Surface Properties and Corrosion Behavior of Co–Cr Alloy Fabricated with Selective Laser Melting Technique

We sought to study the corrosion behavior and surface properties of a commercial cobalt–chromium (Co–Cr) alloy which was fabricated with selective laser melting (SLM) technique. For this purpose, specimens were fabricated using different techniques, such as SLM system and casting methods. Surface hardness testing, microstructure observation, surface analysis using X-ray photoelectron spectroscopy (XPS) and electrochemical corrosion test were carried out to evaluate the corrosion properties and surface properties of the specimens. We found that microstructure of SLM specimens was more homogeneous than that of cast specimens. The mean surface hardness values of SLM and cast specimens were 458.3 and 384.8, respectively; SLM specimens showed higher values than cast ones in hardness. Both specimens exhibited no differences in their electrochemical corrosion properties in the artificial saliva through potentiodynamic curves and EIS, and no significant difference via XPS. Therefore, we concluded that within the scope of this study, SLM-fabricated restorations revealed good surface properties, such as proper hardness, homogeneous microstructure, and also showed sufficient corrosion resistance which could meet the needs of dental clinics.     

In Vivo Corrosion Resistance of Ca-P Coating on AZ60 Magnesium Alloy

Magnesium-based alloys are frequently reported as potential biodegradable orthopedic implant materials. Controlling the degradation rate and mechanical integrity of magnesium alloys in the physiological environment is the key to their applications. In this study, calcium phosphate (Ca-P) coating was prepared on AZ60 magnesium alloy using phosphating technology. AZ60 samples were immersed in a phosphating solution at 37 ± 2 °C for 30 min, and the solution pH was adjusted to 2.6 to 2.8 by adding NaOH solution. Then, the samples were dried in an attemperator at 60 °C. The degradation behavior was studied in vivo using Ca-P coated and uncoated magnesium alloys. Samples of these two different materials were implanted into rabbit femora, and the corrosion resistances were evaluated after 1, 2, and 3 months. The Ca-P coated samples corroded slower than the uncoated samples with prolonged time. Significant differences (p < 0.05) in mass losses and corrosion rates between uncoated samples and Ca-P coated samples were observed by micro-computed tomography. The results indicate that the Ca-P coating could slow down the degradation of magnesium alloy in vivo.     

Three-Dimensional Surface Parameters and Multi-Fractal Spectrum of Corroded Steel

To study multi-fractal behavior of corroded steel surface, a range of fractal surfaces of corroded surfaces of Q235 steel were constructed by using the Weierstrass-Mandelbrot method under a high total accuracy. The multi-fractal spectrum of fractal surface of corroded steel was calculated to study the multi-fractal characteristics of the W-M corroded surface. Based on the shape feature of the multi-fractal spectrum of corroded steel surface, the least squares method was applied to the quadratic fitting of the multi-fractal spectrum of corroded surface. The fitting function was quantitatively analyzed to simplify the calculation of multi-fractal characteristics of corroded surface. The results showed that the multi-fractal spectrum of corroded surface was fitted well with the method using quadratic curve fitting, and the evolution rules and trends were forecasted accurately. The findings can be applied to research on the mechanisms of corroded surface formation of steel and provide a new approach for the establishment of corrosion damage constitutive models of steel.     

Comparing monofractal and multifractal analysis of corrosion damage evolution in reinforcing bars

Based on fractal theory and damage mechanics, the aim of this paper is to describe the monofractal and multifractal characteristics of corrosion morphology and develop a new approach to characterize the nonuniform corrosion degree of reinforcing bars. The relationship between fractal parameters and tensile strength of reinforcing bars are discussed. The results showed that corrosion mass loss ratio of a bar cannot accurately reflect the damage degree of the bar. The corrosion morphology of reinforcing bars exhibits both monofractal and multifractal features. The fractal dimension and the tensile strength of corroded steel bars exhibit a power function relationship, while the width of multifractal spectrum and tensile strength of corroded steel bars exhibit a linear relationship. By comparison, using width of multifractal spectrum as multifractal damage variable not only reflects the distribution of corrosion damage in reinforcing bars, but also reveals the influence of nonuniform corrosion on the mechanical properties of reinforcing bars. The present research provides a new approach for the establishment of corrosion damage constitutive models of reinforcing bars.     

A quantitative study on magnesium alloy stent biodegradation

Insufficient scaffolding time in the process of rapid corrosion is the main problem of magnesium alloy stent (MAS). Finite element method had been used to investigate corrosion of MAS. However, related researches mostly described all elements suffered corrosion in view of one-dimensional corrosion. Multi-dimensional corrosions significantly influence mechanical integrity of MAS structures such as edges and corners. In this study, the effects of multi-dimensional corrosion were studied using experiment quantitatively, then a phenomenological corrosion model was developed to consider these effects. We implemented immersion test with magnesium alloy (AZ31B) cubes, which had different numbers of exposed surfaces to analyze differences of dimension. It was indicated that corrosion rates of cubes are almost proportional to their exposed-surface numbers, especially when pitting corrosions are not marked. The cubes also represented the hexahedron elements in simulation. In conclusion, corrosion rate of every element accelerates by increasing corrosion-surface numbers in multi-dimensional corrosion. The damage ratios among elements with the same size are proportional to the ratios of corrosion-surface numbers under uniform corrosion. The finite element simulation using proposed model provided more details of changes of morphology and mechanics in scaffolding time by removing 25.7% of elements of MAS. The proposed corrosion model reflected the effects of multi-dimension on corrosions. It would be used to predict degradation process of MAS quantitatively.     

Diverse bacterial groups are associated with corrosive lesions at a Granite Mountain Record Vault (GMRV)

Aims: This study applied culture‐dependent and molecular approaches to examine the bacterial communities at corrosion sites at Granite Mountain Record Vault (GMRV) in Utah, USA, with the goal of understanding the role of microbes in these unexpected corrosion events. Methods and Results: Samples from corroded steel chunks, rock particles and waters around the corrosion pits were collected for bacterial isolation and molecular analyses. Bacteria cultivated from these sites were identified as members of Alphaproteobacteria, Gammaproteobacteria, Firmicutes and Actinobacteria. In addition, molecular genetic characterization of the communities via nested‐polymerase chain reaction‐denaturing gradient gel electrophoresis (DGGE) indicated the presence of a broad spectrum of bacterial groups, including Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. However, neither cultivation nor molecular approaches identified sulfate‐reducing bacteria (SRB), the bacteria commonly implicated as causative organisms were found associated with corrosive lesions in a process referred to as microbially influenced corrosion (MIC). The high diversity of bacterial groups at the corrosion sites in comparison with that seen in the source waters suggested to us a role for the microbes in corrosion, perhaps being an expression of a redox‐active group of microbes transferring electrons, harvesting energy and producing biomass. Conclusions: The corrosion sites contained highly diverse microbial communities, consistent with the involvement of microbial activities along the redox gradient at corrosion interface. We hypothesize an electron transport model for MIC, involving diverse bacterial groups such as acid‐producing bacteria (APB), SRB, sulfur‐oxidizing bacteria (SOB), metal‐reducing bacteria (MRB) and metal‐oxidizing bacteria (MOB). Significance and Impact of the Study: The characterization of micro‐organisms that influence metal‐concrete corrosion at GMRV has significant implications for corrosion control in high‐altitude freshwater environments. MIC provides a potential opportunity to further our understandings of extracellular electron transfer and interspecies communications.     

Microbiological corrosion of a Sn base alloy

Babbitt alloy is generally used as an antifriction coating of bearings in plate mills. Samples of corroded alloy which were analyzed showed a localized attack which penetrated the whole thickness in small areas.The bacterium Pseudomonas maltophilia was isolated from the rolling solution and from the lubricant oil in contact with the coating of the bearings. The damage which occurred in service was electrochemically reproduced. Cultures of the bacterium in a nutrient medium were used as electrolyte in the presence of the different substrates.By SEM and EDAX analysis it was shown that the attack nucleates and propagates selectively in the Sn-Sn matrix, while the Cu rich phase remains unaffected.The oligodynamic action of the Sn²⁺ ion on the growth of the bacterium was related to the nutritional requirements of the bacterium and to the selectivity of the attack on the alloy.     

Long-term corrosion and leaching of depleted uranium (DU) in soil

Corrosion and leaching of depleted uranium (DU) was investigated for 3 years using six DU munitions (145–264 g DU) each buried in a column with a soil core of about 3.3 kg dry soil mass. The columns were installed in an air-conditioned laboratory. Each week they were irrigated and ²³⁸U was determined in the effluents by inductively coupled plasma mass spectrometry. In addition, ²³⁵U was measured occasionally to assure that the ²³⁸U was predominantly from the DU munition. On average, 14.5 g corresponding to 7.9% of the initial DU mass was corroded after 3 years, indicating an increased corrosion as compared to the first year of observation. The leaching rates increased much stronger than the corrosion rates by factors of more than 100, resulting in a mean total amount of leached ²³⁸U of 13 mg as compared to 0.03 mg after the first year. Uranium species identified in the seepage water by time-resolved laser-induced fluorescence spectroscopy were mainly hydroxo and carbonate compounds, while those in the corroded material were phosphate compounds. It is concluded that the dramatic increase of the leaching and its large temporal variability do not allow any extrapolation for the future. However, the high ²³⁸U concentrations observed in the seepage water highlight the need for further investigations on the transport of ²³⁸U through soil, in particular with regard to the potential future ²³⁸U contamination of groundwater in areas affected by DU weapons.     

Molecular analysis of microbial diversity in corrosion samples from energy transmission towers

Microbial diversity in corrosion samples from energy transmission towers was investigated using molecular methods. Ribosomal DNA fragments were used to assemble gene libraries. Sequence analysis indicated 10 bacterial genera within the phyla Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. In the two libraries generated from corroded screw-derived samples, the genus Acinetobacter was the most abundant. Acinetobacter and Clostridium spp. dominated, with similar percentages, in the libraries derived from corrosion scrapings. Fungal clones were affiliated with 14 genera belonging to the phyla Ascomycota and Basidiomycota; of these, Capnobotryella and Fellomyces were the most abundant fungi observed. Several of the microorganisms had not previously been associated with biofilms and corrosion, reinforcing the need to use molecular techniques to achieve a more comprehensive assessment of microbial diversity in environmental samples.     

Corrosion of Iron by Iodide-Oxidizing Bacteria Isolated from Brine in an Iodine Production Facility

Elemental iodine is produced in Japan from underground brine (fossil salt water). Carbon steel pipes in an iodine production facility at Chiba, Japan, for brine conveyance were found to corrode more rapidly than those in other facilities. The corroding activity of iodide-containing brine from the facility was examined by immersing carbon steel coupons in “native” and “filter-sterilized” brine samples. The dissolution of iron from the coupons immersed in native brine was threefold to fourfold higher than that in the filter-sterilized brine. Denaturing gradient gel electrophoresis analyses revealed that iodide-oxidizing bacteria (IOBs) were predominant in the coupon-containing native brine samples. IOBs were also detected in a corrosion deposit on the inner surface of a corroded pipe. These results strongly suggested the involvement of IOBs in the corrosion of the carbon steel pipes. Of the six bacterial strains isolated from a brine sample, four were capable of oxidizing iodide ion (I^?) into molecular iodine (I₂), and these strains were further phylogenetically classified into two groups. The iron-corroding activity of each of the isolates from the two groups was examined. Both strains corroded iron in the presence of potassium iodide in a concentration-dependent manner. This is the first report providing direct evidence that IOBs are involved in iron corrosion. Further, possible mechanisms by which IOBs corrode iron are discussed.     

Cytologic diagnosis of schistosomiasis in routine urinary specimens. A case report

A voided urine specimen from a 29-year-old male living in New York was sent for cytologic study, which revealed five schistosome ova, two with terminal spines, and one free miracidium in a cytocentrifuge specimen. The patient, who had been in West Africa three years earlier, underwent cystoscopy, with the finding of bladder mucosal ulcerations. Subsequent cytologic specimens, bladder biopsy and wet-mount preparations established a diagnosis of Schistosoma haematobium infection, which was treated, apparently successfully, with Metrifonate. The case is presented to focus attention on the cytologic diagnosis of S. haematobium in routine urinary specimens since the opportunity to make such a diagnosis is increasing in the continental United States as more Americans visit areas of endemic infestation and more residents of those areas immigrate to this country.     

Metal corrosion by aerobic bacteria isolated from stimulated corrosion systems: Effects of additional nitrate sources

Many microorganisms are reported to influence the corrosive behaviour of mild steel and stainless steel in different habitats. In this study, 40 bacterial strains were isolated from corroded mild steel and stainless steel coupons in the nitrate supplemented environments. The corrosion abilities of the isolates against the mild steel and stainless steel coupons were tested with or without additional nitrate sources. The presence of bacterial isolates alone stimulated the corrosion of mild steel coupons. Most of the bio-corrosion processes of mild steel coupons were mitigated by adding nitrate supplement with bacterial isolates. The effects of bacterial isolates and additional nitrogen sources on corrosion of stainless steels were varied. Not all bacterial isolates stimulated the corrosion on stainless steel during the study period. Unlike the effects on mild steel coupons, additional NaNO₃ might stimulate, retard the corrosion rate by the bacterial isolates or have limited effects. Similar results were obtained when NH₄NO₃ was used. Phylogenetic analysis demonstrated that all isolates were closely related. The majority of the bacterial isolates from corroded metal coupons were identified as Bacillus species. Others were identified as Pseudomonas sp., Marinobacter sp., and Halomonas species. The results prove that the isolated aerobic microorganisms do play a role in the corrosion process of stainless and mild steel. Adding additional nitrate sources might be a tool to mitigate corrosion of mild steel which was stimulated by the presence of bacteria. However, to prevent the corrosion of stainless steels, it might need a trial and errors approach in each case.     

Importance of Hydrogen Sulfide, Thiosulfate, and Methylmercaptan for Growth of Thiobacilli during Simulation of Concrete Corrosion

Biogenic sulfuric acid corrosion of concrete surfaces caused by thiobacilli was reproduced in simulation experiments. At 9 months after inoculation with thiobacilli, concrete blocks were severely corroded. The sulfur compounds hydrogen sulfide, thiosulfate, and methylmercaptan were tested for their corrosive action. With hydrogen sulfide, severe corrosion was noted. The flora was dominated by Thiobacillus thiooxidans. Thiosulfate led to medium corrosion and a dominance of Thiobacillus neapolitanus and Thiobacillus intermedius. Methylmercaptan resulted in negligible corrosion. A flora of heterotrophs and fungi grew on the blocks. This result implies that methylmercaptan cannot be degraded by thiobacilli.     

可降解镁合金材料在医学领域的研究和应用现状

作为最有潜力的第三代生物材料,新型可降解镁合金具有良好的生物相容性,与人体骨骼相近的力学性能,可避免二次手 术带来的不良影响等诸多优点,已成为当今研究的热点之一。然而镁合金在医学中的应用也受到其降解速度过快和随之引起机 械完整性丧失的影响。随着对镁合金研究的深入,在控制降解方面的研究已有显著成效。目前关于镁合金的研究主要集中在改善 其生物相容性、耐腐蚀性和机械性能等方面。本文将从镁合金降解产物对机体的影响,降解速度的控制和在医学中应用对其在当 今科研领域的研究进行综述。     

Surface Modification of Biodegradable Mg-4Zn Alloy Using PMEDM: An Experimental Investigation,Optimization and Corrosion Analysis

ObjectivesMagnesium alloys are the potential candidate for metallic implants due to their excellent mechanical characteristics, biodegradable nature, and properties similar to human bone. However, a high degradation rate is primary obstacle in implementing these alloys as biodegradable orthopedic implants. Powder-mixed electric discharge machining (PMEDM) is an emerging method of surface modification of metallic alloys that can be implemented to improve the corrosion resistance of Mg alloys. Therefore, PMEDM using zirconium (Zr) and manganese (Mn) powder particles has been proposed to modify the surface characteristics of Mg-4Zn alloy.Materials and MethodsIn the present work, Zr and Mn powders have been used in varying concentrations during PMEDM of Mg-4Zn alloy. Experiments were conducted as per mixed design L18 orthogonal array (OA). Taguchi and Grey Relational Analysis (GRA) have been used to optimize the process parameters. Analysis of response characteristics, namely material removal rate (MRR), surface roughness (SR), and thickness of the alloyed layer (TAL), has been carried out at different values of input variables (like powder additives (P_a), powder concentration (C_p), peak current (I_p), pulse on time (T_on) and duty cycle (DC)). The corrosion analysis was carried out by immersing the specimen (machined at an optimized setting) in simulated body fluid (SBF).ResultsIt is observed from the analysis that C_p, I_p, and T_on play a pivotal role in evaluating response characteristics. The favorable setting suggested by the gray approach is P_a: Zr; C_p: 2 g/l; I_p: 4A; T_on: 50 μs; DC: 80%, while responses at this setting are confirmed by confirmation experiments with MRR: 32.14 mm³/min; SR: 5.578 μm and TAL: 8.28 μm. The immersion test signifies that the corrosion rate (CR) of PMEDMed sample (3.20 mm/year) is 40.74% lesser than the corrosion rate of polished sample (5.40 mm/year).ConclusionZr powder shows better performance in terms of higher MRR, lower SR and higher TAL as compared to Mn powder during the PMEDM process. The corroded surface of polished sample exhibited larger size micro pits and cracks than the machined sample, which concluded that surface modification of MZ-4Zn alloy via PMEDM is a powerful tool to enhance its corrosion resistance.     

Marine ‘copper-tolerant’ sulphate reducing bacteria and their effects on 90/10 copper-nickel (CA 706)

Copper and nickel ‘tolerant’ marine sulphate reducing bacteria (SRB) were isolated from 90/10 copper-nickel and shown to attach and grow on the alloy. Their effects upon the corrosion resistance of the alloy, using energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and electrochemical polarisation analyses, were shown to be identical to those produced by synthetic addition of sulphide to test solutions reported by others. Thus attached SRB may have a role in 90/10 copper-nickel corrosion as long as they also possess transient oxygen tolerance.     

Molecular analysis of microbial diversity in corrosion samples from energy transmission towers

Microbial diversity in corrosion samples from energy transmission towers was investigated using molecular methods. Ribosomal DNA fragments were used to assemble gene libraries. Sequence analysis indicated 10 bacterial genera within the phyla Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. In the two libraries generated from corroded screw-derived samples, the genus Acinetobacter was the most abundant. Acinetobacter and Clostridium spp. dominated, with similar percentages, in the libraries derived from corrosion scrapings. Fungal clones were affiliated with 14 genera belonging to the phyla Ascomycota and Basidiomycota; of these, Capnobotryella and Fellomyces were the most abundant fungi observed. Several of the microorganisms had not previously been associated with biofilms and corrosion, reinforcing the need to use molecular techniques to achieve a more comprehensive assessment of microbial diversity in environmental samples.     

一件出土饱水木漆器文物中可培养细菌的鉴定及对木材的腐蚀作用

【背景】饱水木质文物易受到微生物侵害,目前国外围绕饱水木质文物微生物病害已开展多方面研究,并取得阶段性进展,而国内在饱水木质文物微生物学技术方面的报道比较少。【目的】研究保藏水环境中出土饱水木漆器F446及水中细菌的种类,以及对木材的腐蚀作用。【方法】采用16S rRNA基因序列分析方法及生理生化试验,对饱水木漆器F446及水环境中细菌进行鉴定,并选取典型菌按5×10~8个/瓶菌量接种马尾松心材(悬于无菌自来水中),37°C培养120 d,测试木材的损失率。【结果】从F446文物和水样中分离的53株细菌中,21株被鉴定为芽孢杆菌属(Bacillus),为优势菌属,其中蜡样芽孢杆菌(B.cereus)19株,病研所芽孢杆菌(B.idriensis)和苏云金芽孢杆菌(B.thuringiensis)各1株;11株菌被鉴定为短杆菌属(Brevibacterium),此外还有4株短波单孢菌属(Brevundimonas),5株粪产碱杆菌(Alcaligenes faecalis),5株Altererythrobacter,2株水氏黄杆菌(Flavobacterium mizutaii);另外,还有解糖假苍白杆菌(Pseudochrobactrum saccharolyticum)、梭型芽孢杆菌(Lysinibacillus fusiformis)、Leucobacter aridicollis、Ochrobactrum pseudogrignonense、类芽孢杆菌属(Paenibacillus)菌株各1株。菌株A5、A6分别为类芽孢杆菌(Paenibacillus)和Altererythrobacter属中的疑似新种。从典型菌中选取15株菌回接木材进行腐蚀试验,结果显示,9株细菌与对照组比较存在极显著差异,说明这些菌对马尾松木材有一定的腐蚀作用,但是腐蚀率非常低,最高仅1.38%,表明这些细菌对试验木材马尾松腐蚀并不严重。【结论】F446木漆器文物样品中优势菌属为芽孢杆菌属(Bacillus),水样中优势菌属依次为短杆菌属(Brevibacterium)、短波单孢菌属(Brevundimonas)和Altererythrobacter。从F446木漆器文物和水样中分离出的细菌对木材的降解非常缓慢,短期内腐蚀作用有限。     

Spark plasma sintering synthesis of porous nanocrystalline titanium alloys for biomedical applications

The reason for the extended use of titanium and its alloys as implant biomaterials stems from their lower elastic modulus, their superior biocompatibility and improved corrosion resistance compared to the more conventional stainless steel and cobalt-based alloys [Niinomi, M., Hattori, T., Niwa, S., 2004. Material characteristics and biocompatibility of low rigidity titanium alloys for biomedical applications. In: Jaszemski, M.J., Trantolo, D.J., Lewandrowski, K.U., Hasirci, V., Altobelli, D.E., Wise, D.L. (Eds.), Biomaterials in Orthopedics. Marcel Dekker Inc., New York, pp. 41-62]. Nanostructured titanium-based biomaterials with tailored porosity are important for cell-adhesion, viability, differentiation and growth. Newer technologies like foaming or low-density core processing were recently used for the surface modification of titanium alloy implant bodies to stimulate bone in-growth and improve osseointegration and cell-adhesion, which in turn play a key role in the acceptance of the implants. We here report preliminary results concerning the synthesis of mesoporous titanium alloy bodies by spark plasma sintering. Nanocrystalline cp Ti, Ti-6Al-4V, Ti-Al-V-Cr and Ti-Mn-V-Cr-Al alloy powders were prepared by high-energy wet-milling and sintered to either full-density (cp Ti, Ti-Al-V) or uniform porous (Ti-Al-V-Cr, Ti-Mn-V-Cr-Al) bulk specimens by field-assisted spark plasma sintering (FAST/SPS). Cellular interactions with the porous titanium alloy surfaces were tested with osteoblast-like human MG-63 cells. Cell morphology was investigated by scanning electron microscopy (SEM). The SEM analysis results were correlated with the alloy chemistry and the topographic features of the surface, namely porosity and roughness.