No 2 (2023)

The article presents the results of U-Pb dating (SHRIMP-II, the Center for Isotope Research of the A.P. Karpinsky Russian Geological Research Institute) of zircon grains from leucogranite dating back to the final formation stage of the Reftinsky gabbro-granitoid massif, which is one of the largest magmatism areas of this type in the Urals. The intrusive formations of the dated magmatism episode form a sub-meridionally elongated chain of small (up to 5 km in diameter) bodies, which intrude the Silurian plagioclase granitoids building up the main part of the massif. These bodies are dominated by granodiorites, granites, and leucogranites with some gabbro, gabbronorites, diorites, and quartz diorites. By the chemical composition, the study rocks belong mainly to the moderate-potassium calc-alkaline series. The silica-rich petrographic rock varieties have a high-potassium composition. The concordant age of zircons from leucogranites is 396 ± 3 Ma. So, the formation of zircons falls in the same time interval with a significant episode of endogenous activity, i.e. the existence of the Devonian island arc within the Middle Urals (from the second half of the Emsian through the beginning of the Frasnian).

Ultrabasic dike formations developed within the Kosyuskoe, Novobobrovskoe and Oktyabrskoe rare-metal-to-rare-earth ore fields, are attributed to alkaline picrites by the petrographic, petrochemical and geochemical characteristics. The rocks contain high amounts of V, Cr, Ni being typical of ultrabasic rocks. The processes of fenitization increase the content of Th, REE, Y, Pb in the rocks and so cause the appearance of ore minerals (monazite, xenotime, phosphates, and Th and Pb sulfides). The age identified by the ⁴⁰Ar/³⁹Ar method by phlogopite is 598.1±6.2 Ma. This time period is reconstructed for the plume impulse within the Chetlas Kamen of the Middle Timan.

Left tusk’s fragments of the Pleistocene walrus were studied. Its fossil remains were found on the bank of the Pechora River in 2009. The analyses covered granulometric, chemical and normative-mineral composition of grounds inside the bones; thermal properties, chemical and microelemental composition of the tusk; X-ray diffraction parameters and chemical composition of bone bioapatite; macrostructure, elemental and amino acid composition of bone organic matter; isotopic composition of carbon, oxygen in bioapatite and carbon, nitrogen in bone collagen. Bioapatite was identified for moderately isotopically light carbon, characteristic of extracave fossil bones of the Pleistocene animals, and isotopically heavy oxygen, typical of seawater bicarbonate. The isotopic data for the organic matter of the Pechora walrus correlated with the similar characteristics of marine animals but simultaneously indicated not a mollusk diet, typical of modern walruses, but a fish diet. The latter fact evidenced the habitat and the diet of the Pechora walrus being untypical for marine predators.

Mica are a group of minerals with a perfect cleavage. They can split into very thin leaves with equivalent surfaces. Among all known mineral mica species, muscovite and phlogopite are highly important industrially because can be easily split into thin leaves and simultaneously have very high electrical characteristics, incombustibility and a great chemical fastness. Additionally, they are thermally and chemically resistant, poorly hygroscopic, as well as flexible, resilient and transparent as thin leaves. Not only muscovite and phlogopite but also biotite and vermiculite are of practical importance. Biotite is sometimes used to replace muscovite or phlogopite. Vermiculite is a hydrated biotite; it can be hardly split into thin leaves, has low electrical properties and is poorly thermally-resistant. Affected by high temperatures, mica releases water and so gradually loses its brightness and transparency, strongly swells, splits and becomes fragile. Thus, the properties of mica affected by high temperatures largely reduce. Therefore, in order to apply the mineral in materials and devices operating at a very high temperature, we should decide for a relevant type of mica which thermal resistance meets the operating conditions. By the results of the differential-thermal analysis, the mica crystal structure increases in swelling. The authors have identified a temperature range in frames of which mica retains its working properties. Visual changes in swelling in the temperature range of 20–1200 °C have been identified and analyzed. The questions of mica thermal stability for its long-term use in the electric and radio industry have been solved. The technical use of mica in more critical cases has a temperature limit of 600–650 °C. The significant residual swelling allows for the practical use of mica as a heat insulating material.

The authors have developed a three-stage technology for making dense Ti₃SiC₂–TiB₂–(TiC)–SiC ceramic composites of a leucoxene concentrate being a product of previous treatment of titanium-containing sandstones. The first stage means the synthesis of agglomerated Ti₃SiC₂–TiB₂–SiC powders which may significantly differ in SiC content. The synthesis proceeds by the method of the vacuum carbosilicothermic reduction of leucoxene concentrate using SiC as a reducing agent with addition of B₄C as a solid boron-containing component. The second stage is etching the obtained powders with hydrofluoric acid in order to remove the by-products of silicide composition having been formed of impurities in leucoxene concentrate. At the final third stage, the purified Ti₃SiC₂–TiB₂–(TiC)–SiC powders are hot-pressed in a graphite die under 30 MPa at a temperature of 1500-1550 °C. The end product is Ti₃SiC₂–TiB₂–(TiC)–SiC ceramic composites with nearly absolute pore-free microstructure.