Thermodynamic Stability Diagrams Research Articles

Novel applications of ferroalloys for manufacturing of ultra-clean CoCrFeMnNi high-entropy alloy by slagging method

The present study provides a benchmark of a sustainable solution utilizing ferroalloys to prepare ultra-clean CoCrFeMnNi high-entropy alloy (HEA). The designed CaO-MgO-Al2O3 slags saturated with CaAl2O4-MgAl2O4 (CA-MA, Slag A) and CaO-MgO (C-M, Slag M) were used to refine the HEA in Al2O3 and MgO refractory in an induction furnace under high-purity Ar atmosphere at 1773 K. The characteristics of non-metallic inclusions in the sampled HEA at different time intervals were quantitatively investigated. The results showed that three types of inclusions, i.e., sulfide (MnS), oxide, and complex type (oxide+sulfide), were found in the HEA regardless of refractory and slag types. The oxide inclusions such as MnAl2O4 and MgAl2O4 spinel particles can exist stably in the HEA melted in Al2O3 and MgO refractories with slag A and slag M, respectively. This fact is also confirmed not only by the electrolytic extraction method with elimination of the alloy matrix affection but also by the thermodynamic stability diagram for the HEA. For the structure of the complex inclusions, the core of oxide inclusions usually can act as the subsequent nucleation site for MnS since the precipitation temperature of the oxide inclusions (above the liquidus temperature of the HEA, TL ≅ 1623 K) is higher than that of MnS (below the solidus temperature of the HEA, TS ≅ 1573 K). The HEA melted in the MgO refractory with slag M had a higher cleanliness compared with that melted in the Al2O3 refractory with slag A, indicating that the MgO refractory with C-M saturated CaO-MgO-Al2O3 slag is suitable for producing an ultra-clean CoCrFeMnNi HEA prepared by the ferroalloys feedstock as the raw materials.

Development of a Model to Estimate the Thermodynamic Stability of Organic Substances in Leaching Processes

The leaching processes for metals using organic substances represent a sustainable approach to recover precious minerals from solid matrices. However, the generation of organometallic species and the lack of thermodynamic diagrams make it difficult to advance the understanding of their behavior and optimize the process. In this work, a thermodynamically and stoichiometrically consistent mathematical model was developed to estimate the thermodynamic stability of organic substances during the leaching process, and iron leaching with oxalic acid was used as a case study. The Pourbaix and the global thermodynamic stability diagrams for the system were developed in this study. Using a Gaussian®, it was estimated that the Gibbs free energy formation for Fe(C2O4)22−, Fe(C2O4)21−, and Fe(C2O4)33− was −1407.51, −2308.38, and −3068.89 kcal/mol. A set of eleven independent reactions was formulated for the sixteen species involved in the leaching process, and its stability functions in terms of Eh and pH were calculated to generate a 3D global thermodynamic stability diagram. According to the Eh-pH diagrams for the leaching process, ferrioxalate was identified as the most stable and predominant species in the leaching process at pH above 6.6 under reductive conditions. The mathematical model developed in this work resulted in a thermodynamic tool for predicting leaching processes.

Na0.5Bi0.5TiO3 phase relations: Thermodynamics and phase equilibria in the systems Bi2O3 – TiO2, Na2O – TiO2, and Na2O – Bi2O3 – TiO2

The lead-free piezoelectric material sodium bismuth titanate (NBT, Na0.5Bi0.5TiO3) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi2O3 – TiO2 and Na2O – TiO2 and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na2O – Bi2O3 – TiO2 were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na2O – Bi2O3, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na2O, Bi2O3, and TiO2 thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi12TiO20-x / Bi12-xTi1+xO20+0.5x, pyrochlore (Bi2Ti2O7 / NawBi2-xTi2-yO7-z), BTO (Bi4Ti3O12 / NaxBi4Ti3O12+0.5x), and NBT (Na0.5Bi0.5TiO3 / Bi1±xNaxTiO3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na2O – Bi2O3· TiO2 and its binary subsystems.

A DFT Study on Heterogeneous Pt/CeO2(110) Single Atom Catalysts for CO Oxidation

AbstractUnderstanding strong metal‐support interactions is crucially important for developing atom‐efficient transition metal heterogeneous catalysts. Herein, we performed a density functional theory study of highly dispersed Pt on CeO2(110). Various surface models are compared in terms of thermodynamic stability, electronic properties and energy diagrams for CO oxidation. Pt prefers square‐planar oxygen coordination in all models with a +2 state. The structures with a single Pt atom exhibit a low CO oxidation activity. A higher activity is predicted by replacement of a surface Ce by two Pt atoms. The high activity of this highly stable structure stems from the coordinative unsaturation of one of the Pt atoms and the presence of a neighboring two‐fold O atom. The CO oxidation occurs via a Mars‐van Krevelen mechanism. A compared to single‐atom catalysts based on Pt in interaction with CeO2(111) emphasizes the strong dependence of catalytic activity on the ceria surface termination.

Thermodynamic stability diagram of the copper/water/amylxanthate flotation system

The purpose of this work was to obtain the thermodynamic stability diagram that characterizes the copper/water/amylxanthate flotation system, as part of the theoretical foundation necessary for the analysis of the copperion flotation process with the flotation collector reagent potassium amylxanthate. From the system of fundamental chemical reactions and with the help of the Medusa software, the Eh-pH diagram was obtained, in which the stability zones of the different chemical species are defined and it is established that in the pH range from 4 to 13, the xanthogenic species of copper(I) and (II) coexist, whose ratio decreases with the increase of pH.

Preparation of Electroformed Copper-Nickel Multi-Nano-Layers and Characterization of Their Electromagnetic Shielding Effectiveness

Thin copper-nickel foil with multi-nano layers was prepared by pulse-electroforming to develop a high performance electromagnetic shielding material for electronic devices. The pulse electroforming conditions of the aqueous solution chemistry were selected based on the aqueous copper-nickel-sulfur phase diagram and an evaluation of the deposition rate using the finite element method based on the current distribution in front of a cathodic electrode. The thermodynamic stability diagram revealed that the coppernickel multi-nano layers could be formed at pH<4 and ΔE>1.0 V in a modified sulfide bath. The electro-formed copper-nickel multi-layer was well produced at the pulse plating conditions of –0.2V<sub>SHE</sub>, –0.5 mA/cm<sup>2</sup>, and 25 seconds for copper layer and –1.7 V<sub>SHE</sub>, –50 mA/cm<sup>2</sup> and 80 seconds for nickel layer, which was composed of about 25 nm thick copper and about 30 nm thick nickel rich phases, respectively. The average deposition rate of the copper-nickel foil with multi-nano layers was estimated by the finite element method to be about 0.115 mm/sec, which was in good agreement with the real value of the thin multi-nano layered copper-nickel foil. The effectiveness of the electromagnetic shielding of the copper-nickel mesh with multi-nano layers was more than 30% higher than that of copper mesh in the frequency range of 8.2 and 12.5 GHz.

Impact of evaporation on groundwater salinity in the arid coastal aquifer, Western Saudi Arabia

Understanding groundwater salinization and pollution in the arid coastal aquifer is crucial due to complex geochemical processes and sources. This study intends to evaluate the impact of evaporation on groundwater salinity in the arid coastal aquifer, Al Lusub basin, Saudi Arabia using geochemical and multivariate statistical tools. Groundwater samples were collected (n = 52) and analysed for major and minor ions. Groundwater is brackish and shallow wells have higher salinity compared to deeper ones. Hierarchical cluster analysis (HCA) classified the wells into three groups (CG1, CG2, CG3). In these cluster groups, salinity is in the order of CG1(1448 mg/l) < CG2 (3704 mg/l) < CG3(11018 mg/l). PHREEQC modelling reveals that groundwater in this basin is saturated with carbonate, sulphate (CG2, CG3), fluorite (CG3) and silicate minerals, and under-saturated with chloride and hydroxide minerals. Thermodynamic stability diagrams confirm the silicate weathering and kaolinite equilibrium. Precipitation of carbonate minerals at high salinity due to evaporation reduces Ca activity in the groundwater, which triggered the solubility of gypsum and fluorite through common ion effect. Pearson correlation analysis, principal component analysis, ionic ratios (Na/Cl, Cl/Br and F/Cl) and ionic deltas (+ΔBr, +ΔF, +ΔCa, +ΔSO4, +ΔNO3, −ΔNa and −ΔK) justified that non-saline sources and processes, namely evaporation, reverse ion exchange, mineral dissolution and wastewater infiltration predominantly affected the water chemistry in this aquifer. Repeated irrigation practice with high salinity groundwater leads to salt accumulation in the vadose zone due to evaporation, which flushed by the subsequent irrigation events and resulted in higher salinity and NO3− in the groundwater. Hence, sustainable groundwater management and smart irrigation should be implemented.

Water-rock interaction and mixing processes of complex urban groundwater flow system subject to intensive exploitation: The case of Mexico City

In complex aquifer systems subject to intensive exploitation it is important to investigate hydrogeochemical processes in the components to understand the hydrodynamics of groundwater. In this respect, understanding the hydrochemical mechanisms of water-rock interactions and mixing processes eventually leads to the development of appropriate strategies for a sustainable groundwater management. In this study, we analyze water-rock interactions processes of the so-called Anáhuac groundwater system underlying part of the Mexico Valley comprising Mexico City and its suburbs. This intensively exploited system has four flow components: 1) local flow, 2) intermediate flow, 3) cold regional flow, and 4) hot regional flow. This is studied using inverse geochemical models, which consider uncertainties of analytical data and constraints from thermodynamic stability diagrams, speciation-solubility models, and petrographic data. Three representative modeling sections were selected for the implementation of the mass-balance approach. The general conceptual model in two sections suggests that rainwater infiltrates the subsoil and begins to dissolve CO2 in the unsaturated zone; by reaching the saturated zone it reacts with silicate minerals of the host rock producing the final chemical composition of waters. On the other hand, the third section shows mixing as the main groundwater process, as well as water-rock interactions. In general, the identified processes of water-rock interaction are dissolution of CO2, dissolution of calcite, gypsum, and halite, Ca/Na ion-exchange, and weathering of silicate minerals such as biotite, muscovite, plagioclase, epidote and pyroxene, and precipitation of kaolinite, SiO2 and Fe (OH)3. Changes between local and intermediate flow components suggest dissolution of andesite rocks and precipitation of pyrite. Changes between local flow component and the cold regional component are explained by large flow trajectories. Transformations between local and hot regional components indicate mixing flows and a deep circulation influenced by the geothermal gradient. The combination of the methods used in this study can be applied in other similar geoenvironments of the world and assist local water authorities to adequately address and manage groundwater.

Geochemical evolution of groundwater in hard-rock aquifers of South India using statistical and modelling techniques

ABSTRACTMultivariate statistical analysis and inverse geochemical modelling techniques were employed to deduce the mechanism of groundwater evolution in the hard-rock terrain of Telangana, South India. Q-mode hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to extract the hydrogeochemical characteristics and classify the groundwater samples into three principal groups. Use of thermodynamic stability diagrams and inverse geochemical modelling in PHREEQC identified the chemical reactions controlling hydrogeochemistry of each of the groups obtained from statistical analysis. The model output showed that a few phases are governing the water chemistry in this area and the geochemical reactions responsible for evolution of groundwater chemistry along the flow path are (i) dissolution of evaporite minerals (dolomite, halite); (ii) dissolution of primary silicate minerals (albite, anorthite, K-feldspar, biotite); (iii) precipitation of secondary silicate minerals (kaolinite, quartz, gibbsite, Ca-montmorillonite) along with anhydrite and calcite; and (iv) reverse ion exchange processes.

Energies of Mixing (Interaction Parameters), Substitution Limits, and Phase Stability of Solid Solutions Lu1 − xLnxVO4 (Ln = Ce—Yb, Sc, Y)

The energies of mixing (interaction parameters) and temperature ranges of stability of solid solutions Lu1 − xLnxVO4 (where Ln is a rare-earth element (REE), scandium, or yttrium) with the zircon structure were calculated using the crystal-energy theory of isomorphous miscibility. It was shown that, with increasing atomic number of REE in the Ce—Lu series, the calculated energies of mixing and critical decomposition temperatures of the solid solutions regularly decrease. The substitution limits at various temperatures, the thermodynamic phase stability, and the temperature of transition to a metastable state were determined. The thermodynamic stability diagram of the REE vanadate solid solutions Lu1 − xLnxVO4 was presented. The results of the work can be used for searching the compositions of matrices and activators of new laser and other materials.

Structures and thermodynamic stability of cobalt molybdenum oxide (CoMoO4-II)

This contribution reports density functional theory (DFT) calculations on structural and electronic properties of bulk and surfaces of cobalt molybdenum oxide CoMoO4-II; i.e., a material that enjoys a wide array of chemical catalytic and optical applications. Estimated lattice constants and atomic charges for bulk CoMoO4-II reproduce limited analogous experimental measurements. Bader's charges confirm the ionic nature for metal-O bonds in bulk and surfaces of CoMoO4-II. Plotted partial density of states reveal a narrow band gap of 1.8 eV for bulk CoMoO4-II. We found that cleaving bulk of CoMoO4-II along the low-Miller indices afford twelve distinct surfaces. Upward displacement of oxygen atom becomes evident when contrasting bulk positioning of atoms with relaxed surfaces. The two mixed Mo/O- and Co/O–terminated surfaces dominate the thermodynamic stability diagram at 1 atm and 300 – 1400 K, and across a wide range of oxygen chemical potential. The presence of surface oxygen atoms in these stable surfaces is expected to facilitate the occurrence of oxygen reduction reactions as experimentally demonstrated. Likewise, the adjacent surface cations (Mo4+/Co2+) and anions (O2−) serve as Lewis-acid pairs; i.e., very potent active sites in prominent catalysis reactions.

Study of hydrochemical and bacteriological characteristics in Bouhamdane watershed waters, NE Algeria

ABSTRACTThis study aims to determine the physicochemical and bacteriological parameters of surface and groundwater of Bouhamdane basin, located in the North-eastern part of Algeria. Water resources in this area constitute the main source for public drinking, agricultural and industrial supplies in the region. For this purpose, a total of 20 water samples were collected from the Zenati and Bouhamdane rivers, wells and springs and have been analysed for 19 physicochemical elements. Total Coliforms, faecal Coliforms, faecal Streptococci and sulphite-reducing Clostridium were also investigated. The results showed that the water samples have pH values ranging between 6.48 and 8.11, electrical conductivity ranges between 348 and 2150 μS/cm and Nitrate amounts range between 6.16 and 65.2 mg/L. High concentrations of fluoride were noted in the North-eastern part of the study area and the phosphates were relatively high in surface water samples (up to 6.45 mg/L). Hydrochemical facies using Piper diagram indicates that waters are mainly of Cl-Na-K and HCO3-Na-K types. According to thermodynamic calculations and stability diagrams, the chemical evolution of waters is mainly controlled by water–rock interactions. The bacteriological analysis showed that 35% of 20 samples are contaminated, which can represent an important threat for the riparians.

Corrosion behavior of Hastelloy® C–4® Ni–Cr–Mo–Fe alloys for coal gasification syngas plants

Abstract A mechanistic exposure experiment was performed on welded samples of the commercially available Haynes® Hastelloy® C–4® Ni-Cr-Mo-Fe alloy (65 wt.-% Ni, 16 wt.-% Cr, 16 wt.-% Mo, 3 wt.-% Fe, 2 wt.-% Co, 1 wt.-% Mn, 0.7 wt.-% Ti, 0.5 wt.-% Cu, 0.08 wt.-% Si and 0.01 wt.-% C) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin-si, South Korea. The alloy samples were preoxidized at 400 °C under a stagnant air atmosphere for 24 h prior to exposure to the corrosive environment (60 % CO, 28.4 % H2, 2.5 % CO2, 0.8 % CH4, 600 ppm H2S and 110 ppm carbonyl sulfide under 2.005 MPa pressure and 170 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference of the corrosion mechanism was supplemented with morpholo...

Aqueous and Surface Chemistries of Photocatalytic Fe-Doped CeO2 Nanoparticles

The present work describes the effects of water on Fe-doped nanoparticulate CeO2, produced by flame spray pyrolysis, which is a critical environmental issue because CeO2 is not stable in typical atmospheric conditions. It is hygroscopic and absorbs ~29 wt % water in the bulk when exposed to water vapor but, more importantly, it forms a hydrated and passivating surface layer when immersed in liquid water. In the latter case, CeO2 initially undergoes direct and/or reductive dissolution, followed by the establishment of a passivating layer calculated to consist of ~69 mol % solid CeO2·2H2O and ~30 mol % gelled Ce(OH)4. Under static flow conditions, a saturated boundary layer also forms but, under turbulent flow conditions, this is removed. While the passivating hydrated surface layer, which is coherent probably owing to the continuous Ce(OH)4 gel, would be expected to eliminate the photoactivity, this does not occur. This apparent anomaly is explained by the calculation of (a) the thermodynamic stability diagrams for Ce and Fe; (b) the speciation diagrams for the Ce4+-H2O, Ce3+-H2O, Fe3+-H2O, and Fe2+-H2O systems; and (c) the Pourbaix diagrams for the Ce-H2O and Fe-H2O systems. Furthermore, consideration of the probable effects of the localized chemical and redox equilibria owing to the establishment of a very low pH (&lt;0) at the liquid-solid interface also is important to the interpretation of the phenomena. These factors highlight the critical importance of the establishment of the passivating surface layer and its role in photocatalysis. A model for the mechanism of photocatalysis by the CeO2 component of the hydrated phase CeO2·2H2O is proposed, explaining the observation of the retention of photocatalysis following the apparent alteration of the surface of CeO2 upon hydration. The model involves the generation of charge carriers at the outer surface of the hydrated surface layer, followed by the formation of radicals, which decompose organic species that have diffused through the boundary layer, if present.

The role of intrinsic vacancy defects in the electronic and magnetic properties of Sr3SnO: a first-principles study

The thermodynamic stability diagram and formation energies of intrinsic vacancy defects in Sr3SnO. Sr and O vacancy containing Sr3SnO is non-magnetic, while ferromagnetism is achieved in Sn deficient Sr3SnO.

Corrosion behavior of welded Ni-Co-Cr-Si alloys during exposure in integrated coal gasification combined cycle syngas plants

Abstract The corrosion behavior of commercially available and welded Haynes® 160® Ni-Co-Cr-Si alloy samples was investigated by exposure to coal-gasifying integrated coal gasification combined cycle pilot plant facilities under typical conditions as 2.005 MPa and 160 to 300 °C. The morphological and microstructural analyses of the exposed samples were conducted using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis on the external surface of the recovered corrosion test samples to obtain information of the corrosion scale. These analyses based on the pre- and post-exposure corrosion test samples combined with thermodynamic Ellingham-Pourbaix stability diagrams provided preliminary insight into the mechanism of the observed corrosion behavior prevailing in the piping materials that connected the particulate removal unit and the water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material wastage was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested: the observed material waste and corrosion behavior of the Haynes® 160® Ni-Co-Cr-Si alloy samples cut off from the coal syngas integrated coal gasification combined cycle plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered. This contribution supplements the already published studies of Haynes® 556® Fe-Ni-Cr-Co alloys and Haynes® 230® nickel-based superalloys and completes the comprehensive series of such coal-gasifying integrated coal gasification combined cycle pilot plant exposure tests using the facilities affiliated with the Institute for Advanced Engineering.

First Principles Design of Hybrid Cathode Architectures Based on LiMn2O4 Spinel Oxides

LiMn2O4 (LMO) can deliver a reasonable discharge capacity of ~130 mAh g-1, where the three-dimensional lithium ions diffusion channel in the spinel structure allows a rapid de-/intercalation reaction. There are several drawbacks of the spinel LMO including a severe capacity fade during cycling due to a Jahn-Teller (JT) distortion and Mn2+ dissolution. This Mn dissolution presumably starts at the particle surface; and therefore, it is essential to completely understand of the surface structure and its stability. We have recently constructed the thermodynamic stability diagram of LMO using density functional calculations (DFT) to investigate how stability of bulk LMO and LMO surfaces correlate as a function of oxygen and lithium chemical potentials.1 We have also suggested that Li-excess environments and too high temperatures should be avoided upon synthesis to yield particles with less (001) LMO facet, i.e., the surface that is more prone to Mn dissolution. Furthermore, we have recently provided a novel strategy to suppress Mn dissolution and the JT distortion by investigating the spinel LMO (001) surface with a single layer of graphene using DFT.2 Our theoretical calculation in Ref. 2 suggests that the interaction between the graphene sheet and the LMO (001) surface suppresses the Mn3+ disproportionation reaction into Mn2+ and Mn4+. While all surface Mn atoms at the LMO (001) have an oxidation state of +3, we find that the (001) Mn atom that chemically bonds with graphene adopts an electron configuration that has a clear +4 character with an empty eg band. By analyzing the (001) LMO surface Mn-O bond distance, we observe that the JT distortion is reduced as the oxidation state of surface Mn shifts to Mn4+ in the presence of the graphene sheet. A chemical bonding between graphene and LMO on the (001) surfaces provides an underlying mechanism that electronically modifies the LMO (001) surfaces, and subsequently stabilizes them against Mn3+ disproportionation reaction and the JT distortion by converting (001) surface Mn3+ to Mn4+. Our advanced first-principles computations shed lights on the development of alternative hybrid Mn-cathode architecture approaches that can overcome the key shortcomings in these cathode materials.

Composite Microstructure and Formation Mechanism of Calcium Phosphate Conversion Coating on Magnesium Alloy

In order to improve the biodegradability and surface biocompatibility of magnesium (Mg) alloys, a calcium phosphate conversion coating (CPCC) was deposited onto an AZ60 Mg alloy. The coating's components and composite microstructure and its formation mechanism were studied using electrochemical measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy and by developing a thermodynamic stability diagram. The results revealed that the presence of Mg2+ originating from the electrochemical reaction of the Mg alloy could affect the precipitation of different coating components. Because the concentration of Mg2+ at the solution/coating interface continuously changed, three layers of the conversion coating were progressively produced. The inner layer was composed of magnesium hydrogen phosphate trihydrate (MHPT, MgHPO4·3H2O) and had a thickness of ∼1.1 μm. The middle layer was ∼1.6 μm thick and consisted of dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O), magnesium whitlockite (MWH, Ca9Mg(HPO4)(PO4)6), and MHPT. The top layer was ∼2.3 μm thick and was composed of a combination of DCPD and MWH.

Corrosion behavior of Haynes® 230® nickel-based super-alloys for integrated coal gasification combined cycle syngas plants: A plant exposure study

Abstract The corrosion behavior of commercially available Haynes® 230® nickel-based alloy samples was investigated by exposure to coal-gasifying integrated coal gasification combined cycle pilot plant facilities affiliated with the Institute for Advanced Engineering (2.005 MPa and 160-300 °C). The morphological and microstructural analyses of the exposed samples were conducted using scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis on the external surface of the recovered corrosion test samples to obtain information of the corrosion scale. These analyses based on the pre- and post-exposure corrosion test samples combined with thermodynamic Ellingham-Pourbaix stability diagrams provided preliminary insight into the mechanism of the observed corrosion behavior prevailing in the piping materials that connected the particulate removal unit and water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material wastage was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested: the observed material waste and corrosion behavior of the Haynes® 230® nickel-based alloy samples cut off from the coal syngas integrated coal gasification combined cycle plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered. This contribution continues the already published studies of the Fe-Ni-Cr-Co alloy Haynes® 556®.

Corrosion behavior of Haynes® 556® Fe-Ni-Cr-Co alloy for integrated coal gasification combined cycle syngas plants: A plant exposure study*

Abstract A corrosion exposure test was performed on a commercially available Haynes® 556® Fe-Ni-Cr-Co alloy sample to investigate its solid/gas reaction behavior in integrated coal gasification combined cycle pilot plant facilities affiliated with the Institute for Advanced Engineering (2.005 MPa and 160–300 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed and the post-exposure samples were examined ex-situ by morphological and microstructural SEM and EDS analyses on the external surfaces to obtain information on the corrosion scale and provide insight into the mechanism of the observed corrosion behavior in the piping materials connecting the particulate removal unit and water scrubber of the integrated coal gasification combined cycle pilot plant. Uniform material thinning was observed after 46 hours of operation, and a preliminary corrosion mechanism was suggested. The observed material wastage and corrosion behavior of the Haynes® 556® Fe-Ni-Cr-Co alloy sample cut off from the coal syngas IGCC plant were explained by the formation of discontinuous (complex) oxide phases and subsequent chlorine-induced active oxidation under the predominantly reducing environment encountered.