Localized corrosion behavior of 316L stainless steel in the presence of sulfate-reducing and iron-oxidizing bacteria

Localized corrosion behavior of 316L stainless steel was investigated in the presence of sulfate-reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) isolated from cooling water system using polarization measurement, scanning electron microscopy (SEM) examinations and energy dispersive spectrum (EDS) analysis. The results show the corrosion potential (E_corr) and breakdown potential (E_b) of SS decreased in turn with the presence of IOB, SRB and SRB + IOB, indicating decreased relative resistance to localized corrosion. E_corr in the sterile medium remained virtually unchanged with exposure time, indicating that localized attack did not occur. However, micrometer-scale pitting was observed on the SS surface in the presence of bacteria. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB yielded the highest corrosion rate. The presence and metabolic activities of bacteria on SS surface produce environments that can alter rates of partial reactions in corrosion processes and shift corrosion mechanisms. The most severe microbiologically induced corrosion takes place in aquatic solution where physiological groups of aerobic and anaerobic microorganisms interact.     

Bioleaching of spent hydro-processing catalyst using acidophilic bacteria and its kinetics aspect

Bioleaching of metals from hazardous spent hydro-processing catalysts was attempted in the second stage after growing the bacteria with sulfur in the first stage. The first stage involved transformation of elemental sulfur particles to sulfuric acid through an oxidation process by acidophilic bacteria. In the second stage, the acidic medium was utilized for the leaching process. Nickel, vanadium and molybdenum contained within spent catalyst were leached from the solid materials to liquid medium by the action of sulfuric acid that was produced by acidophilic leaching bacteria. Experiments were conducted varying the reaction time, amount of spent catalysts, amount of elemental sulfur and temperature. At 50 g/L spent catalyst concentration and 20 g/L elemental sulfur, 88.3% Ni, 46.3% Mo, and 94.8% V were recovered after 7 days. Chemical leaching with commercial sulfuric acid of the similar amount that produced by bacteria was compared. Thermodynamic parameters were calculated and the nature of reaction was found to be exothermic. Leaching kinetics of the metals was represented by different reaction kinetic equations, however, only diffusion controlled model showed the best correlation here. During the whole process Mo showed low dissolution because of substantiate precipitation with leach residues as MoO3. Bioleach residues were characterized by EDX and XRD.     

Ni-Mn基磁性形状记忆合金第二相的形成及其对相变和性能的影响

Ni-Mn基磁性形状记忆合金具有良好的温度场和磁场诱发的形状记忆效应、超弹性、磁热效应、磁阻效应、弹热效应、交换偏置效应等功能特性。作为一种新型多功能材料,有望应用于驱动器、传感器等多个工程领域。本文详细阐述了包含第二相的Ni-Mn基磁性形状记忆合金的研究现状,梳理和总结了第二相的形成及其对马氏体相变、功能特性和力学性能的影响,提出了一些有待解决的问题,如第二相对包括磁性形状记忆效应在内的磁功能特性的影响,并指出未来应着重于研究第二相形成与演化过程的热力学/动力学因素,对第二相进行合理调控,从而优化合金功能特性。     

Synthesis of nanoamorphous germanium and its transformation to nanocrystalline germanium

A simple reaction between a mild reducing agent such as a trialkoxysilane and Ge^IV species such as germanium tetraalkoxides in a room‐temperature water/alcohol solution produces silica‐coated ultrasmall (2–3 nm) amorphous germanium nanoparticles (na‐Ge/SiO₂). The initial reaction involves the straightforward hydrolysis and condensation of the precursors, Ge(OCH₂CH₃)₄ and (CH₃CH₂O)₃SiH, where the reaction rate depends on the water concentration in the reaction medium. These processes can be further accelerated by adding acid to the reaction medium or carrying out the reaction at higher temperatures. At low water contents (up to 50% water/ethanol) and low acid concentrations, the reaction proceeds as a clear solution, and no precipitation is observed. The initially colorless clear solution progressively changes to pale yellow, yellow, orange, red, and finally dark red as the na‐Ge particles grow. Evaporation of the solvent yields a reddish‐brown powder/monolith consisting of na‐Ge, embedded in an encapsulating amorphous silica matrix, na‐Ge/SiO₂. The formation of na‐Ge proceeds extremely slowly and follows a first‐order dependence on both water concentration and diameter of the na‐Ge particles under the reaction conditions used. Annealing of the na‐Ge/SiO₂ powder under an inert atmosphere at 600 °C produces ultrasmall germanium nanocrystals (nc‐Ge) embedded in amorphous silica (nc‐Ge/SiO₂). Freestanding, colloidally stable nc‐Ge is obtained by chemical etching of the encapsulating silica matrix.     

Preparation of polybenzoxazine foam and its transformation to carbon foam

An organic foam derived from a new type of phenolic resin, namely polybenzoxazine, was successfully prepared with a noncomplex and economical foaming method by using azodicarbonamide (AZD) as a foaming agent. The influence of foam density on the physical and mechanical properties of the foams was studied. All resulting polybenzoxazine foams and carbon foams exhibit a tailorable uniform microstructure. Polybenzoxazine foams showed a density in the range of 273–407 kg/m³, and a compressive strength and a compressive modulus in the range of 5.2–12.4 MPa and 268–681 MPa, respectively. The foam density not only affects the physical and mechanical properties, but also affects the deformation response of the foam. In addition, the polybenzoxazine foam was further transformed into carbon foam by carbonization at 800 °C under an inert atmosphere, and its properties were examined.     

Formation of γ-alumina nanorods in presence of alanine

Boehmite and alumina nanostructures were prepared using a simple green sol-gel process in the presence of alanine in water medium at room temperature. The uncalcined (dried at 200 °C) and the calcined materials (at 500, 600 and 700 °C for 4 h) were characterized using XRD, TEM, SEM, N₂ physisorption and TGA. Nanorod aluminas with a possible hexagonal symmetry, high surface area and relatively narrow pore size distribution were obtained. The surface area was enhanced and crystallization was retarded as the alanine content increased. The morphologies of the nanoparticles and nanorods were revealed by a transmission electron microscope (TEM).     

Formation and transformation of carbon nanoparticles under electron irradiation

This article reviews the phenomena occurring during irradiation of graphitic nanoparticles with high-energy electrons. A brief introduction to the physics of the interaction between energetic electrons and solids is given with particular emphasis on graphitic materials. Irradiation effects are discussed, starting from microscopic mechanisms that lead to structural alterations of the graphite lattice. It is shown how random displacements of the atoms and their subsequent rearrangements eventually lead to topological changes of the nanoparticles. Examples are the formation of carbon onions, morphological changes of carbon nanotubes, or the coalescence of fullerenes or nanotubes under electron irradiation. Irradiation-induced phase transformations in nanoparticles are discussed, e.g. the transformation of graphite to diamond, novel metal-carbon phases in nanocomposite materials or modified phase equilibria in metal crystals encapsulated in graphitic shells.     

Formation and transformation of BaGeO3

β-barium metagermanate (BaGeO₃), in its high-temperature form, was formed metastably at 630–660°C from an amorphous material prepared by the simultaneous hydrolysis of barium and germanium alkoxides. The transformation of BaGeO₃ was studied by thermal analysis and high-temperature X-ray diffraction.     

Formation of AlPO4-15 and CoAPO-15 in the presence of hexamethylenetetramine

Two materials, AlPO₄-15 and CoAPO-15, with the same aluminophosphate lattice have been obtained by hydrothermal synthesis in the presence of hexamethylenetetramine (HMTA). Their formation is attributed to the influence of species that arise through the decomposition of HMTA, the latter process taking place under synthetic conditions. The Co²⁺ ion in CoAPO-15 occupies tetragonally deformed octahedral sites, and this causes a slight expansion of the unit cell of CoAPO-15 in comparison to that of AlPO₄-15. The Co²⁺ ion is coordinated not only by the O atoms of the system but also by NH₃ molecules.     

Formation and optical properties of gold nanoparticles synthesized in the presence of double-hydrophilic block copolymers

In this article, we present a systematic, controlled synthesis of water-dispersed, polymer-stabilized Au nanoparticles with different sizes by either self-reduction or ultraviolet (UV) irradiation-enhanced reduction in the presence of double hydrophilic block copolymers with different functional patterns. The morphology of the particles was found to be spherical, triangular, truncated triangular, and hexagonal under various conditions. In addition, both the particle size and shape could be controlled by variation of the functional group pattern of the block copolymers. With a hexacyclen functional block, we achieved a perfect match to the Au (111) face, resulting in extremely thin free-standing triangular and hexagonal nanoplatelets that show interference patterns in the electron beam due to deformations in the sub-Angstrom range. UV-visible spectra show that the plasmon absorption band can be fine tuned, depending on the type of the polymer and the irradiation power. The influence of the functional polymer groups and the irradiation on the formation of gold nanoparticles was investigated in more detail.     

Bioanalytical method development and its application to pharmacokinetics studies on Simvastatin in the presence of piperine and two of its synthetic derivatives

Piperine has been widely used as a bioenhancer. Simvastatin belongs to a group of medicines known as statins. It acts by inhibiting HMG CoA reductase and acts primarily as a hypolipidemic agent. In this study some derivatives of Piperine were synthesized. They were studied for their bioenhencing effect (10?mg kg^?1) and this effect was compared with that of Piperine. The pharmacokinectic profile of Simvastatin alone and in combination with Piperine and Piperine derivatives were investigated by validated HPLC method as per USFDA guidelines. It was seen that the two synthesized derivatives of Piperine significantly improved the bioavailability of Simvastatin in Wistar rats. The 5-(benzo) [1,3]dioxol-5-yl)-N-(pyridin-4-yl)penta-2,4-dienamide was better amongst the synthesized in increasing the bioavailability of Simvastatin in Wistar rat.     

Pitting initiation of 316L stainless steel in the media of sulfate-reducing and iron-oxidizing bacteria

Pitting corrosion behavior of stainless steel 316L in the presence of aerobic and anaerobic bacteria isolated from cooling water system in oil refinery was investigated using open circuit potential measurement, electrochemically impedance spectroscopy, scanning electron microscopy examinations, and energy dispersive spectrum analysis. The results show the corrosion potential (E _cor) and polarization resistance (R _p) decrease in the presence of sulfate-reducing bacteria (SRB), iron-oxidizing bacteria (IOB), and a combination of SRB and IOB, in comparison with those observed in the sterile medium for the same exposure time. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB created the highest corrosion rate. The metabolic activity of bacteria and the integrality and compactness of biofilm influenced the pitting corrosion process, increased the corrosion damage degree of the passive film, and accelerated the pitting corrosion. It is suggested that SRB and IOB in influencing the pitting corrosion of 316L SS is highlighted. The text was submitted by the authors in English.     

Development of “Macroscopic Composition Gradient Method” and its application to the phase transformation

A new characterization method, “Macroscopic Composition Gradient (MCG) Method” is proposed to investigate the phase transformations near the phase boundaries. The MCG method is a new technique to investigate the phase transformations in various composition alloys by utilizing a single specimen having the macroscopic solute composition gradient. Since the macroscopic composition gradient in the MCG alloy is so prepared as to cross over the phase boundary, the morphological transition of critical phenomena at the phase boundary can continuously be investigated by means of analytical transmission electron microscopy. By utilizing the MCG method, the various kinds of phase transformation, such as the coherent and incoherent precipitation boundaries, the order/disorder phase transition and the morphological change at the spinodal line have successfully been investigated. Furthermore, to an important thing, the critical size of precipitate-nucleus and the nucleation rate near the solubility limit can be experimentally obtained for respective nucleus. The phase decomposition of supersaturated solid solution progresses by a mechanism of spinodal decomposition even in the N-G region of phase diagram. On the basis of experimental results, the application limit of the conventional nucleation theory is investigated, and hence the failure of Boltzmann–Gibbs free energy becomes obvious in the early stage of phase decomposition.It is noteworthy that the present experiment is systematically conducted for the alloy composition range very close to the solubility limit. Such critical phenomena of phase transformation have been scarcely examined in the past. The MCG method proposed here is considered to open a new way to investigate the critical phenomena in the phase boundary.     

Reduction of Cr(VI) facilitated by biogenetic jarosite and analysis of its influencing factors with response surface methodology

In this paper, the facilitating role of biogenetic jarosite in the reduction of Cr(VI) by sulfide and its mechanism were investigated through batch experiments and analysis of X-ray photoelectron spectrum (XPS). To study the effects of operational parameters on the reduction of Cr(VI) by sulfide, four operational parameters (pH of solution, operation temperature, loading of jarosite and reaction time) were considered as input variables for response surface methodology (RSM). Graphical response surfaces and contour plots were used to evaluate the effect of interaction between operational parameters on the reduction of Cr(VI). The results suggest that a cycle process of converting Fe(III) to Fe(II) occurred on the surface of jarosite and markedly accelerated the reduction of Cr(VI) by sulfide. For example, the efficiency of Cr(VI) reduced by sulfide increased from 20.5% to 100% when jarosite (1 g/L) was added to the homogenous reaction system at pH = 8 within 40 min. The analysis of variance (ANOVA) revealed a high coefficient of determination (p-value < 0.0001, R² = 97.99%, Adj-R² = 95.98%) between experimental Cr(VI) removal efficiency and predicted one by RSM developed model. The Pareto analysis results demonstrated that the pH of solution was the most significant term of the developed model. Operation temperature, loading of jarosite and reaction time exhibited synergistic effects on the reduction of Cr(VI), and the effect of interaction between independent factors on the response factor can't be ignored.     

Kinetics of the anatase–rutile transformation in TiO2 in the presence of Fe2O3

The anatase–rutile phase transition in TiO₂ in the presence of Fe₂O₃ was investigated in air and argon atmospheres by means of X-ray diffraction and scanning electron microscopy. Isothermal curves of rutile transformed from anatase as a function of time were obtained between 825 and 950 °C. The data were well fitted by various rate laws. In the presence of Fe³⁺, the anatase–rutile transition temperature is lower and the transformation rate in air is higher than the corresponding one in pure TiO₂. The transformation in the presence of Fe³⁺ in an argon atmosphere is more rapid than in air. The enhancement effect of Fe³⁺ on the anatase–rutile transformation in both atmospheres is understood on the basis of the formation of oxygen vacancies.     

Martensitic transformation in zirconia containing ceramics and its applications

An introduction to tetragonal (t) → monoclinic (m) martensitic transformation in zirconia containing ceramics, especially tetragonal zirconia polycrystalline (TZP) was presented. Thermodynamics, crystallographics and kinetics of t → m martensitic transformation in TZP were emphasized. Transformation toughening and shape memory effect (SME) associated with t → m martensitic transformation in the TZP were reviewed. Perspective of future challenges was briefly mentioned at the end.     

黄钠铁矾渣制备镍锌铁氧体及其表征

利用化学共沉淀法,以黄钠铁矾渣为原料制备镍锌铁氧体。以正丁胺为沉淀剂,在室温条件下,通过共沉淀铁、镍、锌(镍、锌由硫酸锌、硫酸镍按Ni0.5Zn0.5Fe2O4比例补加)制备镍锌铁氧体样品。采用SEM、XRD和FT-IR对该样品进行表征。结果表明,制备所得的样品为镍锌铁氧体。同时,通过磁滞回线显示,镍锌铁氧体比饱和磁化强度为9.04A·m2/kg,比剩余磁化强度为0.65 A·m2/kg,矫顽力为2.47kA/m,具有软磁材料的低比剩余磁化强度和低矫顽力的特性。