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Abstract  

A series of anion-cation surfactants modified organoclays are prepared by incorporating both cationic surfactant, hexadecyltrimethylammonium bromide (HDTMAB), and anionic surfactant, sodiumdodecyl sulfonate (SDS), to montmorillonite. The added amounts of surfactant varied from 0.2 to 4.0 CEC of the used montmorillonite, similar to those reported in literature. A combination of elemental analysis, X-ray diffraction and thermogravimetric analysis is used in the characterization of the resulting organoclays. The experimental results show that anionic surfactants can not be intercalated into the montmorillonite whereas they can be loaded onto cationic modified montmorillonite, resulting in a further increase of organic carbon content of the resulting organoclays. This study demonstrates that SDS can be intercalated into montmorillonite interlayer space through the interaction with HDTMAB rather than by ion exchange. The intercalation of SDS results in an increase of the basal spacing of the resulting organoclays when comparing with HDTMAB modified montmorillonite and higher decomposition temperature of the intercalated surfactants when comparing with them in bulk state. These new insights are of high importance in the application of organoclays in the fields of remediation of polluted water and synthesis of clay based nanocomposites.

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The lipophilicity of a series of pyrrolyl-acetic acid derivatives, inhibitors of the aldose reductase enzyme, was assessed by reversedphase thin layer chromatography (RP-TLC). The role of the carbon content of the stationary phase in reproducing the octanol-water partitioning was examined using RP-18F254S and RP-8F254S plates. Retention on RP-8 plates was found to be more uniform, while these plates exhibit some advantages for the lipophilicity assessment of acidic compounds, compared to the most commonly used RP-18 plates. However, in both cases, different energetics between octanol-water partitioning and RP-TLC retention seem to be involved. On both plates the influence of ionization of the acid functional group was found to be more pronounced on retention in comparison with previous findings for basic compounds. Both sets of R Mw values were compared with HPLC chromatographic indices, reported previously. They were found to correlate better with logk w values, if the latter have been determined in the presence of noctanol as mobile phase additive. In all cases, best relationships were obtained with R Mw(C18). The performance of R Mw indices in regression equations modeling the aldose reductase inhibitory activity was evaluated. Results were comparable with those previously generated using logP. Both R Mw(C8) and R Mw(C18) proved to perform equally well as lipophilicity indices in correlating biological activity, if combined with the ionization correction term Q and Abraham’s basicity term B as additional parameters.

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Differential thermal studies of peat and brown coal are described at high gas pressures (0.3–2.1 MPa). The experiments were performed with samples of different particle size in nitrogen, hydrogen and carbon dioxide atmospheres. The total reaction heats were plotted vs. the carbon content and a decrease was observed above 68% carbon.

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Abstract  

In the14C-dating by accelerator mass spectrometry (AMS) iron and copper oxide are used during sample preparation. In an investigation on the origin of the14C-blank, which in practice determines the dating limit of AMS, the carbon contamination was measured in both reagents by deuteron activation analysis via the12C(d,n)13N reaction. A first batch of iron was analysed radiochemically and a carbon concentration of 37.6 g/g was found with a standard deviation of 2.7 g/g (3 analyses). In a second batch of iron concentrations between 66 and 150 g/g were found for 6 instrumental analyses, suggesting an inhomogeneous distribution of carbon. The carbon content in copper oxide was 17.8 (3.5) g/g for 3 instrumental analyses, but preference should be given to a radiochemical analysis. These figures indicate that the carbon impurities found in iron and copper oxide are possible causes of the14C-blank. However, a final conclusion can only be drawn if the14C concentration of the contaminating carbon and the amount of carbon released during sample preparation are known.

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Abstract  

This paper describes development work to prepare a method to measure absolute239Pu content and Pu-isotopics by ICP-MS in acidified Hanford DOE-site samples which are very high in90Sr,99Tc, and137Cs radioactivity and which are frequently high in organic carbon content. Samples with very large90Sr and137Cs contents have historically been difficult to analyze for Pu content by each of three alpha-counting techniques in use at SRS, and analysis by ICP-MS in these samples is complicated by the high organics content. We report an ion exchange chemical preparation to obtain fraction of Pu that does not contain any fission product contribution and no interfering organics to allow measure of absolute239Pu and of239Pu through241Pu isotopics by ICP-MS. The method uses a242Pu spike to measure Pu recovery and is demonstrated in this paper with three distinct commercially available resins and with over 300 samples. Measured absolute239Pu contents in sixty-three spiked/unspiked duplicates have agreed within 15% precision. Overall242Pu recoveries were near 90% with 25% precision. Comparisons of absolute239Pu contents measured directly on three samples agreed within the quoted 25% uncertainty.

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Abstract  

A method has been developed using thermoanalytical techniques for the analysis of residues from coal-burning fluidised bed plant where limestone is used as a sulphur scavenger. This completely eliminates the need for lengthy wet chemical analyses and allows the derivation of parameters necessary for efficient plant operation, such as limestone addition rate, calcium utilisation efficiency and calcium to sulphur mole ratio. The method also gives values for the unburned carbon content and the ratio of coal ash to limestone derivatives in the sample.

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Abstract  

Yttrium isopropoxide, an yttrium oxide precursor, is sometimes used as a sintering aid for producing aluminum nitride ceramics. In the present work, this sintering aid was used with isopropanol as the solvent and polyethyleneimine as the dispersing agent. After initial ball milling and drying steps, the burnout behaviour of samples taken from isostatically pressed pellets was studied by thermal analysis in nitrogen and air. In addition to the milled and pressed pellets, each component was also analyzed separately. Complete conversion to yttrium oxide, with no residual carbon, would be a desirable property of this system. However, during the preparation of the aluminum nitride pellet, there was only partial yttrium isopropoxide decomposition. The nitrogen burnout residue contained carbon formed from the yttrium isopropoxide and dispersant overlapping thermal decomposition, mostly from an intermediary decomposition stage of the former that occurs between 300 and 550°C. The residual carbon content and the previous yttrium isopropoxide decomposition were estimated by thermogravimetry.

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The influence of scale on the discernment of plant community patterns was examined using vegetation-environment data collected from a subalpine wet meadow in south-coastal British Columbia. Species cover data were recorded in 225, 0.25 m2quadrats systematically located at 5m intervals in a 40 m x 120 m sampling grid. Environmental data consisted of quadrat elevations as well as measured and kriged estimates of five soil variables (carbon content, pH, electrical conductivity, percent sand, and percent clay). Sampling scale was adjusted by aggregating neighbouring quadrats into composite sampling units; analytical scale was altered by varying the intercept level in dendrograms from minimum increase of sum of squares cluster analysis of the vegetation data corresponding to the different sampling scales. The resulting classifications were evaluated for their ability to explain variation in the vegetation data and in the environmental data. The vegetation variation explained by the classifications was highest at the smallest sampling scale indicating that vegetation heterogeneity is fine grained. In contrast, the environmental variation explained was higher for the classifications based on the larger composite sampling units implying a coarser scaling of abiotic conditions within the study area. These results were consistent with the recognition of three main zones along a drainage gradient within the sampling grid. upper mixed-forb, middle heath, and lower sedge. There was also evidence that the orientation of rectangular sampling units parallel to the drainage gradient leads to higher levels of explained variation. This study reaffirms the need for careful consideration of alternatives both in field sampling and analytical phases of vegetation research to ensure that description and interpretation of patterns adequately address study objectives and that vegetation-environment relationships are more completely investigated from a hierarchical perspective.

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Kátai J. — Vágó I. — Lukács V.E. (2005): Relationships between the carbon content and some microbial characteristics int he different soil types. Cereal Research Communications Vol. 33 No. 1 389–392.p. Lukács V

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The thermal properties of complex carbon-silica adsorbents (carbosils) were investigated using differential thermal analysis. The adsorbents were prepared by pyrolysis of methylene chloride. Pyrolysis reaction on silica surface was carried out at different temperatures (400–700 °C) and at different pressures of CH2Cl2 vapours. Thermal analysis was carried out in air atmosphere. The following parameters characterizing the properties of the adsorbents were determined: carbon content, specific surface area, carbon layer thickness, pore volume, mean pore radius, differential of heats of adsorption ofn-hexane and benzene, and micrographs. The correlation between topography and morphology of carbon deposits (dependent on the parameters of the pyrolysis process) and the courses of DTA and TG curves corresponding to individual carbosils have been determined.

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