Bahne C. Cornilsen

Structural comparison of nickel electrodes and precursor phases

Abstract In this paper we summarize our previous Raman spectroscopic results and discuss important structural differences in the various phases of active mass and active mass precursors. Raman spectra provide unique signatures for these phases, and allow one to distinguish each phase, even when the compound is amorphous to X-rays ( i.e. , does not scatter X-rays because of a lack of order and/or small particle size). The structural changes incurred during formation, charge and discharge,d cobalt addition, and ageing will be discussed. The oxidation states and dopant contents are explained in terms of the nonstoichiometric structures.

Structural models for nickel electrode active mass

Abstract Raman spectroscopic data allow one to distinguish nickel electrode active mass, alpha- and beta-phase materials. Discharged active mass is not isostructural with beta-Ni(OH)2. This is contrary to the generally accepted model for the discharged beta phase of active mass. It is concluded that charged active mass displays a disordered and nonstoichiometric, non-closepacked structure of the , NiOOH structure type. Raman spectral data and X-ray diffraction data are analyzed and shown to be consistent with this structural model.

Solid state vibrational spectra of calcium pyrophosphate dihydrate

Abstract The Raman and IR spectra of triclinic Ca 2 P 2 O 7 2H 2 O are interpreted using factor group analysis. Solid state effects, factor group splitting and two-site splitting, must be considered to explain the spectra; site group or free ion group models are inadequate. The simple unit cell of this pyrophosphate allows unambiguous assignment of the eight PO stretching modes in order of decreasing energy: 4 v a PO > v s PO > v a PO > v a POP > v s POP . Comparison of these spectra with those for pyrophosphates exhibiting larger unit cells demonstrates that the number of factor group split symmetric PO stretching modes, v s PO , in the Raman spectra is proportional to the unit cell size. These spectra uniquely characterize this medically interesting material which can cause in vivo crystal-induced inflammation in tissues.

Bonding anomalies in the rare earth sesquioxides

Raman and IR vibrational spectra of C-type rare earth sesquioxides exhibit anomalous wavenumber decreases for europium (f6) and ytterbium (f13) oxide which have not been previously reported. Because of the large shifts observed for the Raman spectra, the IR band positions have been re-examined. Smaller, but definite decreases have been observed in the IR spectra as well. Scatter in the literature data had obscured these anomalies. The anomalies correlate with thermodynamic properties and indicate weaker bonding for these two oxides. It is suggested that these anomalies are caused by electron-phonon interaction, involving low-lying f-states which are below the Fermi level for europium and ytterbium. Therefore, these data provide another example of a system in which 4f electronic structure significantly influences chemical bonding. We suggest that it is due to the presence of the unique, low-lying electronic energy levels in these two elements, and not simply the result of the number of f electrons (half-full or full). Literature results suggest the anomalies are not due to “mixed valence” for Eu2O3 and Yb2O3; however, further research is needed to explain the origin more completely. Raman band positions are reported for the first time for several of the oxides.

Infrared and raman spectra of metal 1,2,4,5-benzenetetracarboxylates: Evidence for very short, strong hydrogen bonds

Abstract Salts of 1,2,4,5-benzenetetracarboxylic acid with copper, aluminum, ammonium, cobalt(II), thallium(I), tin(II), uranyl ion, zinc, manganese, iron(II), nickel, potassium and sodium have been prepared and characterized by their IR spectra. The salts of aluminum, ammonium, thallium(I), tin(II), zinc, iron(II), nickel, potassium and sodium had not been reported before with adequate characterization. Raman spectra of selected compounds also aided structural interpretation. The IR spectra of Na 2 C 10 H 4 O 8 ·2H 2 O, Fe(C 10 H 5 O 8 ) 2 ·12H 2 O, Zn(C 10 H 5 O 8 ) 2 ·12H 2 O, Ni(C 10 H 5 O 8 ) 2 ·12H 2 O, (NH 4 ) 3 C 10 H 3 O 8 ·H 2 O and CoC 10 H 4 O 8 ·6H 2 O indicate very short, strong hydrogen bonds in these compounds. The IR and Raman spectra can be used to determine the mode of coordination (if any) of the carboxylate groups of 1,2,4,5- benzenetetracarboxylate to metal ions.

Raman spectral observation of a new phase observed in nickel electrodes cycled to failure

A ‘new phase’ is reported in nickel electrodes from NiH2 boilerplate cells which were cycled to failure in electrolyte of variable KOH concentration (21–36%). Raman spectra clearly show the presence of this phase, and these spectra have been used to estimate the amounts present on these electrodes. Ten of twelve electrodes examined contain this new phase. The cycle life at higher KOH concentrations (31 and 36%) was greatly reduced, and nickel electrodes from these cells exhibited extensive amounts of this new phase. The presence of this ‘new phase’ correlates with cell failure defined by low end of discharge voltages. It is proposed that the lowered capacity and failure of these electrodes was caused by loss of active mass and formation of a phase with reduced electrochemical activity. These results indicate that formation of this new phase is accelerated at higher KOH concentrations.

Gelation Point In Borosilicate Sols From Rheological Experiments

Dynamic oscillatory experiments are used to monitor the gelation of the borosilicate systems prepared through the sol-gel process from metal alkoxides. The rheological experiments show that tan δ = G”/G’ is independent of frequency at the gel point in agreement with the results of others on organic gelling systems. The dynamic moduli at the gel point followed power-law behavior with respect to frequency. The power-law exponent is found to be ∼0.70. The apparent fractal dimension, dp, of the network cluster at the gel point is determined. The d F values for the samples ranged from 2.5 to 3.8 depending on the final structure of the evolved products at the gel point. The large values (d F > 3) exclude a simple geometric interpretation of the results. The effect of processing parameters, such as composition of reactants and temperature, on the resulting microstructures near the gel point is discussed.

Microwave Drying of Borosilicate Gels

Microwave processing was carried out on SiO 2 -B 2 O 3 solutions and gels prepared by sol-gel methods. Monolithic gels were prepared from alcoholic solutions of trimethylborate and tetraethylorthosilicate using a two-step hydrolysis process. A novel technique of Liquid State Processing (LSP) was employed for the first time, and it was found to be faster and more effective than the conventional processing techniques. The structural evolution of the dried products was followed using FTIR. The effect of processing was examined via surface area analysis (BET), electron microscopy, and FTIR. The microwave drying has been compared with conventional oven drying and vacuum drying techniques. Shorter processing times, improved microstructures, and unique properties have been obtained.

Measurement of Nonstoichiometry in BaTiO3 Using Raman Spectroscopy

The nonstoichiometry and point defect accommodation in low temperature (900°C) BaTiO3 influences the Raman spectrum. Therefore it is possible to monitor this nonstoichiometry and to use this technique to study the point defect chemistry of BaTiO3. Earlier research by Eror and Loehr indicated that the half-band width of a 525 cm-1 vibrational band broadened in Ba-excess or Ti-excess material.1 This observation is confirmed. We also report variation of Raman band intensities with changes in oxygen nonstoichiometry as well as Ba/Ti ratio. These dependencies are expected to be indicative of the defect species which influence the band shapes. The origin of the spectral parameter changes is not completely understood, although it is believed to be related to disorder introduced by the point defects,1,2 or changes in polarizability induced by electronic structure changes near point defects, vacancies or dopants. Vibrational spectra can be more sensitive than neutron scattering for the study of low level defect concentrations (<1%).2 For example, between 10 and 550 ppm of nickel vacancies have been detected in NiO using disorder activated Raman scattering. The presence of doubly ionized nickel vacancies was indicated by the oxygen partial pressure dependence of the data.