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An Analysis of Glass–Ceramic Research and Commercialization

An Analysis of Glass–Ceramic Research and Commercialization

An analysis of –ceramic research

and commercialization Credit: Schott North America

Ceran glass-ceramic cooktop by Schott North America. rial. Although Réaumur had succeeded in converting glass into a polycrystalline mate- By Maziar Montazerian, Shiv Prakash Singh, and Edgar Dutra Zanotto rial, unfortunately the new product sagged, deformed, and had low strength because of 4,5 lass has been an important mate- uncontrolled surface crystallization. rial since the early stages of civiliza- The late Stanley Donald Stookey of Corning Glass Works G (now Corning Incorporated, Corning, N.Y.) discovered glass– tion. Glass–ceramics are polycrystalline mate- ceramics in 1953.6–8 Stookey accidentally crystallized Fotoform—a rials obtained by controlled crystallization photosensitive glass containing nanopar- ticles dispersed in the glass matrix. From the parent glass of certain that contain one or more Fotoform, Stookey and colleagues at Corning Incorporated, crystalline phases dispersed in a residual which holds the first patent on glass–ceramics, derived the glass– glass matrix. The distinct chemical nature ceramic Fotoceram. The main phases of this glass-ceramic are lithium disilicate (Li2Si2O5) and quartz (SiO2). of these phases and their nanostructures or Since then, the glass–ceramics field has matured with funda- microstructures have led to various unusual mental research and development detailing chemical composi- tions, nucleating agents, heat treatments, microstructures, proper- combinations of properties and applications ties, and potential applications of several materials.3,5,9–15 A recent in the domestic, space, defense, health, elec- article revealed that the term “crystallization” is the top keyword in the history of glass science.16 However, researchers still are tronics, architecture, chemical, energy, and keen to understand further the kinetics of transformation from waste management fields.1–3 glass to a polycrystalline material and to study the associated changes in thermal, optical, electrical, magnetic, and mechanical In 1739, French chemist René-Antoine properties. Nonetheless, several commercial glass–ceramic inno- Ferchault de Réaumur was the first person vations already have been marketed for domestic and high-tech known to produce partially crystallized glass.4 uses, such as transparent and heat-resistant cookware, fireproof doors and windows, artificial teeth, bioactive materials for Réaumur heat-treated soda–lime–silica replacement, chemically and mechanically machinable materials, glass bottles in a bed of gypsum and sand and electronic and optical devices. Review articles surveyed the properties and existing uses of for several days, and the process turned glass–ceramics and suggested several possible new applications for the glass into a porcelain-like opaque mate- these materials.9–17 Here we report on the results of a statistical

30 www.ceramics.org | American Ceramic Society Bulletin, Vol. 94, No. 4 Capsule summary

BACKGROUND ANALYSIS KEY POINT Glass–ceramics are polycrystalline materials Through a database search of published papers The field of glass–ceramics has grown during the derived from glass with distinct properties that and filed patents, the authors statistically evalu- past 60 years and continues to show signs of ex- give them unique applications in domestic, ate the evolution of scientific and technological ponential growth. Analysis of patent applications space, defense, health, electronics, architecture, research and development of glass–ceramics has identified a few areas of promising growth chemical, energy, and waste management. during the past 60 years. that may serve as a guide for future commercial endeavors in this field of unique materials. search evaluating the evolution of scientific words in patent titles from FPO records glass–ceramic publications lies between and technological research and develop- from January 2001—December 2013. In these two extremes. Figure 1 shows that, ment of glass–ceramics during the past this case, we searched granted patents using either search strategy, the number 60 years. We made an electronic search and patent applications and found 1,964 of articles shows some annual fluctua- of published research articles, granted records. After sorting and eliminating sis- tion, although both strategies reveal an patents, and patent applications since the ter patents submitted to different offices, exponential increase. Currently, about discovery of glass–ceramics in 1953. we identified 1,000 single granted patents 500–800 papers on glass–ceramics are For a more in-depth assessment and applications, which we categorized published annually. of recent trends and developments manually according to main property or The 40 most prolific authors (not shown in this field, we manually searched proposed use of the glass–ceramic. here) include researchers with 40–130 and reviewed 1,000 granted patents published articles on several aspects of and applications filed during the past Published glass–ceramic papers glass–ceramic materials. The first paper on decade. Here we break down these Searching Scopus for keywords only glass–ceramics listed in the Scopus database numbers into main property classes in article titles provided cleaner results is authored by W.W. Shaver and S.D. (thermal, mechanical, optical, electrical, than searching within abstracts, but this Stookey in 1959, which proposes the name etc.) and proposed applications. The limited search failed to capture all glass– of Pyroceram for the new class of materi- overall objective of this short article is ceramic publications. The search yielded als.18 A second paper, authored by G.W. to give students, academics, and indus- 7,040 papers, which, thus, represents McLellan in the same year, discusses pos- trial researchers some insight about the only a lower bound. Conversely, expand- sible applications of glass–ceramics in the evolution of and perspectives for appli- ing the selected keyword search to article automotive industry.19 cations of this class of materials. We titles, abstracts, and keywords yielded Figure 2 reveals the number of publica- hope it also may be a useful source of 12,806 papers, including several that are tions authored by researchers with par- ideas for new research projects. only minimally related to glass–ceram- ticular affiliations, most of which are uni- ics. Therefore, the actual number of versities. Kyoto University in Japan holds Database search We surveyed the Scopus Elsevier, Free Patents Online (FPO), and Derwent World Patents Index (DWPI) databases for patents and papers published in glass–ceramic science and technology. We searched the Scopus database for scientific publications 1955—2014 using the keywords “sittal”, “vitroceramic*”, “glass–ceramic*”, or “glass ceramic*” in the article title or, in a separate search, in the title, abstract, and keywords. Number of papers Keywords “glass–ceramic” and “glass ceramic” predominate by a large margin. We then sorted articles by publication year, affiliation, and country. Additionally, we extracted DWPI records of granted patents by searching for keywords “glass–ceramic*”or “glass ceramic*” in patent titles from 1968—July Year

2014. We ranked the number of pub- Credit: E.D. Zanotto lished patents per year as well as the most Figure 1. Number of published articles per year extracted from the Scopus database by prolific companies from the records. searching the keywords “sittal”, “vitroceramic*”, “glass–ceramic*”, or “glass ceramic*” Further, we searched the same key- in article titles (blue) or in article titles, abstracts, or keywords (red).

American Ceramic Society Bulletin, Vol. 94, No. 4 | www.ceramics.org 31 An analysis of glass–ceramic research and commercialization

patents. However, this particular search engine provided no other pos- sible search strategies. With this restrictive search strategy, the total number of glass–ceramics patents granted—which thus represents a minimum—up to December 2013 is 4,882. Although granted patents have Affiliation fluctuated somewhat over the years, the number has steadily grown in the past two decades (Figure 3). During 1975– 1979 and 2003–2008, total patents declined monotonically, whereas the number increased 1994–1998. Overall, about 220 new patents are granted each Number of papers year. Our analysis reveals that glass– Credit: E.D. Zanotto Figure 2. Total glass–ceramic publications in the Scopus database from 1955–July 2014, ceramic technology is growing rapidly sorted by affiliation. Counted articles contained keywords “sittal”, “vitroceramic*”, and several potential new products are “glass–ceramic*”, or “glass ceramic*” in the article title. emerging every year. the top position with 157 articles, fol- research with 1,557 papers, followed by Further, we searched DWPI for key- lowed by several Chinese and European researchers from the U.S. (718 papers), words “glass–ceramic*” or “glass ceram- universities and two institutions in emerg- Japan (663 papers), (462 papers), ic*” in patent titles and found that sev- ing countries—Iran University of Science and the United Kingdom (404 papers). eral companies around the world manu- and Technology in Tehran, Iran, and Most countries in this ranking are industri- facture glass–ceramic products (Table 1). the National Research Center in Cairo, ally developed. However, it is somewhat Several companies hold glass–ceramics Egypt. The only company in this ranking surprising that several emerging countries, patents, but only some are commercial- is Corning Incorporated, and it is no sur- such as India, Brazil, Egypt, Iran, Turkey, izing such products. Likewise, some com- prise that most scientific research in this and Romania, also are well ranked. panies manufacture and sell commercial field is conducted in academia. However, glass–ceramics, although they are not patent rankings tell a different story. Patents for glass–ceramics among the top patenting companies. In terms of statistics by country, In addition to publications related to Figure 4 shows the 20 most prolific Chinese investigators –ceramic glass–ceramics, analysis of the status of companies from DWPI that were grant- glass–ceramic ed glass–ceramic patents in 1968–2014. patents com- Schott AG, Corning Incorporated, piles an overall Kyocera, and hold view of techno- the top four positions. All others are logical develop- Japanese, German, or American compa- ments in the nies, with the exception of dental glass– field. Similar ceramic company Ivoclar Vivadent from to searching Liechtenstein. Some companies, such as the publica- Owens–Illinois, were very active during tions database, the 1970s—when they filed several pat- searching the ents on glass–ceramics—but then halted their activity in this field. However, most

Number of patents DWPI patent database for key- of these companies still engage in R&D words “glass– and manufacture various types of com- 5,9 ceramic*”or mercial glass–ceramics. “glass ceram- ic*” only in Commercial applications of patent titles glass–ceramics provided clean- DWPI allows automatic breakdown of er results, but granted patents per field, which reveals Year a wide spectrum of knowledge, spanning Credit: E.D. Zanotto this limited Figure 3. Number of patents granted per year, extracted from the search failed from traditional fields, such as chemis- DWPI database by searching for keywords “glass–ceramic*” or to capture all try, engineering, and , “glass ceramic*” in the patent title. glass–ceramic to unexpected areas, such as polymer

32 www.ceramics.org | American Ceramic Society Bulletin, Vol. 94, No. 4 science, food science, and environmental fields (Figure 5). For a more comprehensive view, we manually searched the FPO database, which allows separate searching of Figure 4. Twenty com- granted patents and patent applications, panies with the most by reading abstracts (and some text) of glass–ceramic patents name Company about 2,000 of the most recently filed granted 1968–2014, extracted from and granted patents. records in the DWPI Glass–ceramics with specific properties, database by search- such as thermal (e.g., low thermal expan- ing for the keywords sion, insulating, high thermal stability, etc.), “glass–ceramic*” or electrical, (e.g., high ionic conductivity), “glass ceramic*” in or optical (e.g., high transparency, high the title. Number of patents luminescence efficiency) properties, have attracted considerable attention from indus- tries and technologists in the past decade. Table 1. Prominent companies and some of their glass–ceramic inventions5,9–11 This special interest has resulted in more Company Product Crystal type Applications than 550 patents on various glass–ceramics Lithium silicate Photosensitive and etched patterned materials intended for electronic components, wiring Schott, Germany β-quartz(ss) Telescope board substrates, cooktop panels, insulators, Ceran/Robax β-quartz(ss) Cookware, cooktops, and oven doors sealants, heat reflector substrates, and more Nextrema Lithium Fireproof window and doors (Table 2). Some patents also have been Pyroceram β-spodumene(ss) Cookware granted for glass–ceramics with architec- Fotoform/Fotoceram Lithium silicate Photosensitive and etched patterned materials tural, biological, magnetic, armor, energy, Cercor β-spodumene(ss) Gas turbines and heat exchangers nuclear, and waste immobilization applica- Corning Inc., U.S. Centura Barium silicate tions and for applications in combined Vision β-quartz(ss) Cookware and cooktops fields, such as electrooptics. 9606 Cordierite Radomes Overall trends in current patent appli- Mica Machinable glass–ceramics cations—which are more recent than 9664 Spinel–enstatite Magnetic memory disk substrates granted patents—are decreased electrical, DICOR Mica Dental restorations electronic, and magnetic applications and increased dental, biomedical, opti- ML-05 Lithium disilicate Magnetic memory disk substrates cal, energy, chemical, waste manage- Neoparies β-wollastonite Architectural glass–ceramics Nippon Electric ment, refractory, and “other” applica- Firelite β-quartz(ss) Architectural fire-resistant windows Glass, Japan tions for glass–ceramics. These results Neoceram N-11 β-spodumene(ss) Cooktops and kitchenware suggest that those areas are potential Narumi β-quartz(ss) Low-thermal-expansion glass–ceramics thrust fields for advanced technology. Neoceram N-0 β-quartz(ss) Color filter substrates for LCD panels The above-listed trend applications are Cerabone A-W Apatite–wollastonite Bioactive implants in line with current demands of new Ivoclar Vivadent IPS Series Leucite/lithium Dental restorations products, suggesting prospects for indus- AG, Liechtenstein silicate/leucite–apatite trial growth in these areas. Keralite β-quartz(ss) Fire-resistant windows and doors Eurokera, U.S./France Eclair β-quartz(ss) Transparent architectural glass–ceramics Future growth Keraglas β-quartz(ss) Cookware and cooktops A great deal already is known about Asahi Glass Co., Japan Cryston β-wollastonite Architectural glass–ceramics glass–ceramics, but several challenges and Kyushu Co., Japan Crys-Cera Calcium metaphosphate Dental restorations opportunities in glass–ceramics research Leitz, Wetzlar Co., Germany Ceravital Apatite –ceramics and development remain to be explored LiC-GC Nasicon(ss) Lithium-conducting glass–ceramics Ohara Inc., Japan for desired properties and new applica- TS-10 Lithium disilicate Magnetic memory disk substrates tions of these materials. A few important Owens-Illinois, U.S. Cer-Vit β-spodumene(ss) Cookware and kitchenware areas for further exploration follow. Pentron Ceramic Inc., U.S. 3G OPC Lithium disilicate Dental crowns Fundamental and technological studies PPG, U.S. Hercuvit β-spodumene(ss) Cookware and domestic-ware Vitron, Germany Bioverit series and Mica/mica–apatite/ and machinable glass–ceramics • Search for new or more potent Vitronit phosphate type nucleating agents for the synthesis of Sumikin Photon, Japan Fotovel/ Photoveel Mica type Dental and insulator materials glass–ceramics using data mining tech- Yata Dental MFG Co., Japan Casmic Apatite–magnesium titanate Bioactive and dental glass–ceramics niques, theoretical equations, and mod-

American Ceramic Society Bulletin, Vol. 94, No. 4 | www.ceramics.org 33 An analysis of glass–ceramic research and commercialization

• Fabrication of 2-D and 3-D single within glass matrices via direct laser heating or photothermal-induced crystallization; and • Understanding the role of the residual glass phase in the properties of glass–ceramics. Desired material properties • Highly bioactive glass–ceramics for or drug delivery and for preventive treatments that slow down dete-

Subject area rioration and maintain health of tissues; • Development of harder, stiffer, stronger, and tougher glass-ceramics, for instance, HV > 11 GPa, E > 150 GPa, four-point-fracture strength > 400 MPa, 1/2 and KIC >3 MPa∙m ; • Nanocrystalline glass–ceramics with greater transparency in the , visible, or infrared spectral regions; Number of patents

Credit: E.D. Zanotto • Highly transparent and efficient Figure 5. DWPI database breakdown of number of patents granted in various fields scintillator glass–ceramics; and by searching keywords “glass–ceramic*” or “glass ceramic*” in patent titles from • Glass–ceramics with ionic conduc- 1968–2014. tivities >10–3 S/cm.

Table 2. Proposed uses for glass–ceramics in patent applications and granted patents in Possible applications FPO database from January 2001–July 2014 • Glass–ceramics for solar cell appli- cations with improved optical, thermal, Subject Number of patents Proposed uses electrical, and mechanical properties Applications Granted for use as substrates, matrices, and solar Thermal 141 145 Cookware, cooktops, hot plates, low-thermal-expansion glass–ceramics, sealants, and fireproof windows and doors concentrators; Electrical 52 95 Solid electrolytes, lithium-ion-conducting glass–ceramics, and substrates • Glass–ceramics as self-healing seal- Electronics 24 96 Electronic components, substrates for electronic devices, and plasma display panels ant materials with high longevity for fuel Optical 63 55 Transparent glass–ceramics, luminescent glass–ceramics, colored glass–ceramics, cells and electronic devices; lasers, lens, and mirrors • Glass–ceramics as smart architectur- Dental 38 21 Dental restorations and dental prosthetic devices al building materials with antifungal and Mechanical 29 30 Abrasives, machinable glass–ceramics, and high-strength glass–ceramics self-cleaning properties; automatic energy Chemical 25 23 Catalytically active glass–ceramics, photocatalyst supports, -resistant glass– generators for building energy consump- ceramics, ion-exchanged glass–ceramics, and glues tion, multisensor security, and antifire Architecture 15 13 Decorative substrates and building construction glass–ceramics systems; and materials with dynamic Biology 17 10 Bioactive scaffolds, antimicrobial glass–ceramics, antiinflammatory glass–ceramics, and glass–ceramic powders for cosmetics color-changing abilities; Energy 10 7 SOFCs, LEDs, and solar cells • Glass–ceramic compositions for immobilization of nuclear waste products; Magnetic 6 11 Magnetic head actuators, magnetic information storage media, and substrates for magnetic storage devices • Glass–ceramics to replace existing Armor 8 7 Bulletproof and missileproof glass–ceramic components and bulletproof vests materials (polymers) currently used in a variety of electronic products, such as eling rather than empirical trials; of photothermal-induced nucleation; computers, mobile phones, IC chips, • Development of stronger, chemically • Engineering adequate matrices for and mother boards, to address future resistant –ceramics with development of hierarchical nanostruc- environmental problems associated with novel electric and optical properties; tured glass–ceramics based on variations electronics waste; • Development of new or improved in size, distribution, and composition of • Glass–ceramics for nanopatterning crystallization processes, such as microwave nanoscale crystals; and nanolithography in high-tech materials; heating, biomimetic assemblage of crystals, • Confinement of the glassy phase • Glass–ceramics for treatment of cancer textured crystallization, laser crystallization, (nanoglass) within the glass–ceramic using thermal or photosensitive therapies; and electron beam crystallization; matrix by reverse engineering based on • Glass–ceramics for components • Deeper understanding and control novel synthesis processes; in space research and similar sophisti-

34 www.ceramics.org | American Ceramic Society Bulletin, Vol. 94, No. 4 cated environments; S.D. Stookey—although he passed away 4R.-A.M. Réaumur, “The art of matching a new grid of porcelain,” Memories Acad. Sci., Paris, 377–88 (1739). • Ultrafast crystallizable chalcogenide on November 4, 2014, his important dis- 5W. Höland and G. Beall, Glass–ceramic technology, 2nd Ed. glass–ceramics for rewritable optical coveries and legacy will remain forever. American Ceramic Society, Westerville, Ohio, and Wiley, disks and PRAM devices; and The authors thank the São Paulo New York, 2012. • Glass–ceramics with low thermal Research Foundation for financial sup- 6S.D. Stookey, “Photosensitively opacifiable glass,” U.S. conductivity, high electrical conductivity, port of this research project, and they Pat. No. 2 684 911, 1954. 7S.D. Stookey, “Chemical machining of photosensitive and adequate Seebeck coefficient developed also acknowledge Brazil’s National glass,” Ind. Eng. Chem., 45, 115–18 (1953). into thermoelectric power generators, which Council for Scientific and Technological 8S.D. Stookey, “Catalyzed crystallization of glasses in theo- could produce renewable and sustainable Development and The World Academy ry and practice,” Ind. Eng. Chem., 51 [7] 805–808 (1959). energy in vehicle exhaust manifolds, furnace of Sciences for Ph.D. fellowships granted 9A.Sakamoto and S. Yamamoto, “Glass–ceramics: exhausts, and building windows. to Maziar Montazerian. The authors also Engineering principles and applications,” Int. J. Appl. Glass Sci., 1 [3] 237–47 (2010). In addition, other unexpected applica- appreciate the critical comments of Mark 10G.H. Beall, “Milestones in glass–ceramics: A personal tions will probably emerge that require Davis, George Beall, and Atiar Rahaman perspective,” Int. J. Appl. Glass Sci., 5 [2] 93–103 (2014). new combinations of material properties. Molla. Edgar Dutra Zanotto is indebted 11W. Pannhorst, “Recent developments for commercial to the knowledgeable members of the applications of low expansion glass–ceramics,” Glass Technol.- Eur. J. Glass Sci. Technol. Part A, 45 [2] 51–53 (2004). Past growth in research expected Crystallization and Glass–Ceramics 12R.D. Rawlings, J.P. Wu, and A.R. Boccaccini, “Glass– to continue Committee of the International ceramics: Their production from wastes—A review,” J. Statistics on published scientific Commission on Glass for enlightening Mater. Sci., 41 [3] 733–61 (2006). articles and patents indicate that glass– discussions during the past 30 years. 13L.L. Hench, “Glass and glass–ceramic technologies to trans- form the world,” Int. J. Appl. Glass Sci., 2 [3] 162–76 (2011). ceramic research has grown exponential- 14M.J. Davis, “Practical aspects and implications of inter- ly during the past 60 years, with no signs About the authors faces in glass–ceramics: A review,” Int. J. Mater. Res., 99 [1] of slowing down. The above analysis pro- All authors are from the Department 120–28 (2008). vides an overall picture in terms of num- of Materials Engineering at the 15E.D. Zanotto, “Glass crystallization research—A 36-year Center for Research, Technology, and retrospective. Part II, Methods of study and glass–ceram- bers as well as traditional and new areas ics,” Int. J. Appl. Glass Sci., 4 [2] 117–24 (2013). Education in Vitreous Materials at of applications for the advancement of 16J.C. Mauro and E.D. Zanotto, “Two centuries of glass glass-ceramics. Commercially successful Federal University of São Carlos, Brazil. research: Historical trends, current status, and grand products include those intended for challenges for the future,” Int. J. Appl. Glass Sci., DOI: 10.1111/ijag.12087 (2014). domestic and high-tech applications— References 17E.D. Zanotto, “A bright future for glass–ceramics,” Am. 1 such as cookware, chemically or mechan- P.W. McMillan, Glass–ceramics. Academic Press, New Ceram. Soc. Bull., 89 [8] 19–27 (2010). York, 1979. ically machinable materials, telescope 18W.W. Shaver and S.D. Stookey, “Pyroceram,” SAE 2 J.F. MacDowell, “Glass–ceramic bodies and methods of Technical Papers, 90428, 1959. mirrors, hard-disk substrates, cooktop making them,” U.S. Pat. No. 3 201 266, 1965. 19G.W. McLellan, “New applications of glass and glass– plates, artificial , and dental pros- 3 V. Marghussian, Nano-glass ceramics: Processing, properties, ceramics in the automotive industry,” SAE Technical st theses—but the breadth of uses proposed and applications, 1 Ed. Elsevier, New York, 2015. Papers, 91753, 1959. n in patents is much wider. Analyses of patent applications of glass–ceramics Realizing the potential of glass–ceramics in industry versus number of granted patents in the by John C. Mauro, Corning Incorporated past decade reveal significant growth in The accidental discovery of glass–ceramics by machining behavior of the glass–ceramic materials dental, biomedical, waste management, S. Donald Stookey in 1953 revolutionized the glass are also of critical concern. industry by enabling new properties, such as ex- and optical applications. Successful design of next-generation indus- ceptionally high fracture toughness and low thermal We hope this report serves as a trial glass–ceramic products should be aided by expansion coefficient compared with traditional a renewed focus on the fundamental physics and motivation and guide for students, pro- glasses. Although glassy materials are noncrystalline chemistry governing these high-tech materials. fessors, technologists, and researchers by definition, glass–ceramics are based on controlled Although the thermodynamic and kinetic aspects nucleation and growth of crystallites within a glassy when thinking of future research direc- of crystallization are of the utmost importance matrix. Concentration, size, and chemistry of the tions and, most importantly, encourages for designing industrial materials, there remains crystallites can be controlled through careful design insufficient theoretical understanding of these basic researchers to dig deeper to find new of the base glass chemistry and the heat-treatment processes in glass–ceramics. Future development of glass–ceramic compositions, nucleating cycle used for nucleation and crystal growth. These new theoretically rigorous modeling capabilities will composition and process parameters give new agents, and heat treatments that lead to hopefully enable quantitatively accurate predictions dimensions for optimizing the properties of industrial novel structures and properties. Such of glass–ceramic microstructures and properties. glass–ceramics. considerations may result in materials A detailed understanding of glass–ceramic materials Table 1 provides an excellent summary of com- with uniquely organized nanostructures is an exceptionally challenging problem, especially mercialized glass–ceramic products. The success of for many-component oxide systems that are the or microstructures or with useful combi- these products is based on achieving unique com- basis for most industrial glass–ceramic products. nations of properties that are well suited binations of attributes, including appropriate optical, However, this presents a unique opportunity to build thermal, mechanical, and biological properties, often for new applications. a solid foundation for realizing the many exciting fu- which cannot be achieved by an “ordinary” non- ture applications of glass–ceramics described in the crystalline glass. For many of these products, such accompanying article and to train the next generation Acknowledgments as MACOR and dental glass–ceramics, forming and The authors dedicate this article to of industrial glass–ceramic scientists.

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