Long Periods Of Immersion Research Articles

Monitoring of silver alloy tarnishing in sulphides by electrochemical noise measurements: Application of statistical and recurrence plot analysis

Silver historical artefacts were manufactured using Ag‒Cu alloys; these can tarnish in environments containing sulphides (H2S, COS), causing changes in their aesthetics and, occasionally, complete loss. This creates problems for their conservation and restoration. In this study, the tarnishing process of Ag-Cu alloys (0.925, 0.800, and 0.720) immersed in (NH4)2S for 48 h was evaluated by electrochemical noise (EN) measurements. To relate the EN to the corrosion process, the EN data were subjected to direct examination and statistical and recurrence analyses. The Cu anodic behaviour controlled the icorr, the process was chaotic at the beginning (localized corrosion), and at longer immersion periods, the process became stochastic (passive condition). Based on the maximum line and the determinism percentage, a localized corrosion stage occurred at the beginning, followed by passivation that controlled the corrosion mechanism of the silver alloys.

Long-Term Performance of Reference Electrodes in Alkaline Radioactive Waste Storage Environments

Accurate measurements of corrosion potential are important for assessing the likelihood of internal localized corrosion and stress corrosion cracking of carbon steel tanks used for storing radioactive wastes. Reference electrodes in underground radioactive waste storage tanks are challenging to deploy, and more difficult to extract and replace frequently due to radiological exposure and disposal constraints. Hence, electrodes that exhibit stable performance over long periods of immersion in these waste environments are desirable. The present study evaluates the stability of reference electrodes used in radioactive waste storage tanks over a much longer period than previously studied. Long-term tests on Ag/AgCl and Hg/HgO reference electrodes were performed in nonradioactive simulants formulated from wastes stored at the Hanford site. Electrode degradation, which was studied by various in situ and ex situ evaluation techniques, was correlated to changes in electrode fill chemistry from waste intrusion via the porous frit junction. An intentional contamination study was performed to better understand and predict contamination effects on electrode potential drift.

Electrochemical Corrosion Behavior in Simulated Body Fluid of a Metastable β‐Type Ti29Nb13Ta4.6Zr Biomedical Alloy with Improved Mechanical Properties

Herein, the mechanical properties and corrosion behavior in simulated body fluid of the β‐type Ti29Nb13Ta4.6Zr alloy (TNTZ) are investigated and compared to Ti6Al4V alloy. The samples are obtained from the solution‐treated (ST) and water‐quenched TNTZ bars. Following quenching, the bars are cold rolled aged (CRA) at 673 K for 20 min in order to reach a desired combination of high yield strength and low elastic modulus. The corrosion tests are conducted using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) during a long period of immersion in physiological Ringer's solution (up to 144 h), and the mechanical behaviors are assessed through uniaxial tensile tests. The results show that both TNTZ ST and CRA conditions have lower Young's moduli than Ti6Al4V. However, with CRA treatment, the alloy is significantly strengthened due to a homogeneous precipitation of nanometer‐sized α‐phase with lenticular morphology in the β‐matrix. Potentiodynamic polarization and EIS results reveal that both TNTZ CRA and Ti6Al4V passivate under testing conditions, and the passive current density is very low, providing corrosion resistance in the potential range studied. The EIS results also reveal that the passive film formed on the surface of both materials is highly corrosion resistant.

Assessment of the inhibitive performance of a hydrazone derivative for steel rebar in a simulated concrete medium: Establishing the inhibition mechanism at an experimental and theoretical level

In the present work, a low-cost and practical approach based on an eco-friendly corrosion inhibitor is suggested for protecting steel rebar. To this end, a new hydrazone derivative, namely N'-(furan-2-ylmethylene)-2-(5-methoxy-2-methyl-1H-indol-3-yl) acetohydrazide (FMAH) was synthesized and its corrosion inhibition characteristics for steel rebar (STR) in chloride contaminated simulated concrete pore solutions (ClSCPS) were evaluated using experimental and theoretical methods. The electrochemical studies, which were conducted at several periods ranging from 1 h to 30 d indicated that the addition of FMAH to the ClSCPS significantly improved the passive film formation. It considerably increased film and charge transfer resistances at an early immersion stage, then decreased at longer immersion periods. Potentiodynamic polarization curves (PPCs) revealed that the investigated compound could be categorized as a mixed inhibitor with a predominance anodic effect. The gravimetric and potentiodynamic polarization studies confirmed corrosion inhibition efficiencies of 80.9% and 81.1%, respectively, for 1.0 mmol.L-1 FMAH after 30 d of exposure. Surface characterization of corroded and inhibited STR surface by X-ray photoelectron spectroscopy (XPS), SEM coupled with EDS, Raman spectroscopy, atomic force microscopy (AFM) and X-ray diffraction spectroscopy (XRD) revealed that inhibitor molecules chemically adsorbed on the STR forming a highly resistant protective layer against corrosive species. Theoretical modeling of inhibitor’s adsorption on the iron surface by the self-consistent-charge Density-functional tight-binding (SCC-DFTB) indicated the formation of several covalent bonds between carbon and oxygen atoms with the iron atoms. The analysis of FMAH-Fe (110) adsorption systems by projected density of states revealed that FMAH molecules adsorbed on the iron surface through a charge transfer process. The interesting results from the present work would open great opportunities for exploring the anti-corrosion performance of the investigated compound in concrete.

Rivers as a potential dispersing agent of the invasive tree Acacia dealbata

BackgroundThe silver wattle Acacia dealbata is a fast-growing tree from Australia that has become naturalised in different regions of the world, attaining invasive status in most of them. In Chile, A. dealbata reaches large abundances along banks and floodplains of invaded fluvial systems, suggesting that rivers may act as a vector for seed dispersal. As hydrochory has not been documented previously in this species, the aim of this study is to evaluate the potential for water dispersal of seeds of this invasive tree along rivers.MethodsSeed samples from rivers were collected at three sites along two A. dealbata-invaded rivers within the Cachapoal basin, central Chile. Number of seeds collected was contrasted versus hydraulic and local conditions with RDA. Seed buoyancy and sedimentation velocity were determined and compared between sites with an ANCOVA. Finally, the probability of seed germination after long periods of immersion in water was assessed, simulating transport conditions in the flow. Germination results were tested with a GLM.ResultsResults indicate that increasing abundance of A. dealbata seeds in the flow is related to the level of turbulence of the flow. Seeds display high floatability but their sedimentation velocity is high when they do sink. Finally, silver wattle seeds can germinate after long periods (many weeks) of immersion in water; however, their probability of germination depends to a large extent on whether seeds are scarified or not.ConclusionsBased on the evidence collected, we suggest that the seeds of A. dealbata have the necessary traits to be dispersed by rivers, this being the first research testing this hypothesis. The success of hydrochory of A. dealbata would depend on river flow turbulence, and whether there are natural mechanisms for scarifying the seeds either before or during transport. The proposed methodology can be used to assess river hydrochory for any tree species.

Corrosion mechanisms of AZ31 magnesium alloy: Importance of starting pH and its evolution

AbstractThis article aims at improving the understanding of the corrosion mechanism of AZ31 magnesium alloys during a long period of immersion in an aqueous electrolyte. In particular, the influence of the starting pH of the electrolyte on the oxidation of AZ31 alloy and its evolution due to corrosion phenomena were investigated. Several electrolytes with different pH values containing or not chlorides were used. The electrochemical properties of the metal substrate in these electrolytes were studied as a function of immersion time by electrochemical impedance spectroscopy. The kinetics of the reactions were determined by potentiodynamic polarization as well as dihydrogen evolution measurements by eudiometry. All these tests were carried out while the sample surface and electrolyte volume remained constant. The corrosion products generated on the alloy surface were analyzed by X‐ray photoelectrons spectrometry. This study has shown that the evolution of the corrosion rate and the corrosion products depends greatly on the initial pH and the nature of the used electrolyte. Alkaline electrolyte leads to a passive protective layer that can be locally destroyed by chloride ions. For a neutral chloride electrolyte, the strong increase of the pH due to the magnesium corrosion is not able to form a protective layer by precipitation of corrosion products. The kinetic and the corrosion extent are affected by the pH changes.

Evaluation of fungal biomass developed from cocoa by-product as a substrate with corrosion inhibitor for carbon steel

The fungal biomass of cocoa bean shell (FBCS) obtained by solid-state fermentation (SSF) with Penicillium roqueforti was used as a natural corrosion inhibitor of carbon steel in an acidic solution with 0.5 mol.L−1 HCl. The evaluation of the corrosive process was carried out using gravimetric, electrochemical, and surface analysis techniques. The gravimetric test data were used to calculate the corrosion rate, current density, and efficiency. Electrochemical measurements provided the polarization curves and the electrochemical impedance spectroscopy (EIS). Finally, the surface analysis was performed using an optical microscope. From Tafel's extrapolation, the largest deviation was noticed at 69.9 mV, confirming that FBCS acted as a partially cathodic inhibitor. Inhibitor molecules were physically adsorbed on the carbon steel surface and the adsorption mechanism followed the Langmuir isotherm model. The results of the EIS confirmed the gravimetric results. FBCS inhibited the acid corrosion of carbon steel AISI 1008 at a concentration range from 0.44 g.L−1 to 1.77 g.L−1, and the higher the concentration, the higher the inhibition rate. The maximum corrosion inhibition efficiency was 93%. The EIS by time results showed that the FBCS should not be applied for very long periods of immersion in the electrolyte. The maximum inhibition efficiency was verified within 12 hours of immersion (95.96%). Therefore, this study encourages the use of FBCS as inhibitor due to good inhibit efficiency and to be environmental friendly, as well as the use of others news materials, such as biomass resulting from the fermentation of other residues, proposed in an unprecedented way in this work.

An additively manufactured magnesium-aluminium alloy withstands seawater corrosion

Magnesium, the lightest structural metal, has inherently poor corrosion resistance. In this study, we developed a magnesium-aluminium Mg-10.6Al-0.6Zn-0.3Mn alloy, additively manufactured by laser powder bed fusion. We reveal that this alloy has a record low degradation rate amongst all magnesium alloys in practically relevant corrosive solutions, and it even withstands seawater corrosion. As tested by a number of methods, the alloy shows even more enhanced passivation with longer immersion periods. The alloy surface following immersion maintained a nearly corrosion-free appearance and was determined to have a thin aluminium-containing surface film, due to surface enrichment of aluminium from the supersaturated matrix. Aluminium enrichment near the sample surface was also observed when the sample is immersed in phosphoric acid or exposed to atmosphere at room temperature. This study demonstrates the prospects for additively manufactured ultra-lightweight magnesium structure with outstanding corrosion resistance.

Micro Raman and XPS surface analysis to understand the electrochemical behaviour of AZ31 and AZ91 magnesium alloys as temporary implant materials.

Degradable metals and alloys have a potential use for surgical orthopedic applications. In this work, surface oxide/hydroxides formed by degradation, are evaluated in two commercial magnesium alloys (AZ31 and AZ91 alloys) by Raman, electrochemical and X-ray spectroscopic techniques. Electrochemical and surface/composition characterization of the AZ31 and AZ91 alloys are developed in contact with Hanks‘ Buffered Salts Solution (HBSS) at 37 °C. AZ31 alloy shows lower corrosion resistance than AZ91 in HBSS at 37 °C, both for short (24 h) and long (17 days) periods of immersion. The surface analysis demonstrate that on both alloys there are abundant corrosion products and the presence of compounds related to apatite. These results show that layers of magnesium oxide and hydroxide can be formed on the alloys surfaces, which gives them a certain degree of protection. The simulated body fluids contain different amounts of Ca2+ ions, carbonates / bicarbonates and phosphates, in addition to the Mg2+ ions (and other cations such as Al3+ and Zn2+) coming from the biomaterial corrosion environment. Thus, specific surface conditions can vary, such as the local pH value, and different corrosion products can precipitate which have different substrate protection properties. These corrosion products can slow down the degradation and influence the adsorption of proteins and cellular adhesion to the Mg surface by changing its chemistry and topography. The use of compositional (Raman and X-ray spectroscopies) and electrochemical (EIS and polarization curves) techniques, allows to do generate advances in the surface and degradation knowledge of typical Magnesium alloys like AZ31 and AZ91, for possible use as temporary implants. Even the analysis was carried out under static conditions, the systematic approach done is complete to picture the degradation mechanism of these alloys. Flow laboratory experiments are consider important to include as future work.

Inhibition performance of 4-mercaptopyridine toward the corrosion of carbon steel in hydrochloric acid solution

The corrosion inhibition performance of 4-mercaptopyridine (4MP) as corrosion inhibitor for A3 steel has been studied using electrochemical method. The maximum inhibition efficiency value is 96.3% at 0.25 h and the inhibition efficiency is higher than 89.4% after immersion of the electrode in hydrochloric acid solution for 33 h. XPS results and frontier orbital calculation results show 4MP molecule adsorb on steel surface mainly through sulfhydryl groups and N atoms. Molecular dynamic simulation results show that an inhibitor layer formed on metal surface in the beginning while the inhibitor film changes from monolayer type to bilayer type with the increasing of time, the corrosion resistance and the corrosion inhibition efficiency of the adsorbed inhibitor film was improved. The phenomenon supplies new perspective for the designing of the molecules used as inhibitors, which is beneficial for the improvement of the adsorption durability of the potential used inhibitor after long period of immersion in acid medium.

The nature of the copper sulfide film grown on copper in aqueous sulfide and chloride solutions

AbstractIn this paper, the properties of copper sulfide films formed both anodically and naturally in deaerated/anoxic aqueous sulfide and chloride solutions were investigated using a series of electrochemical and surface analytical techniques. A combination of cyclic voltammetric, corrosion potential (Ecorr), and cathodic stripping voltammetric experiments showed that the sulfide film growth kinetics and film morphologies were controlled by the supply of SH− from the bulk solution to the copper surface. There was no passive barrier layer observed on the copper surface under either electrochemical or corrosion conditions. The film morphology was dependent on the type and concentration of anions (SH−, Cl−) present in the solution. Scanning electron microscopy on both surfaces and focused ion beam‐cut cross‐sections showed the growth of a thin, but porous, base layer of chalcocite (Cu2S) after short immersion periods (up to 2 hr) and the continuous growth of a much thicker crystalline outer deposit over longer immersion periods (≥36 hr), suggesting a solution species transport‐based film formation process and the formation of an ineffective thin “barrier‐type” layer on copper.

Corrosion protection properties of anodized AA2024T3 alloy sealing with organic-based species

The present study investigates the effect of EDTA disodium salt and Monosodium citrate treatments to improve the corrosion resistance of anodized aluminum alloys coated with sol–gel. The anticorrosive properties were studied by Electrochemical Impedance Spectroscopy (EIS) technique. The chemical and morphological characterization were carried out by Focus Ion Beam (FIB), Field Emission Scanning Microscopy (FESEM) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The results suggests that the addition of any of these salts in the sol–gel film improves the corrosion resistance of the anodized aluminum alloy. Very stable and high impedance values are obtained after a long period of immersion in 0.1 M NaCl solution. The best results are obtained with the addition of 0.5 g L−1 EDTA disodium salt and 1 g L−1 monosodium citrate. The improvement of the corrosion properties is attributed to the changes in sol–gel formation that produce a more compact protective barrier with the COO− groups, which can prevent the entry of aggressive electrolyte by repulsion of charges.

Development of New Wrought Mg Alloys: Improving the Corrosion Resistance by Addition of Alloying Elements

Magnesium (Mg) alloys constitute an attractive structural material for transportation industries, due to their low density and high strength/weight ratio. However, high susceptibility to corrosion of Mg alloys limits their use. Therefore, there is a growing interest for development of new Mg alloys with good mechanical properties and superior corrosion resistance. Production of wrought Mg alloys results in enhancement of mechanical properties, whereas addition of alloying elements may result in improved corrosion behavior. In this study we distinguish the role of aluminum, zinc, tin and calcium additions on the corrosion performance of new wrought Mg alloys. Overall, addition of alloying elements resulted in precipitation of second phase particles with cathodic behavior (relatively to Mg matrix). This enhanced the micro-galvanic effects and the corrosion resistance in short periods of immersion was deteriorated. However, in longer periods of immersion the passive characteristics of the oxide layer played a significant role in improving the alloys' corrosion resistance. The contribution of each element to the oxide layer will be discussed in detail. In general, the quantities of alloying element should be sufficient to stabilize the corrosion products layer; yet as low as possible, in order to reduce the micro-galvanic effects.

Visualisation of latent fingerprints on non-porous object immersed in stagnant tap water using safranin-tinted Candida rugosa lipase reagent

Waterways have been used for disposing evidence by perpetrators, especially during homicide, rendering difficulties for forensic fingerprint investigators since water may destruct the amino acid components of fingerprints. Although the use of small particle reagent for visualising the lipid components of a fingerprint has been suggested, its use has been associated with numerous human as well as environmental toxicities, and hence, must be reduced. Therefore, this present research that developed a new environmentally-friendly safranin-tinted Candida rugosa lipase reagent (i.e. Lipase-Glutaraldehyde-Safranin, Lip-GA-Saf) for visualising latent fingerprints on non-porous surface (aluminium foils) immersed for up to 4 weeks in stagnant tap water acquires forensic significance. Results revealed that the quality of latent fingerprints (Fingermark Quality Scale) developed using Lip-GA-SAF was statistically better in all the four different durations of immersion than that of using SPR (p<0.05). Declining quality of fingerprints over longer period of immersion was also observed for both the Lip-GA-SAF reagent and SPR developed fingerprints. Considering the better quality of fingerprints developed using Lip-GA-SAF reagent, its usefulness in forensic practical caseworks appears promising.

Relation Between Zn Additions, Microstructure and Corrosion Behavior of New Wrought Mg-5Al Alloys

In the present study, the effect of varying Zn additions (0.93–3.16 wt%) on the corrosion resistance of wrought Mg-5Al alloys was studied and related to the microstructure changes. Three secondary phases were found: Al–Mn, β-Mg17Al12 enriched with Zn, and Φ-Mg21(Al, Zn)17; the latter observed only in alloys with relatively high Zn content. The corrosion behavior in short periods of immersion is related to pitting corrosion, and strongly influenced by micro-galvanic effects between the secondary phase particles and the α-Mg matrix. In long periods of immersion, a protective layer is formed, and filiform corrosion observed for alloys with Zn content above 1 wt%. However, the micro-galvanic effects still play a crucial role in deterioration of corrosion resistance in alloys with relatively high Zn content. These effects depend on the cathodic behavior of the particles, and on the total number of the particles presented on the alloy’s surface.

Long duration stabilization of porous silicon membranes in physiological media: Application for implantable reactors.

The natural biodegradabilty of porous silicon (pSi) in physiological media limits its wider usage for implantable systems. We report the stabilization of porous silicon (pSi) membranes by chemical surface oxidation using RCA1 and RCA2 protocols, which was followed by a PEGylation process using a silane-PEG. These surface modifications stabilized the pSi to allow a long period of immersion in PBS, while leaving the pSi surface sufficiently hydrophilic for good filtration and diffusion of several biomolecules of different sizes without any blockage of the pSi structure. The pore sizes of the pSi membranes were between 5 and 20 nm, with the membrane thickness around 70 μm. The diffusion coefficient for fluorescein through the membrane was 2 × 10-10 cm2 s-1, and for glucose was 2.2 × 10-9 cm2 s-1. The pSi membrane maintained that level of glucose diffusion for one month of immersion in PBS. After 2 months immersion in PBS the pSi membrane continued to operate, but with a reduced glucose diffusion coefficient. The chemical stabilization of pSi membranes provided almost 1 week stable and functional biomolecule transport in blood plasma and opens the possibility for its short-term implantation as a diffusion membrane in biocompatible systems.

Long-term stainability of interim prosthetic materials in acidic/staining solutions.

To evaluate the long-term color stainability, translucency, and contrast ratio (CR) of different resins used to fabricate interim prostheses after immersion in acidic/staining solutions. A total of 160 specimens were divided into 16 groups (n = 10) according to the material (heat-polymerized acrylic resin [HPAR], auto-polymerized acrylic resin [APR], nanoparticulated bis-acrylic resin [BR], and prefabricated poly(methyl methacrylate) block for CAD/CAM [CADR]) and immersion solutions (artificial saliva, cola beverage, coffee, and red wine). A spectrophotometer was used before and after each immersion period (7, 14, 28, 90, and 180 days). Color differences (CIEDE2000 and CIELab) were calculated. A three-way repeated-measures analysis of variance and Bonferroni test (α = .05) were used. After 180 days, the APR presented the highest value for coffee and the CADR presented the smallest value for the cola (P < .001). For the CR, the highest values were obtained at 180 days for BR in coffee (1.35) and wine (1.18) (P < .001). Higher translucency parameters were obtained in the BR and CADR in the initial, 14, 28, and 90 days (P < .001). From the greatest to the smallest staining potential, the solutions were classified as: wine > coffee > cola beverage > saliva, while for the materials as: APR > BR > HPAR > CADR. The knowledge of the long-term optical behavior of interim prosthetic materials is important for clinicians to decide which material to use to match the dietary intake of their patients and their esthetic demands. Prefabricated blocks for CAD/CAM systems have been shown to maintaining their optical characteristics even after a long period of immersion in acidic/staining solutions.

Performance of heat and ambient cured geopolymer concrete exposed to acid attack

This paper presents an experimental investigation on the acid resistance of GPC cured under heat regime and GPC composites (GPCC) cured under ambient conditions. The GPC samples were prepared under heat curing at a temperature of 60°C for a period of 48 h, whereas the GPCC samples were prepared with a combination of 80% fly ash and 20% slag. The specimens of GPC and their composites were exposed to 2% and 10% sulfuric acid and nitric acid solutions for a period of 6 months. The parameters that were examined during the experimental investigation are weight loss, compressive strength loss and the maximum depth of penetration of acid. The results indicated that the weight loss is relatively lower in the GPC samples compared with that in the GPCC samples, particularly at the initial periods of immersion. However, the residual strengths of the GPCC samples at longer periods of immersion are higher than those of the GPC samples. It was also found that compressive strength loss and depth of penetration were observed to be less in the GPCC samples compared with those of the GPC samples.

Corrosion Behavior of Different Brass Alloys for Drinking Water Distribution Systems

Some α + β’ brass components of drinking water distribution systems in Morocco underwent early failures and were investigated to assess the nature and extent of the corrosion attacks. They exhibited different corrosion forms, often accompanied by extensive β’ dezincification. In order to offer viable alternatives to these traditional low cost materials, the corrosion behavior of two representative α + β’ brass components was compared to that of brass alloys with nominal compositions CuZn36Pb2As and CuZn21Si3P, marketed as dezincification resistant. CuZn21Si3P is a recently developed eco-friendly brass produced without any arsenic or lead. Electrochemical tests in simulated drinking water showed that after 10 days of immersion CuZn21Si3P exhibited the highest polarization resistance (Rp) values but after longer immersion periods its Rp values became comparable or lower than those of the other alloys. After 150 days, scanning electron microscope coupled to energy dispersive spectroscopy (SEM-EDS) analyses evidenced that the highest dezincification resistance was afforded by CuZn36Pb2As (longitudinal section of extruded bar), exhibiting dealloying and subsequent oxidation of β’ only at a small depth. Limited surface dealloying was also found on CuZn21Si3P, which underwent selective silicon and zinc dissolution and negligible inner oxidation of both α and κ constituent phases, likely due to peculiar galvanic effects.

EFFECT OF IMMERSION TIME OF SHALLOT EXTRACT AND ATONICON SEED GERMINATION OF SHALLOT

The need for raw materials of fried onions derived from 'lembah palu Shallot tubers variety is high enough and can not be fulfilled, because the productivity is still low. This study aimed to find the type of plant growth regulator substances (PGR) with a long period of proper immersion to improve the germination of Shallot tuber. The research was conducted on Mei until June 2017 in Bulupontou Village, Sigi Regency. The study used two factorial Randomized Block Design (RBD). First factor of type RGS: (Z1) onion extract 100 g/l water, and (Z2) atonic 5 ml/l water. The second factor was long seed immersion in PGR: (T1)=30 min; (T2)=60 minutes; (T3)=90 minutes, and (T4)=120 minutes. Each treatment was represented 20 plants and repeated 3 times, so it was used 480 plants. The results showed that (i) red onion tubers soaked with Shallot extract 100 g/liter of water for 30-90 minutes yielded 100% Germinations, and tubers soaked in red onion extract for 30 minutes resulted in germination rate 31.3%/etmal, (ii) the type of growth regulator of shallot extract and atonic (PGR) effect was not significant on the germination of shallot; and (iii) the 30 minute long growth regulator immersion produced the highest hypothetical vigor index.