Thermal properties of pressure sintered alumina–graphene composites

Journal of Thermal Analysis and Calorimetry - The work concerns the alumina–graphene materials sintered by two different pressure methods. The different particle sizes of graphene were used....     

Investigation of the electrokinetic properties of paraffin suspension. 2. In cationic and anionic surfactant solutions

Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential.     

Study of the winter and summer changes of the air composition in the church of Szalowa, Poland, related to conservation

The St. Michael Archangel’s Church in Szalowa, Poland, was selected for closer investigation with respect to the indoor/outdoor air exchange and its influence on the air quality and work arts preservation. Chemical composition, size and abundance of particulate matter and concentration of gases NO₂, SO₂, O₃ inside and outside the church were determined. To study seasonal variation of the weather condition (temperature, inversion level, wind direction) and the influence of seasonal sources of the air pollution (like heating of the nearby houses), samples were collected in winter and summer time. It was stated that suspended particulate matter inside the wooden church has in general an outdoor source. Several groups of particles were distinguished such as the organic ones, soil dust, nitrates and sulphates. In case of organic and soil dust particles, the concentration inside was higher than outside. From the results, in comparison to literature data, one can conclude that accumulation of particulate suspended matter in the church is more intense than in other types of buildings. Gaseous pollutants were detected but their concentration was negligible.     

Structure of mercaptobiphenyl monolayers on mercury

The molecular-scale structure and phase behavior of single-component Langmuir films of 4'-methyl-4-mercaptobiphenyl (MMB) and 4'-perfluoromethyl-4-mercaptobiphenyl (FMMB) on mercury were studied using surface tensiometry, grazing incidence X-ray diffraction, and X-ray reflectivity. At low coverages, a condensed but in-plane disordered single layer of surface-parallel molecules is found for both compounds. At high coverages, both compounds exhibit in-plane-ordered phases of standing-up molecules. For MMB, the biphenyl core dominates the structure, yielding a centered-rectangular unit cell with an area A(x) of 21.8 A(2)/molecule, with molecules tilted by approximately 14 degrees from the surface normal in the nearest-neighbor direction, and a coherence length xi of >1000 A for the crystalline domains. For FMMB, the perfluoromethyl group dominates the structure, yielding a hexagonal unit cell with untilted molecules, an area A(x) of 24.2 A(2)/molecule, and a much smaller xi of approximately 110 A. The structure is discussed in comparison with self-assembled monolayers of MMB on crystalline Au(111) and similar-length alkanethiolate SAMs on Au(111) and on mercury. The differences in the structure are discussed and traced to the differences in the substrate's surface structure, and in the molecular cross section and rigidity.     

A new route to alumoxane gel: a versatile precursor to gamma-alumina and alumina-based ceramic oxides

We present a new route for the preparation of gamma-alumina and YAG nanoparticles. Metal salts of ethylhexanoic acids provide good solubility in hydrocarbon solvents and allow efficient ultrasonication. The sonication product is an alumioxane gel, which can reversibly collapse and reform, depending on the solvent used. The dried gel nanoparticles are calcined at temperatures significantly lower than those used in conventional syntheses, resulting in gamma-alumina nanoparticles. This is due to the complete mixing of elements at the atomic level and the small size of the formed nanoparticles.     

The centralizer near-ring of an inverse semigroup of endomorphisms of a group

Let G be a group and S an inverse semigroup of endomorphisms of G. The simplicity of the centralizer near- ring MS(G) = {fε M(G)‖foα = αo f, ?αεS} is characterized. The necessary and sufficient conditions are given for simplicity of M_s(G) in terms of the structure of G and S.     

Mechanism of adsorption in cylindrical nanopores: the roles of fluctuations and correlations in stabilizing the adsorbed phase

The mechanism of the adsorption in nanometric cylindrical pores has been studied using grand canonical Monte Carlo simulations. The results have been analyzed from the point of view of microscopic correlations. It has been shown that the correlations between the energy components and between the energy and the number of adsorbed particles provide crucial information concerning the microscopic mechanism of the formation of adsorbed layers. Typical susceptibility functions have been calculated. They give the relations between the statistical correlations and the stability of the adsorbed system in different stages of adsorption. The numerical calculations have been carried out for Kr atoms adsorbed in an MCM-41 model porous material with pores of diameter d = 4 nm. The smooth-wall model as well as the model of a wall with micropores have been discussed.     

Preliminary thermal characterization of natural resins from different botanical sources and geological environments

The preliminary studies on thermal behavior of differently aged natural resins from Russia (Khatanga), Dominican Republic (El Valle), Colombia and Poland (Jantar) were performed. Thermal stability and behavior under elevated temperature were investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC), while the differences in the structure and composition by FT-IR spectroscopy. Analyzed resins show different thermal effects during heating suggesting that possible post-reactions and structural changes occurred. TG results indicated that Dominican, Russian and Colombian resins present relatively high thermal stability under air conditions in the range of 228–300 °C, whereas the mass loss of 5mass% at about 217 °C was observed for Baltic amber. During DSC experiments, the analyzed resins expose thermal events which make impossible determination of glass transition temperature in a raw sample. The results indicate that both TG and DSC cannot be considered as methods for age dating of natural resins and more advanced techniques should be applied. Careful analysis of FT-IR data in the carbonyl region may provide additional information about the composition and history of the natural resin.