Extinction coefficients of the OH bands in the IR spectra of basic and water-enriched silicate and aluminosilicate glasses

Abstract

OH bands in the MIR and NIR spectra of selected silicate and aluminosilicate glasses were studied. The spectra of basic and water-enriched samples were compared. The ratio of the absorption coefficients of the IR bands at 3550 and 2800 cm-1 attributed to weakly and strongly hydrogen-bonded OH species, respectively, increases by more than 15 up to 70 % with water content in the glasses. These IR findings were confirmed by 1H MAS NMR measurements for a sodium calcium silicate glass. The practical extinction coefficients ε3550, pract and ε4500 increase with the water content for the alkali calcium silicate glasses as well as for the glasses with the components RO (R = Sr, Ba), AI2O3 and SiO2. For the basic glasses the values of ε3550, pract and ε4500 vary from 15 to 40 1 ∙ mol-1 ∙ cm-1 and from 0.16 to 0.41 1 ∙ mol-1 ∙ cm-1, respectively. No changes in these coefficients were found for glasses of the compositions (in mol%) 33 CaO ∙ y Al2O3 ∙ (67-y) SiO2 ( y = 5, 8, 12) with values about 60 and 0.65 1 ∙ mol-1 ∙ cm-1 for ε3550, pract and ε4500 and for bottle glasses. Furthermore, some changes were obtained in the glass network due to the hydration procedure. Α very small amount of fourfold coordinated aluminium (less than 0.3 mol% AI2O3) was found by 27Al MAS NMR measurements in a hydrated glass with the nominal composition (in mol%) 16 Na2O ∙ 10 CaO ∙ 74 SiO2. IR reflectance measurements suggest an incorporation of aluminium in the glass network for strontium aluminosilicate glasses. Thus, the increase in the practical extinction coefficients of the OH bands can be caused by an increasing water content as well as by small changes in the glass composition due to the hydration procedure. Α satisfactory agreement was found between water concentration values which were determined by NRA (nuclear reaction analysis) experiments and those which were calculated from IR measurements by the so called two-band method with composidon independent extinction coefficients for the OH bands at about 3550 and 2800 cm-1.