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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Effect of secondary gas-phase reactions (SGR) in pyrolysis of carbon feedstocks for anisotropic carbon materials production – 3: Modifying non-coking coal tar through co-pyrolysis of coal with linear low-density polyethylene and high-impact polystyrene

Herein, this work focuses on co-pyrolysis experiments of Utah Sufco coal with linear low-density polyethylene (LLDPE) and high-impact polystyrene (HIPS). These two plastic types have differing pyrolysis chemistries and have different hydrogen transfer behavior. Similar to earlier work in this series of papers, controlled secondary gas-phase reactions during pyrolysis were used to induce cracking and condensation reactions among the pyrolytic tar species. Co-pyrolysis tests were performed with feed plastic percentages ranging from 10-20 wt% and pyrolysis SGR temperatures ranging from 800-900°C. Analyses of the intermediate tar products showed that oxygen contents and aromaticity were substantially different, depending on the plastic, and resulting pitch softening points and mesophase contents also varied greatly depending on the starting plastic feedstock used. Most of the synergies observed in the co-pyrolysis results were negative, except for the oxygen content. Oxygen contents were higher than expected when LLDPE was used, resulting in reactive pitches with softening points > 350°C. On the other hand, oxygen contents were lower than expected when HIPS was used, resulting in less reactive pitches. Ultimately, only the HIPS/coal samples created at the SGR temperature of 900°C had reasonable softening points at or under 350°C, making them the only samples created in this work potentially suitable for mesophase pitch-based carbon fiber production. The success in creating fusible mesophase pitches from co-pyrolyzing HIPS with Utah Sufco coal is likely attributed to the fact that polystyrene is a stronger hydrogen acceptor rather than donor, which should facilitate more cracking rather than stabilizing tar oxygen functional groups, making the tar species ultimately less reactive during thermal conversion to mesophase pitch.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2022

Effect of secondary gas-phase reactions (SGR) in pyrolysis of carbon feedstocks for anisotropic carbon materials production – 2: Effects of SGR on tars produced from varying ranks of coal

Herein, this work explores the extent to which secondary gas-phase reactions (SGR) in pyrolysis can be used to modify coal tar chemistries from coals of different ranks in favor of improved anisotropy formation in their respective pitches. Pyrolysis was performed on four different coals of varying bituminous rank (Utah Sufco, Wyoming PRB Black Thunder, Illinois #6, and West Virginia Flying Eagle), with SGR temperatures ranging from 800 to 900° C and nominal SGR gas-phase residence times from 1 to 2.5 s. The oxygen content, aliphatic content, and molecular weight distributions of the coal tar samples were measured to indicate the changes with increasing levels of SGR, and microscopy was also used to measure changes in anisotropy formation in the resulting pitch samples. Generally, for all coals tested, increased levels of pyrolysis SGR led to decreased oxygen and aliphatic content, increased molecular weight sizes, and improved anisotropy formation. However, it was clear that the extent of these property changes depended on the chemistry and rank of the starting coal feedstock. Despite the relatively high rank of the Illinois #6 coal, its respective pitch samples performed poorly in improving anisotropy formation, due to its high sulfur content. The PRB, Sufco, and Flying Eagle coals performed better in their anisotropy formation than Illinois #6, depending on their respective coal ranks. Statistical analysis (analysis of variance, ANOVA) performed on the sample characterization data also suggests that SGR temperature is consistently the most dominant and significant effect on the resulting coal products.

01 COAL, LIGNITE, AND PEAT↗
NASA NTRS1994

Origins of interstellar and solar system: Carbonaceous materials

Carbon is a crucial atom in cosmochemistry. It is well-established that carbon is synthesized in stellar interiors after the main sequence, is ejected by red giants as small carbonaceous grains during their 'carbon star' phase, resides in the interstellar medium, and was later incorporated into the solar system. The mechanisms of carbon grain formation and later chemical processing are complex because, with only small thermodynamic differences, carbon can take on a bewildering variety of forms: diamond; oxides; carbides; graphite; aliphatic hydrocarbons; polycyclic aromatic hydrocarbons (PAH's); fullerenes; amorphous carbon; and other compounds. These are evidence for many of the forms of carbon found in astronomical observations. We seek to understand the possible astrophysical sites and conditions of the origins of different forms of carbon by combining state-of-the-art capabilities of carbon chemistry with astrophysical modeling. The work is a collaboration between Prof. Frenklach, a leading carbon materials scientist with both laboratory and computer modeling expertise and Prof. Feigelson, an astrophysicist with interests in star formation. The largest effort under this grant was devoted to developing this concept into a comprehensive quantitative model. In addition to explaining the astronomical properties of red giants producing carbonaceous grains, our model also can incorporate recent meteoritic findings. Finally, our induced nucleation grain formation model provides a natural explanation for the widespread presence of PAH emission bands in the Galactic interstellar medium. A brief synopsis of other activities sponsored under this grant and a list of publications from this grant is included.

Feigelson, Eric D.↗
DOE OSTI2020

Fabrication of field-effect transistors with transfer-free nanostructured carbon as semiconducting channel material

Carbon nanostructures as active channel material in field effect transistors (FETs) are appealing in microelectronics for their improved performance such as high speed and low energy dissipation. However, these devices require the incorporation of nanostructure transfer steps in the fabrication process flow, which makes difficult its application in large scale integration circuits. Here we present a novel method for the fabrication of FETs with nanostructured carbon in the channel with p-type semiconducting properties and intermediate drain-source current (IDS) on/off ratio. The method is based on the use of Ni nanoparticles in the source-drain gap region as seed material for the formation of carbon nanostructures in the FET channel. FETs without Ni nanoparticles in the channel showed no modulation of IDS as a function of gate voltage. The device fabrication process does not require any carbon nanostructure transfer steps since it directly forms carbon nanostructures electrically connected to the device's source and drain electrodes via electron-beam evaporation of carbon and conventional lithographic processes. Since all device fabrication steps are compatible with Si technology processes, they are capable of being further optimized following process development protocols practiced by the semiconductor industry.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2014

Improved Composites Using Crosslinked, Surface-Modified Carbon Nanotube Materials

Individual carbon nanotubes (CNTs) exhibit exceptional tensile strength and stiffness; however, these properties have not translated well to the macroscopic scale. Premature failure of bulk CNT materials under tensile loading occurs due to the relatively weak frictional forces between adjacent CNTs, leading to poor load transfer through the material. When used in polymer matrix composites (PMCs), the weak nanotube-matrix interaction leads to the CNTs providing less than optimal reinforcement.Our group is examining the use of covalent crosslinking and surface modification as a means to improve the tensile properties of PMCs containing carbon nanotubes. Sheet material comprised of unaligned multi-walled carbon nanotubes (MWCNT) was used as a drop-in replacement for carbon fiber in the composites. A variety of post-processing methods have been examined for covalently crosslinking the CNTs to overcome the weak inter-nanotube shear interactions, resulting in improved tensile strength and modulus for the bulk sheet material. Residual functional groups from the crosslinking chemistry may have the added benefit of improving the nanotube-matrix interaction. Composites prepared using these crosslinked, surface-modified nanotube sheet materials exhibit superior tensile properties to composites using the as received CNT sheet material.

polymer matrix composite↗
NASA NTRS1983

Present state of boron-carbon thermoelectric materials

Boron-carbon p-type thermoelectric materials show promise for use in advanced thermal-to-electric space power conversion systems. Here, recent data on the thermoelectric properties of boron-carbon materials, such as B9C, B13C2, B15C2, and B4C, are reviewed. In particular, attention is given to the effect of the compositional homogeneity and residual impurity content on the Seeback coefficient, electrical resistivity, and thermal conductivity of these materials. The effect of carbon content for a given level of impurity and degree of homogeneity is also discussed.

Elsner, N. B.↗
DOE OSTI2023

An innovative carbonated cementitious material and its printability and carbon mineralization capacity

The main goal of this research is to develop a carbonated cementitious material (CCMs) mix design and demonstrate its rapid stiffening for manufacturing 3D printed or precast elements for building construction (i.e., concrete with enhanced durability and CO 2 capture efficiency). The material development employs hydrated Ca(OH) 2 , and its distinct reaction with CO 2 to form CaCO 3 . Different formulations and additives including polymer materials enable the thermomechanical properties that give these CCMs 3D printability comparable with cement materials used for similar applications. Here, printable and castable CCM formulations were successfully developed and demonstrated to mineralize CO 2 to form up to 57% CaCO 3 .

36 MATERIALS SCIENCE↗
NASA NTRS1987

Materials property definition and generation for carbon-carbon and carbon phenolic materials

A data base program to generate statistically significant material-property data for carbon-carbon and carbon phenolic materials to be used in designs of Space Shuttle is described. The program, which will provide data necessary for thermal and stress modeling of Shuttle nozzle and exit cone structures, includes evaluation of tension, compression, shear strength, shear modulus, thermal expansion, thermal conductivity, permeability, and emittance for both materials; the testing of carbon phenolic materials also includes CTE, off-gassing, pyrolysis, and RTG. Materials to be tested will be excised from Space Shuttle inlet, throat, and exit cone billets and modified involute carbon-carbon exit cones; coprocessed blocks, panels, and cylinders will also be tested.

Canfield, A. R.↗
DOE OSTI2025

Logical approach to tritium vacuum pump selection for fusion applications

Vacuum pumps have been used for tritium processing since the 1940s following the isolation of pure tritium. The largest problem facing tritium vacuum pumps is the tritium radioactive decay. The beta particles, recoil energy, and subsequent radical formations are detrimental to most carbon-based materials. Carbon materials, such as plastics, elastomers, carbon fiber, activated carbon, etc., react with tritium to form methane and in the process strip material from the carbonbased material. Other reactions can be self-catalyzing, as is the case with nitrogen and tritium forming tritiated ammonia at room temperature and pressure. Tritium also readily isotopically exchanges with surface -OH groups, increasing the amount of protium in the gas stream while creating a tritium holdup on the surface. Metals are the preferred material when working with tritium, but tritium will permeate into and through almost all metals at some point. The entrapped tritium can decay inside the metal, creating local helium distortions that can impact the structural properties above and beyond the hydrogen embrittlement issue tritium can cause.

Angelette, Lucas M. [Savannah River National Labor↗
NASA NTRS1990

On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous, or short-range ordered, carbon identified by conventional TEM imaging and SAED may show evidence for sp(3) bonds in EELS spectra. It is suggested that complex, nanometer-scale, mineralogical interrelations are common to all elemental carbons irrespective of their origin. The subsequent thermal history, or energy balance, will determine the ultimate microstructure.

Rietmeijer, Frans J. M.↗