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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

High-Temperature-Performance Cyanate Ester Composites with Carboranes

Cyanate ester (CE) is an important class of materials among high-temperature performance thermosets. It is used in aerospace launch vehicles, heat sinks, booms, and trusses of satellites etc. due to its high glass transition temperatures (>220°C), excellent thermal stability, and low flammability. Current approaches to improve the thermal stability of CE include incorporation of siloxanes or phosphorus- based flame retardants (PFRs). In this work, we have explored boron-based hydroxy (PD) and epoxy (EP) functionalized carborane additives to improve the thermal properties of CE. Carborane fillers were solvent blended at various mass loadings in the resin and cured to study their effect on thermal properties. PD and EP carboranes react with CE to form iminocarbonate and oxazolidinone linkages respectively. Cure kinetics studies at different wt% loadings explained that carboranes catalyze the curing reaction by reducing curing activation energy by about 54% and 26% for 10 wt% loadings of PD and EP carboranes respectively. In addition, carborane-filled cyanate ester (CE) nanocomposites demonstrate an exceptionally high thermal stability as compared to the pristine resin in air and inert environment. Our thermogravimetric analysis (TGA) experiments show that the ultimate char yield of the resin can be increased from 0% to as high as 76% and 82% with 30 wt% PD and EP carborane loading respectively at 1000 °C in air. The initial degradation temperature T d;5 of the composites decreased with increasing carborane loadings in both air and argon. For instance, T d;5 for CE was 465 and 471.6 °C in argon and air while that for P20 was 437.4 and 452.1 °C. Modulated TGA studies gave evidence of the effect of carboranes on degradation kinetics and the mechanism of the resin in air and inert environment. The effect of bonding between carboranes and CE at various loadings on the thermal expansion of the matrix was also studied using Thermomechanical Analyzer (TMA). PD carborane reduced the T g for P20 to about 225 °C while CE had T g >350 °C.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Reduced graphene oxide catalytically enhances the rate of cyanate ester curing under variable frequency microwave heating

Here, the curing of Lonza Primaset PT-30 novolac cyanate ester resin and EPON 826 bisphenol-A diglycidyl ether were investigated using convective thermal heating and variable frequency microwave (VFM) heating. The addition of 1 part per hundred reduced graphene oxide (r-GO) to PT-30 novolac cyanate ester increased the VFM cure rate compared to thermal heating. Curing it at 160°C for 240 min with VFM heating resulted in a 55% degree of cure compared to a 26% degree of cure with thermal heating. This observed VFM rate enhancement is due to selective microwave heating of the r-GO particles in the resin resulting in increased r-GO catalytic activity toward cyanate ester curing. It is both a thermal and catalytic effect, the latter of which is absent when r-GO is added to a bisphenol-A diglycidyl ether resin with o-phenylenediamine hardener. Impurities present in the PT-30 matrix do not appear to contribute to its overall cure kinetics, nor do they participate in the observed VFM rate enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2024

MOLLER Spectrometer Magnet Design With Measured Mechanical Properties of Irradiated S2-Glass Reinforced Cyanate Ester Resin at Elevated Temperature

Here, the aim of this study was to retire the risk of maintaining the integrity of S2-glass reinforced CTD-403 (a cyanate ester resin) that is exposed to radiation and elevated temperature over the life of the measurement of a lepton–lepton electroweak reaction (MOLLER) experiment in experimental Hall A at Jefferson Lab, Newport News, VA. In this article, the shear strength and flexural modulus of irradiated S2-glass reinforced CTD-403 specimens were measured at 65 °C (the magnets are to operate at less than 65 °C) under two scenarios: vacuum and gaseous nitrogen. The testing method is the short-beam shear (SBS) test according to ASTM D2344. The specimens were exposed to neutrons and gamma rays up to 124 MGy. The results show that specimens have excellent resistance against radiation, only 23% degradation of apparent shear strength with 124 MGy at 65 °C under vacuum. At the highest dose areas of the coils, tungsten plates are used to reduce the radiation dose to the resin system. The conclusion is that S2-glass reinforced CTD-403 is well-suited for electrical insulation of MOLLER magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanical Properties of High-Temperature Fiber-Reinforced Thermoset Composites with Plain Weave and Unidirectional Carbon Fiber Fillers

Fiber-reinforced thermoset composites are a class of materials that address the arising needs from the aerospace and hypersonic industries for high specific strength, temperature-resistant structural materials. Among the high-temperature resistant thermoset categories, phenolic triazine (PT) cyanate esters stand out thanks to their inherent high degradation temperature, glass transition temperature, and mechanical strength. Despite the outstanding properties of these thermosets, the performance of carbon fiber composites using PT cyanate esters as matrices has not been thoroughly characterized. This work evaluated PT and carbon fiber composites’ compressive properties and failure mechanisms with different fiber arrangements. A PT resin with both plain weave (PW) and non-crimped unidirectional (UD) carbon fiber mats was analyzed in this research. Highly loaded thermoset composites were obtained using process temperatures not exceeding 260 °C, and the composites proved to retain compressive strength at temperatures beyond 300 °C. Compressive testing revealed that PT composites retained compressive strength values of 50.4% of room temperature for UD composites and 61.4% for PW composites. Post-compressive failure observations of the gage section revealed that the mechanisms for failure evolved with temperature from brittle, delamination-dominant failure to shear-like failure promoted by the plastic failure of the matrix. This study demonstrated that PT composites are a good candidate for structural applications in harsh environments.

Hall, Samuel Ernesto↗
DOE OSTI2025

Extreme Thermal Stabilization of Carborane–Cyanate Composites via B–N Dative-Bonded Boroxine Barriers

Enhancing the thermal stability of cyanate ester (CE) resins is crucial for high-temperature aerospace applications. This study elucidates the degradation mechanisms of CE composites reinforced with carborane additives, focusing on the formation of boron–nitrogen (B–N) dative bonds and their role in improving thermal resistance. Using thermogravimetric analysis, we examined char formation and evolved gases at multiple degradation stages. Reaction sequences and char products were characterized via Fourier transform infrared spectroscopy (FTIR), solid-state 13C and 11B NMR, and evolved gas analysis using mass spectrometry and FTIR. The solid-state 11B NMR was instrumental in detecting various boron oxidation states and the formation of B–N dative bonds during decomposition. These bonds facilitate cross-linking in the char phase, enhancing material integrity at elevated temperatures. However, in inert environments, the volatility of boron additives like carborane limits their effectiveness. These findings advance the understanding of CE composite degradation mechanisms and offer critical insights for developing high-temperature-resistant materials for aerospace applications.

Fourier transform infrared spectroscopy↗
DOE OSTI2025

Predicting Thermoset Resin Cure Kinetics for Composite Processing

Predicting a material’s thermal properties is not only useful for designing parts but also for defining processing parameters. This is especially applicable to wet-filament winding operations and the production of composite parts using thermoset res ins. For these, the formation of cross-linking bonds is affected by time and temperature, but the degree of cross-linking can be modeled using phenomenological methods. In the current study, the Kissinger and Flynn/Wall/Ozawa methods were both used to calculate kinetic parameters and produced values that were in agreement with each other. The kinetic parameters activation energy ( E a ) and pre-exponential factor (𝐴) calculated from exothermic peak data increased between an epoxy and resole phenol resin system, with a cyanate ester having the highest. The successful application of both methods suggests applicability to future studies for developing cure recipes.

36 MATERIALS SCIENCE↗