Preparation of Nano-Engineered Platelets Using Vacuum Roll Coating, 18-R9625Printer Friendly Version
Inclusive Dates: 04/01/06 Current
Background - Vacuum deposition of a thin film onto a substrate and the subsequent comminuting of the film into a flake or 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 due to 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 1) establish a coating capability amenable to producing prototype quantities greater than 100 grams), 2) develop multilayer platelets with unique functionalities based on their design, composition, and construction, and 3) collect characterization and performance data for nanoengineered platelets for hydrogen storage, that are synergistic with the newly established DOE National Testing Laboratory for Solid-State Hydrogen Storage Technologies.
Accomplishments - Per the plan, Task 1: Coating Capability Design & Fabrication, 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. While this platform is one of only a handful capable of these platelets worldwide, each area for improvement has not required extensive capital investment but only minor modifications that when integrated enable dramatic improvements in capabilities. The chamber is presently operating 15 hours per day, five days per week, utilizing a split shift schedule. In six months, the equipment has been modified and material has been developed for this internal research project, four client-funded projects, and five proposals.
The second task of material development has concentrated on fabricating multi-layer 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. Electron beam evaporation of an alloy source material in a roll coating configuration was anticipated to require process and product development to achieve optimum structure and stoichiometry in the film. The initial LaNi5 was e-beam deposited, and the coated film was passed through a water/acetone (30/70) mixture to form the free standing platelets.
While the LaNi5 is a good demonstration system, lighter materials based on aluminum, such as catalytically-activated sodium aluminum hydride (NaAlH4), have a greater potential for achieving or exceeding the targets for gravimetric energy density and will be developed through the end of the internal research project.
The third task of Characterization & Evaluation has been focused on the elemental and structural properties of the deposited LaNi5 platelets. Surprisingly, compositional analysis found little evidence of lanthanum present. Subsequent samples of the source material and the crucible used in the e-beam deposition found stoichiometric quantities of lanthanum present. A subsequent investigation of the e-beam deposition conditions and the chamber environmental influences is underway to better understand where the lanthanum is going during deposition. Even without the La present, the platelets did exhibit hydrogen storage capacities when evaluated in the DOE-sponsored hydrogen storage testing facility at SwRI.