| The role of transition elements in alkali aluminosilicate liquids was investigated by studying glasses quenched from liquids. Liquid compositions were taken from the Na(,2)O-Al(,2)O(,3)-SiO(,2) and K(,2)O-Al(,2)O(,3)-SiO(,2) systems. Experimentally, the study consisted of three parts: (1) a vibrational spectroscopic investigation of the binary and ternary host glasses which was interpreted in terms of the liquid structure, (2) a study of the electronic spectra of several transition metal ions in sodium silicate glasses which was interpreted in terms of the local environment of the transition metal ions in silicate liquid, and (3) the measurement of Ni('+2) absorption spectra as a function of oxygen fugacity in the melt and the calculation of the activity coefficient of NiO in several alkali silicate and alkali aluminosilicate liquids.;Absorption spectra were measured by glasses doped with manganese, cobalt, and nickel. Samples fused in Pt crucibles at atmospheric conditions stabilize Mn('+3), Co('+2), and Ni('+2) in the liquids. In order to stabilize Mn('+2) in the liquids, samples were fused in covered graphite crucibles at 1400(DEGREES)C, resulting in a P(,O(,2)) (TURNEQ) 10('-17) atm. Liquid sample batches were poured into graphite molds and quenched. From the optical data obtained from these samples and from data in the literature, it seems apparent that transition metal ions occupy several different types of sites in silicate liquids: (1) Highly charged ions like Cr('+6) form separate molecular entites in the liquid, (2) Cr('+3) and Mn('+3) form octahedral quasi-complexes by locally distorting the silicate liquid structure, (3) Fe('+3) and Co('+2) from tetrahedral quasi-complexes in a similar manner, (4) Mn('+2) and Fe('+2) do not appear to complex but occupy network modifier sites with octahedral symmetry, and (5) Ni('+2) occupies a network modifier site of unknown symmetry.;A series of glasses doped with nickel were made for seven compositions in the Na(,2)O-Al(,2)O(,3)-SiO(,2) and K(,2)O-Al(,2)O(,3)-SiO(,2) systems. In each series, the oxygen fugacity of the furnace atmosphere was varied from atmospheric conditions to f(,O(,2)) (TURNEQ) 10('-13) atm. The absorption spectrum of Ni('+2) was used as a colorimetric method to determine the f(,O(,2)) at which the Ni('+2) was reduced to Ni('0). From this data, the activity of NiO in the glass was calculated. The results indicate that Ni('+2) is excluded from highly polymerized melts. The calculated activity coefficients for NiO in silicate liquids may correlate with the changes in melt structure observed by vibrational spectroscopy.;The results of this study do not support the hypothesis that crystal field effects are responsible for transition metal enrichment of early fractionating phases during crystallization of silicate liquids. This enrichment is more likely due to the incompatibility of transition metal ions in highly polymerized silicate structures. Crystal field effects are still thought to control the distribution of a given transition metal ion between competing crystal sites and the distribution of different transition metal ions competing for a given crystal site.;The vibrational spectroscopic study of alkali silicate and alkali aluminosilicate glasses included both Raman and infrared spectroscopic measurements. Samples were obtained by drawing rods and sheets directly from liquid batches. The Raman data indicate the existence of discrete structural units in the liquids (i.e., sheets, chains, and SiO(,4)('-4) monomers). As the alkali concentration increases the silicate network breaks down into simpler structual units. Infrared data indicate that Al('+3) enters network-modifier sites in ternary liquids if the total Al(,2)O(,3) concentration is less than 1 weight %. Above this concentration, Al('+3) enters tetrahedral network-forming sites which are coordinated only by bridging oxygens. |
