Hydrophobicity effects in the condensation of water films on quartz

The surface forces of thin water films condensed onto crystalline quartz plates have been investigated by ellipsometric measurements of film thickness as a function of disjoining pressure. Quartz substrates ranging from fully hydroxylated (contact angle − 0°) to completely dehydroxylated (contact angle − 45°) were used and the results obtained related to the theoretically predicted van der Waals and electrostatic forces present in the system. Water films on fully hydroxylated quartz are much thicker than expected, whereas films on fully dehydroxylated quartz are close to the Lifschitz prediction of dispersion forces. As the extent of dehydroxylation decreases, the adsorption isotherm approaches that obtained on fully hydroxylated quartz.     

Thermal characterization of HCN polymers by TG-MS, TG, DTA and DSC methods

This paper presents a thermogravimetry (TG) study of hydrogen cyanide polymers, synthesized from the reaction of equimolar aqueous solutions of sodium cyanide and ammonium chloride. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were also used to evaluate the thermal behaviour of these black polymers, which play an important role in prebiotic chemistry. A coupled TG-mass spectrometer (MS) system allowed us to analyze the principal volatile thermal decomposition and fragmentation products of the isolated HCN polymers under dynamic conditions and an inert atmosphere. After dehydration, a multi-step decomposition occurred in this particular polymeric system, due to the release of ammonia, hydrogen cyanide (depolymerization reaction), isocyanic acid (or cyanic acid) and formamide; these two latter species allow us identify bond connectivities. Finally, data collected from TG experiments in an oxidative atmosphere showed significant differences at higher temperatures, above 400 °C. According to these results, the different techniques of thermal analysis here applied have demonstrated to be an adequate methodology for the study and characterization of this complex macromolecular system, whose structure remains controversial even today.     

Thermal properties of xenon adsorbed on graphite

We report theoretical results for dynamical and thermodynamic properties of the bare graphite (0001) surface, and with a physisorbed monolayer of xenon. The surface vibrations of graphite are less pronounced than those in more isotropic crystals. The surface-excess specific heat of the bare surface peaks at 45 K, that of the xenon at 13.5 K.     

Formation of B-C-N Ceramics Investigated by Emanation Thermal Analysis, TG and DTA

Processes taking place during formation of B-C-N ceramics by thermal treatment of organic precursors were investigated using emanation thermal analysis (ETA), differential thermal analysis (DTA) and thermogravimetry (TG). An additional information about thermal behavior of precursors used for preparation of BC4N, BN and CNx ceramic systems by heating in argon up to 1100°C was obtained. The ETA enabled us to characterize microstructure changes in the samples at in situ conditions of thermal treatment. A good agreement of ETA, TG and DTA results was found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal study of date kernels via TG and DTA

Thermal analyses was performed on Egyptian date kernels to assess the value of the products as possible sources of valuable compounds. It also furnished technical data necessary for determination of the optimum degree of temperature for the design and operation of units for the pyrolytic processing of date kernels.Two different sets of experiments were carried out, involving thermogravimetry (TG) and differential thermal analysis (DTA).The TG results revealed a purely kinetically controlled, first-order reaction. The activation energy and the Arrhenius constant were 8.17 kJ/mol and 0.0115 min^–1, respectively.The DTA results indicated the nature of the reactions involved in the pyrolysis and the corresponding products.

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Zusammenfassung Ägyptische Dattelkerne wurden thermisch untersucht, um die Möglickkeit einer Verwendung als Quellen für wertvolle Verbindungen zu ergründen. Außerdem wurden technische Daten ermittelt, die zur Festlegung der Optimumtemperatur für die Gestaltung und den Betrieb der Geräte zur pyrolytischen Behandlung von Dattelkernen benötigt werden. Es wurden zwei Versuchsreihen durchgeführt, bei denen einerseits Thermogravimetrie (TG) und andererseits Differentialthermoanalyse (DTA) Anwendung fand. Die TG Ergebnisse eröffnen eine rein kinetisch kontrollierte Reaktion erster Ordnung. Die Aktivierungsenergie und die Arrheniuskonstante betrugen 8,17 kJ/mol bzw. 0,0115 min^–1. DTA Resultate gaben Auskunft über den Charakter und Reaktionsprodukte der Reaktionen bei der Pyrolyse.

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The authors wish to express their sincere appreciation to Prof. Dr. S. G. Serag El-Din, Professor of the Chemical Engineering Department, Cairo University, and Dr. H. H. Abou El-Naga, Manager of Analytical and Research Centre, Misr Petroleum Company, for their sincere and helpful co-operation.     

Viscoelastic properties of cationic starch adsorbed on quartz studied by QCM-D

The adsorption and viscoelastic properties of layers of a cationic polyelectrolyte (cationic starch, CS, with 2-hydroxy-3-trimethylammoniumchloride as the substituent) adsorbed from aqueous solutions (pH 7.5, added NaCl 0, 1, 100, and 500 mM) on silica were studied with a quartz crystal microbalance with dissipation (QCM-D). Three different starches were investigated (weight-average molecular weights M(w) approximately 8.7 x 10(5) and 4.5 x 10(5) with degree of substitution DS = 0.75 and M(w) approximately 8.8 x 10(5) with DS = 0.2). At low ionic strength, the adsorbed layers are thin and rigid and the amount adsorbed can be calculated using the Sauerbrey equation. When the ionic strength is increased, significant changes take place in the amount of adsorbed CS and the viscoelasticity of the adsorbed layer. These changes were analyzed assuming that the layer can be described as a Voigt element on a rigid surface in contact with purely viscous solvent. It was found that CS with low charge density forms a thicker and more mobile layer with higher viscosity and elasticity than CS with high charge density. The polymers adsorbed on the silica even when the ionic strength was so high that electrostatic interactions were effectively screened. At this high ionic strength, it was possible to study the effect of molecular weight and molecular weight distribution of the CS on the properties of the adsorbed film. Increasing the molecular weight of CS resulted in a larger hydrodynamic thickness. CS with a narrow molecular weight distribution formed a more compact and rigid layer than broadly distributed CS, presumably due to the better packing of the molecules.     

Thermal characterization of asphalt mixtures by TG/DTG, DTA and FTIR

The quality of a road relies on the good use of the on road surface and its maintenance along the years. The technology used and the corrections contributes to the prevention of early road destructions. Pavement with polmyer and others additives exhibits greater resistance to rutting, thermal cracking, and decreased fatigue damage, stripping and temperature susceptibility. Samples of CAP 40, SBS 440/02, L 1861/04, L 784/05 and L 2000/04 were analyzed by thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and FTIR. Thermal characterizations showed that the main decomposition stage refers to asphaltenes and samples with additives exhibited a slight increase in thermal stability. The kinetic study, by Kissinger, showed that the sample with the highest stability was the SBS 440/02. Fourier transform infrared spectroscopy (FTIR) analysis suggested that these asphalt samples were originated from light oil.     

States of water adsorbed on perindopril crystals

The relationship between the structural state of adsorbed water, the crystal structure of the substances, and the solubility of the perindopril salt C₁₉H₃₂N₂O₅ · C₄H₁₁N in water was studied by IR spectroscopy and X-ray diffractometry. The high-frequency shift of the stretching vibrations of adsorbed water and the solubility depend on the crystal structure of the drug substance. A reversible chemical reaction occurred between the adsorbed water and the perindopril salt.     

Amino-acid and water molecules adsorbed on water clusters in a beam

Water clusters (H2On and (D2On (n相似文献   

Effect of adsorbed water on the electrorheology of silica suspensions

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η^*|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water.     

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.     

TG and DTA Study of the Thermal Dehydration of Metal-exchanged Zeolite-4A Samples

Zeolite-4A is a hydrated aluminosilicate which becomes more hydrated when exchanged with transition metals. In this work, the dehydration kinetics of cobalt, nickel and copper(II)-exchanged zeolite-4A were studied by means of TG and DTA over the temperature range from 20 to 500°C, and the numbers of water molecules in the metal-exchanged zeolite samples were calculated. It was observed that, as the ionic radius of the hydrated metal increased, the number of water molecules also increased. The loss of water from the zeolite samples generally occurred in the temperature range 100–300°C and was manifested in the DTA graphs by an extended endothermic effect. The DTA curves demonstrated that the peak position shifted towards lower temperatures as the metal concentration increased or, in other words, the water of hydration increased. The kinetic parameters (order of reaction and activation energy) were calculated via the Coats and Redfern method. The process of dehydration was found to follow first-order kinetics. This revised version was published online in August 2006 with corrections to the Cover Date.     

The adsorption of liquid water on the surface of quartz

Conclusions Liquid water has positive adsorption on the surface of quartz; the value of the specific adsorption decreases with increasing temperature, comprising 9·10^–10 g/cm² at 0° and 4·10^–10 g/cm² at 70°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1276–1280, June, 1972.     

Thermal behavior of aluminum powder and potassium perchlorate mixtures by DTA and TG

In this work the thermal decomposition characteristics of micron sized aluminum powder + potassium perchlorate pyrotechnic systems were studied with thermal analytical techniques. The results show that the reactivity of aluminum powder in air increases as the particle size decreases. Pure aluminum with 5 μm particle size has a fusion temperature about 647 °C, but this temperature for 18 μm powder is 660 °C. Pure potassium perchlorate has an endothermic peak at 300 °C corresponding to a rhombic-cubic transition, a fusion temperature around 590 °C and decomposes at 592 °C. DTA curves for Al₅/KClO₄ (30:70) mixture show a maximum peak temperature for thermal decomposition at 400 °C. Increasing the particle size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature increased by enhance in the aluminum content of the mixture.     

Thermal decomposition of silver cyano complex and characterization its decomposition products by ETA,DSC, DTA and TG

It was found by DTA and TG that [Phenyl₂I][Ag(CN)₂] in the solid state is chemically stable on heating in argon up to 160°C. During heating to higher temperatures it decomposes, forming volatile products such as [Phenyl]I, [Phenyl]NC and (CN)₂ [1]. After heating the sample to 500°C metallic silver resulted. The volatile and intermediate solid products were analysed by IR-spectroscopy.It was found by means of DTA and ETA that an isophase reversible transition takes place when the sample is heated and cooled, not higher than 100°C. At heating higher than 100°C the sample melts (melting pointT _m=135°C). The enthalpy melting was determined by means of DSC (H=–28 kJ·mol^–1).By means of ETA the disorder degree of the final decomposition product was estimated. The value of the activation energy of radon diffusion in the temperature range 720°–500°C equals 32.6 kJ·mol^–1.Dedicated to Prof. I. N. Bekman Moscow State University at the occasion of his 50th birthday     

Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina

Nanometric Fe₂O₃ particles could be inserted inside the internal pore volume of SBA-15 mesoporous silica and mesoporous alumina supports, when Fe(III) chelates (EDTA, gluconate or citrate) were used as impregnating precursors. The oxidative degradation of the chelating anions was followed by combined TG-DTA. Strong chelate-SiOH interactions (case of bulky EDTA), favored by the mesopore curvature, yield sub-nanometric extremely well dispersed Fe₂O₃ particles preferentially located at the micropore mouths (confinement effect). Fe₂O₃ even more strongly interacts with alumina walls, generating either (Fe,Al)₂O₃ mixed phases or Fe-aluminate micro domains. These iron-based mesoporous alumina composites proved very active catalysts in total oxidation of phenol at ambient conditions, with extremely low iron leaching (0.2%).