Electron Probe X-ray Microanalysis Research Articles

Effect of Ce on structural evolution and corrosion resistance of HRB500E rebar corrosion layer

HRB500E rebar is a low-alloy high-strength steel with excellent mechanical properties and good plasticity but suffers from deficient corrosion resistance. This can be solved by adding trace elements, including rare earth elements. Herein, the corrosion-resistant behavior of rebar was evaluated by weightlessness testing and electrochemical measurements, and the effects of Ce on the structural evolution of the corrosion product layer were investigated by scanning electron microscopy (SEM), Electron Probe X-ray Micro-Analyzer (EPMA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that adding Ce to the rebar improved the densification of the reinforcing surface corrosion products, as well as reduced the corrosion rate of the experimental rebar. Compared to C0 sample without Ce, the rebar sample containing 0.044 wt.% Ce displayed increased Ecorr by 0.051 V, decreased Icorr by 15.573 mA cm−2, enhanced Rc of the corrosion product layer by 112.71 Ω cm2, incremented α-FeOOH content in the corrosion product layer, and boosted ratio of α/γ* in the corrosion product layer by 10.11%. Furthermore, the oxide (CeO2) formed by Ce in the corrosion layer of the rebar bar surface existed in the rust layer, resulting in a stable corrosion product layer with improved blocking ability of the corrosive medium. Overall, the addition of Ce at certain ratios looks promising to produce HRB500E rebar with excellent corrosion resistance and extended service life under harsh conditions.

Integrated experimental and thermodynamic modeling study of slag-matte-metal equilibrium in the Pb–Fe–O–S–Si-(Al, Ca, Zn) systems at 1100–1200 °C

Integrated experimental and thermodynamic modeling study was undertaken to characterize the effect of Al, Ca and Zn on the partitioning of elements between the slag, matte and metal phases in the Pb–Fe–O–S–Si-(Al), (-Ca), and (-Zn) systems in equilibrium with tridymite at 1100–1200 °C. The experimental methodology involved closed system equilibration in sealed ampoules, quenching and electron probe X-ray microanalysis (EPMA) of compositions of phases. FactSage thermodynamic database obtained by combining earlier assessments of sub-systems was used to plan the targeted experiments, and the results of new experiments were used to improve the thermodynamic database. Important effects were revealed for the conditions of the present study: CaO decreases the concentration of Pb and S in slag; Al2O3 has small effect on Pb in slag, but significantly decreases the concentration of S in slag; ZnO has small effect on Pb in slag, but increases the concentration of S in slag. These experimentally measured effects were reproduced by the model.

Characterizing oxidation, thickness, and composition of metallic glass thin films with combined electron probe microanalysis and X-ray photoelectron spectroscopy

Metallic glass thin films (MGTFs) are a recently developed class of alloy coatings with potential applications ranging from biomedical devices to electrical components. Their tribological performance in service conditions is dictated by MGTF bulk composition but can be limited by the native oxide surface that inevitably forms upon exposure to atmosphere. Surface oxidation, thickness, and composition of ZrCuNiAl MGTFs were characterized using a combination of X-ray photoelectron microscopy (XPS) and electron probe microanalysis (EPMA). MGTF samples with nominal thicknesses of 50, 500, and 1500 nm were sputtered onto Si and SiN wafer substrates within a high vacuum deposition chamber and their amorphicity was confirmed by X-ray diffraction. XPS depth profiling identified the thin film composition and showed that the surface oxide was dominated by a mixed layer of mostly ZrO2, a little oxidized Al, and some metallic Zr. EPMA X-ray intensities were acquired as a function of beam energy to excite characteristic X-rays from different depths of the MGTFs and reconstructed using open-source thin film analysis software BadgerFilm, to determine the composition and thickness of sample layers. EPMA results constrain the composition to be Zr54Cu29Al10Ni7 within 0.7 at. % variation and total thicknesses to be 49, 470, and 1546 nm. Using the oxide composition identified from XPS depth profiling as an input for BadgerFilm analysis, EPMA results indicate the surface oxidation layer on each of the thin film samples was 6.5 ± 1.1 nm thick and uniform across a 0.25 mm region of the film.

Experimental Investigation of Phase Equilibria in the Al–Mo–Hf Ternary System at 400 °C and 600 °C

This study investigates the phase equilibria of the Al-Mo-Hf ternary system at 400 °C and 600 °C using X-ray diffraction (XRD) and electron probe microanalysis (EPMA/WDS) techniques. Seven three-phase and five two-phase regions were identified at 400 °C, while eight three-phase and four two-phase regions were identified at 600 °C. Despite variations in the solid solubility ranges of certain compounds, the distribution of phase zones in the isothermal cross-section remained consistent at both temperatures. Using the experimental results and logical deductions, isothermal cross-sections were constructed for the Al-Mo-Hf ternary system at 600 °C and 400 °C.

High-Temperature Cyclic Oxidation Behavior and Microstructure Evolution of W- and Ce-Containing 18Cr-Mo Type Ferritic Stainless Steel.

Due to the recurrent starting and stopping operations of automobiles during service, their engines' hot ends are continually subjected to high-temperature cyclic oxidation. Therefore, it is crucial to develop ferritic stainless steels with better high-temperature oxidation resistance. This study focuses on improving the high-temperature cyclic oxidation performance of 18Cr-Mo (444-type) ferritic stainless steel by alloying with high-melting-point metal W and the rare earth element Ce. For this purpose, a high-temperature cyclic oxidation experiment was designed to simulate the actual service environment and investigate the high-temperature cyclic oxidation behavior and microstructure evolution of 444-type ferritic stainless steel alloyed with W and Ce. The oxide structure and composition formed during this process were analyzed and characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS) and electron probe X-ray micro-analyzer (EPMA), in order to reveal the mechanism of action of W and Ce in the cyclic oxidation process. The results show that 18Cr-Mo ferritic stainless steel alloyed with W and Ce exhibits an excellent resistance to high-temperature cyclic oxidation. The element W can promote the precipitation of the Laves phase between the matrix and the oxide film, and the small-sized Laves phase can inhibit the interfacial diffusion of oxidation reaction elements and prevent the inward growth of the oxide film. The element Ce can refine oxide particles and reduce the thickness of the oxide film. CeO2 particles within the oxide film can serve as nucleation sites for the formation of oxide particles from reactive elements, and they also contribute to pinning the oxide film, thereby enhancing its adhesion.

Studying the features of complex beryllium-containing silicate phases co-crystallization in zonal samples using the x-ray electron probe microanalysis method

Research subject. Silicate ingots containing four species-forming components Be, Mg, Al, and Si and belonging to the crystallization region of beryllium indialite (with the formula of Mg2BeAl2Si6O18 and a beryl-type structure). Aim. To investigate the fundamental problem of identifying the patterns of matter differentiation and the stable and metastable phase formation in silicate matrices. Methods. The evolution of the phase composition of silicate melts was registered using a temperature gradient method. Results. New data on the features of phase transformations in silicate melts belonging to the region of beryllium indialite were obtained by electron probe microanalysis (EPMA). Co-existing metastable and stable mineral phases were identified, and the similarity of their compositions with different structures was shown. The nature of impurity phases at each stage of crystallization was established. Conclusions. The evolutionary sequence of phase associations ensuring the crystallization of beryllium indialite and metastable phases of a similar composition, the nature of which is determined by the initial ratio of components, was experimentally recorded. The range of possible phase associations that co-crystallize or replace a stable phase with a beryl structure in melts from the region of existence of beryllium indialite in the BeO–MgO–Al2O3–SiO2 system was extended. The selectivity of the coloring element chromium entry into various phases of the studied system is shown depending on the capabilities of their structure. The addition of a chromophore is a reliable criterion for visualizing successive layers, zones, and areas of changing phase associations in the final ingot.

The Effect of W, Cr, Mo Content on the Microstructure and Mechanical Properties of the Weld Interface of TiC Cermet and Low-Carbon Steel

In this study, the influence of W, Cr, and Mo on the microstructure and mechanical properties of the arc-welded interface of TiC cermet and low-carbon steel was investigated. MIG arc welding was employed to deposit muti-alloyed low-carbon steel flux-cored wire onto the surface of the TiC cermet to create the arc-welded interface. Analysis of the microstructure, phase composition, and shear fracture of the interface were conducted by OM (optical microscopy), SEM (scanning electron microscope), EMPA (Electron Probe X-ray Micro-Analyzer), and XRD (X-ray diffraction) methods. The results indicate that the order of influence on the performance of the welded interface is perceived as Cr > W > Mo. The preferred ratio of element content is W at 1.0 wt.%, Cr at 0.5 wt.%, and Mo at 2.0 wt.%. During the arc-welding process, W and Mo formed a rim structure of TiC particles to inhibit the dissolution of TiC particles, while Cr formed dispersed carbides in the bonding phase. The synergistic impact of these components resulted in the simultaneous enhancement of both the TiC particles and the bonding phase. This led to a significant increase in the shear strength of the TiC cermet welded interface to 787 MPa, marking an 83% improvement compared to the welded interface without reinforcement, which exhibited a shear strength of 430 MPa.

Analysis of slag chemistry in WEEE smelting using experimental and modelling study of the “CuO0.5”-ZnO-FeO-FeO1.5-CaO-SiO2-AlO1.5 system in equilibrium with Cu metal

The variability of the composition of recycled copper-containing materials requires enhanced control and understanding of slag chemistry in the secondary pyrometallurgical processing, when compared to primary copper smelting. In the black copper route for recycling waste electronic and electrical equipment (WEEE), slags exhibit high concentrations of alumina and zinc oxide. The simplest system governing phase equilibria at the reducing smelting stage of the black copper process is “CuO0.5”-ZnO-FeO-FeO1.5-CaO-SiO2-AlO1.5. In the present study, slags within this system were equilibrated with liquid copper Cu and solid Fe metallic alloys, quenched and characterized by the Electron Probe X-ray Microanalysis (EPMA). The range of compositions was selected based on the information about the process available in literature. The study focused on the liquidus and proportion of solid spinel in the temperature range from 1100 to 1300 °C. Precise control of the proportion of solids can enhance the stability of refractory materials against corrosive slags while maintaining entrained metal droplets at reasonably low level. Additionally, experimental correlations between the solubility of copper in the oxide liquid and the partial pressure of oxygen were developed for the Zn-free slags in equilibrium with metallic copper at 1200 and 1300 °C. All experimental results were compared to thermodynamic predictions using recent models and FactSage® software. Uncertainties were identified to be used in further model improvement.

Development and application of matte/speiss/metal thermodynamic database for optimization of processing of drosses, dusts and reverts from lead, zinc and copper production

Detrimental elements such as arsenic and antimony tend to accumulate in dusts and drosses of lead-zinc as well as copper smelters. These by-products are commonly treated in dedicated reductive smelting units producing Cu-rich matte, As-Sb-collecting speiss and Pb-rich metal, as well as liquid slag. Such process would have a complex distribution of elements (Cu, Fe, Pb, Zn, Ni, Sn, Sb, As, Ag, Au, S, etc.) among four liquid phases. Thermodynamic calculations can be used for predictions and optimization of such processes. They must rely on accurate models developed in integration with experimental program. Present study reports results of recent progress in experimental and modelling studies of As, Sb-containing speiss systems and demonstration of calculations relevant for industrial conditions. Experimental methodology consisted of equilibration, quenching and electron probe X-ray microanalysis. Calculations were performed using FactSage software and thermodynamic database developed based on the dedicated recent experiments. The main findings of the paper are: a set of binary and ternary diagrams relevant to matte and speiss formation conditions; distribution of Ag and Au among liquid Pb and speiss in key quaternary systems; and distributions of 10 main elements for industrially relevant matte/speiss/metal multicomponent equilibria.

Fundamental experimental and thermodynamic modelling study in support of the lead battery recycling slag

Antimony, tin, and other higher value metals, as well as elements such as arsenic and lead, can be found in the slags produced during the lead battery recycling process. Gopher Resources operates lead battery recycling furnaces that use sodium slag systems for which there has been less thermodynamic research than more common slag systems. Better thermodynamic information could help improve the process efficiency and control of these furnaces, as well as the recovery of higher value metals. The present study focuses on experimental research and thermodynamic modeling of slags belonging to the Na-Si-Fe-O system, with minor elements including S, Sb, Sn, Pb, and As. Examples of important systems studied extensively for the first time include Fe-Sb-Si-O and Na-Sn-Si-O. Phase equilibria methods are used to determine all the interaction parameters between the impurity metals and the main components of the slag. The experimental methodology involves equilibration, quenching, and electron-probe X-ray microanalysis of the samples. The modified Quasichemical model is used to describe the thermodynamics of the slags. The model also takes into account possible formation of matte/metal/speiss liquids, and numerous solid phases, which is important for understanding of fundamentals operation of various process units.

Metallogenetic epoch and material source of Be-pegmatite differentiated from biotite granite in Mufushan complex

The Mufushan Complex (MFSC) is a significant rare metal mineralized in the central China district and is renowned for its marked economic value of rare metal deposits. While the main rare metal mineralization (RMM) stage in the MFSC relates to the magmatic event of two-mica monzogranite, the mineralization event related to biotite monzogranite remains unknown. To fill this gap, this study focuses on porphyritic biotite monzogranite and adjacent Be-rich pegmatite samples obtained from Changqing Pegmatite No. 1, which is situated in the southeastern part of the MFSC. We subjected these samples to zircon U–Pb dating and Hf isotope analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and utilized an electron probe X-ray microanalyzer (EPMA) and LA–ICP–MS to examine the major and trace elements present in the muscovite samples. Our findings revealed precise chronological data for the geological history of Changqing, pinpointing the intrusion age of biotite monzogranite to 145.8 ± 1.1 Ma and the crystallization age of Be-rich pegmatite to 144.9 ± 1.1 Ma, firmly situating these events within the Late Jurassic to Early Cretaceous epoch. Regarding isotopic composition, zircon εHf (t) for granite ranged from −9.29 to −5.09, and their corresponding TDM2 ranged from 1788 to 1520 Ma. Similarly, zircon εHf (t) for pegmatite ranged from −7.89 to −5.47, and their corresponding TDM2 ranged from 1699 to 1544 Ma. These isotopic signatures strongly indicate a shared origin for the initial magma of granite and pegmatite. The partial melting of the thick Lengjiaxi Group tasedimentary strata serves as a material source for RMM. The transition from granite to pegmatite exhibits remarkable constancy in the primary components of muscovite. By examining its geochemical attributes, we observed synchronous decreases in FeO, MgO, SiO2, MnO, Be, Rb, and Cs, coupled with synchronous increases in Nb and Ta contents, along with Ta/Nb values. These findings strongly imply that the Changqing biotite monzogranite and Be-rich pegmatite originate from the continuous differentiation and evolution of a common magmatic source, establishing a clear genetic relationship between them. The MFSC has its origins in three distinct stages of magmatic activity and RMM spanning from 160 Ma to 120 Ma. Considering the distribution patterns of similar pegmatite veins, the metallogenic potential observed during the biotite granite stage may serve as an external indicator of marked mineralization within large batholiths.

Phase equilibria in the NiO-ZnO-SiO2 and PbO-NiO-ZnO-SiO2 systems

Experimental investigation and thermodynamic modeling of the phase equilibria in the (PbO)-NiO-ZnO-SiO2 system has been undertaken to characterize Ni behavior in high-Zn slags. Phase equilibria data at 790–1700 °C were obtained through equilibration of synthetic mixtures in sealed silica ampoules or Pt-Ir / Au foils, rapid quenching, and electron probe X-ray microanalysis. Phase equilibria and liquidus isotherms of the NiO-ZnO-SiO2 system in the tridymite/cristobalite SiO2, monoxide (Ni,Zn)O, zincite (Zn,Ni)O, olivine (Ni,Zn)2SiO4 and willemite (Zn,Ni)2SiO4 phase fields were measured and the extent of the 2-liquid immiscibility gap over cristobalite was determined. Additional solid solutions: larsenite Pb(Zn,Ni)SiO4 and melilite Pb2(Zn,Ni)Si2O7 were measured in the PbO-NiO-ZnO-SiO2 system. It was found that NiO partially substitute ZnO in larsenite and melilite and may form a complete range of solubility in barysilite Pb8(Zn,Ni)Si6O21. New data were used for developing a thermodynamic database to describe the Pb/Cu-containing complex system for characterizing Ni behavior in Zn-containing slags.

Behavior of Tantalum in a Fe-Dominated Synthetic Fayalitic Slag System—Phase Analysis and Incorporation

Pyrometallurgical processes produce slags that may contain valuable elements because of their high oxygen affinity. However, the concentration is extremely low, which causes losses. In fact, these elements, for example, tantalum and rare earth elements, are less than 1% recycled. To return such technologically important elements to the material cycle, pyrometallurgically is used to enrich them in the simplest possible compounds within the slag, which have favorable properties for recovery (morphology, crystal size, magnetic properties), allowing further mechanical separation. The purpose of modification of the slag system is to obtain engineered artificial minerals” (EnAM), a process in which targeted minerals with high element concentration are formed. In this article, this approach is investigated using tantalum-rich fayalitic slag, since this slag is commonly found in the industry for the pyrometallurgical treatment of waste electric and electronic equipment. Synthetic fayalitic slags in reducing environment under different cooling rates were produced with Ta addition. The characterization of the produced samples was carried out using powder X-ray diffraction (PXRD) and electron probe microanalysis (EPMA). Additionally, the speciation of Fe and Ta was accessible through X-ray absorption near-edge structure (XANES) spectroscopy. EPMA also provided a semiquantitative assessment of the Ta distribution in these individual compounds. In these slags, tantalum accumulated in perovskite-like oxidic and silicate compounds as well as in magnetic iron oxides. The enrichment factor is highest in tantalite/perovskite-type oxides (FexTayO6, CaxFeyTazO3) with up to 60 wt.% Ta and ‘tantalomagnetite’ (FeII(FeIII(2−5/3xTax)O4) with a maximum of ~30 wt.% Ta (only fast cooling). This is followed by a perovskite-like silicon containing oxide (XYO3) with 12–15 wt.% Ta (only slow cooling), and a hedenbergite-like compound (XYZ2O6) with a varying content of 0.3–7 wt.%. The Ta concentration in pure Fe, Fe(1-x)O, hercynitic spinel and hematite is negligible. Despite the very low phase fraction, the most promising EnAM compound is nevertheless perovskite-like tantalum oxide, as the highest enrichment factor was obtained. Tantalum-rich magnetite-like oxides also could be promising.

Influence of Si contents on the microstructure and corrosion resistance of the Zn−Al−Mg−Si alloys

Hot dip galvanized products are widely used in various aspects of production and life due to their excellent corrosion resistance. Some studies have added a fourth trace alloying element to the zinc aluminum magnesium coating to form a quaternary alloy for better performance. This article prepared two different types of Zn−Al−Mg alloy ingots with trace amounts of Si added by induction melting, consisting of Zn1Al1Mg0.01Si and Zn1Al1Mg0.05Si, and solidified them in a heating furnace with argon gas protection atmosphere. The precipitation process of Zn1Al1Mg(0.01,0.05)Si alloy components under non equilibrium and equilibrium solidification conditions was calculated. The initial crystalline phase of the alloy and the initial solidification temperature were predicted through phase diagram calculations. The microstructure and phase types of the alloy were analyzed using scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM). The electrochemical Tafel curves of Zn1Al1Mg(0.01,0.05)Si with different Si contents showed that the Zn1Al1Mg0.05Si has the highest corrosion potential and Zn1Al1Mg0.01Si has the lowest corrosion current which means the 1Al1Mg0.01Si alloy possesses the highest corrosion resistance. The Nyqust curves and bode curves also showed that the practical impedance of 1Al1Mg0.01Si alloy is higher than that of 1Al1Mg0.05Si. Moreover, electron probe X-ray micro-analyzer(EPMA) reveals the distribution of Si elements in the Zn1Al1Mg(0.01,0.05)Si. At present, there is little research on the microstructure and properties of quaternary alloys containing silicon. Therefore, studying the influence of silicon content on the microstructure and properties of alloys is of great significance.

Integrated Experimental Phase Equilibria and Thermodynamic Modelling Research and Implementation in support of progress of process pyrometallurgy towards sustainability

Responding to the many sustainability challenges facing the metallurgical industry, we report progress that has been made on the development of predictive tools that can be applied to a wide range of technologies. The aim is to provide accurate, fundamentally-based thermodynamic tools that can be used by industry to improve process efficiencies, metal recoveries and productivities, and reduce energy requirements of pyrometallurgical systems. The program involves an integrated experimental and thermodynamic modelling research on phase equilibria in complex multi-component, multi-phase gas-slag-matte-speiss-metal-solids system with the Cu2O-PbO-ZnO-FeO-Fe2O3-CaO-Al2O3-MgO-SiO2-S major and As-Sn-Sb-Bi-Ag-Au-Ni-Co-Cr-Na minor elements. The experiments involve high temperature equilibration in controlled gas atmospheres, rapid quenching and direct measurement of equilibrium phase compositions with quantitative microanalytical techniques, including electron probe X-ray microanalysis and Laser Ablation ICP-MS. The thermodynamic modelling is undertaken using FactSage software package with advanced thermodynamic solution models. The continuing development of analytical and research methodologies has resulted in significant advances in predictive capability. Implementation of the results of fundamental studies involves ongoing collaboration of researchers and industry technologists, and the provision of advanced professional training. An overview of recent progress in research, implementation and applications in industrial practice will be presented in the paper.

On phase stability and phase relations of topologically close packed phases in binary Cr-Os system over the temperature range of 900–1300 ℃

Osmium (Os) addition has been found to be beneficial in enhancing the creep resistance and microstructure stability of nickel-based single-crystal superalloys. The phase stability and phase relationship of topologically closely packed (TCP) phases in a binary Cr-Os system is thus essential for developing a better understanding of the constitutional effects of Os in multicomponent nickel-based single-crystal superalloys, but are still not fully understood in the literature. In this paper, a series of Cr-Os alloys were prepared, and the phase constituents and the microstructure of both as-cast and annealed alloys over a temperature range of 900–1300 ℃ were analyzed using the X-ray diffraction (XRD) and electron probe microanalysis (EPMA) techniques. The experimental results show that (Cr) solution, (Os) solution and Cr2Os phases are formed during solidification. After long-term annealing at 900–1300 ℃, the phase constituents and the microstructure of the alloys display obvious changes. Based on the measured data, the phase stability and phase equilibria of TCP between 900 and 1300 ℃ in the binary Cr-Os system are accordingly updated. The stability results for the two TCP phases in the binary Cr-Os system demonstrate that the Cr3Os phase exists stably, while the Cr2Os phase decomposes into Cr3Os and (Os) at 900–1300 ℃.

P phase precipitation and strengthening behavior of a novel polycrystalline Ni3Al-based intermetallic alloy at 1100 °C

The microstructural evolution and strengthening behavior of a polycrystalline Ni3Al-based intermetallic alloy were investigated during varying durations of thermal exposure at 1100 °C. The study focused on the topologically closed-packed orthorhombic P phase precipitate, which was found to form in the interdendritic γ channel and grow in the γ'-matrix after thermal exposure. The morphology of the P phase evolved from needle-like to lath-like and then to blocky-like. The crystal structure and composition of the precipitates were analyzed using scanning transmission electron microscopy (STEM) and electron probe X-ray microanalysis (EPMA). The chemical composition of the P phase changed continuously during thermal exposure and the P phase was related to the γ'-matrix by three sets of orientation relationships (OR). The alloy's tensile properties and creep fracture time were enhanced during thermal exposure at 1100 °C for 2000 h due to P phase precipitation at grain boundaries or within the grain. Based on the experimental evidence of this study and theoretical strengthening behavior reported in the literature, a novel mechanism for in-situ precipitation strengthening was proposed.

Influence of V doping on the microstructure, chemical stability, mechanical and tribological properties of MoS2 coatings

PurposeThis study aims to investigate the effect of V doping on the microstructure, chemical stability, mechanical and vacuum tribological behavior of sputtered MoS2 coatings.Design/methodology/approachThe MoS2-V coatings are fabricated via tuning V target current by magnetron sputtering technique. The structural characteristic and elemental content of the coatings are measured by field emission scanning electron microscopy, X-ray diffractometer, electron probe X-ray micro-analyzer, Raman, X-ray photoelectron spectroscopy, high resolution transmission electron microscope and energy dispersive spectrometer. The hardness of the deposited coatings are tested by a nanoindentation technique. The vacuum tribological properties of MoS2-V coatings are studied by a ball-on-disc tribometer.FindingsIntroducing V into the MoS2 coatings results in a more compact microstructure. The hardness of the coatings increases with the doping of V. The MoS2-V coating deposited at a current of 0.2 A obtains the lowest friction coefficient (0.043) under vacuum. As the amount of V doping increases, the wear rate of the coating decreases first and then increases, among which the coating deposited at a current of 0.5 A has the lowest wear rate of 2.2 × 10–6 mm3/N·m.Originality/valueThis work elucidates the role of V doping on the lubrication mechanism of MoS2 coatings in a vacuum environment, and the MoS2-V coating is expected to be applied as a solid lubricant in space environment.

Phase composition and liquidus temperatures of the CaO–SiO2–MgO-13 wt%Al2O3–TiO2 system in reduction conditions

Effects of TiO2, binary basicity and MgO content on the liquidus temperatures of TiO2–CaO–SiO2–MgO–Al2O3 slags were experimentally studied in equilibrium with carbon. The experimental techniques include high temperature equilibration, quenching and Electron Probe X-ray Microanalysis (EPMA). It was found that the major primary phase in the composition range investigated is M3O5 (M = Ti, Mg, Al). The liquidus temperatures increase with increasing TiO2 and MgO contents, whereas decrease with increasing CaO/SiO2 mass ratio. The experimentally determined liquidus temperatures are much higher than the predicted ones by FactSage and the primary phases between the experiment results and predictions are also different. The mole fractions of Al2TiO5 and Ti3O5 in the M3O5 phase decrease, but MgTi2O5 increases with increasing MgO content and CaO/SiO2 in the samples. Moreover, the proportions of Al2TiO5 and MgTi2O5 in the M3O5 phase decrease, while Ti3O5 proportion in the M3O5 phase increases with increasing the reaction time. The mole ratio of Ti3+/Ti4+ in the M3O5 phase decreases with MgO content and CaO/SiO2 mass ratio in the samples but increases with increasing reaction time.

Combustion Characteristics of Boron-Iron Powder with Micro-Zone Compounding

ABSTRACT Boron-iron composite powders with a D50 value of < 0.5 μm and iron contents of 5, 10, and 20 wt.% were prepared via a combination of electro-explosive and roll-grinding methods. High-resolution transmission electron microscopy and electron probe X-ray microanalysis revealed evidence of boron-ion micro-zone composites. Ignition tests using a 150-W laser in a pure oxygen atmosphere indicated that the boron-iron composite powder effectively reduced the ignition delay of boron (224.8 ms), with 5 wt.% boron-iron composite powder exhibiting a reduced ignition delay of 106.1 ms. Thermal analysis tests in a pure oxygen atmosphere indicated that iron not only promoted the exothermic reaction of boron but also significantly promoted its oxidation. A comparison of the oxygen bomb calorific values of the composite powder, the original boron powder, and simple mixed powder revealed that the simple mixed iron did not improve the combustion performance of boron, whereas the composite powder generally improved the boron calorific value (12967 J/g), with the 10 wt.% boron-iron composite powder exhibiting a boron calorific value of 21,189 J/g. The addition of iron improved the combustion behavior, stabilized the combustion flame, and improved the combustion quality. An elevated iron content resulted in an increased sensitivity of the powder to the ambient pressure, and an elevated pressure effectively increased the burning rate. The experimental results indicated that iron generally improved the ignition and combustion performance of boron with low and high iron contents, respectively.