This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were main...This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were mainly MnO and Mn_(2)SiO_(4).Combined with the electrochemical measurements,the corrosion resistance of HZCC showed an increase followed by a decrease with increasing Mn concentration,which was related to the Mn_(2)SiO_(4) and SiO_(2) on the surface of low carbon steel.The excessive Mn concentration resulted in the loss of SiO_(2) and aggregation of Mn_(2)SiO_(4) on the low carbon steel surface,which caused the aggregation of Zr compounds on the surface and reduced the uniformity of the coating.Meanwhile,a moderate amount of Mn addition would be beneficial to increase the adhesion of organic coatings.展开更多
A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears ...A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears to consist of a thin and cracked coating with a scattering of spherical particles.The corrosion behavior of the substrate and conversion coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).Compared with AZ31B magnesium alloy,the corrosion current density of the conversion coating is decreased by two orders of magnitude.The total impedance of the V/Ce conversion coating rise to 1.6×10^(3)Ω·cm^(2)in contrast with2.2×10^(2)Ω·cm^(2)of the bare AZ31B.In addition,the electrical conductivity of the coating was assessed by conductivity meter and Mott-Schottky measurement.The results reveal a high dependence of the conductivity of the coating on the semiconductor properties of the phase compositions.展开更多
The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution at room temperature. The formation process and the anti-corrosion perform...The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution at room temperature. The formation process and the anti-corrosion performance of the conversion coating were investigated using electrochemical test and salt spray test (SST), respectively. The electrochemical test shows that the Zr/Ti and ATMP coating improves the corrosion resistance of AA6061 as good as the chromate (VI) coating. But the results of SST show that the corrosion resistance of Zr/Ti and ATMP coating is not as good as the chromate (VI) coating. The corrosion area is less than 2% after 72 h.展开更多
The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optim...The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optimum processing parameters on corrosion resistance of RECCs, such as density of treating solution, temperature and time of coating formation were discussed. Protective performance of conversion coatings on magnesium alloy was evaluated by moisture/heating test, anodic polarization, etc. The results show that Ce-based RECCs under moisture/heating condition can remain intact, with high coverage and no obvious corrosion phenomenon. Corrosion potential increases and passive phenomenon occurs while current density decreases, therefore Ce-based RECCs can improve corrosion resistance of AZ91 magnesium alloy. The morphology of Ce-based RECCs prepared under optimum process through SEM observation is found to be a few particles coherent to the base coating, and the coating has no cracks and exhibits apparent corrosion resistance during corrosion courses of AZ91 magnesium alloy.展开更多
The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope ...The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope and X-ray diffraction. The corrosion resistance of the coating was studied by salt spray and damp test, and the corrosion tendency during salt immersion test was analyzed. The results show that the phase composition before and after pre-treatment is almost changeless, and the deep microflaw appears between a andβ phases during acidic pickling. The phosphate conversion coating is mainly composed of Mg, MgO, and some amorphous phase, and it can provide a good protection for the AZ31B alloy. Results from corrosive morphology indicate that the growth and the corrosion resistance of the phosphate conversion coating are related to the forming process of the AZ31B matrix.展开更多
A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investiga...A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO2 in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.展开更多
This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the...This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h,which showed the enhancement of charge transfer resistance(Rt) and coating film resistance(Rc),i.e.,the corrosion resistance of the conversion coated samples was improved.The best protection ef...展开更多
Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge ...Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge is their high susceptibility to corrosion,thereby limiting their usability.The considerably lower reduction potential of Mg compared to other metals makes it vulnerable to galvanic coupling.The oxide layer on Mg offers little corrosion resistance because of its high porosity,inhomogeneity,and fragility.Chemical conversion coatings(CCs)belong to a distinct class because of underlying chemical reactions,which are fundamentally different from other types of coating.Typically,a CC acts as an intermediate sandwich layer between the base metal and an aesthetic paint.Although chromate CCs offer superior performance compared to phosphate CCs,yet still they release carcinogenic hexavalent chromium ions(Cr^(6+));therefore,their use is prohibited in most European nations under the Registration,Evaluation,Authorization and Restriction of Chemicals legislation framework.Phosphate-based CCs are a cost-effective and environment-friendly alternative.Accordingly,this review primarily focuses on different types of phosphate-based CCs,such as zinc,calcium,Mg,vanadium,manganese,and permanganate.It discusses their mechanisms,current status,pretreatment practices,and the influence of various parameters-such as pH,temperature,immersion time,and bath composition-on the coating performance.Some challenges associated with phosphate CCs and future research directions are also elaborated.展开更多
Globally,vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period...Globally,vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period.In this context,magnesium(Mg)plays a major role in the production of biodegradable implants owing to their characteristic degradation nature under the influence of body fluids.Also,Mg is one of the essential nutrients required to perform various metabolic activities by the human cells,and therefore,the degraded Mg products will be readily absorbed by the nearby tissues.Nevertheless,the higher corrosion rate in the biological environment is the primary downside of using Mg implants that liberate H2gas resulting in the formation of cavities.Further,in certain cases,Mg undergoes complete degradation before the healing of damaged bone tissue and cannot serve the purpose of providing mechanical support.So,many studies have been focused on the development of different strategies to improve the corrosion-resistant behavior of Mg according to the requirement.In this regard,the present review focused on the limitations of using pure Mg and Mg alloys for the fabrication of medical implants and how the calcium phosphate conversion coating alters the corrosive tendency through the formation of hydroxyapatite protective films for enhanced performance in medical implant applications.展开更多
The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge...The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48% (mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061A1 composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The ca-thodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.展开更多
Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new princ...Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new principles regarding the design of conversion bath were proposed.The treatment bath should be composed of species that can be categorized into two groups:the first group of species that react with Mg substrate to increase the local p H at the interface;the second group that precipitate and contributes to the growth of coating.The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group.By this way,a thick and crack-free two-layered conversion coating is obtained.Moreover,the nature of the adjustment of TA/p H and the roles of the oxidizing agent and catalyst were discussed.展开更多
A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have c...A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have concentrated on the formation of passive film from simple MIS. No.1 solution using immersion. The morphology of passivated surfaces was examined using scanning electron microscopy (SEM). The corrosion resistance of the passivated surfaces and the painted surface was assessed using electrochemical techniques as well as humidity and salt fog tests. It was concluded that the surface treatment magnesium alloy by MIS.No.1 solution is more effective than that by chromate coating treatment, and the MIS.No.1 coating is also suitable for painting's pretreatment.展开更多
A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp w...A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp was then studied according to this method. The results revealed that the Ce conversion coating on the anodized AI6061/SiCp consisted of Al oxide, Ce oxide and Ce hydroxide. The state of Ce element exhibited the mixture of Ce3+ and Ce4+. Some of Cell I was oxidized to be CelV in the outer layer coating.展开更多
The impact of phytic acid concentration,immersion time and soaking temperature on phytic acid conversion coating of the Mg-Li alloy are studied.The surface morphology and the corrosion of the phytic acid conversion co...The impact of phytic acid concentration,immersion time and soaking temperature on phytic acid conversion coating of the Mg-Li alloy are studied.The surface morphology and the corrosion of the phytic acid conversion coating are tested by using scanning electron microscopy and the electrochemical analyzer.The results show that phytic acid concentration and immersion time,soaking temperature affects the microstructure and corrosion resistance of the phytic acid conversion coating.There is a passivation interval with a smaller capacitor and larger resistor in the phytic acid conversion coating.The phytic acid conversion coating is made up of white particle and flake film.展开更多
A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple ...A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple simulative experiment accords with the actual immersion,and it can be substantially used to simulate the behavior of LY12 aluminum alloy in thefilm-forming process. It is showed that the formation of the coating is quickened in CeCl_3 solutioncontaining KMnO_4 compared with that not containing KMnO_4. XPS results reveal that the coatingformed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation ofREM conversion coating changes when KMnO4 is added.展开更多
In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphol...In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid,exhibited excellent corrosion resistance and behavior.展开更多
The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coati...The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.展开更多
The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significant improvement in corrosion resistance for Mg. Magnesium phosphate coating improves the corrosion resistance of Mg, good ...The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significant improvement in corrosion resistance for Mg. Magnesium phosphate coating improves the corrosion resistance of Mg, good bioactivity, promotes cell viability and cyto-compatibility and exhibits antibacterial activity. However, rapid dissolution in Mg in acidic magnesium phosphate containing solutions leads to the development of an inhomogeneous coating. The present study attempts to prevent the excessive dissolution of Mg by forming a fluoride conversion coating as a pre-treatment in the first stage followed by deposition of magnesium phosphate coating in the second stage to develop magnesium fluoride-magnesium phosphate duplex coatings. The morphological features, structural characteristics, nature of functional groups, corrosion behavior in Hanks’ balanced salt solution and bioactivity in simulated body fluid are assessed to ascertain the suitability of the magnesium fluoride-magnesium phosphate duplex coating in controlling the rate of degradation of Mg and improving its bioactivity using uncoated Mg and fluoride conversion coated Mg as reference. The findings of the study reveal that the magnesium fluoride-magnesium phosphate duplex coating could offer an excellent corrosion resistance and improve the bioactivity of Mg.展开更多
Jiuhe Corporation developed a new surface pretreatment for producing a phosphate-free and colored zirconium conversion coating on cold-rolled steel(CRS).Scanning electron microscopy(SEM)and energy-dispersive spectrosc...Jiuhe Corporation developed a new surface pretreatment for producing a phosphate-free and colored zirconium conversion coating on cold-rolled steel(CRS).Scanning electron microscopy(SEM)and energy-dispersive spectroscopy(EDS)were applied to study the surface morphology and elemental composition of the golden yellow-colored conversion coating.Elec trochemic al impedance spectroscopy(EIS)was used to investigate the electrochemical performance of the conversion coatings with different colors.The corrosion resistance properties of the powder coatings were characterized using the neutral salt spray test(NSS)and the tape adhesion test.The EIS and NSS results demonstrate that the colored zirconium conversion coatings exhibit excellent corrosion resistance properties compared with the bare CRS.The golden yellow-colored conversion coating has a maximum EIS value(748Ω·cm^(2))and achieves 0 mm degree of corrosion,as stipulated by EN ISO 4628-8.This paper proposes a hypothesis concerning the ZrO_(2)-(β-FeOOH)-polymer conversion reaction to explain the color changes.展开更多
In the present review,the formation of superhydrophobic(SHP)structures on the surface of Mg alloys was investigated.Different methods including hydrothermal technique,chemical and electrochemical deposition,conversion...In the present review,the formation of superhydrophobic(SHP)structures on the surface of Mg alloys was investigated.Different methods including hydrothermal technique,chemical and electrochemical deposition,conversion and polymer coating,and etching routes were discussed.The superhydrophobicity could form on the surface of Mg alloys by the application of different chemical,electrochemical,and physical methods followed by the immersion of these alloys in the solution containing modifying agents including fatty acids or long-chain molecules.The formed morphology,composition,and contact angle were reported and the effect of synthesis route on these characteristics was reviewed.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51974069)the National Key R&D Program of China(No.2019YFE0123900)the Special Fund for Basic Scientific Research of Central Colleges(N2125035).
文摘This study revealed the effect of Mn on the formation of hybrid zirconium-based conversion coatings(HZCC)on low carbon steel.The XPS results indicated that the Mn compounds on the surface of low carbon steel were mainly MnO and Mn_(2)SiO_(4).Combined with the electrochemical measurements,the corrosion resistance of HZCC showed an increase followed by a decrease with increasing Mn concentration,which was related to the Mn_(2)SiO_(4) and SiO_(2) on the surface of low carbon steel.The excessive Mn concentration resulted in the loss of SiO_(2) and aggregation of Mn_(2)SiO_(4) on the low carbon steel surface,which caused the aggregation of Zr compounds on the surface and reduced the uniformity of the coating.Meanwhile,a moderate amount of Mn addition would be beneficial to increase the adhesion of organic coatings.
基金financially supported by the National Key Research and Development Program of China (Nos. 2016YFB0301105 and 2017YFB0702100)。
文摘A V/Ce conversion coating was deposited in the surface of AZ31B magnesium alloy in a solution containing vanadate and cerium nitrate.The coating composition and morphology were examined.The conversion coating appears to consist of a thin and cracked coating with a scattering of spherical particles.The corrosion behavior of the substrate and conversion coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).Compared with AZ31B magnesium alloy,the corrosion current density of the conversion coating is decreased by two orders of magnitude.The total impedance of the V/Ce conversion coating rise to 1.6×10^(3)Ω·cm^(2)in contrast with2.2×10^(2)Ω·cm^(2)of the bare AZ31B.In addition,the electrical conductivity of the coating was assessed by conductivity meter and Mott-Schottky measurement.The results reveal a high dependence of the conductivity of the coating on the semiconductor properties of the phase compositions.
基金supported by the Science and Technology Plan Project of Liaoning Province,China(No.2006221011).
文摘The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution at room temperature. The formation process and the anti-corrosion performance of the conversion coating were investigated using electrochemical test and salt spray test (SST), respectively. The electrochemical test shows that the Zr/Ti and ATMP coating improves the corrosion resistance of AA6061 as good as the chromate (VI) coating. But the results of SST show that the corrosion resistance of Zr/Ti and ATMP coating is not as good as the chromate (VI) coating. The corrosion area is less than 2% after 72 h.
文摘The feasibility of forming pollution-free and environmentally benign Ce-based rare earth conversion coatings (short for RECCs) on AZ91 magnesium alloy to enhance corrosion resistance was studied. The effect of optimum processing parameters on corrosion resistance of RECCs, such as density of treating solution, temperature and time of coating formation were discussed. Protective performance of conversion coatings on magnesium alloy was evaluated by moisture/heating test, anodic polarization, etc. The results show that Ce-based RECCs under moisture/heating condition can remain intact, with high coverage and no obvious corrosion phenomenon. Corrosion potential increases and passive phenomenon occurs while current density decreases, therefore Ce-based RECCs can improve corrosion resistance of AZ91 magnesium alloy. The morphology of Ce-based RECCs prepared under optimum process through SEM observation is found to be a few particles coherent to the base coating, and the coating has no cracks and exhibits apparent corrosion resistance during corrosion courses of AZ91 magnesium alloy.
基金supported by the National Natural Science Foundation of China(No.50474007)Science and Technology Project of Jiangxi Provincial Departmentof Education (No.[2006]1)
文摘The morphology change of the magnesium matrix after pre-treatment and the morphology as well as the phase composition of chemical conversion coating formed by phosphate were studied using scanning electron microscope and X-ray diffraction. The corrosion resistance of the coating was studied by salt spray and damp test, and the corrosion tendency during salt immersion test was analyzed. The results show that the phase composition before and after pre-treatment is almost changeless, and the deep microflaw appears between a andβ phases during acidic pickling. The phosphate conversion coating is mainly composed of Mg, MgO, and some amorphous phase, and it can provide a good protection for the AZ31B alloy. Results from corrosive morphology indicate that the growth and the corrosion resistance of the phosphate conversion coating are related to the forming process of the AZ31B matrix.
基金Funded by the National Natural Science Foundation of China (No.50603003)
文摘A novel Mg-Li alloy was treated in a cerium nitrate solution and cerium chemical conversion coating was obtained on the alloy. Then the forming process, structure and corrosion resistance of the coating were investigated. The influential factors of cerium conversion coating were discussed through orthogonal experiments, and the optimum processing parameters were confirmed. XPS spectra displayed that the conversion coating consisted of cerium compounds, and the major component of the protective layer was a mixture of Ce (IV) oxide and Ce (IV) hydroxide. In addition, XRD pattern illustrated that there was crystalline CeO2 in the conversion coating. Analysis by SEM showed that the cerium conversion coating was uniform with a fiber-like morphology. The thickness of the conversion coating was 12 μm. The results of electrochemical potentiodynamic polarization and hydrogen evolution measurement indicated that the cerium conversion coating provided effective protection to the novel Mg-Li alloy.
基金supported by Higher Education Commission of Pakistan
文摘This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h,which showed the enhancement of charge transfer resistance(Rt) and coating film resistance(Rc),i.e.,the corrosion resistance of the conversion coated samples was improved.The best protection ef...
基金Uchchatar Avishkar Yojna(UAY)(Phase II)project(codeIITBBS_004)Prime M inister’s Research Fellows(PMRF)。
文摘Magnesium(Mg)and its alloys are lightweight as well as biocompatible and possess a high strength-to-weight ratio,making them suitable for many industries,including aerospace,automobile,and medical.The major challenge is their high susceptibility to corrosion,thereby limiting their usability.The considerably lower reduction potential of Mg compared to other metals makes it vulnerable to galvanic coupling.The oxide layer on Mg offers little corrosion resistance because of its high porosity,inhomogeneity,and fragility.Chemical conversion coatings(CCs)belong to a distinct class because of underlying chemical reactions,which are fundamentally different from other types of coating.Typically,a CC acts as an intermediate sandwich layer between the base metal and an aesthetic paint.Although chromate CCs offer superior performance compared to phosphate CCs,yet still they release carcinogenic hexavalent chromium ions(Cr^(6+));therefore,their use is prohibited in most European nations under the Registration,Evaluation,Authorization and Restriction of Chemicals legislation framework.Phosphate-based CCs are a cost-effective and environment-friendly alternative.Accordingly,this review primarily focuses on different types of phosphate-based CCs,such as zinc,calcium,Mg,vanadium,manganese,and permanganate.It discusses their mechanisms,current status,pretreatment practices,and the influence of various parameters-such as pH,temperature,immersion time,and bath composition-on the coating performance.Some challenges associated with phosphate CCs and future research directions are also elaborated.
文摘Globally,vast research interest is emerging towards the development of biodegradable orthopedic implants as it overcomes the toxicity exerted by non-degradable implants when fixed in the human body for a longer period.In this context,magnesium(Mg)plays a major role in the production of biodegradable implants owing to their characteristic degradation nature under the influence of body fluids.Also,Mg is one of the essential nutrients required to perform various metabolic activities by the human cells,and therefore,the degraded Mg products will be readily absorbed by the nearby tissues.Nevertheless,the higher corrosion rate in the biological environment is the primary downside of using Mg implants that liberate H2gas resulting in the formation of cavities.Further,in certain cases,Mg undergoes complete degradation before the healing of damaged bone tissue and cannot serve the purpose of providing mechanical support.So,many studies have been focused on the development of different strategies to improve the corrosion-resistant behavior of Mg according to the requirement.In this regard,the present review focused on the limitations of using pure Mg and Mg alloys for the fabrication of medical implants and how the calcium phosphate conversion coating alters the corrosive tendency through the formation of hydroxyapatite protective films for enhanced performance in medical implant applications.
文摘The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48% (mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061A1 composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The ca-thodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.
基金financial support from the National Natural Science Foundation of China(51531007 and 51771050)China Postdoctoral Science Foundation(2019M651128)+1 种基金the National Program for Young Top-notch Professionalsthe Fundamental Research Funds for the Central Universities(N170205002)
文摘Cracking and low thickness are major obstacles to the high corrosion performance of conversion coating on magnesium alloy.In this work,the ratio of total acidity to p H(TA/p H)was applied as an indicator,and new principles regarding the design of conversion bath were proposed.The treatment bath should be composed of species that can be categorized into two groups:the first group of species that react with Mg substrate to increase the local p H at the interface;the second group that precipitate and contributes to the growth of coating.The species belong to second group exists in a supersaturated state and its precipitation process is almost independent on the reactions of the species in first group.By this way,a thick and crack-free two-layered conversion coating is obtained.Moreover,the nature of the adjustment of TA/p H and the roles of the oxidizing agent and catalyst were discussed.
文摘A no pollution organic acid based conversion coating solution MIS. No.1 has been examined as to its suitability as possible replacement for chromate containing formulations on magnesium alloys. Investigations have concentrated on the formation of passive film from simple MIS. No.1 solution using immersion. The morphology of passivated surfaces was examined using scanning electron microscopy (SEM). The corrosion resistance of the passivated surfaces and the painted surface was assessed using electrochemical techniques as well as humidity and salt fog tests. It was concluded that the surface treatment magnesium alloy by MIS.No.1 solution is more effective than that by chromate coating treatment, and the MIS.No.1 coating is also suitable for painting's pretreatment.
基金This work has been carried out with the support of The Chinese Postdoctoral Science Fund and The Special Funds for the Major State Basic Research Projects G19990650.
文摘A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced. The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites AI6061/SiCp was then studied according to this method. The results revealed that the Ce conversion coating on the anodized AI6061/SiCp consisted of Al oxide, Ce oxide and Ce hydroxide. The state of Ce element exhibited the mixture of Ce3+ and Ce4+. Some of Cell I was oxidized to be CelV in the outer layer coating.
基金Funded by the Key Laboratory of Superlight Materials and Surface Technology,Ministry of Education
文摘The impact of phytic acid concentration,immersion time and soaking temperature on phytic acid conversion coating of the Mg-Li alloy are studied.The surface morphology and the corrosion of the phytic acid conversion coating are tested by using scanning electron microscopy and the electrochemical analyzer.The results show that phytic acid concentration and immersion time,soaking temperature affects the microstructure and corrosion resistance of the phytic acid conversion coating.There is a passivation interval with a smaller capacitor and larger resistor in the phytic acid conversion coating.The phytic acid conversion coating is made up of white particle and flake film.
基金[This work was financially supported by the National Natural Science Fund of China (No.59771067).]
文摘A Cu/Al galvanic couple was established to study the influence of the oxidantKMnO_4 on the film-forming process of rare earth metal (REM) conversion coating on LY12 aluminumalloy. It is found that the galvanic couple simulative experiment accords with the actual immersion,and it can be substantially used to simulate the behavior of LY12 aluminum alloy in thefilm-forming process. It is showed that the formation of the coating is quickened in CeCl_3 solutioncontaining KMnO_4 compared with that not containing KMnO_4. XPS results reveal that the coatingformed on cathode is composed of oxide or hydroxide of Ce and Mn, so the mechanism of formation ofREM conversion coating changes when KMnO4 is added.
基金financially supported by National Key Research and Development Program of China (Nos. 2017YFB0103904, 2016YFB0301105)National Natural Science Foundation of China (No. 51804190)+2 种基金Youth Science Funds of Shandong Academy of Sciences (No. 2020QN0022)Youth Innovation and Technology Support Program of Shandong Provincial Colleges and Universities (No. 2020KJA002)Jinan Science & Technology Bureau (No. 2019GXRC030)。
文摘In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid,exhibited excellent corrosion resistance and behavior.
文摘The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.
基金University Grand Commission(UGC)for providing a research fellowship to support this research program under the non-net category。
文摘The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significant improvement in corrosion resistance for Mg. Magnesium phosphate coating improves the corrosion resistance of Mg, good bioactivity, promotes cell viability and cyto-compatibility and exhibits antibacterial activity. However, rapid dissolution in Mg in acidic magnesium phosphate containing solutions leads to the development of an inhomogeneous coating. The present study attempts to prevent the excessive dissolution of Mg by forming a fluoride conversion coating as a pre-treatment in the first stage followed by deposition of magnesium phosphate coating in the second stage to develop magnesium fluoride-magnesium phosphate duplex coatings. The morphological features, structural characteristics, nature of functional groups, corrosion behavior in Hanks’ balanced salt solution and bioactivity in simulated body fluid are assessed to ascertain the suitability of the magnesium fluoride-magnesium phosphate duplex coating in controlling the rate of degradation of Mg and improving its bioactivity using uncoated Mg and fluoride conversion coated Mg as reference. The findings of the study reveal that the magnesium fluoride-magnesium phosphate duplex coating could offer an excellent corrosion resistance and improve the bioactivity of Mg.
基金financially supported by Shenzhen Technology Development Project(No.CXZZ20140902141250786)Guangdong Science and Technology Project(No.2014A010105004)。
文摘Jiuhe Corporation developed a new surface pretreatment for producing a phosphate-free and colored zirconium conversion coating on cold-rolled steel(CRS).Scanning electron microscopy(SEM)and energy-dispersive spectroscopy(EDS)were applied to study the surface morphology and elemental composition of the golden yellow-colored conversion coating.Elec trochemic al impedance spectroscopy(EIS)was used to investigate the electrochemical performance of the conversion coatings with different colors.The corrosion resistance properties of the powder coatings were characterized using the neutral salt spray test(NSS)and the tape adhesion test.The EIS and NSS results demonstrate that the colored zirconium conversion coatings exhibit excellent corrosion resistance properties compared with the bare CRS.The golden yellow-colored conversion coating has a maximum EIS value(748Ω·cm^(2))and achieves 0 mm degree of corrosion,as stipulated by EN ISO 4628-8.This paper proposes a hypothesis concerning the ZrO_(2)-(β-FeOOH)-polymer conversion reaction to explain the color changes.
文摘In the present review,the formation of superhydrophobic(SHP)structures on the surface of Mg alloys was investigated.Different methods including hydrothermal technique,chemical and electrochemical deposition,conversion and polymer coating,and etching routes were discussed.The superhydrophobicity could form on the surface of Mg alloys by the application of different chemical,electrochemical,and physical methods followed by the immersion of these alloys in the solution containing modifying agents including fatty acids or long-chain molecules.The formed morphology,composition,and contact angle were reported and the effect of synthesis route on these characteristics was reviewed.