Amorphous silicoboron carbonitride ceramic with very high viscosity at temperatures above 1500°C

Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si1.7C1.0+/-0.1N1.5) alloy with an apparent glass-transition temperature (T-g) of 1400 degrees-1500 degrees C was studied. In this study, the creep behavior of silicoboron carbonitride (Si(2)B(1.0)C(3.4)N2(.3)), which seems to have a T(g)value of >1700 degrees C, was examined. Both materials exhibited a three-stage creep behavior. In stage I, the creep rate declined, because of densification, In stage II, the strain rate approaches a steady state. In stage III, it resumes a declining strain rate, which ultimately decreased below the measurement limit of the system. At 1550 degrees C in stage II, the viscosity of silicoboron carbonitride was six orders of magnitude higher than that of fused silica, Among the Si-C-N ceramics, only chemical-vapor-deposited and reaction-bonded silicon carbides seem to have greater creep resistance than the silicoboron carbonitrides at temperatures >1550 degrees C.