Identification and Characterization of New Materials for Construction of Heating Plates for High-Temperature Guarded Hot Plates

摘要

The selection of a material for making the hot and cold plates of high-temperature guarded hot plates (HTGHPs) working up to 800 degrees C is still an issue. The material must be machinable, have a high mechanical stability to keep the high level of flatness of the plates and have a high thermal conductivity and a high resistance to oxidation when used in air. Nickel 201 alloy has been used in several instruments, but has shown, sometimes, problems of mechanical stability. The total hemispherical emissivity of the plates must be higher than 0.8 as recommended by the standards. Three ceramic materials, a silicon infiltrated silicon carbide (SiSiC), a machinable aluminum nitride and a sintered aluminum nitride (AlN) with high thermal conductivity claimed at ambient temperature, were selected for tests in thermal conductivity and opacity to thermal radiation. Three paints withstanding high temperatures were tested in total hemispherical emissivity and durability at high temperature. Above 600 degrees C, Nickel 201 alloy has a higher thermal conductivity than the three ceramics. Below 600 degrees C, the SiSiC and the sintered AlN have a thermal conductivity significantly higher than Nickel 201, but the sintered AlN shows a wide transparency spectral band at short wavelengths (below 6.5 mu m). Above 300 degrees C, the three paints have a total hemispherical emissivity above 0.8. One of the paints has polluted the specimens of an insulation material tested in thermal conductivity up to 650 degrees C. The other two can be recommended to coat the hot and cold plates of HTGHPs used up to 800 degrees C.