High Viscosity Thermal Protection Materials.
Abstract
Vacuum hot pressing of scaled-up rocket nozzles and leading edge specimens of the tungsten-silica composition encountered devitrification problems. Rates between 4 and 16C per minute were found most apt to produce the undesired crystallization. Batch ball milling time was found to effect the particle size, strength, Young's modulus, oxidation resistance and electrical resistivity of dense hot pressed compacts. Modulus of rupture reached a peak 14000 N/sq cm (20,000 psi) at a batch mean particle size of 1.9 microns resulting from 8 hours of ball milling. Prolonging milling to 48 hours further reduced the particle size and unfortunately the modulus of rupture as well. Electrical resistivity jumped sharply from a value of 0.5 milliohm-centimeters after 24 hours of milling to 3.2 milliohm-centimeters after 48hours. Resistance to oxidation in the 800 to 1400C range was poor but appeared to increase with both ball milling time and oxidation temperature. Scanning electron microscope micrographs confirmed the existence of a continuous tungsten skeleton throughout the silica. Excessive ball milling destroyed the tungsten skeleton and produced more isolated tungsten particles accounting for the drop in mechanical properties and the increase in electrical resistance and resistance to oxidation. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 24, 1970
- Accession Number
- AD0868327
Entities
People
- Roger E. Wilson
Organizations
- Naval Ordnance Laboratory