Irradiated cubic single crystal SiC as a high temperature sensor
Radiation is known to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation flux on the order of 2⋅10 20 neutrons/cm 2 at 0.18 MeV causes over 3% volume lattice expansion. Radiation-induced strain (measurable by X-Ray diffraction) can be relieved when the annealing temperature exceeds the temperature of irradiation. Based on this effect the original technology of maximum temperature measurement was developed a while ago. Single crystal SiC sensor small size (200-500 microns), wide temperature range (150-1450 °C), “no-lead” installation, and exceptional accuracy make it very attractive for use in small, rotating and “hard-to-access” parts, including, but not limited to gas turbine blades, space shuttle ceramic tiles, automobile engines, etc. With the advances in X-Ray diffraction measurements, crystal and thin film growth techniques, it is the time to revise and update this technology. Modeling radiation damage, as well as annealing effects are also beneficial.
Irradiated Single Crystals for High Temperature Measurements in Space Applications
While spacecrafts experience temperatures from -120 to 110°C on the orbit, their surface reaches extremely high temperatures, well above 1000 °C, during descent into the atmosphere due to aerodynamic heating. Sophisticated insulation systems are designed for thermal protection. One of the steps in designing a protection system is experimental temperature measurements. Neutron flux induces point defects formation and accumulation in diamond and SiC single crystals, which causes overall lattice expansion. During thermal annealing this process is reversed, so the annealing temperature and time result in the “reduced” lattice parameter (measured by X-Ray diffraction), which allows determining the maximum temperature, if the exposure time is known. This paper describes the use of irradiated single crystal high temperature sensors for measuring temperatures in thermal protection systems during spacecraft descent, as well as other space applications. These additional applications include measuring the furnace temperature during single crystal growth in space at zero gravity, and measuring the rocket combustion chamber turbo pump temperature.
CAUSES OF FLUCTUATIONS IN R&D EXPENDITURES A QUANTITATIVE ANALYSIS
Introduction 124 The stylised facts of R&D in OECD economies 124 The determinants of business R&D expenditures 127 Modelling R&D expenditures 130 Conclusion 135 Bibliography 137 Annex: The model 138