Two Centuries of Glass Research: Historical Trends, Current Status, and Grand Challenges for the Future

International Journal of Applied Glass Science, 5 [3] 313–327 (2014) DOI:10.1111/ijag.12087

John C. Mauro*,† Science and Technology Division, Corning Incorporated, Corning, New York, 14831

Edgar D. Zanotto* Department of Materials Engineering (DEMa), Center of Research, Technology, and Education in Vitreous Materials (CeRTEV), Federal University of Sao~ Carlos (UFSCar), Sao~ Carlos, SP, 13.565-905, Brazil

The field of glass science and technology has a remarkable history spanning about two centuries of research. In this article, we analyze the number of research papers and patents related to glassy and amorphous materials in the published literature. The publication rate has increased roughly exponentially since 1945. Within the most recent decade, China has become the clear dominant player in the global glass research community, while the publication rate has declined in many of the historically most prolific countries. Oxide glasses, metallic glasses, amorphous carbon, and amorphous silicon have drawn the most research attention overall and are still given the greatest focus today. Publication data are also analyzed in terms of the properties under study, author keywords, affiliation, and primary characterization techniques. We find that the level of published (fundamental) glass research from industrial laboratories has dropped significantly, despite the opportunities for new breakthroughs to solve some of the most challenging problems facing the world today. But, surprisingly, the number of patents issued worldwide has surpassed the number of published scientific articles, indicating a very high level of activity in technological research.

Introduction history. Indeed, glassy materials have proven to be one of the key enablers of modern human civilization. The history of glassmaking dates back more than Throughout most of history, the understanding of glass 5000 years, making glass one of the most important was strictly empirical, based on trial-and-error experi- and impactful materials throughout recorded human mentation. The first modern scientific research on glass was published starting in the eighteenth century by *Member, The American Ceramic Society. 1 †[email protected] Lomonosov, who performed the first systematic studies © 2014 The American Ceramic Society and Wiley Periodicals, Inc. of glass composition–property relationships. This early This is an open access article under the terms of the Creative Commons Attribution License, research in glass also includes the 1827 work by Grif- which permits use, distribution and reproduction in any medium, provided the original work 2 is properly cited. fiths on the dissolution of glass in water and several 314 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014 papers by the great Michael Faraday, who published to the following subject areas: materials science, engi- some of the earliest studies on glass technology.3,4 neering, chemistry, physics, earth sciences, and multidis- Other pillars of glass science and technology in the late ciplinary fields. While we do not evaluate the quality of 1800s and early 1900s were Otto Schott, William E.S. glass publications in this article, and the question of Turner, F. W. Preston, and George W. Morey. quality itself is a subjective and potentially controversial Our understanding of glassy materials has grown matter, the quantity of publications—regardless of immensely in the nearly two centuries that have fol- impact—is an effective and objective proxy for the level lowed this groundbreaking work. Advances in glass of activity in the research of glass. science and technology have served as essential ingre- Although our primary interest is in glass, we also dients for modern day society, including architecture, include the keyword “amorphous”, since the terms transportation, medicine, energy, science exploration, “glassy” and “amorphous” are sometimes used inter- and the communication and display of information. changeably in the literature. Here, we remind the Given the amazing amount of progress in the under- reader that glasses and amorphous solids are thermody- standing and application of glassy materials, especially namically distinct classes of noncrystalline solids, with in recent decades, it is perhaps helpful to take a step glasses having a short-range order similar to that found back to analyze the current state of glass science and in the corresponding molten state, and amorphous sol- the historical trends that have led us to where we are ids having a short-range order distinct from that of the today. Such exercise may also prove helpful in con- liquid. Also, a glass exhibits a continuous relaxation to sidering what might come next for glassy materials the liquid state upon heating, whereas an amorphous and their opportunities for future impact on global solid does not. For more information on the differences society. between glasses and amorphous solids, we refer the In a previous article published in this journal,5 we reader to Gupta.6 reviewed the current status of academic glass research Our search strategy described above was chosen to in the United States, considering all glass-related arti- minimize the number of nonglass articles, that is, those cles published in six of the top glass science journals articles that make use of glass but where the primary during the time frame of 2007 to 2013. In the current focus is not on the scientific or technological aspects of article, we broaden this analysis to consider all of the glass itself. With this chosen search strategy, we obvi- published literature in glass science and technology, ously miss many real glass-related articles. However, dating back nearly two centuries. Our goal is to provide this approach ensures that we have a much cleaner a global view of the historical trends and current status dataset to work with and still have more than enough of glass research, as well as our thoughts on opportuni- data to obtain decent statistics. ties for glass science and technology in the future. We The total number of glass-related publications reg- hope this article will help contribute to a global discus- istered at SCOPUS is about 650,000 considering any sion on future directions for glass, building on the of the keywords (“glass,” “amorphous,” etc.) in the arti- immense framework of understanding and literature cle title, keyword list, or abstract, and accounting for published by our forerunners in the field. all types of documents, including letters, conference proceedings, errata, and technical notes. When we restrict the keywords to the title of the publication Methodology only, the number of documents is reduced to approxi- mately 230,000. For a cleaner dataset, we further In this study, we consider the publications cataloged restrict our search to journal articles only. Using this in the “Physical Sciences” library of the SCOPUS biblio- most restrictive strategy, our search resulted in a total graphic database from Elsevier, which comprises 7200 of about 120,000 glass-related articles from the SCO- journal titles. We specifically search for articles with the PUS database, including all families of glasses (oxide, words “glass,” “glasses,” “vitreous,” “amorphous,” or metallic, organic, polymeric, and so on). A similar “non-crystalline” in the title of the article. To focus on search performed in the Web of Science (Thomson papers pertinent to glass science and technology, we Reuters Scientific) yielded a comparable number, viz., exclude all papers with “spin,” “substrate,” or “electrode” about 176,000 papers. The articles obtained through in either the title or abstract, and we restrict our search this search strategy were sorted according to a variety of www.ceramics.org/IJAGS Two Centuries of Glass Research 315

fields, including publication date, journal title, country (a) of origin, affiliation, and type of glass study. 5.0 We also performed a parallel search of the patent 4.5 literature using the Derwent Innovations Index 4.0 (Thomson Reuters Scientific). This search covered pat- 3.5 ents granted between 1963 and 2013 using the same 3.0 2.5 keywords as in the SCOPUS search in the patent titles. 2.0 Glasses Inorganic Glasses This search resulted in about 370,000 patents issued 1.5 Refractories worldwide. The patents obtained were sorted according 1.0 to date issued and grantee. Semiconductors 0.5 Composites

Log[Number of Publications] 0.0 Results Year From 1837 to 1913, the number of glass-related (b) journal articles published satisfying the abovementioned 4.5 criteria fluctuated from around one to five articles per 4.0 year. Within the ensuing 100 years (1913–2013), the 3.5 number of publications per year increased by more than 3.0 three orders of magnitude. Figure 1 shows a comparison 2.5 2.0 of the number of glass-related publications with article Glasses counts for five other types of materials. Here, we con- 1.5 Inorganic Glasses sider both search strategies: including any of the specified 1.0 Refractories keywords in the article title, abstract, or keyword list 0.5 Semiconductors Composites

(Fig. 1a) or keywords appearing in the article title only Log[Number of Publications] 0.0 (Fig. 1b). From the mid-1940s to the early 1970s, there was a significant increase in the publication rate for all five of the materials classes listed. The growth rate then Year slowed in the 1970s, but the actual numbers continued Fig. 1. Number of publications per year in the SCOPUS data- to increase, reaching about 5500 glass-related papers per base by material type: (a) including all types of publications (let- year (considering keywords in the article titles only). It is ters, notes, conference proceedings, etc.), all areas of knowledge, interesting to note that “glasses” and “inorganic glasses” and the main keywords “glass,” “glasses,” “amorphous,” “vitre- (meaning inorganic, nonmetallic glasses—including both ous,” or “non-crystalline” in the article title, abstract, or keyword oxides and chalcogenides) were about the same until the list; and (b) using a restricted search with the main keywords early 1970s, just after metallic glasses were discovered (in only in the article title, and selecting only articles published in hard science journals. the 1960s) and jointly with organic and polymer glasses became as popular as traditional inorganic glasses. The material class exhibiting the highest growth rate is “com- growing steadily since the 1940s and reached a higher posites,” which also includes a number of types of “glass number/year than those of published scientific articles. matrix” and “glass fiber” composites. Among the various About 370,000 glass-related patents have been granted types of material systems under consideration, the only worldwide in the last 50 years, including 98,000 new exception to the observed exponential growth pattern is patents in the past 4 years. Surprisingly, this is more “refractories,” which nearly saturated in the 1970s and than number of glass-related publications in the SCO- has thenceforth been fluctuating at around 250 articles PUS database (>200,000) over the same 50 years. One per year. must be aware, however, that it is a common industrial For comparison, Fig. 2 shows the number of pat- practice to register several related patent applications in ents granted by decade, as determined through the Der- different countries on the same invention. Therefore, went Innovation Index. The number of granted patents the number of patents is always greater than the actual concerning glasses and amorphous materials has been number of unique inventions being disclosed. 316 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

120,000 and the University of Tokyo are also in the top ten. 100,000 The Russian Academy of Sciences (which includes several different laboratories throughout the Russian 80,000 Federation) is second in this list. Several European and 60,000 Chinese universities also appear among the most pro- 40,000 liﬁc institutions overall.

20,000 Interestingly, in the United States, the most pro-

Number of Patents Granted ductive institution overall (Bell Labs) is an industrial 0 1971-1980 1981-1990 1991-2000 2001-2010 research laboratory rather than a university. Corning Incorporated is also high on the list; IBM Thomas J. Fig. 2. Number of patents granted worldwide by decade. Here, Watson Research Center and Philips Research also we consider any of the keywords “glass,” “glasses,” “amorphous,” appear further down on the ranking. These are the only “vitreous,” or “non-crystalline” in the title of the patent. Between 1963 and 2013, a total of about 370,000 glass-related patents four company laboratories listed among the world’s top have been issued worldwide. 160 most prolific institutions in glass science. Other top institutions in the United States include several Most Prolific Institutions universities (Massachusetts Institute of Technology, the Pennsylvania State University, and Stanford University) Figure 3 plots the total number of glass-related and a U.S. government research laboratory (Argonne papers from 1850 to 2013 by affiliation. The most pro- National Laboratory). lific institution is Tohoku University in Japan, where In Figure 4, we show a similar ranking by institu- the group led by Prof. Akihisa Inoue has published tion, but considering only the most recent 4 years about 2500 articles related to metallic glasses. Other (2010–2013). Tohoku University is still in the lead, Japanese universities, including Kyoto University, followed again by the Russian Academy of Sciences. Osaka University, the Tokyo Institute of Technology, However, a number of Chinese universities have over-

Tohoku University 2857 Russian Academy of Sciences 1762 Kyoto University 1182 CNRS 1074 Osaka University 890 Tokyo Institute of Technology 856 University of Cambridge 843 Shanghai Ins Optics Mechanics Chin Acad Sci 840 University of Tokyo 679 Alcatel-Lucent Bell Labs 661 Chinese Academy of Sciences 661 Massachusetts Institute of Technology 643 Institute Metal Res Chinese Acad Sci 596 Friedrich Schiller Universität Jena 574 Pennsylvania State University 567 1850-2013 State Scientific-Research Institute Glass 565 Argonne National Laboratory 541 IoP Chinese Academy of Sciences 538 Indian Institute of Science 527 Universite Pierre et Marie Curie 526 Tsinghua University 515 Corning Incorporated 510 Stanford University 496 University of Sheffield 492 0 500 1000 1500 2000 2500 3000 Number of Publications

Fig. 3. Total number of publications in glass science (1850–2013), sorted by affiliation. Tohoku University of Japan leads this ranking, a direct result of the extremely prolific research work on metallic glasses of the group lead by Prof. Akihisa Inoue. Overall, there is a mix of Japanese, Russian, European, Chinese, Indian, and American institutions. It is relevant to stress the presence of Bell Labs and Corning Incorporated as the only two company laboratories within the 25 most prolific institutions in this ranking. www.ceramics.org/IJAGS Two Centuries of Glass Research 317

Tohoku University 445 Russian Academy of Sciences 257 Shanghai Institute Optics Mech Chinese… 204 Ningbo University 173 Harbin Institute of Technology 170 Chinese Academy of Sciences 159 CNRS Centre National Recherche Sci 157 University Science and Technology Beijing 155 Graduate Univ Chinese Academy of Sciences 152 Tsinghua University 147 South China University of Technology 139 Technische Universität Dresden 134 Central South University China 129 Leibniz Inst Festkorper Werkst. 125 University of Tennessee, Knoxville 124 2010-2013 Wuhan University of Technology 124 National Research Center, Cairo 117 Inst Metal Re Chinese Academy of Sciences 117 Hong Kong Polytechnic University 115 Universite de Rennes 1 115 Osaka University 114 IoP Chinese Academy of Sciences 107 Friedrich Schiller Universität Jena 107 Zhejiang University 102 Kyoto University 102 0 50 100 150 200 250 300 350 400 450 500 Number of Publications

Fig. 4. Number of publications by affiliation in recent years (2010–2013). Tohoku University of Japan still leads the ranking. How- ever, there has been a significant change in the mix of the most prolific institutions. There is now a clear dominance of Chinese institutions, followed by Japanese, then a few German and French, plus one Egyptian and one American university. It is worth mentioning that Corning Incorporated (#55 most prolific institution) is the single industrial company that appears in the ranking of the 160 most prolific institutions in this time period. taken many of the European and American institutions Fig. 6, the United States has the greatest cumulative from the previous figure. There is no longer any indus- number of publications overall, followed by Japan and trial research laboratory near the top of list. Except for China. Russia and three European countries (Germany, Corning Incorporated (the #55 most prolific institution France, and the United Kingdom) follow. Outside of in 2010–2013), there is no industrial laboratory among Europe, India and South Korea also have very strong the top 160 most prolific organizations. rankings. Next, we consider the top institutions in terms of However, the more recent trends paint a different the number of glass-related patents granted. Figure 5 picture, as depicted in Fig. 7(a). Here, we plot the shows the cumulative number of patents granted to the number of glass-related publications for the top ten twenty most prolific industrial companies in the past most prolific countries in 1850–2013 as a function of 4 years (2010–2013). Japanese companies lead the year. The output from Chinese institutions has grown overall ranking by a large margin. Asahi Glass and Nip- precipitously in recent years, surpassing that of every pon Electric Glass are first and second, respectively. other country. India and South Korea have also grown Corning Incorporated (U.S., #3), Saint-Gobain rapidly, while the rate of growth in research activity has (France, #6), and Schott (Germany, #8) are the only slowed down or even become negative in all other eight non-Asian companies among the top twenty. It is inter- countries in this list, starting in the mid-nineties. The esting to note that six universities and (surprisingly) a precipitous rise of Chinese research has coincided with dozen individual inventors (all Asian) also appear a distinct slowing of the growth rate in the United among the top 100. States. While this slowdown in the United States is troubling, the situation is dramatically worse in several Most Prolific Countries of the other top countries, including Japan, Germany, and Russia, all of which actually produced fewer We now turn our attention to the breakdown of research publications in 2001–2010 compared to glass-related publications by country. As depicted in 1991–2000. 318 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

ASAHI GLASS CO LTD 1128 NIPPON ELECTRIC GLASS CO 728 CORNING INC 559 HOYA CORP 404 MATSUSHITA DENKI SANGYO KK 319 SAINT-GOBAIN GLASS FRANCE 318 SHARP KK 315 SCHOTT AG 280 SAMSUNG ELECTRONICS CO LTD 244 LG DISPLAY CO LTD 237 OHARA KK 221 2010-2013 BOE TECHNOLOGY GROUP CO LTD 213 CENTRAL GLASS CO LTD 211 SEKISUI CHEM IND CO LTD 203 SUMITOMO ELECTRIC IND LTD 203 SEIKO EPSON CORP 199 HON HAI PRECISION IND CO LTD 197 TOYOTA JIDOSHA KK 193 CHINA TRIUMPH INT ENG CO LTD 191 CANON KK 187 0 200 400 600 800 1000 1200 Number of Patents Granted

Fig. 5. Number of glass-related patents granted in 2010–2013, sorted by institution. Japanese companies lead the overall ranking by a large margin. Asahi Glass and Nippon Electric Glass are ﬁrst and second, respectively. Corning Incorporated (U.S., #3), Saint-Gobain Glass (France, #6), and Schott AG (Germany, #8) are the only non-Asian companies among the top twenty.

United States 21524 Japan 14113 China 13675 Russian Fed. + Russia 10274 Germany 8941 France 7165 United Kingdom 6361 India 5352 Italy 3693 South Korea 3097 Spain 2728 Canada 2073 Poland 1835 1850-2013 Brazil 1751 Taiwan 1480 Egypt 1425 Netherlands 1404 Australia 1322 Ukraine 1283 Czech Republic 1225 Switzerland 997 Israel 909 0 5000 10000 15000 20000 25000 Number of Publications

Fig. 6. Most proliﬁc countries in the history of glass research (1850–2013). The United States is the leader overall, followed by Japan and China.

Figure 7(b) shows the number of glass-related pub- steady growth in the past 50 years, except for Spain lications for the second half of the top twenty most and the Netherlands, with stagnant research activity in proliﬁc countries in 1850–2013. They all showed the past 20 years, and Brazil, which has shown a signif- www.ceramics.org/IJAGS Two Centuries of Glass Research 319

(a) icant growth rate from the early 1990s until about 2005, but has since shown declined research activity. In Figure 8, we compare the distribution of recent glass-related publications from China versus that of the United States. While the number of publications from China has surged beyond that of the United States, the types of material systems under study are not too dis- similar. There is somewhat more emphasis on metallic glasses in China and on polymeric glasses in the United States. The percentage of articles on silicate glasses is similar for both countries. Beyond China, other countries showing notable increases in research activity include India and South Korea. Figure 9 shows the ranking of countries for the most recent 4 years (2010–2013), indicating that India has now surpassed both France and Russia. Other countries showing recent high rates of research produc- tivity include Poland, Taiwan, and Egypt.

(b) (a)

(b)

Fig. 7. (a) Number of glass-related publications for the top ten most prolific countries in 1850–2013. The output from Chinese institutions has grown precipitously in recent years, surpassing that of every other country. India and South Korea have also grown rapidly, while the rate of growth in research activity has slowed down or even become negative in all eight other countries in this list, starting in the mid-1990s. (b) Number of glass- related publications for the second half of the top twenty most prolific countries in 1850–2013. They all showed steady growth in the past 50 years, except for Spain and the Netherlands, which had stagnant research activity in the past 20 years, and Brazil, which has shown a significant growth rate from the early 1990s until about 2005, but has since shown declined research Fig. 8. Distribution of recent publications in (a) China and activity. (b) the United States by glass type. 320 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

China 4751 United States 2454 Japan 1549 Germany 1314 India 1283 France 1146 Russian Federation 976 South Korea 882 United Kingdom 765 Italy 603 Spain 481 Poland 366 Taiwan 364 2010-2013 Egypt 352 Australia 335 Brazil 323 Canada 315 Iran 292 Ukraine 239 Turkey 236 Hong Kong 213 Czech Republic 210 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Number of Publications

Fig. 9. Number of glass-related publications by country in the most recent 4 years. The dominance of China is clear, nearly doubling the output of the next most proliﬁc country (the United States).

J Non-Crystalline Solids 10472 Steklo i Keramika (Russian) 4578 Physical Review B 4108 J Applied Physics 3730 Applied Physics Letters 3054 J Materials Science 2266 Physical Review Letters 1576 J Magnetism Magnetic Materials 1473 J Chemical Physics 1426 J American Ceramic Society 1396 Materials Science Engineering A 1388 J Alloys and Compounds 1342 Solid State Communications 1325 J Physics Condensed Matter 1099 1850-2013 J Materials Science Letters 1030 Thin Solid Films 914 Macromolecules 912 Fizika i Khimiya Stekla (Russian) 814 Polymer 811 J Materials Research 778 Physics and Chemistry of Glasses 770 Materials Letters 759 Physica B Condensed Matter 649 0 2000 4000 6000 8000 10000 12000 Number of Publications

Fig. 10. Cumulative number of glass-related publications by journal from 1850 to 2013. Journal of Non-Crystalline Solids leads this journal ranking by a large margin. It is interesting to note that several physics (more than chemistry) journals and materials science journals follow in the ranking. Two polymer journals also appear. Among the specialized journals, only three journals: Steklo I Keramika (Russian), Fizika I Khimiya Stekla (Russian), and Journal of the American Ceramic Society appear among the top 30. www.ceramics.org/IJAGS Two Centuries of Glass Research 321

Most Prominent Journals Material Systems

Within the glass science community, Journal of In Figure 12, we plot the total number of papers Non-Crystalline Solids (JNCS) is clearly the single most published in the period 1850–2013 by the type of mate- signiﬁcant journal, publishing more than double the rial system under study. In this case, the above-listed glass number of glass-related articles as the next most popu- types were searched in the article title, keyword list, and lar journal, as shown in Fig. 10. The historical domi- abstract. Metallic glasses, oxide glasses, amorphous carbon, nance of this journal is maintained even today. As and amorphous silicon have received the most attention depicted in Fig. 11, in recent years, JNCS still pub- overall. (Amorphous silicon and carbon, we note, are not lishes more than double the number of glass-related actually glasses at all, i.e., they do not undergo a glass tran- papers compared to the next most popular journal. sition.) Among oxide glasses, silicates have received the Beyond JNCS, physics journals including Physical most attention (not surprisingly), followed by phosphates. Review B, Applied Physics Letters, and Journal of Chem- With regard to the several application types of glassy mate- ical Physics are excellent sources of glass-related rials (last 7 columns), glass composites are the most popu- research. Overall physics journals are more popular lar, followed by bio-glasses, semiconductor glasses, and than chemistry journals for glass research, although glass-ceramics, which are all nearly tied for second place. the Journal of Physical Chemistry B appears on our list In Figure 13, we see that the same four types of of highest ranked journals for recent years (Fig. 8). glasses have retained their dominance in the most Materials science journals such as Acta Materialia are recent 4 years. Among the oxide glasses, silicates con- also well represented in this ranking. Another note- tinue to lead over other types. For the various applica- worthy trend is an increase in the number of relevant tion types (last 7 columns), glass composites, bio- specialized journals in recent years compared to prior glasses, and glass-ceramics are now the top three. For history. more details, we refer the interested reader to several

J Non-Crystalline Solids 920 Applied Physics Letters 449 J Alloys and Compounds 439 J Applied Physics 413 J American Ceramic Society 298 Physical Review B 286 J Chemical Physics 214 Intermetallics 213 Physical Review Letters 207 Optics Express 176 Acta Materialia 164 Materials Science Engineering A 163 Physica B Condensed Matter 161 Ceramics International 158 Materials Letters 155 J Materials Science 146 2010-2013 Scripta Materialia 143 Glass and Ceramics Translation 139 Materials Chemistry and Physics 133 J Physical Chemistry B 129 Optics Letters 114 PCG European J Glass Science Tech B 113 GC Journal of Functional Materials 112 J Applied Polymer Science 111 Glass Physics and Chemistry 108 Int J Applied Glass Science 106 0 100 200 300 400 500 600 700 800 900 1000 Number of Publications

Fig. 11. Number of glass-related publications by journal in recent years (2010–2013). Journal of Non-Crystalline Solids continues to lead the journal ranking. Physics (more than chemistry) and materials science journals follow in the sequence. More specialized journals now appear among the top 30: Journal of the American Ceramic Society, Ceramics International, Glass and Ceramics (Steklo I Keramika in Russian), Physics and Chemistry of Glasses—European J. Glass Science & Technology B, Glass Physics and Chemistry (Fizika I Khi- miya Stekla in Russian), and the new International Journal of Applied Glass Science in this order. 322 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

Fig. 12. Total number of publications in the period 1850– Fig. 13. Number of publications in 2010–2013 for various 2013 registered in the SCOPUS database for various types of types of glasses and amorphous solids. As in the previous figure, glasses and amorphous solids. In this case, to widen our search, the keywords were searched in the article title, keyword list, and the keywords were searched in the article title, keyword list, and abstract. The research activity in metallic glasses, amorphous car- abstract. Research activity in metallic glasses, amorphous carbon, bon, and oxide glasses still dominates. Research in amorphous sil- and oxide glasses dominate. Research in amorphous silicon is also icon continues to be significant. Silicates continue to lead over very significant. Among the oxide glasses, silicates dwarf that of the other types of oxide glasses. Glass composites, bio-glasses, and every other type of oxide system, as expected. With regard to sev- glass-ceramics are the top three most studied types of application- eral types of application-oriented glasses (last 7 columns), glass oriented glasses (last 7 columns). composites is the top, whereas bio-glasses, semiconductor glasses, and glass-ceramics are about even in second. + “nucleation” + “crystal growth.” The next most recent review articles related to the current status and popular set of keywords include those related to “glass – future directions of glass-ceramic research.7 9 transition” and other dynamic and thermodynamic properties. Research Areas Finally, in Figs 18 and 19, we consider the popu- larity of various characterization techniques, both his- In Figures 14 and 15, we consider the most fre- torically and in recent years. The preferred quently studied types of glass properties, both histori- characterizations techniques have been and still are X- cally and in recent years. Optical and mechanical ray methods, thermal analysis, electron microscopy, sev- properties have received the most attention overall, with eral types of optical spectroscopies, and some types of mechanical properties becoming the most popular in computer simulations methods such as molecular recent years. Thermal and rheological properties have dynamics. also received considerable attention from researchers, both historically and today. In Figures 16 and 17, we plot the most fre- Grand Challenges for the Future quently selected keywords chosen by authors when submitting their manuscripts. Crystallization dominates While the field of glass science is growing healthily due to the strong activity in the metallic glass com- in a global sense, many of the countries with tradition- munity. This is even clearer if one sums the number ally strong glass research programs have clearly fallen of papers having the keywords “glass forming ability” behind fast-growing newcomers, particularly China. www.ceramics.org/IJAGS Two Centuries of Glass Research 323

Optical 14300

Mechanical 12950

Thermal and Rheological 7565

Chemical 5725 1850-2013

Electric and Magnetic 3576

0 2000 4000 6000 8000 10000 12000 14000 16000

Number of Publications

Fig. 14. Total number of glass-related publications by property type. Optical and mechanical properties have garnered the most attention overall.

Mechanical 3581

Optical 2372

Thermal and Rheological 950

Electric and Magnetic 758 2010-2013

Chemical 391

0 500 1000 1500 2000 2500 3000 3500 4000

Number of Publications

Fig. 15. Number of publications by property type in recent years (2010–2013).

Crystallization 8807 Glass Transition 8390 Composition 3708 Thermodynamic Properties 2854 Activation Energy 2586 Structure 2028 Phase Transitions 1679 Nucleation 1578 Diffusion 1430 Sintering 1417 Relaxation 1330 1850-2013 Interfaces 1190 Chemical Bonds 1183 Reaction Kinetics 1152 Energy Transfer 1025 Phase Separation 943 Crystal Growth 880 Glass Forming Ability 816 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Number of Publications

Fig. 16. Most frequent keywords chosen by authors when submitting their glass-related papers. Crystallization is the most popular topic, followed by glass transition. 324 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

Crystallization 2833 Glass Transition 1952 Morphology 1166 Activation Energy 739 Sintering 450 Energy Transfer 405 Glass Forming Ability 376 Thermodynamic Stability 313 Phase Separation 249 2010-2013 Amorphous Structures 217 Dynamics 216 Kinetics 209 Nucleation 207 0 500 1000 1500 2000 2500 3000

Number of Publications

Fig. 17. Most popular keywords selected by authors in recent years (2010–2013). Again, crystallization is the most popular topic, followed by glass transition.

X-Ray 6926 DSC + DTA 5440 Scanning Electron Microscopy 3525 Transmission Electron Microscopy 2694 Molecular Dynamics 2253 Computer Simulation 2204 Raman Spectroscopy 1633 FTIR Spectroscopy 1233 X-Ray Photoelectron Spectroscopy 1226 Absorption Spectroscopy 1084 1850-2013 Spectroscopic Analysis 949 Thermoanalysis 930 Nuclear Magnetic Resonance Spec 828 Atomic Force Microscopy 828 Emission Spectroscopy 802 Spectroscopy 740 0 1000 2000 3000 4000 5000 6000 7000 8000 Number of Publications

Fig. 18. Total number of glass-related publications organized by characterization technique.

This raises the question of how the downward trajecto- ciently in many developing countries, except perhaps ries in these countries can be reversed so that they can India, Brazil, and Egypt, the only three among the top continue to succeed in a much more competitive global 20 most prolific countries in glass research. environment. The answer to this question has clear rel- Related to this issue is the unfortunate decline of evance for the long-term quality of life in the United industrial research in the fundamental sciences. Before States, Japan, and many European countries, where the the breakup of AT&T, the most creative and most pro- rate of research has either dramatically slowed or has lific research laboratory in the world was an industrial shown significant declines in recent times. Glass laboratory (Bell Labs)10 not affiliated with any univer- research and development have also not grown suffi- sity. Today, Corning Incorporated stands as the only www.ceramics.org/IJAGS Two Centuries of Glass Research 325

X-Ray Diffraction 2404 Scanning Electron Microscopy 1376 DSC + DTA 1111 Molecular Dynamics 733 Transmission Electron Microscopy 644 Computer Simulation 323 X-Ray Photoelectron Spectroscopy 282 2010-2013 Emission Spectroscopy 259 Atomic Force Microscopy 230 Thermoanalysis 225 Finite Element Method 207 0 500 1000 1500 2000 2500 3000

Number of Publications

Fig. 19. Most popular characterization methods in recent years (2010–2013). large company that routinely publishes fundamental In lieu of proposing more specific research topics, research in the peer-reviewed glass and glass-ceramics here, we would like to suggest several broader “grand literature. In the case of Corning, this comes from rec- challenge” problems for glass science and technology. ognition that the long-term future of the company is We propose these challenges in a similar spirit as the dependent on having a healthy pipeline of fundamental Grand Engineering Challenges promulgated by the and exploratory research activities.11 This type of U.S. National Academy of Engineering. These grand research is encouraged and promoted, as it is recog- challenges are formulated in terms of questions that nized that the most significant scientific and technologi- address some of the most pressing issues facing our cal breakthroughs require a sufficient focus on world today, as well as the potential role of glassy fundamental understanding and scientific exploration. materials in solving these problems: However, Corning is one of the few large companies in 1. How can glass be used to combat global warm- the materials sector that still demonstrates a consistent ing?13 commitment to basic research. This positive corporate 2. How can glass help enable the next generation of attitude toward basic research will need to spread to renewable energy?14,15 other companies before the state of industrial glass 3. How can glass help to store energy, for example, research as a whole can move beyond incremental with new solid state batteries?16 development work to more longer-term fundamental 4. How can glass be used to enable safe, affordable research.12 This is the only way that any hope of signif- drinking water and a clean, pollution-free atmo- icant—and potentially revolutionary—breakthroughs sphere? can be achieved. 5. How can glass be used to reduce energy consump- With the hope of stimulating a renewed interest in tion and eliminate waste?17 fundamental glass research, recently, we published a list 6. How can glass be used to fight disease and – of nearly 100 open questions grouped into twelve differ- improve human health?18 24 ent areas of glass research.5 Each of these questions 7. What is the future role of glass in information and addresses an area that we feel is not currently being given communication technology?25 enough attention in the research community. The pro- 8. Can ultra-strong, high-toughness glasses be devel- posed research areas discussed in this prior work all have oped to improve safety in architectural and other ample room for new and exciting breakthroughs in fun- structural applications?26 damental science. At the same time, many of them 9. How can strong, lightweight glass boost the future address problems of practical industrial concern. We will of transportation, for example, in electric cars? not repeat these suggestions here, as the interested reader 10. Can we develop ultra-light, strong glass containers can find the full list of topics in ref. 5. that reduce waste and energy consumption? 326 International Journal of Applied Glass Science—Mauro and Zanotto Vol. 5, No. 3, 2014

11. Can ultra-fast switching chalcogenide glasses be scientific articles. This demonstrates the very high level developed into nonvolatile memory media that of activity on (practical) technological research. could be the basis for glass computers?27 It is our hope that a renewed focus on glass and 12. Can ultra-clean optical fibers reach the ultra-low materials education, starting at a young age, will help loss absorption limit? encourage more students to pursue careers in science, 13. Can ultra-strong (>10 GPa), tough, low density, technology, and engineering. We have also proposed a corrosion-, and abrasion-resistant glasses be devel- series of “grand challenge” questions regarding the use oped and applied for a number of high-tech appli- of new glassy materials for solving some of the world’s cations? most pressing issues. Answers to these questions are left 14. Can glass be used as efficient drug or nutrient as a research challenge to glass scientists and technolo- delivery media for agriculture, animals, and gists, and as an exercise for the reader! humans? 15. Can glass be manufactured at large scale in a totally sustainable, environmentally friendly way? Acknowledgments This is by no means a complete list. We encourage the reader to think of other ways in which advances in We are grateful for valuable discussions with Dan- glass science and technology can potentially contribute iel J. Vaughn, Charles S. Philip, Michael S. Pambian- improvements to global health and prosperity. We also chi, Jeffrey T. Kohli, Douglas C. Allan, Adam J. refer the reader to additional publications by Bange Ellison, David L. Morse, M. K. Badrinarayan, Gary S. 28 29 and Weissenberger-Eibl, Rohrer, Zanotto and Calabrese, Martin J. Curran, and Daniel Ricoult of 30 31 Coutinho, and Hench discussing future opportuni- Corning Incorporated. We also thank Eduardo B. Fer- ties for glass and ceramic materials. reira, Ana C.M. Rodrigues, Maziar Montazerian, and Ligia Diniz of CeRTEV for their insightful suggestions, and the Brazilian Agency Fapesp—S~ao Paulo Research Conclusions Foundation—project no. 2013/07793-6 (CeRTEV) for generous funding. Between 230,000 (keywords in the article title) and 650,000 (keywords in all fields) papers have been published in nearly two centuries of research in glass References science and technology. The publication rate has increased roughly exponentially since 1945. While the 1. A. C. Wright, B. A. Shakhmatkin, and N. M. Vedishcheva, “The Chemi- United States is the most prolific country overall, in cal Structure of Oxide Glasses: A Concept Consistent with Neutron Scat- – recent years, China has taken a commanding lead. tering Studies?” Glass Phys. Chem., 27 [2] 97 113 (2001). 2. T. 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