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  • 1
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    High energy collimating fine grids (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The objective of this project was to demonstrate the fabrication of extremely tight tolerance collimating grids using a high-Z material, specifically tungsten. The approach taken was to fabricate grids by a replication method involving the coating of a silicon grid substrate with tungsten by chemical vapor deposition (CVD). A negative of the desired grid structure was fabricated in silicon using highly wafering techniques developed for the semiconductor industry and capable of producing the required tolerances. Using diamond wafering blades, a network of accurately spaced slots was machined into a single-crystal silicon surface. These slots were then filled with tungsten by CVD, via the hydrogen reduction of tungsten hexafluoride. Following tungsten deposition, the silicon negative was etched away to leave the tungsten collimating grid structure. The project was divided into five tasks: (1) identify materials of construction for the replica and final collimating grid structures; (2) identify and implement a micromachining technique for manufacturing the negative collimator replicas (performed by NASA/JPL); (3) develop a CVD technique and processing parameters suitable for the complete tungsten densification of the collimator replicas; (4) develop a chemical etching technique for the removal of the collimator replicas after the tungsten deposition process; and (5) fabricate and deliver tungsten collimating grid specimens.
    Keywords: SPACE RADIATION
    Type: NASA-CR-197688 , NAS 1.26:197688 , ULT/TR-94-6505
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Niobium matrix composites for high temperature turbine blades, phase 2 (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This program demonstrated the feasibility of fabricating fiber-reinforced MMC (niobium matrix) turbine blades to net shape by chemical vapor infiltration (CVI). A controllable, repeatable niobium infiltration process was developed, and the kinetics of both deposition and infiltration were studied. Several continuous refractory fibers (Nicalon, Nextel 440, FP-Al2O3, HPZ, and tungsten mesh) were investigated as potential reinforcements for strengthening niobium. Thermodynamic and experimental evaluation indicated FP-Al2O3 and tungsten to be the most chemically compatible with niobium, while Nicalon, FP-Al2O3, and tungsten were found to be best with regard to reinforcing capability. Finally, a protective coating for iridium was found to provide substantial oxidation protection to the niobium blade matrix.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-194257 , NAS 1.26:194257 , ULT/TR-91-7188
    Format: text
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    NASA TECHNICAL REPORTS
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