Water Vapor Oxidation Research Articles

Effect of Sc on the Water Vapor Oxidation Behavior of FeCrAl Alloys at 1000 °C

Effect of Sc on the Water Vapor Oxidation Behavior of FeCrAl Alloys at 1000 °C

Effect of Sc and Gd co-doping on the oxidation behavior of FeCrAl alloys in water vapor environment at 1000°C

Rare earth Sc, Gd double doped alloys FeCrAl-xScxGd with different compositions (x=0.25, 0.5, 1.0, 2.0) were prepared by vacuum hot press sintering, and their microstructures were investigated. The double-doped alloy FeCrAl-xScxGd was also oxidized with the single-doped alloys FeCrAl-xSc and FeCrAl-xGd (as a control variable) at high temperature water vapor oxidation at 1000 ℃ for 100 h, and the oxidation kinetic curves were investigated. It is concluded that they have positive effects on the enhancement of the oxidation resistance of FeCrAl alloys in different aspects, while there is no "synergistic effect" of Sc and Gd rare earth elements on the oxidation kinetics of FeCrAl alloys. In FeCrAl alloys, the element Gd not only exists as Gd monomer, but also forms two intermetallic compounds of Gd and Fe, Fe5Gd and Fe9Gd, and the oxide Gd3Fe2Al3O12, which hinders the outward diffusion of Al and reduces its oxidation rate. The element Sc, on the other hand, undergoes longitudinal segregation at the oxide grain boundaries and produces a pinning effect on the alumina scale, which enhances the bonding at the oxide scale/alloy interface, thus preventing the growth of new oxide grains and the generation of new nucleation sites at the alumina scale/alloy interface, thus having a positive effect on the alloy.

Water vapor oxidation behavior and mechanism of high-entropy (TiZrNbTaCr)C at 1200°C

High-entropy (TiZrNbTaCr)C ceramics with different Cr content were oxidized at 1200°C in water vapor. Zr6(Nb, Ta)2O17, (Nb, Ta)2O5 and (Ti, Nb, Ta, Cr)O2 were initial oxidation products. After a 4-h oxidation, TiO2-(Nb, Ta)2O5 was produced and changed from Ti(Nb, Ta)2O7 to Ti2(Nb, Ta)10O29 with increasing Cr content, resulting in better oxidation resistance. TiO2-(Nb, Ta)2O5 with large size and relatively dense microstructure impeded the inward diffusion of water vapor, slowing down the oxidation rate and causing the change of oxidation kinetics from linear to parabolic. The formation process of the oxide scale was discussed and the corrosion mechanism was proposed.

Effect of Bias Voltage on Structure, Mechanical Properties, and High-Temperature Water Vapor Corrosion of AlCrNbSiTi High Entropy Alloy Coatings

Fuel cladding tubes are devices used in reactors to encapsulate fuel clots and transmit heat to coolants. However, zirconium alloy materials which are widely used in the fuel cladding pipe of pressurized water reactors have noticeable safety risks in resisting design basis accidents. Therefore, it is very important to improve the corrosion resistance of fuel envelope tubes to high-temperature water vapor oxidation. High-entropy alloys are considered to be a potential protective coating material for cladding tubes. In this study, AlCrNbSiTi high-entropy alloy (HEA) coatings were prepared by magnetron sputtering at different bias voltages. The effect of bias on coating morphologies, structure, mechanical properties, and resistance to high-temperature water vapor corrosion were studied. Experimental results showed that the bias significantly affects the coating surface roughness. In terms of mechanical properties, the sample at 50 V bias exhibited maximum hardness and elastic modulus of 18.2 GPa and 232.4 GPa, respectively. The highest adhesive force of the coating to the substrate of 36 N was obtained at 100 V bias. The optimum water vapor corrosion resistance of the AlCrNbSiTi HEA coating was achieved at 50 V bias, in which sample-point corrosion was the main corrosion failure mechanism.

Oxidation in Water Vapor of Inconel 625 Fabricated by Additive Manufacturing

Oxidation in Water Vapor of Inconel 625 Fabricated by Additive Manufacturing

Preparation and characterization of smart indicator films based on gellan gum/modified black rice anthocyanin/curcumin for improving the stability of natural anthocyanins

In order to improve the stability of natural anthocyanins in intelligent packaging materials, this work first modified black rice anthocyanins (BRA) by acylation with acetic acid, then modified the acylated BRA by co-coloring with different ratios of curcumin (CUR), and finally added the mixed indicator to gellan gum (GG) to develop intelligent packaging films with good stability. The UV spectroscopy results showed that acetic acid had successfully modified the BRA, while the thermal, photostability and pH stability of the modified black rice anthocyanin (MBRA) were significantly enhanced. The indicators of BRA, MBRA and MBRA mixed with CUR showed excellent pH sensitivity in different buffer solutions. The SEM, FT-IR and XRD results indicated apparent crystalline aggregates on the surface of the films added with a high concentration of CUR. Compared with GG-BRA film, GG-MBRA film improved all properties except for antioxidant performance. Notably, the GG-MBRA/CUR series composite films exhibited significant improvements over the GG-BRA and GG-MBRA films in terms of optical characteristics, mechanical properties, water vapor barrier, oxidation resistance, and color stability; meanwhile, all films exhibited excellent pH sensitivity. Considering all the properties of the films, GG-MBRA/CUR3 film has tremendous potential as a smart indicator film for improving freshness accuracy.

Preparation of VO2/graphene/SiC film by water vapor oxidation

Abstract Vanadium dioxide (VO2) has attracted extensive attention due to the specific metal-insulator phase transition as well as the wide device applications. The practical performance of VO2-based device strongly depends on the quality of VO2, since the higher quality of VO2 film always shows much more pronounced phase transition behavior. Thus, the preparation of high quality VO2 film is essential and highly desirable. In this work, we have prepared high-quality VO2 film on SiC substrate by water vapor oxidation with graphene (G) buffer layer, which showed excellent phase transformation properties. Compared with the VO2/SiC sample without G buffer layer, the VO2/G/SiC films show the resistance changes up to four-orders of magnitude across the phase transition boundary and superior optoelectronic properties, which indicates the significant role of G layer in the film growth process. The current study not only provides an economical and feasible method for VO2/G/SiC thin film preparation with high quality, but also supply some clues for the application of G-based VO2 devices in the future.

Effect of soy protein isolate nanoparticles loaded with litsea cubeba essential oil on performance of lentinan edible films

Environmental issues caused by plastic packaging materials have gotten increasingly severe, and substantial research has been conducted on environmentally friendly active packaging materials. In this study, the Litsea cubeba essential oil loaded soy protein isolate nanoparticles (LSNPs) with appropriate particle size, high storage stability and salt solution stability were fabricated. The LSNPs with the highest encapsulation efficiency of 81.76 % were added into the lentinan edible film. The microstructures of the films were observed by scanning electron microscopy. The physical properties of the films were measured. The results show that the lentinan film with LSNPs in the volume ratio of 4:1 (LF-4) had the highest elongation at break of 196 %, the lowest oxygen permeability of 12 meq/kg, and good tensile strength, water vapor barrier property, antibacterial property, oxidation resistance and thermal stability. The study suggested that LF-4 film could inhibit the growth of bacteria and delay the oxidation of lipid and protein on beef surface for 7 d.

Effect of Oxygen on Water Vapor Oxidation of Fe by Oxygen Partial Pressure Control Using Gas Sensor

An oxygen pump sensor was installed in front of an oxidation furnace to supply and discharge oxygen to the Ar–H2O atmosphere and accurately control the oxygen partial pressure in the atmosphere. Furthermore, the oxidation rate was set after the oxidation furnace. It was measured by an oxygen sensor and a hydrogen sensor. Pure iron was used as the sample. The purpose of this study was to clarify the oxidation behavior of water vapor and oxygen. As a result, it was clarified that the amount of hydrogen generated by the oxidation of water vapor and Fe decreases when oxygen is supplied. In addition, when the oxygen supply amount increased, oxidation by the water vapor did not occur. On the other hand, it was clarified that when oxygen in the atmosphere is discharged, oxidation by oxygen is suppressed and only oxidation by the water vapor occurs. In the cross-sectional microstructure after oxidation, Fe3O4 was formed in the outer layer in the environment where the oxygen was discharged, but by supplying oxygen, the oxide layer became thicker and Fe2O3 was formed in the outer layer. The mass gain increased as the oxygen was supplied. Considering the ratio of oxidation by water vapor and oxidation by oxygen, it was clarified by this method that the mass gain is greater when the oxidation by oxygen is dominant.

Gradient structural-phase states and properties of surface layer after nitro-oxidation

The phase equilibrium is considered, the formation of nitride phases during gas nitriding due to the presence of carbon in the iron steel matrix in all formed structural-phase states of the nitride layer, carbides are released, the dispersion and dispersion of which in the nitride layer depends on the nitrogen potential of the saturating atmosphere. During subsequent oxidation in water vapor, simultaneously with the formation of a surface oxide film during the exposure period, especially in water vapor with additives of complexion agents, during reaction-diffusion, gradient structural-phase states of low-nitrogen carbonitride, oxycarbonitride, and nitride phases are formed in the nitride layer. At the same time, the presence of oxygen in the furnace atmosphere positively affects the formation of the nitride layer and the internal nitriding zone. The corrosion resistance of gradient nitride-oxide diffusion coatings depends on the presence of a surface oxide layer consisting of magnetite and the ratio of modified nitrides and γ'-phase composition. At the same time, in the composition of the nitride layer, the composition of oxycarbonitrides with a larger proportion of the γ'-phase has the highest corrosion resistance with a lower rate of development of corrosion damage on the surface. The presence of a surface oxide layer in the structural-phase states of the nitride-oxide layer, providing a positive property gradient, can provide conditions for external friction during sliding friction.

Structural-phase transformations during nitro oxidation of steels and surface properties

Structural and phase changes in the surface diffusion layer during gas nitriding of steel were studied, with the formation of a crystallographic structure of the nitride layer for subsequent oxidation in water vapor. The conditions for forming carbides and nitrocarbides with simultaneous diffusion of nitrogen and decarburization of the steel matrix are determined depending on the nitrogen potential of the saturating medium. The structural-phase states of the surface diffusion layer with a stepwise change in the nitrogen potential during nitriding at the first stage and followed by oxidation at the second stage, the formation of a surface oxide layer, as well as the conditions for participation in mutual diffusion processes of carbon in the nitride layer, decarburized from the steel matrix with the formation compositions of modified nitride phases. The nitride-oxide layer’s corrosion properties and gradient properties in various structural-phase states of nitride phase compositions have been studied.

Characterisation of AlCrCuFeMo x high entropy alloys for nuclear fuel cladding

High entropy alloys (HEAs) have great potential used for accident-tolerant fuel (ATF) due to their excellent properties. The ATF properties of AlCrCuFeMo x HEAs were systematically investigated. The AlCrCuFeMo x had the typical dendrite morphology and Cu and Al elements segregated in the interdendrite region. After 1200°C water vapour oxidation, compact and continuous α-Al2O3 oxide film formed on the surface and effectively protected the inner from further oxidation. When x = 1, the HEA had the best oxidation resistance (59 mg/dm2 weight gain after 1 h), two orders lower than that of the traditional Zr-1Nb alloy for nuclear fuel cladding. Under normal operation water condition, the performance of the present HEAs is not as good as Zr-1Nb due to the segregation of Cu and dispersed Al2O3 formed on the surface.

The enhanced thermal shock resistance and combustion efficiency of SiC reticulated porous ceramics via the construction of multi-layer coating

SiC reticulated porous ceramic (SRPC) as the key component determined the service life and combustion characteristics of porous burner. The novel multi-layer struts were constructed to synergistically improve the oxidation resistance and infrared radiation of SRPC, including microporous cordierite coating, dense mullite transition layer, SiC skeleton and filling layer. The continuous mullite transition layer significantly improved the resistance to water vapor oxidation of SRPC, also their strength and thermal shock resistance were enhanced because the elimination of strut defects in multi-layer struts. In addition, the microporous cordierite coating generated from the burnt out of pitch increased the burner surface temperature from 764.4 °C to 1061.7 °C, and obviously reduced the CO/NOx emission due to its improved infrared radiation property. Furthermore, the porous cordierite coating enhanced the heat radiation of SRPC, thus increasing the heating rate of the burner from 29.4 °C/min to 33.1 °C/min in the process of water heating.

Breakaway oxidation behavior of Fe-based cylinder coating with eutectic ceramics in water vapor at 650 °C

In this study, we investigate the oxidation behavior of a Fe-based cylinder coating mixed with 35 wt% eutectic ceramic particles. About 250 μm thick coatings were produced on the cylinder surface by using internal rotating plasma spraying. The cylinder coatings were placed in an environment at 650 °C to experience air plus water vapor oxidation as well as air oxidation. In order to do the analysis, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), energy dispersive x-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used. The results show that after spraying, the Fe-based coating has less defects and a uniform and dense structure, in which Al2O3, Al2O3/ZrO2 and a small amount of ZrO2 are evenly distributed. In addition, Al2O3/ZrO2 ceramic particles play a certain role in delaying the breakaway oxidation in the following stage. The oxidation behavior of the Fe-base coating is obviously different from that of traditional alloys. The oxidation rate in the aqueous atmosphere is higher than that in the air. This is mainly reflected in the diffusion of elements, the formation and volatilization of oxides, and the formation and aggregation of pores, which therefore play important roles in the breakaway oxidation. The role of ceramic particles in the oxidation of coatings, the reasons for the high oxidation rate, and the breakaway oxidation mechanism of Fe-based coatings in water vapor were analyzed.

Oxidation behaviors of matrix-grade graphite during water vapor ingress accidents for high temperature gas-cooled reactors

Water ingress into cores of high temperature gas-cooled reactors (HTGRs) can cause serious safety problems in graphitic components, especially for matrix graphite, which is more vulnerable than nuclear graphite. In this study, oxidation behaviors of a matrix-grade graphite, ARB-B1, were investigated under simulated water ingress accidental conditions. The oxidation tests were conducted in water vapor/helium mixed atmospheres at elevated temperatures up to 1200 °C. Oxidation rates and activation energy were evaluated by mass loss measurements. The activation energy was 121.5 kJ/mol in the considered temperature range, indicating only one oxidation regime−in-pore diffusion assisted by cracks. The cracks originated from the fabrication process, acting as penetration paths for the oxidant, played an important role in the oxidation behaviors. Ungraphitized binder oxidation occurred at all temperatures, while apparent oxidation of filler particles started from 1100 °C. Moreover, oxidation effects on compressive properties and hardness of the matrix graphite were discussed in terms of oxidized microstructures. This first detailed study on matrix graphite oxidation in water vapor provides important kinetics knowledge and microstructural and mechanical data for accidental scenarios of HTGRs as well as for development of new matrix graphite materials.

Investigation on the water vapor oxidation of Super304H at 600 ℃

Steam oxidation is the main limited factor for the heat-resistant steel in fossil power plant. Disclosing the oxidation mechanism and kinetics could be helpful for the daily inspection to ensure the safety operation. To investigate the water vapor oxidation behavior of Super304H, the oxidation test was conducted at 600 ℃ for 25, 50, 100, 150 and 200 h in flowing steam. The structure and compositions of the oxide layers were investigated by line-scanning of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Surface morphology was observed after the oxidation test. The oxide phases were identified by XRD. The results showed that the oxide layer was duplex structure consisted of a Fe3O4 - Fe2O3 outer layer and an inner oxide layer which contained nickel oxide, Cr2O3, and FeCr2O4. As the oxidation time increased, the thickness of the total oxide layer and inner layer both increased. After 100 h oxidation, oxide layer exfoliation occurred and resulted in rapid growth of new oxide layer in the exfoliation region.

Thermodynamic and Chemical Analysis of Water-Coal Fuel Ignition and Combustion in Adiabatic Combustion Chamber

The article presents results of improvement of physicochemical model of coal-water fuel ignition and combustion processes, taking into account ash content and release of volatile substances of solid phase. In this case, model of ignition and combustion of two systems of atomized coal-water fuel: drops and pure coal particles is taken as a basis. As a result of the analysis, the influence of ash content of coal-water fuel on output of combustible gases and content of water vapor in furnace atmosphere was established. Based on comparison of the diffusion coefficients of gases and the calculated values of equilibrium constants of reaction in combustion zone, conclusion has been of the leading role of water vapor oxidation of carbon in vortex adiabatic furnace. Performed numerical calculations have shown that combustion process of the above inhomogeneous systems (droplets and particles) in an adiabatic furnace within a short time becomes identical. Concentrations of volatile substances, oxygen (O2) and carbon dioxide (CO2) in various sections of the furnace have been established

Effect of the Fuel Equivalence Ratio on the Mechanisms of Thiophene Oxidation in Water Vapor at Increased Density of the Reagents.

The article presents the results of a study of thiophene oxidation in high-density C4H4S/O2 mixtures (ρThi = 0.12 and 0.15 mol/dm3, ρO2 = 0.74–1.26 mol/dm3), diluted with water vapor and argon (dilution level xD = 35–65% mol), at uniform heating (1 K/min) of a stainless-steel tubular reactor up to 823 K. It is established that the temperature of thiophene oxidation onset weakly depends on the nature of the diluent and the oxygen content in the reaction mixture. From the time dependences of the reaction mixtures on temperature and pressure, it follows that the oxidation of thiophene in the water vapor and argon media proceeds according to the mechanisms of homogeneous and heterogeneous reactions. Upon oxidation of thiophene in the stoichiometric mixtures in argon with a small amount of water vapor, as well as in the lean mixtures in water vapor, the contribution of reactions on the surface of the Pt–Rh/Pt thermocouple, inserted into the center of the reaction volume, is increased. Upon oxidation of thiophene in water vapor in the fuel-enriched and stoichiometric mixtures, reactions on the oxidized surface of the reactor wall (primarily iron oxides) prevail. Increasing the density of water vapor both reduces the contribution of heterogeneous reactions on the reactor wall and prevents complete carbon burnout. It is shown that the neutralization of sulfuric acid, resulting from the oxidation of thiophene, with calcium carbonate reduces the corrosion of stainless steel. The X-ray diffraction analysis revealed the presence of ferrochromite, iron and chromium oxides, iron, nickel, and chromium sulfates in the corrosion products.

Water vapor volatilization and oxidation induced surface cracking of environmental barrier coating systems: A numerical approach

A numerical model is developed for surface crack propagation in brittle ceramic coatings, aiming at the intrinsic failure of rare-earth silicate environmental barrier coating systems (EBCs) under combustion conditions in advanced gas turbines. The main features of progressive degradation of EBCs in such conditions are captured, including selective silica vaporization in the top coat due to exposure to water vapor, diffusion path-dependent bond coat oxidation, as well as crack propagation during cyclic thermal loading. In light of these features, user-defined subroutines are implemented in finite element analysis, where surface crack growth is simulated by node separation. Numerical results are validated by existing experimental data, in terms of monosilicate layer thickening, thermal oxide growth, and fracture behaviors. The experimentally observed quasi-linear oxidation in the early stage is also elucidated. Furthermore, it is suggested that surface crack undergoes rapid propagation in the late stage of extended thermal cycling in water vapor and leads to catastrophic failure, driven by both thermal mismatch and oxide growth stresses. The latter is identified as the dominant mechanism of penetration. Based on detailed analyses of failure mechanisms, the optimization strategy of EBCs composition is proposed, balancing the trade-off between mechanical compliance and erosion resistance.

NITRO-OXIDATION PRODUCTS FROM STRUCTURAL STEELS

The article examines the technology of nitro-oxidation, which consists of nitriding in separated ammonia at the first organize and oxidation in water vapor at the second stage of the process, studied the structure and phase composition of the diffusion nitride-oxide layer, providing high physico-mechanical and physicochemical surface characteristics, competitively capable of galvanic strategies of getting a coating, the conceivable outcomes of regulating the structure and phase composition of the nitride-oxide layer are being investigated to obtain a diffusion coating composition with predetermined properties.