Differential Dissolution Research Articles

Differential dissolution of biogenic silica significantly affects the utility of sediment diatoms as paleoceanographic proxies

AbstractDiatoms and biogenic silica (biogenic Si) in sediments are commonly analyzed as paleoceanographic environmental indicators. However, the correspondence between these sedimentary components and their counterparts in the water column above can vary over time and space. This study, undertaken in the northern South China Sea, compares diatoms and biogenic Si in sinking particles from the water column with those in surface sediments below. The results indicate substantial losses of diatoms and biogenic Si during sinking and burial, along with changes in diatom assemblages. About 6% of diatoms sinking from 1000 m depth are estimated to be preserved in sediments: 32% are recycled in the water column and 62% are lost at the sediment–water interface. Approximately, 12% of biogenic Si is preserved in sediments: 6% is remineralized in the water column and 82% is lost at the sediment–water interface. The differences between diatom and biogenic Si preservation and remineralization are likely due to differences in dissolution resistance among the various diatom species and between diatoms and other silicifiers (e.g., radiolarians), along with effects of lateral transport. This variability introduces uncertainties into paleoceanographic inferences made from these two proxies from the sediments. Thalassionema nitzschioides was found to dominate sediment assemblages, which we attribute to its great resistance to dissolution, and to be negatively correlated with diatom sinking fluxes. These properties suggest that in the northern South China Sea, T. nitzschioides may potentially be useful as an indicator of low paleoproductivity (e.g., as seen during strong El Niño events).

Results of studies on the development of an immuno-enzymed test system for diagnosing infectious enterotoxemia in animals

Research materials on the development of an enzyme-linked immunosorbent assay for the determination of specific antibodies to Cl. perfringens bacteria were presented. Strains of Cl. perfringens were used as production strains: No. 28 (type A), LD-1 (type B), No. 392 (type C), No. 213 (type D). To obtain antigen, a daily suspension of Cl perfringens bacteria, containing 20 billion microbial cells in 1 cm3 (5 billion microbial cells of each serotype), was sounded on an ultrasonic disintegrator at a frequency of 20 MHz for 15 minutes at 4 °C, then the endotoxin was precipitated with ammonium sulfate and purified by differential dissolution of the precipitate in 0.02 M phosphate buffer, followed by dialysis against tap water. Control positive serum with specific antibodies of at least 1:12800 to antigens of Cl. perfringens bacteria was obtained by hyperimmunization of cattle with corpuscular antigens and toxoids. The basic conditions of the ELISA reaction were standardized. Determination of the concentration of sorption of the antigen was carried out by parallel testing of various dilutions of the conjugate. The most acceptable titer of the blood serum of animals was found at a dilution of the conjugate of 1:2500 and a concentration of the sorbed antigen of 5-8 μg/cm3. The production test of the enzyme immunoassay test system was carried out in cattle farms in three regions of the Russian Federation, unfavorable for anaerobic enterotoxemia in calves.

Sustainable development of geological resources: the Characteristics of Red Karst Landscape and Tourism Development in Tongren, Guizhou

<abstract> <p>China is rich in karst resources and famous for its karst landscape. As a part of karst, the popularity of red karst is obviously low and has received little attention; moreover, the related scientific research and tourism development are relatively immature. Therefore, this paper takes the red karst in Tongren, Guizhou as the research object, analyzes the characteristics and causes of the red karst, comprehensively evaluates its landscape value, and puts forward development strategies and protection suggestions. Through the above research, the following three research results are obtained. (1) On the basis of a field investigation and a literature review, the geographical situation, background, and landscape characteristics of the red karst landform and its surrounding areas in Tongren City were investigated in detail. It forms isolated peaks, rock walls, protruding rocks, stone pillars, and other forms. The most prominent features of the red karst landscape in Tongren City are that the color is red and white, and the shape is concave and convex in order. (2) Geochemical test and structural data collection and analyses of the collected samples were performed. The obtain concave layer rock is dolomitic limestone, and that convex lay rock is argillaceous dolomitic limestone. Because the convex layer rock sample is high in silicon element content, the convex layer rock sample is not easy to be weathered, is rich in clay mineral, and is not easy to be corrode; the convex layer rock sample gradually protrudes with the passage of time to form an uneven shape. The red karst landform is developed in either the rock stratum or tectonic zone with moderate tectonic deformation intensity. First, the formation of a single-layer honeycomb morphology requires that the rock stratum is subjected to a sufficient horizontal compressive stress at a certain burial depth. Second, it is necessary to widely exist in areas with relatively gentle rock formation occurrence; too strong of a structural deformation will make the rock formation occurrence steep, which is not conducive to the occurrence of differential dissolution between adjacent strata. (3) Through the construction of an evaluation index system, the red karst in Tongren City is evaluated, and it is concluded that the geological heritage value is high, and the development and utilization conditions are weak. The conclusion of this article is a supplement to the geological and geomorphological system characteristics of southern karst. From the perspective of world natural heritage, the study enriches the academic evidence of red karst and enables its exemplary role to be well played. From the perspective of the tourism development value, more people should be made aware of the diverse types of karst landforms, which provide experience and suggestions for the value of landforms, tourism resources, and tourism development in similar areas.</p> </abstract>

Determining the Phase Composition of Copper Ferrite Samples by a Standardless Differential Dissolution Method

Determining the Phase Composition of Copper Ferrite Samples by a Standardless Differential Dissolution Method

Differential dissolution of interlayer, octahedral and tetrahedral cations of vermiculite in oxalic acid

AbstractPhysical and/or chemical changes such as refinement, component dissolution, exchange/adsorption, structural evolution and recombination of phyllosilicate minerals occur continuously in a naturally weakly acidic water environment. To compare the differential dissolution of cations that occupy various sites in vermiculite, trioctahedral vermiculite was dissolved in various concentrations of oxalate for 24 h and in 0.2 M oxalate for various durations. The concentration of ions in the leaching solution and the phase, structure and morphology of the original samples and acid-leached samples were analysed. Structural analysis showed that the 001 reflections of vermiculite gradually shifted to a higher angle and eventually disappeared after the dissolution of interlayer cations caused by acid leaching. The amount and rate of dissolution of each cation in the vermiculite showed that the octahedral cation Mg2+ is more soluble than Fe2+ and Fe3+. The dissolution rates of Al3+, Mg2+ and Ca2+ were greatest in the first 4 h and then decreased gradually. Amorphous silicon dioxide and calcium oxalate were formed during acid leaching, and calcium oxalate was formed in the first 4 h. After leaching with oxalate for various periods, the cation-exchange capacity (CEC) of the samples first increased and then decreased. Micromorphology analysis showed that the acid erosion process started from the edges. The results of this work contribute to our understanding of many natural geochemical processes, and they will be useful for several applications such as soil improvement, ecological restoration and environmental protection.

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

A research on excavation compensation theory for large deformation disaster control and a review on the multiphysical–multiscale responses of salt rock for underground gas storage

Foraminifera dissolution phases in the upper cretaceous succession of Jebel Duwi, Egypt

The present work examines the function of differential dissolution in planktic and benthic foraminifera and introduces the major factors that affect dissolution in early Mid-Maastrichtian Event MME and Late Maastrichtian Event LME paleoenvironmental reconstructions. Two observations on foraminifera dissolution in the Dakhla Formation, where planktic foraminifera are more susceptible to dissolution than benthic foraminifera in the Hamama Member of the Jebel Duwi section, Eastern Desert (Egypt). They are characterized by a decline in the planktic/benthic (P/B) ratio and a rise in the agglutinated percentage. The results of those observations are used for revealing foraminiferal dissolution in these two zones (Racemiguembelina fructicosa CF4a and Pseudoguembelina palpebra CF2). During these two zones, there were excessive relative abundances of agglutinated foraminifera, indicating that these two intervals witnessed severe carbonate dissolution. The high total organic carbon (TOC) and low pH due to the presence of a lot of organic matter in the black shale’s of the Dakhla Formation of the upper Maastrichtian age is the explanation for the observed dissolution that has nothing to do with oceanographic or volcanic processes. The presence of pyrite within the black shale interval suggests low oxygen conditions and the potential for meteoric water to react with the pyrite and form sulfuric acid. This acid could dissolve any carbonate material well after the original deposition.

Defect Structure of Nanocrystalline NiO Oxide Stabilized by SiO2

In this paper, structural features of the NiO-SiO2 nanocrystalline catalyst synthesized by the sol-gel method were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and differential dissolution (DD). The XRD pattern of NiO-SiO2 significantly differs from the “ideal” NiO pattern: the peaks of the NiO-like phase are asymmetric, especially the 111 diffraction peak. The NiO-SiO2 nanocrystalline catalyst was investigated by means of XRD simulations based on two approaches: conventional Rietveld analysis and statistical models of 1D disordered crystals. Through a direct simulation of XRD profiles, structural information is extracted from both the Bragg and diffuse scattering. XRD simulations showed that the asymmetry of all the diffraction peaks is due to the presence of two NiO-like oxides with different lattice constants and different average sizes: ~90 wt% of mixed Ni-Si oxide (Ni:Si = 0.14:0.86) with average crystallite sizes (D ~ 27.5 Å) and ~10 wt% of pure NiO (D ~ 50 Å). The high asymmetry of the 111 diffraction peak is due to the appearance of diffuse scattering caused by the inclusion of tetrahedral SiO2 layers between octahedral NiO layers. Such methods as TEM and DD were applied as independent criteria to prove the structural model, and the results obtained confirm the formation of mixed Ni-Si oxide.

Study of diagenitic processes and surface texture of the oldest river terrace deposits in Shirqat area- northern Iraq

The recent project deals with the diagenitic processes and surface textures of the oldest river terraces deposits in Shirqat area, the diagenitic processes compiled with Cementation, Compaction and Dissolution. The carbonate minerals represent the cementic materials while the point contact compaction represent the degree of compaction in this sediments because the small thickness of the overburden sediments and the secondary effects of differential dissolution. The surface texture is very developed in the large size of sediment included pebble, cobble and boulders which form very developed surface texture formed order and disorder forms as well as smooth surface texture.

Geochemical behavior of stable strontium isotopes during continental weathering process: A review

Continental weathering, an important geological process that affects the formation and evolution of the earth, involves the interaction of matter and energy among the lithosphere, atmosphere, hydrosphere, and biosphere. Stable Sr isotope (δ88/86Sr) is a novel non-traditional stable isotope. It has been widely discussed in tracing continental weathering, studying marine Sr cycle, and analyzing biogeochemical behavior in recent years. Its combination with 87Sr/86Sr can indicate the source of Sr and the mass fractionation of geological processes, which has incomparable advantages over other isotopic systems, such as Li, Mg, and Ba. However, owing to the small mass difference (2%) between 86Sr and 88Sr, fractionation is not significant, which makes the measurement of the ratio δ88/86Sr difficult and limits its application to trace continental weathering.In this study, major developments and challenges in using stable Sr isotopes to trace continental weathering are reviewed, when considering high-precision testing methods, characteristics of δ88/86Sr in natural reservoirs, and geochemical behaviors. The high-precision measurement methods currently used for stable Sr isotopes mainly include multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and thermal ionization mass spectrometry (TIMS), both of which involve chemical purification by a cation exchange column or Sr specific resin, coupled with various methods for quality discrimination correction. The present analytical precision for the determination of δ88/86Sr in geological samples is 0.02‰ ∼ 0.08‰. The δ88/86Sr varies widely in natural reservoirs. In particular, the range of δ88/86Sr values in extraterrestrial reservoirs, the biosphere, the lithosphere, and the hydrosphere are -1.73‰ to +0.66‰, -0.87‰ to +0.85‰, -0.20‰ to +0.53‰ and -0.45‰ to +0.66‰, respectively. Stable Sr isotope fractionation occurs in the processes of differential dissolution of primary minerals (Δ88/86Sr = -0.13‰), formation and adsorption of secondary minerals (Δ88/86Sr = -0.15‰), precipitation of carbonate (Δ88/86Sr = -0.20‰), and biological processes (Δ88/86Sr = -0.15‰), which causes the δ88/86Sr in fluid (solid) phase to δ88/86Sr increases (decrease). Previous research on the fractionation mechanisms and constraint conditions of stable Sr isotopes during continental weathering is insufficient. Thus, promoting a wide application of stable Sr isotopes to trace continental weathering through the combination of field profiles, laboratory experiments and theoretical calculation is urgently warranted.

The Formation of Atolls: New Insights From Numerical Simulations

AbstractSeveral theories have been proposed to explain atoll formation. While karst dissolution during glacial periods and preferential coral reef accretion along raised bank margins during deglaciations and interglacials have been invoked to explain atoll formation, the respective roles of karst dissolution and reef margin construction in atoll formation have not been adequately evaluated by simulations. In this study, we conducted three‐dimensional numerical simulations of the Quaternary development of Meiji Atoll in the southern South China Sea based on interpreted data from a 2020‐m‐deep borehole drilled on its northeast rim in 2018. Our results suggest that the origin of atolls is more likely due to spatially differential dissolution across margin and interior areas (i.e., minimal along margins and maximal in bank centers) rather than preferential reef accretion along margins of flat‐topped banks. Preferential reef accretion along margins of flat‐topped banks that can result in central lagoons and atoll morphology can hardly result in the formation of lagoonal patch reefs that reach mean sea level. Preferential reef accretion along margins is mainly predicated on the karst‐induced morphology that has a central depression surrounded by raised rims, that is, using antecedent karst morphologies. If topographic highs in the lagoon are similar in elevation to the margins, reef accretion on these topographic highs can be similar to that observed on the margins, resulting in lagoonal patch reefs that reach mean sea level. Our simulation shows that spatially differential dissolution across margin and interior areas is a critical driver of worldwide central lagoons and atoll formation.

CO2-enriched CBM accumulation mechanism for low-rank coal in the southern Junggar Basin, China

This paper mainly focused on the genesis of coalbed methane (CBM), CO2 origin and the CBM accumulation mechanism in the southern Junggar Basin using a combination of geochemical and geological analysis methods. From this work, it is found that the degree of early coalification and the current structural and hydrogeological conditions jointly determine the regional differences in CBM genesis, accumulation and gas-bearing capacity. Microbial (biogenic) gases are widely developed in the whole study area, while their generation types and contributions vary greatly in different areas and structural belts. The CBM in the eastern Urumqi (ER) and Jimusaer (JMSE) areas is primary microbial (biogenic gas) that have been generated through CO2 reduction pathway and mixed with a small amount of early mature thermogenic gas. The Baiyang River (BYR) area has a mixed gas source of early mature thermogenic gas, primary microbial gas and secondary microbial gas. The CBM in other areas is mixed gas of thermogenic and secondary microbial origins. Abnormally high CO2 concentration and extremely positive δ13C-CO2 are all related to microbial methanogenesis. The CO2 in the ER and JMSE areas and partial CO2 in the BYR area are produced by the microorganism-mediated degradation of sedimentary organic matter. The selective consumption by microbial reduction and differential dissolution of groundwater result in an increase in CO2 concentration with increasing burial depth in the ER and BYR areas. The CO2 in other areas is originally derived from the deoxidation reaction of early coalification which then undergoes secondary biotransformation. The CO2 intervention commonly runs through the whole process of CBM accumulation in low-rank coal in the study area. Due to isotope fractionation caused by groundwater flow and differential modification of microorganisms, the vertical variations of δ13C-CH4 and δ13C-CO2 are positively correlated with burial depth, and the genetic types and gas-bearing characteristics of CBM have obvious vertical zoning under the condition of high-dip structures.

Optimization and evaluation of resveratrol amorphous solid dispersions with a novel polymeric system.

The preparation of amorphous solid dispersions using polymers is a commonly used formulation strategy for enhancing the solubility of poorly water-soluble drugs. However, a single polymer often does not bring significantly enhance the solubility or amorphous stability of a poorly water-soluble drug. We found an application of a unique and novel binary polymeric blend in the preparation of solid dispersions. The main purpose of this study is to optimize and evaluate resveratrol (Res) amorphous solid dispersions with a novel polymeric system of poly (vinyl pyrrolidone) (PVP) and carboxymethyl chitosan (CMCS). The influence of three different release factors, the ratio of CMCS to the polymer mixture (CMCS% = X1), the ratio of Res to the polymer mixture (Res% = X2) and the surfactant (Tween 80 = X3), on the characteristics of released Res at various times (Q5 and Q30) was investigated. The computer optimization and contour plots were used to predict the levels of the independent variables as X1 = 0.17, X2 = 0.10 and X3 = 2.94 for maximized responses of Q5 and Q30. Fourier transform infrared spectroscopy (FTIR) results revealed that each polymer formed hydrogen bonds with Res. The solid performance and physical stability of the optimized ternary dispersions were studied with scanning electron microscopy (SEM), powder X-ray diffraction (XRD), modulated differential scanning calorimetry (MDSC) and dissolution testing. SEM, XRD and MDSC analysis demonstrated that the Res was amorphous, and MDSC showed no evidence of phase separation during storage. Dissolution testing indicated a more than fourfold increase in the apparent solubility of the optimized ternary dispersions, which maintained high solubility after 90 days. In our research, we used CMCS as a new carrier in combination with PVP, which not only improved the in vitro dissolution of Res but also had better stability.

Fluid-rock interactions and porosity genesis in deep clastic reservoirs: A perspective of differential oil charge intensity

Fluid-rock interactions are important factors affecting pore genesis and hydrocarbon accumulation in sedimentary basins. Different responses and processes will occur under differential oil or gas charge intensities, which is important for reservoir evaluation and prediction, but few studies focus on this topic. To fill this knowledge gap, petrologic, major element, and isotopic study were conducted in conglomeratic reservoirs of the late Permian Upper Wuerhe Formation (P3w) in the Shawan Sag, Junggar Basin, northwestern China. The results show that tuff and volcanic debris are enriched in the formation, and laumontites generally occur as cements due to the alteration of volcanic materials. In oil and gas reservoirs undergoing strong hydrocarbon charge, laumontite and calcite cements generally exist, and partial of cements, as well as some debris and feldspar, are dissolved, forming abundant secondary porosity. The two cements also exist in the water-bearing and dry layers, but both of them are only pratially dissolved. This differential dissolution implies the reformation of acidic hydrocarbon-bearing fluid in clastic reservoirs. Mineral assemblages show that laumontite and small amounts of early-stage calcite precipitated during eodiagenesis. During the continuous compaction of the reservoir, first-stage hydrocarbon charge occurred in the Middle Jurassic when primary porosity almost disappeared. Hydrocarbon charge inhibited the precipitation of laumontite and calcite, promoting their dissolution. Second-stage hydrocarbon charge in the Early Cretaceous further caused more extensive dissolution of laumontite and calcite, forming abundant secondary pores. Authigenic quartz, kaolinite and late-stage calcite precipitated as the associated minerals of laumontite dissolution. Late-stage calcite is characterized by Mn-rich (>2.5%) and δ13C depleted deviations (−19.5‰ ∼ −14.3‰, VPDB), recording the strong activities of hydrocarbon-bearing fluids. This study emphasizes the importance of reservoir reconstruction after hydrocarbon charge and suggests favourable hydrocarbon accumulations may be found in deeply buried clastic reservoirs.

Study on the driven mechanism of hydrologic drought based on the lithology-combined structure of the Karst drainage basin in South China

Abstract Hydrologic drought, considered as a typical natural phenomenon in the background of global climate changes, is the continuation and development of meteorological and agricultural droughts, and is the ultimate and most thoroughly drought. The research area controlled by the 55 hydrological sections in South China is selected in this paper, and the intensity and frequency of hydrologic droughts are analyzed by the Standardized Runoff Index (SRI), and the driven mechanism of watershed lithologies to hydrologic droughts is discussed. The results show that (i) the hydrological drought of Karst drainage basins is shown the gradual aggravation from the west to east parts in South China, with the significant north–south stripe distributions at the SRI_3 and SRI_6; (ii) the occurring probability of hydrological droughts is the Limestone-type Karst Basin (II and III, 0.17) < Dolomite-type Karst Basin (I and IV, 0.22) < Non-Karst Basin (V, 0.25) in terms of combination types of basin lithologies, and (iii) the Karst Basin (I and III, 0.18) < Semi-Karst Basin (II and IV, 0.2) < Non-Karst Basin (V, 0.25) in terms of basin lithologies. Therefore, this proves that the most water-stored spaces are found in Karst Basins under the differential dissolution or erosion effects of soluble water, followed by in the Semi-Karst Basin, the least water-stored spaces in the Non-Karst Basin.

Origin of authigenic albite in a lacustrine mixed-deposition sequence (Lucaogou Formation, Junggar Basin) and its diagenesis implications

Authigenic albites occur widely in clastic reservoirs with important implications for diagenesis and reservoir formation. The middle Permian Lucaogou Formation in the Jimusaer Sag (Junggar Basin, NW China), where major exploration breakthroughs in shale oil have been achieved, reveals a new phenomenon that authigenic albites are abundant in unique mixed carbonate–volcanic–clastic sequences. This has not been reported in the literatures. To fill the knowledge gap, the origin of these authigenic albites and their relationship with dissolution pores (i.e. diagenesis implications) were investigated. Results show that two types (I and II) of authigenic albite were identified within the shale oil reservoirs. Euhedral Type I authigenic albites with 3–10 μm only occur in dolarenite intraclasts and are symbiotic with amorphous dolomite minerals with a pure chemical composition of >99% albite-end-member content. Larger Type II authigenic albites with 10–50 μm are widely distributed in reservoirs, primarily in dissolution pores, and coexist with authigenic dolomite minerals or dolomite overgrowths. Their chemical composition is less pure with anorthite-end-member contents that range from undetectable to 9.77%, with an average of 1.34%. A symbiotic relationship, pure chemical composition, size, and euhedral morphology indicate that Type I authigenic albites precipitated during syngenetic hydrothermal action. However, the morphology of dissolution pores, residual symbiotic “orthoclase”, impure chemical composition and carbon–oxygen isotope indicate that Type II were the products of the dissolution and reprecipitation of “perthite” crystal pyroclasts influenced by acid organic fluids in latter diagenesis. The differential dissolution of “orthoclase” and “albite” components in “perthite” crystal pyroclasts formed enormous intergranular secondary pores in the presence of dolomite minerals in the shale oil reservoirs.

The role of titanite in shaping the geochemistry of amphibolite-derived melts

Titanite, one of the major accessory phases in middle to lower crustal rocks, could play an important role in shaping trace element as well as radiogenic isotope compositions in amphibolite-derived melts. Petrographic, zircon U/Pb, whole-rock element and isotope (Sr and Nd) data on a suite of leucosomes, and titanite Nd isotope compositions from the migmatitic amphibolite complex, southern Liaoning, indicate that (1) the amphibolite with a protolith age of ~2450 Ma underwent low-degree partial melting at ~160 Ma and produced two groups of leucosome; (2) these leucosomes preserved a large magnitude of Nd isotope disequilibrium with up to ~10 epsilon units of difference with respect to their sources; (3) differential dissolution of titanite during partial melting might lead to negative correlations between Nd isotope compositions and respective Ti or V contents (proxy of the amount of titanite presented). These data indicates that during low-degree partial melting of mafic rocks, titanite stays as a residue phase due to either unfavorable texture or melting (temperature or fluid) conditions and leads to the development of melts with depletion in Ti-affinity elements, REE, and a large positive shift in Nd isotope compositions. Similar to other accessory phases (e.g., zircon, apatite, and monazite) in metasedimentary sources, this contribution presents another case that could be common in high-grade metamorphic terranes in which titanite could be a key phase that controls key trace element (e.g. NbTa, V, and REE) budget and Nd isotope compositions in melts derived from low-pressure melting of amphibolite or mafic rocks in various tectonic environments.

High-Resolution Lithographic Patterning with Organotin Films: Role of CO2 in Differential Dissolution Rates

Details of the chemistry enabling the patterning of organotin photoresists to single-digit-nm resolution continue to engage study. In this report, we examine the contributions of atmospheric gases to the differential dissolution rates of an n-butyltin oxide hydroxide photoresist. Cryo scanning tunneling electron microscopy (cryo-STEM) produces a micrograph of the latent image of an irradiated resist film, readily distinguishing exposed and unexposed regions. Temperature-programmed desorption mass spectrometry (TPD-MS) and cryo electron energy loss spectroscopy (cryo-EELS) show that irradiated films are depleted in carbon through desorption of butane and butene. Upon aging in air, irradiated films absorb H2O, as previously established. TPD-MS also reveals a previously unrecognized absorption of CO2, which correlates to a heightened dissolution contrast. This absorption may play an active role in determining intrinsic patterning performance and its variability based on changes in atmospheric-gas composition.

The Formation of Mn-Ce Oxide Catalysts for CO Oxidation by Oxalate Route: The Role of Manganese Content.

The Mn-Ce oxide catalysts active in the oxidation of CO were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transition electron microscopy (TEM), energy dispersive X-Ray (EDX), and a differential dissolution technique. The Mn-Ce catalysts were prepared by thermal decomposition of oxalates by varying the Mn:Ce ratio. The nanocrystalline oxides with a fluorite structure and particle sizes of 4–6 nm were formed. The introduction of manganese led to a reduction of the oxide particle size, a decrease in the surface area, and the formation of a MnyCe1−yO2−δ solid solution. An increase in the manganese content resulted in the formation of manganese oxides such as Mn2O3, Mn3O4, and Mn5O8. The catalytic activity as a function of the manganese content had a volcano-like shape. The best catalytic performance was exhibited by the catalyst containing ca. 50 at.% Mn due to the high specific surface area, the formation of the solid solution, and the maximum content of the solid solution.

Differential Dissolution Stoichiographic Method in Investigation of the Chemical Composition of Functional Materials

This paper presents examples that characterize various aspects of the possibility of determining the phase composition of solid multielement substances and materials containing nanostructured forms of their components by a differential dissolution stoichiographic method. The use of stoichiography makes it possible to detect and quantitatively determine both known and unknown crystalline and amorphous phases of constant and variable composition without standards of solid phases. The use of stoichiographic methods and ideas of nonequilibrium thermodynamics allows one to gain fundamentally new data on solid-state transformations of multielement, multiphase substances and materials.