Bill Bergman

Synthesis of LiCoO2 starting from carbonate precursors I. The reaction mechanisms

Abstract The reaction mechanisms during calcination of a Li 2CO 3/Co 3O 4 mixture in air and CO 2 were monitored by thermogravimetry, differential thermal analysis and complementary calcinations at 300 and 500 °C. It was determined how weight reduction, specific surface area and the formation of phases develop. Below 400 °C the main process is the decomposition of CoCO 3. Formation of LiCoO 2 starts above 400 °C but at high O 2 partial pressures some Li 2CO 3 seems to react already at 300 °C.

Influence of residual stress on elastic modulus and hardness of soda-lime glass measured by nanoindentation

The influence of stress on the elastic modulus E and hardness H in soda-lime glass was studied in the Vickers residual stress field by nanoindentation. The Oliver–Pharr method of analysis first gave higher values of E and H, but after correcting for the pileup contact areas around the nanoindents, results consistent with literature values were obtained at regions in the stress field where the stresses were either low or close to zero. Determination of the pileup contact areas was made possible by the use of the atomic force microscope, which has facility for generating cross-section images of the indents. The elastic modulus was found to decrease with stress, which is explained with reference to the influence of applied stresses on the Si–O–Si bond angle. The hardness on the other hand did not depend on the stresses except in the region very close to the edge of the Vickers indent where the stresses are high.

Synthesis and Performance of LiCoO2 Cathodes for the Molten Carbonate Fuel Cell

A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650-degrees-C. Electrodes were tape cast in a nona ...

Effect of sintering procedures in development of LiCoO2-cathodes for the molten carbonate fuel cell

Abstract LiCoO 2 -powder was synthesized from carbonate precursors by calcination in air. Greentapes were tape-cast using a non-aqueous slurry and 10 μm plastic spheres as pore formers. Sintering was carried out in air at 850–950°C and in argon/air at 500/750°C. The two sintering procedures led to very different sub-micron morphologies, with the primary particles being much smaller in the latter case. The electrochemical performance at 650°C, in terms of overpotential at 160 mA/cm 2 , for the air- and argon/air-sintered electrodes was 57 and 81 mV, respectively. The potential drop due to contact resistance between electrode and current collector was estimated to be 100 and 70 mV, respectively. The electrode materials were characterized by scanning electron microscopy (SEM), Hg-porosimetry, the BET-method (N 2 -adsorption), X-ray diffractometry (XRD), flame atomic absorption spectrometry (F-AAS), carbon analysis and a van der Pauw conductivity measurement set-up.

The influence of different oxides on the formation of Si2N2O from SiO2 and Si3N4

Abstract Si2N2O powder has been produced by reacting SiO2 and Si3N4 in the presence of a liquid phase obtained by the addition of Al2O3, Y2O3, and MgO. The phase changes occurring during the reaction have been quantified by X-ray diffraction. The reaction has been studied at different temperatures and periods of time. The grain size of the starting materials has a large influence on the conversion to Si2N2O, and, by using a fine-grained SiO2, a substantial conversion to Si2N2O was obtained within 1 h at 1500°C for the Y2O3-containing material.

Synthesis of LiCoO2 starting from carbonate precursors II. Influence of calcination conditions and leaching

Abstract The effect of initial Li:Co ratio, calcination atmosphere, temperature, leaching in H 2 O or acetic acid solution on reaction completeness, final Li:Co ratio, primary particle size, conductivity and its sensitivity to different atmospheres has been investigated. The calcination gas composition was found to be very important. A powder with a primary particle size of 100–300 nm and with less than 3 wt.% of unreacted Li 2 CO 3 was obtained.

The SiAlON system at temperatures of 1700–1775°C

Abstract Mixtures of Si 3 N 4 , SiO 2 , Al 2 O 3 and AlN have been used to prepare series of specimens heat treated at 1700, 1730, 1750 and 1775°C. The phase relations of the liquid-rich area of the SiAlON system were studied in detail by X-ray diffraction and scanning electron microscope analysis. Each specimen was chemically analysed after the heat treatment to determine any changes in the overall composition. Finally, the observations have been used to obtain a slightly revised phase diagram at a temperature range of 1700–1730°C for the system Si 3 N 4 -SiO 2 -Al 2 O 3 -AlN.

Determination of contact angle in porous molten-carbonate fuel-cell electrodes

A method of capillary rise (gravimetrically measured) has been investigated for determination of the electrolyte contact angle in porous electrodes for the molten-carbonate fuel cell. The experiments were conducted on LiCoO{sub 2} electrodes in air, at different temperatures (555 to 740 C), to monitor the influence of the temperature on the contact angle. The results indicate that the contact angle decreases with increasing temperature. The results obtained were of good reproducibility, and the method shows promise as a useful tool in characterization of wetting phenomena in porous fuel-cell electrodes, making it possible to study electrodes as manufactured, and under electrochemical conditions. The wetting-in was characterized also by post-test measurements, and it was found that the wetting-in front (i.e., from no electrolyte to fully flooded), extends over several millimeters.

LiFeO2 ­ LiCoO2 ­ NiO Cathodes for Molten Carbonate Fuel Cells

Dissolution of the state-of-the-art lithiated nickel oxide cathode is a major obstacle for the development of molten carbonate fuel cell (MCFC) technology. LiFeO2 and LiCoO2 were reported earlier as the most promising alternative materials; however, they do not satisfactorily substitute for the state-of-the-art cathode material. A solid solution consisting of LiFeO2, LiCoO2, and NiO is expected to posses some desirable properties of these three materials. Powder compositions in the LiFeO2-NiO binary system and a ternary subsystem with a constant 50:50 molar ratio of LiFeO2:NiO were prepared by the Pechini method. After preliminary powder characterizations, the feasibility of new materials for MCFC cathode application was studied. Electrical conductivity and microstructural characteristics were investigated, first in the form of bulk pellets and then in ex situ sintered porous gas diffusion cathodes. Finally, the electrochemical performance of selected cathodes was evaluated by short-time laboratory scale cell operations. The electrical conductivity of the ternary compositions with 50:50 molar ratio of LiFeO2:NiO increases significantly with increasing LiCoO2 content up to about 25 mol %. Further increase of LiCoO2 content decreases conductivity. The cell study indicates the possibility of preparing cathodes suitable for MCFC application with a considerably high LiFeO2 content.

Thermodynamic assessment of the system CoO-MnO

The thermodynamic properties of pure MnO and NiO were analyzed in terms of the Debye model and a model for the magnetic transitions. The classical formula R In (β+ 1) for the magnetic entropy was found to overestimate the effect of magnetic ordering in these systems. A previous interpretation of the data for NiO was corrected. Thermodynamic functions were derived for the solid and liquid states and are given as analytic expressions. A previous assessment of the Gibbs energy of the solid solution (Mn, Ni)O from activity data was modified on statistical grounds. The results indicate that there should be a miscibility gap below 41O°C. By estimating the Gibbs energy of the liquid phase, it was possible to calculate the complete phase diagram.