Microstructure Of Oxide Films Research Articles

Effect of Boron Content in LiOH Solutions on the Corrosion Behavior of Zr-Sn-Nb Alloy.

In pressurized water reactors, LiOH may be concentrated in some areas, leading to the accelerated corrosion of fuel claddings. Injecting boric acid into primary coolants can mitigate the accelerated corrosion effect of LiOH on Zircaloys, but the effects of boron content on the corrosion behavior of the Zr-Sn-Nb alloy are still unknown. This work focused on the corrosion and hydrogen absorption behavior at 360 °C/18.6 MPa in 100 mg/kg LiOH solutions with 0 mg/kg, 50 mg/kg, and 200 mg/kg boron contents for up to 510 days, aiming to study the effect of boron content on corrosion resistance in LiOH solutions. Corrosion kinetics, microstructures of oxide films, hydrogen absorption concentrations and hydride morphology were obtained after the test. The results show that injecting boron in LiOH solutions can significantly reduce the corrosion weight gain, hydrogen concentration, and hydrogen length of Zr-Sn-Nb alloys, that is, improving corrosion resistance effectively. During the oxidation of the Zr-Sn-Nb alloy, B3+ and Li+ incorporate in oxide films. The incorporation of Li+ may lead to the generation of oxygen vacancies, which can carry oxygen from the solutions to O/M interface, accelerating corrosion. The incorporation of B3+ in oxide films will slow down the oxidation of Zr-Sn-Nb alloys by reducing the oxygen vacancies caused by Li+ aggregation.

Effect of yttrium on the formation, microstructure and high-temperature oxidation resistance of the oxide film on the surface of FeCr alloy

Yttrium was diffused into the surface layer of FeCr alloy using an electrodeposition–thermal method via yttrium nitrate solution and diffusion annealing at 1000 °C. Y-doped FeCr samples exhibited excellent high-temperature oxidation resistance. The mass gains and spallation of Y-doped FeCr samples were only 0.51–0.64 mg/cm2 and 0.19–0.25 mg/cm2, respectively, and much lower than the alloy without yttrium (20.7 mg/cm2 and 9.08 mg/cm2, respectively) when oxidized in air at 900 °C for 200 h. The presence of yttrium increased the number of oxide nucleation sites, led to the transformation of the oxide from the Cr2O3 phase to the spinel (FeCrY)3O4 phase and accelerated the rapid formation of a continuous oxide film in the initial oxidation stage. The yttrium content affected the formation and microstructure of oxide film due to the lattice distortion of the FeCr phase. Excess Y induced formation of Y2O3 at grain boundaries, which further increased the bonding force between the oxide film and the substrate. A first-principles calculation confirmed that the bond strength between Y and other atoms was improved significantly. The length of the CrY bond showed little change under an external stress, which increased the bonding strength of the FeCr/Cr2O3 interface.

Oxidation kinetic behavior and microstructure mechanism of GH3536 alloy fabricated by laser powder bed fusion

This study comprehensively investigates the oxidation kinetics of laser powder bed fusion (LPBF) processed GH3536 superalloy at 950 °C. The oxidation kinetics and oxide film microstructure characteristics are analyzed and the underlying mechanism is discussed, by comparing with the conventionally manufactured wrought GH3536 samples under the exactly same test condition. The oxidation rate of LPBF samples is faster at initial stage and then tends to flatten out with increase of heating duration time. The finer and equiaxed chromia crystals formed in LPBF GH3536 surface can effectively improve the oxidation resistance comparing to the columnar structure chromia in wrought GH3536. The oxide film with excellent protection in LPBF GH3536 provides an important contribution to the application of GH3536 at high temperature.

Influence of Ammonia on the Corrosion Behavior of a Zr–Sn–Nb Alloy in High Temperature Water

Corrosion behaviors, microstructures of oxide films, and hydrogen absorptions of a Chinese domestic Zr alloy in 6.7 × 10−3 mol/L ammonia solution and 2.9 × 10−4 mol/L LiOH+9.3 × 10−2 mol/L H3BO3 solution at 360 °C, 18.6 MPa were studied. Weight gains, oxide film thicknesses, and hydrogen absorptions showed that the corrosion rate in the ammonia solution is a little higher than that in the boron–lithium solution. There is no significant difference in the microstructure and crystalline structure between the oxide films formed in the two types of solutions. The element distributions along the depth direction of the oxide films showed the existence of nitrogen in the oxide film formed in ammonia solution. Moreover, nitrogen was found to be segregated in local areas in a range of about 2 μm from the oxide/metal interface. The corrosion behavior of the Chinese domestic Zr alloy in 360 °C aqueous solution shows no difference with other Zr alloys.

Discovery and Temperature Dependence of α-Fe2O3 in Oxide Film on Iron Bonded Wheel and Effect Mechanism of Temperature

Polishing of oxide film on ELID wheel surface has an important effect on grinding surface quality. First, electrochemical reaction of oxide film was researched, and transformation mechanism of component of oxide film under grinding temperature was proposed. The phase compositions, generation and transformation mechanism of the α-F2O3 in the oxide film was measured by XRD, XPS, FITR. The microstructure of oxide film was observed by using TEM. Researched results show, α-F2O3 in the oxide film have been found, the content and transformation of α-F2O3 are closely related to the grinding temperature. Iron oxide in oxide film is transformed into α-F2O3 with temperature gradually, and nano grain α-F2O3 with high purity, good crystal lattice, and grain size 10–80 nm is formed when grinding temperature is 600 °C. TEM analyzed shows, the grain in oxide film is spherality, and film structure is formed with multiple particles α-F2O3. The film structure reveals that polishing mechanism of oxide film isn’t independent act of single particle, but is cooperative behavior of multiple particles α-F2O3.

Microstructure evolution for oxide film of anodic aluminum foil used in high voltage electrolytic capacitor

The oxide film of anodic aluminum foil is the main working medium of aluminum electrolytic capacitor, and its quality directly affects the electrical performance of capacitor. The fabrication of anodic aluminum foil is conducted by a multiple-step anodizing process, including hydration, formation, heat treatment and phosphoric acid treatment. The microstructure evolution for oxide film of anodic aluminum foil during preparation process is studied quantitatively in this paper. The results show that, the pores area on the foil surface keeps decreasing after hydration and subsequent formation. However, after phosphoric acid treatment, the pores area stops decreasing and increases to a local maximum value. The length distribution of ‘corn-flake’ structures keeps increasing, from the range of 60–120 nm to 100–140 nm. After phosphoric acid treatment, the petal edges become serrated, and many small corrosion holes with the length of 20–30 nm are left inside. The thickness of the outer amorphous layer in the anodized oxide film keeps decreasing from the initial 390 nm to the final 90 nm. In contrast, the thickness of the inner dense layer keeps increasing from the initial 130 nm to the final 550 nm. The decreasing trend of grain size continues until the end of preparation process, and reaches the final value of 10 nm. The analysis of microstructure of oxide film is helpful for obtaining optimal process parameters and improving performance of aluminum foil.

Oxide film prepared by selective oxidation of stainless steel and anti-coking behavior during n-hexane thermal cracking

In order to reduce coke formation on the substrate surface, selective oxidation pre-treatments were systematically assessed for 316L stainless steel under H2-H2O atmospheres at 650 °C–950 °C and 0.1 MPa for 10 h. The phase constitution, elemental composition and surface morphology of oxide films were characterized by a combination of SEM, XRD, and EDS. The results showed that the oxidation temperature had a great influence on the morphology and microstructure of oxide films. The Mn and Cr content on the metal surface gradually increased with the increasing exposure temperature. The element composition was mainly associated with MnCr2O4 and Cr2O3. Thickness of oxide films was evaluated in various conditions. The anti-coking performance was evaluated by the n-hexane thermal cracking. It was found that the amount of the coke deposited on the oxidized tube was much smaller than that on the untreated tube, with an average anti-coking ratio of 83.2%. Moreover, the morphologies of carbon deposits were mainly filamentous on the inner surface of untreated tube, but granular for the case of the oxidized tubes.

Properties of α-Fe2O3 in Oxide Film of α-Fe Grinding Wheel Without Abrasive Particles

The properties and the formation mechanism of α-Fe2O3 in oxide film on α-Fe bonded grinding wheel without abrasive grains were researched. The content of α-Fe2O3 in oxide film was measured by XRD and XPS, the results show that there are more α-Fe2O3 in the oxide film of the α-Fe bonded grinding wheel without abrasive grains than that of the iron bonded grinding wheel with abrasive grains. The microstructure of oxide film of α-Fe bonded grinding wheel without abrasive grains was measured by SEM and TEM, the results show that the oxide film formed on the surface of α-Fe bonded grinding wheel without abrasive grains was more smooth, uniform, continuous and it’s granularity is finer, which was beneficial to ultra-precision polishing. The experimental results show that the α-Fe bonded grinding wheel without abrasive grains is more suitable for ELID (Electrolytic In-process Dressing) ultra-precision polishing.

Oxidation of TbFe2: Microstructure of oxide-film by both theory and experiment

TbFe2 owing to its highest magnetostriction finds significant application in defence. However, its quality degradation due to oxidation poses an enormous challenge for being scaled up in a device. To this end, a detailed study by means of both the theory and experiment is performed here to understand the oxide-film overgrowth due to dry, thermal oxidation of TbFe2. Then these results are discussed and compared, which is found to be in agreement with each other. Understanding developed in this study would help in tuning the substrate constituents for higher temperature application, where oxidation of the substrate is a major concern.

The influence of annealing on yttrium oxide thin film deposited by reactive magnetron sputtering: Process and microstructure

Yttrium oxide thin films were prepared by reactive magnetron sputtering in different deposition condition with various oxygen flow rates. The annealing influence on the yttrium oxide film microstructure is investigated. The oxygen flow shows a hysteresis behavior on the deposition rate. With a low oxygen flow rate, the so called metallic mode process with a high deposition rate (up to 1.4µm/h) was achieved, while with a high oxygen flow rate, the process was considered to be in the poisoned mode with an extremely low deposition rate (around 20nm/h). X-ray diffraction (XRD) results show that the yttrium oxide films that were produced in the metallic mode represent a mixture of different crystal structures including the metastable monoclinic phase and the stable cubic phase, while the poisoned mode products show a dominating monoclinic phase. The thin films prepared in metallic mode have relatively dense structures with less porosity. Annealing at 600 °C for 15h, as a structure stabilizing process, caused a phase transformation that changes the metastable monoclinic phase to stable cubic phase for both poisoned mode and metallic mode. The composition of yttrium oxide thin films changed from nonstoichiometric to stoichiometric together with a lattice parameter variation during annealing process. For the metallic mode deposition however, cracks were formed due to the thermal expansion coefficient difference between thin film and the substrate material which was not seen in poisoned mode deposition. The yttrium oxide thin films that deposited in different modes give various application options as a nuclear material.

Effect of Surface State on Nodular Corrosion Resistance of Zircaloy-4 Alloy

The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in superheated steam at 500 °C/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide microstructure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.

Microstructural characterization of CoMnFeO4thin films deposited by radio-frequency sputtering

CoMnFeO4 thin films are stable materials useful to study the influence of radio-frequency sputtering experimental conditions, on the microstructure of oxide films. From various techniques of electronic microscopy, gas adsorption techniques and ellipsometry measurements, it was shown that such oxides films prepared with 0.5 Pa sputtering argon pressure and 5 cm target–substrate distance are very dense. On the other hand, the samples obtained under higher pressure and/or longer distance, are microporous. This porosity is mainly due to shadowing and energetic effects of sputtered particles. According to different characterization techniques, a simple model is proposed to describe the microstructure of the films studied.

The Microstructure and Capacitance Characterizations of Anodic Titanium Based Alloy Oxide Nanotube

This paper presents a simple anodization process to fabricate ordered nanotubes (NTs) of titanium and its alloys (Ti-Mo and Ti-Ta). TiO2, MoO3, and Ta2O5are high dielectric constant materials for ultracapacitor application. The anodic titanium oxide contains a compact layer on the NT film and a barrier layer under the NT film. However, the microstructure of oxide films formed by anodic Ti-Mo and Ti-Ta alloys contains six layers, including a continuous compact layer, a continuous partial porous layer, a porous layer, a net layer, an ordering NT film, and an ordering compact barrier layer. There are extra layers, which are a partial porous layer and a porous layer, not presented on the TiO2NT film. In this paper, we fabricated very high surface area ordered nanotubes from Ti and its alloys. Based on the differences of alloys elements and compositions, we investigated and calculated the specific capacitance of these alloys oxide nanotubes.

Oxidation Behaviors of DO<sub>3</sub> Type Fe<sub>3</sub>Si Based Intermetallics at 900°C

In the present work, intermetallics Fe3Si and Fe3 (Si1-xAlx) (x=0.33, 0.67, 0.80) produced by arc melting, were evaluated regarding the oxidation at 900°C in air. The test preformed was the isothermal and cyclic oxidation. The microstructures of oxide films were analyzed by XRD, SEM, EDS, EPMA. The result showed that the four kinds of intermetallics had good oxidation resistance at 900°C.The addition of Al element can increase the oxidation resistance of Fe3Si based intermetallics. The oxidation kinetics of the four intermetallics follows the rule of the parabola. The main oxidation product of Fe3Si is SiO2.The kinetics of oxidation reaction is mainly controlled by Si diffusion. The oxidation product of three Al alloying Fe3Si based intermetallics is Al oxide. Al moves outward from the substrate to form a protective oxide film which restrained the diffusion of Si and Fe outward.

Liquid Oxide Flow during Oxidation of Zirconium Diboride-Silicon Carbide Ultra High Temperature Ceramics

Recent ideas on the oxidation of ZrB2-SiC are presented, emphasizing the behavior of the boria-silica-zirconia liquid (BSZ liquid) which forms during oxidation and flows to transport silica and zirconia to the surface of the scale. Oxide film microstructure is strongly influenced by the boron oxide, which acts as a volatile flux.

Nanoscale duplex oxide growth during early stages of oxidation of Cu-Ni(100)

for pure metals hold during the initial oxidation of Cu-Ni alloys. Our ex situ TEM observation of oxidized Cu-Ni samples revealed that Cu2O islands nucleate preferentially on top of NiO islands rather than on bare Cu-Ni surface regions between NiO islands, an intriguing phenomenon defying the expectation based on prevailing knowledge of passivation. Our results demonstrate the importance of oxygen partial pressure in controlling the microstructure of oxide films during alloy oxidation, which have significant technological implications for controlled oxide growth.

Effect of surface nanocrystallization on the corrosion behavior of Zircaloy-4

The contrastive corrosion experiments between surface nanocrystallined Zircaloy-4 and coarse-grained Zircaloy-4 under the condition of 673 K/10.3 MPa in pure water are carried out, and the microstructure of oxide films has been studied. The results indicate that the growth rate of oxide films formed on the nanocrystalline Zircaloy-4 is lower than that of oxide films formed on the coarse-grained Zircaloy-4. Simultaneously, the oxide/metal interface of the former is more regular and glossy than that of the latter. For nanocrystalline Zircaloy-4, the low oxygen diffusion rate through the oxide/metal interface can hinder the reaction of oxygen ion with metal ion. Furthermore, more tetragonal ZrO2 are observed in the oxide films, which can delay the martensite phase transition from tetragonal to monoclinic phase in oxide films.

Effects of lanthanum ion-implantation on microstructure of oxide film formed on Co-Cr alloy

Isothermal and cyclic oxidizing behavior of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 °C in the air by thermal-gravimetric analysis (TGA). Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the morphology and structure of oxide film after oxidation. Secondary ion mass spectrum (SIMS) method was used to examine the binding energy change of chromium caused by La-doping and its influence on the formation of Cr 2O 3 film. Laser Raman spectrum was used to examine the stress changes within the oxide film. It was found that lanthanum implantation remarkably reduced isothermal oxidizing rate of Co-40Cr and improved anti-cracking and anti-spalling properties of Cr 2O 3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr 2O 3 oxide and increased high temperature plasticity of the oxide film. Lanthanum mainly existed on the outer surface of Cr 2O 3 oxide film in the form of fine La 2O 3 and LaCrO 3 spinel particles.

Microstructure, porosity and roughness of RF sputtered oxide thin films: Characterization and modelization

Spinel CoMnFeO 4 thin films are stable materials useful to study the influence of radio-frequency (RF) sputtering experimental conditions on the microstructure of oxide films. It has been demonstrated by various techniques such as electronic and atomic force microscopy (AFM), gas adsorption techniques and ellipsometry, that films prepared with 0.5 Pa sputtering argon pressure and 5 cm target–substrate distance are very dense. On the other hand, the samples obtained under higher pressure and/or longer distances are microporous with a mean pore size generally lower than 2 nm. The specific surface areas of such films reach about 75 m 2/g. According to the simple model proposed, the films are made of three layers. From the bottom to the top of the film, the first one at the interface with the substrate is 100% dense. The second layer is made of cylindrical rods set up according to a compact plane. Its porosity is due to the lattice interstices. Hemispheric domes covering each rod make up the third layer, which displays a degree of roughness related to the shape and the hexagonal arrangement of the domes. The surface enhancement factor (SEF), the porosity and roughness, calculated from the model, are in corroboration with the experimental values. The porosity factor is however slightly underestimated by the model for very porous samples.

Effect of Water Chemistry and Composition on Microstructural Evolution of Oxide on Zr Alloys

Abstract The microstructure of oxide films formed on Zircaloy-4 and Alloy No. 3, which has a composition similar to ZIRLO™, was investigated by high resolution transmission and scanning electron microscopy, and by scanning probe microscopy after corrosion tests performed at 360°C/18.6 MPa in deionized water or lithiated water with 0.01 M LiOH. The microstructural evolution of the oxide films was analyzed by comparing the microstructure at different depths in the oxide layer. The defects, consisting of vacancies and interstitials, such as points, lines, planes, and volumes, were produced during the oxide growth. Monoclinic, tetragonal, cubic, and amorphous phases were detected and their coherent relationships were identified. The characteristic of oxide with such microstructure had an internal cause, and the temperature and time were the external causes that induced the microstructural evolution during the corrosion process. The diffusion, annihilation, and condensation of vacancies and interstitials under the action of stress, temperature, and time caused stress relaxation and phase transformation. It was observed, in the middle of the oxide layer, that the vacancies absorbed by grain boundaries formed pores to weaken the bonding strength between grains. Pores formed under compressive stress lined up along the direction parallel to the compressive stress. Thus, cracks developed from the pores were parallel to the oxide/metal interface. Li+ and OH− incorporated in oxide films were adsorbed on the wall of pores or entered into vacancies to reduce the surface free energy of the zirconium oxide during exposure in lithiated water. As a result, the diffusion of vacancies and the formation of pores were enhanced, inducing the degradation of the corrosion resistance. The relationship between the corrosion resistance of zirconium alloys and the microstructural evolution of oxide films affected by water chemistry and composition is also discussed.