铀钚金属表面抗腐蚀性研究进展

金属铀钚表面的腐蚀与防腐蚀一直受到关注,章综述了自1994年来作实验室在铀钚金属表面抗腐蚀性方面的研究进展。用X射线光电子能谱（XPS）、气相色谱（GC）等方法系统地分析研究了金属铀和U3O8与CO、CO2、H2等气体的相容性及其表面化学行为,铀试样在CO气氛中的贮存氧化增重及δ－Pu金属和铀试样在该气氛贮存期气相组成变化;应用改进的量子力学计算方法对金属铀钚化合物的分子结构、势能函数、光谱性质、热力学性质和动力学性质进行了系统研究;应用热力学平衡原理方法研究了铀和钚在还原气氛中的表面化学反应。通过实验与理论结合的系统研究,揭示了铀与上述气体介质相互作用的规律,得到一系列具有实际应用和理论意义的实验研究和理论计算结果,为进一步深化铀钚金属抗腐蚀研究奠定了基础。研究结果表明CO的存在有利于抑制铀钚金属的表面氧化腐蚀。     

预氧化对TP347H锅炉钢650℃水蒸气中腐蚀的影响

超临界发电锅炉在650℃水蒸气中常发生腐蚀,针对此问题进行了锅炉钢表面化学预氧化防护研究。先将锅炉钢TP347H放入管式炉中,管式炉通流量为20 mm/s的氧气,温度300℃下氧化2 h,利用重量法研究了氧化层对锅炉钢的防护效果,利用扫描电子显微镜观察了材料的表面形貌,结合产物成分分析得到以下结论：TP347H锅炉钢在300℃氧化2 h,可生成约0.2μm的氧化膜;这种氧化膜使材料在650℃水蒸气中腐蚀速度比未预氧化的材料降低了87.5%;表面没有氧化的TP347H锅炉钢在高温水蒸气中腐蚀后,产物为2层,表层主要为Fe的氧化物,底层为Fe、Cr、Ni的氧化物,2层间结合强度较差,外层产物容易脱落,而表面氧化后的试样腐蚀产物为单层,腐蚀产物中为Fe、Cr、Ni的氧化物,涂层与基体结合强度好,腐蚀产物不易脱落。     

金属铀热氧化腐蚀的红外和拉曼光谱分析

为了进一步认识金属铀环境腐蚀的规律,采用傅里叶变换红外和显微激光拉曼光谱技术,获得了金属铀与空气热氧化反应产物的红外和拉曼光谱图.实验结果表明,随着温度的升高,铀表面首先出现活性腐蚀亮斑,并逐渐积累长大,主要氧化产物UO2在260℃以上开始转化为U3O8.同时,200℃以上温度条件下,铀表面的热氧化腐蚀速率明显高于较低温度时的氧化反应.研究结果将为改善防腐措施、提高核燃料的安全可靠性提供有价值的参考信息.     

碳钢在H2S／CO2体系中的应力腐蚀开裂机理

应力腐蚀开裂是含H2S／CO2天然气输送管线腐蚀破坏的主要形式,探究其开裂机理有利于实施有效的防护,目前相关研究尚不够深入。采用扫描电子显微镜（SEM）和X射线衍射（XRD）等表面分析技术对U形环X52钢试样在H2S／CO2介质中的应力腐蚀开裂（SCC）行为进行了研究,并分析探讨了其发生SCC的机理。结果表明：X52钢...     

Q235B钢在船舶尾气脱硫液中的腐蚀行为

碱液脱硫是当前尾气处理领域的研究热点,产生的脱硫液是一个新的腐蚀体系.为了探究船舶尾气脱硫液对Q235B钢的腐蚀影响,通过浸泡试验并结合失重法,研究了Q235B钢在船舶尾气脱硫液中的腐蚀行为,并利用SEM、EDS、EPMA和XRD对浸泡后样品的锈层结构、组成、元素分布以及表面形貌进行分析.结果表明:腐蚀初期,碳钢表面沉积一层墨绿色絮状腐蚀产物,微观结构为花瓣状,主要成分为Fe(OH) 2,Fe(OH)3、Fe2O3·H2O,腐蚀类型以全面腐蚀为主;随着腐蚀时间延长,腐蚀产物发生变化,腐蚀受到抑制;在腐蚀35 d后,腐蚀转而以点蚀为主,红褐色的腐蚀产物为团簇状且致密排布,主要成分为Fe2O3·H2O、Fe3O4、FeSO4·4H2O.基于试验结果,推导出Q235B钢在脱硫液中的腐蚀机理:腐蚀初期主要以吸氧腐蚀为主;随着时间延长腐蚀受到抑制,腐蚀以FeSO4的氧化水解形成酸、酸的循环再生机制进行.     

金属间化合物的高温腐蚀与防护

综述了有序金属间化合物，主要是Ｎｉ－Ａｌ，Ｔｉ－Ａｌ和Ｆｅ－Ａｌ系金属间化合物高温腐蚀与防护方面的研究结果，包括它们的氧化腐蚀机理、合金元素对其氧化腐蚀性能的影响以及它们所需的高温涂层等。     

金属间化合物的高温腐蚀与防护

综述了有序金属间化合物，主要是Ｎｉ－Ａｌ，Ｔｉ－Ａｌ和Ｆｅ－Ａｌ系金属间化合物高温腐蚀与防护方面的研究结果，包括它们的氧化腐蚀机理、合金元素对其氧化腐蚀性能的影响以及它们所需的高温涂层等。     

铀及其合金表面防护技术的概况及展望

铀作为核能材料,应用很广泛.但铀的化学性质非常活泼,极易腐蚀,研究者们对其表面防护技术进行了许多研究,总结了铀及其合金各种表面防护技术的发展及应用,并对未来的发展趋势进行了展望.     

阳极氧化法制备TiO2纳米管阵列

采用阳极氧化法在乙二醇体系电解液中制备TiO2纳米管阵列,获得了长度为15~20μm的底端纳米管与顶端纳米线的新型复合结构。讨论了电解液中不同含水量对该复合结构形成的影响,并采用两步阳极氧化法对该结构的形成机理进行了分析。结果表明,当乙二醇体系电解液含有0.4%(质量分数)NH4F和2%(体积分数)H2O时,电解液腐蚀速度适中,纳米管上端部分被选择性腐蚀,最终形成纳米管与纳米线的复合结构。     

变电站端子箱铜包铝电缆屏蔽线的腐蚀现象、机理与防护措施

变电站端子箱中的铜包铝电缆屏蔽线腐蚀严重,通过对其腐蚀产物及横截面的电镜(SEM)扫描、能谱(EDS)和X射线衍射分析,分别用稀HCl,NaCl和NaOH溶液进行盐雾腐蚀,验证了其腐蚀机理;又分别采用K2 Cr2O7,苯丙三氮唑和823溶液进行了防护效果试验.结果表明:腐蚀产物中存在Cl元素,AlCl3及CuCl等物质,阻火泥和屏蔽线外包覆材料中也有大量Cl元素;HCl溶液使铜包铝电缆屏蔽线腐蚀速率最快;823溶液浸泡对铜包铝电缆屏蔽线的防护效果最好.     

Computational Simulation of Redox Reactions within a Metal Electrospray Emitter

A computational simulation of the oxidation of chemical species inside a metal emitter electrospray ion source, in the context of electrospray mass spectrometry (ES-MS), has been developed. The analysis code employs a boundary integral method for the solution of the Laplace equation for the electric potential and current and incorporates standard activation and concentration polarization functions for the redox-active species in the system to define the boundary conditions. This paper provides a demonstration of the capability of this simulation method. Due to the approximate nature of some of the input data, and certain simplifying assumptions, the present results must be considered semiquantitative. The specific system modeled consisted of a 100-μm-i.d., inert metal capillary ES emitter and a spray solution composed of an analyte dissolved in CH(3)CN/H(2)O (90/10 v/v). Variable parameters included the concentration (i.e., 5.0, 10, 20, and 50 μM) of the easily oxidized analyte ferrocene (Fc, dicyclopentadienyl iron) in the solution, and solution conductivities of 1.9, 3.8, and 7.6 × 10(-)(7) Ω(-)(1)/cm, with an operational flow rate of 5.0 μL/min and ES currents on the order of 0.05 μA. Under these defined conditions, the two most prominent reactions at the emitter metal/solution interface were assumed to be H(2)O oxidation (2H(2)O = O(2) + 4H(+) + 4e(-)) and ferrocene oxidation (Fc = Fc(+) + e(-)). Using this model, it was possible to predict the interfacial potentials, as well as the current density for each of the reactions, as a function of axial position from the emitter spray tip back upstream, under the various operational conditions. The simulations show that the majority of the current from the redox reactions is generated within a 200-300-μm region near the spray tip. The lower the value of E(0) for a specific reaction, the further upstream from the tip the reaction extends.     

Chromium behavior during cement-production processes: a clinkerization, hydration, and leaching study

The behavior of chromium during the production of cement clinker, during the hydration of cement and during the leaching of cement mortars was investigated. The microstructures of clinker and mortar properties were investigated using free lime, XRD, SEM/EDS, and TG/DTA techniques. Chromium was found to be incorporated in the clinker phase. The formation of new chromium compounds such as Ca(6)Al(4)Cr(2)O(15), Ca(5)Cr(3)O(12), Ca(5)Cr(2)SiO(12), and CaCr(2)O(7), with chromium oxidation states of +3, +4.6, +5, and +6, respectively, was detected. After the hydration process, additional chromium compounds were identified in the mortar matrix, including Ca(5)(CrO(4))(3)OH, CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), with chromium oxidation states of +4.6, +6, and +6, respectively. Additionally, some species of chromium, such as Cr(3+) from Ca(6)Al(4)Cr(2)O(15) and Cr(6+) from CaCr(2)O(7), CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), were leached during leaching tests, whereas other species remained in the mortar. The concentrations of chromium that leached from the mortar following U.S. EPA Method 1311 and EA NEN 7375:2004 leaching tests were higher than limits set by the U.S. EPA and the Environment Agency of England and Wales related to hazardous waste disposal in landfills. Thus, waste containing chromium should not be allowed to mix with raw materials in the cement manufacturing process.     

Oxidation of cyanide in aqueous solution by chemical and photochemical process

Cyanide waste is found predominantly in industrial effluents generated from metallurgical operations. The toxicity of cyanide creates serious environmental problems. In this paper, oxidation of cyanide in aqueous solution was investigated using chemical and photochemical process. Chemical oxidation was studied at room temperature using H2O2 as oxidant and Cu2+ as catalyst. Photochemical oxidation was studied in an annular type batch photoreactor of 1l capacity using 25 W low-pressure (81.7% transmission at 254 nm wavelength) ultraviolet (UV) lamp along with H2O2 as oxidant. The effect of Cu2+ catalysis was also studied. It was observed that in absence of UV source, the degradation of cyanide by H2O2 alone was very slow, whereas copper ions accelerated the rate of reaction thereby acting as catalyst. Copper formed a complex with cyanide ion, i.e. tetracyanocuprate which had greater affinity for H2O2. Cyanate hydrolysis was also favoured by copper ions. As Cu2+ ion concentration was increased, rate of degradation also increased. Photochemical oxidation by H2O2 and Cu2+ was found to be the best system for cyanide degradation. CN- (100 mg/l) was degraded to non-detectable level in 9 min at pH 10.0 with optimum H2O2 dose of 35.5 mM and Cu2+ dose of 19 mg/l. Reaction kinetics of cyanide oxidation was found to be pseudo-first order and the rate constant has been determined for different processes.     

Electrochemiluminescence of copper(I) bis(2,9-dimethyl-1,10- phenanthroline)

The electrochemical and electrochemiluminescence (ECL) properties of Cu[dmp]2+ (dmp = 2,9-dimethyl-1,10-phenanthroline) have been investigated. ECL has been observed for Cu(dmp)2+ in aqueous, nonaqueous, and mixed solvent solutions using tri-n-propylamine as an oxidative-reductive coreactant. The ECL intensity peaks at potential corresponding to oxidation of both the coreactant and Cu(dmp)2+. The peak potential corresponding to maximum ECL emission is approximately 500 mV more anodic than corresponding oxidative peak potentials, indicating that the ECL emission may be due to the formation of either the *Cu(dmp)2+ metal-to-ligand charge-transfer excited state or an excited-state product of Cu(dmp)2+ oxidation. ECL efficiencies (phiecl = photons generated per redox event) are solvent-dependent (phiecl (CH3CN) > phiecl (50:50 (v/v) CH3CN:H20) > phiecl (H2O)) and correspond fairly well with photoluminescence efficiencies. Increased ECL efficiencies (> or = 50-fold) are observed in the presence of the nonionic surfactant Triton X-100.     

Green synthesis of uniform magnetite (Fe3O4) nanoparticles and micron cubes

Single-crystalline Fe3O4 microcubes were obtained through a green hydrothermal procedure using Fe3+, Fe2+ and H2O2 as starting materials. The structures and morphologies of the as-prepared samples were characterized in detail by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) respectively. Magnetite (Fe3O4) cubes averaging 3 microm in diameter were synthesized by H2O2 oxidation of Fe3+ and Fe2+ under neutral conditions. The contrastive experiments were designed to elucidate the effects of Fe3+, Fe2+ and H2O2 on the morphology of the final products. Irregular and ellipsoidal Fe2O3 structures were obtained by H2O2 oxidation of Fe3+ and Fe2+ respectively. Meanwhile, Fe3O4 nanotubes and nanoparticles were obtained when H2O2 was replaced by NH4HCO3 and urea respectively. The results show that H2O2, Fe3+ and Fe2+ in the reactive system play critical roles in obtaining micrometric cube-like Fe3O4. While, other nanometric Fe2O3 and Fe3O4 particles with tube-like and other morphologies could also be developed by controlling the reaction parameters.     

Reaction of ozone with uranium(IV) oxalate in water

Decomposition of aqueous suspensions of uranium(IV) oxalate under the action of an ozone–oxygen mixture was studied. The process occurs in two steps. In the first step, the U(IV) oxidation with the formation of oxalic acid uranyl solutions prevails. The second step involves decomposition of oxalate ions and hydrolysis of uranyl ions. An increase in temperature accelerates the transformation of uranium(IV) oxalate into uranium(VI) hydroxide compounds. In solutions containing KBr or UO₂Br₂, the following reaction occurs: O₃ + Br^– → O₂ + BrO^–. The arising hypobromite ions and hypobromous acid oxidize uranium(IV) oxalate extremely efficiently. The possible mechanism of ozonation of aqueous uranium(IV) oxalate suspensions is discussed.     

Chemical shift of U L3 edges in different uranium compounds obtained by X-ray absorption spectroscopy with synchrotron radiation

Uranium L₃ X-ray absorption edge was measured in various compounds containing uranium in U⁴⁺, U⁵⁺ and U⁶⁺ oxidation states. The measurements have been carried out at the Energy Dispersive EXAFS beamline (BL-08) at INDUS-2 synchrotron radiation source at RRCAT, Indore. Energy shifts of ~ 2–3 eV were observed for U L₃ edge in the U-compounds compared to their value in elemental U. The different chemical shifts observed for the compounds having the same oxidation state of the cation but different anions or ligands show the effect of different chemical environments surrounding the cations in determining their X-ray absorption edges in the above compounds. The above chemical effect has been quantitatively described by determining the effective charges on U cation in the above compounds.     

Novel active heterogeneous Fenton system based on Fe3-xMxO4 (Fe, Co, Mn, Ni): the role of M2+ species on the reactivity towards H2O2 reactions

In this work, the effect of incorporation of M2+ species, i.e. Co2+, Mn2+ and Ni2+, into the magnetite structure to increase the reactivity towards H2O2 reactions was investigated. The following magnetites Fe3-xMnxO4, Fe3-xCoxO4 and Fe3-xNixO4 and the iron oxides Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 were prepared and characterized by M?ssbauer spectroscopy, XRD, BET surface area, magnetization and chemical analyses. The obtained results showed that the M2+ species at the octahedral site in the magnetite strongly affects the reactivity towards H2O2, i.e. (i) the peroxide decomposition to O2 and (ii) the oxidation of organic molecules, such as the dye methylene blue and chlorobenzene in aqueous medium. Experiments with maghemite, gamma-Fe2O3 and hematite, alpha-Fe2O3, showed very low activities compared to Fe3O4, suggesting that the presence of Fe2+ in the oxide plays an important role for the activation of H2O2. The presence of Co or Mn in the magnetite structure produced a remarkable increase in the reactivity, whereas Ni inhibited the H2O2 reactions. The obtained results suggest a surface initiated reaction involving Msurf2+ (Fe, Co or Mn), producing HO radicals, which can lead to two competitive reactions, i.e. the decomposition of H2O2 or the oxidation of organics present in the aqueous medium. The unique effect of Co and Mn is discussed in terms of the thermodynamically favorable Cosurf3+ and Mnsurf3+ reduction by Femagnetite2+ regenerating the active species M2+.     

Monitoring the speciation of aqueous free chlorine from pH 1 to 12 with Raman spectroscopy to determine the identity of the potent low-pH oxidant

The speciation of aqueous free chlorine above pH 5 is a well-understood equilibrium of H2O + HOCl <==> OCl- + H3O+ with a pKa of 7.5. However, the identity of another very potent oxidant present at low pH (below 5) has been attributed by some researchers to Cl2(aq) and by others to H2OCl+. We have conducted a series of experiments designed to ascertain which of these two species is correct. First, using Raman spectroscopy, we found that an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+ is unlikely because the "apparent pKa" increases monotonically from 1.25 to 2.11 as the analytical concentration is increased from 6.6 to 26.2 mM. Second, we found that significantly reducing the chloride ion concentration changed the Raman spectrum and also dramatically reduced the oxidation potency of the low-pH solution (as compared to solutions at the same pH that contained equimolar concentrations of Cl- and HOCl). The chloride ion concentration was not expected to impact an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+, if it existed. These observations supported the following equilibrium as pH is decreased: Cl2(aq) + 2H2O <==> HOCl + Cl- + H3O+. The concentration-based equilibrium constant was estimated to be approximately 2.56 x 10(-4) M2 in solutions whose ionic strengths were approximately 0.01 M. The oxidative potency of the species in low pH solutions was investigated by monitoring the oxidation of secondary alcohols to ketones. These and other results reported here argue strongly that Cl2(aq) is the correct form of the potent low-pH oxidant in aqueous free-chlorine solutions.