Water Vapor (water + vapor)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by Water Vapor

  • water vapor permeability
  • water vapor transmission rate

  • Selected Abstracts


    Alumina Volatility in Water Vapor at Elevated Temperatures

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004
    Elizabeth J. Opila
    The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250 and 1500C, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process. [source]


    Oxidation and Volatilization of Silica Formers in Water Vapor

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003
    Elizabeth J. Opila
    At high temperatures, SiC and Si3N4 react with water vapor to form a SiO2 scale. SiO2 scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming SiO2 and the other removing SiO2, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved. After steady state is achieved, the oxide found on the surface is a constant thickness, and recession of the underlying material occurs at a linear rate. The steady-state oxide thickness, the time to achieve steady state, and the steady-state recession rate can be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate also can be determined from parameters that describe a water-vapor-containing environment. Accordingly, maps have been developed to show these steady-state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of SiO2 formers in water-vapor-containing environments, such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4. [source]


    Oxidation of Acetaldehyde and Propionaldehyde on a VOx/TiO2 Catalyst in the Presence of Water Vapor

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2006
    W. Ya.
    Abstract The partial oxidation of acetaldehyde and propionaldehyde on a TiO2 supported VOx catalyst in the presence of water vapor was investigated at temperatures from 120 to 280,C. Depending on the kind of aldehyde and reaction temperature, the selective oxidation to the appropriate carboxylic acid and an oxidative splitting to lower carboxylic acids took place. Acetaldehyde was oxidized to acetic acid with selectivities up to 82,% at ,,200,C whereas propionic acid was formed only with selectivities of about 20,% at ,,140,C in the oxidation of propionaldehyde. The oxidative cleavage of propionaldehyde led to the formation of more acetic acid than formic acid, which was in agreement with the higher formation of COx compared to that in the acetaldehyde oxidation. The presence of water and the increasing concentration of oxygen in the feed was found to enhance the selectivity towards the formation of C1 to C3 carboxylic acids by inhibiting the total oxidation of aldehydes and carboxylic acids. [source]


    ChemInform Abstract: A Dawson-Type Dirhenium(V)-Oxido-Bridged Polyoxotungstate: X-Ray Crystal Structure and Hydrogen Evolution from Water Vapor under Visible Light Irradiation.

    CHEMINFORM, Issue 43 2008
    Chika Nozaki Kato
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Nanostructure Copper-exchanged ZSM-5 Catalytic Activity for Conversion of Volatile Organic Compounds (Toluene and Ethyl Acetate)

    CHINESE JOURNAL OF CHEMISTRY, Issue 2 2010
    S. Ali Hosseini
    Abstract Gas phase catalytic oxidation of ethyl acetate and toluene was examined over copper modified ZSM-5 catalysts under atmospheric pressure. Nanostructure of ZSM-5 was characterized by XRD, SEM and TEM techniques. Elemental composition of ZSM-5 was determined using EDX, ICP-AES and XPS techniques. Results of catalytic studies showed better catalytic activity of Cu-ZSM-5 catalysts than those of parent ZSM-5 and HZSM-5, which revealed catalytic role of copper ions in the Cu-ZSM-5 catalysts. Effects of some parameters over catalytic conversion of these compounds were also studied. Ethyl acetate showed more reactivity than toluene over the Cu-ZSM-5 catalysts. Furthermore, the catalytic activity of Cu-ZSM-5 catalysts increased with increasing the copper loadings. The conversion behavior of a binary mixture of ethyl acetate and toluene was different from that of a single form. A promotive and inhibitive behavior was observed for conversion of ethyl acetate and toluene in the binary mixture, respectively. Water vapor as co-feed had an inhibitive effect on conversion of organic compounds over the Cu-ZSM-5 catalysts. [source]


    Heat transfer research on vapor-gas mixture with condensation in a vertical tube

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2002
    L. Jia
    Abstract The convection-condensation heat transfer of vapor-gas mixtures in a vertical tube was studied theoretically and experimentally. The effects of the condensation of a small amount of water vapor (8 to 20%) on heat transfer in a vertical tube were discussed. Comparisons show that theoretical solutions obtained through modified film model and experimental results are in good agreement. The results show that the condensation heat transfer of a small amount of water vapor and single-phase convection heat transfer in the vapor-gas mixtures are of the same order of magnitude, and these two modes of heat transfer could not be neglected. 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(7): 531,539, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10055 [source]


    An experimental study on vapor condensation of wet flue gas in a plastic heat exchanger

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2001
    L. Jia
    Abstract An experimental system investigating condensation heat transfer of wet flue gas was set up, and the heat transfer performance of vapor-gas mixture with vapor condensation was discussed. The experimental results of laminar flow in a plastic longitudinal spiral plate heat exchanger were obtained and are in good agreement with the modified classical film model. It is shown that the plastic air preheater can avoid acid corrosion in the low-temperature field for the boiler using fuel containing sulfur and recover latent heat of the water vapor of the wet flue gas. Also some SO2 was scrubbed during the vapor condensing process in the heat exchanger. 2001 Scripta Technica, Heat Trans Asian Res, 30(7): 571,580, 2001 [source]


    Measured concentrations of combustion gases from the use of unvented gas fireplaces

    INDOOR AIR, Issue 5 2010
    P. W. Francisco
    Abstract, Measurements of combustion product concentrations were taken in 30 homes where unvented gas fireplaces were used. Measurements of CO, CO2, NOx, NO2, O2 (depletion), and water vapor were taken at 1-min interval. The analyzers were calibrated with certified calibration gases for each placement and were in operation for 3,4 days at each home. Measured concentrations were compared to published health-based standards and guidelines. The two combustion gases that exceeded published values were NO2 and CO. For NO2, the Health Canada guideline of 250 ppb (1-h average) was exceeded in about 43% of the sample and the World Health Organization (WHO) guideline of 110 ppb (1-h average) was exceeded in 80% of the sample. Carbon monoxide levels exceeded the U.S. EPA 8-h average standard of 9 ppm in 20% of the sample. Moisture problems were not evident in the test homes. An analysis of the distribution of CO showed that the CO is dispersed throughout the home almost immediately upon operation of the fireplace and that the concentrations throughout the home away from the immediate vicinity of the fireplace are 70,80% of the level near the fireplace. Decay analysis of the combustion gases showed that NO was similarly stable to CO and CO2 in the indoor environment but that both NO2 and water vapor were removed from the air at much greater rates. Practical Implications Previous studies on unvented gas fireplaces have made assumptions of how they are operated by users. This article presents the results of field monitoring of 30 unvented gas fireplaces under normal operation, regardless of whether users follow industry recommendations regarding installation, usage patterns, and maintenance. The monitoring found that health-based standards and guidelines were exceeded for CO in 20% of homes and for NO2 in most homes. There were no identified moisture problems in these homes. Nearly, half of the fireplaces were used at least once for longer than 2 h, counter to manufacturers' intended usage as supplemental heating. This demonstrates that given actual usage patterns and compared to current health-based thresholds, these appliances can produce indoor air concentrations considered to be unhealthy to at least sensitive or at-risk individuals. [source]


    Extended Lifetime of Organic Field-Effect Transistors Encapsulated with Titanium Sub-Oxide as an ,Active' Passivation/Barrier Layer

    ADVANCED MATERIALS, Issue 19 2009
    Shinuk Cho
    A thin capping layer of titanium sub-oxide (TiOx) prepared by sol,gel synthesis from titanium alkoxides extends the lifetime of organic FETs. The TiOx layer functions as an ,active' passivation/barrier layer that actually removes oxygen and water vapor from the organic semiconductor. The results demonstrate a significant improvement in the lifetime of organic field-effect transistors when exposed to air. [source]


    Controlled Etching of Carbon Nanotubes by Iron-Catalyzed Steam Gasification,

    ADVANCED MATERIALS, Issue 21 2007
    W. Xia
    A localized etching method based on catalytic steam gasification was developed to modify carbon nanotubes in a pre-determined manner. The etching, occurring only at the interface, created different etching patterns depending on the iron catalyst by means of an eco-friendly, low-cost process using water vapor. Both the surface roughness and the number of surface defects such as edge planes were significantly enhanced. [source]


    Kinetics and mechanism of the oxidation of carbon by NO2 in the presence of water vapor

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2009
    M. Jeguirim
    The kinetics and mechanism of the oxidation of carbon by NO2 in absence and presence of water vapor were studied in a fixed bed reactor. The rate of carbon oxidation by NO2 is enhanced in the presence of water vapor in the range of temperature 300,400C. The benefit effect of water is attributed to the intermediate formation of traces of nitric and nitrous acids, which enhance the rate of the carbon oxidation without modifying the global mechanism reaction. Therefore, water acts as a catalyst for the carbon oxidation by NO2. A kinetic mechanism derived from this parametric study shows a decrease in the activation energy of carbon oxidation by NO2 in the presence of water vapor. This result is in agreement with the experimental observation. 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 236,244, 2009 [source]


    Snow disappearance in Eastern Siberia and its relationship to atmospheric influences

    INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007
    Yoshihiro Iijima
    Abstract In the present study, we examine the climatological features and interannual variations in snow disappearance within the Lena River Basin, Eastern Siberia, during a recent 15-year period (1986,2000), and the relationship of snow disappearance to atmospheric conditions. According to the climatology of the day of the year on which snow disappears, the boundary of snow disappearance within the Lena River Basin migrates rapidly northward from mid-April until early June, with minimum interannual variation occurring in the middle part of the basin. In addition, the preceding snow disappearance is apparent in the central Lena River Basin. Melting of snow within the Lena River Basin commonly occurs within 30 days of complete snow disappearance under certain atmospheric conditions: daily mean air temperature in excess of , 10 C, greater than 2 hPa of water vapor pressure, and, hence, more than 170 W m,2 of downward longwave radiation under clear sky conditions. Composite analysis using a reanalysis dataset demonstrates that the increase in air temperature and water vapor that accompanies snow melting is due to wet (and warm) air advection in conjunction with enhanced water vapor convergence over the central Lena River Basin during the 30-day period prior to snow disappearance. Copyright 2006 Royal Meteorological Society. [source]


    The Planck,Benzinger thermal work function in the condensation of water vapor

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2006
    Paul W. Chun
    Abstract Based on the Planck,Benzinger thermal work function using Chun's method, the innate temperature-invariant enthalpy at 0 K, ,H0(T0), for the condensation of water vapor as well as the dimer, trimer, tetramer, and pentamer form in the vapor phase, was determined to be 0.447 kcal mol,1 for vapor, 1.127 for the dimer, 0.555 for the trimer, 0.236 for the tetramer, and 0.079 kcal mol,1 for the pentamer using ,G(T) data reported by Kell et al. in 1968 and Kell and McLaurin in 1969. These results suggest that the predominant dimeric form is the most stable of these n -mers. Using Nemethy and Scheraga's 1962 data for the Helmholtz free energy of liquid water, the value of ,H0(T0) was determined to be 1.21 kcal mol,1. This is very close to the value for the energy of the hydrogen bond EH of 1.32 kcal mol,1 reported by Nemethy and Scheraga, using statistical thermodynamics. It seems clear that very little energy is required for interconversion between the hypothetical supercooled water vapor and glassy water at 0 K. A hypothetical supercooled water vapor at 0 K is apparently almost as highly associated as glassy water at that temperature, suggesting a dynamic equilibrium between vapor and liquid. This water vapor condensation is highly similar in its thermodynamic behavior to that of sequence-specific pairwise (dipeptide) hydrophobic interaction, except that the negative Gibbs free energy change minimum at ,Ts,, the thermal setpoint for vapor condensation, where T,S = 0, occurs at a considerably lower temperature, 270 K (below 0C) compared with ,350 K. The temperature of condensation ,Tcond, at which ,G(T) = 0, where water vapor begins to condense, was found to be 383 K. In the case of a sequence-specific pairwise hydrophobic interaction, the melting temperature, ,Tm,, where ,G(Tm) = 0 was found to be 460 K. Only between two temperature limits, ,Th, = 99 K and ,Tcond, = 383 K, where ,G(Tcond) = 0, is the net chemical driving force favorable for polymorphism of glassy water and hypothetical supercooled water vapor. Analysis of the water vapor condensation process based on the Planck,Benzinger thermal work function confirms that a thermodynamic molecular switch occurs at 10 K, wherein a change of sign in [,Cp(T)]cond leads to a true negative minimum in the Gibbs free energy of vapor condensation, and hence a maximum in the related equilibrium constant, Kcond. 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


    Effect of EVA as compatibilizer on the mechanical properties, permeability characteristics, lamellae orientation, and long period of blown films of HDPE/clay nanocomposites

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
    Juliano Marini
    Abstract Two ethylene-vinyl acetate (EVA) resins with 19% (EVA19) and 28% (EVA28) of vinyl groups were used as compatibilizers for nanocomposites of high-density polyethylene (HDPE) and nanoclays. Two nanoclays were also used, one with a nonpolar surfactant (C15A) and another with a polar surfactant (C30B). The HDPE/EVA19/C15A formed an intercalated structure, while the HDPE/EVA28/C30B had surfactant loss. Blown films of these compositions were produced. A two-phase morphology made of HDPE and EVA/nanoclay particles was observed, which was responsible for the increase in water vapor and oxygen permeability rates of the films. The elastic modulus E along the transverse direction of the films was higher than along the machine direction due to preserved orientation given by the spiral die; the lamellae orientation was measured by small-angle X-rays diffraction. The highest E was observed in the HDPE/EVA19/C15A film due to stronger interactions. The long period of the HDPE lamellas was not affected by the presence of the EVA and nanoclay. A model was proposed to explain the improvement in elastic modulus due to the processing conditions and components' interactions. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Bio-hybrid nanocomposite coatings from sonicated chitosan and nanoclay

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
    Jari Vartiainen
    Abstract Nanocomposite films and coatings with improved properties were produced from ultrasonic dispersed chitosan and hydrophilic bentonite nanoclay. Bio-hybrid coatings were applied onto argon,plasma-activated LDPE coated paper. The intercalation of chitosan in the silicate layers was confirmed by the decrease of diffraction angles as the chitosan/nanoclay ratio increased. Nanocomposite films and multilayer coatings had improved barrier properties against oxygen, water vapor, grease, and UV-light transmission. Oxygen transmission was significantly reduced under all humidity conditions. In dry conditions, over 99% reduction and at 80% relative humidity almost 75% reduction in oxygen transmission rates was obtained. Hydrophilic chitosan was lacking the capability of preventing water vapor transmission, thus total barrier effect of nanoclay containing films was not more than 15% as compared with pure chitosan. Because to very thin coatings (,1 ,m), nanoclay containing chitosan did not have antimicrobial activity against test strains. All coating raw materials were "generally recognized as safe" (GRAS) and the calculated total migration was in all cases ,6 mg/dm2, thus the coatings met the requirements set by the packaging legislation. Processing of the developed bio-hybrid nanocomposite coated materials was safe as the amounts of released particles under rubbing conditions were comparable with the particle concentrations in a normal office environment. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Reliable production of highly concentrated bioethanol by a conjunction of pervaporation using a silicone rubber sheet-covered silicalite membrane with adsorption process

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004
    Toru Ikegami
    Abstract For the production of highly concentrated bioethanol by pervaporation using an ethanol-permselective silicalite membrane, pervaporation performance was investigated using a silicalite membrane entirely covered with a silicone rubber sheet to prevent direct contact with acidic compounds. By using a resistance model for membrane permeation, the separation factor of the covered silicalite membrane towards ethanol can be estimated from the individual pervaporation performances of the silicalite membrane and the silicone rubber sheet. No decrease in the ethanol concentration through the silicone rubber sheet-covered membrane was caused when ethanol solutions containing succinic acid were supplied. By directly passing the permeate-enriched ethanol vapor mixed with water vapor through a dehydration column packed with a molecular sieve of pore size 0.3 nm, highly concentrated bioethanol up to 97% (w/w), greater than the azeotropic point in the ethanol/water binary systems, can be obtained from 9% (w/w) fermentation broth. Copyright 2004 Society of Chemical Industry [source]


    MASS TRANSFER IN PACIFIC HAKE (Merluccius australis) PACKED IN REFRIGERATED MODIFIED ATMOSPHERE

    JOURNAL OF FOOD PROCESS ENGINEERING, Issue 6 2001
    R. SIMPSON
    ABSTRACT The objective of this research was to develop, and experimentally validate a fully mathematical model, to predict mass transfer phenomena in Pacific Hake (Merluccius australis) packed in refrigerated modified atmosphere. A mathematical model to predict mass transfer of CO2, O2, N2 and water vapor was developed and validated. The diffusion model was developed utilizing Fick's second law, considering fish fillet as an infinite slab and applied to Pacific Hake (lean fish species) under refrigeration conditions. CO2 diffusivity of Pacific Hake was determined by an inverse procedure at OC and resulted in a value of 5.19 10,10 [m2/s] that is in accordance with values reported in the literature. However, postmortem variations of pH could affect solubility and diffusivity of CO2 in fish muscle. [source]


    Evaluation of the Genotoxicity of Chitosan Nanoparticles for Use in Food Packaging Films

    JOURNAL OF FOOD SCIENCE, Issue 6 2010
    Renata De Lima
    Abstract:, The use of nanoparticles in food packaging has been proposed on the basis that it could improve protection of foods by, for example, reducing permeation of gases, minimizing odor loss, and increasing mechanical strength and thermal stability. Consequently, the impacts of such nanoparticles on organisms and on the environment need to be investigated to ensure their safe use. In an earlier study, Moura and others (2008a) described the effect of addition of chitosan (CS) and poly(methacrylic acid) (PMAA) nanoparticles on the mechanical properties, water vapor, and oxygen permeability of hydroxypropyl methylcellulose films used in food packaging. Here, the genotoxicity of different polymeric CS/PMAA nanoparticles (size 60, 82, and 111 nm) was evaluated at different concentration levels, using the,Allium cepa,chromosome damage test as well as cytogenetic tests employing human lymphocyte cultures. Test substrates were exposed to solutions containing nanoparticles at polymer mass concentrations of 1.8, 18, and 180 mg/L. Results showed no evidence of DNA damage caused by the nanoparticles (no significant numerical or structural changes were observed), however the 82 and 111 nm nanoparticles reduced mitotic index values at the highest concentration tested (180 mg/L), indicating that the nanoparticles were toxic to the cells used at this concentration. In the case of the 60 nm CS/PMAA nanoparticles, no significant changes in the mitotic index were observed at the concentration levels tested, indicating that these particles were not toxic. The techniques used show promising potential for application in tests of nanoparticle safety envisaging the future use of these materials in food packaging. [source]


    Influence of Exposure to Light on the Sensorial Quality of Minimally Processed Cauliflower

    JOURNAL OF FOOD SCIENCE, Issue 1 2007
    Susana Sanz Cervera
    ABSTRACT:, The impact of lighting on minimally processed cauliflower packaged in 4 different film types (PVC and 3 P-Plus) has been measured and quantified. The effect on the sensorial quality of storage at 4 C in darkness and partial or continuous lighting was evaluated. The gas concentrations in the packages and the weight losses were also determined. Atmosphere composition inside the packages depended on both the permeability of the film used for the packaging and exposure to light. Samples stored with lighting maintained the gaseous exchange between plant tissue and the atmosphere inside the packages for longer periods than in samples kept in darkness. This prompted a greater loss of water vapor as well as the development of atmospheres with low levels of O2 and high levels of CO2 in the samples packed with less permeable films. The most important aspect in sensory evaluation was color. In instrumental color evaluation, coordinates h* and L* were the main means for estimating color evolution. The presence of light accelerated browning in the cut zones. The development of abnormal coloring in these areas marked the end of shelf life for minimally processed cauliflower. Among the sensory attributes studied, color was the most affected by exposure to light. Samples packed in P-Plus 120 film displayed the lowest level of color deterioration in the cut zones. However, under lit conditions, the low permeability of this film caused atmospheres with very low O2 contents and high CO2 contents. These atmospheres produced a loss of texture and the development of off-odors. [source]


    Lipid Addition to Improve Barrier Properties of Edible Starch-based Films and Coatings

    JOURNAL OF FOOD SCIENCE, Issue 6 2000
    M.A. Garca
    ABSTRACT: Effects of formulation (lipid presence, type of starch, and plasticizer) on microstructure, water vapor (WVP) and gas (GP) permeabilities of films and coatings were analyzed. Plasticizer was necessary to maintain film and coating integrity and to avoid pores and cracks. Films made from high amylose starch showed lower WVP and GP than regular corn starch films; permeabilities of films with sorbitol (20 g/L) were lower than those with glycerol. The addition of 2g/L sunflower oil to the formulations decreased WVP of starch-based films; X-ray diffraction and Differential Scanning Calorimetry experiments demonstrated that films with plasticizer and lipid showed lower crystalline-amorphous ratio compared to films without additives. Microstructural observations helped explain the decrease of the film permeabilities during storage. [source]


    Four beds pressure swing adsorption for hydrogen purification: Case of humid feed and activated carbon beds

    AICHE JOURNAL, Issue 9 2009
    Ana M. Ribeiro
    Abstract The novelty of this manuscript is the study of purification of hydrogen from a mixture of H2/CO2/CH4/CO/N2 saturated in water vapor. Simulations results of fixed bed behavior and of an eight steps PSA process are presented using an activated carbon as adsorbent. Several operating conditions were considered, namely different feed flow rates, humid/dry feed and adiabatic/nonadiabatic operation. Simulation with single column PSA showed that a 99.9979% purity hydrogen stream could be obtained with a recovery of 71.3% and a productivity of 63.9 mol/kgads/day. The simulation of a four columns PSA predicted a decrease in H2 purity to 99.8193% for the same operating conditions, due to the impurities present in the recycled stream of the continuous multicolumn process. To increase the hydrogen purity above 99.99%, the feed time was decreased 25%. Thus, the multicolumn simulation predicted a hydrogen recovery, purity, and productivity, respectively, of 62.7%, 99.9992%, and 55.2 mol/kgads/day. 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


    Limitations of amorphous content quantification by isothermal calorimetry using saturated salt solutions to control relative humidity: Alternative methods

    JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2010
    Nawel Khalef
    Abstract Despite the high sensitivity of isothermal calorimetry (IC), reported measurements of amorphous content by this technique show significant variability even for the same compound. An investigation into the reasons behind such variability is presented using amorphous lactose and salbutamol sulfate as model compounds. An analysis was carried out on the heat evolved as a result of the exchange of water vapor between the solid sample during crystallization and the saline solution reservoir. The use of saturated salt solutions as means of control of the vapor pressure of water within sealed ampoules bears inherent limitations that lead in turn to the variability associated with the IC technique. We present an alternative IC method, based on an open cell configuration that effectively addresses the limitations encountered with the sealed ampoule system. The proposed approach yields an integral whose value is proportional to the amorphous content in the sample, thus enabling reliable and consistent quantifications. 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2080,2089, 2010 [source]


    Michael Polanyi and the discovery of co-catalysis: Discussion of an autobiographical letter from Michael Polanyi, FRS to Peter H. Plesch of 17 December 1963

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004
    P. H. Plesch
    Abstract The origin of this memoir was a letter from Michael Polanyi (M. P.) to the present writer (P. H. P.) about their researches in the mid-1940s into the mechanism of what are now called cationic polymerizations, at the University of Manchester (England). M. P. analyzes his tactics and the mistakes made in directing this research. When the Manchester-trained researchers made little progress with what was a very recalcitrant problem, M. P. thinking that scientists from a different background might be more sucessful, got P. H. P., from Cambridge, to work with an Oxford-trained chemist. They recognized that the likely cause of the irreproducibility of these polymerizations was the apparatus used which permitted access of atmospheric moisture to the reaction mixtures containing the moisture-sensitive catalytic metal halides. Because the only method for following the very fast polymerizations was by monitoring the accompanying temperature rise, and the reactions had to be done below ambient temperature, the reaction vessel needed to be adiabatic, that is a Dewar (Thermos) flask; hence the problem of how to cool its contents. The solution was P. H. P.'s invention of the pseudo-Dewar vessel, the Dewar space of which, instead of being evacuated permanently, could be filled with air or evacuated. This device permitted the reaction mixture to be made up and cooled, and the reactions to be started without contact with the atmosphere. Thus it was found that isobutene polymerizations, which had stopped unaccountably, could be restarted by water vapor. P. H. P. termed water a "co-catalyst". The consequent "Manchester" theory recognized the monohydrate of TiCl4 as a protonic acid and saw the initiation as due to the protonation of the monomer, with the formation of a tert -carbenium ion, and these ions, formed repetitively, became the propagating species. The Manchester theory was rapidly accepted because it could also explain observations on other related reactions. The involvement of ions established a link with non-aqueous electrochemistry. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1537,1546, 2004 [source]


    Simple sample transfer technique by internally expanded desorptive flow for needle trap devices

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2008
    In-Yong Eom
    Abstract Needle trap devices (NTDs) are improving in simplicity and usefulness for sampling volatile organic compounds (VOCs) since their first introduction in early 2000s. Three different sample transfer methods have been reported for NTDs to date. All methods use thermal desorption and simultaneously provide desorptive flow to transfer desorbed VOCs into a GC separation column. For NTDs having ,side holes', GC carrier gas enters a ,side hole' and passes through sorbent particles to carry desorbed VOCs, while for NTD not having a ,side hole', clean air as desorptive flow can be provided through a needle head by a air tight syringe to sweep out desorbed VOCs or water vapor has been reported recently to be used as desorptive flow. We report here a new simple sample transfer technique for NTDs, in which no side holes and an external desorptive flow are required. When an NTD enriched by a mixture of benzene, toluene, ethylbenzene, and xylene (BTEX) or n -alkane mixture (C6,C15) is exposed to the hot zone of GC injector, the expanding air above the packed sorbent transfers the desorbed compounds from the sorbent to the GC column. This internal air expansion results in clean and sharp desorption profiles for BTEX and n -alkane mixture with no carryover. The effect of desorption temperature, desorption time, and overhead volumes was studied. Decane having vapor pressure of ,1 Torr at 20C showed ,1% carryover at the moderate thermal desorption condition (0.5 min at 250C). [source]


    Surface Enthalpy, Enthalpy of Water Adsorption, and Phase Stability in Nanocrystalline Monoclinic Zirconia

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009
    A. V. Radha
    A fundamental issue that remains to be solved when approaching the nanoscale is how the size induces transformation among different polymorphic structures. Understanding the size-induced transformation among the different polymorphic structures is essential for widespread use of nanostructured materials in technological applications. Herein, we report water adsorption and high-temperature solution calorimetry experiments on a set of samples of single-phase monoclinic zirconia with different surface areas. Essential to the success of the study has been the use of a new ternary water-in-oil/water liquid solvothermal method that allows the preparation of monoclinic zirconia nanoparticles with a broad range of (BET) Brunauer,Emmett,Teller surface area values. Thus, the surface enthalpy for anhydrous monoclinic zirconia is reported for the first time, while that for the hydrous surface is a significant improvement over the previously reported value. Combining these data with previously published surface enthalpy for nanocrystalline tetragonal zirconia, we have calculated the stability crossovers between monoclinic and tetragonal phases to take place at a particle size of 28 6 nm for hydrous zirconia and 34 5 nm for anhydrous zirconia. Below these particle sizes, tetragonal hydrous and anhydrous phases of zirconia become thermodynamically stable. These results are within the margin of the theoretical estimation and confirm the importance of the presence of water vapor on the transformation of nanostructured materials. [source]


    Water Vapor Corrosion Behavior of Scandium Silicates at 1400C

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009
    Zhiliang Hong
    The corrosion behavior of scandium silicates with different scandia contents were investigated in an atmosphere of 50%H2O,50%O2 water vapor with a total pressure of 1 atm at 1400C. The weight changes of scandium silicates as a function of annealing time were recorded to illustrate the corrosion behavior of these materials. The phases of as-prepared and corroded materials were compared by using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the water vapor does not corrode the scandium disilicate. The weight gain during corrosion is attributed to the hydroxylation of free scandia. [source]


    Low-Temperature Aging Behavior of Alumina-Toughened Zirconia

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008
    Jens Schneider
    The corrosion of alumina-toughened zirconia (ATZ) as a consequence of hydrothermal treatment was investigated, especially the transformation kinetics from tetragonal zirconia to the monoclinic phase. For this purpose, polished ATZ specimens (Ra<5 nm) were aged in water vapor at different temperatures ranging from 70 to 134C. The fraction of the monoclinic phase was determined using X-ray diffraction and Rietveld refinement. The isothermal transformation curves obtained were fitted to the Mehl,Johnson,Avrami equation by least squares. An Arrhenius plot of the fitted transformation rates was used to determine the activation energy and the pre-exponential factor. Following this procedure, the kinetic parameters of the phase transformation were extrapolated down to body temperature and the formation of the monoclinic phase was simulated. In addition, optical interferometry on well-polished specimens (Ra<2 nm) was alternatively used to calculate the monoclinic fraction from the histogram dataset. The results agree very well with those of the X-ray measurements. Additionally, the development of surface roughness with increasing aging time is discussed. [source]


    Sintering Behavior of Gehlenite.

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007
    Macro-/Mesoporous Gehlenite, Mechanical, Microstructure, Part I: Self-Forming, Physical Properties, Pore-Forming Mechanism
    A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaOAl2O3SiO2) ceramic (abbreviated C2AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore self-forming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore self-forming ability over a very wide range of temperature from 900 to 1450C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C2AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C2AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 ,m, corresponding to a porosity of 75%,80%, respectively. The porous ceramic can preserve nanometer-sized (26,50 nm) crystallites up to 1000C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 1000C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied. [source]


    Alumina Volatility in Water Vapor at Elevated Temperatures

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004
    Elizabeth J. Opila
    The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250 and 1500C, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process. [source]


    Oxidation and Volatilization of Silica Formers in Water Vapor

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003
    Elizabeth J. Opila
    At high temperatures, SiC and Si3N4 react with water vapor to form a SiO2 scale. SiO2 scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming SiO2 and the other removing SiO2, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved. After steady state is achieved, the oxide found on the surface is a constant thickness, and recession of the underlying material occurs at a linear rate. The steady-state oxide thickness, the time to achieve steady state, and the steady-state recession rate can be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate also can be determined from parameters that describe a water-vapor-containing environment. Accordingly, maps have been developed to show these steady-state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of SiO2 formers in water-vapor-containing environments, such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4. [source]