Richard D. Granata

Positron annihilation lifetime study of PTFE/silica composites

Positron annihilation lifetime spectroscopy (PALS) was used to study the microstructure of PTFE/silica composites. The positron lifetimes (τ n ) and intensities (I n ) of PTFE and the composites (30-62% silica) were measured at room temperature as a function of specimen thickness. Four lifetime components were found in PTFE and the composites. The longer lifetime components, τ 3 = 1.4 ns and τ 4 = 4.4-4.1 ns, were interpreted to be due to the presence of two different sized free volume cavity distributions within the PTFE/silica composites. A strong silica concentration dependence was found in the bulk intensities (I 3b and I 4b ). The I 3b value increased from 13.0% in PTFE to 28.2% in the 62% composite, while the I 4b value decreased from 17.5% in PTFE to 4.5% in the 62% composite. The smaller-void size, free volume fraction (τ 3 I 3b ) values increased linearly between 0 and 100% silica concentration, while the larger void size, free volume fraction (τ 4 I 4b ) values decreased nonlinearly with silica concentration. Since silica has a long lifetime component (τ 3 = 1.6 ns), this behavior is ascribed to silica particles occupying the large free volume cavities (370 A 3 ) in the PTFE/silica composites.

Quantitative Evaluation of Steel Corrosion in Microenvironments Using the Corrosion Coulometer

A corrosion sensor, termed a corrosion coulometer, has been developed for use on steel structures. The corrosion coulometer quantifies the corrosion occurring on a steel element due to atmospheric conditions such as dust, debris, humidity, condensation and electrolytic species. Use of inexpensive monitors to accurately assess the condition of structural systems can have a major impact on reducing the costs of maintaining the infrastructure. This paper presents results from application of corrosion monitors on weathering steel bridges, at an outdoor exposure site and under laboratory conditions. The emphasis is the quantitative relationship between coulometer and adjacent panel corrosion penetration data. More detailed discussion focusing on corrosion coulometer sensor design considerations is available [1].

Electrochemical impedance spectroscopic study of encapsulated triple tracks test (TTT) circuits

Electrochemical impedance spectroscopy (EIS) is effective for studying the reliability of protective coatings on microelectronic packaging devices. Triple track test (TTT) circuits were evaluated as a function of exposure time at 121/spl deg/C and 2 atm pressure. Specimens were deliberately contaminated by various chemicals and particles before coating. The impedance of some specimens decreased after the first 10 hours in the Pressure Cooker Test (PCT) while some lasted more than 150 hours in the PCT without an appreciable change in the impedance values. Impedance of the specimens changed appreciably due to water uptake in the epoxy coatings. The ionic contamination trapped under the coating caused faster failure in the TTT with respect to clean specimens. Water diffused to the polymer/gold interface causing a change in the dielectric properties of the specimen, shown as a shift in the EIS spectrum. This shift was observed in EIS spectra for most of the specimens which were exposed for more than 150 hours. The change suggests water that penetrated the coating made a conductive pathway to the interfacial region, a common cause of debonding between the metal (or ceramic) polymer interface. In one case (specimens contaminated by SiO/sub 2/ particles) the shift was not observed-suggesting that SiO/sub 2/ particles do not accelerate the adhesive failure at the metal (or ceramic)/polymer interface. The calculated saturated volume fraction of water at the metal (or ceramic)/polymer interface was 1.1/spl plusmn/0.1.

Factors affecting the pH developed within carbon steel crevices

Abstract The pH within a carbon steel crevice exposed to a chloride medium is 10–12 upon first exposure. Long-time exposure results in a near neutral pH. Removal of electrolyte from the exterior of the crevice causes the pH to become 4–5.

Characterizing copper surfaces using a polysulfide reagent

Abstract Copper immersed in a 0.025 M Na2S4 solution at pH 11 turns black at a characteristic time that is controlled by the presence of films or contaminants on the copper surface. The color change occurs coincident with an abrupt change in the corrosion potential. It is hypothesized that the rate-controlling step is the conversion of elemental copper and/or copper (I) to the copper(II) valence state. The rate of this reaction is controlled by the chemical nature of the copper surface. The procedure shows promise for characterizing the cleanliness of copper surfaces.