The preparation of aluminumcontaining silicon carbide

SiC(Al)

fibers by using polyaluminocarbosilane (PACS) and polycarbosilane (PCS) blends as precursors was investigated.The solubility parameter of PACS was determined to be 18 MPa1/2by dissolving PACS in solvents with different solubility parameters.It was very close to the solubility parameter of PCS (18.4 MPa1/2)

indicating the possible compatibility of PACS and PCS.After PACS and PCS both were dissolved in xylene

a translucent yellow blend of PACS and PCS

B-PACS

was obtained by distillation.The composition and structure of BPACS

PACS and PCS were characterized by chemical analysis

GPC and FTIR.It was found that B-PACS with desirable Al contents could be obtained by adjusting the ratio of PACS (Al content 1.25 wt%) and PCS.The Si—H bond content can be indicated by A2100 cm-1/A1250 cm-1

where A2100 cm-1

A1250 cm-1 are the absorbance of Si—H bonds at 2100 cm-1 and CH3 bonds at 1250 cm-1

respectively.The FTIR results showed that the Si—H bond content of B-PACS was higher than that of PACS

while their Al contents were the same.PCS with a higher Si—H content might be responsible for the higher Si—H content of B-PACS.GPC results showed that B-PACS had a high molecular weight fraction as compared with PACS of the same Al content.The apparent activation energy of flow for B-PACS and PACS (Al content 0.6 wt%) was determined by the relationship between temperature and melt viscosity.They were 200 kJ/mol and 255 kJ/mol

respectively.The better spinnability of B-PACS was approved by spinning experiments

and finer BPACS green fibers were obtained.The tensile strength of Si-Al-C-O fibers from PACS and B-PACS were 2.0 GPa and 2.4 GPa

respectively.The higher strength of Si-Al-C-O fibers from B-PACS might be related with the finer diameter of the green fibers and the high molecular weight fraction in B-PACS.The SiC(Al) fibers derived by curing PACS and B-PACS green fibers at 1800℃ in Ar were compact and smooth

while the SiC fibers derived from PCS had pores and defects.The introduction of Al into SiC fibers may reduce the growth of SiC crystallites in fibers.The average sizes of SiC crystallites in fibers derived B-PACS

PACS and PCS were 8.5 nm

9.6 nm and 14 nm

respectively.