Diffusion Fundamentals (E-Journal)
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High Temperature Fast Field Cycling Study of Crude Oil
Get PDFA set of crude oil samples with different composition and characteristics is studied by means of Fast Field Cycling (FFC) 1H relaxometry, which probes the distribution of longitudinal relaxation times T1 as a function of the Larmor frequency. Investigation of T1 profiles at different temperatures is able to provide an insight into the dynamics and structural changes of oil components, with our particular interest being the high temperature behaviour of asphaltene. It is well-known that asphaltenes tend to form porous clusters in crude oils, which can cause severe problems for the process of oil extraction. Therefore, FFC experiments are conducted on Stelar Spinmaster FFC2000 in the temperature range 203K < T <443K, where the upper limit of 443K is aimed at approximating the typical maximal in-situ well temperatures. FFC relaxometry data of crude oils at such a high temperature are obtained for the first time with the use of a specially modified NMR probe. Inverse Laplace transformation is applied to the longitudinal agnetization decays, yielding T1 distributions at different frequencies. A comparative analysis of these distributions for different Larmor frequencies and temperatures showed that there is a systematic variation of the frequency dependence of T1 correlating with the asphaltene content in the samples, at temperatures similar to the well conditions
Spinodal decomposition of solutions during crystallization
Get PDFThe modern theory of phase transitions cannot explain the results of many experiments of interphase mass transfer. One reason for this is the assumption that during crystallization the solution is in the metastable state. The decomposition of the solution occurs by binodal scenario in this case. Crystallization nuclei form and grow in solution. The purpose of this study to show that in many cases the solution during crystallization is in an unstable state. The unstable condition leads to decomposition the solution by spinodal scenario
On the Carbon Kinetics in Martensite, relevance to Nanosegregation at Dislocations and Grain Boundaries
Get PDFThis short communication is devoted to the room temperature processes of diffusion and redistribution of dissolved carbon atoms in martensite to the nanosegregation regions at dislocations and grain boundaries. It is related to the DF7 contribution of M. Lavrskyi et al. on the carbon kinetics in martensite [1] and to the DF7 contribution of Yu. Nechaev on the compound-like nanosegregation at dislocations and grain boundaries in metallic materials
