From their glorious past, starting with their accidental ...

(Credit: Schott North America.) A bright future for glass-ceramics

From their glorious past, starting with their accidental discovery, to

successful commercial products, the impressive range of properties

and exciting potential applications of glass-ceramics indeed ensure

a bright future!

by Edgar Dutra Zanotto

Glass-ceramics were discovered – somewhat accidently
– in 1953. Since then, many exciting papers have
been published and patents granted related to glass-ceram-
ics by research institutes, universities and companies
worldwide.
Glass-ceramics (also known as vitro-
cerams, pyrocerams, vitrocerâmicos,
vitroceramiques and sittals) are
produced by controlled crystal-
lization of certain glasses
– generally induced by
nucleating additives.
This is in contrast
with sponta-
neous sur-
face crys-
tallization, which is
normally not wanted in glass
manufacturing. They always con-
tain a residual glassy phase and one or more
embedded crystalline phases. The crystallinity varies
between 0.5 and 99.5 percent, most frequently between
30 and 70 percent. Controlled ceramization yields an
array of materials with interesting, sometimes unusual,
combinations of properties.

American Ceramic Society Bulletin, Vol. 89, No. 8 19

A bright future for glass-ceramics

Unlike sintered ceramics, glass- Fig. 1. Standing, from left to right, TC-7 members Ralf Muller, Guenter VoelKsch, Linda
ceramics are inherently free from poros- Pinckney, Edgar Zanotto, Wolfgang Pannhorst, Takayuki Komatsu, Miguel Prado,
ity. However, in some cases, bubbles or Michael Budd, Joachim Deubener, Wolfram Hoeland and Ian Donald. Sitting are distin-
pores develop during the latter stages of guished guests George Beall and Donald Stookey. Picture taken in Jackson Hole, Wyo.,
crystallization. Glass-ceramics have, in September 2006.
principle, several advantages.
hot-pressing techniques. The sintering (114 articles), Schott Glaswerke (69),
• They can be mass produced by any route also is attractive to produce glass- IBM (65), Nippon Electric Glass Co.
glass-forming technique. ceramics from reluctant glass-forming (30), Ivoclar Vivadent AG (29), NEC
compositions, which could be made as Corp. (24), Aerospace Corp. (20) and
• It is possible to design their nano- a “frit,” molded and sinter-crystallized. Toyota TI (18).
structure or microstructure for a given Commercial applications of sintered
application. glass-ceramics include devitrifying frit There are far too many papers
solder glasses for sealing TV tubes, and patents to be cited in this short
• They have zero or very low porosity. cofired multilayer substrates for elec- “insight” article. Thus, we will direct
• It is possible for them to combine tronic packaging, marblelike floor and the interested reader to a limited num-
a variety of desired properties. wall tile (Neopariés and similar brands) ber of key books and papers, including
One example of the fourth advan- and some bioactive glass-ceramics. some of our own. The fundamentals
tage is combining very low thermal References 1–6 provide a list of recent behind the understanding and control
expansion coefficient with transparency articles and reviews on the fundamen- of glass crystallization concern the
in the visible wavelength range for tals of the sinter-crystallization process. mechanisms, thermodynamics and
cooking ware. Another is combining kinetics of crystal nucleation, growth
very high strength and toughness with Patents and papers and overall crystallization. Several
translucency, biocompatibility, chemi- An idea of the scientific and com- groups have focused on such studies
cal durability and relatively low hard- during the past century. Interested
ness for dental applications. mercial importance of glass-ceramics readers are invited to check References
Glass-ceramics are normally pro- comes from a search on Free-patents 7–9 for reviews on the basics of inter-
duced in two steps. First, a glass is Online, which comprises granted pat- nal and surface nucleation in glasses.
formed by a standard glass-manufactur- ents or applications in the United Readers are referred to classical text-
ing process. Second, the glass article States, Europe and Japan. About 2,400 books in References 10–12 and review
is shaped, cooled and reheated above granted or filed U.S. patents appear articles in References 13–16 for more
its glass transition temperature. The with the keywords “glass ceramic” in detailed information on glass-ceramics.
second step is sometimes repeated as a the abstract. There also are about 1,500
third step. In these heat treatments, the European and 2,700 Japanese patents. Discovery of glass-ceramics
article partly crystallizes in the interior. There is some overlap in these num- Natural glass-ceramics, such as
In most cases, nucleating agents (e.g., bers, because the same patent is often
Pbna2oOsbel5e,glCmasres2tOcaol3smo, rfplFuoeosi2rtOiido3e)ns,atrZoerbOaod2o,dsTetditOhtoe2,the deposited in different countries. some types of obsidian, “always” have
nucleation process. existed. Synthetic glass-ceramics were
A less frequently used method is to A similar search for published papers serendipitously discovered in 1953.
induce and control internal crystalliza- in the Scopus database with the same Stanley Donald Stookey, then a young
tion during the cooling path of a molten keywords yields about 10,000 articles. researcher at Corning Glass Works,
viscous liquid. This process is used some- These are very impressive numbers for meant to anneal a piece of a lithium
times to form relatively coarse-grained such a narrow field within all the numer- disilicate glass with precipitated silver
glass-ceramics from waste materials to be ous materials classes and types. This sug- particles (meant to form a permanent
used in the construction industry. gests that plenty is already known about photographic image) in a furnace at
Glass-ceramics also can be produced glass-ceramics technology. A similar 600°C. He accidentally overheated the
by concurrent sinter-crystallization of search in Scopus indicates that, since glass to about 900°C. “Damm it, I’ve
glass-particle compacts. In this case, 1960, the most prolific companies in ruined a furnace!” Stookey thought.
crystallization starts at glass–particle glass-ceramics research are Corning Inc. Instead of a melted pool of glass, the
interfaces. A main advantage of the
sinter-crystallization process is that
nucleating agents are not necessary,
because the particle surfaces provide
nucleation sites. A disadvantage of this
method is 0.5 to 3.0 percent residual
porosity. However, this can be some-
times minimized or even eliminated by

20 American Ceramic Society Bulletin, Vol. 89, No. 8

astonished Stookey observed a white modern and very inter-
material that had not changed shape.
esting glass-ceramics,
He then accidentally dropped the
piece on the floor, but it did not shat- is represented by
ter, contrary to what might normally
have been expected from a piece of Corning’s Fotoceram
glass! He was surprised by the unusual
toughness of that material. Stookey (also invented by
had accidentally created the first glass-
ceramic, denominated Fotoceram.17 Stookey) and Schott’s

In their book, Volfram Hoeland and Foturan. These glass-
George Beall mention that “knowledge
of the literature, good observation skills ceramics can be pat- Fig. 2 Glass-ceramic teeth.
and deductive reasoning were clearly terned by ultraviolet
evident in allowing the chance events
to bear fruit.” This glass-ceramic was light and selectively crystallized by ther- wnuitchleTatiiOon2 are the most commonly used
later known also as Pyroceram. This first mal treatments. The crystallized regions agents. The main crystalline
synthetic glass-ceramic eventually led
to the development of CorningWare in then are completely dissolved by acid phase is a β-quartz solid solution, which
1957.17 It also influenced the develop-
ment of Vision, a transparent cookware. etching. The patterned glass can be used is highly anisotropic and has an overall
CorningWare entered the consumer
marketplace in 1958 and became a mul- as-is or can be heated once more to form negative TCE. LAS glass-ceramics can
timillion dollar product.
polycrystalline glass-ceramic plates that sustain repeated and quick tempera-
The scientific and commercial
importance of glass-ceramics was recog- have high-precision holes, channels or ture changes of 800°C to 1000°C. The
nized by the International Commission
on Glass, which established TC-7, any desired intricate pattern. The prod- dominant crystalline phase of these
the “Nucleation, Crystallization and
Glass-Ceramic Committee” (www.icg. ucts are used in electronics, chemistry, glass-ceramics, β-quartz solid solution,
group.shef.ac.uk/tc7.html) about three acoustics, optics, mechanics and biology has a strong negative CTE.
decades ago. Figure 1 shows some past
and present TC-7 members and guests. in applications that include microchan- Keatite solid solution (β-spodumene)

Commercial glass-ceramic nels in optical fibers, ink-jet printer also has a negative CTE, higher than
products
heads, substrates for pressure sensors and β-quartz solid solution. The negative
The first commercially viable glass- acoustic systems in head-phones.10–12 CTE of the crystal phase contrasts
ceramic was developed in the aerospace
industry in the late 1950s as radomes Consumer products with the positive CTE of the residual
to protect radar equipment in the
nosecones of aircraft and rockets. Glass- glass. Adjusting the proportion of these
ceramics used in these applications
must exhibit a challenging combina- Corning, Schott, St. Gobain, phases offers a wide range of possible
tion of properties to withstand critical
conditions resulting from rain erosion Nippon, Ohara, Ivoclar and few others CTEs in the finished composite. For
and atmospheric reentry: homogeneity;
low dielectric constant; low coefficient presently produce commercial glass- most current applications, a low or zero
of thermal expansion; low dielectric
loss; high mechanical strength; and ceramics for consumer and special- CTE is desired. A negative CTE also is
high abrasion resistance. Glass-ceramics
now are used in nosecones of high- ized markets. We could not confirm possible. At a certain point, generally
performance aircraft and missiles. No
glass, metal or single crystal can simul- whether Fuji Photo, Japan; Pittsburg between 60 and 75 percent crystallin-
taneously meet all of these relevant
specifications.10 Plate Glass, U.S.; NGK Insulators, ity, the overall negative expansion of

Another class of traditional, but still Japan; Sklo Union, Czech Republic; the crystal phase(s) and the positive

CBP Engineering, U.K.; International expansion of the residual glass phase

Ceramics, U.K.; and Konstantinovskii, cancel each other. Thus, the glass-

Russia; remain active in the glass- ceramic as a whole has a TCE that is

ceramic business.11 very close to zero. But such a balance

A range of commercially successful is not straightforward, because the rela-

glass-ceramics for consumer applica- tive stiffness of the glass and crystal

tions include famous brands of low- phases also is important.

expansion products that are resistant Glass-ceramics also can be adjusted

to thermal shock: CorningWare; and to match the CTE of the material to

Vision – a transparent glass-ceramic. which they will be bonded. LAS glass-

Cooktop plates, such as Schott’s Ceran, ceramics were originally developed

Eurokera’s Kerablack and Nippon for use in mirrors and mirror mounts

Electric Glass’ Neoceram also are avail- of astronomical telescopes. They now

able. These products rely on their rela- have become known and have entered

tively high toughness (compared with the domestic market through their use

glasses), appealing aesthetics and very in cooktops, cookware and bakeware as

low thermal expansion coefficient. well as high-performance reflectors for

The most important system commer- digital projectors. Other well-known

cially is the Laid2dOit–iAonl2aOl c3–oSmiOpo2n(eLnAtsS,) brands of these low-expansion glass-
system with ceramics are Ceran, Kerablack and

NsAuasc22hOOa5saanCnddaOKS2n,OMO.2gF.OiZn,riOnZgn2 Oiang,ecBnoatmsObi,niPnc2lauOtdi5oe,ns Neoceram (cooktops); and Robax,
Keralite and Neoceram (stoves and fire-
places). Nippon Electric Glass’s related

American Ceramic Society Bulletin, Vol. 89, No. 8 21

A bright future for glass-ceramics

Fig. 3. Micrographs of open and partially blocked dentin tubules by Biosilicate glass- voltages, various frequencies and high
cermic powder. RHS – results of a clinical study of dentin sensitivity level of 160 teeth: temperatures. When properly baked out,
Initial and after 1 to 6 applications of Biosilicate. (Reprinted from a research report for machinable glass-ceramics will not out-
Vitrovita – Glass-Ceramic Innovation Institute.) gas under vacuum environments. They
can be machined to complicated shapes
products in this area include Firelite applications include precision optics, and precision parts with ordinary metal-
fire-rated glass. The same class of mate- working tools, quickly and inexpensively.
rial was also used until the late 1990s mirror substrates for large astronomi-
as CorningWare dishes, which could Machinable glass-ceramics require no
be taken from the freezer directly to cal telescopes, mirror substrates for postfiring after machining. This means
the oven with no risk of thermal shock that specifications can be met without
damage. These low-CTE glass-ceramics X-ray telescopes, optical elements for having to resort to costly machining with
are the most successful commercial diamond tools. Typical Macor applica-
glass-ceramics thus far developed.10–12 comet probes, ring laser gyroscopes tions include insulators and supports for
vacuum environment feed-troughs; spac-
Thermal uses of glass-ceramics and standards for precision measure- ers, headers and windows for microwave
Another particularly important mate- tube devices; sample holders for micro-
ment technology. Other great low-CTE scopes; aerospace components; welding
rial is Zerodur, a semitransparent, non- nozzles; fixtures; and medical equipment.
porous glass-ceramic made by Schott. glass-ceramics success stories are Ceran Some dental and some bioactive glass-
Zerodur has an extremely low CTE (0.00 ceramics also are machinable using mod-
± 0.02 × 10–6/K between 0°C and 50°C), panels for cooktops and Robax for fire- ern CAD–CAM techniques.10–12
which can even become zero or slightly
negative in some temperature ranges. places and stoves.10–12,14 Construction materials
Another unique characteristic of this Several authors, especially in the
glass-ceramic is its exceptionally good Another relevant thermal property
homogeneity. Even in large material United Kingdom, Eastern Europe,
blocks, it is almost impossible to mea- of glass-ceramics is their limiting use Cuba, Italy and Brazil have developed
sure the fluctuations in mechanical and many glass-ceramics made from a wide
thermal properties. Its good transparency temperature. Because of their residual variety of waste materials, such incin-
in the range 400 to 2,300 nanometers erator ashes, blast furnaces slags, steel
allows a verification of internal quality. glass phase, most glass-ceramics flow and slags and sugar-cane ashes. Their com-
Therefore, it can be ensured that neither position and predominant crystal phases
bubbles nor inclusions go undetected. deform at relatively low temperatures, vary widely. These low-cost, dark-
colored (because of the high level of
Because of its unique properties, typically below about 700°C. However, transition elements in wastes) materials
Zerodur is a preferred material for are generally strong, hard and chemi-
lightweight honeycomb mirror mounts some notable exceptions exist. An cally resistant. Their intended use is for
made for satellite mirrors. Other typical abrasion and chemically resistant parts
example is a celsian glass-ceramic in the or floor and wall tile used in chemi-
cal, mechanical and other heavy-duty
hSarOs u–sBeatOem–Apel2rOat3u–rSeisOa2s system, which industries or construction.
high as 1,450°C
A high-end-use construction and
and CTEs that match silicon, SiC and architecture glass-ceramic is Neopariés,
which was pioneered by Nippon
Smie3Nrc4i.aTl theims mpeartaetruiraelsis(1m,6e5lt0a°bCle).a18t com- Electric Glass about 20 years ago and
continues to be used. This glass-ceramic
Machinable glass-ceramics is one of the few commercial products
Macor, Dicor, Vitronit, Photoveel made by sintering, and its main crystal
phase is wollastonite (calcium metasili-
and other brands of machinable glass- cate). Neopariés is a pore-free, partially
ceramics rely on mica crystals in their crystallized material with a soft rich
microstructure. Their high CTE readily appearance similar to marble and gran-
matches most metals and sealing glasses. ite. However, it has none of the main-
They exhibit zero porosity and, in gen- tenance problems of natural stone and
eral, are excellent insulators at high is an attractive material for exterior and
interior building walls and table tops.

Because of the growing concern

22 American Ceramic Society Bulletin, Vol. 89, No. 8

about sustainability and exhausting conductivity makes Table I. Relevant properties of bioactive glass-ceramics
reserves of natural stones, the use of them comfort-
glass-ceramics as a construction materi- able in the mouth. Glass-ceramic
al deserves much attention. References ——————————————————————
11 and 19–21 discuss these uses further. Moreover, the mate- Highly bioactive
rial is extremely Property Cerabone Bioverit I glass ceramic
High-strength glass-ceramics durable, and it is
11–020T.–h52e5M0aPvMear∙mPaga1e)/2)afrnoadfctmtuorouesgtshtgrnleaensssgs-tc(heKr(IacSm≈f ≈ics relatively easy to Bioactivity class B† B† A‡
are generally higher than those of com-
≈me0r.c7iaMl Pglaa∙smse1s/2)(.SGf ≈la5ss0-–c7e0raMmiPcas;wKitIch Machinability Low Good Fair
especially high strength and tough-
ness have been reported by George manufacture to cus- Density (g/cm3) 3.1 2.8 2.6
Beall and colleagues10 for canasite
MglaPsas-.mce1ra/2m).icS(oSmf ≈ew3h0a0t MsmPaal;leKrIcb≈ut5 tomized units. All- Three-point flexural strength (MPa) 215 140–180 210
still impressive values of strength and
t2o.3u–g2h.n9eMss P(Saf∙m≈13/25) 0h–a4v0e0bMeePnar;eKpIoc r≈ted ceramic restorations Young’s modulus (GPa) 120 70–90 70
for the lithium disilicate IPS e.max
Press developed by Wolfram Hoeland can be used to cover Vickers hardness (HV) 680 500 600
and other Ivoclar researchers.10 The
common feature of these glass-ceramics even dark tooth Toughness (MPa∙m1/2) 2.0 1.2–2.1 0.95
is their lath-shaped crystals that lead to
crack deflection and toughening. cores (e.g., if the Slow crack growth index 33

Other successful strategies to tooth is severely dis- †Biomaterial class B bonds only to bone. ‡Biomaterial class A bonds to hard (bone) and soft (cartilage)
increase strength and toughness include
fiber reinforcement, chemical strength- colored or a titanium tissues.
ening by ion-exchange methods and
development of a thin surface layer abutment is used).
with a lower thermal expansion than Current lithium disilicate glass-ceram- in Table I.
the interior to induce a compressive Cerabone – developed by Tadashi
surface layer. All these concepts have ics – e.g., Ivoclar’s IPS e.max – are ideal
been demonstrated for a few glass- for fabricating single-tooth restorations Kokubo and produced by Nippon
ceramic compositions. However, they (Fig. 2). This innovative glass-ceramic Electric Glass Co. Ltd. – is prob-
are far from being fully explored, and, produces highly esthetic results. Its hard- ably the most widely used bioactive
thus, there is much scope for further glass-ceramic for bone replacement.
research. Another important aspect ness is similar to that of natural teeth,
that needs further study is effect of and it is two to three times stronger than Numerous clinical trials have shown
the type (compressive versus tensile) other dental glass-ceramics. The mate- intergrowth between this glass-ceramic
and magnitude of the internal residual rial can be either pressed or machined and human bone. Tadashi informed us
stresses that are always present and are to the desired shape in the dental labo- in 2009 that about 50,000 successful
maximum at the crystal–glass inter- implants already have been made using
faces. Values of 0.1 to 1.0 gigapascals ≈2ra.3t3o–6r20y.–.94BM0e0cPaMau∙smPea1o/)2f(asinitnsdghtlieog-uhegdhsgtnereeVnssg-nt(hKotI(ccS≈hf ed Cerabone. Bioverits are machineable
have been reported in some glass- glass-ceramics that are very useful,
ceramics. These stresses certainly affect
the overall mechanical performance of beam)), restorations fabricated with this because they can be easily modified
the material. A few papers have dealt during clinical procedures. Bioverit II is
with residual stresses in glass-ceramics, material can be cemented by various
including References 16 and 22–24. techniques. These glass-ceramics possess especially good in this respect.10,11,25–27
A different type of highly bioactive
Dental glass-ceramics true-to-nature shade behavior, natural-
All-ceramic dental restorations are looking esthetics, natural-looking light glass-ceramic was developed by Peitl et
transmission, versatile applications and a al.28 in 1995. This is a low-density glass-
attractive to dentists and patients, comprehensive spectrum of indications. ceramic in the Na-Ca-Si-P-O system
because they are biocompatible, have that has a Young’s modulus closer to
superior aesthetics and their low thermal
Bioactive glass-ceramics that of cortical bone and much higher

Bioactive glass-ceramics form in-situ bioactivity than previous bioactive glass-
a biologically active layer of hydroxy- ceramics. This particular combination of
carbonate apatite (the mineral phase of properties is desired for several applica-
bone and teeth) that bonds to bone and tions. This glass-ceramic is about 30 to
teeth and sometimes even to soft tissue. 50 percent crystalline, and its main phase
tisriNalsa2fOor∙2mCiadOdl∙e3-SeaiOr b2.oTnheerefpirlsatccelmineincatsl
Moreover, load-bearing applications
require excellent mechanical properties.
Many products have reached commer- in 30 patients yielded very positive
cial success: Cerabone A-W (apatite– results. Table I summaries the main prop-
wollastonite), Ceravital (apatite–devit- erties of some bioactive glass-ceramics.
rite), Bioverit I (mica–apatite), Bioverit A new glass-ceramic based on the
II (mica) and Ilmaplant L1 and AP40. same Na-Ca-Si-P-O system (Biosilicate)
They have been used as granular fillers, but with some compositional modifica-
artificial vertebrae, scaffolds, iliac spac- tions and greater than 99.5 percent
ers, spinous spacers, intervertebral spac- crystallinity recently was developed by
Zanotto and colleagues.29–32 This glass-
ers, middle-ear implants and as other
types of small-bone replacements. Some ceramic is as bioactive as the “gold stan-
of their interesting properties are listed dard” bioglass 45S5 invented by Larry

American Ceramic Society Bulletin, Vol. 89, No. 8 23

A bright future for glass-ceramics

Fig. 4. From left to right: parent glass, glass-ceramic with 97 percent crystallinity sated by additional Li+ ions, leading to
and glass-ceramic with 50 percent crystallinity. Grain size is about 20 micrometers. theSLoim1+exMauxTthi2o–xr(sPcOla4i)m3 sythstaetmt.he main
advantage of obtaining such materials
Hench. Clinical tests of treatment with route for tumor treatment has been fol- by the glass-ceramic route would be a
Biosilicate powder for dentin hypersensi- lowed by several authors. Several other decreased porosity if compared with
tivity in 160 sensitive teeth conducted by compositions have been and are pres- ceramic materials obtained by the clas-
dentist Jessica Cavalle are shown in Fig. ently being tested in various laboratories. sical sintering route. However, one
3. After the first treatment, one-third feature that has been scarcely explored,
of the teeth lost their sensitivity. After Electrically conducting and is that, if the parent glass presents
six applications of Biosilicate powder, internal nucleation, one may easily and
94 percent of the teeth were cured. This insulating glass-ceramics effectively control, for instance by dou-
powdered glass-ceramic also can be use- Electrically insulating materials, such ble-heat treatments, the microstructure
ful for making small sintered bones and of the glass-ceramic to further increase
bioactive scaffolds, such as those shown as spinel–enstatite, canasite and lithium its conductivity.36
in the studies of Enrica Verné33 and Aldo
Boccaccini34 and their colleagues. disilicate glass-ceramics (made by Solid oxide fuel cells are ceramic
solid-state energy conversion devices
Another interesting class of bioactive Corning) as well as TS-10 glass-ceramic that produce electricity by electrochemi-
glass-ceramics is heat-generating bioac- cally combining fuel (e.g., hydrogen gas
tive or biocompatible glass-ceramics substrates (made by Ohara) are used or natural gas) and oxidant (e.g., air)
intended for use for hyperthermic treat- gases across an ionic conducting oxide at
ment of tumors. For instance, in one in magnetic media disks for hard disk operating temperatures of about 800°C.
study by Koichiro et al.,35 glass plates of The planar SOFC configuration provides
Frtehese2uOclt3hi–neBgm2Ogicla3a–slsPc-2coOemr5apwmoesiircteicoconenrCtaamainOizien–dSg.imOTah2–ge- drives. These materials offer the key a simple manufacturing process and high
netite and wollastonite crystals showed current densities, but it requires hermetic
high-saturation magnetization. This properties necessary for today’s higher sealing to prevent fuel–oxidant mixing
glass-ceramic formed a calcium- and and to electrically insulate the stack.
phosphorous-rich layer on its surface and areal density, smaller, thinner drive
tightly bonded with bone within about A suitable sealing material must
eight weeks of implantation. The par- designs. These glass-ceramics have meet several criteria: chemical stability
ent glass did not form the calcium- and at 800°C under oxidizing and reducing
phosphorous-rich layer and did bond high toughness, provide low surface wet atmospheres (air, hydrogen gas);
with bone at 25 weeks. Under an exter- electrically insulating; chemical com-
nal magnetic field, granules of this glass- roughness and good flatness, ultralow patibility (i.e., must not poison other
ceramic filled in rabbit tibias heated cell components); ability to form a seal
surrounding bone to more than 42°C glide heights and excellent shock resis- at about 900°C that results in a her-
and maintained this temperature for 30 metic bond with high strength; CTE of
minutes.35 Since then, this promising tance.10 10–12 ppm/K; and long-term reliability
during high-temperature operation and
On the other hand, lithium-ion- during thermal cycles to room tempera-
ture. In the scientific literature phos-
conducting glass-ceramics are promising phosilicate, boron-free alkaline-earth
silicates and borosilicate glass-ceramics,
solid electrolytes for lithium batteries. SfsoeiarOlii2nn,sghtaaanvpcepelbiSceaerOtnio–snuLsga.g327OesS3t–eevAdelfr2oaOrl 3Sr–eOBse2FaOCrc3–h
groups in the world are attempting to
Sufficiently high conductivity at ambi- develop such materials.

ent temperature (10–3 (Ω∙cm)–1) has Some groups have experimentally
been demonstrated when precursor demonstrated the possibility of produc-
ing glass fibers of the famous BISCO
glasses crystallize in the highly conduc- s(uBpi2eSrcr2oCnadCucut2iOng8)–syasntedmth–enwhcricyhstaalrleizinnogt
them to produce glass-ceramic supercon-
tive nanoscale application specific inte- ductors.38

grated circuit structure. Systems derived Last, but not least, several glass-
ceramics-containing piezoelectric and
from tehxeteLnisTivi2e(lPyOst4u)d3 iceodm. Ipnosfaitciot,npharatviael
been

substitution of Ti4+ by a trivalent cation,

M3+, such as Al3+, Ga3+, In3+, Sc3+, Y3+,

La3+, Cr3+ or Fe3+, generates a deficiency

in positive charges, which is compen-

24 American Ceramic Society Bulletin, Vol. 89, No. 8

ferroelectric phases have been studied. als that absorb UV, reflect IR and are less than about 200 nanometers and has
These areas for glass-ceramics applica- transparent to visible light; materials a small or moderate crystallized frac-
tions have not yet been fully explored. that absorb UV and fluoresce in red/IR; tion of 1 to 70 percent. However, an
substrates for arrayed waveguide grat- interesting new discovery was recently
Transparent glass-ceramics ing; solid-state lighting – white light; reported by Berthier da Cunha and
Some successful and many trial opti- and laser pumps. Ohara’s WMS-15 colleagues.42,43 They developed a large-
glass-ceramic substrates, a commer- grain (about 10–50 micrometer), highly
cal applications have been proposed for cially available product, have improved crystalline (97 percent) and transparent
transparent glass-ceramics: cookware transmittance and exceptionally low glass-ceramic, as shown in Fig. 4.
(Vision) that allows continuous visual- surface roughness values. They enable
ization and monitoring of the cooking manufacturers to produce leading-edge Mark Davis16 mentions in his 2008
process); fireplace protection; transpar- dense wavelength division multiplexer review paper that “many of the exotic
ent armors for visors or vehicle windows; and gain-flattening filters. The WMS optical features now demonstrated in
substrates for LCD devices; ring laser substrates facilitate the production of glass-ceramics (e.g., SHG, lasing, elec-
gyroscopes; missile noses; fiber grating special filters.10,11 trooptical effect) have not yet been
athermalization; precision photolithog- made into a commercial product.”
raphy; printed optical circuits; and small One interesting case of optical appli-
or very large telescope mirrors (Zerodur). cation is the photothermal refractive Glass-ceramic armor
In this last example, the telescope’s glass-ceramic produced by photother- Some patents have been filed and
optical components are required to over- mo-induced crystallization. PTR glass,
come distortions caused by temperature invented by Stookey, is an iron bro- others have been granted for inven-
fluctuations. Therefore, glass-ceramics mine sodium zinc aluminosilicate glass tions related to armor materials for
with zero expansion are highly suitable. doped with silver, cerium, tin or anti- the protection of people or equipment
mony that can be locally crystallized against high-speed projectiles or frag-
The keen interest in glass-ceramics by UV exposure in selected regions fol- ments. Ceramic materials are used
for optical applications is caused by lowed by heat-treatment above its glass particularly in armors for which low
their advantages over glasses, single- transition temperature. weight is important: bullet-proof vests;
crystals and sintered transparent and armor for automobiles, aircraft and
ceramics. Unlike glasses, glass-ceramics However, PTR glass-ceramic has helicopters, especially in cockpits or
demonstrate properties similar to those reached the consumer market during seats and for protection of functionally
of single crystals. In contrast with the past 15 years thanks to the develop- important parts. The first and still-used
single crystals or sintered ceramics, ment of Bragg gratings and other types ceramic armor materials consist of high-
glass-ceramics can be made in intricate of volume holograms for laser devices dmeondsuitlyusisaqnuditheahrdigAh,l2aOb3o,uatlt4hgoruagmhsitpser
shapes and sizes by fast and cost-effi- (narrow-band spectral and angular fil- cubic centimeter. Other very hard, but
cient glass-manufacturing processes. ters, laser beam deflectors, splitters and less dense materials, such as SiC and
attenuators). Leon Glebov and his team Bte4mCp, ecraantubreespbroydcuocsetdlyomnalynuatfavceturyrihniggh
Transparent glass-ceramics based on at the College of Optics and Photonics processes and are, hence, expensive.
fluoride, chalcogenide and oxyfluoride (CREOL), University of Central Florida,
doped with rare-earth ions have been have been responsible for this develop- Most glass-ceramics have lower hard-
successfully used for wavelength up- ment. At least two companies produce ness and Young’s modulus than the
conversion devices for europium-doped such Bragg gratings. This glass-ceramic above-described ceramics, but have
waveguide amplifiers. Transparent is interesting because of the low amount the great advantage of low density
mullite-, spinel-, willemite-, ghanite- of its crystal phase, less than 1 percent and much lower cost. Moreover, glass-
and gelenite-based glass-ceramics of nanosized NaF, and the intricate pho- ceramics can be transparent to visible
doped with transition-metal ions have tothermal crystallization mechanism of light. Alstom’s Transarm, a transparent
been developed for use in tunable and PTR glass is yet scarcely known!40–41 glass-ceramic armor is based on lithium
infrared lasers, solar collectors and disilicate. It originally was developed for
high-temperature lamp applications. To be transparent in the visible protective visors for bomb disposal work.
Glass-ceramics that exhibit second har- range, a glass-ceramic must have one or Another example is Schott’s Resistan,
monic generation and materials with a combination of the following charac- a range of low-expansion glass-ceramics
high Kerr constant for electrooptical teristics: the crystal size must be much that can be opaque or transparent and
devices have been developed as well. less than the wavelength of visible are intended for substrates for vehicular
The combination of several properties light (i.e., less than 200 nanometers); and personal armor systems.
is the hallmark for their success.39 and the birefringence must be very low
or there must be negligible difference Little has been published and patent-
Other optically active applications between the refractive indexes of the ed on this particular use of glass-ceram-
include luminescent glass-ceramics for residual glass matrix and the crystals. ics, compared with other applications,
solar concentrators, up-conversion and The vast majority of existing transpar- because of the sensitive nature of this
amplification devices; illumination ent glass-ceramics relies on crystal size
devices using IR; heat-resistant materi-

American Ceramic Society Bulletin, Vol. 89, No. 8 25

A bright future for glass-ceramics

military-related research. For more infor- • Optical properties: Articles are listed above (and not listed) and their
mation the reader is referred to patents translucent or opaque, opalescent, fluo- exciting potential applications, glass-
granted to Michael Budd and colleagues. rescent, and colored and photo-induc- ceramics have indeed a bright future! n
tion nucleations are possible.
Concluding remarks Editor’s note
Mark Davis mentions in his review All of the glass-ceramic products
An impressive variety of glass- article, that “… as George Beall pointed
ceramics has been developed during the out to me some years ago, although the cited in this article have registered
past six decades. Yet, many others with number of glass-ceramics in total that trademarks held by the companies that
unusual and unforeseen properties and [make it] into commercialization is quite produced them.
applications are likely to be discovered small, once they do make it, they exist
in the future. as a viable product typically for decades.” About the author
This is certainly true: From several Edgar Dutra Zanotto is chair of the
Glass-ceramics possess many favor- thousand patents, only a few dozen glass-
able features. ceramics products have reached the mar- Nucleation, Crystallization and Glass-
ket. However, most of them – or their Ceramics Committee (TC 7) of the
• Composition: 1052 compositions updated versions – remain there, and International Commission on Glass
can, in principle, be vitrified by com- some have sold millions! and head of the Vitreous Materials
bining and varying by 1 mole percent Laboratory, Department of Materials
of all the 80 “friendly” elements of the Much is already known about glass- Engineering, Universidade Federal
periodical table, which could then be ceramic technology, but many challeng- de São Carlos, São Carlos, SP, Brazil
crystallized to form a glass-ceramic.44 es in glass-ceramic research and devel- (www.lamav.ufscar.br).
opment are ahead. They include the
• Forming: Articles of any shape search for new compositions (and there Acknowledgments
can, in principle, be made by rolling, are many alternatives to explore), other I am indebted to Donald Stookey
casting, pressing, blowing, drawing or and more potent nucleating agents, and
by any other glass-processing method new or improved crystallization pro- for discovering glass-ceramics! I also
that already exists or may be invented. cesses. Challenges include microwave deeply thank my former and present
heating, biomimetic microstructures, TC-7 colleagues and friends – from
• Thermal treatment: Crystallization textured crystallization demonstrated by whom I learned much about the intri-
is induced on the cooling path, in one Christian Russel of the OSI in Jena and cacies of glass crystallization, proper-
step or multiple steps. laser crystallization demonstrated by ties and applications of glass-ceramics
Taka Komatsu of Tohoku University in during the past three decades: Peter
• Microstructure: Articles can Japan. A deeper understanding and con- James, Mike Weinberg, Stvan Szabo
be engineered from nanograins, trol of photothermal-induced nucleation (all deceased), Tadaski Kobubo,
micrograins or macrograins; low or high associated or not with chemical etch- Klaus Heide, Wolfgang Pannhorst,
crystallinity; zero, low or high porosity; ing; the development of harder, stiffer, Linda Pinckney, Ian Donald, Guenter
one or multiple crystal phases; random stronger and tougher glass-ceramics; and Volsksh, Taka Komatsu, Akihiko
or aligned crystals; and surface-induced glass-ceramics with increased transpar- Sakamoto, Michael Budd, Maria
or internal crystallization. ency or conductivity are also timely. Pascual, Miguel Prado, Vlad Fokin, Jeri
Sestak, Mark Davis, Gilles Querel, Jojo
• Thermal properties: Thermal A wide range of potential properties Deubener, Ralf Mueller, Falk Gabel and
expansion can be controlled – nega- of glass-ceramics is possible because Robert Hill.
tive, zero or highly positive; stability can of the ability to design their composi-
range from about 400°C to 1,450°C; and tion, thermal treatment and resulting Thanks also to Christian Ruessel for
low thermal conductivity is common. microstructure. This, combined with hosting several dozen internship students
the flexibility of high-speed hot-glass from LaMaV at the famous Otto-Schott
• Mechanical properties: Articles forming will ensure continued growth Institute in Jena. To Leon Glebov,
have much higher strength and tough- of glass-ceramic technology. As in their Larissa Glebova, Julien Lumeau, Vlad
ness than glasses, but the limits are far serendipitous discovery, “luck” based on Fokin, Gui Parent and all the members
from being reached, possibility to be systematic exploratory research, solid of the photothermo-induced nucle-
further strengthened by fiber addition, understanding of glass structure, relax- ation research team. To Larry Hench,
chemical and thermal methods. They ation, crystallization and properties, as Oscar Peitl, Murilo Crovacce, Renato
are hard, some are machinable. well as knowledge of the vast literature Siqueira, Alex Fraga, Marina Ismael
and deductive reasoning, may allow and Bruno Poletto – LaMaV’s bio glass-
• Chemical properties: Articles are other great inventions to bear fruit. ceramics team. To Miguel Prado, Ralf
resorbable or highly durable. From their glorious past, starting with Muller, Catia Fredericci, Edu Ferreira,
their accidental discovery, to their very Anne Barbosa, Vivi Oliveira and Rapha
• Biological properties: Articles are successful commercial products as well (Bode) Reis – the sinter-crystallization
biocompatible (inert) or bioactive. as their impressive range of properties team of LaMaV. To Ana Rodrigues, JL

• Electrical and magnetic properties:
Articles have low or high dielectric
constant and loss, high breakdown volt-
age, ionic conducting or insulating,
superconducting, piezoelectric and fer-
romagnetic properties.

26 American Ceramic Society Bulletin, Vol. 89, No. 8

and their students – the ionic conduct- 12P.W. Mc Millan, Ed., Glass Ceramics, 2nd ed. Biomed. Mater. Res., 82A, 545–57 (2007).
ing glass-ceramics team of LaMaV. To Academic Press, New York, 1979.
Vlad Fokin, Juern Schmelzer, Dick 32C. Tirapelli, H. Panzeri, E.H.G. Lara, R.G.Soares,
Brow, Joe Zwanziger, Aldo Boccacini, 13P.F. James, “Glass-Ceramics: New Compositions O. Peitl and E.D. Zanotto, “The Effect of a Novel
Alicia Duran, M.J. Pascual, Marcio and Uses,” J. Non-Cryst. Solids, 181, 1–15 (1995). Crystallised Bioactive Glass-Ceramic Powder on
Nascimento, Mariana Villas Boas, Dentine Hypersensitivity: A Long-Term Clinical
Daniel Cassar, Leo Gallo, Tiago Mosca, 14W. Pannhorst, “Glass-Ceramics: State-of-the- Study,” J. Oral Rehab., (2010), accepted for publica-
Diogo Alves and all past collaborators Art,” J. Non-Cryst. Solids, 219, 198–204 (1997). tion.
on fundamental studies on nucleation
and crystallization. To Gui Parente, 15G.H. Beall and L.R. Pinckney, “Nanophase Glass- 33C. Vitale-Brovarone, F. Baino and E. Verné,
Michael Budd, Mark Davis and George Ceramics,” J. Am. Ceram. Soc., 82, 5–16 (1999). “High-Strength Bioactive Glass-Ceramic Scaffolds
Beall for their valuable critical review for Bone Regeneration,” J. Mater. Sci.-Mater. Med.,
of this manuscript. Finally, I thank the 16M.J. Davis, “Practical Aspects and Implications 20, 643–53 (2009).
Brazilian funding agencies Capes, CNPq of Interfaces in Glass-Ceramics: A Review,” Int. J.
and Fapesp for continuously supporting Mater. Res., 99, 120–28 (2008). 34O. Bretcanu, C. Samaille and A.R. Boccaccini,
the vitreous materials research group of “Simple Methods to Fabricate Bioglass®-Derived
UFSCar during the past 34 years. 17S.D. Stookey, Ed., Explorations in Glass. American Glass-Ceramic Scaffolds Exhibiting Porosity
Ceramic Society, Westerville, Ohio, 2000. Gradient,” J. Mater. Sci., 43, 4127–34 (2008).
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