The Mechanism of Dezincification and the Effect of Arsenic. I.

Abstract

Copper formed by dezincification of brass shows, in microsections, a dense layer at the surface roughly proportional in thickness to the depth of dezincificatton. The underlying copper frequently shows growth rings of alternate, more or less dense copper layers, sometimes incorporating bands of cuprous oxide, and a narrow band of dense copper is usually observed adjacent to the advancing corrosion front. These features are explained, and have been reproduced in laboratory experiments, on the basis of a redeposition theory of dezincification.

The first step in either dezincification or pitting corrosion of brass is dissolution of both copper and zinc, the copper forming cuprous chloride. In pitting corrosion the cuprous chloride is precipitated and subsequently hydrolysed or oxidised to secondary corrosion products. In dezincification, it is reduced to copper close to the point at which it first forms.

Beta- and non-arsenical alpha-brass both reduce cuprous chloride to copper (the beta much more readily), but arsenical alpha does not. These differences between the three types of brass are reflected in their relative susceptibility to dezincification. The reasons for these differences will be reported in Part II of the paper.     

Kinetics of mild steel corrosion in aqueous formic acid solutions

Abstract

The kinetics of the corrosion of mild steel in formic acid solutions of different concentrations has been studied at 25, 35 and 45°C. The corrosion rate was evaluated by weight loss and electrochemical polarisation techniques. There is good agreement between the data obtained by the two techniques. The maximum corrosion rate was observed in close vicinity of 20% formic acid solution. The anodic polarisation curves show active corrosion behaviour of mild steel over the whole range of potential at each concentration and temperature. The shape of anodic and cathodic polarisation curves was found to be almost independent of the temperature and the concentration of formic acid. However, the curves bodily shift towards the lower or higher current density side with the change in the concentration of the electrolyte. With the increase in temperature, the shift of polarisation curve regularly occurs towards the higher current density side. The surface morphology of the specimens has been studied by scanning electron microscopy. The micrographs indicate uniform corrosion of mild steel in formic acid solution.

On a étudié la cinétique de corrosion de l’acier au carbone en solutions d’acide formique à différentes concentrations, à 25, 35 et 45°C. On a évalué la vitesse de corrosion par des techniques de perte de poids et de polarisation électrochimique. Il y a un bon accord entre les données obtenues par les deux techniques. On a observé la vitesse maximale de corrosion dans une solution de près de 20% d’acide formique. Les courbes de polarisation anodique montrent un comportement de corrosion active de l’acier au carbone pour la gamme complète de potentiel à chaque concentration et température. On a trouvé que la forme des courbes de polarisation anodique et cathodique était presque indépendante de la température et de la concentration de l’acide formique. Cependant, le c?ur des courbes se déplace du côté d’une densité de courant plus faible ou plus élevée avec un changement de concentration de l’électrolyte. Avec une élévation de la température, le déplacement de la courbe de polarisation se produit régulièrement du côté d’une densité de courant plus élevée. On a étudié la morphologie de la surface des échantillons au moyen du microscope électronique à balayage. Les micrographes indiquent une corrosion uniforme de l’acier au carbone dans une solution d’acide formique.     

有限板多孔MSD的应力强度因子计算

首先阐明组合法求解有限板多孔MSD( multiple site damage)应力强度因子的基本原理,然后就组合法运用中比较难以解决的多孔边裂纹间的修正系数问题,提出一种基于复变函数法的有效解决方法.将完善后的组合法应用于有限板多孔MSD应力强度因子的求解,计算某型飞机典型铆接壁板无主裂纹和含主裂纹两种情况的数值算例.通过与有限元结果的比较可知,该方法的计算结果精确、可靠,计算过程简单、易行.提出的近似解析方法能很好地应用于任意分布的有限板多孔MSD裂纹结构,在工程断裂问题中有较好的应用价值.     

Combination treatment of alkaline electrolyzed water and citric acid with mild heat to ensure microbial safety, shelf-life and sensory quality of shredded carrots

The objective of this study was to determine the synergistic effect of alkaline electrolyzed water and citric acid with mild heat against background and pathogenic microorganisms on carrots. Shredded carrots were inoculated with approximately 6-7 log CFU/g of Escherichia coli O157:H7 (932, and 933) and Listeria monocytogenes (ATCC 19116, and 19111) and then dip treated with alkaline electrolyzed water (AlEW), acidic electrolyzed water (AcEW), 100 ppm sodium hypochlorite (NaOCl), deionized water (DaIW), or 1% citric acid (CA) alone or with combinations of AlEW and 1% CA (AlEW + CA). The populations of spoilage bacteria on the carrots were investigated after various exposure times (1, 3, and 5 min) and treatment at different dipping temperatures (1, 20, 40, and 50 °C) and then optimal condition (3 min at 50 °C) was applied against foodborne pathogens on the carrots. When compared to the untreated control, treatment AcEW most effectively reduced the numbers of total bacteria, yeast and fungi, followed by AlEW and 100 ppm NaOCl. Exposure to all treatments for 3 min significantly reduced the numbers of total bacteria, yeast and fungi on the carrots. As the dipping temperature increased from 1 °C to 50 °C, the reductions of total bacteria, yeast and fungi increased significantly from 0.22 to 2.67 log CFU/g during the wash treatment (p ≤ 0.05). The combined 1% citric acid and AlEW treatment at 50 °C showed a reduction of the total bacterial count and the yeast and fungi of around 3.7 log CFU/g, as well as effective reduction of L. monocytogenes (3.97 log CFU/g), and E. Coli O157:H7 (4 log CFU/g). Combinations of alkaline electrolyzed water and citric acid better maintained the sensory and microbial quality of the fresh-cut carrots and enhanced the overall shelf-life of the produce.     

良好分散尼龙6/多壁碳纳米管复合材料的研究

采用柔和混合法制备纳米粒子良好分散的尼龙-6/多壁碳纳米管(PA6/MWNTs)复合材料,采用差示扫描量热仪(DSC)和广角X射线衍射法(XRD)研究了MWNTs对PA6基体结晶熔融行为的影响。DSC结果表明,MWNTs的加入大幅度地提高了PA6的结晶温度(最高提高约20℃),基体的结晶度也有所提高,说明良好分散的MWNTs在PA6结晶过程中呈现明显的异相成核作用;XRD结果证实,分散良好的MWNT促进PA6形成α晶型,抑制γ晶型的形成。同时,MWNT的加入导致复合材料出现熔融双峰现象,其形状随MWNT含量的变化而改变,双峰结构可能是由于熔融过程中伴随着重结晶而引起的。     

Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media

The inhibiting effect of two Schiff bases on the corrosion of the mild steel (MS) in 1 M HCl has been studied by electrochemical impedance spectroscopy (EIS) and Tafel polarisation measurements. The Schiff bases, 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ether (L₁) and 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ethane (L₂), were synthesized using 3-carboxaldehydethiophene and its corresponding amine. Polarisation curves reveal that both compounds are mixed type (cathodic/anodic) inhibitors and inhibition efficiency (% IE) increases with increasing concentration of compounds. It is suggested that their effects depend on their concentrations and the molecular structures. Adsorption of compounds on mild steel surface is spontaneous and obeys Langmuir’s isotherm.     

Investigation of the effect of disulfiram on corrosion of mild steel in hydrochloric acid solution

The corrosion inhibition properties of disulfiram (DSR) for mild steel in HCl solution were analyzed by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy, scanning electron microscopy and gravimetric methods. Physical adsorption is proposed for the inhibition and the process followed the Langmuir adsorption isotherm and kinetic/thermodynamic model of El-Awady et al. Constant phase elements describing the non-ideal characteristics of the electrochemical interface are introduced. The occurrence of inductive loop is also dealt with, through the introduction of an inductive element L. The use of these elements significantly improved the quality of fit of simulation to the EIS data.     

Mono- and dicationic benzothiazolic quaternary ammonium bromides as mild steel corrosion inhibitors. Part I: Gravimetric and voltammetric results

Seven quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl using gravimetric and polarisation techniques. For comparison gravimetric experiments were carried out in 1 M H₂SO₄ as well. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. The polarisation curves revealed that the inhibitors were of mixed type. The adsorption of almost all inhibitors was well described by the Frumkin isotherm. The adsorption isotherm parameters were determined. Conformational changes in the molecular structure favour the adsorption and thus increase the inhibitive effect.     

Theoretical investigation of corrosion inhibition effect of imidazole and its derivatives on mild steel using cluster model

Interaction energies of imidazole and its seven derivatives on the surface of mild steel were calculated via a cluster model by using quantum chemical calculations at density functional theory level. The mild steel surface and its adsorption sites were considered as some clusters taken from two-layered (0 0 1) planes and the quantum chemical calculations which were carried out consist of adsorption of the inhibitor molecules on the surface of these clusters. It is shown that 90% of inhibition variations of the imidazole derivatives are described by considering perpendicular interaction of the inhibitors by iron atom in the mild steel unit cell.     

Inhibition effects of 2,5-dimercapto-1,3,4-thiadiazole on the corrosion of mild steel in sulphuric acid solution

The effect of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) on the corrosion of mild steel (MS) in 1.0 M H₂SO₄ was investigated. DMTD acted as a mixed-type inhibitor without change of the mechanism of hydrogen evolution. The inhibition efficiency increased with the increase in concentration of DMTD but decreased with the increase of temperature. Adsorption of the inhibitor on the MS surface obeyed the Langmuir adsorption isotherm. The potential of zero charge suggests MS surface is positively charged in 1.0 M H₂SO₄. Thermodynamics and quantum chemical calculations reveal that the adsorption process of DMTD includes electrostatic interaction and electron donor–acceptor interactions.