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Thermodynamic Considerations (thermodynamic + consideration)
Selected AbstractsThermodynamic Consideration on Solid Transition of CdSe Nanocrystals Induced by Pressure.CHEMINFORM, Issue 7 2004Q. Jiang No abstract is available for this article. [source] Thermodynamic Considerations in Solid Adsorption of Bound Solutes for Patient Support in Liver FailureARTIFICIAL ORGANS, Issue 7 2008John F. Patzer II Abstract:, New detoxification modes of treatment for liver failure that use solid adsorbents to remove toxins bound to albumin in the patient bloodstream are entering clinical evaluations, frequently in head-to-head competition. While generally effective in reducing toxin concentration beyond that obtainable by conventional dialysis procedures, the solid adsorbent processes are largely the result of heuristic development. Understanding the principles and limitations inherent in competitive toxin binding, albumin versus solid adsorbent, will enhance the design process and, possibly, improve detoxification performance. An equilibrium thermodynamic analysis is presented for both the molecular adsorbent recirculating system (MARS) and fractionated plasma separation, adsorption, and dialysis system (Prometheus), two advanced systems with distinctly different operating modes but with similar equilibrium limitations. The Prometheus analysis also applies to two newer approaches: sorbent suspension reactor and microsphere-based detoxification system. Primary results from the thermodynamic analysis are that: (i) the solute,albumin binding constant is of minor importance to equilibrium once it exceeds about 105 L/mol; (ii) the Prometheus approach requires larger solid adsorbent columns than calculated by adsorbent solute capacity alone; and (iii) the albumin-containing recycle stream in the MARS approach is a major reservoir of removed toxin. A survey of published results indicates that MARS is operating under mass transfer control dictated by solute,albumin equilibrium in the recycle stream, and Prometheus is approaching equilibrium limits under current clinical protocols. [source] ChemInform Abstract: MgCl and Mg2Cl2: From Theoretical and Thermodynamic Considerations to Spectroscopy and Chemistry of Species with Mg,Mg Bonds.CHEMINFORM, Issue 3 2009Ralf Koeppe 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] Evaluation of initiator systems for controlled and sequentially curable free-radical/cationic hybrid photopolymerizationsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005Joe D. Oxman Abstract Free-radical/cationic hybrid photopolymerizations of acrylates and epoxides were initiated using a three-component initiator system comprised of camphorquinone as the photosensitizer, an amine as the electron donor, and a diaryliodonium salt. Thermodynamic considerations revealed that the oxidation potential of the electron donor must be less than 1.34 V relative to SCE for electron transfer with the photoexcited camphorquinone to take place. This electron transfer leads to the production of the active centers for the hybrid polymerization (two radicals and a cation). Further investigation revealed that only a subset of electron donors that meet the oxidation potential requirement resulted in polymerization of the epoxide monomer; therefore, a second requirement for the electron donor (pKb higher than 8) was established. Experiments performed using a combination of electron donors revealed that the onset of the hybrid system's cationic polymerization can be advanced or delayed by controlling the concentration and composition of the electron donor(s). These studies demonstrate that a single three-component initiator system can be used to initiate and chemically control the sequential curing properties of a free-radical/cationic hybrid photopolymerization and is a viable alternative to separate photoinitiators for each type of polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1747,1756, 2005 [source] Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas BuffersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006Abdul-Majeed Azad High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source] Morphology prediction of ternary polypropylene composites containing elastomer and calcium carbonate nanoparticles fillerJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007C. G. Ma Abstract In this work, the morphology was studied in ternary composites of polypropylene (PP) with nanosized calcium carbonate (nano-CaCO3) fillers and elastomer inclusions and the thermodynamic consideration was used to analyze the formation of phase structure of the composites. The wetting coefficient (,a), interfacial tension (,AB), and work of adhesion (WAB) were calculated to predict dispersion state of nano-CaCO3 fillers. A comparison of the prediction and SEM analysis was given. The results show that three types of phase structures were formed: an encapsulation of the filler by elastomer, a separate dispersion of the filler and elastomer, and a particular structure of the filler at the PP/elastomer interface. The predictions by ,a were all successfully supported-up by SEM analysis and the predictions by WAB were however trustless. Both ,AB and WAB can predict a separate dispersion or an encapsulation phase structure, but they were not available for the particular structure of the filler at the PP/elastomer interface. ,a was competent and favored for the prediction of all three types of morphology among the three parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1578,1584, 2007 [source] Dielectric studies of molecular motions in amorphous solid and ultraviscous acetaminophenJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2005G.P. Johari Abstract The dielectric permittivity and loss spectra of glassy and ultraviscous states of acetaminophen have been measured over the frequency range 10 Hz,0.4 MHz. The relaxation spectra show an asymmetric distribution of times expressed in terms of the Kohlrausch exponent, ,, which remains constant at 0.79,±,0.02 over the 305,341 K range. The dielectric relaxation time increases on cooling according to the Vogel,Fulcher,Tammann equation. However, the values of the parameters are considerably different from the values deduced from earlier work by other researchers using the heat capacity of ultraviscous acetaminophen and relating it to its molecular mobility. The calorimetric glass softening temperature of 296 K obtained from differential scanning calorimetry is close to the value measured from dielectric relaxation. The equilibrium permittivity of ultraviscous acetaminophen decreases on heating like that of a normal dipolar liquid, as anticipated from the Curie law. But, its value decreases rapidly with time when it begins to crystallize. The equilibrium permittivity of this crystal phase is ,3.1 at 300 K and increases with temperature, which indicates a partial, orientational-disordering of its structure. The results show limitations of the procedures used in the modeling of the kinetics of molecular motions, that is, estimating physical stability, using thermodynamic considerations based on thermal analyses of the amorphous solid phase of acetaminophen. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2207,2223, 2005 [source] Studies on nylon-6/EVOH/clay ternary compositesPOLYMER COMPOSITES, Issue 1 2006N. Artzi Nylon-6 (Ny-6)/EVOH blends are interesting host multiphase systems for incorporation of low clay contents. The Ny-6/EVOH blend is a unique system, which tends to chemically react during melt-mixing, affecting thermal, morphological and mechanical properties of the ternary systems containing clay. The addition of clay seems to interrupt the chemical reaction between the host polymers at certain compositions, leading to lower blending torque levels when clay is added. A competition between Ny-6 and EVOH regarding the intercalation process takes place. Ny-6 seems to lead to exfoliated structure, whereas EVOH forms intercalated structure, as revealed from XRD and TEM analyses, owing to thermodynamic considerations and preferential localization of the clay in Ny-6. Hence, the ternary systems have combined intercalated and delaminated morphology or complete exfoliated morphology depending on blend composition and clay content. Selective extraction experiments (gel content) indicate the formation of chemical reaction between the Ny-6 and EVOH, and give an indirect indication of the polymer content residing in the galleries. The thermal properties of the polymers were found to be affected by the occurrence of chemical reaction, the level of intercalation and exfoliation and plasticizing effect of the low molecular weight onium ions treating the clay. Of special interest is the increased storage modulus attained upon the addition of only 1.5 wt% clay. POLYM. COMPOS. 27:15,23, 2006. © 2005 Society of Plastics Engineers [source] Precursor-derived Si,(B,)C,N ceramics: thermolysis, amorphous state and crystallization,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2001Joachim Bill Abstract The preparation of silicon nitride- and carbide-based ceramics by solid-state thermolysis of polysilazanes and polysilylcarbodiimides is described. Results on the ceramization of the preceramic compounds and the architecture of the corresponding amorphous states obtained by spectroscopic means and by X-ray and neutron scattering are reviewed. Fundamental correlations between the composition and structure of the preceramic compounds and the architecture of the amorphous state are revealed. Furthermore, the crystallization behavior of the amorphous precursor-derived Si,C,N ceramics is treated. Moreover, the influence of boron on the thermal stability of the amorphous state is described. The high-temperature behavior of these Si,B,C,N solids can be correlated with their phase composition. Ceramic materials with compositions located close to the three-phase equilibrium SiC,+,BN,+,C exhibit a high temperature stability up to 2000,°C. This effect is accompanied by the formation of a metastable solid consisting of Si3N4 and SiC nanocrystals that are embedded in a turbostratic B,C,N matrix phase. Based on thermodynamic considerations, a model for the high-temperature stability effect is proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Recent Advances in CO2 Capture and UtilizationCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 11 2008Kerry Yu Dr. Abstract Energy and the environment are two of the most important issues this century. More than 80,% of our energy comes from the combustion of fossil fuels, which will still remain the dominant energy source for years to come. It is agreed that carbon dioxide produced from the combustion process to be the most important anthropogenic greenhouse gas leading to global warming. Atmospheric CO2 concentrations have indeed increased by almost 100,ppm since their pre-industrial level, reaching 384,ppm in 2007 with a total annual emission of over 35,Gt. Prompt global action to resolve the CO2 crisis is therefore needed. To pursue such an action, we are urged to save energy without the unnecessary production of carbon emissions and to use energy in more efficient ways, but alternative methods to mitigate the greenhouse gas have to be considered. This Minireview highlights some recent promising research activities and their prospects in the areas of carbon capture and storage and chemical fixation of CO2 in constructing a future low-carbon global economy with reference to energy source, thermodynamic considerations, net carbon emissions and availability of reagents. [source] | |||||||||||||