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: 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. DOI:10.1016/j.ceramint.2013.07.032 · 2.09 Impact Factor
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ABSTRACT: Hydroxyapatite (HAp) nanostructures may be an advanced candidate in biomedical applications for an apatite substitute of bone and teeth than other form of HAp. In contrast, well-defined size and shape control in synthesizing HAp nanostructures is always difficult. In this study, hydroxyapatite nanorods (HAp NRs) were prepared by simple hydrothermal method with controlling the reaction time without using any surfactant or templating agents. The nanostructure clearly depicts the growth stages of the HAp NRs by increasing the reaction time. The synthesized HAp has the rod like morphology with uniform size distribution with the aspect ratio of about 8–10. Transmission electron microscopic (TEM) and high resolution TEM (HRTEM) images show that the growth direction of the HAp is parallel to the (001) plane. The interplanar distances measured in segments (fringes) of the HRTEM micrograph were ~0.35nm, corresponding to the interplanar spacing of the (002) plane of the hexagonal HAp. X-ray diffraction (XRD) measurements indicate that the improved crystallinity of the HAp by increasing the reaction time. The mechanical studies reveal that the improved tensile strength and the abrasion resistance are observed for the HAp nanorods reinforcing with high molecular weight polyethylene (HMWPE). KeywordsNanorods–Hydroxyapatite–Polyethylene–TEM–Mechanical properties–Biocompatible implants–NanomedicineJournal of Nanoparticle Research 01/2011; 13(5):1841-1853. DOI:10.1007/s11051-010-9932-3 · 2.28 Impact Factor
Conference Paper: On the effect of smart antennas on error statistics and TCP performance[Show abstract] [Hide abstract]
ABSTRACT: We present some results on the statistics of the packet error process and on the resulting throughput of TCP when a smart antenna system is used to transmit signals from a base station to wireless users. Multiple users are assumed to be present, and the propagation environment considered includes frequency selective fading. The main results presented involve the tradeoffs between various systems parameters. It is shown that smart antennas have the potential to improve the wireless channel adequately, thereby essentially solving the performance problems which affect TCP. It is also shown that the whole complexity of these scenarios can be essentially summarized by the fading rate (Doppler frequency) and by the average packet error rate, thereby allowing the introduction of the concept of an "equivalent single-antenna system" and the scalability of the many available results for the latter caseVehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd; 02/2001