Following a long period of qualitative assessment of environmental cracking phenomenology, there has been recent emphasis on developing quantitative, mechanistically-based predictive models. This focus is driven by scientific and engineering concerns. For example, neither pressure vessel design nor evaluation codes incorporate the contribution of environmental cracking under static loading, nor do they differentiate between the large possible variations in both environment and material chemistry. Similarly, while numerous scientific hypotheses have been proposed to explain the crack advance process and related, contributing phenomena, ultimately their validity must withstand the scrutiny of quantification and comparison to measured cracking kinetics and observed component lifetimes.

The benefits and approaches involved in predicting environmental cracking based on mechanistic modeling of crack advance and its underlying phenomena are discussed. The benefits and approaches involved in predicting environmental cracking based on mechanistic modeling of crack advance and the underlying phenomena are discussed. The formulation of a quantitative model from fundamental mechanisms has progressed most rapidly for the film rupture / slip dissolution mechanism of environmental crack advance. Specifically, for iron and nickel base alloys in high temperature water, identification, quantification and integration of the important underlying parameters has led to algorithms which predict crack growth rates over a wide continuum in static and dynamic stressing, metallurgical microstructure and solution chemistry applicable to light water reactors. For widely studied systems, e.g., stainless and low alloy steels in 288°C water, the predictions are within a factor of 2–3 for 90% of the data which span “initiation”, the possible roles of contributing, “secondary” crack advance processes in oxidation-based mechanisms, such as environmentally enhanced cleavage, spontaneous oxidation, etc.

Similar efforts to identify and quantify the critical parameters and underlying processes in crack advance mechanisms involving hydrogen embrittlement, environmentally assisted cleavage, etc. are summarized. Conceptual approaches to and progress toward integrating these models with in-situ chemical and crack monitoring devices, with the goal of providing on-line evaluation, control and lifetime prediction of environmental cracking, are also discussed.

The chromium composition along the grain boundaries of sensitized austenitic stainless steel are calculated using several different quantitative theories of sensitization. The results of the calculations are compared to measured values of the chromium composition along the grain boundary in an effort to assess the validity of the various theories. The experimental results point out two facts not previously emphasized in prior studies: (1) the amount of carbide precipitation required to sensitize austenitic stainless steel is small; (2) significant de-sensitization does not occur until after large amountsof carbide precipitation have occurred.

An experimental method that is able to verify and to characterize the damage zone developed in front of crack tip under time-dependent fatigue crack propagation has been established. The crack growth rate was found to decrease exponentially in the damaged zone. Such a crack growth behavior can be described by a mathematical model which only requires three parameters: initial crack growth rate, (da/dN)q; normal crack growth rate (da/dN)o; and damaged zone size, D. An analyticat relationship has been developed to correlate the temperature and the time of sustained loading to the size of the induced damaged zone.

Contrary to limited published information on the subject, magnesium die casting alloys are shown to be susceptible to stress corrosion cracking (SCC), requiring only partial immersion in distilled water. Also described is evidence that this SCC results from a cathodic process, with perhaps hydrogen-assisted cracking and film rupture both playing roles.

The study of radiation effects in complex silicate glasses has received renewed attention because of their use in special applications such as high level nuclear waste immobilization and fiber optics. Radiation changes the properties of these glasses by altering their electronic and atomic configurations. These alterations or defects may cause dilatations or microscopic phase changes along with absorption centers that limit the optical application of the glasses. Atomic displacements induced in the already disordered structure of the glasses may affect their use where heavy irradiating particles such as alpha particles, alpha recoils, fission fragments, or accelerated ions are present. Large changes (up to 1%) in density may result. In some cases the radiation damage may be severe enough to affect the durability of the glass in aqueous solutions.

In this paper, we review the literature concerning radiation effects on density, durability, stored energy, microstructure and optical properties of silicate glasses. Both simple glasses and complex glasses used for immobilization of nuclear waste are considered.

Different structure types related to the hexagonal tungsten bronze structure have been observed in the AxCrF3 sytem (A= K, Rb) by electron diffraction and high resolution electron microscopy. These structures decomposed into alkali metal and CrF3 in the electron beam. The former evaporates, leaving the original structure highly unstable. CrF3 crystallizes via a highly disordered phase to a distorted ReO3–type structure.

A review of methods for predicting the lifetime of protective organic coatings on steel is presented in terms of a model which includes the steps of defect formation, transport of corrodents, loss of adhesion, and corrosion. Electrochemical impedance methods and acoustic techniques have played important roles in characterizing how the four processes interact and depend on coating processes and environmental effects. A major result of this work has been the observation that both the anodic and cathodic partial processes of the corrosion reaction limit adhesion of organic coatings on steel by generating tensile stresses and polymer degradation, thereby limiting the life of the protective system.

The effectiveness of phthalocyanines and polyphthalocyanines as corrosion inhibiting coatings for protection of steel have been studied. The metallo-phthalocyanines studied included phthalocyanine tetracarboxylates of Fe(III), Co(II), VO(IV), Cr(III), Si(IV) and Zn(II). Polymeric phthalocyanine coatings based on Fe(III) polyphthalocyanines gave the highest inhibitor efficiency of 82%, as confirmed by AC impedance analysis. The polymerization was achieved by simple dip coating followed by heat treatment of the coated surface at 450°C in an inert atmosphere. The resulting coating is adherent and electrically conducting when appropriately doped. Our recent findings indicate that the inhibition efficiencies can be further improved by introducing a long alkyl chain into the phthalocyanine molecule.

Semiconductor and insulator coatings, appropriately configured in Metal-Semiconductor (MS) and Metal-Insulator (≈20–100Å)-Semiconductor (MIS) structural formats, are shown to result in the formation of a built-in active electronic barrier on metal surfaces. This interfacial electronic barrier impedes the transfer of electrons from the metal to oxidizing species present at the metal surface, thereby providing protection against corrosion. The effectiveness of the electronic barrier concept has been confirmed using weight-loss, and cathodic and anodic polarization measurements on aluminum samples coated with indium tin oxide ITO (semiconductor) and SiO2 (thin oxide/insulator) films. In particular, Al-ITO, Al-ITO-Si3N4, Al-SiO2-ITO, and Al-SiO2-ITO-Si3N4 structures were fabricated and tested in a 1% NaCl, pH-2 solution. The films were grown using chemical vapor deposition (CVD) and spray techniques to ensure high quality and reproducibility. Aluminum samples tested included commercial purity, high purity (polycrystalline and single crystalline), and alloy (7075-T6). The MS and MIS configurations were found to provide superior corrosion protection as compared to conventional insulating films (e.g., Al-Si3N4). The active electronic barrier approach is a generic methodology to inhibit corrosion, and it can be realized using other semiconductor/insulator combinations including semiconducting polymer coatings.

Since the seminal work of Friedman and Smith [1] obsidian hydration dating (OHD) has undergone several important stages of development and refinement. This paper will summarize the history of research and developments as to elucidate some areas for future research.

Archaeologists have taken a pragmatic and empirical approach towards OHD and hydration rate determination. They would like OHD to become an absolute chronometric technique. Geochemists and material scientists have sought to understand the hydration process from an environmental, chemical and thermodynamic perspective. As suggested by the literature, obsidian hydration appears to be a diffusion, reaction and dissolution process dependent on the chemical and thermal history of the hydration environment. Although there appear to be certain central tendencies, however, there are discrepancies between empirical archaeologically-derived data and theoretical models.

California offers a rich data base for synthesis and testing of hydration models. There are over 25 natural obsidian sources many of whose chemical and physical properties have been measured by Ericson [2]. Obsidians have been distributed aboriginally as artifacts into diverse environments. Intensive excavations, underwritten by extensive land development, have contributed to development of a number of source-specific hydration rates for single sources. Reanalysis of the California data warrants future examination to advance our understanding of obsidian hydration dating on a world wide basis.

Chemical analysis of typical obsidians place them with a group of silica- and alumina-rich glasses constructed of a three dimensional framework of silica and alumina tetrahedra with nearly all tetrahedra sharing corners. Raman and infrared spectra of unweathered obsidians confirm the high degree of polymerization as well as some additional structural disorder. Analysis of dissolution rates of various glasses shows obsidian to be among the most stable, comparable to the most durable synthetic glasses. Surface layers on glasses can be chemically characterized by depth-profiling techniques such as SIMS and SIPS that give depth-concentration profiles for individual elements. Hydration rinds on glasses can be structurally characterized by infrared spectroscopy which shows both hydration and re-polymerization as the rinds age. Because obsidians are already completely polymerized glasses, their hydration rinds are mainly a result of hydrolysis and alkali exchange.

The results of a series of hydration experiments on natural glasses (Hawaiian basalt, obsidian) and the nuclear waste glass WV-44 done to examine laboratory methods of accelerating reaction processes are summarized. The glasses were reacted in hydrothermal solution and in saturated vapor water. It was found that different reaction rates and processes were found using the differing conditions, and that laboratory efforts to accelerate and duplicate natural processes must account for the physical processes that occur naturally.

The rate of many processes, including the diffusion of water into rhyolitic volcanic glass (obsidian), as well as the racemization of amino acids is temperature dependent, and a knowledge of temperatures integrated over time periods of at least a year is necessary to quantify these processes. The construction and properties of simple devices consisting of small plastic containers that change weight at a rate that is a function of temperature and the activity of water will be described. The cells function because water diffuses through the plastic across a constant vapor-pressure gradient. This vapor-pressure gradient is maintained constant between the substances within the cell and the materials outside the cell. The plastic cells are usually filled with water and surrounded by a dehydrating agent, such as silica gel. A better arrangement is to fill the cell with a mixture of solid sodium chloride (NaCl) and a saturated solution of NaCl, and to surround the cell with pure water. A number of plastics have been investigated, including polycarbonate, polystyrene, tefzel, polyallomer, and methacrylate. The cells have been sealed by various methods including screw caps, room-temperature vulcanizing silicone rubber sealant, and rubber stoppers. The final design consists of a small cell made of a polycarbonate plastic centrifuge tube containing solid NaCl plus NaCl-saturated solution sealed with a rubber stopper and placed in a polypropylene tube containing pure water. Our aim has been to develop cells that are sufficiently sensitive to yield a precision of ±0.2°C when exposed for one year at temperatures that range from 0° to 40°, and that will fit into metal fittings that can be screwed into standard 3/4-inch plastic water pipe (approximately 1 inch outside diameter).

Various theoretical models that have been proposed to correlate glass durability to their composition for a wide variety of silicate, borosilicate, and aluminosilicate glasses are examined. Comparisons are made between the predictions of these models and those of an empirical formulation extracted from existing data in the present work. The empirical approach provides independent confirmation of the relative accuracy of the silica release rate predictions of the different theoretical models in static leaching systems. Extensions of the empirical approach used in this work are discussed.

Hydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.

Induced obsidian hydration experiments have been conducted over the last six months at Sonoma State University. Our initial focus has been to assess the influence of experimental conditions on hydration development within a thermally controlled pressure reaction vessel. Although an ultimate goal is to calculate source-specific rates for local obsidians, given current uncertainties regarding the ability to reliably express hydration widths as calendar years, a more immediate goal is to develop a means to compare hydration rim measurements of samples from one obsidian source relative to another so that archaeological assemblages containing obsidians from two or more sources can be placed into a time series. Induced hydration experiments are expected to provide data that illustrate the relationship between hydration measurements of different obsidians with temporal equivalency. Results and implications of initial experiments are discussed.

Samples of wet 13th-14th c. Grisaille window glass, visually sorted according to their extent of corrosion, were examined for physical changes while air-drying and solvent-drying. Polished cross-sections of the samples were examined with a JEOL-35CF SEM with a LINK AN 10,000 dispersive x-ray analyzer. Elemental distribution maps showed distinct alterations in the positioning of elements according to the corroded nature of the glass.