HIGH-TEMPERATURE CONTAINERLESS LASER PROCESSING OF DIELECTRIC SAMPLES IN MICROGRAVITY - STUDY OF AERODYNAMIC TRAPPING

We present here the results of work on microgravity laser materials processing and containerless trapping (or positioning) in gas flows. Basic principles are explained and the experimental apparatus is described. Spherical samples can be trapped in appropriately constructed subsonic diffusers. Anisotropic pressure distributions generate restoring forces which depend on diffuser geometry, sample size and gas flow rate. Different diffuser designs were tried in KC-135 parabolic flights with sample diameters up to 8 mm and densities up to 9 g/cm(3) (tempered steel). All samples were trapped with flow rates as low as 2.71/min. Containerless dielectric samples (alumina and other oxide compounds) were CO2 laser beam heated to temperatures beyond the melting point (over 2,300 K) and rapidly cooled and undercooled in microgravity (up to > 300 K/s of radiative cooling). NMR spectra of SiO2-Y2O3 indicate better sample homogeneity when microgravity processed.