DETERMINATION OF THE THERMAL DIFFUSIVITY OF TRANSPARENT MATERIALS BY A NEW THERMOGRAPHIC EXPRESS METHOD

The thermophysical characteristics of nonmetallic materials (in particular, thermal conductivity and thermal diff usivity) account for their heat-insulating properties, the quality of processing in various laser technologies, and also signifi cantly aff ect the optical strength of power optics materials. Determination of thermophysical characteristics by traditional methods requires laborious manufacturing of specimens of certain sizes and two-sided access to them, which prevents the use of nondestructive testing of large workpieces and fi nished products. The article describes a nondestructive thermographic method of measuring the thermal diff usivity of transparent and semitransparent materials, which does not require cutting out samples from the test object and two-sided access to it. To increase the coeffi cients of absorption and emission of visible and infrared radiation of the accessible surface, thin opaque coatings or targets with a diameter of several tenths of a millimeter were used. The method was tested on eight optically transparent polymeric, amorphous, and crystalline materials diff ering in composition, spectral characteristics of light absorption, surface condition and overlapping about 2 orders of magnitude in thermal diff usivity. The described procedure demonstrated a small random error (0.5% for polymethyl methacrylate, 1.1% for polycarbonate, 2.3% for fused quartz, 3.3% for monocryslalline NaCl) at a speed of about 10 s, which makes it possible to use it for rapid diagnostics of newly created heat-shielding materials and elements of power optics.
   
Author:  Yu. I. Golovin, A. I. Tyurin, D. Yu. Golovin and A. A. Samodurov
Keywords:  thermal diff usivity, thermography, point stepwise laser heating, optically transparent materials
Page:  266