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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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NASA NTRS1975

The preparation and properties of aluminum nitride films

Aluminum nitride films have been deposited on silicon substrates at 800-1200 C by the pyrolysis of an aluminum trichloride-ammonia complex, AlCl3.3NH3, in a gas flow system. The deposit was transparent, tightly adherent to the substrate, and was confirmed to be aluminum nitride by X-ray and electron diffraction techniques. The deposited aluminum nitride films were found to be polycrystalline with the crystallite size increasing with increasing temperature of deposition. Other properties of aluminum nitride films relevant to device applications, including density, refractive index, dissolution rate, dielectric constant, and masking ability, have been determined. These properties indicate that aluminum nitride films have potential as a dielectric in electronic devices.

Chu, T. L.↗

NASA NTRS2011

Demonstration/Validation of Environmentally-Preferable Coatings for Launch Facilities

Kennedy Space Center (KSC) is responsible for a number of facilities/structures with metallic structural and non-structural components in a highly corrosive environment. Metals require periodic maintenance activity to guard against the insidious effects of corrosion and thus ensure that structures meet or exceed design or performance life. The standard practice for protecting metallic substrates in atmospheric environments is the application of an applied coating system. Applied coating systems work via a variety of methods (barrier, galvanic and/or inhibitor) and adhere to the substrate through a combination of chemical and physical bonds. Maintenance at KSC and other NASA Centers is governed by NASA-STD-50088 (Protective Coating of Carbon Steel, Stainless Steel, and Aluminum on Launch Structures, Facilities, and Ground Support Equipment) which establishes practices for the protective coating of ground support equipment and related facilities used by or for NASA programs and projects. The Standard is for the design of non-flight hardware used to support the operations of receiving, transportation, handling, assembly, inspection, test, checkout, service, and launch of space vehicles and payloads at NASA launch, landing, or retrieval sites. These criteria and practices contained within the Standard may be used for items used at the manufacturing, development, and test sites upstream of the launch, landing, or retrieval sites. The objective of this effort is to demonstrate and validate environmentally-preferable alternatives in accordance with NASA-STD-50088 and KSC requirements which can then be added to the Approved Products List. This Test Protocol contains the critical requirements and tests necessary to qualify alternatives for structural steel applications. These tests were derived from engineering, performance, and operational impact (supportability) requirements defined by a consensus of KSC participants. A Test Report will document the results of the testing as well as any test modifications made during the execution of the testing. Users of this Test Protocol should check the project's Test Report for additional test details or minor modifications that may have been necessary in the execution of the testing. The technical stakeholders will have agreed upon test procedures modifications documented in the Test Report.

Lewis, Pattie↗

NASA NTRS1989

Tribological properties of ceramic/Ti3Al-Nb sliding couples for use as candidate seal materials to 700 deg C

Tribological properties of Ti3Al-Nb intermetallic disks sliding against alumina-boria-silicate fabric were ascertained in air at temperatures from 25 to 700 C. These materials are candidates for sliding seal applications for the National AeroSpace Plane. The tests were done using a pin on disk tribometer. Sliding was unidirectional at 0.27 m/sec under a nominal contact stress of 340 kPa. Gold sputter or ion plating deposited films were used to reduce friction and wear. Rhodium and palladium films were used beneath the gold lubricating films to prevent diffusion of the substrate into the gold at high temperature. The friction and wear of the unlubricated specimens was unacceptable. Friction coefficients were generally greater than 1.0. The ion plated gold films, when used with a rhodium diffusion barrier reduced friction by almost a factor of 2. Wear was also substantially reduced. The sputter deposited films were not adherent unless the substrate was sputter cleaned immediately prior to film deposition. Palladium did not function as a diffusion barrier.

Dellacorte, Christopher↗

NASA NTRS1990

Tribological properties of ceramic-(Ti3Al-Nb) sliding couples for use as candidate seal materials to 700 C

Dellacorte, Christhopher↗

DOE OSTI2023

Effect of an oxide layer on high velocity impact of tantalum particles characterized using molecular dynamics

Micro-cold spray, also commonly referred to as the aerosol deposition method or vacuum kinetic spraying, is a process for depositing nanostructured films of metals and ceramics by impacting solid nanoparticles at high velocity onto a substrate at room temperature and at low pressures. Tantalum films deposited by micro-cold spray are desirable because tantalum is non-reactive to certain molten metals and can therefore serve as a non-reactive barrier coating. However, unlike most other metals deposited by micro-cold spray, tantalum quickly forms an oxide layer when exposed to air. In the deposition of films using traditional cold spray with much larger particles, native oxides must fracture for particle–substrate bonding to occur. Furthermore, the fraction of the particle that is oxidized in micro-cold spray and the strain rates experienced by the particles upon impact are both much larger than in cold spray, suggesting that the role of the oxide on film deposition may be distinct. The effect of this oxide layer on particle deformation and adherence to a substrate under high strain rates is studied using molecular dynamics simulations. The effect of oxide layer thickness, particle diameter, and impact velocity are examined.

42 ENGINEERING↗

NASA NTRS1999

The Mars Environmental Compatibility Assessment MECA Abrasion Tool

The Mars Environmental Compatibility Assessment (MECA) experiment, an instrument suite to be flown on Mars Surveyor 2001, will include a tool for doing simple mineralogical scratch and streak tests on particles from the Martian regolith. The Abrasion Tool will be applied to particles that adhere to highly polished substrates of various hardnesses. Granular soil components will be subjected to a compressive force of about 3 N using a leaf spring. The spring will be applied with a paraffin actuator capable of a 0.76 mm throw to achieve a maximum displacement of about 7.5 mm at the tip of the tool. The pressure per grain will be dependent on the grain size, the number of grains that adhere to the substrate and the number of grains in compression. The pressure per particle is expected to be on the order of 100 MPa - 1 GPa. The MECA sample wheel containing the substrates will be rotated after the particles are placed in compression to produce scratches or pits. A primary goal of the Abrasion Tool is to identify quartz (Mohs' hardness = 7) using substrates of varying hardnesses. Quartz is considered hazardous to future human explorers of Mars because it can cause silicosis of the lungs if it is of respirable size. It is also hazardous to machinery, structures, and space suits because of its ability to abrade and scratch surfaces. Since large quantities of minerals harder than quartz are not expected, any scratches produced on polished quartz substrates might be reasonably attributed to quartz particles, although there may be minerals such as impact metamorphic diamond in the soils. Careful calibration of the tool will be necessary to ensure that grains are not overloaded; for example, a steel ball pressed into glass will produce a Hertzian fracture, even though it is softer than glass. Other minerals, such as magnetite (Mohs'hardness = 6.5) have been shown to scratch glass ceramics such as Zerodur (Mohs' hardness = 6.5). Thus, minerals can be differentiated: note that regardless of the mineral species, if any particle is harder than 6.5 it will certainly be an interesting discovery for both planetary geology and human exploration concerns. The scratches will be identified using the 6X optical microscope and profiled with the atomic force microscope included in the MECA instrument suite. Analysis of the scratch morphology will yield evidence concerning the shape of the particle responsible for producing each scratch. For example, angular grains should leave vertical cracks with microconchoidal lateral chipping, while rounded grains might leave chattermarks, or nested partial Hertzian cracks. Particle shape can thus be inferred from these indentation modes, as well as material hardness. In addition, particle size information may also be available if pits caused by rolling particles can be identified. Converse to scratching, the minerals may be crushed at their contact points, and be smeared onto the target substrates to leave what geologists refer to as "streaks". These are coldwelded trails of mineral material that have structure and color indicative of mineral composition. The AFM will determine the morphology of these streaks, while the microscope will ascertain the color. On the harder substrates, we might expect streaking to dominate; on the softer substrates, scratching may dominate. Progressions of material interactions across the substrate selection will be a valuable source of data for mineral discrimination. It should also be noted that many minerals have coatings (such as iron oxides), and these will have to be differentiated from the host mineral grains; laboratory tests will establish the effects of such coatings on the scratch results. Finally, we note that the microscope will provide corroborative data regarding likely mineral species by grain shapes, fracture patterns, surface textures, colr, and UV fluorescence reactions.

Kuhlman, K. R.↗

NASA NTRS1969

Fundamental considerations for future solid lubricants

Properties important to the performance of solid lubricants are discussed. Those properties include shear characteristics, coherence between particles, resistance to cold flow, adherence to the substrate, applicable chemical thermodynamics and kinetics of materials and environments, polymorphism, and rheology. The following generalizations are made: (1) chemical thermodynamics and kinetics are powerful tools for use in determining the useful environments and methods of application for solid film lubricants; (2) the primary requirement for a solid lubricant is low shear strength; (3) the rheology of solid film constituents and formulations is likely to be of vital importance to performance and life; and (4) adherence and mobility of surface films is another primary requirement for long lived solid lubricants.

Johnson, R. L.↗

NASA NTRS2018

Inkjet Printing of Conductive Carbon Nanotubes

Systems and methods for forming conductive materials. The conductive materials can be applied using a printer in single or multiple passes onto a substrate. The conductive materials are composed of electrical conductors such as carbon nanotubes (including functionalized carbon nanotubes and metal-coated carbon nanotubes), grapheme, a polycyclic aromatic hydrocarbon (e.g. pentacene and bisperipentacene), metal nanoparticles, an inherently conductive polymer (ICP), and combinations thereof. Once the conductive materials are applied, the materials are dried and sintered to form adherent conductive materials on the substrate. The adherent conductive materials can be used in applications such as damage detection, particle removal, and smart coating systems.

Roberson, Luke B.↗

DOE OSTI2021

Enhanced oxidation resistance of (Mo 95 W 5 ) 85 Ta 10 (TiZr) 5 refractory multi-principal element alloy up to 1300°C

Refractory-metal-based alloys are a potential replacement of current nickel-based superalloys due to their excellent mechanical strength at extremely high temperatures. However, severe oxidation in a high-temperature working environment limits their application. To address this challenge, a two-step coating process (including a Mo precoat and a Si-B pack cementation) was applied to an innovative refractory multi-principal element alloy (RMPEA) (Mo 95 W 5 ) 85 Ta 10 (TiZr) 5 . The coating is composed of an aluminoborosilica glass layer on top of a RMPEA-Si-B multilayered structure. Here, the coating effectively protects the RMPEA from oxidation in high-temperature environments, as demonstrated by phase-stable operation at 10–20% higher temperatures over state-of-the-art systems without any forced-cooling system. Following an isothermal exposure at 1300 °C, the weight change of the coated sample follows a paralinear kinetics with a minor weight loss of 4.2 mg/cm 2 after 50 h. Thermal cycling tests between 1300 °C and room temperature in air resulted in the total weight gain of only 2.6 mg/cm 2 after 450 cycles. The coating shows an excellent adherence to the substrate with a boride layer acting as a barrier that maintains the coating integrity. This two-step Mo-Si-B coating method can be adapted to provide environmental resistance to a wide range of RMPEA.

36 MATERIALS SCIENCE↗

NASA NTRS1979

Study of composites as substrate materials in large space telescopes

Nonmetallic composites such as the graphite/epoxy system were investigated as possible substrates for the primary mirror of the large space telescope. The possible use of fiber reinforced metal matrix composites was reviewed in the literature. Problems arising out of the use of composites as substrate materials such as grinding, polishing, adherence of reflective coatings, rigidity of substrate, hygrospcopici tendency of the composites, thermal and temporal stability and other related problems were examined.

Sharma, A. V.↗

NASA NTRS1981

Development of Improved Rhenium Coatings for Fluorine Engine Thrust Chambers

Coating trials were undertaken to evaluate the application of rhenium to carbon-carbon composite sheet by plasma spraying. Optimum spray parameters and coating thickness were identified for production of coatings free from continuous defects and with adequate adherence to the substrate. A tungsten underlayer was not beneficial and possibly detracted from coating integrity. Stress calculations indicated that the proposed operating cycle of the rocket engine would not cause spalling of the rhenium coating. Calculations indicated that permeation of gases through the coating would not be significant during the expected life of the thrust chamber. The feasibility of applying rhenium coatings by laser melting was also studied. Poor wetting of the composite surface by the liquid rhenium precluded production of uniform coatings. Borate/carborate fluxes did not improve wetting characteristics.

Barton, K. J.↗

NASA NTRS1982

Refractory coatings

A thin sputtered film is discussed which exhibits improved adherence to a substrate and has improved friction and wear characteristics. Each substrate is placed directly below a titanium carbide target of a commercial radiofrequency diode apparatus in a vacuum chamber. Nitrogen is bled into the system through a nozzle resulting in a small partial pressure of about 0.5% to 2.5% during the first two minutes of deposition. The flow of nitrogen is then stopped, and the sputtering ambient is reduced to pure argon through a nozzle without interrupting the sputtering process.

Brainard, W. A.↗

NASA NTRS1994

Morphological Differentiation of Colon Carcinoma Cell Lines in Rotating Wall Vessels

The objectives of this project were to determine whether (1) microgravity permits unique, three-dimensional cultures of neoplastic human colon tissues and (2) this culture interaction produces novel intestinal growth and differentiation factors. The initial phase of this project tested the efficacy of simulated microgravity for the cultivation and differentiation of human colon carcinoma in rotating wall vessels (RWV's) on microcarrier beads. The RWV's simulate microgravity by randomizing the gravity vector in an aqueous medium under a low shear stress environment in unit gravity. This simulation achieves approximately a one-fifth g environment that allows cells to 'float' and form three-dimensional relationships with less shear stress than in other stirred aqueous medium bioreactors. In the second phase of this project we assessed the ability of human colon carcinoma lines to adhere to various substrates because adhesion is the first event that must occur to create three-dimensional masses. Finally, we tested growth factor production in the last phase of this project.

Jessup, J. M.↗

NASA NTRS2002

Electrical Characterization of Polyaniline/polyethylene Oxide Nanofibers for Field Effect Transistors

Nanofibers comprised of polyaniline/polyethylene oxide (PANI/PEO) are being developed for novel logic devices. We report the electrical conductivity of PANI/PEO nanofibers with diameters in the 100 to 200 nm range. We measured conductivity values of approx. 0.3 to 1.0 S/cm, which is higher than the values reported for thicker nanofibers, but less than the bulk value of PANI. The electrical measurements were performed by depositing the fibers on pre-electroded, oxidized silicon (Si) substrates. The excellent adherence of the nanofibers to the SiO2 as well as the gold (Au) electrodes may be useful in the design of future devices.

Mueller, Carl H.↗

NASA NTRS1996

Silicone Contamination Camera for Developed for Shuttle Payloads

On many shuttle missions, silicone contamination from unknown sources from within or external to the shuttle payload bay has been a chronic problem plaguing experiment payloads. There is currently a wide range of silicone usage on the shuttle. Silicones are used to coat the shuttle tiles to enhance their ability to shed rain, and over 100 kg of RTV 560 silicone is used to seal white tiles to the shuttle surfaces. Silicones are also used in electronic components, potting compounds, and thermal control blankets. Efforts to date to identify and eliminate the sources of silicone contamination have not been highly successful and have created much controversy. To identify the sources of silicone contamination on the space shuttle, the NASA Lewis Research Center developed a contamination camera. This specially designed pinhole camera utilizes low-Earth-orbit atomic oxygen to develop a picture that identifies sources of silicone contamination on shuttle-launched payloads. The volatile silicone species travel through the aperture of the pinhole camera, and since volatile silicone species lose their hydrocarbon functionalities under atomic oxygen attack, the silicone adheres to the substrate as SiO_x. This glassy deposit should be spatially arranged in the image of the sources of silicone contamination. To view the contamination image, one can use ultrasensitive thickness measurement techniques, such as scanning variable-angle ellipsometry, to map the surface topography of the camera's substrate. The demonstration of a functional contamination camera would resolve the controversial debate concerning the amount and location of contamination sources, would allow corrective actions to be taken, and would demonstrate a useful tool for contamination documentation on future shuttle payloads, with near negligible effect on cost and weight.

Source record↗

NASA NTRS2009

Electrostatic Switching in Vertically Oriented Nanotubes for Nonvolatile Memory Applications

We have demonstrated electrostatic switching in vertically oriented nanotubes or nanofibers, where a nanoprobe was used as the actuating electrode inside an SEM. When the nanoprobe was manipulated to be in close proximity to a single tube, switching voltages between 10 V - 40 V were observed, depending on the geometrical parameters. The turn-on transitions appeared to be much sharper than the turn-off transitions which were limited by the tube-to-probe contact resistances. In many cases, stiction forces at these dimensions were dominant, since the tube appeared stuck to the probe even after the voltage returned to 0 V, suggesting that such structures are promising for nonvolatile memory applications. The stiction effects, to some extent, can be adjusted by engineering the switch geometry appropriately. Nanoscale mechanical measurements were also conducted on the tubes using a custom-built anoindentor inside an SEM, from which preliminary material parameters, such as the elastic modulus, were extracted. The mechanical measurements also revealed that the tubes appear to be well adhered to the substrate. The material parameters gathered from the mechanical measurements were then used in developing an electrostatic model of the switch using a commercially available finite-element simulator. The calculated pull-in voltages appeared to be in agreement to the experimentally obtained switching voltages to first order.

plasma-enhanced chemical vapor deposition (PECVD).↗

DOE OSTI2020

Superhydrophobic coating and process of making same

An improved superhydrophobic coating and a process of making it is provided herein. More particularly, a robust superhydrophobic coating is produced by using carbon dioxide to enhance the integration of a binder material into the superhydrophobic coating. The carbon dioxide may be used to infiltrate and fill the interstitial voids of a superhydrophobic material, such as diatomaceous earth. Consequently, occupying these voids in the superhydrophobic material effectively blocks other components (e.g., binders) from entering the voids. As a result, the coating formulations of the present invention are more robust and may strongly adhere to the substrates to which they are applied.

36 MATERIALS SCIENCE↗

NASA NTRS2003

Process for Smoothing an Si Substrate after Etching of SiO2

A reactive-ion etching (RIE) process for smoothing a silicon substrate has been devised. The process is especially useful for smoothing those silicon areas that have been exposed by etching a pattern of holes in a layer of silicon dioxide that covers the substrate. Applications in which one could utilize smooth silicon surfaces like those produced by this process include fabrication of optical waveguides, epitaxial deposition of silicon on selected areas of silicon substrates, and preparation of silicon substrates for deposition of adherent metal layers. During etching away of a layer of SiO2 that covers an Si substrate, a polymer becomes deposited on the substrate, and the substrate surface becomes rough (roughness height approximately equal to 50 nm) as a result of over-etching or of deposition of the polymer. While it is possible to smooth a silicon substrate by wet chemical etching, the undesired consequences of wet chemical etching can include compromising the integrity of the SiO2 sidewalls and undercutting of the adjacent areas of the silicon dioxide that are meant to be left intact. The present RIE process results in anisotropic etching that removes the polymer and reduces height of roughness of the silicon substrate to less than 10 nm while leaving the SiO2 sidewalls intact and vertical. Control over substrate versus sidewall etching (in particular, preferential etching of the substrate) is achieved through selection of process parameters, including gas flow, power, and pressure. Such control is not uniformly and repeatably achievable in wet chemical etching. The recipe for the present RIE process is the following: Etch 1 - A mixture of CF4 and O2 gases flowing at rates of 25 to 75 and 75 to 125 standard cubic centimeters per minute (stdcm3/min), respectively; power between 44 and 55 W; and pressure between 45 and 55 mtorr (between 6.0 and 7.3 Pa). The etch rate lies between approximately equal to 3 and approximately equal to 6 nm/minute. Etch 2 - O2 gas flowing at 75 to 125 stdcm3/min, power between 44 and 55 W, and pressure between 50 and 100 mtorr (between 6.7 and 13.3 Pa).

Turner, Tasha↗