Innovations in Corrosion and Materials Science (Discontinued) - Volume 8, Issue 1, 2018

Background: The problems in the electrochemical synthesis of Au-Sn alloy from aqueous and non-aqueous solutions concerning Au : Sn ratio and phase composition control, as well as the stability of the solutions and mechanisms of the alloying are discussed. The information is presented on the methods of Au-Sn eutectic synthesis by layer-by-layer gold and tin deposition and by simultaneous metals electrochemical reduction. The importance of this alloy synthesis is stipulated by its unique properties determining application as a solder in electronics and instrumentation. Method: The analysis is performed on the effect of tin and gold compounds composition and concentration in the solutions for electrochemical gold, tin and Au-Sn alloy deposition, the nature of a solvent, the value of pH in aqueous solutions, the availability of different additives on the stability of electrolytes, current efficiency, the rate of coatings deposition, and their chemical and phase composition. Results: The reasons for the instability of aqueous electrolytes such as Sn(II, IV) compounds hydrolysis, and Au(I, III) compounds reduction in the solution together with the causes of small tin content in the alloys which is largely stipulated by a great difference between gold and tin electrode potentials, are analyzed. The known methods of these drawbacks of diminution are described. Conclusion: The conceptions about mechanisms of electrochemical simultaneous reduction of Sn(II, IV) and Au(I, III) from aqueous and non-aqueous electrolytes are considered. The advantages and weak aspects of the usage of non-aqueous electrolytes based on glycols, mixtures of choline chloride with urea and/or glycols are shown.

Background: This study is aimed at evaluating the content of mercury in 17 samples of beauty creams. These beauty creams have been procured from local market. Objective: The potential use of graphene modified glassy carbon electrode in electrochemical detection of mercury ions present in beauty cream samples has been demonstrated. The content of Hg was measured by electrochemical method. Method: The analyses were preceded by acid digestion of the creams and Scanning Electron Microscope and Raman spectroscopy was used for characterization of the samples. The quantification of Hg was performed by graphene modified glassy carbon electrode. The presence of graphene sheets on the glassy carbon electrode greatly enhanced the electrochemical response for mercury. Results: The electrode's performance was accurate and sensitive for the detection of mercury ions in real samples. Cyclic Voltametry measurements showed a well-defined HgCl2 redox peaks present in control. Detection of Hg2+ was achieved in the range of 5 mM to 10-7mM with a limit of detection of 10- 6 mM. The performance of the electrode was also studied by recording nyquist plot for the sample cream which showed the maximum presence of Hg2+. Conclusion: The results of the creams showing the presence of mercury were also confirmed by the Atomic Absorption Spectroscopy (AAS).Therefore, our method is potentially suitable for routine mercury ions sensing in beauty cream samples. The fabricated device shows good electronic stability, excellent lower detection limit and high sensitivity for real-time detection of Hg2+ in beauty creams.

Background: Due to the increase in the number of sour wells in today's oil and gas industry, reservoir souring and related acidizing issues must be considered as an essential concern for material selection which significantly affect the application and performance of alloy steels. Objective: The influence of deposited corrosion product layers on the electrochemical behavior of 13% chromium stainless steel was investigated in an acidic solution to study the effect of a deposited elemental sulfur and FeS layer on the electrochemical behavior of 13% chromium steel with particular emphasis on the role of temperature, chloride concentration and morphological characterization of corrosion products. Method: Cyclic polarization and also linear polarization resistance techniques were applied to measure the corrosion parameters such as corrosion rate, Ecorr, Epit and Ipass of 13% chromium steels at various temperatures and chloride concentrations. All the electrochemical measurements were performed at 25 and 75°C with addition of 0, 10 and 20 g/L NaCl in 0.01 M hydrochloric acid solution. Surface measurement techniques such as SEM, EDS, and AFM were applied for morphological analysis of the corrosion products. Results: The results showed that both temperature and chloride concentration had significant effects on corrosion parameters; however, these effects on the corrosion rates in the presence of elemental sulfur were significantly higher than those in the presence of an iron sulfide layer or without any initial deposited layer on the sample surface. Conclusion: Environmental variables, such as temperature and chloride concentration have an important role in the corrosion resistance of 13% chromium steel which can indicate either protective or destructive effects on the corrosion behavior of steel.

Background: Harsh coastal environment has detrimental results on the mechanical performance of the reinforced concrete structures. Corrosion damage and its consequences are not included in the existing regulations, concerning reinforced concrete structures, given that only recently scientific community demonstrated interest on the specific issue. Nevertheless, scientific research requires the application of methods for rapid simulation and reproduction-qualitatively and quantitatively- of the corrosion phenomena. Objective: The purpose of the present paper is to present some parameters affecting the experimental results, obtained from the electrochemical corrosion method, on both quality and quantity, given that no commonly accepted protocol has prevailed so far. Method: One of the most widespread accelerated corrosion techniques, used for the goals of the present study, is electrochemical corrosion method. Using this method, natural corrosion can be simulated and damage accumulation, which often occurs during the lifecycle of a reinforced concrete structure, can be evaluated. Results: It has been established that for higher current densities, higher mass loss rates have been recorded for the same exposure period. Furthermore, comparing short and long series of specimens, of the same diameter, for the same corrosion duration, seems that short samples record higher mass loss percentages and more intense pitting. Conclusion: Analysis of the research results allows us to conclude that long- bare steel bar specimens record milder corrosion damage than short-bare specimens. This is related to the presence of factors favoring corrosion initiation. Moreover, given that corrosion effect is initially concentrated in small areas, the behavior of long- embedded specimens, against corrosion, can be simulated with the corresponding behavior of short- bare specimens.

Background: Fiber reinforced ceramic matrix composites are developed to improve the mechanical properties as well as to decrease the crack propagation and brittleness of monolithic ceramics. Objective: In this work, natural amorphous silica fibers and amorphous colloidal silica were used to obtain fiber reinforced ceramic matrix composites. Method: Initially, a small fraction of natural amorphous silica fibers was milled to reduce the particles size distribution to reach an intermediate size between natural amorphous silica fibers and amorphous colloidal silica. Subsequently, compositions containing 10 to 40 wt% of natural amorphous silica fibers were homogenized, uniaxially pressed (100 MPa), dried and fired at different temperatures (1000, 1100 and 1200°C, 10°C/min) in an oxidant atmosphere. Furthermore, the obtained composites samples were characterized according to their physical, thermal, structural, microstructural and mechanical properties. Results: SEM analysis showed that natural amorphous silica fibers are characterized by an acicular shape with aspect ratio, L/D = 18 ± 1.2. The obtained composites have shown relatively strong interfacial bond between matrix and fibers. However, the results suggest enough interfacial adhesion between fibers and matrix for composites containing 30% of natural amorphous silica fibers. Moreover, they exhibit a low coefficient of thermal expansion (0.63 x 10-6°C-1), an appropriated relative density and a significant increase (45%) in fracture toughness. Conclusion: The composites produced are promising materials for a wide range of advanced engineering applications, remarkably in the building industry, machinery, aviation industry, and architecture.

Background: The present paper investigates the corrosion inhibition of copper using six corrosion inhibitors namely: 4-phenyl thiosemicarbazide (PTSC), Salicylaldehydethiosemicarbazone (STSC). 5-Mercapto-1-methyle tetrazole (MMT), 5-(3-Pyridyl)-1H-tetrazole (PyTA), 5-phenyl-1-Htetrazole (PTA) and 5-Amino-tetrazole monohydrate (ATA). Method: Copper samples were tested using potentiodynamic polarization technique in the absence and in the presence of corrosion inhibitors. Results: Results show that tetrazole derivatives show high inhibition efficiencies (≥90%) in comparison to thiosemicarbazide derivatives (<80%). The highest inhibition efficiency of 92.9% was shown by ATAH at 2000 ppm. The order of inhibition efficiencies of the tested compounds was as follows: PTA≈ATA >PyTA> MMT > STC > PTSC.