一种用于嗜酸性氧化亚铁硫杆菌液氮保藏的新型保护剂的保藏效果(英文)

对一种用于嗜酸性氧化亚铁硫杆菌液氮冷藏新型保护剂GP的保藏效果进行研究。依据最大细胞复苏率及最高亚铁氧化活性确定该新型保护剂的最佳使用浓度。结果表明,保护剂的最佳浓度为30%,在此浓度下细胞复苏率达到84.4%,且能在120h内完全氧化培养基中的亚铁,培养6d后菌体浓度达到5.8×107cell/mL。此外,解冻细胞在9K培养基中培养6d后,对活细胞复苏的最佳GP残留浓度为0.6%(体积分数)。在此浓度下,菌株DC完全氧化亚铁需要108h,并且最终菌体浓度为6.8×107cell/mL.因此,GP是一种简单、有效的嗜酸性氧化亚铁硫杆菌液氮保藏的冷冻保护剂。     

氧化亚铁硫杆菌浸矿体系中黄铁矿的电化学行为(英文)

运用循环伏安、稳态极化扫描和交流阻抗等电化学测试方法,研究黄铁矿在氧化亚铁硫杆菌浸矿体系和无菌酸性体系下的电化学氧化机理。结果表明,在无菌和A.ferrooxidans菌存在的条件下,黄铁矿的氧化反应分为两步:第一步是黄铁矿氧化生成元素S;第二步是元素S被氧化生成SO42-。加入A.ferrooxidans后黄铁矿的氧化机理没有发生改变,但是氧化速度加快。随着黄铁矿与A.ferrooxidans作用时间的延长,极化电流密度增加,黄铁矿表面钝化膜溶解的点蚀电位降低。在细菌存在的条件下,电极的阻抗值下降,表明微生物的存在加速了黄铁矿电极的腐蚀作用,有利于黄铁矿的氧化溶解。     

Bioleaching of pyrite by A. ferrooxidans and L. ferriphilum

Pyrite oxidation rates were examined under various conditions in the presence of A.ferrooxidans and L.ferriphilum,in which different pulp concentration,inoculation amount,external addition of Fe3+ and initial pH value were performed.It is found that A.ferrooxidans and L.ferriphilum show similar behaviors in the bioleaching process.The increasing pulp concentration decreases the leaching rate of iron,and external addition of high concentration Fe3+ is also adverse to leaching pyrite.The increased inoculation amount and high initial pH value are beneficial to leaching pyrite,and these changed conditions bring more obvious effects on leaching pyrite by L.ferriphilum than by A.ferrooxidans.The results also show that adjusting the pH values in leaching process baffles leaching pyrite due to the formed jarosite.Jarosite formed in leaching process was observed using XRD,SEM and energy spectrum analysis,and a considerable amount of debris with a crystalline morphology is present on the surface of pyrite.The results imply that the indirect action is more important for bioleaching pyrite.     

The effect of denitrifying Fe-oxidizing bacteria TPH-7 on corrosion inhibition of sodium molybdate

The corrosion process characteristics in the presence of thermophilic strain TPH-7 were investigated. The results showed that (1) by adding Na₂MoO₄ to the sterilized solution, the steel could be well protected with the increasing of the concentration from 0 to 100 mg/l, which caused the decreasing of corrosion current; (2) in the solution with strain TPH-7 and Na₂MoO₄, corrosion product formed and corrosion current decreased slightly. Based on the SEM observation, strain TPH-7 would adhere to the steel surface to interfere with the corrosion inhibition process of steel by molybdate. Therefore, 100 mg/l Na₂MoO₄ could not inhibit the MIC caused by strain TPH-7.     

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR() and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR() to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved  + GR() or GR() alone) and various atmospheres (N₂:H₂ or N₂:CO₂:H₂). In the first part of the study, CO₂ was deliberately omitted so as to avoid the formation of carbonated compounds, and GR() was the only source of sulphate. Cell concentration increases from 4 × 10⁷ to 7 × 10⁸ cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR()/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO₂ and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR() into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO₃.     

Microbial corrosion of galvanized steel by a freshwater strain of sulphate reducing bacteria (Desulfovibrio sp.)

Microbially influenced corrosion of galvanized steel was investigated exposing coupons (2.0 × 2.0 cm) to culture of sulphate reducing bacteria strain Desulfovibrio sp. The coupons were exposed to the SRB culture for 4, 8, 24, 72, 96, 168, 360 and 744 h along with a control set in uninoculated medium. The results from the present study suggest that SRB were responsible for the corrosion of the galvanized steel. The corrosion rate of galvanized steel was not be correlated with the number of sessile SRB cells. Also Desulfovibrio sp. had an ability to produce EPS (Extracellular Polimeric Substances) and biodegrade the carbohydrate, that is the predominant component of the EPS produced by them. When Desulfovibrio sp. cells were in logarithmic phase, the concentration of dissolved zinc in the bulk solution was very toxic for Desulfovibrio desulfuricans.     

Influence of thermal aging on sulfate-reducing bacteria (SRB)-influenced corrosion behaviour of 2205 duplex stainless steel

Microbiologically-influenced corrosion behaviour of thermally aged 2205 duplex stainless steel in comparison to the as-received material was studied by exposing the coupons for 40 days in chloride medium containing sulfate-reducing bacteria (SRB). Coupons exposed to the sterile medium were used as control. Electrochemical studies suggest a sharp drop in corrosion potential and increase in the anodic current for the coupons exposed to SRB. The austenite phase was found to be selectively attacked in presence of SRB for as-received material. Even though enhanced selective etching of austenite was noticed for thermally aged material, presence of actively corroding locations adjacent to the σ-phase protect the austenite phase.     

Development and evaluation of whole-genome oligonucleotide array for Acidithiobacillus ferrooxidans ATCC 23270

To effectively monitor the characteristic of Acidithiobacillus ferrooxidans ATCC 23270 at the whole-genomic level,a whole-genome 50-mer-based oligonucleotide microarray was developed based on the 3 217 ORFs of A.ferrooxidans ATCC 23270 genome.Based on artificial oligonucleotide probes,the results showed that the optimal hybridization temperature was 45℃. Specificity tests with the purified PCR amplifications of 5 genes(Sulfide-quinone reductase,Cytochrome C,Iron oxidase,Mercuric resistance protein,Nitrog...     

De-alloying of 316 stainless steel in the presence of a mixture of metal-oxidizing bacteria

The corrosion behavior of 316 stainless steel was investigated in the presence of a mixture of metal-oxidizing bacteria isolated from marine environments. Ennoblement of stainless steel in the presence of these bacteria can lead to localized corrosion that confirmed by ESEM images. The corrosion rate of the metals also increased. EDS results showed that these bacteria caused the segregation of Si elements in the metal structure and promoted the depletion of Cr and Fe contents in the corrosion products. Thus, the de-alloying of stainless steel can occur in the presence of metal-oxidizing bacteria.     

The influence of sulphate-reducing bacteria biofilm on the corrosion of stainless steel AISI 316

This work investigates microbially-influenced corrosion (MIC) of stainless steel AISI 316 by two sulphate-reducing bacteria, Desulfovibrio desulfuricans and a local marine isolate. The biofilm and pit morphology that developed with time were analyzed using atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) results were interpreted with an equivalent circuit to model the physicoelectric characteristics of the electrode/biofilm/solution interface. D. desulfuricans formed one biofilm layer on the metal surface, while the marine isolate formed two layers: a biofilm layer and a ferrous sulfide deposit layer. AFM images corroborated results from the EIS modeling which showed biofilm attachment and subsequent detachment over time.     

Influence of thermal stabilization treatment on the subsequent microstructure development during directional solidification of a Ti–46Al–5Nb alloy

Directional solidification (DS) experiments with thermal stabilization (TS) treatments were performed on Ti–46Al–5Nb (at.%) alloys in a Bridgman-type furnace using a quenching technology. Influence of the TS treatment on mushy zone and directional growth afterwards were investigated. The results show that the length of the mushy zone decreases but the β dendrite spacing in directional growth significantly increases with increasing TS time. During the DS process, β dendrite spacing is more homogeneous and its growth direction is more inclined to parallel to the axial direction with increase of the TS time. Al solute concentration in the mushy zone in a steady-state is always lower than that in original as-cast alloys. The mushy zone with the columnar β and α grains is easily produced after TS treatment on the alloys with microstructures of the directional dendrite segregation morphology before DS starting. TS treatment results in the redistribute of solute Al thus changes the phase constituent in the mushy zone. An appropriate TS is necessary to produce the L + β + α region in the mushy zone, which is of great benefit to control DS microstructures of TiAl peritectic alloys.     

Corrosion of carbon steel C1010 in the presence of iron oxidizing bacteria Acidithiobacillus ferrooxidans

In this study, corrosion behaviors of carbon steel C1010 in the presence of an acidophilic, iron-oxidizing bacterial species Acidithiobacillus ferrooxidans were examined. Results showed that A. ferrooxidans cells, with or without attaching to C1010 steel, accelerated its corrosion at a rate of 3–6× those of acidic water, at a pH of 2, without cells. A. ferrooxidans oxidized Fe²⁺ to Fe³⁺ as an energy source and the produced Fe³⁺ rapidly oxidized Fe⁰ to Fe²⁺ was proposed and verified as the reason. In addition, severe pitting corrosion was found on the C1010 steel surface in solutions containing A. ferrooxidans cells.     

The effects of sulfate reducing bacteria on corrosion of carbon steel Q235 under simulated disbonded coating by using electrochemical impedance spectroscopy

The effect of sulfate reducing bacteria (SRB) on the corrosion of the carbon steel Q235 has been investigated in the crevice under the simulated disbonded coating in the soil-extract solutions (SES). The results of electrochemical impedance spectroscopy (EIS) show that the corrosion rate is inhibited in the SES with SRB during the stationary phase of SRB, but enhanced during the death phase. The comparison of the polarization (R_p) and the charge transfer resistances (R_t) has indicated that the biofilm seriously influences the reactive procedure of metal/solution interface. SRB is found in the pits on the surface of the steel.     

Synergistic effect of sulfate-reducing bacteria and elastic stress on corrosion of X80 steel in soil solution

In this paper, the individual and simultaneous effects of stress and sulfate-reducing bacteria on corrosion of X80 steel were conducted by electrochemical impedance spectroscopy, scanning electron microscope and X-ray photoelectron spectroscopy. Both elastic stress and activity of SRB enhance corrosion of the steel and, furthermore, they have synergistic effects on corrosion behavior of the steel. The activities of SRB give rise to the initiation of pits, and the applied elastic stress keeps and promotes the growth of pits. The activities of SRB and the applied elastic stress induce tiny secondary corrosion pitting at the bottom of the primary pitting.     

Surface chemistry and corrosion behaviour of 304 stainless steel in simulated seawater containing inorganic sulphide and sulphate-reducing bacteria

Although many studies have been carried out regarding the role of sulphide anions in promoting microbial corrosion of various metal substrates, very little is known about the differences between inorganic sulphide and biogenically-derived sulphide by sulphate-reducing bacteria (SRB) and what the reasons for differing corrosion behaviour between the two types of sulphide may be towards common metals. In this study, various electrochemical and surface analytical techniques were employed to study the effect of the inorganic and biogenic sulphide (active SRB present) on the surface chemistry and corrosion behaviour of 304 stainless steels in a simulated seawater-based modified Baar’s (SSMB) medium. Clear differences in the surface chemistry of the sulphurised passive film by inorganic and biogenic sulphide (active SRB present) were quantified by X-ray photoelectron spectroscopy (XPS). The transformation of metal sulphides in abiotic and biotic sulphide solutions with the exposure time was correlated with different corrosion behaviour of 304 stainless steels.     

Crystal growth of TiAl alloys

The growth of TiAl alloys over a range of Al concentrations has been considered for ingots processed by the floating zone technique. For Al-rich alloys, single crystals of γ-TiAl cannot be grown for compositions below Ti-54 at% Al since a banded microstructure forms due to the limitations imposed by the L + → γ peritectic reaction. However, near stoichemetric TiAl crystals can be grown by the traveling solvent method when using a TiAl---Co flux, although optimum processing conditions have not yet been realized. For Ti-rich alloys, evidence of a growth morphology consisting of β-phase dendrites embedded within a continuous matrix of the peritectic -phase is found for ingots processed up to 200 mm h⁻¹. The final lamellar orientation of the ingot is then determined by the orientation of the peritectic -phase and not by that of the leading β dendrites.     

Molecular-dynamics simulation of the synthesis of intermetallic Ti–Al

In the present paper, results of a molecular-dynamics simulation study of the synthesis of intermetallic Ti–Al in the regime of thermal explosion at constant volume are reported. The structure of the polycrystalline intermetallic compound formed upon cooling was studied, and the dependence of crystallite sizes on the cooling rate was examined.     

The effect of sensitization on the hydrogen-enhanced fatigue crack growth of two austenitic stainless steels

Fatigue crack growth tests were performed to evaluate the susceptibility to hydrogen-enhanced crack growth of AISI 304 and 316 stainless steels (SSs). Sensitization treatment at 650 °C 100 h played little effect on the fatigue crack growth behavior in air, regardless of testing specimens. However, hydrogen accelerated the fatigue crack growth of various specimens to different degrees; sensitized specimens were more susceptible as compared with the un-sensitized ones.

Fatigue fracture appearance of various specimens tested in air exhibited mainly transgranular fatigue fracture together with rarely intergranular fracture and twin boundary separation. Meanwhile, intergranular fracture was found for sensitized specimens tested in hydrogen. Extensive quasi-cleavage fracture related to the strain-induced martensite accounted for the hydrogen-accelerated fatigue crack growth of unstable austenitic SSs. On the other hand, the lower susceptibility of 316H specimens could be attributed to the partial austenite transformation, as evidenced by a mixture of transgranular fracture feature and quasi-cleavage.