The relationship between phase equilibria in the PbF2−AlF3 system and the solidification behavior of several ternary lead aluminum fluoride compounds was explored. A partial binary phase diagram for the PbF2−AlF3 system was determined from differential thermal analysis, annealing and directional solidification studies. The compounds AlF3, Pb3Al2F12, Pb9Al2F24, and a PbF2 solid solution were identified by x-ray diffraction, energy dispersive and microprobe analysis. The previously reported phases PbAlF5 and PbAl2F8 were not observed. Directional solidification studies showed that it is possible to grow crystals of AlF3, Pb3Al2F12, and the PbF2 solid solution from nonstoichiometric PbF2−AlF3 melts. The compound Pb9Al2F24 was found to decompose on heating by a peritectoid reaction (forming two other solids) and thus could not be solidified directly from a PbF2−AlF3 melt.

Small angle neutron scattering (SANS) was employed to characterize the pore structure of nanophase TiO2 ceramic materials compacted at different temperatures. Nanophase samples, produced by inert gas condensation, were compacted at 25, 290, 413, and 550 °C using a pressure of ≍1 GPa. The pore size distribution of the sample compacted at room temperature was very broad, with sizes ranging from ≍3–30 nm and pores comprising 38% of the sample volume. Compaction at 290 and 413 °C reduced the pore volume to 25% and 20%, respectively, by eliminating pores at both the small and large ends of the distribution. Compaction at 550 °C resulted in a pore volume that was less than 8%. Complications in the SANS analysis arising from the scattering from grain boundaries are discussed. The results from SANS are compared with those derived from nitrogen absorption, BET, measurements.

The reaction between tantalum ethoxide and an inorganic, silicon-carbon based polymer known as polycarbosilane resulted in a modified polymer that could be thermally converted into a binary ceramic of SiC and TaC. In this report, the initial reaction of the precursors and the high temperature transformations that resulted in the mixed ceramic carbide are discussed. The synthesis of this modified polymer was characterized using 29Si, 13C NMR, and infrared spectroscopy. The reaction involved cross-linking of polycarbosilane through bridging carbon bonds and the formation of Si–OCH2CH3 ligands. According to these data and to the low-angle x-ray diffraction data, the structure of the reaction product can be described as a network of modified polycarbosilane with intimately dispersed tantalum oxide particles. The structural transformations that occurred during inert atmosphere pyrolysis of the polymer product were determined using 29Si, 13C MAS NMR, infrared and x-ray diffraction spectroscopy. Inert atmosphere pyrolysis at temperatures below 500 °C involved continued cross-linking of polycarbosilane through the endothermic formation of bridging carbon bonds. During pyrolysis at 500 °C, an exothermic reaction between the modified polycarbosilane and the intimately dispersed tantalum oxide particles was observed. This reaction involved the formation of an inorganic, amorphous oxycarbide phase that can be described as a continuous network of C–Si–O and C–Ta–O bonds. At pyrolysis temperatures exceeding 1000 °C, carbothermal reduction of the oxide constituents initiated. Further pyrolysis at temperatures exceeding 1200 °C resulted in the crystallization of zinc-blend β–SiC and NaCl structured TaC.

A systematic investigation of the microstructural evolution of fast fired, sol-gel derived Pb(Zr, Ti)O3 films (Zr/Ti = 54/46) was performed by analytical transmission electron microscopy (TEM). It was found that the nucleation and growth of the sol-gel PZT films were influenced by the precursor chemistry. The precursor solution was composed of Pb 2-ethylhexanoate, Ti isopropoxide, and Zr n-propoxide in n-propanol. Porous and spherulitic perovskite grains nucleated and grew from a pyrochlore matrix for NH4OH-modified films, but no chemical segregation was found. These thin films consisted completely of porous spherulitic PZT grains (∼2 μm) when the firing temperature was increased. Chemical phase separation with regions of Zr-rich pyrochlore particles separated by Zr-deficient perovskite grains was observed in the initial stages of nucleation and growth for CH3COOH-modified PZT films. This phase separation is attributed to the effect of acetate ligands on the modification of molecular structure of the PZT precursor. Firing the acid-modified films at higher temperatures for long times resulted in porous perovskite grain structures. The residual porosity in these films is suggested to be a result of differential evaporation/condensation rates during the deposition process and the gas evolution at high temperatures due to trapped organics in the films. Dielectric and ferroelectric properties were correlated to the microstructure of the films. Lower dielectric constants (∼500) and higher coercive fields (∼65 kV/cm) were found for the acid-modified PZT films with phase separation in comparison to those measured from the sol-gel films with a uniform microstructure (∽ > 600, Ec < 50 kV/cm). All films fired at 650 °C showed relatively good remanent polarization on the order of 20 μC/cm2.

A well-characterized Synroc was subjected to durability tests in de-ionized water at 70 °C and 150 °C, and silicate and bicarbonate solutions at 70 °C, to study the effect of temperature and solution composition on the mechanisms of aqueous alteration. SEM and TEM were used before and after durability experiments to characterize the primary and secondary phases in and on the Synroc samples, and to describe changes in morphology and chemistry. Leachant compositions after durability testing were analyzed using ICP/OES and ICP/MS and have been reported elsewhere.8 After durability testing, titaniferous surface layers were observed primarily on perovskite, the most soluble Synroc phase. Electron microscopy demonstrates that the surface layer formed at 70 °C is an amorphous Ti–O film and is fine grained anatase at 150 °C. Congruent dissolution is the major mechanism of perovskite alteration. However, at 150 °C, selective loss of Ca and Sr may occur locally. A number of additional secondary phases were identified, including Al–oxide/hydroxide, Fe–oxide, REE-bearing Ti–oxides, and several silicate phases. The abundance and composition of the secondary phases are related to solution composition and temperature.

A thorough investigation of the microstructure of single SCS-6 SiC fibers widely used as reinforcements in metal-matrix and ceramic-matrix composites has been made. Various techniques of electron microscopy (EM) including scanning (SEM), conventional transmission (TEM), high resolution (HREM), parallel electron energy loss spectroscopy (PEELS), and scanning Auger microscopy (SAM) have been used to analyze and characterize the microstructure. The fiber is a complicated composite consisting of many different layers of SiC deposited on a carbon core and different carbonaceous coatings covering the SiC layers. The structural and chemical aspects of each layer are characterized and discussed.