Precursor impregnation and pyrolysis (PIP) processing of barium Aluminosilicate- Nicalon composites

摘要

Efforts were made to evaluate the utility of thepolymer precursor method of processing Nicalon fiberreinforced barium aluminosilicate (BAS) composites. A novelprecursor, synthesized in one step from BaO, Al(OH)_3 andSiO_2 was used. This precursor, with a ceramic yield of ? 30 wt.percent, was used to assess three forms of PIP processing. Fiberpreforms consisting of 4-12 0/90 deg cross-woven Nicalon plieswere impregnated with precursor/ethanol solutions at ambientpressure and under vacuum/pressure. Impregnated preformswere typically fired in air to 550 deg C to remove carbon andform a structurally intact composite. Cycle times were 12 h.Amorphous densities approaching 60-70 percent of theory (ruleof mixtures) were achieved with the fewest PIP cycles by theapplication of vacuum to the samples before infiltration, the useof pressure to infiltrate the samples and increasing the ceramiccontent of the precursor solution. Strontium aluminosilicate(SAS) was added to promote the hexagonal to monoclinic phase transformation.