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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Lignin-Derived Carbon Fiber as a Co-Product of Refining Cellulosic Biomass

Lignin by-products from biorefineries has the potential to provide a low-cost alternative to petroleum-based precursors to manufacture carbon fiber, which can be combined with a binding matrix to produce a structural material with much greater specific strength and specific stiffness than conventional materials such as steel and aluminum. The market for carbon fiber is universally projected to grow exponentially to fill the needs of clean energy technologies such as wind turbines and to improve the fuel economies in vehicles through lightweighting. In addition to cellulosic biofuel production, lignin-based carbon fiber production coupled with biorefineries may provide $2,400 to $3,600 added value dry Mg-1 of biomass for vehicle applications. Compared to producing ethanol alone, the addition of lignin-derived carbon fiber could increase biorefinery gross revenue by 30% to 300%. Using lignin-derived carbon fiber in 15 million vehicles per year in the US could reduce fossil fuel consumption by 2-5 billion liters year-1, reduce CO2 emissions by about 6.7 million Mg year-1, and realize fuel savings through vehicle lightweighting of $700 to $1,600 per Mg biomass processed. The value of fuel savings from vehicle lightweighting becomes economical at carbon fiber price of $6.60 kg-1 under current fuel prices, or $13.20 kg-1 under fuel prices of about $1.16 l-1.

09 BIOMASS FUELS↗
DOE OSTI2013

Structure-based discovery of fiber-binding compounds that reduce the cytotoxicity of amyloid beta

Amyloid protein aggregates are associated with dozens of devastating diseases including Alzheimer’s, Parkinson’s, ALS, and diabetes type 2. While structure-based discovery of compounds has been effective in combating numerous infectious and metabolic diseases, ignorance of amyloid structure has hindered similar approaches to amyloid disease. Here we show that knowledge of the atomic structure of one of the adhesive, steric-zipper segments of the amyloid-beta (Aβ) protein of Alzheimer’s disease, when coupled with computational methods, identifies eight diverse but mainly flat compounds and three compound derivatives that reduce Aβ cytotoxicity against mammalian cells by up to 90%. Although these compounds bind to Aβ fibers, they do not reduce fiber formation of Aβ. Structure-activity relationship studies of the fiber-binding compounds and their derivatives suggest that compound binding increases fiber stability and decreases fiber toxicity, perhaps by shifting the equilibrium of Aβ from oligomers to fibers.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1972

Design and fabrication of engineering model fiber-optics detector

The design and fabrication of an annular ring detector consisting of optical fibers terminated with photodetectors is described. The maximum width of each concentric ring has to be small enough to permit the resolution of a Ronchi ruling transform with a dot spacing of 150 microns. A minimum of 100 concentric rings covering a circular area of 2.54 cm diameter also is necessary. A fiber-optic array consisting of approximately 89,000 fibers of 76 microns diameter was fabricated to meet the above requirements. The fibers within a circular area of 2.5 cm diameter were sorted into 168 adjacent rings concentric with the center fiber. The response characteristics of several photodetectors were measured, and the data used to compare their linearity of response and dynamic range. Also, coupling loss measurements were made for three different methods of terminating the optical fibers with a photodetector.

Mcsweeney, A.↗
NASA NTRS1973

Factors affecting miniature Izod impact strength of tungsten-fiber-metal-matrix

The miniature Izod and Charpy impact strengths of copper, copper-nickel, and nickel-base superalloy uniaxially reinforced with continuous tungsten fibers were studied. In most cases, impact strength was increased by increasing fiber or matrix toughness, decreasing fibermatrix reaction, increasing test temperature, hot working, or heat treating. Notch sensitivity was reduced by increasing fiber content or matrix toughness. An equation relating impact strength to fiber and matrix properties and fiber content was developed. Program results imply that tungsten alloy-fiber/superalloy matrix composites can be made with adequate impact resistance for turbine blade or vane applications.

Winsa, E. A.↗
NASA NTRS1972

The effects of matrix and interface modification on local fractures of carbon fibers in epoxy.

This paper examines the fracture mechanisms which occur in the matrix and interfacial region surrounding a fiber when the fiber fails under axial load. Both tensile and compressive behavior of carbon fibers in an epoxy-novolac system are treated for specimens having very low fiber concentrations. First, the fracture mechanisms are isolated and identified and then means for controlling the propagation or containment of fiber fractures are explored. Sequences of photographs showing progressive damage with increasing load are presented for each loading condition. Effects of fiber orientation are also treated.

Mullin, J. V.↗
NASA NTRS1974

Effect of chromia doping of thermal stability of silica fibers

Commercial silica fibers of the type being evaluated for reusable surface insulation for reentry vehicles were found to be porous and composed of subfibers. The effect on shrinkage and devitrification of soaking such silica fibers in water, acetic acid, chromium acetate, and chromium nitrate solutions was studied. Felted specimens made of chromia-doped fibers shrunk only about one-half as much as those made of untreated fibers after exposure in air for 4 hours at 1300 C. The devitrification rate of fibers given prolonged soaks in chromium nitrate was as low as that of as-received fibers.

Zaplatynsky, I.↗
NASA NTRS1975

Carbide coated fibers in graphite-aluminum composites

The NASA-supported program at the Los Alamos Scientific Laboratory (LASL) to develop carbon fiber-aluminum matrix composites is described. Chemical vapor deposition (CVD) was used to uniformly deposit thin, smooth, continuous coats of TiC on the fibers of graphite tows. Wet chemical coating of fibers, followed by high-temperature treatment, was also used, but showed little promise as an alternative coating method. Strength measurements on CVD coated fiber tows showed that thin carbide coats can add to fiber strength. The ability of aluminum alloys to wet TiC was successfully demonstrated using TiC-coated graphite surfaces. Pressure-infiltration of TiC- and ZrC-coated fiber tows with aluminum alloys was only partially successful. Experiments were performed to evaluate the effectiveness of carbide coats on carbon as barriers to prevent reaction between alluminum alloys and carbon. Initial results indicate that composites of aluminum and carbide-coated graphite are stable for long periods of time at temperatures near the alloy solidus.

Imprescia, R. J.↗
NASA NTRS1976

Further development of high temperature-resistant graphite fiber coupling agents

Potential coupling agents for graphite fibers were screened by their effect on the weight losses of Thornel 300, HMS, and HTS fibers at 588K for 200 and 400 hours. Unidirectional laminates were made from HMS and HTS fibers, untreated, and treated with each of the seven coupling agents. The matrix of all laminates was PMR polyimide (PMR-PR). On the basis of the best overall retention of elevated temperature interlaminar shear strength after 200 hours at 588K, composite weight after 200 hours at 588K, and fiber weight after 400 hours at 588K, ventromer T-1 applied from aqueous solution and pyrolyzed PPQ were selected for further evaluation as coupling agents for HTS fiber while ventromer T-2 and pyrolyzed PPQ were selected as coupling agents for HMS fiber. It was shown that pyrolyzed PPQ as a coupling agent improves the oxidative stability of HTS/PMR-PI composites.

Griffin, R. N.↗
NASA NTRS1976

Fiber distributed feedback laser

Utilizing round optical fibers as communication channels in optical communication networks presents the problem of obtaining a high efficiency coupling between the optical fiber and the laser. A laser is made an integral part of the optical fiber channel by either diffusing active material into the optical fiber or surrounding the optical fiber with the active material. Oscillation within the active medium to produce lasing action is established by grating the optical fiber so that distributed feedback occurs.

Elachi, C.↗
NASA NTRS1977

Residual stresses in boron/tungsten and boron/carbon fibers

By measuring the change in fracture stress of 203 micrometer diameter fibers of boron on tungsten (B/W) as a function of fiber diameter as reduced by chemical etching, it is shown that the flaws which limit B/W fiber strength are located at the surface and in the tungsten boride core. After etching to a diameter of 188 micrometers m virtually all fiber fractures were caused by core flaws, the average strength being 4.50 GN/sq m. If both the surface and core flaws are removed, the fracture strength, limited by flaws in the boron itself, is approximately 6.89 GN/sq m. This was measured on B/W fibers which were split longitudinally and had their cores removed by chemical etching. The longitudinal residual stress distribution was determined for 102 micrometer diameter B/W and B/C fibers.

Behrendt, D. R.↗
NASA NTRS1978

Axial residual stresses in boron fibers

The axial residual stress distribution as a function of radius was determined from the fiber surface to the core including the average residual stress in the core. Such measurements on boron on tungsten (B/W) fibers show that the residual stresses for 102, 142, 203, and 366 micron diameter fibers were similar, being compressive at the surface and changing monotonically to a region of tensile within the boron. At approximately 25 percent of the original radius, the stress reaches a maximum tensile stress of about 860 mn/sq.m and then decreases to a compressive stress near the tungsten boride core. Data were presented for 203 micron diameter B/W fibers that show annealing above 900 C reduces the residual stresses. A comparison between 102 micron diameter B/W and boron on carbon (b/C) shows that the residual stresses were similar in the outer regions of the fibers, but that large differences near and in the core were observed. The effects of these residual stresses on the fracture of boron fibers were discussed.

Behrendt, D. R.↗
NASA NTRS1978

Wide temperature range fiber optic cable: Cable design study

Factors considered in the design and fabrication of a single fiber optic cable intended for spacecraft applications in an environment of temperature extremes from -160 C to 125 C include: abrasion resistance, low temperature flexibility, small size, low weight, and overall temperature stability. Specific requirements were identified for fiber core and overall diameters, fiber loss and NA, and cable tensile load. The single fiber cable will be fabricated by using a chemical vapor step index fiber of .125 mm coated to .3 mm with RTV silicone and then extruded with a jacket of Teflon PFA to a diameter of .5 mm. Six yarns of 1420 denier unimpregnated Kevlar 49 with a helical lay of 1.3 inches will surround the jacketed fiber under an extrusion of PFA. The finished cable diameter will measure 1.8 mm, and the weight of one kilometer length will be approximately 4350grams.

Speed, E. U.↗
NASA NTRS1979

Mechanisms of boron fiber strengthening by thermal treatment

The fracture strain for boron on tungsten fibers was studied for improvement by heat treatment under vacuum or argon environments. The mechanical basis for this improvement is thermally-induced axial contraction of the entire fiber, whereby strength-controlling core flaws are compressed and fiber fracture strain increased by the value of the contraction strain. By highly sensitive measurements of fiber density and volume, the physical mechanism responsible for contraction under both environments was identified as boron atom diffusion out of the fiber sheath. The fiber contracts because the average volume of the resulting microvoid was determined to be only 0.26 plus or minus 0.09 the average atomic volume of the removed atom. The basic and practical implications of these results are discussed with particular emphasis on the theory, use, and limitations of heat-induced contraction as a simple cost-effective secondary processing method.

Dicarlo, J. A.↗
NASA NTRS1979

Carbon fiber behavior in an enclosed volume

Tests were performed to evaluate the behavior of single carbon fibers existing in an enclosed space such as a room of a building. Three general phenomena were explored: the concentration decay rate of a fiber-charged room, the degree of uniform mixing of fibers within a room, and the effects of fibers being redisseminated off deposition surfaces within a room. The results were required in understanding the ratio of total indoor fiber exposure to total outdoor fiber exposure, a quantity essential to risk analysis. Results indicate that decay rate is predictable within acceptable limits and that homogeneous mixing can always be assumed. Some factors of redissemination are identified and effects discussed.

Harvey, M. C.↗
NASA NTRS1979

Mechanisms of boron fiber strengthening by thermal treatment

The fracture strain for boron on tungsten fibers can be improved by heat treatment under vacuum or argon environments. The mechanical basis for this improvement is thermally-induced axial contraction of the entire fiber, whereby strength-controlling core flaws are compressed and fiber fracture strain increased by the value of the contraction strain. By highly sensitive measurements of fiber density and volume, the physical mechanisms responsible for contraction under both environments was identified as boron atom diffusion out of the fiber sheath. The fiber contracts because the average volume of the resulting microvoid was determined to be only 0.26 + or - 0.09 the average atomic volume of the removed atom. The basic and practical implications of these results are discussed with particular emphasis on the theory, use, and limitations of heat-induced contraction as a simple cost-effective secondary processing method.

Dicarlo, J. A.↗
NASA NTRS1980

Burning characteristics and fiber retention of graphite/resin matrix composites

Graphite fiber reinforced resin matrix composites were subjected to controlled burning conditions to determine their burning characteristics and fiber retention properties. Small samples were burned with a natural gas fired torch to study the effects of fiber orientation and structural flaws such as holes and slits that were machined into the laminates. Larger laminate samples were burned in a modified heat release rate calorimeter. Unidirectional epoxy/graphite and polyimide/graphite composites and boron powder filled samples of each of the two composite systems were burn tested. The composites were exposed to a thermal radiation of 5.3 Btu/sq ft-sec in air. Samples of each of the unfilled composite were decomposed anaerobically in the calorimeter. Weight loss data were recorded for burning and decomposition times up to thirty-five minutes. The effects of fiber orientation, flaws, and boron filler additives to the resins were evaluated. A high char forming polyimide resin was no more effective in retaining graphite fibers than a low char forming epoxy resin when burned in air. Boron powder additions to both the polyimide and the epoxy resins stabilized the chars and effectively controlled the fiber release.

Bowles, K. J.↗
NASA NTRS1980

Effects of carbon/graphite fiber contamination on high voltage electrical insulation

The contamination mechanics and resulting failure modes of high voltage electrical insulation due to carbon/graphite fibers were examined. The high voltage insulation vulnerability to carbon/graphite fiber induced failure was evaluated using a contamination system which consisted of a fiber chopper, dispersal chamber, a contamination chamber, and air ducts and suction blower. Tests were conducted to evaluate the effects of fiber length, weathering, and wetness on the insulator's resistance to carbon/graphite fibers. The ability of nuclear, fossil, and hydro power generating stations to maintain normal power generation when the surrounding environment is contaminated by an accidental carbon fiber release was investigated. The vulnerability assessment included only the power plant generating equipment and its associated controls, instrumentation, and auxiliary and support systems.

Garrity, T.↗
NASA NTRS1980

Evaluation of micron size carbon fibers released from burning graphite composites

Quantitative estimates were developed of micron carbon fibers released during the burning of graphite composites. Evidence was found of fibrillated particles which were the predominant source of the micron fiber data obtained from large pool fire tests. The fibrillation phenomena were attributed to fiber oxidation effects caused by the fire environment. Analysis of propane burn test records indicated that wind sources can cause considerable carbon fiber oxidation. Criteria estimates were determined for the number of micron carbon fibers released during an aircraft accident. An extreme case analysis indicated that the upper limit of the micron carbon fiber concentration level was only about half the permissible asbestos ceiling concentration level.

Sussholz, B.↗