Film Breakdown Research Articles

Experimental investigations into triplex hybrid process of GA-RDECDM during subtractive processing of MMC’s

ABSTRACTThe use of Al-6063 SiCp metal matrix composites (MMCs) in electronic packaging applications, heat sinks for printed circuit boards and for microwave housings necessitates certain degree of machining operations to meet the specifications of the product. The various conventional and non-conventional machining processes had been used to machine the MMCs. But all such processes have their limitations in providing the desired outcomes. Therefore, the present research endeavor, a new process variant of ECDM for the machining of Al-6063 SiCp MMCs. The developed grinding assisted rotary disk electrochemical discharge machining (GA-RDECDM) process integrates the concept of triplex hybridization. In GA-RDECDM, an abrasive coated rotary disk was used as a tool electrode. The abrasive coated disk provides micro gaps between the tool electrode and work material surface and thereby it results in thin and stable gas film formation. The breakdown of thin and stable gas films produce high frequency, low intensity discharges and consequently improves the machining performance. The additional abrasion action imparted by rotating disk ensures the continuation of ECDM process. The influence of various process parameters including applied voltage, pulse on time, electrolyte concentration and the disk rotation rate on width over cut (WOC) and depth were experimentally investigated. Multi criteria optimization using desirability approach predicts the parametric combination of applied voltage of 99V, pulse on time of 3 ms, electrolyte concentration of 17%wt./vol. and disk rotation rate of 30 rpm as the optimum setting for fabrication of slits on the MMCs. The underlying process mechanism is also investigated and presented with appropriate illustrations. The major contribution of the present research work is the development of a novel method for the fabrication of the slits on MMCs.

Experimental Study of the Breakdown Characteristics of Polypropylene Films Under Nanosecond Voltage Pulses

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon.

Stability of the film flow passing round the cross-section elements in the area of high density irrigation

The paper studies the loss of stability of a liquid film using regular surface roughness. The model of the breakdown process is described and the conditions for the formation of a liquid film breakdown are determined experimentally. It was found that there are two characteristic modes, namely drop and film regimes. Using the methods of thermal anemometry, data were obtained on the distribution of the droplet sizes after a film breakdown and the dependence of the We number on the projection arrangement height was plotted.

Revealing How Alkali Cations Affect the Surface Reactivity of Stainless Steel in Alkaline Aqueous Environments

Stainless steel is a ubiquitous structural material and one that finds extensive use in core-internal components in nuclear power plants. Stainless steel features superior corrosion resistance (e.g., as compared to ordinary steel) due to the formation of passivating iron and/or chromium oxides on its surfaces. However, the breakdown of such passivating oxide films, e.g., due to localized deformation and slip line formation following exposure to radiation, or aggressive ions renders stainless steel susceptible to corrosion-related degradation. Herein, the effects of alkali cations (i.e., K+, Li+) and the interactions between the passivated steel surface and the solution are examined using 304L stainless steel. Scanning electrochemical microscopy and atomic force microscopy are used to examine the inert-to-reactive transition of the steel surface both in the native state and in the presence of applied potentials. Careful analysis of interaction forces, in solution, within ≤10 nm of the steel surface, reveals that the interaction between the hydrated alkali cations and the substrate affects the structure of the electrical double layer (EDL). As a result, a higher surface reactivity is indicated in the presence of Li+ relative to K+ due to the effects of the former species in disrupting the EDL. These findings provide new insights into the role of the water chemistry not only on affecting metallic corrosion but also in other applications, such as batteries and electrochemical devices.

CHRONIC TEARING INDUCED BY APREMILAST – A PHOSPHODIESTERASE 4 INHIBITOR

Introduction Apremilast is a phosphodiesterase 4 inhibitor approved for the treatment of psoriatic arthritis and moderate to severe plaque psoriasis. It exerts an anti-inflammatory effect by means of elevating intracellular cAMP levels. This case reveals a novel adverse reaction, chronic excessive tearing secondary to apremilast, diagnosed through history and drug challenge. Case Description A 53-year-old female was referred to the allergy service for evaluation of “conjunctivitis” associated with chronic bilateral epiphora without itch of 18-month duration. Oral antihistamines, punctal plugs, and topical steroids failed to provide relief. The patient noted tear reduction the day after forgetting to take apremilast. Symptoms fully resolved within two days of intentionally stopping the medication. She had taken apremilast daily for 18 months to control psoriasis. She remained asymptomatic throughout a one-month discontinuation trial. Five days after restarting apremilast she developed epiphora that progressively worsened in a stepwise pattern. Symptoms resolved after the second discontinuation with no recurrence. Discussion Dry eye disease involves breakdown of tear film that results in ocular dehydration and irritation. Elevating cAMP has been shown to stimulate lacrimal gland secretion and increase tear volume. For this reason, PDE-4 inhibitors have been investigated as possible topical agents for dry eye disease. Histological similarities between corneal epithelial cells and thin skin help to explain why drugs indicated for hyperproliferative skin disorders, such as dupilumab and corticosteroids, have unintended effects on the eye. Although this reaction was not life-threatening, it caused significant morbidity and extensive utilization of the healthcare system.

Size matching effect between anion vacancies and halide ions in passive film breakdown on copper

Different types of anion vacancies were optimized in passive films on copper via first-principles calculations based on density functional theory, and numerous potentiodynamic polarizations were performed to evaluate the size matching effect between anion vacancies and halide ions in passive film breakdown on copper. The size of the anion vacancies decreased to some extent compared with the corresponding atom due to the surface relaxation effect, and electrochemical experiments showed that the pitting potential for an oxide passive film on copper followed the order F− < Cl− < Br−, while this order was Cl− < F− < Br− for a sulfide passive film, which was attributed to the integrated effect of the energy of anion vacancy expansion and the Gibbs energy of dehydration. The pitting potential orders were the same on pre-oxidized or pre-sulfided copper with that of fresh copper in the same solution. Meanwhile, iodide ions were not compared due to the formation of poorly soluble copper iodides. The ratio of pit depth to pit mouth diameter on copper decreased with increasing pit volume, resulting in shallow pits with large mouth; thus, the catalytic-occluded cell effect was not obvious for copper.

A combined numerical and experimental approach for determining the contact temperature in an industrial ironing operation

Tribological conditions in forming operations depend on several parameters such as tool-workpiece interface pressure, surface expansion, sliding length, sliding speed, tool and workpiece materials and the roughness of the parts. Among indirect parameters, the most influential one is the tool-workpiece interface temperature, which directly influences the lubricant performance. Prior to testing new tribo-systems to determine their limits of lubrication, it is therefore important to find the interface temperature. However, measurement of the interface temperature in metal forming is difficult. The present work investigates the determination of the interface temperature in an industrial ironing operation, where severe process parameters lead to lubricant film breakdown and galling after several strokes. The methodology combines finite element simulations and experimental measurements. The overall procedure is based on a steady-state thermal analysis to determine the temperature distribution within the tool and a transient thermo-mechanical analysis of the ironing process when steady-state conditions are achieved. Results show that the proposed methodology applied to a single stroke can effectively and accurately predict the interface temperature in the test tool, thus avoiding the otherwise required thermo-mechanical FEM analyses of hundreds of strokes to reach steady-state. Furthermore, the influence of parameters, such as the predicted steady-state tool temperature, the friction coefficient and the heat transfer coefficient on the contact temperature, is analysed. It is concluded that the frictional heating is the primary cause for the peak temperature. By calibration of the friction coefficient and the heat transfer coefficient to ensure matching of the numerical results and the experimental measurements, a maximum tool-workpiece interface temperature of 158 °C was determined during the forward stroke and 150 °C during the backward stroke.

Influence of PbO content on the dielectric failure of Nb‐doped {100}‐oriented lead zirconate titanate films

AbstractA series of niobium‐doped, {100} textured, “gradient free,” lead zirconate titanate (PNZT) films with different PbO contents were fabricated by the chemical solution deposition method. The films’ PbO content was controlled by changing the average PbO content in the solution from 114.7 to 117 at.%. During the dielectric breakdown process of 1.5 μm thick PNZT films with Pt top and bottom electrodes, two phenomena were observed: cracking and thermal breakdown of the piezoelectric film. At 150°C, with an applied 400 kV/cm electric field, the crack density of PNZT films induced by electromechanical failure increased from 0.060/μm to 0.090/μm as the solution's PbO content increased from 114.7% to 117%. In addition, the films showed higher crack densities and more frequent thermal breakdown events when the electric field was oriented downward (from top to bottom electrode) compared with an upward oriented electric field (from bottom to top electrode). The films with higher PbO content had a lower breakdown strength. Also, all films showed lower breakdown strength when measured in the field down direction. The Schottky barrier height (SBH) decreased from 0.82 ± 0.06 to 0.68 ± 0.04 eV in the field up direction measurement as the PbO content increased. The SBH value did not show significant change in the field down direction measurement. This suggests that the asymmetry in the film/electrode interfaces is a function of the PbO content in the original solution.

Polarity Effect and Dielectric Breakdown of Composite Ferroelectric Films as the Dielectric for Electrowetting Systems

In this paper, we study the electrical properties and breakdown phenomena of BaTiO3/Teflon composite ferroelectric thin film in electrowetting systems. The experimental results showed that the electrowetting effect and the breakdown voltage depend on DC voltage polarity, and this polarity dependence is closely related to the thickness of the ferroelectric film. Under AC voltages, the breakdown voltage increased directly with voltage frequency. These results are useful for designing reliable EWOD devices with low operation voltages and high robustness.

Study on Aging Effect of Adhesion Strength Between Polyimide Film and Copper Layer

This paper experimentally confirmed that the adhesion strength of the copper layer formed on the surface of the polyimide film by wet plating greatly changes with the aging time. The adhesion strength of the copper layer showed a rapid increase from 4 to 10 h after aging had begun and then converged to a value without a significant change. The adhesion enhancement between polyimide film and copper layer by aging is due to the interlocking effect caused by the volume expansion of copper oxide (CuO) formed in the polyimide, the increased mobility of copper particles enlarged by the decrease of impurities in the copper layer grain boundaries, and the consequent change of the crystal structure of the copper layer leading to the internal stress reduction. Such adhesion improvement can be confirmed by the progress of the cohesive failure indicating the breakdown of the polyimide film.

Single Event Experiment: A Powerful Approach for Studying Passivity Breakdown and Pitting Corrosion

Prediction of material lifetime such as stainless steels requires a clear understanding of passivation, corrosion, and pitting mechanisms. Despite its ubiquity and its history, the mechanisms of pitting are poorly understood, mainly because the stochastic behavior of the phenomenon, which results in many individual processes occurring simultaneously on the material surface. It is thus necessary to devise experiments which allow to work on a single pit for a better understanding of mechanisms governing pitting from its initiation to the propagation or its repassivation. Different experimental setup allowing the local injection of aggressive species such as chloride ions, have thus been developed [1-3], including a flow micro-device allowing a single pit to be initiated and then propagated over long time [4-6]. In this work, we show that we were able to reproduce, at will, the pitting of 316L stainless steel in order to study its propagation at various stages and to revisit the different parameters involved in the pitting process. Thanks to a statistical analysis performed on identical experiments, it was possible to build some zone diagrams showing the stability of pits as a function of the chloride concentration, the pit dimensions, and the electrode potential. Interestingly, the chemistry inside the pit was also studied as a function of the electrode potential. These experiments were performed with a specific experimental setup in order to measure the pitting current of a single pit simultaneously with the Raman spectrum thus opening new insight in the identification of species inside the pit. It was also possible to link the sulphate concentration (and thus the pH variation) inside the pit to the current as a function of time. [1] K. Fushimi, K. Azumi, M. Seo, Use of a liquid-phase ion gun for local breakdown of the passive film on iron, J. Electrochem. Soc., 147 (2000) 552-557. [2] K. Fushimi, M. Seo, Initiation of a local breakdown of passive film on iron due to chloride ions generated by a liquid-phase ion gun, J. Electrochem. Soc., 148 (2001) B450-B456. [3] C. Gabrielli, S. Joiret, M. Keddam, H. Perrot, N. Portail, P. Rousseau, V. Vivier, Development of a Coupled SECM-EQCM Technique for the Study of Pitting Corrosion on Iron, J. Electrochem. Soc., 153 (2006) B68-B74. [4] N. Aouina, F. Balbaud-Celerier, F. Huet, S. Joiret, H. Perrot, F. Rouillard, V. Vivier, A flow microdevice for studying the initiation and propagation of a single pit, Corros. Sci., 62 (2012) 1-4. [5] S. Heurtault, R. Robin, F. Rouillard, V. Vivier, Initiation and propagation of a single pit on stainless steel using a local probe technique, Faraday Discuss., 180 (2015) 267-282. [6] S. Heurtault, R. Robin, F. Rouillard, V. Vivier, On the Propagation of Open and Covered Pit in 316l Stainless Steel, Electrochim. Acta, 203 (2016) 316-325.

(Corrosion Division Morris Cohen Graduate Student Award) Local Hydrogen Detection Techniques for Atmospheric Uptake in Ultra-High Strength Steels

Hydrogen embrittlement (HE) is a concern specifically in ultra-high strength steels (UHSS) prevalent in key structural and vehicle components. In full immersion environments, hydrogen production and uptake in high strength materials has been well documented, such as in the case of cathodic protection. However, for atmospheric exposures, there is a large lack of information regarding hydrogen production and uptake. Under atmospheric conditions, acidic pits can form in UHSS due to the breakdown of the passive film, metal dissolution, hydrolysis, and acidification which are prone to local H production and uptake. An understanding of the effects of marine aerosols, industrial pollutants, and other environmental factors, such as UV and relative humidity, on hydrogen production and uptake in UHSS is necessary to develop new alloys with improved corrosion resistance as well as to anticipate and manage the effects of environment severity on embrittlement susceptibility of currently employed UHSS. However, at present, the majority of available techniques for the measurement of hydrogen dissolved in metals and effective hydrogen diffusivity (DH,eff) lack spatial resolution at the micrometer scale. This is not only of significance for atmospheric exposures, with localized H uptake occurring at pits and/or within droplets, but is also of great importance since the hydrogen-metal interactions and processes occurring at the micrometer to nanometer length scales govern hydrogen embrittlement (HE). This presentation discusses and demonstrates select novel local hydrogen probes; the Scanning Kelvin Probe (SKP) and the Scanning Electrochemical Microscope (SECM). The detection of the spatial distribution of diffusible H concentrations was demonstrated on pre-exposed metallic surfaces with the SKP and SECM. SKP and SECM scans of H uptake in samples from controlled atmospheric pre-exposures are also presented. The application of these techniques is shown to provide local and spatial information on H concentrations produced through atmospheric corrosion. An understanding of the H severity at this local scale can provide significant information on severity of atmospheric exposure environments in terms of H production, uptake, and transport. Furthermore these techniques are adaptable to even higher resolution measurements with the application of the SKP atomic force microscope (SKPFM) or SECM-AFM. Acknowledgement: Research was sponsored by the US Air Force Academy under agreement number FA7000-13-2-0020 and ONR under PROJ0007990. The authors would like to acknowledge the Army Research Laboratories, as well as Monash University, in particular Dr. Sebastian Thomas and Prof. Nick Birbilis. The research was partially supported by a 2014 Australia Endeavour Award Research Fellowship with support from Dr. Kishore Venkatesan and Dr. Ivan Cole at CSIRO.

Application of Channel Flow Double Electrode to pH Detection of Magnesium Dissolution during Anodic Polarization

An elucidation of magnesium dissolution mechanisms is one of the key issues for wider usage of magnesium and its alloys in industry because the magnesium has high reactivity in aqueous solutions. The hydrogen evolution rate is increased with positive polarization from the open circuit potential, which is the so called negative difference effect (NDE).1,2 The real-time hydrogen measurement methods have been developed to investigate the NDE.3-6 Authors7 developed a pH sensing channel flow double electrode (CFDE) in order to investigate the pH changes due to the magnesium dissolution. Our group8-10 have been applied the CFDE for analysis of dissolution mechanisms of copper and copper alloys because the oxidation state of the metal ions dissolved from the metal working electrode (WE) can be detected by arranging a detecting electrode (DE) downstream of the WE. In the pH sensing CFDE, the DE was used as the pH sensor, namely, the hydroxide ions generated during the anodic polarization of magnesium WE can be detected at the pH sensor. It indicates that this method allows for the estimation of the hydrogen evolution rate from pH values without the hydrogen gas collection. In addition, a video recording of the WE surface was performed during the measurement in this system. In the present study, the magnesium dissolution during anodic polarization was examined by the pH sensing CFDE. The relationship between the breakdown of the oxide film formed on the magnesium surface and increase of pH was discussed, and the hydrogen evolution rate was estimated from the pH values. References G. Song, A. Atrens, D. St John, X. Wu and J. Nairn, Corros. Sci., 39, 1981 (1997).G. S. Frankel, A. Samaniego and N. Birbilis, Corros. Sci., 70, 104 (2013).M. Curioni, Electrochim. Acta, 120, 284 (2014).S. Lebouil, A. Duboin, F. Monti, P. Tabeling, P. Volovitch and K. Ogle, Electrochim. Acta, 24, 176 (2014).S. Fajardo and G. S. Frankel, Electrochim. Acta, 165, 255 (2015).Y. Hoshi, R. Takemiya, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 163, C303 (2016).Y. Hoshi, K. Miyazawa, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 165, C243 (2018).M. Itagaki, M. Tagaki, T. Mori and K. Watanabe, Corros. Sci., 38, 601 (1996).Y. Hoshi, M. Itagaki, K. Tabei and I. Shitanda, J. Solid State Electrochem., 19, 3551 (2015).Y. Hoshi, T. Oda, I. Shitanda and M. Itagaki, J. Electrochem. Soc., 164, C450 (2017).

Effects of iron content on the microstructure and corrosion behavior of Ti-30Zr-5Al-3V-xFe alloys

The microstructure and corrosion behavior of the hot-rolled Ti-30Zr-5Al-3V-xFe alloys were investigated. All the alloys are composed of α and β phases. With the increase of Fe content, α laths gradually decreases and the relative content of β phase increases. Potentiodynamic polarization curves recorded in 3.5% NaCl and 5% HCl solutions show that all the alloys exhibit a passivation behavior at potential in the range of 0.25–1.25 V (SCE). An evident change in corrosion current density is presented for all of the alloys in both solutions, which can be attributed to the passive film breakdown caused by pitting corrosion. All the alloys exhibit more positive pitting potential compared with the typical 304 stainless steel. The impedance spectra were fitted using equivalent circuit with two time constants. The alloys with different Fe contents exhibit capacitive behavior with phase angles closed to −80° and high impedance values at low frequency. Containing Fe alloys exhibit commendable combination of mechanical properties and corrosion resistance, which is markedly superior to the typical 304 stainless steel although the corrosion resistance decreases by the addition of Fe. The relative content of α and β phases and the segregations of Fe and V elements are identified as the main factors that affect the corrosion resistance of the hot-rolled alloys.

Corrosion studies of rebar in contact with saturated solution produced by leaching of Portland Type-II cement: examining the effects of chloride, carbonation and an amorphous silica additive

ABSTRACTThis study examined the effects of silica addition on electrochemical behavior of rebar in native pH 12.5 saturated solutions prepared by leaching of Portland Type-II cement, and in solutions reduced by CO2 to pH 9. Cyclic polarizations showed that at pH 12.5 the silica additive increased the threshold concentration required for pitting from 100 to 105mM, and from 0.3 mM to 0.5 mM at pH 9. Passivation kinetic exponents were consistently larger for solutions with either pH when silica was present. The silica additive provided the passive film with generally increased resistance and lower capacitance, as confirmed by electrochemical impedance spectroscopy. Charge carrier densities calculated from Mott-Schottky plots were on the order of 1020 (cm-3), increasing significantly after the passive film breakdown. Raman spectroscopy of rebar samples immersed in saturated cement solutions showed films predominantly composed of iron oxyhydroxides with a new shoulder attributed to amorphous silica.

Dielectric breakdown of alumina thin films produced by pulsed direct current magnetron sputtering

Alumina films (~2 μm thick) were deposited with a mixed Cu/Al interlayer onto copper. Direct current (DC)/Pulsed DC (PDC) magnetron sputtering techniques were independently compared for reactive alumina sputtering. In DC sputtered films, elemental aluminium of 9.2 at.% and nano-crystallites were present within the x-ray amorphous matrix, resulting from target arcing. Defects lead to premature dielectric breakdown/increased current leakage. PDC sputtering improved film quality by removing crystallites, metallic clusters and through thickness cracking. Time dependent dielectric breakdown (TDDB) measurements were carried out using conductive atomic force microscopy identified an improvement in dielectric strength (166 to 310 V μm−1) when switching from DC to PDC deposition power. TDDB suggested that at high applied field the dominant pre-breakdown conduction mechanism was Fowler-Nordheim tunnelling in DC films. Tensile pull-off adhesion ranged from 56 to 72 MPa and was highest following incorporation of an Cu/Al blended interfacial layer. Scratch testing indicated various cracking/buckling failures.

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

A measurement method using electrical impedance has been developed for simultaneous quantifications of the thickness (h) and breakdown ratio (α) of oil films in elastohydrodynamic (EHD) contacts. First, based on simplified geometrical and electrical models of EHD contacts, theoretical expressions of h and α were derived as explicit functions of the measured electrical impedance by using the Lambert function. Then, to verify the proposed measurement principle, oil film thickness measurements were conducted by using the electrical method together with the optical interferometry method in a ball-on-disc-type apparatus, which utilized the lubricated contact between a steel ball and a glass disc with a transparent conductive layer (i.e., an indium tin oxide layer). As a result, it was confirmed that the measured h-values obtained by the electrical method agreed well with those obtained by the optical method, under various test conditions with changing the entrainment speed, slide-to-roll ratio, normal load, and viscosity. Besides, it was also confirmed that the measured α-values obtained by the electrical method showed consistent correlations with the film parameter and the friction coefficient. It is hoped that the developed electrical method will be applied to practical metal-to-metal contacts (e.g., the contacts in practical ball bearings) to understand invisible behaviors of oil films in EHD contacts.

Alloy design employing high Cr concentrations for Mo-free stainless steels with enhanced corrosion resistance

In this study, we demonstrate the strategic replacement of Mo with excess Cr in Fe-Cr alloys and report their corrosion resistances. To better understand pitting corrosion, the electrochemical properties of the passive films observed on different alloys (Fe-20Cr-2Mo and Fe-25Cr) were compared. Mo-free Fe-25Cr offered comparable or better pitting corrosion resistance than Fe-20Cr-2Mo during film breakdown, repassivation, and pit propagation stages. We investigated the reason for enhanced stability against pitting corrosion as a result of Mo exclusion in such alloys. Mo accelerated co-dissolution of Fe and Mo itself, consequently enriching Cr on the surface and ultimately promoting onset of passivity.

SALT CONDENSATE рН EFFECT ON PITTING CORROSION OF ALUMINUM ALLOYS

Background The late stages of oil fields development include the technologies increasing oil recovery, and therefore oil production is carried out in conditions of its high water cut, which leads to increased equipment corrosion at production, preparation, storage, transport and processing facilities oil. Technological fluids high aggressiveness is associated with the presence of dissolved gases, mechanical impurities, salt ions, water-soluble naphthenic and mineral acids and bases, as well as microorganisms whose life-activity products cause active biocorrosion of the metal. According to statistics of oil and gas equipment failures and destruction, it can be noted that corrosion of metal and the formation of its products, contributing to the transported raw materials contamination, represent the main complications that significantly reduce its resource. Aims and Objectives Impact assessment of corrosive environment pH on the pitting corrosion development in formation water. Results Studies have shown that an increase in the pH of a water-salt solution saturated with chlorine ions promotes the substantial shift of the aluminum alloy surface stationary electrode potential (up to 900 mV) in the negative direction. This contributes to the cathodic corrosion reactions enhancement and the breakdown of passive films. Passive film breakdown causes the pitting corrosion development. According to the forecast, if the pH is increased to 14, the corrosion rate can be increased to 17 mm/year. Characteristics and composition of alkaline salt condensate require constant monitoring. With significant local increase in the condensate pH, it is necessary to protect the aluminum alloy surface with paint and varnish. Taking into account the study results and following the recommendations made will significantly increase the life of pontoons, reservoirs and other structures during their operation in the oil and gas industry.

Inclination dependence of planar film boiling stability

Understanding the dynamics of film boiling is crucial for predicting its heat transfer properties. Besides the complete breakdown of film boiling (Leidenfrost point), the most prominent transition is the change from a steady state to an unstable and oscillating vapor film. Here we consider the stability of saturated planar non-horizontal film boiling, with particular attention given to its dependence on inclination angle. Based on the lubrication approximation and a quasi-equilibrium evaporation model, we derive a model for transient film boiling dynamics. We investigate the stability of its steady-state solution by locally applying potential flow linear stability analysis. We show how the behavior will be an inclination dependent mixture of Kelvin–Helmholtz and Rayleigh–Taylor type instabilities, and a relatively simple stability criterion is derived. We also show how the transient lubrication model is incapable of predicting the former kind of instability. The model’s ability to predict the inclination dependence of stability limits is tested against an experimental data set from the literature, and we see that the model displays reasonable accuracy considering its lack of free empirical parameters.