Energy and Resource Saving of Steelmaking Process: Utilization of Innovative Multi-phase Flux During Dephosphorization Process

An increase in the utilization efficiency of CaO, one of the major fluxing agents used in various steelmaking processes, is required to reduce the amount of discharged slag and energy consumption of the process. The authors have intensively focused on the development of innovative dephosphorization process by using so called “multi-phase flux” composed of solid and liquid phases. This article summarizes the research on the above topic done by the authors, in which the formation mechanisms of P₂O₅-containing phase during CaO or 2CaO·SiO₂ dissolution into molten slag, the phase relationship between solid and liquid phases at equilibrium, and thermodynamic properties of P₂O₅-containing phase have been clarified. The reactions between solid CaO or 2CaO·SiO₂ and molten CaO-FeO _x -SiO₂-P₂O₅ slag were observed by dipping solid specimen in the synthesized slag at 1573 K or 1673 K. The formation of the CaO-FeO layer and dual-phase layer of solid 2CaO·SiO₂ and FeO _x -rich liquid phase was observed around the interface from the solid CaO side toward the bulk slag phase side. Condensation of P₂O₅ into 2CaO·SiO₂ phase as 2CaO·SiO₂-3CaO·P₂O₅ solid solution was observed in both cases of CaO and 2CaO·SiO₂ as solid specimens. Measurement of the phase relationship for the CaO-FeO _x -SiO₂-P₂O₅ system confirmed the condensation of P₂O₅ in solid phase at low oxygen partial pressure. The thermodynamics of 2CaO·SiO₂-3CaO·P₂O₅ solid solution are to be clarified to quantitatively simulate the dephosphorization process, and the current results are also introduced. Based on the above results, the reduction of CaO consumption, the discharged slag curtailment, and energy-saving effects have been discussed.     

A Combined Thermodynamic/Kinetic Modeling Approach to Predict SiC Recession Due to SiO2 Scale Volatility Under Combustion Environments

A computational approach, which targets on the prediction of SiC recession caused by SiO₂ scale volatility under combustion environments, was developed in this study. In this approach, thermodynamic calculation was integrated with a gaseous-diffusion model to calculate the fluxes of volatile species, such as SiO(g), Si(OH)₄(g), SiO(OH)₂(g), and SiO(OH)(g), produced by the reaction of SiO₂ scale with the combustion air. The resulted weight loss of SiC was then calculated under a variety of combustion environments. The benefit of using environmental barrier coating (EBC) in the protection of SiC from recession was demonstrated by the calculation. It is shown that the weight loss of SiC-based ceramics could be significantly reduced when EBCs, such as mullite (Al₆Si₂O₁₃ or written as 3Al₂O₃·2SiO₂) or SrAS₂ (SrO·Al₂O₃·2SiO₂), are used. The effects of combustion conditions, such as temperature and total pressure, on the volatility of SiO₂ scale were also discussed.     

Corrosion Resistance Enhancement of AZ91D Magnesium Alloy by Electroless Ni-Co-P Coating and Ni-Co-P-SiO2 Nanocomposite

Electroless Ni-Co-P coating and Ni-Co-P-SiO₂ nanocomposites were successfully applied on AZ91D magnesium alloy via environmentally friendly cerium-lanthanum-permanganate treatment and their properties were compared with traditionally binary Ni-P coating. The prepared coatings were analyzed using scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Moreover, the corrosion behavior of the coatings in 3.5 wt.% NaCl was evaluated by two electrochemical methods. It is found that the Ni-Co-P coating possesses more uniform and compact structure and better corrosion protection characteristics in comparison with the Ni-P coating. The plating rate of Ni-Co-P bath is relatively lower than the Ni-P bath, but it significantly increases after addition of SiO₂ nanoparticles more probably due to adsorption of silica nanoparticles on alloy surface. The corrosion resistance of Ni-Co-P-SiO₂ composite coatings was superior with respect to Ni-P and Ni-Co-P coatings due to formation of thick and compact coating with tortuous grain boundaries.     

Synthesis and characterization of iron oxide nanoparticles by solvothermal method

In the present work iron oxide nanoparticles have been synthesized by alkaline solvo thermal method using anhydrous ferric chloride, sodium hydroxide, polyethylene glycol and cetyl trimethyl ammonium bromide and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermal Gravimetric Analysis (TGA). XRD indicated that the product is a mixture of different phases of iron oxide viz. gamma-Fe₂O₃ (maghemite, tetragonal), Fe₂O₃ (maghemite, cubic), Fe₃O₄ (magnetite, cubic) and ?-Fe₂O₃(epsilon iron oxide). FESEM studies indicated that size of the particles is observed in the range of about 19.8 nm to 48 nm. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR spectra indicated absorption bands due to O-H stretching, C-O bending, N-H stretching and bending, C-H stretching and Fe-O stretching vibrations. TGA curve represented weight loss of around 3.0446 % in the sample at temperature of about 180°C due to the elimination of the water molecules absorbed by the nanoparticles from the atmosphere.     

Microstructure and Mechanical Properties of AlN/Cu Brazed Joints

In this study, the AlN/Cu bonding was explored using the brazing technique. During AlN/Cu brazing, the temperature was set at 800, 850, and 900 °C for 10, 20, 30, and 60 min, respectively. We studied the bonding mechanism, microstructure formation, and the mechanical characteristics of the bond. The reaction layer developed at the interface of AlN/Cu is observed to be TiN. The activation energy of TiN is about 149.91 kJ/mol. The reaction layer thickness is linearly dependent on the temperature and duration at 800 and 850 °C for 60 min and 900 °C for 30 min. However, the growth of the reactive layers decreases gradually at 900 °C when the duration changed from 30 to 60 min. The strength of the specimens with thickness ranging between 1 and 1.5 μm is 40-51 MPa.     

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.     

Oxidation Potentials in Matte Smelting of Copper and Nickel

The oxidation potential, given as the base-ten logarithm of the oxygen partial pressure in bars and the temperature [log pO₂/T, °C], defines the state of oxidation of pyrometallurgical extraction and refining processes. This property varies from copper making, [?6/1150]; to lead/zinc smelting, [?10/1200]; to iron smelting, [?13/1600]. The current article extends the analysis to the smelting of copper and nickel/copper sulfide concentrates to produce mattes of the type Cu(Ni)FeS(O) and iron silicate slags, FeO_xSiO₂—with oxidation potentials of [?7.5/1250].     

Effect of applied potential on fatigue crack propagation behavior of API X80 steel in seawater

In the present study, the fatigue crack propagation (FCP) tests were conducted on X80 steel in air and artificial seawater (ASW) under various applied potentials to establish optimum and safe working limits of cathodic protection (CP). The slow strain rate test (SSRT) was also conducted on the X80 BM specimens in ASW under CP potential to identify the susceptibility of hydrogen affecting the FCP behavior. The CP potential of ?850 and ?1,050 mV_SCE suppressed the environmental effect of seawater on the FCP behavior of X80 BM and WM specimens, showing almost identical da/dN-ΔK curves for both air and ASW environments. The SSRT in ASW under CP potential of ?1,050 mV_SCE suggested that the X80 BM specimen steel is susceptible to hydrogen embrittlement, but the effect of hydrogen was believed to be marginal in affecting the FCP behavior of the X80 specimens at a loading frequency of 10 Hz. The FCP behavior of high strength X80 steel is discussed based on the fractographic observation to understand the FCP mechanism in seawater under various CP potentials.     

Assessment of Abrasive Wear of Nanostructured WC-Co and Fe-Based Coatings Applied by HP-HVOF,Flame, and Wire Arc Spray

Thermal spray processes have been widely used to minimize losses caused by wear mechanisms. Sprayed deposits using conventional wire and powder materials have been long solving tribological problems in engineering equipment. More recently, the option for new different technologies and consumables like nanostructured powder materials and nanocomposite cored wires have expanded the possibilities for technical solutions. Cored wire technology allows the use of compositions that cannot be drawn into wire form like carbides in metallic matrix and high-temperature materials, thus, intensifying the use of spraying processes with low operating cost to demanding wear and corrosion applications. The objective of this work was to study the mechanical characteristics and wear performance of coatings obtained by Flame, Wire Arc, and HVOF spraying using selected nanostructured WC10Co4Cr, WC12Co, and Fe-based 140 MXC powder and wire materials. Abrasive wear performance of the coatings was determinate following the ASTM G-65 standard. Based on the results, a higher abrasive wear resistance was found for the HVOF-sprayed WC10Co4Cr nanostructured coating.     

Overview of SIMS-Based Experimental Studies of Tracer Diffusion in Solids and Application to Mg Self-Diffusion

Tracer diffusivities provide the most fundamental information on diffusion in materials, and are the foundation of robust diffusion databases that enable the use of the Onsager phenomenological formalism with no major assumptions. Compared to traditional radiotracer techniques that utilize radioactive isotopes, the secondary ion mass spectrometry (SIMS)-based thin-film technique for tracer diffusion is based on the use of enriched stable isotopes that can be accurately profiled using SIMS. An overview of the thin-film method for tracer diffusion studies using stable isotopes is provided. Experimental procedures and techniques for the measurement of tracer diffusion coefficients are presented for pure magnesium, which presents some unique challenges due to the ease of oxidation. The development of a modified Shewmon-Rhines diffusion capsule for annealing Mg and an ultra-high vacuum system for sputter deposition of Mg isotopes are discussed. Optimized conditions for accurate SIMS depth profiling in polycrystalline Mg are provided. An automated procedure for correction of heat-up and cool-down times during tracer diffusion annealing is discussed. The non-linear fitting of a SIMS depth profile data using the thin-film Gaussian solution to obtain the tracer diffusivity along with the background tracer concentration and tracer film thickness is demonstrated. An Arrhenius fit of the Mg self-diffusion data obtained using the low-temperature SIMS measurements from this study and the high-temperature radiotracer measurements of Shewmon and Rhines (Trans. AIME 250:1021-1025, 1954) was found to be a good representation of both types of diffusion data over a broad range of temperatures between 250 and 627 °C (523 and 900 K).     

Laboratory Produced P/M Aluminum 2XXX + Zr Sheet

Laboratory procedures were established to produce advanced aluminum 2XXX+ Zr alloy powder metallurgy sheet in the T8X temper. The sheet was tested for tensile and Kahn Tear properties in the longitudinal and long transverse directions. The results from the laboratory-produced sheet were compared to the results of a pilot-scale NASA contractual study which used the same alloy powders, leading to the conclusion that laboratory-scale sheet properties are good to excellent predictors of the pilot-scale tensile properties and tear notch toughness values. Tear resistance toughness at pilot scale was not satisfactorily predicted by the laboratory results.     

Impedance of NiSi electrode in sulfuric-acid solution in the region of passive and transpassive states

The behavior of an NiSi electrode in 0.5 M H₂SO₄ in the region of passive and transpassive state (from 0.50 to 2.1 V (versus SHE)) is studied. The conclusion is made about formation of oxide film close to SiO₂ by composition on the electrode surface in the passivation process. Equivalent electric circuit modeling passive and transpassive state of nickel silicide is proposed. Thickness of oxide film and its specific resistance depending on electrode potential are calculated basing on the impedance data.     

Effect of B2O3 on the Structure and Viscous Behavior of Ti-Bearing Blast Furnace Slags

This study provided a fundamental analysis of the viscous behavior and structure of Ti-bearing blast furnace slags modified by different B₂O₃ additions with a basicity (CaO/SiO₂) range of 0.5–0.9. The viscosity of slag melts was measured by rotating cylinder method, and the results showed that both slag viscosity and apparent activation energy for viscous flow remarkably decreased with B₂O₃ addition. To connect the viscosity variation of slags to the melt structure, Fourier transformation infrared spectroscopy analysis was performed. The results indicated that B₂O₃ acted as a typical network forming oxide, which was introduced into the network and existed dominantly as a two-dimensional structure, BO₃ triangular. With the increase of B₂O₃ content, the stretching vibration of BO₃ triangular gradually became more pronounced, which resulted in a simpler and less complex structure and caused the decrease of slag viscosity.     

In-Situ Agglomeration and De-agglomeration by Milling of Nano-Engineered Lubricant Particulate Composites for Cold Spray Deposition

Nano-engineered self-lubricating particles comprised of hexagonal-boron-nitride powder (hBN) encapsulated in nickel have been developed for cold spray coating of aluminum components. The nickel encapsulant consists of several nano-sized layers, which are deposited on the hBN particles by electroless plating. In the cold spray deposition, the nickel becomes the matrix in which hBN acts as the lubricant. The coating demonstrated a very promising performance by reducing the coefficient of friction by almost 50% and increasing the wear resistance more than tenfold. The coatings also exhibited higher bond strength, which was directly related to the hardenability of the particles. During the encapsulation process, the hBN particles agglomerate and form large clusters. De-agglomeration has been studied through low- and high-energy ball milling to create more uniform and consistent particle sizes and to improve the cold spray deposition efficiency. The unmilled and milled particles were characterized with Scanning Electron Microscopy, Energy-Dispersive X-Ray Spectroscopy, BET, and hardness tests. It was found that in low-energy ball milling, the clusters were compacted to a noticeable extent. However, the high-energy ball milling resulted in breakup of agglomerations and destroyed the nickel encapsulant.     

Effects of Nitrogen Content on the Phase and Resistivity of TaN Thin Films Deposited by Electron Beam Evaporation

A series of amorphous electron beam evaporated Ta and TaN films with N/Ta ratio from 0 to 1.15 were deposited on Si/SiO₂ substrates at 200°C. As N/Ta ratio increases, the TaN films undergo phase changes from pure metallic Ta to a mixture of Ta, Ta₂N, and nitrogen-rich TaN films. The electrical resistivity of the Ta and TaN films increased from 242 µΩ-cm to 1126 µΩ-cm with increasing N/Ta ratio. X-ray diffraction patterns revealed the development of different phases of TaN that are in agreement with the TaN phase diagram. The presence of different phases on the film surface was also confirmed by x-ray photo-emission spectroscopy (XPS) analysis. Groups of Ta4f doublet related to different TaN phases were observed in the core-level spectra of TaN films. Field-emission scanning electron microscopy images revealed that surface morphology also varied with the phase change in TaN films. The N/Ta ratios from energy-dispersive x-ray generally agreed with those from the XPS analysis.     

Processing and designing parts using structural reaction injection molding

A new process called structural reaction injection molding (SRIM) has been developed to combine the high strength and modulus properties of fiber reinforced composites with the advantages of the reaction injection molding process. Along with the process, a new reactive resin has been developed expressly for the structural RIM process. With the new resin and SRIM process conventional design methods can be used, but the designer must also consider several facets of the structural RIM process.     

The Center for Microanalysis of Materials

“Excuse me,” said a graduate student that I’ve not seen before, “I’d like to get some time on the Auger.” “Fine” I reply, “If you are going to need a lot of time, Nancy will train you so that you can use the machine yourself. If it’s only a small project, she’ll work with you. In either case, see Nancy to get a session scheduled.” Shaking off the last remnants of sleep, I realize that I’ve forgotten the most important question, “Oh, just a minute …. Why? … I mean, what do you want to find out?” And so begins a discussion which leads to the recommendation that, instead of Auger spectroscopy, the student use a combination of SIMS and STEM. We schedule time appropriately.     

Effect of conditions of formation of composite pyrographite/Nafion-polyaniline-Pt anode upon electrooxidation of methanol

The effect of the conditions of formation (regime of formation and sequence of deposition of composite components, pH of the solution) of a multicomponent composite anode including polyaniline, Nafion, and platinum on the activity of such an anode in the course of electrocatalytic oxidation of methanol is studied. An explanation of the observed regularities of platinum and polyaniline codeposition is suggested on the basis of the data on the electrode surface topography obtained using the atomic force microscopy technique.     

Microstructural study of NiCrAlY electrodeposits

Pulse electrodeposition technique was used to co-deposit Ni with NiCrAlY powder on Ni-based high temperature alloy substrate. Pure nickel anode was immersed in a standard Watt’s bath containing fine particles of NiCrAlY powder that were entrapped during electrodeposition to form a NiCrAlY electrodeposit on cathode specimen surface. Diffusion heat treatment was conducted in argon at ≈1150°C and the samples were oxidized at 1000°C in air. Scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction were used to characterize the microstructure and identify the phases. Pulse electrodeposition resulted in dense and fine-grained deposit with the formation of Al₂O₃ oxide at the coating surface after exposure to high temperature.     

The properties and applications of rhenium produced by CVD

Rhenium possesses a unique combination of properties that make it an excellent choice for many applications demanding high-temperature strength, wear resistance and erosion resistance. While the major use of rhenium is still in bimetallic catalysts, renewed interest in improved propulsion and space-power systems has led to increased development of rhenium as a structural material. Recent investigations have illustrated the tremendous advantages of rhenium in certain structural applications.Thesuperior performance of rhenium can be attributed to its chemical inertness, superior high-temperature strength and room-temperature ductility. In several demanding applications, many of rhenium's properties can be optimally exploited by using chemical vapor deposition.