Aging of carbons

The hgure also shows that loading the carbon with hnely dispersed palladium has a further accelerating effect on surface oxidation, which is most pronounced with the carbon black. This can be explained by dissociative adsorption of O2 molecules on the metal surface and oxygen spillover. Platinum had a similar effect. Palladium (200 p.mol/g) was deposited on the carbons by incipient wetness impregnation followed by H2 reduction at 523 K the dispersion was about 25% with Norit and 15% with Corax 3. 

Sample N Content (irmoPg) Catalytic Activity (p,moiyg H2S03 g) Acidic Surface Sites (ftmol/g) Basic Surface Sites (itmol/g)  

Clearly, these changes in the surface chemistry of carbons during storage negatively affect the reproducibility of measurements after some time has passed. The samples are not the same as they were a year or two ago. They must be characterized anew if additional measurements are to be done. 

Some CO2 is evolved in the aging reaction. A continuous conversion of carbon to CO2 could be achieved by treating carbons with oxygen in 0.01 to 0.2 N NaOH at 353 K. An oxygen stream was passed through a suspension of the carbon, and from time to time aliquot samples were taken. After acidifying in a closed vessel, the CO2 liberated was carried by a gas stream to a conductivity cell filled with a 

01 M Ba(OH)2 solution, and the drop in electrical conductivity was measured, taking into account the small carbonate contamination of the NaOH solutions (see Section 7.3.1). The oxidation rate increased with increasing NaOH concentration [40,163]. Some CO was also formed, about 5 to 7% of the quantity of CO2 [163]. The conversion rate increased markedly after treatment with NH3 at 1173 K, from zero to 44 p.mol C02/g h with activated carbon Eponit and from 10 to 15.5 p.mol C02/g h with furnace black Corax 3 [163]. 

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Cheng H, Edwards RL, Mttrrell MT, Benjamin TM (1998) Uranium-thorittm-protactinium dating systematics. Geochim Cosmochim Acta 62 3437-3452 Cherdyntsev W, Kazachevskii IV, Kttz mina YA (1965) Age of carbonate determined from the isotopes of thorium and uranium. Geochem Int 2 749-756... 

Radiocarbon dating relies on the fact that carbon exists naturally in several isotopic forms. All of them are virtually identical chemically, but they can be distinguished with special methods of analysis. One isotope, carbon-14, provides a kind of elemental clock that reveals the age of carbon-rich materials from living organisms. This technique is one of the most valuable of the many uses that chemists, geologists, medical biologists, and other scientists have found for isotopes the sibling forms that every element displays. 

Radiocarbon Dating. This is a method of estimating Ihe age of carbon-containing materials by measuring the radioactivity of the carbon in them. The validity of this method rests upon certain observations and assumptions, of which the following statement is a brief summaiy. The cosmic rays entering the atmosphere undergo various transformations, one of which results in the formation of neutrons, which in turn, induce nuclear reactions in the nuclei of individual atoms of the adnosphere. The dominant reaction is... 

Menendez, I., and Fuertes A.B. (2001) Aging of carbon membranes under different environments. Carbon 39, 733-740. 

In carbon dating, the relative amounts of carbon isotopes are compared. Since carbon isotopes decay at a regular rate, this information can be used to find the age of carbon compounds. However, the isotopic ratios of carbon on this planet are different from those on Earth. The isotopic ratios of carbon on this planet are 80.2 % 12C, 19.3% 13C, and 0.5% 14C. 

Because C-14 with a half-life of 5700 years occurs in nature, it can be used to determine the age of carbon-containing artifacts. The basis for such determinations is the loss of C-14 that was trapped in the artifact (animal, human, fired pottery, and so on). The related art and science of carbon dating are fairly complex and thus subject to significant uncertainties. 

Kuretzky, T. and Boehm, H.-P. (1994). Effect of water vapor and of platinum metals on the aging of carbon at moderate temperatures. In Extended Abstracts and Programme, Carbon 94, International Carbon Conference, Granada, Spain. University of Granada Press, pp. 262-3. 

Kamen, and it has a imirn oT about 5730 years, Libby soon realized that this isotope provides a valuable means of determining the age of carbon-containing materials. 

The aging of carbon materials in acetonitrile-based electrolyte is very slow and at least several weeks are required to register the measurable changes even when conditions for accelerated aging (increased potential) are provided. 

Zhu, M., C. J. Weber, Y. Yang et al. 2008. Chemical and electrochemical ageing of carbon materials used in supercapacitor electrodes. Carbon 46 1829-1840. 

Wadhwa M, Lugmair GW (1996) The formation age of carbonates in ALH 84001. Abstract Meteorit Planet Sci 3LA145 Wagstaff J, King EA (1981) Micrometeorites and possible cometary dust from Antarctic ice cores. Lunar Planetary Science Conference, vol. 13(3). LPI, Houston, Texas, pp 1124-1126... 

Source Reprinted from Gourdin C, Ageing of carbon fibres of various origins, SAMPE, Bourdeaux, 49-61, Oct 17-20, 1983. 

Buggy and Carew have reported the effect of thermal ageing of carbon fiber/PEEK [234]. The theoretical modulus based on the Law of Mixtures for a 61% high strength carbon fiber (YM = 227 GPa) and 39% PEEK (YM = 3.9 GPa) is ... 

In exploring the question of the earliest date for human presence in Brazil, Steelman and coworkers apply the plasma chemical procedure to extract carbon from both the pigments of a rock painting from Toca do Serrote de Bastiana and the accretions covering its surface. The accretions were found to contain both monohydrate of calcium oxalate and calcium carbonate. The radiocarbon age of the oxalate carbon was determined to be 2540 60 B.P. while the radiocarbon age of carbon extracted from the pigment was determined to be 3730 90 B.P. These ages are much more recent than the 30,000-40,000 B.P. age determined by electron spin resonance and thermoluminescence of the accretions, but are consistent with dates of other pictographs in the same shelter. 

Iskanderova, A. D. Preliminary data on determination of the absolute age of carbonate sediments by the method of ordinary lead. Akad. Nauk SSSR Kom. Opredeleniyu Absolyut. Vozrasta Geol. Formatsii Trudy, sess. 13, 449—455 (1966). 

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