High-temperature electron emission and vaporization of selected refractory materials
The emission of electrons from heated refractory metals is the driving reaction in the direct conversion of heat to electricity by thermionic energy conversion. Electron emission is quantified by the work function. In this paper, the work functions of important refractory metals and alloys in the technology of thermionic energy conversion were measured. The metals studied were osmium, iridium, ruthenium, rhenium, and molybdenum. Alloy systems included tungsten and osmium; tungsten and iridium; tungsten and rhenium, tantalum and osmium; and niobium and ruthenium. The highest work function for any of the metals was found for a (110) single crystal of iridium. For the alloys a W-3%Ir exhibited the highest work function. The basic thermionic emission behavior varied for different materials. Some materials had work functions which were constant with changes in temperature, pressure, or chemical composition while others varied markedly. In addition to work function studies, a unique high temperature sublimation mass spectrometer was designed and fabricated for the study of vaporization phenomena. Metals and alloys were allowed to vaporize freely into vacuum and their vapors were analyzed by mass spectrometry. Activation enthalpies of vaporization were measured and compared to reported heats of vaporization for the pure metals. Standards were used to calculate surface activities and to estimate vaporization rates. Spectral normal emissivities were measured at a wavelength of 0.65 {mu}m. A knowledge of the emissivity for these materials will allow accurate temperature measurement of future investigations without the need for black body cavities.
- Research Organization:
- Arizona State Univ., Tempe, AZ (United States)
- OSTI ID:
- 5582825
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
300403* -- Thermionic Converters-- Materials
Components
& Auxiliaries
ALLOY SYSTEMS
ALLOYS
BINARY ALLOY SYSTEMS
CONVERSION
DIRECT ENERGY CONVERSION
ELECTRON EMISSION
ELEMENTS
EMISSION
EMISSIVITY
ENERGY CONVERSION
ENTHALPY
FUNCTIONS
HEATING
IRIDIUM
IRIDIUM ALLOYS
METALS
MOLYBDENUM
NIOBIUM ALLOYS
OPTICAL PROPERTIES
OSMIUM
OSMIUM ALLOYS
PHYSICAL PROPERTIES
PLATINUM METAL ALLOYS
PLATINUM METALS
REFRACTORY METALS
RHENIUM
RHENIUM ALLOYS
RUTHENIUM
RUTHENIUM ALLOYS
SURFACE PROPERTIES
TANTALUM ALLOYS
THERMIONIC CONVERSION
THERMIONIC EMISSION
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
TRANSITION HEAT
TUNGSTEN ALLOYS
VAPORIZATION HEAT
WORK FUNCTIONS