Protective Oxide Research Articles

Improved oxidation protective ability of SHS powder-synthesized ZrB2-MoSi2-SiC-Si coating on carbon/carbon composites

ZrB2-MoSi2-SiC-Si coatings were prepared by gaseous silicon infiltration on the carbon/carbon composites, and the powders synthesized by the self-propagating high-temperature synthesis method (SHS) were used as the raw materials to benefit the oxidation protective ability of the coatings. The ZrB2-MoSi2-SiC-Si coatings prepared from commercial powders (CP coated samples) were used as a comparison. After sintering, the structure of the coating prepared with SHS powders is denser than the CP coated sample with a density of 3.5 g/cm3. After 62 h of oxidation tests at 1500 °C, the mass loss of the SHS coated sample was only 0.28 %, which was 32 % lower than that of the CP coated sample. The ability of SHS coatings to exhibit better oxidation protection is attributed to the higher oxidation stability and sintering activity of the SHS powders than that of commercial ones.

In Situ High-Temperature TEM Observation of Inconel Corrosion by Molten Chloride Salts with N2, O2, or H2O

In situ transmission electron microscopy (TEM) diffraction and imaging techniques are used to monitor and quantify corrosion of Inconel-625 by pure molten chloride salts (MgCl2 − NaCl − KCl) at 500 °C–800 °C in 1.0 atm inert N2 or pure O2, or by salts which are controllably hydrated in a high vacuum chamber. The isothermal corrosion rate R in inert N2 increases from 203 ± 30 μm year−1 at 700 °C to 463 ± 30 μm year−1 at 800 °C. An oxygen ambient causes a six-fold increase to R = 1261 ± 170 μm year−1 at 700 °C. Salt hydration dramatically accelerates corrosion to R> 3 × 105 μm year−1 at 700 °C while it leads to a more moderate R = 95 ± 20 and 486 ± 30 μm year−1 at 500 °C and 600 °C, respectively. These isothermal corrosion rates indicate that the molten chloride corrosion is significantly accelerated by salt hydration at temperatures above 600 °C, where corrosion is aggravated by increased generation and solubility of corrosive HCl gases. Hence, to reduce rate of corrosion it is important to both avoid incorporation of H2O into the system at each stage and ensure proper flushing of the system before increasing the temperature beyond 600 °C. Compositional analysis of the corroded cells indicate that corrosion in O2 ambient is dominated by oxidation of metals by O2 gas dissolved in the chloride melt, but corrosion in H2O ambients is caused by chlorination of metals by dissolved HCl gas and MgOH+ ions. So, to reduce rate of corrosion, steps should be taken to tailor chloride melt compositions that has low solubility for HCl and O2. All of our corroded samples exhibit passive-protective oxide layers of Cr, Mg, and Ni. In addition, distinct volatile compounds of Ni, Mo and Cr involving NiCl2, (Na,K)2MoO4 and CrO2(OH)2 are detected in N2, H2O, and O2 ambients, respectively. We believe that corrosion acceleration can be minimized by minimizing formation of volatile by-products or promoting reactions that could convert these volatile compounds to solid phases, as these volatile compounds led to destruction of protective oxide layers.

Suppression of Sn whisker growth from SnAgCu solder alloy with TiO2 and ZnO reinforcement nano-particles by increasing the corrosion resistance of the composite alloy

The main joining process of the electronic industry is still soldering with different alloys of Sn. This work studied the relationship between Sn whisker growth and corrosion resistance of 99Sn0.3Ag0.7Cu–TiO2/ZnO (0.25wt%) composite solder alloys in a corrosive environment via scanning electron microscopy and focused ion beam techniques. The corrosive environment test showed that the application of TiO2 and ZnO nano-particles almost totally suppressed the Sn whisker growth and improved the corrosion resistance of the composite solder alloys compared to the reference 99Sn0.3Ag0.7Cu alloy. The microstructural analysis of the reference 99Sn0.3Ag0.7Cu solder alloy showed that the volumetric increase of the corroded β-Sn grains resulted in local mechanical stress in the solder joints, which was released by Sn whisker development. However, in the composite solder joints, the increased grain boundary fraction and segregation of the TiO2 and ZnO nano-particles to the grain boundaries resulted in a relatively uniform and compact protective oxide layer at the β-Sn grain boundaries. This suppressed the formation of SnOx, and via this, the corrosion-induced whisker growth.

Comparative hot corrosion performance of arc ion plated NiCoCrAlYSiHf coating in Na2SO4/NaCl/V2O5-media via high-current pulsed electron beam

The surface of NiCoCrAlYSiHf coating was modified by high-current pulsed electron beam (HCPEB), and the hot corrosion behavior of the coatings in different salts of Na2SO4/K2SO4, Na2SO4/NaCl, and Na2SO4/V2O5 at 900 °C was studied. Microstructural results show that after HCPEB irradiation, the surface of coating was remelted, and a polished, purified, compact, and refined remelted layer was formed; a large number of Y-enriched nanoparticles and high-density dislocation entanglement structures were uniformly distributed in the remelted layer. The results of the hot corrosion test show that the irradiated effects promoted the formation of a continuous and dense protective oxide film in different molten salt environments, effectively prevented the hot corrosion damage of the coating. This significantly reduces the corrosion weight gain, and reduced the corrosion rate by about one order of magnitude compared with the original ones. HCPEB technology significantly improves the hot corrosion resistance of NiCoCrAlYSiHf coating.

Numerical Analysis of Gas-Dynamical and Mechanical Oxidation Protection Against of the Heat-Affected Zone During Coaxial Laser Cladding

Numerical Analysis of Gas-Dynamical and Mechanical Oxidation Protection Against of the Heat-Affected Zone During Coaxial Laser Cladding

Role of Mn Alloying Element on the Oxide Growth Behavior of 800H Nickel-Based Alloy at 900°C

The addition effect of Mn alloying element on the oxide growth behavior of 800H nickel-based alloy has been study in this paper. The alloy was experienced a cyclic oxidation at 900 °C. The cyclic oxidation test was carried out at oxidizing temperature for one hour followed by cooling at about 200 °C for 20 minutes for each cycle. The test samples were exposed to the cyclic condition up to 150 cycles. The oxidized samples of selected cycles were characterized in term of oxidation kinetic, phase analysis using x-ray diffraction (XRD) spectrometer and oxide scale morphology in plan and cross-sectional view by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. As a results, the oxidation kinetic exhibited a weight gain pattern as the exposure cycle increase. Several protective oxide phases which are Cr2O3 and MnCr2O4 oxides were formed. In addition, continuous oxides scale was formed on the sample surface with evidence of Cr-Mn and Cr-rich oxide as detected by EDX analysis.

Effect of Nb on Oxide Formation by Isothermal Oxidation of Solution Treated Fe-40Ni-24Cr Ni-Based Alloy

The study on solution treated Fe-40Ni-24Cr Ni-based alloy on the isothermal oxidation has been investigated. The solution treatment process has been done at two temperatures, which are 1100°C and 1200°C. The alloys were soaking for 3 hours, followed by rapid cooling using water cooled. The solution treated Fe-40Ni-24Cr Ni-based alloy were experienced an isothermal oxidation test at 700°C for 500 hours exposure time. The effect of Nb alloying element on the oxide growth behavior has been characterized in termed of plan and cross sectional view using scanning electron microscope with energy dispersive x-ray spectrometer. As a results, good protective oxide scale has formed on the fine grain solution treated sample with homogeneous and dense oxide structure. On the other hand, coarse grain solution treated sample demonstrated an oxide exfoliation after 500 hours exposure around the overgrown Nb-rich oxide precipitate area, hence indicating poor oxidation protection.

Short-term oxidation behavior of 304 stainless steel in N2-21 vol％O2 environment between 900 and 1200 °C

Oxidation behavior and microstructure evolution of 304 stainless steel at 900–1200 °C in N2-21 vol％O2 were investigated. At 900 °C, Cr2O3 protective oxide is formed on the surface of the steel. With the increase in temperature (1100 °C), an inner oxide layer is formed consisting of two phases (Fe, Cr)3O4 oxide and remaining Ni-Fe metallic. The oxide scale formed at 1200 °C has a unique morphology consisting of the inner Cr-rich oxidation region, middle gap region, outer porous Fe3O4 oxide region, and outermost dense Fe2O3 oxide scale. A discontinuous SiO2 layer appears in the oxide scale.

Roles of Al2O3 coating layer on an ordered mesoporous Ni/m-Al2O3 for combined steam and CO2 reforming with CH4

To enhance catalytic and thermal stability of Ni nanoparticles for a combined steam and CO2 reforming with CH4 (CSCR), the utilization of an ordered mesoporous Al2O3 support with ∼6 nm of average pore diameter (Ni/m-Al) was proposed in terms of spatial confinement effects of the Ni nanoparticles with the help of successive Al2O3 overlayer protective layers (Ni/m-Al@Al). At an optimal amount of Al2O3 coating layers less than ∼3 wt%, the much higher catalytic activity and stability were observed on the Ni/m-Al@Al(3). The synergy effects of Al2O3 overlayers on the ordered mesoporous Ni/m-Al were mainly attributed to the formation of strongly interacted Ni-Al2O3 interfaces as supported by its higher XPS binding energy in the spatially restricted mesoporous m-Al channels with the protective metal oxide overlayers. Those structures were also responsible for the suppressed migrations of the spatially confined Ni nanoparticles to the outer m-Al surfaces by Al2O3 protective overlayers, which resulted in an excellent long-term stability with small coke depositions by preserving the original Ni nanoparticle sizes.

Influence of Ti on Oxide Formation During Isothermal Oxidation of 800H Ni-Based Alloys

In this research, a 800H Ni-based alloy was experienced a solution treatment procedure at two different temperatures. The solution-treated alloys were undergo a high-temperature oxidation under isothermal conditions at 500°C for 500 hours in laboratory air. The alloy was characterized using OES, XRD, SEM and FESEM equipped with an EDX spectrometer. It was found that the solution-treated alloy at 950°C produced a small grain size, and alloy treated at 1100°C produced a large grain size. The XRD results show that various oxides phases were detected. The oxidation kinetics followed the parabolic rate law indicating the oxide was formed based on diffusion-controlled oxide growth rate. The alloys with small grain sizes exhibited a lower oxidation rate, hence have excellent oxidation resistance. This is due to the accessibility of the high ion diffusion route through the grain boundaries of small-grained alloy and thus permits the speedy establishment of the initial oxide layer. Uniform oxide scale formed on a small-grained oxidized sample with visible overgrow discrete oxide particle comprised of Ti-rich oxide. The large-grained oxidized sample indicates evidence of oxide exfoliation indicating poor oxidation protection.

Versatile Zirconium Oxide (ZrO2) Sol-Gel Development for the Micro-Structuring of Various Substrates (Nature and Shape) by Optical and Nano-Imprint Lithography

Zirconium oxide (ZrO2) is a well-studied and promising material due to its remarkable chemical and physical properties. It is used, for example, in coatings for corrosion protection layer, wear and oxidation, in optical applications (mirror, filters), for decorative components, for anti-counterfeiting solutions and for medical applications. ZrO2 can be obtained as a thin film using different deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). These techniques are mastered but they do not allow easy micro-nanostructuring of these coatings due to the intrinsic properties (high melting point, mechanical and chemical resistance). An alternative approach described in this paper is the sol-gel method, which allows direct micro-nanostructuring of the ZrO2 layers without physical or chemical etching processes, using optical or nano-imprint lithography. In this paper, the authors present a complete and suitable ZrO2 sol-gel method allowing to achieve complex micro-nanostructures by optical or nano-imprint lithography on substrates of different nature and shape (especially non-planar and foil-based substrates). The synthesis of the ZrO2 sol-gel is presented as well as the micro-nanostructuring process by masking, colloidal lithography and nano-imprint lithography on glass and plastic substrates as well as on plane and curved substrates.

The influence of V addition on the structure, mechanical properties, and oxidation behaviour of TiAlSiN coatings deposited by DC magnetron sputtering

The influence of V content on the morphology, structure, hardness (H) and reduced Young's modulus (E), adhesion, and oxidation resistance of TiAlSiN coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing V contents from 0, 4.8 and 11.0 at.%. All coatings exhibit a fcc type structure. The coating with 4.8 at.% of V shows the highest values of H and E, whereas the values are similar for the reference coating and the coating with 11.0 at.% of V. The coatings adhere well to the substrates and show a dense and compact columnar growth extending from the adhesive interlayer to the top surface of the coatings. The dynamic thermal gravimetric oxidation curves reveal that V additions decreases the onset point of oxidation significantly and degrades the oxidation resistance of the coatings. A dual oxide layer is formed on the top surface of the reference coating: an outer porous Ti–Al–O rich layer with plate-like features on the top, which classified to TiO2 (rutile and anatase) and Al2O3 phases, and an inner Ti–Si–O rich layer with Al depletion that identified as mixture of amorphous Si–O and Ti–Si–O protective oxides. The diffusion of V to the top surface governs the oxidation process of the V-containing coatings, i.e. increasing V concentration leads to disrupt the formation of the protective continuous oxide layers easily.

Corrosion polarization and passivation behavior of selected stainless steel alloys and Ti6Al4V titanium in elevated temperature acid-chloride electrolytes

AbstractThe corrosion polarization behavior of 439ll ferritic (439ll), 316L austenitic (316L), and NO7208 nickel-chromium-aluminum-iron (NO7208) stainless steels, and Ti6Al4V titanium (Ti6Al4V) alloys was studied in 4 M H2SO4+ 5% NaCl solution at 35 and 70°C. Corrosion rate (CR) of the alloys were generally higher at 70°C. NO7208 and 439ll alloy exhibited higher resistance to general corrosion at 35°C (0.067 and 0.050 mm/year) while Ti6Al4V was the most reactive (0.506 mm/year). Passivation behavior was evident on the plots of NO7208 and Ti6Al4V alloys. NO7208 pitted at 1.04 V with passivation range of 0.17 V. Metastable pitting occurred at 0.02 V and ceased at 0.19 V. Pitting was absent from the polarization plot of Ti6Al4V though it exhibited metastable pitting at −0.39 V and passivated at −0.21 V. At 70°C, NO7208 alloy exhibited the lowestCR(0.392 mm/year), while Ti6Al4V was the most reactive at 21.868 mm/year.CRof the alloys increased by 97.63%, 91.18%, 82.83%, and 97.69% at 70°C. Corrosion potential of the alloys shifted cathodically at 35 and 70°C signifying dominant cathodic processes. Ti6Al4V exhibited passivation behavior at 70°C with no pitting evidence. Open circuit potential measurement showed that Ti6Al4V was the most electronegative and NO7208 alloy was the most electropositive due to the significant growth of its protective oxide. Grain boundary corrosion was visible on 439ll and 316L at 35°C and total surface deterioration at 70°C. Pseudo corrosion pits were visible on NO7208 and Ti6Al4V alloy at 35°C. At 70°C, total surface degradation was visible on Ti6Al4V and grain boundary corrosion on NO7208.

Comparative analysis reveals distinctive genomic features of Taiwan hot-spring cyanobacterium Thermosynechococcus sp. TA-1.

Thermosynechococcus is a genus of thermophilic unicellular cyanobacteria that dominates microbial mats in Asian non-acidic hot springs. These cyanobacteria are the major primary producers in their ecological niches and are promising sources of thermostable enzymes for biotechnology applications. To improve our understanding of these organisms, we conducted whole-genome sequencing of a novel strain for comparative analysis with other representatives in the same genus. This newly characterized strain, Thermosynechococcus sp. TA-1, was isolated from the Taian hot springs in Taiwan. Analyses based on average nucleotide identity (ANI) and genome-scale phylogeny suggested that TA-1 and another Taiwanese strain CL-1 belong to a novel species-level taxon. Two metagenome-assembled genomes (MAGs) originated from India represent the sister group, and Thermosynechococcus elongatus PKUAC-SCTE542 from China is the next closest lineage. All cultivated strains and MAGs from Japan form a separate monophyletic clade and could be classified into two species-level taxa. Intriguingly, although TA-1 and CL-1 share 97.0% ANI, the genome alignment identified at least 16 synteny breakpoints that are mostly associated with transposase genes, which illustrates the dynamic nature of their chromosomal evolution. Gene content comparisons identified multiple features distinct at species- or strain-level among these Thermosynechococcus representatives. Examples include genes involved in bicarbonate transportation, nitric oxide protection, urea utilization, kanamycin resistance, restriction-modification system, and chemotaxis. Moreover, we observed the insertion of type II inteins in multiple genes of the two Taiwanese strains and inferred putative horizontal transfer of an asparagine synthase gene (asnB) associated with exopolysaccharides gene cluster. Taken together, while previous work suggested that strains in this genus share a highly conserved genomic core and no clear genetic differentiation could be linked to environmental factors, we found that the overall pattern of gene content divergence is largely congruent with core genome phylogeny. However, it is difficult to distinguish between the roles of phylogenetic relatedness and geographic proximity in shaping the genetic differentiation. In conclusion, knowledge of the genomic differentiation among these strains provides valuable resources for future functional characterization.

Lignin and fungal abundance modify manganese effects on soil organic carbon persistence at the continental scale

Manganese (Mn) may play an outsized role in soil biogeochemical cycles relative to its abundance. The role of Mn-facilitated oxidation of biomacromolecules during litter decomposition is well-established, but the balance between Mn-promoted soil organic carbon (SOC) oxidation and long-term SOC protection in mineral soils is unknown, especially in subsoils. In this study, we used soils collected across the US National Ecological Observatory Network (NEON) to assess the distribution of Mn and relationships between Mn abundance and SOC concentration, potential mineralization, and persistence at a continental spatial scale. Total reducible Mn was not spatially correlated to site moisture (Spearman’s Rho = 0.24), highlighting that Mn abundance may influence SOC cycling independently from other moisture-driven soil chemical properties (e.g., reactive iron and aluminum). However, Mn effects on SOC cycling depended on depth, soil, or site-level properties. In particular, fungal:bacterial biomass ratio, proportion of SOC in the free light fraction, lignin abundance, and/or proportion of undegraded organic matter mediated the effect of Mn on SOC cycling metrics. For example, the effect of Mn on SOC concentration in subsoils shifted from positive (approximately +270 % relative to mean subsoil SOC) to negative (−125 %) with increasing fungal:bacterial ratio. We propose that convergence of high Mn, lignin-rich substrates, and fungal:bacterial ratio amplifies lignin mineralization in surface soils, but does not result in higher net SOC turnover due to fungal biomass stabilization. In contrast, we suggest that Mn abundance promotes smaller, but more persistent SOC stocks in subsoils by accelerating SOC transformation from particulate to microbial biomass pools.

On thermal stability and oxidation behavior of metastable W–Zr thin-film alloys

The thermal stability and oxidation behavior of metastable W–Zr thin-film alloys with up to 83 at.% Zr were thoroughly investigated with a focus on the effect of gradual substitution of Zr for W. The films were prepared by dc magnetron co-sputtering of W and Zr targets in argon on unheated and unbiased substrates. The experiments showed that a supersaturated α-W(Zr) solid solution structure of as-deposited W-rich films with up to 19 at.% Zr is highly thermally stable up to 1200 °C in argon and the thermal stability of the W–Zr thin-film metallic glasses (33–83 at.% Zr) decreases with increasing Zr content. Nevertheless, the thermal stability of the W–Zr thin-film metallic glass with 33 at.% Zr reaches 1420 °C, which is very high value for binary metallic glass. The annealing of W-rich films (0–24 at.% Zr) in air leads to the formation of a protective surface oxide layer, which serves as a more effective oxygen diffusion barrier due to an increasing packing factor and amorphization with Zr addition. On the other hand, no protective surface oxide layer is grown during the annealing in air in the case of the W–Zr thin-film metallic glasses and the oxidation leads to the formation of compact, homogeneously oxidized substoichiometric W–Zr–O films with an amorphous structure and enhanced mechanical properties before reaching the final mass gain.

Impact of NaCl impurity on corrosion of 316 L steel in molten nitrate salts for thermal energy storage: An electrochemical study

AbstractThe impact of NaCl impurity on corrosion of stainless steel (SS) 316 L in binary nitrate salts (60 wt% NaNO3 + 40 wt% KNO3) was systematically investigated at 565°C via electrochemical measurements. SS 316 L exhibits active dissolution behavior in salts containing 0–1.4 wt% NaCl. The influence of NaCl impurity shows a strong time dependence according to the negligibly affected corrosion current density obtained from a short‐time potentiodynamic polarization sweep. The corrosion process of 316L in salts with NaCl‐free is controlled by ions transport through the oxide layer. With the presence of NaCl impurity, it is controlled by higher rate of ions transport and the diffusion of metal chlorides. The alternation in basicity in the corrosion front caused by chloride ions increases the solubility of chromium oxide and hence the dissolution of chromium oxide, which can lead to the formation of a less protective oxide layer.

Analysis of surface roughness and oxidation of FeNi-based metal amorphous nanocomposite alloys

We report on a systematic investigation of newly developed (Fe 70 Ni 30 ) 80 Nb 4 B 14 Si 2 metal amorphous nanocomposites (MANCs) and the factors affecting their surface roughness, including oxide formation and phase evolution during the nanocrystallization process. Analysis of surface roughness using atomic force microscopy (AFM) revealed an average roughness of 9.33 nm after heat treatment compared with as-cast amorphous ribbons, which exhibited a roughness of 4.21 nm. A surface oxide layer thickness has been determined using X-ray photoelectron spectroscopy (XPS). For samples annealed at 400 °C for 1 h, 450 °C for 1 h, and 550 °C for 3 h in air, the average surface oxide layer thickness was determined to be 10.9, 11.7, and 54.4 nm, respectively. It was observed that oxygen is enriched at the outermost surface and decreases rapidly as the XPS sputtering depth increases. Fe-oxide appeared as a predominant metal oxide at the top surface, followed by the presence of Nb oxide. A boron content increase was observed at the interface between the top surface oxide layer and the bulk of the sample. A protective surface oxide layer on FeNi-MANCs, such as observed in this work, can provide sufficient electrical insulation to reduce interlaminate eddy current losses and lower overall losses in magnetic components. • Surface roughness and oxidation of FeNi-based metal amorphous nanocomposites. • Surface roughness in amorphous ribbon using atomic force microscopy (AFM). • Crystallization and activation energies in metal amorphous nanocomposite ribbons. • Phase fractions in metal amorphous nanocomposite ribbons. • Surface oxides partitioning in amorphous and nanocrystalline alloys.

Improving oxidation resistance of porous FeAl-based intermetallics with high boron/yttrium alloying

The coalloying with high contents of chromium (Cr), boron (B) and yttrium (Y) for porous B2-structured FeAl intermetallics fabricated through reactive synthesis was conducted. The oxidation behaviors of porous FeAl-based materials were investigated by evaluating the pore-structure evolution, oxidation kinetics and oxide-scale configuration. The results show that with the coalloying of high contents of Cr, B and Y, the oxidation mass gains of porous FeAl materials at 600−800 °C are significantly reduced. The combination of B enriched on the surface of oxide scales and Y located at the scale−metal interface promotes the formation of thin protective nodular α-Al2O3 oxide scales. It is indicated that introducing relatively high contents of reactive elements such as B and Y can benefit the selective growth of α-Al2O3 scales at relatively low temperatures without pre-treatment.

Enhanced corrosion resistance in accident-tolerant FeCrAl alloy by water-assisted laser surface modification

FeCrAl alloys have been widely developed as an alternative accident-tolerant cladding material in light water reactors since the Fukushima nuclear accident in 2011. A large thermal neutron cross-section is the most severe challenge for FeCrAl alloys in the final commercial use, and a thinner cladding was necessary to overcome this, which led to higher corrosion resistance requirements. To address this issue, a surface treatment process is described here to enhance the corrosion resistance of the FeCrAl alloy via a water-assisted laser modification. By varying the laser power and laser scanning speed, the relationship between corrosion and processing parameters was investigated to better understand the mechanism with various characterizations. A heat-transfer model with boiling heat transfer boundary conditions was built and simulated using a finite element method to reveal the change in temperature field during processing. A corrosion test was performed with a simulated light water reactor (LWR) hydro-thermal environment for 120 h. The corrosion rate and oxide film thickness of the water-assisted laser modified FeCrAl alloy sample decreased by 83 % and 50 %, respectively, compared to the as-received one, and this was ascribed to the formation of protective oxide film during laser processing, along with grain refinement and elimination of holes and scratches.