Electron Probe X-ray Microanalysis Research Articles

Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS2.

Ternary potassium-iron sulfide, KFeS2, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, etc. While some of the measurements can be satisfactorily described, the deficiency of the entropy changes upon the magnetic transition and the spin state of the iron ion remains a challenge for the further understanding of magnetism. In this work, high-quality single-crystalline samples of KFeS2 were grown by the Bridgman method, and their stoichiometry, crystal structure, and absence of alien magnetic phases were checked, utilizing wave-length dispersive X-ray electron-probe microanalysis, powder X-ray diffraction, and 57Fe Mössbauer spectroscopy, respectively. An ab initio approach was developed to calculate the thermodynamic properties of KFeS2. The element-specific phonon modes and their density of states (PDOS) were calculated applying the density functional theory in the DFT + U version, which explicitly takes into account the on-site Coulomb repulsion U of electrons and their exchange interaction J. The necessary calibration of the frequency scale was carried out by comparison with the experimental iron PDOS derived from the inelastic nuclear scattering experiment. The infrared absorption measurements confirmed the presence of two high-frequency peaks consistent with the calculated PDOS. The calibrated PDOS allowed the calculation of the lattice contribution to the specific heat of KFeS2 by direct summation over the phonon modes without approximations and adjustable parameters. The temperature-dependent magnetic specific heat evaluated by subtraction of the calculated phonon contribution from the experimental specific heat provides a lower boundary for estimating the reduced spin state of the iron ion.

Phase transformations and thermodynamic properties of oxide systems

A new approach to obtain amorphous oxides was investigated both theoretically and experimentally using X-ray diffraction (XRD) and electron probe microanalysis (EPMA) techniques. In this work, the conventional sol-gel method was modified by the addition of malic acid as an oxidizing agent and successfully applied to obtain two oxides Al2O3 & Fe2O3 with the amorphous structure. The results of the modified sol-gel method were compared to those obtained by thermal decomposition of corresponding salts, and the advantage of new technique was clearly demonstrated. Thermal stability of the obtained amorphous oxides was examined by the differential scanning calorimetry (DSC). It was found that amorphous Al2O3 is stable up to 790 – 810 °C, while amorphous Fe2O3 recrystallises at about 160 – 180 °C, depending on the heating rate.

Phase equilibria in TiO2-rich part of the MgO–CaO–TiO2 system at 1500–1600 °C

The equilibrium phase relations of the MgO–CaO–TiO2 system were investigated at 1500–1600 °C in air using the high-temperature isothermal equilibration of samples in platinum crucibles followed by the rapid quenching technique. The phase compositions were analyzed using an electron probe X-ray microanalyzer (EPMA). The isothermal sections at 1500 °C and 1600 °C were constructed based on the experimentally determined liquid phase compositions. The present results deviate significantly from previous observations as well as the predictions by MTDATA and FactSage using their oxide databases, in particular in the perovskite primary phase field.

Phase equilibria in Ni–Ti–Ta ternary system

Phase diagrams of two isothermal sections of the Ni–Ti–Ta ternary system at 1000 and 1200 °C in a full composition range were determined by X-ray diffraction and electron probe microanalysis. The experimental results indicated a ternary compound τ phase with low solid solubility and composition ranges of (16.3–22.4) at.% Ta, (15.9–24.1) at.% Ti and (58.5–60.0) at.% Ni at 1000 °C. The two terminal solid solutions (bcc-(Ta) and β-Ti) formed a continuous solid solution at 1000 and 1200 °C. A certain amount of Ti can dissolve into Ni–Ta intermetallic compounds near the Ni–Ta side, with the highest value of 21.9 at.% observed in the Ni2Ta compound at 1000 °C.

Integrated experimental and thermodynamic modeling study of phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal for characterizing refractory-slag interactions

An integrated experimental and thermodynamic modeling study of the phase equilibria in the ‘CuO0.5’-MgO-SiO2 system in equilibrium with liquid Cu metal has been undertaken to better understand the reactions between MgO-based refractories and liquid slag in copper converting and refining processes. New experimental phase equilibria data at 1250–1680 °C were obtained for this system using a high-temperature equilibration of synthetic mixtures with predetermined compositions in silica ampoules or magnesia crucibles, a rapid quenching technique, and electron probe X-ray microanalysis of the equilibrated phase compositions. The system has been shown to contain primary phase fields of cristobalite (SiO2), tridymite (SiO2), pyroxene/protoenstatite (MgSiO3), olivine/forsterite (Mg2SiO4), periclase (MgO), and cuprite (Cu2O). Three regions of 2-liquid immiscibility were found—two in the high-silica range of compositions above the cristobalite primary phase field (close to ‘CuO0.5’-SiO2 and MgO–SiO2 binaries) and one in the low-SiO2, high-‘CuO0.5’ compositional region above the periclase and olivine phase fields. The results obtained in this study indicate that silica in high-copper refining slags likely led to olivine and pyroxene phase formation, increased solubility of MgO in liquid slag, and decline in the performance of MgO-based refractories. New experimental data were used in the development of a thermodynamic database describing this pseudo-ternary system.

Investigation on the Matte/Slag/Spinel/Gas Equilibria in the Cu-Fe-O-S-SiO2-(CaO, Al2O3) system at 1250 °C and pSO2 of 0.25 atm

ABSTRACT The equilibrium-phase relations between copper mattes and spinel-saturated iron silicate slags were investigated at 1250°C and pSO2 of 0.25 atm. The experiments were conducted in synthesized spinel crucibles (Fe3O4) in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature isothermal equilibration/quenching technique. The equilibrium-phase compositions were characterized using an electron probe X-ray microanalyzer. The compositions of matte and slag were displayed as a function of matte grade or oxygen partial pressure. The present results obtained at spinel saturation in the matte-slag equilibrium system were compared with observations in the literature. This study improves the experimental thermodynamic data on the matte-slag-spinel-gas equilibria systems.

SPECIATION FEATURES OF GOLD IN ORES AND MINERALS OF THE NATALKINSKOE DEPOSIT (NORTH-EAST RUSSIA)

The distribution and speciation features of gold in ores and minerals of the Natalkinskoe gold deposit (North-East Russia) are studied using light microscopy (LM), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), X-ray electron probe microanalysis (EPMA), "phase" chemical analysis with atomic absorption spectrometry (PCA-AAS) and atomic absorption spectrometry with analytical data selections for single crystals (AAS-ADSSC). The vein and streaky-vein ores are high-grade ores, whereas veinlet-disseminated ores are less rich and disseminated ores are poor in gold. Up to 85 % of the gold in the ores is in a free native state, associated with quartz and sulfide minerals. LM, SEM-EDX and EPMA reveal that the predominant gold grains are 0.01 to 2.00 mm in size and at a fineness of 720 to 900 ‰. The finely dispersed and submicron elemental gold particles (Au0) amounted to 20 % and are mainly enclosed into arsenopyrite and pyrite. According to PCA-AAS data, the highest Au concentrations (up to 1383 ppm) are recorded in arsenopyrite; lower contents are typical of pyrite (up to 158.2 ppm). In these sulfides, two non-mineral species of "invisible" Au are the structurally bound and surface-bound species recognized by AAS-ADSSC. The structural Au is included in the mineral structure. The surface-bounded Au prevails and is confined to nano-sized, non-autonomous phases (NAPs) on the sulfide surface. In common with "invisible" Au, the micro-sized particles of native gold are often observed on the surface and within the surface layers of sulfide crystals. This is consistent with the model of post-growth transformations of nano-sized NAPs, resulting in the formation of nano and micro-sized Au0 particles. It is expected that the major part of gold contained in arsenopyrite and pyrite as finely dispersed and submicron particles, as well as the surface-bound gold in NAPs, can be won with modified current schemes of gold concentration, which enhances the value of the gold ore mining.

Experimental phase equilibria study and thermodynamic modelling of the PbO-“FeO”-SiO2-ZnO, PbO-“FeO”-SiO2-Al2O3 and PbO-“FeO”-SiO2-MgO systems in equilibrium with metallic Pb and Fe

Phase equilibria of the PbO-“FeO”-SiO2-ZnO, PbO-“FeO”-SiO2-Al2O3 and PbO-“FeO”-SiO2-MgO slags with liquid Pb metal, solid or liquid Fe metal and solid oxides (cristobalite and tridymite SiO2, willemite (Zn,Fe)2SiO4, wustite (Fe,Al)O1+x, spinel (Fe,Al)3O4, olivine Fe2SiO4, corundum (Al,Fe)2O3, mullite Al6Si2O13 and pyroxene (Mg,Fe)SiO3) were investigated at 1125–1670 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica, corundum or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Si, Zn, Al and Mg concentrations in the liquid and solid phases with the electron probe X-ray microanalysis (EPMA) was used. Present data can be used to improve the thermodynamic models for all phases in this system.

Integrated Experimental and Thermodynamic Modeling Investigation of Phase Equilibria in the PbO\u2013MgO\u2013SiO2 System in Air

Magnesium oxide-based refractory materials are used industrially to contain the chemically aggressive slags present in lead smelting systems. In the present study an integrated experimental and thermodynamic modeling approach was taken to provide fundamental information on the chemical reactions taking place in these systems. New experimental phase equilibria and liquidus data were obtained for the PbO–MgO–SiO2 system in air in the temperature range 750 °C to 1740 °C. In the MgO–SiO2 binary, new experimental results were obtained at 1550 °C to 1740 °C and compared to the available thermodynamic data in the literature. The experiments were carried out using the high-temperature equilibration of oxide powder mixtures followed by rapid quenching of the samples. Electron probe X-ray microanalysis (EPMA) was used to determine the compositions of the solid and liquid phases present at equilibrium conditions. Phase equilibria and liquidus isotherms in the cristobalite and tridymite (SiO2), pyroxene (protoenstatite MgSiO3), olivine (forsterite Mg2SiO4), barysilite (Pb8MgSi6O21), massicot (PbO) and periclase (MgO) primary phase fields were measured, and the extent of the high-silica two-liquid immiscibility gap in equilibrium with cristobalite was determined. The experimental results were used to optimize the parameters in a thermodynamic database that was subsequently used to describe this multi-component, multi-phase system and predict the liquidus for the PbO–MgO–SiO2 system. The new data were used to characterize the chemical interactions of magnesia-based refractory with PbO–MgO–SiO2 slags.

Effect of Chromium on Microstructure and Oxidation Wear Behavior of High-Boron High-Speed Steel at Elevated Temperatures.

In order to investigate the effect of Cr content on the microstructures and oxidation wear properties of high-boron high-speed steel (HBHSS), so as to explore oxidation wear resistant materials (e.g., hot rollers), a scanning electron microscope, an X-ray diffractometer, an electron probe X-ray microanalysis and an oxidation wear test at elevated temperatures were employed to investigate worn surfaces and worn layers. The results showed that the addition of Cr resulted in the transformation of martensite into ferrite and pearlite, while the size of the grid morphology of borides in HBHSSs was refined. After oxidation wear, oxide scales were formed and the high-temperature oxidation wear resistance of HBHSSs was gradually improved with increased additions of Cr. Meanwhile, an interaction between temperature and load in HBHSSs during oxidation wear occurred, and the temperature had more influence on the oxidation wear properties of HBHSSs. SEM observations indicated that a uniform and compact oxide film of HBHSSs in the worn surface at elevated temperatures was generated on the worn surface, and the addition of Cr also reduced the thickness of oxides and inhibited the spallation of worn layers, which was attributed to improvements in microhardness and oxidation resistance of the matrix in HBHSSs. A synergistic effect of temperature and load in HBHSSs with various Cr additions may dominate the oxidation wear process and the formation and spallation of oxide films.

Various Carbon Materials Action on the Burning Rate Modifiers of Low-Calorie Double-Base Propellant

ABSTRACT The effect of a combined ballistic modifier consisting of copper or nickel salts and carbon materials, such as carbon black and multi-walled carbon nanotubes, on the burning rate and the structure of the quenched combustion surface of low-calorie double-base propellant have been studied. Carbon nanotubes individually have a tangible effect on the burning rate, comparable to individual ballistic modifiers. CNT have the most significant effect on the efficiency of nickel-containing modifiers, significantly exceeding the impact of soot. Using scanning electron microscopy and X-ray electron-probe microanalysis, it has been established that CNT forms a more developed and more robust carbon frame on the combustion surface than carbon black. Significant burning rate growth is observed only when a carbon frame on the combustion surface is formed and substantial accumulation of the modifier particles occurs. The greater the degree of carbon frame coverage of combustion surface with the modifier, the greater the catalytic effect.

NEW DATA ON THE CRYSTAL-CHEMISTRY OF METAMICT MINERALS FROM THE VELYKA VYSKA SYENITE MASSIF (UKRAINIAN SHIELD)

The structural properties and composition of metamict minerals, namely allanite, chevkinite, and britholite, occurring as inclusions in allanite from feldspar syenites of the Velyka Vyska massif (Korsun-Novomyrgorod pluton, Ukrainian Shield) were investigated by X-ray diffraction and electron probe microanalysis (EPMA). The age of the syenites is 1.7-1.8 Ga, which corresponds to their formation ages within the Ukrainian Shield. X-ray analysis shows that of the original samples of chevkinite and allanite give a broad diffraction peak between 16—28° 2Θ as well as Bragg reflections in the region of the most intense reflections of semimetamict allanite and britholite, indicating the metamict state of chevkinite and the semimetamict state of allanite. The content of radioactive Th found in the chevkinite (0.25-0.33 apfu) is higher compared to its amount in allanite (0.024-0.033 apfu). Calculated unit-cell parameters of the chevkinite and allanite samples showed that their structures underwent significant changes after annealing. There is a slight distortion of the chevkinite unit cell related to a decrease in the a and an increase in b and c edges. A decrease in b and the increase in c in the allanite is caused by a redistribution of cations in the structure and an oxidation of iron, Fe2+ → Fe3+, during heating. Thereby the stability of the allanite structure decreases and it ultimately breaks down. The structural sites A and A2 in chevkinite and allanite are mainly occupied by REEs of the cerium group. The amount of Y is minor. The substitution mechanism А2(REE)3+ + М3М2+ → А2Са2+ + М3М3+(allanite) and M2Fe3+ + M3,4Ti4+↔ M2Fe2+ + M3,4Nb5+ (chevkinite) occur. The M2 site in the structure of chevkinite and M3 in allanite contain more Fe2+ than Fe3+. This leads to a weakening of the bonds in their structures, and a stepwise breakdown and partial or total metamictization of their structures. The britholite inclusions in allanite belong to the Y variety. They were probably formed much later than allanite and chevkinite in the Velyka Vyska massif. According to the EPMA results, namely BSE-images and REE content determinations, allanite and chevkinite formed almost simultaneously.

Experimental investigation of the Ni-V-W ternary phase diagrams

Phase equilibria in the Ni-V-W ternary system have been experimentally investigated. The phases and their compositions of Ni-V-W alloys annealed at 900 and 1100 °C were studied via X-ray diffraction (XRD) and electron probe micro-analysis (EPMA) measurements. The isothermal section measured at 1100 °C showed a three-phase region of fcc + bcc + (σ). Two three-phase regions [fcc + bcc + (σ) and WNi4 + WNi + bcc] were detected in the samples annealed at 900 °C. No ternary compounds were detected in the present work. The solubility of V in the Ni-W binary compounds, i.e. WNi4, WNi, W2Ni, at 900 °C was found to be extremely small (maximum 1.12 at. % V). The solubilities of W in (σ) at 900 and 1100 °C were found to be 2.14 at. % and 3.17 at. %, respectively. The complete isothermal sections at 900 and 1100 °C of the Ni-V-W system were then constructed, which are needed for a thermodynamic optimization of the ternary system.

EXPERIMENTAL METHODS FOR STUDYING THE RESOURCE VALUE OF DUMP BLAST FURNACE SLAGS

The study of the properties of blast-furnace slags requires an integrated approach, including various research methods. The purpose of the work is to substantiate the resource value of the Zaporizhstal dump blast furnace slag. The research methods were used: X-ray phase, petrographic, gamma-spectrometric analysis and electron probe microanalysis. The slag is dispersed into fractions, since the slag minerals have different hardness. Fractions (mm) were investigated in the work: >20 2.5–5, <0.63. X-ray phase analysis made it possible to reveal in the crystalline part of blast-furnace slag minerals that are technically valuable in the production of binders: 3CaO∙2SiO2, SiO2, 2CaO∙Al2O3∙SiO2, α-2CaO∙SiO2, 2CaO∙MgO∙2SiO2, α-CaO∙SiO2. Minerals akermanite, bredigite, pseudo-wollastonite have hydraulic activity. It is shown that the mass fraction of the amorphous component is half the mass of the blast furnace slag. The high content of substances in the amorphous state confirms the possibility of sorption of extraneous ions and compounds. The found elements Potassium, Sodium, Sulfur, Chlorine, Cuprum and Titanium are not part of the minerals. Slag contains less than 1% of the total amount of Fe, Ti and Cu, belonging to the 3rd class of hazardous substances. The maximum content of Potassium, Sodium and Titanium is typical for the fraction 2.5–5 mm. The most basic is the fraction <0.63 mm (pH 9.7), for the 2.5–5 mm fraction pH 9.1, the most acidic fraction >20 (pH 8.2). By the value of the toxicity index (4.3–5.4) and the III hazard class, dump blast furnace slag «Zaporizhstal» as a moderately hazardous waste can be used as a secondary raw material in the construction industry. The database on the content of natural radionuclides in technogenic raw materials has been updated. It has been proven that slag and its individual fractions contain natural radionuclides 40К, 226Ra, 232Th. The main contribution to the value of Сef is made by the 226Ra radionuclide, then by 232Th. The excess of specific activity is expressed for the 2.5–5 mm fraction. The I class of radiation hazard is defined, which allows the use of slag in construction without restrictions. Dump blast furnace slag «Zaporizhstal can be recommended in the production of inorganic binders « by the totality of chemical indicators.

Experimental phase equilibria studies in the “CuO0.5”-CaO-SiO2 ternary system in equilibrium with metallic copper

Phase equilibria studies were undertaken on the “CuO0.5”-CaO-SiO2 system in equilibrium with metallic copper to provide fundamental information on the reactions taking place between slags and refractory materials in metallurgical furnaces. The liquidus isotherms between 1160 and 1706 °C in the tridymite and cristobalite (SiO2), cuprite (Cu2O), pseudowollastonite (CaSiO3), rankinite (Ca3Si2O7) and dicalcium silicate (Ca2SiO4) primary phase fields, and the 2-liquid miscibility gaps in the silica-rich corner and low-silica area of the system, were experimentally determined using the equilibration and quenching technique, followed by the electron probe X-ray microanalysis (EPMA) of phase compositions. The liquidus surface of the “CuO0.5”-CaO-SiO2 system has been constructed. The dissolution of copper oxide in the tridymite and cristobalite (SiO2) was shown to be negligible. The data obtained are used for the optimization of the thermodynamic database for the copper-containing systems.

Experimental Determination of Phase Equilibria in the Na2O-SiO2-WO3 System

The present study investigated phase equilibria in the Na2O-SiO2-WO3 system experimentally using high-temperature equilibration, quenching, and electron probe X-ray microanalysis (EPMA). New thermodynamic information on the Na2O-SiO2-WO3 system was derived based on the newly obtained experimental results and data from the literature. The primary phase fields of sodium metasilicate, sodium disilicate, and tridymite were determined along with the isotherms at 1073, 1173, and 1273 K. The solubilities of WO3 in SiO2, Na2Si2O5, and Na2SiO3, and the solubility of SiO2 in Na2WO4 were accurately measured using EPMA. Comparisons between the existing and newly constructed phase diagram were carried out and the differences are discussed. The phase equilibrium data will be beneficial to the future development of sustainable tungsten industries and thermodynamic modelling in WO3 related systems.

Effect of laser surface cleaning of corroded 304L stainless steel on microstructure and mechanical properties

In this study, a high-power Nd:YAG laser is used to remove a corrosion layer on the surface of 304L stainless steel (SS304L). A laser power of 1140 W with different hatch distances and the number of repetitions is employed for corrosion removal. As shown by an electron probe X-ray microanalyzer, corrosion removal is successfully achieved via laser surface cleaning (LSC) with the small hatch distance or the large number of repetitions. However, corrosion residues remain at the surface of SS304L after the LSC process with the large hatch distance and the small number of repetitions. The effect of LSC process on the microstructure and mechanical properties of SS304L is investigated. The electron backscatter diffraction and transmission electron microscopy analyses reveal that the microstructure of SS304L depends significantly on the LSC conditions. In the LSC process with the large hatch distance and the small number of repetitions, only an increase in dislocation density is discovered. However, the LSC process with the small hatch distance or the large number of repetitions introduces dense dislocation structures, deformation twins, grain refinement, and precipitation. This microstructural alteration owing to the LSC process modifies the mechanical properties of SS304L in terms of hardness and tensile strength.

Development of a cleaner route for Aluminum–Vanadium alloy production

Aluminum–Vanadium (AlV) alloy is essential for high-performance titanium material. Calcium fluoride (CaF2) is currently used in AlV production and has inevitable drawbacks in terms of product quality and environmental impact. In order to avoid its potential hazards, lime (CaO) as an alternative flux material in producing AlV alloy has been investigated in laboratory and by industrial trials in the present study. The samples were analyzed by Electron Probe X-ray Micro-analyzer (EPMA) and X-ray Diffraction (XRD), regarding the phases formed and corresponding compositions. A slag with good fluidity can protect inner alloy from being oxidized and also promotes the separation between slag and alloy, with a goal to reduce alloy inclusions in slag to enhance the yield. The results showed that using CaO as flux with appropriate amount greatly improved the yield and quality of the AlV alloy and avoided environmental pollution caused by fluoride evaporations.

Metallization by Sputtering to Improve the Bond Strength between Zirconia Ceramics and Resin Cements

Zirconia has been used as a prosthesis material for over a decade because of its excellent mechanical properties and esthetics. The surface treatment for zirconia generally involves sandblasting and the application of primers for favorable bond strength between the surface and resin. However, sandblasting causes the microcracking and chipping of the zirconia surface. To overcome these challenges, the metallization of the zirconia surface was performed. Ti and Au were sputtered on yttria stabilized zirconia (YSZ) disks and heated to 800 °C for 15 min in air. These disks were bonded to stainless-steel rods using resin cement. Then, shear bond strength tests were performed using an Instron-type testing machine. The shear bond strength of the Ti sputtering group was significantly higher than that of the other groups. According to the results of X-ray photoelectron spectroscopy and electron probe microanalysis, the Ti-sputtered YSZ surface contained both sub-titanium oxide and titanium oxide before heating. Sub-titanium oxide was converted to titanium oxide by heating. These results suggest that metallization using Ti is effective for zirconia surface treatment to improve the shear bond strength between YSZ and resin cement. This metallization technique for YSZ has potential in clinical applications.

Experimental Measurements of Slag/Matte/Metal/Tridymite Phase Equilibria in the Cu-Fe-O-S-Si System at 1200ºC

ABSTRACT An experimental study has been carried out to determine the compositions of the slag/matte/metal/tridymite phases in equilibrium in the Cu-Fe-O-S-Si system at 1200℃. The measurements covered the full range of matte compositions from copper-free mattes to white metal, i.e. from 0 to 80 wt% of copper in matte. The research methodology involved high-temperature equilibration, quenching of the samples and accurate measurement of the phase compositions by electron probe X-ray microanalysis. The oxygen concentrations in mattes were directly measured using the EPMA. A comprehensive set of experimental equilibrium data has been obtained for coexisting matte, slag, Cu-Fe metal alloy and Fe-Cu metal alloy phases. It has been shown that solid iron-copper alloys were present at matte grades below 56 wt% Cu, while liquid copper-iron alloys were formed for matte grades higher than 56 wt% Cu. The experimental measurements have been compared with data reported in the literature and the trends calculated using the thermodynamic model descriptions of the system.