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Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
The cyclo-silicates are obtained when the two oxygen atoms of each SiO4 anion unit share two corners of a tetrahedron, resulting in the formation of a closed ring anionic ion (Si3O9)6–. The silicon/oxygen atomic ratio 1:3. An example is benitoite silicate, BaTi (Si3O9).
Feedstock Chemistry in the Refinery
Published in James G. Speight, Refinery Feedstocks, 2020
In support of the participation of asphaltene constituents in sediment or coke formation, it has been reported that the formation of a coke-like substance during viscous feedstock upgrading is dependent upon several factors (Storm et al., 1997): (i) the degree of polynuclear condensation in the feedstock, (ii) the average number of alkyl groups on the polynuclear aromatic systems, (iii) the ratio of heptane-insoluble material to the pentane-insoluble/heptane-soluble fraction, and (iv) the hydrogen-to-carbon atomic ratio of the pentane-insoluble/heptane-soluble fraction. These findings correlate quite well with the proposed chemistry of coke or sediment formation during the processing of heavy feedstocks and even offer some predictability since the characteristics of the whole feedstocks are evaluated.
Metal Zeolite Catalysts
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
The selectivity of hydrocracking catalysts can be changed considerably by varying the type of cracking components. A broad classification of catalyst characteristics is given in Table 8. Within the series of potential hydrogenation components, the ranking Ni-W > Ni-Mo > Co-Mo > Co-W has been reported. Pt when not sulfided, is the most active hydrogenation component. The atomic ratio of: group VIII metalgroup VIII metal+group VIb metal=0.25
Evaluations of the Effect of Heterogeneity in HALEU Systems Using Modified Critical Benchmarks
Published in Nuclear Science and Engineering, 2022
Joseph A. Christensen, R. A. Borrelli
Based on some previous work,2 a relationship between the effect of heterogeneity and minimum critical volume was observed with regard to both the size of the particles in the multiplying system and the fuel-to-water ratio, which is also sometimes known as the moderator ratio. Generally, this ratio is easily expressed as an atomic ratio of fuel (235U) and the primary moderator element (hydrogen). This is a convenient parameter for use in comparison between moderated systems and is frequently available in the International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook3 (ICSBEP Handbook) alongside the benchmark evaluation and development parameters. Accordingly, we selected this parameter as an initial focus to help investigate the effects of heterogeneity in the systems under evaluation. It is recognized that the systems in this work have moderator ratios that are generally considered under-moderated in that they would achieve smaller mass or volume if the moderator ratio is increased and that there are other related parameters such as the average energy of neutrons causing fission (ANECF) that may be evaluated similarly and may provide different results; such an evaluation is included in our future work.
Structure and optical properties of CrOxNy films with composition modulation
Published in Surface Engineering, 2020
Yanyan Yuan, Bingye Zhang, Jian Sun, Philippe Jonnard, Karine Le Guen, Yuchun Tu, Chao Yan, Rui Lan
Figure 5 shows the phase structures of the chromium oxynitride thin films. In addition, the XRD pattern of the Si substrate is also shown here for comparison. There is no diffraction peak of the Si substrate in the measurement range. The samples prepared using Cr2O3 target with N2 reactive gas show an intense peak located at around 2θ = 57.5°, which corresponds to CrO3(003). Otherwise, a shoulder located at 2θ = 56° along the strong peak appeared, which probably corresponds to Cr2N (112). A weak peak located at 2θ = 77.5° probably corresponds to CrO3 (402). The results are in agreement with the XPS-derived Cr/O ratio. When the sample prepared using CrN target with 10 sccm of oxygen flow rate, the peak position is same as these prepared using Cr2O3 target. However, the sample deposited using Cr2O3 target with 5 sccm of oxygen flow rate shows an intense peak located at 2θ = 56°, which corresponds to Cr2N (112). It is not in agreement with the XPS-derived atomic ratio. But one thing should be noted that the XPS-derived atomic ratio is from the sample surface. However, the XRD pattern shows the whole sample information.
Performance Restoration of a Tritium-Aged LaNi4.25Al0.75 Sample
Published in Fusion Science and Technology, 2020
Gregory C. Staack, David W. James
Hydride behavior can be compared using pressure-composition response curves collected at constant temperature (isotherms). The composition of a hydride is typically expressed as the hydrogen-to-metal atomic ratio Q/M (where Q represents hydrogen isotopologues protium, deuterium, or tritium). For an absorption isotherm, equilibrium pressure measurements are taken after an aliquot of gas is added to the system. Likewise, for a desorption isotherm, equilibrium pressure measurements are taken after an aliquot of gas is removed from the system. The quantity of tritium absorbed or desorbed by the hydride is inferred from changes between before and after PVT measurements of the gas phase. Isotherms reveal the plateau pressure, reversible capacity, and heel of a material.