Voltammetric behaviour of an archeaological bronze alloy in aqueous chloride media

The interface archaeological bronze alloy‐chloride media was characterized by using linear sweep rate cyclic voltammetry. The electrochemical behaviour of the Cu‐Sn alloy being different from pure copper and pure tin. In fact, the voltammograms show an anodic peak and two cathodic peaks. Surface examination revealed a compact layer which spread over the ancient material. The influence of different parameters such as scan rate, chloride concentration and repetitive cycling on the voltammetric response of the archaeological bronze was also studied. The results indicate that patina layer formation is a spreading process over the electrode surface leaving only small pores. Diffusion of the halide controls the growing rate of this layer. Two other anodic peaks are evidences when potential cycling increases. The oxidation became more difficult as a result of a constant layer thickness.     

Morphology and mechanisms of formation of natural patinas on archaeological Cu–Sn alloys

Natural patinas on archaeological bronzes (Cu–Sn alloys) have been classified and characterized in order to get a deeper insight into their formation mechanisms. From examinations of cross-sections on archaeological artefacts, two classes of corrosion structures were defined (Type I and Type II), using both optical and electron microscopies, EDSX, XRD, IRS and a statistical treatment of data (Principal Components Analysis). A Type I structure (even surface) is defined as a two-layer passivating deposit due to an internal oxidation with a decuprification process (i.e. selective dissolution of copper). A Type II structure (coarse surface) corresponds to more severe attacks, such as pitting but also general uneven corrosion; it is modelled by a three-layer structure, characterized by the presence of cuprous oxide and by an increase in the chloride content at the internal layer/alloy interface related with selective dissolution of copper. A phenomenological model to explain the formation of bronze patinas is developed on the basis of a decuprification phenomenon.     

Analysis of Oxides Formed on the Surface of the Alloy 690 in Hydrogenated Supercritical Water

The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.The oxides on me surface of the alloy 690 exhibited multi-layer structure:an outer layer consisted of granular crystallites(NiO and NiFe_2O_4) and a compact inner layer(spinel and Cr_2O_3).Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium,whereas the inner layer was enriched in chromium and iron but depleted in nickel.The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr_2O_3 layer.Besides,Cr_2O_3 nodules were readily observed at the oxides/alloy interface.     

Effect of Technical Parameters on Surface Morphology of Electrodeposition of Iridium Layer in Aqueous System

在水体系中利用直流电沉积的方法以IrCl3为主盐在铂基体上制备出了Ir层。利用SEM、EDS和XPS对不同工艺参数下所制备Ir层的表面形貌及成分进行了分析,并最终获得了最优的电沉积工艺条件。结果表明:IrCl3主盐浓度对Ir层形貌有较大影响,浓度太低时电沉积的铱层太薄,导致铱层易起皮或产生裂纹,故适当提高主盐的浓度有利于改善Ir层质量;在一定的pH值范围内,电沉积所制备的Ir层表面形貌差别不大,表面均比较平整,Ir颗粒比较均匀、致密;电流密度对Ir层表面形貌尤其是对Ir层结晶颗粒的大小和致密性影响较大;电沉积溶液的温度太低时,不能沉积出Ir层,温度太高时,则沉积出的Ir层粗糙、表面形貌不均匀。     

Corrosion behaviour of Cu-10Sn bronze in aerated NaCl aqueous media - Electrochemical investigation

Investigation of the electrochemical behaviour of Cu-10Sn (wt.%) alloy has been conducted in aerated aqueous chloride solutions and compared to that of pure Cu and Sn. Cathodic and anodic bronze behaviours have been investigated in function of the chloride concentrations (0.1-0.001 M), the rotation speed of the electrode and the potential sweep rate after 1-h immersion time in open-circuit conditions. At the corrosion potential, the corrosion behaviour appears determined by the charge-transfer controlled reduction of oxygen and the mixed charge- and mass-transfer controlled electrodissolution. In 0.1 M NaCl solution, three anodic regions are evidenced corresponding to: (I) a dissolution part from Eoc value, (II) a maximum current region corresponding to peaks formation and (III) a large current plateau. A partial protective effect of the corrosion product layer is observed at high anodic potential. It has been interpreted as the result of a 3D growth mechanism involving the formation of stable tin species in the layer according to a “pore resistance model”. Results on synthetic alloy are compared with those obtained on an archaeological bronze with a similar composition immersed in the same medium. Equivalent interface behaviour is evidenced between the synthetic and the archaeological bronzes.     

Interfacial layer on archaeological mild steel corroded in carbonated anoxic environments studied with coupled micro and nano probes

The interfacial layer formed on archaeological artefacts corroded during 450 years in carbonated anoxic water was studied using FEG–SEM, Raman, STEM, STXM. This layers forms between the metallic substrate and an outer carbonate layer. Interfacial layer shows various thicknesses from about 100 nm to several μm. It is made of a mix of iron oxides (maghemite or magnetite). A formation mechanism is proposed and based on slight pH increase at the interface. D₂O labelling experiments show that the penetration of water in the pore network seems to be significantly hindered at the interface by the presence of the oxide layers.     

中碳钢盘条的高温氧化行为研究

针对中碳钢盘条的高温氧化问题,利用热重分析仪对45钢和40Cr钢盘条的高温氧化行为进行了试验研究;采用场发射电子探针表征了氧化铁皮厚度及截面微观形貌,对氧化铁皮形貌演变规律以及合金元素在氧化铁皮与基体界面处的分布规律进行了研究分析。结果表明:45钢和40Cr钢盘条的氧化增重曲线在1 050~1 250 ℃范围内遵循抛物线规律,当氧化条件相同时,相比于常规低碳钢,其氧化激活能较高,抗氧化性能更好;氧化铁皮呈典型的3层结构,从外到里分别为Fe₂O₃、Fe₃O₄及FeO,并且在氧化铁皮与基体界面处存在合金元素富集层;45钢盘条在高温氧化时,Cr元素分布不明显,Si元素在氧化铁皮与基体界面处有少量富集,Mn元素在氧化铁皮中均匀分布;40Cr钢盘条在氧化铁皮与基体界面处不仅有富Si层,还明显存在一层均匀完整的富Cr层,由于合金元素富集层阻碍了Fe²⁺向外扩散,提高了盘条的高温抗氧化性能。     

Effect of Oxidation on the Bonding Formation of Plasma-Sprayed Stainless Steel Splats onto Stainless Steel Substrate

Stainless steel splats were deposited on 304 stainless substrates with different thicknesses of oxide layer to examine the effect of substrate oxidation on splat morphology and splat-substrate interface bonding by inert low-pressure plasma spraying. The cross sections of splats showing the splat-substrate interface were prepared by focus ion beam (FIB). The splat morphology and splat-substrate interface bonding state were characterized by scanning electron microscopy. The interface bonding was also examined by an electrolytic etching process. Results showed that with increasing oxide layer thickness and surface roughness, the morphology of splat changed from disk shape to splashed finger-like shape. The examination into the interface bonding by using FIB-prepared cross-sectional samples revealed that the splat interface bonding depended on the oxide roughness and composition. The interface bonding with a ratio of 44% was formed at the inner part of a splat on the pre-oxidized substrate when iron oxide presented on the surface, and the roughness of oxide scale was <5 nm. When the pre-oxidizing temperature exceeded 800 °C, the surface roughness increased to 14 nm and chromium oxide covered the pre-oxidized surface, resulting in no effective bonding forming at the whole interface. Thus, surface roughness and oxide composition have a significant influence on the splat interface bonding formation.     

堆焊铜合金/35CrMnSiA接头的界面结构特征

采用冷体TIG堆焊方法在钢质基体上堆焊铜合金层,重点分析了其微观组织.通过显微镜(OM)、扫描电镜(SEM)观察了界面、铜合金层及基体的组织形貌特征, 分析了焊接工艺对铜合金层中泛铁量的影响.通过能谱 (EDXA)研究了铜合金层内和界面的成分变化,发现在焊接过程中发生了基体元素向铜合金层中溶解和某些铜合金层元素向基体扩散,在由CuSi3形成的铜合金层中有Fe2Si生成,在由B30形成的铜合金层中存在树枝晶组织.而且,焊接工艺不当时,因界面处存在低熔共晶进而出现渗透裂纹.     

Multisecular corrosion behaviour of low carbon steel in anoxic soils: Characterisation of corrosion system on archaeological artefacts

In the context of the prediction of materials behaviour used in the nuclear waste storage, the understanding of iron corrosion mechanisms in anoxic environment is of great importance. Information can be obtained using complementary analytical tools. Interactions between burial soil and archaeological artefacts are studied by performing on site soil measurements. Moreover, archaeological artefacts are studied on transverse sections using a combination of microbeam techniques. The specific interest of this project lies in the study of ferrous thick corrosion layers formed in anoxic environments.     

SnS2 -SnO2 / 石墨烯复合材料的合成及其电化学储锂性能的研究

目的制备高容量和循环性能稳定的锂离子电池复合电极材料。方法通过L-半胱氨酸(Lcys)辅助水热法合成SnS2-SnO2/石墨烯复合纳米材料,采用XRD,SEM,TEM和HRTEM技术对其进行结构表征,并采用循环伏安、恒流充放电和电化学阻抗技术研究了其电化学贮锂性能。结果随着水热溶液中L-cys的量增加,复合材料中少层数结构SnS2的含量也增加。当Sn4+/L-cys的物质的量之比为1∶4时,制得了SnS2/石墨烯复合纳米材料,而且石墨烯的存在在一定程度上抑制了SnS2沿c轴方向的生长,减少了层状SnS2的层数。结论由于二维层状结构的SnS2具有与石墨烯类似的微观结构和形貌,与石墨烯的复合具有更好的匹配性和相互协同效应,增强了SnS2/石墨烯复合材料的电化学贮锂性能,使其具有较高的可逆储锂容量、良好的循环性能和增强的倍率特性。     

Al-Al 爆炸焊接界面边侧与中心区域差异定量评价

由于边侧稀疏波的作用,爆炸焊接界面边界与中心区域形貌结构存在差异。然而学术上对焊接界面形貌差异分析仍处于定性水平,尚未建立定量分析方法。据此,本文尝试对爆炸焊接界面形貌差异开展定量化评价。研究过程中首先建立冲击波作用下金属复板弹粘塑性模型以分析波状界面的形成,并开展2024Al对称爆炸焊接;随后运用三维超景深显微镜获得界面形貌图像,结合冲量理论,定义中心区域与边侧区域分界线;最后基于分形理论计算图像轮廓分维与多重分维谱。由分维与多重分形谱数据可定量表征界面的起伏程度与表面最大、最小概率分布,从而实现焊接界面形貌差异定量描述。     

硼掺杂对钛基金刚石薄膜附着力的影响

采用微波等离子体化学气相沉积(MPCVD)技术在钛基片上沉积了掺硼金刚石薄膜,并对掺杂前后的薄膜形貌及结构进行了检测.结果表明掺杂元素对形貌和结构有很大的影响,同时掺杂后薄膜与基底附着力有所下降.掠角衍射(GIXD)检测表明,中间层的主要成分是TiC和TiH_2.随着硼的加入,两者的含量增加.薄膜与基底的附着力下降的原因主要是受中间过渡层成分和残余应力增加的共同影响.     

Buried iron archaeological artefacts: Corrosion mechanisms related to the presence of Cl-containing phases

Deterioration after excavation of archaeological iron artefacts buried in soil is often associated with the presence of Cl-containing phases in corrosion products, leading to serious problems for conservation of metallic objects of cultural heritage. Thus, in order to better understand the corrosion process related to the presence of chlorine, some high-resolution techniques of materials characterisation are implemented. Particularly this paper shows the great utility of the combination of micro-X-ray diffraction, micro-Raman spectroscopy and micro-X-ray absorption spectroscopy. The analyses are realised on the cross sections of iron corroded objects excavated on archaeological sites dated from the 12th to the 16th century AD. In addition to the common oxyhydroxide containing chloride, akaganeite (β-FeOOH) often mentioned in the literature, a ferrous hydroxychloride β-Fe₂(OH)₃Cl was also found in the corrosion layers. In order to explain the corrosion system formed during burial, a corrosion mechanism including the presence of chlorine, is proposed.     

Sulfathiazole as potential corrosion inhibitor for copper in 0.1 M NaCl

Effects of sulfathiazole (ST) on copper corrosion as a corrosion inhibitor in 0.1 M NaCl solutions have been studied using potentiodynamic polarization, open circuit potential, electrochemical impedance spectroscopy with scanning electron microscopy (SEM). Potentiodynamic polarization measurements indicated that the presence of ST in chloride solutions affects mainly the cathodic process and decreases the corrosion current and shifts the corrosion potential towards more negative values. The adsorption of inhibitor on the copper surface obeys the Langmuir adsorption isotherm. The adsorption free energy of ST on copper (?33.47 kJ/mol) shows a strong adsorption of the inhibitor on the metal surface. The effect of temperature on the inhibition efficiency of sulfathiazole was examined with Arrhenius equation and activation energies in 0.1 M NaCl with and without inhibitor were calculated. Impedance data were analyzed using an appropriate equivalent circuit model for the electrode /electrolyte interface. SEM measurements also exhibited that the ST molecules are strongly adsorbed on the copper surface.     

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.     

The mechanism of periodic layer formation during solid-state reaction between Mg and SiO2

The as yet unresolved microstructure of the periodic layers formed in the reactive diffusion system Mg/SiO₂ was clarified by using high-resolution field-emission SEM. The periodic layered structure actually consists of the single-phase layer of Mg₂Si and the two-phase layer of (Mg₂Si + MgO) alternated within the reaction zone. According to the experimental observations and in line with the diffusion-induced stresses model, the mechanism controlling this phenomenon could be attributed to the stresses induced by the difference in interface growth rates of Mg₂Si and MgO phases within the layer. When the elastic deformation of the slow-growing aggregated-MgO phase reaches its elastic maximum, it will be split off from the reaction front by the neighboring Mg₂Si phase and a new periodic layer forms. The computer simulation results are coinciding well with the experimental data.     

Ni-CNTs增强颗粒对Sn58Bi-0.1Er焊点组织与力学性能的影响

采用真空熔炼方法制备了不同Ni-CNTs含量的Sn58Bi-0.1Er钎料合金,研究不同Ni-CNTs含量对Sn58Bi-0.1Er复合钎料在Cu基板上的润湿性能的影响,并对不同Ni-CNTs含量下接头界面处金属间化合物的组织形貌及接头的剪切性能进行了分析.结果表明,当Ni-CNTs增强颗粒的添加为0.01％～0.05...     

焊接能量对Mg/Ti超声波焊接接头微观组织与力学性能的影响

采用超声波焊接技术对Mg/Ti异种金属进行了焊接,研究了不同焊接能量对接头界面峰值温度、界面形貌、界面原子扩散程度以及力学性能的影响规律。研究发现:Mg/Ti超声波焊接接头整体界面较平直,局部界面有较小起伏,未发现裂纹、未熔合等缺陷,也未看到明显的反应层;随着焊接能量的增大,界面峰值温度升高,原子扩散层厚度增大,连接区面积逐渐增大,接头力学性能得到提高,而能量达到2000J时镁侧母材出现裂纹;接头断裂模式分为界面断裂和纽扣断裂,界面断裂时断裂发生在镁侧扩散层区域和镁侧非扩散层区域。扫描电子显微镜和X射线衍射仪分析表明,Mg/Ti连接界面区域无明显的金属间化合物生成。     

Process analysis of direct laser melting to fabricate layered hybrid beads

The successful fabrication of layered hybrid beads by DLM process is limited by dissimilar melting ranges of different powders.For the application of DLM process into manufacturing industries,target mechanical properties of final product must be achieved.Process analysis was performed for the DLM fabrication of layered hybrid beads by using stainless steel (SS 316L) and titanium powders.For the analysis of fabrication characteristics,single hybrid bead was formed using SS316L powder onto the base plate and then Ti powder was melted onto the previous melted layer.In addition,multi-layer hybrid beads were fabricated for the analysis of the layering effects between them.From these studies,the effects of the processing parameters,such as laser power,scan rate and scan line spacing on surface morphology were characterized and optimum processing conditions for the DLM fabrication of layered hybrid beads were developed.