Needle-like Oxide Research Articles

The Mechanism of Oxide Growth on Pure Aluminum in Ultra-High-Temperature Steam

A high-temperature water steam (H2O(g)) between 300 °C and 1000 °C reacted with the Al surface in this study. The Al surface states were characterized and analyzed using XRD °C, XPS, and SEM after and before the reaction, and the effects and mechanism of H2O(g) on the Al surface morphology and chemical composition were studied. The experiment showed that for an Al sheet reacting with H2O(g), its oxide layer morphology changed from nano-needle to flaky and granular oxides gradually with the rise of temperature, and finally the Al surface became porous as a whole. Its oxide crystals were amorphous and were determined to be aluminum oxide (Al2O3) using XPS. The needle-like oxide in the Al sheet surface tended to grow toward the surface, and no obviously inward oxidizing corrosion layer occurred in the aluminum substrate; the oxide layer between the oxide and Al sheet substrate was compact, and could effectively prevent the infiltration and corrosion of water molecules.

Novel Nanoporous Carbon/Iron Oxide Catalyst for SO2 Degradation

A green chemistry approach for fabrication of active carbon, enriched with remediated iron is shown. Detailed characterization (HRSTEM, STM, and N2 adsorption) was performed, followed by active carbon soaking in iron and manganese ionic solutions obtained from remediated mining sludge. Novel forms of active carbons with round or needle-like oxide particles on the surface were obtained by combining these materials. The materials were tested as filters for sulfur dioxide, on sulfur-rich coals fume. After adsorption, the iron structures seem to play a stronger catalytic role in the filter regeneration, transforming the adsorbed sulfur dioxide into sulfuric acid.

Effects of temperature on oxidation behaviours of 35CrMo in high temperature flue gas environment

The pipelines made by alloy 35CrMo are widely used in the process of flue gas injection. Therefore, corrosion behaviours of alloy 35CrMo have been investigated at varied temperatures, namely 120 °C, 150 °C, 200 °C and 250 °C, with same experimental pressure of 9 MPa and flus gas environment. Scanning electron microscopy was employed to examine the morphologies and microstructures of the oxide films. The results indicated that moderate temperature stands an essential role in the reaction mechanism and aggressive effects. In addition to increase in the diffusion rate of both alloy ions and corrosive gas, temperature can also reform the morphology of oxides by resulting in larger oxide particles and thicker oxide films, plus the transmission from needle-like oxides to spherical oxides.

Effects of iron content in Ni[sbnd]Cr[sbnd]Fe alloys on the oxide films formed in an oxygenated simulated PWR water environment

The iron content in NiCrFe alloys strongly affected the properties of oxide films after 1012 h of immersion in an oxygenated simulated PWR primary water environment at 310 °C. Increasing the iron content in the alloy increased the porosity and thickness of the outer layer and the inner layer. Increasing the iron content in the alloy increased the amount of spinel needle-like oxides and decreased the amount of NiO particles in the outer layer. Cellular oxide in the inner layer was nickel-rich in the center and chromium-rich at the edge.

Influence of Oxidation Temperature on Photocatalytic Activity of Cr-TiO<sub>2</sub> Coatings by Mechanical Coating Technique

The photocatalyst coatings on alumina (Al2O3) balls had been prepared by mechanical coating technique (MCT) and subsequent oxidation process with Ti powder and Cr powder, and the influence of oxidation temperature on the photocatalyst composite coatings (Cr-TiO2) were investigated. The contrast experiments of the oxidation temperature and the usage of Cr powder had been carried out. The crystal structure and microstructure of the coatings were investigated. Photocatalytic activity of the coatings was evaluated and discussed. The XRD results showed that the mixed-phase of anatase (A) and rutile (R), and mass fraction of rutile (XR) had been increased with adding Cr, especially under 973 K. The SEM images indicated that the needle-like oxide was formed at the temperature of 973 K. The photocatalytic activity is relatively higher at 973 K under both of ultraviolet (UV) and visible light (VL). At the same time, the influence on photocatalytic activity of the photocatalyst coatings under UV or VL by adding Cr would guide the direction for the improvement of photocatalytic activity.

Characterization of oxide films formed on Alloy 600 and Alloy 690 in simulated PWR primary water by using hard X-ray photoelectron spectroscopy

Oxide films on Alloy 600 and Alloy 690 formed during exposure to the simulated primary side water of a pressurized water reactor were characterized using hard X-ray photoelectron spectroscopy. The specimens were immersed in a solution containing 500 ppm B + 2 ppm Li with or without dissolved hydrogen at 320 or 360 °C for 24 h. Photoelectrons generated in the oxide films with thickness up to 25 nm and in the substrate alloy underneath the oxide films could be observed simultaneously without any destructive techniques such as sputtering. The oxide films were composed of an inner oxide layer of mainly Cr and a covering hydroxide layer of Ni and Cr, with needle-like oxides distributed on the outermost surface. In addition, alloyed Cr was depleted from the substrate alloy directly underneath the oxide layer. Even though the Ni-based alloys examined were mainly composed of Ni, almost no Ni oxide was present in the oxide films formed in solution with dissolved hydrogen. Most of Ni was incorporated as hydroxide. However, Cr was incorporated both in the hydroxide and the inner oxide layers.

ANALYSIS OF SURFACE OXIDE FILM FORMED ON ELETROPOLISHED ALLOY 690TT IN HIGH TEMPERATURE AND HIGH PRESSURE WATER WITH SEQUENTIALLY DISSOLVED HYDROGEN AND OXYGEN

The electropolished(EP) alloy 690 TT samples were first oxidized in the simulated B and Li containing primary water with 2.5 mg/L H2 at 325 ℃ and 15.6 MPa for 720 h, and then half of the samples were continuously immersed in this solution with 2.0 mg/L O2 for another 720 h. The microstructures and chemical composition of the oxide films formed under the above two conditions were analyzed. The results show that the dual layered oxide film formed under the single hydrogen water chemistry is mainly composed of spinel oxides. The outer layer is composed of big oxide particles rich in Ni and Fe and the underlying loose needle-like oxides rich in Ni.The inner layer is continuous Cr-rich oxides. The oxide film formed on EP alloy 690 TT under the hydrogen/oxygen water chemistry also shows a dual layered structure. The surface morphology and chemical composition of the outer layer are similar to the oxide film formed under the hydrogen water chemistry. However, the inner layer is changed to the nano-sized Ni O. The stable phase region in the potential-p H diagram for the Ni oxides is enlarged by the later dissolved oxygen. As a result, the oxygen promotes the fast growth of the outer needle-like oxides rich in Ni. Further, the oxygen promotes the dissolution of the inner Cr- rich oxides formed under the hydrogen water chemistry and increases the corrosion rate of the EP alloy 690 TT. Electropolishing treatment can not reduce the corrosion rate of alloy 690 TT in the simulated primary water with sequentially dissolved hydrogen and oxygen.

Analysis of Surface Oxide Films Formed in Hydrogenated Primary Water on Alloy 690TT Samples With Different Surface States

Oxidation of Alloy 690TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 × 10−6 B and 2.3 × 10−6 Li with 2.5 × 10−6 dissolved H2, at 325 °C and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion: an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones. Samples of ground Alloy 690TT showed superior resistance to intergranular attack (IGA).

Effect of cerium addition on oxidation behavior of 25Cr20Ni alloy under low oxygen partial pressure

The influence of Ce addition on the oxidation behavior of 25Cr20Ni alloy at 950 °C under low oxygen partial pressure was investigated. The oxidized samples were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and scratch tester to obtain the oxide phases, morphology, thickness, composition and adhesion property of the oxide scales. The experiment results indicated that a small amount of Ce addition (0.02 wt.% or 0.05 wt.%) promoted oxidation resistance and inhibited the growth of the needlelike oxide. The Ce addition also decreased the formation of MnCr2O4 but promoted the SiO2 formation underneath the Cr2O3, which largely contributed to the improvement of oxide scale spallation resistance. For the sample with 0.3 wt.% Ce addition, the oxidation rate significantly increased and the spallation resistance of the oxide scale decreased.

CORROSION BEHAVIOR OF NUCLEAR GRADE ALLOYS 690 AND 800 IN SIMULATED HIGH TEMPERATURE AND HIGH PRESSURE PRIMARY WATER OF PRESSURIZED WATER REACTOR

The corrosion behaviors of nuclear grade commercial alloys 690 and 800 were studied by in situ electrochemical measurements using a self-built high temperature and high pressure water loop system,combining with SEM observation and XPS analysis.The results show that the corrosion potentials of alloys 690 and 800 decrease gradually with immersion time increasing,while the immersion time has no obvious impact on the result from electrochemical impedance spectroscopy(EIS).A large number of needle-like oxides have been found on the surface of alloy 690 after being exposed to high temperature and high pressure water for 408 h.For alloy 800,except needle-like oxides,many particle oxides are also observed.For alloy 690,Cr is rich at inner side of oxide film,while it is rich at outer side of oxide film for alloy 800.Alloy 690 shows better corrosion resistance than alloy 800 in high temperature and high pressure water.After immersion experiment,the contents of Ni~(2+),Cr~(3+) and Fe~(3+) ions in the test water solutions are 0.1×10~(-6),0.1×10~(-6) and 0.3×10~(-6),respectively.

Influence of dissolved oxygen on oxide films of Alloy 690TT with different surface status in simulated primary water

Oxidation of Alloy 690 with different surface conditions were performed in oxygenated primary water containing B and Li at 325 °C and 15.6 MPa for 2 months. Oxide scales were analyzed using various methods. Results showed triple-layer oxide films were formed: the outmost layer with dispersed big oxide particles; the intermediated layer with loose sheet-like or needle-like oxides and the inner layer with incompact cellular oxides, which were lack of protectiveness. Oxide morphologies were affected by the surface status of samples. Dissolved oxygen increased the intergranular attack (IGA) sensitivity of Alloy 690TT. Growth mechanism of the oxide film was discussed.

ANALYSES OF SURFACE OXIDE FILMS ON ELECTROPOLISHED ALLOY 690TT AFTER IMMERSION FOR DIFFERENT TIMES

The corrosion of Ni base alloys in high temperature and high pressure water is affected by samples surface statuses.The morphologies and structures of surface oxide films grown on electropolished(EP) alloy 690TT after immersion in the simulated hydrogenated primary water of pressured water reactors(PWRs) for different times were analyzed by AFM,SEM,TEM,EDS and XPS.After immersion for 15 and 35 h,the EP alloy 690TT samples were covered with columnar oxides. With the increase of the immersion time,the sample surfaces were covered with scattered big oxide particles and loose needle-like oxides.Regardless of the immersion time,the formed oxide films are composed of spinel oxides and metallic Ni.After immersion for 720,1440 and 2160 h,the oxide films are composed of three layers:the outmost layer is the separated big oxide particles which are rich in Fe and Ni:the intermediate layer is the loose needle-like oxides rich in Ni;the inner layer is the continuous and compact Cr oxides.The peak decomposition of the XPS revealed that the Cr oxides in the inner layer are probably Cr_2O_3.Only the inner layer in the oxide film could restrain the outward diffusion of metal atoms and also the inward diffusion of the oxygen atoms and then played the role of barrier layer well. Electropolishing treatment disadvantaged the fast growth of protective oxide film on alloy 690TT in the studied solution.The average corrosion rate of the inner layer does not decrease gradually with increasing the immersion time.After immersion for 2160 h,the oxide film still could not protect the matrix from further corrosion.

Oxidation Behavior of 2Cr12NiMoWV Steel in High-Temperature and High- Pressure Water Vapor

Discrete mass gain method is adopted to determine the oxidation kinetic behaviors of 2Cr12NiMoWV steel in water vapor at 540°C and 17.5 MPa. Results indicate that the kinetic curve of the oxidation experiences a dramatic turning where the oxidation has lasted 20h, namely, the oxidation is faster than before the oxidation point of 20h, then oxidation rate is greatly reduced;, and after the oxidation has lasted for 300h, its reaction is inhibited to enter into a relatively stable period. The test analysis of oxide film under scanning electronic microscopy and electronic probe microanalyser shows that the formation process of the oxide film is as follows: needle-like oxide nuclei → short-strip oxide → fine equiaxed crystal grains → large equiaxed crystal grains or columnar crystal particles. The alloying elements involved in oxidation represent the law as follows: Fe, Mo and Si react with vapor at the initial stage of oxidation reaction to form Mo and Si-contained Fe-rich oxide. As the oxidation reaction proceeds, Cr gathered at the interface between the surface oxide film and the matrix, is internally oxidized. The Mo, Si and Cr in the surface oxide will be continuously volatilized with the occurrence of oxidation reaction.

Steam Oxidation Behaviour of Ni-Based Alloys

The steam oxidation behavior and the oxide scale structure of Ni-based alloys containing 20 to 25 mass% Cr content were studied. The oxidation test was carried out from 550 to 700°C at 50°C intervals for 100 hours in steam. All Ni-based alloys used showed good steam oxidation resistance; higher Cr containing alloys have a little better oxidation resistance than lower Cr containing alloys. The kinetics of the oxidation rate of all Ni-based alloys used was estimated as the temperature parameter in a 100 hour test and as the temperature and time parameters, respectively. These equations could be useful for industrial applications. The oxide scale of Alloy 625 was composed of two layers. The outer layer was composed of needle-like oxides and the inner layer was composed of isometric oxides. The oxide scale was composed of Cr2O3 type. The Cr/Ni ratio in the oxide scale at 700°C was by one order larger than that at 650°C. The oxidation resistance of Ni alloys is maintained by a uniform Cr2O3 layer which is composed of high Cr content.

Growth of Cu-Oxide Protrusion by Ar Ion Irradiation

Cu2O conical micron-scale protrusions have been grown on a preoxidized Cu surface by the Ar ion beam irradiation at 9 kV for 5-20 min in the low vacuum. This Ar ion irradiation is based on the ‘Transcription Method’ which has been originated by B.-S. Xu and S.-I. Tanaka in 1996 to form nanoparticles. Ar ion irradiation induced needle-like nanostructures composed of Cu2O and CuO which were randomly nucleated on Cu surface by the oxidation at 623 K for 10 min in the air. The obtained Cu2O conical protrusions have a controllable length of up to 14.6 μm with diameter in the range of 0.8 μm by changing the Ar ion irradiation angle to the surface. The mechanism of the formation of the conical protrusions is proposed that Cu atoms on the Cu surface activated and sputtered by the Ar ion irradiation diffuse on the surface of needle-like oxide as nuclei along the Ar ion track and react with residual oxygen atoms to grow the conical Cu2O protrusions.

Surface morphology of scale on FeCrAl (Pd, Pt, Y) alloys

The high temperature oxidation behavior of Fe–20Cr–4Al, floating zone refined (FZ) Fe–20Cr–4Al, Fe–20Cr–4Al–0.5Pd, Fe–20Cr–4Al–0.5Pt and Fe–20Cr–4Al–(0.01, 0.02, 0.05, 0.1, 0.2, 0.5)Y alloys was studied in oxygen for 0.6–18 ks at 1273–1673 K by mass gain measurements, X-ray diffraction and scanning electron microscopy. The mass gains of FeCrAl, FZ FeCrAl, FeCrAlPd and FeCrAlPt alloys showed almost the same values. Those of FeCrAl–(0.01, 0.02, 0.05, 0.1, 0.2, 0.5)Y alloys decreased with increasing yttrium of up to 0.1% followed by an increase with the yttrium content after oxidation for 18 ks at 1473 K. Needle-like oxide particles were partially observed on FeCrAl alloy after oxidation for 7.2 ks at 1273 K. These oxide particles decreased in size with increasing oxidation time of more than 7.2 ks at 1473 K, and then disappeared after oxidation for 7.2 ks at 1573 K. It is suggested that a new oxide develops at the oxygen/scale interface. The scale surface of FeCrAl alloy showed a wavy morphology after oxidation for 7.2 ks at 1273 K which then changed to planar morphology after an oxidation time of more than 7.2 ks at 1573 K. On the other hand, the scale surfaces of other alloys were planar after all oxidation conditions in this study. The scale surfaces of FeCrAl, FZ FeCrAl, FeCrAlPd and FeCrAlPt alloys were rough, however, those of FeCrAl–(0.1, 0.2, 0.5)Y alloys were smooth. The oxide scales formed on FeCrAl–(0.1, 0.2, 0.5)Y alloys were found to be α-Al 2O 3 with small amounts of Y 3Al 5O 12, and those of the other alloys were only α-Al 2O 3.

Influence of Dissolved Hydrogen on Structure of Oxide Film on Alloy 600 Formed in Primary Water of Pressurized Water Reactors

In order to investigate the relationship between the susceptibility of primary water stress corrosion cracking (PWSCC) in Alloy 600 and the content of dissolved hydrogen (DH) in the primary water of pressurized water reactors (PWR), structural analysis of oxide films formed under four different DH conditions in simulated primary water of PWR was carried out using a grazing incidence X-ray diffractometer (GIXRD), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). In particular, to perform accurate analysis of the thin oxide films, the synchrotron radiation of SPring-8 was used for GIXRD. It has been observed that the oxide film is mainly composed of nickel oxide, under the condition without hydrogen. On the other hand, needle-like oxides are formed at 1.0 ppm of DH. In the environment of 2.75 ppm of DH, the oxide film has thin spinel structures. From these results and phase diagram consideration, the condition around 1.0 ppm of DH corresponds to the boundary between stable NiO and spinel oxides, and also to the peak range of PWSCC susceptibility. This suggests that the boundary between NiO and spinel oxides may affect the SCC susceptibility.

Oxide particle densities in internally oxidised Ag-Cd alloys: Part 2 Alloys with ternary additions

The densities of oxide particles are studied as a function of depth below the surface of internally oxidised Ag–9·5 at.-%Cd alloys with additions of ~0·2 or 2 at.-%Al, Mn, Ni, Sn, or Zn. Because of its low diffusivity and low free energy of oxide formation, Ni has no influence on particle density. Tin forms needlelike oxides and reduces the particle density as a result of geometric effects. Zinc has a marked effect on particle shape with platelike precipitates which coalesce during subsequent precipitation of CdO, but does not greatly affect particle density. Both Al and Mn increase particle density up to two orders of magnitude. Planar size distributions are presented which indicate that two types of nucleation site are present in the Mn containing alloys. In the alloy containing 0·15 at.-%Al the Al2O3 particles are too fine to act as nuclei for CdO precipitation; two types of band both with a narrow size distribution of CdO particles, but with slightly different size and largely different density are formed. Heterogeneous nucleation and depletion of the centre region of sample sheets, both of which result from the counterdiffusion of the oxidising elements, are shown to have a great influence on particle density, resulting in a more homogeneous distribution of particle densities over the sample cross-section than that predicted by available theories.MST/900b

Dispersibility of Magnetic and Nonmagnetic Iron(III) Oxides in Cyclohexane and Effect of Water on the Stability

Abstract The dispersion stability of needlelike and octahedral iron(III) oxides of magnetic or nonmagnetic particles in cyclohexane solutions of sodium 1,2-bis(2-ethylhexyloxycarbonyl)ethanesulfonate (Aerosol OT or AOT) was studied on anhydrous and hydrous systems. The dispersion stability of the anhydrous system was examined for seven kinds of oxides. The sedimentation velocity of dispersions, the histograms of particle distribution, the adsorption of Aerosol OT on the particles and zeta potential were measured. Potential energies of the interaction between a pair of particles were calculated for the anhydrous system. It was suggested from the calculation of potential energies that the magnetic attractive force, which is a function of the strength of the saturation magnetization and the volume of particle, is a main factor affecting the flocculation of the magnetic particles in cyclohexane as well as in 2-butanone reported in the previous papers. The study of the dispersion stability of the hydrous system was done for three kinds of needlelike oxides. The relatively stable region appeared in the lower concentration range of water. The stability decreased at the fixed water concentration followed by marked flocculation (“floc formation” region). It was considered that the appearance of the “floc formation” is caused by the formation of thick hydration layer on the oxide surface and the decrease of zeta potential.

Ag-Cd-Sn合金の内部酸化における酸化物の析出挙動

Ag-Cd and Ag-Cd-Sn alloys containing 10∼17 mass%Cd and 0.5∼1.5 mass%Sn were oxidized at 973 and 1073 K under oxygen pressures of 2.1×104 and 1.0×105 Pa in order to investigate the precipitation behavior of oxides during internal oxidation. Microstructures, distribution of Cd and Sn in oxides, and oxide phases were investigated by optical microscopy, electron probe X-ray microanalysis, and X-ray diffraction, respectively. Oxidation tendency of solute elements were estimated with an EPMA, by utilizing oxide enrichment produced at the oxidation front when oxidation conditions were changed rapidly to higher temperature and lower oxygen pressure.The results obtained are as follows:(1) Massive oxides in Ag-Cd alloys were changed into fine needle-like oxides by addition of Sn. The most remarkable effect was obtained with 0.5%Sn.(2) Oxide phases precipitating at 973 K were identified as CdO, Cd2SnO4, and CdSnO3. CdO and Cd2SnO4 precipitated at 1073 K.(3) SnO2 or composite oxides of CdO and SnO2 precipitated followed by precipitation of CdO on the oxides. It was considered that SnO2 converted into composite oxides by reaction with CdO.