A mathematical model has been used to compute temperature profiles in ceramic preforms that are heated by microwaves. The temperature profiles were then input to a second part of the model describing chemical vapor infiltration of the preform, that is the diffusion of gaseous reactants, heterogeneous reaction, and evolution of the pore structure. Equations were solved numerically for parameters corresponding to the infiltration of SiC preforms by pyrolysis of trichloromethylsilane. While based on some simplifications, the model leads to the conclusion that infiltration proceeds more rapidly, and to a greater extent, with microwave heating/external cooling than in isothermal infiltration. The model suggests that infiltration might be optimized by manipulation of microwave power and external cooling. The computed extent of infiltration is seen to be very sensitive to the initial pore size.

The mullite formation process in both single phase and diphasic sol-gel precursors to mullite was studied using dynamic x-ray diffraction (DXRD). A metastable, tetragonal-like mullite phase was observed in all the single gels at temperatures from 980 °C to 1200 °C, but not in any of the other precursors. The tetragonal to orthorhombic mullite transformation was very slow as the lattice parameters, a and b, split and moved gradually away from each other as a result of a gradual decrease of alumina content in the mullite solid solution with increasing temperature from 1100 °C to 1200 °C. The formation of tetragonal mullite coincides with that of the Al–Si spinel. The occurrence of tetragonal mullite or the spinel (or both) is determined mainly by the processing conditions of the sol-gel precursors.

Two sets of submicronic mullite whiskers, which have potential applications for fiber reinforced composites or as a thermal insulator, have been characterized to be tetragonal or orthorhombic using x-ray and electron microscopy techniques. The whiskers decompose upon heating under vacuum with a continuous loss of silicon and reduction in oxygen content up to the limit for which pure aluminum metal and α-alumina are formed.

This paper describes the preparation and compositional analysis of multilayer thin-film coatings prepared using sol-gel techniques. Alternate layers were labeled with an iron tag, derived from hydrolyzed 1,1'-bis(triethoxysilyl)ferrocene. Iron-free layers were composed of SiO2 derived from hydrolyzed tetraethylorthosilicate (TEOS). Analyses of these systems were based on Rutherford Backscattering Spectrometry (RBS) and Cross-Sectional Transmission Electron Microscopy (XTEM). The depth profile of iron, measured by RBS, yielded thicknesses (1000–1600 Å) for the individual layers that could be verified independently by XTEM.

Colloidal amorphous lead niobate particles of different composition and morphologies were obtained by a metal-chelate decomposition method. The nature of the dispersions depended on the conditions of the preparation of the complexes, pH, aging time, and temperature. The structural and chemical changes of the so prepared powders on calcination were investigated by thermal and x-ray diffraction analyses. Chemical mechanisms of the formation and transformation of the particles are suggested.

The high temperature equilibrium conductivity (950 °C–1050 °C) of congruent LiNbO3 can be resolved into two components: an electronic portion that is dependent on the oxygen partial pressure and an ionic portion that is pressure independent. It is shown that the two components can be obtained from an analysis of the total equilibrium conductivity measured as a function of oxygen partial pressure. The ionic transport number (fractional ionic conductivity) thus obtained is compared with that obtained from an oxygen concentration cell measurement. The two techniques are found to be in excellent agreement, confirming the experimental validity of the defect chemistry method. From the temperature dependence of the ionic conductivity, the activation energy (138 kJ/mol [1.43 eV]) for the ionic transport is obtained. The results are in good agreement with the value previously obtained for the oxygen chemical diffusivity.

Polyvinyltoluene (PVT) latex particles were etched with O2 or CF4/O2 plasma and polystyrene (PS) latex by the O2 plasma. While the effect of these treatments on the surface topology and the specific surface area was minor, the electrokinetic measurements showed a significant change in the surface charge characteristics. The interpretation of the results in terms of a surface complexation model, taking the Stern–Gouy–Chapman structure of the interfacial layer into consideration, yielded the values of the corresponding equilibrium constants, which indicated that the chemical nature and the density of the surface charged groups were altered by plasma attacks.

Ultra-thin films of polyamic acid (BTDA-ODA type) are prepared by spin coating a very dilute solution onto bare or metallized silicon wafers (estimated thickness 25 ± 5 Å). The XPS analysis of the various polymer/metal interfaces suggests the occurrence of acid-base type interaction between the carboxylic groups of the polymer and the oxides and hydroxides that cover the Ni and Cr surfaces. When these systems are in situ cured, the XPS analysis shows the occurrence of a variety of chemical interfacial reactions. In particular: (i) when the substrate is a naturally passivated Ni layer, the complete destruction of the polymer is observed; (ii) when the substrate is a naturally passivated Si wafer, no relevant interaction occurs; (iii) for a naturally passivated Cr and an oxidized Ni surface, partial decomposition of the polymer is observed. The above effects are explained in terms of the acid or basic properties of the oxidized layers that cover the metal surfaces, and in terms of their stability toward heating.

Silicone oil vapor deposition and Ar+ ion irradiation can form an adhesive carbonaceous film on a steel substrate. The friction coefficient μ of the coated substrate is found to be very low for sliding against a steel ball both in air (μ ∼ 0.04) and in N2 gas (μ < 0.02). The duration of the low friction state is comparatively long and is 5 × 103–1.5 × 104 cycles for a film 0.15 μm thick. X-ray photoemission spectroscopy, infrared reflection spectra, and Raman measurements indicate that the film mainly consists of amorphous carbon containing Si and O.