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Development of pyrolysis optimization methodology for carbon/carbon materials


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop and demonstrate a methodology for design and optimization of pyrolysis schedules to generate desirable carbon matrices for carbon-carbon composites. DESCRIPTION: Carbon-carbon composites (CCCs) have been utilized for hypersonics applications for decades. For much of that time, the state of the art in source materials, particularly for the matrix phase, has advanced slowly or not at all. Recently, however, a spate of new potential materials (particularly polymer resins) have been developed and are being evaluated as possible precursors for CCCs. The development and commercialization of these polymers represents an exciting opportunity to meaningfully advance the state of the art in CCC fabrication. However, to date, the manufacture of CCCs is still a long and expensive process, and the urgent and increasing DoD need for these materials in the short and medium term necessitates efforts to bring article lead times and cost down. Since CCC costs are primarily driven not by precursor material costs, but by processing costs, it is important to assess new potential precursor material solutions by the impact of their use on the efficiency of downstream processing steps, i.e., densification cycles. However, the efficacy of a given potential material solution is driven not only by the chemistry of the matrix precursor material, but by how that chemistry behaves during the pyrolysis cycle to which the material is subjected to render a carbon matrix [1]. The nature of the pyrolysis cycle determines several important factors of the resulting matrix and composite. First, the details of the pyrolysis cycle can affect the resulting char yield [2], which is a metric that receives a large amount of attention from polymer developers as they develop new materials. Second, the differences in pyrolysis cycle can influence the microstructure of the resulting voids left behind after pyrolysis [3], which can be large drivers of the efficiency of subsequent densification cycles. That is, for the purposes of redensification, it is desirable to have voids which are 1) of a size which can be efficiently filled by the carbon medium used downstream, and 2) highly connected throughout the part rather than closed and isolated. Third, the pyrolysis cycle parameters should allow for volatiles generated during the pyrolysis to leave the material quickly enough to avoid generating excessive pore pressures [4], which can lead to undesirable outcomes including destructive delaminations, which may render a CCC part unusable. Currently, there are no commercially available methods to guide resin development or to optimize the pyrolysis of new resins with an aim to improving any of the above metrics. Therefore, we seek the development of novel tools and approaches to optimization of pyrolysis cycles that will allow for more cost effective and efficient densification of CCCs for hypersonics applications. Such tools should be robust and broadly applicable to different chemistries of interest, rather than tailored exclusively to one particular chemistry, and be transitionable to DoD and industry partners. PHASE I: The offeror shall develop a method to optimize the pyrolysis cycle for one carbon precursor (e.g., resin or pitch) material of interest to the DoD hypersonics community. This method shall be demonstrated to achieve meaningful improvement of some aspect of the resulting carbon matrix in a CCC that is expected to result in materially improved efficiency of downstream densification cycles. Measured improvement will be in the context of a composite form relevant to DoD hypersonics needs, i.e., either a continuous fiber 2D or 3D woven carbon form of at least ½” thickness. Metrics of improvement may include 1) increase in char yield, wherein the offeror will show at least 10% improvement in char yield over the baseline case; 2) improved void microstructure for efficient redensification, wherein the improvement may be compared to the baseline case using void characterization techniques including, but not limited to, mercury intrusion porisimetry, pycnometry, computed tomography, or diffusivity measurement; or 3) any other reasonable metric commonly accepted by the CCC community as an indicator of expected improvement in densification efficiency. The baseline in all cases will be defined as a temperature ramp from room temperature to 1000°C at a rate of 5°C/min in an inert atmosphere, or some other reasonable pyrolysis cycle in common use in the industry. The offeror may make use of industry- and DoD-derived databases of pyrolysis processes if these are available, but as these will largely be proprietary, the offeror may need to conduct pyrolysis cycles independently to establish the necessary datasets for development of the tool. The offeror is encouraged to keep in mind the need to deliver a product that can be readily transitioned and commercialized at the end of the period of performance. PHASE II: The offeror shall expand the method developed in Phase I to demonstrate the broad applicability of the method to at least two additional carbon matrix precursor chemistries of interest to the DoD hypersonics community. The offeror will demonstrate improvement of pyrolysis cycle for downstream reinfusion/densification with, e.g., demonstration of more complete and uniform infusion of polymer resin into pyrolyzed composite compared to baseline. (Additional pyrolysis and reinfusions beyond this are not required.) The offeror shall deliver a method and toolset that can be readily transitioned and commercialized. The toolset may be standalone software, software modules that can be integrated into existing commercial software, an analytical model, or any other similar transitionable knowledge product. PHASE III DUAL USE APPLICATIONS: The offeror is expected to aggressively pursue opportunities to market the method developed herein for use in CCC fabrication for DoD-relevant hypersonics applications. REFERENCES: 1. “Simulating the Initial Stage of Phenolic Resin Carbonization via the ReaxFF Reactive Force Field”, De-en Jiang, Adri C. T. van Duin, William A. Goddard III, and Sheng Dai; J. Phys. Chem. A, 2009 2. “Modification of the pyrolysis/carbonization of PPTA polymer by intermediate isothermal treatments”, Alberto Castro-Muñiz, Amelia Martínez-Alonso, Juan M.D. Tascón; Carbon, 2008 3. “Effect of processing parameters on the mechanical properties of carbonized phenolic resin”, Chul Rim Choe, Kwang Hee Lee, Byung Il Yoon; Carbon 1992 4. “Stress and damage development in the carbonization process of manufacturing carbon/carbon composites”, Tiantian Yin, Yu Wang, Linghui He, Xinglong Gong; Comp. Mat. Sci., 2017 KEYWORDS: Carbon-carbon; pyrolysis; optimization; polymer design; hypersonics; materials; processing.
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