INVESTIGATION OF BORIDE COMPOUNDS FOR VERY HIGH-TEMPERATURE APPLICATIONS
A comprehensive study of the properties of high-purity well- characterized sanaples of TiB/sub 2/, ZrB/sub 2/, HfB/sub 2/, NbB/sub 2/, a nd TaB/sub 2/ was performed. Floating zone refining and highpressure hot pressing were used to prepare single crystal and polycrystalline material respectively. An investigation of the sintering mechanism of TiB/sub 2/ was performed. Powder purification procedures by acid leaching and vacuum heating were examined. Properties measured included lattice parameter, x-ray thermal expansion, linear thermal expansion, electrical resistivity, and microhardness. These quantities were obtained for materials which satisfied the sample requirements for the various experiments. Measurements were generally performed between room temperature and 1000 deg C. Thermal conductivity measurements between 1000 and 2000 deg C are in progress. Thermal properties measured included specific heat, vapor pressure, and heat of formation. The latter is in progress. Phase boundary experiments were performed in Zr-B system and the current status of the phase diagrams of these materials was reviewed. Kinetic studies were performed to elucidate the mechanism of oxidation and to study the nature of protective coatings which are produced by some of these materials in oxidizing atmospheres. An integrated thermodynamic analysis of the diborides was completed. On the basis of current vapor pressure and oxidation data, HfB/sub 2/ and ZrB/sub 2/ are shown to be the most likely candidates for high temperature applications requiring oxidation resistance. The available description of the compositional dependence of the boron activity in these compounds indicates that metal-rich deviations from stoichiometry in these compounds will probably result in additional enhancement of the oxidation resistance. Other variations in composition suggested by the results of the present study include additions of Ta and Nb or Y and La. These elements might serve to impede diffusion of oxygen through the oxide surface layer. Additions of silicon to the pure diborides might also provide enhanced oxidation resistance. (auth)
- Research Organization:
- ManLabs. Inc., Cambridge, Mass.
- NSA Number:
- NSA-18-010539
- OSTI ID:
- 4103221
- Report Number(s):
- RTD-TDR-63-4096(Pt.I)
- Country of Publication:
- United States
- Language:
- English
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Ultra high temperature ceramics for hypersonic vehicle applications.
RESEARCH ON PHYSICAL AND CHEMICAL PRINCIPLES AFFECTING HIGH TEMPERATURE MATERIALS FOR ROCKET NOZZLES. Quarterly Progress Report, April 1, 1963-June 30, 1963
Related Subjects
COATING
CORROSION PROTECTION
CRYSTALS
DIFFUSION
ELECTRIC CONDUCTIVITY
EXPANSION
GRAIN BOUNDARIES
HAFNIUM BORIDES
HARDNESS
HEATING
HIGH TEMPERATURE
HOT WORKING
IMPURITIES
LANTHANUM
LATTICES
LAYERS
LEACHING
MEASURED VALUES
METALS, CERAMICS, AND OTHER MATERIALS
MONOCRYSTALS
NIOBIUM
NIOBIUM BORIDES
OXIDATION
OXIDES
OXYGEN
PHASE DIAGRAMS
POWDERS
PREPARATION
PRESSURE
REACTION KINETICS
REFINING
SILICON
SINTERING
SPECIFIC HEAT
STABILITY
SURFACES
TANTALUM
TANTALUM BORIDES
TEMPERATURE
THERMAL CONDUCTIVITY
TITANIUM BORIDES
USES
VACUUM
VAPORS
VARIATIONS
X RADIATION
YTTRIUM
ZIRCONIUM BORIDES