Formation of material prescribed phase composition from refractory filler silica powder modified with alkoxide and sol-gel composite

Creation of ceramics and refractories with improved physicomechanical properties is possible with use of nanomaterials in their technology. Introduction of SiC nanoparticles into a ceramic material charge by using modified filler powders is proposed. Fillers modified with tetraethoxysilane during grinding leads to powder crystal structure breakdown and SiC mechanochemical synthesis. The amount of -SiC synthesized in this way depends on the amount of modifying additive. Results are provided for modified filler phase composition before and after heat treatment at 1000°C, and mechanochemically synthesized SiC thermal stability is established. It is shown that sintering of modified electro-corundum worsens with an increase in amount of synthesized silicon carbide nanoparticles. The difference is demonstrated in phase composition formation with heat treatment of a mixture of modified and normal finely ground electrocorundum with a sol-gel binder and firing up to 1600°C. Silicon carbide nanoparticle synthesis does not exceed 3 – 7 % in both cases. Recommendations are given for use of corundum filler with a different amount of modifying additive

Synthesis of β-SiC in the intermediate layer of corundum coatings based on a sol-gel binder for protecting graphite objects from oxidation

A coating is developed for protecting graphite from oxidation at 2023 – 2223 K. The efficiency of the protective action of a corundum coating based on a sol-gel binder increases due to creating a dense intermediate layer between the graphite substrate and the coating as a result of its self-reinforcement with fibers of mullite crystals and -SiC nanoparticles. Components of a modifier and sol-gel binder, but not carbon of the graphite substrate, provide synthesis of β-SiC

Features of high-strength composite material structure creation

The basis of technology proposed is use of a sol-gel method for preventing polycrystalline corundum fiber from crystallization during heating to high temperature and for low-temperature synthesis of prescribed phases in a corundum matrix with the aim of improving the operating properties of composite materials based on corundum. As a result of firing a charge based on corundum powder modified with tetraethoxysilane and polycrystalline corundum fiber modified with ethylsilicate-32 at 1360°C materials are created with very good strength properties. The materials exhibit electrical insulation properties and are stable in ionized gas streams at the level of known analogs as a result of creating self-reinforced mullite and β-SiC corundum matrix, reinforced with polycrystalline fiber and rapidly sintered due to presence of silicon oxynitride

Sicilian byzantine icons through the use of non-invasive imaging techniques and optical spectroscopy: The case of the madonna dell’elemosina

The iconographic heritage is one of the treasures of Byzantine art that have enriched the south of Italy, and Sicily in particular, since the early 16th century. In this work, the investigations of a Sicilian Icon of Greek-Byzantine origin, the Madonna dell’Elemosina, is reported for the first time. The study was carried out using mainly non-invasive imaging techniques (photography in reflectance and grazing visible light, UV fluorescence, infrared reflectography, radiography, and computed tomography) and spectroscopic techniques (X-ray fluorescence and infrared spectroscopy). The identification of the constituent materials provides a decisive contribution to the correct historical and artistic placement of the Icon, a treasure of the Eastern European historical community in Sicily. Some hidden details have also been highlighted. Most importantly, the information obtained enables us to define its conservation state, the presence of foreign materials, and to direct its protection and restoration

Oxidation resistance of nano-reinforced PC-refractories modified with phenol formaldehyde resin. Part 4. Thermodynamic evaluation of phase formation within Mg–O–C–Al, Mg–O–C–Ni and МgO‒Al₂O₃‒NiO‒SiO₂ systems using SiC + Al + Ni (NiO) complex antioxidant

Results are given for the synthesis and co-existence of phases formed from components of complex organic- inorganic antioxidant formed during modification of phenol-formaldehyde resin (PFR) and graphite with silica alkoxide and inorganic or organic nickel precursors. Thermodynamic analysis is given for the Mg–Al–C and Mg–O–Ni–C systems. It is shown that the periclase and carbon can coexist with aluminum and nickel, and also that oxidized antioxidants Al₂O₃ and NiO can interact respectively with the periclase and with the synthesized SiC formed during modification of PFR with silica. In considering the NiO‒MgO‒Al₂O₃‒SiO₂ system it is established that during service noble spinel will be synthesized from the complex antioxidant components, facilitating an increase in PC-refractory durability in service

Oxidation-resistant nano-reinforced PC-refractories of modified phenol formaldehyde resin. Part 3. Formation mechanism of organic-inorganic complexes during low-temperature synthesis of nanoparticles of additional antioxidants and their effectiveness

SiC nanoparticles that could be used as an antioxidant for periclase-carbon (PC) refractories were synthesized from the organic—inorganic complex (‒СН₃)‒(SiO₂)n that formed during heating of silicon alkoxide and thermal destruction of its gels. Use of phenolformaldehyde resins modified with silicon alkoxide and its sols was proposed and enabled the formation of an organic—inorganic complex (-СН₃)‒(SiO₂)n‒С with a high C content. This increased the yield of SiC synthesized in the carbon binder. The addition of Ni precursors (additional antioxidant) formed an even more complicated organic—inorganic complex. Use of the complex (‒СН₃)‒(SiO₂)n‒Ni(NiO)‒С together with Al improved the operating characteristics of the PC refractories. It was found that their resistance to oxidation was increased after the complex antioxidant Al + SiC + Ni(NiO) formed

Drought soil legacy overrides maternal effects on plant growth

Maternal effects (i.e. trans-generational plasticity) and soil legacies generated by drought and plant diversity can affect plant performance and alter nutrient cycling and plant community dynamics. However, the relative importance and combined effects of these factors on plant growth dynamics remain poorly understood. We used soil and seeds from an existing plant diversity and drought manipulation field experiment in temperate grassland to test maternal, soil drought and diversity legacy effects, and their interactions, on offspring plant performance of two grassland species (Alopecurus pratensis and Holcus lanatus) under contrasting glasshouse conditions. Our results showed that drought soil legacy effects eclipsed maternal effects on plant biomass. Drought soil legacy effects were attributed to changes in both abiotic (i.e. nutrient availability) and biotic soil properties (i.e. microbial carbon and enzyme activity), as well as plant root and shoot atom 15N excess. Further, plant tissue nutrient concentrations and soil microbial C:N responses to drought legacies varied between the two plant species and soils from high and low plant diversity treatments. However, these diversity effects did not affect plant root or shoot biomass. These findings demonstrate that while maternal effects resulting from drought occur in grasslands, their impacts on plant performance are likely minor relative to drought legacy effects on soil abiotic and biotic properties. This suggests that soil drought legacy effects could become increasingly important drivers of plant community dynamics and ecosystem functioning as extreme weather events become more frequent and intense with climate change. A plain language summary is available for this article.</p

Spatial complementarity and the coexistence of species

Coexistence of apparently similar species remains an enduring paradox in ecology. Spatial structure has been predicted to enable coexistence even when population-level models predict competitive exclusion if it causes each species to limit its own population more than that of its competitor. Nevertheless, existing hypotheses conflict with regard to whether clustering favours or precludes coexistence. The spatial segregation hypothesis predicts that in clustered populations the frequency of intra-specific interactions will be increased, causing each species to be self-limiting. Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade. In this study we create an individual-based model in homogeneous two-dimensional space for two putative sessile species differing only in their demographic rates and the range and strength of their competitive interactions. We fully characterise the parameter space within which coexistence occurs beyond population-level predictions, thereby revealing a region of coexistence generated by a previously-unrecognised process which we term the triadic mechanism. Here coexistence occurs due to the ability of a second generation of offspring of the rarer species to escape competition from their ancestors. We diagnose the conditions under which each of three spatial coexistence mechanisms operates and their characteristic spatial signatures. Deriving insights from a novel metric — ecological pressure — we demonstrate that coexistence is not solely determined by features of the numerically-dominant species. This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community. Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation

Photoactive Properties of Transport Sol-Gel Layers Based on Strontium Titanate for Perovskite Solar Cells

In this work, we have investigated the photocurrent and spectral sensitivity of the silicon/SrTiO3:xNb/perovskite structures. The sol–gel method carried out the deposition of undoped SrTiO3 layers as well as niobium-doped (SrTiO3:Nb) layers at atomic concentrations of 3 and 6% Nb. The perovskite layer, CH3NH3PbI3_xClx, has been deposited by the vacuum co-evaporation technique. The layers have been characterized by scanning electron microscopy and X-ray diffraction measurements. The volt–ampere characteristics and spectral sensitivity of the fabricated samples have been measured under illumination with selective wavelengths of 405, 450, 520, 660, 780, 808, 905, 980, and 1064 nm of laser diodes. We have shown that for different configurations of applied voltage between silicon, SrTiO3:xNb, and CH3NH3PbI3_xClx, the structures are photosensitive ones with a variation of photocurrent from microamperes to milliamperes depending on Nb concentration in SrTiO3, and the highest photocurrent and spectral sensitivity values are observed when a SrTiO3:Nb layer with 3 at.% of Nb is used. A possible application of the proposed structure with a SrTiO3:Nb layer for perovskite solar cells and photodetectors is being discussed