Titanium has been found to offer several advantages over molybdenum as the material used to construct electrostatic-accelerator and -screen grids for ion thrusters for spacecraft. These advantages could also be expected to extend to the manufacture of grids for ion accelerators used in scientific research and the fabrication of semiconductors.
Titanium was chosen as the result of a search for a grid material that is less vulnerable to sputter erosion and from which grids could be fabricated at acceptably low cost. At a given current density, the volumetric rate of sputter erosion of titanium is about half that of molybdenum. Hence, in comparison with a thruster containing molybdenum grids operating at a given beam current density, a thruster of the same size containing titanium grids can last about twice as long; alternatively, the thruster containing titanium grids can last about the same amount of time when operated at twice the beam current density. Similarly, accelerators containing titanium grids could be operated at higher voltages.
The strength-to-weight ratio of titanium exceeds that of molybdenum, making it possible to reduce the weights of ion accelerators. The substitution of titanium for molybdenum does not entail any increase in the complexity of ion-accelerator design.
Titanium grids can be fabricated by use of photochemical-etching and hydroform processes heretofore used to make molybdenum grids for Glenn Research Center. Previously, attempts at photochemical etching of titanium were thwarted by the corrosion-resistant nature of titanium, but recent advances in photochemical etching have overcome this obstacle.
Finally, titanium offers the advantage of lower cost: at the time of reporting the information for this article, the cost per unit weight of titanium was 43 percent less than that of molybdenum.
This work was done by Vincent K. Rawlin of Glenn Research Center and George C. Soulas of Dynacs Engineering Co. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center,
Commercial Technology Office,
Attn: Steve Fedor,
Mail Stop 4—8,
21000 Brookpark Road,
Cleveland, Ohio 44135.
Refer to LEW-16893.