Short Periods Of Immersion Research Articles

Progressive failure characteristics and water-induced deterioration mechanism of fissured sandstone under water–rock interaction

Stability of engineered rock mass can be significantly affected by the combined action of fissures and water. In this study, uniaxial compression tests of fissured sandstone under natural state and water-chemical environments were conducted, accompanied by acoustic emission and digital image correlation to monitor the whole failure process. The results indicate that the strength and elastic modulus of fissured sandstone in the saturated state were lower than those in the natural state. The inside structural changing of dried specimen after water–chemical environments immersion had a weak influence on the strength and elastic modulus, but the peak strain and yield deformation would significantly increase. Characteristic stress determination methods were identified applicable to fissured sandstones under water–rock interactions. The σci/σf (the ratio of crack initiation stress to peak strength) could be largely degraded by the presence of water, while the impact on σcd/σf (the ratio of crack damage stress to peak strength) was weak. The structural changing could also significantly reduce σci/σf. However, only the σcd/σf ratio in the acid water environment exhibited the obvious reduction. The presence of water could also influence the crack initiation and failure mode of fissured sandstone. After a short period of immersion (45 d), the strength and elastic modulus degradation of fissured sandstone was mainly caused by the water–rock physical reaction, while the change in the peak strain was jointly affected by the water–rock chemical and water–rock mechanical reactions. The σci/σf ratio was affected by the water–rock chemical and water–rock mechanical reactions, while the σcd/σf ratio was affected only by the water–rock chemical reaction. Moreover, the water–rock mechanical reaction significantly changed the initiation mode of fissured sandstone. The water-induced deterioration mechanism of fissured sandstone was lastly revealed by these results, which could provide an important reference for evaluating the stability of water-rich engineered rock mass.

Effectiveness and cytotoxicity of two desensitizing agents: a dentin permeability measurement and dentin barrier testing in vitro study

BackgroundWhen evaluating the efficacy and safety of various desensitizing products in vitro, their mechanism of action and clinical utility should be considered during test model selection. This study aimed to evaluate the effects of two desensitizers, an in-office use material and an at-home use material, on dentin specimen permeability, and their dentin barrier cytotoxicity with appropriate test models.MethodsTwo materials, GLUMA desensitizer (GLU) containing glutaraldehyde and remineralizing and desensitizing gel (RD) containing sodium fluoride and fumed silica, were selected. Human dentin specimens were divided into three groups (n = 6): in groups 1 and 2, GLU was applied, and in group 3, RD was applied and immersed in artificial saliva (AS) for 24 h. Dentin specimen permeability before and after each treatment/post-treatment was measured using a hydraulic device under a pressure of 20 cm H2O. The perfusion fluid was deionized water, except in group 2 where 2% bovine serum albumin (BSA) was used. The representative specimens before and after treatment from each group were investigated using scanning electron microscopy. To measure cytotoxicity, test materials were applied to the occlusal surfaces of human dentin disks under which three-dimensional cell scaffolds were placed. After 24-h contact within the test device, cell viability was measured via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays.ResultsGLU significantly reduced the dentin permeability and occluded the dentinal tubules when 2% BSA was used as perfusion fluid. RD significantly reduced dentin permeability and occluded the tubules, but permeability rebounded after AS immersion. GLU significantly decreased cell viability, but RD was non-cytotoxic.ConclusionsIn vitro GLU application induced effective dentinal tubule occlusion only following the introduction of simulated dentinal fluid. RD provided effective tubule occlusion, but its full remineralization potential was not realized after a short period of immersion in AS. GLU may harm the pulp, whereas RD is sufficiently biocompatible.

Assessing writing development during study abroad

Abstract In research about second language (L2) development during study abroad (SA), writing is underrepresented. This is partly due to the difficulty of designing adequate tasks and measures to gauge writing development during a short immersion period. Our study explores the applicability of a narrative task assessed in terms of both linguistic complexity, accuracy, and fluency (CAF) and functional adequacy (FA), a novelty in SA writing research. Texts written by 30 advanced students of L2 German before and after SA were analysed. The results show moderate correlations between the measures for fluency and lexical variation and two FA dimensions. This suggests that, in the SA context, CAF and FA develop together to a certain extent, although the constructs are conceptually different.

Biljni materijali kao inhibitor zelene korozije za odabrane legure gvožđa - pregled

The importance of corrosion studies brings to the forefront economic losses, damage, and safety issues of metals deterioration in the construction industry. Although the choice of a material and use of inhibitors can contribute to its resistance to environmental corrosion behavior, the structural deterioration of metals can be exacerbated under operation conditions. In this review, highlights of research findings published in the past five years on the use of plant materials as corrosion inhibitors for variants of steel: carbon steel, mild steel, stainless steel are provided. It elucidates the meaning of green inhibitors and their types. It also presents the methods employed to ascertain the inhibition efficiencies of the plants/plant parts listed and the parameters considered in the corrosion inhibition analyses. The major gaps or limitations identified in the reported research findings include experimentation at constant temperatures and short immersion periods for the alloys. Due to the fact that, if these extracts were to be deployed for industrial use, they'd be subjected to more hazardous conditions, such as higher temperatures, pressures, etc., this paper proposes that their investigations as potential inhibitors on the laboratory/pilot scale be performed at higher temperatures and longer immersion times which may as such provide more comprehensive knowledge on the environmental/climatic requirements for their application. Additional improvement strategies are also suggested. The list of extracts, however, is not exhaustive.

Enhanced protection of hybrid polyetherimide-ZnO or CuO bilayer composite coatings against mild steel corrosion in chloride media

Protective bilayer composite coatings based on polyetherimide (PEI) containing ZnO or CuO particles were applied on mild steel (MS) by the sol-gel dip coating method and exposed to aggressive NaCl solutions. Scanning electron microscopy (SEM) analysis revealed the formation of homogenous coatings and X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis confirmed the presence of ZnO or CuO. Although attenuated total reflectance (ATR) proved that the polymer structure was not affected by the presence of the oxide particles, water contact angle revealed that PEI-CuO fallen within the hydrophobic range, whereas PEI alone and PEI-ZnO presented a hydrophilic behaviour. Upon immersion, the PEI-CuO coating was preserved, whereas the PEI and PEI-ZnO coatings were more susceptible to damage and the exposed MS presented different corrosion profiles, depending on being previously coated with blank PEI or PEI-ZnO coatings. The corrosion resistance was investigated by electrochemical impedance spectroscopy (EIS) and demonstrated that the barrier properties of the composite coating and the corrosion resistance of MS, over a short period of immersion, were improved with PEI-CuO. The coating modified with CuO particles, immersed for 8 days in NaCl, presented impedance values above 5 × 105 Ω.cm2, and represented a protective efficiency greater than 99% compared to PEI alone, or to the coating modified with ZnO for which the impedance was in the order of 103 Ω.cm2.Therefore, the most protective composite coating, due to the presence of CuO, brings potential to be explored as an anti-biofouling solution.

Spectroscopic Investigations of 316L Stainless Steel under Simulated Inflammatory Conditions for Implant Applications: The Effect of Tryptophan as Corrosion Inhibitor/Hydrophobicity Marker

In this paper, the conformational changes of tryptophan (Trp) on the corroded 316 L stainless steel (SS) surface obtained under controlled simulated inflammatory conditions have been studied by Raman (RS) and Fourier-transform infrared (FT-IR) spectroscopy methods. The corrosion behavior and protective efficiency of the investigated samples were performed using the potentiodynamic polarization (PDP) technique in phosphate-buffered saline (PBS) solution acidified to pH 3.0 at 37 °C in the presence and absence of 10−2 M Trp, with different immersion times (2 h and 24 h). The amino acid is adsorbed onto the corroded SS surface mainly through the lone electron pair of the nitrogen atom of the indole ring, which adopts a more/less tilted orientation, and the protonated amine group. The visible differences in the intensity of the Fermi doublet upon adsorption of Trp onto the corroded SS surface, which is a sensitive marker of the local environment, suggested that a stronger hydrophobic environment is observed. This may result in an improvement of the corrosion resistance, after 2 h than 24 h of exposure time. The electrochemical results confirm this statement—the inhibition efficiency of Trp, acting as a mixed-type inhibitor, is made drastically higher after a short period of immersion.

“Soapy water” transformation of the “condenser” with self-cleaning ability and antibacterial activity

Superhydrophobic materials exhibit diverse application potential in various fields due to their excellent self-cleaning properties. However, it is still challenging to prepare bionic superhydrophobic materials employing the green methods. In this study, the “condenser” (simulated by a red copper spiral tube) with excellent self-cleaning properties and antibacterial activity has been prepared by a simple one-step “soapy water” immersion process without introducing any other reagents. The results demonstrate that the Cu[CH3(CH2)10COO]2 lamellar nanostructures are formed on the surface of “condenser” owing to the oxidation of copper upon immersion in the sodium laurate aqueous solution. The as-formed nanostructures exhibit excellent self-cleaning performance and can significantly inhibit the growth and proliferation of Escherichia coli and Staphylococcus aureus, which is significant for the upgradation of the safety and comfort features of the new generation air-conditioners. Moreover, the ruptured superhydrophobic coating on the copper tube can be effectively restored by a facile re-soaking process. Therefore, the present approach, with simple one-step solution-immersion process, low cost, short immersion period, environmental friendliness and optimal applicability to a variety of metal structures of different shapes, represents a promising strategy for fabricating the low-cost superhydrophobic surfaces applicable to the condenser and heat transfer systems, thereby, promoting the development of the self-cleaning and antibacterial smart devices.

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.

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.

Fatigue behaviour of dry or partially saturated hot mix asphalt (HMA)

AbstractThis paper analyses the water, the degree of saturation, and the void content effects on the fatigue behaviour of hot mix asphalt (HMA) samples mixed in the laboratory. Some results on stiffness are also given. Fatigue characterization was carried out through a uniaxial tension‐compression (T‐C) test performed in a controlled‐strain mode, at 10°C and 10 Hz, on cylindrical samples. Our results show that the stiffness is not significantly affected by the water. This finding could be attributed to the short period of immersion of samples in water, low testing temperature, low void content of tested samples, and high viscosity of bitumen used. Furthermore, the fatigue resistance of HMA partially saturated with water (PSW) is lower than the one obtained for dry materials.

Microbiologically influenced corrosion mechanism of 304L stainless steel in treated urban wastewater and protective effect of silane-TiO2 coating

Microbiologically influenced corrosion (MIC) of bare and silane-TiO2 sol-gel coated stainless steel (SS) was studied in treated urban wastewater (TUWW). Combining the electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET) showed that SS surface colonization occurs, at earlier stages, by iron-oxidizing bacteria (IOB), and later by sulphate-reducing bacteria (SRB). The SVET results showed that chemical corrosion process and bacterial respiration led to the depletion of dissolved oxygen, creating a differential aeration cell and thus a localized corrosion phenomenon. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that the growth of a bacterial biofilm on 304L SS was a dynamic process, stimulating the localized oxidation of SS. To improve corrosion protection, a silane-TiO2 sol-gel coating for SS is proposed. SEM showed that the coating reduced bacterial adhesion and EIS study demonstrated that the coating improved the barrier properties and corrosion resistance of 304L SS in TUWW over a short period of immersion.

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.

Using Macro and Micro Electrochemical Methods to Understand the Corrosion Behavior of Stainless Steel Thermal Spray Coatings & Mg/Al Diffusion Couples

High-velocity oxygen fuel (HVOF) thermal spray coatings are desirable for their excellent erosion resistance. However, the fabrication process can lead to a decrease in corrosion resistance in comparison to the original bulk material. Stainless steel coatings on stainless steel substrates were produced using varying deposition parameters to investigate the corrosion properties of the resulting composite steels and elude the corrosion mechanism. Potentiodynamic polarization measurements carried out in corroding environments demonstrated the rate of degradation of the Fe-Cr alloy. After short immersion periods, both the coatings and sintered powder pellets for the same alloy showed iron-like active corroding behavior and no passivation regions on the anodic branch. Over time, the coating’s corrosion behavior began to change to signify similar results to that of pure chromium. Ex-situ electron microscopy and elemental composition revealed a Cr oxide rich layer left on the coating’s surface. Furthermore, chemical etching and digestion revealed microstructural changes between the powdered material and the bulk sheet metal such as Cr rich inclusions, known to be responsible for initiating intergranular corrosion. Micro electrochemical techniques including scanning electrochemical microscopy and scanning micro capillary method were employed over the coatings and powdered material, respectively, to prove that the lack of protective passivity the thermal spray coatings possess is mostly inherited from the atomized powdered stainless steel material.

Experimental Study on the Effect of Moisture Content on Bituminous Coal Porosity Based on 3D Reconstruction of Computerized Tomography

Bituminous coal in the Xutuan Coal Mine of the Huaibei Mining Bureau (China) is the research object of this study. The influence of moisture content on the porosity of the bituminous coal was investigated from a microscopic perspective by using a high-solution 3D X-ray micro-analyzer. The threshold segmentation method was used to segment the scanning slices of the coal samples. The threshold values of the various media were in the following order (from large to small): minerals, water, matrices, and fractures. The scanning volume and actual volume proportions of the different media in the coal samples with different moisture contents were calculated. The accuracy of the computerized tomography (CT) scanning method in measuring the coal moisture content was verified by comparison with the results obtained using the weighing method. 3D reconstructed coal samples, with different moisture contents, were analyzed, as well as separately reconstructed fractures and water in the coal samples with different moisture contents. The heterogeneity and anisotropy of the coal mass were explained quantitatively by the CT scanning intensity. A commonly used fracture classification method indicated that the primary fracture in the coal sample was a type A fracture. The results of the analysis of water in the coal fracture indicated that the porosity of bituminous coal decreased with the increase in moisture content in conditions of atmospheric pressure and a short immersion period. However, a certain level of porosity remained evident, and the degree of fracture development of the coal samples remained unchanged. This is attributed to the minor volumetric change in the minerals in the coal samples, as the water does not completely occupy the fractures in the coal samples, and the dissolution of the minerals by water is therefore not significant. The reasons for the moisture content affecting gas adsorption, seepage, and strength of a coal body were analyzed from a microscopic perspective. In addition, the types of fractures and water in the coal samples were classified by employing statistics and analyses of volume, surface area, specific surface area, and aspect ratio of the fractures and the water in the coal samples with different moisture contents.

Using macro and micro electrochemical methods to understand the corrosion behavior of stainless steel thermal spray coatings

High-velocity oxygen fuel thermal spray stainless steel coatings are desirable for their excellent erosion resistance. However, the fabrication process can lead to a decrease in corrosion resistance in comparison to the original bulk material. Here we produced stainless steel coatings on stainless steel substrates using varying deposition parameters to investigate the corrosion properties of the resulting composite steels and elucidate the corrosion behavior both on the macro and micro scale. Macro potentiodynamic polarization measurements carried out in corroding environments demonstrated the rate of degradation of the Fe-Cr alloy coating. After short immersion periods, the coatings showed iron-like active corroding behavior and no passivation regions on the anodic branch. Over time, the coating’s corrosion behavior began to change to signify similar results to that of pure chromium. Ex-situ electron microscopy and elemental composition revealed a Cr oxide rich layer left on the coating’s surface. Micro electrochemical techniques including scanning electrochemical microscopy and scanning micropipette contact method were employed over the coatings and powdered material, respectively, to show that the lack of protective passivity the thermal spray coatings possess is mostly inherited from the atomized powdered stainless steel material.

Recycling waste materials in geopolymer concrete

The widespread industry adoption of geopolymer concrete has the potential to positively contribute to environmental sustainability in both the industrial and construction sectors, through the recycling of waste materials, and the reduction in carbon emissions. Extensive research has been conducted into geopolymers during the past two decades, demonstrating the potential for the alkali-activated cement to replace ordinary Portland cement. However, there are a number of challenges facing the adoption of geopolymers. Much of the research into geopolymers uses sodium silicate solution as the alkali activator. Studies have noted that sodium silicate solutions are highly corrosive, and, as such, can be defined as user-hostile systems. Alternative alkali activators, such as potassium silicate solutions, have been proposed as more user-friendly and therefore more favourable for industry adoption. The highly variable nature of waste materials needs to be a focus of future research, with mix designs that focus on locally available waste materials with minimal processing. Much research has focused on heat-cured geopolymers; however, this increases the embodied energy while reducing the environmental benefit, which also acts as a limiting factor for in situ applications. Research into ambient temperature curing, addressing the issues of compressive strength, the rate of strength development, and curing time is required. Durability issues need to be addressed with studies finding the compressive strength of geopolymers being reduced after relatively short time periods of immersion in water, and potential problems relating to chloride induced corrosion of reinforcing steel. Further research is recommended for developing standardized leachate analysis for geopolymers containing recycled waste materials. The objective of this paper is to review the research into waste-incorporated geopolymers and highlight the barriers to industry adoption with a view to pointing the way forward for future research.

Role of Sn in microstructure and corrosion behavior of new wrought Mg-5Al alloy

The effect of Sn additions on the microstructure and corrosion behavior of new wrought Mg-5Al-xSn (x = 0.71, 1.47, 2.44, and 3.09 wt%) was studied through optical and electron microscopy, XRD, hydrogen evolution test, and electrochemical measurements. Increasing of the Sn content was followed an increase in the quantity of Sn dissolved in the Mg matrix and precipitation of Mg2Sn intermetallics when Sn content exceeded 1.47 wt%. The corrosion mode in a short immersion period was pitting corrosion; presence of cathodic sites (i.e., Mg2Sn intermetallics) deteriorated the alloys' corrosion resistance. However, with a long immersion period the corrosion mode of the alloys with Sn content above 0.71 wt% was mixed pitting and filiform corrosion, indicating that a passivation layer was formed on the alloys' surface and increased their corrosion resistance.

Microstructural, protective, inhibitory and semiconducting properties of PEO coatings containing CeO2 nanoparticles formed on AZ31 Mg alloy

The aim of this study is to investigate the effects of presence of cerium oxide nanoparticles on the microstructure, protective properties and inhibitory properties, while also enquiring into plasma electrolytic oxidation (PEO) coatings semiconductors properties, which were formed in a phosphate electrolyte solution, applied on AZ31 Mg alloy. According to the SEM/elemental map, Ce has been deposited in the oxide coating structure, and results in the changing of the morphology and coating thickness. According to the results of potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS), during the short and long immersion period of up to 16 days, the presence of optimum level of CeO2 in the phosphate electrolyte solution (3 g/l) results in the highest protection properties for PEO coating. Furthermore, the EIS test following the PDS, indicated the inhibitory effects of the cerium products, while the results of Mott-Schottky (M-S) test indicated a decrease in the donor concentration with presence of optimum CeO2 and thus, a drop in the tendency to undergo corrosion reactions. Thermodynamic investigations have shown that the formation of corrosion products which contain Ce is possible and stable, hence leading to the improvement of the protective properties of PEO coatings.

Modeling of water diffusion mechanism in polypropylene/date palm fiber composite materials

The aim of this work is to model the water absorption mechanism of the polypropylene/date palm fibers composite materials after their exposure at different immersion conditions. For short immersion period, a model combining the Fick’s law and the time temperature stress principle has been proposed to describe the water absorption mechanism. However, it has been noted that, after a saturation time, the water diffusion mechanism leads to a physical degradation and a mass loss into the composite material, especially under high temperatures and long times of water immersion. Microscopic observations have revealed a decrease of the interfacial adhesion between the fibers and the matrix and fiber degradations. A general new model describing the evolution of the water uptake mechanism and the degradation phenomenon has been also proposed in the present work. A good agreement between the theoretical and experimental data has been obtained.

The effect of pulse waveforms on surface morphology, composition and corrosion behavior of Al2O3 and Al2O3/TiO2 nano-composite PEO coatings on 7075 aluminum alloy

Plasma electrolytic oxidation was employed to produce Al2O3 and Al2O3/TiO2 composite coatings from a silicate based electrolyte on 7075 aluminum alloy using unipolar and bipolar waveforms with cathodic duty cycle of 20 and 40%. The results showed that the surface morphology of the coatings is dependent on the applied waveform. Pancake like morphology was converted to crater like by altering waveform from unipolar to bipolar. Higher thickness, lower porosity, and thus, higher corrosion protection were achieved using the bipolar waveform at higher cathodic duty cycle of 40%. The incorporation of TiO2 nano-particles in the coatings decreased the thickness, increased the micro-cracks and widened the micro-pores on coating surface when unipolar waveform was applied. It was found that TiO2 nano-particles have been incorporated into the coatings in their original crystalline structure, i.e. rutile, which was categorized in the “inert incorporation” mode and this incorporation has not changed the matrix micro-structure, i.e. γ-alumina. In addition, the incorporated amounts of TiO2 nano-particles were constant and showed no reasonable relation with the applied waveform. The corrosion results indicated that although the composite coating produced at unipolar waveform shows the highest corrosion resistance at short periods of immersion due to repairing mechanism, it degrades at a higher rate. However, for the composite coatings produced using the bipolar waveform with the higher cathodic duty cycle of 40%, the maximum corrosion protection was achieved at long term immersion. Repairing mechanism is plugging the micro-pores in the inner compact layer which was found more effective for the coatings with lower porosity. Accordingly, it was concluded that the corrosion protection of the coatings with higher “intrinsic resistance” get more benefit from the repairing mechanism too.