In this paper,X-ray photoelectron spectroscopy,X-ray diffraction,scanning electron microscopy and Raman spectroscopy were employed to study the surface physical and chemical properties of silicon carbide fi-bers with low oxygen and high carbon.Results show that fiber surface is smooth and compact,and disorderd free carbon exists in the surface of the fibers,which is in accordance with the chemical compositon of fibers.Al-so,the surface of fibers is mainly composed by SiOx Cy ,followed by SiC,and SiO2 .The fiber surface physical and chemical properties can help the combination of fibers and matrix with proper strength,which is beneficial to enhance the strength and improve the fracture toughness of the composite materials.

SiNO ceramic has very excellent comprehensive properties and is one of the best candidates for ceramic matrix composites.In this work,influences of pyrolysis and curing conditions on the SiNO ceramic prepared with pyrolysis nitridation are systematically studied.The results show that decarbonization is completed before 800 ℃ with carbon residue lower than 1%(by mass).After pyrolysis in N2,nitrogen content is as high as 35.65%(by mass).Oxidation curing before ammonolysis can improve ceramic yield.The ceramic yield is 61.84%(by mass)but the nitrogen content decreases significantly(below 20%)by mass,and the product is amorphous SiNO ceramic.Therefore,high-yield and low-carbon-content SiNO ceramic can be prepared with pyrolysis nitridation of polycarbosilane.

In this work,it was systematically studied that how oxygen content of cured cobalt-containing polycar-bosilance (PCS)fibers influences the structure and properties of cobalt-containing silicon carbide(Co-SiC)fi-bers.Compared to cured Co-PCS-air fibers,Co-PCS-O2 fibers have a higher oxygen content and higher ceramic yield.For Co-PCS-O2 fibers derived from cured Co-PCS-O2 ,lower pyrolysis temperature was required to reach maximum mechanical properties.And higher SiCx Oy content,higher growing speed and final sizes ofβ-SiC and CoSi grains and lower electrical conductivity were observed.Co-PCS-O2 fibers have a electrical conductivity con-trollable between 100- 103Ω??cm and were magnetic to some degree,enabling this kind of fibers to have the po-tential to be used as wave-absorbing materials.

Cobalt-containing silicon carbide (Co–SiC) fibers were synthesized through a colloidal method.

In this work,PCS fibers,cured with different oxygen contents,were conducted by pyrolysis nitrida-tion for carbon removal and amination in the ammonia atmosphere,and then through condensation/nitridation reaction at high temperature in the nitrogen atmosphere to produce silicon oxynitride fibers.Results of XRD, EPMA and TEM showed that,all of the elements in the ceramic fibers dispersed uniformly,and as the oxygen content in the cured fibers increased,it also increased in the ceramic fibers but with a drop in mechanical prop-erties.However,the ceramic yield rose first and then fell because of the phase decomposition at high tempera-ture.Indicated by the results of XRD and TEM,even after heat treatment at 1 500 ℃,ceramic fibers were still amorphous regardless of how much the oxygen content was.The oxygen maybe play a role like impurity in the fibers,which inhibites the crystallization of silicon nitride.

In this work,PCS cured fibers were pyrolysis nitridation in the ammonia atmosphere for carbon re-moval and amination,and then condensation/nitridation reaction at high temperature in the nitrogen to produce Si3 N4 fibers.Results showed that as-prepared Si3 N4 fibers were colorless and transparent.What was more,the skin of the fiber was smooth and the cross section was rather dense without identifiable defects.This paper also discussed the mechanism of nitridation and the influence of pyrolysis conditions on the structure and properties of Si3 N4 fibers.The results of FT-IR spectra and elemental analysis showed that the carbon content was ex-tremely low after amination and pyrolysis,which was less than 1%,while the nitrogen content increased with the elevated pyrolysis temperature,and the oxygen content first increased and then decreased with the elevated pyrolysis temperature.The fibers were amorphous when the pyrolysis temperature was less than 1500℃,while the tensile strength reached a maximum at 1300℃.The processes of pyrolysis nitridation were a process of de-carburization and ammonification,and then condensation/nitridation at high temperature in the nitrogen,finally producing Si3 N4 fibers.