Extension Of Immersion Time Research Articles

Corrosion characteristic of vitallium 2000 CoCrMo casting alloy in fluoride containing artificial saliva

In order to reveal the effect of fluoride ions (F−) on the passive film corrosion resistance and composition of CoCrMo dental prosthesis. The passivity of casting Vitallium 2000 CoCrMo series alloy was systematically studied by adopting electrochemical and surface techniques. The results show that F− have a certain effect on the passive film corrosion resistance of casting CoCrMo in oral environment, and the increase of F− concentration weakens the passive film corrosion resistance. With the increase of F− concentration, the open circuit potential moves negatively, the corrosion current density increases, the polarization resistance decreases, and the defect density in the passive film increases. With the extension of immersion time, the corrosion resistance of alloy will be enhanced and shows: AS > AS + 0.5 wt% NaF > AS + 1 wt% NaF. The addition of F− can decrease Co, Cr and Mo peaks sharply and promote the dissolution of the passive film. The result of present study could regulate and guide the application dose of oral fluorine-containing products.

Surface corrosion mechanism of ceramic proppant caused by formation water

AbstractThe performance of ceramic proppant tended to deteriorate during service, and one of the main reasons was the formation of water corrosion on the proppant surface. The proppant was isothermally soaked in formation water and the proppant immersed for different times was characterized by X‐ray fluorescence spectroscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier‐transform infrared spectroscopy, and scanning electron micrscopy. It is found that Cl− in the formation water can migrate to the proppant surface by diffusion and cause corrosion, which degrades its performance. Silica of the proppant can react with Cl− of formation water to form SiCl4, which will rapidly hydrolyze to produce opaque silica gel or silicic acid gel coating the proppant surface. With the extension of immersion time, the gel becomes thicker and more, promoting the degradation of the proppant. This will provide some theoretical guidance for alleviating the degradation of proppant.

Study on corrosion resistance of passive sealant to Fe-based amorphous coating at atomic-scale

Pore defect elimination is the most effective way to prolong the service life of Fe-based amorphous coating. In this study, the passive sealant (PSG) was successfully prepared by the sol–gel method, and the sealing and passive film continuous repair were completed in one-step. Three-dimensional X-ray tomography (3D-XRT) was used to reveal the PSG penetration depths, which was more than 180 μm and resulted in a significant rising of the coating density. The ferric phosphate film formed on the interface of the sealant/coating changed the semiconductor properties of the passive film. The results of Mott-Shottky test showed that the donor density (Nd) decreased by 5 orders of magnitude, which slowed down the diffusion rate of the point defect of the passive film, and the thickness of the passive film increased from 2.37 nm to 12.04 nm. With the extension of immersion time, the concentration of Fe2O3 and Cr2O3 increased by 183.5 % and 93.5 %, respectively. In addition, the increasing concentrations of Fe3+/Fe2+ and Cr3+/Cr0 also demonstrated the improvement of the coating’s passive ability. This study provides a low-cost and a simple strategy for one-step completion of coating sealing and passive film repair to extending the service life of Fe-based amorphous coating.

Constructing passivation film on plain carbon steel similar to that on 316L stainless steel

A high corrosion-resistant passivation film with cerium-molybdenum-chromium-nickel ions has been synthesized on plain carbon steel rebar through a chemical transformation method which significantly lowered the pitting susceptibility of the rebar in the chloride-containing concrete environment. The results indicated that the prepared film has a re-passivation self-healing property in a concrete environment with a concentration of 0.1 M NaCl, which is similar to the behavior of 316L stainless steel. The charge transfer resistance increased markedly with the extension of immersion time, reaching 3.70 × 106 Ω cm2 in about 1500 h of immersion (about 10 times of the initial Rt value). The high corrosion resistance mechanism of the film was discussed here in depth.

Insight on corrosion behavior and mechanism of AA2219 friction stir welded joint in N2O4 medium

This paper investigated the corrosion behavior of AA2219 friction stir welded joints in N2O4. The results showed that with the extension of immersion time, corrosion behaviors such as pitting, intergranular corrosion, and exfoliation corrosion occurred in both base material and weld nugget zone, but there are differences in corrosion sensitivity, and the corrosion behavior mechanism and corrosion sensitivity differences were further analyzed. Pitting was caused by the dissolution of the aluminum matrix near the intermetallic Al2Cu. In addition to the potential differences, intergranular corrosion was also related to grain boundary misorientation and differences in grain boundary precipitates. Corrosion products observed visually at the intergranular corrosion position were helpful in understanding the corrosion mechanism. This work is the first to systematically investigate and report the evolution in corrosion behavior and mechanism of AA2219 FSW in N2O4, which can be a reference for the study of aerospace aluminum alloy materials.

Corrosion Behavior of High-Strength C71500 Copper-Nickel Alloy in Simulated Seawater with High Concentration of Sulfide

The corrosion behavior of high-strength C71500 copper-nickel alloy in high concentrations of sulfide-polluted seawater was studied by potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), immersion testing, and combined with SEM, EDS, XPS, and XRD surface analysis methods. The results showed that the C71500 alloy shows activation polarization during the entire corrosion process, the corrosion rate is much higher (0.15 mm/a) at the initial stage of immersion, and the appearance of diffusion limitation by corrosion product formation was in line with the appearance of a Warburg element in the EIS fitting after 24 h of immersion. As the corrosion process progressed, the formed dark-brown corrosion product film had a certain protective effect preventing the alloy from corrosion, and the corrosion rate gradually decreased. After 168 h of immersion, the corrosion rate stabilized at about 0.09 mm/a. The alloy was uniformly corroded, and the corrosion products were mainly composed of Cu2S, CuS, Cu2(OH)3Cl, Mn2O3, Mn2O, MnS2, FeO(OH), etc. The content of Cu2S gradually increased with the extension of immersion time. The addition of S2- caused a large amount of dissolution of Fe and Ni, and prevented the simultaneous formation of a more protective Cu2O film, which promoted the corrosion process to some extent.

Mechanical effect of clay under the acid-base action: A case study on montmorillonite and illite

To study the mechanical effect of clay under acidic and basic conditions, typical clay minerals, montmorillonite and illite, were taken as the main research objects in this study. The variation law and mechanism of the cohesive force and internal friction angle were studied by immersing the remoulded soil in HNO3 solution with pH = 3 and NaOH (alkaline waste liquid) with pH = 13.5, respectively. It was found that, under acidic conditions, a corrosion reaction between clay minerals and nitric acid occurred. Except for the medium-term, the cohesion generally shows a decreasing trend, and the internal friction angle has little change. Under alkaline conditions, the cohesion of montmorillonite-quartz sand remoulded soil decreased briefly in the early immersion stage of and increased in the middle and late stages. The internal friction angle increases steadily with the extension of immersion time. The cohesion of illite-quartz sand remoulded soil also decreased first and then increased, while the internal friction angle changed little. X-ray diffraction analysis shows that montmorillonite and illite will corrode under acidic conditions, and no new material will be generated, resulting in a decrease in soil cohesion. Under alkaline conditions, montmorillonite was seriously depleted, resulting in the formation of zeolite minerals (zeolite X, garronite) and new cement hydrated calcium silicate CSH (xonotlite). Strong alkali reacts with illite to generate sodium metaaluminate (NaAlO2) and liquid cement Na2SiO3 (sodium silicate). The formation of new cements is the main reason for the increase in cohesion under acid-base conditions, and chemical corrosion and ion exchange cause a decrease in cohesion.

Highly effective Q235 steel corrosion inhibition in 1 M HCl solution by novel green strictosamide from Uncaria laevigata: Experimental and theoretical approaches

Traditional corrosion inhibitors are not popular due to high toxicity. Instead, green corrosion inhibitors are appearing. Here, strictosamide as a green corrosion inhibitor was firstly separated from Uncaria laevigata, showing excellent solubility in hydrochloric acid solution. By means of electrochemical test, morphology measurement, and theoretical analysis, the corrosion inhibition ability of strictosamide on Q235 steel in corrosive medium was evaluated. Electrochemical results suggested that strictosamide revealed significant corrosion inhibition efficiency of 94.25% at 25 °C. Moreover, the inhibition effect was still strong with extension of immersion time, and the highest inhibition efficiency reached up to 94.90% for 48 h at 160 mgL−1. After the samples were immersed in the inhibited solution for 24 h, scanning electron microscopy and atomic force microscopy observations indicated that strictosamide was firmly attached to Q235 steel surface by making a protective film. Then, according to X-ray photoelectron spectroscopy results, Fe-N bonds existed on the steel showed the presence of chemisorption between metal ions and strictosamide molecules. Mainly because N atoms were complexed with Fe (II) to form stable complexes attached to the active position on steel. Hence, the stability and compactness of the adsorption film on metal surface were strengthened. Additionally, the inhibition mechanism of strictosamide was illustrated by molecular dynamics. Overall, strictosamide may exhibit the potential to replace the traditional toxic corrosion inhibitors in the industry.

Pressure sensitive adhesive based on PFBA monomer for ePTFE bonding

AbstractExpanded polytetrafluoroethylene (ePTFE) has superior properties such as compression creep resistance and compression resilience, but it is difficult to bond with other materials due to its low surface energy, high crystallinity and highly symmetrical structure. In this paper, a new type of pressure‐sensitive adhesive is prepared from butyl acrylate, glycidyl methacrylate and unique pentafluorobenzyl acrylate, in which pentafluorophenyl group is introduced to provide steric hindrance to avoid clustering and increase the affinity with ePTFE simultaneously. The thermal stability of this pressure‐sensitive adhesive is approximately 250°C; the contact angle can reach 110.7°; the peel strength can reach 19 N/25 mm, comparable to literature values. The shear holding power at room temperature can be maintained over 100 h, and increases with the extension of immersion time in water, 5 times that of the literature report. This new adhesive can aptly solve the adhesion challenges with the use of ePTFE in complex environment.

Accelerated degradation of quaternary ammonium functionalized anion exchange membrane in catholyte of vanadium redox flow battery

Anion exchange membranes (AEMs) are a type of important separators for vanadium redox flow batteries (VRFBs) with unique advantage in mitigating the permeability of vanadium ions by Donnan repulsion. So far, the degradation mechanism of quaternary ammonium functionalized AEMs in acidic and oxidative VRFBs catholyte is still unclear. Herein, we report the accelerated degradation of a homemade quaternary ammonium functionalized AEM (QA-OMPFEK-20) in the catholyte of VRFBs. The experimental results show that the VO2+ species in the catholyte are reduced to VO2+ gradually with the extension of immersion time. The ion exchange capacity (IEC) of the QA-OMPFEK-20 was decreased to 88.7% of its original value after 30 days of immersion. 1H NMR, Fourier-transformed infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were used to probe the changes in chemical environment of QA-OMPFEK-20. The degradation mechanism was then proposed as the critical attack of VO2+ ions on the ether bond of backbone and the C-N bond of quaternary ammonium groups, leading to the decrease of both molecular weight and IEC.

Long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coatings in sulfide-containing 3.5 wt.% NaCl solution

In this work, Cr3C2–NiCr coatings were fabricated by high-velocity oxygen-fuel (HVOF) spraying. Under the help of scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and optical microscope (OM), the phase compositions and microstructure of the coatings were characterized. The long-term corrosion behavior of HVOF sprayed Cr3C2–NiCr coating (HC) and Q345 steel was probed in 3.5 wt.% NaCl solution (S1) and 3.5 wt.% NaCl solution containing 20 ppm Na2S (S2). With the extension of immersion time, the corrosion rate of HC in different solutions showed an overall trend of increasing first and then decreasing. The corrosion rate of Q345 steel in both of the solutions showed a growing trend, while the trend in the sulfide-containing solution was even sharper. The corrosion rates of HC in S1 and S2 were both lower than those of Q345 steels, especially in S2. Owing to the generation of the dense protective film on the HC surface as well as the accumulation of corrosion products, after 70 d of immersion, HC exhibited better corrosion resistance in S2 than that in S1.

Double-layer peelable coating with eminent mechanical properties and anti-permeability

The inferior resistance to liquid permeation is a typical drawback of common peelable coatings, which can not only shorten their service life under the liquid environments, but also restrict their large-scale application in this field. To solve these problems, a scheme of double-layer composite coating has been proposed by incorporating two typical one-component coatings and its effect on the improvement of the anti-permeability of original peelable coating was investigated. The results revealed that the Double-Layer Peelable Coating (DLPC) exhibited an optimal comprehensive performance on both flexibility and anti-permeability, which can be applied on a variety of different substrate surfaces (such as metals, woods and glasses etc.).Then the evolution of the mechanical properties of the coatings under continuous immersion in 3.5 wt% NaCl solution was tracked by peel and tensile tests, and the anti-permeability was also monitored using electrochemical impedance spectroscopy (EIS) technology and water absorption test. The results demonstrated that although the mechanical properties and anti-permeability of both peelable coatings deteriorated with the extension of immersion time, their response trends were obviously different. The service life of the DLPC has increased by about 648 h compared with the mono-layer peelable coating. Besides, the results of resistance to acids, alkalis aqueous solutions and neutral salt spray also verified the effectiveness of double-layer composite coating.

One-step preparation and characterization of a Ce-La-Y ternary rare earth conversion coating on magnesium alloy AZ91D

A cerium-lanthanum-yttrium (Ce-La-Y) ternary rare earth conversion coating (TRECC) was prepared on magnesium alloy AZ91D with one-step chemical conversion, and the microstructure, composition and protection of Ce-La-Y@TRECC were characterized. Ce-La-Y@TRECC exhibited a crystal-cluster and mud-crack microstructure; crystal-clusters were exquisite and regular, and mud-cracks formed a continuous network. Ce-La-Y@TRECC was composed of O, Ce, La and Y mainly; however, three RE elements presented different distribution characteristic that the simultaneous presences of Ce, La and Y at coating outer side and the only presence of Ce at coating inner side. The average thickness of Ce-La-Y@TRECC was 3.68 μm; in 3.5 wt% NaCl solution, the coating resistance of Ce-La-Y@TRECC decreased and the corrosion weight-loss velocity of Ce-La-Y@TRECC coated AZ91D increased with the extension of immersion time, and the total failure of Ce-La-Y@TRECC consumed ten days.

Effect of Immersion in Water or Alkali Solution on the Structures and Properties of Epoxy Resin.

The durability of fiber-reinforced polymer (FRP) composites is significantly dependent on the structures and properties of the resin matrix. In the present paper, the effects of physical or chemical interactions between the molecular chain of the epoxy resin matrix and water molecules or alkaline groups on the water absorption, mechanical structures, and microstructures of epoxy resin samples were studied experimentally. The results showed that the water uptake curves of the epoxy resin immersed in water and an alkali solution over time presented a three-stage variation. At different immersion stages, the water uptake behavior of the resin showed unique characteristics owing to the coupling effects of the solution concentration gradient diffusion, molecular hydrolysis reaction, and molecular segment movement. In comparison with the water immersion, the alkali solution environment promoted the hydrolysis reaction of the epoxy resin molecular chain. After the immersion in water or the alkali solution for one month, the water uptake of the resin was close to saturate, and the viscoelasticity was observed to decrease significantly. The micropore and free volume space on the surface and in the interior of the resin gradually increased, while the original large-scale free volume space decreased. The tensile strength decreased to the lowest point after the immersion in water and the alkali solution for one month, and the decrease percentages at 20 °C and 60 °C water or 60 °C alkali solution were 24%, 28%, and 22%, respectively. Afterward, the tensile strength recovered with the further extension of immersion time. In addition, it can be found that the effect of the alkali solution and water on the tensile strength of the epoxy resin was basically the same.

Influence of Humidity on the Elastic Modulus and Axis Compressive Strength of Concrete in a Water Environment.

Concrete structures are often in different humidity conditions that have a significant impact on the elastic modulus of concrete, therefore, systematic research on the evolution of the law of concrete elastic modulus under different humidity conditions is needed. In this study, the variation laws of the water saturation of concrete specimens with strength grades C15, C20, and C30 were obtained, and then the influence laws of the water saturation on the concrete axial compressive strength were carried out, and the prediction model of elastic modulus of concrete with respect to water saturation was constructed. The results showed that the water saturation of concrete with strength grades C15, C20, and C30 increased with an extension of immersion time, and the water saturation showed an approximately linear rapid growth within three soaking hours, reaching 47.56%, 71.63%, and 47.29%, respectively. Note, the concrete reached saturation state when the soaking time was 240 h. The axial compressive strength with strength grades C15, C20, and C30 decreased with increased water saturation, and the axial compressive strength of saturated concrete decreased by 27.25%, 21.14%, and 20.76%, respectively, as compared with the dry state concrete. The elastic modulus of concrete with strength grades C15, C20, and C30 increased with increased water saturation, and the elastic modulus of saturated concrete was 1.18, 1.19, and 1.24 times higher than those of dry concrete, respectively.

Study on the migration of four phthalates from plastic food contact materials to food simulants

The ultra performance convergence chromatography method was developed to detect the migration of four phthalates (PAEs) in plastic food contact materials. Plastic food contact materials samples are immersed with oil-based (isooctane) and water-based simulants (10% ethanol, 4% acetic acid and water), respectively. The pre-treatment method of four kinds of PAEs in the simulated immersion solution was optimized. The relationship between migration behaviour and the simulants, migration temperature and migration time were studied. The results show that PAEs were more likely to migrate in oily simulants. Within a certain range, the migration amount increased with the extension of immersion time. The migration rate and amount enhanced with the temperature.

An in-depth study of photocathodic protection of SS304 steel by electrodeposited layers of ZnO nanoparticles

Thin layers of ZnO nanoparticles were deposited potentiostaticly on the surface of stainless steel 304 (SS304) at various potentials (−0.7 V, −1.0 V, −1.3 V, −1.6 V) to study the effect of photo-generated cathodic protection on the substrate. Electrochemical methods of open circuit potential (OCP), potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were employed to investigate the electrochemical behaviors of ZnO-covered SS304 system (ZnO/SS304) in 3.5 wt% NaCl solution under the conditions with and without UV illumination. It is found that the ZnO nanoparticles deposited at −1.0 V was in the shape of hexagonal nanorods, which caused a negative shift to lowest OCP upon UV illumination. Polarization curves were also performed on ZnO/ITO glass system to reveal the photoelectrochemical behavior of ZnO nanoparticles only. Possible anodic and cathodic reactions on the ZnO/SS304 and ZnO/ITO systems at the absence and presence of light illumination have been analysed and discussed in detail. It is found that traditional Tafel extrapolation of the polarization curves cannot be used to get the free corrosion current density of ZnO/SS304 system under light illumination due to the superposition of photo-generated current density. The charge transfer resistance obtained from EIS also includes the influence from the photo-generated reactions on the ZnO/SS304 system. Long-term immersion of the ZnO/SS304 in NaCl solution indicates that the ZnO nanorods underwent morphological transitions to nanotubes at 5 days and finally to needles and thin plates at 10 days. Correspondingly, the photocathodic protection of the ZnO layer decreases with the extension of immersion time. The transformation in morphology is postulated to be caused by the attack of Cl− ions on the surface of ZnO nanoparticles.

Corrosion Resistance of Zinc Phosphate Conversion Coatings on AZ91D Surface

Magnesium alloys have been widely applied in many fields, because of their high strength-to-weight ratio. However, magnesium alloys have high chemical activity and are easily corroded. The poor corrosion resistance of magnesium alloys greatly limits its further application. In this paper, the zinc phosphate conversion coatings were prepared on the surface of AZ91D magnesium alloys. Nano-zinc oxide was the source of zinc and the zinc phosphate conversion coatings were prepared by the given process: 1.25 g/L NaNO3, 3 g/L C6H8O7 H2O, 2.5 g/L NaF, 5.5 g/L ZnO, 12.5 mL/L H3PO4, reaction temperature 50°C, reaction for 30 minutes. The full immersion uniform corrosion test was conducted for the fabricated coatings. The morphology and composition of corrosion in different corrosion stages were characterized by XRD, SEM and other microscopies. The results showed that: (1) the corrosion process of the conversion coatings could be divided into three stages: the dissolution of the conversion coatings, the corrosion of the matrix and the deposition of insoluble matter; (2) XRD analysis and other methods found that the pine-needle magnesium oxychloride compounds were formed in the process of immersion firstly, and it was dissolved into Mg(OH)2 over time; (3) With the extension of immersion time, Mg(OH)2 increased continuously and played a major role in corrosion prevention. The deposited Mg(OH)2 was divided into two layers. In the initial deposition stage, it was mainly evenly dispersed on the surface of the alloy to form a tightly arranged inner layer. Afterwards, the crystals of Mg(OH)2 agglomerated and formed a sphere, becoming the outer layers.

Ca-P spots modified zirconia by liquid precursor infiltration and the effect on osteoblast-like cell responses.

Ca-P spots modified zirconia by liquid precursor infiltration and the cell responses were investigated. Pre-sintered zirconia specimens were immersed in Ca-P precursor solution. After dense sintering, scanning electron microscopy showed Ca-P spots were formed on the zirconia and anchored with zirconia substrates. The distribution density was increased with the extension of immersion time. Energy dispersive spectrometer confirmed the stoichiometric Ca/P ratio was about 1.67. After hydrothermal treatment, Ca-P spots turned into rod crystals where diffraction peaks of tricalcium phosphate and hydroxyapatite were detected by X-ray diffraction, and Ca2+ and PO43- release decreased slightly (p>0.05). There was no significant decrease on three-point bending strength (p>0.05). Osteoblast-like MC3T3-E1 cells attached and spread well and showed higher proliferation on Ca-P spots modified zirconia (p<0.05), though its initial alkaline phosphatase activity was not significant high (p>0.05). In conclusion, Ca-P liquid precursor infiltration is a potential method to modify the zirconia ceramics for improving bioactivity.

Semiconductor Property and Corrosion Behavior of Passive Film Formed on Steel with Zinc Coating in 5% NaCl Solution

The initial stage of corrosion behavior and the semiconductor property of a passive film formed on steel with zinc coating were investigated in 5 wt.% NaCl solution using scanning electrochemical microscopy (SECM), electrochemical impedance spectroscopy (EIS), potential-capacitance measurement and the Mott–Schottky analysis method. The SECM test results reveal that the Faradic currents on the tip of the ultramicro electrode decreased with the extension of immersion time, suggesting that the coating was slowly degrading, and the water and ions gradually permeated into the coating. The tip current remained stable without obvious bursting and swelling, which revealed that no blister occurred inside the coating. EIS results also support the above conclusion, especially for long-term immersion. The potential-capacitance and Mott–Schottky analysis show that the water and ions gradually entered into the coating during the immersion process, while at the same time the coating showed the characteristics of n-type semiconductor. As the time elapsed, the capacitance value decreased and the thickness of the space charge layer declined. The decrease in the slope of the Mott–Schottky curves suggested the simultaneous increase of the carrier density, and the coating was degrading. SEM observation also exhibits an obvious coating degradation after immersion compared with the previous coating without immersion in solution.