Papers by Keyword: Organic Precursor

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: A new preparation method was developed to produce Si₃N₄-SiO₂-Si₂N₂O composites for broad band radome applications. The three-dimensional cross-linked polyphenylsiloxane (PPS) was used as an organic precursor. The composites obtained through react bonding between Si and the precursor powders in the stream of N₂ were examined. The conversion of the PPS polymer to the ceramic was examined by TG analysis and conventional X-ray diffraction (XRD) techniques. It was found that the ceramics contained a primary Si₂N₂O phase, some β-Si₃N₄ phase and a minor α-SiO₂ phase. Despite low density (1.7-2.0g•cm^-3), the flexural strengths of the composites reaches 195Mpa at room temperature. The ceramic has excellent dielectric properties with dielectric constants as low as 3.2-5.5.