Improvement of the laser flash method to reduce uncertainty in thermaldiffusivity measurements

Abstract

The National Metrology Institute of Japan (NMIJ) has improved thelaser flash technique to reduce uncertainty in thermal diffusivitymeasurements of solid materials above room temperature. An advanced laserflash apparatus was constructed after the following technical improvements hadbeen made. (i) Uniform pulse heating of a specimen was achieved with animproved laser beam using an optical fibre (decreasing the error due tononuniform heating). (ii) A fast infrared radiation thermometer with anabsolute temperature scale was developed (decreasing the error due tononlinear temperature detection). (iii) A new data analysis algorithmemploying curve-fitting method whereby the entire region of the temperaturehistory curve is fitted by the theoretical solution under the real boundarycondition was introduced (decreasing the heat loss error). The precision andaccuracy of the apparatus were demonstrated by measuring specimens ofglassy carbon which is a candidate reference material for a thermaldiffusivity standard to be supplied by the NMIJ.