A new surface protection process was developed to magnesium alloy against corrosion in aggressive environments.Firstly,a phosphate coating was formed on rinsed magnesium alloy.Then,powder painting was carried out on t...A new surface protection process was developed to magnesium alloy against corrosion in aggressive environments.Firstly,a phosphate coating was formed on rinsed magnesium alloy.Then,powder painting was carried out on the phosphated magnesium alloy.Surface morphologies and phase compositions of the phosphate coating were investigated by X-ray diffraction(XRD) and scanning electron microscope(SEM) .The results show that the phosphate coatings formed in bath containing earth additives at room temperature have dense and fine microstructure.The phosphate coating provides excellent paint adhesion to the magnesium alloy. Salt spray tests indicate that the corrosion resistance of the phosphate coating plus paint could meet the demand of magnesium alloy automobile components in aggressive environments.展开更多
The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate （CAP） coatings deposited under different process voltages in the range of 150-400 V on the commercially pure titani...The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate （CAP） coatings deposited under different process voltages in the range of 150-400 V on the commercially pure titanium （Ti） and Ti-40%Nb （Ti-40Nb） （mass fraction） alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300-400 V, the crystalline phases, such as CaHPO4 and β-Ca2P207, were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases： CaTi4（PO4）6, β-Ca2P2O7, TiP2O7, TiNb（PO4）3, TiO2, NbO2, and Nb2O5. The applied voltage and process duration in the ranges of 200-250 V and 5-10 min, respectively, revealed the coating formed on Ti and Ti-40Nb with optimal properties： thickness of 40-70μm, porosity of 20%-25%, roughness （Ra） of 2.5-5.0 μm, adhesion strength of 15-30 MPa, and Ca/P mole ratio of 0.5-0.7.展开更多
The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and...The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and a square pulse potential with frequency of 1 Hz and voltage of 110 V was applied between the inner and outer surfaces of the alumina cup. Surface morphology of CP coatings during different deposition periods was observed by a Philips XL-30 scanning electron microscope （SEM）. Compositional analysis was examined by EDAX. The mechanism of nucleation and growth of CP coating was discussed. SEM result indicates that the coating comprises of a large number of tiny needle-like grains and has a porous microstructure. There is a strong bond between the deposited layer and Al2O3 substrate, which may be due to the gentle growth of the biomimetic method. The EDAX analysis indicates that main composition of the coating is calcium and phosphor. The formation of CP coating may be contributed to the stimulation of electric pulse and the high ions concentration which is 1.5 times of the concentration of SBF solution （1.5SBF solution）. Such surface functionalization method by electric pulse potential can be used to prepare CP coating on various electric-insulating bioinert materials for improving their bioactive character.展开更多
In order to obtain a more protective phosphate conversion coating with a denser architecture,the nucleation kinetics of phosphate chemical conversion coating on Mg-Gd-Y-Zr magnesium alloy was tuned in this work.A pret...In order to obtain a more protective phosphate conversion coating with a denser architecture,the nucleation kinetics of phosphate chemical conversion coating on Mg-Gd-Y-Zr magnesium alloy was tuned in this work.A pretreatment process was proposed and organic additives were incorporated,which aims at increasing the ionic produce(J_(sp))at the interface for increasingσ,and decreasing the critical ionic product(J_(C,sp)),respectively.Results prove that the pretreatment of bare alloys in a phosphate bath could increase the ion products of MgHPO_(4)/MnHPO_(4).The addition of benzalkonium chloride could neutralize the charges of crystals,and in turn promote the nucleation kinetics.A denser and more protective conversion coating could consequently be obtained.展开更多
The authors regret that due to negligence,the picture was misplaced in the original manuscript,resulting in Fig.6d being incorrectly included.The correct version of Fig.6d is provided below for reference.This error do...The authors regret that due to negligence,the picture was misplaced in the original manuscript,resulting in Fig.6d being incorrectly included.The correct version of Fig.6d is provided below for reference.This error does not affect the conclusions of the study,and we apologize for any confusion it may have caused.展开更多
The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating （Zn-Ca-P coating） on Mg-Li-Ca alloy was investigated. The mor...The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating （Zn-Ca-P coating） on Mg-Li-Ca alloy was investigated. The morphologies, elemental distribution and chemical structures of the coatings were examined via SEM, EPMA, EDS, XRD and FT-IR. The corrosion resistance was assessed by hydrogen evolution, potentiodynamic polarization and EIS. The results show that the coating is composed of single element Zn and ZnO at below 45 ℃;whereas the coatings are predominantly characterized by Zn3（PO4）2·4H2O and small amount of element zinc and ZnO at above 50 ℃. Mg-Li-Ca alloy with Zn-Ca-P coatings prepared at 55 ℃ has the highest corrosion resistance. However, the hydrogen evolution rates of the coatings obtained at 40-50 ℃ is accelerated due to the galvanic corrosion between the imperfection of the single element Zn coating and the Mg substrate.展开更多
A SnO2-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition.The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure an...A SnO2-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition.The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 mm.The surface of the coating became smooth with an increase additive amount of the SnO2 nanoparticles.The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO2 were reduced compared to the coating without SnO2 and the bare AZ31 substrate,indicating an improvement in the corrosion resistance of the SnO2-doped coating.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
The influence of different surface coatings of NiTi shape memory allays was examined using in vitro testing methods. Plates of superelastic nickel-titanium shape memory allay （ NiTi ） were coated with calcium phosph...The influence of different surface coatings of NiTi shape memory allays was examined using in vitro testing methods. Plates of superelastic nickel-titanium shape memory allay （ NiTi ） were coated with calcium phosphates （ hydroxyapatite ） by high-temperature plasma-spraying or by dip-coating. The biocompatibility was tested in vitro by cultivation of isolated human granulocytes and whole blood cells. As substrates, pure NiTi, plasma-spray-coated NiTi and dip-coated NiTi were used. Isolated granulocytes showed an increased adhesion to both calcium phosphate-coated NiTi samples. Compared to non-coated NiTi or dip-coated NiTi, the number of dead granulocytes adherent to plasma-sprayed surfaces was significantly increased （ p 〈 0.01 ）. Whether the d/f- ferences in apoptosis of granulocytes on dip-coated vs plasma-sprayed coatings observed are due to differences in material surface morphologies has to be analyzed in further studies. Because of the cellular interactions with the coating layers, h is likely that the results obtained are not caused by the underlying NiTi but due to the coating itself.展开更多
The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were ...The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were successfully prepared by adding ultra-high deacetylated chitosan in a phosphate bath.The chemical composition of the prepared composite film was investigated by X-ray photoelectron spectroscopy(XPS)and Fourier trans-form infrared spectroscopy(FT-IR),and the morphology and fracture of the composite film were characterized by scanning electron microscope(SEM).Potentiodynamic polarization curves and electrochemical impedance spec-troscopy were used to study the corrosion behavior of the coated alloys.The results showed that when pH=2.5 and the chitosan concentration was 5.0 g/L,chitosan was deposited in the phosphate coating in the form of inclusions.In addition,the potentiodynamic polarization curves of the composite films show that the corrosion potential is positively shifted by 0.6 V compared to the monolayer phosphate coating,indicating improved corro-sion resistance.This work shows that highly deacetylated chitosan can be co-deposited with phosphate to form a dense composite film on the surface of magnesium alloys in one step,thereby improving the corrosion resistance of the alloy.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
The possible application of magnesium(Mg)in glaucoma surgical treatment has been investigated in our previous work.In this paper,the degradation behavior and biocompatibility of Mg coated with hydroxyapatite(HA)and di...The possible application of magnesium(Mg)in glaucoma surgical treatment has been investigated in our previous work.In this paper,the degradation behavior and biocompatibility of Mg coated with hydroxyapatite(HA)and dicalcium phosphate dihydrate(DCPD)in eye environment were evaluated,and uncoated Mg was used for comparison.It was found that uniform corrosion occurred macroscopically to the coated Mg samples in sodium lactate ringer’s injection(SLRI)as well as in the rabbit eyes.In micro-scale,the corrosion was characterized by local cracking and pitting primarily.Mg and calcium(Ca)were incorporated into the surface corrosion products and a multi-layer structure was formed.Compared to other samples,HA-coated Mg slowed down dramatically the alkalinity of the solution and the ion release of the sample,and exhibited the lowest corrosion rate in SLRI,which was about 0.22 mm/a.In terms of biocompatibility,fibroblasts demonstrated high viability in the HA-coated and DCPD-coated Mg groups(p<0.05)in vitro.In vivo,HA-coated Mg was found to show lower inflammatory response and fibrosis than the other groups did,as indicated by hematoxylin-eosin and immunofluorescence staining.During the degrading process of HA-coated Mg in the rabbits’eyes,no inflammation was found in the anterior chamber,lens,and vitreous body.HA-coated Mg was fully biodegraded fifteen weeks post-operation,and the scleral drainage channel(SDC)was formed without obvious scarring.It is concluded that HA-coated Mg implantation is a promising adjunctive procedure to improve the success rate of trabeculectomy.Statement of significance:Magnesium(Mg)has shown to be a potential biomaterial for ophthalmic implants in our previous work.However,inflammatory response resulted from the low corrosion resistance of Mg is a major concern.It is shown here that Mg coated with different calcium phosphates can improve these properties in varying degrees and keep the scleral drainage channel unobstructed and unscarred.Based on our in vitro and in vivo studies,HA-coated Mg exhibited a better degradation behavior and excellent biocompatibility.The scleral drainage channel still exists and aqueous humor flows out smoothly after the full degradation of the implant.It is concluded that HA-coated Mg is a promising biomaterial to increase the therapeutic efficiency of trabeculectomy for glaucoma.展开更多
In deaerated 0.05 M,0.1 M,0.2 M and 0.5 M K_(2)HPO_(4) solutions with pH 9.5,AZ31 magnesium(Mg)alloy was subjected to potentiostatic polarization at−0.8 VSCE to deposit a phosphate conversion coating.The morphology,st...In deaerated 0.05 M,0.1 M,0.2 M and 0.5 M K_(2)HPO_(4) solutions with pH 9.5,AZ31 magnesium(Mg)alloy was subjected to potentiostatic polarization at−0.8 VSCE to deposit a phosphate conversion coating.The morphology,structure,chemical composition,and protective performance of the conversion coating during the formation process were characterized.The results showed that amorphous Mg(OH)_(2) and MgHPO_(4) and crystallized KMgPO_(4)·6H2O(struvite-K)were successively deposited on the surface of AZ31 Mg alloy in the four solutions.MgHPO_(4) was converted from Mg(OH)_(2),while struvite-K was transformed from MgHPO_(4).The distribution of Mg(OH)_(2),MgHPO_(4) and struvite-K along the thickness of the coating difers with K_(2)HPO_(4) concentration.As the concentration of K_(2)HPO_(4) increased,the coating time was gradually shortened,and the coating was gradually thinned.Meanwhile,the ratio of the nucleation rate to the growth rate of struvite-K crystal nuclei increased,resulting in a decrease in the size of struvite-K crystal.When the concentration of K_(2)HPO_(4) increased from 0.05 to 0.1 M,the content of struvite-K increased,and the protective performance of the coating was enhanced.However,as the concentration of K_(2)HPO_(4) continued to increase to 0.5 M,the content of struvite-K and the protective performance of the coating decreased.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
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
Silicate sol post-treatment was applied to form a complete composite coating on the phosphated zinc layer. The chemical compositions of the coatings were investigated using XPS. The coated samples were firstly scratch...Silicate sol post-treatment was applied to form a complete composite coating on the phosphated zinc layer. The chemical compositions of the coatings were investigated using XPS. The coated samples were firstly scratched and then exposed to the neutral salt spray(NSS) chamber for different time. The microstructure and chemical compositions of the scratches were studied using SEM and EDS. And the non-scratched coated samples were compared. The self-healing mechanism of the composite coatings was discussed. The results show that during corrosion, the self-healing ions in composite coatings dissolve, diffuse and transfer to the scratches or the defects, and then recombine with Zn2+ to form insoluble compound, which deposits and covers the exposed zinc. The corrosion products on the scratches contain silicon, phosphorous, oxygen, chloride and zinc, and they are compact, fine, needle and flake, effectively inhibiting the corrosion formation and expansion of the exposed zinc layer. The composite coatings have good self-healing ability.展开更多
Hydroxylamine sulfate （HAS） and sodium nitrite are used as the accelerators for zinc phos- phate coating on high carbon steel. Phase evolution of phosphate coating was investigated by X-ray diffraction. It is found ...Hydroxylamine sulfate （HAS） and sodium nitrite are used as the accelerators for zinc phos- phate coating on high carbon steel. Phase evolution of phosphate coating was investigated by X-ray diffraction. It is found that the phosphating coatings are mainly composed of hopeite Zn3Fe（PO4）2.4H2O and phosphophyllite Zn2Fe（PO4）2.4H2O. The microstructural changes of the phosphate coating, as a function of phosphating time, were evaluated by scanning elec- tron microscopy. Four-ball friction experiments reveal that hydroxylamine sulfate instead of sodium nitrite can effectively reduce the friction coefficient of lubricated phosphating coat- ing. Therefore, it may be expected that HAS will be widely used as a fast and ECO-friendly accelerator in phosphate industry.展开更多
A phosphate solution free of chromate, fluoride and nitrite was prepared and an environment-friendly film was obtained on AZ31 magnesium alloy surface via the chemical deposition method. The morphology, composition, p...A phosphate solution free of chromate, fluoride and nitrite was prepared and an environment-friendly film was obtained on AZ31 magnesium alloy surface via the chemical deposition method. The morphology, composition, phase structure and its corrosion resistance were studied. The effects of film-forming temperature and free acid on corrosion resistance, microstructure and electrochemical behavior of the film were discussed. The results indicate that the corrosion resistance of AZ31 with the phosphate film was better than blank AZ31 substrate, which was most attributed to the great inhibitive action on the anodic dissolution and cathodic hydrogen evolution of the film.展开更多
It was ascertained that when a RE element was added in bath,the sample was improved on the anti-corrosion power of the coating because of the increasing of covering rate of formless crystal Zn2Fe(PO4) 2·4H2O(mark...It was ascertained that when a RE element was added in bath,the sample was improved on the anti-corrosion power of the coating because of the increasing of covering rate of formless crystal Zn2Fe(PO4) 2·4H2O(marked P) crystals and the ratio of P/(P+H) (H was the mark of Zn3(PO4) 2 crystal) in the coating,combination of which with components parsing by EDS indicated that the sequence of contribution elements P and Zn to erosion resistance of coatings was P】Zn. And the correlative mechanism was discussed,which made it clear that owing to the particularity of the outer-shell electron structure and larger ionic radius,RE was so easy to be polarized and metamorphosed itself that it adsorbed lightly on the basic body to pose gels. They efficiently reduced the activation energy which was required for formation of a new solid phase of phosphates and made it also possible to engender effectively active nucleation regions of cathode and anode under low temperature phosphating condition,which was propitious to formation,densification and uniformization of the phosphate crystal nucleus and growth of the crystallite and coating buildup. Thus it could be seen that REN played the role of surface regulator and accelerant,which speeded up the phosphating,as well as bids amount of porosity of the coating fall to improve the corrosion resistance of the coating.展开更多
To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) steel was post-sealed with cerium nitrate solution. The morphology, composition, corrosion resistance of the coatings ...To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) steel was post-sealed with cerium nitrate solution. The morphology, composition, corrosion resistance of the coatings was investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and neutral salt spray (NSS) tests. The results show that after post-sealing the phosphated HDG samples with cerium nitrate solution, the pores among the zinc phosphate crystals are sealed by the compounds containing phosphorus, oxygen and cerium; the zinc phosphate crystals are covered by the flocculent cerium compounds; and the continuous composite coatings are formed on HDG steel. The corrosion resistance of the composite coatings, which increases with the increase in phosphating time and cerium nitrate post-sealing time, is far higher than that of the single phosphate coatings. The composite coatings with the optimal corrosion resistance are obtained for phosphating 300 s and post-sealing 300 s; and the corrosion resistance is more outstanding than that of the chromate coatings.展开更多
基金Projects(Y20090108,G20080115)supported by Education Department of Zhejiang and Technology Department of Wenzhou,China
文摘A new surface protection process was developed to magnesium alloy against corrosion in aggressive environments.Firstly,a phosphate coating was formed on rinsed magnesium alloy.Then,powder painting was carried out on the phosphated magnesium alloy.Surface morphologies and phase compositions of the phosphate coating were investigated by X-ray diffraction(XRD) and scanning electron microscope(SEM) .The results show that the phosphate coatings formed in bath containing earth additives at room temperature have dense and fine microstructure.The phosphate coating provides excellent paint adhesion to the magnesium alloy. Salt spray tests indicate that the corrosion resistance of the phosphate coating plus paint could meet the demand of magnesium alloy automobile components in aggressive environments.
基金Project(III.23.2.5)supported by the Fundamental Research Program of the Siberian Branch of Russian Academy of SciencesProject(15-03-07659)supported by the Russian Foundation for Basic Research+1 种基金Project(CR16-22)supported by the China and Russia on the Implementation of Inter-governmental ScientificTechnological Cooperation Projects of the Notice(NSC foreign word[2012]No.269)
文摘The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate （CAP） coatings deposited under different process voltages in the range of 150-400 V on the commercially pure titanium （Ti） and Ti-40%Nb （Ti-40Nb） （mass fraction） alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300-400 V, the crystalline phases, such as CaHPO4 and β-Ca2P207, were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases： CaTi4（PO4）6, β-Ca2P2O7, TiP2O7, TiNb（PO4）3, TiO2, NbO2, and Nb2O5. The applied voltage and process duration in the ranges of 200-250 V and 5-10 min, respectively, revealed the coating formed on Ti and Ti-40Nb with optimal properties： thickness of 40-70μm, porosity of 20%-25%, roughness （Ra） of 2.5-5.0 μm, adhesion strength of 15-30 MPa, and Ca/P mole ratio of 0.5-0.7.
文摘The preparation of calcium phosphate （CP） coating on alumina ceramics using electric pulse stimulating methoe has been investigated. The cup-shaped alumina ceramics were soaked in a simulated body fluid （SBF）, and a square pulse potential with frequency of 1 Hz and voltage of 110 V was applied between the inner and outer surfaces of the alumina cup. Surface morphology of CP coatings during different deposition periods was observed by a Philips XL-30 scanning electron microscope （SEM）. Compositional analysis was examined by EDAX. The mechanism of nucleation and growth of CP coating was discussed. SEM result indicates that the coating comprises of a large number of tiny needle-like grains and has a porous microstructure. There is a strong bond between the deposited layer and Al2O3 substrate, which may be due to the gentle growth of the biomimetic method. The EDAX analysis indicates that main composition of the coating is calcium and phosphor. The formation of CP coating may be contributed to the stimulation of electric pulse and the high ions concentration which is 1.5 times of the concentration of SBF solution （1.5SBF solution）. Such surface functionalization method by electric pulse potential can be used to prepare CP coating on various electric-insulating bioinert materials for improving their bioactive character.
基金the National Natural Science Foundation of China(No.52201066 and No.U21A2045)LiaoNing Revitalization Talents Program(NO.XLYC2002071)+2 种基金Gratitude is also expressed to the support from the Shanghai Aerospace Science and Technology Innovation Fund(SAST2020-046)the Fundamental Research Funds for the Central Universities(N2224002-21)the Natural Science Foundation of Shanghai(20ZR1424200).
文摘In order to obtain a more protective phosphate conversion coating with a denser architecture,the nucleation kinetics of phosphate chemical conversion coating on Mg-Gd-Y-Zr magnesium alloy was tuned in this work.A pretreatment process was proposed and organic additives were incorporated,which aims at increasing the ionic produce(J_(sp))at the interface for increasingσ,and decreasing the critical ionic product(J_(C,sp)),respectively.Results prove that the pretreatment of bare alloys in a phosphate bath could increase the ion products of MgHPO_(4)/MnHPO_(4).The addition of benzalkonium chloride could neutralize the charges of crystals,and in turn promote the nucleation kinetics.A denser and more protective conversion coating could consequently be obtained.
文摘The authors regret that due to negligence,the picture was misplaced in the original manuscript,resulting in Fig.6d being incorrectly included.The correct version of Fig.6d is provided below for reference.This error does not affect the conclusions of the study,and we apologize for any confusion it may have caused.
基金Project(51241001)supported by the National Natural Science Foundation of ChinaProject(ZR2011EMM004)supported by the Natural Science Foundation of Shandong Province,China+1 种基金Project(SKLCP21012KF03)supported by the Open Foundation of State Key Laboratory for Corrosion and Protection,ChinaProject(TS20110828)supported by Taishan Scholarship Project of Shandong Province,China
文摘The influence of phosphating bath at different temperatures on the formation and corrosion property of calcium-modified zinc phosphate conversion coating （Zn-Ca-P coating） on Mg-Li-Ca alloy was investigated. The morphologies, elemental distribution and chemical structures of the coatings were examined via SEM, EPMA, EDS, XRD and FT-IR. The corrosion resistance was assessed by hydrogen evolution, potentiodynamic polarization and EIS. The results show that the coating is composed of single element Zn and ZnO at below 45 ℃;whereas the coatings are predominantly characterized by Zn3（PO4）2·4H2O and small amount of element zinc and ZnO at above 50 ℃. Mg-Li-Ca alloy with Zn-Ca-P coatings prepared at 55 ℃ has the highest corrosion resistance. However, the hydrogen evolution rates of the coatings obtained at 40-50 ℃ is accelerated due to the galvanic corrosion between the imperfection of the single element Zn coating and the Mg substrate.
文摘A SnO2-doped dicalcium phosphate coating was prepared on AZ31 alloy by means of hydrothermal deposition.The results showed that the coating possessed a globular morphology with a long lamellar crystalline structure and a thickness of approximately 40 mm.The surface of the coating became smooth with an increase additive amount of the SnO2 nanoparticles.The corrosion current density and hydrogen evolution rate of the coating prepared in presence of SnO2 were reduced compared to the coating without SnO2 and the bare AZ31 substrate,indicating an improvement in the corrosion resistance of the SnO2-doped coating.
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.
文摘The influence of different surface coatings of NiTi shape memory allays was examined using in vitro testing methods. Plates of superelastic nickel-titanium shape memory allay （ NiTi ） were coated with calcium phosphates （ hydroxyapatite ） by high-temperature plasma-spraying or by dip-coating. The biocompatibility was tested in vitro by cultivation of isolated human granulocytes and whole blood cells. As substrates, pure NiTi, plasma-spray-coated NiTi and dip-coated NiTi were used. Isolated granulocytes showed an increased adhesion to both calcium phosphate-coated NiTi samples. Compared to non-coated NiTi or dip-coated NiTi, the number of dead granulocytes adherent to plasma-sprayed surfaces was significantly increased （ p 〈 0.01 ）. Whether the d/f- ferences in apoptosis of granulocytes on dip-coated vs plasma-sprayed coatings observed are due to differences in material surface morphologies has to be analyzed in further studies. Because of the cellular interactions with the coating layers, h is likely that the results obtained are not caused by the underlying NiTi but due to the coating itself.
基金supported by the National Natural Science Founda-tion of China(52075112,51971071,52011530025)Natural Science Foundation of Heilongjiang Province(JJ2019LH1520).
文摘The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were successfully prepared by adding ultra-high deacetylated chitosan in a phosphate bath.The chemical composition of the prepared composite film was investigated by X-ray photoelectron spectroscopy(XPS)and Fourier trans-form infrared spectroscopy(FT-IR),and the morphology and fracture of the composite film were characterized by scanning electron microscope(SEM).Potentiodynamic polarization curves and electrochemical impedance spec-troscopy were used to study the corrosion behavior of the coated alloys.The results showed that when pH=2.5 and the chitosan concentration was 5.0 g/L,chitosan was deposited in the phosphate coating in the form of inclusions.In addition,the potentiodynamic polarization curves of the composite films show that the corrosion potential is positively shifted by 0.6 V compared to the monolayer phosphate coating,indicating improved corro-sion resistance.This work shows that highly deacetylated chitosan can be co-deposited with phosphate to form a dense composite film on the surface of magnesium alloys in one step,thereby improving the corrosion resistance of the alloy.
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.
基金supported by the Natural Science Foundation of Chongqing(Grant No.csts2018jcyjAX0016)Funded by the Senior Medical Talents Program of Chongqing for Young and Middle-aged.
文摘The possible application of magnesium(Mg)in glaucoma surgical treatment has been investigated in our previous work.In this paper,the degradation behavior and biocompatibility of Mg coated with hydroxyapatite(HA)and dicalcium phosphate dihydrate(DCPD)in eye environment were evaluated,and uncoated Mg was used for comparison.It was found that uniform corrosion occurred macroscopically to the coated Mg samples in sodium lactate ringer’s injection(SLRI)as well as in the rabbit eyes.In micro-scale,the corrosion was characterized by local cracking and pitting primarily.Mg and calcium(Ca)were incorporated into the surface corrosion products and a multi-layer structure was formed.Compared to other samples,HA-coated Mg slowed down dramatically the alkalinity of the solution and the ion release of the sample,and exhibited the lowest corrosion rate in SLRI,which was about 0.22 mm/a.In terms of biocompatibility,fibroblasts demonstrated high viability in the HA-coated and DCPD-coated Mg groups(p<0.05)in vitro.In vivo,HA-coated Mg was found to show lower inflammatory response and fibrosis than the other groups did,as indicated by hematoxylin-eosin and immunofluorescence staining.During the degrading process of HA-coated Mg in the rabbits’eyes,no inflammation was found in the anterior chamber,lens,and vitreous body.HA-coated Mg was fully biodegraded fifteen weeks post-operation,and the scleral drainage channel(SDC)was formed without obvious scarring.It is concluded that HA-coated Mg implantation is a promising adjunctive procedure to improve the success rate of trabeculectomy.Statement of significance:Magnesium(Mg)has shown to be a potential biomaterial for ophthalmic implants in our previous work.However,inflammatory response resulted from the low corrosion resistance of Mg is a major concern.It is shown here that Mg coated with different calcium phosphates can improve these properties in varying degrees and keep the scleral drainage channel unobstructed and unscarred.Based on our in vitro and in vivo studies,HA-coated Mg exhibited a better degradation behavior and excellent biocompatibility.The scleral drainage channel still exists and aqueous humor flows out smoothly after the full degradation of the implant.It is concluded that HA-coated Mg is a promising biomaterial to increase the therapeutic efficiency of trabeculectomy for glaucoma.
基金financially supported by the National Natural Science Foundation of China(No.52373322).
文摘In deaerated 0.05 M,0.1 M,0.2 M and 0.5 M K_(2)HPO_(4) solutions with pH 9.5,AZ31 magnesium(Mg)alloy was subjected to potentiostatic polarization at−0.8 VSCE to deposit a phosphate conversion coating.The morphology,structure,chemical composition,and protective performance of the conversion coating during the formation process were characterized.The results showed that amorphous Mg(OH)_(2) and MgHPO_(4) and crystallized KMgPO_(4)·6H2O(struvite-K)were successively deposited on the surface of AZ31 Mg alloy in the four solutions.MgHPO_(4) was converted from Mg(OH)_(2),while struvite-K was transformed from MgHPO_(4).The distribution of Mg(OH)_(2),MgHPO_(4) and struvite-K along the thickness of the coating difers with K_(2)HPO_(4) concentration.As the concentration of K_(2)HPO_(4) increased,the coating time was gradually shortened,and the coating was gradually thinned.Meanwhile,the ratio of the nucleation rate to the growth rate of struvite-K crystal nuclei increased,resulting in a decrease in the size of struvite-K crystal.When the concentration of K_(2)HPO_(4) increased from 0.05 to 0.1 M,the content of struvite-K increased,and the protective performance of the coating was enhanced.However,as the concentration of K_(2)HPO_(4) continued to increase to 0.5 M,the content of struvite-K and the protective performance of the coating decreased.
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.
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.
基金Project(2012J05099)supported by the Natural Science Foundation of Fujian Province,ChinaProject(YKJ10021R)supported by the Scientific Research Project of Xiamen University of Technology
文摘Silicate sol post-treatment was applied to form a complete composite coating on the phosphated zinc layer. The chemical compositions of the coatings were investigated using XPS. The coated samples were firstly scratched and then exposed to the neutral salt spray(NSS) chamber for different time. The microstructure and chemical compositions of the scratches were studied using SEM and EDS. And the non-scratched coated samples were compared. The self-healing mechanism of the composite coatings was discussed. The results show that during corrosion, the self-healing ions in composite coatings dissolve, diffuse and transfer to the scratches or the defects, and then recombine with Zn2+ to form insoluble compound, which deposits and covers the exposed zinc. The corrosion products on the scratches contain silicon, phosphorous, oxygen, chloride and zinc, and they are compact, fine, needle and flake, effectively inhibiting the corrosion formation and expansion of the exposed zinc layer. The composite coatings have good self-healing ability.
基金This work was supported by the Bengbu Yucheng New Materials Science and Technology Ltd. （No.2012QTXM0375） and the Natural Science Foundation of Anhui Province （No.1208085QE99）.
文摘Hydroxylamine sulfate （HAS） and sodium nitrite are used as the accelerators for zinc phos- phate coating on high carbon steel. Phase evolution of phosphate coating was investigated by X-ray diffraction. It is found that the phosphating coatings are mainly composed of hopeite Zn3Fe（PO4）2.4H2O and phosphophyllite Zn2Fe（PO4）2.4H2O. The microstructural changes of the phosphate coating, as a function of phosphating time, were evaluated by scanning elec- tron microscopy. Four-ball friction experiments reveal that hydroxylamine sulfate instead of sodium nitrite can effectively reduce the friction coefficient of lubricated phosphating coat- ing. Therefore, it may be expected that HAS will be widely used as a fast and ECO-friendly accelerator in phosphate industry.
基金Projects (2011CL08, 2011CL01) supported by Open Fund of Material Corrosion and Protection Key Laboratory of Sichuan Province, ChinaProject (2011RC02) supported by Talent Introduction Funds of Sichuan University of ScienceProject (12ZA261) supported by Key Project of Education Department of Sichuan Province, China
文摘A phosphate solution free of chromate, fluoride and nitrite was prepared and an environment-friendly film was obtained on AZ31 magnesium alloy surface via the chemical deposition method. The morphology, composition, phase structure and its corrosion resistance were studied. The effects of film-forming temperature and free acid on corrosion resistance, microstructure and electrochemical behavior of the film were discussed. The results indicate that the corrosion resistance of AZ31 with the phosphate film was better than blank AZ31 substrate, which was most attributed to the great inhibitive action on the anodic dissolution and cathodic hydrogen evolution of the film.
文摘It was ascertained that when a RE element was added in bath,the sample was improved on the anti-corrosion power of the coating because of the increasing of covering rate of formless crystal Zn2Fe(PO4) 2·4H2O(marked P) crystals and the ratio of P/(P+H) (H was the mark of Zn3(PO4) 2 crystal) in the coating,combination of which with components parsing by EDS indicated that the sequence of contribution elements P and Zn to erosion resistance of coatings was P】Zn. And the correlative mechanism was discussed,which made it clear that owing to the particularity of the outer-shell electron structure and larger ionic radius,RE was so easy to be polarized and metamorphosed itself that it adsorbed lightly on the basic body to pose gels. They efficiently reduced the activation energy which was required for formation of a new solid phase of phosphates and made it also possible to engender effectively active nucleation regions of cathode and anode under low temperature phosphating condition,which was propitious to formation,densification and uniformization of the phosphate crystal nucleus and growth of the crystallite and coating buildup. Thus it could be seen that REN played the role of surface regulator and accelerant,which speeded up the phosphating,as well as bids amount of porosity of the coating fall to improve the corrosion resistance of the coating.
文摘To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) steel was post-sealed with cerium nitrate solution. The morphology, composition, corrosion resistance of the coatings was investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and neutral salt spray (NSS) tests. The results show that after post-sealing the phosphated HDG samples with cerium nitrate solution, the pores among the zinc phosphate crystals are sealed by the compounds containing phosphorus, oxygen and cerium; the zinc phosphate crystals are covered by the flocculent cerium compounds; and the continuous composite coatings are formed on HDG steel. The corrosion resistance of the composite coatings, which increases with the increase in phosphating time and cerium nitrate post-sealing time, is far higher than that of the single phosphate coatings. The composite coatings with the optimal corrosion resistance are obtained for phosphating 300 s and post-sealing 300 s; and the corrosion resistance is more outstanding than that of the chromate coatings.
