SEARCH · Engineering Papers

Results for “TiC”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS1997

Observational Evidence for Mixing and Dust Condensation in Core-Collapse Supernovae

Recent findings of isotopic anomalies of Ca-44 (the decay product of Ti-44) and the enhanced ratio of Si-28/Si-30 in SiC grains X, TiC subgrains, and graphite dust grains within primitive meteorites provides strong evidence that these presolar grains came from core-collapse supernovae. The chemical composition of the presolar grains requires macroscopic mixing of newly nucleo-synthesized elements from explosive silicon burning at the innermost zone of the ejects to higher velocities where C exists and where C/O > 1 in either the outer edge of the oxygen zone or in the He-C zone. To date, the only core-collapse supernova observed to form dust is the brightest supernova of the past four centuries, SN1987A in the Large Magellanic Cloud. Observations of SN1987A confirm large scale macroscopic mixing occurs in the explosions of massive stars. Rayleigh-Taylor instabilities macroscopically mix most of the ejects into regions which are still chemically homogeneous and which cool with different time scales. Only small clumps in the ejects are microscopically mixed. Observations show that dust condensed in the ejects of SN1987A after approx.500 days in the Fe-rich gas. Neither silicates nor SiC grains were seen in the dust emission spectrum of SN1987A. SN1987A, the Rosetta Stone of core-collapse supernovae, shows that while the mixing required to explain presolar grains occurs, the rapid cooling of the Fe zone and the sustained high temperatures of the O-Si, O-C, and He-C zones favor the formation of iron-rich rather than oxygen- or carbon-rich grains.

Wooden, Diane↗

NASA NTRS2004

Evolution of In-Situ Generated Reinforcement Precipitates in Metal Matrix Composites

Due to certain inherent advantages, in-situ production of Metal Matrix Composites (MMCs) have received considerable attention in the recent past. ln-situ techniques typically involve a chemical reaction that results in precipitation of a ceramic reinforcement phase. The size and spatial distribution of these precipitates ultimately determine the mechanical properties of these MMCs. In this paper we will investigate the validity of using classical growth laws and analytical expressions to describe the interaction between a precipitate and a solid-liquid interface (SLI) to predict the size and spatial evolution of the in-situ generated precipitates. Measurements made on size and distribution of Tic precipitates in a Ni&I matrix will be presented to test the validity of such an approach.

Sen, S.↗

NASA NTRS2005

History of Presolar Grains

Papers on the History of Presolar Grains. This has been a very productive period in which much of the laboratory work conducted in the previous year and during this funding cycle were brought to completion. In the last year we have published or submitted for peer review 4 research papers, 4 review papers, and 11 abstracts in research areas supported under this grant. Brief synopses of the results of the research papers are presented, followed by short summaries of the topics discussed in the review papers. Several areas of research are of course being actively pursued, and the appended list of abstracts gives citations to this ongoing work. In a paper submitted to the Astrophysical Journal, the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, with and without previously formed internal crystals of titanium carbide (TIC) are reported.

Bernatowicz, Thomas J.↗

NASA NTRS2005

Constraints on Grain Formation Around Carbon Stars from Laboratory Studies of Presolar Graphite

We report the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, either with or without internal crystals of titanium carbide (TiC). In addition to providing detailed information about stellar nucleosynthesis, the structure and composition of presolar grains give unique information about the conditions of grain formation. In the present work we use laboratory observations of presolar graphite to gain insight into the physical conditions in circumstellar outflows from carbon AGB stars. The periodic pulsation of AGB stars enhances the gas density through shocks in the stellar atmosphere above the photosphere, promoting the condensation of dust grains. Copious mass outflow occurs largely because grains are coupled to the radiation field of the star, which accelerates them by radiation pressure; momentum is in turn transferred to gas molecules by collisions with grains. The dust/gas mixture is effectively a two-component fluid whose motion depends on atmospheric structure and which, in turn, influences that structure. In particular, the radiation pressure on the grains determines the velocity field of the outflow and thus the density distribution, while the density distribution itself determines the conditions of radiative transfer within the outflow and thus the effective radiation pressure.

Bernatowicz, T. J.↗

NASA NTRS2005

Surface and Internal Structure of Pristine Presolar Silicon Carbide

Silicon carbide is the most well-studied type of presolar grain. Isotope measurements of thousands [1,2] and structural data from over 500 individual grains have been reported [3]. The isotope data indicate that approximately 98% originated in asymptotic giant branch stars and 2% in supernovae. Although tens of different polytypes of SiC are known to form synthetically, only two polytypes have been reported for presolar grains. Daulton et al. [3] found that for SiC grains isolated from Murchison by acid treatments, 79.4% are 3C cubic beta-SiC, 2.7% are 2H hexagonal alpha-SiC, 17.1% are intergrowths of and , and 0.9% are heavily disordered. They report that the occurrence of only the and polytypes is consistent with the observed range of condensation temperatures of circumstellar dust for carbon stars. Further constraint on the formation and subsequent alteration of the grains can be obtained from studies of the surfaces and interior structure of grains in pristine form, i.e., prepared without acid treatments [4,5]. The acid treatments remove surface coatings, produce etch pits around defect sites and could remove some subgrains. Surface oxides have been predicted by theoretical modeling as a survival mechanism for SiC grains exposed to the hot oxidizing solar nebula [6]. Scanning electron microscopy studies of pristine SiC shows some evidence for the existence of oxide and organic coatings [4]. We report herein on transmission electron microscopy studies of the surface and internal structure of two pristine SiC grains, including definitive evidence of an oxide rim on one grain, and the presence of internal TiC and AlN grains.

Stroud, Rhonda, M.↗

NASA NTRS2001

Uncertainties in the Thermal and Mechanical Properties of Particulate Composites Quantified

Particle-reinforced composites are candidate materials for a wide variety of aerospace and nonaerospace applications. The high costs and technical difficulties involved with the use of many fiber-reinforced composites often limit their use in many applications. Consequently, particulate composites have emerged as viable alternatives to conventional fiber-reinforced composites. Particulate composites can be processed to near net shapepotentially reducing the manufacturing costs. They are candidate materials where shock or impact properties are important. For example, particle-reinforced metal matrix composites have shown great potential for many automotive applications. Typically, these materials are aluminum matrix reinforced with SiC or TiC particles. Reinforced concrete can also be thought of as a particle-reinforced composite. In situ ceramics can be modeled as particulate composites and are candidate materials for many high-temperature applications. The characterization of these materials is fundamental to their reliable use. It has been observed that the overall properties of these composites exhibit scatter because of the uncertainty in the constituent material properties, and fabrication-related parameters.

Murthy, Pappu L. N.↗

NASA NTRS2005

Microbiological Characterization and Concerns of the International Space Station Internal Active Thermal Control System

Since January 1999, the chemical the International Space Station Thermal Control System (IATCS) and microbial state of (ISS) Internal Active fluid has been monitored by analysis of samples returned to Earth. Key chemical parameters have changed over time, including a drop in pH from the specified 9.5 +/- 0.5 ta = 58.4, an increase in the level of total inorganic carbon (TIC), total organic carbon (TOC) and dissolved nickel (Ni) in the fluid, and a decrease in the phosphate (PO,) level. In addition, silver (AS) ion levels in the fluid decreased rapidly as Ag deposited on internal metallic surfaces of the system. The lack of available Ag ions coupled with changes in the fluid chemistry has resulted in a favorable environment for microbial growth. Counts of heterotrophic bacteria have increased from less than 10 colony-forming units (CFUs)/l00 mL to l0(exp 6) to l0(exp 7) CFUs/100 mL. The increase of the microbial population is of concern because uncontrolled microbiological growth in the IATCS can contribute to deterioration in the performance of critical components within the system and potentially impact human health if opportunistic pathogens become established and escape into the cabin atmosphere. Micro-organisms can potentially degrade the coolant chemistry; attach to surfaces and form biofilms; lead to biofouling of filters, tubing, and pumps; decrease flow rates; reduce heat transfer; initiate and accelerate corrosion; and enhance mineral scale formation. The micro- biological data from the ISS IATCS fluid, and approaches to addressing the concerns, are summarized in this paper.

Roman, Monsi C.↗

NASA NTRS2003

Particulate Titanium Matrix Composites Tested-Show Promise for Space Propulsion Applications

New manufacturing technologies can now produce uniformly distributed particle strengthened titanium matrix composites (TMCs) at lower cost than many types of continuous-fiber composites. The innovative process results in near-final-shape components having a material stiffness up to 26-percent greater than that of components made with conventional titanium materials. This benefit is achieved with no significant increase in the weight of the component. The improved mechanical performance and low-cost manufacturing capability motivated a review of particulate-reinforced metal composite technology as a way to lower the cost and weight of space-access propulsion systems. Focusing on the elevated-temperature properties of titanium alloy Ti-6Al-4V as the matrix material, researchers at the NASA Glenn Research Center conducted experiments to verify the improved performance of the alloy containing 10 wt% of ceramic titanium carbide (TiC) particles. The appropriate blend of metal and ceramic powder underwent a series of cold and hot isostatic pressing procedures to yield bar stock. A set of round dogbone specimens was manufactured from a small sample of the bars. The TMC material proved to have good machinability at this particle concentration as there was no difficulty in producing high-quality specimens.

Thesken, John C.↗

NASA NTRS2007

Wear Behavior of Low-Cost, Lightweight TiC/Ti-6Al-4V Composite Under Fretting: Effectiveness of Solid-Film Lubricant Counterparts

The wear behavior of low-cost, lightweight 10-wt% TiC-particulate-reinforced Ti-6Al-4V matrix composite (TiC/Ti- 6Al-4V) was examined under fretting at 296, 423, and 523 K in air. Bare 10-wt% TiC/Ti-6Al-4V hemispherical pins were used in contact with dispersed multiwalled carbon nanotubes (MWNTs), magnetron-sputtered diamondlike carbon/chromium (DLC/Cr), magnetron-sputtered graphite-like carbon/chromium (GLC/Cr), and magnetron-sputtered molybdenum disulphide/titanium (MoS2/Ti) deposited on Ti-6Al-4V, Ti-48Al-2Cr-2Nb, and nickel-based superalloy 718. When TiC/Ti-6Al-4V was brought into contact with bare Ti-6Al-4V, bare Ti-48Al-2Cr-2Nb, and bare nickel-based superalloy 718, strong adhesion, severe galling, and severe wear occurred. However, when TiC/Ti-6Al-4V was brought into contact with MWNT, DLC/Cr, GLC/Cr, and MoS2/Ti coatings, no galling occurred in the contact, and relatively minor wear was observed regardless of the coating. All the solid-film lubricants were effective from 296 to 523 K, but the effectiveness of the MWNT, DLC/Cr, GLC/Cr, and MoS2/Ti coatings decreased as temperature increased.

Miyoshi, Kazuhisa↗

NASA NTRS2007

Design of an Integrated-System FARAD Thruster

Pulsed inductive plasma accelerators are spacecraft propulsion devices in which energy is stored in a capacitor and then discharged through an inductive coil. The device is electrodeless, inducing a current s heet in a plasma located near the face of the coil. The propellant is accelerated and expelled at a high exhaust velocity (order of 10 km/s) through the interaction of the plasma current and the induced magne tic field, The Faraday Accelerator with RF-Assisted Discharge (FARAD) thruster is a type of pulsed inductive plasma accelerator in which t he plasma is preionized by a mechanism separate from that used to for m the current sheet and accelerate the gas. Employing a separate preionization mechanism allows for the formation of an inductive current s heet at much lower discharge energies and voltages than those used in previous pulsed inductive accelerators like the Pulsed Inductive Thr uster (PIT). In this paper, we present the design of a benchtop FARAD thruster with all the subsystems (mass injection, preionization, and acceleration) integrated into a single unit. Design of the thruster follows the guidelines and similarity performance parameters presented elsewhere. The system is designed to use the ringing, RF-frequency s ignal produced by a discharging Vector Inversion Generator (VIG) to p reionize the gas. The acceleration stage operates on the order of 100 J/pulse and can be driven by several different pulsed powertrains. These include a simple capacitor coupled to the system, a Bernardes and Merryman configuration, and a pulsecompression circuit that takes a temporally broad, low current pulse and transforms it into a short, h igh current pulse. A set of applied magnetic field coils are integrated into the system to guide the preionized propellant as it spreads ov er the face of the inductive acceleration coil. The coils are operate d in a pulsed mode, and the thruster can be operated without using the coils to determine if there is a performance improvement gain realiz ed when an applied field is present.

Polzin, K.A.↗

NASA NTRS2009

Measurement and Analysis of a Ferroelectric Field-Effect Transistor NAND Gate

Previous research investigated expanding the use of Ferroelectric Field-Effect Transistors (FFET) to other electronic devices beyond memory circuits. Ferroelectric based transistors possess unique characteris tics that give them interesting and useful properties in digital logic circuits. The NAND gate was chosen for investigation as it is one of the fundamental building blocks of digital electronic circuits. In t his paper, NAND gate circuits were constructed utilizing individual F FETs. N-channel FFETs with positive polarization were used for the standard CMOS NAND gate n-channel transistors and n-channel FFETs with n egative polarization were used for the standard CMOS NAND gate p-chan nel transistors. The voltage transfer curves were obtained for the NA ND gate. Comparisons were made between the actual device data and the previous modeled data. These results are compared to standard MOS logic circuits. The circuits analyzed are not intended to be fully opera tional circuits that would interface with existing logic circuits, bu t as a research tool to look into the possibility of using ferroelectric transistors in future logic circuits. Possible applications for th ese devices are presented, and their potential benefits and drawbacks are discussed.

Phillips, Thomas A.↗

NASA NTRS2010

International Space Station (ISS) Internal Active Thermal Control System (IATCS) New Biocide Selection, Qualification and Implementation

The Internal Active Thermal Control System (IATCS) aboard the International Space Station (ISS) is primarily responsible for the removal of heat loads from payload and system racks. The IATCS is a water based system which works in conjunction with the EATCS (External ATCS), an ammonia based system, which are interfaced through a heat exchanger to facilitate heat transfer. On-orbit issues associated with the aqueous coolant chemistry began to occur with unexpected increases in CO2 levels in the cabin. This caused an increase in total inorganic carbon (TIC), a reduction in coolant pH, increased corrosion, and precipitation of nickel phosphate. These chemical changes were also accompanied by the growth of heterotrophic bacteria that increased risk to the system and could potentially impact crew health and safety. Studies were conducted to select a biocide to control microbial growth in the system based on requirements for disinfection at low chemical concentration (effectiveness), solubility and stability, material compatibility, low toxicity to humans, compatibility with vehicle environmental control and life support systems (ECLSS), ease of application, rapid on-orbit measurement, and removal capability. Based on these requirements, ortho-phthalaldehyde (OPA), an aromatic dialdehyde compound, was selected for qualification testing. This paper presents the OPA qualification test results, development of hardware and methodology to safely apply OPA to the system, development of a means to remove OPA, development of a rapid colorimetric test for measurement of OPA, and the OPA on-orbit performance for controlling the growth of microorganisms in the ISS IATCS since November 3, 2007.

Wilson, Mark E.↗

NASA NTRS2011

International Space Station (ISS) Internal Active Thermal Control System (IATCS) New Biocide Selection, Qualification and Implementation

Wilson, Mark E.↗

NASA NTRS2011

Oxide Scales Formed on NiTi and NiPtTi Shape Memory Alloys

Ni-49Ti and Ni-30Pt-50Ti (at.%) shape memory alloys were oxidized isothermally in air over the temperature range of 500 to 900 C. The microstructure, composition, and phase content of the scales were studied by SEM, EDS, XRD, and metallography. Extensive plan view SEM/EDS identified various features of intact or spalled scale surfaces. The outer surface of the scale was a relatively pure TiO2 rutile structure, typified by a distinct highly striated and faceted crystal morphology. Crystal size increased significantly with temperature. Spalled regions exhibited some porosity and less distinct features. More detailed information was obtained by correlation of SEM/EDS studies of 700 C/100 hr cross-sections with XRD analyses of serial or taper-polishing of plan surfaces. Overall, multiple layers exhibited graded mixtures of NiO, TiO2, NiTiO3, Ni(Ti) or Pt(Ni,Ti) metal dispersoids, Ni3Ti or Pt3Ti depletion zones, and substrate, in that order. The NiTi alloy contained a 3 at.% Fe impurity that appeared in embedded localized Fe-Ti-rich oxides, while the NiPtTi alloy contained a 2 v/o dispersion of TiC that appeared in lower layers. The oxidation kinetics of both alloys (in a previous report) indicated parabolic growth and an activation energy (250 kJ/mole) near those reported in other Ti and NiTi studies. This is generally consistent with TiO2 existing as the primary scale constituent, as described here.

Smialek, James L.↗

NASA NTRS2012

TEM Observation of the Ti Interlayer Between SiC Substrates During Diffusion Bonding

Diffusion bonding was carried out to join SiC to SiC substrates using titanium interlayers. In this study, 10 m and 20 m thick physical vapor deposited (PVD) Ti surface coatings, and 10 and 20 m thick Ti foils were used. Diffusion bonding was performed at 1250 C for PVD Ti coatings and 1200 C for Ti foil. This study investigates the microstructures of the phases formed during diffusion bonding through TEM and selected-area diffraction analysis of a sample prepared with an FIB, which allows samples to be taken from the reacted area. In all samples, Ti3SiC2, Ti5Si3Cx and TiSi2 phases were identified. In addition, TiC and unknown phases also appeared in the samples in which Ti foils were used as interlayers. Furthermore, Ti3SiC2 phases show high concentration and Ti5Si3Cx formed less when samples were processed at a higher temperature and thinner interlayer samples were used. It appears that the formation of microcracks is caused by the presence of intermediate phase Ti5Si3Cx, which has anisotropic thermal expansion, and by the presence of an unidentified Ti-Si-C ternary phase with relatively low Si content.

Tsuda, Hiroshi↗

NASA NTRS2002

The Halite-Bearing Zag and Monahans (1998) Meteorite Breccias: Shock Metamorphism, Thermal Metamorphism and Aqueous Alteration on the H-Chondrite Parent Body

Zag and Monahans (1998) are H-chondrite regolith breccias comprised mainly of lightcolored metamorphosed clasts, dark clasts that exhibit extensive silicate darkening, and a halite-bearing clastic matrix. These meteorites reflect a complex set of modification processes that occurred on the H-chondrite parent body. The light-colored clasts are thermally metamorphosed H5 and H6 rocks that were fragmented and deposited in the regolith. The dark clasts formed from light-colored clasts during shock events that melted and mobilized a significant fraction of their metallic Fe-Ni and troilite grains. The clastic matrices of these meteorites are rich in solar-wind gases. Parent-body water was required to cause leaching of chondri tic minerals and chondrule glass; the fluids became enriched in Na, K, CI, Br, AI, Ca, Mg and Fe. Evaporation of the fluids caused them to become brines as halides and alkalies became supersaturated; grains of halite (and, in the case of Monahans (1998), halite with sylvite inclusions) precipitated at low temperatures (less than or equal to 100 C) in the porous regolith. In both meteorites fluid inclusions were trapped inside the halite crystals. Primary fluid inclusions were trapped in the growing crystals; secondary inclusions formed subsequently from fluid trapped within healed fractures.

Rubin, Alan E.↗

NASA NTRS2013

Characterization of Heat Melt Compactor (HMC) Product Water

The Heat Melt Compactor (HMC) is designed to sterilize and process wastes produced during space missions. Benefits of the HMC include reduction of biohazards to the crew, reduction in volume of wastes that would otherwise require storage, production of radiation shielding tiles, and recovery of water and other resources. Water reuse is critical onboard spacecrafts; it reduces the need for resupply missions and saves valuable storage space. The main sources of water in HMC batches are food, beverages, shampoo, disinfecting wipes, toothpaste, and diapers. Water reclaimed by the HMC was analyzed for concentrations of Na+, NH4+, K+, Mg2+, Ca2+, Cl-‐, NO2-‐, Br-‐, NO3-‐, PO43-‐, SO42-‐, total organic carbon (TOC), total inorganic carbon (TIC), % total solids, and pH. The data are discussed in relation to the current water input characteristics established for the International Space Station Water Processor Assembly system. Batches with higher than average amounts of food produced HMC product water with higher sulfate content, and batches with higher proportions of disinfectant wipes and food yielded HMC product water with higher ammonium concentration. We also compared theoretical chemical composition of HMC product water based on food labels and literature values to experimental results.

Heat Melt Compactor↗

NASA NTRS2016

Characterization of Candidate Materials for Remote Recession Measurements of Ablative Heat Shield Materials

A method of remotely measuring surface recession of a material sample in a plasma flow through emission spectroscopy of the post shock layer was characterized through experiments in the NASA Langley HYMETS arc jet facility. Different methods for delivering the seed products into the Phenolic Impregnated Carbon Ablator (PICA) material samples were investigated. Three samples were produced by seeding the PICA material with combinations of Al, Si, HfO2, VB2, Al2O3, SiO2, TiC, HfC, NaCl, and MgCl2 through infusing seed materials into a core of PICA, or through encapsulating seed material in an epoxy disk, mechanically bonding the disk to a PICA sample. The PICA samples seeded with the candidate tracers were then tested at surface temperatures near 2400 K under low pressure air plasma. The emission of Al, Ti, V, Na, and Mg in the post-shock layer was observed in the UV with a high resolution imaging spectrometer viewing the whole stagnation line from the side, and from UV to NIR with a fiber-coupled miniaturized spectrometer observing the sample surface in the wavelength range from 200 nm to 1,100 nm from the front through a collimator. Al, Na, and Mg were found to be emitting in the post-shock spectra even before the recession reached the seeding depth - therefore possibly characterizing the pyrolysis process rather than the recession itself. The appearance of Ti and V emission in the spectra was well correlated with the actual recession which was monitored through a video of the front surface of the sample. The applicability of a seed material as an indicator for recession appears to be related to the melting temperature of the seed material. Future parametric studies will be carried out in low power plasma facilities at the University of Kentucky.

Butler, Bradley D.↗