Attack Of Water Research Articles

Anisotropic Hydrolysis Susceptibility in Deformed Polydimethylsiloxanes.

Chemical reactions involving the polydimethylsiloxane (PDMS) backbone can induce significant network rearrangements and ultimately degrade macro-scale mechanical properties of silicone components. Using two levels of quantum chemical theory, we identify a possible electronic driver for chemical susceptibility in strained PDMS chains and explore the complicated interplay between hydrolytic chain scissioning reactions, mechanical deformations of the backbone, water attack vector, and chain mobility. Density functional theory (DFT) calculations reveal that susceptibility to hydrolysis varies significantly with the vector for water attacks on silicon backbone atoms, which matches strain-induced anisotropic changes in the backbone electronic structure. Efficient semiempirical density functional tight binding (DFTB) calculations are shown to reproduce DFT predictions for select reaction pathways and facilitate more exhaustive explorations of configuration space. We show that concerted strains of the backbone must occur over at least a few monomer units to significantly increase hydrolysis susceptibility. In addition, we observe that sustaining tension across multiple monomer lengths by constraining molecular degrees of freedom further enhances hydrolysis susceptibility, leading to barrierless scission reactions for less substantial backbone deformations than otherwise. We then compute chain scission probabilities as functions of the backbone degrees of freedom, revealing complicated configurational interdependencies that impact the likelihood for hydrolytic degradation. The trends identified in our study suggest simple physical descriptions for the synergistic coupling between local mechanical deformation and environmental moisture in hydrolytic degradation of silicones.

Hydrolytic crack in a rubbery network

We report an experimental finding that a crack advances in a polydimethylsiloxane (PDMS), under a small stress, in a moist environment. PDMS chains consist of siloxane bonds with methyl side groups. The methyl groups make PDMS hydrophobic, and PDMS hydrolyzes extremely slowly under no stress. Nonetheless, we find that a crack advances under the combined attack of water and stress. Our experimental data support the hypothesis that PDMS is susceptible to stress-assisted hydrolysis, but show that the activation area for PDMS is smaller than that for silica by two orders of magnitude. We attribute this large difference to the molecular structures of the two materials: a glassy network and a rubbery network, respectively. This finding suggests that stress-assisted reaction should concern many elastomers and gels in engineering and medicine.

Kinetics of environmentally assisted cracking in SiNx barrier films

Kinetics of environmentally assisted subcritical cracking in SiNx barrier films is studied by in situ optical microscopy experiments and quantum chemical molecular orbital theory simulations. The activation volume of 0.83–1.11 cm3/mol and the activation energy of 138 kJ/mol (1.43 eV) are experimentally measured for subcritical crack growth in moist air. The quantum chemical simulations reveal the molecular mechanism of stress corrosion in mechanically strained SiNx under water attack, and the predicted activation energy and activation volume are in good agreement with the experimental results. The combined experimental and modeling studies provide a fundamental understanding of subcritical crack growth in SiNx barrier films for flexible electronic device applications.

Durability characteristics of lightweight rubberized concrete

This study experimentally investigates the durability characteristics of rubberized concrete up to 30% rubber content. The durability characteristics including the carbonation depth, standard potential, water absorption, and initial rate of absorption of rubberized concrete were investigated. The experimental results have shown that rubberized concrete absorbed more water than conventional concrete, and the water absorption increased with the rubber content. Therefore, rubberized concrete is more susceptible to water, chloride, and chemical attacks. The carbonation depth of rubberized concrete was also higher than that of the conventional concrete and it increased with the rubber contents, indicating more susceptibility to corrosion. Although the estimated service life of rubberized concrete is shorter than that of conventional concrete, with 15% rubber contents it exceeds 50 years according to fib CEB-FIP [1] and AS 3600 [2]. Rubberized concrete thus can be used for structural components with sufficient strength and adequate service life up to 15% rubber content. In addition, the pre-treatment methods with NaOH or water were found to have considerable effects on carbonation depth but marginal effects on the water absorption and standard potential of rubberized concrete.

Hydrolysis and condensation of ZIF-8 in water

Recent studies have shown that zeolitic imidazolate framework-8 (ZIF-8) crystallites are not stable in aqueous solution under ambient conditions. When immersed in water, ZIF-8 crystallites are hydrolyzed to zinc and imidazolate ions, which can be condensed to form a new solid substance upon removal of water by evaporation. The present work demonstrates such ZIF-8 phase shift substance is of crystalline structure but does not belong to any known (pseudo)polymorphs of ZIF-8, ZIF-L, dia(Zn), or decomposed product of ZIF-8: Zn(OH) 2 and 2-methylimidazole. FTIR characterization shows the co-existence of Zn–O and Zn–N bond in the new substance, confirming the partial cleavage of Zn–N bond in ZIF-8 building unit in the hydrolysis step. EDS quantification for the ZIF-8 phase shift substance gives a C:N:Zn:O atomic ratio of 40:20:5:4. Based on EDS and FTIR results, the chemical formula of Zn 5 (HMIM) 4 (MIM) 6 (OH) 4 for the building unit of such substance is proposed consisting of four partially hydrolyzed and one undisturbed secondary ZIF-8 building units. The ZIF-8 phase shift substance is crystalline with a nearly identical atomic composition as ZIF-8 (except for increased oxygen content), suggesting it might be a novel pseudo-polymorph of ZIF-8. The hydrolysis and condensation of ZIF-8 can be described by a mechanism that includes (1) hydrolysis of ZIF-8 through cleavage of Zn–N bond to form zinc and imidazolate ions and partially hydrolyzed ZIF-8 units and (2) condensation of these ions and clusters with the help of hydrogen bond to form the new structure of ZIF-8 phase shift substance. • Hydrolysis of ZIF-8 in water proceeds via partial cleavage of Zn–N bonds. • Hydrolysis and condensation of ZIF-8 leads to a new crystalline substance with same composition as ZIF-8. • Improved stability of ZIF-8 can be achieved by protecting Zn–N coordination bond from water attack.

Covalent binding of uracil DNA glycosylase UdgX to abasic DNA upon uracil excision.

Uracil DNA glycosylases (UDGs) are important DNA repair enzymes that excise uracil from DNA, yielding an abasic site. Recently, UdgX, an unconventional UDG with extremely tight binding to DNA containing uracil, was discovered. The structure of UdgX from Mycobacterium smegmatis in complex with DNA shows an overall similarity to that of family 4 UDGs except for a protruding loop at the entrance of the uracil-binding pocket. Surprisingly, H109 in the loop was found to make a covalent bond to the abasic site to form a stable intermediate, while the excised uracil remained in the pocket of the active site. H109 functions as a nucleophile to attack the oxocarbenium ion, substituting for the catalytic water molecule found in other UDGs. To our knowledge, this change from a catalytic water attack to a direct nucleophilic attack by the histidine residue is unprecedented. UdgX utilizes a unique mechanism of protecting cytotoxic abasic sites from exposure to the cellular environment.

High-Temperature Grafting Silylation for Minimizing Leaching of Acid Functionality from Hydrophobic Mesoporous Silicas Used as Catalysts in the Liquid Phase.

Ordered-hexagonal silica materials, such as Mobil crystalline material-41 and Santa Barbara amorphous-15, have important applications in heterogeneous catalysis and biomass conversion due to their chemical stability and mesoporous structure. Low-temperature grafting (LG) is one of the most common functionalization methods used to modify the acidity/basicity or hydrophobicity/hydrophilicity of the surface. However, the materials prepared by this method are prone to leaching of functional groups into the reaction medium. The exact nature of the leaching phenomenon has not been fully addressed in the literature. In this contribution, we have investigated this process at the molecular level by combining well-controlled reaction experiments and several characterization techniques (Fourier transform infrared, 1H-29Si cross-polarization magic-angle spinning NMR, X-ray diffraction, thermogravimetric analysis, and N2 adsorption-desorption). We have found that leaching is originated by the presence of terminal surface silanols, which render the catalysts susceptible to the attack of water and polar compounds. Hence, instead of simple detaching of functional groups, leaching can be better described as a partial dissolution of the surface layers of the silica, which of course also removes the functional groups during this process. Therefore, an effective strategy to minimize leaching is to reduce the density of free silanols via full functionalization of the surface. We propose a novel silylation method, high-temperature grafting, which allows the grafting process to be conducted at high temperatures (180 °C) under solvent-free conditions. By this method, a more complete silylation of surface silanols can be obtained. Consequently, the samples prepared by this high-temperature grafting method show to be highly stable during acid-catalyzed alkylation reaction, conducted under severe conditions (high temperature and in the presence of polar solvents).

Performance of New Non-Clinker Aluminum Dross Cement Curing Agent

The growth of China's aluminum industry makes more and more waste aluminum dross, although there are some ways for recycling aluminum dross, but still cannot absorb its output. This paper attempts to develop an effective concrete curing agent with high content of aluminum ash so as to effectively solve the problems of waste residue accumulation. The properties of a new aluminum dross cement-curing agent based on industrial solid wastes combined with an activator are evaluated through orthogonal testing using standard testing methods for compressive strength, bending strength, setting time, soundness, and the water requirement of standard consistency. The influence of the curing conditions and the water to cement ratio on the strength obtained with the aluminum dross curing agent was also studied along with the durability to water erosion, resistance to sulfate attack and stability when subjected to dry/wet cycles or high temperature. The results obtained demonstrate that this new clinker-free aluminum ash curing agent provides good mechanical properties and a high resistance to water and sulfate attack. This material was also found to be suitable for use as a curing agent in soil solidification.

Montmorillonite with unique interlayer space imparted polymer scaffolds with sustained release of Ag+

Abstract Polyglycolic acid (PGA) has been a potential scaffold material due to its good biocompatibility and processibility, but its poor mechanical properties and over fast degradation restricted its application in bone repair. Meanwhile, it is worth noticing that bacterial infection is a common problem in bone repair. In this study, montmorillonite (MMT), with unique interlayer space, was introduced to PGA scaffolds prepared via additive manufacturing to address the problems. The results indicated MMT acted as rigid reinforcements dispersing well in the PGA matrix, which effectively transferred and absorbed the stresses in the matrix, thereby significantly increasing the compressive properties and hardness of the scaffolds. Moreover, MMT played the role of impermeable barriers in the matrix, hindering the diffusion of water and its attack on the matrix, which inhibited the hydrolysis and hence significantly decreased the degradable rate. More importantly, Ag+ was loaded into the interlayer space of MMT via ion exchange and was further chemically reduced to metallic Ag with higher stability. The impermeable layered structure of MMT presented dual barrier effects on the release of Ag+ via inhibiting the attack of water on Ag from outside and the diffusion of Ag+ from inside. Hence, the scaffolds exhibited a sustained Ag+ release and a long-lasting antibacterial property.

Alkyne Activation with Gold(III) Complexes: A Quantitative Assessment of the Ligand Effect by Charge-Displacement Analysis.

A quantitative assessment of the Dewar-Chatt-Duncanson components of the Au(III)-alkyne bond in a series of cationic and dicationic bis- and monocyclometalated gold(III) complexes with 2-butyne via charge-displacement (CD) analysis is reported. Bonding between Au(III) and 2-butyne invariably shows a dominant σ donation component, a smaller, but significant, π back-donation, and a remarkable polarization of the alkyne CC triple bond toward the metal fragment. A very large net electron charge transfer from CC triple bond to the metal fragment results, which turns out to be unexpectedly insensitive to the charge of the complex and more strictly related to the nature of the ancillary ligand. The combination of σ donation, π back-donation, and polarization effects is in fact modulated by the different ligand frameworks, with ligands bearing atoms different from carbon in trans position with respect to the alkyne emerging as especially interesting for both imparting Au(III)-alkyne bond stability and inducing a more effective alkyne activation. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-alkyne is made by performing a comparative study in a model nucleophilic attack of water to the alkyne triple bond. Smaller π back-donation facilitates alkyne slippage in the transition states, which is energetically less demanding for Au(III) than for Au(I), and suggests a greater propensity of Au(III) to facilitate the nucleophilic attack.

Influence of Chemical Stability on the Fabrication of MnGa-based Devices

Ferromagnetic films of L10-ordered MnGa have shown promise not only in the applications in ultrahigh-density magnetic recording and spintronic memories, oscillators, and sensors, but also in controllable studies of novel electrical transport phenomena. However, the stability of MnGa in chemicals and oxygen plasma that are commonly used in the standard micro-/nano-fabrication process has unsettled. In this work, we report a systematic study on the chemical stability of the MnGa films in acids, acetone, ethanol, deionized water, tetramethylammonium hydroxide (TMAOH) and oxygen plasma. We find that MnGa is very stable in acetone and ethanol, while can be attacked substantially if soaked in TMAOH solution for sufficiently long time. Deionized water and acids (e.g., HCl, H3PO4 and H2SO4 solutions) attack MnGa violently and should be avoided whenever possible. In addition, oxygen plasma can passivate the MnGa surface by oxidizing the surface. These results provide important information for the fabrication and the integration of MnGa based spintronic devices.

Kinematic Analysis of the Kick Start Underwater Phase of Young Male Swimmers

Introduction: The introduction of a starting block with an adjustable and slanted footrest has caused the development of a new starting technique - the Kick Start. Therefore, research on swim start seems necessary, particularly concerning the Kick Start underwater phase. Aim: The study aim was to characterise the underwater phase of the Kick Start among young, male, competitive swimmers. Basic procedures. The study included 32 male, youth, competitive swimmers (mean age=16.61 years, height=1.80 m, body mass=72.47 kg, FINA Points=617). Participants executed three freestyle Kick Starts recorded using an underwater high-speed camera. Videos were kinematically analysed using the Skill Spector programme. Then, k-means clustering was applied. Results. Participants were classified into three clusters. Cluster FT (“flat trajectory”) comprised swimmers with a ”flat” course of underwater movement - low value of the angle of water attack (KA=0.92o), maximum depth of the head (hmax=0.85 m), distance (dmax=0.71 m), and time to maximum depth of the head (tmax=0.51 s). Group MT (“moderate trajectory”) had moderate values of the above-mentioned parameters (KA=10.27o, hmax=0.93 m, dmax=1.03 m, tmax=0.60 s), while Cluster DT (“deep trajectory”) achieved the highest values (KA=15.74o, hmax=1.05 m, dmax=1.38 m, tmax=0.73 s). The time to reach 15 m in Cluster FT was about 0.3 s slower than in Group MT and DT, although this dissimilarity was not significant. Conclusions. The course of underwater movement is mostly affected by the angle at which swimmers submerge. There is no “ideal” way to perform the underwater phase, however, it should not be executed too close to the water surface.

Mechanical Properties and Corrosion Resistance of Cement Concrete Containing Sea Sand or Sea Water

ABSTRACT Through the test of 27 groups of specimens, the influence law on compressive strength and expansion under sea salt corrosion by type of cement, fly ash substitute rate of cement, fly ash substitute rate of fine aggregate, water-binder ratio, type of fine aggregate, and immersion method were analyzed. The corrosion resistance of reinforced concrete under sea water attack was also studied in this research. The experimental results indicate that the influence of various factors on the compressive strength is correlative, and the interaction effects of the type of cement and type of fine aggregate, type of cement and immersion method on the compressive strength are correlative; fly ash substitute rate of fine aggregate, water-binder ratio, type of fine aggregate and immersion were all had significant effects on the expansion at each age. The immersion method had the most significant effect on the expansion. The type of fine aggregate has a significant effect on all tests, but other more correlative factors can be used to improve the deterioration of cement mortar caused by sea sand. Replacement of 10% or 20% aggregate by fly ash gives no apparent improvement in preventing the expansion of cement mortar in sea water exposure. The concrete test results indicate that no serious detrimental effect was found for the corrosion inhibitor in reinforced concrete.

Confined Pt11+ Water Clusters in a MOF Catalyze the Low‐Temperature Water–Gas Shift Reaction with both CO2 Oxygen Atoms Coming from Water

AbstractThe synthesis and reactivity of single metal atoms in a low‐valence state bound to just water, rather than to organic ligands or surfaces, is a major experimental challenge. Herein, we show a gram‐scale wet synthesis of Pt11+ stabilized in a confined space by a crystallographically well‐defined first water sphere, and with a second coordination sphere linked to a metal–organic framework (MOF) through electrostatic and H‐bonding interactions. The role of the water cluster is not only isolating and stabilizing the Pt atoms, but also regulating the charge of the metal and the adsorption of reactants. This is shown for the low‐temperature water–gas shift reaction (WGSR: CO + H2O → CO2 + H2), where both metal coordinated and H‐bonded water molecules trigger a double water attack mechanism to CO and give CO2 with both oxygen atoms coming from water. The stabilized Pt1+ single sites allow performing the WGSR at temperatures as low as 50 °C.

Confined Pt1 1+ Water Clusters in a MOF Catalyze the Low-Temperature Water-Gas Shift Reaction with both CO2 Oxygen Atoms Coming from Water.

The synthesis and reactivity of single metal atoms in a low-valence state bound to just water, rather than to organic ligands or surfaces, is a major experimental challenge. Herein, we show a gram-scale wet synthesis of Pt1 1+ stabilized in a confined space by a crystallographically well-defined first water sphere, and with a second coordination sphere linked to a metal-organic framework (MOF) through electrostatic and H-bonding interactions. The role of the water cluster is not only isolating and stabilizing the Pt atoms, but also regulating the charge of the metal and the adsorption of reactants. This is shown for the low-temperature water-gas shift reaction (WGSR: CO + H2 O → CO2 + H2 ), where both metal coordinated and H-bonded water molecules trigger a double water attack mechanism to CO and give CO2 with both oxygen atoms coming from water. The stabilized Pt1+ single sites allow performing the WGSR at temperatures as low as 50 °C.

Metal Oxidation States for the O–O Bond Formation in the Water Oxidation Catalyzed by a Pentanuclear Iron Complex

Understanding the water oxidation mechanism, especially how the O–O bond formation takes place, provides crucial implication for the design of more efficient molecular catalysts for water oxidation in artificial photosynthesis. Density functional calculations have here been used to revisit the mechanism of O–O bond formation catalyzed by a pentanuclear iron complex. By comparing energetics for O–O bond formation at different oxidation states, it is suggested that the formally Fe5III,III,III,IV,IV state is the best candidate for the coupling of two oxo groups, with a barrier of 17.3 kcal/mol, rather than the previously suggested lower oxidation state of Fe5II,II,III,IV,IV. Importantly, the first water insertion into the Fe5III,III,III,III,III complex is associated with a barrier of 18.8 kcal/mol. The calculated barrier is somewhat overestimated as discussed in the text. Other possible reaction pathways, including water attack at the Fe5III,III,III,IV,IV state, coupling of oxo and hydroxide at the Fe5III,II...

Direct oxygen isotope effect identifies the rate-determining step of electrocatalytic OER at an oxidic surface

Understanding the mechanism of water oxidation to dioxygen represents the bottleneck towards the design of efficient energy storage schemes based on water splitting. The investigation of kinetic isotope effects has long been established for mechanistic studies of various such reactions. However, so far natural isotope abundance determination of O2 produced at solid electrode surfaces has not been applied. Here, we demonstrate that such measurements are possible. Moreover, they are experimentally simple and sufficiently accurate to observe significant effects. Our measured kinetic isotope effects depend strongly on the electrode material and on the applied electrode potential. They suggest that in the case of iron oxide as the electrode material, the oxygen evolution reaction occurs via a rate-determining O−O bond formation via nucleophilic water attack on a ferryl unit.

Mercerizing Extraction and Physicochemical Characterizations of Lignocellulosic Fiber from the Leaf Waste of Mikania micrantha Kunth ex H.B.K

ABSTRACTInvasive plants can grow rampantly and spread fast in large amount, which can be economically invoked for generating value-added products. In this study, lignocellulosic fiber was extracted from the leaf waste of a luxuriant invasive plant, Mikania micrantha Kunth-ex H.B.K. by mercerization process. After the alkaline treatment, the lignocellulosic biomass remained at 38.54% resulting from the large removal of extractive impurities. The lignocellulosic fraction in the mercerized leaf fiber was improved from 56.59% to 83.96%. The chemical composition analysis showed the cellulose fraction was increased by 11.17% while the hemicellulose and lignin fractions were found to be decreased by 4.89% and 6.28%, respectively. The FT-IR and TGA results further affirmed the change in chemical composition of the lignocellulosic fiber. Furthermore, an increase in cellulose fraction raised the fiber crystallinity index from 11.0% to 36.7%. The SEM study revealed that the surface morphology of lignocellulosic fiber changed from smooth surface into rough corrugated ridges, which affirmed the increase in crystallinity, resulting from the removal of wrapped cementing materials. In subsequent, the lignocellulosic fiber exhibited more pervious to water attack with an increase in moisture absorption from 119.22% to 410.19%.

δ13C and δ18O Stable Isotope Analysis Applied to Detect Technological Variations and Weathering Processes of Ancient Lime and Hydraulic Mortars

Samples of mortars were collected from lime and hydraulic mortars affected by environmental degradation. A total of 63 samples were obtained from Hellenistic, Late Roman and Byzantine historic constructions located at Kavala, Drama and Makrygialos in North Greece. Samples were collected in sections from the surface up to 6 cm deep using a drill-core material. The first sample was collected from the external layer, while the internal samples were collected each 1cm beeper from the previous, in order to monitor the moisture ingress. Isotopic data will make it possible to create an ideal Hellenistic and Byzantine mortar layer and to provide weathering gradients. The isotopic values comprise a range of δ13C and δ18O values from −17.1‰ to 1.2‰ and −25.9‰ to −2‰, respectively. The weathering process of Hellenistic and Byzantine are expressed, by the regression lines δ18Ocalcite matrix = 0.6 × δ13Ccalcite matrix − 1.9 and δ18Ocalcite matrix = 0.6 × δ13Ccalcite matrix − 2.0 for hydraulic and Lime mortars respectively. Pronounced isotopic shift to heavy or light δ13C and δ18O in the carbonate matrix was attributed to the primary source of CO2 (atmospheric versus biogenic) and H2O (evaporation of local primary water), in residual limestone and in secondary processes such as recrystallization of calcite with pore water and salts attack. Exogenic processes related to biological growth are responsible for further alterations of δ18O and δ13C in lime mortars. This study indicated that stable isotope analysis is an excellent tool to fingerprint the origin of carbonate, the environmental setting conditions of mortar, origin of CO2 and water during calcite formation and to determine the weathering depth and the potential secondary degradation mechanisms.

Interactive Effects of Water Chemistry, Hydrodynamics, and Precipitated Calcium Carbonate Causing Erosion Corrosion of Copper in Hot Water Recirculation Systems: Case Study and Experimental Work

Erosion corrosion, or flow-induced failure, of copper is a complex phenomenon driven by a multitude of water quality, hydrodynamic, and electrochemical factors. This most common form of corrosion attack in hot water is likely to increase with newer Legionella risk-management regulations promulgating increased water recirculation, hotter water temperatures, and higher chlorine disinfectant dose. The current work reports findings from an investigation into widespread copper plumbing failure due to erosion corrosion in a large building complex by systematically exploring the effects of relevant water chemistry and hydrodynamic variables on localized erosion corrosion attack. The results seriously call into question decades of conventional wisdom by demonstrating that hard waters are not inherently less aggressive than soft water; in fact, if calcium carbonate solids form they can become even more aggressive. Entrained particles significantly accelerated attack on copper pipe walls, especially in high-turbulence areas like bends. This is the first research study to reliably reproduce rapid erosion corrosion failures in realistic potable water chemistry in the laboratory.