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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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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Prediction of curing kinetics of resorcinol‐added resole phenolic resins using differential scanning calorimetry for the fabrication of carbon/carbon composites

Phenolic resins are commonly used as carbon precursors for the fabrication of carbon/carbon composites due to their high carbon yield and aromatic nature. To decrease curing times, acid catalysts are generally used, but the addition of resorcinol was found to have a similar effect while being incorporated into the resin matrix with no contamination or corrosion issues. In this work, the curing kinetics of pure, 10, 20, and 30 wt% resorcinol-added phenolic resins were investigated through differential scanning calorimetry. Heating rates of 0.5, 1, 2.5, and 5°C min -1 were used with several curing models to predict isothermal curing. Averaged mean absolute error (MAE) for the isoconversional mathematical approaches namely Kissinger–Akahira–Sunose (MAE = 12.9 min), Flynn–Wall–Ozawa (15.8 min), and Vyazovkin (14 min) show that these methods provide the best predictions, attributed to their adoption of an activation energy that depends on the extent of cure (E a (α)). The Kissinger method (MAE = 36 min), which depends only on peak temperature with a constant activation energy assumption, and the data noise sensitive Friedman model (MAE = 1144.7 min) provide the least accurate results. Thermogravimetric analysis revealed that resorcinol decreases the curing times by up to 71% without lowering carbon yield.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Storing Co 2 in Built Infrastructure: Co 2 Carbonation of Precast Concrete Products

The overall objective of the proposed study was to advance the technical understanding of CO 2 incorporation into novel cementitious materials for the development of high value products that provide a net reduction in carbon emissions. This project combined two primary phases of research that addressed technical barriers related to (i) optimizing CO 2 storage capability of cementitious materials, (ii) evaluating and enhancing physical properties of novel carbonated materials, and (iii) assessing the reductions in life cycle CO 2 emissions attributed to CO 2 carbonation of precast cementitious materials. Engineered cementitious composites (ECC) are a class of highly ductile concrete composites that have been shown to be very durable when used in the built environment. CO 2 carbonation of ECC was examined in this study and it was found that precast ECC specimens could sequester up to 35% CO 2 by cement mass after 24 hours of curing at a CO 2 pressure of 0.5 MPa and 23°C and had a strain capacity of 3%. Carbonation conditions were optimized at the bench-scale and then utilized to create full-scale CO 2 -cured ECC railroad ties that were field tested on a train track. Rail ties were selected for this initial assessment of CO 2 storage in precast concrete materials due to the large market for concrete ties in the railroad industry. Although the full-scale rail ties passed all of the required American Railway Engineering and Maintenance-of-Way Association qualifying mechanical tests, on-track testing of the CO 2 -cured ECC rail ties was unsuccessful due to fiber alignment in the ECC the during the rail tie casting process which prevented the material from achieving the expected level of strain capacity. This result highlights the challenge in scaling up bench-scale processes to full-scale product manufacturing and requires additional investigation into the casting process of large-scale infrastructure elements using ECC combined with carbonation curing. Life cycle assessment of a CO 2 -cured ECC rail tie versus a traditional concrete rail tie indicates that the ECC tie can have lifecycle carbon savings of between 11% and 51% depending on how much longer its useful lifetime is compared to traditional concrete rail ties. Both carbon and cost savings are driven by a reduction in the need to replace broken rail ties, so the key factor is the extent to which a CO 2 -cured ECC rail tie will have increased lifetime durability compared to alternative rail ties.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRSDate not supplied

Detection and Localization of a Fold, Twist, and Overlaps within Tow-Steered Composite Panels During Autoclave Cure

Because of the anisotropic properties of carbon fiber reinforced polymer (CRFP) composites, novel layup architectures, such as tow-steering, can be used to tailor mechanical properties of the composite structure to the loading condition during use. In this work, a tow-steered composite panel was de-signed, laid up using the Integrated Structural Assembly of Advanced Com-posites (ISAAC) automated fiber placement (AFP) machine located at the NASA Langley Research Center (LaRC), and cured while simultaneously be-ing inspected using an ultrasonic inspection system operating inside the auto-clave. The composite panel contained overlaps that are intrinsic to the tow-steered design and had intentionally introduced layup defects including folds, wrinkles, splices, tow twists, foreign object debris (FOD), gaps, and additional overlaps. The inspections during the cure cycle focused on the ar-ea within the laminate containing a fold, a twist, and intrinsic overlaps. The ultrasonic inspections performed during the cure cycle were analyzed and compared to post-cure ultrasonic inspections of the entire laminate.

Composites↗
NASA NTRSDate not supplied

Detection and Localization of a Fold, Twist, and Overlaps within Tow-Steered Composite Panels During Autoclave Cure

Because of the anisotropic properties of carbon fiber reinforced polymer (CRFP) composites, novel layup architectures, such as tow-steering, can be used to tailor mechanical properties of the composite structure to the loading condition during use. In this work, a tow-steered composite panel was de-signed, laid up using the Integrated Structural Assembly of Advanced Com-posites (ISAAC) automated fiber placement (AFP) machine located at the NASA Langley Research Center (LaRC), and cured while simultaneously be-ing inspected using an ultrasonic inspection system operating inside the auto-clave. The composite panel contained overlaps that are intrinsic to the tow-steered design and had intentionally introduced layup defects including folds, wrinkles, splices, tow twists, foreign object debris (FOD), gaps, and additional overlaps. The inspections during the cure cycle focused on the ar-ea within the laminate containing a fold, a twist, and intrinsic overlaps. The ultrasonic inspections performed during the cure cycle were analyzed and compared to post-cure ultrasonic inspections of the entire laminate.

Composites↗
NASA NTRS2014

Applying a Stiffened Stitched Concept to Shear-Loaded Structure

NASA and The Boeing Company have worked to develop new low-cost, lightweight composite structures for aircraft. A stitched carbon-epoxy material system was developed to reduce the weight and cost of transport aircraft structure, first in the NASA Advanced Composites Technology (ACT) Program in the 1990's and now in the Environmentally Responsible Aviation (ERA) Project. By stitching through the thickness of a dry carbon fiber material prior to cure, the need for mechanical fasteners is almost eliminated. Stitching also provides the benefit of reducing or eliminating delaminations, including those between stiffener flanges and skin. The stitched panel concept used in the ACT program used simple blade-stiffeners as stringers, caps, and clips. Today, the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept is being developed for application to advanced vehicle configurations. PRSEUS provides additional weight savings through the use of a stiffener with a thin web and a unidirectional carbon rod at the top of the web which provides structurally efficient stiffening. Comparisons between stitched and unstitched structure and between blade-stiffened and rod-stiffened structure are presented focusing on a panel loaded in shear. Shear loading is representative of spar loading in wing structures.

Jegley, Dawn C.↗
NASA NTRS2013

Applying a Stitched, Rod-Stiffened Concept to Heavily Loaded Structure

NASA and the Boeing Company have worked to develop new low-cost, light-weight composite structures for aircraft. A stitched carbon-epoxy material system was developed to reduce the weight and cost of transport aircraft wing structure, first in the NASA Advanced Composites Technology (ACT) program in the 1990's and now in the Environmentally Responsible Aviation (ERA) Project. By stitching through the thickness of a dry carbon fiber material prior to cure, the labor associated with panel fabrication and assembly can be significantly reduced and the need for mechanical fasteners is almost eliminated. Stitching provides the benefit of reducing or eliminating delaminations, including those between stiffener flanges and skin. Stitching also reduces part count, and therefore, cost of the structure. The stitched panel concept used in the ACT program in the 1990's used simple blade-stiffeners as stringers, caps and clips. Today, the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept is being developed for application to advanced vehicle configurations. PRSEUS provides additional weight savings through the use of a stiffener with a thin web and a unidirectional carbon rod at the top of the web which provides structurally efficient stiffening. A comparison between the blade-stiffened structure and PRSEUS is presented focusing on highly loaded structure and demonstrating improved weight reduction.

Jegley, Dawn C.↗
NASA NTRS1994

The effect of Low Earth Orbit exposure on some experimental fluorine and silicon-containing polymers

Several experimental fluorine and silicon-containing polymers in film form were exposed to low Earth orbit (LEO) on a Space Shuttle flight experiment (STS-46, Evaluation of Oxygen Interaction with Materials, EOIM-3). The environmental parameters of primary concern were atomic oxygen (AO) and ultraviolet (UV) radiation. The materials were exposed to 2.3 plus or minus 0.1 x 10(exp 20) oxygen atoms/sq cm and 30.6 UV sun hours during the flight. In some cases, the samples were exposed at ambient, 120 C and 200 C. The effects of exposure on these materials were assessed utilizing a variety of characterization techniques including optical, scanning electron (SEM) and scanning tunneling (STM) microscopy, UV-visible (UV-VIS) transmission, diffuse reflectance infrared (DR-FTIR), x-ray photoelectron (XPS) spectroscopy, and in a few cases, gel permeation chromatography (GPC). In addition, weight losses of the films, presumably due to AO erosion, were measured. The fluorine-containing polymers exhibited significant AO erosion and exposed films were diffuse or 'frosted' in appearance and consequently displayed dramatic reductions in optical transmission. The silicon-containing films exhibited minimum AO erosion and the optical transmission of exposed films was essentially unchanged. The silicon near the exposed surface in the films was converted to silicate/silicon oxide upon AO exposure which subsequently provided protection for the underlying material. The silicon-containing epoxies are potentially useful as AO resistant coatings and matrix resins as they are readily processed into carbon fiber reinforced composites and cured via electron radiation.

Connell, John W.↗
NASA NTRS2004

High Temperature Transfer Molding Resins: Preliminary Composite Properties of PETI-375

As part of an ongoing effort to develop materials for resin transfer molding (RTM) of high performance/high temperature composites, a new phenylethynyl containing imide designated as PETI-375 has been under evaluation. PETI-375 was prepared using 2,3,3 ,4 - biphenyltetracarboxylic dianhydride (a-BPDA), 1,3-bis(4-aminophenoxy)benzene and 2,2 - bis(trifluoromethyl)benzidine and endcapped with 4-phenylethynylphthalic anhydride. This material exhibited a stable melt viscosity of 0.1-0.4 Pa sec at 280 C. High quality, void-free laminates were fabricated by high temperature RTM using unsized T-650 carbon fabric and evaluated. After curing for 1 hour at 371 C, the laminates exhibited a glass transition temperature of approx. 375 C by thermomechanical analysis. The laminates were essentially void and microcrack free as evidenced by optical microscopic examination. The chemistry, physical, and composite properties of PETI-375 will be discussed.

Connell, J. W.↗
DOE OSTI2022

Microbial Curing of Cement for Energy Applications

Rutgers University, Lawrence Livermore National Laboratory, and the University of Arizona executed this program over 36 months with a 4-Task Program: (M1)-Microbial Engineering (M2)-Microstructure Modelling, (M3) Cement and Concrete Formulation, (M4)-Techno-economic analysis (TEA) and lifecycle assessment (LCA). This program developed a new carbonate cement concrete manufacturing process called microbial curing (MBC). MBC utilizes in-situ microbial production of CO 2 that dissolves into pore-bound water to carbonate a cementitious material creating a bonding matrix of CaCO 3 and SiO 2 that hardens and densifies the material. This is the first work of this type where calcium silicate was used in microbial studies. All other work reported in the literature always used a soluble form of calcium. This final report describes the work done in the final quarter, the best procedures and results, and the final techno-economic and lifecycle analyses. This quarter, we cast and cured twenty-five (4”x8”) cylinder samples. The compressive strength, split tensile, Young’s modulus, chloride permeability, and creep measurements were performed. These measurements demonstrated that MBC of calcium silicate concrete exhibits scaling problems due to the escape of ammonia gas, a product of the microbial reaction to generate CO 2 . As curing proceeds, the ability for the gas to escape from within the cylinder is restricted by the outer cylindrical portions densifying, making the outer portion highly impermeable to gas flow. In contrast, the small samples cured are uniformly cured, forming materials whose mechanical properties are 7x better than the large samples. This problem needs to be solved before this technology can be commercialized. The techno-economic and lifecycle analyses indicate that the technology developed in this program exhibits a significant opportunity to reduce the cost of cement and CO 2 emissions associated with concrete, provided the curing issue associated with larger samples can be addressed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Impacts of Curing-Induced Phase Segregation in Silicon Nanoparticle-Based Electrodes

We report the investigation of silicon nanoparticle composite anodes for Li-ion batteries, using a combination of two nm-scale atomic force microscopy-based techniques: scanning spreading resistance microscopy for electrical conduction mapping and contact resonance and force volume for elastic modulus mapping, along with scanning electron microscopy-based energy dispersion spectroscopy, nanoindentation, and electrochemical analysis. Thermally curing the composite anode—made of polyethylene oxide-treated Si nanoparticles, carbon black, and polyimide binder—reportedly improves the anode electrochemical performance significantly. This work demonstrates phase segregation resulting from thermal curing, where alternating bands of carbon and silicon active material are observed. This electrode morphology is retained after extensive cycling, where the electrical conduction of the carbon-rich bands remains relatively unchanged, but the mechanical modulus of the bands decreases distinctly. These electrical and mechanical factors may contribute to performance improvement, with carbon bands serving as a mechanical buffer for Si deformation and providing electrical conduction pathways. This work motivates future efforts to engineer similar morphologies for mitigating capacity loss in silicon electrodes.

25 ENERGY STORAGE↗
NASA NTRS2010

High Temperature VARTM of Phenylethynyl Terminated Imides (PETI) Resins

Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications a void fraction of less than 2% is desired. In the current study, two PETI resins, LARCTM PETI-330 and LARCTM PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 C and 371 C. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly (typically < 3%) for carbon fiber biaxially woven fabric. Photomicrographs of the panels were taken and void contents were determined by acid digestion. For carbon fiber uniaxial fabric, void contents of less than 2% have been obtained using both PETI-8 and PETI-330. Mechanical properties of the panels were determined at both room and elevated temperatures. These include short beam shear and flexure tests. The results of this work are presented herein.

Ghose, Sayata↗
NASA NTRS2017

Carbon-On-Carbon Manufacturing

The presently disclosed technology relates to carbon-on-carbon (C/C) manufacturing techniques and the resulting C/C products. One aspect of the manufacturing techniques disclosed herein utilizes two distinct curing operations that occur at different times and/or using different temperatures. The resulting C/C products are substantially non-porous, even though the curing operation(s) substantially gasify a liquid carbon-entrained filler material that saturates a carbon fabric that makes up the C/C products.

Mungas, Gregory S.↗
NASA NTRS2010

Phenylethynyl Terminated Imide (PETI) Composites Made by High Temperature VARTM

Fabrication of composite structures using vacuum assisted resin transfer molding (VARTM) is generally more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, a void fraction of <2% is desired. In the current study, two PETI resins, LARC. PETI-330 and LARC. PETI-8 have been used to fabricate test specimens using HT-VARTM. The resins were infused into carbon fiber preforms at 260 C and cured between 316 and 371 C. Photomicrographs of the panels were taken and void contents were determined by acid digestion. Modifications to the thermal cycle used in the laminate fabrication have reduced the void content significantly; typically .3% for carbon fiber biaxially woven fabric and less than 2% for carbon fiber uniaxial fabric. Mechanical properties (short beam shear and flexure) of the panels were determined at both room and elevated temperatures. The results of this work are presented herein. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

Chose, Sayata↗
NASA NTRS2001

ODC-Free Solvent Implementation for Phenolics Cleaning

During phenolic liner manufacture, resin-impregnated (pre-preg) bias tape of silica, glass, or carbon cloth is tape-wrapped, cured, machined, and then wiped with 1,1,1 tri-chloroethane (TCA) to remove contaminants that may have been introduced during machining and handling. Following the TCA wipe, the machined surface is given a resin wet-coat and over-wrapped with more prepreg and cured. A TCA replacement solvent for these wiping operations must effectively remove both surface contaminants, and sub-surface oils and greases while not compromising the integrity of this interface. Selection of a TCA replacement solvent for phenolic over-wrap interface cleaning began with sub-scale compatibility tests with cured phenolics. Additional compatibility tests included assessment of solvent retention in machined phenolic surfaces. Results from these tests showed that, while the candidate solvent did not degrade the cured phenolics, it was retained in higher concentrations than TCA in phenolic surfaces. This effect was most pronounced with glass and silica cloth phenolics with steep ply angles relative to the wiped surfaces.

Wurth, Laura↗
DOE OSTI2026

Impact of DMP-30 catalyst concentration on the degradation and kinetics of bisphenol A epoxy thermosets cured with linear amine hardener

Epoxy thermosets are a crucial component in carbon-fiber composites, serving as the organic binding matrix. Catalysts are commonly used in prepolymer formulations to accelerate curing of the thermosets. However, the impact of catalysts on the thermal stability, degradation pathways, and kinetics of the final thermoset is poorly understood. Here, in this work, Product-Specific Kinetics (PSK) analysis was utilized with isoconversional kinetics to provide a first look into the degradation kinetics of major pyrolysis pathways in bisphenol A (BPA) epoxy resins and determine the impact of altering catalysis concentrations on these kinetic pathways. Results revealed new insights into previously identified degradation pathways, provided evidence of multiple degradation pathways for some products, and showed that use of excess catalyst results in polymer network alterations and reduced thermal stability of the thermosets.

Bisphenol A↗
DOE OSTI2020

Materials for the biorefinery: high bio-content, shape memory Kraft lignin-derived non-isocyanate polyurethane foams using a non-toxic protocol

Polyurethanes are among the top six polymers produced in the world and are widely used in the automotive, furniture, construction and appliance industry for their light weight, impact resistance, and insulating properties. However, the use of hazardous diisocyanates used in polyurethane formulations has led many to search for more sustainable alternatives. The lignin component of biomass has been targeted to replace the often toxic and petroleum-derived precursors to polymer synthesis in support of the biorefinery concept where natural materials are used as the feedstock for commodity plastics. The use of lignin is often hampered due to its low reactivity, heterogeneity and the necessity of employing extensive purification and/or functionalization measures to ensure materials are of comparable quality. In this report, a unique method is presented for the synthesis and processing of a non-toxic, non-isocyanate polyurethane foam utilizing unmodified Kraft lignin and a biobased curing agent. Here, raw Kraft lignin is functionalized with green organic carbonates and a non-toxic approach is taken to solubilize the precursors with a curing agent from renewable fatty acids enabling rapid gel-times. For the first time, a NIPU foam from lignin is synthesized while the structure–property relationship of different reaction mixtures is studied demonstrating shape memory capacity and 100% biobased carbon content.

36 MATERIALS SCIENCE↗