Unilamellar vesicles, formed spontaneously by mixing single-tailed cationic (cetyl trimethyl ammonium tosylate, CTAT) and anionic aqueous solutions of (sodium dodecyl benzene sulfonate, SDBS) surfactants have been used as reactors for the aqueous phase precipitation of nanometer sized particles within their inner cores. AlCl3 solution was encapsulated within these vesicles, aluminum ions were replaced with sodium ions in the extravesicular phase, and sodium hydroxide was then added to the extravesicular region. Hydroxyl ions penetrate through the vesicle walls and react with the available aluminum in the intravesicular region to form the product. The morphology and sizes of these particles were examined by transmission electron microscopy, while their phase and crystalline nature were probed by electron and x-ray diffraction. The product particles were nanometer-sized with near spherical morphology. Good control of particle size was achieved by varying the initial concentration of electrolyte. Single particle electron diffraction revealed a symmetric pair of spots, indicating that the particles were either single crystals or polycrystalline with á low number of grain boundaries or defects. Although wide area electron diffraction showed that the product was δ–Al2O3, powder x-ray diffraction revealed that these particles were, in fact, Al(OH)3. It is likely that heating of these nanoparticles by the high energy electron beam in a high vacuum environment causes a phase transformation, resulting in the difference between the electron and x-ray diffraction results. These results represent the first demonstration of precipitation within vesicles produced spontaneously by mixing appropriate ratios of inexpensive single-tailed surfactants, and may potentially make intravesicular precipitation a commercially viable route for making nanometer-sized particles.

Diphasic yttrium-aluminum garnet (Y3Al5O12, YAG) sols were made by hydrolysis of aluminum and yttrium isopropoxides. The sols were gelled across TEM grids to make films. The films were heat-treated up to 1550 °C for as long as 300 h. Heat-treatments of bulk gel were also done. Microstructure and phase evolution were observed by TEM. Some observations were done in situ in a TEM hot-stage. YAG fraction and grain size, matrix grain size, nuclei/area, and film thickness were measured. Bulk samples were characterized by x-ray, DTA, and TGA. Yttrium-aluminum monoclinic (YAM) and transition alumina appeared at 800 °C. YAG nucleated between 800 °C and 950 °C. Nucleation was weakly correlated with the transient presence of YAlO3 garnet, and was eventually site-saturated at 0.3/μm3. The change in grain growth rate of the YAM and transition alumina matrix correlated with the change in the growth rate of YAG. Between 850 °C and 1000 °C YAG growth had t1/2 dependence and 280 kJ/mole activation energy. Below 850 °C nucleation was continuous, and growth had t0.85 dependence. Above 1000 °C YAG growth had t1/4 dependence, and the matrix grains coarsened with t1/4 dependence. Thicker films reacted faster because the nuclei/area and the growth rate after nucleation scaled with thickness. YAG growth was accompanied by formation of 20–100 nm subgrains. In the late stages of matrix grain coarsening there was also some reaction to YAG by a different process. Nucleation and growth kinetics are compared with other systems. Possible mechanisms are discussed.

The time-differential perturbed angular correlation technique has been used to investigate the thermal behavior of a ZrO2−13.6 mole % MgO ceramic between room temperature and 1423 K. Two different quadrupole hyperfine interactions corresponding to a tetragonal structure have been found to result on cooling the ceramic from the single-phase cubic field. One of them agrees with that depicting the pure t-ZrO2 tetragonal phase and the other one has been interpreted as describing a high-MgO-content nontransformable t'–ZrO2 phase. As temperature increases, the latter gives rise to a similar but fluctuating interaction related to the oxygen vacancies mobility and which shows a thermal behavior analogous to that already reported for the stabilized cubic ZrO2. Above 1100 K these dynamic t'-sites transform into pure tetragonal ones which behave ordinarily, suffering the t → m phase transition when cooling to room temperature. Differences found between TDPAC results and information drawn from other techniques are discussed.

The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients (Kd) at a small fractional exchange in nitrate media. All metal ions studied showed linear relationships with a slope of −2 on the log-log plot of Kd vs [HNO3] which clearly indicated that the adsorption process is an “ideal” ion-exchange. The selectivity increased in the following order: Pb ≫ Mn > Co > Cu > Hg > Cd > Zn > Ni. The high selectivity of the manganic acid was successfully utilized in the removal of Co2+ from seawater and tap water.

An experimentally verified model, which quantifies the degradation and diffusion of organic vehicle during pyrolysis of a ceramic molding in the shape of an infinite cylinder, has been modified to accommodate the various effects of porosity development as degradation proceeds. Thus, in the first case, a shrinking radius has been taken into account as organic matter recedes. Secondly, the formation of uniformly distributed porosity is considered as organic vehicle is removed. In each of these instances, the model predicts the critical heating rate and temperature at which boiling occurs in the ceramic body, giving rise to internal defects for various cylinder radii.

The mechanical properties of hot isostatically pressed monolithic Si3N4 and Si3N4−20 vol. % SiC composites have been studied by microindentation at temperatures up to 1400 °C. Indentation crack patterns and microstructures have been examined by optical microscopy, scanning electron microscopy, and transmission electron microscopy. It is shown that dense Si3N4 base materials can be synthesized by HIPing without densification aids. Both the monolithic Si3N4 and the Si3N4/SiC composites exhibit high hardness values which gradually decrease with increasing temperature. Both types of material show low fracture toughness values apparently because of strong interfacial bonding. On the other hand, the fracture toughness of the composite is about 40% higher than that of the monolithic material, due to the presence of the 20 vol. % SiC whiskers. A crack deflection/debonding mechanism is likely to be responsible for the higher toughness observed in the composite. High resolution electron microscopy shows that the grain boundaries in both samples contain a thin SiO2 layer.

Raman spectra are reported for fresnoite-type [Ba2Ti(Si, Ge)2O8] materials. Single crystal and glasses of the endmember compositions, Ba2TiSi2O8 (BTS) and Ba2TiGe2O8 (BTG), along with crystalline powders along the pseudobinary join, Ba2TiSi−xGe2−xO8, are discussed. The polarized single-crystal Raman spectra of BTS show the vibrational bands of the Si2O7 and TiO5 molecular groups. The v (Si–O–Si) mode is found at 666 cm−1, and is relatively weak. The strongest bands in the BTS single crystal spectra are found at 858 cm−1 and 873 cm−1. These are attributed to the v (SiO3) modes and the stretching of a short Ti–O bond, with mixing between them evident. The BTG single crystal polarized Raman spectra show the vs(Ge–O–Ge) mode at 521 cm−1, and a strong band at 841 cm−1 assigned to the stretch of the short Ti–O bond. The angular dependence of the TO-LO splitting is cataloged for the A1(z) stretching modes. The vibrational characteristics of both BTS and BTG are dominated by the molecular groups, and do not show behavior indicative of a sheet structure composed of TiO5 and (Si, Ge)2O7 groups. Raman investigation of the crystalline powders points to the presence of Si2O7, Ge2O7, and SiGeO7 groups within the nonendmember compositions. The BTG glass spectra show correspondence with the BTG crystalline Raman spectra; the vs(Ge–O–Ge) mode occurs at 518 cm−1 in the glass. Fivefold coordinated titanium may be present in the BTG glass, as revealed by a very strong band at 824 cm−1 in the I spectrum. BTS glass spectra also show some similarity with the BTS crystalline spectrum; the strongest band is found at 836 cm−1 in the I glass spectrum. Through comparison with other titania-silicate glasses, we conclude that the BTS glass has a structure similar to the crystalline phase.

During the pyrolysis of cured hydridopolysilazane (HPZ) polymer to form Si–C–N ceramic fibers, large quantities of unpaired electrons are produced. For such materials dynamic nuclear polarization (DNP) provides a means of enhancing the intensity of the NMR signal, and supplies information on the localization or delocalization of unpaired electrons. 29Si, 1H, and 13C DNP gives enhancements of 250 for 13C and at least 800 for 29Si. 13C and 29Si DNP-DPMAS experiments yield the following results: (i) there are at least two distinct types of carbon, sp2 and sp3; (ii) there is a distribution of sp3 silicon environments; (iii) the unpaired electrons behave as fixed paramagnetic centers; and (iv) the unpaired electrons are distributed homogeneously throughout the sample. Proton DNP spectra can be obtained even though hydrogen is only a trace element in the finished ceramic.

Magnetic Resonance Imaging (MRI) is applied to porous ceramic materials to study structural properties. In ceramics, processing differences create inhomogeneous binder distribution in the materials which can cause the formation of regions with differing densities and voids. These defects can be observed with MRI using solvent permeation. Fractional porosity obtained by using image intensity measurements and weight gain due to solvent permeation can be correlated. Dark regions in the image are due to defects such as closed voids, pockets of binder, or agglomerates. Defects such as voids or agglomerates usually have different magnetic susceptibilities. This difference causes artifacts in the image. By exploiting the increase in signal loss using a gradient-echo sequence, apparent enhancement of voids in ceramics is achieved.

The contact radii arising from surface forces were determined for cross-linked polystyrene particles having radii between 1.5 and 10 μm in contact with SiO2/silicon substrates using scanning electron microscopy. It was observed that the contact radius varied approximately as the particle radius to the 0.42 ± 0.13 power. These results are consistent with the theories that assume plastic response of the materials, such as that proposed by Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984)] but are inconsistent with the predictions of models which assume only elastic response, such as that of Johnson, Kendall, and Roberts [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London A 324, 301 (1971)]. The thermodynamic work of adhesion, calculated from the experimental results, was found to be 0.32 J/m2, which is significantly smaller than that reported previously on a similar system.

A simple atomistic approach to the mechanical strength and the fracture toughness of brittle materials is made by the use of a universal expression for binding potential energy versus atomic separation curves. The scaling factors for the atomic separation and for the energy amplitude successfully apply to describing the intrinsic fracture toughness K* in a scaled dimensionless form. It is demonstrated that the intrinsic fracture toughness combined with a stress shielding coefficient (SSC) yields the fracture toughness of real materials. Microfracture mechanisms for crack-tip stress-shielding processes, as well as the interrelationship between the stress intensity- and the potential energy-derived fracture toughness, are addressed.

Mathematical models emulating DSC/DTA traces of fusion and first-order decomposition were developed. A computer program is described that uses the simplex numerical optimization algorithm to determine the coefficients for the model equations that best fit experimental data, by the criterion of least-squared error. Use of the program permitted deconvolution of various superimposed endotherms.