Polymer‐Derived SiBN Fiber for High‐Temperature Structural/Functional Applications

Abstract

We report the fabrication of a SiBN fiber through pyrolysis of a novel polyborosilazane polymer. Preliminary findings show that this new ceramic fiber demonstrates structural/functional properties with high mechanical strength, a low and thermally stable dielectric constant, and excellent hightemperature resistance. Because of this combination of desirable properties, SiBN ceramic fiber has the potential to resolve a wide number of todays material challenges in high-temperature, radar-wave-transmitting applications.The rapid development of the aerospace industry and the generation of new high mach number aircrafts require new materials for electromagnetic windows or radomes to meet the stringent requirements of greater speed, higher temperature, and longer flight times. Such materials must have low density, high thermal stability, and a low and thermally stable dielectric constant with high mechanical strength. The ceramic fiber reinforced nitride ceramic matrix composites (FRCMCs) offer several advantages, such as high working temperatures, low ablation, and high mechanical strengths in high-temperature applications. [1,2] However, the mechanical and physical performances of FRCMCs are greatly influenced by the properties of the reinforcing fibers. The thermomechanical and -chemical properties of fibers always prescribe the atmosphere, temperature, and weaving capabilities in composite manufacture.[1] Therefore, performances of FRCMCs depend on the right selection of fibers with proper chemical and physical properties. [1,3] For composites to be useful in the above-described environments, the fibers should be lightweight, structurally stable, and mechanically strong at elevated temperatures. Moreover, they must possess excellent and thermally stable dielectric properties.Clearly, the selection of fibers suited for such applications is limited. Those fibers prepared from polymer pyrolysis are particularly attractive because of their fine diameter and flexibility to allow weaving and braiding. Furthermore, with this method, fiber properties, including density, dielectric properties, and tensile strength, can be tailored through control of the starting polymer and the curing and the pyrolysis steps. [3,4] Presently, SiC fibers, quartz fibers, Si 3 N 4 fibers, [5,6] and BN fibers [7][8][9][10] are the fibers available with potential applications in such areas. Each of these fibers has its individual peculiarities in properties. SiC fibers are the well-established fibers with excellent mechanical performances and thermal resistance, however, the inefficient dielectric properties resulting from the high carbon content cannot meet the practical requirements. [11,12] Quartz fibers are one of the most commonly used reinforcements in radome composites because of their excellent dielectric properties. [13][14][15][16] However, their low mechanical property at high temperature is the critical drawback, limiting their application to more hostile conditions. [1,16,17] In addition, quartz fibers are intrinsically prone to crys...

Microstructures and Properties of Ceramic Fibers of h-BN Containing Amorphous Si3N4

“…Table 3 summarizes the dielectric properties of BN fiber and composite fiber. The dielectric properties of other wave-transparent fibers [17] are also listed in Table 3. The dielectric constant and loss tangent of the BN/Si 3 N 4 composite fiber were 3.06 and 2.94 × 10 −3 , slightly higher than those of the h-BN fiber.…”

Fabrication and properties of borazine derived boron nitride matrix wave-transparent composites reinforced by 2.5 dimensional fabric of Si–N–O fibers

“…BN fiber also displays excellent high-temperature resistance and dielectric properties. However, the relative low oxidation temperature (~900 ºC) of the fiber makes it unsuitable for longtime use at elevated temperatures, especially for those BN f /BN composites [7,8]. In comparison, those polymer pyrolysis derived Si-B-N fiber, Si 3 N 4 fiber and Si-N-O fiber are particularly attractive because of their designable composition, fine flexibility as well as excellent high-temperature properties.…”

“…Ceramic fiber reinforced boron nitride ceramic matrix composites (FRCMCs), such as SiO 2f /BN, SiO 2f /Si 3 N 4 -BN, BN f /BN and SiBN f /BN composites, are attractive radome candidates for they combine the excellent dielectric properties and thermal resistance of BN ceramic with a non-brittle mechanical behavior [3][4][5][6][7][8]. However, the high temperature performance of the FRCMCs depends largely on the properties of the reinforcing fiber.…”

Nearly stoichiometric BN fiber by curing and thermolysis of a novel poly[(alkylamino)borazine]

“…Above 600 8C, carbon content decreased slower and reduced to 0.14 wt% at 1200 8C. With very low carbon content and nearly stoichiometric composition, the BN fiber is deemed to possess low dielectric constant and find application in wave transparent composites [5,25].…”