Volatile Surface Research Articles

The compositional dependence of the saturation surface of H 2O + CO 2 fluids in silicate melts

The volatile saturation surface in H 2O–CO 2–silicate melt systems is modeled by applying thermodynamic equilibrium between gaseous and liquid volatile components. The whole database of existing saturation data in the C–O–H–silicate liquid systems has allowed us to re-calibrate a previously developed fully multicomponent H 2O–CO 2 saturation model [Papale, P., 1999. Modeling of the solubility of a two-component H 2O + CO 2 fluid in silicate liquid. Am. Mineral., 84, 477–492]. The new database nearly doubles the previous one, greatly improving the performances of the whole model, which now adopts a significantly lower number of model parameters with respect to the previous calibration. The multicomponent H 2O + CO 2 saturation model is fully non-ideal, the only assumption being that the excess Gibbs free energy of the silicate mixture can be represented by an expansion of first-order symmetric interaction terms. No a-priori assumption is made on the P– T dependence of the volatile–oxide interaction terms, meaning that no assumption is made on the partial molar volume and enthalpy of the dissolved volatiles. The whole treatment is evaluated by restrictive statistical algorithms, which confirm the model validity on an extended database. The model allows to investigate extensively the dependence of the complex volatile saturation surface on composition. In order to explore the non-linear behaviors implicit in the physics of the dissolution process, the model is employed in a series of calculations aimed at illustrating some of the compositional features of the volatile saturation surface in both one-component and two-component volatile conditions. The results show compositional-dependent minima and maxima, some of which are known from the experiments. Non-ideal behavior is enhanced in two-component fluid phase conditions and pressures above a few hundreds MPa, where calculated isobaric H 2O–CO 2 saturation curves reveal the possible existence of a maximum in CO 2 saturation at non-zero H 2O contents. Due to the compositional dependence of the volatile saturation surface, it is outlined the important role played by redox conditions, especially in iron-rich melt systems like basalts.

Effects of 160 MeV Ni12+ ion irradiation on HCl doped polyaniline electrode

Conducting polymers are suitable as electrode materials for high performance supercapacitors because of their high specific capacitance and high dc conductivity in the charged state. Ion beam (energy >1 MeV) irradiation of materials is a novel technique to modify their properties. Polyaniline conducting polymer thin films doped with HCl are synthesized electrochemically on indium tin oxide coated glass substrates and are irradiated with 160 MeV Ni12+ ions at different fluences, namely, 5 × 1010, 5 × 1011 and 3 × 1012 ions cm−2. The dc conductivity measurements of the irradiated films showed up to 70% increase in conductivity, which may be due to the increase of carrier concentration in the polymer film as observed in UV-Vis spectroscopy and other effects like the cross linking of polymer chains, bond breaking and creation of defects sites. An x-ray diffractogram study shows that the degree of crystallinity of polyaniline increases upon swift heavy ion (SHI) irradiation with the increase in ion fluence. The capacitance of the irradiated films is lowered but that of the supercapacitors with irradiated films showed enhanced electrochemical stability compared with the devices with unirradiated films while characterized for a cycle life up to 10 000 cycles. This effect could possibly be ascribed to the stabilization of volatile surface groups upon SHI irradiation.

The influence of ultrasound power on multibubble sonoluminescence intensity from aqueous solutions containing surface active solutes

Water soluble surface active solutes have been found to affect the intensity of multibubble sonoluminescence (MBSL) in aqueous solutions. For example, the presence of charged surfactants enhances the MBSL intensity relative to that observed from pure water, whereas the presence of volatile surface active solutes decreases the MBSL intensity in reference to pure water [J. Phys. Chem. B 101, 10845 (1997)]. Further investigations on how ultrasound power influences the effect of surface active solutes on MBSL intensity have shown that ultrasound power plays an important role in governing the above mentioned effects. The relative enhancement in MBSL intensity by charged surfactants has been found to vary with changes in ultrasound power level; the relative enhancement decreases with an increase in the ultrasound power level. Also, the extent of MBSL quenching by alcohols has been found to increase with an increase in the applied ultrasound power level; no SL quenching at lower power levels and >80% SL quenching at higher power levels have been observed. The influence of ultrasound power on the population of ‘‘active’’ bubbles and the cavitation bubble temperature, in aqueous solutions containing surface active solutes, will be discussed in order to rationalize the observed experimental data.

Preparation and characterization of electroconductive polypyrrole copolymer Langmuir–Blodgett films

We successfully synthesized an amphiphilic pyrrole derivative, 12-pyrrolyl dodecanoic acid (PDA) and fabricated the Y-type multilayer PDA Langmuir–Blodgett (LB) films by the conventional vertical dipping method. We, however, could not obtain an electroconductive polymer LB film from PDA alone. We, therefore, carried out in situ copolymerization of pyrrole and PDA at the air–water interface by spreading the mixture solution of pyrrole and PDA with various feed ratio in chloroform onto a subphase containing 1 wt.% FeCl 3. We confirmed that the well ordered electroconductive Y-type poly(PPy-co-PDA) LB film was successfully prepared with the feed mole ratio of 300:1 (pyrrole:PDA) under the condition of surface pressure 33 mN/m, pH 5.3, and 17 °C. Poly(PPy-co-PDA) LB multiplayer film showed the fairly high electrical conductivity of 2.3×10 −3 S/cm and extremely smooth surface. We expect the electrically conducting polymer film with good structural order can be applied to many potential application fields such as volatile organic sensor, biosensor, or surface acoustic wave devices.

Behavior of ceria as an actinide surrogate in electroslag remelting and refining slags

Downsizing and decommissioning of nuclear facility operations is increasing the stockpile of various different grades of radioactive scrap iron (RSI). Disposal of this material not only represents significant resource and value lost but also necessitates long term monitoring for environmental compliance. The latter results in additional recurring expense. It is desirable to be able to decontaminate the RSI to a very low level that can be recycled or used for fabrication of containers for RSI disposal instead of using virgin metal to fabricate the container. Electroslag remelting and refining (ESR) is often used for decontaminating radioactive contaminated sources of scrap iron, such as stainless steel. Nonradioactive oxides of cerium are used to simulate the radioactive oxide contaminants of uranium and plutonium. The success of the ESR process is strongly dependent on having the right thermo-physical-and-chemical slag properties. In this article, we measured the following relevant slag properties: capacity to incorporate the radioactive contaminant (simulant), volatilization rate and volatile species, electrical conductivity, viscosity, surface tension, and slag-metal partition coefficient, as a function of temperature. The impact of these properties on the ESR decontamination process is discussed.

Fluorescence visualization of a convective instability which modulates the spreading of volatile surface films

The spontaneous spreading of a thin liquid film along the surface of a deep liquid layer of higher surface tension is a ubiquitous process which provides rapid and efficient surface transport of organic or biological material. For a source of constant concentration, the leading edge of a nonvolatile, immiscible film driven to spread by gradients in surface tension is known to advance as t3/4 in time. Recent experiments using laser shadowgraphy to detect the advancing front of spreading films indicate, however, that immiscible but volatile sources of constant concentration spread with a reduced exponent according to t1/2. Using a novel technique whereby fluorescent lines are inscribed in water, we have detected the evolution of a thermal instability beneath the leading edge of volatile films which strongly resembles a Rayleigh-Bénard roll. We propose that the increased dissipation from this rotational flow structure is likely responsible for the reduction in spreading exponent. This observation suggests a conceptual framework for coupling the effects of evaporation to the dynamics of spreading.

Boundary conditions in a multicomponent gas mixture flow past a volatile nonspherical surface at knudsen numbers 0.01 and 0.3

The paper presents the boundary conditions of a temperature-and concentration-inhomogeneous multicomponent gas flow past a slightly curved nonspherical surface in the presence of slow evaporation and condensation processes.

In Vitro Eye Irritation Studies on Organosilicon Compounds

AbstractThe development of alternatives to in vivo eye irritation testing in animals is spurred by humane, scientific, and economic considerations. Two commercially available in vitro assays (Epi-Ocular Tissue Model OCL-100 and Skin2 ZK-1200 model) and a third published assay, the Bovine Corneal Opacity and Permeability Assay (BCOP), were used to assess the eye irritancy potential of several organosilicon (OS) compounds to evaluate their suitability for testing silicone polymers and other materials. The Skin2 ZK-1200 model (nine OS compounds) was generally applicable for the in vitro assessment of eye irritancy of liquid silicone polymers. However, some effort will be required to overcome the problem of working with viscous pastes and volatile low surface tension test materials for which variable results were observed. The correlation of the Skin2 model in vitro eye irritancy results with known in vivo data was generally good for silicone polymers, although some alkoxysilanes do not appear to give in vitr...

96/05299 The release of nitrogen during the combustion of coal chars: The role of volatile matter and surface area

96/05299 The release of nitrogen during the combustion of coal chars: The role of volatile matter and surface area

The release of nitrogen during the combustion of coal chars: the role of volatile matter and surface area

The effect of pyrolysis conditions on the release of nitrogen during char combustion was investigated. A fluidized bed pyrolysis unit was used to produce several chars at different temperatures and pressures from a Spanish coal. In this way, a number of chars differing in volatile matter and specific surface area were obtained. Gas evolution profiles of CO, CO 2, NO and N 2 from temperature-programmed char combustion were recorded by a thermogravimetric analyser linked to a quadrupole mass spectrometer. The NO evolution profiles show two zones whose intensity depends on the volatile matter and specific surface of the chars. These zones of NO release are attributed to two different nitrogen sources. The fraction of the total nitrogen char released as NO depends on the volatile matter and the specific surface of the chars. The higher the volatile matter and the lower the surface area, the higher the NO/N ratio, i.e. the fraction of the char nitrogen that is released as NO. The nitrogen released as NO + N 2 accounts for nearly all the nitrogen in chars of low surface area and high volatile matter. This is not the case for the chars of high specific surface and low volatile matter, showing that other nitrogen species, probably N 2O, are formed during oxidation of such chars. The results are discussed on the basis of the mechanisms proposed in the literature for NO release that involve primary NO formation and subsequent reduction to N 2 and N 2O by CO and char carbon.

Development of Aroma Volatiles and Color during Postharvest Ripening of `Kent' Strawberries

`Kent' strawberries were harvested at red, pink, and white stages of development, and stored at 15C in the light. Fruit were sampled over a 10-day period and evaluated for volatile production and surface color. Volatile production by red and pink fruit peaked after 4 days of storage. Maximum volatile production by red fruit was 8- and 25-fold greater than maximum production by pink and white fruit, respectively. Aroma volatiles were not detected in the headspace over white berries until 4 days following harvest after which volatile production increased through the tenth day of storage. Changes in the surface color of white berries during postharvest ripening coincided with the production of volatiles. In another experiment, red, pink, and white `Kent' strawberries were stored for 3 days at 10 or 20C in the dark or light. Fruit were then evaluated for volatile production, weight loss, anthocyanin content, and surface color changes. White berries produced volatile esters after 3 days of storage at 20C in the light. Both light and temperature influenced the relative production of the volatiles produced by pink fruit. Fresh weight loss, color change, and anthocyanin content were temperature and light dependent.

Etching of Si surfaces with hot chlorine beams: Translational and vibrational excitation of the incident chlorine particles

A systematic study of etching of Si(100) and Si(111) and Ar+ bombarded Si(100) (surface with defect sites) with chlorine has been carried out. We have compared the reactivity of atomic and molecular chlorine, and studied the effect of translational and vibrational excitation of the etchant on the etch rate. Similar etch rates were obtained on the Si(100) and Si(111) single crystal surfaces. On both surfaces the major etch products were SiCl4 at Ts<500 K and SiCl2 at Ts≳600 K. Some SiCl desorption was obtained at Ts≳1100 K. We have outlined the conditions under which the etch rate, at constant incident flux, is adsorption and desorption limited. On the Si(100) and Si(111) surfaces we found that when the etch rate is reaction limited, higher etch rate can be obtained with atomic chlorine than with molecular chlorine. In the adsorption limited regime, translational excitation of both atomic and molecular chlorine results in a higher etch rate than that obtained with slow atomic and molecular chlorine. Vibrational excitation of Cl2 does not result in an enhancement of the etch rate on the single crystal surfaces studied. In the desorption limited regime the etch rate is primarily determined by the surface temperature. The nature of the etchant particles does not have a significant effect. On Ar+ bombarded Si(100), we obtained a small increase in the etch rate with translationally and vibrationally excited Cl2, and comparable enhancement is obtained with Cl2 that is only translationally excited. The difference in the etch properties of the single crystalline and Ar+ bombarded silicon surfaces points to the importance of surface defects in etching. The present results show that at room temperature the low etch rate of silicon single crystal surfaces with chlorine, as compared to etching with fluorine, is due to the low formation rate of volatile surface products.

An analytic solution of the problem of the temperature jumps and vapour density over a surface when there is a temperature gradient

An analytic solution of the Boltzmann equation with a BGK (Bhatnagar, Gross and Krook) collision operator is constructed in the problem of the temperature jumps and the density of a rarefied gas in the half-space above a volatile surface, where a constant temperature gradient is specified far from the surface. The necessary numerical calculations are carried out. A canonical-matrix method with a normal form at infinity is simultaneously developed to solve the Riemann-Hilbert vector boundary-value problem. The proof of the expansion of the solution of the boundary-value problem considered in generalized eigenvectors of the corresponding characteristic equation is reduced to the solution of this problem.

Surface analysis of cubic silicon carbide (001)

Cubic β-SiC(001) surfaces were cleaned in ultra-high vacuum by heating within a Si atomic flux, allowing contaminant species to desorb while continuously replenishing volatile surface Si. Using this technique, surface compositions ranging from Si-rich to Si-deficient were prepared. Surfaces were subsequently characterized using Auger electron, electron energy loss. X-ray photoelectron, and ultraviolet photoelectron spectroscopies as well as low energy electron diffraction. Data are presented for a range of surface compositions which result in formation of several reconstructions: (3 × 1), c(4 × 2), (2 × 1), c(2 × 2), and (1 × 1). Results are interpreted based on surface models which include ordered arrays of surface Si dimers for Si-rich and Si-terminated surfaces and graphite formation for Si-deficient surfaces.

Polymer melt devolatilization mechanisms

AbstractScanning electron microscopy (SEM) was used to study the mechanism of falling‐strand devolatilization of polymer melts. Polystyrene and low‐density polyethylene were enriched with styrene and hexane, respectively, and were subsequently extruded as thin strands at various conditions. The polymer strands were exposed to superheat conditions for preset periods of time ranging from tenths to tens of seconds. The strands were then frozen, fractured, and studied by SEM. Devolatilization was found to proceed through a blistering mechanism, both on the surface of the strands and on the surfaces of volatile bubbles formed within the core of the melt. At all volatile concentrations surface blistering and foaming preceded bubble growth in the core, and occurred before the strands foamed. A mechanism for the observed polymer melt devolatilization is proposed.

ON THE FATE OF SINUSOIDAL RADIATION TO A VOLATILE OPAQUE LIQUID

A method was developed that predicts the energy distribution of sinusoidal radiation incident on a volatile opaque liquid surface. The energy is absorbed by the liquid phase, absorbed by the gas phase and used to furnish the heat of vaporization of the volatile liquid. In an example of heptane and air, 94.8% of the energy conducted into the liquid phase 1.0% was conducted into the gas phase and 4.2% was required for the heal of vaporization The method could be used to determine the emissivity of a material radiating to a volatile opaque liquid. Results may also find application in reducing hydrocarbon emissions from fixed-roof tanks by as much as 30% if aluminum instead of steel tank domes were used

Dynamic hydration effects in an electron microscope cold stage.

Water can be a substantial proportion of the residual gas in modern electron microscopes even when frozen hydrated specimens are not used. During measurements of the mass thickness of thin collodion film specimens at low temperatures, it was found that a volatile surface layer (condensed water) modified the apparent rate of mass loss induced by radiation exposure. Mass loss can be enhanced by the presence of water (specimen "etching"), or mass loss can be masked by the dynamic adsorption of water to the specimen surface. The microscope or the grid can be a secondary source of the water; even with cold anticontaminator plates in the vicinity of the specimen, water can be desorbed by x-rays or backscattered electrons. In one typical situation, the mass loss rate appears reduced (due to water adsorption), but the ultimate damage is greater (due to etching). These results illustrate that care must be taken in interpreting mass thickness measurements made in the presence of water and that the lowest stage temperature does not necessarily produce the best observation conditions for all specimens.

Nucleation of Gaas on Vicinal Si(100) Surfaces

ABSTRACTWe investigate the nucleation of epitaxial GaAs grown on vicinal Si(100) surfaces by Molecular Beam Epitaxy. We find that the vicinal surface structure is highly sensitive to the surface cleaning process, and that in-situ desorption of a volatile surface oxide at 900°C appears to result in significant step mobility, resulting in the formation of low angle surface facets. Nucleation of GaAs then occurs on these facets, raising the possibilty of influencing the heteroepitaxial nucleation and growth processes by influencing the substrate surface “template” at the surface cleaning stage.

Large seasonal variations in Triton's atmosphere

Triton's seasons differ materially from those of Pluto owing to four important differences in the governing physics: First, the obliquity of Triton is significantly less than Pluto's obliquity. Second, Triton's inclined orbit precesses rapidly about Neptune so that a complicated seasonal variation in the latitude of the Sun occurs for Triton. Third, Neptune's orbit is much more circular than Pluto's orbit so that the sunlight intercepted by Triton's disk does not vary seasonally. Finally, Triton's atmosphere cannot be saturated at the lower latitudes so that the mass of the atmosphere is controlled by the temperature of the high-latitude ices or liquids (polar caps), as for CO 2 on Mars. The consequences of Triton's entire surface being covered with volatile substances have been examined. It is found that the circularity of Neptune's orbit then implies that Triton would have hardly any seasonal variation at all in surface temperature or atmospheric bulk, in spite of the complicated precessional effects of Triton's orbit. The only seasonal effect would be the migration of surface ices and liquids. This scenario is ruled out because it implies a column CH 4 abundance much higher than that observed and because it quickly depletes the lower latitudes of volatiles. It is concluded that Triton's most volatile surface substances are probably relegated to latitudes higher than 35° and probably form polar caps. The temperature of the polar caps should be nearly equal, even during midwinter/midsummer when the insolation of the summer pole is greatest. If the summer pole completely sublimates during one of the “major” summers, Triton's atmosphere may begin to freeze out over the winter caps. It is therefore expected that Triton's atmosphere undergoes large and complex seasonal variations. Triton is currently approaching a “maximum southern summer”, and over the remainder of this century, a dramatic increase in CH 4 abundance above the current upper limit of 1 m-Am may be witnessed.

Identification of host plant attractants for the carrot fly,Psila rosae

Cold-trapped carrot leaf volatiles were analyzed by gas chro-matography with an outlet splitter to a flame ionization detector and to a carrot fly antennogram preparation as the second detector (GC-EAD). Strongest EAD responses were elicited by products whose elution temperatures corresponded to the propenylbenzenes,trans-methylisoeugenol (3,4-dimethoxy-1-propenylbenzene) andtrans-asarone (2,4,5-trimethoxy-1-propenylbenzene) and, to a lesser extent, by-products matching the elution temperatures of the leaf aldehydes hexanal, (E)-2-hexenal, and heptanal, and of the terpenes linalool and caryophyllene. The identity of the propenylbenzenes was confirmed by gas chromatography-mass spectrom-etry. GC-EAD permitted accurate estimation of the olfactory thresholds; it was lowest fortrans-asarone at 500 attogram (5 × 10(-16)g)/ml of air passing over the antenna. Both the leaf aldehydes and propenylbenzenes were attractive when tested individually in the field with yellow sticky traps; fly captures were linearly related to the quantity of propenylbenzenes applied per trap. A combination oftrans-asarone and hexanal was more attractive than either compound singly, suggesting that the fly is adaptively equipped to respond to a mixture of compounds emanating from carrot foliage. In laboratory choice tests, flies were more attracted by vapors from intact carrot foliage than by that from a nonhost; leaf odor alone also mediated oviposition. We conclude that through the selectivity and sensitivity of its response to foliar volatiles, the carrot fly may achieve host-plant orientation and also at close range, in union with its response to less volatile leaf surface components, selection of an oviposition site.