Intercalation and exchange reactions of clay minerals and non-clay layer compounds

Presently, a large variety of layered materials are synthesized that are able to intercalate neutral guest molecules or to exchange inorganic and organic ions for interlayer ions. Several of these materials are also found as minerals.The intracrystalline reactivity of a few selected compounds will be described and compared to clay minerals:

Polymeric phosphonium salts as a novel class of cationic biocides. V. Synthesis and antibacterial activity of polyesters releasing phosphonium biocides

Polyesters were prepared which retained phosphonium biocides as counter ions of sodium sulfonate moieties incorporated into the polymers, and surface antibacterial activity of the polyester films against Staphylococcus aureus and Escherichia coli was explored. These films exhibited a high surface antibacterial activity against S. aureus and E. coli, particularly against S. aureus, and the activity was affected by the structure and the compositional ratio of the phosphonium salts. Amount of the released phosphonium salts was very small, so that liberation of the phosphonium biocides can be expected to occur over a long period. Morphological changes of the cells of S. aureus and E. coli in contact with the polyester films were evaluated by scanning electron microscopy. It was found that the surface antibacterial activity of the polyester films was rather bacteriostatic than bactericidal as evidenced by no morphological changes of the bacterial cells in contact with the phosphonium biocides © 1993 John Wiley & Sons, Inc.     

Gas-Chromatographic Studies of the Interaction between Water and Methanol Molecules and the Surface of Carbon Materials

The gas-chromatographic method is used to study the interaction of water and methanol molecules with active hydrophilic centres existing at the surface of thermally exfoliated graphite and graphitized thermal carbon black. The concentration of carboxyl and phenol hydroxyl groups at the surface of these sorbents is determined, and heats of adsorption of the studied molecules are shown to be and 28−25 kJ/mol, respectively. It is also shown that adsorption of water at the hydrophilic centres at lowest relative pressure values takes place with formation of clusters consisting of n = 2 water molecules.     

The influence of minor components on the structural reorganization in glassforming materials

Correlation of structure parameters of glasses and related crystals formed in homogeneous or heterogeneous nucleation processes by thermal treatment is discussed on the basis of DTA, TG and EGA measurements in relation to the textural patterns of the materials. For cordierite glass, crystallization of metastable disordered cordierite polymorphs is related to an exothermic heat evolution and simultaneous with a small weight loss (appr. 0.025%). By MS-EGA, evolution of water was determined during the transformation of the metastable melt to a metastable intermediate crystalline phase. Interpretation of the crystallization by comparing the available structure parameters of cordierite glasses and crystals alone is insufficient to explain the role of water in the kinetics of crystallization. Optical and electron microscopy of the primary crystallization phenomena show the metastable solid solution with low quartz-type structure. Interpretation of the crystallization behaviour in terms of conventional theory of nucleation and crystal growth is impossible.     

Crystallite Nanosize Effect on the Structural Transitions of WO3 Studied by Raman Spectroscopy

Nanocrystallites of tungsten oxide samples of 2, 4, 16, 35 and 60 nm of diameter were prepared by cryosol and pyrosol techniques. The pressure- and temperature-induced phase transitions of these samples were monitored by Raman spectrometry from 0.1 MPa to 34 GPa and from 77 to 1200 K. The tetragonal (α)-orthorhombic (β)-monoclinic (γ) transitions in these nanometric samples are strongly downshifted in temperature by comparison with the bulk WO₃. For instance, the tetragonal phase which exists above 1171 K for the bulk tungsten oxide can be stabilized at 700 K for the 35 nm sample. In the same way, the monoclinic P2₁/n-monoclinic P2₁/c high-pressure-induced transition is slightly shifted from 0.1 GPa to a higher pressure (1.5 GPa). The discussion of these transition-line shifts is based on thermodynamic considerations in which the surface energy of crystallites plays an important role.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO_4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点。综述了锂离子电池正极材料LiFePO_4的研究进展。系统地阐述了LiFePO_4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望,并提出了下一步可能的研究趋势。     

Development of a chemical vapor sensor using piezoelectric quartz crystals with coated unusual lipids

Piezoelectric quartz crystal sensors were developed using lipids with various properties for highly sensitive detection of chemical vapors. Lipids with varying lengths of alkyl chains were coated onto 10 MHz AT-cut quartz crystal resonators and the response of these modified crystals to chemical vapors were measured. It was shown that hydrophilic compounds, such as ethanol and methanol, could be recognized efficiently by lipids having shorter alkyl chains, whereas lipids with longer alkyl chains showed affinity to more hydrophobic vapors, such as toluene, hexane and cyclohexane. Frequency changes caused by adsorption of alcohols could be enhanced when cholesterol was co-immobilized in the lipid layer. To confirm the assumption that the sensor-response might be affected by the properties of lipids derived from acyl chains, we have examined the effects of two types of newly synthesized unusual lipids on sensor response. When lipids having one triple bond each at different positions on their alkyl chains were coated onto quartz crystals separately, lower responses were observed compared to responses obtained for a sensor with immobilized, saturated phosphatidylcholine. Lipids containing -branched acyl chains, however, showed good affinity for organic vapors, and sensor responses improved 4–5-fold. Moreover, these sensors were shown to have sensitivity of the same order as the humans' sense of smell (10⁻⁵–10⁻⁶ w/w in liquid paraffin) when measured using standard odorants (isovaleric acid, skatole, etc.) for an olfactometry established in Japan.     

Rigid nanoscopic containers for highly dispersed, stable metal and bimetal nanoparticles with both size and site control

We demonstrate a novel strategy for the preparation of mesoporous silica-supported, highly dispersed, stable metal and bimetal nanoparticles with both size and site control. The supporting mesoporous silica, functionalized by polyaminoamine (PAMAM) dendrimers, is prepared by repeated Michael addition with methyl acrylates (MA) and amidation reaction with ethylenediamine (EDA), by using aminopropyl-functionalized mesoporous silica as the starting material. The encapsulation of metal nanoparticles within the dendrimer-propagated mesoporous silica is achieved by the chemical reduction of metal-salt-impregnated dendrimer-mesoporous silica by using aqueous hydrazine. The site control of the metal or bimetal nanoparticles is accomplished by the localization of inter- or intradendrimeric nanoparticles within the mesoporous silica tunnels. The size of the encapsulated nanoparticles is controlled by their confinement to the nanocavity of the dendrimer and the mesopore. For Cu and Pd, particles locate at the lining of mesoporous tunnels, and have diameters of less than 2.0 nm. For Pd/Pt, particles locate at the middle of mesoporous tunnels and have diameters in the range of 2.0-4.2 nm. The Pd and Pd/Pt nanoparticles are very stable in air, whereas the Cu nanoparticles are stable only in an inert atmosphere.     

Mechanical behaviour of biodegradable agricultural films under real field conditions

The mechanical behaviour of various types of biodegradable materials depends on their chemical composition and additives, the processing characteristics and the application conditions. The environmental conditions during storage and usage of these materials strongly influence their mechanical properties and behaviour. Ageing and degradation during the useful lifetime of biodegradable agricultural films causes losses in the mechanical performance of the material, as measured by monitoring the evolution of some of the critical mechanical properties. Such losses may be comparable to the corresponding losses of the conventional polyethylene agricultural films due to ageing, or they may be more drastic. In the present paper, the overall mechanical and ageing/degradation behaviour of experimental specially designed and manufactured low-tunnel and mulching biodegradable films, exposed to full-scale field conditions is analysed. Selected critical mechanical properties of these films manufactured with different grades of Mater-Bi material and additives, different thickness and processing schemes and exposed to real cultivation conditions in four different locations in Europe are investigated in the laboratory and compared against the corresponding behaviour of conventional agricultural films at various stages of their exposure time.