Oceanic strike-slip faults represent active fluid conduits in the abyssal sub-seafloor

We present pore-fluid geochemistry and heat-flow data along the SWIM1 fault in the Horseshoe Abyssal Plain (northeastern Atlantic Ocean). The SWIM1 fault is part of the transcurrent plate boundary between Africa and Eurasia and cuts through as much as 5-km-thick sediments overlying >140 Ma oceanic lithosphere. In a number of places, restraining segments (as long as 15 km) of the SWIM1 fault generate anticlines (positive flower structures) that protrude as ~100-m-high hills above the abyssal plain. Heat flow and gradients of dissolved constituents in pore water are enhanced at these seafloor highs. Transport-reaction modeling confirms that slow advection of deep-seated fluids, depleted in Mg and enriched in Sr and CH4, can explain the observations. The geochemical signature is similar to the one observed at deep-sea mud volcanoes located eastward on the SWIM1 fault. The upward-migrating fluids have interacted with carbonate rocks at maximum 5 km depth, which represent the oldest sedimentary unit on top of the basement. We argue that deep-rooted fluids can generally be mobilized and transported upward along flower structures that formed in restraining-bend segments of long strike-slip faults. Such tectonic settings represent largely unrecognized corridors for mass exchange between lithosphere and ocean.

A New Dynamic Modeling Approach to Predict Microbial Methane Generation and Consumption in Marine Sediments

Methane, as a clean energy source and a potent greenhouse gas, is produced in marine sediments by microbes via complex biogeochemical processes associated with the mineralization of organic matter. Quantitative modeling of biogeochemical processes is a crucial way to advance the understanding of the global carbon cycle and the past, present, and future of climate change. Here, we present a new approach of dynamic transport-reaction model combined with sediment deposition. Compared to other studies, since the model does not need the methane concentration in the bottom of sediments and predicts that value, it provides us with a robust carbon budget estimation tool in the sediment. We applied the model to the Blake Ridge region (Ocean Drilling Program, Leg 164, site 997). Based on seafloor data as input, our model remarkably reproduces measured values of total organic carbon, dissolved inorganic carbon, sulfate, calcium, and magnesium concentration in pore waters and the in situ methane presented in three phases: dissolved in pore water, trapped in gas hydrate, and as free gas. Kinetically, we examined the coexistence of free gas and hydrate, and demonstrated how it might affect methane gas migration in marine sediment within the gas hydrate stability zone.

Asymmetric misfit nanotubes: Chemical affinity outwits the entropy at high-temperature solid-state reactions

Asymmetric two-dimensional (2D) structures (often named Janus), like SeMoS and their nanotubes, have tremendous scope in material chemistry, nanophotonics, and nanoelectronics due to a lack of inversion symmetry and time-reversal symmetry. The synthesis of these structures is fundamentally difficult owing to the entropy-driven randomized distribution of chalcogens. Indeed, no Janus nanotubes were experimentally prepared, so far. Serendipitously, a family of asymmetric misfit layer superstructures (tubes and flakes), including LaX-TaX2 (where X = S/Se), were synthesized by high-temperature chemical vapor transport reaction in which the Se binds exclusively to the Ta atoms and La binds to S atoms rather than the anticipated random distribution. With increasing Se concentration, the LaS-TaX2 misfit structure gradually transformed into a new LaS-TaSe2-TaSe2 superstructure. No misfit structures were found for xSe = 1. These counterintuitive results shed light on the chemical selectivity and stability of misfit compounds and 2D alloys, in general. The lack of inversion symmetry in these asymmetric compounds induces very large local electrical dipoles. The loss of inversion and time-reversal symmetries in the chiral nanotubes offers intriguing physical observations and applications.

The development of methods for the research and synthesis of solid phases by the scientific school of Ya. A Ugai. Review

The scientific school founded by Yakov A. Ugai has existed at Voronezh State University for over fifty years. One of its focus areas has been the development of physics and chemistry for obtaining solid phases in systems with volatile components. This determined the necessity to develop methods for the investigation of vapour pressure (tensimetric methods). This article only focuses on some of the works by the VSU staff dedicated to the study and construction of P-T-x diagrams. This review analyses phase equilibria and the nature of the intermediate phases in the AIV – BV, AIV – BV – СV, and AIII – BVI systems.Owing to the special nature of the cation-cation and anion-anion bonds, these compounds have highly specific properties that make them promising materials (2D materials in particular). The article presents an overview of works devoted to the construction of P-T-x diagrams and the investigation of defect formation processes in binary and ternary systems based on AIVBV compounds. It should be emphasised that the known techniques needed updating due to the high values of vapour pressure. This allowed conducting experiments at pressures of about 35-40 atmospheres. The study of the AIII - BVI systems,on the contrary, is complicated by low values of vapour pressure over indium and gallium chalcogenides and the complex composition of the vapour. For such systems the auxiliary component method was developed. The possibilities of its application are wide and are not limited to AIIIBVI compounds. A new method for nonstoichiometry regulation was developed and applied using non-destructive selective chemical transport reactions (i.e. with the participation of an auxiliary component). This method is based on the introduction or removal of one of the sample components by means of a selective chemical transport reaction. In conclusion, the development of methods for the research and synthesis of intermediate phases with variable compositions (properties) was analysed based on the example of the discussed systems.

Modeling of nonlinear processes of nucleation and growth of GaSxSe1–x(0 ≤ х≤ 1) solid solutions

The results on the study of modeling and physico-chemical study of the kinetics ofnucleation and growth of GaSxSe1–x(0 ≤ х≤ 1) solid solution. The nucleation heterogeneous process and growth of GaSxSe1–xcrystals have been studied and simulated taking into account nonlinear equations considering the kinetic behavior of crystallizing phases.GaSxSe1–xsingle and nanocrystals were grown from solution, melt, and by chemical transport reaction through steam. GaSxSe1–xcrystals were grownbychemical transport reaction in a two-tem-perature gradient furnace in a sealed quartz ampoule. Iodine was used as a transporting additive. Using the Fokker–Planck equation, the evolution of the distribution function of crystals of solid solutions of the GaS–GaSe system by size at the nucleation time is studied by a numerical method. For the convenience of comparing theory with experimental data, we used the GaS1–xSex(x= 0.7 molar fraction of GaSe) composition of the solid solution. The Monte Carlo method is used to approximate the time evolution of the nucleation of two types of particles for the GaS0.3Se0.7 solid solution, simulated by a constant nucleus size. The results of modeling non-linear crystallization processes are consistent with experimental data.

NEW POSSIBILITIES OF LOW-TEMPERATURE GENERATION OF ACTIVE CENTERS DURING HETEROGENEOUS-HOMOGENEOUS ACTIVATION OF PROPANE ON SILICA GEL SURFACE, MODIFIED WITH ZnO BY THE SOL-GEL AND CHEICAL TRANSPORT REACTION METHODS

By the example of heterogeneous catalytic oxidation of propane the process of peroxide radicals transfer from the surface of catalysts into the reactor volume is studied. For comparison ZnO/SiO2 contacts obtained by depositing the active phase on the silica surface by sol-gel and chemical transport reaction (CTR) were used. It was established that for the case both the temperature of the radicals transfer from the surface to the volume and the value of the activation energy are lower than in the case. It was shown that the modification of the silica gel surface with zinc oxide by the CTR method is more effective as compared with the sol-gel method. It is established that in both cases the active phase of the catalyst exhibits paramagnetic properties. On the basis of the given, semi-artificial kinetic method of radical detachment, the obligatory mechanism of activation failed.

X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1)

Single crystals of 2H and 3R niobium diselenide were grown by a chemical transport reaction. The current determinations by single crystals X-ray diffraction reveal a non-stoichiometric composition. The structures are built from Se—Nb—Se slabs with Nb in trigonal prismatic coordination whereas the extra or additional Nb atoms are located in the octahedral holes between the slabs giving rise to the formula 2H and 3R-Nb1+xSe2 with 0.07 < x < 0.118. In particular, vacancy and Nb-Nb interactions may play an important role on the non-stoichiometry and the stacking mode in NbSe2. By increasing the number of additional Nb atoms in the pure 2H-NbSe2, a transition 2H to 3R polytype should occur in order to minimize the Nblayer—Nbextra—Nblayer repulsions between these adjacent slabs. The theoretical study shows that both 2H and 3R-Nb1+xSe2 are thermodynamically stable in the range 0 < x < 0.1.