Sections of the CO(NH2)2-NH4NO3-CH3CONH2-H2O quaternary system

Four sections of the urea-ammonium nitrate-acetamide-water system were studied by the visual polythermal method over wide temperature and concentration ranges. The system was found to be of the simple eutonic type. The corrosion activity of some mixtures of liquid fertilizers at various temperatures was determined.     

Effect of acidity level Ro(H) on the corrosion of steel in concentrated HCL solutions

The corrosion of a carbon steel in (0.5 – 9.0 M) HCl media using weight loss, electrochemical polarization and polarization resistance measurements was investigated. The corrosion data are discussed as function of the Strehlow acidity function R_o(H) which is the extension of pH in concentrated solutions. Weight loss, corrosion current densities and resistance polarization values show a linear behaviour with the R_o(H) acidity function. The corrosion potential-R_o(H) plot is also linear using the ferricinium (Fc⁺) / ferrocene (Fc) reference electrode in concentrated acid solutions.     

混凝土中钢筋的腐蚀行为研究

本文探讨了在不同 pH和Cl- 含量的模拟混凝土孔隙液介质中 ,混凝土中钢筋的腐蚀电化学行为 .电化学技术测试结果表明 ,正常情况下 ,钢筋在混凝土中受到高碱性环境的保护 ,耐蚀性好 .但随着介质 pH的降低、Cl- 含量的上升 ,钢筋腐蚀电流升高 ;动电位阳极极化曲线的测试表明 ,钢筋的维钝电流增大 ,击穿电位负移 ,混凝土中钢筋的耐蚀性下降 .这是钢筋表面钝性受破坏的缘故 .     

Corrosion resistance of molybdenum silicides in aqueous solutions

The corrosion performance of Mo-22Si and Mo-25Si alloys in 0.5 M sodium chloride (NaCl) and 0.5 M sodium hydroxide (NaOH) solutions, at room temperature, was evaluated using electrochemical techniques. In 0.5 M NaCl, additionally, the effect of solution pH (3, 7 and 10) and concentration (0.1, 0.5 and 1.0 M) was studied using techniques such as potentiodynamic polarization curves, linear polarization resistance and electrochemical noise in current. The alloy contained either -Mo or Mo₅Si₃ phases in a Mo₃Si matrix. Polarization results showed that only the alloys containing 22Si developed a passive film in 0.5 M NaOH solution, whereas the alloy containing 25Si was passivated only in 0.5 M NaCl, pH 10 solution. In 0.5 M NaCl, pH 7 and 0.5 M NaOH solutions, the alloy with 25Si was the one with the highest corrosion rate, whereas the one containing 22Si was the most corrosion resistant. In NaCl solutions, the alloys exhibited a localized type of corrosion, but not in NaOH solutions. Alkaline NaCl solutions increased the corrosion rate of the 75Mo-25Si alloy with respect to acidic or neutral solutions, whereas diluted (0.1 M) or concentrated (1.0 M) NaCl solutions produced lower corrosion rates than the 0.5 M NaCl solution. Some localized type of corrosion occurred in the NaCl solutions, due to a selective corrosion of the -Mo and Mo₅Si₃ phases with respect to the Mo₃Si matrix.     

醋酸介质中溶解氧对不锈钢和磷脱氧铜腐蚀行为影响

应用极化曲线法和溶解氧测量技术研究不锈钢_2 0 6和磷脱氧铜在醋酸介质中的腐蚀行为以及过程的控制特征 .分析在含氧及采用抗坏血酸去除部分溶解氧的醋酸介质中 ,醋酸浓度、氯度、温度对上述两种金属腐蚀行为的影响因素 ,为石油化工中的醋酸设备的正确选材及有效防腐提供理论和实验依据     

Liquid chromatographic determination of urea in water-soluble urea-formaldehyde fertilizer products and in aqueous urea solutions: collaborative study

Water soluble urea-formaldehyde (UF) fertilizers, manufactured by complex reaction of urea and formaldehyde, typically contain varying amounts of unreacted urea. A liquid chromatography method for the analysis of urea in these products, and in aqueous urea solutions, was collaboratively studied. An amine chromatography column was used to separate the unreacted urea from numerous UF reaction products present in these liquid fertilizers. Unreacted urea was determined by using external urea standards with UV detection at 195 nm. The standards and test samples were prepared in the mobile phase of 85% (v/v) acetonitrile in water. Ten laboratories analyzed 5 different UF-based commercial products containing unreacted urea in the range of 6 to 17% by weight, and 5 different concentrations of urea in water equivalent to commercial products of that nature. The aqueous urea solutions contained 2-20% urea (w/w). The range of s(R) values for the 5 UF-based commercial fertilizers was 0.49-1.02 and the %RSD(R) was 1.94-6.14. The s(R) range for the 5 urea solutions was 0.10 to 0.79 and the %RSD(R) range was 2.54 to 4.88. The average recovery of urea from the aqueous urea solutions was 96-103%. Therefore, this method is capable of monitoring urea nitrogen manufacturers' label claims and total nitrogen claims in those cases where urea is the sole source of plant food nitrogen. Based on the collaborative study data, the authors recommend this method be approved for AOAC Official First Action status.     

The effect of chloride concentration and pH on pitting corrosion of AA7075 aluminum alloy coated with phenyltrimethoxysilane

The effect of chloride ion concentration and pH of solution on the corrosion behavior of aluminum alloy AA7075 coated with phenyltrimethoxysilane (PTMS) immersed in aqueous solutions of NaCl is reported. Potentiodynamic polarization, linear polarization, open circuit potential, and weight loss measurements were performed. The surface of samples was examined using SEM and optical microscopy. Elemental characterization of the coating by secondary ion mass spectrometry indicates an intermediate layer between coating and aluminum alloy surface. The corrosion behavior of the aluminum alloy AA7075 depends on chloride concentration and pH of solution. In acidic or neutral solutions, general and pitting corrosion occur simultaneously. On the contrary, exposure to alkaline solutions results in general corrosion only. Results further reveal that aluminum alloy AA7075 is susceptible to pitting corrosion in all chloride solutions with concentrations between 0.05 M and 2 M NaCl; an increase in the chloride concentration slightly shifted both the pitting and corrosion potentials to more active values. Linear polarization resistance measurements show a substantially improved corrosion resistance value in case of samples coated with PTMS as compared to uncoated samples in both neutral (pH = 7), acidic (pH = 0.85 and 3), and alkaline chloride solutions (pH = 10 and 12.85). The higher corrosion resistance of the aluminum alloy coated with PTMS can be attributed to the hydrophobic coating which acts as a barrier and prevents chloride ion penetration and subsequent reaction with the aluminum alloy.     

温度和溶液pH值交互作用对X80钢在模拟土壤环境中腐蚀行为的影响

利用循环伏安法（CV）、电化学阻抗谱（EIS）和Mott-Schottky曲线研究了温度和溶液pH值交互作用下X80钢在模拟土壤环境中的腐蚀性能。结果表明：低pH值条件下X80钢表面会形成一层稳定性差的腐蚀膜;高pH值条件下X80钢表面会形成一层保护性强的腐蚀膜。随着pH值得增大和温度的降低X80钢表面所成腐蚀膜的膜电阻和传递电阻增大,这表明随着pH值得增大和温度的降低X80钢表面所成腐蚀膜对基体的保护性增强。X80钢在模拟土壤环境中表面所成腐蚀膜呈n型半导体特性,膜内施主密度随介质pH值增大而降低,随溶液温度升高而增大。平带电位和pH值之间呈现线性关系。     

Use of rare earth metal salt solutions for corrosion protection of aluminum alloys and mild steel

The rare earth metal salt (REMS) compounds which are non-toxic and inexpensive have been used successfully for the corrosion protection of commercial aluminum alloys as well as of mild steel. The resistance to localized corrosion of aluminum alloys such as Al 2024, Al 6061 and Al 7075 has been greatly improved by immersion in hot cerium salt solutions. Cerium oxides/hydroxides were formed at sites where intermetallic compounds containing copper were located and eliminated the formation of local cathodes. REMS solutions were also used for sealing of anodized layer on Al alloys replacing toxic chromates. In addition to increased corrosion resistance excellent paint adhesion was observed. Cerium nitrate and yttrium sulfate solutions produced the most satisfactory results. Cerium salts were also applied successfully as inhibitors and as pretreatment for the corrosion protection of carbon steel in hot NH₃/water solutions used in absorption heat pumps. Factorial design experiments have been used to determine the optimum concentrations of CeCl₃ and H₂O₂ as well as the treatment time used in the cerating process for mild steel. The corrosion protection provided by the cerated layer was further improved by cathodic polarization in cerium chloride. A dual corrosion protection strategy employing cerating and addition of a REMS to the working solution is expected to provide long-lasting corrosion protection of mild steel. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth. This article was submitted by the author in English.     

Application of Polytyramine Nanoparticles to the Corrosion Protection of Copper

Electrochemical polymerization of tyramine was achieved on copper electrode surface from tyramine in 0.3 M oxalic acid (pH=1.2) solution by using cyclic voltammetry technique. The formation of polytyramine nanoparicles (PTN) were characterized by cyclic voltammetry (CV), fourier transform infrared‐attenuated total reflectance (FTIR‐ATR) spectroscopy and scanning electron microscopy (SEM). The corrosion behavior of PTN coated copper was investigated by means of the change of open circuit potential with exposure time (E_ocp t), electrochemical impedance spectroscopy (EIS) and anodic polarization curves in 3.5 % NaCl solutions at room temperature. The obtained results showed the shift of corrosion potential toward positive values for electropolymerized copper and a significant decrease in corrosion current and corrosion rate in comparison with bare copper, so that the PTNs coating could be used as an important protection against corrosion of copper.     

Determination of metal corrosion rate using the pH-metry by the method of compensating additives

A possibility for determining the metal corrosion current in the acidic solutions in the absence of external polarization is considered. The calculations are based on the analysis of time dependence of the amount of electrolyte with a lower pH value (as compared with the pH value of the working solution), which was introduced into the measuring cell in order to compensate an increase of the pH value in the course of corrosion.     

扫描电化学显微镜原位表征pH值对核电蒸汽发生器合金腐蚀行为的影响

用扫描电化学显微镜(SECM)和电化学阻抗谱(EIS)原位表征了溶液pH值对核电蒸汽发生器800 合金溶液中的腐蚀行为的影响. 实验结果表明：在酸性氯化钠溶液中,SECM探针渐进曲线为正反馈,表明800合金为活化阳极溶解,腐蚀电位下的EIS 图呈现完整的单容抗弧特征;而在中性或者碱性溶液中,SECM探针渐进曲线为负反馈,表明800 合金为自钝化,不同阳极电位下的EIS 图均呈现不完整的容抗弧特征,但随着阳极极化电位的增加,EIS 谱容抗弧半径减小,表明钝化膜的耐蚀性下降;SECM二维扫描图像结果显示探针电流增加,表明电极表面活性增加,即钝化膜的溶解速度增加. 而在中性或者碱性溶液中的SECM二维图像中均可观察到若干活性点,这可能与晶界或者金属夹杂物等有关.     

硫酸根离子对铁在弱碱性溶液中阳极溶解和钝化行为的影响

采用浸泡实验, 电化学测试和表面分析技术研究了硫酸根离子浓度对铁在稀碳酸氢钠溶液中开路状态和阳极极化行为的影响. 在无硫酸根离子及含有少量硫酸根离子的碳酸氢钠溶液中, 铁的开路电位约为(-0.225±0.005) V, 并呈现钝化状态, 其电化学阻抗很大, 腐蚀速率较低. 在含有较高浓度硫酸根离子的碳酸氢钠溶液中, 铁的开路电位为(-0.790±0.010) V并呈现活性溶解状态, 其电化学阻抗较小, 腐蚀速率较高, 同时阳极极化曲线上能观察到活化-钝化转变现象. 由于铁在含有较高浓度硫酸根离子的碳酸氢钠溶液中处于活化状态, 阳极极化曲线上存在数个电流峰. 足够高的硫酸根离子浓度会导致铁表面预先形成或转变而成的氧化膜失效. 相比于自然曝氧状态, 在除氧条件下较低的硫酸根离子浓度即可引起铁在碳酸氢钠溶液中由钝态向活性溶解态的转变.     

Material Analysis of Steel Corrosion Products in Water Coolants of Thermal and Nuclear Power Plants

The poor informativity of conventional elemental analysis in the industrial control of equipment corrosion at thermal and nuclear power plants was discussed. A set of methods was proposed for the material analysis of steel corrosion products. The set includes spectrophotometry for determining the chemical composition of hydroxo complexes in aqueous solutions and various versions of Mossbauer spectroscopy for identifying and determining corrosion products in the solid phase of suspensions, loose deposits, and corrosion films on steel surfaces.     

Effects of exposure time on the anodic dissolution of Monel-400 in aerated stagnant sodium chloride solutions

The anodic dissolution of Monel-400 (63.0% Ni, 28–34% Cu) alloy after its immersion in freely aerated stagnant 3.5% NaCl solutions for 0, 24, and 72 h has been investigated. The study was carried out using a variety of electrochemical techniques and gravimetric measurements after varied exposure periods (5–160 days). The work was complemented by scanning electron microscopy and energy dispersive X-ray analyzer (SEM/EDX) investigations. The electrochemical measurements showed that Monel suffers both general and pitting corrosion. The severity of uniform corrosion decreased, while pitting one increased with increasing the immersion time to 24 h and further to 72 h before measurements. Gravimetric data indicated that the weight loss increased, while the corrosion rate decreased for Monel with time. SEM images and EDX profile analyses confirmed that the corrosion of Monel after 160 days immersion in NaCl solutions occurs due to the selective dissolution of nickel.     

Sorption extraction of lanthanides from phosphoric acid solutions

The possibility of sorption extraction of lanthanides from nitric-phosphoric and phosphoric acid solutions with inorganic sorbents based on hydrated titanyl hydrophosphate was studied. New technological solutions were suggested for lanthanide sorption from the products which are formed in processing of the Khibiny apatite concentrate on mineral fertilizers (frozen nitric-phosphoric acid extract, a product of nitric acid decomposition of apatite, and the production phosphoric acid from the dihydrate process).     

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduces pitting potential. In addition, the influence of the post-processing heat treatment temperature was recognized. Penetrating attacks occurred either on after low temperatures stress relieving or specimens without any treatment, promoted by selective dissolution of the α-Al phase stimulated by galvanic coupling with noble silicon precipitates at the border of the melt pool. Such penetrating morphology was not observed after heat treatments at high temperature.     

Inhibition of steel corrosion by calcium benzoate adsorption in nitrate solutions: theoretical and experimental approaches

The inhibitive effects of calcium benzoate on steel corrosion were studied in sodium nitrate solutions at room temperature. Corrosion parameters of the steel/nitrate and steel/benzoate + nitrate interfaces were obtained from polarization curves. Adsorption parameters of benzoate on steel in sodium nitrate solutions were determined through changes in the degree of surface coverage by the inhibitor, as a function of concentration, time, and adsorption potential. The most likely adsorption configuration of benzoate on iron was envisaged with the help of semiempirical calculations such as extended Hückel calculations. A two-dimensional flat configuration was involving at least two metal atoms, one interacting with the phenolic group and the other with the carboxylate moiety. The effect of chloride on the corrosion inhibition of benzoate was analyzed by exposing the metal to different chloride solution concentrations, from which corrosion parameters were calculated and compared with those in nitrate solutions.     

A study of the sulfuric acid leaching of rare-earth elements,phosphorus, and alkali metals from phosphodihydrate

The leaching of rare-earth elements, phosphorus, and alkali metals from phosphodihydrate, obtained in processing of the Khibiny apatite concentrate into mineral fertilizers, with sulfate solutions with a sulfuric acid concentration c(H₂SO₄) = 0.5−4 wt % was studied.     

Corrosion behavior of aluminum exposed to a biodiesel

Aluminum was exposed to biodiesel with different levels of contaminants and impurities, and its corrosion behavior was evaluated by conventional electrochemical techniques. It was found that the corrosion behavior of aluminum in biodiesel contaminated with alkalis is similar to the corrosion behavior of aluminum in aqueous solutions. In addition, it was demonstrated that corrosion of aluminum can be used as a quantitative indication of the biodiesel purity.