Chemical Phase Analysis Research Articles

Hydrogen Generation From Ferrous Saponite in Reaction With H2S‐Containing Fluid: Relevance to Early Martian Habitability

AbstractMolecular hydrogen is an important gas species for understanding the early Martian climate and redox chemistry. Through ancient aqueous alterations of crustal rocks, ferrous (Fe(II)) saponite formed abundantly on Mars. Subsequent intrusions of hydrothermal fluids may have resulted in a chemical reaction between the dissolved volatiles and the nearby rocks. Here we propose a new H2 generating reaction between ferrous saponite and H2S‐containing fluids, which is possible on early Mars. A series of hydrothermal experiments at a relatively low temperature of 90°C were performed under anoxic conditions using synthesized ferrous saponite to compare the resulting H2 concentration among various gas and fluid compositions. Based on the relationship with the existence of H2S, reaction time, fluid pH, dissolved iron concentration, and amount of minerals, we found that high levels of H2 (∼0.1 mmol/g ferrous saponite) were generated in the presence of H2S most rapidly in moderate pH conditions. Our microscopic chemical analysis of mineral phases suggested that ferrous saponite served as both the iron source of pyrite precipitation and the electron source to form H2. Our results suggest that intrusions of H2S‐containing fluids into the saponite‐containing crust of Mars would generate H2, which could potentially provide locally concentrated chemical energy for chemoautotrophic life.

Correlative morphological, elemental and chemical phase analyses at the micrometric scale of powdered materials: Application to nuclear forensics

To characterize a mixture of powders using several analytical techniques, it is necessary that successive analyses be carried out on well-identified and localized particles, so that each characterization corresponds to a given powder. In this publication, powdered nuclear materials are characterized at the morphological and elemental levels with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and at the chemical level with a micro-Raman spectrometer (MRS). However, to avoid a time-consuming and insufficiently accurate microparticle relocation process between SEM/EDS and MRS, micro-Raman analyses are carried out inside the SEM using a coupling device. In this way, all three pieces of information are obtained for exactly the same micrometric spot, without moving the sample or relocating the microparticles analyzed. The information can therefore be combined to characterize each component of the mixture. In this article, we describe in detail the methodology we have developed and optimized for morphological, elemental and chemical analysis of microparticles using a combined SEM/EDS and SRM. This methodology has been applied to powdered nuclear materials in two international nuclear forensics exercises. In the first exercise, named CMX-6, the combined use of the two instruments identified the presence of PuO2 microparticles and several uranium compounds (UO2, U3O8, UO2F2) in both materials. In the second exercise, called CMX-7, the methodology developed enabled us to distinguish two chemical phases of uranium, a uranyl oxy-hydroxide and a uranyl nitrate, each characterized by specific morphologies and the detection or non-detection of a minor elemental constituent (calcium).

Synthesis and alloying of zinc sulfide in a homogeneous system based on dodecane, its identification and optical properties

Zinc sulfide doped with Mn2+ ions was synthesized in a homogeneous dodecane medium by the method of emerging reagents. By methods of chemical and X-ray phase analysis, IR spectroscopy, electron microprobe microscopy, identification of products was carried out, photographs of the surface of powder particles (SEM) were recorded. Based on the totality of the results, a conclusion is made about the formation of nanoscale objects having a polytype structure with a predominance of distorted cubic crystals forming agglomerates up to 10 microns in size in ZnS powder and up to 100 microns in ZnS–Mn powder. The formation of nanoscale ZnS particles is confirmed by spectral data. The effect of manganese ions on the photoluminescence (FL) of the powder is manifested by a change in the type of the descending branch of the ZnS–Mn FL band, it is associated with recombination processes at the levels of defects formed by Mn2+ ions in the ZnS structure at their low concentration.

The Waelz Slag from Electric Arc Furnace Dust Processing: Characterization and Magnetic Separation Studies.

The Waelz slag generated during electric arc furnace dust processing is an iron-rich product with significant amounts of iron, zinc and copper. About 600-800 kg of the Waelz slag is generated per ton of the dust processed. The Waelz slag samples from two different plants were thoroughly characterized using inductively coupled plasma optical emission spectroscopy (ICP-AES), X-ray diffraction analysis (XRD), chemical phase analysis, Mössbauer spectroscopy and other supporting methods. The phase distribution of iron, zinc and copper was determined in the Waelz slag samples. Low-intensity wet magnetic separation was tested for the iron recovery from the Waelz slag samples. It was found that the Waelz slag samples have complex chemical and mineralogical compositions, which can impede the selective recovery of valuable elements. The obtained results indicate that the chemical and mineralogical composition of the Waelz slag samples has a considerable effect on the magnetic separation indexes. The experiments showed that the iron concentrates with Fe contents of 73% and 46.8% with the metallization degrees of 87.2% and 57.5% and the iron recovery degree of 54.8% and 52.9% were obtained at optimal conditions for two different samples, respectively, without selective segregation of Cu and Zn in the magnetic or non-magnetic fraction.

Mechanical Properties and Corrosion Resistance of Hot-Pressed Dysprosium Molybdate Samples

The purpose of this work was to study the consolidation features using hot pressing method of dysprosium molybdate billets and to study their mechanical properties and corrosion resistance.Methods. The technological and physical properties of the mechanosynthesised dysprosium molybdate powder were investigated. Properties and structure of the obtained dysprosium molybdate powder were studied by methods of chemical and X-ray phase analyses and scanning electron microscopy. Bulk density of dysprosium molybdate powder was studied according to GOST 19440-94. Flowability of dysprosium molybdate powder was determined according to GOST 20899-75. The specific surface of dysprosium molybdate was determined using a specific surface analyser NOVA 1200e (USA) by the method of low-temperature nitrogen adsorption (BET). X-ray phase analysis of mechanosynthesised dysprosium molybdate powder was carried out on a diffractometerResults. The bending strength of hot-pressed dysprosium molybdate specimens was determined, it was found that the highest value of the bending strength was recorded for these specimens at a pressing pressure of 35 MPa and is 314 MPa. The corrosion resistance of hot-pressed dysprosium molybdate samples in aqueous coolant at a temperature of 100 °C was studied. It was recorded that the mass of the mechanosynthesised dysprosium molybdate specimens remained practically unchanged throughout the corrosion resistance test in aqueous coolant.Conclusion. Tests on corrosion resistance have shown absence of change of mass of samples from dysprosium molybdate during 60 hours. The bending strength of samples from dysprosium molybdate obtained by hot pressing at pressure 35 Pa, temperature 1400 oÑ and time of holding under pressure 5 min is 314 MPa.

Еlectrochemical behavior of cadmium by alternating current polarization in hydrocloric acid solution

This paper presents the results of a study of the electrochemical behavior of a cadmium electrode in aqueous solutions of hydrochloric acid under polarization by stationary and non-stationary currents and shows the possibility of synthesis of its chloride. The purpose is to develop the electrochemical behavior of cadmium under alternating current polarization in a solution of perchloric acid. Methods. During the study, it was found that when two cadmium electrodes are polarized with an alternating current of 50 Hz, their dissolution does not occur, however, when one electrode is replaced with a titanium one, cadmium is intensively dissolved. Results and discussion. The influence of the main parameters, such as the duration of electrolysis, current density, concentration and nature of the electrolyte on the electrochemical process has been studied. A schematic diagram of an installation for dissolving cadmium by polarization with a non-stationary current is proposed. It is shown that on the titanium electrode in the range of 20-80 kA/m2, the current yield of the dissolution of the cadmium electrode gradually increases, and with a current density equal to 80 kA/m2, the current yield reaches 135%. Conclusion. It is shown that with alternating current polarization, the rate of chemical dissolution of cadmium, increases with the release of hydrogen. During the experiment, with the polarization of the cadmium electrode by alternating current, the possibility of obtaining cadmium chloride was shown. Based on chemical and X-ray phase analyses, it was proved that cadmium forms compounds CdCl2∙H2O.

Synthesized-Hydroxyapatite Powder from Anadara Granosa Shells using Deposition Time Method for Biomedical Applications

Hydroxyapatite (HAp) powder, one of the biomaterials derived from natural sources, could be used in biomedical applications. In this research, the synthesized-HAp powder from Anadara Granosa shells as raw materials had a high calcium carbonate content with variations in deposition time using the precipitation method. Variations of deposition time used were 0 (S0), 24 (S24), and 48 (S48) hours. Fourier Transform Infrared (FTIR), X-Ray Diffractions (XRD), and Scanning Electron Microscopy (SEM) were used to investigate the chemical structure, phase analysis, and morphology of the synthesized HAp powder. FTIR results of the S0, S24, and S48 showed that the functional groups , and were formed at variations in the deposition time. The XRD results showed that the smallest of crystallite size of S48 was 26.03 nm, and the crystallinity degree of S24 was 38.74%. The grain dispersity of the synthesized-hydroxyapatite powder from SEM results were uniform, agglomeration, and spherical, irregular shape. The Ca, P, Mg, and Si compositions were shown in the synthesized-hydroxyapatite powder. The deposition time affects the synthesized-Hydroxyapatite (HAp) powder from the Anadara Granosa shell, and it is a potential raw material for biomedical applications.

RESEARCH AND DEVELOPMENT OF TECHNOLOGY FOR PRODUCTION OF SODIUM FLUORIDE, AMORPHOUS SILICA AND LIQUID GLASS FROM A MIXTURE OF FLUOROSILICIC AND HYDROFLUORIC ACIDS

In article presents the results of processing of a mixture of fluorosilicic and hydrofluoric acids – a by-product of fluoride salts and phosphate fertilizers production in order to obtain sodium fluoride, silica gel (amorphous silicon oxide) and liquid glass. On this basis, the optimal technological parameters of the interaction of a mixture of FSA and hydrofluoric acid with sodium hydroxide were determined depending on temperature, process duration and sodium hydroxide concentration. It was found that at temperature 25 ºC, process duration 15 min, sodium hydroxide concentration 45% wt. the degree of sodium fluoride extraction reaches more than 93%. Also, sodium fluoride dissolved during the reaction after hydrolysis of sodium metasilicate with precipitation and filtration of silica gel is returned back to the production cycle for preparation of the required sodium hydroxide solution. It was determined that treatment of amorphous silica forming with 10 % sodium hydroxide solution for 60 min. and temperature 85-90 ºC yields liquid glass. The results of the conducted research are confirmed by chemical and X-ray phase analyses, which gives grounds for the introduction of this technology in the industry. In addition, on the basis of the conducted researches the basic technological scheme of processing of the mixture of FSA and hydrofluoric acid was developed in order to obtain sodium fluoride, amorphous silica and liquid glass.

ВЫПУСК ОПЫТНО-ПРОМЫШЛЕННЫХ ПАРТИЙ КРИОЛИТА С ИСПОЛЬЗОВАНИЕМ ХЛОРИДА И ГИДРОКСИДА НАТРИЯ И ИХ ИСПЫТАНИЯ ПРИ ПРОИЗВОДСТВЕ АЛЮМИНИЯ

The paper presents the results of pilot batch production of cryolite using sodium chloride and sodium hydroxide by hydrochemical method, physical and chemical studies of the obtained products, as well as their testing in aluminium electrolysers with measurements of technological parameters before and after use. The conducted studies have shown that the process of production of a pilot batch of cryolite by hydrochemical method from hydrofluoric acid using aluminium hydroxide, sodium chloride and sodium hydroxide solutions proceeds at a temperature of 25 °C for 30-45 min. In this case, the yield of cryolite according to the first embodiment using sodium chloride is more than 80 %, since during the reaction a side hydrochloric acid is formed, which dissolves more than 15 % of the cryolite. When sodium hydroxide is used, the process proceeds similarly to the first variant with an increase in cryolite yield of more than 90%. According to pilot tests, the first variant produced 600 kg of cryolite and the second variant produced 620 kg of cryolite. The reliability of the process of cryolite production with the use of sodium chloride and hydroxide was confirmed by chemical and X-ray phase analyses using the modernised Dron-2 unit. It was found that the analysed samples correspond to the reference cryolite, indicating the interaction of sodium chloride and sodium hydroxide with fluoroaluminium acid. Also the obtained synthetic products have successfully passed pilot tests in aluminium electrolysers of JSC "TALCO" with control of technological parameters. On the basis of conducted researches the basic technological scheme of cryolite production by hydrochemical method with application of hydrofluoric acid, aluminium hydroxide, sodium chloride and hydroxide was developed. As a result of the research it was found out that the technology of cryolite production with the use of sodium chloride and hydroxide is easy to implement and cost-effective due to low energy consumption of production and the use of local mineral raw materials.

Separation and recovery of zinc from blast furnace dust via coordination leaching of Cl− and hydrolysis of NH4+

Blast furnace dust (BFD) is a by-product of iron-making process, a typical hazardous waste containing abundant recyclable components. In this study, a NH4Cl cooperative coordination leaching method was proposed for the selective separation and recovery of zinc from BFD. The thermodynamic analysis results revealed that ZnO and ZnSO4 from BFD can be converted to zinc-chlorine coordination compounds (ZnCli2−i, i = 1,2,3,4) in the cooperative actions of NH4+ and Cl− ions. The experimental results showed that the leaching efficiency of zinc reached 85.64% while iron and carbon was enriched from 46.76% to 57.96% under the optimal experimental conditions. The leaching residue with a total content 2.53% of Zn, Cl, K and Na can be returned to sintering for the recovery of iron and carbon. Moreover, the XRD, SEM-EDS and chemical phase analysis results of BFD and residue demonstrated that a small amount ZnO, ZnS and ZnFe2O4 were not leached and remained in the leaching residue. Additionally, a novel method of low-temperature crystallization was adopted to recover zinc from filtrate. The crystallization efficiency of zinc reached 80.96% and the obtained crystal was confirmed to be special Zn(NH3)2Cl2. Thus, this work not only achieved the separation and recovery of zinc from BFD, but also solved the disposal problem of leaching residue and crystallization solution, providing a guidance for the resource utilization of hazardous BFD.

Use of laser cladding for the synthesis of coatings from high-entropy alloys reinforced with ceramic particles

The purpose of this work was to develop methods for obtaining composite coatings based on high-entropy alloys by laser cladding from mixtures of low-entropy powders. Powders of pure copper (Cu), titanium carbide (TiC), aluminum oxide (Al2O3), as well as commercial powders of low- and medium-entropy alloys were used for the implementation of laser additive technologies. The powder particle size ranged from 40 to 150 µm. Coatings were obtained using an ytterbium fiber-optic laser on a steel substrate. The structure of experimental samples was studied on a scanning electron microscope. In order to confirm the composition of the zones found in the studied samples (for chemical and structural analysis of phases in the studied samples), X-ray spectral microanalysis was performed using an energy-dispersive X-ray spectrometer. The phase structure of the obtained samples was studied by X-ray phase analysis using a powder diffractometer using Cu-Kα radiation. The technique used made it possible to obtain composite coatings with inclusions of Al2O3 and TiC. The results of the work open the way to the development of technologies for producing, by laser cladding, highly functional coatings from high-entropy alloys strengthened with reinforcing ceramic particles or from composite materials based on high-entropy alloys, using a combination of commercially available powders of low-entropy and medium-entropy alloys.

Characteristics of Gold Minerals in Gold Concentrate with a High Copper Content and Effective Gold Recovery via Flotation and Ammonia Pretreatment–Cyanidation Leaching

The characteristics of ultrafine gold minerals in gold concentrate with a high copper content produced by a large gold mining company in Shandong Province were determined via chemical composition analysis, phase analysis, and mineral liberation analysis. The results showed that the concentrate contained 48.13 g/t gold, which was mainly in the form of native gold and electrum. Regarding the gold mineral particles, 57.65% were completely liberated and 35.75% were associated with chalcopyrite and pyrite. The remainder mainly comprised wrapped intergrowths. The cumulative distributions of native gold and electrum fractions with diameters of less than 75 µm were 82.55% and 90.15%, respectively. Enhanced Cu–S bulk flotation, and then, Cu–S separation from the raw material were proposed to effectively enrich the gold minerals and decrease the treatment throughput during the leaching operation. The optimized conditions yielded a concentrate with a high copper content (3.89% Cu and 545.62 g/t Au contents, and 83.15% Cu and 77.54% Au recoveries) and a concentrate with a high sulfur content (0.059% Cu and 15.03 g/t Au contents, and 83.15% Cu and 21.28% Au recoveries). The capacity of the subsequent leaching process was reduced by 25%. Ammonia pretreatment was introduced to decrease the adverse effect of copper on cyanidation leaching for the copper concentrate. Under the optimized leaching conditions, gold dissolution reached 99.76%, which was approximately 4% higher than that obtained via direct leaching. The NaCN consumption decreased over 10 kg/t. These results could serve as a valuable reference for the economic and green utilization of gold resources from concentrate with a high copper content.

Extraction of Germanium from Low-Grade Germanium-Bearing Lignite by Reductive Volatilization.

Germanium (Ge) as an important strategic metal is widely used in many modern-technology fields such as optical fiber and thermal solar cells. In this study, the volatilization behavior of Ge from low-grade germanium-bearing lignite was investigated in detail through reductive volatilization. The results indicated that temperature and air flow rate in the semi-closed roasting system played a significant role in the process. The optimal volitation efficiency of Ge reached 98% at 1100 °C for 2 h with air flow rate of 0.7 L/min in a maffle furnace, respectively. Under optimal conditions, the contents of Ge lowered to 30 ppm in the roasting residue. Analysis of the enriched ash yielded 71,600 ppm for Ge. Chemical phase analysis of the Ge in the enrichment ash showed that soluble Ge accounted for 82.18% of the total Ge, which could be viewed as an excellent material for Ge extraction by chlorinated distillation.

On the reasons for the premature failure of safety valve springs in the equipment of the primary oil refining

The reasons for the premature failure of a spring made of steel 50KhFA used in the safety valve of the column head part of the flare facility were analyzed. The failure of the spring occurred after 7 years of operation at a temperature below 90°C in a working environment of light oil products (sulfurous gasoline). Visual and measurement control, chemical analysis of the steel composition, energy-dispersive X-ray spectroscopy (EDS) of metal in local areas, macro- and microstructural analysis, macro- and electron fractography, phase chemical and X-ray structural analysis, hardness and microhardness tests and reductive heat treatment were used in the research. The data on the characteristic external signs, typical micro damages, and the mechanism of destruction under low-temperature hydrogen sulfide corrosion of steel 50KhFA with hydrogenation, the most dangerous accompanying process, were gained in the study. According to the results obtained, the chemical composition and hardness of the spring metal meet the requirements of the standards for steel 50KhFA. The microstructure of the studied metal is tempered martensite with a decarburized layer up to 0.158 mm in thickness present on the surface. The analysis of the results showed that the premature failure of the spring is attributed both to technological heredity and contact with the working environment unauthorized by the project. An ulcerative damage of the metal surface and penetrating of corrosion products into the depth of metal due to violation of the integrity of the spring coating were revealed, which indicates a low resistance of 50KhFA steel to low-temperature hydrogen sulfide corrosion. The failure occurs predominantly near non-metallic inclusions along the boundaries of primary austenitic grains, where the largest precipitates of chromium carbides are located, as well as along the interphase boundaries of oriented carbide plates.

Phase equilibria and microstructure development in Mg-rich Mg-Gd-Sr alloys: Experiments and CALPHAD assessment

Mg-Sr alloys are promising to fabricate orthopedic implants. The alloying of rare earth elements such as Gd may improve the comprehensive mechanical properties of Mg-Sr alloys. The information on the phase diagram and the microstructure development are required to design chemical composition and microstructure of Gd alloyed Mg-Sr alloys. The phase equilibria and the microstructure development in Mg-rich Mg-Gd-Sr alloys (Gd, Sr < 30 at. %) are experimentally investigated via phase identification, chemical analysis, and microstructure observation with respect to the annealed ternary alloys. The onset temperatures of liquid formation are measured by differential scanning calorimetry. A thermodynamic database of the Mg-rich Mg–Gd–Sr ternary system is developed for the first time via CALPHAD (CALculation of PHAse Diagram) approach assisted by First-Principles calculations. The thermodynamic calculations with the developed database enable a well reproduction of the experimental findings and the physical-metallurgical understanding of the microstructure formation in solidification and annealing.

Mineral forms of tungsten at the Porokhovskoe and Yugo-Konevskoe deposits (South Urals)

The ore hand specimens and technological ore samples from the Porokhovskoe and Yugo-Konevskoe W greisen deposits in the South Urals are studied. The major W minerals of primary ores at both deposits include hubnerite and scheelite. The secondary and accessory minerals are pyrite, chalcopyrite and molybdenite, rare minerals include sphalerite, galena, bismuthinite, aikinite, unidentifed chalcogenides and sulfosalts, magnetite, rutile, ilmenite, titanite and columbite. The veins are mainly composed of quartz and muscovite with subordinate calcite, dolomite and fuorite, rare chlorite and amphibole and accessory zircon, apatite and uraninite. No zonation in the distribution of wolframite with various Fe content is identifed relative to the Yugo-Konevsky granite pluton, however, wolframite of the Northern area of the Porokhovskoe deposit is enriched in Fe compared to that of the Central area and Yugo-Konevskoe deposit. In addition to veined wolframite and scheelite, the oxidized ores also contain Fe and Mn oxyhydroxides, malachite, pyromorphite and bromargyrite. Tungsten is part of Mn and Fe oxyhydroxides, which replace wolframite and less often sulfdes. The WO3 content of pseudomorphic Mn and Fe oxyhydroxides after hubnerite reaches 18 wt. %. Single grains of stolzite and russellite are found. According to the results of phase chemical analysis of technological samples, the amount of tungstite in oxidized ores is minor, therefore all ores of both deposits were ascribed to primary type. Keywords: South Urals, Porokhovskoe deposit, Yugo-Konevskoe deposit, tungsten, hubnerite, scheelite, stolzite, trace elements.

Improving the technology of copper-zinc ore beneficiation of a Uralian-type pyrite deposit

Introduction and research objective. Copper-zinc ore of pyrite deposits of the Uralian type are refractory. Difficulties in beneficiation are due to their material composition: fine coarseness and emulsion impregnation of ore minerals in each other, a large amount of flotation-active pyrite, a high content of finely dispersed and submicroscopic gold in sulfides, etc. In the course of pyrite ore processing at dressing mills, 83–91% of copper and 10–45% of gold are extracted into copper concentrates, and 46–78% of zinc and 5–15% of gold are extracted into zinc concentrates. Increasing the process performance of pyrite deposit ore processing is a promising and urgent task. Methods of research included copper-zinc pyrite ore material composition study through quantitative chemical analysis, chemical phase analysis for the forms of copper, zinc, gold and silver compounds, and mineralogical analysis. Technological studies were carried out by flotation and gravity methods using a centrifugal concentrator and a concentration table. Conclusions. In the course of pyrite deposit copper-zinc ore beneficiation at the dressing mill, the effect of circulating concentration of gold in the coarse copper concentrate regrinding cycle was established. The results of studies on the centrifugal concentration of gold in a centrifugal concentrator with further secondary cleaning of its heavy fraction on a concentration table show the possibility of obtaining a gravity product with a mass fraction of gold up to 200 g/t under its operational extraction up to 29%. It was noted that the integrated flotation-gravity technology for copper-zinc ore beneficiation will increase the through extraction of gold into marketable mineral products by more than 1.5%. The use of a combination of butyl potassium xanthate and FRIM-2920 reagent-collector in the copper-zinc pyrite ore flotation technology contributes to increased extraction of copper and gold into copper concentrate by 0.87% and 3.22%, respectively, and zinc into zinc concentrate by 0,4%. Increasing the pulp temperature in the zinc flotation cycle to 40–45 °C and returning the control zinc flotation concentrate and tailings from the first cleaning flotation of zinc to the II main zinc flotation allows increasing the mass fraction of zinc in the zinc concentrate from 48.5 to 51.1% under a simultaneous increase in the extraction of zinc into zinc concentrate from 62.6 to 65.6%.

Precipitation behavior of γ′ precipitates in 21Cr-32Fe-41Ni heat-resistant alloy at different aging temperatures

The precipitation behavior of γ′ precipitates and mechanical properties of 21Cr-32Fe-41Ni alloy at different aging temperatures were investigated by scanning electron microscopy, transmission electron microscopy, chemical phase analysis, mechanical property tests. The results showed that the precipitates in 21Cr-32Fe-41Ni alloy included γ′ precipitates, MC phases, σ phases after aging heat treatment. There were two precipitation modes of γ′ precipitates: intragranular dispersed precipitation and grain boundary discontinuous precipitation. The number and size of intragranular γ′ precipitates increased with the increase in aging temperature. During the coarsening process, the γ′ precipitates were kept spherical. When the aging temperature was above 740 ℃, the discontinuous precipitation reaction occurred under the combined effect of grain boundary migration and solute diffusion-controlled equilibrium phase growth. According to SEM images, there were four different kinds of morphologies of discontinuous precipitated cellular γ′ at the grain boundaries. They were lamellae precipitates, short rod precipitates, granular precipitates and bidirectional parallel precipitates. When the aging temperature was between 650 ℃ and 740 ℃, the strength of the alloy increased rapidly due to the precipitation of a large number of intragranular spherical γ′, and the precipitation of grain boundary cellular γ′ was one of the main reasons for the toughness of alloy decreased rapidly above 740 ℃.

Thermal stability of linear siloxanes and their mixtures

The working fluid thermal stability is one of the crucial features of an effective organic Rankine cycle. Hexamethyldisiloxane (MM - C6H18OSi2) and octamethyltrisiloxane (MDM - C8H24O2Si3) are siloxane fluids currently exploited in high temperature organic Rankine cycles. However, data about their thermal stability are scarce or absent in literature. This manuscript presents a study of their behavior and decomposition at operating temperatures in the range 270–420°C.The assessment of thermal stability can be performed with several methods, which are either based on pressure anomalous variation in isothermal stresses or on the deviation of the saturation curves experimentally obtained before and after the fluid is thermally stressed. An enhanced method is proposed here, based on chemical analysis of both vapor and liquid phases of the sample before and after it is subjected to thermal stress. A comparison of the pre- and post-stress vapor–liquid equilibrium curve complements the analysis.Results proved a higher stability for MM than for MDM. Moreover, due to the current interest in applying mixtures in organic Rankine cycles, an equimolar mixture of MM and MDM was also tested, which exhibit a behavior that appears to be different from the simple superimposition of pure fluid ones.

Optimization of preparation parameters of ceramic pot water filters for potential application of microbial and fluoride removal from groundwater

The need to make clean water accessible and affordable for low-income countries is crucial. This study examines the suitability of various clays for Ceramic Pot Water Filters production and groundwater treatment for effective microbe and fluoride removal. For this study, three clays were collected from different geographical locations in Ethiopia,i.e., Hosaenna Clay, Babawuha Clay, and Leku Clay. Organic additives such as sawdust and eragrostis tef husks were used to increase the porosity of the Ceramic Pot Water Filters. The Atterberg limit and particle size distribution tests revealed that BC and HC have moderate to high plasticity and mouldability, making them suitable for CPWF production. The clay chemical composition, phase analysis, and thermal properties were determined using XRF, XRD, and TGA/DTA. The turbidity, fluoride level, total dissolved solids, and pH of the groundwater decreases, from 13 to 0.45 NTU, from 3.4 to 0.053 mg/100 mL, from 1245 to 360 mg/l, and from 8.4 to 7.3, respectively; all of which are within the acceptable range of WHO drinking water standards. Microbial removal tests show that the CPWFs removed 99.3%–100% of total coliform bacteria and 98.48%–100% of fecal coliform bacteria from groundwater. Therefore, this work paves the way to fabricate a clay-based ceramic water filter for low-income countries to provide affordable household groundwater treatment technology for microbial and excess fluoride removal.