Importance

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Abstract

Ion exchangeable glass compositions containing from 50 to 90 mole percent GeO.sub.2, from 5 to 30 mole percent Al.sub.2 O.sub.3, from 3 to 30 mole percent Li.sub.2 O, up to 30 mole percent Na.sub.2 O and up to 30 mole percent K.sub.2 O are provided. In another aspect, minor amounts of anhydrous fluorides and chlorides corresponding to these oxides are added to the glass compositions to aid in water removal. Glass articles formed of the germanate glass compositions of the present invention are readily ion exchangeable when contacted with certain salts. Strengthened germanate glass articles are also provided having an inner tension region and an outer compressive surface layer which provide good mechanical strength for the formed glass article. The strengthened germanate glass articles are made using the ion exchangeable germanate glass compositions of the present invention. The compressive surface layer of the strengthened germanate glass articles are formed by contacting the surface of the glass article with a suitable salt, preferably a molten alkali salt, in an ion exchange process. The surface compressive layer of the strengthened germanate glass article has a lower concentration of lithium ions than the inner tension region and has a higher concentration of select ions provided by the salt bath.

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First Claim