there was no degradation in thermophysical properties of carbon composite during processing. These results reveal high efficient reinforcement of different morphological silicon carbide in carbon composite, demonstrate a new mechanism of carbon composite reinforcement and suggest a new direction to carbon composite reinforcement. Graphical AbstractJournal of Materials Science 10/2014; 49(19). · 2.31 Impact Factor