Glasses as engineering materials: A review

EUGEN AXINTE GLASSES AS ENGINEERING MATERIALS: A REVIEW MATERIALS & DESIGN - VOLUME 32, ISSUE 4 FEATURED IN THE

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Materials and Design 32 (2011) 1717–1732

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Review

Glasses as engineering materials: A review Eugen Axinte ⇑ Gh. Asachi Technical University of Iasi, Faculty of Machine Manufacturing & Industrial Management, 59A, Prof. Dimitrie Mangeron Blvd., Romania

a r t i c l e

i n f o

Article history: Received 15 September 2010 Accepted 24 November 2010 Available online 28 November 2010 Keywords: Glasses Constitution Environmental performance

a b s t r a c t Glass products have applications in design engineering, and they can solve many special problems. These materials can work in situations in which plastics and metals would fail and need to be part of designer’s repertoire. In some situations, by using these materials, some difficult problems would be solved. This paper contains a number of chapters as follows: a brief about ceramics family, a short history of glass, a brief about physics and the technology of glass fabrication, recently developed glasses with special destinations, testing methods and news about glass parts processing (grinding, waterjet processing, laser cutting, nanoimprint lithography, etc.). The last chapter of this review paper contain some strategic lines of glass usage in industry and estimations about the future of glass development. Ó 2010 Elsevier Ltd. All rights reserved.

1. The ceramics family Cermets and ceramics are becoming the tool materials for the present and future. By using the cemented carbides at wood working tools (as saw blades, cutting wheels), the wear was reduced significant. Coated cemented carbides displaced the high-speed steel for cutting tools and also high production press dies use the cemented carbide tooling. Ceramics are taking a lot of high-temperature machine tasks, are substrates for computer chips, and are used for prosthetic devices. Glasses and carbon products have applications in design engineering and they can solve many special problems. These materials can work in situations in which plastics and metals would fail and need to be part of designer’s repertoire; sometimes, using these materials, some difficult problems would be solved. Ceramics are defined as solids composed of compounds that contain metallic and/or non-metallic elements, and the atoms of compounds are held together with strong atomic forces (ionic or covalent bonds). The spectrum of ceramic uses is presented in Fig. 1. The ceramics with high strength and the best toughness (as aluminum, zirconias, oxides, silicon carbides) were named in 1980 as ‘‘structural ceramics’’. In Japan, these ceramics were called ‘‘fine ceramics’’. In 1990, the (ASTM) Committee for ceramics (C28) named this ceramics ‘‘advanced ceramics’’. The definition given by C28 for this class of materials is highly engineered, high-performance, predominantly non-metallic, inorganic, ceramic material having specific functional attributes (by standard ASTM C1145) [1].

⇑ Tel./fax: +40 232217290 (office), mobile: +40 722892926. E-mail address: [email protected] URL: http://www.cm.tuiasi.ro/html/ro/tcm.htm 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.11.057

Glasses are not ceramics (by previous definition of ceramics), but they are used for similar type of things as ceramics and have some properties that are typical for ceramics. The most common property of ceramics, glasses, and cements is brittleness. The measure of crack propagation tendency, fracture toughness, is lower at ceramics family than at metals, as is shown in Fig. 2.

2. Brief history of glass: past and present of glass It is not exactly known when, where, or how humans first learned to make glass. The legends tells us that a Phoenician sailor (by other historians, a Roman sailor), cooking the evening meal on a beach, sets the pots on top of stones of natron (a natural mixture of sodium carbonate decahydrate, sodium bicarbonate along with small quantities of household salt). As the cooking fire heated both these stones and the sand below, an unknown liquid began to flow and that was the origin of man-made glass. In [2] is demonstrated and argued that in ancient times, soda glasses with high alumina concentrations are quite rare around the Mediterranean area or in the Middle East. The few available examples include European Iron-Age dark blue glass colored with cobalt-rich alum that contains up to 8% of alumina. Mineral soda–alumina (m-Na–Al) glass has been found across a vast area stretching from Africa to East Asia. m-Na–Al glass appears around the 5th c. B.C. and is relatively common for periods as late as the 19th c. A.D. It is particularly abundant in South Asia, where raw materials to produce m-Na–Al glass are readily available and was likely manufactured there; however, the number and the importance of the manufacturing centers are unknown as archaeological information is extremely scarce. The interpretation of data obtained using compositional analysis on a large corpus of artifacts (486) shows that at least five subgroups of m-Na–Al glass can be

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E. Axinte / Materials and Design 32 (2011) 1717–1732

Fig. 1. The spectrum of ceramics uses.

Fig. 2. The fracture toughness of different materials.

identified using the concentrations of calcium, magnesium, uranium, barium, strontium, zirconium, and cesium measured with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). From this data, it is possible to infer the existence of several m-Na–Al glass-making centers, not all of them located in South Asia as previously assumed. They were operating over different time periods and were connected to different exchange networks. It is historically accepted that the first manufactured glass was in the form of a glaze on ceramic vessels, about 3000 B.C. The first glass vessels were produced about 1500 B.C. in Egypt and Mesopotamia. The glass industry was extremely successful for the next 300 years and then declined. It was revived in Mesopotamia in the 700 B.C. and in Egypt in the 500 B.C. For the next 500 years, Egypt, Syria, and the other countries along the eastern shore of the Mediterranean Sea were glassmaking centers. Glass manufacturing developed in the Roman Empire and spread from Italy to all Roman provinces. The first four centuries of Christian Era is called the First Golden Age of Glass. In the middle ages, by the time of the Crusades, glass manufacture had been revived in Murano island, near Venice, where soda lime glass, known as crystal, was

developed (this period is known as the Second Golden Age of Glass). In North America (United States), the first factory known was a glass plant built at Jamestown, Virginia, in 1608, but failed within a year. The Jamestown colonists tried glassmaking again in 1621, but an Indian attack in 1622 and the scarcity of workers ended this attempt in 1624. The glass industry was reestablished in America in 1739, when Caspar Wistar built a glassmaking plant in Salem County, New Jersey. This plant operated until 1780. In 1820, Bakewell, Page, & Bakewell Co. from Pittsburgh, Pennsylvania, introduced the first real development in production glassblowing since the blowpipe, a development that would change how glass was used forever. They patented a process of mechanically pressing hot glass. After 1890, glass uses and manufacturing developments increased so rapidly as to be almost revolutionary. The late 1900s brought new important specialty glasses. Among the new specialty glasses were transparent glass–ceramics, which are used to make cookware, and chalcogenide glass, an infraredtransmitting glass that can be used to make lenses for night-vision goggles. The science and engineering of glass as a material was much better understood, and in the late 1950s, Sir Alastair Pilkington introduced a new revolutionary production method (float glass production), by which 90% of flat glass is still manufactured today. In the 1970s, optical fibers were developed for use as ‘‘light pipes’’ in laser communication systems. These pipes maintain the brightness and intensity of light being transmitted over long distances. Types of glass that can store radioactive wastes safely for thousands of years were also developed during the 1970s. 3. Brief about physics of glass: how it is made Generally, solids (metals) have a three-dimensional periodic structure (crystalline structure). But also exists solids with a randomized three-dimensional structure – these solids are called amorphous or glassy (Fig. 3). A lot of materials such as organic polymers and metal alloys are able to form under special conditions amorphous structures. An inorganic amorphous or glassy solid is a high-speed cooled liquid (cooled fast enough to prevent crystallization).

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Fig. 3. Crystalline structures (a) amorphous randomized structures (b) and the molecular structure of silica-based glass (c).

The relationship between the oxygen and the cation of the oxide compound essentially influences the glass-forming ability of an oxide. There are four types of oxides used in glass fabrication (see Table 1). At room temperature, glasses are very viscous structures (1018 Pa s – glass viscosity vs 1 Pa s – water viscosity). Viscous flow of glass at room temperature occurs in a geological timescale. With increasing temperature, the glass viscosity decreases as is shown in Fig. 4. There are five very important temperatures, called ‘‘standard points’’, associated with the viscous flow (melting) of glass. The strain point is the maximum temperature supported by glass for structural applications. A review and the description of standard points is given by Table 2. After the glass was formed, it is cooled to a temperature nearly above the strain point, where it will retain its shape and resist flow. At this point, the glass parts are annealed to relieve the internal stresses. A glass part that is incorrectly annealed will fracture or crack at ambient temperature. The behavior of specific density of glass as a function of the temperature is illustrated by graph from Fig. 5. It is observed that at glass transition temperature exists an inflexion point. After this point, the glass viscosity decreases, specific volume abruptly increases, and the specific density has a greater rate of decreasing. This behavior has major consequences for design and manufacture of molds. In [3], Fluegel developed an accurate glass viscosity model relevant to commercial application through statistical analysis and based on all composition–property data available in SciGlass. The viscosity model for predicting the complete viscosity curve of glass was developed using a global statistical approach and more than 2200 composition–viscosity data for silicate glasses collected from over 50 years of scientific literature, including soda–lime–silica container and

Fig. 4. Dynamic viscosity of glass vs heating temperature.

float glasses, TV panel glasses, borosilicate fiber wool and E-type glasses, low expansion borosilicate glasses, glasses for nuclear waste vitrification, lead crystal glasses, binary alkali silicates, and various other compositions. All that is required to make glass is sand, soda, a little lime, and a lot of heat. The typical process of glasses fabrication is shown in Fig. 6.

Table 1 Types of oxides used in glass fabrication. No.

Oxide type

Characteristics

Examples

1

Main glass former oxides

Suitable structures and low crystallization rates

SiO2 B2O3 GeO2 P2O5 Al2O3; Bi2O3 WO3; MoO3 TiO2; ZnO; PbO; Zr2O3 MgO CaO Na2O K2O

Form glass under slow cooling rates 2 3 4

Conditional glass formers oxides Intermediate oxides Network modifier oxides

Form glass under certain conditions Cannot form glass themselves but form glass in mixture with former oxides Cannot form glass themselves nether in mixture with former oxides

They can modify the properties of glass by affecting Si–O bonds

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Table 2 The standard points of glass. No.

Standard point name

Viscosity (Pa s)

Temperature descriptions

1 2

Working point Softening point

103 106.6

3

Glass transition temperature Annealing point Strain point

1012

At this temperature, the viscosity is sufficiently low for glass forming. Casting processes are possibly below 10 Pa s viscosity At this temperature, the viscosity is sufficiently low for glass to slump under own weight. Near below this temperature glass is stiff, but a little effort is necessary for yield and flow Range of temperatures at which glass transitions from super cooled liquid in a solid state

1013.4 1013.6

Internal stresses are relieved in minutes Internal stresses are relieved in hours

4 5

1 Pa s (SI) = 0.1 P (P – poise, physics system of units).

tured in glass pieces by different techniques as blowing, molding, casting, injection, extrusion, and wire drawing. Commercial glasses are silica-based glasses with additional oxides (see Table 1). The presence, type, and the quantity of one or many oxides give the glass type and also have major influences on the glass properties and utilization. For example, a colored glass is obtaining by addition of a metallic oxide (iron oxide for green glass, cobalt oxide for blue glass). Crystalline glass–ceramics are obtained by the introduction of titanium oxide in melted glass. Titanium oxide initiates the crystallization and the material obtained is up to 96% crystalline [1]. The mechanical and physical properties of glasses are essentially determined by their composition, but a general view can be given:

Fig. 5. The evolution of specific density vs temperature (———— specific volume vs temperature).

The mixture of refined sand (SiO2) and additional basic oxide is heated in furnace (gas or electric) at a temperature higher than 1200 °C. Essentially, the main role of this additional oxides (as CaO, Na2O, K2O) is to reduce the working point of the mixture. A pure silicone oxide (quartz) is refractory, with a softening point near 1500 °C or higher. Then, the melted composition is manufac-

a. b. c. d. e. f. g.

Glasses are harder than metals. Glasses have tensile strength in the range 24–69 MPa. Glasses are brittle and have low ductility. Glasses have a low coefficient of thermal expansion. Glasses have a low coefficient of thermal conductivity. Glasses are good electrical insulators. Glasses are resistant to acids, solvents, chemicals, water and saline water and alkaline solutions. h. Some glasses can be used at high temperatures (700 °C – soda lime for windows; 1580 °C – fused quartz–silica). Selection of the main mechanical and physical properties of amorphous glass and crystalline glass–ceramic is presented in

Fig. 6. Basic technology for glass fabrication (integrated with the recycling process).

E. Axinte / Materials and Design 32 (2011) 1717–1732 Table 3 Mechanical properties of glasses vs other engineering materials. Hardness, HV

Young modulus of elasticity, E (GPa)

Material

Flexural strength (MPa)

Compressive strength (MPa)

Silica (amorphous glass) Crystalline glass–ceramic Plastic (polycarbonate) Carbon steel Cemented carbide

98

1860

600

69

103

344

250

64

89.6 275 1400

4.1. Advances in glass and glass–ceramics design and manufacture

275 4000

100 1000

200 612

Thermal conductivity (W/m °C)

Coefficient of thermal expansion, 20–100 °C (10 6 m/m °C)

Electrical resistivity (O m)

2304

34

1

107

2592

33

9.4

1012

1296

0.2

6.7

8 1014

8064 16,000

47 86

11.9 7.4

20 6 10

Density (kg/ m3)

Silica (amorphous glass) Crystalline glass–ceramic Plastic (polycarbonate) Carbon steel Cemented carbide

8

Tables 3 and 4. For comparison, in tables are presented some properties of a plastic (polycarbonate), a carbon steel, and a cemented carbide WC with 6% cobalt. Optical properties of glasses make them preferable in the construction of lenses and windows. The very low coefficient of thermal expansion of high silica glasses makes them extremely resistant at thermal shocks and also makes them favorite for laboratory glass instruments (tubes, retorts) and light bulbs. The crystalline glass with elasticity modulus above 130 103 MPa has good shock resistance. 4. Advances in glass family development The glass family is huge and is in continuous enrichment. Year after year, new types of glass with new properties extend their utilization domain. The utilization domain of glass in engineering design have a lot of facets: from banal windows or bottles to antinuclear radiation containers; from architectural and structural glasses to photosensitive glass devices used in machine controls; from food preparation tanks to newest optical fibers. The enormous variety of existent glass types, rapid development of new and innovative glasses, developments in glass fabrication and development of glass-manufacturing processes make the classification of glasses extremely difficult. After the product types, a first classification can be done for the main glass industries, as in Table 5 (based on http://www.glassonweb.com/ description-in section directory).

Table 5 Classification of main glass industries. Main glass industries Flat glass

Hollow glass

A list of glass types in the flat glass industry is starting from basic glass types as float glass, mirrors, and trough security types to special glass types like electrochromic and photovoltaic glass (see Table. 6). A large spectrum of designer’s interests for these glass products are also observed. A simplified classification is based on the chemical composition and follows the crystallization model (Table 7).

2.28

Table 4 Physical properties of glasses vs other engineering materials. Material

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Automotive glass

Art glass

Optical glass

Glass fibers

Glass Wool

In [4], Hampshire revealed some advances in the domain of oxynitride glasses. This work is a complete review of the development of oxynitride glasses and outlines the effect of glass composition, especially nitrogen content and also cation ratios, on properties and relates this to structural features within the glass. Nucleation and crystallization studies are also outlined. Oxynitride glasses are prepared by mixing appropriate powders – silica, alumina, the modifying oxide(s) plus silicon nitride or aluminum nitride – in isopropyl alcohol in a ball mill with sialon milling media, followed by evaporation of the alcohol. Glasses (50–60 g) are melted in boron nitride-lined graphite crucibles under 0.1 MPa nitrogen pressure at 1600–1750 °C for 1 h, after which it is quickly removed from the furnace and poured into a preheated graphite mold at 850–900 °C. The glass is annealed at this temperature for 1 h to remove stresses and then slowly cooled. The main conclusions of the study are that oxynitride glass formation occurs in a number of M–Si–O–N, M–Si–Al–O–N and M–Si–Mg–O–N systems, and using normal melting processes, up to 30 equiv.% nitrogen can be dissolved in the glass. An innovative approach, using metal precursors, allows much more N to be dissolved into some M–Si–O–N glasses. As nitrogen content increases, properties such as glass transition temperature, elastic modulus, viscosity, hardness, and slow crack growth resistance increase while thermal expansion coefficient decreases as a result of increased cross-linking of nitrogen within the glass network. Spectroscopic studies have identified the structural features of glasses and the role of nitrogen as a network ‘‘former’’. Many studies on crystallization of oxynitride glasses have been carried out, which have identified suitable two-stage heat treatments for nucleation and growth of crystal phases, to form glass–ceramics with significant increases in strength and elastic modulus over the parent glasses. Addition of fluorine extends glass formation in oxynitride systems and allows dissolution of higher levels of nitrogen into glasses. Fluorine lowers glass transition temperature but does not have any effect on elastic modulus or microhardness. Nitrogen may be dissolved in phosphate glasses with consequent improvements in chemical durability and increases in many physical and mechanical properties [4]. New advances in structural glasses domain are described by Royer-Carfagni and Silvestri [5]. The authors developed an innovative point-fixing system (called Gecko system) for frameless glass glazing that exploits the enhanced mechanical properties of a new generation of ionoplast polymer interlayers. Laminated glass connected with the new device exhibits a noteworthy resistance and interesting post-glass-breakage performances. To achieve a fail-safe performance, the key point is to attach the polymeric interlayer of laminated glass directly to metallic holders, so that the interlayer itself may act as a confining membrane even after glass-breakage. This technology is possible only if the polymeric materials present sufficiently high mechanical properties and adhere well to both glass and metals. The Gecko system is presented in Fig. 7 (from [5]). After the testing of the system in different conditions (tests at room temperature, tests on aged samples and tests at low and high temperatures), the authors have demonstrated that the polymer can be easily curved by slightly heating the material, and even when the radius of curvature is very small, no considerable decay

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E. Axinte / Materials and Design 32 (2011) 1717–1732 Table 6 Glass types in flat glass industry and the designers spectrum of interests. Designer’s interests Flat glass industry

Automotive/ aerosapce

Common glasses (basic and decorative)

Special glass types

Float glass Body tinted glass Reflective glass Low glass Mirror Insulating glass Enameled/screen printed glass Pattern glass Antique mirror Photovoltaic glass X-ray protection glass Electrically heated glass Electrochromic glass Liquid crystal glazing Self-cleaning glass Sand-blasted glass Acid-etched glass Bent glass Tempered glass Laminated glass Fire-resistant glass Wired glass Alarm glass Antireflective glass

Architecture construction

Physics/chemistry/ electronics

x x x x x

x x

x x x

x

x x x x x x

x x x x x x x

x x x x x x x x x x x x x x x x

x x x x x x x x x x x x x x

Table 7 Simplified glasses classification. No.

Type

Description/key words

1

Ordinary – amorphous glasses a. Quartz b. Silica glass c. Na–Ca silicate glass Glass–ceramics

Amorphous structure; silica base; high commercial spectrum

2

3

Bulk metallic glasses BMGs

Glass–ceramics are manufactured through the controlled crystallization of a specially formulated glass – a high density of crystalline nuclei (Ti, Zr, P2O5) is generated in the molten glass. Glass–ceramics are useful in thermally hazardous conditions. Good resistance to erosion and pressure and the excellent hardness make glass–ceramics widely used in industrial purposes. Moreover, glass–ceramics are very good electrical insulators Bulk metallic glasses (BMGs) are metallic materials with a disordered atomic-scale structure, produced directly from the liquid state during cooling (the rapid cooling, on the order of millions of degrees a second, is too fast for crystals to form and the material is ‘‘locked in’’ a glassy state), are called ‘‘glasses’’, or amorphous metals and they are commonly referred as ‘‘metallic glasses’’ or ‘‘glassy metals’’. BMGs have been paid great attentions for its theoretical and practical reasons since the bulk amorphous Pd–Cu–Si and Pd–Ni–P alloys was first synthesized by water quenching method in 1974. More recently, batches of amorphous steel have been produced that demonstrate strengths much greater than conventional steel alloys. The most useful property of bulk amorphous alloys is that they are true glasses, which means that they soften and flow upon heating. This allows for easy processing, such as by injection molding, in much the same way as polymers. Bulk metallic glasses have been commercialized for use in medical devices, and as cases for electronic equipment

of the mechanical properties has been observed. In any case, the viscoelastic nature of the polymer renders the response strongly dependent upon the load duration and environmental temperature. However, the confinement effect produced by the attached glass or metal enhances the mechanical strength of the bent appendix, which results much higher than that of the plain polymer especially at relatively high temperatures. The post-glassbreakage testing shows that the interlayer remains attached to the metallic holders even after complete breakage of both glass plies, thus acting as a confining membrane that prevents the detachment of the glass fragments. In [6], Fujimoto describes a new infrared luminescence from bismuth (Bi)-doped glass. In this work, the author will introduce the basic properties of Bi-doped silica glass (BiSG), such as a phase diagram and spectroscopic properties, and then mainly talk about the origin of luminescent center. After the discovery of a new infrared luminescent bismuth center, several research groups started to

study its applications, such as optical amplification or laser oscillation using Bi luminescent materials. Optical amplification around 1.3 lm with Bi-doped multicomponent glass fiber is useful for metropolitan area network optical amplifiers [7]. A large study about advances in multicomponent silicate glasses and their glass–ceramics derivatives for dental applications is presented by ElBatal et al. [8]. X-ray diffraction patterns reveal the formation of lithium disilicate as a major phase together with other subsidiary phases precipitated during the crystallization process according to the other constituent oxides. Infrared spectra show mainly characteristic bands due to silicate network. In [9] is statistically analyzed the relation between the chemical composition and the density of silicate glass melts at temperatures of 1000–1400 °C. The analysis was carried out on all 140–260 available values in the SciGlass information system for compositions containing more than 40 mol% silica, less than 40 mol% boron oxide, varying amounts of Al2O3, Li2O, Na2O, K2O, MgO, CaO, PbO,


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Fig. 7. The Gecko system with indication of the bent polymeric interlayer [5]. (a) Section; (b) front view of a prototype.

and other minor components. A model based on multiple regression was developed. The 95% confidence interval of the mean model prediction on the density was 0.5–3%, depending on the composition of interest. The prediction of density as a function of temperature made possible the estimation of the coefficient of thermal expansion in the molten state to within 20–40% error with a 95% level of confidence. The effects of the composition of silicate glass melt density and thermal expansion are investigated: boron oxide, B2O3, decreases the density of silicate glass melts based on its low molecular mass; lithium oxide, Li2O, slightly decreases the density of silicate glass melts; alumina, Al2O3, clearly increases the glass melt density at high temperatures (1200–1400 °C); sodium oxide, Na2O, does not have a strong influence on the glass melt density within the studied temperature range because of the interplay between its medium molecular weight, its influence on the thermal expansion, and component interactions. At 1400 °C, adding Na2O appears to decrease the density, whereas at lower temperatures, the influence of Na2O addition is not readily recognized; potassium oxide, K2O, decreases the density of silicate glass melts; magnesium oxide, MgO, might not decrease the glass melt density despite its low molecular weight, because it does not appear to increase the thermal expansion coefficient significantly;

calcium oxide increases the glass melt density due to its relatively high molecular weight and the moderate influence on the thermal expansion coefficient; lead oxide, PbO, has a very high molecular weight; therefore, it increases the glass melt density significantly. An example for glass designer’s use is given in Fig. 8 (from [9]). The authors recommend that for glass design through property modeling, evaporation losses during glass batch melting and possible influences of the oxidation states of transition metal oxides must be taken into account. Advances in environmental glass industrialization are extracted from [10–12] and are listed as follows: Ref. [10] presents glasses obtained from melting mixtures of industrial wastes (panel glass from cathode ray tubes, mining residues from feldspar excavation, and lime from fume abatement systems of the glass industry). Micro- and macrocellular sintered glass–ceramics were manufactured. Microcellular glass–ceramics, with a closed porosity, were prepared by the direct foaming of the glass mass, determined by viscous flow sintering of fine powders ( 100 A – 100; B – >50; C – 25 to 50; D < 25 A < 50; B – 50 to 99; C – 100 to 200; D > 200 A < 25; B – 25 to 50; C – 51 to 75; D > 75 A – no problems; B – minor problems; C – serious legal problems; D – under severe legal restriction A – quickly degrades; D – unlimited lifetime A – 100; B – 50 to 100; C < 50; D = 0 A – no social or political problems; D – social malign; political restrictions

materials) will find increasing application in biological and medical areas. Materials such as photochromic, electrochromic, and thermochromic glasses, which respond to external stimuli, are being developed with various, sometimes unusual, applications. Revolutionary materials, as the flexible ceramic heat shield material (ZircoFlex), are recently developed and fabricated by using a new technology in which the ceramic material is sprayed in the form of thousands of individual ‘platelets’ onto the surface of the aluminum backing foil (see Fig. 20). Early applications for ZircoFlex™ foil are coming from the automotive industry, where the foil can be used to protect sensitive components from heat in increasingly crowded engine bays. Al Gore (former US vice president) became the publicly recognizable face of the environmental issue after his Oscar-winning documentary movie An Inconvenient Truth (2006). This documentary helped enormous to make the issue of global warming a recognized problem worldwide. By winning of Nobel Peace Prize in 2007, Al Gore brought once more to the forefront the problem of global warming. The first impact on glass industry was produced by switching on large scale to compact fluorescent light bulbs (by the replacing of incandescent bulbs 4200 + tons of carbon were offset). Glass industry has successfully reacted to environmental issues by offering a variety of applications to make buildings more energy efficient and ecologically friendly. Today’s glass can be practically custom-made to fit into any environmental conditions and offer specific appearances and performance. The latest development in the industry has been the introduction of self-cleaning glass. While progress in the glass industry continues, we can expect glass in the near future that will react to external stimuli, the socalled ‘‘smart glasses’’, offering maximum comfort and excellent energy efficiency inside buildings. Some glass applications also use alternative natural resources to preserve the environment in which we live. Some states have begun to regulate or even stimulate the introduction of such energy-preserving applications [36]. The modern glass industry have a huge contribution through development and the introduction of new energy-efficient glass products and applications, some issues in glass manufacturing and processing still must be addressed in the future. A great challenge for the actual and the future glass industry is to increase the contribution to environment preservation. According to the criteria of environment-friendly selection of materials (Table 9 [37]), the weakness of glass is the ‘‘embedded energy’’. The embedded energy for glass mass unit can be rated at D (>200), the worst as possible. The challenge for researchers and glass industry is to act for significant decreasing of embedded energy in glass mass unit. There are two possible ways to solve this desiderate: (a) continuous developing of high-efficiency furnaces; (b) continuously developing of new glass compositions, with lower glass transition temperatures. The synergetic effect of simultaneous applying of both ways could offer a good future for glass industry. Most recent tendencies are to use the green energy (wind and solar) in producing and manufacturing of glasses.

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