Extension Of Oxidation Time Research Articles

Magnetic properties of an Fe-based amorphous soft magnetic composite prepared via in-situ steam oxidation

Reducing the core losses of motors and transformers is an important way to address the global environment and energy resource problems. Soft magnetic composites (SMCs) comprising of electrically insulated ferromagnetic powder has shown vast potential for applications at low to high applied frequencies. In this work, in-situ steam oxidation was used to coat the surface of amorphous Fe75.5Si4B6P8C6Mo0.5 powder with an insulating layer. The thickness and composition of the Fe-oxide layer were controlled by tuning the in-situ steam oxidation time, and more cracks and Fe2+ were formed on the powder surface with the extension of oxidation time. The magnetic Fe-oxide layer of amorphous powder not only plays an insulating role to reduce the Pe, but also affects the magnetic coupling of particles that leads to the change of Ph. And the amorphous SMCs with 10 h in-situ steam oxidation treatment exhibits good comprehensive soft magnetic properties, i.e., the magnetic loss (Pcv), effective permeability (μe) and DC bias are 61.44 W/kg (50 mT, 100 kHz), 30.4 (to 10 MHz) and 71.5% (100 Oe), respectively.

Microstructural evolution of thermally grown oxide of an arc ion plated MCrAlX coatings after high-current pulsed electron beam treatment

An arc ion-plated NiCoCrAlYHfSi coating modified by a high-current pulsed electron beam (HCPEB) was examined in this study. The dynamic growth behavior and formation mechanisms of the thermally grown oxide (TGO) of the original and modified coatings were thoroughly compared by isothermal oxidation at 1050 °C. HCPEB irradiation led to the transformation of the rough original coating into a flat, smooth, and dense structure. Furthermore, Y-Al nanoparticles and high density of dislocations were also obtained in the modified layer. These modification characteristics can establish favorable conditions for the rapid accumulation and stable growth of the protective Al2O3 particles. With the extension of oxidation time, the CrO3 formed in the oxide film left many small pits after volatilization, but these pits were filled with Al2O3 particles. Compared with the oxide film of the original coating, the TGO of the modified coating is flat, continuous, and dense, and its growth rate is notably slower. Also, the growth of Ni, Cr, and Co rich oxides was expectantly restrained. Obviously, the HCEPB technique has the capacity to change the growth behavior of the TGO and significantly enhance the coating's resistance to high-temperature oxidation.

High temperature oxidation behavior of porous MoAlB ceramic from 800 °C to 1100 °C in air

MoAlB possesses the characteristics of both metals and ceramic materials, which has attracted extensive attention due to its excellent high-temperature oxidation resistance. For this reason, porous MoAlB is considered applicable to the practice of filtration under harsh environment. In this study, the high-temperature oxidation behavior of porous MoAlB ceramics is systematically studied at the temperatures ranging from 800 to 1100 °C. According to the results, the porous MoAlB exhibits good oxidation resistance at a maximum temperature of 1000 °C. The oxidation kinetics of porous MoAlB can be divided into three stages, and the estimated activation energies of the three stages are 253.83 kJ·mol−1, 367.48 kJ·mol−1 and 317.84 kJ·mol−1, respectively. In the stable stage at 1000 °C, the quadratic mass gain per unit area shows linearity over time, and the oxidation rate of porous MoAlB reaches 37.31 mg2·cm−4·h−1. As revealed by the analysis of the composition and microstructure of oxide layers, the main components of the oxide layer include MoO3, MoO2, Al2O3, B2O3. With the extension of oxidation time, the content of Al2O3 in the oxide films increases. The average pore size, permeability and open pore porosity of porous MoAlB show a trend of first decreasing and then tending to be stable. In addition, a discussion is conducted on the high-temperature oxidation mechanism of porous MoAlB.

Effect of SiO2 content on the oxidation resistance of SiO2–B4C-glass coating for alumina–carbon refractories

To improve the oxidation resistance of alumina–carbon refractories, SiO2–B4C-glass composite coating was prepared by slurry brushing method on the surface of refractories. Effect of SiO2 content on the oxidation resistance of the coating was studied. Oxidation resistance mechanism and failure reason of the SiO2–B4C-glass coating were discussed. Results showed that introducing SiO2 could increase viscosity activation energy and elevate the glass layer's viscosity at high temperature. With the increase of SiO2 content, the glass viscosity at high temperature gradually increased. When SiO2 content was too low, the glass exhibited smaller viscosity and larger fluidity, so the glass layer was easy to be washed away. When SiO2 content was too high, the glass phase with high viscosity and low fluidity could not uniformly cover on the surface of alumina–carbon refractories. The composite coating with SiO2 content of 55 wt% exhibited excellent oxidation resistance, which could effectively protect alumina–carbon refractories at 800 °C for 100 h with weight loss of only −1.721%. Excellent oxidation resistance of the coating mainly depended on the glass layer with good self-healing ability. With the extension of oxidation time, the coating thickness decreased, leading to the relatively poor self-healing ability and reduced weight gain rate of the coating.

Oxidation Behavior and Interfacial Bonding Properties of NiCrAl Alloys

AbstractThe oxidation behavior and oxidation kinetics of NiCrAl alloy were studied by XRD, SEM and the thermogravimetric analysis method. The adhesion strength of the films was characterized by micron scratch tester. The results show that the oxide film has not formed at 600 °C and 700 °C, and an oxide layer of Al2O3 has formed at 800 °C. Moreover, an oxide layer composed of Cr2O3 and Al2O3 has formed at 900 °C. After oxidation at 800 °C for 100 h, partial θ‐Al2O3 has transformed to steady‐state α‐Al2O3 and a dense oxide film of Al2O3 with the thickness of about 620 nm has formed on the surface of the NiCrAl alloy. The oxidation kinetics curve of the alloy obeys the parabolic law and there are two oxidation rate constants in the oxidation process. The oxidation rate constant of 1.58×10−4 mg2⋅cm−4⋅h−1 in the early oxidation period (0∼12 h) and the oxidation rate constant of 1.04×10−4 mg2⋅cm−4⋅h−1 in the late oxidation period (12∼100 h) indicate that the oxidation resistance ability of the alloy increases with the extension of oxidation time. With the increase of the oxidation time, the interface bonding strength between the oxide film and the substrate can be improved and reaches 5.21 N at 800 °C for 100 h.

Porous SiC–Si3N4 composite ceramics with excellent EMW absorption property prepared by gelcasting using DMAA

The porous SiC–Si3N4 composite ceramics with good EMW absorption properties were prepared by combination of gelcasting and carbothermal reduction. The pre-oxidation of Si3N4 powders significantly improved the rheological properties of slurries (0.06 Pa s at 103.92 s−1) and also suppressed the generation of NH3 and N2 from Si3N4 hydrolysis and reaction between Si3N4 and initiator APS, thereby reducing the pore defects in green bodies and enhancing mechanical properties with a maximum value of 42.88 MPa. With the extension of oxidation time from 0 h to 10 h, the porosity and pore size of porous SiC–Si3N4 composite ceramics increased from approximately 41.86% and 1.0–1.5 μm to 46.33% and ~200 μm due to the production of CO, N2 and gaseous SiO, while the sintering shrinkage decreased from 16.24% to 10.50%. With oxidation time of 2 h, the Si2N2O fibers formed in situ by the reaction of Si3N4 and amorphous SiO2 effectively enhanced the mechanical properties, achieving the highest flexural strength of 129.37 MPa and fracture toughness of 4.25 MPa m1/2. Compared with monolithic Si3N4 ceramics, the electrical conductivity, relative permittivity and dielectric loss were significantly improved by the in-situ introduced PyC from the pyrolysis of three-dimensional network DMAA-MBAM gel in green bodies and the SiC from the carbothermal reduction reaction between PyC and SiO2 and Si3N4. The porous SiC–Si3N4 composite ceramics prepared by the unoxidized Si3N4 powders demonstrated the optimal EMW absorption properties with reflection loss of −22.35 dB at 8.37 GHz and 2 mm thickness, corresponding to the effective bandwidth of 8.20–9.29 GHz, displaying great application potential in EMW absorption fields.

Oxidation properties of tri-layer ytterbium-disilicate/mullite/silicon-carbide environment barrier coatings for Cf/SiC composites

Mullite (Al6Si2O13) and ytterbium disilicate (Yb2Si2O7) powders were synthesized by the solvent gel (sol-gel) method. To improve the oxidation resistance of Cf/SiC composites at high temperatures, a novel tri-layer Yb2Si2O7/Al6Si2O13/SiC environment barrier coatings (EBCs) was deposited on the surface of Cf/SiC composites by chemical vapor deposition (CVD) and air spray sol-gel methods. Results show that Yb2Si2O7/Al6Si2O13/SiC coating lost its ability to protect Cf/SiC composites in the air environment at 1773 K due to the Yb2Si2O7 particles in Yb2Si2O7 top coating diffused into the Al6Si2O13 middle coating, which eventually form a eutectic interface with the extension of oxidation time. However, Yb2Si2O7/Al6Si2O13/SiC coating can efficiently prevent the oxidation of Cf/SiC composites at 1673 K for 150 h with a weight loss of 2.69 × 10−3 g·cm−2. The growth of grains and the disappearance of micro-holes in Al6Si2O13 and Yb2Si2O7 coatings deposited by air spray sol-gel method led to the excellent oxidation resistance of Yb2Si2O7/Al6Si2O13/SiC coating.

Deterioration mechanism of minced mutton induced by Fenton oxidation treatment

This study aims to investigate the effects of protein oxidation on the quality characteristics of minced mutton oxidized at 1, 3 and 5 h in Fenton oxidation system. The results showed that with the extension of oxidation time, the cooking loss, freeze-thaw loss and pH value of the minced mutton significantly increased, while the emulsification performance decreased. Compared with the control group, the peak area of immobilized water (T22) and free water (T23) in the oxidation treatment group gradually decreased. Scanning electron microscope (SEM) showed that the hole number of the minced mutton increased and the surface became uneven with the extension of oxidation time. The solubility of salt-soluble proteins showed a decreasing trend with the extension of the oxidation time. Compared with the control, the secondary structure of the protein in the oxidized samples were destroyed. As the oxidation time increased, the α-helix content of minced mutton protein significantly reduced, while the percentage of random coils significantly increased. These results indicated that minced mutton protein had undergone significant oxidation in the Fenton oxidation system, resulting in the changes of quality and structure.

Interdiffusion Behaviour of NiCoCrAlY Coating and N5 Single Crystal Superalloy

This paper aims at investigating the microstructure and phases evolution of single crystal superalloy/high temperature protective coating during high temperature static oxidation, and exploring the influence of element interdiffusion behaviour on microstructure and phase evolution of the single crystal superalloy substrate. A NiCoCrAlY high-temperature protective coating was deposited on the Ni-based single-crystal superalloy by low-pressure plasma spraying technology. The coated samples were subjected to static oxidation for 200 h at a constant temperature of 1100 °C. Scanning electron microscope, energy dispersive spectrometer and X-ray diffraction were used to characterise the microstructure and phase after interdiffusion between the coating and the substrate at high temperature. The results showed that a dense thermally grown oxide layer was formed on the surface of the NiCoCrAlY coating after oxidation for over 100 h. The only interdiffusion zone was formed after oxidation for 50 h, while both interdiffusion zone and secondary reaction zone could be observed after oxidation for over 100 h. The thickness of interdiffusion zone and secondary reaction zone is increased with the extension of oxidation time, and the grain growth of topological close-packed phase in the secondary reaction zone is found. Al, Cr and Co in the coating diffuse from the coating to the substrate, while Ni and refractory materials like Ta, Mo, Re and W diffuse from the coating to the substrate. The interdiffusion of coating and substrate leads to the instability of γ/γ′ phase in the substrate, which finally results in the formation of W, Re and Cr-rich needle-like topological close-packed phase in the substrate.

Micro-arc oxidation behavior of fly ash cenospheres/magnesium alloy degradable composite and corrosion resistance of coatings

In order to reduce the degradation rate of fly ash cenospheres (FACs)/magnesium alloy (MA) degradable composite, the protective micro-arc oxidation (MAO) coatings were prepared on the composite. The corrosion resistance of the coatings was evaluated by immersion tests and potentiodynamic polarization tests in 3 wt% KCl solution. The results indicated that FACs and Mg2Si did not participate in the coating-forming reaction. During the initial period of MAO, the growth rate of the coating on α-phase was faster than that on β-phase. FACs and Mg2Si had a hindering effect on the growth of the coating and were gradually covered by the coating. With the extension of oxidation time, the thickness of the coating increased, and the growth mechanism changed from outward growth to simultaneous inward and outward growth. The microstructure of the coating changed from through-pores to complex porous structure with prolonged oxidation time. Both the immersion tests and the potentiodynamic polarization curves showed that the coating significantly improved the corrosion resistance of the composite, and the coating obtained with longer oxidation time showed better corrosion resistance.

Effect of High Temperature Oxidation on Infrared Irradiation of Stainless Steel 304

The effect of 304 stainless steel oxidation at 800℃ for 0.5, 2, 10, 25, 100 and 200 h, respectively, on its weight gain, surface microphotograph, composition, and infrared emissivity were investigated in the paper. The results show that, with increasing the oxidation time, the weight gain rate decreased gradually. At the initial stage of surface oxidation, Fe oxide was mainly formed. The surface composition changed from Fe oxide to large flake Cr Mn oxide with the increasing of oxidation time. Polished and unoxidized stainless steel 304 showed low infrared emissivity, the infrared emissivity increased rapidly with the extension of oxidation time.

High temperature mechanical retention characteristics and oxidation behaviors of the MoSi2(Cr5Si3)\u2014RSiC composites prepared via a PIP\u2014AAMI combined process

In the present paper, MoSi2(Cr5Si3)—RSiC composites were prepared via a combination of precursor impregnation pyrolysis (PIP) and MoSi2—Si—Cr alloy active melt infiltration (AAMI) process. Composition, microstructure, mechanical retention characteristics, and oxidation behaviors of the composites at elevated temperature were studied. X-ray diffraction (XRD) pattern confirms that the composites mainly compose of 6H—SiC, hexagonal MoSi2, and tetragonal Cr5Si3. Scanning electron microscopy (SEM) image reveals that nearly dense MoSi2(Cr5Si3)—RSiC composites exhibiting three-dimensionally (3D) interpenetrated network structure are obtained when infiltrated at 2173 K, and the interface combination of the composites mainly depends on the composition ratio of infiltrated phases. Oxidation weight gain rate of the composites is much lower than that of RSiC matrix, where MoSiCr2 possesses the lowest value of 0.1630 mg·cm−2, about 78% lower than that of RSiC after oxidation at 1773 K for 100 h. Also, it possesses the highest mechanical values of 139.54 MPa (flexural strength σf and RT) and 276.77 GPa (elastic modulus Ef and RT), improvement of 73.73% and 29.77% as compared with that of RSiC, respectively. Mechanical properties of the composites increase first and then decrease with the extension of oxidation time at 1773 K, due to the cooperation effect of surface defect reduction via oxidation reaction and thermal stress relaxation in the composites, crystal growth, and thickness increase of the oxide film. Fracture toughness of MoSiCr2 reaches 2.24 MPa·m1/2 (1673 K), showing the highest improvement of 31.70% as compared to the RT value.

Growth of Ga-doped ZnO films by thermal oxidation with gallium and their optical properties

Metal gallium was evaporated onto ZnS films by physical vapor deposition method and then the thermal oxidation in the air was subsequently performed for the growth of Ga-doped ZnO films. The microstructures, photoluminescence (PL) and optical absorption properties of the Ga-doped ZnO films prepared under different deposition and oxidation conditions were investigated. The results showed that certain Ga doping can decrease the defects level, improve the crystallinity of ZnO films, and it became more effective with the extension of oxidation time. As the oxidation time increased, the Ga-doped ZnO films became more compact and uniform, displaying higher crystallinity. In addition, the optical band gaps of the ZnO films increased, the PL intensity of the visible emission decreased, and the luminescent center of the visible emission changed. Among them, the 505 nm emission resulted from oxygen vacancy, while the 539 nm emission was associated with oxygen interstitial.

Corrosion Behavior of MAO-Treated Magnesium Alloy in Hank’s Solution

In this paper, the magnesium alloy AZ91D as biological implant material was treated by micro-arc oxidation. The effects on the coating growth of oxidation time and terminal voltages in zirconium solution and silicate solution were investigated respectively. Immersion and electrochemical tests were applied to study the corrosion behavior of AZ91D alloy in Hank’s solution. The results revealed that the coating thickness increases and the corrosion rate in immersion test decreases as the extension of oxidation time and the rising of terminal voltage. The corrosion rate of the alloy in the immersion test treated in zirconium solution varies with the terminal voltages and that in silicate solution depends on the coating thickness. In the polarization curves test, the corrosion current of the MAO treated alloy is two orders of magnitude lower than that of original samples and the polarization curves in zirconium solution show bigger anode and cathode polarizability which indicates that the MAO coating has a strong blocking effect of the corrosion. The corrosion resistance of MAO treated magnesium AZ91D improves significantly.

Fabrication and Mechanism of Titania Nanotube Arrays by Anodization in DMSO Electrolyte

Titania nanotube arrays were synthesized via anodic oxidization of titanium foil in dimethyl sulfoxide (DMSO) solution containing 2 wt% HF and 3 wt% H2O at 40 V. The microstructure of the arrays was characterized with scanning electron microscopy (SEM). The results show that morphology of titania nanotube arrays is evidently influenced by the anodization time, and with the extension of oxidation time, the better morphology could be obtained. The possible formation mechanism of titania nanotube arrays has been discussed.

Interface of wet oxidized AlGaAs/GaAs distributed Bragg reflectors

The interface of wet oxidized Al0.97Ga0.03As/GaAs in a distributed Bragg reflector (DBR) structure has been studied by means of transmission electron microscopy and Raman spectroscopy. With the extension of oxidation time, the oxide/GaAs interfaces are not abrupt any more. There is an amorphous film near the oxide/GaAs interface, which is Ga2O3 related to the prolonged heating. In the samples oxidized for 10 and 20 min, there are some fissures along the oxidized AlGaAs/GaAs interfaces. In the samples oxidized or in situ annealed for long time, no such fissures are present due to the complete removal of the volatile products.

Time dependence of wet oxidized AlGaAs∕GaAs distributed Bragg reflectors

The time dependence of wet oxidized AlGaAs∕GaAs in a distributed Bragg reflector (DBR) structure has been studied by mean of transmission electron microscopy and Raman spectroscopy. The wet oxidized AlGaAs transforms from an initial amorphous hydroxide phase to the polycrystalline γ-Al2O3 phase with the extension of oxidation time. The thickness of oxide layers will contract due to the different volume per Al atom in AlGaAs and in the oxides. In the samples oxidized for 10 and 20 min, there are some fissures along the AlGaAs∕GaAs interfaces. In the samples oxidized longer, although no such fissures are present along the interfaces, the whole oxidized DBR delaminates from the buffer.