Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics.

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.

Compact fiber-coupled UV-NIR hyperspectral imaging sensor for characterizing ultra-high temperature ceramic materials.

A compact fiber-coupled hyperspectral imaging sensor (HSIS) operating within the range of ultraviolet to near-infrared (UV-NIR) wavelengths is designed and developed for the remote recording of two-dimensional (2D) spectrally resolved thermal radiation and chemiluminescent emission from ultra-high-temperature ceramics (UHTCs). Using simulations, the entire system is optimized to improve the collection efficiency and minimize aberrations. The design, construction, and characterization of the HSIS sensor are discussed in detail. We present the 2D spectrally resolved measurements of the simultaneous thermal radiation and BO2∗ chemiluminescent emission from a commonly used UHTC (HfB2-SiC) material under high-heat-flux conditions. Our results show that BO2∗ chemiluminescence corresponds directly to material ablation and can be used to track the formation of the protective heat-resistant glass/oxide layer. Furthermore, the temperature measurements demonstrate the heat distribution properties of the sample and indicate the locations at which BO2∗ chemiluminescence is possible. These results highlight the application prospects of the compact fiber-coupled HSIS for high-temperature material characterization in practical arc-jet facilities with limited optical access.