Zinc Surface Research Articles

Moving Boundary Simulation of Iron-Zinc Sacrificial Corrosion under Dynamic Electrolyte Thickness Based on Real-Time Monitoring Data

The electrolyte film thickness condensation and evaporation is an important parameter for complexity of atmospheric corrosion. Atmospheric corrosion rate of zinc at the west coast of Singapore was measured for one year using an electrical resistance monitoring system. The analysis of the data reveals that significant corrosion rates only occur at specific hours on dry days. The beginning of this period corresponds to falling temperature and rising relative humidity resulting in the formation of a film of moisture on the zinc surface and the end corresponds to a point that this film dries as the temperature increases. This finding allowed the drying rate of the moisture film to be estimated for input into a moving boundary simulation model of the galvanic corrosion in scratched and zinc coating samples. The simulation results showed that the maximum corrosion rate occurs at electrolyte thickness of about 8 μm. Moreover, the simulation suggested that cut-edge is a more harmful defect than scratch, which was confirmed by the appearance of iron corrosion products on atmospheric exposed cut-edge samples whereas scratched samples were not corroded after one week of exposure. Finally, moving boundary simulation allowed to predict the changes to the geometry of the corroding electrodes.

Maltodextrin for corrosion mitigation of zinc in sulfamic acid: Electrochemical, surface and spectroscopic studies

Maltodextrin (MLD), a biopolymer was introduced as a novel green inhibitor to mitigate the corrosion of zinc in sulfamic acid medium by weight loss and by electrochemical methods. Conditions were optimized to obtain maximum inhibition efficiency. Thermodynamic parameters were evaluated. The surface morphology was studied by SEM, EDX, AFM analysis. Adsorption of inhibitor was re-affirmed by FT-IR spectroscopy, Atomic absorption spectroscopy (AAS), Raman spectroscopy and powder X-ray diffraction (XRD) analysis. Maximum efficiency of 72% was observed for the addition of 400 ppm of MLD. Surface morphology and spectroscopic studies confirmed the adsorption of MLD onto the surface of zinc. Results obtained by classical and electrochemical methods are in good agreement with one another. Maltodextrin emerged as an effective eco -friendly green inhibitor.

Salt Preform Texturing of Absorbable Zn Substrates for Bone-implant Applications.

Surface roughness is an important factor in improving the bone-implant contact area to enhance bone regeneration, yet this aspect has not been applied to absorbable metals. Textured zinc surfaces with varying degrees of surface roughness were produced using a salt-preform method with fine- and coarse-grained salts and compared to a polished control sample. The resulting surfaces were characterized by scanning electron microscopy (SEM), surface roughness, corrosion rates, and in vitro cytotoxicity. The resulting textured surfaces exhibit micron-sized cavities and increased roughness consistent with the initial salt particle size. The corrosion rate was shown to accelerate significantly as compared to the polished control sample, and pre-osteoblasts displayed healthy morphologies on the textures. The results confirm textured zinc surfaces support cell adhesion and can be used to control the corrosion rate. This study represents an important intermediate step that can be applied to porous absorbable metal scaffolds for bone-implant applications.

Experimental Research and Theoretical Analysis of Surface Contact Angles of Different Materials

Surface properties play an important role in the formation of frost crystals. The smaller the contact angle formed by droplets on the metal wall, the larger the contact area with the cold surface, thus accelerating the freezing process and making frost crystals easier to form. In this paper, the water droplets on the surface of zinc, aluminium, brass and red copper with the same specifications were observed microscopically. The images were binarized by Rising View software. The contact angles of the surfaces of different materials were measured, and the theoretical analysis and calculation were made by geometric method. It is found that the water droplets are spherical coronal on the horizontal surface. With the increase of the inclination angle of the specimen, the water droplets will incline downward, and the contact angle of the surface will be larger in front and smaller in back, and the difference between the two is equal to the inclination angle of the specimen. When the inclination angle exceeds the critical inclination angle, the water droplets will slip and no longer adhere to the metal surface.

Effect of Phenols on Biological Zinc Corrosion

It has been shown that treating a zinc surface with phenols (phenol, 2,6-di-tert-butyl-4-methylphenol (ionol), hydroquinone, pyrocatechol, 3,5-di-tert-butyl-pyrocatechol) increased the corrosive damage of the metal caused by microorganisms. It has been suggested that corrosion stimulation was caused by radical processes involving phenols adsorbed on the metal surface and products of oxygen biotransformation by microorganisms.

An in situ IR-Vis Sum Frequency Generation Spectroscopy study of cyanide adsorption during zinc electrodeposition

In this paper, we demonstrate the feasibility of in situ non-linear IR-Vis Sum Frequency Generation (SFG) Spectroscopy investigations at zinc surfaces in electrochemical ambient. We investigated both zinc electrodeposition onto an extraneous electrode and adsorption on polycrystalline zinc. Electrodeposition studies were carried out onto a polycrystalline gold cathode in contact with a Zn-cyanocomplex solution containing free CN−, while adsorption studies were carried out on a polycrystalline zinc electrode in contact with a free-CN− solution. In both experiments, we monitored the spectroscopic features associated with the internal stretching of the adsorbed cyanide (ca. 2100 cm−1) that we exploited as local Au and Zn site probes. Spectroelectrochemical results were complemented by cyclic voltammetric measurements. This proof-of-principle study is encouraging in the view of more concrete applications regarding additive adsorption at zinc electrodes, aiming at a fundamental understanding of the cycling stability of zinc battery anodes.

Additively manufactured biodegradable porous zinc

Additively manufacturing (AM) opens up the possibility for biodegradable metals to possess uniquely combined characteristics that are desired for bone substitution, including bone-mimicking mechanical properties, topologically ordered porous structure, pore interconnectivity and biodegradability. Zinc is considered to be one of the promising biomaterials with respect to biodegradation rate and biocompatibility. However, no information regarding the biodegradability and biocompatibility of topologically ordered AM porous zinc is yet available. Here, we applied powder bed fusion to fabricate porous zinc with a topologically ordered diamond structure. An integrative study was conducted on the static and dynamic biodegradation behavior (in vitro, up to 4 weeks), evolution of mechanical properties with increasing immersion time, electrochemical performance, and biocompatibility of the AM porous zinc. The specimens lost 7.8% of their weight after 4 weeks of dynamic immersion in a revised simulated body fluid. The mechanisms of biodegradation were site-dependent and differed from the top of the specimens to the bottom. During the whole in vitro immersion time of 4 weeks, the elastic modulus values of the AM porous zinc (E = 700–1000 MPa) even increased and remained within the scope of those of cancellous bone. Indirect cytotoxicity revealed good cellular activity up to 72 h according to ISO 10,993–5 and -12. Live-dead staining confirmed good viability of MG-63 cells cultured on the surface of the AM porous zinc. These important findings could open up unprecedented opportunities for the development of multifunctional bone substituting materials that will enable reconstruction and regeneration of critical-size load-bearing bone defects. Statement of significanceNo information regarding the biodegradability and biocompatibility of topologically ordered AM porous zinc is available. We applied selective laser melting to fabricate topologically ordered porous zinc and conducted a comprehensive study on the biodegradation behavior, electrochemical performance, time-dependent mechanical properties, and biocompatibility of the scaffolds. The specimens lost 7.8% of their weight after4 weeks dynamic biodegradation while their mechanical properties surprisingly increased after 4 weeks. Indirect cytotoxicity revealed good cellular activity up to 72 h. Intimate contact between MG-63 cells and the scaffolds was also observed. These important findings could open up unprecedented opportunities for the development of multifunctional bone substituting materials that mimic bone properties and enable full regeneration of critical-size load-bearing bony defects.

Evaluation of surface activity of hot-dip galvanized steel after alkaline cleaning

The surface activity of hot-dip galvanized steel was evaluated after alkaline cleaning by exposing the cleaned specimens in humid supercritical carbon dioxide, followed by extraction and quantification of the formed corrosion products. Different free alkalinities of the cleaning bath were studied to obtain information on the evolution of zinc surface activity at different levels of surface etching. Surface reactivity of uncleaned galvanized steel is restricted and local, with major contributions from grain boundaries and intermetallic particles. Formation of zinc corrosion products took place in uncleaned samples exclusively on and around these sites. Al2O3 removal by alkaline cleaning gradually increased the surface activity. The major increase in surface activity was achieved when increasing the free alkalinity from 0.5 to 4.0 mEq/L, which was shown by formation of zinc corrosion products within zinc grains. The surface activity was confirmed by applying a titanium hexafluoride pretreatment on the cleaned panels and measuring the lateral microscale uniformity of the formed layer. The uniformity increased when larger areas of galvanized steel became activated by alkaline cleaning. Reactivity of zinc is rather difficult to quantify when setting up an industrial cleaning sequence for galvanized steel. Controlled exposure of cleaned samples in humid supercritical carbon dioxide, followed by quantification of oxidized zinc, provides a straightforward method to evaluate zinc reactivity.

The Influence of Dimethyl Sulfoxide as Electrolyte Additive on Anodic Dissolution of Alkaline Zinc-Air Flow Battery

The present work describes the effects of dimethyl sulfoxide (DMSO) in KOH aqueous electrolyte on the performance of a zinc-air flow battery. Aqueous electrolytes containing 7 M KOH and (0 to 20)% v/v DMSO were studied revealing a critical role of DMSO on the dissolution and deposition of zinc. The anodic zinc dissolution process was studied via cyclic voltammetry, Tafel polarization and electrochemical impedance spectroscopy (EIS). The presence of DMSO showed improved zinc dissolution performance with the highest peak of zinc dissolution being the electrolyte containing 5% v/v DMSO. Tafel analysis demonstrated a significant decrease in polarization resistance and an increase in corrosion rate due to the introduction of DMSO to the electrolyte. This suggests that DMSO has the ability to suspend zinc oxide in the electrolyte, thus preventing passivation of the zinc surface. EIS results revealed that by adding DMSO to the electrolyte, charge transfer resistance increased. This is attributed to the formation of passive layers having arisen from DMSO adsorption, the formation of zincate ions in the vicinity of the zinc surface, and the deposition of discharged products. A difference in Nyquist plots was observed for 20% v/v DMSO/KOH and 0% v/v DMSO/KOH electrolytes implying non-Debye relaxation behavior taking place due to the surface effects. The electrolytes were implemented in a zinc-air flow battery. Maximum power densities of 130 mW/cm2 (5% v/v DMSO) and 125 mW/cm2 (20% v/v DMSO) were obtained and were observed to be about 43% and 28% higher than that of the DMSO-free electrolyte. Results indicated that when 20% v/v DMSO was added to KOH solution, there was 67% zinc utilization efficiency (550 mAh/g) which provided 20% improvement in discharge capacity. Further, the battery with 20% v/v DMSO demonstrated excellent cyclability. Overall, DMSO shows great promise for enhancement of zinc dissolution/deposition in zinc-air batteries.

Experimental investigation of steam-air condensation on containment vessel

Steam condensation heat transfer is the primary cooling strategy of the passive containment cooling system in some of the third generation reactors. In this study, a series of experiments were performed to investigate the steam condensation on a 1.5 × 0.6 m2 rotatable inorganic zinc surface, with surface inclination angle from horizontal to 60°. The condensate flow on the condensing surface at different inclination angles is photographed and analyzed. The results show that the effect of inclination angle on condensation heat transfer coefficient could be influenced by air fraction. Furthermore, considering the existence of air and overpressure, a semi-empirical correlation based on Nusselt model is developed to precisely predict the steam condensation heat transfer coefficient on the inorganic zinc surface. Since the surface condition of the experimental condensing surface is the same as that of the actual containment vessel, the experimental results would have certain reference values to the containment response analysis of the postulated accidents.

A Metal-Air Scavenger from Hydrogel Electrolytes for Powering Robotics

The low gravimetric and volumetric energy densities of energy storage technologies are principal limitations for realizing the full potential of modern robotics technologies[1]. In many cases, the size and weight of energy storage technologies required to power robotic systems are too large or massive for a robot to carry untethered. Therefore, most robotic systems are tethered, or constrained to limited operational times and long-recharging times over which they remain unused. Energy storage technologies are particularly limiting for micrometer to centimeter scale robots, vehicles, and sensors, as microbatteries dominate the size and mass of the corresponding devices [2,3]. One approach to overcome the energy limitations of batteries is to use battery chemistries with increased energy density. Metal-air batteries are particularly appealing due to their high energy densities. Iron-air, zinc-air, and aluminum-air batteries have 1229, 1535, and 8076 Wh/kg theoretical energy densities [4], which is 5 – 32 X larger than commercial lithium ion batteries. Practical metal-air batteries, however, only achieve a fraction of the theoretical energy density (350 – 500 Wh/kg for Zn-air, for example) and suffer from poor and inefficient rechargeability. Although promising, realizing rechargeable metal-air batteries with near theoretical energy densities is likely several years or decades away. New approaches for powering robots that take advantage of specific environments or use-cases are required to realize untethered robotic systems in the near future. In a conventional battery, active materials are stored in a rigid package so that the maximum volumetric energy density is the energy available in the lowest capacity electrode divided by the total battery volume or mass. A robot, therefore, is required to carry both the active material mass as well as the packaging and electrolyte required for the battery to work. In metal-air batteries, the pertinent electrode is the solid metal anode which oxidizes to produce electrons and, typically, a metal hydroxide or metal oxide. An electrolyte connects the metal anode to a thin porous cathode that reduces oxygen in the air. Metal-air batteries have high energy densities because oxygen for the cathode reaction can be extracted from the air and therefore does not contribute to the battery mass or volume. Electrons from the anode are transferred to the cathode through the robot electronics, powering the robot. In this work, we present a metal-air scavenger (MAS), which is a device that extracts electrical energy from external metal surfaces to power centimeter scale or smaller robots, vehicles, and electronics. The MAS undergoes the same chemical reactions as a metal-air battery, but is only composed of a polymer electrolyte and cathode current collector so that both the anode and cathode active materials are external to the device. The powered devices, therefore, only need to carry the mass of the electrolyte and cathode current collector. We show that, when stationary, a MAS extracts near the theoretical capacity of aluminum and zinc surfaces, as well as extracts up to 1,450 mAh/g from iron surfaces. The maximum power densities of a MAS on aluminum, zinc, and iron surfaces are 130, 80, and 25 mW/cm2. A principal advantage of the MAS is that it can continue to power a device as it moves across a metal surface, so that the total mass and volume of metal oxidized are many multiples of the mass and volume of the device. We demonstrate the utility of a MAS by powering a 5 x 4 x 2 cm electric vehicle on aluminum and zinc surfaces with a 2 x 2 x 0.3 cm MAS. The MAS powered the vehicle over many square feet of metal surface and at up to 8 mm/s velocity. The MAS concept presented here takes advantage of the prolific variety of external metal energy sources available in modern urban environments. We believe the MAS will find utility in many applications, lead to further unconventional methods for powering robotic systems, and open new materials development opportunities. Yang, Guang-Zhong, et al. "The grand challenges of Science Robotics." Science Robotics3.14 (2018): eaar7650.St. Pierre, Ryan, and Sarah Bergbreiter. "Toward Autonomy in Sub-Gram Terrestrial Robots." Annual Review of Control, Robotics, and Autonomous Systems(2019).Oudenhoven, Jos FM, Loïc Baggetto, and Peter HL Notten. "All‐solid‐state lithium‐ion microbatteries: a review of various three‐dimensional concepts." Advanced Energy Materials1.1 (2011): 10-33.Li, Yanguang, and Jun Lu. "Metal–air batteries: will they be the future electrochemical energy storage device of choice?." ACS Energy Letters2.6 (2017): 1370-1377. Figure 1

(Invited) Formation, Characterization and Applications of Nanowire Films Formed By Anodizing of Metals

Anodizing of metals and alloys is a simple electrochemical process to form various nano-structured oxide films, including self-ordered nanoporous and nanotubular films. Typical examples are nanoporous alumina films with honeycomb morphology and nanotubular array of anodic titanium oxide. Recently, several nanowire-type anodic films have been prepared on metals, including aluminum, copper and zinc. The formation mechanism of of the nanowire films may be different from those of the nanoporous and nanotubular anodic films. Here, our recent studies on the formation, characterization and applications of the anodic nanowire films on metals are presented. When zinc plate was anodized at a constant voltage in KHCO3 aqueous electrolytes, nanowires were covered on the entire zinc surface. From the SEM observations, it was found that pits were initially formed on zinc surface. The low-voltage SEM observations disclosed that some small pits were covered with a thin passive film, and in such pits nanowires were preferentially nucleated probably because of the increased concentration of dissolved Zn2+ ions in the pits. Then, the nanowires were grown radially over the pits and covered the entire zinc surface. The nanowires were not composed of ZnO. XPS and FT-IR analyses of the nanowire films indicated the presence of carbonate and hydroxide species; the nanowire consisted of basic zinc carbonate. TEM observations confirmed the single crystalline nature of the as-formed nanowires. The basic zinc carbonate was converted to ZnO without changing the nanowire morphology by heat treatment in air, although single crystalline nanowires changed to polycrystalline one. In addition, slit-type nanopores were introduced into the nanowires so that the specific surface area of the nanowire films was highly enhanced by the heat treatment. The nanowire films exhibits unique wettability to liquids. The as formed nanowire films showed superhydrophilicity with a water contact angle close to 0o and after organic coating the surface changed to superhydrophobic with a water contact angle greater than 150o. Such surface may have many potential applications.

Kinetics of Zinc Corrosion in Concrete as a Function of Water and Oxygen Availability.

This paper studies the effect of water as an oxidation agent and also of oxygen on zinc corrosion kinetics in active state in concrete, using high-sensitivity electrical resistance sensors. It was proven that zinc corrosion in active state is strongly affected by the presence of water at its surface. Zinc corrosion in real concrete in the absence of water can be misinterpreted as salt passivity. The presence of oxygen results in an increase of zinc corrosion rate, however at pH 12.6, passivity can occur. It was verified that corrosion products consisting primarily of Ca[Zn(OH)3]2·2H2O cannot effectively passivate zinc surface in concrete, even after 1800 h of exposure and zinc, or hot-dip galvanized steel can corrode at an unacceptable corrosion rate (more than 4 µm·a−1).

Preparation of polypyrrole coated zinc anode electrode for inhibition corrosion of secondary zinc ion battery

In this work, polypyrrole coated onto zinc surface anode electrode was successfully prepared via cyclic voltammetry deposition. The different PPy thickness layer on zinc electrode is controlled by the different numbers of deposited cycles at 3, 5, 7 and 10 cycles. The surface morphology development of polypyrrole nano/micro structure covering on zinc surface was examined by Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy. The electrochemical activity of polypyrrole coated zinc electrode is characterized by linear polarization, cyclic voltammetry and galvanic static charge-discharge, indicating that the anti-corrosion PPy surface covering on Zn electrode can yield the highest value of corrosion inhibition efficiency of 67% and serve as high redox layer to improve the charge performance.

Fabrication of ZnO nanotube layer on Zn and evaluation of corrosion behavior and bioactivity in view of biodegradable applications

Biodegradable materials are of great interest for the development of temporary implants. While most works have focused on Mg-based materials, recently, zinc and zinc based alloys are attracting increasing attention in this field. In this work, large scale area of flower structure zinc oxide nanotube (ZnO NT) layers were manufactured on the surface of pure zinc via anodic oxidation. Surface morphology and composition were characterized with SEM, XRD and XPS. The length of ZnO NTs was approximately 18 μm. Electrochemical tests in SBF solution showed that ZnO NT layers enhanced the electrochemical activity of pure zinc, from the perspective of degradation rate, the Zn/ZnO NT composite is more suitable for bone fixation compared with pure zinc. Immersion tests demonstrate that more Ca/P deposition occurs on the surface of ZnO NT samples, indicating a better biocompatibility compared with pure zinc. In addition, ZnO NTs have a large number of potential applications, such as use for drug release, or based on their catalytic and semiconductive properties.

A Study of the Effect of Nano Zinc Oxide on Cure Characteristics and Mechanical Properties of Rubber Composites

This study investigates the effect of nano zinc oxide on cure characteristics and mechanical properties of natural rubber composites in comparison with the effect of conventional zinc oxide. Six rubber compounds were prepared with nano zinc oxide (particle size = (10-30) nm and surface area = (30-60) m2/g) and levels of (0,0.4,0.8,1.2,1.6,2) phr (parts per hundred parts of rubber weight). Six rubber compounds were prepared with conventional zinc oxide levels of (0,2,4,5,6,8) phr. The cure rate index was improved by 48.29% and torque difference was improved by 4.77%. The tensile strength was improved by 7.37% and the modulus at 300% was improved by 3.27%, while the hardness was decreased by 5.73%. The using of nano zinc oxide instead of conventional zinc oxide reduced the amount of zinc oxide inside rubber composites by 75%.

Fabrication of durability superhydrophobic LDH coating on zinc sheet surface via NH4F-assisted in-situ growth and post-modification for enhancing anti-corrosion and anti-icing

In this work, a superhydrophobic layered double hydroxide (LDH) coating was fabricated on zinc sheet surface by in-situ growth and post-modification technology. The obtained zinc sheet exhibited excellent superhydrophobicity with a water contact angle (WCA) of 160° and a water sliding angle (WSA) of 5o. To determine the mechanical stability, chemical stability, storage stability of the superhydrophobic LDH coating on zinc surface, sandpaper abrasion test, tape-peeling test, immersion test and long-term exposure to the outdoors were employed. The results of stability test suggested that the LDH coating on zinc surface possessed excellent superhydrophobic stability (WCA > 150°, WSA < 10°) during all kinds of harsh conditions except pH = 1, indicating the superior adaptability to outdoor environment. More importantly, the superhydrophobic LDH coating on zinc surface exhibited excellent anti-corrosion efficiency (η = 99.99%) and delay icing ability (t = 75 min), which was beneficial to the application of zinc in a variety of practical fields.

Passivation and Depassivation Behavior of Zinc in Concrete

Steel rebar in concrete structure is in a passive state due to high pH in sound concrete. However, depassivation takes place by neutralization of concrete due to CO2 gas and penetration of chloride through the concrete. To extend the life time of concrete structure, it is of great importance to examine the degradation of concrete and corrosion of steel rebar. Recently, hot-dip galvanized steel rebar and epoxy-coated rebar are being used. They are expected for long durability. For the galvanized steel rebar, it has been reported [1] that zinc becomes passive by formation of Ca(Zn(OH)3)2・2H2O in simulated concrete solutions, although zinc generally corrodes in high alkaline solutions. In this study, passivation and depassivation behavior of zinc has been investigated in simulated concrete solutions, and fresh concrete. Special attention has been paid to effect of mass transfer in the concrete on the passivation and depassivation. Difference from carbon steel in passivation and depassivation was also discussed. A pure zinc plate and carbon steel plate were used as the specimens, and they were buried in epoxy resin as working electrodes. Two test solutions of a saturated Ca(OH)2 solution (pH12.5) and fresh mortar (water: cement: sand = 0.6:1:2) simulating concrete environment were employed. To determine a critical chloride concentration for the depassivation, NaCl was added into the test solutions and mortar. EIS was measured at certain intervals of the test, and Ecorr was continuously measured. To characterize the corrosion products, the surface and the cross-section were observed by SEM, and elemental analysis was conducted by EDX. The corrosion products were identified by XRD. The corrosion potential of zinc gradually shifted in positive direction, and reached around -0.5 V vs. SSE after 400 h in a saturated Ca(OH)2 solution. On the other hand, in a fresh mortar, it jumped up to about -0.5 V after 20 h. The charge transfer resistance (R ct) of zinc in the Ca(OH)2 solution and mortar was in the other of 106 Ω∙cm2 after the positive shift to -0.5 V in the both solutions. Since the R ct value was comparable to that of carbon steel in the same solutions, the zinc surface was passivated in the both solutions. The different time to passivation could be attributed to the difference of mass transfer of dissolved zinc ions. A compact Ca(Zn(OH)3)2∙2H2O film was observed in the whole surface of the passivated zinc. The passivation might occur due to highly protective Ca(Zn(OH)3)2∙2H2O film. On the other hand, in Ca(OH)2 solution at pH10.5, the R ct of zinc was about 104 Ω∙cm2, where porous ZnO was observed on the surface. In the presence of chloride, zinc and carbon steel were depassivated in the saturated Ca(OH)2 solution at pH12.5, when chloride was increased by 0.05 M. On the other hand, zinc and carbon steel were passivated in the fresh mortar containing 0.05 M NaCl. The film of Ca(Zn(OH)3)2∙2H2O was detected on the zinc surface in the mortar containing 0.05 M NaCl. They were depassivated in the fresh mortar when NaCl was higher than 0.5 M. A critical chloride concentration for the depassivation in the mortar was much higher than in mortar. This might be attributed to the difference of mass transfer. The threshold of chloride concentration for the depassivation of zinc in mortar (pH12.5) was almost same as that of carbon steel. Reference[1] Z.Q.Tan et al.,Corr. Sci., 50(2008),2512

Zinc Oxidation in Limited Volume of Alkaline Electrolyte

Studies of zinc electrode oxidation under the conditions of limited volume of alkaline electrolyte are carried out. It is shown, that at anodic polarization below 7–8 mV the zinc surface is covered by phase layer of zinc oxides and hydroxides. The last ones hinder diffusion of ions participating in electrochemical reactions. Then, formation of zincate complex [\(\rm{Zn}(OH)\begin{array}{c}2-\\ 4\end{array}\)] starts, with the slow diffusion stage of hydroxide ions to the anode surface. At polarization from 0.08 to 0.12 V formation of supersaturated zincate electrolyte occurs, and its decomposition with formation of the loose zinc oxide layer. At polarization above 0.12 V, nonporous oxide film is formed on zinc surface; zinc oxidation process proceeds by solid-phase mechanism.

Controlled adsorption of titanium(IV) oxide particles on electroplated zinc coatings to improve the corrosion resistance of chromium(VI)‐free conversion layers

AbstractAdsorption of nano‐scaled titanium(IV) oxide particles on electroplated zinc is performed by a simple dip‐coating technique in an aqueous titanium(IV) oxide suspension prepared with a stirred media mill. X‐ray photoelectron spectroscopy, scanning electron microscopy and X‐ray fluorescence spectroscopy are carried out to investigate the composition of the zinc surface and the thickness and porosity of the adsorbed titania films. The zinc surface formed during the electrodeposition process is of oxyhydroxide nature and the thickness of the adsorbed titania particle layer is controlled by the pH value and the solid concentration of the suspension. In the range of 10 wt.%–30 wt.% titanium(IV) oxide, a linear dependence between the titania film thickness and the solid content of titania particles in the suspension is found. Highest film thicknesses are obtained in alkaline media (pH≥9). At 13.5 wt.% titania particles and pH values below pH = 2.4, the titania particle film is not closely packed and the zinc layer underneath is still visible in electron microscopy, which is a prerequisite for imbedding these particles by a thin second zinc layer for formation of a robust chromium(VI)‐free passivation layer containing the titania particles.