Experiments to produce polycarbosilazane resin and high‐strength silicon carbide–silicon nitride (SixNyCz) fibers as well as resin/fiber characteristics are reported. Polycarbosilazane resin was drawn into fibers from the melt and subsequently treated and pyrolyzed into SixNyCz fibers. These materials are characterized by high tensile modulus (29 × 106 psi for 0.4‐mil diameter) and high electrical resistivity (6.9 × 108 Ω·cm for 0.6‐mil diameter).

The development of silicon carbide-silicon nitride (SIC-Si3N4) fibers by the pyrolysis of polycarbosilazane precursors that was carried out in this laboratory is reviewed. Precursor resin, which was prepared by heating tris(Nmethylamino]methylsilane or tris(N-methylaminolphenylsilane to about 520°C. was drawn into fibers from the melt and then made unmeltable by humidity conditioning at 100°C and 95 percent relative humidity. The humiditytreated precursor fibers were pyrolyzed to ceramic fibers with good mechanical properties and electrical resistivity. For example, SiC-Si3N4 fibers derived from tris(N-methylamino)-methylsilane had a tensile rupture modulus of 29 X lo6 psi and electrical resistivity of 6.9 x 1 O8 R-cm, which is 10l2 times greater than a value obtained for graphite fibers.

A thermal conductivity measuring apparatus that uses heat flow sensors to measure the heat flux through samples was constructed of inexpensive materials. This device was used to measure the thermal conductivity (k) of two composites used in the space program that consist of fibrous or granular components embedded in a resin matrix. The k‐values that were determined ranged from 0.035 to 0.059 Btu/h‐ft2‐°F/ft (−163 to 553°F) and 0.029 to 0.035 Btu/h‐ft2‐°F/ft (77 to 212°F). Thermal conductivity values of the composites conformed to the rule of mixture. The accuracy of the system was found to be comparable to the guarded hotplate and it requires neither a skilled operator nor extensive maintenance.

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