bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Magnetic Field on Anodic Dissolution and Pitting of Iron in a Molybdenum Nitrate Solution with Chlorides
Authors: Li Hongjuan , Ling Sichun , Ma Jiarong , Xiong Qi , Lu Zhanpeng
Published: February 2020

Magnetic fields would affect electrochemical reactions for metallic materials in aqueous solutions. The main effect of a magnetic field applied on an electrochemical system is the introduction of additional forces on the ions in the electrolyte, such as Lorentz-force driven magnetohydrodynamics (MHD) effect and Kelvin-force-driven magnetic field gradient force (MFGF) effect. There are some published reports on the influence of magnetic fields on the pitting corrosion, and apparently contradictory results have been reported. In this work, we focused on the effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride ions.

The typical potentiodynamic polarization curves of iron in a 0.2 mol L-1 Na2MoO4 +0.2 mol L-1 NaCl solution at a potential sweep rates of 0.833 mV/s and under 0 T and 0.4 T magnetic field are shown in Fig. 1. Magnetic field decreased the limiting current densities at high potentials. The results in Fig. 1 were confirmed by potentiostatic polarization measurements, which were used to study the effect of magnetic field on the anodic corrosion of iron. After a relatively long period of polarization at 0.4V(SCE) at 0T, imposing a magnetic field will result in a sudden increase and then a slowly decrease of the current density, as shown in Fig. 2(a). The electrode surface morphologies after potentiostatic polarization at 0.4V for 200s under 0T are shown in Fig. 2(b), which are corresponded to the conditions in Fig. 2(a). The pits have propagated deeply. The mass transfer process between occluded pit bottom and the pit mouth would became difficult with the deepening of the pits. The retarding effect of magnetic field on anodic dissolution of iron in a molybdenum nitrate solution with chloride is ascribed to its effect on the mass-transport process between the occluded pit bottom and the pit mouth and finally the resultant disturbance of the autocatalysis process involved in pitting

Figure 1
Characteristics of the Oxide Films Formed on Ni-Base Alloy Cladding in Hydrogenated High Temperature Water
Authors: Jia Yibo , Ling Sichun , Zhang Kun , Ma Jiarong , Xiong Qi , Lu Zhanpeng
Published: February 2020

The oxide film formed on low alloy steel-nickel-base alloy (Alloy 52M) clad weld in simulated pressurized water reactor (PWR) primary water environments can be affected by the heterogeneities in structure and chemical composition as the result of cladding and machining process. The surface morphology and the cross-section of the oxide films were observed by scanning electron microscopy and (SEM) and transmission electron microscopy (TEM). After immersion in 325 oC hydrogenated PWR primary water for 146h, more oxide particles formed on the cladding alloy were found at the location close to the cladding fusion line than at the location far away from the fusion line. The microstructure and chemical composition in the weld at various distance from the weld fusion line is characterized by metallography, SEM-EDS and electron backscattering diffraction. Ni and Cr contents in the cladded Ni-base alloy increased with increasing the distance from the fusion line, while Fe content decreased with increasing the distance from the fusion line. A higher iron content in the cladding alloy corresponded to more oxide particles formed on the surface after the immersion in PWR primary water. After immersion in hydrogenated high-temperature water for 1860 h, the morphologies of the oxide film formed on the cladded Ni-base alloy at different locations became similar. The cross-sectional observation shows that the oxide film exhibits a double structure with the external layer enriched in iron and the internal layer enriched in chromium.

Figure 1
Corrosion Monitoring and Inhibition of Buried Pipes in a Nuclear Power Plant Using a FEM Method or Mixed Inhibitors
Authors: Kim Ki Tae , Hur Seung Young , Yoo Young Ran , Kim Young Sik
Published: February 2020

Several kinds of pipes in a nuclear power plant were buried in the soil. In order to control the corrosion problems, cathodic protection has been applied to protect the corrosion process in the outer surface of pipes and several corrosion inhibitors have been used to minimize the corrosion in the inner surface of the pipes. This work focused on the corrosion monitoring of the outside of coal tar-coated pipes buried in a nuclear power plant using a FEM method and the corrosion inhibition of the inside of the pipes using mixed inhibitors. The pipes buried in a nuclear power plant were ductile cast iron and these have been suffered under very high cathodic protection condition beyond the appropriate condition. However, cathodic potential measured in the site reveals the non-protected status. Converting from 3D CAD data of the power plant to appropriate type for a FEM simulation was performed and cathodic potential under the applied voltage and current was calculated using the primary and secondary current distribution physics conditions. FEM simulation for coal tar-coated pipe without defects showed the over-protection condition if the pipes are well-coated. On the other hand, we compared the different inhibition mechanisms of organic inhibitor with that of anodic inhibitor. When ethanolamines or nitrite or molybdate were added separately to tap water for inhibiting the corrosion of ductile cast iron, large amounts of inhibitor were needed. However, when mixed inhibitors were added, their amounts were greatly reduced and we found the synergistic effect and also proposed the new mechanism.
Effect of Pad Type on Passivation Film Formation Relevant to Copper Chemical Mechanical Planarization
Authors: Mlynarski Amy , Mistry Neera , Shuchi Halima , Keleher Jason J.
Published: February 2020

Copper (Cu) chemical mechanical planarization (CMP) is an extremely critical step in the manufacturing of ultra-large-scale integrated (ULSI) semiconductor devices. By optimizing the synergistic relationship between a chemical dispersion, referred to as a slurry, and mechanical parameters, global planarization is able to be achieved utilizing CMP. Traditional slurries for Cu CMP promote Cu oxidation, promoting the creation of a passivation film which readily able to be removed by the same mechanical process. However, the efficiency of film removability is strongly correlated to the molecular structure of the passivating agent and also the composition of the polyurethane polishing pad. This work aims to mechanistically understand the relationship between molecular structure of the passivating agent and the pad type on the modulation of the passivation film formed. The film formation kinetics and characteristics were studied through various electrochemical techniques and surface spectroscopy. Results have indicated that the film is directly correlated to the molecular structure of the passivating agent, and the ease of removing the film is strongly contingent on the type of polyurethane pad implemented in the CMP polishing process.
Corrosion Characteristics and Workability of Cold Rolled Ti-4Mo-X (1, 2, 3, 4 Cr or V) Ternary Alloys
Authors: Lee Gunhee , Lee Kwangmin
Published: February 2020

The beta phase stability of titanium alloys can be generally described by means of molybdenum equivalence (Moeq). In this study, Ti-4Mo-X (1, 2, 3, 4 wt.% Cr or V) alloys were prepared by means of vacuum arc remelting under argon atmosphere in order to enhance the workability of Ti-4Mo-X alloys and corrosion resistance. The corrosion properties, microstructural evolution and plastic workability were investigated following uniaxial cold rolling. The corrosion evaluation was conducted in a standard three-electrode cells in naturally aerated Ringer’s physiological solution at 37±1 ℃. Optical micrograph showed an increase of acicular β phases after cold rolling. XRD results showed a higher intensity of β phase in the cold rolled specimen compared to as-homogenized one. The formation of β phase was responsible for the improved workability of Ti alloys. The maximum reduction ratio of the cold rolled specimens without any presence of cracks were 72.8% and 39.4% for Ti-4Mo-4Cr and Ti-4Mo-4V alloys, respectively. The corrosion properties of the alloy were relatively dependent on the cold rolling. Ti-4Mo-4Cr alloy showed the lowest corrosion current density with 6.71E10-9/cm2.
Mechanistic Study of Zr Based Nano-Anti-Corrosion Surface Pretreatment
Authors: Liu Xiaoyang , Jiang Hua , Ge Mingyuan , Kisslinger Kim , Nazaretski Evgeny , Williams Garth J. , Thieme Juergen , Petrash Stan , Vonk Donald , Foster Kate , Chen-Wiegart Yu-chen Karen
Published: February 2020

Most metals used in manufacturing require surface treatment for essential functionalities, including: corrosion resistance, paint adhesion, surface appearance, and/or tactile finishing. Chemical conversion coating is one of the surface treatment methods that provides anti-corrosion properties, and widely used in automobile and other industries. Here we investigated an environmentally friendly chemical conversion method, Zr-based, dilute hexafluorozirconic acid (H2ZrF6) treatment. This method attracted attention because it is phosphate-free and easy to apply, however without clear reaction mechanism. This study focuses on the elemental distribution of the coatings, the change of element concentration and species during the immersion treatment using in situ synchrotron X-ray fluorescence microscopy (XRF) and X-ray Absorption Spectroscopy (XAS). Also, we treated the sample in the solution at certain temperature and time range. Scanning electron microscopy (SEM) and focus ion beam (FIB)-SEM were also used to see the surface and cross-section morphology change before and after the surface treatment. Then by comparing the coating thickness, surface cluster density and cluster size to seek the kinetics of coating formation process. As such, we could determine the mechanism of the coating formation via surface chemical conversion.

Figure 1
The Corrosion Behavior of a Fully Homogenized Equimolar Co-Cr-Fe-Ni-Mn and Co-Cr-Fe-Ni-Al High Entropy Alloys in Sulfuric Acid and Saline Solutions
Authors: Yen Chao Chun , Huang Chun Yuan , Tsai Min Chen , Tsai Ming Hung , Yen Shiow Kang
Published: February 2020

The hardness of CoCrFeNi has been enhanced from Hv 100 to 495 by the addition of Al to form equimolar CoCrFeNiAl high entropy alloy (HEA) and further homogenization annealing treatment at 1100℃ for 48 hr. It is finally composed of FCC and two disordered BCC (1 and 2) crystal structures, transformed form one disorder and the other order BCC structures in as-casted specimen. It is known that the corrosion resistance of CoCrFeNiAlx is deteriorated with the amount of order BCC phase and/or x increasing, and it is the worst one when x equals to 1. However through a suitable homogenization annealing treatment to avoid the formation an order BCC phase, the equimolar CoCrFeNiAl HEA has shown the similar corrosion resistance to CoCrFeNi in 0.5M H2SO4 and 3.5 wt.% NaCl aqueous solution. It is speculated that the order BCC phase which is more stable than the disorder one should play an important role on accelerating corrosion current, possibly acting as a cathode in galvanic corrosion. In contrast, both disorder BCC structures diminish the tendency of galvanic corrosion. However the addition of Mn to form CoCrFeNiMn equimolar HEA, only one FCC structure, has worsened in the corrosion resistance, since the Ksp of corrosion product Mn(OH)2 is much higher than those of Al(OH)3 and Cr(OH)3, leading to the less protection effect on corrosion. Besides, the absorption of O2 and/or H2O on equimolar HEAs has been simulated by the first principle to correlated the corrosion behaviors.
Effect of Imidazoline Corrosion Inhibitors on Erosion/Corrosion Processes - an Electrochemical Investigation
Authors: Mobarakinejad Ali
Published: February 2020

Erosion-corrosion is a concern for oil and gas pipelines [1]–[3]. The simultaneous influence of fluid parameters such as velocity, turbulence, fluid regime and the characteristics of the corrosion scales formed on the pipe surface can accelerate erosion-corrosion inside oil and gas pipelines [4]. Corrosion inhibitors, made of imidazoline derivatives, are widely used in oil industry to prevent internal corrosion of pipelines. In this work, the influence of an imidazoline corrosion inhibitor on erosion-corrosion rates, in flowing fluid condition, is electrochemically investigated. The test electrolyte is synthesized to simulate condition of a multiphase gas pipeline. Electrochemical Impedance Spectroscopy (EIS) was used to measure the corrosion rate in presence of varying concentration of corrosion inhibitors. A cylindrical working electrode with a rotational speed of 1200 (rpm) was employed to simulate the dynamic behavior of the flowing fluid inside wet gas pipelines.

The results revealed that corrosion inhibitor films could be readily removed from the steel surface by the erosional behavior of the flowing fluid if the adhesion factor of the surface films are not sufficient. This would expose the bare metal to the corrosive medium. The consequence of such phenomena is the lifespan reduction of pipelines and thus occurrence of immature erosion-corrosion failures. This study demonstrated that the adhesion force of the corrosion inhibitor films are directly related to the thickness of the formed film on the pipe surface and the shear stress generated by flow at the steel surface.

References:

[1] H. Mansoori, D. Mowla, F. Esmaeelzadeh, and A. H. Mohammadi, “Case Study: Production Benefits from Increasing C-Values,” OIL GAS J., vol. 111, no. 6, pp. 64–69, 2013.

[2] H. Mansoori, R. Mirzaee, A. H. Mohammadi, and F. Esmaeelzadeh, “Acid Washes, Oxygenate Scavengers Work Against Gas Gathering Failures,” OIL GAS J., vol. 111, no. 7, pp. 106–111, 2013.

[3] H. Mansoori, R. Mirzaee, F. Esmaeelzadeh, and D. Mowla, “Altering CP Criteria Part of Unified Anti-SCC Approach,” Oil Gas J., vol. 111, no. 12, pp. 88–93, 2013.

[4] H. Mansoori, R. Mirzaee, F. Esmaeilzadeh, and et al., “Pitting corrosion failure analysis of a wet gas pipeline,” Eng. Fail. Anal., vol. 82, pp. 16–25, Dec. 2017.
Synergetic Properties of Some Polymers with Antiscaling and Anticorrosive Action for Industrial Cooling Water Systems Protection
Authors: Branzoi Florina , Branzoi Viorel
Published: February 2020

In this study, to examine synergistic effect of various combinations of the following polymers: PSO-1 (an oligomer phosphinosuccinic in neutralized state) and PMA-M1 (mixture by weight ratio 1/1 from 2-phosphonobutane-1-2, 4 tricarboxilic acid with polymaleic acid) were investigated as corrosion inhibitors for carbon steel of type OL 37, OLC 45 and for copper and brass. Using the microwaves energy, new polymers with antiscaling and anticorrosive properties were synthesized in microwaves field. These new polymers were obtained by radical polymerization of acrylic and/or acrylsulfonate water-soluble monomers in presence of microwaves field chain transfer agents, under the action of peroxidic initiators. The inhibitive properties of these organic compounds were analyzed by electrochemical measurements, FT-IR spectroscopy and by scanning electron microscopy (SEM) of the electrode surface. Also, a variety of short-time corrosion tests on laboratory scale were used to determine the performance and application parameters under different environmental conditions. The metallographic micrographies and scanning electron microscopy made before and after the potentiodynamic polarizations pointed out the evolution of the corrosion process.

The inhibition activity analysis of the organic compounds was made by assuming that, the mechanism of inhibition by organic molecules is chemisorption and that the energetic of the corrosion process per se is unaffected by the addition of substituients on the parent compound. We presume that, these organic compounds inhibit corrosion of these materials by a protective mechanism, forming insoluble complexes and repairing the porous oxide layer. The addition of these new organic polymers offers protection by forming an adsorption organic barrier film at the electrode surface. The corrosion parameters obtained from polarization curves and from EIS spectra are in good concordance and point out the inhibitory action of these new organic polymers.

The addition of the organic inhibitors led in all the cases to inhibition of the corrosion rate. The organic compounds used are adsorbed on the electrode surface according to a Langmuir isotherm. The inhibition process was attributed to the formation of the adsorbed film on the metal surface that protects the metal against corrosive agents. The EIS measurements have confirmed this protection and pointed out the formation of adsorption layers on the electrode surface

The negative value of thermodynamic parameter like Gibbs free energy of adsorption indicates the spontaneity of adsorption process. Moreover, characterization utilizing FT-IR confirms the adsorption of inhibitors and the constitution of corrosion products on the materials surface. EIS and potentiodynamic polarization results demonstrate its corrosion protection capacity
A Novel Inhibitor for L921A alloy Steel in a 3.5 % NaCl Solution
Authors: Yong Xingyue , Chen Zhenglin , Zhou Lin , Jiang Lin , Chen Rihui
Published: February 2020

Corrosion inhibitors, acting as an effective method at lower operating cost, are often used to protect metallic materials from corrosion. Although many kinds of corrosion inhibitors have been used in circulating cooling water systems, a few papers have been published for introducing the applications of corrosion inhibitors in chloride media. By comparison, it is difficult to develop a novel inhibitor for alloy steels in chloride solutions or sea water.

In this paper, a novel corrosion inhibitor for L921A alloy steel in a 3.5% NaCl solution was formulated by weight loss in conjunction with orthogonal tests. The inhibitory efficiency of this novel inhibitor was over 95.0%. It was found by electrochemical polarization that this novel inhibitor was a mixed type of inhibitor which had an ability to improve the pitting corrosion resistance of L921A alloy steel in a 3.5% NaCl solution. EIS spectra showed that L921A alloy steel in a 3.5% NaCl solution was subjected to pitting corrosion, due to that EIS spectrum with two time constants of L921A alloy steel in a 3.5% NaCl solution was composed of a capacitive loop at high frequency region and an inductive loop at low frequency region. However, EIS spectrum with two time constants consisted of a capacitive loop at high frequency region and a Warburg line at low frequency region when the novel inhibitor was added into a 3.5% NaCl solution. The thickness of inhibitory film increased with increasing immersion time, resulting in the increment of the electrochemical impedance of corrosion process of L921A alloy steel in a 3.5% NaCl solution. Finally, the formation of the inhibitory film was further studied by EDX and XPS technology.

Key words: alloy steel; chloride solution, inhibitor; EIS, XPS; inhibitory mechanism
Investigation of Pit Initiations on Copper during Anodic Polarization By Real-Time Surface Observation System with Channel Flow Double Electrode
Authors: Hoshi Yoshinao , Oda Tomohiko , Shitanda Isao , Itagaki Masayuki
Published: February 2020

A pitting corrosion on copper tube is a serious problem because it may lead to a leak accident. Though the conditions related to the pit initiations on copper were reported 1, 2, the mechanisms associated with the pit initiations on copper have not been clarified yet.

In order to investigate pit initiations on copper, we previously developed a real-time surface observation system with a channel flow double electrode (CFDE) 3. Our group 4-7 applied the CFDE to investigation of anodic dissolution mechanisms of metals and alloys because metallic ions dissolved from working electrode (WE) can be detected by arranging a detecting electrode (DE) downstream of the WE. The developed system enables us the in-situ surface observation of copper during anodic polarization since a video recording can be carried out during the measurement. In the present study, the pit initiations on coper during anodic polarization was discussed based on the results of the dissolution currents of cupric or cuprous ions and in-situ surface observation of copper surface.

References

H. S. Campbell, J. Inst. Metals, 77, 345 (1950).

R. May, J. Inst. Metals, 82, 65 (1953).

Y. Hoshi, T. Oda, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 164, C450 (2017).

M. Itagaki, M. Tagaki, T. Mori and K. Watanabe, Corros. Sci., 38, 601 (1996).

M. Itagaki, M. Tagaki and K. Watanabe, Corros. Sci., 38, 1109 (1996).

M. Itagaki, T. Mori and K. Watanabe, Corros. Sci., 41, 1955 (1999).

Y. Hoshi, M. Itagaki, K. Tabei and I. Shitanda, J. Solid State Electrochem., 19, 3551 (2015).
A New and Cheap Methodology to Study Tridimensionally Pitting Corrosion in Stainless Steel
Authors: Coelho Dyovani , Cuadros Linares Oscar , Oliveira Aloadir , Andrade Marcos , Rios Emerson , Zimer Alexsandro Mendes , Mascaro Lucia Helena , Batista Neto Joao do Espirito Santo , Bruno Odemir Martinez , Pereira Ernesto Chaves
Published: February 2020

According to NACE International, the global cost generated by corrosion is about US$ 2.5 trillion and up to 35% could be saved by using corrosion control practices[1]. However, the correct choice of the method to control the corrosion it is tied to the knowledge of how the process happens. In this aspect, the pitting corrosion on stainless surfaces is extremely worrying. This kind of corrosion is a localized form which cavities are produced in the materials, but it is more difficult to detect, predict and avoid or minimize. Here is proposed a new and cheap methodology to study the tridimensional format of the pitting corrosion using reconstruction of segmented images. The pitting were produced by polarization of stainless steel AISI 304 at 0.46 V (vs Ag/AgCl/KCl satured) into 0.1 mol L-
1 HCl during 10 minutes at 25 °C. Afterwards, the samples were cut, washed with pure water, dried and immersed into resin keeping the plane of surface in a perpendicular direction to the base of resin block. Next, the resin block was polished using sandpaper (mesh 2000) and alumina slurry (1 μm). Every 8 μm of scraping one optical microscopy image of the surface-bulk of the sample was taken. This procedure allowed a side view of the pitting detailing its shape and extension. Finally, the segmented images were reconstructed in a tridimensional one, which shows in detail the shape and extension of each pitting in the surface of stainless steel. Now, the distribution of pitting and its shape variation could be related to the other physical and chemical signals monitored during the pitting formation, as current intensity or chemical composition. This methodology, although destructive, is easily applicable and allows to evaluate in an inexpensive and reproducible way the pitting formation.
Impedance Analysis of Ti-Based Porous Alloy
Authors: Sancy Mamié , Guerra Carolina , Silva Daniela , Walczak Magdalena , Aguilar Claudio
Published: February 2020

Ti-based alloys as porous materials with low elastic modulus has been recently developed due to the evident need to avoid the stress shielding problems related to stiffness mismatch related to human bone. In this work, Ti-30Nb-13Ta-2Mn alloy as porous material was obtained by powder metallurgy using (NH4)2(CO3) as space-holder. Powders and space-holder were mixed together and compacted with 400 MPa stress. (NH4)2(CO3) particles were removed from the compacts during sintering at 1250 °C for 3 h in Ar atmosphere. The porosity and active area of the porous electrode were estimated by using Archimedes methods and BET analysis. In addition, the surface analysis was carried out by SEM and XRD. Finally, electrochemical measurements such as open circuit potential curves, polarization curves and electrochemical impedance spectroscopy were carried out in a simulated blood plasma fluid called Ringer’s solution at 37 ºC. Results revealed foams with heterogeneous pore distribution in diameter as well as length. The electrochemical results showed that the corrosion potential was shifted to more negative values and the anodic and cathodic current were increased as a function of exposure time. On the other hand, impedance analysis displayed an impedance of the de Levie associated to the anodic response in parallel with an interfacial impedance attributed to cathodic response. Additionally, an evolution of the passive oxide layer as a function of exposure time was observed, which was mainly formed at the pore walls and, the cathodic reaction related to the oxygen reduction reaction took place mainly outside the pore.

Reference

E. Orazem and B. Tribollet, Electrochemical Impedance Spectroscopy, 2nd Edition, John Wiley & Sons, Inc. Hoboken, New Jersey (2017) 322-332.

O.E. Barcia, E. D’Elia, I. Frateur, O.R. Mattos, N. Pébère, B. Tribollet, Application of the impedance model of de Levie for the characterization of porous electrodes, Electrochimica Acta 47 (2002) 2109-2126.
(Invited) High Temperature Corrosion of Chromia-Forming Alloys By CO2: Effects of H2o and so2
Authors: Xie Yun , Yu Chun , Nguyen Thuan Dinh , Zhang Jianqiang , Young David John
Published: February 2020

Hot CO2 gas is surprisingly corrosive to chromia forming alloys as a result of internal carburisation, which decreases the ability of an alloy to form a protective Cr-rich oxide scale. Comparison of Fe- and Ni- base alloys reacted with Ar-20CO2 shows that the latter can provide superior performance, by virtue of their better resistance to carburisation. Experiments with model Fe-Cr and Ni-Cr alloys at 650oC show that addition of water vapour to the gas is detrimental to the performance of Fe-based alloys: chromia grains are refined, leading to enhanced diffusion and accelerated scale growth; large chromia platelets grow from the scale, generating stress and leading to premature failure; the nucleation and growth of Fe-rich nodules leads to breakaway corrosion. Nickel-base alloys of marginal chromium content undergo internal oxidation in dry CO2, accompanied by buckling of surface regions in wet CO2.

Addition of 0.5% SO2 to Ar-20CO2 is mildly detrimental to the performance of Fe-Cr alloys, causing a slight acceleration in the nucleation and growth of Fe-rich oxide nodules. The addition of 20% water vapour to Ar-20CO2 is also detrimental, promoting Fe-rich oxide growth and breakaway corrosion. However, the simultaneous addition of H2O and SO2 to Ar-20CO2 leads to complete passivation of the alloy surface by a slow growing Cr2O3 scale. These effects are discussed in terms of grain boundary segregation and diffusion of impurity species within the chromium oxide.
Oxide Stability in High-Temperature High-Velocity Steam
Authors: Opila E.
Published: February 2020

Recent development of a high-temperature high-velocity steam jet furnace has allowed the rapid evaluation of oxide stability toward formation of gaseous metal hydroxides. Temperature dependent results have been obtained for the formation of the gaseous species Si(OH)4, TiO(OH)2, TaO(OH)3 and Al(OH)3 from their respective binary metal oxides SiO2, TiO2, Ta2O5, and Al2O3 by simple recession measurements. Results are compared to calculated equilibrium partial pressures and available literature data in an effort to establish the relevance of this technique for establishing equilibrium conditions. Challenges for adapting this technique to explore the stability of complex silicates such as Y2Si2O7 in high-temperature high-velocity steam are also described. Finally, the advantages and disadvantages of utilizing the steam jet technique for establishing oxide stability in high-temperature high-velocity steam are summarized.
Influence of Ni and Cu on Oxide-Scale Structure of Steel
Authors: Harashima Aya , Kondo Yasumitsu
Published: February 2020

In steel products, high surface quality is required in addition to characteristics corresponding to intended use. For improving surface quality of steel products, it is important to control structure of oxide scales. In hot rolling process, heterogeneous structure of oxide scales, such as uneven scale/steel interface, causes surface defects. For steels containing Ni, it has been reported that structure of oxide scales at the scale/steel interface is characteristic and complicated. Consequently, in this report, Ni and Cu, which are nobler than Fe, are focused on, and the effects of these elements on structure of oxide scales of steels are investigated. Fe-10mass%Ni and Fe-10mass%Cu alloys were oxidized at 1000°C or 1200°C in an atmosphere of 10%O2+20%H2O+70%N2 for 1800s.

　In all cases, uneven scale/steel interfaces are observed (see Fig.1). In case of Fe-Ni alloy, Ni-enriched metal phase of complicated form is observed in oxide scales. Concentration of Ni in metal phase increases as it approaches the surface. On the other hand, in case of Fe-Cu alloy, precipitation of Cu phase is observed. Cu precipitates as particles in oxide scale at 1000°C, while it precipitates as a layer at the scale/steel interface under oxide scale at 1200°C.

　With regard to the uneven scale/steel interface, it should be caused by the property that both Ni and Cu are nobler than Fe. The mechanism can be explained as follows: first, selective oxidation of Fe proceeds, and Ni or Cu enriches at the scale/steel interface. Then, internal oxides of Fe precipitate and Ni or Cu enriches around them. Finally, with proceeding of such heterogeneous oxidation, internal oxides of Fe and those locally Ni- or Cu-enriched area are simultaneously occluded into the scale/steel interface, and therefore uneven scale/steel interface forms.

　With regard to the different structure of oxide scales at the scale/steel interface in Fe-Ni and Fe-Cu alloys, that is, enrichment of Ni and precipitation of Cu, it should be caused by the difference of the solid solubility limit of Ni and Cu to austenite. According to the phase diagram of Fe-Ni alloy, Ni dissolves in austenite completely at both 1000°C and 1200°C. On the other hand, according to the phase diagram of Fe-Cu alloy, Cu dissolves in austenite partly at both 1000°C and 1200°C. Because the solid solubility limit of Cu to austenite is just about 10% at 1200°C, Cu which exceeds its solid solubility limit with proceeding of oxidation of Fe should precipitate as liquid phase at the scale/steel interface. Although both Ni and Cu are nobler than Fe, different structure of oxide scales forms at the scale/steel interface in Fe-Ni and Fe-Cu alloys corresponding to the solid solubility limit to austenite.

Figure 1
Understanding Corrosion of Ni-Cr Alloys in Molten Chloride Salts
Authors: Raiman Stephen S , McMurray Jake , Mayes Richard , Abney Carter , Keiser James , Pint Bruce
Published: February 2020

Molten chloride salts possess many attractive properties for use as a coolant and storage medium in advanced nuclear reactors and in concentrating solar power systems. Among the many challenges is the corrosion of salt-facing structural components. In molten halide salts, the passive films that typically form on the surface of corrosion resistant alloys either do not form, or are unstable due to the very low oxygen activities. Therefore, corrosion of materials is dependent largely on interfacial dissolution reactions between the molten salt and the bare metal surface in which alloy constituents with the most stable chlorides tend to be the most likely to dissolve.

For most common structural alloys, chromium has the most stable chloride, and thus selective dissolution of chromium from the alloy into the salt is the dominant form of material degradation in molten halides. While this fact is well known and backed-up by experimental data, the mechanism of chromium depletion from alloys is not yet known. To truly understand corrosion in molten salts, the mechanism of chromium depletion from alloys must be understood and quantified.

This talk will discuss results of a combined experimental and computational strategy aimed at fundamentally understanding corrosion of alloys in molten chloride salts. Controlled capsule tests are conducted in which model Ni-Cr alloys are exposed to molten KCl-MgCl2 at temperatures in excess of 600°C to measure degradation in molten salt. In an effort to maintain greater control of the molten salt environment, new processes to sufficiently purify salts are discussed. Quantification of salt impurities is matched to corrosion results in an effort to quantify the effect of salt impurity concentrations on corrosion rates. Traditional experimentation is coupled with x-ray spectroscopy and thermodynamic modeling to identify relevant reactions and to develop a thermodynamic description of the alloy-salt system.

This work is funded by the Laboratory Directed Research and Development Fund at Oak Ridge National Laboratory.
(Invited) Chromia Semiconducting Properties Study: A Textbook Case?
Authors: Latu-Romain Laurence , Parsa Yohan , Wouters Yves
Published: February 2020

Chromia, Cr2O3, is the protective layer of a large family of metallic alloys denominated as chromia-formers. The chromia structure is particularly complex [1] and merits to be studied if one wants to try to improve its chemical durability.

In this work, oxidation of pure Cr is studied as a function of temperature (from 800 °C to 900 °C) and oxygen partial pressure p(O2) (from 10-14 to 10-12 atm.) Chromia semiconducting properties are investigated by photoelectrochemistry at macroscopic, mesoscopic and microscopic scales, whereas its morphological and structural properties are studied by Transmission Electron Microscopy with orientation mapping tool (called ASTAR). By associating these two techniques -which gives respectively the type of semiconduction and the oxide growth direction- it becomes possible to identify the nature of the major point defects in chromia [2].

In every case, the morphology of the oxide scale is duplex (see Fig. 1). It is revealed that the morphology is linked to the growth direction and not to the nature of the major point defect: anionic (inward) growth leads to equiaxed grains whereas cationic (outward) growth is conducive to columnar grain formation.

Finally by tuning the oxygen partial pressure, chromia semiconducting properties can be controlled. In particular when p(O2) increases from 10-14 to 10-12 atm., the type of semiconduction of the external chromia subscale changes from n-type to p-type ; and, for intermediate conditions, chromia is insulating [3]. The growth of such stoichiometric chromia layer may be helpful for the optimization of chemical durability of chromia forming alloys.

References

[1] A. Holt, P. Kofstad, Electrical conductivity and defect structure of Cr2O3. I. High temperatures ( > ~ 1000°C), Solid State Ionics, 69 (1994) 127-136.

[2] L. Latu-Romain, Y. Parsa, S. Mathieu, M. Vilasi, M. Ollivier, A. Galerie, Y. Wouters, Duplex n- and p-type chromia grown on pure chromium: a photoelectrochemical and microscopic study, Oxid. Met. 86(5) (2016) 497-509

[3] L. Latu-Romain, Y. Parsa, S. Mathieu, M. Vilasi, A. Galerie, Y. Wouters, Towards the growth of stoichiometric chromia on pure chromium by the control of temperature and oxygen partial pressure, Corros. Sci. (2017) DOI 10.1016/j.corsci.2017.07.005

Figure 1: ASTAR grain orientation maps recorded with a probe size of 1 nm and a step size of 3 nm (see color codes on the left) of Cr2O3 grown on pure Cr (a) at 800 °C during 60 min at a p(O2) of 10-14 atm, (b) at 850 °C during 30 min at a p(O2) of 10-13 atm, (c) at 900 °C during 30 min at a p(O2) of 10-12 atm. From [3].

Figure 1
(Invited) Developing Environmental Barrier Coatings Resistant to Molten Calcium-Magnesium-Aluminosilicate (CMAS)
Authors: Wiesner Valerie L , Harder Bryan J , Garg Anita , Bansal Narottam P
Published: February 2020

In order to improve fuel efficiency in commercial aircraft engines, ceramic matrix composites (CMC) are considered a leading material system to replace metal-based turbine engine components, due to their lower density and high-temperature capabilities compared with traditional metallic structural materials. However, silicon-based CMCs are susceptible to oxidation and corrosion in the harsh combustion environment found in air-breathing turbine engines. Environmental barrier coatings (EBCs) are being developed and applied to protect and to enhance durability and service life of CMC components for application in the hot-section of engines.

The development of robust EBCs is threatened by sand, volcanic ash and other particulate debris, which are routinely ingested by aircraft engines in varying geographic regions. At temperatures >1200°C, these particulates melt, yielding molten calcium-magnesium-aluminosilicate (CMAS) deposits. These deposits can significantly reduce the durability of present and future engine component materials, particularly EBCs designed to protect silicon-based ceramic matrix composites (CMC). Near target operating temperatures (~1500°C) of future CMC-based aircraft engines, molten CMAS behaves like a viscous melt that can infiltrate and chemically interact with protective coatings, causing premature failure of the EBC system and ultimately the overall CMC engine component.

Degradation of candidate EBC materials based on rare-earth silicates by molten CMAS will be presented with a focus on recent work, as well as methods of evaluating the complex high-temperature materials interactions, accomplished at NASA Glenn Research Center.
The Mechanisms of Spinel/Solid Solution Formation and Wear in Gasification High Chrome Oxide Refractories Caused By Carbon Feedstock Impurities
Authors: Bennett James P , Kwong Kyei-Sing , Nakano Jinichiro , Nakano Anna , Nealley William
Published: February 2020

Gasification is a term used to describe the process of converting high carbon materials (such as coal and petcoke) into H2 and CO gases used in the production of power or as a feedstock material in chemical production. High temperature slagging gasifiers are operated between 1325-1575oC; a temperature range that oxidizes, transforms, and/or melts organo-metallic and mineral impurities in the carbon source; forming molten particles that coalesce into slag. By-products from the gasification of a carbon feedstock constitute about one wt pct of petcoke to about 10 wt pct or more for coal. To protect the gasification chamber from the severe service environment, they are lined with high chrome oxide refractories, a material which slowly interacts with the slag, and which need to be replaced every 6-36 months. Longer and predictable service life of the refractory liner is desired. Refractory wear is caused by interactions between the slag and refractory, leading to chemical dissolution or spalling (chemical or structural) of the liner. The chemical and physical nature of the wear, along with a thermodynamic study of process are discussed; with emphasis on the role of slag Al, Mg, Fe, and V interactions with refractory brick to form spinel/solid solution structures.
(Invited) All-Inorganic Water-Dispersible Silicon Quantum Dots
Authors: Fujii Minoru , Sugimoto Hiroshi , Kano Shinya
Published: February 2020

A colloidal solution of Si quantum dots (QDs) is a versatile material useful for electronics, optoelectronics and biophotonics. Recently, we have developed a new type of all-inorganic Si QDs that can be dispersed in alcohol and water almost perfectly without organic ligands. The unique property of the QDs arises from the heavily B and P codoped crystalline Si shell, which induces negative potential on the surface and prevents agglomeration of Si QDs in polar solvents. Thanks to the shell, the luminescence property is very insensitive to the environment and to the chemical treatment. To the ligand-free surface of codoped Si QDs, molecules in a solution can easily access, and thus a variety of charge-transfer-induced processes such as a photocatalytic effect are expected.

In this presentation, we first discuss the structure of codoped Si QDs based on the data obtained by atom probe tomography. We then discuss the size dependence of the HOMO and LUMO level energies measured from the vacuum level by combining photoemission yield spectroscopy and photoluminescence spectroscopy. Furthermore, we show density of state spectra of single codoped Si QDs obtained by scanning tunneling spectroscopy and discuss the size dependence of the in-gap donor and accepter states, onset of the conduction and valence band edges, and the ionization energies of dopants. From these data, we will identify the origin of the luminescence in B and P codoped Si QDs. We demonstrate that the codoped Si QDs exhibit efficient luminescence in the energy ranges below and above bulk Si band gap. The below bulk band gap luminescence opens up a new application of codoped Si QDs as a phosphor in the second biological window (1000-1300 nm). We also discuss charge transfer between Si QDs and adsorbed molecules. We show charge-transfer-induced reversible enhancement and quenching of photoluminescence of Si QDs and the photocatalytic activity to adsorbed molecules. We can produce a variety of nanocomposites composed of codoped Si QDs and noble metal (Au, Ag and Pt) nanostructures. We discuss the enhanced optical response due to the coupling with the localized surface plasmon resonances of metal nanostructures. By using the colloidal solution of codoped Si QDs, we can produce the monolayer film, the multilayer film and the dense solids. In these films, we discuss the energy transfer between QDs. Finally, we show electrical transport properties of the films and demonstrate the possible application as electronic devices.
A Method to Improve Quantum Efficiency of Phosphors in the Submicron Size Regime Using a Flux for Solid State Lighting Applications
Authors: Ha Jungmin , Novitskaya Ekaterina , Hirata Gustavo , Zhou Chenhui , Ridley Robyn , Graeve Olivia A , Wang Zhenbin , Ong Shyue Ping , McKittrick Joanna
Published: February 2020

Micron sized phosphors have been widely studied by using a solid-state reaction method for application in near UV-emitting LEDs. This method produces large crystallite size powders, but have higher quantum efficiencies than smaller crystallite size powders. For the phosphor configuration, the packing density of these large particles on the device is thus low and generates substantial light-scattering. To overcome this issue, phosphors with a small, narrow size distribution are required. If the particle radii are < ~400 nm, scattering from these particles will be negligible on visible and UV radiation. However, submicron-sized phosphors with nano-sized crystallites have poor quantum efficiency compared to micron-sized phosphors with micron-sized crystallites.

An addition of flux (NH4F, NH4Cl, or H3BO3) to the CaMgSi2O6:Eu2+ phosphors during synthesis was performed and the effect of the flux on the crystallite size and quantum efficiency of nanocrystalline and submicron phosphors particles was examined. The use of NH4F or NH4Cl increased the crystallite size in the submicron sized particles, which yielded an increase in emission intensity and quantum efficiency. Adding the H3BO3 flux crystallized SiO2 and changed lattice parameters, degrading the luminescent properties. Excessive NH4Cl was also examined and it resulted in nucleation of a second phase and changed lattice parameters with no improvement in luminescent properties. These results demonstrate that a careful selection and use of a flux is a method to improve the quantum efficiency of submicron particles sized phosphors. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).
(Invited) Strain Assisted Band Gap Engineering of SiGe Core–Shell Nanowires using Low-Temperature Condensation Process
Authors: Berbezier Isabelle , David Thomas , Ronda Antoine , Favre Luc , Gailhanou Marc , Gentile Pascal , Buttard Denis , Calvo Vincent , Amato Michele , Aqua Jean-Noël
Published: February 2020

Selective oxidation of the silicon element of silicon germanium (SiGe) alloys during thermal oxidation is a very important and technologically relevant mechanism used to fabricate a variety of microelectronic devices. We show a two-step epitaxy/condensation process at low temperature to produce atomically flat Ge rich layer fully strained and free of defects. We demonstrate that the condensation based process enables the total inhibition of the classical ATG morphological instability, together with the hindering of dislocations for critical thickness much greater than those commonly obtained by direct deposition. Those behaviors could be explained by the injection of self-interstitials in the Ge-rich layers during condensation.

An integrative approach involving vapor–liquid–solid (VLS) growth followed by selective oxidation steps to the construction of core–shell nanowires and higher-level ordered systems with scalable configurations is used. We contrast this strategy that uses reaction-diffusion-segregation mechanisms to produce coherently strained structures with highly configurable geometry and abrupt interfaces with growth-based processes which lead to low strained systems with non uniform composition, three-dimensional morphology, and broad core–shell interface. We specially focus on SiGe small core–shell nanowires and demonstrate that they can have up to 70% Ge-rich shell and 2% homogeneous strain with core diameter as small as 14 nm. Key elements of the building process associated with this approach are identified with regard to existing theoretical models. Moreover, starting from results of ab initio calculations, we discuss the electronic structure of these novel nanostructures as well as their wide potential for advanced device applications. Similar core-shell structures can be formed around small nanocrystals for photonic applications.
Atomic Layer Deposition of ZnO and Doped ZnO As Alternative Transparent Conducting Oxides for Photovoltaics
Authors: Ryan Louise P , Walsh Adrian , McCarthy Melissa M. , Monaghan Scott , Modreanu M , Romanitan Cosmin , Chaix-Pluchery Odette , O'Brien S , Pemble Martyn E , Povey Ian M
Published: February 2020

Organometallic halide perovskite solar cells have gained considerable interest in recent times, with low cost and high power conversion efficiencies [1]. However, such cells are not without problems such as, stability, scalability and the need for a low thermal budget in the fabrication of tandem structures. In this work, we examine the transparent conducting electrode where the current materials of choice are FTO and ITO which require a higher process temperature (>450oC).

Zinc oxide thin films have attracted significant attention as transparent conducting oxides due to their diverse electrical and optical properties. ZnO is an n-type semiconductor with a direct band gap of 3.3 eV. It is optically transparent in the UV/visible and infrared spectra and exhibits promising electrical properties.

ALD has distinct characteristics that make it a prospective deposition method of ZnO and doped ZnO, low temperature, conformal and large surface area coating capabilities. The deposition of ZnO and doped ZnO has previously been reported. In this work, an ALD process has been developed to deposit ZnO as a potential TCO in solar cells.

ZnO was deposited using low temperature atomic layer deposition (ALD). Subsequently, zinc oxide was doped with Al, Ti and Hf and the electrical, optical and structural properties were analyzed to determine the effect of doping on ZnO. The presented results revealed that Ti-doped ZnO was the suitable TCO candidate with a sheet resistance value of 41 Ω/□ and electron mobility of 12.8 cm2/Vs. In addition to promising electrical properties, Ti-doped ZnO also exhibited high optical transparency of >80% in the UV/ visible and IR ranges. We demonstrate that ALD of Ti-doped ZnO could be a viable alternative to ITO and FTO for TCO materials in photovoltaics. Preliminary data from perovskite solar cells fabricated with a ZnO based transparent conducting electrode are presented and discussed.

[1] https://www.nrel.gov/pv/assets/images/efficiency-chart.png