Small Amount Of Graphite Research Articles

Oxidation rates of carbon particles in methane-air flames

Small amounts of graphite were introduced into a laminar, flat, low-pressure, fuel-lean methane-air flame. The mean initial diameter of the particles was about 4 μm. The rate of oxidation of the particles was observed by optical means as they passed through the flame. In addition, measurements of particle and gas temperatures were used to estimate the heat released by the surface reaction. The results were found to be reasonably consistent with those found from more direct measurements of particle size. The study showed a very considerable enhancement (by a factor of up to 5) of the carbon oxidation rates in the main gaseous flame reaction zone as compared with the burned gas region, thus indicating the importance of the flame radicals O, OH, and H in controlling the oxidation. Consideration of the collision frequencies with the external surface area showed, however, that the bulk gas-phase concentrations of the radicals were insufficient for their direct diffusion and reaction to be able to account for the enhancement. At the same time consideration of the particle properties excludes porosity effects as a means of rate enhancement. An outline mechanism whereby the radicals catalyze attack by molecular oxygen is proposed. The CO arising from the char oxidation mechanism is simultaneously coupled with the other reactions involved in the CH 4-air kinetic scheme. Numerical simulation shows the mechanism to be consistent with the observations if radical recombination at the particle surface is also included.

Graphite formation in the Hiroshima fire storm

In order to investigate what might be the composition and optical properties of particles that could lead to a “nuclear winter,” a search has been made for particles that had been generated in urban fire storms. Deposits containing small amounts of graphite have been found on an artifact from the Hiroshima fire storm. The fire storm was initiated on August 6, 1945, by the atomic bomb detonation. The particles were rained out of the atmosphere in the “black rain” that commenced following the urban fire storm. Initial studies using electron microscopy have revealed that the particles consist of a mixture of clay and amorphous sooty carbon. Scanning electron photomicrographs have suggested the presence of graphite. Its presence has been confirmed using laser Raman spectroscopy (LRS), surface ionization mass spectroscopy (SIMS), and electron scattering for chemical analysis (ESCA). Significant amounts of the sooty material consists of clay, and the graphite is probably present as short-range ordered structure in sooty microspheres. The results of this study are presented with a discussion of conditions that may lead to graphite formation.

Bulk standards for low-temperature biological x-ray microanalysis

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

A mixed compound of the KNH 3C ternary system having marked stability in air

A newly synthesized stage 1 KNH 3C ternary compound with I c ≅ 5.4Å, coexisting with a minor component with I c ≅ 8.3 Å, was found to be unusually stable in air, oxygen atmosphere and acid solutions. The compound preparation procedures were as follows: 1. (1) The well known compounds of K(NH 3) 2C 12 or K(NH 3) 2C 28 were prepared. 2. (2) The KNH 3GICs thus obtained were submitted to deammoniation treatment by evacuation at temperature between 16 and 400 °C. 3. (3) The deammoniated compound was again allowed to react with potassium vapor by the two-bulb method. On exposure to air, this compound was transformed very slowly to higher stage compounds. After 3 months of exposure, a considerable amount of the stage 1 compound still remained, accompanied by higher stage compounds and a small amount of graphite.

Some geological implications of equilibrium between graphite and a C‐H‐O gas phase at high temperatures and pressures

The occurrence of graphite as a common accessory mineral in meteorites and in terrestrial metamorphic and igneous rocks gives particular importance to the study of equilibrium between graphite and a coexisting gas phase. By using a simplified model in which T, Pgas, and fO2 are independently specified for the system C‐H‐O, values of PCO2, PCO, PH2O, PH2 and PCH4 in a gas phase in equilibrium with graphite have been calculated for a wide range of geologically possible conditions by means of a high‐speed computer. The numerical results support the following general conclusions: (1) The assumption that Pgas = PH2O + PCO2 is significantly in error for many graphite‐bearing mineral assemblages. (2) Methane, CH4, may be a significant to dominant constituent of the gas phase in many possible geological environments involving moderate reduction; in particular, the occurrence of graphite with reduced minerals such as fayalite, wüstite, and iron is indicative of a methane‐rich gas phase. (3) Under metamorphic conditions, pure water is not stable with graphite, but graphite can coexist with a gas phase rich in CO2. (4) Original graphite in a sediment will stabilize increasingly reduced mineral assemblages during progressive thermal metamorphism. (5) The presence or absence of even small amounts of graphite can explain PO2 gradients observed over short distances or between adjacent layers in metamorphic rocks. (6) It is possible that the terrestrial atmosphere could have evolved by conversion of original methane to water and CO2 by reaction with graphite and other accessory minerals within the primordial earth at temperatures of 600° to 1000°C. Material requirements for such a conversion are not unreasonable, and the process itself is consistent with many proposed models for the origin of the earth.