Effects Of Chemical Degradation Research Articles

Parameterizations of US wildfire and prescribed fire emission ratios and emission factors based on FIREX-AQ aircraft measurements

Abstract. Extensive airborne measurements of non-methane organic gases (NMOGs), methane, nitrogen oxides, reduced nitrogen species, and aerosol emissions from US wild and prescribed fires were conducted during the 2019 NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality campaign (FIREX-AQ). Here, we report the atmospheric enhancement ratios (ERs) and inferred emission factors (EFs) for compounds measured on board the NASA DC-8 research aircraft for nine wildfires and one prescribed fire, which encompass a range of vegetation types. We use photochemical proxies to identify young smoke and reduce the effects of chemical degradation on our emissions calculations. ERs and EFs calculated from FIREX-AQ observations agree within a factor of 2, with values reported from previous laboratory and field studies for more than 80 % of the carbon- and nitrogen-containing species. Wildfire emissions are parameterized based on correlations of the sum of NMOGs with reactive nitrogen oxides (NOy) to modified combustion efficiency (MCE) as well as other chemical signatures indicative of flaming/smoldering combustion, including carbon monoxide (CO), nitrogen dioxide (NO2), and black carbon aerosol. The sum of primary NMOG EFs correlates to MCE with an R2 of 0.68 and a slope of −296 ± 51 g kg−1, consistent with previous studies. The sum of the NMOG mixing ratios correlates well with CO with an R2 of 0.98 and a slope of 137 ± 4 ppbv of NMOGs per parts per million by volume (ppmv) of CO, demonstrating that primary NMOG emissions can be estimated from CO. Individual nitrogen-containing species correlate better with NO2, NOy, and black carbon than with CO. More than half of the NOy in fresh plumes is NO2 with an R2 of 0.95 and a ratio of NO2 to NOy of 0.55 ± 0.05 ppbv ppbv−1, highlighting that fast photochemistry had already occurred in the sampled fire plumes. The ratio of NOy to the sum of NMOGs follows trends observed in laboratory experiments and increases exponentially with MCE, due to increased emission of key nitrogen species and reduced emission of NMOGs at higher MCE during flaming combustion. These parameterizations will provide more accurate boundary conditions for modeling and satellite studies of fire plume chemistry and evolution to predict the downwind formation of secondary pollutants, including ozone and secondary organic aerosol.

In-Situ Fatigue Lifetime Modeling of a Reinforced Membrane by Projecting Critical Accumulated Plastic Dissipation Energy from Pressure Differential-Accelerated Mechanical Stress Tests

Polymer electrolyte fuel cells (PEFCs) have become increasingly appealing over internal combustion engines because of their high efficiency, low operating temperature, and zero CO2 emissions. Nevertheless, the transportation sector necessitates high durability and reliability, which may be difficult to predict for emerging technologies. A crucial aspect is the ability of the thin membranes that conduct ions in PEFCs to endure the chemical and mechanical stresses that arise during dynamic operations. For mechanical fatigue, temperature and relative humidity (RH) fluctuations induce dynamic stresses that lead to the formation and propagation of microcracks in the membrane. As the membrane is confined by other components in the membrane-electrode assembly (MEA), changes in temperature and humidity can generate thermal and swelling strains in the membrane, leading to dynamic and residual stresses [1].The US Department of Energy sets a passing criterion of 20,000 RH cycles for mechanical fatigue assessment. However, many modern reinforced membranes have already passed this threshold without failing [2]. Therefore, Ref [3] introduced a pressure differential between the cathode and anode sides of the membrane at 80°C to speed up the testing. In this research, the pressure differential-accelerated mechanical stress test (ΔP-AMST) method was applied to a reinforced membrane at two different temperatures and with four times faster humidity cycles in a wider range of ΔPs. This objective is to project the mechanical fatigue lifetime from the ΔP-AMST to the membrane under its in-situ conditions by using the critical accumulated plastic dissipation energy (CAPDE) in ΔP-AMSTs and the plastic dissipation energy (PDE) during a single cycle of humidity that the membrane experiences under complete fuel cell settings. The first step involves performing a series of ∆P-AMST, and in the second step, a finite element model (FEM) for ∆P-AMST based on the developed constitutive model for the tensile tests that covers temperature, humidity, and swelling strain impacts is built, and therefore its S-N curve is extracted. Next, a FEM model for a complete fuel cell is created, and the mechanical fatigue life is estimated by dividing the CAPDE in ∆P-AMST by the PDE in one cycle of the in-situ modeled membrane by considering amplitude stress as a link between the full fuel cell model and ∆P-AMST, as illustrated in Figure 1 and verified by previous studies [4,5]. In the final step, we will also discuss opportunities to integrate the present mechanical fatigue model with a chemical degradation module to simulate its impacts on fatigue lifetime. This integration includes the two main effects of chemical degradation, which are reflected in the thickness of the reinforced membrane [6] and its updated CAPDE [7]. Acknowledgments The authors gratefully acknowledge AVL Fuel Cell Canada and Mitacs for supporting this project. The authors also thank Roger Penn and Amy Nelson for technical advice.

Effect of Chemical Degradation of Sodium Alginate on Capsaicin Encapsulation

Capsaicin is known as an oily extract of paprika that is characterized by pungent taste and bioactivity. It also may cause irritation to the mouth and stomach which is why is so important to immobilize capsaicin on a carrier to prevent it. The usage of alginate oligomers, which has an antioxidant potential compared to alginate, is of benefit because it may be used in the immobilization of bioactive substances that are fragile to oxidation. The purpose of this study was to use sodium alginate oligomers as a coating material in the encapsulation process of paprika oleoresin. Alginate oligomers were produced by chemical degradation with hydrogen peroxide. The characteristics of the samples were obtained by measuring the viscosity, the contact angle of the surface, and the surface tension of solutions. The obtained solution of alginate oligomers served as the carrier material for the immobilization of capsaicin. Capsules were prepared by ionic gelation using a calcium chloride solution as a crosslinking agent. In this way, capsules without and with the core (capsaicin) were prepared and their ability to scavenge free radicals (DPPH) and iron-reducing properties (FRAP) were determined. The stability of the capsules was examined by thermal decomposition and under conditions of the gastric and small intestine, and capsaicin content was detected using high-performance liquid chromatography. It was found that alginate oligomers could be used in the encapsulation of bioactive compounds and the efficiency was above 80%. Capsule production from alginate oligomers affected their thermal stability. The use of alginate derivatives as a carrier increased the antioxidant properties of the finished product, as well as its ability to reduce iron ions. The use of alginate oligomers as a coating material prevented the active substance from being released too early in the conditions of the small intestine, prolonged the stability of the capsules, and supported their durability in gastric conditions.

The Effect of Chemical Degradation and Polishing on the Gloss of Composite Dental Materials.

This aim of this study was to investigate surface gloss changes of different composite dental materials after chemical degradation or polishing. Five different composites were used (Evetric, GrandioSO, Admira Fusion, Filtek Z550, Dynamic Plus). The gloss of the tested material was measured with a glossmeter before and after chemical degradation in different acidic beverages. Statistical analysis was performed using a t-test for dependent samples, ANOVA, and a post hoc test. For comparison between groups, a level of significance was set at 0.05. Initial gloss values ranged from 51 to 93 at baseline to 32 to 81 after chemical degradation. The highest values were obtained for Dynamic Plus (93.5 GU) and GrandioSO (77.8 GU), followed by Admira Fusion (82 GU) and Filtek Z550 (70.5 GU). Evetric showed the lowest initial gloss values. After acidic exposures, the gloss measurements revealed different patterns of surface degradation. The results showed that the gloss of the samples decreased with time regardless of the treatment. The interaction between chemical-erosive beverages and the composite could lead to a decrease in the surface gloss of the composite restoration. The nanohybrid composite showed less gloss changes under acidic conditions, suggesting that it is more suitable for anterior restorations.

3D zero-thickness interface model for fracture of cement-based materials with chemical degradation

In the framework of the Finite Element Method, zero-thickness interface elements have been widely used to model fracturing processes in quasi-brittle materials in a broad variety of problems. In particular, interface elements equipped with elastoplastic constitutive laws that account for the softening of the material strength parameters due to the fracturing mechanical work has been proved to accurately reproduce observed fracture propagation behaviour in concrete. Along this line, this paper presents the extension of an existing constitutive law of this kind to include the effect of chemical degradation of the material in the formation of fractures. The law is defined in terms of the normal and shear stresses on the average plane of the crack and the corresponding normal and shear relative displacements. A hyperbolic cracking (plastification) surface in the stress state determines the crack initiation. The softening of the cracking surface is governed by two history variables: an internal variable that accounts for the dissipated fracturing (plastic) work, and an external variable to be provided by a chemical degradation model that accounts for the effect of chemical degradation on the strength parameters. After a detailed discussion of the formulation, the main characteristics of the proposed law are illustrated with a number of academic examples for different combinations of mechanical loading and chemical degradation sequences. The model is finally validated against experimental results from the literature consisting of three-point bending tests performed on mortar samples previously exposed to an aggressive solution for different time periods.

Effects of chemical degradation on longitudinal fracture of non-homogeneous beams: an analytical study

An analytical study of the chemical degradation of the material and its effects of on longitudinal fracture behaviour of continuously non-homogeneous cantilever beam is carried-out. The chemical degradation is described by decreasing of the elasticity modulus of the non-homogeneous material with time. The fracture is studied by analyzing of the strain energy release rate. For this purpose, the strain energy release rate is derived as a function of time with taking into account the chemical degradation and the non-homogeneity of the material. The time-dependent fracture is analyzed also by applying the J-integral with considering the chemical degradation for verification. The variation of the strain energy release rate with the time due to the chemical degradation is studied and discussed in detail.

Failure of fluorocarbon copolymer pipes subjected to mechanical strain in an alkaline environment

A failure analysis was carried out on leaking fluorocarbon-based copolymer pipes used in a cleaning and disinfection plant. Pipes conveyed a solution of sodium hydroxide and showed leaking after two months of service. Leaks originated from reddish-colored cuts located on the bending curves of the external surface of the pipes. Experimental findings and literature review pointed out that a combined effect of chemical degradation and mechanical strain (similar to stress corrosion cracking) triggered the failure. This type of degradation developed in high pH hydroxide solution due to dehydrofluorination of the exposed surface, starting material embrittlement and formation of crazes and microcracks. An applied mechanical deformation accelerated the crack opening and the solvent diffusion, up to the consequent pipe leaking and failure.

Four-dimensional in situ imaging of chemical membrane degradation in fuel cells

Chemical membrane degradation is considered a key impeding issue for durability of polymer electrolyte fuel cells. Chemical additives have been developed to mitigate this phenomenon by preventing radical attack and associated membrane thinning. In this work, a 4D in situ X-ray visualization approach is adopted to examine the pure chemical degradation effects of non-reinforced, mechanically reinforced, and mechanically and chemically reinforced fuel cell membranes. The 4D approach is achieved by non-invasive, identical location 3D (x, y, z) imaging of the fuel cell at different lifetime stages (t). Observations show that local membrane thinning culminating in electrode-shorting under land regions is the key failure mode for non-reinforced and mechanically reinforced membranes without chemical additives. The ePTFE layer within the mechanically reinforced membrane does not prevent electrode shorts and exhibits divot formation. Preferential shorts under the land regions show that mechanical stresses due to clamping pressure can accelerate electrode shorting at advanced stages of chemical degradation. In contrast, the mechanically and chemically reinforced membrane sustains significantly longer test duration without failure and significant membrane thinning, highlighting the radical scavenging effect. No membrane pinhole or crack development is observed in any of the three membranes, suggesting that such failures require additional mechanical degradation.

Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment

Stellite 6 (Co-29.5%Cr-5%W-1.2%C in wt%) is traditionally used as a hardfacing material in the primary circuit of pressurised water reactors (PWRs) due to its good corrosion and wear resistance in water at up to 300 °C. In this study, pin-on-disc type sliding contact tribocorrosion testing was conducted on HIPed Stellite 6 at 20 °C and 250 °C using a bespoke tribometer to simulate a primary circuit environment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize, for the first time, the material affected by tribocorrosion. Whilst the material loss increases by 16–39 times when the test temperature is increased from 20 °C to 250 °C, the mechanisms of degradation and deformation remain largely unchanged. Furthest from the sliding contact, strain is principally accommodated by the deformation-induced transformation of the γ Co-based matrix to ε-martensite. Closer to the sliding contact, the ε-martensite phase accommodates further strain via twinning and dislocation slip. At the sliding contact the intense deformation generates a nanocrystalline structure. The tribologically affected material is resistant to plastic strain localisation; this confines wear to the nanoscale where the synergistic effects of chemical degradation and mechanical deformation permit the removal of nanoscale particulates (corrosion enhanced nanowear (tribocorrosion)). The increased wear rate at 250 °C is attributed to a temperature dependent increase in corrosion enhanced nanowear. The degradation mechanisms revealed are important for the design of future hardfacings.

Modeling proton-exchange-membrane fuel cell performance/degradation tradeoffs with chemical scavengers

One of the primary limiting factors for proton-exchange-membrane (PEM) fuel-cell lifetime is membrane degradation driven by operational stressors such as generation of highly reactive radical species, which result in cell failure and voltage decay. To extend the lifetime of the membrane, cerium ions are added to the membrane to mitigate the effects of chemical degradation by scavenging radicals produced by crossover of reactant gases across the PEM. Although cerium has shown to be very effective at reducing chemical degradation during PEM fuel cell operation, the cerium ions also lead to a decrease in performance due to changes in the membrane transport properties and possible site blockage in the catalyst layers. In this paper, a full-cell, transient performance and durability model is presented in which a micro-kinetic framework accounts for gas crossover induced degradation and concentrated-solution theory describes transport in the PEM. The transport model takes into account the coupled nature of the electrochemical driving forces that cause transport of cerium ions, protons, and water. The cell model predicts the migration of cerium out of the membrane and into the catalyst layers and its impact on performance. A comparison between dilute-solution-theory and concentrated-solution-theory models shows how water management in the cell also effects cerium distribution, where higher relative humidity leads to better retention of cerium in the membrane. A voltage loss breakdown shows that cerium leads to performance losses in the cell both by decreasing proton activity and by modifying transport properties of water and protons through the membrane. Transient simulations show that the optimal tradeoff between performance and durability metrics is reached at low cerium concentrations in the membrane (less than 1% of membrane sulfonic acid sites occupied by cerium for our analysis). Finally, analysis of membrane thickness and catalyst layer thickness as design parameters shows that thicker membranes and thinner catalyst layers best optimize both performance and durability.

Effects of conjoint mechanical and chemical stress on perfluorosulfonic-acid membranes for fuel cells

To improve the lifetime of proton-exchange membrane (PEM) fuel cells, it is necessary to provide a better understanding of the degradation mechanisms of the perfluorosulfonic acid (PFSA) membranes during fuel cell operation. Despite quantities of work focusing independently on chemical or mechanical degradation, only a few concerned the effect of both combined. The purpose of this study is to analyze the effects of conjoint chemical and mechanical stress on PFSA membranes via an ex-situ approach. First, an investigation of the effects of chemical degradation by radical attacks (i.e. exposure to Fenton reagents) on PFSA membranes was carried out. The results confirm that the chemical decomposition of PFSA membranes is significantly influenced by the concentration of Fenton's reagents, both chemically and morphologically. Second, a custom-made device was developed to examine the impact of coupled chemical and mechanical degradations. The initial results show that fully hydrated membranes seem to withstand severe sinusoidal constraints as no crack formed. However, the application of cyclic compression resulted in accelerated chemical decomposition of PFSA membranes. The results also demonstrate that some microstructural changes can appear and lead to a slight increase in the hydrogen crossover that can be detected before it impacts the cell performances.

CFD Simulation of an Industrial PEM Fuel Cell with Local Degradation Effects

AbstractThe polymer electrolyte membrane (PEM) fuel cell model of a commercial software package is presented. The basic performance model is extended by two chemical degradation effects: ionomer degradation and carbon corrosion including platinum oxidation. The ionomer degradation model describes the ionomer mass loss due to hydrogen peroxide formation and subsequent attack of the ionomer by radicals. The carbon corrosion model calculates the carbon mass loss caused by carbon oxidation and the active area reduction due to platinum oxidation. The degradation models are coupled with an agglomerate model of the catalyst layer. The model is validated against measurements on an industrial cell. For these measurements, the cell is equipped with a segmented measuring board, which is used to measure the current density distribution and high frequency resistance of every segment. In order to test the predictability of the model under different operating conditions, measurements for stoichiometry and pressure variations are carried out. Calculated and measured current density distributions of the cell, aged by an accelerated stress test, are compared for the validation of the degradation model. Moreover, 3D simulation results of the fresh and aged cells are analyzed in detail and the influence of operating conditions on fuel cell aging is pointed out.

In situ measurements of viscoelastic properties of biomass during hydrothermal treatment to assess the kinetics of chemical alterations

This work aimed to use continuous measurements of viscoelastic properties to evaluate the effect of hydrothermal treatment on poplar samples. Different conditions (temperature and pre-soaking liquid: acidic, neutral and alkaline) were tested on wood in both tangential and radial directions. Two viscoelastic properties were determined: the modulus of elasticity and the stress relaxation. The applicability of these properties as indicators of the kinetics of biomass deconstruction was also evaluated, thanks to the chemical analyses performed on the treated solid and the recovered liquid phase. The ultimate goal is to build a macroscopic indicator capable of establishing rules to optimize the hydrothermal treatment before the explosion stage. The joint use of the two parameters succeeded in revealing the effects of chemical degradation, including the coexistence of cleavage and re-condensation and the impact of process conditions (temperature, residence time, and pre-soaking liquid). The monotonous behavior of stress relaxation is a major asset as a possible macroscopic indicator of biomass deconstruction.

Drivers for the cracking of multilayer polyamide‐based backsheets in field photovoltaic modules: In‐depth degradation mapping analysis

AbstractThere is a lack of understanding on the root cause of cracking of photovoltaic (PV) backsheets due to the challenge of multilayer characterization and the complicated failure modes at the submodule level. In this work, the in‐depth degradation mapping of field‐exposed polyamide‐based (PA‐based) PV module backsheets was studied, with the major focus on the identification of underlying drivers for the through cracking (in between the solar cells). PV modules were retrieved from five different locations, comprising a variety of climates, including humid subtropical, hot‐summer Mediterranean, tropical savanna climate, and hot arid. A suite of microscale cross‐sectional characterizations, including chemical changes, fluorescence intensity, and modulus as a function of distance from the air surface of the backsheet, was performed. Results showed more advanced signs of degradation of the inner layer than the outer layer in the cracking region. Increases in the modulus were identified as the major indicator for the cracking. Moreover, a rudimentary test by immersion in acetic acid, which forms during photodegradation of the ethylene‐vinyl acetate copolymer (EVA) encapsulant, showed the first‐time direct evidence that acetic acid can largely accelerate the chemical degradation and facilitate the cracking of PA inner layer. This study suggests that the field cracking of PA‐based backsheet can be attributed to the combined effects of chemical degradation and physical reorganization (chemi‐crystallization) under cyclic thermomechanical stresses. Therefore, it is important to consider effects of local microclimates and interlayer infection to understand the heterogeneous nature of backsheet failures.

Demonstration of the MOEX Process Using Additive-Manufacturing-Fabricated Annular Centrifugal Contactors

ABSTRACTAdditive manufacturing/3D printing is a rapidly maturing field with potential advantages for the fabrication of chemical processing equipment. A demonstration of the molybdenum solvent-extraction process, developed to recover Mo for the production of 99Mo/99mTc from enriched 98Mo or 100Mo, was accomplished using a nine-stage bank of additive-manufacturing-fabricated 2-cm annular centrifugal contactor-separator devices. The results from the demonstration are presented along with the benefits and shortcomings of the 3D printed contactors. This paper also discusses recent developments in the design of 3D printed contactors in order to improve reliability and mitigate the effects of chemical degradation of additive-manufacturing media.

Modeling Impact of Ce on Fuel-Cell Performance and Durability

Throughout the lifetime of a polymer-electrolyte fuel cell, the membrane undergoes chemical degradation that causes defects to form and grow, contributes to a loss of performance, and can lead to cell failure. A combination of accelerated stress tests (ASTs)1-2 and modeling studies3-4 have been performed on this topic to better understand membrane degradation mechanisms and how to mitigate them5-6. During fuel-cell operation, formed peroxide radicals due to reactant gas crossover attack the polymer backbone and end chains, leading to membrane thinning and formation and growth of defects such as cracks and pinholes. This study builds upon our previous modeling study on membrane degradation to analyze the addition of chemical scavengers into the fuel-cell membrane to mitigate the effects of chemical degradation via radical attack. The developed model is transient and 1D across the fuel-cell sandwich. The transport and concentration of cerium is modeled using an ion-transport model based on concentration solution theory, thereby allowing the evaluation of how water gradients also move cerium ions throughout the ionomer, resulting in nonintuitive distributions. The model results also show how drive-cycle testing impacts the performance of the cell and the location of cerium, where relaxation of the applied gradients help redistribute the cerium in the ionomer. The purpose of the study is to optimize the cerium amount in both the membrane and catalyst layers by balancing effects of mitigation of chemical degradation and performance due to the impact of cerium on the ionomer material properties. For the latter, a key feature is accounting for the nonlinearities induced by the impacts of cerium on membrane and catalyst-layer ionomer properties. Acknowledgements The authors would like to thank Hans Johansen for helpful discussions and Los Alamos National Laboratory for providing material property data. Funding support was supplied by the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-AC02-05CH11231. References R. Borup, et al., Chem. Rev., 107, 3904 (2007)F. A. de Bruijn, et al., Fuel Cells, 8, 3 (2008).R. Singh, et al., J. Electrochem. Soc., 165, F3328 (2018)K. H. Wong and E. Kjeang, J. Electrochem. Soc., 166, F128 (2019).M. Zatón, et al., Sustainable Energy & Fuels, 1, 409 (2017).F. D. Coms, et al., in The Chemistry of Membranes Used in Fuel Cells: Degradation and Stabilization, 1st ed., S. Schlick Editor, John Wiley & Sons, Inc. (2018).

SPATIAL DISTRIBUTION AND DEGRADATION RISK ASSESSMENT OF SOME CULTIVATED ALLUVIAL SOILS OF AL-AZHAR UNIVERSITY, ASSIUT GOVERNORATE, EGYPT

This research aims to characterize soils of Al-Azhar university of Assiut and mapping them on a large scale for more information. Moreover, assessment the risk of soil degradation for understanding the current situation of land uses and its management. The characteristics of the investigated soils ranged from 1.39 to 2.72%, 1.37 to 1.48 dSm−1, 2.07 to 4.85% and slowly to very slowly permeable as weighted means for CaCO3 content, salinity, sodicity and permeability condition, respectively. The soils could be divided into two mapping unites; (1) nearly level deep fine textured soils which is the major one, (2) nearly level deep moderately fine textured soils. High hazard of compaction covered the total area as a result of human activities along with very high values of physical degradation and low to moderate effects of chemical degradation threaten the studied soils. Anthropogenic factor had a clear impact on processes of land degradation and actual hazard in terms of inadequate soil management, intensive irrigation procedures, using heavy machinery and absence of conservation measures. The running situation of land degradation within the studied area is very serious and misses a correct land use planning and management.

Effect of Chemical Degradation on Surface Roughness and on Color Stability of Micro hybrid and Nanofilled Composites

ResumoA resina composta é o material restaurador mais utilizado atualmente. Apesar de seu sucesso clínico, o material está sujeito a alterações em suas propriedades físicas, quando exposto ao meio bucal. O objetivo foi avaliar a influência da degradação química na estabilidade de cor e na rugosidade superficial de resinas micro-híbrida e nanoparticulada. Foram confeccionados 40 discos (6,0mm x 2,0mm) da resina composta micro-híbrida (Z250XT) e 40 da resina nanoparticulada (Z350XT). Após a análise da cor inicial e da rugosidade inicial, 10 discos de cada resina foram imersos em saliva artificial (Controle, pH=6,4), suco de laranja (pH= 3,4), refrigerante de limão (pH=2,9) e vinho tinto (pH=3,1), por 4 horas por dia (37ºC) durante 30 dias. Após, foram realizadas as leituras finais de cor e rugosidade. Os dados obtidos para a estabilidade de cor foram analisados pelo Teste de Kruskal-Wallis, seguido pelo Teste de Dunn (α=5%). Para a análise da rugosidade foi utilizado o Teste t para amostras pareadas (α=5%). O manchamento provocado pela saliva artificial, suco de laranja e refrigerante foi similar, mas foi estatisticamente diferente do manchamento produzido pelo vinho, em ambas as resinas testadas. O vinho produziu o mesmo grau de manchamento nas resinas micro-híbrida e nanoparticulada. Foi observado que o suco de laranja, o refrigerante e o vinho promoveram aumento da rugosidade superficial dos discos de resina. Diante disso, concluiu-se que o vinho alterou a cor de resinas compostas micro-híbrida e nanoparticulada, e que a rugosidade superficial dos discos de resina foi alterada por todas as bebidas utilizadas.Palavras chave: Resinas Compostas. Corantes. Cor.Abstract Composite resin is the most used restorative material. Despite its clinical success, it is susceptible to changes in its physical properties when exposed to the oral environment. The aim was to evaluate the influence of acidic beverages on the color stability and on the surface roughness of the nanofilled and micro hybrid composite. Forty discs (6.0mm x 2.0mm) of the micro hybrid composite (Z250XT) and 40 of the nanofilled composite (Z350XT) were manufactured. After the measurement of the initial color and the initial roughness, 10 discs of each composite were individually immersed in artificial saliva (control, pH = 6.4), orange juice (pH=3.4), lime soda (pH = 2.9) and red wine (pH = 3.1) during 4 hours per day at 37°C for 30 days. At the end of the experiment, the final analysis of color and surface roughness were performed. The data obtained for the color stability were analyzed by Kruskal-Wallis and Dunn’s test (α= 5%). For the analysis of the surface roughness, the t test for related samples was used (α= 5%). The color changes promoted by artificial saliva, orange juice and soda were similar, but they were statistically different from staining produced by wine, in both tested composites. Wine produced the same degree of staining in both composites. Orange juice, soda and red wine increased the surface roughness of the composite discs. It was concluded that red wine significantly changes the color of micro hybrid and nanofilled composites. Furthermore, all beverages increased the surface roughness of the composites tested in the study herein.Keywords: Composite Resins. Coloring Agents. Color.

A numerical study of chemical degradation effects on elastic-plastic behavior of sandstone

In this paper, an elastic-plastic damage model is first proposed for a class of semi-brittle rocks. This model is then applied to investigate effects of chemical degradation on mechanical behavior of a red sandstone. Experimental data obtained from three groups of samples, respectively, immersed in water and two acid solutions will be analysed. Chemical degradation effects on both elastic modulus and compressive strength will be discussed in term of the solution acidity. The relationship between the solution acidity and chemical damage will be established.

Octadecyl Amine Functionalized Graphene Oxide towards Hydrophobic Chemical Resistant Epoxy Nanocomposites

AbstractIn this research study, graphene oxide (GO) was synthesized using an improved Hummers method and thence oxygen‐based functional groups were replaced with octadecyl amine. Afterwards, epoxy‐based nanocomposites containing GO and GO‐octadecyl amine (GO‐ODA) were fabricated via a vacuum shock technique. The chemical resistance of the fabricated nanocomposites against various solvents, namely xylene, toluene and distilled water, was investigated and the effect of chemical degradation on the hardness and structural stability of the nanocomposites was examined. Besides, SEM, contact angle and AFM analyses were conducted to evaluate morphology, hydrophobicity and roughness of the nanocomposites prior to and following the chemical degradation. The obtained results illustrated that the reinforcement of the epoxy‐based nanocomposites with GO‐ODA and GO, in order, enhanced chemical resistance, hardness, roughness, and hydrophobicity of the nanocomposites. For instance, after incorporating GO and GO‐ODA into the epoxy resin, the average roughness of the neat epoxy resin reduced 84.0% and 94.1%, the hardness of the neat epoxy resin increased from 80 to 82 and 86 kgf/mm2, and the contact angle of the epoxy resin changed from 76° to 71° and 85°, respectively. In brief, outcome of this study reveals that GO‐ODA can be used as an efficient filler to develop effective hydrophobic polymeric shields against chemical degradation.