Rapid RF-based curing of nano-filled polycarbosilanes to produce silicon carbide structures
Abstract
Scientific Objectives: The objective of the proposed work is to evaluate the hypothesis that exposure to RF fields (~10 MHz Ð 10 GHz) will cause susceptor-loaded polycarbosilanes to undergo uniform volumetric heating and rapid curing to form silicon carbide (SiC). SiC-based composites are frequently used to meet a wide range of defense and aerospace needs as lightweight composites, semiconductors, and hard substrates for radar or power management. These materials may be prepared by high-temperature curing of polycarbosilanes (pre-ceramic polymers with Si-C backbones that act as SiC pre-cursors). Our prior ARO-funded work shows that exposure of carbon nanotube (CNT) networks in polymers to RF fields can generate a rapid, localized heating response, which has utility in welding and/or curing polymers. In the proposed work, we examine the RF dielectric coupling and heating response of CNT-loaded polycarbosilane, including high-temperature curing to form SiC structures; we will utilize theory and experiment to show how these properties connect to the underlying resistive/capacitive interactions in the CNT network. Research Plan: We will carry out experiments on RF-curing of polycarbosilanes in two overall research thrusts. In Thrust 1, we characterize the dielectric and heating properties of polycarbosilanes as a function of CNT loading, RF frequency, and temperature. We then study the RF-induced curing of the polycarbosilane to amorphous SiC; preliminary data show the first-ever demonstration of low-frequency (100 MHz) RF-curing of polycarbosilanes. Both the process (heating) and the results will be characterized using thermogravimetric, electromagnetic, and dielectric analysis, with special attention on uniformity of the cured samples. In Thrust 2, we extend this concept to include additional fillers in order to produce robust SiC structures. We will determine how CNT and SiC fillers affect the dielectric properties and RF energy coupling (heating response) as a function of RF frequency. We then examine the use of SiC particles as fillers to decrease porosity in RF-cured samples and then study the backfill-and-cure cycling process with RF as the energy source. Mechanical properties will be determined by four-point bending tests. We also demonstrate that this process can be extended to rapid layer-by-layer buildup of uniform SiC structures by depositing polycarbosilane and scanning the samples over RF applicators. Given the proper rheological properties, such a process may even be carried out in a mold-free setup. Finally, we examine how RF-curing of CNT-loaded polycarbosilane will function in an infiltrated ceramic matrix composite (CMC) reinforced with carbon or SiC fibers. Outcomes and Significance to ARO: The proposed work generates new fundamental knowledge in the area of energy-coupled-to-matter with RF interactions with CNT-loaded polycarbosilane as a model system for field-heated-curable resins. The rapid heating response of the system may enable new SiC-based structures and processing techniques. Our experimental plan will connect the as-measured properties to the underlying microstructure of the CNT network and the dynamic dielectric properties of the matrix as it cures to form SiC. This work will affect a wide range of scientific communities, from ceramics to polymer composites and RF/microwave engineering.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1810109
Entities
People
- Micah J Green
Organizations
- Army Contracting Command
- Texas Engineering Experiment Station
- United States Army