Preceramic Polymers; Synthesis, Processing, Modeling, and Derived Ceramics: Preceramic Polymers and Polymer Derived Ceramics II
Sponsored by: ACerS Engineering Ceramics Division
Program Organizers: Matthew Dickerson, Air Force Research Laboratory; Gurpreet Singh, Kansas State University; Paolo Colombo, University of Padova; Günter Motz, Universität Bayreuth
Wednesday 2:00 PM
October 20, 2021
Room: B230
Location: Greater Columbus Convention Center
Session Chair: Gurpreet Singh, Kansas State University
2:00 PM
Effect of Pendant Groups on the Mass Yield, Density and Process Modeling of Polycarbosilanes during Pyrolysis: Thomas Key1; Garth Wilks2; Michael Cinibulk2; 1UES Inc; 2Materials & Manufacturing Directorate, Air Force Research Laboratory, RXCC
As preceramic are pyrolyzed, they undergo multiple thermal decomposition reactions. Differences in initial composition leads to differences in thermal decomposition of the polymers. These differences then affect the evolution of density of the polymers in a ways that dramatically affect their volume yield as a function of pyrolysis temperature. Experimental data indicated that the material models addressing volumetric changes during pyrolysis must be able to address both the temperature and time at temperature dependent changes in mass and material density, because density is not a simple function of mass yield. The model analysis of the materials performance revealed two major spikes in the rate of volume shrinkage where the first is initially driven by changes in mass changes but is quickly overcome by density’s dominant contribution to changes in volume for both peaks. This indicates the importance changes in material density in predicting the volume yield of preceramic polymers.
2:20 PM Invited
Atomistic Simulations of Polymer Pyrolysis: Peter Kroll1; 1University of Texas at Arlington
Polymer-derived ceramics are processed via the thermal treatment of polymer precursors. Chemical reactions during thermal processing convert the hybrid organic-inorganic polymer into an amorphous ceramic. A persistent challenge is to address how precursor architecture and processing conditions affect a final material. Computational studies of the principal chemical reactions during processing are scarce, not at least due to the complexity of the problem arising on different time and length scales.Here we present atomistic simulations of the polymer pyrolysis of polysiloxanes and polysilazanes. We use both ab-initio as well as empirical reactive force field (ReaxFF) Molecular Dynamic Simulations. We observe detailed mechanisms of cross-linking and elimination reactions, yielding intra- and inter-chain coupling. Kumada-like rearrangements incorporate carbon into the -Si-O- and -Si-N- polymer backbone. Segregation of excess carbon occurs into poly-aromatic hydrocarbons. Continuing annealing goes along with significant mass loss, and systems evolve into SiCO and SiCN ceramics, respectively.
2:50 PM
Organics Matter: Common Features in Energetics of Polymer Derived Ceramics, Metal Organic Frameworks, and other Hybrid Materials: Alexandra Navrotsky1; 1Arizona State University
Hybrid materials are solids containing both organic and inorganic constituents bound together in crystalline or amorphous structures, often showing distinct ordering and/or phase separation on the nanoscale. Relatively strongly bound examples include simple salts of organic cations, hybrid perovskites where organic cations substitute for large inorganic ones, polymer derived ceramics and their precursors, and metal organic frameworks (MOFs), in which inorganic nodes are connected by organic linkers. More weakly bound examples include intergrowths of organic and inorganic films or fibers, where the interactions occur mainly at interfaces. Advanced solution calorimetry measures their formation energetics. The organic ion, linker, or layer plays a dominant role in energetics because of its ability to change its geometric configuration, affecting both vibrational and electronic structures, and giving rise to interplay between enthalpy and entropy effects.
3:10 PM
Thermal and Rheological Properties of Preceramic Polymer Grafted Nanoparticles: Kara Martin1; Ravichandran Kollarigowda2; Caitlyn Clarkson3; Christina Thompson4; Subramanian Ramakrishnan2; Matthew Dickerson5; 1UES, Inc; 2FAMU-FSU College of Engineering; 3NRC Research Associateship Program; 4Southwest Ohio Council for Higher Education (SOCHE) Program; 5Air Force Research Lab
Ceramic matrix composites (CMC) offer unique material properties, including extreme temperature stability, making them advantageous for use in aerospace research. CMCs can be fabricated through polymer infiltration and pyrolysis (PIP), which requires repetition for full part densification due to porosity formed from polymer thermolysis. Addition of inorganic fillers can offset porosity but the dispersion rheology can be poor due to particle aggregation. Grafting polymers to fillers is a dependable method for stabilizing polymer/particle mixtures, but is an unexplored area for preceramic polymers. In this presentation, we detail our method of hydrosilylation grafting-from used to graft polycarbosilane brushes on silica. We demonstrate how changing the brush composition can impact rheological and thermal behaviors of the grafted particle, as well as the ceramic composite. The goal of this research is to design new preceramic materials that maintain advantageous rheological properties for common processing methods like PIP.
3:30 PM Break
3:50 PM Invited
Molecules, Polymers, and Rings: Preceramic Compounds for AsB Formation: Brandon Ackley1; Rory Waterman2; 1ARCTOS Technology Solutions; 2University of Vermont
Boron arsenide has been proposed as a semiconductor for solar applications due to its band gap (1.82 eV) and excellent thermal conductivity (1,300 W/mK at 300 K). Cubic arsine borane (AsB) is formed via the reaction of elemental boron and arsenic at temperatures over 1,100 °C, yet the formation of pure AsB is challenging due to the decomposition of AsB to boron subarsenide (As2B12) at 920 °C. The degradation to As2B12 hinders traditional processing and formation methods, however, using cyclic arsineborane preceramic molecules and polymers allows for the formation of AsB without detectable amounts of As2B12 as observed through XRD. There is no appreciable difference in ceramic obtained by using precursors with molecular weights ranging from 700 Da to 2,400 Da, though it is suspected that weak bonds between As and B prevent longer chain growth. This method was expanded and used in the formation of other III/V ceramics.