INFLUENCE OF SURFACE PRE-HEATING ON THE NITRIDING DEPTH OF STEEL 25CrMoVA USED COMPLEX ION-PLASMA TREATMENT

In the method of nitriding elements, various methods of their thermal heating are used. The simplest heating method in ion-plasma nitriding is heating by bombarding the surface first with low-energy gas ions and then with metal ions with energies up to several kiloelectronvolt. Elements exposed to ion bombardment have a welldeveloped surface that is free from contaminants and facilitates the diffusion of nitrogen into the depth of the metal during nitriding. The paper studies the effect of various preliminary heating methods on the nitriding depth in the complex ion-plasma hardening technology of 25CrMoVA steel. A JSM 7000-1F scanning electron microscope equipped with an X-ray spectral energy dispersive microanalysis attachment was used to diagnose changes occurring on the surface of the samples and at depth; the hardness was measured using a Nanoindentor G200 device. The preliminary heating of the samples was carried out both with the use of bombardment with Ti or Mo ions, and without its direct effect on the heated surface. In the experiment, differences in the depth of hardening of the nitrided layer of steel are observed when it is heated in different ways. When bombarded with Mo ions, the greatest depths of hardening were obtained in comparison with other preliminary heating conditions. It is shown that these differences are associated with the features of the morphology of the steel surface formed as a result of sputtering processes. The formation of nitride compounds in its surface layer can serve as a barrier that slows down the penetration of nitrogen into the metal. It is shown that with complex treatment in the process of deposition of a nitride coating on the surface of nitrided steel, an additional increase in the depth of hardening of the nitrided layer occurs.

Three β-Glucuronosyltransferase Genes Involved in Arabinogalactan Biosynthesis Function in Arabidopsis Growth and Development

Arabinogalactan proteins (AGPs) contain arabinogalactan (AG) polysaccharides that are biologically relevant to plant growth processes. Here, the biochemical and physiological roles of three Golgi localized β-glucuronosyltransferase genes (GLCAT14A, GLCAT14B and GLCAT14C) in Arabidopsis thaliana, responsible for the addition of glucuronic acid to AG chains, were further investigated using single, double and triple glcat14 mutant plants. These proteins were localized to the Golgi apparatus when transiently expressed in Nicotiana benthamiana. Sugar analysis of AGP extracts from Arabidopsis stem, leaf and siliques showed a consistent reduction in glucuronic acid in glcat14 mutants relative to wild type, with concomitant effects resulting in tissue-specific alterations, especially in arabinose and galactose sugars. Although we observed defects in trichome branching in glca14a/b and glca14a/b/c mutants, scanning electron microscope analysis/energy dispersive microanalysis (SEM/EDX) showed no difference in the calcium content of trichomes in these mutants relative to wild type. Immunoblot analyses of the stem and leaf showed a reduction in AGPs as detected with the LM2 antibody in glcat14a/b and glcat14a/b/c mutants relative to wild type. The current work exemplifies the possibility of conducting structure-function assessment of cell wall biosynthetic genes to identify their physiological roles in plant growth and development.

Effect of Heat Treatment on the As-Cast Microstructure and Hardness of NiSi3B2 Alloy

Cast Ni-Si-B alloys have the potential for high-temperature applications because of their high resistance to wear, impact, corrosion, and oxidation at elevated temperatures due to an appropriate balance of hard phases and austenite that ensures a good compromise between toughness and hardness. In this work, NiSi3B2 specimens, fabricated by the lost-wax casting process, were investigated. Given the complex multiphase cast microstructure, a differential scanning calorimeter (DSC-TGA) analysis was employed to characterize the reactions that occur during solidification and the resulting phases were characterized using scanning electron microscopy (SEM), with energy-dispersive microanalysis (EDS) and backscattered electron (BSE) image and X-ray diffraction (XRD). Due to the presence of hard phases, machining of the Ni-Si-B components can pose additional difficulties. Therefore, the conditions of the solution heat treatment, which might lead to the homogenization of the microstructure, consequently improving its machinability, were also investigated. The results of the heat-treated samples indicated that the dissolution of the eutectic constituent is accompanied by a significant decrease in the hardness (approximately 17%). It is important to emphasize that the solution heat treatments carried out reduced the hardness without affecting the percentage of borides, which will allow improving the machinability without adversely affecting the alloy performance in service.

Destruction of microplastics in the natural environment

<p>Morphological structure and chemical composition of environmental microplastics (MPs) extracted from water and bottom sediments of Lake Onego were studied. Raman spectroscopy was used to identify MPs polymer types and scanning electron microscopy with energy dispersive microanalysis was used to study the morphology and trace elements composition of inclusions on their surface. The features of the destruction of MPs, as well as the presence of various chemical elements on their surface including heavy metals, were investigated. Four main mechanisms of MPs microdestruction have been identified: (1) Local destruction of monophasic MPs caused by local oxidation and cleavage of thin flakes and fragments with the formation of nanoscale plastics. (2) The destruction of multiphase microplastics predominantly determined by the selective destruction of one of the phases of the composite, for example, the ligament scission between the individual components of the plastic with their separation. (3) Microbiological destruction of MPs under the influence of diatoms by fixing spores of diatoms on defects of MPs with their subsequent growth, deflection, and separation of nanoscale polymer particles. (4) Mineralogical destruction of MPs associated with the sorption of chemical elements and crystallization of nanocrystals, which under appropriate conditions begin to grow and break-up the MPs accelerating the process of its destruction. The last mechanism have not yet been reported. These mechanisms initiate nanoplastics formation, which increases particles mobility in the aquatic environment and their threat to water organisms. At the same time, the fouling with diatoms (with a silica shell) and the sorption of heavy elements increase the bulk specific density of MPs and contribute to its accumulation in bottom sediments.</p><p>The study was supported by the Russian Science Foundation grant number 19-17-00035.</p>

A study of radicals in industrial raw cristobalite powders

We report the results of an experimental multianalytical characterisation of industrial cristobalite powders, used as raw materials for artificial stone production. Cristobalite is considered a serious threat to human health. The study was carried out through X-ray diffraction (XRD), scanning electron microscopy with energy dispersive microanalysis (SEM/EDS), continuous-wave (cw) and pulse electron paramagnetic resonance (EPR) spectroscopy. Our results point out a sub-micrometric size of the structural coherence in cristobalite, associated with numerous stacking defects. Moreover, the material was found characterised by the presence of superoxide radicals, whose persistence appears conceivably long. Radicals in a material synthesized through a high-temperature treatment were generated during the grinding step in the industrial production of cristobalite. During this process, in fact, both superoxide generation and structural defectivity are induced. Indeed, cristobalite powders already result activated by a radical population, before any kind of process in artificial stone production.

Alcoxotechnology for obtaining heat-resistant materials based on rhenium and ruthenium

Objectives. To develop physical and chemical bases and methods to obtain rhenium–ruthenium isoproxide Re4-yRuyO6(OPri)10 —a precursor for obtaining a high-temperature alloy—from ruthenium acetylacetonate and rhenium isoproxide acquired by electrochemical methods.Methods. IR spectroscopy (EQUINOX 55 Bruker, Germany), X-ray phase and elemental analyses, energy-dispersive microanalysis (EDMA, SEM JSM5910-LV, analytical system AZTEC), powder X-ray diffraction (diffractometer D8 Advance Bruker, Germany), experimental station XSA beamline at the Kurchatov Synchrotron Radiation Source.Results. The isoproxide complex of rhenium–ruthenium Re4-yRuyO6(OPri)10 was obtained, and its composition and structure were established. Previously conducted quantum chemical calculations on the possibility of replacing rhenium atoms with ruthenium atoms in the isopropylate complex were experimentally proven, and the influence of the electroconductive additive on the composition of the obtained alloy was revealed.Conclusions. Physical and chemical bases and methods for obtaining rhenium–ruthenium isoproxide Re4-yRuyO6(OPri)10 were developed. The possibility of using rhenium–ruthenium Re4-yRuyO6(OPri)10 as a precursor in the production of ultra- and nanodisperse rhenium–ruthenium alloy powders at a record low temperature of 650°C were shown.

PROSPECTS FOR USING BENTONITE CLAYS IN CONCRETE COMPOSITES

В работе представлен опыт практического использования бентонитовых глин, свидетельствующий о широком его применении во многих областях промышленности, и в частности в строительной индустрии, как перспективный материал для получения современных строительных композитов. Исследованиям подвергались бентониты местной сырьевой базы, на основании которых представлены результаты отбора проб, энергодисперсионный микроанализ и химический состав. Проведенные исследования подтверждают наличие необходимого оксидного и минерального составов, что позволит в дальнейшем получать строительные композиты, активированные щелочным затворителем. The paper presents the experience of the practical use of bentonite clays, which indicates its widespread use in many areas of industry, and in particular in the construction industry, as a promising material for obtaining modern building composites. The bentonites of the local raw material base were studied, on the basis of which the results of sampling, energy dispersive microanalysis and chemical composition are presented. The studies carried out confirm the presence of the necessary oxide and mineral compositions, which will allow in the future to obtain building composites activated with an alkaline grout.

The Cannero Castle (Italy): Development of Radiocarbon Dating Methodologies in the Framework of the Layered Double Hydroxide Mortars

ABSTRACTThe mortar samples of the Castle of Cannero (Lake Maggiore, Italy) have been characterized and radiocarbon (14C) dated. The presence of LDH phases was identified. The hydraulic reaction was evaluated by a multi-analytical approach. Careful extraction, preparation and purification of the binder fraction have been performed. Contaminations due to LDH phases have been removed allowing reliable absolute dating of the structures.Non-hydraulic lime-based mortars represent only part of the binding materials found in archaeological and historical structures, and a new challenge is the application of 14C dating techniques on mortars that feature hydraulic reactions. This research work aims at 14C dating a series of Mg-rich hydraulic mortars from the Castle of Cannero (Lake Maggiore, Italy), from which both charcoals and mortar samples were collected. A multi-analytical approach employing X-ray powder diffraction (XRPD), optical microscopy (OM), and scanning electron microscopy/energy-dispersive microanalysis (SEM-EDS) was adopted in order to carefully characterize the samples. A wet gravimetric separation for the extraction of the fine fraction mainly composed by the mortar binder was carried out and the binder fraction was characterized by XRPD in order to investigate the presence of contaminants. The binding fractions are characterized by the widespread occurrence of hydrotalcite-type minerals, considered contaminants in 14C dating of mortars because of their capability to exchange carbonate anions even after the hardening process. A further purification treatment by thermal decomposition was performed before 14C dating by AMS. The obtained dates were consistent with archaeological expectations, confirming the potential of the developed purification methodology for hydraulic mortars dating.

PREPARATION OF LIQUID-GLASS SILICATE-SODIUM ALKALINE SOLUTIONS FROM SILICON-CONTAINING ADDITIVES

В основу получения бетонных композитов на вяжущих щелочной активации положен отечественный и зарубежный опыт применения шлакощелочных композитов в строительстве. В данной работе проведен энергодисперсионный микроанализ исследуемых бесклинкерных композиций на основе щелочных силикат натриевых растворов из кремнеземсодержащих горных пород. Разработанные рецептуры бесклинкерных вяжущих на основе высокодисперсных порошков различной природы, затворенных щелочным раствором, приготовленным мокрым способом при температурах до 950С и атмосферном давлении. Данная технология позволит расширить область применения щелочных цементов и получать бетоны с заданными свойствами. Работа выполнена в рамках исследований по реализации научного проекта 1848200001 Высококачественные бетоны с повышенными эксплуатационными свойствами на основе местного природного и техногенного сырья , получившего поддержку Российского фонда фундаментальных исследований (РФФИ). Alkaline mixing cements in which the alkaline metals will be the active component can interact with aluminosilicate minerals during hydration to form strong and insoluble compounds. The basis for the production of concrete composites on alkaline binding binders is based on domestic and foreign experience in the use of slag base composites in construction. In this work, an energy dispersive microanalysis of the clinkerfree compositions under study based on alkaline silicate sodium solutions from silicacontaining rocks was carried out. Developed formulations of clinkerless binders on the basis of highly dispersed powders of various nature, closed with an alkaline solution prepared by the wet method at temperatures up to 95 C and atmospheric pressure. This technology will allow you to expand the scope of alkaline cements and get concretes with desired properties.