Papers by Keyword: Polycarbosilane

Abstract: Since mesoporous silica such as MCM-41 and SBA-15 was developed, the study of the properties of high-surface area materials was accelerated. Moreover, the mesoporous silica is used as a template to produce high-surface materials by nanocasting technology. The purpose of this paper is the synthesis of a high surface silicon carbide sphere by the nanocasting technology. In this study, KCC-1 silica sphere was used as a template, and polycarbosilane and poly (phenyl carbosilane) were selected for precursor of silicon carbide. Carbosilane polymer gives advantage of synthesis silicon carbide under low temperature, and hollow spheres were produced. In this study, the polycarbosilane was more effective for the synthesis of SiC hollow spheres by inversion of template structure showing a fibrous morphology on the sphere wall. And it was confirmed that the sphere was composed of nanosized SiC crystals, and has high surface area using TEM, XRD and BET analysis.

Abstract: The pyrolysis kinetic behaviors and reaction mechanism of polycarbosilane (PCS) were characterized by means of XRD, SEM and on-line TG-DSC-FTIR-MS coupling technique, which showed that the pyrolysis process accorded with the F2 integral model (300-600°C), and the values of apparent activation energy (E_a) and pre-exponential factor (A) were 56.10KJ/mol and 10.84, respectively. During the pyrolysis process, PCS was converted into amorphous inorganic solid from organic polymer with breakage and rearrangement of chemical bonds, then to well-defined crystal structure of good thermal stability. Furthermore, the weight loss occurred mainly among 300°C and 800°C with CH₄, (CH₃)₄Si,(CH₃)₃SiH,(CH₃)₂SiH₂ and other silane gases releasing from pyrolysis product leading to the conversion from organic polymers to inorganic ceramic. The pyrolysis product was converted into β-SiC crystal completely at 1400°C, and the crystallization of α-SiC phase occurred after 1550°C which might influence the stability of SiC matrix. Key words:polycarbosilane, organic precursor, pyrolysis kinetic behavior

Abstract: SiC-Ti functionally graded material (FGM) was prepared by polymer-derived method in order to resolve connection problem between the ceramic matrix and its composite materials, as well as metal at high-temperature. Gradient materials were fabricated successfully by polymer-derived method combined with hot-press sintering process at 1300. The microstructure of the prepared samples was studied, and the results revealed that this FGM had a compact structure, without obvious interface between different layers. The distribution of elements was gradient according to the SEM and EDX results.

Abstract: Polycarbosilane (PCS) is one of precursor systems applied in industry for the Polymer Infiltration Pyrolysis (PIP) processing of C or SiC fiber reinforced SiC matrix composites (Cf/SiC or SiCf/SiC CMC) materials. In this work, a series of PCS-derived SiC specimens treated at 300, 550, 800, and 1100 °C was studied by XRF, IR, XRD and XPS methods. The results show that a slight amount of PCS molecules with low softening point evaporates below 300 °C; the cross-link between PCS chains takes place to form a 3D -Si-C-Si- network via the reaction between -Si-CH3, -Si-CH2-Si- and -Si-H groups in the temperature range of 300-550 °C; an amorphous phase of SiC was observed when PCS was heated up to 800 °C, which indicates the completion of transformation from organic to inorganic; above 800 °C, β-SiC domain grows. Furthermore, a surface structure evolution of PCS-derived SiC specimens with temperature is proposed after the analyzing the XPS spectra.

Abstract: Non-oxide ceramics derived from organo-elemental precursors in the system Si-N-C has attracted much attention for its excellent properties. Typically, the Si-N-C ceramic shows homogeneous elemental distribution, better high-temperature stability and oxidation resistance which making them attractive for applying in various branches of technology. A novel amorphous ceramic is fabricated from precursors mixed by polysilazane (PSZ) and polycarbosilane (PCS). The Si-N-C ceramics (PSZ/PCS=2 (w/w)) are heat-treated between 1200°C and 1500°C in nitrogen to crystallization of microcrystalline α-Si3N4 and nanocrystalline SiC. The obtained Si-N-C ceramics are characterized by density, ceramic yield, porosity, X-ray diffraction and Scanning electron microscope to analyze the crystallization and microstructure. The experimental results indicate that the ratio of PSZ/PCS and the annealing temperature have a big influence on the crystallization behavior.

Abstract: Polycarbosilane (PCS), an important precursor for manufacture of silicon carbide (SiC) ceramics, was prepared and analyzed to determine its chemical composition. The major elements of silicon (Si) and carbon (C) in Si-C backbones and side chains in PCS represent more than 80% with minor elements of oxygen and hydrogen being less than 20%. In this work, a conventional potassium silicofluoride volumetric method was explored and modified for establishing a standard routine procedure to evaluate Si content in PCS. The optimal conditions were investigated using an orthogonal designed four-factor-three-level normal experimental scheme. The suitable parameters and standard procedure to analyze Si in PCS were obtained.

Abstract: Polycarbosilane (PCS) was introduced into preforms to prepare W-ZrC cermets by reactive melt infiltration (RMI). Properties and microstructure of the preforms and cermets were analyzed with XRD, SEM and EDS. The preforms had an open porosity of 42.0 %, and the WC particles were cemented by the pyrolysate of PCS. W-ZrC cermets were prepared by heating Zr2Cu covered preforms to 1300 °C for 3 h. XRD revealed that the resulting cermets were made up of W, ZrC and W2C. The cermets had an open porosity of 3.5 %, a flexural strength of 354.0 MPa, a flexural modulus of 192.5 GPa and a flexural toughness of 5.72 MPa·m1/2 .

Abstract: A melt-spinnable precursor for SiC based fibers was prepared from blend polymers of polycarbosilane (PCS) and modified polymethylsilane (M-PMS). The blend polymers cured at 320°C are different from M-PMS and PCS. The ceramic yield of these blend polymers is about 83%. The C/Si ratio of M-PMS/PCS derived ceramics (pyrolyzed at 1250°C) is linear to the content of MPMS in M-PMS/PCS. After melt spinning, thermal oxidation curing, and pyrolysis, Si-C-O fibers were obtained. The diameter and the tensile strength of the resulted fibers are 16.5μm and 1.62GPa, respectively.

Abstract: Nano silicon carbide ceramics were prepared via precursor pyrolysis. Polycarbosilane (PCS) and divinylbenzene (DVB) were selected as a precursor to silicon carbide ceramics and a cross-linking reagent for PCS, respectively. The cross-linking properties and pyrolysis of PCS and DVB were investigated by changing the mass ratios of PCS/DVB. The mass ratio of PCS/DVB has a great effect on silicon carbide ceramic yield. The cured PCS/DVB with a mass ratio of 1:0.5 has the highest SiC ceramic yield (63.1%) at the temperature up to 1500 °C and its pyrolyzates consiste of nano silicon carbide with a diameter of 10-40 nm. The microstructures of the nano silicon carbide ceramics were characterized by SEM and XRD. The pyrolysis behavior of the cured PCS/DVB was characterized by thermogravimetry in nitrogen atmosphere.

Abstract: Silicon carbide (SiC) based fibers with continuous pore structures were synthesized by the precursor method using a polycarbosilane (PCS) and polymethylhydrosiloxane (PMHS) polymer blends. The pore formation process can be explained by hydrogen gas dissolution in the polymer melt and desaturation process of the dissolved gas during the fiber spinning. We investigated the effect of PMHS additives with different chemical and physical natures on the obtained pore structures, because PMHS decomposition process played a role of hydrogen gas source. The individual polymer melts were characterized by viscosity measurement, gas chromatograph analysis and thermogravimetric (TG) analysis in order to obtain details of pore structure control.