Pannhorst, Wolfgang

English

Repositorium für Naturwissenschaften und Technik  (TIB Hannover)

N e w D e v e l o p m e n t s in t h e F i e l d o f G l a s s C e r a m i c sW o l f g a n g P a n n h o r s tSCHOTT Glas, Hattenbergstr. 10 , 5 5 1 2 2 MainzUsing Raman spectroscopy the description of the nucleation process in a modelcomposition of the commercially important Li20-Al203-Si02 (LAS) glass ceramic Systemhas been extended successfully to a more complex composition. Α quantitative descriptionwith crystal densittes up to 10^^ crystals/cm^ was obtained for a model composition with a molar ratio for Li02/Al203 of less than  1 and  1 mol% Zr02 / 2 mol% Ti02 as nucleatingagents. Düring nucleation all Zr02 precipitates as ZrTi04 while the remaining Ti02 stays inthe glass network in 4-fold coordination.The commercial low thermal expansion glass ceramics based on the LAS System areroutinely used in cooktop panels, telescope min-or Substrates and laser gyroscopes;development projects for cook top panels address shaped panels and panels for gasStoves; recently LAS glass ceramics have found application as wafer stages in microlithography and as reflectors in beamers. Currently, the glass ceramic Zerodur for opticalprecision applications is under redevelopment to apply it as mirror Substrate for theExtreme UV Lithography (EUVL). In EUV-lithography transmissive optics are replaced byreflective optics to process Si wafers at a wavelength of 13,8 nm. The introduction of EUVlithography into the market is expected for 2 0 0 6 . Although the coefficient of thermalexpansion of curent commercial Zerodur can be specified as low as + 2 0 ppb/K for thetemperature inten^al 0 - 5 0 X this is not low enough for EUVL optics. They require + 5 ppb/Kwithin the temperature inten/al 1 9 - 2 5 X .On a laboratory scale a sintered glass ceramic Zerodur has been developed. By startingwith a fine grained powder of the Zerodur precursor glass dense and opaque bodies ofcomplex shape were fabricated which show identical thermal expansion behaviour asnormal Zerodur. Up to now no product idea has been identified which justifies the costs tobuild up a production technology.Ferrules for optical connectors as well as Substrates for hard disks are glass ceramicproducts which have established themselves as stable products in their markets.-

New Developments in the Field of Glass Ceramics

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New Developments in the Field of Glass Ceramics

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Repositorium für Naturwissenschaften und Technik (TIB Hannover)