Geochemical, Isotopic and Petrological Constraints on the Origin and Evolution of the Recent Silicic Magmatism of the Greater Caucasus

Significant volumes of rhyolites and granites of the Pliocene-Pleistocene age are exposed in the collision zone of the Greater Caucasus, Russia. The volcanic history of the region includes ignimbrites and lavas associated with the Chegem caldera (2.9 Ma) and Elbrus volcano (1.98 and 0.7 Ma) and rhyolitic necks and granites in Tyrnyauz (1.98 Ma). They are characterized by a similar bulk and mineral composition and close ratios of incompatible elements, which indicates their related origin. The 1.98 Ma Elbrus ignimbrites, compared to the 2.9 Ma Chegem ignimbrites, have elevated concentrations of both compatible (Cr, Sr, Ca, Ni) and incompatible elements (Cs, Rb, U). We argue that the Elbrus ignimbrites were produced from magma geochemically similar to Chegem rhyolites through fractionation crystallization coupled with the assimilation of crustal material. The 1.98 Ma Eldjuta granites of Tyrnyauz and early ignimbrites of the Elbrus region (1.98 Ma) are temporally coeval, similar mineralogically, and have comparable major and trace element composition, which indicates that the Elbrus ignimbrites probably erupted from the area of modern Tyrnyauz; the Eldjurta granite could represent a plutonic reservoir that fed this eruption. Late ignimbrites of Elbrus (0.7 Ma) and subsequent lavas demonstrate progressively more mafic mineral assemblage and bulk rock composition in comparison with rhyolites. This indicates their origin in response to the mixing of rhyolites with magmas of a more basic composition at the late stage of magma system development. The composition of these basic magmas may be close to the basaltic trachyandesite, the flows exposed along the periphery of the Elbrus volcano. All studied young volcanic rocks of the Greater Caucasus are characterized by depletion in HSFE and enrichment in LILE, Li, and Pb, which emphasizes the close relationship of young silicic magmatism with magmas of suprasubduction geochemical affinity. An important geochemical feature is the enrichment of U up to 8 ppm and Th up to 35 ppm. The trace element composition of the rocks indicates that the original rhyolitic magma of Chegem ignimbrites caldera was formed at >80%–90% fractionation of calc-alkaline arc basalts with increased alkalinity. This observation, in addition to published data for isotopic composition (O-Hf-Sr) of the same units, shows that the crustal isotopic signatures of silicic volcanics may arise due to the subduction-induced fertilization of peridotites producing parental basaltic magmas before a delamination episode reactivated the melting of the former mantle and the lower crust.

Synthesis, Properties and Aging of ICP-CVD SiCxNy:H Films Formed from Tetramethyldisilazane

Amorphous hydrogenated silicon carbonitride films were synthesized on Si(100), Ge(111), and fused silica substrates using the inductively coupled plasma chemical vapor deposition technique. 1,1,3,3-tetramethyldisilazane (TMDSN) was used as a single-source precursor. The effect of the precursor’s pressure in the initial gas mixture, the substrate temperature, the plasma power, and the flow rate of nitrogen gas as an additional reagent on the film growth rate, element composition, chemical bonding, wettability of film surface, and the optical and mechanical properties of a-SiCxNy:H films was investigated. In situ diagnostic studies of the gas phase have been performed by optical emission spectroscopy during the film deposition process. The long-term stability of films was studied over a period of 375 days. Fourier-transform infrared (FTIR) and X-ray energy dispersive spectroscopy (EDX), and wettability measurements elucidated the oxidation of the SiCxNy:H films deposited using TMDSN + N2 mixture. Films obtained from a mixture with argon had high stability and maintained the stability of element composition after long-term storage in ambient air.

Effect of Er-Rich Precipitates on Microstructure and Electrochemical Behavior of the Al–5Zn–0.03In Alloy

The effect of Er-rich precipitates on microstructure and electrochemical behavior of the Al–Zn–In anode alloy is investigated. The results showed that with the increase in Er content, the microstructure was refined, the amount of interdendritic precipitates gradually increased, and the morphology changed from discontinuous to continuous network gradually. With the addition of Er element, the self-corrosion potential of the Al–5Zn–0.03In–xEr alloy moved positively, the self-corrosion current density decreased, and the corrosion resistance increased. When the Er content was less than 1 wt.%, the addition of Er improved the dissolution state of the Al–5Zn–0.03In–xEr alloy, and increased the current efficiency of the Al–5Zn–0.03In–xEr alloy. When the Er content was more than 1 wt.%, the current efficiency was reduced. The major precipitate of the alloy was Al3Er. According to the element composition of Al3Er in the Al–Zn–In–Er alloy, the simulated-segregated-phase alloy was melted to explain the effect of Al3Er segregation on the electrochemical behavior of alloys, and the polarization curve and AC impedance spectrum of the simulated-segregated-phase alloy and the Al–Zn–In alloy were measured. The results showed that Al3Er was an anodic segregation phase in the Al–Zn–In–Er alloy, and the preferential dissolution of the segregation phase would occur in the alloy, but the Al3Er phase itself was passivated in the dissolution process, which inhibited the further activation of the dissolution reaction of the Al–Zn–In–Er alloy to a certain extent.

Effect of Vacuum Environment on Micro Morphology and Porosity of Lunar Soil Concrete

Lunar soil concrete with sulfur system was prepared. The XRD, XRF and SEM datas of lunar soil concrete under atmospheric pressure and vacuum environment after 28 days of curing were compared. The changes of composition and microstructure during solidification of sulfur lunar soil under vacuum and atmospheric pressure were studied. The changes of porosity under atmospheric pressure and vacuum environment were analyzed and compared. Semi quantitative analysis and evaluation are carried out to compare different experimental phenomena.The results show that the vacuum environment has little effect on the element composition of lunar soil concrete. Sulfur exists in the form of single substance in lunar soil concrete, which has the effect of cementation and bonding. The porosity of lunar soil concrete becomes larger under vacuum environment. It can provide technical reserves for the follow-up utilization of in-situ lunar resources and the construction of lunar scientific research stations.

One-pot hydrothermal synthesis of CuBi2O4/BiOCl p-n heterojunction with enhanced photocatalytic performance for the degradation of tetracycline hydrochloride under visible light irradiation

In our part, we synthesized the CuBi2O4/ BiOCl p-n heterojunction photocatalyst by convenient one-pot hydrothermal method. And the morphology, crystal phase, element composition and optical properties of as-synthesized CuBi2O4/BiOCl were...

Studies on nanocomposites nanoplates and pervoskite nanorod thin films

Nano crystalline nickel oxide thin films of different film thickness were deposited onto glass substrate at 350 oC by varying volume of precursor solution using spray pyrolysis technique. This structural, morphological and microstructure properties were investigated using XRD, FE-SEM and TEM. The element composition was studied using EDAX. It is found that increase in the volume of sprayed solution leads to the increment in film thickness and amelioration of crystallinity of the film. The results are discussed and interpreted.

Monthly variation of micro- and macro-element composition in smooth scallop, Flexopecten glaber (Linnaeus, 1758), from the Çardak Lagoon (Çanakkale Strait, Turkey)

The present study investigated the total elemental composition (Fe, Cu, Mn, Zn, Al, S, B, Na, Mg, K, Ca, P, S) in smooth scallop (Flexopecten glaber) meat collected monthly in the Çardak Lagoon (Turkey) in 2017- 2018. Considering the distribution of elements in terms of quantity during the year, the elements were sorted as S> Na> K> P> Mg> Ca> Fe> Zn> Mn> Al> B> Cu> Se and the heavy metals were below the detection limit. Although the elements were at their highest values during autumn and summer, they were at their lowest values during spring and winter. The differences between the months in terms of Fe, Mn, Mg, and Ca elements were found to be statistically significant (p <0.05). It was determined that the element composition of smooth scallop meat was suitable for consumption in terms of the area where it is collected and is beneficial for health when consumed in the amounts recommended by FAO/WHO, and CODEX. The Hazard Quotient (THQ) and the Hazard Index (HI), which was conducted to evaluate the health risks of consuming smooth

Experimental and Analytical Investigations on Tribological Properties of PTFE/AP Composites

The tribological properties of polytetrafluoroethylene (PTFE)/AP (poly(para-phenyleneterephthalamide) (PPTA) pulp) composites under different test conditions (load: 2N, 10N; frequency: 1 Hz, 4 Hz; amplitude: 2 mm, 8 mm) were holistically evaluated. PTFE/AP composites with different AP mass ratios of 3%, 6%, and 12% as a skeleton support material were prepared. The coefficient of friction (COF) and wear rate were determined on a ball-on-disk tribometer. Furthermore, the morphology, element composition, and chemical structure of the transfer membrane were analyzed accordingly. The relationships between load, frequency, amplitude, and tribological properties were further investigated. According to the wear mechanism, AP enables effective improvement in the stiffness and wear resistance, which is also conducive to the formation of transfer films.