Papers by Keyword: Pre-Ceramic Polymer

Abstract: Non-oxide ceramic SiCN possesses unique physical and chemical properties, which make it a suitable material for various applications such as catalyst support, high temperature semiconducting devices, and metal or polymer matrix composites. In this work, SiCN foams with pore size of 500 and 1000 nm and high BET surface area of 184.5 and 71 m2/g were prepared using preceramic polymer, polyvinylsilazane, as a precursor and polystyrene sphere packed bed as a self-sacrificial template. The polystyrene sphere packed bed was prepared by the natural sedimentation of spheres. After the infiltration and curing of viscous preceramic polymer, the sample was pyrolyzed at 1000 °C under N2 atmosphere to produce the ceramic foams. It is a very simple synthesis because in the process of pyrolysing preceramic polymer, the polystyrene sphere template was removed simultaneously by pyrolysis with no additional etching step. SEM, N2 adsorption-desorption measurement and TGA were used to characterize the obtained samples. It was concluded from the TGA measurement that the obtained SiCN foam possessed very high thermal stability at 1000 °C under air.

Abstract: Ceramic membranes having nano sized pores have great potential for gas separation at high temperature due to their good thermal stability. Moreover, nanoporous silicon carbide membrane has potential application under hydrothermal condition at high temperature. In this research, nanoporous SiC membrane has been developed on the porous alumina plate using preceramic polymers as CVD precursor at 850oC. The preceramic polymer was characterized with Si29 NMR, FT-IR, GC and TGA. The prepared SiC membrane was characterized with SEM and EDS. The hydrogen permeability and selectivity toward nitrogen gas were measured using a GC.

Abstract: Interests on the fabrication of microfluidic devices have increased in the fields of micro total analysis system (μ-TAS) and MEMS (Microelectromechanical systems) due to their chemical inertness and high thermal stability. The thermal characterization of the SiCN preceramic polymer, polyvinylsilazane, showed that the cured polymer has ceramic properties at heat treatment temperature of 600 oC or above. In the characterization of the mechanical properties, the characteristic values of the elastic modulus and hardness notably increased for the heat-treated SiCN. The present study describes the preparation of nano-sized patterns and microfluidic channels using a soft lithographic technique. The study shows that the fabrication of microchannels using the cured inorganic polymers holds tremendous potential in the field of microfluidics, where materials with high optical transparency, thermal stability and chemical inertness are in demand as niche between conventional microfluidics using glass and polymeric materials.

Abstract: This paper reports fabrication of high temperature stable, chemically inert SiC and SiCN monolithic porous microchannels by micromolding in capillaries (MIMIC) method. These types of high surface area materials hold tremendous untapped potential in micro-total analysis systems, micro-reaction technology and clean energy systems. Owing to their excellent durability under harsh conditions, SiC and SiCN micro-components are imperative in fields like fuel cells, for hydrogen generation and as environmental sensors. The report also describes the use of template particles of different size and type with diameter of ranging from 0.5 to 1.5 µm to prepare porous, high temperature stable ceramic microchannels. In the present work, ceramic porous channels have been fabricated via polymer to ceramic conversion route by using commercially available polymer precursors.

Abstract: In this work, ceramic matrix composites (CMC) were prepared by AFCOP process, using a polysiloxane network filled with metallic niobium and aluminum powders as active fillers. The liquid polysiloxane precursor was loaded with a suitable polymer/filler ratio in relation to stoichiometric Nb : C and Al : O molar ratios. Changing Al for a-Al2O3, which acted as an inert filler, non-stoichiometric conditions were obtained. The mixtures were blended, uniaxially warm pressed, and pyrolysed in flowing argon at 800, 1000 and 1200 °C. Thermogravimetry was used to follow the weight changes during the pyrolysis process. X-ray diffraction was used to identify the formation of new crystalline phases, such as Al2O3, NbC, Nb2C and Al3Nb in the composites. Sintered specimens were also characterized by SEM and EDS. The results indicated good potential for this system to obtain multiphasic composite material in the Al-Nb system at lower temperatures.

Abstract: Macroporous SiCBN and BCN ceramic were prepared by infiltrating these preceramic polymers into the colloidal silica crystalline array, followed by pyrolysis at 1400ı and subsequently etching off the silica spheres. It is generally observed by SEM and TEM that a highly ordered and interconnected 'honeycomb' pore structure was obtained by replicating the three dimensional close packed silica spheres which was fabricated by natural sedimentation. And BET surface areas in range 413 ~ 315 m2/g and pore sizes of 113 ~ 395 nm in the porous materials were tailored by controlling the sacrificial silica sphere sizes in range 145~500 nm even under volume shrinkage involved during pyrolytic step. The porous SiCBN ceramics and BCN ceramic showed a slight weight loss of 0.2~0.8% and 4%, respectively, indicating excellent resistance to oxidation.

Abstract: Ceramic foams containing MoSi2 were prepared by a self-blowing process of poly-silsesquioxane with MoSi2 as filler. Ceramic foams prepared by polymer pyrolysis were composed of MoSi2 and silicon oxycarbide glass matrix. Densities, pore sizes and mechanical properties of ceramic foams were depended on the filler content and heating rate for curing of polymer. Depending on the foaming condition, ceramic foams with a density of 1.2∼0.4 and a compressive strength of 3∼30 MPa were obtained.

Abstract: Carbon fibre reinforced SiC (Cf /SiC) as a promising high temperature structural material possesses broad prospects for aeronautical and astronautical applications. Joining technique is very important from both technical and economical points of view. Joining of Cf/SiC to itself has been realized by reaction joining process using a preceramic polymer, polysilazane, as joining material (welding compound). The weld strength of joints is strongly affected by joining temperature and number of times of reinforcement, which comprises infiltration and pyrolysis of polysilazane. Samples were joined at temperatures ranging from 1100oC -1400oC. The maximum weld strength of joints is obtained at 1250oC. The reinforcement can remarkably increase the weld strength of joints. After three times of reinforcement the shearing strength of joints reaches 27.78MPa. Microstructural study and phase analysis reveal that the joining material has transformed into an amorphous ceramic interlayer composed of Si, C and N at 1100~1250oC, which is uniform and densified. The thickness of the interlayer is 2-3µm. The contact at the interfaces is good without obvious cracks and pores. The amorphous ceramic interlayer transforms into crystal SiC and Si3N4 at 1400oC.