Prolonged Exposure To Water Research Articles

Mitigating aging infrastructure risks: An optimized epoxy resin system for water supply pipeline rehabilitation

Urban water supply networks are crucial for ensuring the delivery of safe drinking water to urban populations; however, the aging infrastructure in these systems has led to a rising incidence of leaks and frequent pipeline failures, posing serious risks. Traditional repair approaches encounter limitations in terms of efficiency, durability, and environmental safety, particularly when employed in potable water pipelines. To address these challenges, we developed a novel multi-component amine-cured epoxy resin system specifically optimized for in-situ curing under ambient conditions. This study comprehensively examines the mechanical properties, water absorption behavior, and curing kinetics of this resin system, formulated to reduce volatile organic compound emissions while enhancing durability under prolonged water exposure. Experimental findings demonstrate that the E2 formulation exhibited superior tensile strength, flexural properties, and fracture toughness relative to other formulations, with a two-stage water absorption model accurately predicting resin behavior in moisture-laden environments. Moreover, finite element modeling and laboratory testing confirmed the influence of bubble defects on mechanical performance, and a negative pressure defoaming technique effectively reduced defect volume, resulting in a 17.6% improvement in tensile strength. Collectively, this research advances the practical application of rapid-curing resins, offering a resilient, safe, and sustainable solution for the rehabilitation of aging water pipeline networks.

Water Sorption and Solubility of Highly Aesthetic Single-Shade Nano-Hybrid Resin Composites.

Background A single-shade resin composite is a new type of resin composite that was introduced in 2019. There is not much data regarding the water sorption (Wsp) and water solubility (Wsl) of this type of resin composite. Therefore, this study aimed to investigate Wsp and Wsl and their effects on the surface roughness of a single-shade nano-hybrid resin composite in comparison with a conventional nano-hybrid resin composite in accordance with ISO 4049:2019 (Dentistry - Polymer-based Restorative Materials). Material and methods An in vitro study was performed to investigate the Wsp and Wsl of a single-shade supra-nano-hybrid composite (Omnichroma) and a conventional nano-hybrid composite (Filtek™ Z250 XT) in accordance with ISO 4049:2019. Five disks were prepared of each material with dimensions of 15 ± 1 mm in diameter and 1 ± 0.1 mm in thickness, as per ISO 4049:2019. The results were calculated according to the ISO equations for Wsp and Wsl in µg/mm3. Atomic force microscopy (AFM) was used to analyze the surface roughness (Ra) of test specimens. Results The findings showed that the values of Wsl and Wsp of both materials are comparable and revealed no statistically significant difference (P > 0.05). The AFM images showed a higher Ra post-solubility testing, and the statistical analysis indicated a significant difference for both materials. Conclusions The study concluded that the single-shade resin composite (Omnichroma) and the conventional nano-hybrid composite (Filtek™ Z250 XT) are following the requirements of ISO 4049:2019. The AFM analysis indicated that resin composite surfaces are significantly affected when exposed to water for a prolonged period of time. However, the Ra variations of Filtek™ Z250 XT were higher than Omnichroma specimens. These results indicate that resin composite surfaces can be significantly impacted by prolonged water exposure. This knowledge is critical for enhancing the long-term clinical performance and durability of these dental restorative materials.

Accelerated ageing of 3D printed water purification filters based on PLA reinforced with green nanofibers

This study investigates the ageing behavior of polylactic acid (PLA) and PLA-based biocomposites reinforced with either 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO) - oxidized cellulose nanofibers (TCNF) or chitin nanofibers (ChNF) in water. Fused deposition modeling (FDM) was used to create water filters, which underwent aging tests at various temperatures over 19 weeks. Thermomechanical results show that while the addition of TCNF and ChNF improves the mechanical performance of PLA-based filters in dry conditions, it has the opposite effect after exposure to water. The impact of prolonged water exposure on Young's modulus and toughness was more significant in biocomposites than in unmodified PLA filters. The TCNF/PLA and ChNF/PLA filters saw a substantial ∼10 °C drop in glass transition temperature (Tg) after 3 weeks, while pure PLA remained nearly unaffected for up to 7 weeks. The mechanical tests allowed to estimate the service life of the 3D printed filters using the Arrhenius model. It was shown that the TCNF/PLA and ChNF/PLA filters can be utilized at room temperature water for up to 8 and 5 months, respectively, until they lose 50 % of their initial ability to resist deformation. In the same conditions, PLA filters can serve for up to 3.5 years. In conclusion, this study highlights the importance of considering the degradation behaviour of biocomposites when developing sustainable materials for water treatment applications.

Explanation of the Compensation Law and the Isokinetic Point in the Electrical Conduction of Crosslinked Polyethylene

Thermally activated direct current (DC) electrical conductivity in low-density polyethylene (LDPE) is known to be subject to the compensation law. Accordingly, the preexponential factor follows a specific relation with activation energy, reducing overall changes in conductivity. This relationship is governed by the Meyer-Neldel temperature. However, there is no published evidence for a corresponding isokinetic point, a temperature where the conductivity of all LDPE samples is the same. Here, it is determined that the compensation law applies to both DC and alternating current (AC) conduction for LDPE and for crosslinked polyethylene (XLPE) without an observed isokinetic point. The potential origins of compensation in polyethylene are discussed as well as reasons for similarity between LDPE and XLPE. It is observed that prolonged water exposure removed the compensation behavior. Meanwhile, preheating samples in the oven prior to measurements modifies the compensation behavior and reduced the spread around the isokinetic point. It is thus deduced that an isokinetic point can be observed in polyethylene but is obscured by contributions from water and other impurities.

Painful Plantar Rash with Systemic Symptoms

Painful Plantar Rash with Systemic Symptoms

The Responses to Long-Term Water Addition of Soil Bacterial, Archaeal, and Fungal Communities in a Desert Ecosystem

The response of microbial communities to continual and prolonged water exposure provides useful insight when facing global climate changes that cause increased and uneven precipitation and extreme rainfall events. In this study, we investigated an in situ manipulative experiment with four levels of water exposure (ambient precipitation +0%, +25%, +50%, and +100% of local annual mean precipitation) in a desert ecosystem of China. After 9 years of water addition, Illumina sequencing was used to analyze taxonomic compositions of the soil bacterial, archaeal, and fungal communities. The results showed significant increases in microbial biomass carbon (MBC) at higher amended precipitation levels, with the highest values reported at 100% precipitation. Furthermore, an increase in the bacterial species richness was observed along the water addition gradient. In addition, the relative abundance of several bacterial phyla, such as Proteobacteria, significantly increased, whereas that of some drought-tolerant taxa, including Actinobacteria, Firmicutes, and Bacteroidetes, decreased. In addition, the phyla Planctomycetes and Nitrospirae, associated with nitrification, positively responded to increased precipitation. Archaeal diversity significantly reduced under 100% treatment, with changes in the relative abundance of Thaumarchaeota and Euryarchaeota being the main contributors to shifts in the archaeal community. The fungal community composition was stable in response to water addition. Results from the Mantel test and structural equation models suggested that bacterial and archaeal communities reacted contrastingly to water addition. Bacterial community composition was directly affected by changing soil moisture and temperature, while archaeal community composition was indirectly affected by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes in the desert ecosystem.

Effects of prolonged saline water exposure on the peel strength of polyurea/monel 400 interface

ABSTRACT This study investigates changes in the peel strength of polyurea/monel 400 interfaces after prolonged exposure to saline water. The monel family of alloys is extensively used on marine structures due to its resistance to corrosion, and polyurea has shown considerable promise as a coating material for marine structures to mitigate the damage from blast loading and provide corrosion resistance. In the present work, polyurea was cast on sandblasted and chemically treated Monel 400 bars, which were subsequently immersed in saline water at 70°C for 2, 5 and 8 weeks, respectively, to accelerate the aging process. This high-temperature exposure corresponded to 19, 48 and 76 weeks in the real-life service environment. The peel strengths of the interfaces were measured using the fixed arm peel test at two angles: 90° and 180°. The adhesive energy was computed from the experimentally determined peel strength using models developed by Kendall and Rivlin. The surfaces exposed by peeling were analyzed with the use of an optical microscope to determine the different failure modes at the interfaces. Finally, employing degradation kinetics, a degradation model was established and used to calculate long-term adhesive energy and the degradation rate of the interface. Results showed that prolonged exposure to saline water leads to a drop in the peel strength. For 180° peel test, an 83% decrease in the peel strength of the polyurea/monel 400 interface was observed after 8 weeks of exposure at 70°C. Both peel angles gave similar adhesive energies for the same exposure durations indicating the independence of the adhesive energy on the testing angle. The elastic term contribution to the adhesive energy for all experiments was less than 5.5%. Lastly, the exposure time dependence on the adhesive energy followed first-order degradation kinetics.

Mechanical and Thermal Properties of Montmorillonite-Reinforced Polypropylene/Rice Husk Hybrid Nanocomposites.

In recent years, there has been considerable interest in the use of natural fibers as potential reinforcing fillers in polymer composites despite their hydrophilicity, which limits their widespread commercial application. The present study explored the fabrication of nanocomposites by melt mixing, using an internal mixer followed by a compression molding technique, and incorporating rice husk (RH) as a renewable natural filler, montmorillonite (MMT) nanoclay as water-resistant reinforcing nanoparticles, and polypropylene-grafted maleic anhydride (PP-g-MAH) as a compatibilizing agent. To correlate the effect of MMT delamination and MMT/RH dispersion in the composites, the mechanical and thermal properties of the composites were studied. XRD analysis revealed delamination of MMT platelets due to an increase in their interlayer spacing, and SEM micrographs indicated improved dispersion of the filler(s) from the use of compatibilizers. The mechanical properties were improved by the incorporation of MMT into the PP/RH system and the reinforcing effect was remarkable as a result of the use of compatibilizing agent. Prolonged water exposure of the prepared samples decreased their tensile and flexural properties. Interestingly, the maximum decrease was observed for PP/RH composites and the minimum was for MMT-reinforced and PP-g-MAH-compatibilized PP/RH composites. DSC results revealed an increase in crystallinity with the addition of filler(s), while the melting and crystallization temperatures remained unaltered. TGA revealed that MMT addition and its delamination in the composite systems improved the thermal stability of the developed nanocomposites. Overall, we conclude that MMT nanoclay is an effective water-resistant reinforcing nanoparticle that enhances the durability, mechanical properties, and thermal stability of composites.

Probing the Interfacial Chemistry of Ultrathin ALD-Grown TiO2 Films: An In-Line XPS Study

Ultrathin TiO2 films received renewed attention in the field of photoelectrochemical water splitting as corrosion protection layers for unstable, small-bandgap semiconductors. Because nucleation on the substrate can differ from steady-state growth of the film itself, it is important to understand the nucleation behavior on a specific surface. In this work, we studied the nucleation mechanism of atomic layer deposition-grown TiO2 from TiCl4 and H2O on as-received silicon by means of in-line X-ray photoelectron spectroscopy. Within a region of ∼0.4 nm of the SiO2/TiO2 interface, the presence of Ti3+ states are detected. In this region, the Ti, O, and Cl species are found to be more strongly bonded. At the initial stages of film growth, prolonged TiCl4 exposure is necessary to reach a saturated surface chemistry, which is in contrast to the outcome of growth per cycle saturation curve analysis. A prolonged water exposure experiment suggests that residual chlorine impurities can be prevented by using a suffic...

Otitis externa in military divers: more frequent and less harmful than reported.

Although otitis externa (OE) is a common disease, data related to (military) divers are limited. This study aimed to determine the incidence of OE in military divers during their initial training. We also wished to consider seasonal influences on incidence and whether early detection increases completion of the diving course. From January 2011 to October 2016 the Royal Netherlands Navy Diving School trained 189 divers. Up to December 2015 we used the training records for the analyses. From January 2016 onward all divers were prospectively screened. Pearson's chi-squared 2 and Fisher's exact tests were used to analyse the data. In the 162 included divers, 30 cases of OE were identified. The incidence in 2016 was significantly higher than in 2011-2015 (17/35 (49%) versus 13/127 (10%), P < 0.001). Almost all cases developed after three weeks of diving. No influence of season was found (P = 0.354). Early diagnosis and treatment of OE does not seem to affect completion of diving courses (P = 0.28). Only in three cases did a diver have to discontinue the course due to OE. This study suggests that OE is more frequent among military divers than earlier reported, most likely caused by prolonged water exposure. Diving activities can often be continued with standard topical treatment.

Identifying the Optimal Water-Occluding Earplugs: A Scientific Simulation Study.

Numerous types of water-occluding earplugs are available as a means of preventing infection in patients with external and middle ear disease. However, little is known about the comparative efficacies of these earplugs with prolonged water exposure. In this study, we assessed the water impermeability of various earplug materials to prolonged water exposure. Nine earplugs were tested: cotton wool mixed with petroleum jelly, cotton wool externally coated with petroleum jelly, Blu-Tack, foam earplugs, silicone putty, silicone earplugs, flanged earplugs, and hard and soft silicone custom-moulds. Precision-engineered cups were filled with 30 mL water and sealed with lids that contained a 10 mm diameter hole to simulate the ear canal. The aperture was occluded with different earplugs, and the cup was inverted. Computer software was used to record the water loss to the nearest 10 milligrams 720 times over a three-hour period. The test was repeated five times for each material. The water permeability onset, rate, and total amount of water loss varied markedly between the materials; cotton wool mixed with petroleum jelly demonstrated the fastest onset of leak and the highest rate of water loss (p < 0.00001), as well as the largest amount of cumulative water loss (p = 0.00213). The soft silicone custom-mould plugs, hard silicone custom-mould plugs, foam plugs, and silicone putty demonstrated no leaks. This study demonstrates a wide range of water permeabilities of commonly used ear-occluding materials during prolonged water exposure. We found that the generally suggested regimen of cotton wool mixed with petroleum jelly may be inefficacious for substantial periods of water exposure.

Ultrathin Nafion Film Behavior Under Simulated Hot-Pressing and Operating Conditions of a PEFC

It is now widely accepted that Nafion ionomer in the polymer electrolyte fuel cell (PEFC) catalyst layer exists as a thin film (<10nm in). The impact of thermal annealing on the Nafion® thin films is of particular interest for PEFCs because the membrane electrode assembly (MEA) comprising the catalyst layers (CLs) and the membrane is subjected to a hot pressing step by heating to a temperature ranging 125-195 oC under elevated pressure. In an operating fuel cell, the catalyst layer and ionomer film within experiences prolonged liquid water exposure. The polymer molecules can undergo rearrangement when the chemical/thermal environment is altered. In internal and surface structure change can also impact the wettability and transport behavior of ultrathin ionomer films. In this work, the effects of thermal annealing and liquid water exposure on Nafion®thin films is examined.Recently, we have reported the properties self-assembledultrathin Nafion ionomer film including the characteristic thickness scale (i.e., 4-10 nm) pertinent to PEFC CLs [1]. Film thickness-dependent surface wettability and bulk proton conductivity were notable features of those unannealed films. We also discussed about the surface switchability of ultrathin ionomer film from super-hydrophilic to hydrophobic when the films were subjected to the high temperature annealing [2]. One of the interesting finding was the restricted ionomer mobility with decreasing thickness that required high energy for the switching of surface wettability, generalized as the term “confinement effect”.We have further investigated bulk proton transport of those thermally annealed ultrathin Nafion films by electrochemical impedance spectroscopy (EIS). It was found that proton conductivity diminished more than one order of magnitude regardless of thin film thickness compare to the unannealed counterpart. The reason of that might be the higher extent of morphological rearrangement and reorientation upon annealing as evident in atomic force microscopic (AFM) measurement. Interestingly, liquid water exposure to such those annealed films regenerate the both surface and bulk properties where prolonged water vapor exposure cannot alter such properties. Moreover, the regeneration process is highly thickness dependent. As an example, the proton conductivity of the 55 nm film at 60 oC and different RH has been plotted in terms of treatment condition in the Figure 1. The truncated terms - Un-ann, Ann-1st, WT (24 h) and WT (96 h) have been used for the film treatment conditions - Un-annealed, 1stAnnealed, 24 h Water treated and 96 h Water treated, respectively. It was found that proton conductivity of 24 h water treated film was very similar to the annealed films in the RH range 20 to 96%. In contrast, the conductivity of 96 h water treated film went back to unannealed film after 96 h water treatment at high RH where it did not recover completely at low RH. On the other hand, the regeneration process for the much thinner 10 nm film is much quicker as happened by 24 h water treatment (not in the fig). Surface wettability of the water treated films was also investigated by water contact angle measurement as shown in Figure 2. It is interesting that the surface wettability was also regenerated from hydrophobic to hydrophilic. The process is thickness dependent as well where the regeneration for thinner films is much quicker than that of thicker films. This is completely opposite trend to the annealing effect. However, there is a consistency of surface and bulk regeneration where film thickness is the differentiating parameter.The presentation will discuss the results of the study in more detail. Acknowledgements Financial Early Researcher Awards (Ontario Ministry of Research and Innovation) and Natural Sciences and Engineering Research Council of Canada (NSERC).

Sunscreens may also serve as a barrier to protect skin from prolonged water exposure

Sunscreens may also serve as a barrier to protect skin from prolonged water exposure

Abstracts: Natural moisturizing factors in the stratum corneum II. Regeneration of NMF over time after soaking

pp. 23–29 The detrimental effects of prolonged water exposure on skin are well known. Information on the effects of short‐term exposure, e.g. during bathing, showering, and hand washing, on Natural moisturizing factors (NMF) levels is limited. In an attempt to isolate the effects of soaking on the NMF, a time course for skin sample collection was devised in which adhesive tapes were applied 0.5 and 4 h after soaking of the treated arm. Significant decreases in NMF levels, quantified by high‐performance liquid chromatography analysis of serial tape strips, were observed 0.5 h after soaking, with a replacement of NMF occurring by the four‐hour mark. This replacement corresponds to a parallel rebound in skin pH also observed at these times. Stratum corneum (SC) hydration values, measured instrumentally as the rate of moisture accumulation (MAT), however, were depressed 0.5 h post‐soaking and remained low 4 h later. In addition, significant increases in skin pH were observed during the immediate post‐soak period. These findings suggest that short‐term exposure to water alone produces significant changes in the SC.

An examination of proposed causes of auditory exostoses

Auditory exostoses are a discrete trait, the presence of which may be a product of environmental factors. Water exposure is believed to be associated with the trait's appearance, which has allowed anthropologists to hypothesise about past population subsistence strategies. However, some scholars still contend that water exposure is not necessarily the precipitating factor for its development. This study examined 744 Nubians for exostoses from the following time periods: Kerma, Meroitic, X-group, Christian and a current sample. A total of six male individuals exhibited the characteristic. There is little evidence in the Nubian archaeological record to suggest that marine resources were exploited in a manner that required prolonged water exposure. Moreover, the Nubian groups with auditory exostoses were primarily agriculturists and/or pastoralists. Wind chill and temperature have also been put forth as potential contributors to the development of auditory exostoses, but like other hypotheses, water is also needed in order for wind chill and temperature to incite exostoses. Even though water may have contributed to the development of exostoses for many populations, it is not suitable to cite it as a precipitating factor for the development of auditory exostoses in Nubians. Based on this evidence, other non-water factors may be important in the trait's development. Caution must be used when interpreting exostoses as indicators of a particular water-related activity and trait frequencies must be carefully considered, as low frequencies are not necessarily evidence of water-exposure. Copyright © 2009 John Wiley & Sons, Ltd.

Additive impairment of the barrier function by mechanical irritation, occlusion and sodium lauryl sulphate in vivo

The interaction between potential irritants in the workplace might be important because workers are not usually exposed to a single irritant, but to multiple potentially harmful substances. Physical irritant contact dermatitis caused by friction or mechanical abrasion is a common occupational dermatosis. Prolonged water exposure by occlusion is also common in the workplace. Several studies have revealed the negative effect of the common anionic detergent sodium lauryl sulphate (SLS) on permeability barrier function. To study the additive impairment of permeability barrier function by mechanical irritation combined with 0.5% SLS or prolonged water exposure by occlusion, as models of mild irritation. The volar forearms of 20 healthy volunteers were exposed to mechanical irritation and occlusion with water or 0.5% SLS for four consecutive days in a combined tandem repeated irritation test (TRIT). Permeability barrier function was measured with a Tewameter TM 210. Irritation was assessed with a Chromameter CR 300 and a visual score. Barrier disruption in our model was rated as follows: occlusion with SLS and mechanical irritation > occlusion with SLS > occlusion with water and mechanical irritation > mechanical irritation and occlusion with water > occlusion with a glove and mechanical irritation > mechanical irritation > occlusion with water. Barrier disruption caused by occlusion or mechanical irritation was enhanced by the tandem application. The choice of irritant under occlusion, time of occlusion and order of tandem application all affected the degree of barrier disruption. Evaporimetry was able to detect early stages in the development of an irritant reaction before it became visible. Chromametry was not able to detect this early response. Physical irritants (friction, abrasive grains, occlusion) and detergents such as SLS represent a significant irritation risk and should be minimized, especially when acting together, as shown in our TRIT model.

Effect of prolonged water immersion on equine hoof epidermis in vitro.

To evaluate the effect of prolonged water exposure on tissue mass and solutes of outer and inner layers of the stratum medium, sole, frog, and the stratum medium (SMZA) zona alba layer of horses' hooves. SPECIMEN POPULATION: 10 hooves from 10 horses without foot abnormalities. Hoof wall tissue specimens were obtained and immersed for 10 days in distilled deionized water. Serial changes in mass were recorded during the immersion period. Subsequently, osmolarity and Na+, K, Cl-, and protein concentrations of the immersion solution were quantified. Fully cornified outer hoof wall, sole, and frog epidermal structures increased in mass, whereas the SMZA lost mass when immersed in water. All hoof structures had a variable loss of crystalloids during immersion, but none of the specimens lost proteins. The frog epidermis was distinct in that total solute lost during immersion could not be ascribed to N+, K+, and Cl-. Data support a 2-compartment model for the fully cornified outer stratum medium, frog, and sole that permits the exchange of crystalloids, but not proteins, across the cell membrane and infers that topical agents containing proteins cannot benefit the hoof. The unique osmotic behavior of the SMZA relative to other hoof structures suggests the hypothesis that it is composed of transitional epithelial cells. The solutes lost from frog epithelium are interpreted to reflect its unique lipid composition.

Behaviour of Dioxins, Furans and Metals Associated with Stabilized Msw Combustor Ash in Sea Water

Abstract This report presents the results of a research programme designed to examine the engineering and environmental acceptability of stabilizing municipal solid waste (MSW) combustor ash for artificial reef construction. Municipal solid waste combustor ash was combined with Portland cement to form solid blocks using conventional construction block making technology. the resultant stabilized combustor ash (SCA) blocks were used to construct an artificial habitat in Conscience Bay, Long Island Sound, New York and compared to identical concrete blocks, fabricated using natural aggregates. Over a 4.5 year period divers periodically returned to the site to monitor the interaction of SCA blocks with the marine environment and compare the performance of these blocks with the concrete control blocks. Results show that the SCA blocks retain their strength after prolonged sea water exposure. Contaminants of environmental concern, including metals, dioxins and furans, were retained within the cementitious matrix...

Behavior‐induced auditory exostoses in imperial Roman society: Evidence from coeval urban and rural communities near Rome

Presence and features of auditory exostoses were investigated in two cranial samples of Roman imperial age (1st-3rd century A.D.). The skeletal material comes from the necropolises of Portus (Isola Sacra) and Lucus Feroniae (Via Capenate), two towns along the Tevere River, in close relation with the social and economic life of Rome. Deep-rooted differences between the human communities represented by the skeletal samples (83 and 71 individuals, respectively, in this study) are documented both historically and archaeologically. The results show lack of exostoses in the female sex, a negligible incidence among the males of Lucus Feroniae, but a high frequency in the male sample from Isola Sacra (31.3%). Auditory exostoses are commonly recognised as localized hyperplastic growths of predominantly acquired origin. Features of the exostoses found in the male crania from Isola Sacra (particularly in relation to the age at death of the affected individuals) support this view. Furthermore, several clinical and anthropological studies have pointed out close links between the occurrence of auditory exostoses and prolonged cold water exposure, generally due to the practice of aquatic sports, or to working activities involving water contact or diving. In this perspective, the differences observed between the two Roman populations and between the sexes (in Isola Sacra) appear to result from different social habits: the middle class population of Portus habitually used thermal baths, whereas it is probable that thermae were seldom frequented (if at all) by the Lucus Feroniae population represented in the necropolis (mostly composed by slaves or freedmen farm laborers).(ABSTRACT TRUNCATED AT 250 WORDS)

The adsorption and thermal decomposition of water on clean and oxygen-predosed Al(111)

The adsorption of water on both clean and oxygen-predosed Al(111) has been studied by vibrational spectroscopy using electron energy loss spectroscopy (EELS). At 130 K, adsorption on either surface is competitively associative and dissociative. The dominant dissociation product is a hydroxyl species. On the clean surface, adsorption is predominantly molecular, while in the presence of oxygen, adsorption is predominantly dissociative. In contrast to the low temperature behavior, adsorption of water on clean Al(111) at 300 K is completely dissociative, resulting in oxygen adsorption and surface oxidation. Adsorbed hydroxyl species can be produced at 300 K by prolonged water exposure. Upon heating a low-temperature water layer adsorbed on either surface, molecular water desorption and further decomposition both occur. The production of adsorbed hydroxyl species from water reaches a maximum at 250 K on the clean surface and at 350 K on the oxygen-predosed surface. The hydroxyl species decompose above these temperatures to evolve hydrogen and further oxidize the Al(111) surface.