Hyatt, Lizbeth H. | Search NASA

NASA NTRS1988

Fibers And Composites Derived From Silsesquioxanes

In new method, silsesquioxane powders blended to control ratio of carbon to silicon. Powders melted, and excess silanol groups condense with evolution of water. When melt attains suitable viscosity, extruded into fibers through die or drawn into fibers from melt at uniform rate. Fibers cured and heat treated. Enables easy fabrication of thermally stable fibers from inexpensive silsesquioxane precursors. Impregnation of fibers and preforms without solvent minimizes both shrinkage and formation of voids resulting from volatilization of trapped solvent.

Hurwitz, Frances I.↗

NASA NTRS1987

Silsesquioxanes as precursors to ceramic composites

Silsesquioxanes having the general structure RSiO sub 1.5, where R = methyl, propyl, or phenyl, melt flow at 70 to 100 C. Above 100 C, free -OH groups condense. At 225 C further crosslinking occurs, and the materials form thermosets. Pyrolysis, with accompanying loss of volatiles, takes place at nominally 525 C. At higher temperatures, the R group serves as an internal carbon soruce for carbo-thermal reduction to SiC accompanied by the evolution of CO. By blending silsesquioxanes with varying R groups, both the melt rheology and composition of the fired ceramic can be controlled. Fibers can be spun from the melt which are stable in argon in 1400 C. The silsesquioxanes also were used as matrix precursors for Nicalon and alpha-SiC platelet reinforced composites.

Hurwitz, Frances I.↗