Silicate Composition Research Articles

Retardation Effects of Filter Mud in Molasses on Composite Silicate Cement.

The filter mud in molasses has a significant inhibitory effect on biological activity and cannot be utilised by organisms; therefore, before molasses are biotransformed, the filter mud will be separated and directly discarded in the environment. In this study, the filter mud was used as the retarder of cement concrete OPC 42.5 for the first time. It was found that when 0.2–0.8% filter mud was added to fresh cement concrete OPC PC 42.5, the hardening time of cement slurry was significantly prolonged due to the synergistic retarding effect of sugar, colloid and total cellulose in the filter mud. In addition, the compressive strength of cement concrete mixed with the filter mud in the early stage (<10 days), middle stage (10–100 days) and later stage (180 days) was significantly higher than that of cement concrete and cement concrete mixed with commercial asphalt lignosulfonate. These results showed that the filter mud in molasses could realise harmless and resource utilisation, which could promote the comprehensive utilisation of molasses.

Effect of Temperature on Properties of Concrete in Stirring Process

Taking composite silicate concrete as the research object, the double horizontal shaft mixing method is used to mix concrete. The setting time, strength and workability tests are carried out to study the influence of temperature on the mechanical properties of concrete in the ordinary mixing process. The results show that the temperature has great influence on the setting time, compressive strength and splitting strength of concrete. Reasonable control of cement temperature has important guiding significance and theoretical basis in practical construction application.

Pressure-stabilized hexagonal perovskite-related isolated tetrahedral anion silicate La6Sr3Si6O24

The discovery of new perovskite compounds under high pressure mainly focuses on the ABO3 compositions and the compositions highly deviated from ABO3 are less explored. Here we demonstrate that the La6Sr3Si6O24 silicate composition can be stabilized as a hexagonal perovskite-related structure with isolated tetrahedra anions under high pressure of 6 GPa. The compound adopts 9-layer shifted hexagonal perovskite-like structure with both B-cation and oxygen deficiencies and contains pseudo-cubic (c′) (La/Sr)O2 layers and hexagonal (h) (La/Sr)O3 layers stacked according to (c′hh)3 sequence. This structure features both B-cation vacancy ordering between the two consecutive hexagonal layers and oxygen vacancy ordering in c′-(La/Sr)O2 layers, resulting in isolated tetrahedral SiO4 anions and ionic conduction behavior. This work demonstrates the practicability of accessing new perovskite-related functional materials from the compositions highly deviated from ABO3 under high pressure.

The effects of highly reduced magmatism revealed through aubrites

AbstractEnstatite‐rich meteorites, including the aubrites, formed under conditions of very low oxygen fugacity (ƒO2: iron‐wüstite buffer −2 to −6) and thus offer the ability to study reduced magmatism present on multiple bodies in our solar system. Elemental partitioning among metals, sulfides, and silicates is poorly constrained at low ƒO2; however, studies of enstatite‐rich meteorites may yield empirical evidence of the effects of low ƒO2 on elemental behavior. This work presents comprehensive petrologic and oxygen isotopic studies of 14 aubrites, including four meteorites that have not been previously investigated in detail. The aubrites exhibit a variety of textures and mineralogy, and their elemental zoning patterns point to slow cooling histories for all 14 samples. Oxygen isotope analyses suggest that the aubrite parent bodies may be more heterogeneous than originally reported or may have experienced incomplete magmatic differentiation. Contrary to the other classified aubrites and based on textural and mineralogical observations, we suggest that the Northwest Africa 8396 meteorite shows an affinity for an enstatite chondrite parentage. By measuring major elemental compositions of silicates, sulfides, and metals, we calculate new metal–silicate, sulfide–silicate, and sulfide–metal partition coefficients for aubrites that are applicable to igneous systems at low ƒO2. The geochemical behavior of elements in aubrites, as determined using partition coefficients, is similar to the geochemical behavior of elements determined experimentally for magmatic systems on Mercury. Enstatite‐rich meteorites, including aubrites, represent valuable natural petrologic analogues to Mercury and their study could further our understanding of reduced magmatism in our solar system.

Anti-Stokes fluorescence cooling of nanoparticle-doped silica fibers.

The first observation of cooling by anti-Stokes pumping in nanoparticle-doped silica fibers is reported. Four Yb-doped fibers fabricated using conventional modified chemical vapor deposition (MCVD) techniques were evaluated, namely, an aluminosilicate fiber and three fibers in which the Yb ions were encapsulated in CaF2, SrF2, or BaF2 nanoparticles. The nanoparticles, which oxidize during preform processing, provide a modified chemical environment for the Yb3+ ions that is beneficial to cooling. When pumped at the near-optimum cooling wavelength of 1040 nm at atmospheric pressure, the fibers experienced a maximum measured temperature drop of 20.5 mK (aluminosilicate fiber), 26.2 mK (CaF2 fiber), and 16.7 mK (SrF2 fiber). The BaF2 fiber did not cool but warmed slightly. The three fibers that cooled had a cooling efficiency comparable to that of the best previously reported Yb-doped silica fiber that cooled. Data analysis shows that this efficiency is explained by the fibers' high critical quenching concentration and low residual absorptive loss (linked to sub-ppm OH contamination). This study demonstrates the large untapped potential of nanoparticle doping in the current search for silicate compositions that produce optimum anti-Stokes cooling.

Experimental constraints on truly conjugate alkaline silicate – carbonatite melt pairs

Physical separation of immiscible carbonatites from CO2-bearing alkaline silicate melts is frequently invoked to explain the common presence of carbonatites in alkaline rock suites. We present new isobaric 1.0 GPa crystallization and liquid immiscibility experiments between 1250 and 925°C on chemically complex CO2-bearing subvolcanic basanitic, nephelinitic and nepheline-syenitic compositions from the intrusive complex on Brava Island, Cape Verdes. In the experiments, carbonatites exsolve from silicate melt along the basanite–nephelinite melt fractionation pathway throughout an unmixing temperature window from 1100 to 950°C. Liquid immiscibility is suppressed by 950°C by the onset of alkali-feldspathoid crystallization, which deflects the residual silicate melt away from the two-liquid field. While evolving along the two-liquid field boundary, silicate melt increases in SiO2 from 46 to 51 wt% and decreases in CaO / (Na2O + K2O) (by weight) from 0.83 to 0.12, reproducing the observed compositional array of alkaline silicate subvolcanic rocks from Brava. The conjugate carbonatite melts are moderately alkaline Ca-carbonatites with 5 to 9 wt% SiO2 and CaO / (Na2O + K2O) that decreases from 5.64 at 1100°C to 1.60 at 950°C. These coexisting silicate and carbonatite melt compositions show that previous high-pressure experimental studies have not yielded truly conjugate melt pairs, mainly due to the use of modified starting materials resulting in melt compositions too enriched in alkalis to match the natural alkaline silicate rock record.

Hybrid amorphous-crystalline silicate composites as feasible solid-state electrolytes

Solid-state electrolytes (SSEs) are considered as the most promising materials for enabling the safer, more efficient, and feasible solution to address the market demands for lithium-ion batteries. The current work investigates the production of inorganic SSEs from silicate minerals, which are abundant materials in natural resources (kaolinite) as well as in industrial waste-streams (amorphous silica). The synthesized materials showed high amorphous contents combined with lithium silicate phases at variable proportions, according to the molar proportions of the reacting system. The materials have been characterized with XRD, SEM/EDS, FTIR, TGA-DSC, XPS, EIS, and density measurements. The results showed that hybrid structures of amorphous and crystalline silicates can form an ordered hotchpotch morphology. The best of the hybrid SSEs presented ionic conductivity values of 1.42 × 10-4 and 1.30 × 10-4 Scm−1 for samples with total amorphous contents of 73 and 83 wt%, respectively. The connected structure between amorphous and crystalline phases in a hotchpotch structure is hypothesized to assist the hopping of the Li+ ions via combined mechanisms of segmental motion of the silicates amorphous chains with defects in the crystalline phases. The proposed approach may offer new research paths towards the low-cost scalable production of SSEs.

Self-templating construction of flower-like mesoporous magnesium silicate composites from sepiolite for high-efficiency adsorption of aflatoxin B1

The rational design and fabrication of mesoporous materials with highly exposed surface area are of great significance to address water pollution problems caused by mycotoxins. In this work, a facile self-templating strategy was developed to construct flower-like mesoporous magnesium silicate composites (MMSCs) by subjecting sepiolite to acid bleaching process, followed by hydrothermal reaction. The effect of hydrothermal time on the microstructures and specific surface areas of MMSCs were investigated, and the possible formation mechanism of MMSCs was proposed. The MMSCs synthesized at hydrothermal time of 12 h showed a well aflatoxin B1 (AFB1) adsorption capacity, and the maximum adsorption capacity, calculated from the Langmuir model, was 21.26 mg/g. The high adsorption capacity was mainly attributed to the synergistic effect of flower morphology and mesoporous structure, providing high surface area, and consequently exposing more available adsorption sites (e.g., Si-O-Mg, Mg-OH, and Si-OH), which favored bonding with AFB1. Density functional theory (DFT) calculations revealed that the mechanisms of AFB1 adsorption onto MMSCs were mainly electron donor-acceptor interaction and hydrogen bonding. The strategy proposed here can provide a new avenue for the design of mesoporous materials with high surface area, and resulting materials are promising adsorbents for adsorption of AFB1.

Cement-free refractory concretes. Part 12-2. HCBS and ceramic concretes of siliceous compositions

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Cement-free refractory concretes. Part 12-1. HCBS and ceramic concretes of siliceous compositions

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Micro-Raman water calibration in ultrapotassic silicate glasses: Application to phono-tephrites and K-foidites of Colli Albani Volcanic District (Central Italy)

This study investigates the potential use of micro-Raman spectroscopy for the quantification of water in ultrapotassic silicate glasses. A calibration was developed using experimental phono-tephritic glasses with water content ranging from ~ 1 to ~ 3 wt%. The calibration curve showed a typical direct proportionality between water content and the ratio of high- (3100–3750 cm−1) and low-wavenumber (100–1500 cm−1) spectral regions, with a linear fit coefficient m = 1.74. The comparison with the m coefficients available in literature for other silicate compositions showed a deviation of our composition as a function of some major oxides such as FeO, TiO2 and K2O, highlighting the possible influence of the polymerization degree (NBO/T: non-bridging oxygens per tetrahedron) on m coefficient. In this respect, we observed a linear relationship between m coefficient and NBO/T and a positive correlation between the area underneath the silicate region (100–1500 cm−1) and NBO/T for the phono-tephrite of this study and for other compositions spanning from basalts to phonolite and rhyolites available in literature. For ultrapotassic natural and experimental glasses characterized by the presence of CO2, documented by the carbonate peak at 1062–1092 cm−1, it has been possible to extrapolate the CO2 content by using the model of Morizet et al. (2013) obtaining values of ~ 1.1 ± 0.3 and ~ 1.7 ± 0.2 wt%, respectively. The obtained m coefficient was applied to estimate water content of natural phono-tephritic glasses belonging to the Colli Albani Volcanic District. Moreover, we estimated water content also for some natural K-foiditic glasses from the same volcanic district. Since the m coefficient results to be strongly dependent on the chemical composition of the sample of interest, the coefficient estimated for the phono-tephrites of this study could result in significant overestimation or underestimation of the water content of the Colli Albani Volcanic District K-foiditic natural samples. Thus, we extrapolated the m coefficient for the K-foiditic samples by means of an equation obtained in this study as function of the polymerization degree (NBO/T).

Constraints on Pore Development in Marine Shales of the Upper Yangtze Area, South China: A Comparative Case of Lower Cambrian and Lower Silurian Formations

Both Lower Cambrian and Lower Silurian shale are typical of oil-prone kerogen and siliceous composition, but differ in thermal maturities with 3.56% Ro and 2.31% Ro, respectively. In this paper, pore characteristics were explored between these two shales. All samples were studied by a combination of organic geochemistry, x-ray diffraction, N2 adsorption, helium porosity, and focused ion beam milling and scanning electron microscopy. In particular, N2 adsorption of isolated OM was conducted to compare physical properties of OM-hosted pores, and fractal dimension was exploited to analyze morphologic characteristics of pores. N2 adsorption indicated that the Lower Silurian shale presented superior pore characteristics than the Lower Cambrian shale, in terms of pore volume (PV), pore surface area (PSA), and pore diameter. FIB-SEM manifested that pinhole OM-hosted pores and open-ended dissolved pores were primarily in the Lower Cambrian shale, while cellular OM-hosted pores were dominant in the Lower Silurian shale. Statistical and fractal analysis demonstrated that OM, rather than minerals, played a dominant role in pore development in marine shales at late diagenetic or metamorphic epoch. Furthermore, OM-hosted pores were not increased monotonously with increasing thermal maturity, but presented a unimodal trend, peaking at 2.8% Ro. PV (PSA) of isolated OM in the Lower Silurian shale was approximately 6.6 (4.3) times higher than that in the Lower Cambrian shale. With similar matrix basics and distinctive pore features, a comparison of these two marine shales markedly emphasizes the impact of thermal maturity on the state of OM-hosted pores.

Protocol for selecting exemplary silicate deposit compositions for evaluating thermal and environmental barrier coatings

AbstractA protocol for selecting representative silicate compositions for comparative testing of gas turbine coating materials is presented. It begins with a curated dataset of compositions of engine deposits and naturally occurring siliceous debris including volcanic ashes, sands, and dusts. The compositions are first reduced to the five major oxides—those of Ca, Mg, Fe, Al, and Si—and then distilled further using principal component analysis and k‐means clustering. The process ultimately yields four classes of possible deposits with common chemical characteristics. Each class is represented by a composition centroid and a range in Ca:Si ratios. Key thermophysical properties of the possible deposits are calculated and related to the glass network connectivity, characterized by the Si:O ratio. Finally, deposits from each of these classes are compared in terms of their reactions with prototypical thermal and environmental barrier oxides, with due consideration of the effects of composition variations within each deposit class. The protocol is, in principle, adaptable to datasets compiled by OEMs and researchers in gas turbine coatings.

The partitioning of Cu and Ag between minerals and silicate melts during partial melting of planetary silicate mantles

Geochemical and cosmochemical reservoirs show Cu/Ag variations from 500 to 40,000. To understand magmatic Cu–Ag fractionation and origins of such large Cu/Ag variations, we have measured the partition coefficients of Cu and Ag between minerals and silicate melts (DCu,AgMin/SM) relevant for partial melting of the silicate mantles of Earth, Mars, and the Moon. The experiments were conducted at 1–3 GPa, 1300–1600 °C, and oxygen fugacity ∼2–5 log units below the FMQ buffer. The results show that DCuMin/SM are 0.034–0.109 for olivine, 0.011–0.044 for orthopyroxene, and 0.046–0.092 for clinopyroxene; DAgMin/SM are 0.003–0.012 for orthopyroxene and 0.037–0.093 for clinopyroxene. These DCu,AgMin/SM values increase mainly with increasing pressure and are oxygen fugacity-independent. DAgMin/SM are 0.0005–0.0017 for olivine, which do not show measurable dependence on P–T, oxygen fugacity, or silicate composition. One pair of DCu,AgMin/SM values are 0.0037 and 0.0004 for garnet, respectively; 0.15 and 0.005 for spinel, respectively. These results indicate that Ag is more incompatible than Cu in all mantle minerals. Our DCu,AgMin/SM combined with previous sulfide–silicate melt partition coefficients of Cu and Ag imply that although sulfides host large fractions of planetary mantle Cu and Ag, silicate minerals can be also important Cu and Ag reservoirs, particularly when sulfides occur as monosulfide solid solutions. The application of our DCu,AgMin/SM to various melting models demonstrates that Cu–Ag fractionation occurs during partial melting of the silicate mantles of Earth, Mars, and the Moon; however, the modeled Cu/Ag ratios in basalts agree with their mantle source Cu/Ag ratios within 50% relative. Therefore, the superchondritic but similar Cu/Ag ratios of ∼3000–4000 in mid-ocean ridge basalts, arc basalts, mantle plume-related oceanic island basalts and plateau basalts, and the bulk silicate Earth (BSE) reflect homogeneous distribution of Cu/Ag in Earth’s mantle and limited Cu–Ag fractionation during slab dehydration/melting in subduction zones. However, components with chondritic Cu/Ag ratios (∼600–2300) may exist in the mantle sources of Hawaii oceanic island lavas. The Cu/Ag ratios (∼500–1100) in the Martian basalts and bulk silicate Mars (BSMars) are chondritic, but the Cu/Ag ratio (∼15,000–40,000) in the bulk silicate Moon (BSMoon) is strongly superchondritic. Such largely different Cu/Ag ratios in different planetary reservoirs cannot be explained by magmatic Cu–Ag fractionation, solar nebular process, or core-formation process. We propose that different degrees of planetary melting and evaporation provide a solution because Ag is more volatile than Cu during silicate melt evaporation. The chondritic Cu/Ag ratios in the BSMars could be explained by limited evaporation of planetesimals that delivered Mars’ moderately volatile elements, and the superchondritic Cu/Ag ratios in the BSE may be due to Earth’s accretion of planetesimals with partial evaporative loss of Cu and Ag. However, high degrees of evaporative Cu and Ag loss during the Moon-formation are required to explain the strongly superchondritic Cu/Ag ratios in the BSMoon. Accordingly, Cu/Ag ratios in the bulk silicate planets may provide new insights into the nature of their building blocks.

Microstructural and Chemical Investigations of Presolar Silicates from Diverse Stellar Environments

Abstract We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CBb3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe)2SiO4] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO3) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe)3Si2O5(OH)4], while the other is a nontronite [Na,Fe2(Si,Al)4O10(OH)2.nH2O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al)2O6]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.

Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina

Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.

Differences of Pore Features in Marine Shales between Lower Cambrian and Lower Silurian Formations of Upper Yangtze Area, South China

Lower Cambrian shale and lower Silurian shale are both typical of oil-prone kerogen and siliceous composition, but different in thermal maturities. Porosity differences were determined in marine shales between the two shales. Measurements were utilized including organic geochemistry, XRD, scanning electron microscopy (SEM) and N2 gas adsorption. Pore volume (PV) of lower Silurian shale was approximately 1.5 times higher than that of lower Cambrian shale, and pore surface area (PSA) of lower Silurian shale was almost 2.5 times higher than that of lower Cambrian shale. Lower Cambrian shale and lower Silurian shale possess similar materials, but distinctive thermal degrees. Evolution mechanisms of different types of pores, especially organic matter (OM)-hosted pores, may trigger this different pore features. Pores of rigid framework are the residue of primary interparticle pores during the burial history. Pores associated with clay flakes can be preserved well adjacent to rigid grains or secondary minerals acting as rigid frameworks or grain supporters. Dissolved pores in both lower Cambrian shale and lower Silurian shale barely contribute to the total porosity and mean little to the permeability. Both excessive OM content and over thermal maturity are detrimental to development of OM-hosted pores. Rigid particles, clay flakes, and OM commonly co-exist within shale matrix. Rigid grains act as supporters, clay flakes confine ample space, and OM first migrates into and provides secondary OM-hosted pores. In this condition, pores can be preserved owing to associating matrix with good mechanic and chemical stability. The significant differences of structural settings result into various hydrocarbon explosion efficiency and different pressure circumstance, which consequently leads to the different pore features between the two shales. For lower Cambrian shale, overpressure circumstance diminish if hydrocarbon expels outside of the shale system, and OM-hosted pores destroy through compaction. Sustaining overpressure and abundant residue hydrocarbon (migrated OM) make positive contributions to the pore properties, in terms of numbers, diameters and connectivity of the lower Silurian shale samples.

Литогеохимические характеристики высокосернистых лечебных грязей оз. Нуху-Нур (Иркутская область): сопоставление с лечебными грязями мира

IIn therapeutic mud (peloids) of Lake Nuhu Nur, major oxides, trace elements, and mineral phases are determined from sedimentary columns taken in the central and near-coastal parts of the lake. In the center of the lake, layers with high and low contents of total sulfur (Stot) and S2− alternate. Sulfur is part of sulfates: gypsum, tenardite, and hexahydrite. The distribution of S is generally correlated with Na2O, CaO, Sr, and U with a strong negative correlation with other major oxides and trace elements. In near-coastal parts of the lake, there are layers enriched and depleted with CaO, which strongly correlates with Sr. Lithogeochemical signatures of peloids show concentration of therapeutic components in the bottom sediments of the lake due to processes similar to weathering of rocks of silicic composition in arid climate. In terms of major oxides and trace elements, peloids from Lake Nuhu Nur are generally comparable to those from Wudalianchi (Northeast China), coastal regions of Brazil, as well as Georgia and Spain, but are closest to therapeutic high-sulfur sulfate mud of Kopahue in Argentina.

Properties dependence of castable samples from low-cement silicon carbide castable on the firing temperature and the gas atmosphere

The influence of firing temperature of 1000, 1100, 1200, 1300, 1400, 1580 °C and atmosphere (air and reducing) on the main properties of castable samples from low-cement silicon carbide castable grade of “NKBS” with a combined additive has been investigated.&#x0D; It was shown that, in air with an increase in the firing temperature in the range 1000—1580 °C, the content of silicon carbide in the castable samples decreases. Up to temperatures of 1200—1300 °C, the content of silicon carbide in the castable samples practically does not change, and oxidation slows down due to the formation of a viscous melt of a glassy phase of an alumina silicate composition on the surface of silicon carbide grains. An increase in the firing temperature above 1300 °C leads to a more intense oxidation of silicon carbide grains to SiO2, which causes a change in the porosity, density and strength of the samples. As a result of the carried out studies, it was found that, the using temperature in the air of the above mentioned low-cement silicon carbide castable should not exceed 1300 °C.&#x0D; It was found that, after firing in a reducing atmosphere in the temperature range of 1000—1580 °C in the samples of silicon carbide castable, the content of silicon carbide remains almost the same, and the density and strength increase, which ensures the efficiency of its use for lining thermal units operating in a reducing atmosphere up to temperatures of 1580 °C.

Impact of Carbon Particle Character on the Cement-Based Composite Electrical Resistivity.

Electroconductive cement-based composites are modern materials that are commonly used in many industries such as the construction industry, among others. For example, these materials can be used as sensors for monitoring changes in construction, grounding suspension, and resistance heating materials, etc. The aim of the research presented in this article is to monitor the impact of carbon particle character on cement-based electroconductive composites. Four types of graphite were analyzed. Natural and synthetic types of graphite, with different particle sizes and one with improved electrically conductive properties, were tested. For the analysis of the electrical conductivity of powder raw materials, a new methodology was developed based on the experience of working with these materials. Various types of graphite were tested in pure cement paste (80% cement, 20% graphite) as well as in a composite matrix, which consisted of cement (16.8%), a mixture of silica sand 0–4 mm (56.4%), graphite filler (20.0%) ground limestone (6.7%) and super plasticizers (0.1%). The resistivity and physical-mechanical properties of the composite material were determined. Furthermore, the resistivity of the test samples was measured with a gradual decrease in saturation. It may be concluded that graphite fillers featuring very fine particles and high specific surface are most suitable and most effective for creating electrically conductive silicate composites. The amount, shape and, in particular, the fineness of the graphite filler particles thus creates suitable conditions for the creation of an integrated internal electricity-conductive network. In the case of the use of a coarse type of graphite or purely non-conductive fillers, the presence of an electrolyte, for example, in the form of water, is necessary to achieve a low resistivity. Samples with fine types of graphite fillers achieved stable resistivity values when the sample humidity changed. The addition of graphite fillers caused a large decrease in the strength of the samples.