Nucleation and Condensation of Magnesium Vapor in Argon Carrier

The nucleation and condensation of Magnesium (Mg) vapor carried by argon gas (Ar) were examined. The condensation of Mg vapor at a heat source temperature of 1273–1473 K and Ar flow rate of 0.1–0.4 m3/h was analyzed. The result indicated that the condensation temperature is affected by the heat source temperature and Ar flow rate, and the condensation temperature of Mg vapor was 1013.3 K at a heat source temperature of 1473 K and Ar flow rate of 0.2 m3/h. The effects of Mg vapor partial pressure and temperature of the condensation zone on the nucleation and condensation of Mg vapor carried by Ar were calculated and analyzed in terms of atomic collisions and critical nucleation radius. Increased vapor oversaturation and decreased condensation temperature were favorable for liquid nucleation growth. The Mg condensation products in Ar flow rate of 0.2 m3/h at a heat source temperature of 1473 K were analyzed by XRD, SEM, and EDS, which indicated that the condensed product was of high purity and not easily oxidized in Ar flow. In this paper, the quality of Mg vapor condensation was controlled, which provided the theoretical and experimental basis for a continuous Mg production process.

Permeability alteration by salt precipitation: numerical and experimental investigation using X-Ray Radiography

The injection of a gas phase through a water saturated porous medium can reduce the water saturation not only by displacement mechanisms but also by evaporation mechanisms. In the presence of brine, this process can induce salt crystallization and precipitation within the porous medium with a risk of permeability alteration. In the field of gas production and storage, the occurrence of such a phenomenon can have detrimental consequence on the well productivity or injectivity. In this work, we investigated experimentally and numerically the effect of dry gas injection on salt precipitation and permeability impairment. State of the art equipment designed for high throughput coreflood experimentation was used to capture the dynamic of salt migration using X-Ray radiography. A set of experiments have been conducted on a sample of Bentheimer sandstone (10mm in diameter and 20 mm in length) as well as a two layers composite sample with a significant permeability contrast. Experiments were conducted using Nitrogen and KBr brine with different boundary conditions (i.e. with and without capillary contact). Results showed that salt precipitation results from the interplay of different parameters, namely pressure gradient, brine salinity, capillary forces and vapor partial pressure. Experimental observations indicate that in the case of dry gas injection, salt systematically precipitates but permeability alteration is observed only if a capillary contact is maintained with the brine. We built a 2D flow model integrating two-phase Darcy flow, capillary forces, salt effect on vapor partial pressure, dissolved salt transport, as well as the different PVT equilibria needed to describe properly the systems. Once calibrated, the model showed good predictability of lab scale experiment and thus can be used for parametrical study and upscaled to the well bore scale.

Effects of Annealing Parameters on Epitaxial Graphene on SiC Substrates

The effects of annealing on epitaxial graphene on SiC substrates with various conditions are investigated. Results show that high pressure hydrogen atmosphere is more effective to decouple the epitaxial graphene from SiC substrate than that of a relative lower pressure process. Besides, the characteristic 2D-peak of graphene in Raman spectra disappeared with an annealing temperature 1000 °C, which means that the epitaxial graphene layer was decomposed in this condition. The study also shows that the decomposition of graphene can be effectively suppressed by increasing carbon vapor partial pressure through introducing ethylene during high pressure hydrogen annealing at 1000 °C. And the epitaxial graphene is successfully transferred to quasi free standing graphene by the annealing with an appropriate flow of ethylene.

A New Experimental Method to Determine the Henry’s Law Constant of a Volatile Organic Compound Adsorbed in Soil

This paper presents a new mechanical method to determine Henry’s law constant (HLC) of a volatile organic compound (VOC). This method is an extension of the one proposed by Ouoba et al. (2010) to determine the water activity in porous media. This work focuses on TCE and aims at characterizing its liquid-vapor equilibrium in various cases in the form of a pure liquid phase or dissolved in an aqueous solution, adsorbed or not in a natural soil. A liquid phase is disposed in a closed chamber whose volume can be incrementally increased. The recording of the total gas pressure leads to evaluating the vapor partial pressure of a volatile compound even in the case of an aqueous solution. This method has been validated using various aqueous solutions of TCE and the HLC obtained is in agreement with the literature. Then, the validity of Henry’s law has been asserted in the case of an aqueous solution of TCE adsorbed in a hygroscopic soil. Indeed, a linear relation between the vapor partial pressure of TCE and its concentration has been obtained while the HLC is about 16% lower. This result highlights the influence of adsorption phenomena on vapor/liquid equilibrium.

Effect of O2 Flow Rate on the Morphological and Optical Properties of ZnO Nanocrystals

The morphological and optical properties of ZnO nanocrystals prepared by thermal evaporation of Zn powders were studied at both upstream and downstream under different O2flow rates. The morphological evolution was observed by scanning electron microscopy. With O2flow rates changing from 0.25 sccm to 1 sccm, the caps of the ZnO nanonails become bigger and the stems gradually disappear at upstream, and the diameters at the top of ZnO nanorods become thicker and the length become longer at downstream. Room temperature PL study shows that UV emission is relatively enhanced with increasing O2flow rates. Computational fluid dynamics simulation was performed, which indicates that the morphological evolution of the ZnO structures results from the competition between the axial growth and the radial growth based on different O2and Zn vapor partial pressure.

Air Dehumidification with the Porous Hydrophobic Wall in Underground Tunnel

Air can be dehumidified with the porous hydrophobic wall in mostly underground tunnel in constant zone of subsurface temperature. For water vapor through the wall, it must produce a concentration difference between both sides of the wall. According to this principle, a test is done combined with repair works on an underground tunnel. The hydrophobic porous mortar is scraped on geotextile, which is pasted on the painted original tunnel wall as hydraulic conductivity layer where vapor condense and water flow away. It is recognized that temperature and mass transfer rate is relative to tunnel air velocity, air temperature and partial pressure of water vapor, the temperature in constant zone of subsurface temperature and the saturated water vapor partial pressure. Comparative test results show that the condensation dew on the wall is disappeared completely, the wall dehumidifies air effectively, and saving dehumidifier power is more than 50% in normal humidity range.

Metal Oxide Nanowire Growth via Intermediate Hydroxide Formation:A Thermochemical Assessment

ABSTRACTIn this study we apply reaction thermodynamics to show that a significant volatile hydroxide vapor partial pressure forms at a metal-oxide interface and is a likely precursor source for nanowire growth. The growth of WO3 and CuO nanowires are used as examples for reactions dependent on only H2O and O2+H2O, respectively. Optimal temperatures, H2O (and O2) partial pressures for volatile hydroxide formation are calculated and experimentally investigated. We conclude that metal oxide nanowires can be readily grown at relatively low temperatures (close to or less than 500oC) over short anneal times (tens of minutes). The growth of these metal oxide nanowires, with many oxidation states, by this simple thermal technique is readily suited for a range of emergent large surface area nanostructured optical and electrical applications, including sensing, photocatalysis and ultracapacitors.

Absolute ozone absorption cross section in the Huggins Chappuis minimum (350–470 nm) at 296 K

We report the ozone absolute absorption cross section between 350–470 nm, the minimum between the Huggins and Chappuis bands, where the ozone cross section is less than 10−22 cm2. Ozone spectra were acquired using an incoherent broadband cavity enhanced absorption spectrometer, with three channels centered at 365, 405, and 455 nm. The accuracy of the measured cross section is 4–30%, with the greatest uncertainty near the minimum absorption at 375–390 nm. Previous measurements vary by more than an order of magnitude in this spectral region. The measurements reported here provide much greater spectral coverage than the most recent measurements. The effect of O3 concentration and water vapor partial pressure were investigated, however there were no observable changes in the absorption spectrum most likely due to the low optical density of the complex.