STRUCTURAL INVESTIGATION OF MOLTEN AND GLASSY SILICATES BY MEANS OF INFRARED EMISSION SPECTROMETRY

L'état vitreux est souvent pris comme terme de comparaison à la place de l'état liquide. Pour clarifier la validité de cette substitution on a développé une méthode d'observation directe des vibrations moléculaires des silicates fondus par spectrométrie IR. La méthode consiste essentiellement à combiner deux spectres d'émission d'une couche mince et d'une couche épaisse de l'échantillon placé sur un substrat métallique. Le spectre de transmission peut en être déduit, comme indiqué précédemment. On a mesuré les spectres d'émission IR de silicates alcalins fondus entre 25 000 et 400 000 m-1 et les spectres de transmission obtenus à l'état liquide ont été comparés à ceux à l'état vitreux. Les résultats obtenus sont les suivants : (1) La vitesse de trempe entre 10-2 à 104 K/s a peu d'influence sur les spectres vibrationnels des verres. (2) Bien que l'allure générale des spectres IR des silicates fondus est très semblable à celle des verres, on observe que les fréquences de vibration des silicates fondus se déplacent vers des fréquences plus basses et les largeurs de bande sont plus élevées que pour les verres. (3) Etant donné que la dépendance de ces déplacements est linéaire en fonction de la température pendant la transition de l'état liquide à l'état vitreux, on peut conclure que la structure fondamentale des anions silicate ne diffère pas beaucoup dans les deux cas.In order to clarify the validity of the dummy role of glassy state instead of molten state, the direct method for observing the molecular vibration in molten state has been developed by means of infrared emission spectrometry. The essential feature of this method consists of a combination of the two emission spectra which are obtained from thin and thick layers of the sample on a metal substratum. Transmission spectrum can be obtained from these emission spectra by virtue of the simple relation reported previously. The infrared emission spectra of molten alkaline silicates were measured in a range of wave number from 25 000 to 400 000 m-1 and the transmission spectra obtained in molten state were compared with that of glassy state. The obtained results are summarized as follows : (1) The cooling rate from molten to glassy state in the range of 10-2 to 104 K/s has little influence on the vibrational spectra of the glassy state thus obtained. (2) Although the general pattern of infrared spectra of molten silicates is quite similar to that of glassy state, it is observed that the vibrational frequencies of molten silicates shift toward the lower frequencies and the band shapes are broader than those of glassy state. (3) From the facts that the temperature dependence of these frequency shifts is linear during the transition from molten to glassy state, it may be concluded that the fundamental structure of silicate anion does not differ seriously in both states

Scattering Effect of Iron Metallic Particles on the Extinction Coefficient of CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 Glasses

The extinction coefficient of the CaO-SiO2-B2O3-Na2O-Fe2O3-CaF2 glasses has been studied using a FT-IR and a UV-visible spectrometer in the range of 0.5-5 mu m to investigate thermal radiation through glassy flux film during continuous casting of steels. In present investigations, iron oxide has been reduced to metallic iron droplets by reaction with graphite crucible during melting, which brings considerable increase of the extinction coefficient due to the scattering. To analyze the scattering effect of these droplets on the extinction coefficient, the number density and size parameter of metallic particles have been measured using an automated scanning electron microscope. The number of metallic particles is intensively proportional to boron contents due to the transition of molar structure, BO4 to BO3, with increasing boron oxide. It is found that calculated scattering coefficients based on Mie scattering theory are in good agreement with measured ones. As the increased scattering coefficient of glassy film would not cause any serious side effects on casting operations, utilization of scattering effects is believed to be significantly essential for the future design of commercial mold fluxes.11Nsciescopu