In vitro corrosion and biocompatibility of phosphating modified WE43 magnesium alloy

Phospahting coated WE43 magnesium alloy was prepared by an immersion method. The microstructure, corrosion resistance and biocompatibility of the coated alloy were investigated. Scanning electron microscopy （SEM） and X-ray diffraction （XRD） were used to examine the microstructure and the composition of the coated alloy. The corrosion resistance was studied by means of potentiodynamic polarization method and the biocompatibility of the surface modified WE43 alloy was evaluated by （3-（4,5）-Dimethylthiazol-2, yl）-2,5-diphenyltetrazolium bromide （MTT） and hemolysis test. The results show that the phosphating coating can enhance the corrosion resistance of WE43 alloy and can be a good candidate to increase the biocompatibility of WE43 alloy.

Formation process of composite plasma electrolytic oxidation coating containing zirconium oxides on AM50 magnesium alloy

The formation processes of a composite ceramic coating on AM50 magnesium alloy prepared by plasma electrolytic oxidation （PEO） in a K 2 ZrF 6 electrolyte solution were studied by scanning electron microscope （SEM） and energy dispersive X-ray spectroscope （EDX）. Electrochemical impedance spectroscopy （EIS） tests were used to study the variation of the corrosion resistance of the coating during the PEO treatment. The results show that the coating formed on Mg alloy is mainly composed of MgO and MgF 2 when the applied voltage is lower than the sparking voltage, and zirconium oxides start to be deposited on Mg substrate after the potential exceeding the sparking voltage. The corrosion resistance of the coating increases with increasing the applied voltage.

注氮后纯钛在不同浓度含氟溶液中的腐蚀性研究

目的:通过等离子浸没注入对纯钛试样进行表面改性,探讨其在不同浓度含氟溶液中的耐腐蚀性。方法:利用等离子浸没注入法对纯钛表面进行氮离子注入,用电化学分析测定注氮前后纯钛在不同浓度含氟溶液中的自然腐蚀电位(Ecorr)、腐蚀电流密度(Icorr)、极化电阻(Rp)。扫描电镜(SEM)观察试件表面形态变化。结果:注氮前后纯钛在同种溶液中腐蚀性均有显著差异(p<0.05),纯钛在不同浓度含氟溶液中的腐蚀性也存在显著差异(p<0.05)。扫描电镜观察表明,注氮前纯钛试件表面腐蚀痕迹比注氮后明显,纯钛试件在0.2%NaF人工唾液中腐蚀痕迹更加明显。结论:等离子浸没注氮后的纯钛有较好的耐腐蚀性,纯钛在含0.2%NaF溶液中耐腐蚀性能明显下降。

Surface modification with SiO_2 coating on biomedical TiNi shape memory alloy by sol-gel method

The effect of heat treatment on the transformation temperature of Ti?52.2%Ni (mole fraction) alloy was studied using differential scanning calorimetry (DSC). The transformation temperatures of the alloy can be adjusted effectively by heat treatment. Dense and stable SiO2 coatings were deposited on the surface of the pre-oxidized TiNi alloy by sol?gel method. The bonding strength of films and matrix was (65.9±1.5) N. The electrochemical corrosion test shows that the TiNi alloy with SiO2 coating has excellent corrosion resistance in the Hank’s simulated body fluid. The release behaviors of Ni ion of the alloy with and without SiO2 coating implanted in the acoustic vesicle of guinea pig were studied by EDS testing, which was inhibited effectively by the dense and stable SiO2 coating on the alloy.

Etching Behavior of GaN/GaAs(001) Epilayers Grown by MOVPE

Wet etching characteristics of cubic GaN (c GaN) thin films grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE) are investigated.The samples are etched in HCl,H 3PO 4,KOH aqueous solutions,and molten KOH at temperatures in the range of 90～300℃.It is found that different solution produces different etch figure on the surfaces of a sample.KOH based solutions produce rectangular pits rather than square pits.The etch pits elongate in 1 0] direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers. direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers.

Corrosion degradation behavior of Mg-Ca alloy with high Ca content in SBF

The corrosion degradation behavior of a Mg-Ca alloy with high Ca content aiming for a potential bone repair material in the simulated body fluid（SBF） was investigated.The microstructure and phase constitution of the pristine Mg-30%Ca（mass fraction） alloy were characterized with scanning electron microscopy（SEM） and X-ray diffraction（XRD）.The Mg-30%Ca alloy samples were immersed in the SBF for 90 d,and the morphology,composition and cytotoxicity of the final corrosion product were examined.It is found that Mg-30%Ca alloy is composed of α-Mg and Mg2 Ca phases.During the corrosion process in the SBF,the Mg2 Ca phase acts as an anode and the α-Mg phase acts as a cathode.The final corrosion product of the Mg-30%Ca alloy in SBF includes a small amount of black precipitates and white suspended particles.The white suspended particles are Mg（OH）2 and the black particles are believed to have a core-shell structure.The cytotoxicity experiments indicate that these black precipitates do not induce toxicity to cells.

延长轮胎使用寿命妙诀

轮胎使用寿命的长短,除与作业量多少有关外,关键在于维护保养。轮胎维护保养的妙诀是:「两坚持、两不停、四勤、四慢、八标准。」

压缩式喷雾器使用注意事项

目前农村使用较广的喷雾器是５５２型、５５２丙型压缩式喷雾器。它是一种小型手动喷洒农药药液的机具，只需一人操作，轻便、灵活，适用于小面积的矮秆作物。使用这种喷雾器时应注意以下几点：１新喷雾器在使用前应拆下压盖，向气筒内滴入少许机油润滑皮碗，然后依次装好部件，注意各接头处装入垫圈后再拧紧。２使用前应先加入清水，井把器械上部的放气螺丝拧紧，用手握住铁柄，上下压动３０－５０次（压塞杆进行打气时，应平稳，每次行程应拉足、压足），打开开关进行喷雾，检查各管路接头处是否漏水和漏气，观察喷雾是否正常。如果正常，即可到田间作业，要是喷雾不好，或是漏水漏气，应修好再用。３若加水盖略有漏气，可将桶身摇晃几下。

Electrochemical evaluation of zinc and magnesium alloy coatings deposited on electrogalvanized steel by PVD

Zinc alloy coating attracted much attention due to its high anti-corrosive properties.Particularly,zinc alloy coatings containing magnesium was considered a promising metallic alloy due to a remarkable improvement of corrosion resistance.The proper magnesium content for Zn-Mg alloy coatings was studied.The samples were prepared using thermal evaporation method.The influence of Zn-Mg alloy coating on corrosion resistance was evaluated using immersion test,potentiodynamic test,and galvanic test in 3% NaCl solution at room temperature.The results show that the corrosion resistance of Zn-Mg alloy coatings is strongly dependent on magnesium content.Corrosion potential decreases with increasing magnesium content,whereas current density increases up to 15% magnesium content,and passivity region was found only in Zn-Mg coatings.

Synthesis and in-vitro characterization of biodegradable porous magnesium-based scaffolds containing silver for bone tissue engineering

Infection is a major potential complication in the clinical treatment of bone injuries. Magnesium (Mg)-based composites are biodegradable and antibacterial biomaterials that have been employed to reduce infection following surgical implants. The aim of present study was to synthesize and in-vitro characterize Mg-based scaffolds containing silver for bone tissue engineering. Porous Mg-based scaffolds with four silver concentrations (i.e., 0, 0.5 wt.%, 1 wt.%, and 2 wt.%), denoted by Mg?Ca?Mn-Zn-xAg (MCMZ?xAg)(where x is the silver concentration), were fabricated by the space holder technique. The effects of silver concentration on pore architecture, mechanical properties, bioactivity, and zone of bacterial inhibition were investigated in-vitro. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy were utilized to characterize the obtained scaffolds. In-vitro corrosion test results indicated that the MCMZ scaffolds with lower silver content were more resistant to corrosion than those enriched with higher amounts of silver. Examination of the antibacterial activity showed that the MCMZ?Ag scaffolds exhibited superb potential with respect to suppressing the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), in the inhibition zone around the MCMZ?Ag scaffolds, with increasing in the amount of incorporated silver;however, higher amounts of silver increased the cytotoxicity. Taken together, the results of this study demonstrate that the porous 0.5 wt.% Ag-containing scaffolds with interconnected pores, adequate mechanical properties, antibacterial activity, and cell adhesion are promising with respect to the repair and substitution of damaged and diseased bones.

Effects of cooling rate on bio-corrosion resistance and mechanical properties of Mg-1Zn-0.5Ca casting alloy

Mg?1Zn?0.5Ca alloys were prepared by traditional steel mould casting and water-cooled copper mould injection casting at higher cooling rate. Microstructure, mechanical properties and bio-corrosion resistance of two alloys were contrastively investigated. Grain size reduces remarkably and microstructure becomes homogenous when raising cooling rate. The bio-corrosion behaviour in 3.5% sodium chloride solution (3.5% NaCl) and Hank’s solution at 37°C was investigated using electrochemical polarization measurement and the results indicate that the alloy prepared at higher cooling rates has better corrosion resistance in both types of solution. Further mass loss immersion test in Hank’s solution reveals the same result. The reason of corrosion resistance improvement is that raising cooling rate brings about homogeneous microstructure, which leads to micro-galvanic corrosion alleviation. The tensile test results show that yield strength, ultimate tensile strength and elongation are improved by raising cooling rate and the improvement is mainly due to grain refinement.

Bioactivity,in-vitro corrosion behavior,and antibacterial activity of silver-zeolites doped hydroxyapatite coating on magnesium alloy

Mg-based alloys received significant attention for temporary implant applications while, their applications have been limited by high degradation rate. Therefore, silver-zeolite doped hydroxyapatite（Ag-Zeo-HAp） coating was synthesized on Ti O2-coated Mg alloy by physical vapour deposition（PVD） assisted electrodeposition technique to decrease the degradation rate of Mg alloy. X-ray diffraction（XRD） analysis and field emission scanning electron microscopy（FE-SEM） images showed the formation of a uniform and compact layer of Ag-Zeo-HAp with a thickness of 15 μm on the Ti O2 film with a thickness of 1 μm. The potentiodynamic polarization（PDP） and electrochemical impedance spectroscopy（EIS） tests indicated that corrosion resistance of Mg-Ca alloy was considerably increased by the Ag-Zeo-HAp coating. The bioactivity test in the simulated body fluid（SBF） solution showed that a dense and homogeneous bonelike apatite layer was formed on the Ag-Zeo-HAp surface after 14 d. Investigation of antibacterial activity via disk diffusion and spread plate methods showed that the Ag-Zeo-HAp coating had a significantly larger inhibition zone（3.86 mm） towards Escherichia coli（E. coli） compared with the Ti O2-coated Mg alloy（2.61 mm）. The Ag-Zeo-HAp coating showed high antibacterial performance, good bioactivity, and high corrosion resistance which make it a perfect coating material for biomedical applications.

Role of Ag addition on microstructure,mechanical properties,corrosion behavior and biocompatibility of porous Ti-30 at%Ta shape memory alloys

In the present study,the thermal,mechanical,and biological properties of xAg/Ti-30Ta(x=0,0.41,0.82 and 2.48 at%)shape memory alloys(SMAs)were investigated.The study was conducted using optical and scanning electron microscopy(SEM),X-ray diffractometry(XRD),compression test,and shape memory testing.The xAg/Ti-Ta was made using a powder metallurgy technique and microwave-sintering process.The results revealed that the addition of Ag has a significant effect on the pore size and shape,whereas the smallest pore size of 11μm was found with the addition of 0.41 at%along with a relative density of 72%.The fracture stress and strain increased with the addition of Ag,reaching the minimum values around 0.41 at%Ag.Therefore,this composition showed the maximum stress and strain at fracture region.Moreover,0.82 Ag/Ti-Ta shows more excellent corrosion resistance and biocompatibility than other percentages,obtaining almost the same behaviour of the pure Ti and Ti-6Al-4V alloys,which can be recommended for their promising and potential response for biomaterial applications.

Improvement of in vitro corrosion, wear, and mechanical properties of newly developed Ti alloy by thermal treatment for dental applications

The effects of thermal treatments on the structure, mechanical properties, wear resistance, and in vitro corrosion protection in artificial saliva(AS) were investigated for a newly developed Ti20 Nb13 Zr(TNZ) alloy. XRD and SEM analyses were used for structural and microstructural analysis. The in vitro corrosion properties of the samples were investigated using electrochemical impedance spectroscopy and linear polarization resistance techniques up to an immersion time of 168 h. The tribological characteristics were evaluated with a linear reciprocating tribometer. SEM analysis showed that solution treatment and aging influenced the size and distribution of α phase. The air-cooled and aged samples exhibited the highest microhardness and macrohardness, for which the wear resistances were 25% and 30% higher than that of the untreated sample, respectively. The cooling rate significantly influenced the corrosion resistance of the TNZ samples. The treated samples showed a reduced corrosion rate(50%) for long immersion time up to 168 h in AS. The furnace-cooled and aged samples exhibited the highest corrosion resistance after 168 h of immersion in AS. Among the treated samples, the aged sample showed enhanced mechanical properties, wear behavior, and in vitro corrosion resistance in AS.

Microstructure,anticorrosion,biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications,Mg−6Zn−0.3Mn−xCa(x=0,0.2 and 0.5,wt.%)alloys were prepared by semi-continuous casting followed by hot-extrusion technique.The microstructure and mechanical properties of Mg−6Zn−0.3Mn−xCa alloys were investigated using the optical microscope,scanning electron microscope and tensile testing.Results indicated that minor Ca addition can slightly refine grains of the extruded Mg−6Zn−0.3Mn alloy and improve its strength.When 0.2 wt.%and 0.5 wt.%Ca were added,the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2μm,respectively.Of the three alloys studied,the alloy with 0.5 wt.%Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%.The corrosion behaviour,cell viability and antibacterial activities of alloys studied were also evaluated.Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca2Mg6Zn3 phases.Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg−6Zn−0.3Mn−0.5Ca alloy compared to Mg−6Zn−0.3Mn and Mg−6Zn−0.3Mn−0.2Ca alloys.The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.

Effect of fluoride treatment on corrosion behavior of Mg-Ca binary alloy for implant application

The influence of hydrofluoric acid（HF） treatment on the corrosion behavior of the Mg-0.5Ca alloys was investigated by immersion specimen in sodium hydroxide and HF solutions with various concentrations and durations at room temperature.Microstructural evolutions of the specimens were characterized by atomic force microscopy,X-ray diffraction,field-emission scanning electron microscopy.The corrosion resistance was examined through potentiodynamic polarization and immersion test in Kokubo solution.The results revealed that the fluoride treated Mg-0.5Ca alloys produced by immersion in 40% HF provided more uniform,dense and thicker coating layer（12.6 μm） compared with the 35% HF treated specimen.The electrochemical test showed that the corrosion resistance of fluoride treated specimen was 35 times higher compared with the untreated Mg-0.5Ca alloy specimen in Kokubo solution.In vitro degradation rate of the fluoride treated specimens was much lower than untreated Mg-0.5Ca alloy in Kokubo solution.After immersion test the surface of 40% HF treated sample showed a few corrosion dots,while untreated specimens were fully covered by corrosion products and delamination.Fluoride treated Mg-0.5Ca alloy with 40% HF is a promising candidate as biodegradable implants due to its low degradation kinetics and good biocompatibility.

Zinc-doped hydroxyapatite-zeolite/polycaprolactone composites coating on magnesium substrate for enhancing in-vitro corrosion and antibacterial performance

This work is focused on developing zinc-doped hydroxyapatite-zeolite(Zn HA-Zeo)and polycaprolactone(PCL)composite coatings on magnesium(Mg)substrate to improve the corrosion resistance and antimicrobial properties.Dip-coating technique was used to coat Zn HA-Zeo/PCL on the Mg substrate at room temperature.The samples were subjected to field emission scanning electron microscopy(FESEM),X-ray diffraction(XRD),Fourier transform infrared(FTIR),energy dispersive X-ray spectroscopy(EDX)and antimicrobial potential.Results demonstrated that composite coatings consist of HA,scholzite,zeolite,and PCL phases.EDX spectra indicated the presence of calcium(Ca),silicon(Si),aluminum(Al),zinc(Zn),phosphorus(P)and oxygen(O).The composite surface appeared in spherical-like microstructure on coating with thickness ranging 226-260μm.Zinc-doped HA-Zeo composite coating had a high corrosion resistance and provided sufficient protection to the Mg surface against galvanic corrosion.Doped Zn HA-Zeo coating samples exhibited superior disc inhibition by confirming antimicrobial activity against the E.coli as compared to HA-Zeo sample.Altogether these results showed that the Zn HA-Zeo coatings not only improved the corrosion resistance,but also enhanced the antimicrobial property and hence they can be used as suitable candidates for implant applications.

The Morphology, Phase Composition and Effect of Corrosion Product on Simulated Archaeological Iron

The immersion corrosion of archaeological iron in solution(0.06mol·L- 1NaCl+0.03mol·L -1 Na2SO4+ 0.01mol·L- 1 NaHCO3)simulating soil water composition was presented.The evolution of archaeological iron from iron to iron oxide and to iron oxy-hydroxides compounds was investigated by scanning electron microscope(SEM) and X-ray diffraction(XRD)analysis.According to the morphology,phase composition,and transformation proc- ess,the contributions of each corrosion product to archaeological iron were discussed.