Ceramics-Silikáty 61, (2) 163 - 171 (2017)

The presented work involved model corrosion tests of silica -zirconia glass fibers with two different types of lubrication (Anti-Crack HD with dispersible lubrication and Anti-Crack HP with non-dispersible lubrication). Also the corrosion tests of fibers with lubrication removed by firing was studied. All types of fibers were leached in alkaline solutions (Ca(OH) ₂ with pH 12.7, KOH with pH 12.7 and 14) at temperature of 80°C for 7-42 days. Changes in corrosion solutions composition and in glass surface were measured and characterized (AAS, ICP-OES and SEM-EDS, XRF, XRD resp.). The leaching results were similar for both types of fibers with or without lubrication. After leaching in the Ca(OH)₂ (pH 12.7), the fibers were covered with calcium precipitates. On fibers with lubrication the precipitate contained mainly crystalline calcium carbonate and calcium hydroxide, while on fibers with removed lubrication the precipitate also contained silicate. After the calcium-containing precipitates were removed with an acid solution, pitting corrosion was visible on fibers with lubrication while fibers without lubrication were covered with a corrosion layer without a significant change in the surface composition. The fibers practically did not dissolve in that environment. In KOH (pH 12.7) the fibers slightly dissolved but without visible precipitates, the composition of all types of fibers did not substantially changd In KOH (pH 14) the fibers dissolved more significantly. On the surface of the fibers a ZrO₂ and silica containing corrosion layer was formed. The time dependences of dissolved glass components indicates the incongruent dissolution of the fibers with selective leaching of sodium ions or congruent dissolution followed by precipitation of SiO₂, or SiO₂ with calcium ions from the solution. It is likely that both the created precipitates (calcium or calcium-silica) and the developed corrosion layers (silica -zircon dioxide) may operate as a barrier which slows down further corrosion of glass fibers.