Cr2O3 Film Research Articles

Development of room temperature sensor based on high quality rhombohedral Al2O3:Cr2O3 (1:1) thin film with bone like morphological feature for ultrasensitive detection of NH3 gas

This paper describes the successful preparation of high quality (104) oriented Al2O3:Cr2O3 (1:1) thin film with rhombohedral phase and bone like surface morphology by RF magnetron sputtering technique. Compositional purity and its corresponding chemical states of the elements (Al3+ and Cr3+) present in the deposited films were ascertained by EDX and XPS analyses, respectively. In particular, the film deposited with 300 W RF power not only possess unique morphology (bone like morphology), but also exhibits superior gas sensing performance towards NH3 at room temperature due to its very high surface-to-volume ratio, which provide a more reaction site for NH3 gas molecules. Due to this unique morphological feature, the 1000 °C annealed Al2O3:Cr2O3 (1:1) film exhibited the good selectivity, long-term stability, high sensitivity (sensitivity = 4.14), excellent sensor response (SR = 99.7% for 100 ppm) for diverse range of ammonia concentrations and the film has an ability to respond even at very low concentration (1 ppm level) at room temperature. The probable gas sensing mechanism was also discussed.

Influence of Forging and Annealing on the Microstructure and Corrosion Behavior of Austenitic Stainless Steel

The deformed microstructure and corrosion behavior of 316LN austenitic stainless steel after warm forging and annealing have been explored by using electron backscatter diffraction (EBSD) and electrochemical corrosion test methods in marine environment. An attempt has been made to understand the effect of warm forging and annealing on the microstructure and electrochemical behavior of 316LN stainless steel. The results indicate that the corrosion rate decreases after annealing of forged samples because annealing improves the repassivation capacity of forged samples. In the Tafel plot, the value of Ecorr shifts toward the passive direction after annealing of forged samples which indicates that a more protective passive film of Cr2O3 is formed on the surface of annealed sample after forging. The EBSD micrographs show that refinement of grain occurs after warm forging, and due to refinement, grain boundaries are not clearly visible after forging. EBSD microstructure shows that grain coarsening occurs after annealing of forged sample and the optimum strength and corrosion resistance were observed in annealed sample after forging. The value of impact strength decreases and hardness increases after increasing the percentage of deformation, and optimum impact strength and hardness were observed in annealed sample after warm forging.

Effect of Warm Forging on the Microstructure and Corrosion Behavior of Austenitic Stainless Steel 316LN

Abstract The as-received as well as deformed microstructure and electrochemical corrosion behavior of warm-forged and annealed 316LN austenitic stainless steel have been investigated by using electron backscatter diffraction (EBSD) and electrochemical corrosion test methods. An attempt has been made to understand the effect of warm forging and annealing on the microstructure and electrochemical corrosion behavior of 316LN stainless steel. As-received and deformed microstructures of a sample were observed by EBSD, and from micrographs, it was observed that the refinement of grain occurs after deformation. Microstructural refinement occurs after appropriate annealing of the forged sample because of the revision of alpha ferrite and strain-induced martensite into austenite, which is formed after forging. Annealing treatment after warm forging gives better mechanical strength and optimum corrosion resistance because of the formation of homogeneous and equiaxed strain-free austenite grains. After warm forging, around 85 % of grains show a low misorientation angle of 2.5°, which shows that a lot of dislocation generation occurred during warm forging deformation and that these dislocations aligned themselves to form subgrain boundaries also known as recovery during annealing dislocation. The corrosion rate drastically increases after deformation but decreases after the annealing of deformed samples, which indicates that after appropriate annealing the corrosion resistance and repassivation capacity of materials improved because of the formation of stable oxide of chromium. The value of corrosion current density (Ecorr) shifted toward the passive direction in the Tafel plot after annealing of deformed samples, which indicates that a more protective passive film of Cr2O3 formed on the surface of the annealed sample after warm forging. The surfaces of the samples after an immersion test in the FeCl3 solution have been observed by scanning electron microscopy, and from micrographs, it has been observed that the number of pits is reduced after the annealing of a warm-deformed sample as compared with undeformed samples. The pitting potential of the samples was calculated in a simulated pressurized water reactor environment using the Tafel potentiodynamic polarization test.

Tribocorrosive Study of New and In Vivo Exposed Nickel Titanium and Stainless Steel Orthodontic Archwires

The surface, corrosion and wear properties of new and in vivo exposed nickel titanium (NiTi) and stainless steel (SS) archwires used in orthodontic treatment were investigated. Electrochemical and tribo-electrochemical tests in artificial saliva were performed in order to define corrosion properties and to estimate wear rate of new and in vivo exposed NiTi and SS archwires. The surface chemical analysis of the passive film on the NiTi and SS archwires before and after tribocorrosion tests was performed by Auger Electron Spectroscopy (AES). In vivo exposed NiTi and SS archwires had better electrochemical properties than new archwires due to the protective nature of oral deposits. Total wear and coefficients of friction were higher among in vivo exposed archwires and higher in NiTi archwires in comparison to SS archwires. The estimated thickness of the TiO2 passive film on as-received NiTi is 8 nm, while the passive Cr2O3 film on as-received SS is just 1–2 nm. On in vivo exposed NiTi archwire, a 60–80 nm thick organic film/dental plaque was observed, and on SS, it was thinner, at about 60 nm. This research shows the importance of combining AES with electrochemical testing, to characterize tribocorrosive properties of NiTi and SS orthodontic archwires.

High-rate sputter deposition of chromium oxide thin films using water vapor as a reactive gas

The use of water vapor as a reactive gas under metallic mode for high rate sputter deposition of chromium oxide thin films have been studied in the course of this research. Chromium oxide (Cr2O3) thin films were deposited by an RF magnetron sputtering system with chromium metal as a target and argon (Ar) and water vapor (H2O) as the sputtering gas. Water was injected to the target or substrate surface at an H2O flow ratio of H2O/(H2O + Ar), varied from 0 to 100%. A liquid nitrogen cold trap was placed in the sputtering chamber to adsorb non-reacted H2O molecules.When the cold trap was inactive, the deposition rate and discharge voltage dropped and the transmittance of the films increased above an H2O flow ratio of 10%. Discharge voltage and plasma emission measurements showed that Cr2O3 films were deposited under compound target mode. In contrast, when the cold trap was active, the deposition rate increased with increase in H2O flow ratio and also a gradual increase in the transmittance of the films was observed. Hence, the target surface was considered to be almost in a metallic state and the oxidation proceeded gradually. Results of this study indicate that H2O sputtering using cold trap is a promising method for the formation of chromium oxide thin films at high deposition rates under metallic target mode.

Effect of Aluminum on Microstructure and High-Temperature Oxidation Resistance of Austenitic Heat-Resistant Steel

The ZG40Cr20Ni20Alx (x = 0, 1.76, 3.45, and 5.34) heat-resistant steel has been newly developed on the basis of HK40 steel for aggressive oxidizing environments. The results reveal that the Al greatly enhances the oxidation resistance of ZG40Cr20Ni20 steel at high temperatures. The mass gain of ZG40Cr20Ni20 upon oxidation at 1100 °C for 480 h is up to 103.6 mg/cm2, while the values for the steels containing 1.76 and 3.45 wt% Al are sharply decreased to 6.1 and 5.4 mg/cm2, respectively. Both of their matrix phases are still austenite, which is the same as that of ZG40Cr20Ni20. Their FeCr2O4 spinel oxide scales appear to be more stable under high oxygen partial pressure than that of ZG40Cr20Ni20, and the continuous Cr2O3 film appears between their matrix and spinel oxide. As for the steel with 5.34 wt% Al, the mass gain is only 1.1 mg/cm2. Its matrix is compared to those of austenite and ferrite, and the oxide scale is continuous Al2O3.

Синтез и газовая чувствительность тонких пленок оксида хрома

The thin polycrystal Cr2O3 films were synthesized by RF - magnetron sputtering with followed annealing at T = 673 K in an air atmosphere. The grains diameter in the thin Cr2O3 film is 40–70 nm, Eg = 3.3±0.2 eV. In the temperature range of 303–473 K, the Cr2O3 films show high response to NO2, Н2, vapors of acetone and toluene, weakly react to CH4 and CO and have the relatively weak dependence of resistance on humidity. The qualitative model of the gases influences on the thin Cr2O3 films electrical properties was proposed.

Evaluation corrosion behavior on commercial stainless steel SS 304 in Nano fluids water-Al2O3 system at different pH by Electrochemical Impedance Spectroscopy methods

The corrosion behavior on commercial stainless steel SS 304 in Nano fluids water-Al2O3 system at pH 3 until 7 conditions has been investigated using electrochemical methods. The electrochemical tests were performed with and without the addition chlor to adjust of pH Nano fluid condition. The pH of nano fluid for testing corrosion stainless steel 304 are 3.18,.3.65, and 5. 9. The electrochemical technique used in this study, were open circuit potential (OCP), galvanodynamic polarization and electrochemical impedance spectroscopy (EIS). The results of open circuit potential tests showed that the corrosion potential (Ecorr) values of stainless steel 304 in nanofluid at three pH values are slightly different between pH neutral and acidic. At pH 5.9 corrosion potential more positive compare with at acid pH 3.18. The positive potential of corrosion potential at pH 5.9 due to development of chromium oxide (Cr2O3) film formed on stainless steel is more stable in 5.9 than in acidic with the presence of Cl. However, galvanodynamic polarization of stainless steel SS 304 in nanofluid showed that the lowest corrosion of stainless steel SS 304 in nanofluid at pH 5.9 than stainless steel at condition in acidic pH 3.18 and 3.65. EIS study shows that stainless steel SS 304 in nanofluid showed the higher impedance at higher pH than at in acidic condition at lower pH. The higher impedance indicated that the passive film of Cr2O3 formed on the surface of stainless steel and reduce corrosion rate. In terms of corrosion rate values, stainless steel alloy showed the best corrosion rate in low pH nanofluid compared with high pH value. This shows that the interaction between Nano fluids and the stainless steel have no significant effect onto its corrosion behavior.

Crystalline dependence of spin transmission in Cr2O3 thin films

Spin transmission in Cr2O3 films of different crystalline textures is studied experimentally. With Y3Fe5O12/Cr2O3/Pt trilayer devices, a spin current is injected into Cr2O3 by spin pumping from Y3Fe5O12, and the spin transmission is monitored by the inverse spin Hall voltage (VISHE) in Pt. For (0001) plane textured Cr2O3 films, VISHE vanishes quickly below the Néel temperature. However, the VISHE shows a broad shoulder below the Néel temperature for (112‾0) and (112‾3) plane co-textured Cr2O3. Such a difference in the temperature dependence of Cr2O3 can be understood by the different Néel vector orientations with respect to the injected spin moment direction.

Effects of different alloying additives X (X = Fe, Ni, Mn, Co, Si, Nb, W, Cu, Ce, Y) and water on the structural of Cr2O3 film: a first-principles study

This study investigates the potential effects of different alloying elements X (X = Fe, Ni, Mn, Co, Si, Nb, W, Cu, Ce, Y) in the Cr2O3 (0001) layers with water adsorption by using the first-principles method. For water adsorption, the most stable adsorption site is bridge site. By calculating the adsorption energy of the alloy element doped layer, the distances of top Cr and O layer and charge densities of Cr and O atoms, it is concluded that the vapor corrosion resistance of the oxide film was improved after doping with elements such as Fe, Ni, Mn, Co, Si, Cu, Ce and Y. In particular, the rare elements doped system can obviously enhance resistance to water vapor erosion. By adding YCo and YW, the oxidation film showed better corrosion resistance than single-element doping and CoW co-doping systems.

Investigation of metal elements diffusion in Cr2O3 film and its effects on mechanical properties

Cr2O3 films were deposited on Inconel718 alloy substrate by using an arc ion planting system, and then annealed at 1000 °C in different atmospheres. The diffusion behavior of metallic elements from the substrate in different atmospheres and its effect on mechanical properties of the film were researched. The results show that Ti and Cr elements in the substrate would diffuse to Cr2O3 film surface when the films are annealed in argon, nitrogen and oxygen. A diffusion layer comprised of Cr and TiO2, which could attribute to the residual oxygen in furnace, formed on the surface of the argon-annealed film. In nitrogen atmosphere, Ti and Cr elements were nitrided to form Cr2N and TiN, and then they packed to form a diffusion layer on the film surface. Especially, a mesh-like heave comprised of Cr2O3 and Cr2Ti7O17 formed on the surface of the oxygen-annealed film. However, there is no element diffusion detected in the vacuum-annealed film, while lots of cracks formed on the film surface. Annealing in different atmospheres could improve the adherence strength obviously. The vacuum-annealed film maintains a high hardness, and possesses excellent tribological properties degradation. After argon and nitrogen annealing, the loose diffusion layers result in the hardness decreasing and tribological properties degradation. For the oxygen-annealed film, internal diffusion of oxygen decreases the surface hardness obviously. Moreover, although Cr2Ti7O17 lubricant formed on film surface, the loose surface structure deteriorates the tribological properties.

Preparation and high temperature oxidation behaviors of TiO2/Al2O3/Inconel625 composite coatings on the surface of Q235 alloy at 900 °C

Sol-gel method combined with plasma surfacing was used to prepare TiO2/Al2O3/Incone1625 composite coatings on the surface of Q235 alloys. Oxidation thermodynamic results show the composite coatings caused lower oxidation weight gain than the sample with single coating. Combination of XRD and SEM results illustrates that the surface and cross-sectional morphology were composed of an innermost continuous but not compact enough Cr2O3 layer, the outer layer next to C2O3 was loose and cracked NiO, and the outermost layer was composed of iron oxides for the Incone1625 coated sample. For the composite coating sample, the oxide film was composed of NiO as the outermost layer, Cr2O3 as the inner layer, there was a very thin but continuous layer consisted of Cr2O3 and Al2O3 as the innermost layer. This work shows that TiO2/Al2O3/Incone1625 composite coating improves the high-temperature oxidation resistance properties of the Q235 alloy at 900 °C by promoting the formation of the protective Cr2O3 and Al2O3 film.

Preparation and molten salt corrosion behaviors of TiO2/Al2O3/Incone1625 composite coatings on the surface of Q235 alloy at 900 °C

Sol-gel method combined with plasma surfacing was used to prepare TiO2/Al2O3/Incone1625 composite coatings on the surface of Q235 alloys. To investigate the corrosion resistance of this coatings, samples with Incone1625 single coating and TiO2/Al2O3/Incone1625 composite coating were corroded with NaCl and Na2SO4 salts with the weight ration of 1:1at 900 °C in air for 24 h. Molten salt corrosion thermodynamic results show the composite coatings caused lower oxidation weight gain than the sample with single coating. Combination of XRD and SEM results illustrates that the surface and cross-sectional morphology were composed of an outermost loose and cracked NiO and iron oxides layer for the Incone1625 coated sample. For the composite coating sample, the oxide film was composed of more compact NiO and Cr2O3 as the main layer. There were inner oxidation regions for both samples, but region for sample with composite coating was more thinner than that for sample with single coating. This work shows that TiO2/Al2O3/Incone1625 composite coating improves the molten salt corrosion resistance properties of the Q235 alloy at 900 °C by promoting the formation of the protective Cr2O3 film on the sample surface.

Dispersion of chromia films (eskolaite) in UV-VIS

Abstract Atomic layer deposited polycrystalline Cr2O3 films grown from chromyl chloride and methanol were analysed using spectrophotometry, spectral ellipsometry and atomic force microscopy. The films possessed polycrystalline eskolaite structure with rough sublayer in contact with air. Using the positions and peak widths of the two visible absorption bands as fixed from absorption measurements, we could determine the optical dispersion of the film material in 1.3 – 6 eV energy region. A direct band gap of chromia film grown in these conditions was 3.2 eV, the other also direct absorption band with a gap of 5.15 eV was found situated in UV.

Effect of helium implantation on the hydrogen retention of Cr2O3 films formed in an ultra-low oxygen environment

To simulate and investigate the irradiation damage of neutron and transmutation effect (He production) on the hydrogen isotope trapping behavior, in the present study, a new monoclinic hydrogen permeation barrier composed of Cr2O3 was fabricated and helium implantation with different fluences was tentatively employed. First, pure chromium samples were oxidized in an ultra-low oxygen partial pressure (1.7 × 10−23 Pa) environment to obtain a single Cr2O3 layer. Then a dense layer of helium bubbles was formed in a substrate using a helium ion implantation method. Finally, the samples were treated in a hydrogen plasma environment at 500 °C. The damage, vacancy, and helium distribution in these samples were then simulated by SRIM. The morphology, phase, surface characteristics, thermal desorption, and electrochemical properties were subsequently characterized and evaluated. Thermal desorption spectrum analysis (TDS) was used to study the thermal desorption of hydrogen and helium at different temperatures. Our results showed that the inhibitory effect of the composite hydrogen barrier layer on the hydrogen diffusion in the substrate first increased and then decreased with the increase of the helium ion implantation fluence.

Corrosion-resistant carbide-reinforced martensitic steel by Cu modification

Carbide-reinforced martensitic steels, known as high-speed steels (HSSs), have been used as tool materials in various industries because of their high hardness and wear resistance. Nonetheless, such steels show severe degradation when used in a corrosive environment because typical Cr2O3 films, which generally realise passivity in these alloys, do not often work effectively. Here, we demonstrate that the corrosion resistance of a high-carbon-containing Fe–Cr–W-based alloy in a sulfuric acid solution can be significantly improved by the addition of trace Cu. The enrichment of Cu at the surface of the alloy as corrosion proceeds is key to inhibiting further corrosion. A theoretical model for a micro corrosion cell, which should be applicable to any material employed under the same corrosion conditions in fields such as the chemical and energy industries, was developed to interpret the experimental observations.

Hot Corrosion Performance of Single-Crystal CMSX-4 and CMSX-486 Superalloys in the Mixture of Na2SO4-NaCl Melts

A modification in the chemistry of single-crystal CMSX-4 to produce CMSX-486 superalloy has been reported in the literature to be accomplished without degradation in high-temperature mechanical performance. However, adequate attention has not yet been focussed on the hot corrosion response of the alloy considering its chemical composition modification. This paper reports for the first time that a considerable degradation in the hot corrosion resistance of CMSX-4 occurs by the modification of its chemistry. Corrosion tests at different salt concentrations and temperatures showed that the hot corrosion resistance of CMSX-486 is worse than the conventional CMSX-4 alloy. The difference in the corrosion resistance characteristics of the two alloys is attributable to the nature of the protective oxide layer formed on the materials during hot corrosion. Characterization using various advanced techniques revealed that the oxide layer formed on CMSX-486 consists of less amount of protective and coherent Al2O3 and Cr2O3 film than CMSX-4, and this is the reason for its poor hot corrosion resistance.

Weak ferromagnetism at room temperature in Ti incorporated Cr2O3 thin film

An experimental study of undoped and Ti incorporated Cr2O3 film has been carried out. Apart from structural and morphological modifications due to Ti doping, a striking feature of enhanced weak ferromagnetism at room temperature was observed in the Ti incorporated Cr2O3 film. The X-ray photoelectron spectroscopic data of the films revealed increased number of oxygen vacancies in the Ti incorporated Cr2O3films. The origin of weak ferromagnetism in the Ti incorporated Cr2O3 thin film is assigned to the presence of Ti and the oxygen vacancies.

Temperature dependence of spin Hall magnetoresistance in a Cr2O3 film with a TaOx buffer layer

We study the spin Hall magnetoresistance (SMR) in a Cr2O3/Ta bilayer with a buffered TaOx layer. Comparing the temperature dependence of SMR in Cr2O3 without a TaOx buffer layer, an additional change of sign is observed at 95 K. By means of the analysis of structure and magnetism, the amorphous properties and surface magnetic frustration are responsible for the change of sign in SMR. Our results demonstrate that the transport performance could be used to explore the magnetic textures at the complex interface of antiferromagnet/non-magnetic metal bilayers. Thus, SMR might become a characteristics tool in the field of antiferromagnetic spintronics.

Corrosion Behavior of GH4169 Alloy under Alternating Oxidation at 900 °C and Solution Immersion

In this paper, the corrosion behavior of GH4169 superalloy under alternating oxidation (at 900 °C) and solution immersion (in 3.5% NaCl solution, 30 ± 1 °C) has been studied by SEM, XRD, XPS, and electron probe microanalysis (EPMA). The results show that the alternating environment increases the corrosion rate of GH4169. The reaction of NaCl and Cr2O3 generates various volatile and soluble corrosion products, such as Na2Cr2O7, CrCl3, Cl2, and Na2CrO4, at a high temperature. The destruction of the protective Cr2O3 film leads to the increase of defects in the oxide scale, promoting the formation of oxides, such as NiO and Fe2O3, and changes the composition and structure of the oxide film. After repeated iterations, the mixed oxides will result in the spalling of the oxide film because they can reduce the fracture toughness of the corrosion scale. Therefore, the corrosion is comprehensively intensified.