In this study we examine the potential for using brushite (dicalcium phosphate dihydrate) as a coating for orthopedic implants. It was found that brushite is transformed into a more stable calcium phosphate (hydroxyapatite), regardless of the aqueous transforming media utilized. The transformation was carried out at room temperature in deionized water, deionized water with added calcium ions, and modified Hank's type solution without calcium and magnesium ions, modified Hank's type solution with calcium and magnesium ions, and modified Hank's type solution with added calcium ions. In several of the transformation systems it was noted that brushite provided an increased amount of calcium ions to the transforming media through solubility. The process was monitored using X-ray diffraction, X-ray photoelectron spectroscopy, and dissolution studies. Scanning electron microscopy and energy dispersive spectroscopy were also utilized for characterization. The brushite coatings can be easily achieved electrolytically on conducting substrates. The process is non line of sight, simple, and inexpensive; and when using an electrolyte that can sustain currents of approximately 100 mA/cm2, the necessary coating can be completed in about 3 min.
Polymer-bonded explosives (PBX) fulfil the need for insensitive munitions. However, the environmental impacts of PBX are unclear, even though it is likely that PBX residues from low-order detonations and unexploded ordnance are deposited on military training ranges. The release of high explosives from the polymer matrix into the environment has not been studied in detail, although as polymers degrade slowly in the environment we anticipate high explosives to be released into the environment. In this study, PBXN-109 (nominally 64% RDX) samples were exposed to variable UK climatic conditions reproduced in the laboratory to determine the effects of temperature, UV irradiation and rainfall on the release of RDX from the polymer binder. The most extreme conditions for spring, summer and winter in the UK were artificially reproduced. We found that up to 0.03% of RDX was consistently released from PBXN-109. The rate of RDX release was highest in samples exposed to the summer simulation, which had the lowest rainfall, but the highest temperatures and longest UV exposure. This was confirmed by additional experiments simulating an extreme summer month with consistently high temperatures and long periods of sunlight. These results probably reflect the combination of polymer swelling and degradation when samples are exposed to higher temperatures and prolonged UV irradiation.
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