No abstract

Well defined porous ceramic particle/polymer matrix composites consisting of Si and nanosized ZrO 2 particles have been fabricated by the pyrolysis of phenolic resin at 1123 K in vacuum. Electron probe microanalyser analysis showed that the pyrolysis of the starting materials led to the agglomeration of ZrO 2 particles and the uniformly distribution of Si particles in the matrix. Scanning electron microscopy images showed the formation of spherical pores ranging from 10 mm to several 100 mm in diameter in the composite, resulting in the flexural strength of ,14 MPa. X-ray diffraction analysis suggested that b-SiC might be formed in the composite; and the matrix of porous polymer matrix ceramic composite was amorphous carbon.

The aim of present study is to investigate the effect of preforms on the synthesis of micro β-SiC. For this purpose, preforms were prepared from commercially available phenol resin and silicon powders by pyrolysing at 650°C and 750°C in vacuum. Then, preforms were hot isostatically pressed (HIPed) at 1400°C for 10 min in an argon atmosphere of 50 MPa to synthesize micro β-SiC. X-ray diffraction analyses showed that the formation of β-SiC was enhanced in the specimens prepared by HIPing the preforms pyrolyzed at 750°C, which might be due the more carbonization and the development of porous structure in the range 600-800°C. Scanning electron microscopy observations revealed the formation of micro-crystals (up to 8 μm in size) with facets in the HIPed specimens. In addition, the degree of crystallites in the specimen obtained from the preforms pyrolyzed at 750°C was higher than the preforms pyrolyzed at 650°C. The energy dispersive spectroscopy showed that crystals were of SiC because the atomic ratio of silicon and carbon atoms in the crystals was almost 1 : 1. The density of the specimens obtained by HIPing the preforms pyrolyzed at 750°C was (3.11 g/cm 3 ) more than the specimens obtained by HIPing preforms pyrolyzed at 650°C (2.95 g/cm 3 ). The HIPing process, in addition to densification, led to the formation and growth of β-SiC.

No abstract

A novel two-step process was used to investigate the microstructure and properties of porous CMCs prepared by HIPing the pyrolyzed composites of commercially available ZrO2 (TZ- 3YS), silicon powders and phenolic resin. In the first step, preforms with 70, 80 and 90 mass % of ZrO2 powders were prepared by the pyrolysis of ZrO2 / Si / Phenol Resin composites at 850 oC in vacuum. And, then the pyrolyzed preforms were HIPed at 1400 oC for 30 minutes in Argon atmosphere under a pressure of 50 MPa to fabricate the porous CMCs, in the second step. XRD analyses suggested the formation of β-SiC in the composites below the melting point of silicon. SEM photographs showed that spherical pores of several μm in diameter were uniformly distributed in the matrices of composites and crystals of β-SiC with facets were observed in the pores. EDS analyses showed that the crystals were composed of Si and C with 1 : 1 atomic ratio suggesting that crystal are SiC. The maximum hardness (13.78 GPa) was achieved from the composite with 90 mass % ZrO2, which is more than that of bulk hardness of ZrO2 (10-12 GPa).