Molecular Adsorber Coating (MAC)

materials and coatings
Molecular Adsorber Coating (MAC) (GSC-TOPS-28)
Capturing outgassed volatiles using a simple spray coating
Overview
Goddard Space Flight Center has developed a portfolio of molecular adsorber coatings (MAC) to mitigate issues posed by volatile organic compounds (VOC). Many materials contain gasses that are trapped on or within the surface that, when in vacuum, will escape the host material over time - a process known as outgassing. The extent of outgassing is a function of the material, temperature, and the vacuum level present. To address outgassing issues in spacecraft, NASA has historically used zeolite based molecular adsorbers in spacecraft and instruments to collect and retain outgassed molecular effluent emanating from potting compounds, epoxies, tapes, lubricants, and other spacecraft materials, protecting critical, contamination sensitive, surfaces. Uncontrolled, molecular contamination can cause significant degradation of instrument performance, thermal control properties, solar array efficiency, optical surfaces, laser systems, detectors, cryogenic instruments, and high powered electronics. In an effort to simplify previously flown complex zeolite coated cordierite molecular adsorber puck systems, such as those flown on Hubble Space Telescope (HST), a portfolio of easily produced and applied molecular adsorber coatings have been developed.

The Technology
MAC is a zeolite based coating that captures and traps molecules in its microscopically porous structure. This microscopic nano-textured structure, consisting of large open pores or cavities, within a crystal- like structure, provides a large surface area to mass ratio that maximizes available trapping efficiency. MAC is a durable coating that is applied through spray application. These sprayable coatings eliminate the major drawbacks of puck type adsorbers (weight, size, and mounting hardware requirements), resulting in cost savings, mass savings, easier utilization, greater adsorber surface area, more flexibility, and higher efficiency. This coating works in air, as well as vacuum systems, depending on the application. There is potential for ground based spin-off applications of this coating, particularly in areas where contaminants and volatile compounds need to be collected and contained. Example industries include: pharmaceutical production, the food industry, electronics manufacturing (circuit boards and wafers), laser manufacturing, vacuum systems, chemical processing, paint booths, and general gas and water adsorption.
Figure 2.: Large pores or cavities on the crystal structure of zeolite capture and trap contaminant molecules; Figure 3.: Nano-sized silica molecules of the binder gels around the pigment without blocking the adsorption sites
Benefits
  • Better adsorption than other coating slurries: NASA's MAC is far superior to other adsorber coatings previously tested or developed by NASA GSFC.
  • Coat virtually any surface: NASA's MAC exhibits excellent adhesion to multiple substrates, including but not limited to composites, cellulose based materials, aluminum, and other metals.
  • Easy to formulate & apply: Based upon commercially-available and low-cost chemicals, NASA's MAC can be deposited via simple water-based spray techniques to thicknesses in the 100-250 micron range (i.e., 4-10 mils), depending on application.

Applications
  • General gas and water adsorption
  • Collection and containment of contaminants and volatiles
Technology Details

materials and coatings
GSC-TOPS-28
GSC-16105-1 GSC-17075-1 GSC-17208-1 GSC-17075-2
10787575
Abraham, N., Hasegawa, M., & Straka, S. (2012). Development and testing of molecular adsorber coatings. Optical System Contamination: Effects, Measurements, and Control 2012.
Similar Results
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Air Revitalization for Vacuum Environments
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NEW CFC Front Image
Cryogenic Flux Capacitor
Storage and transfer of fluid commodities such as oxygen, hydrogen, natural gas, nitrogen, argon, etc. is an absolute necessity in virtually every industry on Earth. These fluids are typically contained in one of two ways; as low pressure, cryogenic liquids, or as a high pressure gases. Energy storage is not useful unless the energy can be practically obtained ("un-stored") as needed. Here the goal is to store as many fluid molecules as possible in the smallest, lightest weight volume possible; and to supply ("un-store") those molecules on demand as needed in the end-use application. The CFC concept addresses this dual storage/usage problem with an elegant charging/discharging design approach. The CFC's packaging is ingeniously designed, tightly packing aerogel composite materials within a container allows for a greater amount of storage media to be packed densely and strategically. An integrated conductive membrane also acts as a highly effective heat exchanger that easily distributes heat through the entire container to discharge the CFC quickly, it can also be interfaced to a cooling source for convenient system charging; this feature also allows the fluid to easily saturate the container for fast charging. Additionally, the unit can be charged either with cryogenic liquid or from an ambient temperature gas supply, depending on the desired manner of refrigeration. Finally, the heater integration system offers two promising methods, both of which have been fabricated and tested, to evenly distribute heat throughout the entire core, both axially and radially.
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Particle Contamination Mitigation Methods
The following methods can be used individually or in combination to generate superhydrophobic surfaces: Synthesis of novel copolyimide oxetanes with unique surface properties The technology is the synthesis of a polyimide coating or film with a modified surface chemistry shown in Figure 1. A minor amount of an oxetane reactant containing fluorine is added to the polyimide, and the oxetane preferentially migrates to the surface, enabling relatively high concentrations of fluorine at the surface, without compromising the functional performance of the bulk of the polymide coating/film. The copolymers exhibit mitigation of particle adhesion and fouling from exposure to various particulate and biological contaminants and exhibit reduced surface energy and increased surface fluorine content at extremely low oxetane loadings relative to the imide matrix (see Figure 2). Additionally, the short fluorinated carbon chains do not bioaccumulate, reducing the environmental impact of these materials. Modifying surface energy via laser ablative surface patterning This method uses a laser to create nanoscale patterns in the surface of a material to increase the hydrophobicity of the surface (see Figure 2). The benefits of hydrophobic surfaces include decreases in friction and increases in self-cleaning properties. This is an advantageous method of surface modification because it is fast and single-step, promises to be scalable, requires no chemicals, could be applied to a variety of materials, and does not require a planar surface for patterning.
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Alternative Transparent Coating Lotus Suitable for Optics with Vacuum Deposition Layer
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ISS as seen by STS-124; Photo Credit: NASA on the Commons, https://www.flickr.com/photos/nasacommons/35201127816/in/album-72157648186433655/
Liquid Sorbent Carbon Dioxide Removal System
NASA's Liquid Sorbent Carbon Dioxide Removal System was designed as an alternative to the current CO2 removal technology used on the International Space Station (ISS), which uses solid zeolite media that is prone to dusting, has a low absorption capacity, and requires high regeneration temperatures and frequent maintenance. Motivated by CO2 removal systems on submarines, NASA innovators began investigating the use of liquid sorbents. Liquid sorbents have a capacity four times greater than solid zeolites, require low regeneration temperature, and need fewer unreliable moving mechanical parts than solid based systems. While submarine CO2 scrubbers spray an adsorbing chemical directly into the air stream and allow the liquid to settle, NASA's new system uses a capillary driven 3D printed microchannel direct air/liquid contactor in a closed loop system. The Liquid Sorbent Carbon Dioxide Removal System is robust and reliable, while being low in weight, volume, and power requirements. The system is capable of reaching equilibrium when the liquid sorbent surface is being regenerated at a rate equal to the rate of absorption into the liquid.
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