THE CAUSE OF SURFACE-TENSION INCREASE WITH TEMPERATURE IN MULTICOMPONENT ALUMINOSILICATES DERIVED FROM COAL-ASH SLAGS

An explanation is proposed for the increase of surface tension with temperature in multicomponent aluminosilicate systems such as those derived from coal-ash stags. Two major factors are considered: (1) depolymerization of aluminosilicates caused by rearrangements of intermediate structures in the surface layers, and (2) the increase in surface entropy caused by evaporation of some ash slag components. Electron spectroscopy for chemical analysis spectra were recorded for oxygen Is photoelectrons on quenched bulk slags and on sessile drops to gain insight into the depolymerization of coal-ash stags with temperature. The tests performed on quenched bulk slags indicated replacement of bridging oxygen [Si-O] with non-bridging oxygen atoms [Si-O-] as a function of increasing temperature. Mossbauer spectra showed an increase in ferrous iron from 4% to 12% of total iron as temperature rose from 1400 degrees C to 1500 degrees C. The increase in non-bridging oxygens resulted from the reduction of tetrahedrally coordinated Fe3+ to octahedrally coordinated Fe2+. Also, the intensity of the non-bridging oxygen Is photoelectron peak was higher when detected on the surface of a sessile drop than when detected from the bulk of the drop.