Granata, Richard D.

This research tests the use of sensitized lanthanide ions to determine if they can
detect water-borne explosive traces and produces two designs for a field-deployable
underwater explosive trace detector. 1,1 0-phenanthroline and thenoyltritluoroacetone are
evaluated as sensitizing ligands to absorb energy and initiate the fluorescence process in
europium ions. Different compounds obtained via ligand choice and mixing order are
evaluated for their ability to produce a large fluorescence differential between explosive-laden
and explosive-absent solutions. Optimal excitation and emission wavelengths for
several different compounds are determined, as well as practical wavelengths to be
applied in the field. The effect of methanol as a solvent to deliver the reagents is
evaluated and rough solubility limits are determined. The effects of seawater constituents
on detection are investigated and explosive detection limits are determined. It was found
that this method and device are viable for underwater explosive trace detection. A field-deployable
device is designed, characterized, and proven.

This research tests the corrosion resistance of weathering steel against carbon
steel exposed to dry and humid cycles during laboratory experiments. Various
environments are tested and include the following parameters: chloride
concentration, pH and wetting time. Corrosion values from weight loss analysis are
given and studied for the same environments. X-ray diffraction characterized the
formation of different oxides as a function of the environment and gave a better
understanding on the formation of the protective patina on the weathering steel, and
validated that chamber experiments reproduce field conditions. The study is
supported by the design, test and validation of an easily deployable galvanic
atmospheric corrosion sensor that allowed the monitoring of the corrosion rate on
an hourly basis.

Weathering steel has been a primary construction material for bridges in the
United States. Notches caused by corrosion are observed on the flange of steel
I-beams. These notches reduce the cross section area of the structure and are
threats to bridge safety. A606-04 Type 4 cold rolled weathering steel samples
were studied in this thesis to understand the effect of notches that caused by
corrosion. Weathering steel samples were in the shape of plates, which simulated
flange of I-beams. The plate samples were notched across their surfaces by
applying electrical current through an electrochemical circuit composed of an
anode, a cathode and electrolyte. Sixteen samples were notched and cut into
appropriate shape for fatigue testing. S-N (Stress-Number of cycles to failure)
diagram established from fatigue data indicated that the fatigue strength
decreased below AASHTO category B. Weibull analysis was also performed to
understand the reliability distribution.

Tests in a cyclic chamber and in real atmospheric conditions resulted in the development of an improved corrosion coulometer sensor. First tests showed that it responded well in a reproduced environment but not satisfactorily in a real one, although it seemed to present a good correlation with the weather observations. However, these tests allowed a small time step data analysis of atmospheric corrosion and therefore an improved knowledge of this process. Also discussed are the possible ways of retrieving the corrosion coulometer data wirelessly, thus allowing a real-time analysis of atmospheric corrosion on steel structures. Ideas are proposed for improving both the sensor and the electronic package to make the system an efficient monitor of atmospheric corrosion.

This research investigates the influence of chromate, as a conversion coating and as an inhibitor pigment, on the adhesion of epoxy coatings to an aluminum substrate. Epoxy coatings, with and without strontium chromate (SrCrO4) inhibitor pigment, are prepared according to manufacturers' specifications on AA2024-T3 substrates, with and without chromate conversion coatings. Specimens are exposed in an environmental chamber, cycling between high and low humidity conditions. After exposure, specimens are evaluated using Electrochemical Impedance Spectroscopy (EIS), ASTM D3359 cross-cut tape test, and an Environmental Scanning Electron Microscope. From the evaluation it was determined that under these exposure conditions chromate does not increase the adhesive strength between the aluminum substrate and the epoxy coating system, but does provide corrosion inhibition. Regardless of the pretreatment or the coating system, the coating fails at the interface between the substrate and the coating.

This research used Electrochemical Impedance Spectroscopy (EIS) as a non-destructive technique to evaluate coating performance and determine the electrochemical characteristics of Special Hull Treatments (SHT). The evaluation of the SHT system provided information on its corrosion resistance and cathodic protection-influencing characteristics. The coating's impedance was analyzed while exposed to ambient versus 4.5 MPa pressures and immersion times of 1 to 9 days in seawater. Eleven specimen types were evaluated based on coating seam orientation and composition. The data support the conclusion that there was no effect on impedance values and phase shifts due to orientation, formulation, pressure values or immersion time. However, temperature increase above 30° was shown to decrease the impedance values of the SHT specimens.