Technology
Tougher deck coating made for navy carriers Chemists at the Naval Research Laboratory, Washington, D.C., have developed a longer-lasting coating for the decks of aircraft carriers that they hope eventually may save the Navy millions of dollars in repair costs. Not only is the new coating expected to last about two to two and a half times longer than the coatings that are now used to provide a nonskid surface on carrier decks, explains Robert F. Brady Jr., supervisory chemist and principal investigator on the project, but when they do break down they tend to powder rather than chip. This property is particularly important on an aircraft carrier, Brady says, because chips of deck coating can be sucked into the engines of landing airplanes and cause very expensive damage. Present nonskid coatings on carrier decks must be resurfaced at least twice a year at an annual cost of about $3 million. The new coating would last from 12 to 18 months, Brady estimates, before it would need to be replaced. "There are no rare ingredients or high-cost materials needed for our coating," he adds. He estimates that the cost of the new coating should be comparable to that of conventional ones. The candidate coatings are twocomponent epoxy polyamides. They can be cured at room temperature and use conventional solvents. They are pigmented with titanium dioxide, carbon black, and talc, Brady says. The solvents currently being used
NRL's Brady tests new coating are low-molecular-weight aromatic naphtha and ethylene glycol monoethyl ether. The second of these solvents has been associated with reproductive toxicity in animal tests, however, and one of the aims of present work is to replace it with a less toxic solvent. Brady and associates Larry Kraft and Marina Ambrogi have made test panels of the new coatings which they say outperform conventional products. Laboratory tests will continue for another six to nine months. Then the researchers will take their material to an aircraft carrier for performance testing. D
Sandia unit to study nuclear reactor melts A facility capable of melting and superheating half a ton of uranium dioxide has b e g u n operation at Sandia National Laboratories. Called the large-scale melt facility (LMF), it is the world's largest facility, according to Sandia, for producing melts of reactor fuel similar to those possible in a severe nuclear power reactor accident. Sandia says the LMF will enable it to investigate—on a scale and at temperatures never before possible— the safety-related phenomena that could develop if a reactor core cooling system failed. The facility's 22
August 1, 1983 C&EN
furnace can handle 1100 lb of dep l e t e d u r a n i u m dioxide, w h i c h reacts to high temperatures the same as enriched uranium dioxide in fuel. It can superheat the material to 2700 °C without damage to itself, well above the 1500 °C melting point of steel achievable by current state-ofthe-art industrial furnaces of this scale. The furnace is the heart of the new facility. It is a 1000-Hz, 250-kW induction system. A watercooled copper coil acts as an induction coil that couples to a specially designed graphite holder, called a
susceptor. The susceptor holds a metallic crucible that contains densified uranium dioxide powder. As the coil, wound around the crucible, generates an electric field, it causes current to flow in the susceptor, raising its temperature. In this way, the susceptor heats the 32.5-cmdiameter, 52.5-cm-high metallic crucible and its contents by radiation and conduction. When the uranium dioxide becomes m o l t e n , a shotgunlike device fires two slugs into the crucible base, breeching the crucible and permitting molten uranium dioxide to drain rapidly into the experiment chamber located beneath the furnace. In an experiment, molten uranium dioxide—to which can be added nonradioactive materials such as zirconia and yttria to simulate reactor fuel cladding and fission products—drains rapidly into the experiment chamber that contains solids, gases, or liquids that the melt could encounter during a severe accident. Extensive instrumentation gathers information from inside the experiment chamber. For example, initial tests at LMF are investigating interactions that might occur if molten core materials escaped from a reactor vessel and fell onto the reactor c o n t a i n m e n t structure, typically composed of concrete. According to Sandia, extensive materials R&D was instrumental to successful operation of the furnace. The refractory metal alloy used for the crucible must survive the corrosive effects of molten uranium dioxide on its inside surface and chemical attack on its outside surface due to contact with the susceptor. Early on, Sandia determined that only tantalum and tungsten could be considered for the crucible but that neither alone could withstand attack from both hot graphite and molten uranium dioxide. This determination led to a crucible with a four-layer construction. The outer layer— V4 inch thick—is an alloy of 90% tantalum and 10% tungsten. A 1/10-inch-thick layer of pure tungsten is plasma sprayed to the inside of this outer layer. Next is a zone of tungsten powder 1/8 inch thick, followed by a 1/16-inch-thick inner tungsten liner applied with chemical vapor deposition. D
