My colleague, Wally Hansen, and I have just released a new review paper that may be of interest to those of you in the aerospace industry.

As you know, aerospace has had decades of experience with metal bonding, sealing, and corrosion protection. However, many of these methods have not lent themselves well to automation, and they also generate environmental waste.

But new applications are emerging for atmospherically deposited nano coatings that can address these shortcomings. These nano coatings are formed by direct injection of select vapor chemistries into the plasma jet. Such molecular surface modifications yield long-term, environmentally stable interfaces for bonding.

Cleaning

Plasma surface treatment begins with a fine cleaning of the substrate to remove loosely bound organic contaminants (on metal oxide surfaces, the oxide layer is either removed or pre-conditioned for adhesion).

Atmospheric plasma jets provide a multi-faceted cleaning action. First, the charged species within the plasma neutralizes electrostatically bound particles. Next, a vortex of pressurized gas blows away unbound solids and oils. Finally, the substrate is bombarded by reactive gas plasma species.

Low molecule weight contaminants on the substrate surface are efficiently reduced into nascent compounds and removed from the material system. This final phase of cleaning takes place on the molecular scale.

Coating

After cleaning, a different plasma jet technology deposits a functional coating. The coating thickness is controlled by parameters such as distance to substrate and speed. Coatings have been developed that simultaneously provide adhesion promotion and corrosion protection of the bond line. Furthermore, some of these coatings act as reliable tie layers, effectively bridging contact between inorganic and organic systems. There is opportunity to replace liquid primers or otherwise laborious surface pre-treatments used in composite bonding.

So far, atmospherically deposited plasma coatings have demonstrated utility as a release layer, an adhesion promoter, or a corrosion barrier. In practice, the plasma-deposited nano coating combines with conventional protective top coats to amplify corrosion resistance and suppress ingress at damage sites.

The atmospherically deposited plasma coatings show substantial improvement in corrosion performance even at a thickness of less than 500 nm.

Conclusion

Atmospheric plasma cleaning and coating can offer significant advantages in surface preparation of metals and composite systems for bonding and sealing in the aerospace industry. The technology is scalable and amenable to automation as it enables high-throughput material processing.

Furthermore, some plasma implementations are able to combine multiple process steps into a single step while reducing waste and reducing operating costs – without compromising performance.

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Rocket propulsion has progressed in the over 40 years of space travel. On October 4th 1957 the Soviet Union launched the first artificial earth satellite. The feat was achieved using a 2 stage R-7 ICBM rocket weighing 170 tons. The solid rocket fuel needed to be held at cryogenic temperatures. Although today’s rockets are a lot more high tech most of the fundamental principles of propulsion still persist. Mainly the modern rocket typically utilizes solid rocket fuel. High altitudes are reached through multi-stage systems whereby the burned-out stage drops away relieving cumbersome mass from taxi of the final payload. Surprisingly the velocity with which space is traversed has not appreciably changed since the year 1962. This time of travel is arguably the biggest impedance to human exploration of the solar system. Second is that fact that once the rocket is ignited there is no turning it off; the fuel must be burned to completion. This is sort of suggestive of a one way trip. There is however a new generation of rocket propulsion beyond the horizon. The concept is named Variable Specific Impulse Magnetoplasma rocket or VASIMR.

 

The VASIMR is a plasma based propulsion system. Radio Frequency electric field ionizes the fuel into a plasma. Magnetic field then directs the hot accelerating gas out of the engine generating thrust. Even though the PTS and Plasmatreat organization utilize plasma for a different purpose, there are a couple of parallels that can be drawn. For starters one may envision mission specific gas mixture selection balancing metrics such as thrust, efficiency, and weight. Furthermore a plasma process may start or stop, its intensity regulated, and the gases employed are usually prevalent throughout the solar system. Efficient plasma impulse is ideal in the vacuum of space. There is great appeal in possibly being able to refuel a plasma propulsion system using gases present in the atmosphere of a destination such as mars. To put it in another perspective contemporary space shuttles exhausts propellant at about 6,000 m/s. An RF plasma would potentially expel mass in the range of 30,000 – 300,000 m/s. Here on Earth plasma has enabled myriad industrial and technological possibilities. I will finally conclude with an appropriate adage, “to the moon and beyond.” I am excited to see the field of plasma opportunity expanding into the stars.

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