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.

Group theoretical methods are used to obtain the form of the elastic moduli matrices and the number of independent parameters for various symmetries. Particular attention is given to symmetry groups for which 3D and 2D isotropy is found for the stress-strain tensor relation. The number of independent parameters is given by the number of times the fully symmetric representation is contained in the direct product of the irreducible representations for two symmetrical second rank tensors. The basis functions for the lower symmetry groups are found from the compatibility relations and are explicitly related to the elastic moduli. These types of symmetry arguments should be generally useful in treating the elastic properties of solids and composites.

Solvent induced crazes formed in strained polyimide thin films on different substrates have been studied. A fracture mechanics approach has been used to simulate craze evolution. The experiments and simulations have identified a critical prestrain below which craze formation does not occur. This strain decreases with increase in solvent exposure time, but also exhibits a threshold. Diffusion of the solvent into the film is considered to be responsible for the time-dependent nature of damage formation.

Polyimide is used extensively in a variety of integrated circuit packaging applications. It is a good dielectric material with excellent planarizing capabilities, but like most polymers, it absorbs moisture. This hygroscopic behavior can lead to reliability problems in integrated circuit packages. The effects of variations in process history on moisture uptake are examined using gravimetric measurement techniques. In particular, the effects of cure schedule and exposure to high temperature/high humidity environments (85 °C/85% RH) on steady state moisture uptake are reported. Steady state moisture uptake is shown to be a decreasing function of cure temperature. Samples cured at 250 °C absorb 25% more moisture by weight than do samples cured at 400 °C. Moreover, the steady state moisture uptake in polyimide is greater after the samples have been “aged” in a high temperature and humidity ambient. The bulk and surface chemical composition are also monitored as a function of aging using Fourier transform infrared spectroscopy (FTIR) and electron spectroscopy for chemical analysis (ESCA), respectively. The PI surface chemistry degrades after 700 h in an 85 °C/85% RH environment. The bulk chemical composition appears to be unaffected.

TiB2 conducts the current and forms a liquid phase at the interface with BN. Neighboring crystals of BN and some TiB2 spall due to thermal shock. During pause periods parts of the liquid and fragments are flushed out by the dielectric. Composites rich in TiB2 or with fine TiB2 grains gave high material removal rates. Increasing the amount of the conducting phase by 10% is as effective as decreasing the grain size from 11 to 7 μm. Coarse TiB2 could withstand high pulse durations before wire breaks. Material removal rate increases with pulse duration, frequency, and current. For the same composition and grain size, increasing the pulse duration or current increased the crater depth (the roughness) up to a certain value, beyond which increasing these parameters yielded a smoother surface. The conductivity of the dielectric was effective only for compositions rich in TiB2 content. In such cases, higher water conductivity lowered the energy required for material removal.

The mechanism of fracture arrest in brittle-matrix composites with strong, long fibers is analyzed by using the inclusion method. The maximum stress contribution of the matrix in composites is discussed in this paper. A critical volume fraction of fibers fc is theoretically derived. If the volume fraction f is less than fc, then debonding between fibers and matrix occurs before the crack propagates through the whole section. If f is greater than fc, then no debonding occurs before the crack propagates through the whole section. The value of fc depends on the matrix and fiber properties and the bond character of the interface. To verify the analytical predictions, experiments on fiber reinforced cement composites subjected to uniaxial tension were conducted. The results of the theoretical predictions were also compared satisfactorily with other published experimental data.

The microstructure of air voids in both air-entrained and non air-entrained paste, mortar, and concrete containing silica fume has been studied at different ages (5 min to 60 days) in order to understand how air-entrained voids form in portland cement–silica fume systems. Scanning electron micrographs of air voids are presented for many different ages. The solidification process of portland cement–paste and mortar was frozen at different ages using both a low-temperature scanning electron microscope and freeze drying. During the course of these experiments, it was discovered that air voids can be considered “windows” in the microstructure in which one can observe early hydration features that give insight into the nature of portland-cement systems. A well-developed sheaf of wheat morphology has been observed in concretes incorporating silica fume, and a new interpretation of the microstructure of silica fume concrete is presented.

Berlinite crystals grown in H3PO4, HCl, H3PO4/HCl, H2SO4/HCl, or H3PO4/HCl/H2SO4 solvents are characterized by acoustic microscopy techniques. Surface and subsurface defects can be visualized via acoustical images, whereas elastic parameters of the crystal can be measured on a microscopic scale. They prove to be of great importance in the identification of not only crystal orientations but of preparation methods as well. We show, for example, that a growth in sulfuric and phosphoric mediums improves mechanical behavior of berlinite crystals. Moreover, it seems that anisotropy plays a fundamental role in this characterization technique with an appearance or a disappearance of specific modes.