Phase In Oxide Layer Research Articles

Insight into the effect of Ti substitutions on the static oxidation behavior of (Hf,Ti)C at 2500 ​°C

Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000 ​°C. However, the static oxidation behavior at their potential service temperatures remains unclear. To fill this gap, the static oxidation behavior of (Hf, Ti)C and the effect of Ti substitutions were investigated in air at 2500 ​°C under an oxygen partial pressure of 4.2 ​kPa. After oxidation for 2000 ​s, the thickness of the oxide layer on the surface of (Hf, Ti)C bulk ceramic is reduced by 62.29 ​% compared with that on the HfC monocarbide surface. The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides, HfO2, and carbon. The Ti-rich oxycarbide ((Ti, Hf)CxOy) dispersed within HfO2 formed the major structure of the oxide layer. A coherent boundary with lattice distortion existed at the HfO2/(Ti, Hf)CxOy interface along the (111) crystal plane direction, which served as an effective oxygen diffusion barrier. The Hf-rich oxycarbide ((Hf, Ti)CxOy) together with (Ti, Hf)CxOy, HfO2, and precipitated carbon constituted a dense transition layer, ensuring favorable bonding between the oxide layer and the matrix. The Ti content affects the oxidation resistance of (Hf, Ti)C by determining the oxide layer's phase distribution and integrity.

Regularities of Vacuum Oxidation of Iron in the Range of Low-Temperature Passivation According to the Data of Spectral Ellipsometry

The methods of spectral ellipsometry and nanotomography are used to study the kinetics of formation of oxide layer phase components (magnetite and hematite) on the iron surface under the conditions of vacuum treatment, in the region of low-temperature gas passivation manifestation. In the course of oxidation at the temperature of 300°C and vacuum treatment at 1 Torr, an island and, then, a solid layer of magnetite grows on the surface of iron. Further oxidation results in growth of α-Fe2O3 in the form of plates at the magnetite–gas boundary depthward into magnetite. It forms an island film consisting of hematite microcrystallites on the surface of magnetite when this magnetite surface is coated. Island coalescence occurs under longterm oxidation exposure, which leads to formation of a solid layer consisting of hematite microcrystallites with thin intergrain boundaries. Here, a “puzzle” surface structure is observed, in which crystallite boundaries approximately correspond to their neighbors and, therefore, result in complete coating of the surface. Such a layer efficiently hinders oxygen diffusion, which passivates the metal and prevents formation of a thick magnetite layer.

Stabilization of TiO2–Co3O4 thin films on a glass fiber material by introduction of silica into the matrix

The TiO2–Co3O4–SiO2 oxide system supported on glass fiber was synthesized and studied. The oxide layers attached to the glass fiber surface have a porous structure. Characteristics of thin-film coatings on the glass fiber substrate (oxide layer phase composition and adhesion to the glass fiber surface) depend on the silica concentration. The obtained materials are catalytically active towards the exhaustive oxidation of propane.

Wettability and cellular response of UV light irradiated anodized titanium surface

PURPOSEThe object of this study was to investigate the effect of UV irradiation (by a general commercial UV sterilizer) on anodized titanium surface. Surface characteristics and cellular responses were compared between anodized titanium discs and UV irradiated anodized titanium discs.MATERIALS AND METHODSTitanium discs were anodized and divided into the following groups: Group 1, anodized (control), and Group 2, anodized and UV irradiated for 24 hours. The surface characteristics including contact angle, roughness, phase of oxide layer, and chemical elemental composition were inspected. The osteoblast-like human osteogenic sarcoma (HOS) cells were cultured on control and test group discs. Initial cellular attachment, MTS-based cell proliferation assay, and ALP synthesis level were compared between the two groups for the evaluation of cellular response.RESULTSAfter UV irradiation, the contact angle decreased significantly (P<.001). The surface roughness and phase of oxide layer did not show definite changes, but carbon showed a considerable decrease after UV irradiation. Initial cell attachment was increased in test group (P=.004). Cells cultured on test group samples proliferated more actively (P=.009 at day 2, 5, and 7) and the ALP synthesis also increased in cells cultured on the test group (P=.016 at day 3, P=.009 at day 7 and 14).CONCLUSIONUV irradiation induced enhanced wettability, and increased initial cellular responses of HOS cells on anodized titanium surface.

Electrolytic pickling of the oxide layer on hot-rolled 304 stainless steel in sodium sulphate

Electrolytic pickling of hot-rolled 304 stainless steel in Na 2SO 4 electrolyte was investigated with electrochemical, weight loss and SEM–EDX measurements. Pickling took place upon both active and transpassive polarisations. Mechanism and kinetics of pickling during active and transpassive polarisations were unravelled. Metallic phase in oxide layer was dissolved during active polarisation while the oxide layer was significantly undercut. Chromium oxide in the oxide layer was oxidised to soluble anions during transpassive polarisation, while iron oxide and metallic phase could either be remained or removed. Pickling due to undercutting with active polarisation was highly pronounced.

Analysis on volume fraction and crystal orientation relationship of monoclinic and tetragonal oxide grown on Zr–2.5Nb alloy

Texture and phase volume fraction of the oxide grown on Zr–2.5Nb, in static autoclaves, at 623 K, with lithiated heavy water were investigated. It is found that both monoclinic and tetragonal zirconia are highly textured with {1 0 0}〈1 0 0〉 preferred crystal orientation for the tetragonal phase, and ( 1 0 3 ¯ ) [ 0 1 ¯ 0 ] and ( 1 0 4 ¯ ) [ 4 0 1 ] texture for the monoclinic phase. No change in the texture for both phases was observed with the increase of thickness of the oxide layer. The crystal orientation relationship of both the monoclinic and tetragonal phases was found to be ( 1 0 3 ¯ ) m ‖ ( 1 0 0 ) t or ( 1 0 3 ¯ ) m ‖ ( 1 0 1 ) t and [ 1 0 0 ] t ‖ [ 0 1 0 ] m . The integrated intensity over pole figures was used to calculate the volume fraction of the tetragonal phase in the oxide layer. The volume fraction of the tetragonal phase in the dense oxide layer near the metal–oxide interface was found to be about 8% and gradually decreases with an increase of the oxide thickness.