Corrosion Behavior of Weldments of Ti and Ti- 5Ta for Nuclear Fuel Reprocessing Plants

Corrosion studies on specimens of nuclear- grade type 304L stainless steel, titanium, Ti- 5Ta, and their respective weldments were carried out in a boiling nitric acid medium, as well as in boiling nitric acid containing hexavalent chromium and divalent silver ions. The weldments were prepared using a tungsten inert gas welding process. Titanium and its weldment showed excellent corrosion resistance in both media compared to 304L stainless steel. Specimens of Ti- 5Ta alloy base showed excellent corrosion resistance, whereas its weldment showed higher corrosion rates in boiling nitric acid medium. Scanning electron microscopy and x- ray diffraction analyses were carried out on the tested specimens to examine the scale morphology and the phases present on the surface.     

Beitrag zum Korrosionsverhalten der IVa?, Va? und VIa-Metalle sowie des Rheniums

The corrosion behaviour of IVa, Va and VIa metals as well as Rhenium In general, the non-alloyed metals of groups IVa, Va and VIa of the periodic system as well as Rhenium show a high resistance against corrosion by aqueous solutions, diluted acids and alkalis. Among the IVa metals, Hf shows the highest resistance; like the other IVa metals, it is liable to be strongly attacked by hydrofluoric acid only. Titanium however, which has a high resistance against media containing chlorine or chlorides, is liable to corrode slightly at high temperatures when exposed to diluted, nonoxidant acids or alkaline solutions. Titanum has a high resistance to nitric acid only. Among the Va metals, the corrosion resistance increases greatly from V via Nb to Ta. All three metals are liable to be attacked by hydrofluorid acid; but, with the exception of V, they show a high resistance to other acids and to alkalis. Among the VIa metals, Cr ist the only one to be resistant to nitric acid. On the other hand, nitric acid has a moderate effect on W, and a strong effect on Mo. Yet Mo and W have a high resistance to all other acids, including hydrofluoric acid. Alkalis are liable to attack all VIa metals. Rhenium is a metall with high corrosion resistance. It is only attacked by nitric acid a high temperatures, and by alkalis.     

Corrosion behavior of Hastelloy C22 coating produced by laser cladding in static and cavitation acid solution

The Hastelloy C22 coatings on Q235 steel substrate were produced by high power diode laser cladding technique. Their corrosion behaviors in static and cavitation hydrochloric, sulfuric and nitric acid solutions were investigated. The electrochemical results show that corrosion resistance of coatings in static acid solutions is higher than that in cavitation ones. In each case, coating corrosion resistance in descending order is in nitric, sulfuric and hydrochloric acid solutions. Obvious erosion-corrosion morphology and serious intercrystalline corrosion of coating are noticed in cavitation hydrochloric acid solution. This is mainly ascribed to the aggressive ions in hydrochloric acid solution and mechanical effect from cavitation bubbles collapse. While coating after corrosion test in cavitation nitric acid solution shows nearly unchanged surface morphology. The results indicate that the associated action of cavitation and property of acid solution determines the corrosion development of coating. Hastelloy C22 coating exhibits better corrosion resistance in oxidizing acid solution for the stable formation of dense oxide film on the surface.     

钛合金空蚀损伤及防护的研究进展

钛合金具有密度小、比强度高、耐蚀性好等优势,被广泛应用于诸多工程领域。由于钛合金存在表面硬度低、耐磨性差等缺点,导致其在过流部件中容易发生空蚀损伤,会降低钛合金构件的使用寿命,因此针对钛合金空蚀损伤行为及其防护措施的研究显得极为重要。概述了空蚀现象的作用机理和理论模型,详细介绍了材料自身的力学性能、表面状态、介质类型和溶液温度等对钛合金空蚀行为的影响,着重讨论了针对钛合金空蚀损伤的多种应对措施,如热处理、激光纹理加工、激光气体氮化、化学热处理、离子注入、添加缓蚀剂等技术,总结了相应方法提高钛合金抗空蚀性能的具体原因。其中,热处理技术通过改变钛合金自身的显微组织来提高其抗空蚀性能;激光气体氮化工艺可在钛合金表面形成硬质TiN相,以抵御空泡溃灭时的冲击;化学热处理技术在钛合金表面生成了致密的陶瓷层+固溶扩散层,缓解了空泡的溃灭能,延长了空蚀的孕育期;离子注入技术依靠注入离子在钛合金材料表面产生固溶强化、位错增值强化等效果,降低其空蚀损伤。最后对钛合金空蚀及防护研究的发展方向提出了展望。     

Korrosionseigenschaften dünner Schichten im System Ti?B?N

Corrosion properties of thin coatings in the Ti? B? N system Thin titanium nitride TiN, boride TiB₂ and boronitride Ti(B, N) hard coatings were deposited on titanium substrates by the PVD-process Magnetron-Sputter-Ion-Plating (MSIP). They were characterized by X-ray diffractometry, SEM and WDX-analysis. With increasing B-content the Vickers hardness of the coatings increases. Photoelectron spectroscopic measurements show that all coatings are covered in atmosphere by thin oxid layer. Titanium nitride is electrochemically in 1 N sulphuric acid stable up to 1.3 V (SHE), above 1.3 V it becomes oxidized to titanium oxide TiO₂ and nitrogen N₂. The oxidation products were detected with XPS. Corrosion tests in nitric acid HNO₃ show that the corrosion resistance of titanium nitride is lower than the resistance of titanium. The corrosion of titanium boride and titanium boronitride in sulphuric acid is more intensive compared to titanium nitride. The borides cannot be passivated, but dissolve completely by anodic polarization.     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

EIS characterisation of Ti anodic oxide porous films formed using modulated potential

Titanium, due to its excellent corrosion resistance, good mechanical properties and biocompatibility has been employed in many fields, such as in biomedical and dental implants. A passive oxide film formed on titanium surface is responsible for its high corrosion resistance. In the present study, oxide films were grown on titanium surface employing an anodising procedure using modulated potential, in a hydrofluoric acid solution. Electrochemical impedance spectroscopy was used to study the electrochemical behaviour of anodised Ti surface in a NaCl solution. The dependence of oxide film characteristics on forming conditions was analysed employing equivalent circuits. Samples were observed by scanning electron microscopy, in Jeol-JSM-5900LV microscope of the LME/LNLS, Campinas. It was observed that final anodising potential has an influence on the porous layer film morphology and that the anodising procedure with the chosen solution produces a double layer porous anodic film.     

Inhibitors for the corrosion of reactive metals: Titanium and zirconium and their alloys in acid media

The search for effective corrosion inhibitors for titanium and zirconium in acid media is growing because of the considerable increase in the use of these materials in chemical process equipment. It still remains limited, as appears from this review, because of the exceptionally high corrosion resistance of the metals. Titanium has received the greater attention. Its corrosion rate can be lowered by introduction in the medium of multivalent ions, inorganic and organic oxidants. Care should be taken to hold the concentration at a level exceeding some critical value, otherwise the corrosion rate increases. Complexing organic agents do not show such hazardous behaviour. The very rapid corrosion of titanium and zirconium in fluoride media may be lessened by complexing the fluoride ions. Though rarely encountered, localized corrosion may be avoided by using inhibitors. In some cases good corrosion inhibitors for titanium are dissolution accelerators for zirconium.     

The corrosion behavior of hard W–C system chemical vapor deposition layers in HCl and H<Subscript>2</Subscript>S aqueous solutions

The results of a study of anticorrosion performance of low carbon containing tungsten-based hard chemical vapor deposition (CVD) coatings with microhardness from 5 to 17 GPa are presented in this work. Their high corrosion resistance in hydrochloric acid and hydrogen sulfide solutions is noted, as their corrosion rate does not exceed 6 μm per year in hydrochloric acid solution and 15 μm per year in hydrochloric acid solution saturated with hydrogen. The open circuit potentials correspond to tungsten (VI) oxide formation so the corrosion process supposedly runs in passive state. Taking into account the low porosity of the CVD layers, which is lower than 0.02%, these coatings are promising for application as anticorrosion wear-resistant coatings for chemical and oil and gas apparatus responsible units.     

喷丸和盐酸酸洗对2205双相不锈钢热轧板氧化层微观结构的影响

利用光学显微镜(OM)、X射线衍射(XRD)、扫描电镜(SEM)配合能谱仪(EDS)和X射线光电子能谱(XPS)研究了 2205双相不锈钢热轧板经过退火和喷丸处理后的氧化层组成和结构,并分析了盐酸及混酸(HNO₃+HF)酸洗后表面钝化膜微观组织结构,利用电化学测试手段分析了酸洗后钢的耐蚀性,进一步提出了热轧退火2205双相不锈钢板在喷丸和酸洗过程中氧化层去除演变模型。结果表明:喷丸处理对于2205双相不锈钢表层富Fe氧化物的去除效果明显,但是不能去除内层致密的富Cr氧化层。盐酸预酸洗由外向内可以进一步去除喷丸后致密氧化层,硝酸和氢氟酸终酸洗可去除退火产生的贫Cr层,使得钢表面形成富含Cr₂O₃的钝化膜。2205双相不锈钢经混酸终酸洗后表现出比盐酸预酸洗后更高的自腐蚀电位和更大的容抗弧半径,说明混酸酸洗有利于提高2205双相不锈钢的耐蚀性能。     

Über das Verhalten einiger CrNiMo-Stähle beim Einsatz im chemischen Betrieb

The behaviour of some CrNiMo steels in use at chemical plants A report is given about the behaviour of some highly alloyed CrNiMo steels in use in inorganic-chemical plants. The observations are supported and supplemented by results of potentiostatic tests. In the presence of mixed acids, the corrosion resistance of the steels greatly depends, e.g., on the SO: Cl^? ion ratio. In the presence of Cl^? ions and at higher temperatures, exceeding about 70°C, the resistance is largely influenced by the specifically orientated analytical and structural pattern of the steels. Attention is drawn to the detrimental influence, especially in cast metals and welds, of the concomitant element, silicon, which — if encountered in increasing quantitities — favours the segregation of several corrosion-promoting phases. Examinations of case of damage in practical operation, supported by potentiostatic tests with CrNiMo steels, with and without copper contents, have shown that the presence of copper is apt to reduce the corrosion resistance in media containing hydrochloric acid or chlorine ions. On the other hand, a copper content may be beneficial in sulphate solutions free from chlorine ions.     

Korrosionsinhibitoren in der chemischen Industrie

Corrosion inhibitors in the chemical industries On the basis of some examples form industrial practice potential applications of inhibitors for the solution of specific corrosion problems are shown. It was e.g. possible to prevent corrosion of titanium equipment in a chemical factory by adding chlorine to the hydrochloric acid use for cleaning; in this case chlorine acts as a gaseous passivator. In another case titanium could be protected against attack by formic acid vapours by aerating the vapours; crevice corrosion encountered in this case was suppressed by adequate increases of the aeration rate, the inhibition efficiency being controlled by built-in reference electrodes. Protection by aeration was also successful in the case of columns of CrNiMo steal in contact with contaminated acetic acid. Difficulties were encountered with salt like inhibitors when a liquid as well as a gaseous phase was present. Emphasis is also placed on the importance of water additions to liquid ammonia in the case of steel vessels.     

Effect of potential on the corrosion behavior of a new titanium alloy for dental implant applications in fluoride media

The effect of fluoride ion concentration and pH on the corrosion behavior of TCA (60 Ti 10 Ag 30 Cu), which is a new Ti alloy with low melting point, pure Titanium (Ti), and TAV (TiAl6V4) was examined using open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) at different potentials. Results show that the corrosion resistance of TCA and Ti decrease at anodic potentials compared with results obtained at OCP. At one potential the corrosion resistance decrease depends on NaF concentration and pH. TAV shows less resistance against corrosion in fluoride containing saliva. TCA has potentials more positive than Ti and TAV due to surface enrichment of Cu and Ag as Ti dissolves which accelerates the cathodic reaction. Fluoride ion may not hinder the growth of oxide layers on the surfaces of the electrodes. It will have influence on the properties of the oxide layer causing them to be not protective against corrosion in acid media containing fluoride ions.     

海洋环境钛金属的应用现状及其防护技术研究

钛金属具有优异的耐海水和海洋大气腐蚀性能,因此在海洋装备中有广泛应用。但是钛金属在严酷海洋环境中应用表现出一些不足之处,如耐磨蚀性能差、易生物污损和电偶腐蚀等问题,严重影响了钛金属结构件的长寿命和安全可靠服役。介绍了钛金属在海洋环境中的应用现状,揭示了存在上述不足问题的本质原因。如海洋环境磨损与腐蚀的交互作用导致耐磨性能差的钛金属磨蚀损耗加剧,钛金属良好的生物相容性使其产生严重的生物污损,钛金属相比于其他金属具有较高的正电位,在介质环境中与异种金属偶接时作为阴极被保护从而加速偶接合金的腐蚀。鉴于钛金属优异的海洋耐候性,其在海洋环境中的应用必将越来越广泛,但是合适的表面处理和涂层防护是必不可少的。综述了国内外钛金属在海洋环境应用相关防护技术的研究现状,并对海洋环境中钛金属表面防护技术的发展方向和趋势进行了展望：金属陶瓷涂层和可控纳米结构氧化物陶瓷涂层是海洋环境钛金属运动部件耐磨蚀保护有效的技术手段;防污剂释放型和纳米缓释涂层技术是实现钛金属长效防生物污损很有前途的技术方法;钛金属表面低导电表面改性层的设计和制备可降低与其接触异金属的电偶腐蚀速度。     

A comparison between corrosion performances of titanium grade 2 and 7 in strong reducing acids

Titanium has a good corrosion resistance, owing to a thin, compact oxide layer that is formed spontaneously when the metal is exposed to the environment. However, even titanium can be subject to corrosion, for example, when exposed to reducing strong acids. This paper aims to analyze the differences in corrosion resistance of commercially pure titanium (Ti grade 2) and the most resistant Ti–Pd alloy (Ti grade 7, ∼0.2% Pd) in a strong reducing acid environment. Immersion tests, with results collected in the form of corrosion rates, are provided in the first part of the present work. Corrosion morphology is investigated using optical microscopy and laser profilometry. Then, an electrochemical characterization of both metals has been performed by means of cathodic polarization tests, electrochemical impedance spectroscopy, and linear polarization resistance. Weight loss data, electrochemical tests, and corrosion morphology are in good agreement: H₂SO₄, HCl, and oxalic acid are the most aggressive chemicals for commercially pure titanium. In such conditions, the use of Ti grade 7 appears mandatory.     

Corrosion resistance properties of plasma nitrided Ti-6Al-4V alloy in nitric acid solutions

The corrosion resistance of plasma nitrided Ti-6Al-4V titanium alloy in nitric acid solutions was investigated using polarisation curves, cyclic voltammetry, XRD analysis and surface microhardness. For comparison, untreated alloy samples were tested under the same conditions. While the untreated alloy shows a passive behaviour, the compound layer obtained by glow-discharge nitriding treatment, which is composed of an outer TiN and an inner Ti₂N layer, shows a high electrochemical inertia; however, if the polarisation potential is higher than a threshold or the period of immersion in high oxidising acid solution is sufficiently long, then the compound surface layer will be attacked and removed with corrosion rate higher than in the case of the untreated Ti-6Al-4V alloy. The corrosion resistance of Ti₂N layer results higher in comparison with that of TiN layer.     

Einige Anwendungszwecke für Kunststoffe in Zellstoff-Bleichanlagen

Some applications of plastics in pulp bleaching equipment Polyester resins with a high chlorine dibasic aromatic acid (Het acid) are characterized by a particular chemical indifference and inflammability. They are used with preference in installations contacted by chlorine dioxide and have been used for years, without any damage, in chlorine dioxide installations. The resins are mostly glass fibre reinforced and are resistant to the decompositions gases formed by detonations in such installations. They have also been used successfully for installations where excess chlorine is absorbed by alcaline media. Failures which have occurred in some rare cases - e.g. in hypochlorite solutions - could be attributed to insufficient curing of the resins. Optimum resistance is obtained by curing with a sufficient quantity of benzoyl peroxide + dimethyl aniline and by reducing to a minimum dilution by styrene. The resins offer resistance e.g. to the following media: NaCl, sat. (65°C); sulfuric acid 60% (65°C}); carbon tetrachloride; dimethyl acetamide; chromium sulfate, sat.(65°C).     

Characterisation of titanium oxide films by potentiodynamic polarisation and electrochemical impedance spectroscopy

Abstract

Titanium is used for many applications, ranging from chemical, biomedical, and decorative. Its versatility is due to its excellent mechanical properties, high corrosion resistance and biocompatibility. Moreover, its oxides, grown by anodising techniques, can have different colourations, which make them useful for applications related to art and architecture; in their crystalline form, they show excellent photochemical properties, which are widely used in chemical synthesis and in the cleansing of pollutants. The aim of this work is to characterise the titanium dioxide films, grown anodically in sulphuric acid 0·5 M at three different anodising potentials, by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). When comparing the obtained oxide films, a progressive increment in their crystallinity and electrical resistance was observed with the increase of the anodising potential.     

Effects of nitric acid passivation on the corrosion behavior of ZG06Cr13Ni4Mo stainless steel in simulated marine atmosphere

ZG06Cr13Ni4Mo martensitic stainless steel was nitric acid-passivated to improve its corrosion performance. The effects of nitric acid passivation on the surface morphology, chemical composition, electrochemical properties, semiconductor behavior, and long-term corrosion performance of the stainless steel were investigated using various analytical techniques. An in-depth analysis of X-ray photoelectron spectroscopy (XPS) showed that the passive film formed after the acid passivation process showed high thickness and a duplex character as it consisted of a hydroxide layer and an oxide layer. The oxide layer affected the corrosion resistance and thickness of the passive film. The thickness of the passive film was calculated theoretically as well as experimentally by fitting the electrochemical impedance spectroscopy and XPS results. The electrochemical tests revealed that the dramatic increase in the corrosion resistance of the stainless steel after the passivation was due to the formation of a thick, low-disorder passive film rather than Cr enrichment. The removal of inclusions resulted in higher pitting resistance, whereas the increased roughness showed a negative effect on the corrosion behavior of the stainless steel. During the wet–dry cyclic tests, the modification of the passive film was examined. The passivated stainless steel exhibited good corrosion resistance for up to 50 days of exposure in the simulated environment.     

Morphology and Properties of Coatings Obtained by Plasma-Electrolytic Oxidation of Titanium Alloys in Pyrophosphate Electrolytes

By means of scanning electron microscopy, atomic-force microscopy, X-ray fluorescence analysis, and X-ray spectral microanalysis it was shown that, under plasma-electrolytic oxidation (PEO) of titanium alloys in pyrophosphate electrolytes, well-adhered oxide coatings with microglobular morphology result. It was demonstrated that the chemical and phase composition of the coatings, as well as the surface topography and grain size, can be controlled by changing the concentration of a pyrophosphate electrolyte and a PEO current density. It was established that the resulting oxide layer is highly resistant to abrasive wear and enhances the titanium corrosion resistance in model media (Ringer’s solution) substantially, which suggests that the coatings are promising for use in biological applications.