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Bioorganic comparative analysis of desert soils, Precambrian shales and meteorites by automated pyrolysis-gas chromatography-mass spectrometry system for future Mars soil analysis
Determining composition of pyrolysis products from degradation of ablative materials
Thermal cracking of phenolic-nylon pyrolysis products analyzed on passing through heated char
Rapid linear pyrolysis of polymethyl methacrylate
Charring ablative composites pyrolysis products composition determination, comparing chemical analysis techniques
Hydrocarbons pyrolysis in Knudsen cells at low pressures, using mass spectrometry to study reactions and products
The carbon contents of various lunar soil particle types and sieve fractions of Apollo 15 and 16 samples have been determined by the pyrolysis method. The mineral, glass, and high-grade breccia fragments in the soils examined contain relatively low amounts of carbon (approximately 8, 25, and 25 microg C/g sample respectively in 149-250 micron grains). Most low-grade breccias and all agglutinates examined have high carbon contents (approximately 52 and 80 microg C/g sample respectively), and agglutinate abundance is indicative of the carbon content and maturity of a soil. The distribution of carbon with respect to particle size in mature soils generally reveals a minimum in carbon content at about 100 micron particle diameter. At smaller particle diameters, carbon content is directly proportional to particle surface area and therefore increases with the ratio (surface area)/(particle mass). A model relating the cycle of comminution and aggregation of soil particles to the redistribution of surface implanted carbon is developed.
Pyrolysis of several structurally different amino acids in a column at 500 C showed differences in the mechanisms and final products. The aliphatic protein amino acids decompose mainly by simple decarboxylation and condensation reactions, while the beta amino acids undergo deamination to unsaturated acids. Alpha amino acids with alpha alkyl substituents undergo an unusual intramolecular SN1 reaction with the formation of an intermediate alpha lactone which decomposes to yield a ketone. The alpha alkyl substituents appear to stabilize the developing negative charge formed by partial heterolytic cleavage of the alpha carbon - NH3 bond. The gamma and delta amino acids give 2-pyrrolidinone and 2-piperidone respectively, while the epsilon acids yield mixed products.
A number of spacecraft construction materials are evaluated for the toxic effects of their thermodegradation products on rats. Pyrolysis toxicity testing of pyrolysate fumes establish carbon monoxide, carbon dioxide and hydrogen cyanide as the most common intoxicating agents. Generally, COHb levels of animals expiring in the test chamber suggest higher concentrations of CO are produced with larger samples of most materials.
The hydrogen contents of various Apollo 15 rocks and Apollo 15 and 16 soil particle types and sieve fractions have been determined by the pyrolysis method. The Apollo 15 crystalline rocks analyzed release very little hydrogen (approximately 6 micromoles H/g sample). The mineral, glass, and light-colored breccia fragments in the soils contain approximately 5, 30, and 10 micromoles H/g sample, respectively. The dark breccias and glassy agglutinates examined have much higher hydrogen contents (60 and 110 micromoles H/g sample). For soil particle diameters less than 105 microns, hydrogen content increases linearly with particle surface area per particle mass. The calculated grain surface average concentrations of hydrogen in the Apollo 15 and 16 soils fall short of experimentally determined saturation values by a factor of 20. The volume-correlated component of hydrogen in a soil increases with the maturity of the soil.
The following projects were completed as part of the effort to develop and test economically feasible fire-resistant materials for interior furnishings of aircraft as well as detectors of incipient fires in passenger and cargo compartments: (1) determination of the sensitivity of various contemporary gas and smoke detectors to pyrolysis and combustion products from materials commonly used in aircraft interiors and from materials that may be used in the future, (2) assessment of the environmental limitations to detector sensitivity and reliability. The tests were conducted on three groups of materials by exposure to the following three sources of exposure: radiant and Meeker burner flame, heated coil, and radiant source only. The first test series used radiant heat and flame exposures on easily obtainable test materials. Next, four materials were selected from the first group and exposed to an incandescent coil to provide the conditions for smoldering combustion. Finally, radiant heat exposures were used on advanced materials that are not readily available.
One of the principal factors in animal toxicity studies is the choice of animal species. A limited study of the relative toxicity of the pyrolysis products from cotton and wool indicated that values of concentrations and doses required to produce death in 50% of the test animals obtained with Swiss albino mice were approximately one-half the values obtained with Sprague-Dawley rats. The toxicity of cotton relative to that of wool was the same using Swiss albino mice or Sprague-Dawley rats. Rankings of relative toxicity appear to be more sensitive to differences in apparatus and procedure than to interspecies differences.
An apparatus and procedure for evaluating the toxicity of pyrolysis gases from synthetic polymers are described. In each test, four Swiss albino mice are exposed in a 5-liter chamber to the gases from materials pyrolyzed at 700 C. The apparatus is simple in design, easy to clean, inexpensive and gives reproducible results. Data on several fluorine-containing and polyamide polymers are presented.
This paper considers a model for the pyrolysis of polymers for use in mass loss and smoke density predictions in a fire situation. It is based on the fundamental postulate that the overall rate-limiting reactions are in the relatively low temperature condensed phase; the rate limiting step is the polymer degradation to a vaporizable state. The state of the polymer (chain length) at the surface is specified by the vapor pressure equilibrium criterion. For the case of polymers with inert fillers, like alumina trihydrate, the further assumption is made that the linear regression rate of the material is identical to the unfilled material's at the same surface temperature. The fraction of polymer mass loss converted to smoke is inferred from the literature. The smoke density in the NBS-smoke density chamber is predicted for a polyester and the same polyester with two different loads of alumina trihydrate filler. Diffusional effects in the smoke spreading are considered in an elementary manner. The comparisons with experimental data are encouraging. The overall fire characteristics are predicted using only the fundamental physicochemical property values of ingredients.
The four basic elements in the chemical vapor deposition (CVD) of silicon from silane are analytically treated from a kinetic standpoint. These elements are mass transport of silane, pyrolysis of silane, nucleation of silicon, and silicon crystal growth. Rate expressions that describe the various steps involved in the chemical vapor deposition of silicon were derived from elementary principles. Applications of the rate expressions for modeling and simulation of the silicon CVD are discussed.
Thirty-nine samples of polymeric materials were evaluated to determine the apparent lethal concentrations of their pyrolysis products. The materials were compared on the basis of the apparent lethal concentration for 50 percent of the test animals. Relative toxicity rankings based o apparent lethal concentration values can differ significantly depending on whether they are based on weight of sample charged or weight of sample pyrolyzed. The ranking of polyphenylene sulfide is particularly sensitive to this difference.
The apparent lethal concentrations for 50 percent of the test animals of the pyrolysis products from twelve polymeric materials were studied as a function of temperature and heating rate. The materials were polyethylene, nylon 6, ABS, polycarbonate, polyether sulfone, polyaryl sulfone, wool fabric, aromatic polyamide fabric, polychloroprene foam, polyvinyl fluoride film, Douglas fir, and red oak. The apparent lethal concentration values of most materials vary significantly with temperature and heating rate. The apparent lethal concentration values, based on weight of sample charged, appears to effectively integrate the thermophysical, thermochemical, and physiological responses from a known quantity of material under specified imposed conditions.
Seventy samples of cushioning and upholstery materials used in home furnishings were evaluated for relative toxicity by means of the USF/NASA toxicity screening test. The materials were variably toxic under pyrolysis conditions, and this test appeared suitable for discriminating among them on the bases of time to incapacitation and time to death. The addition of fire retardants to these materials to comply with flammability regulations either had no significant effect on toxicity, or resulted in a reduction in relative toxicity. The modification of materials to comply with California upholstered furniture flammability regulations appears to have resulted in desirable limitations on toxicity. Fifty percent of the 70 materials tested caused incapacitation earlier than did the materials in compliance, and 30 percent caused death earlier.