Date: Dec 15, 2009 Author: Joe Singleton Source: MDA (
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by Joe Singleton/jsingleton@nttc.edu
Rocket nozzle materials developed for improving the performance of missiles might soon find a new home in hospital x-ray equipment and industrial heaters.
Through a 2008 SBIR Phase II contract, MDA funded Plasma Processes, Inc. (Huntsville, AL), to develop a material capable of preventing rocket nozzle erosion caused by high-temperature exhaust. The company determined materials such as tungsten-rhenium or tantalum carbide provided an optimum level of protection against erosion.
To fabricate an erosion-free rocket nozzle, Plasma Processes first fabricates a mandrel that conforms to the internal shape of the object to be manufactured. Then, using its patented plasma gun, tungsten-rhenium or tantalum carbide is vaporized in a stream of argon and hydrogen heated to about 10,000°C. The material, a vacuum plasma spray (VPS), is deposited on the rotating mandrel until the desired thickness has been achieved. Nozzles the same size as those found on small tactical missile can be created in a few minutes' time. Larger nozzles, such as those on booster rockets, tend to take at least two hours. Once the component has cooled, the mandrel is removed, leaving the manufactured part. Electrical-discharge machining may be required to finish the edges.
Contrasted with machining a component from a block of material, net-shape manufacturing, such as Plasma Processes' technique, reduces waste and eliminates cost and time. These reductions allow cost savings to be passed on to the customer, since the ceramic-like materials are very expensive--sometimes thousands of dollars per pound--and very difficult to machine.
Company tests have shown that VPS-manufactured rocket nozzles remain intact with no sign of erosion occurring after ignition, primarily due to the materials' high melting point (3410°C to 3880°C) versus rocket exhaust gas (2500°C to 3000°C). Current nozzle materials erode at a rate of up to 10 mils per second. Erosion resistance helps maintain a rocket's structural integrity, allowing it to travel farther or carry heavier payloads.
Beyond the realm of defense, one possible application for VPS is in hospital x-ray machines, specifically the generators used in computer tomography (CT) scans. To get the highest possible resolution, the CT machine requires higher levels of energy generation. And since x-ray target materials may be similar to the same alloys used in making rocket nozzles, Plasma Processes sees a business opportunity.
Industrial crucibles offer another potential commercial market for Plasma Processes' products. Crucibles used for growing crystals operate at extremely high temperatures. The industry needs high-purity materials that can withstand such high temperatures without contaminating the crystals, and Plasma Processes President Timothy McKechnie thinks his company's products meet such requirements.
Plasma Processes now is focused on determining the best marketing and business strategies to get its technology inserted in defense platforms as well as recognized by the commercial sector. The company also hopes to find partnership opportunities with mid-tier contractors in the near future.
