Journal of the American Ceramic Sociery-Kurkjian and prindle Vol 81. No 4 Cao 30 2::3 a20s0 Fig 3. Soda-lime-silica phase diagram(R S. Roth, T Negas, and L P Cook; Fig 5321 in Phase Diagrams for Ceramists. Vol IV. Edited by G. Smith. American Ceramic Society, Columbus, OH, 1981) to preserve durability as the use of synthetic soda ash(pure possibility with the discovery of extensive deposits in Turkey Na2CO3, with no CaCO3)became wide-spread. This practice Chile, and, in particular, Califomia, in the latter part of the 19th an early in the 19th century because soda ash from the century Leblanc process became available and its use was common noted in an earlier section. Abbe an Schott. d ractice after the 1860s when the Solvay process became the 1880s, were the first to use boron compounds in glass in sig nificant amounts, first in optical glasses, then in glasses for Most of the current commercial glasses are soda-lime-silica laboratory apparatus. Both Faraday and Harcourt had made glasses. It is significant that the compositions of these glasses, some use of boron in glass, but Abbe and Schott clearly estab- used typically for containers and flat glass, has changed little shed that borosilicate glasses had superior resistance than ranging from 10%to 200s from 65% to 75% silica, with alkali soda-lime-silica glasses to chemical attack and had better ther- over the centuries. ra and lime as the balance. althou mal shock resistance because of their lower coefficient of thel nost older soda-lime-silica glasses contained a few percent mal expansion. The introduction of the Auer von Welsbach alumina from raw-material impurities and from refractories, a mantle in gas lamps in 1887 created a need for a lamp cylinder similar amount has been added customarily since Schott, based or chimney with improved resistance to thermal shock. Schott on his observations of Thuringian glasses, demonstrated, in the met this need with a glass containing 15% boric oxide(see late 1880s, that it benefited durability and resistance to devit- glass ll in Table I)having a very low coefficient of expan- rification Glasses with these compositions are relatively easy sion.3640,42 to melt and form, do not devitrify easily, and generally have At about this time in the United States, cracking and break reasonable resistance to attack by moisture. They can be made age of the globes of railroad brakemen's lanterns was a prob- quite color-free and nontoxic with pure raw materials that ar lem when rain showers struck the hot glass. Why Schott heat available worldwide at acceptable cost. 5. 40 resistant glasses were not used to solve this problem is not Improvements in melting technology-e. g, more-resistant known; perhaps it was due to the poor international technical refractories and higher temperatures--have increased chemical communications of the times. Corning Glass Works, the lead- durability through lower alkali and higher lime contents. This ing U.S. manufacturer of lamp chimneys and bulbs for electric trend also has been encouraged by the comparative costs of lamps, was asked to investigate the matter, and it became the soda and lime, and, currently, economic factors are the princi- first assignment of the newly formed research laboratory in pal determinant for soda-lime-silica compositions. Enough is 1908. In 1909, Corning introduced a borosilicate glass that now known about the effects of composition on properties to solved the lantern globe thermal shock problem, but had poor permit major glass constituents to be adjusted several percent- chemical durability. Corning 's first research director, Eugene age points to compensate for differences in raw-material prices C. Sullivan, a chemist hired from the U.S. Geological Survey to reach the lowest-cost composi and William C. Taylor, a young chemist colleague recently from Massachusetts Institute of Technology, worked further on (2) Borosilicate Glasses the problem. By 1912, they had perfected a chemically du- The first new major glass system to be explored beyond the rable, shock-resistant, lead borosilicate glass marketed under soda-lime-silica glasses utilized the other great glass-former the name Nonex (for nonexpanding) that reduced lantern boric oxide, important for its many commercial applications. globe breakage by 60%(see 12 in Table 1). Nonex also Although borax was known and used in the Middle ages as an proved to double the life of the battery jars used by the rail- in practical glassmaking became a realistic roads in their new electrically powered signal systemsto preserve durability as the use of synthetic soda ash (pure Na2CO3, with no CaCO3) became wide-spread. This practice began early in the 19th century, because soda ash from the Leblanc process became available and its use was common practice after the 1860s when the Solvay process became the principal source of soda. Most of the current commercial glasses are soda–lime–silica glasses. It is significant that the compositions of these glasses, used typically for containers and flat glass, has changed little over the centuries, ranging from 65% to 75% silica, with alkali ranging from 10% to 20%, and lime as the balance. Although most older soda–lime–silica glasses contained a few percent alumina from raw-material impurities and from refractories, a similar amount has been added customarily since Schott, based on his observations of Thuringian glasses, demonstrated, in the late 1880s, that it benefited durability and resistance to devit￾rification. Glasses with these compositions are relatively easy to melt and form, do not devitrify easily, and generally have reasonable resistance to attack by moisture. They can be made quite color-free and nontoxic with pure raw materials that are available worldwide at acceptable cost.5,40 Improvements in melting technology—e.g., more-resistant refractories and higher temperatures—have increased chemical durability through lower alkali and higher lime contents. This trend also has been encouraged by the comparative costs of soda and lime, and, currently, economic factors are the princi￾pal determinant for soda–lime–silica compositions. Enough is now known about the effects of composition on properties to permit major glass constituents to be adjusted several percent￾age points to compensate for differences in raw-material prices to reach the lowest-cost composition.43 (2) Borosilicate Glasses The first new major glass system to be explored beyond the soda–lime–silica glasses utilized the other great glass-former, boric oxide, important for its many commercial applications. Although borax was known and used in the Middle Ages as an exotic flux, its use in practical glassmaking became a realistic possibility with the discovery of extensive deposits in Turkey, Chile, and, in particular, California, in the latter part of the 19th century.42 As noted in an earlier section, Abbe and Schott, during the 1880s, were the first to use boron compounds in glass in sig￾nificant amounts, first in optical glasses, then in glasses for laboratory apparatus. Both Faraday and Harcourt had made some use of boron in glass, but Abbe and Schott clearly estab￾lished that borosilicate glasses had superior resistance than soda–lime–silica glasses to chemical attack and had better ther￾mal shock resistance because of their lower coefficient of ther￾mal expansion. The introduction of the Auer von Welsbach mantle in gas lamps in 1887 created a need for a lamp cylinder or chimney with improved resistance to thermal shock. Schott met this need with a glass containing 15% boric oxide (see glass 11 in Table I) having a very low coefficient of expan￾sion.36,40,42 At about this time in the United States, cracking and break￾age of the globes of railroad brakemen’s lanterns was a prob￾lem when rain showers struck the hot glass. Why Schott heat￾resistant glasses were not used to solve this problem is not known; perhaps it was due to the poor international technical communications of the times. Corning Glass Works, the lead￾ing U.S. manufacturer of lamp chimneys and bulbs for electric lamps, was asked to investigate the matter, and it became the first assignment of the newly formed research laboratory in 1908. In 1909, Corning introduced a borosilicate glass that solved the lantern globe thermal shock problem, but had poor chemical durability. Corning’s first research director, Eugene C. Sullivan, a chemist hired from the U.S. Geological Survey, and William C. Taylor, a young chemist colleague recently from Massachusetts Institute of Technology, worked further on the problem.44 By 1912, they had perfected a chemically du￾rable, shock-resistant, lead borosilicate glass marketed under the name Nonext (for nonexpanding) that reduced lantern globe breakage by 60% (see glass 12 in Table I). Nonex also proved to double the life of the battery jars used by the rail￾roads in their new electrically powered signal systems. Fig. 3. Soda–lime–silica phase diagram (R. S. Roth, T. Negas, and L. P. Cook; Fig. 5321 in Phase Diagrams for Ceramists, Vol. IV. Edited by G. Smith. American Ceramic Society, Columbus, OH, 1981). 802 Journal of the American Ceramic Society—Kurkjian and Prindle Vol. 81, No. 4