The soils buried under the early medieval mounds of the 9th and early 11th centuries AD were studied. The reconstruction of environmental trendу and their influence on soils was carried out on the ...basis of a comparative analysis of the properties of soils buried under mounds of different ages, surface soils, and newly formed soil on mound structures supplemented with data on the time of soil formation on sandy parent rocks in the taiga zone. The study area belongs to the Baltic province of soddy-podzolic soils of the southern taiga subzone. Soils buried under mound structures characterize periods with different climatic conditions. Soils that developed before burial in the cool and humid climate of the 8th–9th centuries AD are specified by the mobility of iron compounds in the profile and a morphologically pronounced accumulation of bleached quartz grains in its upper part. The influence of relatively warm and dry climate of the 10th century AD on the processes of soil formation is manifested in the lower mobility of iron compounds, more active humus accumulation, and less pronounced bleaching of mineral grains. The time of formation of the profile of soddy podbur in the material of mound structures was estimated at 1000 years. The construction of the mound structures consisted in successive filling of the mound from the edges to the center of the site, so that the material of middle horizons of the initial natural soil turned out to be in the upper part of the mound.
Co doped bismuth magnesium tantalate with a pyrochlore structure (sp. gr. Fd-3m) was synthesized for the first time using the standard ceramic method. Single phase Bi2Mg1−xCoxTa2O9 samples were found ...to be formed when x < 0.7 in the X-ray phase analysis. However, with a higher cobalt content in the samples, the impurity phase β-BiTaO4 (sp. gr. P-1) is detected, and its amount is proportional to the degree of cobalt doping. The formation of solid solutions is evidenced by a uniform increase in the unit cell parameter of the Co,Mg co doped bismuth tantalate phase with an increase in the content of cobalt ions in the samples from 10.5412(8) (x = 0.3) to 10.5499(8) Å (x = 0.7). The samples exhibit a porous microstructure consisting of chaotically oriented and partially fused elongated grains measuring 1–2 μm. The dependence of the ceramic grain size on the n(Mg)/n(Co) ratio was not determined. X-ray spectroscopy (ear dge X-ray bsorption ine tructure (NEXAFS) and X-ray photoelectron spectroscopy (XPS)) was used to study the charge state of ions in Bi2Mg1−xCoxTa2O9. The NEXAFS and XPS data showed that doping with cobalt and magnesium did not change the bismuth and tantalum oxidation states in pyrochlore; in particular, the ions maintained their oxidation states of Bi(+3), Mg(+2) and Ta(+5). The energy position of the peaks of the Ta4f-, Ta5p-, Ta4d spectra had a characteristic shift towards lower energies compared to the binding energy in pentavalent tantalum oxide Ta2O5. A shift towards lower energies is characteristic of a decrease in the effective positive charge; in particular, for the Ta4f and Ta4d spectra we presented, this energy shift was ΔE = 0.65 eV, and in the region of the Ta4d edge—0.55 eV. This in turn allowed for us to assume that tantalum atoms have the same effective charge +(5-δ). The oxidation state of cobalt ions was predominantly 2+ and partially 3+, according to NEXAFS spectroscopy data.
A global trend in the development of the aluminum industry is connected with the attempts undertaken by all leading companies to find efficient measures for increasing the service life of ...electrolyzers. This is explained by the fact that overhauls prove to be one of the most costly stages in the process of production of aluminum. This is why the development and subsequent implementation of scientific and methodological approaches to the optimization of the startup period is one of the most promising directions directly affecting the duration of the service life of aluminum electrolyzers. We propose a simplified model of heat exchange used to choose the optimal voltage of an electrolyzer in the startup period of operation, when the scull has not been formed yet as an additional heat-insulating layer. This model is based on the ordinary differential equations and the representation of an electrolyzer in the form of a collection of heat-conducting multilayer elements and a heating melt. We present the numerical analyses of the dynamic responses of temperature of the melt and the layers of lining to the control action by voltage.
The possibility of high-temperature solid-phase synthesis of Ni-doped bismuth tantalate pyrochlore, not only from the oxide compounds BiTaO4 and NiO but also using nickel chloride NiCl2 as a ...precursor, was shown for the first time. The concentration range of the formation of nickel pyrochlore Bi2NixTa2O9−δ (0.85 ≤ x ≤ 1.0) at an equal molar ratio of bismuth(III)/tantalum(V) ions was determined. This indicates that the pyrochlore structure may be stable at 20–33% vacant bismuth sublattice. The influence of non-stoichiometric composition relative to bismuth and tantalum, by the example of Bi2±xNiTa2O9−δ and Bi2NiTa2−xO9−δ (x ≤ 0.5) compositions, on the phase composition of ceramics was studied. X-ray powder diffraction phase analysis of Bi2Ni1+yTa1.75−yO9−δ samples made it possible to determine the solubility limit of nickel ions in the tantalum sublattice. It was shown that the molar ratio of metal atoms (Ta, Ni) in the B2O6 (B-Ni(II), Ta(V)) octahedral sublattice of mixed pyrochlores is also limited.
The effect of Zn-doping on the phase composition and optical properties of the Bi2ZnxFe1-xTa2O9.5-Δ (x = 0.3, 0.5, 0.7) was studied. XRD data showed that the samples crystallize in the structural ...type of pyrochlore (sp. gr.Fd-3m). For all the samples, an admixture of bismuth orthotantalate β-BiTaO4 triclinic modification up to 22.5 wt.% is observed. The content of β-BiTaO4 increases with zinc doping. The unit cell parameter of the pyrochlore phase rises from 10.4878 (x = 0.3) to 10.5154 Å (x = 0.7). The samples are characterized by a porous microstructure with indistinct grain boundaries. Zinc oxide has a sintering effect on ceramics. The charge state of the ions in Bi2ZnxFe1-xTa2O9.5-Δ was investigated by X-ray spectroscopy. NEXAFS and XPS data show that zinc doping does not change the oxidation degree of iron and bismuth ions in pyrochlore. The ions are in the charge states Bi(+3), Fe(+3), Zn(+2). In the Ta4fspectrum, an energy shift of the absorption band towards lower energies by ΔE = 0.5 eV is observed, which is typical for tantalum ions with an effective charge of (+5-δ). With the increase of x(Zn), the Bi 4f7/2 and Bi 4f5/2 bands are observed to shift to lower energies due to the distribution of some Zn(II) ions in the bismuth position.
The solid-phase synthesis of multicomponent bismuth tantalates and niobates with pyrochloric structure (space group
Fd-3m
), containing equimolar amounts of transition 3
d
-element atoms, is ...demonstrated. The composition of such pyrochlores can be described by the stoichiometric formula Bi
2
Cr
1/6
Mn
1/6
Fe
1/6
Co
1/6
Ni
1/6
Cu
1/6
Ta(Nb)
2
O
9±∆
. An aspect of the synthesis of pyrochlores is a multi-stage high-temperature process of heat treatment of samples in the range of 650 – 1050°C for 60 h. For pyrochlore based on bismuth tantalate, an impurity phase of triclinic bismuth orthotantalate β-BiTaO
4
(sp. gr. P-1) is formed in trace quantities. Complex pyrochlore based on bismuth niobate is characterized by a dense, low-porous microstructure, in contrast to open, porous tantalum pyrochlore with average grain size equal to about 2 µm. The unit cell parameter for niobium- and tantalum-containing pyrochlores is equal to 10.4927 (10.4922) Å respectively.
The results of geochemical studies of the diamondiferous suevites of the Kara astrobleme (Pay-Khoy) using a new approach based on “area” microprobe analysis of suevite matrix and consolidated impact ...melt aggregates with subsequent data processing by multivariate statistic methods are described for the first time. At least three suevite varieties that differ essentially in geomorphology, mineralogy, petrography, and geochemical features have been recognized. The predominant protoliths of the rocks of the target are proposed for these suevite varieties on the basis of integrated data analysis.
The samples of Ni-doped bismuth magnesium tantalate pyrochlores with the general formula Bi1.4(Mg1–x Ni x )0.7Ta1.4O6.3 (x = 0.3, 0.5, 0.7) were obtained by solid-phase synthesis. The crystal ...structure of the pyrochlore type (sp. gr. Fd3̅m:2) was clarified by the Rietveld method on the basis of X-ray powder diffraction data. The unit cell parameters increase with the decreasing nickel content in the range from 10.5319(1) to 10.5391(1) Å. The electronic state of atoms is established by the XPS method. According to XPS analysis, bismuth atoms have an effective charge of +3, nickel atoms +(2 + δ), and tantalum ions +(5 – δ). The coefficient of thermal expansion of the lattice of the samples was calculated from high-temperature X-ray structural measurements in the range of −180 to 1050 °C. The average values of linear TECs α in the temperature ranges of 30–570 and 600–1050 °C are 5.1 × 10–6 and 8.1 × 10–6 °C–1, respectively. The monotonicity of the change in the thermal expansion coefficient in the temperature range from −100 to 1050 °C indicates the absence of phase transformations. All samples are dielectric and exhibit high activation energies ∼2.0 eV, moderately high dielectric constants ∼24–28, and tangent dielectric losses ∼0.002 at 1 MHz and 21 °C. The electrical properties of the samples are described by a simple parallel equivalent scheme. The chemical composition of the materials has little effect on the polarizability of the medium or on the value of the activation energy of the conductivity. Ionic processes in investigated materials at frequencies 200–106 Hz and at temperatures 100–450 °C were not detected.
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The chronosequence of soils buried under constructions of different ages at the large (3.5 m in height and 74 m in diameter) Shumny Kurgan in the Krasnodar region has been studied. The kurgan was ...built sequentially by the people of Catacomb (28th–22nd centuries BC) and Srubnaya (15th–10th centuries BC) cultures and includes five constructions made of the material of local soils and anthropogenic admixtures. Each of the subsequent constructions overlapped the previous one and went beyond it, covering some additional space. This allows us to study a consecutive series of soils buried under the constructions. During the kurgan building (28th–10th centuries BC), the morphological and physicochemical properties of the soils changed: the content of organic matter and magnetic susceptibility increased, whereas the mixing up of the upper horizons by burrowing animals, the content of carbonates, and the exchangeable sodium percentage decreased. The direction of these changes in the properties of the materials of kurgan constructions over time agree with changes in the properties of corresponding buried soils. For the uneven-aged constructions of the kurgan, local soils were used, which had different properties at the stages of the construction. These soils occupied a significantly larger area than the kurgan, which increases the reliability of the study. Evolutionary changes in the properties of buried soils and earth materials of kurgan structures are indicative of the climatic trend during the long-term kurgan construction—an increase in atmospheric moistening and a decrease in the mean annual temperature from the Early Catacomb to Srubnaya cultures. An independent palynological analysis of buried paleosols confirms this conclusion about the tendency of climate changes. According to micromorphological data, the Early Catacomb time can be additionally characterized as an arid epoch, which manifested itself in soil cracking and accumulation of carbonates in the upper part of soil profiles. Based on the structure and properties of the kurgan, it is possible to identify technologies of the construction, which included tamping down of earthy material in dry and wet states; its mixing; and adding of river silt, charcoal, and bones.
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