Spectrophotometric and Magnetic Studies of Glasses Containing Iron in Relation to Their Structure. Part IV. Borate, Cabal and Phosphate Glasses

JSGT 1954 V38 T244-T270

The study of the colours and magnetic properties of glasses containing iron has been extended to include a number of borate, cabal and phosphate glasses, and the results thus obtained indicate that: (1) In the alkali-borate glasses and borate glasses containing MgO, ZnO, CaO, SrO, BaO, Al₂O₃ and SiO₂, iron can exist in the ferrous, brown ferric, ferroso–ferric and the colourless forms, the amounts of which can be determined by colour analysis as in silicate glasses. In the glasses which contain high proportions of the alkalis, however, a proportion of the iron is present in the form which gives an absorption in the region of 480–520 µm and which has been provisionally identified in Parts I-III as corresponding with the form of iron in an alkali ferrate. The observed and the calculated mass susceptibilities agree closely with each other, except in the glasses containing this form of iron, for all of which the observed mass susceptibilities are lower than the calculated values. (2) In a silica-boric oxide glass the iron exists mainly in the brown ferric and the ferroso–ferric forms, with a small proportion of ferrous iron and a negligibly small proportion of colourless iron. (3) In cabal glasses and the modified cabal glasses the iron is present mainly in the brown ferric and the ferroso–ferric forms, with only small proportions of ferrous and colourless iron; no “ferrate” could be traced in these glasses. For all these glasses the mass susceptibilities calculated from the amounts of iron present in the various forms, as indicated by the colour analysis, agreed closely with the observed values; (4) The transmission curves of the phosphate glasses differ very considerably from the transmission curves of the silicate and borate glasses, and cannot be analysed in terms of optical densities given by the various forms of iron in silicate and borate glasses. In the phosphate glasses the absorption in the 480–520 µm region is high as compared with the absorption in this region given by iron in silicate and borate glasses. Sodium diphospho-ferrate and sodium triphospho-ferrate give similar absorption in the 480–520 µm region, which indicates that in phosphate glasses some of the iron can exist in the same form as in the phospho-ferrates with the Fe³⁺ ion covalently linked with three oxygen ions. (5) The magnetic susceptibility of the iron in ferric phosphate is shown to have the value of approximately 180×10⁻⁶ at 20°C, which corresponds closely with the value of 182·5×10⁻⁶ for the colourless iron in the glasses. This gives very strong support for the view that the colourless form of iron in glasses exists as FeO, groups as in ferric phosphate.

Abd-El-Moneim Abou-El-Azm