Novel Process to Create Structured Membrane Films for Micromachining Applications

The first of Glenn's innovative sealing technologies features an acoustic resonator, which creates acoustic waveforms that generate a sealing pressure barrier blocking fluid flow from an area of high pressure to an area of low pressure. Through the use of resonant macrosonic synthesis (RMS), the device thus permits non-contacting sealing operation. To increase the effect, Glenn researchers discovered that an oscillating driver can be coupled with the resonator to achieve an RMS pressure-multiplying effect. In this way, the combination of the oscillating driver and the resonator cavity can create four to ten times greater pressure at the seal, thereby enabling optimal sealing. These sealing devices are also very versatile for practical applications. The resonators can be selected from several different shapes to produce the desired RMS effect. Moreover, the high and low pressure areas in the application can be in contact with a structure while the resonator is not in contact, allowing a wide array of design strategies to integrate the sealing device. For extremely high-temperature sealing applications, Glenn researchers have devised novel methods for using nickel-based single-crystal superalloys. One process includes fabricating a rapid prototype spring "pattern" to create the required cavity in a ceramic mold, and then casting a coiled spring to form at least one coil spring configuration based on the ceramic mold. The second process includes determining the orientation of the single crystal in a single crystal slab to "harvest" a single crystal spring with optimal properties. In this way, the single crystal preloader can be manufactured in a variety of configurations to meet the requirements of particular applications.

For extremely high-temperature sealing applications, Glenn researchers have devised novel methods for fabricating single-crystal preloaders. NASA's high-temperature preloaders consist of investment cast or machined parts that are fabricated in various configurations from single crystal superalloys. Machined preloaders include a variety of spring configurations, compressed axially or radially, fabricated from single crystal slabs. Before machining, the slabs are carefully oriented in a special goniometer using x-diffraction techniques. This helps to maintain proper crystal orientation relative to the machined part and the applied loads. For more complex geometry components which cannot be easily and economically machined, an investment casting approach would be used. Complex preloader geometries include wire coil springs of various configurations. These single crystal preloaders would be designed with the appropriate stiffness for the intended thermal barrier/seal application and placed underneath, or integrated within, the seal/barrier. At extrememly high temperature, the preload device keeps the seal/barrier mated against the opposing surface as the gap between the two surfaces changes, maintaining contact between surfaces and preventing convective heat transfer.

NASA designed an inflatable habitat intended for space whose exterior incorporates an expandable layer known as the bladder – the main pressure shell of a module to which astronauts may reside while off-world. The bladder is made from a polymer material and is surrounded by protective layers to ensure it is not damaged and does not leak. On every module, there are two areas where the bladder and other flexible layers interface with the ends of a cylindrical core, at the bulkheads. Seals between the non-metallic bladder and the metallic bulkhead are critical in maintaining a safe pressurized environment for astronauts to live and work. With both bulkhead plates assembled, RTV silicone is deposited in specially designed channels which are sandwiched between the plates. After the channels are filled, a cure-in-place seal is formed between the bladder and the bulkhead. The RTV sealing method worked successfully during prototype testing as confirmed by a helium leak test and post-test visual inspection of the seals. In prototype testing, this method created a consistent and reliable seal between the bladder and bulkhead assembly replicated from the inflatable module design. The RTV sealing method may benefit terrestrial applications that may demand cure-in-place internal seals. The method could also innovate manufacturing processes for components by enhancing the speed of assembly while increasing seal integrity.

Approximately 50 inches in diameter, Glenn's unique sealing system consists of multiple elements installed in a recessed rectangular sealing groove. The main sealing function is provided by an elastomer element (e.g., silicone) comprising one or more sealing wall(s) connected by a web. The wall(s) extend above the top of the sealing groove so they are compressed by the opposing mating surface during the sealing process. The retractable shroud element is installed between the wall(s), with its base resting atop the web of the sealing element. The shroud is typically composed of an elastomer material to allow for flexibility (which is essential to retraction), but it can also be made from thin metal or plastic materials. When the seal is no longer in use, a pair of V-shaped shroud "arms" extend upward from the base of the seal to cover the wall(s). A thin metal retainer is installed on top of the shroud, and fasteners pass through holes in the retainer, shroud, and sealing elements to secure the system to the base of the sealing groove. Metal washers are installed in these holes to provide a load path between the metal retainer and the surface of the sealing groove. The system can seal against either a flat metal surface or another seal of the same design. This sealing system has been designed to accommodate multiple sealing cycles and has exhibited extremely low leak rates, making it an attractive solution within a variety of industries from aerospace to agriculture.

JPL's process uses a relatively low-power plasma to remove the indium oxide with less sputtering of the underlying indium, and a second step to remove organics left from the first step. Typical processing time for each step has been 20 minutes, although those times could likely be reduced.