Aggressive Aqueous Environments Research Articles

Influence of electrochemical machining on shape memory and surface characteristics of nickel-titanium-cobalt shape memory alloy: An experimental study

ABSTRACT Electro-chemical machining (ECM) can safely be categorized as being a unique unconventional machining technique, in which the role of thermal defects are not involved. The NiTiCo shape memory alloy has high yield strength coupled with good resistance to aggressive aqueous environments, which makes it a potential candidate for use in several bio-medical applications. This research concentrates on electro-chemical machining of a NiTiCo alloy. Taguchi’s Design of Experiment (DOE) containing three-parameters and three-factors was used to conduct the experimental study. The influence of concentration of the sodium chloride electrolyte, voltage, and frequency on output characteristics, such as (i) material removal rate (MRR), (ii) surface roughness (SR), and (iii) over-cut (OC), was analyzed. Experimental outputs revealed the voltage (45.29%) to be the most influential among the three controlling parameter. Grey relational analysis (GRA) was utilized to discover the ideal parametric relation and optimize machining characteristics.

Performance of permeable concrete mixes based on cement and geopolymer in aggressive aqueous environments

The permeable pavement efficiently manages stormwater, which is acidic and contains fine sediments and heavy metals exhausted by vehicles driving on this material. The heavy metal removal in permeable concrete samples based on geopolymer and Portland cement was examined in this study. Their performance when exposed to strong acids and turbid water were also investigated. They were able to infiltrate 28 L of water in 60 min and gained a compressive strength greater than 25 MPa in 2 weeks after casting. However, it was found that its porous structure was clogged with fine sediments when water containing bentonite clay passed through them for multiple cycles. To evaluate their metal removal capacity, a concentration of 10 mg/l of cadmium-containing solution was passed through such samples for a continuous period of 8 h. They were able to trap nearly 95% of the cadmium ions from the simulated wastewater during the column experiment. Their adsorption behaviour fits well with the pseudo-second-order kinetic and Langmuir isotherm models, implying that the main removal mechanism is chemisorption. To examine their acid resistance capacities, cement- and geopolymer-based mortar samples were exposed to acids for 2 weeks. The acid-exposed samples were severely degraded, as the mass loss in the geopolymer was determined to be 64% lower than that of the cement sample. Geopolymer-based permeable pavements are ecological, harden in moist air, gain higher strength at early ages, are acid resistant, and also remediate groundwater contamination.

Effects and interactions of scouring abrasion and external sulfate attack on deterioration of lining concrete: Experiments and preliminary modeling

The conventional tests of dynamic water scouring abrasion (DWSA) on lining concrete for hydraulic discharge tunnel do not consider concomitant sulfate ions that may exist in aggressive aqueous environment and alter the mechanisms and deterioration kinetics of DWSA. In this study, an abrasion-erosion testing system based on natural conditions of the environment has been used to evaluate the influence of volumetric concentration of sediment and the velocity of the scouring flow on abrasion-erosion synergism of lining concrete. To this end, lining concretes were subjected ambient conditions similar to that in drainage tunnel, spillway and stilling basin geographic locations, while implementing abrasion and accelerated external sulfate attack (ESA) test alternately prior to various physical and microstructural analyses. A dynamically decrease of properties on a macroscopic scale was observed, as well as an increase of precipitated ettringite, leached calcium, harmful pore (>200 nm) and sheeted radial micro-cracks, in lining concretes exposed to sediment-laden flow simulated for discharge, which were involved in the co-occurrence of complex degradation mechanisms in specimens exposed to DWSA-ESA. Results indicate that a water body with a high-velocity flow and a high sediment concentration significantly accelerates the sulfate attack on concrete. In contrast, a water body with a low-velocity flow and a low concentration of sediment alleviates the traverse of sulfate ions in concrete due to the inside-out pressure potential. The implications of these synoptic findings may informatively improve the design of abrasion and erosion resistance for concrete when dual exposure to ESA and abrasion is occurred in hydraulic tunnel engineering.

Multiphysical damage characteristics of concrete exposed to external sulfate attack: Elucidating effect of drying–wetting cycles

Drying–wetting cycles (DWC) are suspected of influencing the performance of concrete under sulfate attack, but the nature and extent of this influence are still unclear. Therefore, this research concerns understanding the effects of drying–wetting regimes. To this end, pastes, mortars, and concretes were subjected to cyclic drying–wetting with an interval of 12, 24, or 48 h prior to various physical and microstructural analyses. Additionally, drastic drying–wetting conditions with forced drying at 60 °C to reduce relative humidity from 100% to 55% and field-like drying–wetting conditions with gentle stepwise drying in the natural environment were adopted to examine the relationship between the laboratory and field testing. The results indicate that the conditioning regime with a dry–wet ratio of 3:1 and a dry–wet interval of 48 h can be considered a means to accelerate external sulfate attack (ESA) in a short duration and take both reliability and reproducibility into account without overly sacrificing the anticipated filed conditions. The results confirm that the drying–wetting cycle length and the drying mode affect the transport and reaction mechanisms of sulfate ions and the degradation kinetics of sulfate attack. The implications of these findings inform the design of drying–wetting regime for aggressive aqueous environments.

On the phase-field modeling of fully coupled chemo-mechanical deterioration and fracture in calcium leached cementitious solids

As it is extremely difficult, if not impossible, to carry out fully coupled chemo-mechanical tests lasting several hundreds of years, a reliable modeling approach is thus indispensable in assessing the integrity, durability and safety of infrastructures under aggressive aqueous environments. In this work, we propose a multi-physical phase-field model for fully coupled chemo-mechanical deterioration and fracture in calcium leached cementitious solids, aiming to predict the long-term behavior of concretes structures. The chemical sub-problem is built upon the mass conservation of calcium ions in pore solution, representing the diffusion–dissolution equilibrium of the leached system. Regarding the mechanical process, the length scale insensitive phase-field cohesive zone model is substantially extended with the calcium dissolution induced deterioration of mechanical properties properly accounted for by a porosity-dependent damage variable. Vice versa, during the leaching process both the transport diffusivity of calcium ions and the dissolution rate of the skeleton are promoted with the crack phase-field incorporated into the chemical sub-problem. The resulting inter-field fully coupled model is validated by several representative numerical examples. Both the sequentially and fully coupled chemo-mechanical problems are studied to verify the detrimental effects of simultaneous chemical attack and mechanical loading on the structural behavior. Based on the fully coupled analysis, an extra example is presented to demonstrate the promising prospects of the proposed model in service-life predictions of concrete structures under concurrent mechanical loading and aggressive environmental attacks.

Conjoint influence of environment and load on fatigue life of a bolted aluminum alloy structure

In this paper, an attempt is made to describe the decline in fatigue life of an aluminum alloy structure containing bolted joints under the conjoint influence of an aggressive aqueous environment and loading that is essentially cyclic in nature. In an attempt to project the real situation experienced by an aluminum alloy structure containing bolted joints while in service, an alternate cycle test method was used to essentially include the damage caused by the environment and cyclic loading. A chloride-containing solution was used to simulate the damage caused to the bolted structure upon exposure of the aluminum alloy structure containing a joint to the environment. The nature of fatigue loading was essentially cyclic tension. It was found that following an observable amount of environment-induced damage caused by exposure to a wet–dry environment followed by cyclic loading, the fracture position revealed a noticeable shift from the centerline of the bolt hole to the loading end. This can be attributed to the occurrence of fretting-related damage at the fine microscopic level. Based on an assumption of an average fracture line, a life prediction model was established. Compared with experimental results, the prediction method considering the fracture position to shift from the centerline of the bolt hole does provide results with a reasonably high degree of accuracy. The method proposed in this study does provide a convincing approach for reliable estimation of life, or endurance, of an aluminum alloy structure containing joints.

Evolution of corrosion damage in an aluminum alloy: an experimental and numerical study

In this paper, the results of a recent study on the environment-induced damage behavior of aluminum (Al) alloy 2024-T3, which is often a preferred choice for use in a spectrum of aircraft structural applications, are presented and discussed. Accelerated corrosion tests by way of exposure of test specimens of the alloy to an aggressive aqueous environment were carried out at ambient temperature (27°C). A numerical approach, based on the meshless peridynamic method, was developed to study the morphology of damage caused by the aqueous environment by way of pitting. To improve the numerical accuracy while concurrently reducing the solution time, an implicit finite-difference method was developed to solve the peridynamic control equation. The numerical algorithm was implemented in a Matlab program and was applied to simulate the evolution of pits resulting as a direct consequence of sustained exposure to the aqueous environment. The numerical predictions accord reasonably well with the experimental findings and results, thereby providing adequate proof that the simulation algorithm based on the meshless peridynamic method is effective at predicting both the nucleation and growth of the damage in the form of pits arising as a direct consequence of exposure to an aggressive aqueous environment.

(Invited) Influence of Current Collector on the Long-Term Performance of Electrochemical Capacitors

Electrochemical capacitors store the energy by the formation of the electrical double-layer at the electrode/electrolyte interface. These devices are characterized by high power density, short charge/discharge time and excellent cycling stability. The main goal of supercapacitor development nowadays is to increase their energy density and mentioned cycling stability. The former parameter could be improved by increasing the capacitance or operating voltage of the system, while the second by preserving current collectors from electrochemical corrosion phenomena. The increase of capacitance could be realized by the so-called pseudocapacitance effect, which can originate from the quick faradaic reactions at the electrode/electrolyte interface. These reactions can be induced by the appropriate modification of electrode in order to enforce the pseudocapacitive effect [1-4]. Electrochemical capacitors are composed of two electrodes separated by a separator and soaked in the electrolyte solution. Electrode material (mainly activated carbon) is coated on the surface of the current collectors made either of metals or stainless steel. In such a case, current collectors are exposed to corrosive electrolytes and can be subjected to corrosion processes [5-7]. There are several methods that are utilized to protect metals and steel from the harmful effects of electrochemical corrosion. One of them is the utilization of ionic liquids (ILs), which are added to an aggressive aqueous environment [8]. They act as corrosion inhibitors. This form of protection is being discussed in the scientific literature from about 20 years. A majority of articles describes the ability of this class of compounds to provide anti-corrosive protection for metal and steel. For these materials, an inhibitive influence on corrosion processes has been documented for dozens of ILs, vastly diversified in their chemical structure. A list of almost 90 investigated substances can be found in the literature [8]. Ionic liquids (ILs) are organic compounds which exhibit ionic structure and melting points below 100 degrees of Celsius. Due to their numerous advantageous properties, from some decades ILs stay in the scope of intense scientific interest, what results in the extensive research on possible ways to utilize them industrially. It covers various fields of IL application, for example as a solvent, an electrolyte, a catalyst, as a pharmaceutical or as corrosion inhibitors.In this work, the influence of ionic liquids additives on the performance of electrochemical capacitors is presented. Strictly, ionic liquids have been added to aqueous 1 M Na2SO4 electrolyte to inhibit corrosion processes on the surface of 316L stainless steel current collectors, which also influence the performance of electrochemical capacitors. Ionic liquids compounds were based on a common 2,5-dihydroxybenzenesulfonic anion. Electrochemical measurements were performed for a 2,5-dihydroxybenzenesulfonic acid, introduced to the electrolyte solution in 4 different concentrations ranging from 0,001% to 1%. Analogous tests were also conducted for 0,1% addition of 6 chosen ILs. All of ILs used in the research were composed of 2,5-dihydroxybenzenesulfonic anion and alkyldimethylammonium cation. The alkyl substituent of this cation varied, including n-ethyl, n-butyl, n-hexyl, cyclohexyl, n-octyl and n-decyl groups. The performed analysis proved an inhibitive effect of investigated compounds on the corrosion processes. The highest effectivities were observed for the ILs with bulkier alkyl substituent (i.e. containing cyclohexyl, n-octyl and n-decyl groups). On the basis of potentiodynamic polarization tests, a mixed corrosion inhibition mechanism was identified, with a predominant influence on the anodic process. Moreover, particular ionic liquids with the best anti-corrosive properties were used as additives to the electrolyte solution in electrochemical capacitors at a concentration of 0.1%. The results of electrochemical tests indicate a significant effect of the addition of ionic liquids on the working parameters of the electrochemical capacitors systems.This work was financially supported by the National Science Centre of Poland granted on the basis of the decision number 2018/31/B/ST8/01619 and by European Research Council (ERC) within ERC-StG-2017 project (grant agreement No. 759603) under the European Union’s Horizon 2020 research and innovation programme. References 1) F. Béguin, V. Presser, A. Balducci, E. Frackowiak, Adv. Mater., 26, 2219 (2014).2) T. Brousse, D. Bélanger, J.W. Long, J. Electrochem. Soc., 162, A5185 (2015).3) M. Graś, Ł. Kolanowski, J. Wojciechowski, G. Lota, Electrochem. Commun., 68, 28 (2018).4) K. Fic, G. Lota, M. Meller, E. Frackowiak, Energy & Environmental Science, 5, 842 5 (2012).5) J. Wojciechowski, Ł. Kolanowski, A. Bund, G. Lota, J. Power Sources 368, 18 (2017).6) E. McCafferty, Introduction to Corrosion Science, Springer, New York (2010).7) R.W. Revie, H.H. Uhlig, Corrosion and Corrosion Control, fourth ed., John Wiley & Sons, New Jersey (2008).8) C. Verma, E.E. Ebenso, M.A. Quraishi, J. Mol. Liq., 233, 403 (2017).

Properties of fly ash blended magnesium potassium phosphate cement cured in presence of sulfuric acid

Magnesium potassium phosphate cement (MKPC) is a new fast hardening and high strength cementitious material, which have attracted more attention in the field of repair and reinforcement for damaged concrete structures due to aggressive aqueous environments. The performance of MKPCs under severe environment are however not be sufficiently investigated. In this work, the effect of fly ash (FA) on the compressive strength development and micro-characteristics of the plain MKPC and FA/MKPC cured for a short of time and then exposed to air/water/sulfuric acid solution, were systematically investigated. The results show that, FA replacement ranges from 25% to 35% is beneficial to the sulfuric acid resistance properties of the MKPCs, in light of the compressive strength retention ratio and compressive strength. The acidic environment obtained by adding the sulfuric acid altered the reaction path of the plain MKPCs and FA/MKPCs with the probable formation of products not identified in the present work, which was detrimental to the properties of MKPC. In the presence of appropriate pH, Mg tends to be trapped to form precipitation of MgSO3·H2O. However, the MgSO3·H2O is quite instable which tends to destabilize when the environment changes. When the plain MKPCs were exposed to sulfuric acid solution, sheet-like crystal groups which were composed of acicular-like crystals, formed and intermixed at the surface of a compact structure.

Chloride Ingress in Cement Mortars Exposed to Acidithiobacillus thiooxidans Bacteria

Concrete structures placed in aggressive aqueous environments are vulnerable to degradation. Majority of studies have linked structural failures to the ingress of deleterious ions into the cement matrix. Some microbial activities may accelerate the penetration of harmful materials into the cement matrix and hence cause pronounced deterioration. This work reports a laboratory‐simulated study carried out to determine the extent of chloride ingress in cement mortars exposed to Acidithiobacillus thiooxidans. Test prisms were cast from Portland pozzolana cement (PPC) and ordinary Portland cement (OPC) with water‐to‐cement ratio maintained at 0.5. Acidithiobacillus thiooxidans bacterial solution of concentration 1.0 × 107 cell/mL was used to prepare microbial mortar prisms, whereas distilled water was used to prepare the control mortar prisms. The test prisms were subjected to porosity and accelerated chloride ingress after 28th day of curing. Compressive strength was determined after the 2nd, 7th, 28th, and 56th days of curing. Apparent diffusion coefficients (Dapp) were estimated from the solutions to Fick’s second law of diffusion. After the 56th day of curing, the microbial‐treated mortars exhibited a significant reduction in compressive strength. The resultant percentage decrease in compressive strength was 30.74% and 19.88% for OPC and PPC, respectively. Further, microbial‐treated mortars demonstrated both high porosity and chloride ingress as compared to the control test mortars. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) analyses showed the formation of new deleterious products in the microbial‐exposed mortars.

Stochastic chemo-physical-mechanical degradation analysis on hydrated cement under acidic environments

The accumulation of material degradation under contact with aggressive aqueous environments could lead to reduced structural reliability. In terms of hydrated cementitious materials, such interactions often result in the chemo-physical-mechanical (CPM) degradation, which represents a multiphysics process of high non-linearity and complexity. By further considering the inevitable uncertainties associated with both the materials and the serving conditions, solving such a process requires novel probabilistic approaches. This paper presents a stochastic chemo-physical-mechanical (SCPM) degradation analysis on the hydrated cement under acidic environment. The SCPM analysis consists of modelling the stochastic chemophysical degradation by finite element method, and assessing the mechanical deterioration through analytical micromechanics. The proposed modelling framework couples the conventional Monte Carlo Simulation with a novel support vector regression algorithm. The present method is able to not only address the detailed degradation mechanisms, but also ensure low computational costs for an accurate SCPM degradation assessment.

Corrosion of stainless steel valves in a reverse osmosis system: Analysis of corrosion products and metal loss

Aggressive aqueous environments in reclaimed water treatment plants can cause corrosion of stainless steel equipment, which may further result in equipment failure. The current study carried out morphological, micro-structural, mineralogical and chemical analyses to understand the differences between corrosion products formed on stainless steel valves at different locations in a reclaimed water plant reverse osmosis system. Correlation between formation of corrosion products and metal loss was studied in depth. For that purpose, a new parameter, namely metal loss percentage (MLP), was introduced to evaluate the extent of metal loss on the surfaces of stainless steel valves. The results showed that the valves had corroded to various extents. The corrosion included pitting, cracking and accumulation of products on the alloy surface. The corrosion products were composed of iron oxides, iron hydroxides, chromium oxide, calcium carbon oxide, siderite and green rust. There was a significant positive correlation between the weight percentage increase in the corresponding elements in these products and MLP on the alloy surface. O and C were among the elements most correlated with metal loss on the alloy surface. The latter correlated linearly with MLP. Based on these results, the reaction pathways for the formation of corrosion products on the surfaces of valves were postulated.

Corrosion-protective coatings based on fluorocarbosilane

This study discusses the effect of 3-(1,1,2,2,3,3,4,4-octafluoropentyloxy)propyltriethoxysilane (OFTES) based coatings on the anti-corrosive properties of 304 type stainless steel, which has not been described to date. The coatings were deposited from methanol using the anhydrous deposition method and influence of the sonication on this process has also been investigated. Anti-corrosive properties of modified and unmodified steel surfaces have been characterized by electrochemical and surface analysis methods. Since silicon is an element capable of forming bonds with both organic and inorganic substrates, these features allow to combine organofunctional silanes with metal as well as steel surfaces through metalOSi covalent bonds. A fluorinated alkyl chain, which is attached to the silicon atom, forms an effective barrier against an aggressive aqueous environment.

The rim zone of cement-based materials – Barrier or fast lane for chemical degradation?

Sophisticated evaluation models for the long-term stability of cement-based systems demand a precise knowledge of the mechanisms of deterioration reactions, particularly respecting a permanent exposure to aqueous environments. Commonly, insights into these mechanisms are deduced from long-term investigations. However, these chemical reactions start immediately after exposure to aggressive environments causing rapid changes of composition and structure. Consequently, properties of its rim zone change, which affects transport processes in aqueous solutions. In laboratory experiments, the influence of these surface processes on the stability of cement-based materials exposed to different chloride solutions was studied as a function of time and temperature. Analysis of compositional and structural changes beneath the surface reveal the role of crystalline covering layers for chemical resistance. Such layers are often described as protective barriers. However, these processes in the rim zone can accelerate chemical degradation and subsequently reduce the resilience of the cement-based materials to aggressive aqueous environments.

Stainless steel corrosion scale formed in reclaimed water: Characteristics, model for scale growth and metal element release

Stainless steels generally have extremely good corrosion resistance, but are still susceptible to pitting corrosion. As a result, corrosion scales can form on the surface of stainless steel after extended exposure to aggressive aqueous environments. Corrosion scales play an important role in affecting water quality. These research results showed that interior regions of stainless steel corrosion scales have a high percentage of chromium phases. We reveal the morphology, micro-structure and physicochemical characteristics of stainless steel corrosion scales. Stainless steel corrosion scale is identified as a podiform chromite deposit according to these characteristics, which is unlike deposit formed during iron corrosion. A conceptual model to explain the formation and growth of stainless steel corrosion scale is proposed based on its composition and structure. The scale growth process involves pitting corrosion on the stainless steel surface and the consecutive generation and homogeneous deposition of corrosion products, which is governed by a series of chemical and electrochemical reactions. This model shows the role of corrosion scales in the mechanism of iron and chromium release from pitting corroded stainless steel materials. The formation of corrosion scale is strongly related to water quality parameters. The presence of HClO results in higher ferric content inside the scales. Cl− and SO42− ions in reclaimed water play an important role in corrosion pitting of stainless steel and promote the formation of scales.

Measurement of Surface Damage through Boundary Detection: An Approach to Assess Durability of Cementitious Composites under Tannery Wastewater

Concrete structures are often subjected to aggressive aqueous environments which consist of several chemical agents that can react with concrete to produce adverse effects. A Central Effluent Treatment Plant consisting of reinforced concrete structures which is being constructed at Savar, Bangladesh, is an example of such a case. The purpose of this treatment facility is to reduce the environmental pollution created by tannery wastewater. However, tannery wastewater consists of several chemicals such as sulfates, chlorides, and ammonium, which, from the literature, are known to generate detrimental effects on concrete. Evaluation of durability of concrete structures in such environments is therefore imperative. This paper highlights a technique of boundary detection developed through image processing performed using MATLAB. Cement mortar cubes were submerged in simulated tannery wastewater and the images of the surface of cubes were taken at several time intervals. In addition, readings for compressive strength and weight were also taken on the same days. In this paper, an attempt is made to correlate the results from image processing with that of strength and weight loss. It was found, within the scope of this study, that the specimens which suffered greater strength and weight loss also underwent greater loss of surface area.

Influence of Shot Peening on Failure of an Aluminum Alloy Exposed to Aggressive Aqueous Environments

Pre-corrosion damage tests were performed on the high strength aluminum alloy (Al-Zn-Mg-Cu) that was subject to shot peening surface treatment. The tests were performed for different time levels and compared one-on-one with the performance and characteristics of the non-shot-peened alloy. The residual stress induced by the shot peening surface treatment for two different intensity levels was measured using the method of incremental drilling of holes. Based on an observation of morphology of corrosion experienced by the aluminum alloy the depth of corrosion was measured using a laser displacement sensor. The surface of the aluminum alloy that was shot peened revealed an overall better resistance to pitting while concurrently revealing evidence of partial degradation. The depth of degradation is related to the residual stress that is induced in the aluminum alloy sample by the shot peening treatment. The key mechanisms that control damage during corrosion of the shot-peened aluminum alloy can be divided into the distinct stages of (a) initial occurrence of uniform corrosion followed by (b) the generation of degradation, and (c) culminating in the initiation of pitting once the depth of degradation reaches a certain level.

Influence of morphology of corrosion on fracture initiation in an aluminum alloy

The image pertinent to the morphology of corrosion is an important feature that is essential for the purpose of evaluating the corrosive behavior of an aluminum alloy that finds selection and use in aircraft structural applications. Characteristic quantities pertinent to damage due to corrosion are extracted based on carefully executed, controlled and monitored experiments. The image processing technique was used to analyze the morphology of corrosion following exposure of an aluminum alloy to aggressive aqueous environment for different lengths of time. Parameters of Area-Box and surface corrosion ratio are introduced to describe the rule for the evolution of pitting corrosion. Based on the gray values for the different regions in an image, a three-dimensional (3-D) solid model was constructed in accordance with the damage data specific to pitting corrosion obtained from the experiments. A finite element analysis procedure was developed and used to predict the stresses and resultant site most susceptible for the onset of crack nucleation, or damage initiation, as a consequence of the pits resulting from exposure of the aluminum alloy to the aggressive environment.

Fluorine and carbon ion implantation and deposition on metals by plasma source ion implantation

Deposition of fluorine containing diamond-like carbon films is an effective solution for the improvement of machine parts in an aggressive aqueous environment when the combination of a hydrophobic surface with good corrosion protection and low friction coefficients is required. Stainless steel and silicon were treated by plasma source ion implantation using the gases CF 4, C 6F 6 and C 6H 5F, in the latter case with previous methane implantation. Depending on the plasma gas there are differences in the fluorine content, depth distribution, film thickness, water contact angle and friction coefficient.

Focused Ion Beam Investigations on Cement Based Materials in Aggressive Aqueous Environments

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.