Photoinitiated oxidation of heterophasic ethylene–propylene copolymers. I. Comparison of oxidation products

Detailed photoproducts from photoirradiation of heterophasic ethylene-propylene copolymers and their fractions have been compared by infrared spectroscopy combined with chemical derivatization. The oxidized films were treated with gaseous NH₃, SF₄, and NO for the rapid identification and resolution of the various carbonyl species, alcohols, and hydroperoxides. The photoproduct formation depends upon the composition of the sample. The heterogeneities in thin films were also determined by micro FTIR spectroscopy. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of olivine LiNiPO4 for aqueous rechargeable battery

LiNiPO₄ belongs to a family of olivine type compounds, with members LiMPO₄ where M = Fe, Mn, Co or Ni are transition metals. The lithium nickel phosphate was prepared and characterized in order to evaluate a new potential cathode material for our ongoing research in aqueous rechargeable batteries. Annealing the final product is critical in obtaining the stoichiometric LiNiPO₄ pure phase; conventional cooling to a room temperature leads to an indication of Li₃PO₄ and NiO secondary phases as impurities. The synchrotron infrared radiation (SR-IR) as a source for IR spectroscopy pins down the differences in the chemical bonding for annealed and conventional cooled LiNiPO₄ samples. The cyclic voltammetric and galvanostatic studies showed annealed LiNiPO₄ is electrochemically active from which lithium ions can be de-intercalated during oxidation process leading to an amorphous NiPO₄ and a minor product of nickel(II) hydroxide (β-NiOOH). During subsequent reduction, lithium ions are not fully intercalated, however, the structure is reversible and adequate for multiple cycles. The high potential in LiNiPO₄ looks to be very attractive in terms of high energy density, given the efficiency is improved.     

Charge transport and structural morphology of HCl-doped polyaniline

The d.c. and a.c. (100 Hz–1 MHz) conductivities of HCl-doped polyaniline have been measured in the temperature range 77–300 K. At 77 K, the a.c. conductivity data, (), can be described by the relation ()=As, where the parameter s lies close to unity and decreases with increase in the doping level. The ratio of measured a.c. to d.c. conductivity shows dispersion at 77 K, which decreases with increase in the doping level. This decrease is found to be sharp around pH3.0. In the temperature range 77–150 K, the observed d.c. conductivity data can be described by Mott's three dimensional variable range hopping (VRH) model. Scanning electron microscopy studies reveal a sharp change in structural morphology of HCl-doped polyaniline at a pH3.0. A strikingly remarkable structural morphology has been observed in the formc of a channel at this pH value. This change is accompanied by a rapid increase in d.c. conductivity, dielectric constant, along with sharp changes in structural morphology, which indicates the existence of a doping-induced structural conductivity correlation in this system. © 1998 Chapman & Hall     

An infrared study of the structure of GeO2-CeO2 thin films

The infrared spectra of amorphous thin films consisting of GeO₂ co-evaporated with CeO₂ are presented and interpreted in relation to the spectrum of the pure amorphous GeO₂ film. The lower frequency side of the broad absorption band within this spectrum peaking at 730 cm^–1 is believed to be due to defect centres similar to the O ₁ ^– and O ₃ ⁺ centres found in a-SiO₂. Absorption at higher frequencies within this band is due to the O stretch vibrations of the Ge-O-Ge linkage. After considering the vibrations of the O ₁ ^– and O ₃ ⁺ centres in detail, it is shown that the band at 495 cm^–1 cannot be due to either of these centres and must therefore by caused by some other reactive defect centres. The variation of the position of the 730 cm^–1 peak within the series of spectra is noted and probable explanations are offered. The optical absorption edge of a-GeO₂ thin film is compared with that of a-SiO and a possible explanation of the basic differences is proposed.     

Measurements of stratospheric aerosols with a combined elastic-Raman-backscatter lidar

Improvements made to the NASA Goddard Space Flight Center Stratospheric Ozone Lidar system have extended its atmospheric-aerosol-measuring capabilities. The methods by which aerosol-scattering ratio, aerosol backscatter, and aerosol extinction are simultaneously derived from lidar data are reported, and results obtained during several intercomparison campaigns at worldwide locations are shown. The results track the evolution of the Mt. Pinatubo aerosol cloud from 1991 to 1994 and report wavelength-dependence information for aerosol backscatter between 308 and 351 nm. Two analysis techniques, a more common inversion method and a combined elastic-Raman-backscatter approach, are also compared.     

Microstructure evolution in nanocrystalline NiTi alloy produced by HPT

A slightly Ni-rich nano-NiTi alloy, deformed by high-pressure torsion (HPT) was investigated. By HPT, almost complete amorphization of initial B2 NiTi is obtained. Crystallization and microstructure evolution during isothermal treatment were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy.The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and the growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing reveals reproducibly non-monotonous trends with annealing time that cannot be explained solely by growth of crystalline volume fractions. The size of nanocrystals increases dramatically after annealing for 5 h. The effective activation enthalpies for stress relaxation (along with crystallization) and grain growth were estimated at 115 and 289 kJ/mol, respectively. The results are discussed with respect to the intricate interdependencies between synthesis and thermal processing pathways and the evolution of the nanoscale microstructure.     

Dynamic effects during sinter forging of axi-symmetric hollow disc preforms

The present paper reports an investigation on the dynamic effects during sinter forging of axi-symmetric hollow disc preforms at room temperature. The preforms have been prepared by compacting the copper metal powder within the closed-cavity circular compaction dies and experiments have been conducted on computer-controlled hydraulic press to investigate the effect of die velocity, i.e. dynamic effects on various deformation characteristics, e.g. flow of material, densification during dry and lubricated interfacial friction conditions, bulging and strains at preform-free surfaces and die loads. The theoretical analysis for die pressure distribution, average die load and bulged profile by ‘upper bound’ approach has been presented. The identification of critical sinter-forging characteristics and their interrelationships are the cornerstones of present study. The effect of die velocity along with other deformation characteristics on die load and inertia energy dissipation has been investigated critically using ‘design of experiment’ technique and the important interactions have been displayed graphically using ‘response surface methodology’ technique. The study on dynamic effects revealed that die velocity is the most critical factor during sinter-forging operations, especially at higher die speeds and hence, inertia energy must be considered during its analysis. The experimental and theoretical results have been found in close agreement with each other and it is expected that the work will be highly useful for the assessment of various deformation characteristics during processing of sintered materials.