Carbonate grains

Both single-layer protective and duplex-layer protective scales have a PBR of 2.1, whereas breakaway scales show a PBR of approximately 2.7, containing around 23% porosityand graphitic carbon grains (up to 6% by weight) between the oxide grains... 

Estimation of pore size distribution is based on the assumption that there is no diffusional coupling between pores of different sizes. Microporous carbonate grain-stones have been identified as an example where this assumption is not valid [31]. 

Fig. 2. EPMA back-scattered electron images of a polished section from Chelehkureh deposit, a) carbonate in a mineralized vein with chalcopyrite b) larger image of carbonate grain marked by + in previous image, c), d) and e) are in turn compositional Mg, Fe and Ca images of that grain.

The shape of the front is given by the spreading of the front around the point S. The spreading depends mainly on toxic mass transfer kinetics between gas and solid phases. Thus numerous parameters can be considered air flow rate, size of the toxic molecule, pore sizes of the carbon, carbon grain diameter. With large pores and small grains, the mass transfer from gas to carbon is very fast the spreading... 

Koike, C., H. Hasegawa, and A. Manabe, 1980. Extinction coefficients of amorphous carbon grains from 2100 A to 340 jam, Astrophys. Space Sci., 67, 495-502. 

When these inclusions are associated with organic matter (which acts as binding material of the carbonate grains and amounts to 5-15% of the rock), they produce clear halos (Figure 6a-d). 

The size of carbon grains in the kinetic experiments was 1-2 mm. Preliminary tests with grains of different sizes had shown that this size range ensured the reaction course in the kinetic region. 

Since there are sufficient evidences about the presence of carbon grains and about the fact that the recombination of H atoms on carbon surface is effective even at low temperatures, we will limit our further discussion to this specific aspect hydrogen and carbon surfaces. 

Small carbon grains are assumed to be the carrier of the prominent interstellar ultra violet absorption at 217 nm. To investigate this hypothesis, we produced small carbon particles by evaporating graphite in an inert quenching gas atmosphere, collected the grains on substrates, and measured their optical spectra. In the course of this work - which in the decisive final phase was carried out with the help of K. Fostiropoulos and L. D. Lamb - we showed that the smoke samples contained substantial quantities of C60. The fullerene C60 (with small admixtures of C70) was successfully separated from the sooty particles and, for the first time, characterized as a solid. We suggested the name fullerite for this new form of crystalline carbon. 

In a further section, we emphasize the mineralogy and chemistry of carbonate skeletal grains, because of their abundance in Phanerozoic sediments, and their potential usefulness in paleoenvironmental interpretation. To provide the reader at this point with some idea of the complexity of skeletal carbonate grains, Tables 5.2 and 5.3 summarize the chemistry, mineralogy and structure of major... 

Pestana H.R. (1977) Guide for the Identification of Carbonate Grains and Carbonate-Producing Organisms. Special Publications No. 13, Bermuda Biological Station for Research, Saint Georges, Bermuda, 53 pp. 

Walter L.M. (1983) The dissolution kinetics of shallow water carbonate grain types Effects of mineralogy, microstructure and dolution chemistry. Ph.D. dissertation, Univ. Miami, Miami, FL. 

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