Part II-A Study of Glasses Consisting of the Oxides of Elements of Low Atomic Weight
JSGT 1956 V40 T097-T138
The Absorptions Characteristic of Certain of the Experimental Glasses
A study has been made of glasses melted mainly from binary and ternary mixtures of the oxides of elements of low atomic weight; the basic oxides used were beryllia, lithia, magnesia, and soda, and the acidic or 'glass-forming' oxides were boric oxide, alumina, and silica. In some cases the number of oxides was increased to four or more in order to elucidate specific points indicated by the observations made on the ternary mixtures. The limitation to the oxides of the elements of low atomic weight was decided upon because the properties of glasses containing such oxides would, it was considered, be most likely to show variations which could be related to structural changes due to differences between the co-ordination numbers of the different ions. In Part I the limits of glass formation in the various systems are described, and deductions are drawn relating to the co-ordination numbers of beryllium and magnesium ions. In Part II the transmissions of the glasses in the visible, ultra-violet and infra-red regions of the spectrum over the range 230 mμ to 15 μ are dealt with. The transmission curves in the visible and ultra-violet regions showed no absorption except the general absorption in the ultra-violet region due to iron in the ferric condition. In the infra-red region the transmission of specimens 2 mm. thick was practically zero at and beyond 6 μ, and in some cases was only very small beyond 3 μ. With very thin films, however, the positions of absorption bands over the whole range to 15 μ could be determined, and these could be attributed to different cation–oxygen systems in the glasses; one result given by this study was that in alkali borates and glasses of high boric oxide content the proportion of BO4 units cannot exceed one-fifth of the total boron–oxygen groups. In Part III observations on the densities, coefficients of thermal expansion, and chemical durabilities of a number of the glasses are described and the variations of these properties are correlated with the conclusions drawn from the work described in Parts I and II.
To ascertain what information relating to the structure of the experimental glasses might be obtainable from a study of their absorption spectra, the absorptions in the infra-red region were investigated and, for the sake of completeness, the visible and ultra-violet regions were also explored.
H. Moore & P. W. McMillan
