Vapor Environment Research Articles

In Situ Characterization of Interfaces Relevant for Efficient Photoinduced Reactions

AbstractSolar energy conversion and photoinduced bioactive sensors are representing topical scientific fields, where interfaces play a decisive role for efficient applications. The key to specifically tune these interfaces is a precise knowledge of interfacial structures and their formation on the microscopic, preferably atomic scale. Gaining thorough insight into interfacial reactions, however, is particularly challenging in relevant complex chemical environment. This review introduces a spectrum of material systems with corresponding interfaces significant for efficient applications in energy conversion and sensor technologies. It highlights appropriate analysis techniques capable of monitoring critical physicochemical reactions in situ during non‐vacuum preparation and photoactivity studies including well‐defined inorganic epitaxial reference surfaces, buried interfaces, and low‐defect nucleation of disjunct epitaxial materials that are analyzed during preparation in chemical vapor environment. Their surfaces are then modified and functionalized in gaseous and liquid environment. Finally, even more complex coupling of inorganic stable photoactive materials with responsive soft matter for bioactivity is reviewed. Interface formation, structure, and/or artificial photochemical interfacial reactions are scrutinized down to the atomic scale in real time, also accounting for equilibrium versus non‐equilibrium, kinetically driven processes, in order to accelerate progresses in the realization of efficient energy materials and in the exploitation of photoinduced processes at interfaces.

In Situ Characterization of Interfaces Relevant for Efficient Photoinduced Reactions

Solar energy conversion and photoinduced bioactive sensors are representing topical scientific fields, where interfaces play a decisive role for efficient applications. The key to specifically tune these interfaces is a precise knowledge of interfacial structures and their formation on the microscopic, preferably atomic scale. Gaining thorough insight into interfacial reactions, however, is particularly challenging in relevant complex chemical environment. This review introduces a spectrum of material systems with corresponding interfaces significant for efficient applications in energy conversion and sensor technologies. It highlights appropriate analysis techniques capable of monitoring critical physicochemical reactions in situ during non-vacuum preparation and photoactivity studies including well-defined inorganic epitaxial reference surfaces, buried interfaces, and low-defect nucleation of disjunct epitaxial materials that are analyzed during preparation in chemical vapor environment. Their surfaces are then modified and functionalized in gaseous and liquid environment. Finally, even more complex coupling of inorganic stable photoactive materials with responsive soft matter for bioactivity is reviewed. Interface formation, structure, and/or artificial photochemical interfacial reactions are scrutinized down to the atomic scale in real time, also accounting for equilibrium versus non-equilibrium, kinetically driven processes, in order to accelerate progresses in the realization of efficient energy materials and in the exploitation of photoinduced processes at interfaces.

Temperature Dependence of the Elastic Properties of Bio Silk Films Crystallized in a Water Vapor or Ethanol Environment

Temperature Dependence of the Elastic Properties of Bio Silk Films Crystallized in a Water Vapor or Ethanol Environment

Investigation of polymer–solvent interactions in poly(styrene sulfonate) thin films

ABSTRACTThe swelling behavior of acid form poly(styrene sulfonate) (PSS‐H) thin films were investigated using in situ spectroscopic ellipsometry (SE) to probe the polymer–solvent interactions of ion‐containing polymers under interfacial confinement. The interaction parameter (χ), related to the polymer and solvent solubility parameters in the Flory–Huggins theory, describes the polymer‐solvent compatibility. In situ SE was used to measure the degree of polymer swelling in various solvent vapor environments, to determine χ for the solvent‐PSS‐H system. The calculated solubility parameter of 40–44 MPa1/2 for PSS‐H was determined through measured χ values in water, methanol, and formamide environments at a solvent vapor activity of 0.95. Flory–Huggins theory was applied to describe the thickness‐dependent swelling of PSS‐H and to quantify the water‐PSS‐H interactions. Confinement had a significant influence on polymer swelling at low water vapor activities expressed as an increased χ between the water and polymer with decreasing film thickness. As the volume fraction of water approached ∼0.3, the measured χ value was ∼0.65, indicating the water interacted with the polymer in a similar manner, regardless of thicknesses. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1365–1372

Stress corrosion crack initiation of Zircaloy-4 cladding tubes in an iodine vapor environment during creep, relaxation, and constant strain rate tests

During accidental power transient conditions with Pellet Cladding Interaction (PCI), the synergistic effect of the stress and strain imposed on the cladding by thermal expansion of the fuel, and corrosion by iodine released as a fission product, may lead to cladding failure by Stress Corrosion Cracking (SCC). In this study, internal pressure tests were conducted on unirradiated cold-worked stress-relieved Zircaloy-4 cladding tubes in an iodine vapor environment. The goal was to investigate the influence of loading type (constant pressure tests, constant circumferential strain rate tests, or constant circumferential strain tests) and test temperature (320, 350, or 380 °C) on iodine-induced stress corrosion cracking (I-SCC). The experimental results obtained with different loading types were consistent with each other. The apparent threshold hoop stress for I-SCC was found to be independent of the test temperature. SEM micrographs of the tested samples showed many pits distributed over the inner surface, which tended to coalesce into large pits in which a microcrack could initiate. A model for the time-to-failure of a cladding tube was developed using finite element simulations of the viscoplastic mechanical behavior of the material and a modified Kachanov's damage growth model. The times-to-failure predicted by this model are consistent with the experimental data.

Synthesis of double carbon dots co-doped mesoporous Al2O3 for ratiometric fluorescent determination of oxygen

A new type of ratiometric fluorescent sensor was fabricated in a facile and low-cost process via sequentially assembling blue-light-emitting luminescent carbon dots (BCDs) and red-light-emitting carbon dots (RCDs) into the pores of mesoporous aluminas (MAs) through hydrogen band interactions. The advantages of the resultant BCDs/RCDs/MAs co-doped materials are that their luminescence exhibits dual characteristic peaks of the BCDs and RCDs under a single excitation wavelength, and that they having high surface-to-volume ratios. The co-doped materials were monitored in different carbon dioxide (CO2), oxygen (O2), nitrogen (N2), and water vapor (H2O) environments. Based on the energy transfer from the RCDs to BCDs, with the addition of oxygen, the characteristic fluorescence intensity of the RCDs is monotonically quenched, but that of the BCDs remains almost unchanged. These results allow for the fabrication of a ratiometric fluorescent sensor using BCDs as reference fluorophores, and RCDs as target sensitive fluorophores. The as-prepared ratiometric fluorescence sensor has a high sensitivity with a linear oxygen volume range from 0 to 100, and exhibits an extremely short response/regeneration time of 2–4s. The BCDs/RCDs/MAs co-doped materials are highly sensitive and selective for the detection of oxygen.

163 - The effect of common transient warming events on post thaw recovery and functionality of human mesenchymal stem cells stored in LN2 vapour environment

163 - The effect of common transient warming events on post thaw recovery and functionality of human mesenchymal stem cells stored in LN2 vapour environment

Exceptional Anti-Icing Performance of Self-Impregnating Slippery Surfaces.

A heat exchange interface at subzero temperature in a water vapor environment exhibits high probability of frost formation due to freezing condensation, a factor that markedly decreases the heat transfer efficacy due to the considerable thermal resistance of ice. Here we report a novel strategy to delay ice nucleation on these types of solid-water vapor interfaces. With a process-driven mechanism, a self-generated liquid intervening layer immiscible to water is deposited on a textured superhydrophobic surface and acts as a barrier between the water vapor and the solid substrate. This liquid layer imparts remarkable slippery conditions resulting in high mobility of condensing water droplets. A large increase of the ensuing ice coverage time is shown compared to the cases of standard smooth hydrophilic or textured superhydrophobic surfaces. During deicing of these self-impregnating surfaces we show an impressive tendency of ice fragments to skate expediting defrosting. Robustness of such surfaces is also demonstrated by operating them under subcooling for at least 490 h without a marked degradation. This is attributed to the presence of the liquid intervening layer, which protects the substrate from hydrolyzation, enhancing longevity and sustaining heat transfer efficiency.

Preparation of a dense ytterbium disilicate layer via dual electron beam physical vapor deposition at high temperature

Ytterbium disilicate (Yb2Si2O7) is promising material for multilayered environmental barrier coatings (EBCs) on SiC fiber reinforced SiC matrix composites (SiC/SiC), because of its excellent volatilization resistance in a water vapor environment and the conformity of its coefficient of thermal expansion to SiC/SiC. A Yb2Si2O7 layer was formed on a mullite substrate, of which the combination was applied to the multilayered EBCs, via electron beam physical vapor deposition (EB-PVD) with dual electron guns using Yb2O3 and SiO2 ingots as vapor sources, simultaneously heating on the substrate at 1523K. The resulting layer consisted of a single-phase of Yb2Si2O7, with the (110) oriented structure. The layer had a highly dense columnar structure extending in the direction of thickness, but not the feather-like structure typical of layers synthesized via conventional EB-PVD techniques. It is expected that the application of dual EB-PVD during heating is useful for the construction of EBCs with excellent gas barrier performance.

Promotion of performances of quantum dot solar cell and its tandem solar cell with low bandgap polymer (PTB7-Th):PC71BM by water vapor treatment on quantum dot layer on its surface

In this study, we propose new treatments on the PbS quantum dot (QD) layer surface by exposing it to air, water vapor and oxygen environments at room temperature.

基于分形理论的不同大气环境对激光传输特性影响的研究

在实验室中模拟平稳大气环境和同等浓度的水蒸气环境与烟雾环境，获取氦氖激光器在三种环境下的激光光斑图像。利用Matlab处理光斑图像得到其灰度图，并提取出光斑轮廓线。编写程序计算光斑的分形维数，得到的结果表明：平稳大气环境对激光传输特性影响较小，分形维数也较小；同等浓度的水蒸气环境和烟雾环境，水蒸气对激光的传输特性影响较大，分形维数较大，光斑直径较大，能量密度较小；可以利用激光光斑分形维数来研究不同环境对激光传输特性的影响。 We simulate stable atmospheric environment and the same concentration of water vapor envi-ronment and smoke environment in our lab, and then we get the laser spot of our helium-neon laser in these three different environments with CCD sensor. Dealing with these images to get grayscale image and extract spots’ contour line. Writing programs to calculate contour lines’ fractal dimension and the result shows that laser’s transmission characteristic is less affected by stable atmosphere environment so that the fractal dimension is the smallest. Comparing to the smog of the same class, the influence of vapor on laser’s transmission characteristic is larger; for the fractal dimension is bigger and the spot’s diameter is larger and the energy density is lower. It is feasible to analyze that how different environments affect laser’s transmission characteristic by means of studying on laser spot’s fractal dimension.

A First-Principles Study of Phase Transition of Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine (HMX) under Static Compression

The issue of HMX phase transition under hydrostatic compression is not clear and experiments show conflicting results. Effective solution via first-principles simulation is challenged by difficulty of accurate prediction of Van der Waals interaction, which exists ubiquitously and is crucial for determining the structure of molecules and condensed matter. We have contributed to this by constructing a set of pseudopotentials and pseudoatomic orbital basis, specialized for molecular systems with C/H/N/O elements. The reliability of the method is verified from the interaction energies of 45 complexes (comparing to the results of coupled cluster with singles and doubles (Triple) (CCSD)(T)) and the crystalline structures of 7 typical explosives (comparing to experiments). Using this method, we complete the phase diagram of HMX under static compression up to 50 GPa. We make it clear that no β→δ/ε→δ phase transition occurs at 27 GPa, which has long been a hot debate in experiments. A possible γ→β phase transition is found at around 2.10 GPa in the environment of vapour. We have also predicted the equation of states for α-, δ-, and γ-HMX, which are experimentally absent.

Local Surface Phase Stability during Cyclic Oxidation Process

Surface properties are essential for many engineering material ́s design issues, such as fatigue and corrosion performances. Austenitic stainless steels used in high-temperature applications, as for instance components in biomass-fired power plants, need sufficient corrosion resistance. At temperatures above 600 °C and in water vapor environment, Cr-vaporization will create Cr-depletion, causing a local change in chemical composition. This local change in chemical composition leads to phase transformation in some austenitic stainless steels. This paper reports the surface properties regarding the local phase transformation during thermal cycling in water vapor environment. Three commercial austenitic stainless steels are investigated, AISI 304, AISI 316L and Sandvik SanicroTM 28. The thermal cycling was performed up to 650 °C in a 15 mol.% water vapor environment. AISI 304 shows local surface phase transformation related to martensitic transformation due to locally changed chemical composition and increase in the martensitic transformation temperature (Ms). However, the other two austenitic stainless steels don’t show this martensitic transformation. The phase transformation and oxidation is discussed using microstructural investigations methods such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS).

Microscopic mechanism for light-induced degradation of silicon solar cell in water vapor environment

Abstract Degradation is the key factor to determine the efficiency and stability of the silicon solar cells, which highly affects their cost and practical performance. Humidity has been well recognized to accelerate the degradation process of the silicon solar cells, but the microscopic mechanism of light-induced degradation in hydrogenated silicon devices at water vapor environment is still elusive. In this paper, combining time-dependent density functional theory with ab initio molecular dynamics (AIMD), we show the water cluster adsorption slightly more elongates the Si-Si bond under illumination compared to the vacuum, which induces electron localization to further greatly facilitate the oxygen molecule absorption and dissociation. This external degradation process is different from the intrinsic degradation mechanisms in hydrogenated silicon devices under light irradiation caused by formation of metastable hydrogen complexes. The transition-state calculations of degradation pathway show the oxidation reaction energy barrier of Si cluster in water vapor environment is lower than that in vacuum, which confirms AIMD observations. Our results not only shed new insight for understanding the microscopic mechanism of light-induced degradation under water vapor, but would also be beneficial for controlling the light-induced silicon degradation of solar cell in real application.

Flame synthesis of novel ternary nanocatalysts Pd/CeO2[sbnd]TiO2 with promotional low-temperature catalytic oxidation properties

One-step flame-assisted spray pyrolysis with highly-quenched premixed stagnation flame is developed to synthesize the supported palladium catalysts on the mixed ceria-titania oxides. Promotional oxygen reducibility and inherent high activity of the catalysts are discovered in contrast to the same loading palladium catalyts on either single support, and the complete methane oxidation is achieved at as low as 450 °C. Palladium valence electronic structure analysis from X-ray photoemission spectroscopy (XPS) indicates that the metal palladium is highly positively charged and electrons transfer from palladium clusters to support oxides during the flame synthesis process. Similar electron transfer can even occur during the cyclic catalytic process for the initially non-charged clusters. From the cyclic experiments, theelectrostatic interaction built up at the metal–support interface plays a major role in the superior sintering resistance for palladium-based catalysts during the combustion process. Moreover, the introduction of water vapor to the feedstock induces a negative effect on the methane oxidation at low temperatures. XPS spectra reveals that the palladium 3d binding energy varies and the interfacial electron transfer flow changes over heating–cooling cycles when exposed to water vapor. More importantly, the excellent thermal stability performances remain even under the water vapor environment.

Mixed-solvent-vapor annealing of perovskite for photovoltaic device efficiency enhancement

The key to improve the photovoltaic performance of perovskite solar cells is the quality of perovskite materials. Here, we report a growth mode that the perovskite precursor film is thermal annealed in mixed anti-solvent (IPA) and solvent (DMF) (100:1, v/v) vapor environment to improve the film quality, which enhances the power conversion efficiency of CH3NH3PbI3 based planar heterojunction solar cell device from 12.2% to 15.1%. After 8 days’ storage without encapsulation, the devices retained about 75% of their original efficiency while devices without solvent annealing reduced to 40% of that. It should be mentioned that by further applying compositional engineering such as using CH3NH3PbI3−xClx perovskite precursor and using interface engineering approach, the efficiency of planar heterojunction solar cell could be further enhanced up to 18.9%. The enhancement in photovoltaic performance and stability is due to the perovskite film quality improvement, with the increased average grain size and crystallinity of perovskite.

Surface enhanced Raman scattering substrate with high-density hotspots fabricated by depositing Ag film on TiO2-catalyzed Ag nanoparticles

Surface enhanced Raman scattering (SERS) has been developed as a powerful tool for detection of ultra-trace molecules, thus at foundation of a number of important technologies, such as chemical analysis and biosensor. Photocatalytic growth of Ag nanoparticles (NPs) by TiO2 film is a cost-effective, facile and surfactantless way to fabricate SERS substrates with high stability and reproducibility, but the SERS activity still needs to be improved. In this work, we report a facile way to improve SERS activity of TiO2-catalyzed Ag NPs by additionally depositing a layer of Ag film using magnetron sputtering. Combining with the advantages of liquid and vapor environment, the Ag NPs size increase to the resonance size without decrease of density, so the spacing of Ag NPs decrease and high-density hotspots can be formed. By optimizing the sputtering time of Ag films, the SERS activity of the Ag NPs/films is improved by a factor of ∼400. This work not only establish a low-cost method for fabricating high-quality SERS substrate, more importantly, propose a novel way to prepare plasmonic nanostructures with high-density hotspots.

Atomic-scale Studies of Uranium Oxidation and Corrosion by Water Vapour.

Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.

Effect of Surface Evaporation on Steady Thermocapillary Convection in an Annular Pool

In order to understand the effect of surface evaporation on thermocapillary convection in an annular pool, a series of numerical simulation on thermocapillary convection of the fluids with Prandtl number from 0.01 to 50 in the pure vapor environment were carried out. The results show that thermocapillary convection is always coupled with the evaporation process on the free surface. With the increase of evaporation Biot number, the surface temperature decreases, and the evaporation mass flux near the hot wall increases obviously. However, near the cold wall, the evaporation mass flux increases first, and then decreases. When Marangoni number is small, the total evaporation mass rate at free surface increases with the increase of evaporation Biot number; when Marangoni number is larger, it increases first and then approaches a constant value. The aspect ratio of the annular pool has a positive influence on the thermocapillary convection strength and the total evaporation mass rate. With the increase of Prandtl number, the surface temperature rises gradually and the evaporative mass flux increases, and the thermocapillary convection cell moves gradually toward the outer wall and the free surface. This effect decreases with the increase of evaporation Biot number When evaporation Biot number is smaller, the total evaporation mass rate increases with the Prandtl number; when Biot number is larger, Prandtl number has little impact on the total evaporation mass rate.

Wicking of liquid nitrogen into superheated porous structures

Evaporation in porous elements of liquid–vapor separation devices can affect the vapor-free cryogenic propellant delivery to spacecraft engines. On that account, the capillary transport of a cryogenic liquid subjected to evaporation needs to be understood and assessed. We investigate wicking of liquid nitrogen at saturation temperature into superheated porous media. A novel test facility was built to perform wicking experiments in a one-species system under non-isothermal conditions. A setup configuration enabled to define the sample superheat by its initial position in a stratified nitrogen vapor environment inside the cryostat. Simultaneous sample weight and temperature measurements indicated the wicking front velocity. The mass of the imbibed liquid nitrogen was determined varying the sample superheat, geometry and porous structure. To the author’s extent of knowledge, these are the first wicking experiments performed with cryogenic fluids subjected to evaporation using the weight–time measurement technique. A one-dimensional macroscopic model describes the process theoretically. Results revealed that the liquid loss due to evaporation at high sample superheats leads to only a slight imbibition rate decrease. However, the imbibition rate can be greatly affected by the vapor flow created due to evaporation that counteracts the wicking front propagation.