Abrupt Increase of the Absorption Coefficient of Alumina at Melting by Laser Radiation and Its Decrease at Solidification

Abstract

Experimental data for the normal-hemispherical reflectivity R of remolded aluminum oxide ceramics for wavelengths of (0.488, 0.6328, 1.15, and 3.39) µm and effective (radiance) temperatures T eff1 and T eff2 for wavelengths of 0.55 µm and 0.72 µm were obtained in the process of rapid subsecond heating by CO 2 laser radiation in air and vacuum from room temperature to the formation of thin molten layers of 0.6 mm to 0.7 mm thickness and of subsequent rapid free cooling with solidification of the melt when the laser radiation was blocked. Experimentally and by numerical simulation of combined radiation and conduction heat transfer, the influence of the heating radiation flux on the formation of the thin melt on the surface of ceramics with an abrupt increase of T eff1 and T eff2 and on the signal of the spectrometer in the infrared range from 2 µm to 11µm at melting and on its decrease at solidification were studied. The radiation heat flux varied from 500 W · cm −2 to 2000 W · cm −2 . It is shown that the determining effect on the temperature field and on the intensity of outgoing radiation is caused by the formation of the isothermal continuous two-phase zone and the abrupt increase (decrease) of the absorption coefficient of the melt. The importance of kinetics in the abrupt change of the absorption coefficient of molten Al 2 O 3 is noted.

Microstructural characterization and tribological behavior of Laser Furnace processed ceramic tiles

“…3.the melt depth increases rapidly as a function of fluence. Thus it seems that a physical phenomenon is associated to this threshold value, consistent with the fact that absorption of laser light is sufficiently different between the solid and liquid surface irradiated[30,[35][36]. It appears here that, once a sufficient volume of liquid pool forms, absorption of laser radiation becomes more effective.Incubation effects are observed, on the other hand, to be cumulative(Figure 8(b)) and exhibit a pronounced effect on melt depth up to an incubation energy value of ca.…”

Process characterization and analysis of ceramic powder bed fusion

“…Figure 1 shows the experimental setup for the measurement of the absorptance. The reflectance (R) was measured using an integrating sphere, and the transmission was assumed to be zero, since the extinction coefficient of molten alumina is relatively high [21,22]. The absorptance (A) is therefore calculated as follows:…”

Atmosphere-Interior Exchange on Hot, Rocky Exoplanets

“…We approximate the solid silicate interior of hot super-Earths as isentropic, consistent with mantle convection models (e.g., van Summeren et al 2011) which show that solidstate convection can even out large inter-hemispheric contrasts in interior temperature. To predict silicateatmosphere compositions, we use the MAGMA code (Fegley & Cameron 1987;Schaefer & Fegley 2004, 2009Schaefer et al 2012) (Fig. 2).…”