•Mg-Zn ferrites prepared by autocombustion, co-precipitation, spray pyrolysis.•Influence of structural features on magnetic properties of ferrites is determined.•The highest magnetization is achieved ...for Mg0.5Zn0.5Fe2O4 nanoparticles.
Structural characteristics and magnetic properties of MgxZn1–xFe2O4 (x = 0.25; 0.5; 0.7) nanomaterials prepared by autocombustion, co-precipitation and spray pyrolysis methods were studied. Different characterization techniques are used to study the structural formation of the generated nanoparticles, namely X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), infrared spectroscopy (FT-IR) and vibrating sample magnetometery (VSM). In case of citrate autocombustion and co-precipitation methods, the magnetization goes through a maximum at Mg0.5Zn0.5Fe2O4 composition, while the dependence on the composition is subtle for spray pyrolysis. An increase in temperature and duration of heat treatment during the synthesis process leads to a particle size growth and to a cation redistribution between spinel sub-lattices. These resulted in a significant increase in the specific magnetization of the particles generated by citrate autocombustion method. The nanoparticles synthesized by co-precipitation method exhibit superparamagnetic behavior with no coercivity at room temperature. Nonetheless, the materials prepared by spray pyrolysis and citrate autocombustion methods are found to possess small coercivity of 30–80 Oe. The highest specific magnetization at room temperature is referring to Mg0.5Zn0.5Fe2O4 nanoparticles obtained by citrate autocombustion method (30 emu/g). The revealed correlations can be used to synthesize spinel ferrite nanoparticles with well-defined collective properties for a wide spectrum of applications.
Abstract
An important quantity determining the choice of technical solutions in design of both surface and underground structures in the permafrost area is the thawing depth of the rocks. To obtain ...simple analytical relations to determine the thawing depth over time, a simple assumption is used: that the initial temperature of the rocks is equal to the melting temperature of ice. The aim of the present work was the assessment of impact of this assumption on the forecast precision. For a quantitative assessment, a simple typical formula recommended by construction norms was used. Functional dependence of the density of the rocks and their heat capacity on the fraction of ice content was considered in the formulas. A rock consisting of a combination of quartz sand and ice was used as an example.Multiple variant calculations were done according to the formulas and their results presented in the form of charts. It was shown that the relative error in determination of thawing depth depends solely on the Stefan criterion and is independent of the thawing duration, thermal conductivity coefficient of the thawing rocks and the air temperature during the thawing. A relation was obtained which allows to quickly assess at which initial values (temperature and ice content of the frozen rocks) it is possible to use the formulas obtained from the simplified calculation models with the assumption that the temperature of the rocks is equal to the melting temperature of ice.
The cytochrome P450 (CYP) superfamily is a diverse and important enzyme family, playing a central role in chemical defense and in synthesis and metabolism of major biological signaling molecules. The ...CYPomes of four cnidarian genomes (Hydra vulgaris, Acropora digitifera, Aurelia aurita, Nematostella vectensis) were annotated; phylogenetic analyses determined the evolutionary relationships amongst the sequences and with existing metazoan CYPs. 155 functional CYPs were identified and 90 fragments. Genes were from 24 new CYP families and several new subfamilies; genes were in 9 of the 12 established metazoan CYP clans. All species had large expansions of clan 2 diversity, with H. vulgaris having reduced diversity for both clan 3 and mitochondrial clan. We identified potential candidates for xenobiotic metabolism and steroidogenesis. That each genome contained multiple, novel CYP families may reflect the large evolutionary distance within the cnidarians, unique physiology in the cnidarian classes, and/or different ecology of the individual species.
This article provides relevant information on the catalysts’ morphological characteristics that allow for the optimal combination of activity and durability of the materials for proton-exchange ...membrane fuel cells. The home-made Pt/C and PtCu/C catalysts have been established to have at least by 20% higher values of the mass activity in the oxygen reduction reaction than the commercial Pt/C analogue (HiSPEC 3000, Johnson Matthey). The detailed analysis of the microstructure by transmission electron microscopy and the electrochemical parameters by electrochemical surface-sensitive methods after the stress testing has allowed estimating the contribution of various mechanisms to the degradation process. After the stress testing, the residual activity in the oxygen reduction reaction of the home-made materials has proved to be at least more than double that of the commercial Pt/C catalyst. A specific feature of this work is the presented correlation between the morphology and the electrochemical behavior of the catalysts, with this interconnection appearing to be a valuable resource for a wide range of scientists.
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•The rapid and facile synthesis methods of the highly active catalysts are presented.•The PtCu/C catalyst is 2.5 times more active in the ORR than the commercial Pt/C.•The testing is conducted within the protocols with the long-term cycling and the potential hold.•The home-made materials are more robust against degradation than the commercial one.•The integrated approach to studying the catalysts' durability is presented.
Heat capacity of dispersed rocks Galkin, A F; Yu Pankov, V
Journal of physics. Conference series,
12/2021, Letnik:
2131, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Abstract
Protection of automobile roads from negative cryogenic processes is a current issue to which significant attention is devoted in both scientific and engineering communities. In many cases ...important for practice, the the thermal factor determines the reliability and security of the use of the road in the cryolithic zone. The heat capacity of dispersed rocks is among the most important indicators of the physical properties determining the intensity of thermal processes in the road surfaces and road foundations. The precision of determination of the total heat capacity of the rocks in thawed and frozen state largely determines the precision of the forecast of the thermal regime of roads in the cryolithic zone. A complex assessment of the impact of ice content of the dispersed rocks on the value of total heat capacity was done. 2D and 3D charts which allow to assess the possible range of change in the heat capacity of the dispersed rocks in thawed and frozen state, in both a wide range and in the typical range of values, were produced. Among the main criteria determining the extent of the seasonal freezing and thawing of the soils of the active layer is the Stefan number, a dimensionless criterion. An overall assessment of the impact of ice content on the ground (rock) foundations of the roads and of the air temperature in the warm period of the year on the quantitative values of the Stefan number was done. Charts allowing to determine in both a wide and typical range the changes of values of the Stefan numbers, permitting to assess the possible range of changes of the Stefan number, were made. It was determined, in particular, that for the typical dispersed rocks of the road foundations in the cryolithic zone the range of change in the Stefan numbers is 2.1-6.5.
We performed a quantitative study of the neuronal population in the spinal cord of mice with acute and chronic model of experimental autoimmune encephalomyelitis. Immunohistological/immunofluorescent ...analysis with motor neuron marker ChAT revealed a significant decrease in the number of motor neurons in the ventral horns of the lumbar spinal cord in the acute form of autoimmune encephalomyelitis, with the further appearance of large empty (containing no motor neurons) areas in the ventral horns in the chronic form. The development of experimental autoimmune encephalomyelitis is accompanied by degradation and death of neurons, in particular ChAT
+
motor neurons.
Nanocrystalline ZnxFe3–xO4 solid solutions (with x=0, 0.18, 0.45, 1) with crystallite sizes of 5–10nm, specific surface of about 180m2/g were synthesized via an inorganic variant of the sol–gel ...approach. The composition and structure of the formed nanoparticles were examined with the help of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, inductively coupled plasma atomic emission spectrometry and Fourier transform infrared spectroscopy. Hysteresis loops recorded for the samples indicate their ferromagnetic behavior at 5K and superparamagnetic behavior at 300K. The highest maximum magnetization of 59emu/g at room temperature corresponds to Zn0.18Fe2.82O4 composition, and at 5K to Zn0.45Fe2.55O4 (86emu/g). The saturation magnetization of the pure magnetite was measured to be respectively 62 and 49emu/g.
•A modified inorganic sol–gel method was applied to prepare ZnxFe3–xO4 nanoparticles.•Nanoparticles exhibit narrow size distribution with a particle size of 5–10nm.•The compositions with a higher magnetization value than magnetite were obtained.•The synthesized ZnxFe3–xO4 nanoparticles with x=0, 0.18, 0.45, 1 are superparamagnetic at room temperature.
Platinum–carbon catalysts are widely used in the manufacturing of proton-exchange membrane fuel cells. Increasing Pt/C activity and stability is an urgent task and the optimization of their structure ...seems to be one of the possible solutions. In the present paper, Pt/C electrocatalysts containing small (2–2.6 nm) nanoparticles (NPs) of a similar size, uniformly distributed over the surface of a carbon support, were obtained by the original method of liquid-phase synthesis. A comparative study of the structural characteristics, catalytic activity in the oxygen electroreduction reaction (ORR), and durability of the synthesized catalysts, as well as their commercial analogs, was carried out. It was shown that the uniformity of the structural and morphological characteristics of Pt/C catalysts makes it possible to reduce the negative effect of the small size of NPs on their stability. As a result, the obtained catalysts were significantly superior to their commercial analogs regarding ORR activity, but not inferior to them in terms of stability.
An important feature of this research is the investigation of the de-alloyed catalysts based on the nanoparticles with a simple structure (alloy) and a complex structure (gradient). The resulting ...samples exhibit the 2–4 times higher mass activity in the ORR compared with the commercial Pt/C. The novelty of this study is due to the application of the express-electrochemical experiment to register the trend of changes in the ORR activity caused by rearranging the structure of bimetallic nanoparticles. The state-of-the-art protocol makes it possible to establish the dependence of properties of the de-alloyed catalysts on the nanoparticles’ structure obtained at the stage of the material’s synthesis. The study shows the possibility of determining the rate of the ongoing reorganization of bimetallic nanoparticles with different architectures. The PtCu/C electrocatalysts for proton-exchange membrane fuel cells presented in this work are commercially promising in terms of both the high functional characteristics and the production by facile one-pot methods.
The majority of prospective deposits of oil and natural gas in the Russian Federation are located in the zones of permanently frozen rocks - the permafrost. This region is characterized not only by ...harsh climatic conditions, causing difficulty in development of the deposits, but also by negative cryogenic processes impacting the reliability of construction and use of various engineering structures. It is necessary to know the regularities of and to be able to forecast the thermal regime of the soils and rocks in order to forecast the degree of influence of cryogenic processes on the engineering structures. In particular, the depth of thawing and freezing of soils in the locations of underground and surface structures, such as pipelines, is of importance. The depth of thawing of soil is an important indicator for the choice of the method of construction on the frozen surfaces. Control of the thawing/freezing depth can be ensured with the use of thermal insulation as well as replacement of the soil itself with an artificial soil with preselected properties. Transportation of oil and natural gas is realized using pipelines laid through frozen rocks. In order to decrease cryogenic impact on the pipes, special thermal insulation beddings replacing a section of soil are used. To determine the thermal insulation properties of beddings made out of polystyrene, variant calculations of thermal conductivity coefficient have been done according to the Odelevski and Schwerdtfeger formulas. Calculations were done for beddings in thawed and frozen state with different polystyrene content concentration. The conclusion is that both formulas can be used for theoretical determination of thermal conductivity coefficient. Absolute and relative errors do not exceed those permissible in engineering calculations for a wide range of conditions.
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