Oxygen Partial Pressure Environment Research Articles

Boosting the electrocatalytic activity of NdBaCo2O5+δ via calcium co-doping as bifunctional oxygen electrodes for reversible solid oxide cells

The oxygen electrode of the solid oxide cells (SOCs) operates under an oxidizing atmosphere. Lattice shrinkage in a high oxygen partial pressure environment results in cation misalignment, leading to a decline in performance. Addressing the drawbacks associated with A-site cation mismatch in LnBaCo2O5+δ double perovskite oxides for reversible solid oxide cells (RSOCs) oxygen electrodes, a novel calcium ion co-doping strategy is proposed. This approach effectively mitigates A-site cation segregation and enhances stability. The glycine-nitrate method was employed to synthesize Nd0.8Ca0.2Ba1−xCaxCo2O5+δ (x = 0–0.2) layered double perovskites oxides co-doped with calcium ions, denoted as NCBCC. NCBCC exhibits excellent compatibility with commonly used electrolytes. The doping of calcium co-doped in NdBaCo2O5+δ decreases the thermal expansion coefficient and improves the electron transfer characteristics. The sample with x = 0.1 exhibited an area-specific resistance (ASR) of 0.024 Ω cm2 when operated at a temperature of 800 °C in air. In the solid oxide fuel cell mode, employing x = 0.1 as an oxygen electrode, the maximum power density achieved was 766 mW cm−2 at 800 °C. In the solid oxide electrolysis cell mode, operating with CO2 and steam at an electrolysis voltage of 1.5 V and a temperature of 800 °C, the corresponding current densities were −1.51 and −1.85 A cm−2, respectively. The incorporation of calcium ions into layered perovskite oxides offers a promising strategy to enhance the performance of oxygen electrodes in RSOCs.

Comparative study of Curcumin and Lucentis on retinal neovascularization

Introduction To investigate the effect of Curcumin on retinal neovascularization in mice with oxygen-induced lesions. Methods 7-day-old (P7) C57/BL6J mice were randomly divided into control group, OIR group, DMSO group, 100 mg/kg, 50 mg/kg and 25 mg/kg curcumin group and Lucentis group (15 mice per group). Mice in the experimental group were fed for 5 days in high oxygen partial pressure environment, and then in normal oxygen air environment for another 5 days. Corresponding interventions were given at 12-16 days of age (P12-16). At 17 days of age (P17), the eyeball was removed and the retina was paved with Isolectin GS-IB4 fluorescence staining. Real-time PCR was used to detect VEGF mRNA levels in tissues and cells. The protein expression level of VEGF was detected by Western blot. Results Immunofluorescence showed that curcumin injection could significantly reduce the formation of retinal neovascularization and astrocyte injury in OIR, and 100 mg/kg curcumin group had the best effect. Compared with the control group, mRNA and protein expression of VEGF in retina of mice in OIR and DMSO groups were significantly up-regulated (P<0.05); Compared with OIR group, curcumin group and Lucentis group were down-regulated (P<0.05). The protein expression and mRNA level of VEGF in HRCECs of curcumin group decreased with the increase of curcumin concentration, and the effect of curcumin group at 80μmol/L was similar to that of Lucentis group. In the HRCECs cultured with the same concentration of curcumin, the protein expression and mRNA level of VEGF decreased with the prolongation of drug intervention time. Conclusion Curcumin can down-regulate the expression of VEGF in retinal tissues and cells, thereby inhibiting retinal neovascularization and HRCECs cell proliferation.

Stable oxygen permeable membrane with Ce0.9Gd0.1O2-δ protective layer for syngas production

The stability of catalytic membrane reactors (CMRs) is crucial for the practical applications in chemical reaction processes. However, currently reported CMRs with perovskite-based oxygen permeable membranes usually show poor stability owing to the over-reduction of Co and Fe ions in perovskite lattice under harsh reducing gas atmospheres and the interaction between membrane and catalyst. Here we developed an oxygen permeable membrane Ce0.9Gd0.1O2-δ-SrCe0.5Fe0.5O3-δ (CGO-SCF) with Ce0.9Gd0.1O2-δ (CGO) protective layer to construct a catalytic membrane reactor packed with Ni/Al2O3 catalyst for partial oxidation of methane. The CGO dense protective layer can effectively avoid the over-reduction of Fe ions in perovskite under harsh reducing gas atmospheres and the interaction between perovskite and Ni/Al2O3. Benefiting from high stability and mixed ionic-electronic conductivity of CGO in a low oxygen partial pressure environment, the developed membrane reactor with a dense CGO thin film was successfully operated with a stable CH4 conversion of 87% and a H2/CO ratio of 2 over 200 h in harsh operating conditions. This strategy proposed here provides insights into the design of highly stable catalytic membrane reactor in harsh conditions.

Protective Effect of Modified Hemoglobin on Rabbits and Goats in High-AltitudeSickness.

The prevalence and severity of high-altitude sickness increases with increasing altitude. Prevention of hypoxia caused by high-altitude sickness is an urgent problem. As a novel oxygen-carrying fluid, modified hemoglobin can carry oxygen in a full oxygen partial pressure environment and release oxygen in a low oxygen partial pressure environment. It is unclear whether modified hemoglobin can improve hypoxic injury on a plateau. Using hypobaric chamber rabbit (5000 m) and plateau goat (3600 m) models, general behavioral scores and vital signs, hemodynamic, vital organ functions, and blood gas are measured. The results show that the general behavioral scores and vital signs decrease significantly in the hypobaric chamber or plateau, and the modified hemoglobin can effectively improve the general behavioral scores and vital signs in rabbits and goats, and reduce the degree of damage to vital organs. Further studies reveal that arterial partial pressure of oxygen (PaO2 ) and arterial oxygen saturation (SaO2 ) on the plateau decrease rapidly, and the modified hemoglobin could increase PaO2 and SaO2 ; thus, increasing the oxygen-carrying capacity. Moreover, modified hemoglobin has few side effects on hemodynamics and kidney injury. These results indicate that modified hemoglobin has a protective effect against high-altitude sickness.

Growth of Mn-Co-Ni-O nanowires by pulsed laser deposition

Manganese-cobalt–nickel oxides (Mn-Co-Ni-O) materials have been widely applied as infrared detectors due to its superior thermistor properties and one-dimensional Mn-Co-Ni-O nanowires are expected to significantly enhance the detecting performance. We herein present a novel approach for successfully growing Mn0.79Co1.71Ni0.50O4 nanowires with Au as catalyst by pulsed laser deposition. The influence of growth parameters on the morphology and structural properties of nanowires was explored, and the optimal growth condition of nanowires was obtained. The growth mechanism of Mn-Co-Ni-O nanostructures under different oxygen partial pressure environments is discussed. The deep understanding of the underlying growth mechanism can stimulate more future research on fabrication of high-quality Mn-Co-Ni-O nanowires.

Shear strength and interfacial characterization of borosilicate glass-to-metal seals

In this work, we present the shear strength and interfacial characterization of 304 stainless steel (304SS) to borosilicate glass seals, with the aim of obtaining the best chemical bonding of seals. Different microstructures and chemical compositions of the interface transition region were achieved by employing various pre-oxidation processes of 304SS, which were conducted in a low oxygen partial pressure environment at 1000, 1050, and 1100 °C for a duration of 30, 45, and 60 min. The results of X-ray diffraction (XRD) reveal that the oxide layer is mostly composed of Cr2O3 and Mn1.5Cr1.5O4, and martensitic transformation occurs in the surface of 304SS substrate. Shear strength test shows that the bonding strength formed by dissolution of oxides is far higher than that formed by interfacial redox (reduction-oxidation) reaction directly between metal and glass. The seals to 304SS pre-oxidized at 1050 °C for 45min exhibit the highest shear strength, yielding an average failure strength of 27 ± 0.5 MPa. The correlations between bubble-free region, element diffusion, interfacial defects, fractured surfaces, and the shear strength were qualitatively discussed, leading to new insights into interfacial bonding properties of the glass-to-metal seals.

Carrier localization in perovskite nickelates from oxygen vacancies

Point defects, such as oxygen vacancies, control the physical properties of complex oxides, relevant in active areas of research from superconductivity to resistive memory to catalysis. In most oxide semiconductors, electrons that are associated with oxygen vacancies occupy the conduction band, leading to an increase in the electrical conductivity. Here we demonstrate, in contrast, that in the correlated-electron perovskite rare-earth nickelates, RNiO3 (R is a rare-earth element such as Sm or Nd), electrons associated with oxygen vacancies strongly localize, leading to a dramatic decrease in the electrical conductivity by several orders of magnitude. This unusual behavior is found to stem from the combination of crystal field splitting and filling-controlled Mott-Hubbard electron-electron correlations in the Ni 3d orbitals. Furthermore, we show the distribution of oxygen vacancies in NdNiO3 can be controlled via an electric field, leading to analog resistance switching behavior. This study demonstrates the potential of nickelates as testbeds to better understand emergent physics in oxide heterostructures as well as candidate systems in the emerging fields of artificial intelligence.

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.

Hydrogen interaction characteristics of a Cr2O3[sbnd]Y2O3 coating formed on stainless steel in an ultra-low oxygen environment

Ceramics are the most promising candidates for tritium permeation barriers for fusion reactors due to their high thermal and chemical stabilities and low hydrogen isotope permeation reduction factors. However, hydrogen embrittlement and a large number of defects in ceramic coatings are new challenges for first wall materials in nuclear reactors. To address this issue, a new Cr2O3Y2O3 coating with a thickness of about 100 nm was synthesized and placed in an ultra-low oxygen partial pressure (8 × 10−20 Pa) environment, in which a compact CrY alloy coating was successfully deposited on the stainless-steel substrate by pulsed electrochemical deposition. The interactions between the coating and hydrogen plasma were comprehensively analyzed and compared via surface analysis techniques, including TEM, XPS and electrochemical impedance spectroscopy (EIS). The mechanical properties of the coating before and after hydrogen permeation were studied by tensile testing. It was found that this ceramic coating effectively reduced the defect concentration and retained a high protective performance upon hydrogen exposure. Therefore, this new Cr2O3Y2O3 coating has potential as a promising hydrogen permeation barrier.

Investigation of local atomic structure of Ni doped SnO2 thin films via X-ray absorption spectroscopy and their magnetic properties

Nanostructured Ni (10 at.%) doped SnO2 thin films were grown on Si (100) substrate via pulsed laser deposition technique in ultrahigh vacuum (UHV) chamber and oxygen partial pressure (Po2) environment. The influence of UHV and Po2 growth conditions on the ferromagnetic (FM) ordering, electronic states and short-range structure around Ni ions embedded in the SnO2 network has been investigated. Synchrotron X-ray diffraction results revealed the single-phase nature of SnO2 rutile structure without any foreign peak, and the mean crystallite sizes were found to be 12 and 25 nm for UHV and Po2 deposited films respectively. The crystal growth in UHV chamber, introduced deliberately the oxygen vacancy (Vo) and reduced partially the valence state of Sn4+ (SnO2) ions to Sn3+ (Sn2O3), whereas the Po2 environment optimized the crystallinity and enhanced the oxygen stoichiometry (O:Sn = 2:1) by healing the oxygen vacancies. These details have been obtained by means of Raman spectra, near edge X-ray absorption fine structure at Ni L3,2, O K edges and XANES spectra at Ni K edge. The films showed FM response and the saturation moments increase clearly from 4.4 emu/cm3 (0.33 µB/Ni) for Po2 deposited film to 5.9 emu/cm3 (0.45 µB/Ni) for the film grown in UHV condition. Hence, the enhanced magnetization in UHV condition gives clear evidence on the importance of oxygen vacancies to activate the FM ordering. The role of Vo2+, in the first-shell of oxygen coordination around Sn/Ni ions, to achieve the FM response has been discussed on the basis of bound magnetic polaron and charge transfer percolation mechanisms.

Precipitation induced crack healing in a Ti2SnC ceramic in vacuum

Self-healing ceramics are able to heal cracks through an oxidative healing mechanism at high temperature in oxidizing environments with the recovery of original performance and functionality. However, the oxidation induced repair may be impossible when the ceramics are used in vacuum or inert atmospheres with low oxygen partial pressures. So far little work has been done on crack healing in vacuum or inert atmospheres. Here we report on the crack healing of a Ti2SnC ceramic in vacuum by a precipitation induced repair mechanism. Cracks induced by thermal shock in Ti2SnC are completely filled by only metallic Sn at temperatures above 800°C for only 1h in vacuum. The electrical conductivity of healed materials is fully recovered, and it even exceeds the initial conductivity. This work might bring a new wave of research on crack healing behavior of ceramics in low oxygen partial pressure environments.

Modelling of Processes inside a Rechargeable Oxide Battery

Renewables requires large storage capacities to ensure continuous electricity supply if photovoltaics or wind turbines are not in operation due to weather conditions. For this purpose, amongst other, solid oxide cells (SOC) are used. At operating conditions at 800 °C they can run in two modes: In fuel cell mode (figure 1) a fuel (hydrogen or methane) is burned to generate electricity in the time of electricity undersupply. During electricity oversupply the surplus electricity can be used to produce hydrogen by running the cell in the electrolyzer mode (figure 2). However, storage and transport of hydrogen is cost intensive and controversial regarding safety issues. High security standards have to be fulfilled which increases additionally running cost of SOCs. Therefore, this study focuses on a new concept of running a SOC without external hydrogen supply. Thus, in particular SOFCs can also be used as stationary large scale batteries, so called rechargeable oxide batteries (ROB). In this case the fuel compartment is sealed-off and filled with an atmosphere of hydrogen and steam. In this atmosphere a metallic component, usually an iron based material, will be converted to a metal oxide during discharging (figure 3) and back to metal during charging by reducing the metal oxide (figure 4). Thus, the iron acts as a storage volume in a certain oxygen partial pressure (pO2) environment to achieve a high as possible current density. A special requirement for this setup is the pO2 has to be held in the range of 10-18 to 10-21 bar in the fuel compartment since as anode built-in Ni-cermet could oxidize above pO2 = 10-16 bar and lead to a breakdown of the cell performance. Additionally, the drop of pO2 between the air and fuel side has a direct influence of the transport of oxygen ions through the electrolyte. A beneficial metal/metal oxide system is iron/iron oxide (Fe/FeO) which results in an open circuit voltage of approximately 1.02 V per cell at 800 °C due to the dissociation pressure of FeO in the range of pO2≈10-18 bar. Oxidation and reduction processes strongly depend on the exact atmospheric compositions, the surface area, the porosity, and the diffusion velocities in the storage component. The latter will change due to the reduction/oxidation (change of pore sizes) during charging and discharging of the battery. Also the formation of dense metallic layers on top of the storage components can massively influence the reaction kinetics regarding a higher cycling number. To analyze the processes inside of an ROB, a 1D and a 2D model are developed to simulate the gas transport in the prevailing H2O/H2 atmosphere from the anode surface to the storage component (and reverse) as well as the gas-solid reaction inside the porous Fe/FeO oxide micro structure. The model is implemented by using the Navier-Stokes equations and the method of finite elements using Matlab. The degradation process reduces the performance of the battery along with its recyclability and lifetime. Therefore the degradation should be held as low as possible. Thus, the model contributes to identifying the critical processes in the battery and will allow further optimization considering the development of the battery design and within the performance enhancement. Figure 1

Distribution of elements between copper and FeOx–CaO–SiO2 slags during pyroprocessing of WEEE: Part 2 – indium

Electronic waste (WEEE) is being generated at a rapidly increasing rate and leading to the removal of scarce and valuable metals from the materials cycle. The search for efficient WEEE reprocessing methods requires reliable data on the distribution of these valuable metals during smelting. In this work the distribution ratio of indium between FeOx–CaO–SiO2 slags and copper was examined at an oxygen partial pressure of 10−8 MPa (10−7 atm) and at 1300°C. The indium distribution ratio was strongly dependant on the CaO content, decreasing as the CaO content increased, but relatively unaffected by the Fe/SiO2 ratio of the slag over the range examined. Indium was inferred to be present in slag as InO1·5. The activity coefficient of InO1·5 was calculated and presented as iso-activity coefficient curves on the copper-saturated FeOx–CaO–SiO2 phase diagram. Volatilisation of indium under the oxidising conditions used in this work was insignificant, and it was shown that this is consistent with theoretical expectations. Only in much lower oxygen partial pressure environments can indium volatilisation be expected.

Resilient, Nanostructured, High-Current, and Low-Voltage Neutralizers for Electric Propulsion of Small Spacecraft in Low Earth Orbit

We report propellantless neutralizers resilient to oxygen and low-vacuum environments based on arrays of Pt-coated, self-aligned, and gated Si field emitters. These devices emit currents in excess of 1 mA at bias voltages of less than 120 V, adequate for neutralizing the plume of a small spacecraft's electric propulsion system. The reported devices produce similar currents at fivefold less voltage and emitting area than state-of-the-art CNT neutralizers. Long-term (3 hours) continuous emission in a 1 μTorr oxygen partial pressure environment was demonstrated, confirming the compatibility of these neutralizers with low Earth orbit (LEO) conditions. A robust processing sequence was developed that could be employed for high-yield fabrication of large-area field emission neutralizers with active areas larger than 10 cm2 for current emission higher than 100 mA.

Effect of environment atmosphere on thermal shock resistance of the ZrB2–SiC–graphite composite

The thermal shock resistance of the ZrB2–SiC–graphite composite was evaluated by measuring the retention of the flexural strength after the electrical resistance heating to the temperature ranging from 1000°C up to 2500°C. The experiment was operated in two different environment atmospheres (pure oxygen and low oxygen partial pressure which mixed O2 and Ar with 1:9) at total pressure 2000Pa. The residual strength for the specimen decreased gradually as the temperature increased up to 2200°C, and it was slightly higher when heated in low oxygen partial pressure environment than in pure oxygen. In contrast to the specimen heated in low oxygen partial pressure environment, the residual strength for the specimen in pure oxygen increased steeply as the temperature increased from 1600°C up to 1800°C. The analysis of the SEM observations combined with EDS confirmed that the surface oxidation played a positive role in the thermal shock resistance of the ZrB2–SiC–graphite composite with different environment atmospheres. The results here pointed out a potential method for charactering the effect of environment atmosphere on thermal shock resistance of the ZrB2–SiC–graphite composite.

Thermal shock resistance of a ZrB2–SiC–graphite composite in low oxygen partial pressure environment

Abstract The heating rate and size effect on thermal shock resistance of a ZrB2–SiC–graphite (ZSG) composite was studied by measuring the retention of the flexural strength after rapid resistance heating in a low oxygen partial pressure environment. The residual strength values for the specimen heated in a low oxygen partial pressure of 200 Pa decreased gradually as the temperature increased under high heating rate of 200 °C/s, 300 °C/s and 500 °C/s, and then increased suddenly when the temperature reached 1800 °C. The residual strength values for the specimen with heating rate of 200 °C/s were obviously greater than others and approximate that of the original specimen. At a temperature above 1800 °C, the residual strength decreased again with increasing temperature under different heating rate. Furthermore, the size effect on thermal shock at different temperature was investigated. The experimental results revealed that thermal shock resistance of the ZSG composite was sensitive to the heating rate and size effect. The microstructure of the ZSG composite in different conditions were also presented and analyzed.

Fabrication of asymmetric tubular mixed-conducting dense membranes by a combined spin-spraying and co-sintering process

Abstract Mixed-conducting dense ceramic membranes have attracted considerable attention because of their potential application in oxygen separation, oxyfuel combustion and catalytic membrane reaction processes. However, the development of robust mixed-conducting membranes with both high permeability and stability is still a major challenge. In this paper, a crack-free asymmetric tubular membrane made of SrCo 0.4 Fe 0.5 Zr 0.1 O 3− δ perovskite oxide was successfully prepared by a combined spin-spraying and co-sintering method, in which the slurry containing powders was sprayed on a rotating green support tube and followed by sintering process. The issue of the shrinkage mismatch between membrane and support was solved by the optimization of processing parameters, i.e. heating rate, sintering temperature and spraying circles. SEM and nitrogen gas-tight test demonstrated that the surface of membrane was dense, continuous and crack-free, and the thickness of the dense layer was about 20 μm. A high oxygen flux of 7.41×10 −7 mol cm −2 s −1 was achieved at 800 °C which was 2.35 times that of symmetric membrane. Long-term oxygen permeation measurement (850 °C, 200 h) showed that the asymmetric membrane was stable under low oxygen partial pressure environment. This work provides a new path for the preparation of asymmetric tubular membrane. This simple and cost-effective fabrication technique can be readily used for mass production.

Reversible catastrophic oxidation of a 38Fe–34Ni–25Cr alloy induced by sodium sulphate at low oxygen potential atmospheres

The chromia-forming nickel-based alloy Haynes® HR-120 was oxidised with and without Na2SO4 deposit in a CO/H2/CO2 (45/45/10%vol.) simulated process atmosphere at 900°C for 96h. During the first hours of oxidation, samples covered by sodium sulphate exhibit higher oxidation rate than non-covered ones. However, after 24h both sulphate-covered and uncovered specimens follow the same linear kinetics. In this very low oxygen partial pressure environment (10−18atm), the presence of Na2SO4 promotes the growth of localized iron-rich oxide nodules leading to the observed accelerated oxidation. The development of these nodules is discussed to be the result of the chromia dissolution induced by a basic fluxing mechanism. As soon as the salt is evaporated, slower kinetics are observed and the nodules disappear. In these specific conditions, the oxidation could be considered as a self-healing process.

Oxidation of Carbon Fiber‐Reinforced Silicon Carbide Matrix Composites at Reduced Oxygen Partial Pressures

Carbon fibers (Polyacrylonitrile‐derived T‐300) and T‐300 carbon fiber‐reinforced silicon carbide composites (C/SiC) were oxidized in flowing 0.1 MPa reduced oxygen partial pressure environments (50% O2, 5% O2, 0.5% O2, and 0.1% O2 in argon). Experiments were conducted at temperatures of 816°, 1149°, 1343°, and 1538°C. The oxidation kinetics were monitored using thermogravimetric analysis. T‐300 fibers were completely oxidized for times between 0.6 and 325 h. C/SiC coupons were oxidized for either 25 or 100 h. Fiber oxidation rates had an oxygen partial pressure dependence with a power‐law exponent close to one but were only weakly dependent on temperature. Fiber oxidation kinetics were consistent with gas‐phase diffusion control at these temperatures. The C/SiC coupon oxidation kinetics showed some variability, attributed to differences in the number and width of cracks in the SiC seal coat. Oxidation of the carbon fibers dominated the coupon oxidation behavior. For C/SiC coupons, low temperatures and high oxygen pressures resulted in the most rapid consumption of the carbon fibers. At higher temperatures, the lower oxidation rates were attributed to crack closure due to SiC thermal expansion, rather than oxidation of SiC. At the highest temperature and lowest oxygen partial pressure, active oxidation of SiC was observed.

Mechanism and Control of Carbon Deposition on High Temperature Alloys

In solid oxide fuel cells, the preferred anode electrode is a cermet of Ni-yttria-stabilized zirconia. When high carbon activity and low oxygen partial pressure environments are encountered in the anode compartment, carbon deposition occurs in concert with a corrosion reaction known as metal dusting. Thus high temperature alloys that could resist the carbon deposition/metal dusting reaction are needed. The present work has led to a carbon deposition-resistant alloy in which the initial rapid formation of a surface MnO layer blocks carbon transfer. Subsequently, a Mn-rich spinel layer develops beneath the MnO layer providing long-term resistance to carbon transfer and corrosion. In the alloy, 20Fe-40Ni–10Mn–30Cr, a layer of MnO forms almost instantaneously when exposed to high carbon activity environments over the temperature range . In the above environment, MnO is an n-type conductor and allows rapid Mn transport via Mn vacancies. Beneath this MnO layer, a diffusion resistant, adherent film develops.