Corrosion Resistance Of Phosphate Coatings Research Articles

PDA@α-ZrP/SiO2 incorporated phosphate coating with enhanced corrosion resistance and friction resistance.

In this study, α-ZrP and SiO2 composite nanomaterials were used to as phosphating accelerators. Experiments show that 2D nanosheets and 0D nanoparticles modified by PDA (PDA@α-ZrP/SiO2) play a synergistic role in effectively increasing the number of phosphate crystals and refining the crystal's size, thereby forming dense and uniform phosphate coatings. The friction resistance and corrosion resistance of phosphate coatings are simultaneously enhanced. Especially when the PDA@α-ZrP/SiO2 addition amount is 0.55 g L-1, the coating porosity of phosphate coating drops from 64.24% to 4.38%. The friction resistance coefficient drops from 0.32 to 0.02 and the polarization resistance increased from 1381 Ω cm2 to 20 520 Ω cm2.

Enalapril maleate as a green accelerator for zinc phosphating coating on low-carbon steel

In this study, enalapril maleate (EM), a green ingredient of an antihypertensive drug, was selected as an accelerator for phosphate coating promoting on low-carbon steel. The scanning electron microscope (SEM), X-ray diffraction (XRD), 3D morphologies, coating weight, coating thickness and free acidity (FA) as well as total acidity (TA) were characterized to analyze the coating performance. Copper sulfate titration, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were performed to evaluate corrosion resistance of phosphate coatings. The DFT computations were applied to explore the phosphating promoting mechanism. The results show that the EM optimal concentration is 1.6 g/L which lowers the operating temperature (form 80 ℃ to 40 ℃), generates the smoothest (Ra = 2.85 μm), the heaviest (28.35 g/cm2) and the thinnest (21.6 μm) coating, and reduces the corrosion rate from 1.099 mpy of blank to 0.0246 mpy. The density functional theory (DFT) results confirm that EM adsorbs on low-carbon steel by electrophilic sites (N10) as well as nucleophilic sites (C10), forms nucleated particles preferentially and accelerates the growth of crystals. Therefore, EM is a green organic compound with high phosphating promotion efficiency which has potential application prospects in industrial phosphating.

Effect of Modifiers Introduced into Cold Phosphating Solutions on the Physical and Mechanical Properties of the Formed Phosphate Films

This work is devoted to the study of the physical-mechanical and protective properties of modified phosphate coatings obtained on steel by cold method. Modifiers introduced into phosphating solutions are buffer additives, stabilize the phosphating process, allow the deposition of coatings at low temperatures, increase the number of active centers on the metal surface, resulting in fine-crystalline uniform coatings of small thickness. It was found that the corrosion rate of modified phosphate films is 2 times less than that of coatings obtained by the traditional method. When the temperature rises above 100 °C, the corrosion resistance of phosphate coatings decreases, and the satisfactory protective properties of the modified films are preserved when heated to 200 °C. Modified phosphate coatings have a high adhesion strength to the metal due to their small thickness. However, thin phosphate coatings have low wear resistance and medium electrical insulation properties.

Evaluation of the Corrosion Resistance of Phosphate Coatings Deposited on the Surface of the Carbon Steel Used for Carabiners Manufacturing

This study aims to evaluate the corrosion resistance of carbon steel, used for carabiners manufacturing, coated with three different types of phosphate layer. The phosphate layers have been obtained by phosphate conversion coating with three different types of phosphate solutions: zinc-based solution, zinc-iron-based phosphate solution, and manganese-based phosphate solution. Additionally, the test was performed on zinc phosphate samples impregnated with molybdenum bisulfate-based oil and zinc phosphate samples further coated with a layer of elastomer-based paint. Considering the areas where the carabiners are used (civil engineering, navigation, oil industry, rescue operations, etc.), the corrosive environments studied are rainwater, Black Sea water, and fire extinguishing solution. The structure of the deposited layers was studied by scanning electron microscopy, while the interface structure between the alloy and corrosive environment was analyzed by electrochemical impedance spectroscopy. According to this study, the corrosion resistance of zinc-based phosphate coated samples and zinc/iron-based phosphate coated samples is higher than that of the studied carbon steel samples, despite the corrosion environment. Also, the most aggressive corrosion environment was the fire extinguishing solution.

Corrosion resistance of black phosphorus nanosheets composite phosphate coatings on Q235 steel

To improve the corrosion resistance of phosphate coatings on Q235 steel, black phosphorus (BP) nanosheets in a phosphating solution were applied. Through X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical tests, the effects of different BP nanosheet concentrations on the composition, morphology, and corrosion resistance of the phosphate coatings were studied. The results indicated that the composition of the phosphating coatings did not change, but their morphology did. The addition of BP nanosheets (0–0.2 g/L) increased the number of sites and decreased the grain size, resulting in the formation of a denser, heavier, and thicker phosphate coating structure. The densest and most uniform coating was obtained at a BP nanosheet concentration of 0.1 g/L. The corrosion current density and rate of the phosphate coating decreased by one order of magnitude. Electrochemical impedance spectroscopy revealed that the coating resistance was four times higher than that of the coating without the BP nanosheets, and the highest corrosion resistance was achieved at this concentration.

Accelerated formation of zinc phosphate coatings with enhanced corrosion resistance on carbon steel by introducing α-zirconium phosphate

In this study, α-zirconium phosphate (α-ZrP) is used as an accelerator for phosphate coatings on carbon steel. A more compact phosphate coating with enhanced corrosion resistance is obtained with the incorporation of α-ZrP. Scanning electron microscopy (SEM) was used to observe the growth of phosphate crystals and the surface morphology of phosphate coatings during the phosphating process. The phosphate crystals composition was analyzed by X-ray diffraction (XRD) spectra. Coating weight and surface roughness tests were also performed. Results of all these characterizations reveal that the incorporation of α-ZrP reduces the phosphate crystals size, coating weight and decreases coating roughness. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests demonstrate that the incorporation of α-ZrP effectively improves corrosion resistance of phosphate coatings (i.e. the corrosion rate is decreased by one order of magnitude). Optimally when the concentration of α-ZrP in the phosphating solution is 0.8 g/L, the minimum corrosion rate (0.17 mpy) is obtained. • α-zirconium phosphate (α-ZrP) is used as a new eco-friendly accelerator of phosphate coatings. • α-ZrP effectively increase phosphating efficiency, reduce the phosphate grain size, and form a denser phosphate coating. • α-ZrP increases the corrosion resistance of phosphate coating by one order of magnitude.

Melatonin as an Accelerating Agent for Phosphate Chemical Conversion Coatings on Mild Steel with Enhanced Corrosion Resistance

Melatonin (MEL), as a new accelerating agent, is applied for phosphate chemical conversion coating on mild steel. Scanning electron microscopy has been applied to observe the morphology of phosphating crystals, showing that the incorporation of MEL results in more dense and uniform phosphate coatings. Electrochemical impedance spectroscopy and potentiodynamic polarization are performed to evaluate corrosion resistance of phosphate coatings. The results show that the corrosion rate of blank phosphate coating is 5.64 mpy, while the corrosion rate of phosphate coating accelerated with 1.25 g l−1 MEL is reduced to 0.04 mpy. In addition, the dry friction test shows that friction coefficient of the phosphate coatings with the introduction of MEL is decreased to 0.3 compared to 0.6 of the blank one, proving that MEL also reduces the friction resistance of phosphate coatings along with improved corrosion resistance.

Incorporation of boron nitride nanosheets in zinc phosphate coatings on mild steel to enhance corrosion resistance

To enhance corrosion resistance of zinc phosphate coatings on mild steel, boron nitride nanosheets (BNs) were introduced into zinc phosphating bath. The effects of BNs on the phase composition, surface morphology and corrosion resistance of phosphate coatings were investigated by varying the concentration of BNs (0.15–0.60 g/L) in the phosphating bath. Results show that the presence of BNs could effectively reduce the crystal sizes of phosphate crystals and thus make BN-incorporated phosphate coatings denser and finer than pure phosphate coatings. Moreover, BN-introduced phosphating bath yields heavier phosphate coatings (25.10 g·m−2). In the electrochemical corrosion measurements, BN-incorporated phosphate coatings display the corrosion current of 3.21 × 10−6 A/cm2, which is one order of magnitude lower than the ones without BNs. Moreover, the time against corrosion of copper sulfate dropping prolongs to 328 s for BN-incorporated samples, which is an increase of 182.75% compared with pure ones.

Study on the Growth and Corrosion Resistance of Manganese Phosphate Coatings on 25Cr2Ni4WA Alloy Steel

The growth process and corrosion resistance of the phosphate coating on 25Cr2Ni4WA alloy steel fabricated by a high temperature manganese phosphating were investigated by XRD, SEM, EDS and electrochemical polarization method, respectively. It is found that the phosphate coating consists of lots of close packed lump crystallites and mainly composed of (Mn,Fe)5H2(PO4)4·4H2O. The coating weight increased rapidly, and then the increase rate slowed down when phosphating process was carried for about 5 min. The corrosion potentials of the phosphated steel shifted positively about 250 mV than the bare steel, indicating that the phosphating can improve the corrosion resistance of the 25Cr2Ni4WA alloy steel.

Effect of Phosphating Technologies on Corrosion Resistance of Phosphate Coatings on 6063 Aluminum Alloy

The basic formulation and technologies of phosphating for 6063 aluminum alloys were discussed to enhance the corrosion resistance. The effect of phosphating time, pH, ZnO, H3PO4 and NaF content on corrosion resistance was investigated using Tafel polarization methods. The results show that the optimum phosphating technologies of 6063 aluminum alloys are as follows: 7 g/L ZnO, 20 mL/L 85% H3PO4, 1.2 g/L NaF, pH 3.0, temperature 45±2°C, phosphating time 7 min. After phosphating treatment the anodic and cathodic corrosion processes of 6063 alloys are suppressed greatly, and the corrosion resistance is enhanced.

Effect of Phosphating Additives on Corrosion Resistance of Phosphate Coatings on AZ91D Magnesium Alloy

AZ91D magnesium alloys were immersed in different phosphating solutions with zinc nitrate and sodium fluoride additives to enhance the corrosion resistance. The devolution law of the Open Circuit Potential (OCP) of AZ91D alloys during phosphating was measured. The corrosion behaviors of AZ91D alloys in 3.5%NaCl solution were investigated using OCP and Tafel polarization methods, and the effect of phosphating additives was discussed. The results show that the changes of the OCP of AZ91D alloys with phosphating time in different phosphating solutions are different; the anodic and cathodic corrosion processes of AZ91D alloys are conspicuously inhibited with phosphate coatings; zinc nitrate and sodium fluoride are benefit to form phosphate coatings with better corrosion resistance. The corrosion potential of AZ91D alloy phosphated in solutions with both zinc nitrate and sodium fluoride is most positive.

Study on the growth and corrosion resistance of manganese phosphate coatings on 30CrMnMoTi alloy steel

Due to containing some alloy elements such as chromium, 30CrMnMoTi steel is usually difficult to be phosphated. In present paper, the growth process of the phosphate coating on 30CrMnMoTi alloy steel fabricated by a high temperature manganese phosphating was investigated. The microstructure, surface morphology, composition and corrosion resistance of the phosphate coatings were analyzed by XRD, SEM, EDS and electrochemical polarization method, respectively. The time dependence of open circuit potential (OCP) and the weight of the coating were also measured. It is found that the phosphate coating is mainly composed of (Mn,Fe)5H2(PO4)4·4H2O and consists of a lot of close packed lump crystallites. Based on the time dependence of morphology and the weight of phosphate films, it shows that the phosphating process mainly includes three stages: corrosion of the substrate, creation and growth of phosphate crystal nucleus and thickening of phosphate coating. For 30CrMnMoTi steel, it takes at least 30seconds and 3minutes for the first and second step, respectively: at the beginning stage of phospahting process, a lot of bubbles emit, then a complete film will form at the end of bubbling, and the nucleation of phosphate film is inhomogeneous, phosphate crystal nucleus usually forms preferentially at grain boundary. The coating weight-time curve is similar to that of the parabolic growth. The electrochemical polarization measurement shows that the corrosion potentials of the phosphated steel shifted positively about 480mV than the bare steel and the results of neutral salt spray test (NSS) could reach 24h, indicating the phosphating improved the corrosion resistance of the 30CrMnMoTi alloy steel.

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd 2O 3 in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn 3(PO 4) 2 · 4H 2O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd 2O 3 reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.

Effect of substrate heat treatment on morphology and corrosion resistance of Zn–Mn phosphate coating

Phosphate coatings are one of the ancient methods for improvement the corrosion resistance of steels. Many researchers have investigated the effect of process parameters on the structure and properties of these coatings, but the influence of substrate microstructure has been less studied. In this article, the effect of heat treatment of AISI 4130 steel on the surface morphology and corrosion resistance of Zn–Mn phosphate coating has been investigated. The steel substrate was subjected to different heat treatments before coating application. X-ray diffraction, optical and scanning electron microscopy were used for phase and microstructure analysis respectively. The corrosion resistance of the coatings was studied by means of salt spray, potentiodynamic polarisation and electrochemical impedance spectroscopy methods. The results showed that the corrosion resistance of phosphate coatings is greatly influenced by substrate microstructure. The finer the steel microstructure, the more condensed becomes the coating morphology and the better its corrosion resistance.

Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing

To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) sheets were post-sealed with sodium silicate (water glass) solutions. The morphology and chemical composition of the composite coatings was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of sodium silicate post-sealing treatment on the corrosion behaviors of phosphate coatings was investigated by neutral spray salt (NSS) tests and electrochemical measurements. The results show that after the silicate post-treatment the pores among zinc phosphate crystals are sealed with the films containing Si, P, O and Zn, leading to the formation of the continuous composite coatings on the surface of HDG steel. The corrosion resistance of the composite coatings depending on concentration of sodium silicate and post-sealing time is greatly improved by the silicate post-treatment. The optimum concentration of silicate and post-sealing time are 5 g/L and 10 min, respectively. Both the anodic and cathodic processes of zinc corrosion on the samples are suppressed conspicuously, and the synergistic protection effect of the single phosphate coatings and the single silicate films is evident. Moreover, the low frequency inductive loop in electrochemical impedance spectroscopy (EIS) is disappeared and the electrochemical impedance values are increased for more than one order of magnitude. The corrosion protection of the composite coatings is comparable to that provided by the chromic acid post-treatment.

Evaluation of the corrosion resistance of phosphate coatings obtained by anodic electrochemical treatment

The corrosion resistance of phosphate coating obtained by anodic electrochemical treatment at 4–6 mA/cm 2 is addressed in this paper. The corrosion performance of these coatings is also compared with the coatings obtained by chemical treatment. The regenerated phosphoric acid under the influence of anodic current causes a large variation in morphological features of the coatings. Immersion and salt spray tests indicate the ability of these coatings to act as a barrier film on mild steel. Polarization and electrochemical impedance spectroscopic (EIS) studies indicate that the corrosion resistance of phosphate coatings obtained by anodic treatment decreases with increase in current density employed for deposition. In spite of their higher coating weight, the corrosion resistance of phosphate coatings obtained by anodic treatment is inferior to those obtained by chemical treatment. The porosity or discontinuities created due to the dissolution of the coating under the influence of anodic current are considered responsible for the inferior corrosion resistance of these coatings. The study concludes that anodic treatment has only a limited scope for preparing phosphate coatings with improved corrosion resistance.

Corrosion resistance of phosphate coatings obtained by cathodic electrochemical treatment: Role of anode–graphite versus steel

The formation of phosphate coatings by cathodic electrochemical treatment using graphite and steel anodes and evaluation of their corrosion resistance is addressed in this paper. The type of anode used, graphite/steel, has an obvious influence on the composition of the coating, resulting in zinc–zinc phosphate composite coating with graphite anode and zinc–iron alloy–zinc phosphate–zinc–iron phosphate composite coating with steel anode. The corrosion resistance of the coating is found to be a function of the composition of the coating. The deposition of zinc/zinc–iron alloy along with the zinc phosphate/zinc and zinc–iron phosphate using graphite/steel anodes has caused a cathodic shift in the Ecorr compared to uncoated mild steel substrates. The icorr values of these coatings is very high. EIS studies reveal that zinc/zinc–iron alloy dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the formation of zinc and iron corrosion products imparts resistance to the charge transfer process and increases the corrosion resistance with increase in immersion time. The corrosion products formed might consist of oxides and hydroxychlorides of zinc and iron. The study suggests that cathodic electrochemical treatment could be effectively utilized to impart the desirable characteristics of the coating by choosing appropriate anode materials, bath composition and operating conditions.

Increasing the corrosion resistance of phosphate coatings by subsequent treatment with inhibitor solutions

Increasing the corrosion resistance of phosphate coatings by subsequent treatment with inhibitor solutions