THERMAL-DIFFUSIVITY MEASUREMENTS IN OPAQUE SOLIDS BY THE MIRAGE TECHNIQUE IN THE TEMPERATURE-RANGE FROM 300-K TO 1000-K

A method to measure the thermal diffusivity of solid samples as a func tion of temperature is presented. The measurement technique is based o n the mirage effect and in its linear zero-crossing relation for the t ransverse deflection, whose slope directly gives the diffusivity of th e material. A 3D theoretical model has been developed in order to incl ude both the effects of the radiative and convective heat transfers be tween the sample and its surroundings, and the temperature dependence of the refractive index and thermal diffusivity of the gas. The model also incorporates the effects introduced by the mirage parameters (siz es of the pump and probe beams, and probe beam height). The samples st udied are opaque and thermally thick, and the applicability of the met hod is restricted to materials with diffusivity > 1 mm2/s. Two experim ental mirage setups are presented, one with the sample being heated in an open environment, and the other with the sample heated within a fu rnace. In the first case the range of measurable temperatures goes fro m ambient to approximately 500 K, whereas in the second the upper limi t is approximately 1000 K. A comparison of the experimental results ob tained with this method with those from the literature on calibrated s amples of pure nickel, pure cobalt, and an AISI-302 alloy of low therm al diffusivity, confirm the validity of the model and method proposed.