Abstract
SummaryIn the course of classical optics manufacturing glass components are in permanent direct contact with aqueous operating materials. Such contact leads to a certain absorption of water and hydrogenous compounds that may induce severe glass defects. In this contribution, absorption of hydrogen and other contaminants during grinding of glass was observed and qualitatively detected via laser‐induced breakdown spectroscopy. It is shown that hydrogen, calcium, magnesium, and carbon are implanted into the glass surface where the contaminant concentration increases over grinding time or contact time of the glass surface with water and the grinding tool, respectively. The contaminants hydrogen, calcium, and magnesium can be attributed to the water used as lubricant. In contrast, carbon most likely originates from wear debris of the used silicon carbide grinding pads. Several possible mechanisms that lead to such surface contamination of glasses during grinding – diffusion, accumulation in micro cracks as well as the formation of hydrated silica – are finally introduced.
Highlights
Classical optics manufacturing is realised by several successive steps
The glass surface measured here was ground with an F320 silicon carbide grinding pad for ten minutes
The same lines for magnesium, calcium, hydrogen, sulphur and sodium as detected in the spectrum taken for the zinc crown glass, see Fig. 1, were identified
Summary
Classical optics manufacturing is realised by several successive steps. Primarily, preforms of optical components are usually cut from glass blocks or bars using circular saws. The glass component is shaped by pre-grinding or roughening, and the optically active surfaces are further smoothed by different grinding or lapping steps. Lapping – referred to as loose abrasive grinding [2] – is performed by a slurry, i.e. a mixture of water and lapping grains such as corundum, aluminium oxide or silicon carbide This process is quite comparable to subsequent polishing where an aqueous suspension is used. Each single process step and especially grinding and lapping comes along with the formation of micro cracks and subsurface damages [1,3] The depth of such defects depends on the grain size and can reach some hundreds of microns [4]. Due to friction between the particular tools and the surface, compara-
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