Carbonate-rich Samples Research Articles

Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis

Rock-Eval pyrolysis is used to rapidly evaluate the petroleum-generative potential and thermal maturity of rocks. Accurate conclusions require programs every 30-60 ft (9-18 m), understanding of interpretive pitfalls, and supporting data, such as visual kerogen, vitrinite reflectance, and elemental analyses. The generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography. Most coals show high S2/S3 (>5) and low HI values (< 300 mg HC/g TOC). Migrated oil and mud additives, which alter Rock-Eval data, can sometimes be removed by special processing. For immature rocks, bimodal S2 peaks and PI values over 0.2 indicate contamination. Pyrolysis downgrades organic-poor, clay-rich rocks, which show lower HI and higher Tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays. Tmax values for small S2 peaks (< 0.2 mg HC/g TOC) are unreliable. Tmax is affected by maturation, organic matter type, contamination, and the mineral matrix. S3 is sensitive to inorganic and adsorbed carbon dioxide, and to instrumentation problems. Acidification of carbonate-rich samples and proper maintenance improves S3 measurement. Constant sample weights (100 mg) are recommended. Below a threshold weight, Tmax increases by up to 10°C, and other parameters decrease. Organic-rich samples, which overload the detector, can be diluted with carbonate. Detector linearity is determined by pyrolyzing various weights of an organic-rich rock.

Sputtering of silicon carbide coatings by low-energy hydrogen ions

Abstract Various types of silicon carbide coatings made by reactive ion-plating have been bombarded with a 3.0 keV H+3 ion beam at temperatures around 500°C. The sputtering yield in stoichiometric samples (i.e. Si : C = 1 : 1) at 500°C was 1.15 × 10 −2 atoms/H+. As the stoichiometry deviates from this point, the sputtering yield has larger values. The temperature dependence of the sputtering yield in stoichiometric samples was negligible below 600°C. No surface topography changes occurred in stoichiometric samples even at a high fluence of 2 × 10 20 H + /cm 2 , while severe erosion took place in non-stoichiometric samples. By Auger electron spectroscopy (AES), carbon exists on the surface in the form of carbide in stoichiometric SiC before and after bombardment, while it exists in the form of graphite in carbon rich samples, which suggests that the bound state of carbon in the form of carbide should correspond to the low sputtering yield in stoichiometric SiC coatings. The surface stoichiometry changes due to hydrogen bombardment were observed by AES, where the carbon population increases in stoichiometric SiC, while it decreases in carbon rich samples, which was supported as well by the results from electron probe X-ray microanalysis.

The geochemistry of the carbonate-rich Espanola Formation (Huronian) with emphasis on the rare earth elements

The Espanola Formation, part of the Lower Proterozoic Huronian sequence, is unique in the Huronian succession in that it contains abundant carbonate material.Chemical analysis of bulk samples suggest that the dominant control on the distribution of Al, Si, Ti, K, P, Rb, Zr, Ba, Zn, Cr, Ni, Li, and Ga is the noncarbonate fraction of the rocks. This terrigenous component was derived from a source compositionally similar to that of other fine-grained Huronian formations. Sr is controlled by the substitution for Ca in calcite and dolomite. Na and Y are strongly affected by both the carbonate and noncarbonate fraction. Cu displays erratic behaviour. Microprobe analyses reveal high concentrations of Fe in calcite and dolomite, possibly related to substitution for Mg. Mn may have had a similar control. Whether this control is related to incorporation of Fe and Mn at the time of deposition, during diagenesis, or during metamorphism is uncertain.The distribution of the rare earth elements is similar to that of normal terrigenous clastic rocks of post-Archean age. However, high concentrations of REE in the soluble portion of carbonate-rich samples may suggest incorporation of REE into the carbonate structure. The lack of anomalous Ce behaviour implies that these rocks were deposited in water not equilibrated with manganese nodule formation.

Superconducting and normal state properties of tantalumcarbonitrides under hydrostatic pressure

We have investigated the formation and the normal- and superconducting properties of TaC x N y . By analogy to NbCN the superconducting transition temperature of the nitrogen-rich samples increases with pressure and decreases for carbon-rich samples. This is correlated with a different resistivity vs temperature behaviour.