Recycling of waste glasses into partially crystallized glass foams

Enrico Bernardo Æ Giovanni Scarinci ÆPaolo Bertuzzi Æ Piero Ercole Æ Ludovico Ramon

Published online: 14 April 2009

� Springer Science+Business Media, LLC 2009

Abstract Waste soda-lime glass, alone or mixed with

wastes from the manufacturing of glass fibers, was suc-

cessfully converted into partially crystallized glass foams

by a particularly simple and economic processing, con-

sisting of a direct heating of glass powders at temperatures

from 900 to 1050 �C. The foaming operated by the oxi-

dation of SiC, inserted as powder additive, was found to

depend on a complex combination of processing tempera-

ture, soaking time, tendency of the investigated glasses

toward devitrification, and amount of MnO2, acting as

oxidation promoter. Selected combinations led to foams

with a good microstructural homogeneity and mechanical

strength, suitable for application as aggregates in light-

weight concrete.

Keywords Glass � Glass–ceramic � Foam � Porosity

1 Introduction

The demand for lightweight aggregates, to be used in

thermally and acoustically insulating concretes [1], is

giving a renewed industrial interest to cellular glasses (also

known as glass foams), compared to other insulating

materials, such as polymeric foams. In fact, besides a

superior chemical and thermal stability, important for

durability and safety reasons (the combustion of polymeric

foams generally leads to the evolution of potentially toxic

gases, while glass foams, due to their inorganic nature, are

un-inflammable), the key advantage of the glass foams is

their significant mechanical strength [2], to be exploited in

cement matrices.

The manufacturing of glass foams is essentially a way

for glass recycling [3, 4]. Unlike the first examples, dating

back to the 1930s, in the current materials the foaming is

not dependent on the direct introduction of gases (blowing)

into molten glass [5], but relies on the reaction of powder

additives (i.e. foaming agents) embedded in a pyroplastic

mass, determined by the viscous flow sintering of fine glass

powders [6–8]. This processing allows, besides significant

energy savings (the viscous flow occurs at much lower

temperatures than those required by the blowing), the

introduction of a variety of recycled glasses, like those

presented here. It must be noted that the form of pellets or

loose pieces, to be used as aggregates, gives additional

economic advantages in the processing: the manufacturing

of large blocks, in fact, is particularly complicated in the

cooling stage, in order to avoid thermal stress failures [2];

in the case of loose pieces, the thermal stress failure is even

exploited for the rupture of large glass foam sheets into

small fragments [9].

This study focuses on three kinds of glasses. The first,

and the most important, consists in waste soda-lime glass,

i.e. a by-product of glass recycling. Although recom-

mended for limiting the consumption of energy and natural

raw materials, the usage of scrap glass in manufacturing

new glass articles is possible only after an expensive

sorting step, aimed at the separation of glass from other

materials, like metallic or ceramic contaminants. This

separation leads to a fraction of almost pure glass, ready for

the industry, and a fraction enriched in contaminants,

which remains practically unemployed, and is mostly

E. Bernardo (&) � G. Scarinci

Dipartimento di Ingegneria Meccanica—Settore Materiali,

Universita di Padova, via Marzolo 9, Padova 35131, Italy

e-mail: enrico.bernardo@unipd.it

P. Bertuzzi � P. Ercole � L. Ramon

SASIL SpA, via Liberta 8, Brusnengo, Biella 13862, Italy

123

J Porous Mater (2010) 17:359–365

DOI 10.1007/s10934-009-9286-3

landfilled [10]. The Italian company SASIL [11] has been

treating, under a proprietary process, this kind of waste

since 2005, developing a refined waste soda-lime glass

named ‘‘glassy sand’’, to be used as secondary raw mate-

rial, in a quantity of about 180,000 ton/year.

The other two glasses consist of industrial residues from

the manufacturing of glass fibres; these two glasses belong

to the CaO–Al2O3–SiO2 system, and they differ from each

other mostly on the basis of the B2O3 content. Due to

remarkable dimensions of the market of glass fibres, there

are large amounts (about 10,000 ton/year) of waste glasses

without any application.

This article illustrates a project of application of all

these waste glasses in cellular glasses, developed by the

usage of SiC as foaming agent, coupled with MnO2. Due to

the observed properties, the foams are quite ready for a

large scale industrial production and application as aggre-

gates in lightweight concrete.

2 Experimental procedure

The chemical compositions of the waste glasses employed

are reported in Table 1. All the glasses were considered

after milling to a size below 50 lm. Soda-lime glass (SL)

or mixtures of soda-lime glass and the other two glasses

(F1 and F2) were added with SiC (mean particle size

\2 lm), at a fixed concentration of 2 wt%, and MnO2

powder (reagent grade, average particle size of about 5 lm,

Mallinckrodt Chemical Inc., St. Louis, MO, USA), in

various amounts. Batches were obtained by dry mixing the

components in a planetary mill for 30 min. Uniaxial

pressing was conducted at 40 MPa in a laboratory press,

and cylindrical pellets of 32 mm in diameter and 5 mm

thick were obtained. The specimens were then fired in air,

in an electric laboratory furnace, with direct insertion at

different maximum temperatures (in the range from 900 to

1050 �C) and with different soaking times (from 15 to

60 min). Natural convection inside the furnace was used

for cooling.

Compressive strength was measured using an UTM

machine (Instron 1121, Norwood, MA, USA) with a

crosshead speed of 1 mm/min on prismatic samples with

an average size of 8 mm 9 8 mm 9 3 mm, cut from

foamed cylindrical pellets. The bulk density of the foams

was determined geometrically on prismatic samples before

mechanical testing. At least five tests were conducted for

each specimen. The morphology of the foams was studied

by means of optical and scanning electron microscopy

(SEM, Philips XL 30, Eindhoven, The Netherlands) and

the crystalline phases present in the foamed pieces were

assessed using X-ray diffraction (Bruker AXS D8

Advance, Karlsruhe, Germany), employing CuKa radiation

(0.15418 nm). The diffraction patterns were analyzed by

means of the Match! Program package (Crystal Impact

GbR, Bonn, Germany), using data from PDF-2 database

(International Center for Diffraction Data—ICDD, New-

town Square, PA).

3 Results and discussion

The amount of SiC, 2 wt%, is equal to that of commercial

foams, used as aggregates for concrete [12]. However, the

present foams feature a secondary foaming component,

consisting of MnO2. This component is aimed at improving

the homogeneity of the foaming provided by SiC. In fact

SiC, like other C-containing compounds, causes the

foaming of softened glass by oxidation, with the develop-

ment of CO and CO2 gases [2]. SiC reacts with the oxygen

in the furnace atmosphere: while the oxygen is directly

available at the surface of pellets, the reaction inside the

body depends on the diffusion of oxygen via the porosity

available. The amount of oxygen present inside the glass

pellets, upon softening (at temperatures above Tg) may not

be sufficient to complete the oxidation reaction. MnO2 was

added as an ‘‘oxidation promoter’’, active in providing

some extra oxygen, as recently shown for Si3N4 [13].

Commercial foams may contain, as oxidation promoters,

some sulphates (as an example CaSO4, i.e. gypsum) [2, 9,

12], being reduced to sulphites and sulphides. The usage of

MnO2 is intended to avoid the development of noxious

gases. The role of the oxide relies on the fact that Mn is a

metal with multiple valence state (Mn4?, Mn3?, and Mn2?)

[14]: the oxide with the highest valence state, MnO2

(pyrolusite), decomposes into oxides with a lower valence

state (Mn2O3, Mn3O4, and MnO) and oxygen [15]. If we

consider the complete reduction (due to the presence of a

reducing agent, such as a C-containing compound), we

have the largest release of oxygen, as follows:

Table 1 Chemical composition of the investigated glasses (wt%)

Oxide Glassy sand (SL) F1 F2

SiO2 72.3 55.3 62.7

Al2O3 2.2 14.0 12.0

Fe2O3 0.3 0.2 0.2

TiO2 0.1 0.2 -

Na2O 12.0 0.6 1.5

K2O 0.9 0.4 0.5

CaO 10.0 22.0 22.0

MgO 2.0 1.0 1.0

B2O3 - 6.2 -

PbO 0.05 - 0.1

Cr2O3 0.15 - -

360 J Porous Mater (2010) 17:359–365

123

2MnO2 ! 2MnOþ O2 ð1Þ

If the oxidation of SiC would be caused only by the

complete reduction of MnO2 into MnO (to be dissolved in

the glass), we would obtain:

SiCþ 4MnO2 ! SiO2 þ CO2ðgasÞ þ 4MnO ð2Þ

Since MnO2 is not the only source for oxygen, the

amount of this oxide, for a homogeneous foaming, may be

significantly lower than that predicted by Eq. 2. In a

previous investigation [10] it was shown that the oxidation

promotion may occur even for a MnO2/SiC weight ratio of

about 1/3. This fact was the reason for the usage of MnO2

in a minimum quantity of 0.7 wt% (the content of SiC

being 2 wt%); other foams were prepared by doubling and

doubling the MnO2 content (1.4, 2.8, and 5.6 wt%), with

the exception of the samples with a content of 8.4 wt%,

corresponding to the MnO2 amount predicted by Eq. 2.

Figure 1 summarizes the effects of processing temper-

ature, time and content of oxidation promoter for waste

soda-lime glass. It has to be highlighted that, in order to

simulate a particularly economic industrial process, the

foaming was achieved by a direct treatment at a tempera-

ture in the range of 900–1050 �C; unlike other experiences,

reported in the literature [16, 17], two step treatments

(nucleation and growth of bubbles) were not applied.

With the same formulation, the evolution of glass/SiC/

MnO2 mixtures was found to depend on a delicate balance

of processing temperature and time. It must be remembered

that a proper selection of the most suitable temperature for

the foaming process is of basic importance, since glass

viscosity (strongly dependent on temperature) and foaming

temperature are strictly related. The optimum range of

foaming temperatures must be selected considering, on the

one hand, the necessary foam stability—controlled by

viscosity—and, on the other hand, the internal cell struc-

ture, which should be characterized by homogeneous pores,

with regular shape and size, and with very thin separating

walls [18]. At the selected temperature, there is a signifi-

cant decrease of density, due to gas release, with increasing

soaking time; however, if the soaking time is excessively

long, the density increases, due to the beginning of the

coalescence of small cells into larger ones [19]. The coa-

lescence is favoured by the reduction of surface energy,

and the dissolution of small cells into larger ones is gen-

erally associated to the thickening of cell walls [2, 10, 13,

20].

The two cases of 0.7 wt% and 5.6 wt% MnO2 are par-

ticularly interesting. With 0.7 wt% MnO2 we observe a

dramatic decrease of density, from 0.9 to 0.4 g/cm3, with

increasing foaming temperature, from 900 to 1000 �C,

coherently with a decrease of glass viscosity. The tem-

perature for a density of 0.4 g/cm3 is 950 �C for a soaking

time of 60 min, 1000 �C for 30 min. For a MnO2 content

of 5.6 wt%, the density of 0.3 g/cm3 (see the horizontal

line in Fig. 1) is achieved for 60 min at 950 �C, 20 min at

1000 �C, and 15 min at 1050 �C. The point for a MnO2

content of 5.6 wt%, 30 min at 1000 �C, corresponding to a

density of about 0.35 g/cm3, much higher than that

achieved for the same MnO2 content and temperature for

20 min, reveals the occurrence of cell coalescence.

The addition of MnO2 adds complexity to the time/

temperature balance. Figure 1 shows that MnO2 effectively

promotes the oxidation only at a relatively low temperature

of 950 �C, with a relatively long soaking time of 60 min.

Under these two conditions, in fact, the density is quite

inversely dependent on the MnO2 content. Higher tem-

peratures probably enhance the oxidation of SiC, so that it

is active even without any oxidation promoter. A shorter

time at 950 �C, i.e. 30 min, gives an anomalous trend (the

density is minimized for a MnO2 content of 0.7 wt%).

Figure 2 illustrates the microstructural changes associ-

ated to different foaming conditions. For the same MnO2

content of 5.6 wt%, the foam obtained after 60 min at

950 �C, shown in Fig. 2a, features a quite homogeneous

cellular structure, with most pores having a diameter

\0.5 mm, while foams obtained at 1000 �C, shown in

Fig. 2c (20 min) and Fig. 2d (30 min) exhibit several lar-

ger pores, indicating some cell coalescence. A significant

coalescence is also observed for the foam obtained after

60 min at 950 �C for a MnO2 content of 8.4 wt% (Fig. 2b):

since MnO2 is not the only source for oxygen, some gas

coming from the reduction of MnO2 into MnO is not useful

for the oxidation of SiC, but acts like a secondary foaming

gas (the decomposition of MnO2 into MnO may be

Fig. 1 Density/temperature/oxidation promoter plot for glass foams

from waste soda-lime glass (the numbers near the symbols refer to the

MnO2 content, in wt%—Triangles: 60 min; Circles: 30 min; Stars:

15 min)

J Porous Mater (2010) 17:359–365 361

123

exploited even as the only foaming reaction, as shown by

Ducman et al. [21]).

A fundamental criterion for evaluating foams obtained

by different processing conditions, as previously shown

[13], is the compressive strength. Classical models for

compressive strength of foams, provided by Gibson and

Ashby [22, 23], predict the dependence of strength (rcr) on

the flexural strength of the solid phase (rfs) and, above all,

on the relative density (qr), i.e. the ratio between bulk

density and true density, as a combination of exponential

and linear terms, as follows:

rcr

rfs

� 0:2ð/qrÞ3=2 þ ð1� /Þqr ð3Þ

The quantity (1 - U) expresses the fraction of solid in

the cell walls; if the foam is open-celled, the pores are fully

interconnected, with material only on the cell edges, so that

U = 1 (1 - U = 0) and the exponential term is dominant;

on the contrary, for a closed-cell foam, U is lower, with the

solid phase constituting mostly the cell walls, thus

enhancing the linear term. Glass foams, however, are not

perfect closed-cell foams. Previous investigations [10, 20,

24] showed that the strength is fitted by relatively high

values for the U parameter, especially for foams with a

poor homogeneity; in fact, inhomogeneous foams generally

feature thick and porous cell walls, possessing a low

mechanical strength.

If we consider the specific compressive strength, i.e. the

ratio between compressive strength and bulk density (the

true density is practically constant), foams with the same

density may possess different values, due to their homo-

geneity. Inhomogeneous foams, associated to high U val-

ues, are more sensible to the exponential term of Eq. 3, so

that they possess low specific compressive strength values.

As reported by Table 2 (reporting the properties of the

lightest foams, i.e. those which could be used as reference

for industrial production) the specific strength is effectively

maximized by the most homogeneous foams, i.e. those

obtained after 60 min at 950 �C and with a MnO2 content

not exceeding 5.6 wt%. With 5.6 wt% MnO2 the foaming

at 1000 �C for 20 min is equivalent to that at 950 �C for

60 min for the density, but not for the strength (there is a

decrease of specific strength of about 50%, not comprised

within the standard deviation).

The specific strength has a quite anomalous increase

(from 3.4 to 6.0 MPa cm3/g) when passing from 20 to

30 min at 1000 �C with 5.6 wt% MnO2. Although with a

poor statistical significance (as shown by Fig. 2 the two

foams are not homogeneous, so that they feature a large

data scatter), the increase could be attributed to the fact that

the glass foams partially crystallized. Figure 3 evidences

the formation of wollastonite (CaSiO3, ICDD PDF # 84-

0654), which effectively increases when passing from 20 to

30 min at 1000 �C (see the height of wollastonite main

peak, at 2h * 30�). The partial crystallization increases

the strength of the solid phase to be considered in Eq. 3,

reasonably due to the residual stresses associated to the

different coefficient of thermal expansion between crystals

Fig. 2 Optical

stereomicroscope images of

selected glass foams from waste

soda-lime glass

362 J Porous Mater (2010) 17:359–365

123

and glass matrix. The crystallization of wollastonite is

quite unusual for soda-lime glass: to our opinion the for-

mation of the specific phase is associated to the very high

specific surface of foams (wollastonite is a well-known

surface nucleating specie) and to the proximity of the

foaming temperature to the temperature range for wollas-

tonite formation (950–1000 �C) [25]). The introduction of

MnO2 could also contribute to the wollastonite formation,

if we consider that Mn ions may be incorporated by wol-

lastonite structure (giving origin, as an example, to busta-

mite Mn2þ2:25Ca0:75Si3O9 [26]); however, patterns with

different MnO2 content (not reported here for the sake of

brevity) did not show any significant variation of intensity

of wollastonite peaks.

The compressive strength values of the best foams, i.e.

those possessing the maximum values of specific strength,

fall in the range of those exhibited by commercial foams

[9]: due to the selection of processing conditions operated

by the microstructural analysis and the calculation of

specific strength, the products are effectively almost ready

for industrial application (which will be possible after large

scale production, to be realized in a specifically designed

kiln).

The approach exploited for waste soda-lime glass was

applied even to mixtures of glassy sand with F1 and F2

glasses. As shown by Fig. 4, mixtures with 50 wt% soda-

lime and 50 wt% F1 glass (SL50–F150) had a poor expan-

sion (the density exceeded 1.2 g/cm3); only mixtures with a

lower content of F1 glass, being 25 wt% (SL75–F125), led

to foams with densities comparable to those achieved with

waste soda-lime glass. The temperature for a substantial

foaming moved from 950 to 1000 �C; interestingly, also in

this case the same density is achievable with different time/

temperature combinations, and the effect of MnO2 is sig-

nificant at a relatively low temperature, for a relatively long

time.

Table 2 Compressive strength

data for selected glass foams

from waste soda-lime glass

Density

range

Bulk

density

(g/cm3)

MnO2

content

(wt%)

Foaming

temperature

(�C)

Soaking

time

(min)

Compressive

strength

(MPa)

Specific

strength

(MPa cm3/g)

[0.4 g/cm3 0.42 ± 0.06 2.8 1000 30 2.6 ± 0.6 6.2 ± 1.6

0.42 ± 0.01 0.7 950 60 3.6 ± 0.7 8.7 ± 1.7

0.41 ± 0.05 0.7 1000 30 2.1 ± 0.3 5.1 ± 1.0

0.3–0.4 g/cm3 0.40 ± 0.04 1.4 1000 30 2.6 ± 0.7 6.5 ± 1.9

0.37 ± 0.03 5.6 1000 30 2.2 ± 0.9 6.0 ± 2.5

0.36 ± 0.02 1.4 950 60 2.3 ± 0.2 6.4 ± 0.7

0.35 ± 0.07 2.8 950 60 2.6 ± 0.7 7.5 ± 2.5

\0.3 g/cm3 0.29 ± 0.01 5.6 1000 20 1.0 ± 0.3 3.4 ± 1.0

0.29 ± 0.01 5.6 950 60 1.7 ± 0.4 6.0 ± 1.4

0.22 ± 0.02 8.4 950 60 0.7 ± 0.1 3.0 ± 0.5

Fig. 3 X-ray diffraction patterns of selected glass-foams (MnO2

content: 5.6 wt%)

Fig. 4 Density/temperature/oxidation promoter plot for glass foams

from waste soda-lime glass mixed with F1 and F2 glasses (the

numbers near the symbols refer to the MnO2 content, in wt%—

Triangles: 60 min; Circles: 30 min)

J Porous Mater (2010) 17:359–365 363

123

The key reason for the increase of foaming temperature

is the tendency of F1 glass toward devitrification, visible

from the X-ray diffraction of SL75–F125, in Fig. 3,

foamed at 1000 �C for 60 min (with 5.6 wt% MnO2, like

the foams from SL glass). The more substantial crystal-

lization in the foam with F1 glass, compared to the foams

from only SL glass, is consistent with the fact that F1

glass has a calcium alumino-silicate composition (with

some B2O3), quite close to that for wollastonite glass–

ceramics [25]. Increases in the foaming temperature and

the proper mixing with soda-lime glass are necessary to

compensate the increases in apparent viscosity provided

by crystal inclusions.

Although still under investigation, the glass-ceramic

foams from mixtures of glassy sand with F2 glass dem-

onstrated interesting features. As shown by Fig. 3, the

mixture with 20 wt% F2 glass (SL80–F220) exhibits a

remarkable crystallization, at a lower temperature and with

a shorter soaking time than for the mixture with 25 wt% F1

glass (SL75–F125); Fig. 3 evidences also that a secondary

phase (sodium–aluminium silicate, Na(AlSiO4), ICDD

PDF # 81-2081) formed in addition to wollastonite.

Table 3 (again reporting the properties of the lightest

foams, i.e. those which could be used as reference for

industrial production) reveals that the mixture with F2

glass generally gives higher specific strength values than

that with F1 glass.

The differences in processing parameters and strength,

to our opinion, depend on a different combination of

foaming and crystallization. An indication of this behavior

may be found in Fig. 5: the cellular structure of SL75–F125

is composed by many round pores, i.e. pores formed in a

viscous mass before crystallization; the cellular structure of

SL80–F220, on the contrary, is composed of pores with an

irregular shape, modified by the crystallization during the

foaming. Foams from F1 glass possess larger pores, with

also some weakening secondary pores in the cell walls and

large openings (Fig. 5a); foams from F2 glass are less

homogeneous, but they feature smaller cells (Fig. 5b),

favorable to mechanical strength [23].

The foams with F1 and F2 glasses are quite comparable to

the high compressive strength foams obtained by Tulyaga-

nov et al. [17], prepared by mixing soda-lime glass with

small amounts of alkali earth aluminosilicate glass powder,

intrinsically prone to be crystallized to anorthite and diop-

side, and SiC at a concentration of 1 wt%. The best results

were obtained for a content of alkali earth aluminosilicate

glass of 3 or 5 wt%, leading to very strong foams (the

Table 3 Compressive strength data for selected glass foams from waste soda-lime glass mixed with F1 and F2 glasses

Composition Density

range

Bulk density

(g/cm3)

MnO2

content (wt%)

Foaming

temperature (�C)

Soaking

time (min)

Compressive

strength (MPa)

Specific strength

(MPa cm3/g)

SL75F125 [0.4 g/cm3 0.47 ± 0.06 0.7 1000 60 3.0 ± 0.7 6.5 ± 1.7

0.3–0.4 g/cm3 0.33 ± 0.04 1.4 1000 60 1.8 ± 0.4 5.3 ± 1.4

\0.3 g/cm3 0.28 ± 0.01 2.8 1000 60 1.3 ± 0.1 4.8 ± 0.4

0.24 ± 0.01 5.6 1000 60 1.0 ± 0.3 4.0 ± 1.3

SL80F220 [0.4 g/cm3 0.40 ± 0.04 8.4 900 30 2.2 ± 0.3 5.5 ± 0.9

0.3–0.4 g/cm3 0.35 ± 0.01 5.6 900 30 2.2 ± 0.4 6.3 ± 1.2

0.33 ± 0.03 5.6 950 30 2.1 ± 0.3 6.4 ± 1.1

Fig. 5 SEM micrographs of samples SL75F125 1000 �C, 60 min,

5.6 wt% MnO2 (a) and SL80F220 900 �C, 30 min, 5.6 wt% MnO2 (b)

364 J Porous Mater (2010) 17:359–365

123

specific strength exceeded 8 MPa cm3/g), while a more

substantial addition, 10 wt%, led to foams effectively sim-

ilar to those obtained from F2 glass mixed with glassy sand

(the specific strength was about 6.9 MPa cm3/g). Although

generally stronger, it must be noted that the foams obtained

by Tulyaganov et al. [17] were obtained by a two step

thermal treatment (heating at 5 �C/min up to 900 �C, hold-

ing for 30 min, further heating at 5 �C/min up to 950 �C and

holding for 30 min), much slower than the treatments here

presented; secondly, the ‘‘crystallizing glass’’ was not

directly available as a waste, like F1 and F2 glasses.

Even if the foams with F2 glass are not stronger than

those obtained from pure glassy sand, they possess a sig-

nificant advantage in the application as aggregates in

concrete. As shown in the literature [27, 28], while glass

foams may experience alkali–silica reaction in concrete

(which depends on the availability of amorphous silica in

the aggregates), partially crystallized foams are expected to

be less reactive [24].

4 Conclusions

We may conclude that:

1. The direct heating of glass powders, together with

suitable additives, at temperatures from 900 to

1050 �C, was successfully applied to waste soda-lime

glass, alone or mixed with wastes from the manufac-

turing of glass fibres, for the obtainment of glass

foams. The process is suitable to valorisation of waste

glasses, since it is particularly simple and economic,

especially if compared to the processes for high

compressive strength foams in the literature.

2. MnO2 effectively promotes the oxidation of SiC,

employed as a foaming agent for soda-lime glass, at

temperatures below 1000 �C; MnO2 refines the micro-

structure, in the sense that improves the gas evolution

in the glass mass, at relatively low temperatures;

3. The foaming of waste glasses is affected by secondary

phenomena, such as cell coalescence and partial devit-

rification of glass, more substantial for mixtures of soda-

lime glass with calcium alumino-silicate glasses;

4. Potential improvements in strength, associated to the

partial crystallization, are counterbalanced by the

weakening effect of inhomogeneous microstructures.

References

1. A. Mueller, S.N. Sokolova, V.I. Vereshagin, Construct. Build.

Mater. 22, 703 (2008). doi:10.1016/j.conbuildmat.2007.06.009

2. G. Scarinci, G. Brusatin, E. Bernardo, in Cellular ceramics,structure, manufacturing, properties and applications, ed. by M.

Scheffler, P. Colombo (Wiley-VCH, Weinheim, 2005), pp. 158–

176

3. P. Colombo, G. Brusatin, E. Bernardo, G. Scarinci, Curr. Opin.

Solid. State. Mater. Sci. 7, 225 (2003). doi:10.1016/j.cossms.

2003.08.002

4. E. Bernardo, G. Scarinci, S. Hreglich, Glass Sci. Technol. 78, 7

(2005)

5. W.O. Lytle, U.S. Patent 2,215,223, 1940

6. B.K. Demidovich, Production and application of glass foam(Nauka i Tekhnika, Minsk, 1972)

7. E.H. Haux, U.S. Patent 2,191,658, 1940

8. W.D. Ford, U.S. Patent 2,691,248, 1954

9. J. Hurley, Glass research and development final report: a UK

market survey for foam glass. (WRAP, The Waste and Resources

Action Programme, 2003), http://www.wrap.org.uk/downloads/

AUKMarketSurveyForFoamGlass.ed91e9c7.358.pdf, Accessed 8

Jan 2009

10. E. Bernardo, R. Cedro, M. Florean, S. Hreglich, Ceram. Int. 33,

963 (2007). doi:10.1016/j.ceramint.2006.02.010

11. http://www.sasil-life.com/pagine_UK/default_uk.html, Accessed

12 March 2009

12. http://www.enco.ch/glass.htm, Accessed 8 January 2009

13. A. Saburit Llaudis, M.J. Orts Tari, F.J. Garcıa Ten, E. Bernardo,

P. Colombo, Ceram. Int. (2008). doi:10.1016/j.ceramint.2008.

10.022

14. J.E. Post, Proc. Natl. Acad. Sci. USA 96, 3447 (1999). doi:

10.1073/pnas.96.7.3447

15. K.L. Berg, S.E. Olsen, Metall. Mater. Trans. 31B, 477 (2000)

16. G. Brusatin, G. Scarinci, L. Zampieri, P. Colombo, in Proceed-ings of the XIXth International Congress on Glass—ICG XIX,

vol. 2 (Society of Glass Technology, Edinburgh, 2001), pp. 17–18

17. D.U. Tulyaganov, H.R. Fernandes, S. Agathopoulos, J.M.F.

Ferreira, J. Porous. Mater. 13, 133 (2006)

18. H. Hojaji, Mater. Res. Soc. Proc. 136, 185 (1989)

19. A.A. Ketov, in Proceedings of the International Symposium onRecycling and Reuse of Glass Cullet, ed. by R.K. Dhir et al.

(Thomas Telford Books, Dundee, 2001), pp. 84–91

20. E. Bernardo, F. Albertini, Ceram. Int. 32, 603 (2006). doi:

10.1016/j.ceramint.2005.04.019

21. Ducman V, Kovacevic M (1997). Key Eng. Mater. 132–

136:2264. doi:10.4028/www.scientific.net/KEM.132-136.2264

22. L.J. Gibson, M.F. Ashby, Cellular solids, structure and proper-ties (Cambridge University Press, Cambridge, 1999), pp. 175–

231

23. E. Bernardo, P. Colombo, in Ceramic science and technology, ed.

by R. Riedel, I.-W. Chen, vol. 1 (Wiley-VCH, Weinheim, 2008),

pp. 407–442

24. E. Bernardo, J. Eur. Ceram. Soc. 27, 2415 (2007). doi:10.1016/

j.jeurceramsoc.2006.10.003

25. W. Holand, G.G. Beall, Glass–ceramic technology (The Ameri-

can Ceramic Society, Westerville, 2002), pp. 110–119

26. http://webmineral.com/data/Bustamite.shtml, Accessed 17 March

2009

27. S. Fotiadou, M.C. Limbachiya, A.N. Fried, J.J. Roberts, in Sus-tainable waste management and recycling of glass waste, ed. by

M.C. Limbachiya, J. Roberts (Thomas Telford Ltd, London,

2004), pp. 305–312

28. M.J.M. Moons, K. Van Breugel, in Sustainable waste manage-ment and recycling of glass waste, ed. by M.C. Limbachiya, J.

Roberts (Thomas Telford Ltd, London, 2004), pp. 197–204

J Porous Mater (2010) 17:359–365 365

123