Effect of Host Media on Microbial Influenced Corrosion due to Desulfotomaculum nigrificans

This article reports about the tests carried to investigate microbial-induced corrosion on stainless steels due to sulfate-reducing bacteria sp. Desulfotomaculum nigrificans in different host media. Stainless steel 304L, 316L, and 2205 were selected for the test. Modified Baar’s media (BM), sodium chloride solution, and artificial sea water (SW) were used as test solutions in anaerobic conditions. Electrochemical polarization and immersion test were performed to estimate the extent of corrosion rate and pitting on stainless steels. SEM/EDS were used to study the details inside/outside pits formed on the corroded samples. Biofilm formed on corroded coupons was analyzed for its components by UV/Visible spectroscopy. Corrosion attack on the test samples was observed maximum in case of exposure to SW followed by NaCl solution, both having sulfide and chloride whereas stainless steel exposed to BM, having sulfide, showed minimum attack. Tendency of extracellular polymeric substances to bind metal ions is observed to be responsible for governing the extent of corrosion attack.     

The Influence of the Desulfovibrio desulfuricans 14 ATCC 27774 on the corrosion of mild steel

The involvement of sulphate‐reducing bacteria (SRB) in microbially influenced corrosion (MIC) of steel and the serious implications associated with their presence in industrial environments have long been known and extensively described. Desulfovibrio desulfuricans ATCC 27774 is an interesting metabolic case of SRB, as it can use both sulphate and nitrate as respiratory substrates during lactate oxidation. This strain has been extensively studied from both a biochemical and structural point of view but, so far, restricted information is available concerning its role in MIC. This work describes a comparative study of the corrosive aggressivity of ATCC 27774 strain towards mild steel when grown either in lactate/sulphate or lactate/nitrate media. The carbon source and electron acceptor's consumption rates were analysed and the metabolic features were correlated with weight loss measurements and SEM observations.     

Biocorrosion and cytocompatibility assessment of NiTi shape memory alloys

Ti-based alloys are characterised by an excellent corrosion resistance, high mechanical performances, an increased biocompatibility, and in particular by the deforming force of NiTi. Five alloys were examined by electrochemical assays and cell culture tests with different cell types. All tests show the high biological and electrochemical performances of Ti6Al4V and NiTi, and in particular a significant influence of living cells on corrosion.     

磷酸钙表面改性镁合金的生物腐蚀性能及细胞相容性(英文)

在镁合金表面制备磷酸钙涂层,利用X射线衍射仪确定涂层的相组成。用扫描电镜观察涂层的微观形貌。结果表明,涂层由板条状的CaHPO4·2H2O晶体组成。采用电化学测试和浸泡实验研究磷酸钙改性镁合金的生物腐蚀性能,并与未改性合金进行对比。通过观察L929细胞在材料表面的粘附生长状况来评价材料的生物相容性。电化学测试结果表明,磷酸钙改性镁合金比未改性合金显示出更好的耐腐蚀性能。浸泡实验表明,磷酸钙涂层可以减缓合金的腐蚀,且在浸泡过程中磷酸钙涂层发生了向羟基磷灰石(HA)的转变。与未改性合金相比,L929细胞在磷酸钙改性镁合金表面显示出良好的粘附、生长和分化特征,表明磷酸钙改性能明显提高基体合金的细胞相容性。     

Fouling and Biocorrosion of a High-Alloy Steel in the Golden Horn Bay

The effect of polluted sea waters of the Golden Horn Bay on the fouling and corrosion of a high-alloyed X18H10T type steel are continued to be investigated. It is shown that the corrosivity of the polluted marine environment increases with the concentration of dissolved oxygen, while that of the control one does with its growing biota determining the biomass and intensity of the metal fouling.     

Effect of Alloyed Mo on Mechanical Properties,Biocorrosion and Cytocompatibility of As-Cast Mg-Zn-Y-Mn Alloys

The influences of Mo contents on mechanical properties,biocorrosion and cytocompatibility of as-cast Mg-6Zn-8.16Y-2.02Mn-xMo(x=0.0,0.1,0.3,0.5,0.7 wt%) alloys were firstly investigated.Appropriate amount of Mo was conducive to grain refinement and the formation of long-period stacking ordered structure with continuous distribution,which was advantageous to mechanical properties and corrosion resistance.Mg-6Zn-8.16Y-2.02Mn-0.3Mo exhibited the ultimate tensile strength of 265.0 MPa,elongation of 13.5% and the lowest weight loss rate in Hank's solution.Moreover,the cell toxicity cultured in 25% extract was evaluated and the alloy with 0.3 wt% Mo exhibited the best cytocompatibility.Thus,the alloy was expected to become a novel biodegradable implant material.     

Biocorrosion of Oil and Gas Field Equipment and Chemical Methods for Its Suppression. I

Main groups of corrosive microorganisms are considered. The parameters of the medium that intensify biocorrosion and the conditions for the formation of biofilms are described. The mechanisms of biocorrosion induced by the main groups of unicellular microorganisms are proposed, and the characteristic types of biodamage, specified.__________Translated from Zashchita Metallov, Vol. 41, No. 4, 2005, pp. 417–426.Original Russian Text Copyright © 2005 by Moiseeva, Kondrova.     

硫酸盐还原菌对低碳钢的腐蚀

本文用失重法测定半连续、不连续培养的硫酸盐还原菌对低碳钢的腐蚀速度,采用线性极化技术测定活性生长的硫酸盐还原菌中低碳钢的线性极化阻力(同时测定自腐蚀电位、菌数、硫化物浓度)随时间的变化,并测量不同电位变化区间的阴阳极恒电位极化曲线。结果表明:在一定Fe2 浓度的硫酸盐还原菌培养基中,硫酸盐还原菌对钢的腐蚀速度与菌的生长时期有密切关系。在活性生长的硫酸盐还原菌系统中一直发生强烈的阴极去极化腐蚀。     

Polarisation of Mild Steel in the Presence of Hydrogen Bacteria and Methane Bacteria

Abstract

The cathodic polarisation behaviour of mild-steel electrodes in a culture of hydrogen bacteria and in methane fermentations has been studied. Negligible cathodic depolarisation was observed and it was concluded that these two groups of bacteria do not participaee significantly in anaerobic microbial corrosion processes.     

Investigation of computer hardware failure due to corrosion

Abstract

Failure analysis was conducted on two failed electronic cardsfrom the Computer Center of the Kuwait Institute for Scientific Research. The results of the elemental analysis indicated that the corrosion product film found on contact pins and soldered through holes was composed of copper and sulphur compounds. Chemical analysis of the air in the computer room indicated a high level of nitrogen oxide (up to 300 ppb), whereas other gases such as H²S and SO² were below the detectahle limits (100 and 200 ppb respectively) of the analytical technique used. It was concluded that the initial high relative humidity ( ～ 75%) had synergised with the strongly oxidising nitrogen oxide and H²S and/or SO² to bring about the corrosion of copper substrate in ‘bare spots’ or gaps in the soldered contacts, causing card failure. Other factors, such as galvanic coupling of the copper substrate with nickel, silver, and gold plates, and the relatively high local temperature, may have accelerated the corrosion process. A decrease in the relative humidity to the optimum value of 45% did not obviate card failure. It was concluded that efficient air filters should be utilised in the computer environment, as electronic equipment can be damaged by levels of pollutant gases 10 times lower than those cited for human safety requirements.     

Toughening of conducting cracks due to domain switching

Recent investigations [Heyer et al., Acta mater. 46 (1998) 6615] of conducting cracks under combined electrical and mechanical loading in piezoelectric ceramics revealed that the fracture load (K_I) changes with applied electric field (K_E). The experimental observations contradict theoretical predictions based on linear piezoelectricity and strip-saturation models. In this paper, interaction between a semi-infinite conducting crack and switching induced strains and polarizations is studied to examine the above discrepancy. New fundamental solutions for the electroelastic field intensity factors induced by transformation strains and polarizations are derived and used to develop a model for variation of fracture toughness due to domain switching. A work energy based criterion for domain switching and a Reuss-type approximation for poly-domain piezoelectrics reported previously are used in the modeling. The influence of electromechanical loading and poling direction on the switching-induced stress intensity factors (toughness variation) is studied for PZT-5H. Under combined electrical and mechanical loading, a positive electric field is found to increase apparent fracture toughness of a crack parallel to the poling direction, while a negative one tends to reduce it. This prediction is consistent with experimental observations.     

Evolution of reinforcement corrosion due to climatic variations

Concrete moisture is the most significant parameter with respect to its durability, however the data on moisture content in real‐size structures are scarce in contrast to the numerous literature published on laboratory experiments. The majority of laboratory tests have been performed in chambers with controlled hydrothermal regime, in general to enable the concrete to reach equilibrium and steady‐state conditions. However, real weather induces permanent non‐steady state situations due to the evolution of temperature and climatic events as snowing or raining. Present paper discusses the effect of climatic events on the hydrothermal performance of concrete and their influence on reinforcement corrosion process. Concerning the moisture level, the degree of saturation, S_W, and not the internal relative humidity has been identified to be the controlling parameter of the corrosion process. The psychometric chart and the S_W‐RH plots are very suitable to study the hydrothermal behaviour. With respect to the corrosion parameters, corrosion potential, resistivity and corrosion rates, they are very influenced by temperature in a complex manner. The temperature is the main factor influencing the degree of saturation in sheltered conditions while rain and snow are so, in unsheltered ones. In opposition, however, what can be expected, climates with higher temperatures are less aggressive than colder ones, except when rain periods are produced during the hotter periods.     

Study of the electrochemical behaviour of 304 stainless steel in postgate medium in the presence and absence of desulfovibrio desulfuricans

A comparative study has been undertaken on the behaviour of AISI 304 steel in Postgate medium with and without the presence of Desulfovibrio desulfuricans subspecies desulfuricans bacteria (strain DSM 642). Electrochemical studies were carried out with open circuit potential measurements, linear polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscopy (SEM). In Postgate medium without bacteria, and as expected in stainless steels, the formation is observed of a protective surface passive film on the AISI 304 steel. On measuring the corrosion potentials (E_corr), it is noted that the potential tends to rise with the immersion time, and in the impedance graphs an increase is observed in the charge transfer resistance and a higher phase angle with respect to the other systems tested. However, in Postgate medium with Desulfovibrio desulfuricans (strain DSM 642), the tendency of the corrosion potentials (E_corr) is not uniform, though the recorded values are less noble than those for the medium without bacteria. A variation is observed in the properties of the layer of corrosion products in the presence of bacteria as the immersion time advances (due to the effects caused by the formation of corrosion products which gives rise to changes in the corrosion speed).     

铁和铁合金的塑性变形与磁化

结晶材料通过塑性变形会发生磁物理量的变化,位错周围的磁矩变化会影响到塑性变形磁性体的磁化过程。研究了矫顽力、渐近饱和区域的磁化率与位错组织的相关关系。纯铁和Ａ533Ｂ钢的变形应力与矫顽力有着一定的相关性,矫顽力随着变形量的增加而增大形成一条曲线。Ａ533Ｂ钢...     

Corrosion of steels due to the action of microorganisms

The susceptibility of variously alloyed structural steels to microbiological corrosion in media enriched with hydrogen sulfide and favorable for reproduction of sulfate-reducing bacteria is studied. It is shown that stainless steels 05Kh17N4DB and especially nitrogen-alloyed steel 05Kh13A possess a higher anti-adhesive capacity with respect to corrosion-active microorganisms and resistance to microbe fouling and formation of corrosion-active biofilms than the conventional structural steel 38KhGM. It is assumed that the action of nitrogen can be connected with formation of biocide substances.     

Damage of stainless steel bars due to atmospheric corrosion

In addition to constructional requirements in civil engineering stainless steels often have to fulfil high visual demands. Unexpected impairments of the visual appearance of stainless steels under low corrosive conditions are a widespread problem today. Frequently it is supposed that this is caused by changes in the alloy composition, worse environmental conditions or improper handling. Within a research project the systematic investigation of several cases of damaged stainless steel bars has shown that the reasons are based on well‐known material defects like chemical inhomogeneities (e.g. precipitations or local carburization) or geometrical defects (e.g. undercuts, rolling defects or shell formation). Thus, the failures could be clearly identified as production failures of the respective semi‐finished products.     

Analysis of pits induced stresses due to metal corrosion

The corrosion damage due to pitting is commonly observed in a wide range of aluminum alloys and structural steels that are being used for aerospace and naval structural applications. In order to predict the nucleation of cracks resulting from nucleation and growth of pits, there is a need to obtain the stress environment around pits. The objective of this study is to investigate the pits induced stresses responsible for possible crack nucleation using the photomicrographs of corroded aluminum 5059 alloy samples using stress analysis. An analysis procedure is developed using CAD and finite element analysis to predict stresses due to single and/or multiple corroded pits. The analysis was performed to investigate stress distributions on the corrosion surface as a function of sensitization time. The results obtained indicate that as the duration of the specimen sensitization increased from 50 days to 74 days, the highest stress levels have increased by about 56%. However, further increase in the sensitization time from 74 to 100 days has very little effect on the stress level. The observed severe exfoliation or the tearing of the sample surface layers in and around the pits is due to the nucleation and coalescence of fine cracks. The cracks are nucleated because of the production and the buildup of differential stresses along the sample thickness.     

Hardening of a bismuth crystal due to electroplastic deformation

The surface texture of a bismuth crystal after deformation of the surface by a diamond pyramid and simultaneous passage of a pulse of high-density electric current is studied. The fact of hardening is established by measuring the microhardness in the zone of the indentation. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 54–56, March, 2007.