Carbon analysis, surface

Surface Carbon Analysis. This method is based on the observation that the presence of carbon on automotive body sheet steel, for instance, can be linked to poor corrosion performance. The carbon content on the surface can be determined by subjecting the body sheet to about 500°C in an oxygen environment and determining the CO2 thus formed. 

Recent developments in Raman equipment has led to a considerable increase in sensitivity. This has enabled the monitoring of reactions of organic monolayers on glassy carbon [4.292] and diamond surfaces and analysis of the structure of Lang-muir-Blodgett monolayers without any enhancement effects. Although this unenhanced surface-Raman spectroscopy is expected to be applicable to a variety of technically or scientifically important surfaces and interfaces, it nevertheless requires careful optimization of the apparatus, data treatment, and sample preparation. 

The long-term stability of the Ru/Ti02 catalyst was studied under various reaction conditions and the spent catalysts were characterized for assessing the reasons of deactivation. It was observed that the rate exhibits a rapid reduction at the initial several hours of reaction, followed by a slow and continuous deactivation. Analysis of the spent catalyst, by H2 adsorption after removing surface carbon, showed that the initial rapid reduction of activity is mainly due to metal sintering, while the continuous and slow deactivation is related to the occurrence of the SMSl phenomenon at the later part of the catalyst bed, where reducing conditions prevail. In order to avoid these processes which lead to catalyst deactivation, Ti02... 

Correlations between surface species and emitted secondary ions are based on characterization of the surface adlayer by adsorption and thermal desorption measurements. It is shown that the secondary ion ratios RuC+/Ru+ and R CTVRuJ can be quantitatively related to the amount of nondesorbable surface carbon formed by the dissociative adsorption of ethylene. In addition, emitted hydrocarbon-containing secondary ions can be directly related to hydrocarbon species on the surface, thus allowing a relatively detailed analysis of the hydrocarbon species present. The latter results are consistent with ejection mechanisms involving intact emission and simple fragmentation of parent hydrocarbon species. 

In the first set of measurements the rate of carbon build-up on a Ni(lOO) surface was measured at various temperatures as follows (1) surface cleanliness was established by AES (2) the sample was retracted into the reaction chamber and exposed to several torr of CO for various times at a given temperature (3) after evacuation the sample was transferred to the analysis chamber and (4) the AES spectra of C and Ni were measured. Two features of this study are noteworthy. First, two kinds of carbon forms are evident - a carbidic type which occurs at temperatures < 650 K and a graphite type at temperatures > 650 K. The carbide form saturates at 0.5 monolayers. Second, the carbon formation data from CO disproportionation indicates a rate equivalent to that observed for methane formation in a H2/CO mixture. Therefore, the surface carbon route to product is sufficiently rapid to account for methane production with the assumption that kinetic limitations are not imposed by the hydrogenation of this surface carbon. 

Organic groups are bound to the silica surface after grinding silica in organic liquids (277). A more controlled substitution of surface silanol groups was reported by Wartmann and Deuel (194). Silica gel which had been treated with thionyl chloride was allowed to react with phenyl lithium. Silicon-phenyl bonds could be detected by infrared spectroscopy. The phenyl content of Aerosil treated in this way as estimated from carbon analysis corresponded to 85% of the silanol groups (188). However, it is not certain whether the reaction... 

A homoleptic bulky a,y-diketonate yttrium complex (fod = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate) was immobihzed on MCM-41.280 ( s = 1140m g, Vp = 0.93 cm g, dp = 2.7 nm) and a monopodaUy anchored surface species 6 has been proposed (Scheme 12.5). As suggested by FTIR (strong band for the Si-OH stretch vibration) as well as metal and carbon analysis (circa 3.4 wt% Y, fod/Y circa 2) only around half of the silanol population has been consumed [110]. 

Applying ion beams, surface-sensitive analysis and modification in atomic and electronic structures of inorganic materials have been developed. Ion beam modification of titanium dioxide (Ti02), carbon-based materials, and the analysis of Nb/Cu multilayers and VO2 using ion beam are described as follows. 

Thermal treatment reduced surface carbon on aminopropylsilane-treated fiber, presumably by desorbing adventitious material. Carbon from the organic substituent on the silane desorbed also, since the nitrogen present before thermal treatment was totally absent afterwards. (The wide scan analysis of heat-treated fibers is incomplete because small concentrations of sulfur, fluorine and phosphorus were present on this sample only. They are considered to be artifacts, deposited perhaps from the inner wall of the chromatographic column during ramping, and are not reported). 

The surface concentration of carbon in the used catalysts is consistent with the bulk carbon analysis, while surface carbon on the fresh and regenerated samples seems disproportionately high. Surface sulfur is consistently lower than the bulk values of Table I indicating the presence of metallic sites on the surface, since these levels on the used catalysts are incomplete for total sulfiding of Co and Mb. 

A variety of measurements, such as total carbon analysis and BET surface area, have been used to determine the effectiveness of the sily-lation reactions and the coverage of the silica surface. From these measurements the percentage of carbon on the surface can be calculated and is used to designate the degree of surface coverage. Values ranging from 2 to 30% carbon have been reported. 

The studies of the composition and state of chemical elements on enzyme-modified wool surfaces (carbon, nitrogen, oxygen, sulphur) as compared to untreated ones were performed by means of XPS analysis (Vacuum System Workshop Ltd., England) using non-monochromatized AlKa radiation with energy 1486.6 eV, 10 kV and 200 W. The base pressure in the analysis chamber was 3 x 10-6 Pa [30], XPS spectra were acquired in the constant analyser transmission mode with energy of electron transmission 22 eV. 

As noted in the table. Lots A and B of the unalloyed LTI carbon were identical, with a carbon/oxygen ratio slightly less than 50 1. No other elements were detected on the surface. Detailed analysis of the C-ls region of these samples shows a small chemically-shifted peak in the major C-ls region indicating what appears to be an ether- or hydroxyl-like carbon-oxygen bond. 

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