Enhanced electrical and thermal conductivities of 3D-SiC(rGO, G x ) PDCs based on polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor containing graphene fillers

Abstract(#br)Lightweight 3D-SiC(rGO, G x ) PDCs were fabricated from polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO) precursor added by different amounts of graphene fillers via direct cold molding and pyrolysis at 1400 °C in an easy manner. Results reveal that SiC(rGO, G x ) PDCs consist of β-SiC nanocrystals homogeneously embedded within amorphous SiO x C y /C free , and graphene is well compatible with SiO x C y /C free for void-free bonded interface, efficiently delaying decomposition of SiO x C y phase into β-SiC. The nanocomposite structure provides an ingenious strategy for constructing complexes with good integrity, high ceramic yield, excellent thermal stability, high electrical and thermal conductivities. This improvement is primarily attributed to the presence of graphene with considerably increasing electric-charge carriers and wider phonon-channel. Such 3D-SiC(rGO, G 20% ) PDCs possess satisfying hardness (12.02 GPa), high electrical conductivity (23.82 S cm −1 ) and thermal conductivity (7.47 W m −1 K −1 ), which make them attractive candidates for microelectromechanical systems (MEMS) devices, energy storage/conversion systems and high precision components, etc

Preparation and characterization of freestanding SiC(Ti, B) films derived from polycarbosilane with TiN and B as additives

Freestanding SiC(Ti, B) films with high temperature resistance were fabricated from polymer precursor of polycarbosilane (PCS) blended with 0.26 wt% TiN and 0.74 wt% B powders. Results reveal that SiC(Ti, B) films with good mechanical properties are uniform and dense. After high temperature annealing at 1500 degrees C in argon, SiC(Ti, B) films exhibit better high temperature resistance as compared to SiC films without additives, which implies their potential applications in ultra-high temperatures (exceeding 1500 degrees C) microelectromechanical systems (MEMS). Sintering additives are effective in suppressing the growth of SiC crystals and decreasing the content of oxygen and free carbon, which is normally beneficial to enhance high temperature resistance of films. (C) 2012 Elsevier Ltd. All rights reserved.Science and Technology Program of Fujian Province [2009H0038]; Fundamental Research Funds for the Central Universities [2010121053]; Aeronautical Science Foundation of China [2011ZF68004]; Specialized Research Fund for the Doctoral Program of Higher Education [20110121120033

Oxidation behavior of Hi-Nicalon SiC monofilament fibres in air and O-2-H2O-Ar atmospheres

An equipment including aircraft engine simulated environmental system and sample loading stage was manufactured for annealing Hi-Nicalon monofilament fibres in corrosive environments. The fibres were exposed in air and 14% H2O/8% O-2/78% Ar atmospheres at 1200 degrees C for 1-100 h, respectively. Experimental results indicate that tensile strength decreases, whereas oxide layer thickness and grain size of SiO2 increase with rising annealing time. The specimens show brittle/flat fracture, most of cracks initiate at the interface between SiC and SiO2 region of fibres. The control effect of water vapor on formation and structural evolution of the passive film was discussed. (C) 2011 Elsevier Ltd. All rights reserved.Science and Technology Program of Fujian Province [2009H0038]; Fundamental Research Funds for the Central Universities [201012 1053]; Aeronautical Science Foundation of China [2011ZF68004]; Specialized Research Fund for the Doctoral Program of Higher Education [20110121120033

Synthesis and characterization of continuous freestanding silicon carbide films with polycarbosilane (PCS)

A technique based on melt spinning of precursor was introduced to produce continuous freestanding SiC films. An equipment including spinneret, mandril, tank and seal groove was designed and manufactured for melt spinning. The polycarbosilane (PCS) precursors were deaerated, melt spun, crosslinked (by oxidation or irradiation), and pyrolyzed at high temperature in order to convert the initial PCS into freestanding SiC films. Our results revealed that the continuous freestanding SiC films, approximately 8 mu m to 190 mu m in thickness depended on setting, were uniform and dense. Their microstructure consisted of amorphous SiOxCy, beta-SiC nano-crystals and free carbon. The photoluminescence (PL) spectrum showed two blue emissions at 416 nm and 435 nm. The continuous freestanding SiC films with high modulus, high density, high surface hardness and optoelectronic properties may have potential applications in microelectromechanical systems (MEMS), advanced optoelectronic devices and such complex-shaped materials. (C) 2008 Elsevier Ltd. All rights reserved.National Natural Science Foundation of China [50532010

Effects of oxidation curing and Al atoms on the formation of near-stoichiometric freestanding SiC(Al) films derived from polyaluminocarbosilane (PACS)

Fundamental Research Funds for the Central Universities [2010121053]; Aeronautical Science Foundation of China [2011ZF68004]; Specialized Research Fund for the Doctoral Program of Higher Education [20110121120033]; Science and Technology Program of Fujian Province [2012H0036]The effects of oxygen pick-up and Al atoms on the formation and microstructure of freestanding SiC(Al) films by melt spinning of polyaluminocarbosilane (PACS) precursor were studied. PACS green films were cross-linked for 1 h, 2 h, 3 h and 4 h, pre-pyrolyzed at 900 degrees C, respectively. They were continuously pyrolyzed at 1800 degrees C to convert initial PACS into SiC(Al) ceramic films. Results reveal that the strict control of oxygen content during the oxidation curing is essential to produce near-stoichiometric SiC(Al) films. The microstructure of the dense films is a mixture of beta-SiC crystals, alpha-SiC nano-crystals, C clusters and a small amount of Al4O4C and Al4SiC4. Al atoms which play important roles as both sintering aids and grain growth inhibitor are well distributed in the films due to the presence of stable composition and structure. SiC(Al) films with excellent mechanical properties would be attractive candidate materials for MEMS in harsh environments. (C) 2013 Elsevier Ltd. All rights reserved

Synthesis and optical properties of metal (M) atom-doped polycarbosilane (PCS) with extended conjugation (M = Al, Dy, Er and Eu)

Fundamental Research Funds for the Central Universities [2010121053]; Aeronautical Science Foundation of China [2011ZF68004]; Specialized Research Fund for the Doctoral Program of Higher Education [20110121120033]; Science and Technology Program of Fujian Province [2012H0036]Optical properties of metal atom-doped polycarbosilane (PCS) which originated from sigma-conjugation effect were studied. Al, Dy, Er and Eu were introduced into PCS by one-pot method to yield polyaluminocarbosilane (PACS), polydysprosiumcarbosilane (PDCS), polyerbiumcarbosilane (PErCS) and polyeuropiumcarbosilane (PECS), respectively. Effects of oxidation curing and ultraviolet (UV) radiation on the photoluminescence (PL) properties of the samples were investigated. PL spectra show strong blue light-emissions and the intensity of PCS is enhanced by adding metal atoms. PACS with extended a-conjugation exhibits an obvious PL red-shift, high intensity, high quantum yield and excellent oxidation resistance as compared with those of others. As treated under UV lamp for 3 h in air, PACS retains good UV resistance performance, owing to the AlOx (x = 4, 5, or 6) groups which effectively extend the sigma-conjugation. The obtained results are expected to have important applications in active sources for electroluminescence (EL) devices, especially suitable for blue emission. (C) 2013 Elsevier B.V. All rights reserved

Oxidation behavior of Hi-Nicalon SiC monofilament fibres in air and O2-H2O-Ar atmospheres

An equipment including aircraft engine simulated environmental system and sample loading stage was manufactured for annealing Hi-Nicalon monofilament fibres in corrosive environments. The fibres were exposed in air and 14% H2O/8% O2/78% Ar atmospheres at 1200掳C for 1-100h, respectively. Experimental results indicate that tensile strength decreases, whereas oxide layer thickness and grain size of SiO2 increase with rising annealing time. The specimens show brittle/flat fracture, most of cracks initiate at the interface between SiC and SiO2 region of fibres. The control effect of water vapor on formation and structural evolution of the passive film was discussed. 漏 2011 Elsevier Ltd

A mini-review on gene delivery technique using nanoparticles-mediated photoporation induced by nanosecond pulsed laser

Nanosecond pulsed laser induced photoporation has gained increasing attention from scholars as an effective method for delivering the membrane-impermeable extracellular materials into living cells. Compared with femtosecond laser, nanosecond laser has the advantage of high throughput and low costs. It also has a higher delivery efficiency than continuous wave laser. Here, we provide an extensive overview of current status of nanosecond pulsed laser induced photoporation, covering the photoporation mechanism as well as various factors that impact the delivery efficiency of photoporation. Additionally, we discuss various techniques for achieving photoporation, such as direct photoporation, nanoparticles-mediated photoporation and plasmonic substrates mediated photoporation. Among these techniques, nanoparticles-mediated photoporation is the most promising approach for potential clinical application. Studies have already been reported to safely destruct the vitreous opacities in vivo by nanosecond laser induced vapor nanobubble. Finally, we discuss the potential of nanosecond laser induced phototoporation for future clinical applications, particularly in the areas of skin and ophthalmic pathologies. We hope this review can inspire scientists to further improve nanosecond laser induced photoporation and facilitate its eventual clinical application.</p