Corrosion Degradation Behavior Research Articles

Biomimetic hydrogel coatings for improving the corrosion resistance, hemocompatibility, and endothelial cell growth of the magnesium alloy

The fast biodegradation and poor biocompatibility of Mg alloys in physiological environments are still the main problems restricting their application in cardiovascular stents. In this study, the hydrogel coatings (SBMA-AAM) with different proportions of methacryloyl ethyl sulfobetaine (SBMA) and acrylamide (AAM) were built on the surface of AZ31B magnesium alloy through ultraviolet (UV) polymerization. The corrosion degradation behavior, hemocompatibility, and endothelial cell (EC) growth performance of the samples were studied in detail. The findings revealed that the uniform and dense SBMA-AAM coatings could significantly enhance the corrosion resistance. In addition, the hydrogel coatings showed excellent hydrophilicity, which increased the albumin adsorption while inhibiting the fibrinogen adsorption, and thus reduced the platelet adhesion and activation and hemolysis rate, accordingly significantly enhancing their anticoagulant performance. Furthermore, SBMA-AAM hydrogel coating promoted the EC adhesion and proliferation and the vascular endothelial growth factor (VEGF) and nitric oxide (NO) secretion of ECs, which is conducive to promoting endothelialization. When the concentration ratio of SBMA and AAM was 1: 2, the modified magnesium alloy showed the best corrosion resistance and biocompatibility. Therefore, the SBMA-AAM hydrogel coating could effectively regulate the corrosion degradation performance and biocompatibility of Mg alloys, laying a foundation for the application of Mg alloys in cardiovascular stents.

Corrosion Degradation Behavior of Bending Aluminum and Copper Materials for Air Conditioning Refrigerant Piping

Introduction Many types copper alloys of refrigerant piping are used for practical use owing to their high workability, thermal conductivity, and weather ability. However, there is concern about depletion, due to consume in large quantities via emerging country and new devices such as electric vehicle and so on. Recently, we focused on aluminum as light metal, and applied for refrigerant piping of air-conditioning equipment. We focused on corrosion factors of piping for inside (refrigerant passage) and outside (atmospheric exposure) and investigated simulated practical used straight sections. As a result, almost equal practicalities were confirmed for both cases of aluminum and copper [1].In actual refrigerant piping, bending sections are always appared utilized alongside straight pipes. When pipes are bent using a bender, tensile stress occurs on the outer surface and compressive stress on the inner surface. Stress corrosion cracking (SCC) can be induced under tensile stress in corrosive environments. Evaluating SCC potential in aluminum piping due to bending is crucial for its long-term use in refrigerant piping. Therefore, in this study, mechanical, electrochemical characteristics, and weather resistance characteristic of bending aluminum and copper piping under tensile stress were investigated to confirm practicality of Al refrigerant piping. Experiments A6063-T83(Al-T) and C1220-1/2H(Cu-H) were used for the aluminum materials and utilized copper materials, respectively. To confirm the electrochemical characteristics in order to investigate the difference in the bending curvature, natural electrode potential measurements were examined at eight bent points (four on the tensile side, four on the compressive side) and one straight segment. The natural potential of the samples was measured using a three-electrode method, with the samples, Pt wire, and Ag/AgCl as working, counter and reference electrodes, respectively, immersed in a 3.0 mol L-1 NaCl solution. Measurements were carried out using a potentiostat (HZ-5000, Hokuto Denko) at 303 K maintained by a constant-temperature water bath. To investigate the corrosion resistance of bending aluminum and copper piping, cyclic degradation test was performed according to the Japanese Automotive Standard JASO M610-92. Each cycle, lasting 8 hours, comprised three steps: 1. neutral saltwater spray (35°C, pH 6.5-7.2, 2h), 2. drying (60°C, 25% RH, 4h), and 3. humidification (50°C, 95% RH, 2h). Specimens were removed at 8h, 24h, 48h, 96h, 192h, 384h, and 496h during the cyclic degradation test for appearance observation. In addition, Samples at 496h, cross-sectional observations using SEM (JSM-7200F, JEOL) were performed after etching the samples at the tensile and compressive sides of the bent sections and the straight segment. Results & Discussion Fig.1 shows the time dependence in the natural electrode potential of tensile side of Cu-H. At all measurement points, stable natural potential of -0.27 V vs. Ag/AgCl(V) and no significant natural electrode potential changes were confirmed during the measurement time. Fig.2 shows the time dependence in the natural electrode potential of tensile side of Al-T. At all measurement points, the average natural potential value remained approximately -0.75 V vs. Ag/AgCl(V) across all measurement points, and no significant natural electrode potential changes were observed during the measurement time. However, deviations in the natural electrode potential values were also slightly observed at measurement points c and d with a large curvature in the bent part. These results suggested that regions with increased curvature due to bending might be occured to destroying to the oxide film on the surface of the Al piping, indicating subtle yet progressing oxidation. Fig 3. shows cross-section SEM images of the tensile and compressive sides of the bent sections and the straight segment of Cu-H after 496h cyclic degradation test. No significant were observed in all observation points.The results of this measurement indicate that the no evidence of corrosion of the copper tube due to tensile stress. Fig 4. shows cross-section SEM images of the tensile and compressive sides of the bent sections and the straight segment of Al-T after 496h cyclic degradation test. Thin oxide observed at all the measurement points, but there were no significant differences observed in its production at each of the measurement locations. In an environment of constant exposure to seawater, such as that encountered in the natural electrode potential measurements, chlorine can cause severe damage to the Al bending piping. On the other hand, cyclic degradation tests ,which simulated actual use for severe weather resistance performances, conditions suggested that the effects of Al bending are minimal, as the oxide film is re-formed during the wet-dry process. Thus we demonstrated that Al bending piping must use in practical useful.[1] S. Uchiyama, et., al., Mater Corros.(Wiley), 74, 344-351 (2023). Figure 1

Corrosion Behavior of Ferritic 12Cr ODS and Martensitic X46Cr13 Steels in Nitric Acid and Sodium Chloride Solutions.

This paper presents corrosion resistance results of a 12Cr ferritic ODS steel (Fe-12Cr-2W-0.5Zr-0.3Y2O3) fabricated via a powder metallurgy route as a prospective applicant for fuel cladding materials. In a spent nuclear fuel reprocessing facility, nitric acid serves as the primary solvent in the PUREX method. Therefore, fundamental immersion and electrochemical tests were conducted in various nitric acid solutions to evaluate corrosion degradation behavior. Additionally, polarization tests were also performed in 0.61 M of sodium chloride solutions (seawater-like atmosphere) as a more general, all-purpose procedure that produces valid comparisons for most metal alloys. For comparison, martensitic X46Cr13 steel was also examined under the same conditions. In general, the corrosion resistance of the 12Cr ODS steel was better than its martensitic counterpart despite a lower nominal chromium content. Potentiodynamic polarization plots exhibited a lower corrosion current and higher breakdown potentials in chloride solution in the case of the ODS steel. It was found that the corrosion rate during immersion tests was exceptionally high in diluted (0.1-3 M) boiling nitric acid media, followed by its sharp decrease in more concentrated solutions (>4 M). The results of the polarization plots also exhibited a shift toward more noble corrosion potential as the concentrations increased from 1 M to 4 M of HNO3. The results on corrosion resistance were supported by LSCM and SEM observations of surface topology and corrosion products.

Effects of MgO nanoparticle addition on the mechanical properties, degradation properties, antibacterial properties and in vitro and in vivo biological properties of 3D-printed Zn scaffolds

Bone tissue engineering is the main method for repairing large segment bone defects. In this study, a layer of bioactive MgO nanoparticles was wrapped on the surface of spherical Zn powders, which allowed the MgO nanoparticles to be incorporated into 3D-printed Zn matrix and improved the biodegradation and biocompatibility of the Zn matrix. The results showed that porous pure Zn scaffolds and Zn/MgO scaffolds with skeletal-gyroid (G) model structure were successfully prepared by selective laser melting (SLM). The average porosity of two porous scaffolds was 59.3 and 60.0%, respectively. The pores were uniformly distributed with an average pore size of 558.6–569.3 μm. MgO nanoparticles regulated the corrosion rate of scaffolds, resulting in a more uniform corrosion degradation behavior of the Zn/MgO scaffolds in simulated body fluid solution. The degradation ratio of Zn/MgO composite scaffolds in vivo was increased compared to pure Zn scaffolds, reaching 15.6% at 12 weeks. The yield strength (10.8 ± 2.4 MPa) of the Zn/MgO composite scaffold was comparable to that of cancellous bone, and the antimicrobial rate were higher than 99%. The Zn/MgO composite scaffolds could better guide bone tissue regeneration in rat cranial bone repair experiments (completely filling the scaffolds at 12 weeks). Therefore, porous Zn/MgO scaffolds with G-model structure prepared with SLM are a promising biodegradable bone tissue engineering scaffold.

Corrosion characteristics of basalt-polypropylene hybrid fiber concrete under the compound salt and drying-wetting cycles

Concrete is widely used in civil engineering due to its superior properties, however, due to its crack-prone nature, its application in marine engineering will generate a large number of micro-cracks, which will affect the durability and service life of the concrete structure. Basalt-polypropylene hybrid fibers have been added to concrete as a new type of hybrid fiber to improve tensile strength. However, the long-term erosion resistance of basalt-polypropylene hybrid fiber concrete (BPHFC) in marine tidal environments has not been well studied. Therefore, the corrosion degradation behavior of BPHFC under the combined action of compound salt (NaCl+Na2SO4) and drying-wetting cycles was investigated using indoor simulation experiments, and analyzed the effects of fiber content and form on the macroscopic properties and sulfate concentration of concrete. In addition, the corrosion deterioration mechanism of BPHFC was revealed using a concrete surface pore structure analyzer, X-ray diffractometer, and field emission scanning electron microscopy. The research results showed that after 60 cycles, the mass loss rate of BPHFC began to increase, and the specimens mixed with 0.1% BF exhibited the smallest mass loss rate. The relative compressive strength (Kn) and relative dynamic elastic modulus showed a tendency to increase and then decrease. Compared with the control specimens, the addition of 0.1% BF, PF, or BF-PF reduced the Kn loss rate of concrete by 24.04%, 13.28%, and 8.10%, respectively, whereas 0.2% BF-PF hybrid fibers increased the Kn loss rate of concrete by 1.62%. The sulfate concentration of BPHFC increased with the number of cycles, and the addition of 0.1% single or hybrid fibers increased the magnitude of the decrease in sulfate concentration during the later stages of erosion. The addition of BF, PF, or hybrid BF-PF reduced the percentage of super-large pores in concrete by 0.67–28.91% after 90 cycles, and addition of BF and PF attenuated the deterioration of concrete pores after erosion. There was a difference in the bonding properties of BF and PF with the concrete matrix, and the corrosion products of BPHFC were mainly ettringite and gypsum. The results of this study contribute to the development and application of BPHFC in marine engineering.

Effect of Zinc Content on Powder Characteristics, Porosity, Microstructure, and Corrosion Behavior of SLM-Printed Mg-xZn-0.2Mn Alloys for Biomedical Applications

This study investigated the effects of Zinc (Zn) content, specifically in the range of 1 wt.% to 7 wt.%, on the powder characteristics, porosity, microstructure, and corrosion behavior of Mg-xZn-0.2Mn alloys produced using selective laser melting (SLM). To evaluate the porosity of the printed parts and various powder attributes, such as size, circularity, void spaces between powders, and inherent imperfections, scanning electron microscopy (SEM) and optical microscopy (OM) were employed. The alloy microstructure, composition, and phase were examined using energy dispersive X-ray (SEM-EDX) and X-ray Diffraction (XRD). The corrosion resistance and degradation behavior were assessed through electrochemical corrosion tests and immersion tests in Hanks’ solution at 37.5 °C, respectively. Finally, OM and SEM-EDX were used to characterize the corrosion products. The findings of this study indicated that the powder size increased with Zn content, maintaining a 0.8 circularity. Powder defects were minimal, with occasional satellite particles. For the SLM-printed samples, it was evident that porosity characteristics could be influenced by Zn content. As Zn content increased, the pore fraction rose from 1.0% to 5.3%, and the pore size grew from 2.2 μm to 3.0 μm. All printed samples consisted of an α-Mg matrix. Additionally, a higher Zn content resulted in more distinct grain boundaries. Corrosion resistance decreased with Zn, leading to more pronounced localized corrosion after immersion in Hanks’ solution. Ca-P was found as white corrosion products on all samples.

Study on glass-forming ability and corrosion performance of Ca-based biomedical materials.

Stress shielding and the need for secondary surgery are the two major challenges faced by permanent metallic implants, and the emerging Ca-Mg-Zn calcium-based bulk amorphous alloys, with Young's modulus comparable to that of human bone, good biocompatibility, and in vivo degradation, are highly promising materials for bioimplants. Few studies have been reported on the glass formation ability (GFA) and corrosion degradation behavior of Ca-Mg-Zn amorphous alloys in the human body. In this work, we discuss a study on Ca53+x Mg20Zn27-x (x = 0, 2, 4, 6, 8, 10) alloys, focusing on changes in Zn content near eutectic points and their impact on microstructure and biological corrosion behavior. A copper mold spray casting method has been developed to prepare amorphous bar alloys and amorphous crystalline composite bar alloys with a diameter of 3 mm, which has been verified by X-ray diffraction, electrochemical treatment, and immersion tests. The experimental results demonstrated that the Ca3Zn and CaZn2 phases were precipitated in the 3 mm bar material Ca53+x Mg20Zn27-x (x = 0, 2, 4), and Ca53+x Mg20Zn27-x (x = 6, 8, 10) was completely amorphous. The Ca63Mg20Zn17 alloy showed the best glass-forming ability, while the Ca59Mg20Zn21 alloy exhibited superior corrosion resistance. Cytotoxicity experiments showed that Ca-Mg-Zn alloys have good biocompatibility and can be used as biomedical materials.

Grain size dependant high-temperature hot corrosion (HTHC) degradation behavior in Alloy 617 during exposure in Na2SO4 + NaCl + V2O5 salt mixture

In the present investigation, the implication of grain size on the high-temperature hot corrosion (HTHC) response in Alloy 617 is studied. Towards this, specific thermal and thermo-mechanical processing schedules were employed to attain a wide range of grain sizes (7–70 µm), while maintaining other microstructural features like Σ3 n (n ≤ 3) boundary fraction, retained strain, and precipitate fraction nearly at constant. Subsequently, these specimens were exposed to Na 2 SO 4 + NaCl + V 2 O 5 (75 wt% + 20 wt% + 5 wt%) salt mixture at 1273 K for 24 h. Post-corrosion analyses reveal the formation of a highly porous and thick oxide scale on the as-received (AR) specimen (~32 µm), a relatively less porous and non-uniform oxide scale on the very coarse-grained specimen (~70 µm), and a homogeneous and dense Cr-rich scale on the very fine-grained microstructure (~7 µm). Such a protective scale on the very fine-grained specimen, developed due to the enhanced diffusivity of Cr, obstructs the entry of corrodents and thereby minimizes the percolation depth (~60 µm). The percolation depth is relatively higher (~130 µm) in the very coarse-grained specimen due to the development of a porous and non-uniform oxide scale. However, its percolation depth is still lower than the AR specimen (~ 305 µm), because of the reduced grain boundary area available for the diffusion of the corrosive species into the substrate. The AR specimen has exhibited the maximum percolation depth due to the simultaneous presence of fine and coarse grains, leading to the failure of both the aforementioned resistive mechanisms i.e., the accelerated formation of a protective Cr-rich scale and lesser availability of diffusion paths for the ingression of the corrosive species. • Very fine and very coarse-grained microstructures are resistant to HTHC damage. • AR specimen with inhomogeneous grain size distribution underwent maximum damage. • Grain refinement accelerates Cr-oxide formation that blocks entry of corrodants. • Grain coarsening decreases the channels for ingression of corrodants into the alloy. • Inhomogeneous grain size distribution in AR fails to activate resistive mechanisms.

Corrosion behavior of AZ31 magnesium alloys coated with PMMA/HA as biodegradable implants

Magnesium alloys' rapid corrosion rates have limited their use as biodegradable implants. As a result, designing a composite coating to slow the corrosion of the AZ31 magnesium alloy is critical. A spin coating process was used to cover an AZ31 alloy with a polymethylmethacrylate (PMMA)/hydroxyapatite (HA) composite coating. The coating characteristics was estimated using AFM, FESEM contact angle, and antibiofilm formation. In addition, potentiodaynamic polarisation and hydrogen evolution measurements were used to assess the coating's corrosion resistance and degradation behavior. In general, corrosion experiments revealed that specimens coated with one or two layers of PMMA polymer were successful in slowing down the rate of corrosion in Ringer's solution. Adding hydroxyapatite particles to the PMMA polymer also considerably reduces the rate of corrosion. Furthermore, the corrosion resistance of the coating with two layers of coatings is greatly improved.

Corrosion mechanism and degradation behavior of basalt fiber-reinforced composites in sulfuric acid solution

Epoxy resins reinforced by basalt fibers were treated with a sulfuric acid solution for different periods and concentrations. The tensile strength of the composites was examined after the treatment. The fracture surfaces were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The tensile strengths of the sulfuric acid solution-treated samples showed a decreasing trend with treating times and concentrations. However, after 250–500 h of treatment time, the tensile strengths showed an increasing trend. Based on the experimental results, the possible corrosion mechanisms were explored. Sulfuric acid leads to insoluble sulfur oxide formation with high C, Ca and Fe element contents on the fiber surface. With the continuation of sulfuric acid reaction, a thin corrosion shell covers the whole fiber surface. The thickest corrosion shell caused a significant increase in the tensile strength at the breaking of basalt fibers.

Corrosion resistance and degradation behavior of anodized Mg-Gd alloys: A comparative study

Abstract A conventional anodic oxidation process was conducted on two Mg-Gd alloys to study the corrosion resistances and degradation behaviors of their anodized films, and a commercial AZ31 alloy was used for comparison. It was found that both the structures and degradation properties of the anodized films of Mg-Gd alloys were quite different from AZ31 alloy. For Mg-Gd alloys, the anodized films contained more crystalline MgO, Mg2SiO4 and Mg3(PO4)2 with lower porosity and small pore size compared with anodized AZ31 alloy. Although the anodized AZ31 alloy showed slightly higher initial corrosion resistance, its long-term degradation performance was uncompetitive compared with two anodized Mg-Gd alloys. And the scanning electrochemical microscopy (SECM) tests also pointed to more uniform degradation behaviors of anodized Mg-Gd alloys. The better long-term degradation performances of anodized Mg-Gd alloys, especially anodized Mg-1Zn-1Gd alloy, were believed to benefit from their different structures, compositions and corrosion products of anodized films compared with anodized AZ31 alloy.

Corrosion Degradation Behavior of Forged Mg-Zn-Zr/-Y Alloy in Simulated Body Fluid

The corrosion degradation rate of pure magnesium and forged Mg-Zn-Zr/-Y magnesium alloy was compared by static immersion corrosion weight loss experiment and electrochemical corrosion experiment at constant temperature (37±0.5°C) and room temperature (25±1°C) SBF to simulate the corrosion degradation rate in body fluids. The results show that the corrosion resistance of magnesium alloy can be improved by adding Zn, Zr, Y compared with pure magnesium. The results of static immersion corrosion test and electrochemical corrosion test of forged Mg-Zn-Zr-Y show that the corrosion resistance of magnesium alloy can be improved by adding Zn, Zr, Y element. The average corrosion rate of the forged Mg-Zn-Zr-Y alloy was 0.62mm/a by weight loss method after 240 h immersion corrosion in SBF at 37 ± 0.5 °C, and the corrosion resistance of forged Mg-Zn-Zr-Y alloy was better than Mg-Zn-Zr alloy.

Corrosion degradation behavior of PBO fibers under strong inorganic acid

Known as the super fiber of the twenty-first century, poly-p-phenylenebenzobisoxazole (PBO) fibers exhibit outstanding strength and modulus, fire and heat resistance, which are superior to those of poly-p-phenylene terephthalamide fiber. However, the poor resistance of acid corrosion is regarded as a fatal weakness, which restricts its application in complicated chemical environment. In present work, PBO fibers were exposed in strong acid solutions under different conditions, and then, surface morphology was observed by optical microscopy and scanning electron microscopy. Substantial changes in functional groups were investigated by Fourier-transform infrared (FTIR) spectroscopy, as well as changes in crystalline structure using differential scanning calorimetry (DSC) and thermal stability using thermogravimetric analysis (TGA). After treatment by H2SO4 and HNO3 solution, the strength of the fibers declines typically, while the modulus increases. It is attributed to the formation of N–H bonds in the vicinity of 3410.0 cm−1 confirmed by FTIR spectra. Hydrogen bonds, derived from N–H bonds, increase the thermal degradation temperature from 716.4 °C (untreated) to 725.6 °C (treated by H2SO4), shown in TGA curves. HNO3 treatment is more destructive than that of H2SO4. There exist longitudinal corrosion cracks after treatment by HNO3 solution. Furthermore, HNO3 solution penetrates into crystalline region and destroys the ordered crystal structure of PBO fibers demonstrated by DSC results.

Preparation and Degradation Behavior of Composite Bio-Coating on ZK60 Magnesium Alloy Using Combined Micro-Arc Oxidation and Electrophoresis Deposition

In this work, ZK60 magnesium alloy was employed as the substrate for producing micro-arc oxidation (MAO) coating containing Ca and P. Electrophoretic deposition (ED) process was conducted on the micro-arc oxidized sample to prepare a hydroxyapatite (HA) layer on the original coating. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze the phase constituents and microstructures of both MAO and MAO-ED coatings. Corrosion resistance and degradation behavior of the coatings in SBF were investigated by electrochemical tests and simulated body fluid (SBF) immersion tests. The results indicate that a dense HA layer about 5μm in thickness has been successfully prepared on the MAO coating. The porosity of the MAO-ED coating decreases from 5.63% before ED process to 0.81%. The Ca/P ratio of the MAO-ED coating is 1.60, indicating a potential biocompatibility. The MAO-ED coating can induce the deposition of bioactive products from SBF. During 10-day SBF immersion test, the weight gain of MAO-ED sample keeps increasing, indicating that the deposition rate of the induced products is always higher than that of corrosion products before the 10 days of immersion. The deposition of induced products effectively protects the substrate from being corroded so that it ensures the good mechanical properties and biocompatibility during the initial stage of implantation. According to the changes in sample morphologies and the electrochemical measurements in SBF, a relevant degradation model has been suggested and the underlying mechanism for degradation behavior is discussed.

In vitro and in vivo studies on the degradation and biosafety of Mg-Zn-Ca-Y alloy hemostatic clip with the carotid artery of SD rat model.

An Mg-Zn-Ca-Y alloy operative clip was developed to overcome the drawbacks of the Ti clips such as ion dissolution inflammation, interference imaging diagnosis, and the potential harm that permanent retention brings to the patient. The structure optimization design of the hemostatic clip was carried out by the finite element numerical simulation method to realize the matching between the structure design and the material properties. Hot extrusion and wire cutting process was used to prepare the Mg-Zn-Ca-Y alloy operative clip. Corrosion degradation behavior of Mg-Zn-Ca-Y alloy in vitro was investigated using electrochemical noise (EN) and immersion test in Simulated body fluid (SBF). The carotid artery of SD rats was clipped using the Mg-Zn-Ca-Y operative clip to evaluate occlusion safety and the complete corrosion degradation behavior and biocompatibility of Mg-Zn-Ca-Y alloy clip in vivo were investigated using micro-computed tomography, histological analysis, and blood biochemical indicators. It was found that the newly designed Mg-Zn-Ca-Y clip can successfully ligate the carotid artery, and no blood leakage occurred after surgery. After eight months, the Mg-Zn-Ca-Y clip degraded utterly. Histological analysis and various blood biochemical parameters in SD rat serum samples collected at different time periods showed no tissue inflammation around the clips.

Corrosion degradation behavior of Mg–Zn–Zr bone screw in vitro and vivo

In this work, in vitro and in vivo corrosion degradation behavior of bone fixation screws made of Mg-3.0 wt%Zn-0.8 wt%Zr alloy (MZZ) aiming for a bone fixation material was investigated. In vitro immersion tests showed the corrosion type of MZZ screws were mainly pitting corrosion and the corrosion degree of the screw body especially the thread part was more severe in contrast to the screw cap. In vivo x-ray imaging analysis showed the joint connecting screw cap with screw body had fractured in three months following surgery. Micro-CT analysis confirmed the experimental results of the above x-ray analysis. And Up to three months after operation, the residual volume fraction (RVF) of screw body and screw cap was maintained about 35% and 45% respectively. Moreover, compared with the screws implanted in the lateral position of the condyle (hereafter, denoted as the condyle), the volume loss of MZZ screws implanted in the region between the trochanter and the medullary cavity (hereafter, denoted as the trochanter) was higher. Histological evaluation showed new bone tissues were generated on the surface of MZZ screws at one month postoperation. And some granular degradation products distributed in the soft tissue surrounding the MZZ screws. Obvious inflammation reaction to periosteal cells cannot be confirmed indicating the good biocompatibility of MZZ screws. Therefore, MZZ screws are expected to apply to medical installations in bone fixation surgery.

Electrochemical characterization of nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy covered with amorphous nickel

Nanocrystalline hydrogen storage La1.5Mg0.5Ni6.5Co0.5 alloy was obtained by mechanical alloying and heat treatment (850 °C/0.5 h). The A2B7 phase is dominant in so synthesized material. Concentration of AB5 phase is close to 3 at. % and is 2.6 times lower than that in Co-free La1.5Mg0.5Ni7 alloy. The La1.5Mg0.5Ni6.5Co0.5 powder fraction of 20–50 μm was encapsulated with thin (0.48 μm thick), amorphous nickel by magnetron sputtering. The electrochemical charge/discharge multicycling of powder composite electrodes was carried out in view of material potential usefulness as electrode material for Ni/MHx batteries. Partial substitution of Ni by Co in La1.5Mg0.5Ni7 nanocrystalline alloy is prone to increase of electrode discharge capacity (up to 14%) and enhances its activation (strong decrease of Nmax cycle and simultaneous increase of QNmax). On the other hand, Co addition worsens corrosion degradation behavior, but the corrosion resistance can be improved (≈30%) by the application of amorphous nickel coating. Finally, Co modified La1.5Mg0.5Ni7 nanocrystalline alloy reveals 15% greater exchange current density of H2O/H2 system and improved hydrogen diffusivity compared to the reference, nanocrystalline Co-free La1.5Mg0.5Ni7 hydrogen storage material.

Microwave-assisted magnesium phosphate coating on the AZ31 magnesium alloy

Due to the combination of many unique properties, magnesium alloys have been widely recognized as suitable metallic materials for fabricating degradable biomedical implants. However, the extremely high degradation kinetics of magnesium alloys in the physiological environment have hindered their clinical applications. This paper reports for the first time the use of a novel microwave-assisted coating process to deposit magnesium phosphate (MgP) coatings on the Mg alloy AZ31 and improve its in vitro corrosion resistance. Newberyite and trimagnesium phosphate hydrate (TMP) layers with distinct features were fabricated at various processing times and temperatures. Subsequently, the corrosion resistance, degradation behavior, bioactivity and cytocompatibility of the MgP coated AZ31 samples were investigated. The potentiodynamic polarization tests reveal that the corrosion current density of the AZ31 magnesium alloy in simulated body fluid (SBF) is significantly suppressed by the deposited MgP coatings. Additionally, it is seen that MgP coatings remarkably reduced the mass loss of the AZ31 alloy after immersion in SBF for two weeks and promoted precipitation of apatite particles. The high viability of preosteoblast cells cultured with extracts of coated samples indicates that the MgP coatings can improve the cytocompatibility of the AZ31 alloy. These attractive results suggest that MgP coatings, serving as the protective and bioactive layer, can enhance the corrosion resistance and biological response of magnesium alloys.

Atmospheric corrosion of Nylon 6,6 in Mauritius

Plastics are being more and more commonly used for outdoor applications in Mauritius. In this context, the atmospheric corrosion degradation behaviour of nylon 6,6 was observed in the Mauritian atmosphere, having a corrosivity category of C3, according to ISO 9223. The crack width, depth and extent of the cracks formed on the surface were investigated using micrometry and image analysis. The changes in the chemical composition of the nylon 6,6 were investigated using the Fourier Transform Infrared spectroscopy technique. It was observed that the nylon 6,6 surface showed a progressive discolouration and a sudden increase in the size of the cracks after around 2 years of exposure. The degree of crack formation in terms of crack width, the depth of degradation and the microhardness of the surface were evaluated and all showed significant degradation only after about 2 years of exposure. Degradation has penetrated the test material within 750 µm from the surface in 4.5 years of exposure. Using the FTIR technique, evidence of chain scission occurring among the polymer chains was observed. Keywords: nylon, atmospheric corrosion, weathering, cracks, FTIR.

Fabrication and Investigation of Thermal and Wear Properties of Zinc Novel Coatings Reinforced with Nano-Al2O3 and Cr2O3 Particles

Abstract The study of the thermal, wear and corrosion properties of developed nanocomposite coatings of Zn-Al2O3 and Zn-Cr2O3 was carried out. The coatings were produced by electrodeposition technique from chloride acidic bath. Laboratory tube furnace was used for the thermal analysis. The wear test was performed using CETR tribo-tester dry reciprocating tester. The hardness properties were investigated using diamond base Dura microhardness tester. Scanning electron microscope (SEM) affixed with energy dispersive spectrometry was used to study the morphological characteristics, before and after wear deformation. The corrosion degradation behavior was observed using linear polarization technique in 3.5% NaCl. In all the interaction, the effects of the incorporated Al2O3 and Cr2O3nanoparticulates on zinc rich coatings were found to have an excellent influence on the wear, corrosion and thermal stability properties. The fabrication and properties exhibited by the alloys were therefore found to be satisfactory and shows good predictability and applicability.