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NASA NTRS1970

Intumescent Coatings as Fire Retardants

The development of fire-retardant coatings to protect surfaces which may be exposed to fire or extreme heat is a subject of intense interest to many industries. A fire-retardant paint has been developed which represents a new chemical approach for preparing intumescent coatings, and potentially, is very important to fire-prevention authorities. The requirements for a superior coating include ease of application, suitability to a wide variety of surfaces and finishes, and stability over an extended period of time within a broad range of ambient temperature and humidity conditions. These innovative coatings, when activated by the heat of a fire, react to form a thick, low-density, polymeric coating or char layer. Water vapor and sulphur dioxide are released during the intumescent reaction. Two fire-protection mechanisms thus become available: (1) the char layer retards the flow of heat, due to the extremely low thermal conductivity; and (2) water vapor and sulfur dioxide are released, providing fire quenching properties. Still another mechanism functions in cases where the char, by virtue of its high oxidation resistance and low thermal conductivity, reaches a sufficiently high temperature to re-radiate much of the incident heat load. The coatings consist of dispersions of selective salts of a nitro-amino-arornatic compound. Specifically, para-nitroaniline bisulfate and the ammonium salt of para-nitroaniline-ortho sulphuric acid (2-amino-5-nitrobenzenesulphuric acid) are used. Suitable vehicles are cellulose nitrate of lacquer grade, a nitrite-phenolic modified rubber, or epoxy-polysulfide copolymer. Three separate formulations have been developed. A solvent is usually employed, such as methylethyl ketone, butyl acetate, or toluene, which renders the coatings suitably thin and which evaporates after the coatings are applied. Generally, the intumescent material is treated as insoluble in the vehicle, and is ground and dispersed in the vehicle and solvent like an ordinary coating pigment. The char found on intumescence is better in terms of yield and physical properties than chars obtained from many previously known intumescent materials. Prior to intumescence, the coating has a density of 85 pounds per cubic foot. After intumescence, the density is approximately 0.3 pounds per cubic loot. The linear expansion of the coatings ranges from 70 to 200 times the applied coating thickness.

Parker, J. A.↗

NASA NTRS2016

TEM Analysis of Interfaces in Diffusion-Bonded Silicon Carbide Ceramics Joined Using Metallic Interlayers

Silicon Carbide (SiC) is a promising material for thermo-structural applications due to its excellent high-temperature mechanical properties, oxidation resistance, and thermal stability. However, joining and integration technologies are indispensable for this material in order to fabricate large size and complex shape components with desired functionalities. Although diffusion bonding techniques using metallic interlayers have been commonly utilized to bond various SiC ceramics, detailed microstructural observation by Transmission Electron Microscopy (TEM) of the bonded area has not been carried out due to difficulty in preparing TEM samples. In this study, we tried to prepare TEM samples from joints of diffusion bonded SiC ceramics by Focused Ion Beam (FIB) system and carefully investigated the interfacial microstructure by TEM analysis. The samples used in this study were SiC fiber bonded ceramics (SA-Tyrannohex: SA-THX) diffusion bonded with metallic interlayers such as Ti, TiMo, and Mo-B. In this presentation, the result of microstructural analysis obtained by TEM observations and the influence of metallic interlayers and fiber orientation of SA-THX on the joint microstructure will be discussed.

Silicon Carbide↗

NASA NTRS2017

TEM Analysis of Diffusion-Bonded Silicon Carbide Ceramics Joined Using Metallic Interlayers

Silicon Carbide (SiC) is a promising material for thermostructural applications due to its excellent high-temperature mechanical properties, oxidation resistance, and thermal stability. However, joining and integration technologies are indispensable for this material in order to fabricate large size and complex shape components with desired functionalities. Although diffusion bonding techniques using metallic interlayers have been commonly utilized to bond various SiC ceramics, detailed microstructural observation by Transmission Electron Microscopy (TEM) of the bonded area has not been carried out due to difficulty in preparing TEM samples. In this study, we tried to prepare TEM samples from joints of diffusion bonded SiC ceramics by Focused Ion Beam (FIB) system and carefully investigated the interfacial microstructure by TEM analysis. The samples used in this study were SiC fiber bonded ceramics (SA-Tyrannohex: SA-THX) diffusion bonded with metallic interlayers such as Ti, TiMo, Mo-B and TiCu. In this presentation, we report the microstructure of diffusion bonded SA-THX mainly with TiCu interlayers obtained by TEM observations, and the influence of metallic interlayers on the joint microstructure and microhardness will be discussed.

Ceramics↗

NASA NTRS2016

Compact, Lightweight, Ceramic Matrix Composite (CMC) Based Acoustic Liners for Reducing Subsonic Jet Aircraft Engine Noise

Recent developments have reduced fan and jet noise contributions to overall subsonic aircraft jet-engine noise. Now, aircraft designers are turning their attention toward reducing engine core noise. The NASA Glenn Research Center and NASA Langley Research Center have teamed to investigate the development of a compact, lightweight acoustic liner based on oxide/oxide ceramic matrix composite (CMC) materials. The NASA team has built upon an existing oxide/oxide CMC sandwich structure concept that provides monotonal noise reduction. Oxide/oxide composites have good high temperature strength and oxidation resistance, which could allow them to perform as core liners at temperatures up to 1000C (1832F), and even higher depending on the selection of the composite constituents. NASA has initiated the evaluation of CMC-based liners that use cells of different lengths (variable-depth channels) or effective lengths to achieve broadband noise reduction. Reducing the overall liner thickness is also a major goal, to minimize the volume occupied by the liner. As a first step toward demonstrating the feasibility of our concepts, an oxide/oxide CMC acoustic testing article with different channel lengths was tested. Our approach, summary of test results, current status, and goals for the future are reported.

testing↗

NASA NTRS2018

Polyurethane Microparticles for Stimuli Response and Reduced Oxidative Degradation in Highly Porous Shape Memory Polymers

Shape memory polymers (SMPs) have been found to be promising biomaterials for a variety of medical applications; however, the clinical translation of such technology is dependent on tailorable properties such as gravimetric changes in degradation environments. For SMPs synthesized from amino-alcohols, oxidation resulting in rapid mass loss may be problematic in terms of loss of material functionality as well as toxicity and cytocompatibility concerns. Control of gravimetric changes was achieved through the incorporation of small molecule antioxidants, either directly into the polymer matrix or included in microparticles to form a SMP composite material. Direct incorporation of small molecule antioxidants, such as phenolic alcohols, was found to alter shape memory attributes and increase elastic modulus at the expense of the strain to failure. Such changes could not ensure retention of the antioxidants and therefore did not increase oxidative stability. However, the inclusion of antioxidants in microparticles was found to produce materials with similar thermomechanical and shape memory properties while increasing oxidative resistance compared to controls. The microparticle composite SMPs also act as a platform for environmental sensing, such as pH-dependent fluorescence shifts and payload release, as demonstrated by fluorescent dyes and the release of antioxidants. The use of polyurethane-urea microparticles in porous SMPs is demonstrated to increase biostability of the materials, by approximately 25%, and ultimately extend their lifespan for use in aneurysm occlusion as determined through calculated in vivo degradation rates corresponding to a porcine aneurysm environment.

Weems, A. C.↗

NASA NTRS2019

TUFROC Thermal Protection System

Toughened Unipiece Fibrous Reinforced Oxidation-resistant Composite (TUFROC) is a tiled Thermal Protection System (TPS) suitable for reusable entry heating at 2900+ °F and with single use potential up to at least 3600 °F. TUFROC was initially developed for NASA's X-37 project and ultimately resulted in use on the Air Force X-37B as the wing leading edge (WLE) of the vehicle. TUFROC has similar high temperature capability compared with carbon/carbon, but is manufactured at an order of magnitude lower cost & faster schedule.

thermal protection system↗

NASA NTRS2019

GRCop-42 Development and Hot-fire Testing Using Additive Manufacturing Powder Bed Fusion for Channel-Cooled Combustion Chambers

GRCop-42 is a high conductivity, high-strength dispersion strengthened copper-alloy for use in high heat flux applications such as liquid rocket engine combustion devices. This alloy is part of the family of NASA-developed GRCop, copper-chrome-niobium alloys. GRCop alloys were developed for harsh environments specific to regeneratively-cooled combustion chambers and nozzles with good oxidation resistance. Significant development was completed on the GRCop-84 and GRCop-42 alloys in the extruded wrought form demonstrating feasibility for combustion chambers. NASA has recently developed a process for additive manufacturing, specifically Powder Bed Fusion (PBF) or Selective Laser Melting (SLM), of GRCop-42 to establish parameters, characterize the material, and complete testing of components with complex internal features. This evolution of the GRCop-42 was based on the successful predecessor development work using GRCop-84 with the motivation of establishing a new copper-alloy option for use in NASA, government, and industry programs with SLM. A few advantages have been shown with the GRCop-42 that include higher conductivity and faster build speeds over the GRCop-84, and a simplified powder supply chain. Initial property development has shown that it is possible to produce high density builds with strengths equivalent to wrought GRCop-42 and a conductivity greater than GRCop-84. The GRCop-42 has completed process development and initial properties have been established. Several demonstrator combustion chambers have also been fabricated with the SLM GRCop-42 that include integral channels and closeouts. Additional test units have been fabricated and are completing substantial hot-fire testing to demonstrate performance of the material, process, and design.

Gradl, Paul R.↗

NASA NTRSDate not supplied

Analysis of PICA-NuSil at the Hypersonic Materials Environmental Test System (HyMETS)

Phenolic Impregnated Carbon Ablator (PICA) gained heritage during the stardust mission and is the baseline material for missions to Mars. The phenolic phase of PICA is friable, and therefore the surface is treated with a siloxane resin (NuSil) to mitigate the shedding of particulate matter. Historically, material response models have not accounted for the presence of this coating. Therefore, a test campaign was executed at the Hypersonic Materials Environmental Test System (HyMETS) to investigate the performance of NuSil under multiple heating rates and gas composition. Sphere-cone models were instrumented with thermocouples to measure the in-depth temperature response, and surface temperatures were monitored with a pyrometer. Furthermore, emission spectrometers were used to collect spectra from species emitting at the surface of the test article and the post-shock stagnation region. Post-test analysis suggests that the coating decomposes according to multiple stages. Inspection of silicon emission data reveals a rapid rise and decline in intensity within the first couple of seconds of testing, which is attributed to pyrolysis of NuSil. Pyrolysis is followed by a stagnation in silicon emission and surface temperature which are attributed to the formation of a thin layer of oxidation-resistant silicon oxycarbide. Moreover, the presence of the silicon oxycarbide layer significantly reduces the in-depth thermal response when compared to the baseline material. Eventually, the silicon oxycarbide layer decomposes via high-temperature reactions, which expose the underlying char layer to a highly reactive flow.

PICA-NuSil↗

NASA NTRSDate not supplied

Exploration of Particle Size Engineering and Microencapsulation Technologies for Multifunctional Applications

There is a critical need for high performance materials for functional and space-based applications, including tires for exploratory rovers and external structures for landing vehicles. Novel ternary borides, such as iron aluminum boride (Fe2AlB2) and molybdenum aluminum boride (MoAlB), have emerged as potential materials for such application owing to their hardness, mechanical behavior and oxidation resistance. In this poster presentation, we will present different methods of fabricating these particles and engineering them for additive manufacturing and other related manufacturing practices. As an integral component of this study, we will demonstrate technologies to (a) synthesize these particles and (b) microencapsulate these particles with bioplastics like polylactic acid (PLA). The resulting particles will be evaluated for their processability as coatings on hydroxyapatite and Inconel particles using microstructural and flowability studies. It is expected that these particles can be used for 3D printing.

ceramics↗

NASA NTRSDate not supplied

Feasibility Testing of Silver Electrolysis for Disinfection of Spacecraft Potable Water Systems

Anodic dissolution of silver electrodes, or “silver electrolysis,” is being investigated as a means of introducing biocidal silver into potable water on exploration spacecraft. A proof-of-concept prototype of a silver electrolysis reactor was developed, and feasibility was demonstrated for imparting a target silver concentration into a spacecraft water system. Prototype testing showed that the primary initial concerns related to the technology - inefficiencies of electrolysis in low conductivity water, the potential formation of resistive oxides on the electrode surfaces, and the potential for release of electrolytically-generated silver particles to the effluent water - were not problematic over the duration of the feasibility testing. The testing also demonstrated advantages of the technology, including the ability to consistently deliver silver at targeted concentrations and the ability to directly correlate the silver concentration to measurements of water conductivity. On the other hand, the reliability of the system has not yet been demonstrated. During prototype testing, intermittent periods of poor reactor performance manifested as a decrease in voltage accompanied by a decrease in silver output. It was determined that the cause of this behavior was silver-based deposits on inter-electrode wetted surfaces forming a conductive “bridge” between electrodes. Ongoing testing and refinement of the prototype reactor design seek to elucidate the root cause the bridging phenomenon and identify associated mitigation strategies. Once resolved, long-term performance testing is planned as part of continued development of the electrolytic silver dosing system.

Silver↗

NASA NTRSDate not supplied

Advanced TUFROC Thermal Protection System Evolution Under Re-entry like Conditions

Toughened Unipiece Fibrous Reinforced Oxidation-resistant Composite (TUFROC) and its successor, Advanced TUFROC, are state-of-the-art thermal protection systems (TPS) for high temperature reusable applications. Originally designed for use on the wing-leading edge of X-37B, TUFROC is an insulative tiled system consisting of a low-conductivity ceramic base, a carbonaceous cap, and multiple coatings for thermal performance. The improved Advanced TUFROC has demonstrated reusability up to 2900 °F and single use capabilities exceeding 3200 °F. This effort explores the evolution of Advanced TUFROC when exposed to re-entry like conditions via arc jet testing. Chemical reactions and constituent migration resulting from the aerothermal heating are known to occur and are studied in detail. Further, the interaction between the multiple constituents and layers will be discussed as this is believed to have a significant impact on the overall performance. Characterization includes structural analysis via optical microscopy, scanning electron microscopy and energy-dispersive x-ray spectroscopy.

Thermal protection system↗

NASA NTRSDate not supplied

New Development Activities at NASA Ames in Reusable TPS Materials

Over the last few years, new activities in rapid, low-cost access to low-earth orbit (LEO) and hypersonic flight have refreshed interest in reusable thermal protection systems (RTPS) that have not had broad application since the Space Shuttle era. Development of novel systems having a greater consideration of full cycle cost (lower cost raw materials, manufacturing, integration, and refurbishment) in addition to improved performance are needed to enable this new generation of space flight. NASA Ames has a long history of RTPS development including invention of flexible blankets such as Advanced Flexible Reusable Surface Insulation (AFRSI), rigid ceramic tiles like Fibrous Refractory Composite Insulation (FRCI) and Alumina Enhanced Thermal Barrier (AETB), and multi-component systems like Toughened Uni-piece Fibrous Reinforced Oxidation-resistant Composite (TUFROC). In much more recent times, NASA Ames is supporting the growing commercial space field through internal research and development efforts for high-risk low TRL materials and collaboration with commercial partners including technology transfer. This talk will discuss the current development efforts that span broadly from updating legacy insulating systems with modern raw materials and processes to totally novel designs for heat pipes with various low-TRL activities in between. It will also discuss Ames’ recent re-investment in experimental capabilities to enable characterization and material testing.

Reusable thermal protection materials↗

NASA NTRSDate not supplied

Novel Ceramic Dispersion Strengthened Refractory Metals for Improved Printability and Properties

Refractory metals and alloys are of major interest for nuclear fusion systems, space nuclear power and propulsion, and hypersonic applications due to their desirable properties at elevated temperatures (>1500°C). Limitations of refractory materials include their low ductility, poor oxidation resistance, and high manufacture cost using traditional techniques. Additive manufacturing (AM) can reduce material waste associated with manufacture, but AM fabrication is impacted by the brittleness of these refractory metals, resulting in excessive cracking during printing. Cracking reduces the effectiveness of hot isostatic pressing (HIP) which is commonly used to improve density and mechanical properties of AM components. The goal of this work is to improve refractory metal printability without majorly affecting the material properties which are the main reason these materials are used. Ceramic nanoparticles have been shown to help improve material properties after heat treatment. Results will be shown that demonstrate the effectiveness of adding nanoparticles to refractory metals. Additionally, there will be discussion regarding how these nanoparticles change the effect of heat treatments such as HIP compared with the AM pure metal samples.

Carly J. Romnes↗

NASA NTRSDate not supplied

New Development Activities at NASA Ames in Reusable TPS Materials

Reusable thermal protection materials↗

NASA NTRS2024

Advanced Lightweight TUFROC Thermal Protection System for Space Plane Applications

Toughened Uni-piece Fibrous Reinforced Oxidation-resistant Composite (TUFROC) represents the state of the art in low-cost, reusable spacecraft Thermal Protection Systems (TPS) with high temperature capability and is flight proven on the USAF X-37B. The two-piece design takes advantage of a low-conductivity porous silica substrate combined with high-temperature-capable carbon cap and surface treatments. NASA has updated the chemical composition of the surface treatments resulting in improved high-heating capability and reusability. The new system, called Advanced TUFROC, experiences a lower surface temperature (by ~80 K) at identical aerothermal heating conditions compared to the original formulation, now called Standard TUFROC. The reduced heating is attributed to the lower catalytic efficiency of the new formulation, which results in reduced exothermic atom recombination rates at the surface. Multiple arc-jet test campaigns demonstrate that Advanced TUFROC has the ability to withstand long and repeated exposures at 1866 K or a shorter duration exposure at 1980 K without recession or damage to TPS. Furthermore, an improved arc-jet article design for assessing 3-dimensional flow over a wing leading edge has been developed and tested. This article allows for assessment of heating at a tile gap under flight-relevant conditions at significantly reduced article fabrication and arc-jet facility configuration costs compared to prior work.

TUFROC↗

NASA NTRSDate not supplied

Reusable TPS Materials Development Activities at NASA Ames

Recent developments in low-cost access to low-earth orbit (LEO) and hypersonic flight are driving renewed demand in reusable thermal protection systems (RTPS) that have not had broad application since the Space Shuttle era. Modern systems will need to consider full cycle cost (lower cost raw materials, manufacturing, integration, and refurbishment) in addition to improved performance to enable this new generation of space flight. NASA Ames Research Center (ARC) has a long history of RTPS development including modern state-of-the-art materials like Alumina Enhanced Thermal Barrier (AETB), and multi-component systems like Toughened Uni-piece Fibrous Reinforced Oxidation-resistant Composite (TUFROC). Now, ARC is supporting the growing commercial space field through internal research and development efforts for high-risk low TRL materials and collaboration with commercial partners including technology transfer. This talk will discuss the current development efforts at ARC that span updating legacy insulating systems with modern raw materials and processes to totally novel designs for heat pipes with various low-TRL activities in between. It will also discuss Ames’ recent re-investment in experimental capabilities to enable characterization and material testing.

Adam Caldwell↗

NASA NTRSDate not supplied

Investigating Material Behavior in Atmospheric Entry Conditions: Arc-Jet Testing Insights from Meteorite Ablation to High-Temperature Coatings.

Arc-jet testing is an indispensable tool in elucidating the complex interactions materials undergo when subjected to the extreme thermal and mechanical stresses of atmospheric entry. By replicating these harsh conditions, arc-jets enable researchers to explore critical phenomena such as ablation, melting, and spallation, generating invaluable data that informs the development of sophisticated, physics-based models. These models are pivotal not only in predicting material performance for spacecraft re-entry systems but also in assessing the threat posed by celestial bodies as they encounter Earth’s atmosphere. One of the leading facilities for such investigations is the Hypersonic Materials Environmental Test System (HyMETS) at NASA’s Langley Research Center. A pioneering test campaign conducted at HyMETS focused on unraveling the ablation mechanisms of an ordinary chondrite meteorite (Tamdakht H5) and a terrestrial analog (basalt). These studies unveiled distinct material behaviors: Tamdakht demonstrated a remarkably stable melt flow, with mass loss primarily driven by the volatilization of elements such as iron and sodium, whereas basalt exhibited more aggressive surface degradation due to the rapid decomposition of hydrated minerals, culminating in significant spallation and surface material ejection. Beyond meteorite analysis, HyMETS has also been integral in the exploration of advanced Thermal Protection Systems (TPS) such as Phenolic Impregnated Carbon Ablator (PICA), a material with extensive flight heritage in missions like Stardust, Mars Science Laboratory, Mars 2020, and Osiris-REx. PICA, when coated with NuSil CV-1144-0—a polysiloxane resin designed to prevent particle shedding—undergoes a remarkable transformation upon heating. The resin pyrolyzes to form a thin, oxidation-resistant silicon oxycarbide layer that profoundly influences the material’s thermal response through a sophisticated four-stage process. Initially, the silicon oxycarbide acts as a formidable barrier, impeding reactive interactions with the PICA char and effectively suppressing surface temperature rise and material recession. However, as the heating persists, the protective layer decomposes via carbothermal reduction, exposing the underlying char, which in turn leads to a dramatic spike in surface temperature and accelerated material erosion. In the final stage, equilibrium is reached, with recession rates aligning with those of the virgin material. This intricate understanding of PICA-NuSil behavior under extreme conditions offers valuable insights, enhancing material response models and advancing the development of next-generation TPS for space exploration.

Chemistry↗

NASA NTRS2026

Hybrid Modeling Study on Grain Evolution in the Metal Welding Process and Its Potential Lunar Application

Metal is most commonly used structural material in a wide range of spacecraft, and welding is the principal method for joining metal components into functional systems. However, conducting welding experiments under extreme environments—such as microgravity or vacuum conditions in space—is prohibitively expensive and experimentally challenging. To overcome these limitations, multi-physics computational welding models provide a cost-effective and versatile alternative. In this work, the authors have developed a coupled thermal (fluid) microstructure simulation framework to model metal welding under varying gravity conditions. The framework integrates a mixed-mode heat transfer formulation (conduction, convection, and radiation) with molten pool fluid dynamics, enabling accurate prediction of temperature fields and weld-pool geometry. A grain growth model is further incorporated to capture the spatial and temporal evolution of microstructure, including grain size distribution and morphological transitions during solidification. This approach provides detailed insight into molten pool evolution and grain-level microstructure development throughout the welding process. By explicitly parameterizing environmental conditions, the model supports extrapolation to off-Earth manufacturing scenarios such as welding on the lunar surface. Tantalum—chosen in this study due to its high melting point, oxidation resistance, and mechanical stability at elevated temperatures—serves as the material system for model demonstration. Beyond Tantalum, the integrated multi-physics framework offers broad applicability for predictive welding simulations of various structural and refractory metals or alloys used in extreme terrestrial or extraterrestrial environments.

kinetic Monte Carlo (SPPARKS)↗