Preparation of Nano-Engineered Platelets Using Vacuum Roll Coating, 18-R9625

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Principal Investigator
Kent Coulter

Inclusive Dates:  04/01/06 – 09/30/07

Background -  Vacuum deposition of a thin film onto a substrate and the subsequent comminuting of the film into a flake/platelet was originally developed in the mid 1980s for pigments that possess unique optical attributes. The attributes that are advantageous for optical pigments are applicable to many nanotechnology developments and in particular in catalytic applications. Recently hydrogen storage has become a “hot topic” in the field of catalysis. The main challenge in the field is to devise new materials or combinations of materials that exhibit high volumetric and gravimetric capacity, fast sorption kinetics at near ambient temperatures, and high tolerance to recycling. Nanostructured composites are considered one of the most promising classes of materials because of the wide composition ranges, structural engineering possibilities and unique chemical properties. This effort focuses on the fabrication, formulation, and utilization of thin-film, multilayer platelets for hydrogen storage.

Approach - In this project, the three components are to:

  • establish a coating capability amenable to producing prototype quantities ( less than 100 grams) of platelet material
  • develop multilayer platelets with unique functionalities based on their design, composition, and construction
  • collect characterization and performance data on nanoengineered platelets for hydrogen storage that are synergistic with the U.S. Department of Energy National Testing Laboratory for Solid-State Hydrogen Storage Technologies.

Accomplishments - Per the plan, the multi-use Stokes vacuum chamber was upgraded and modified to incorporate a web winder, dual e-beam deposition sources and a monitor system that form a modular piece of equipment that has fixed geometries to hold the deposition profile constant with easily installable fittings and connectors.

The second task of material development concentrated on fabricating platelets for application as hydrogen storage materials. Lanthium nickel (LaNi5) as a hydrogen storage material is typically manufactured by high energy mechanical milling, melt spinning or plasma spray techniques with improved hydrogen content correlating with crystallinity in the film. The LaNi5 was e-beam and sputter deposited, and the coated film was passed through a water/acetone (30/70) mixture to form the free standing platelets.

The LaNi5 platelets deposited using electron beam evaporation did exhibit some hydrogen absorption, but the total volume absorbed was immeasurable compared with published theoretical values. The hydrogen sorption behavior of sputter-deposited material was investigated using high-pressure gravimetric analysis, while the magnitude of hydrogen uptake (0.6-1 wt. percent) was consistent with conventional forms of LaNi5. There was little evidence of equilibrium plateaus at the coexistence region of the hydriding phase that are typically seen for metal hydrides.

This program was to establish the facilities and expertise to deposit multilayer thin films that are comminuted into platelets exhibiting nanotechnology performance attributes in prototype quantities ( less than 100g) with a focus on the fabrication, formulation, and utilization of thin-film, multilayer platelets for hydrogen storage. Using existing equipment and infrastructure, SwRI established coating and conversion capabilities, developed processes and procedures for fabrication, and characterized the performance of multilayer platelets for hydrogen storage. While this project focused on nanoengineered platelets with immediate commercial interest, the real benefit of the project was establishing a capability that has application in the rapidly expanding field of nanotechnology.

Platelets of LaNi5 synthesized using magnetron sputtering processes are shown following activation with hydrogen.

 

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