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Journal of Non-Crystalline Solids 368 (2013) 98–104

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Journal of Non-Crystalline Solids
journal homepage: www.elsevier.com/ locate/ jnoncrysol

Effects of nano silica on synthesis and properties of glass ceramics in
SiO2–Al2O3–CaO–CaF2 glass system: A comparison
Debasis Pradip Mukherjee, Sudip Kumar Das ⁎
Department of Chemical Engineering, University of Calcutta, 92, A. P. C. Road, Kolkata, 700 009, India

a r t i c l e

i n f o

Article history:
Received 7 December 2012
Received in revised form 8 March 2013
Available online 9 April 2013
Keywords:
Glass ceramics;
Nano-SiO2;
Crystallization;
DTA;
SEM

a b s t r a c t
Glass ceramics of composition 34SiO2–29Al2O3–25CaO–12CaF2 (wt.%) was made by conventional melting and
quenching process using either normal or nano-SiO2 respectively. The glasses were characterized by differential
thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning

electron microscopy (SEM). The crystallization, microstructure, mechanical and chemical properties were
compared for the two systems. With nano-SiO2 addition, the crystallization peak temperature (Tp) decreases,
activation energy (E) and Avrami parameter (n) have very little change, and the mechanism of crystallization
of the glass ceramics changed from surface crystallization to two-dimensional crystallization. The crystallite
size of nano-SiO2 containing glass is lower than the normal SiO2 containing glass. Introduction of nano-SiO2
particles in glass ceramics gives higher Vickers hardness, shrinkage, lower water absorption, and higher acid
resistance than the normal silica containing glass ceramics, thus making it more useful for industrial building,
internal and external wall facing and tiles applications.
© 2013 Elsevier B.V. All rights reserved.

1. Introduction

2. Experimental procedure

There is considerable interest in the glass ceramic materials for their
clinical and household applications [1]. Glass ceramics can be prepared
either by heat treatment of preformed glass or by sintering techniques
[2,3]. However, the properties depend on the composition of phases
and the microstructure developed during the manufacturing process
[4]. The basic materials are SiO2–Al2O3–CaO and the nucleating agent,
which serve the proper nucleation and crystallization. It is observed
that the use of CaF2 as a nucleating agent in this system gives better
crystallization and microstructure [4].The physical properties like
strength, permeability, chemical resistance and Vickers hardness are
depending on its structure.
The nano-SiO2 has drawn much attention as its application in
industries like the production of pharmaceuticals, pigments and
catalyst etc, [5]. Researchers show that the addition of nano-SiO2 in
concrete improved its mechanical properties [6–14]. The nano-SiO2
has a uniform size and shape. The use nano-SiO2 may provide more

homogeneous distribution within the glass ceramic and hence
enhance properties like hardness, chemical resistance, shrinkage
and water absorption etc. This paper deals with the preparation
of SiO2–Al2O3–CaO–CaF2 glass ceramics using normal silica (BS)
and nano-SiO2 (BNS) and compared their characteristic, physical,
chemical and mechanical properties.

The glass batches with weight percent composition (Table 1) were
prepared using high-purity chemicals of Calcium carbonate, CaCO3
(99.9%, Merck Specialties Private Limited, India), alumina, Al2O3
(99.3%, Merck Specialties Private Limited, India), silica, SiO2 (particle
size 40–150 mesh, 99.8%, Merck Specialties Private Limited, India),
calcium fluoride CaF2 (99.0%, Merck Specialties Private Limited,
India) and nano-SiO2 (particle size 0.014 μ, 99.9%, Sigma-Aldrich,
St. Louis, MO, USA) by the conventional melt-quench technique.
The samples have been designated as BS and BNS respectively. About
100 g of glass batch was mixed thoroughly by attrition mill and then
melted in an alumina crucible in an electrically heated furnace at
1450 °C and kept at this temperature for 1 h in air with intermittent
stirring. The glass melt was poured into a preheated iron mold to make
glass block, followed by annealing at 600 °C for 1 h to removed the internal stresses of the prepared glass followed by natural cooling to room
temperature. The as-prepared annealed block was shaped into desired
dimensions (50 mm × 5 mm × 4 mm) by cutting machine (Buehler,
Lake Bluff, IL). These cut samples were subjected in heat treatment at a
rate 5 °C/min at temperature range from 850 °C to 1150 °C and soaked
for 1 h.

⁎ Corresponding author. Tel.: +91 9830638908.
E-mail address: (S.K. Das).
0022-3093/$ – see front matter © 2013 Elsevier B.V. All rights reserved.

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2.1. Measurement and characterization techniques
The thermal behavior of the glasses was evaluated by differential
thermal analyzer (Pyris Diamond TG/DTA, PerkinElmer, Singapore) in
nitrogen atmosphere (150 ml/min) at constant heating rate 10 °C/min


D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

99

30

4.30

Table 1
Chemical composition of the investigated glass (wt.%).

a

CaO

Al2O3

SiO2

Nano-SiO2

CaF2

BS
BNS

25
25

29
29

34
–

–
34

12
12

25

4.25

20

H v ¼ 1:8544 Â

P
d2

ð1Þ

where Hv is the Vickers hardness number (VHN) in kg/mm 2, P is
the normal load in kg, and d is the average diagonal length of the
indentation in mm.
3. Results and discussion

The DTA curves for two different specimens BS and BNS at a heating
rate of 10 °C/min are shown Fig. 1 (a)–(b) respectively. One exothermic
peak was observed in both the specimens. The exothermic peak
corresponds to wollastonite, anorthite and gehlenite. Nano-SiO2 affected
the glass transition temperature (Tg) and the crystallization peak temperature (Tp) as shown in Fig. 1(b). It can be seen that the crystallization
peak temperature occurred at nearly 951 °C for BS and 895 °C for BNS.
The kinetics of crystal growth can be described from the Johnson–
Mehl–Avrami (JMA) equation [18–21],
n

4.15

o
951.03 C

10
5

4.10

0
4.05
500

600

700

800

900

-5
1000

Temperature(oC)
13.90

b

20
15

13.85

Weight (%)

10
13.80

5

o
895.14 C

0

13.75
-5
-10

13.70
500

600

700

800

900

-15
1000

Temperature(oC)
Fig. 1. (a)–(b) DTA curves of the two glass batches at a heating rate at 10 °C/min.

the reaction rate constant which is related to the absolute temperature
T, as given by Arrhenius type equation,


E
k ¼ ν exp −

RT

ð2Þ

where, v is the frequency factor, R gas constant and E activation energy
of crystal growth. From Eqs. (1) and (2), non–isothermal crystallization
kinetics of glass can be described by the expression [17–20],

3.1. Differential thermal analysis (DTA)

− lnð1−xÞ ¼ ðkt Þ

15

Heat flow endo down (mW)

with α-Al2O3 powder as reference material to evaluate the glass crystallization peak temperature (Tp). 20 mg. of glass samples were taken in
platinum crucible and heated at the rate of 5, 10, 15 and 20 °C/min in
TG/DTA to study the kinetics of crystallization and also to calculate the
activation energy using Kissinger equation and Avrami parameter
using Augis–Bennett equation. Precipitated crystalline phases present
in the heat treated glass ceramics were identify by using X-ray diffractometers (PANalytical PW3040/60, The Netherlands) with Ni filtered
Cu Kα X-rays and a scanning speed of 1°/min. The XRD pattern was
recorded within Bragg angle from 5° to 80° 2θ range. The FTIR spectra
of the heat treated glasses were recorded using a Fourier transform
infrared spectrometer (Alpha FTIR, Bruker, Germany), on potassium
bromide (KBr) pellets prepared by mixing of 2 mg samples to 20 mg
KBr. The microstructures of the samples were carried out by scanning
electron microscope (FEI-QUANTA-200, the Netherland) after polishing
and then chemically etched using 10% HF solution for 15–20 s.

The densities of ceramized glasses were measured via the Archimedes'
method. The chemical resistance was estimated by immersing the rectangular specimens (50 mm × 5 mm × 4 mm) into 150 ml of 0.1 N NaOH
and 0.1 N HCl solutions and reheated at 95 °C for 1 h. The linear shrinkage was calculated from the dimension of bulk and sintered samples.
Water absorption was evaluated by the ISO-standard 10545-3, 1995,
(i.e., weight gain of the samples after immersion into boiling water for
2 h) [15].
The hardness was measured by taking micro-indentation on the
polished surface of the samples. Using 160 microhardness testers
(Carl Zeiss Jena, Germany) equipped with a conical Vickers indenter
at an indent load of 40 g. Ten indents were taken for each sample
with identical loading condition and average of this was used to
calculate the hardness using the standard equation for the Vickers
geometry as [16,17],

Weight (%)

4.20

Heat flow endo down (mW)

Batches

ð1Þ

where x is the volume fraction of crystallized phase at time t, n is the
Avrami exponent related to the mechanism of crystallization, and k is

2

ln

Tp
E
E
¼
þ ln
RT p
Rν
β

ð3Þ

where, Tp is the crystallization peak maximum temperature of the DTA
curve, β heating rate of DTA, R gas constant and E activation energy of
crystal growth. The plots of ln(Tp2/β) versus 1/Tp for two glass samples
are shown in Fig. 2, they are linear in nature. These values of the E and
ν are calculated from the intercept and slope of these straight lines and
reported in Table 2. From the value of activation energy E, the Avrami
parameter (n) is calculated by using the Augis–Bennett equation [22],
2

n¼

2:5 RT p
Â
ΔT
E

ð4Þ

D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

13.0

Table 3
JCPDS files used to identify the crystalline phase formed at different temperatures.

2
ln( T p /

12.0

11.5

11.0

10.5

10.0
10.2

10.4

10.6

10.8

11.0

11.2

11.4

(1/Tp) x104
Fig. 2. Variation of ln(Tp2/β) vs. 1/Tp for BS and BNS glass batches.

where, ΔT is the full width of the exothermic peak at half maximum
intensity. The Avrami exponent (n) depends upon the actual nucleation
and crystal growth mechanism. According to the JMA theory, Avrami
exponent (n) is also related to crystallization pattern, n ≅ 2 means that
the surface crystallization dominants the overall crystallization, n ≅ 3
means two dimensional crystallization, n ≅ 4 means that three dimensional crystallization for bulk materials [23–25]. Table 2 shows the
Avrami exponents that were 2.69 and 2.85 respectively, which are
close to 3, and this means that bulk nucleation and two dimensional
growths occur for the glass-ceramics.
3.2. X-ray diffraction analysis (XRD)
The JCPDS reference files are used to identify the crystal phases
formed in the glass ceramics batches are shown in Table 3. In BS,
at 850 °C, peaks of anorthite (CaAl2Si2O8) and wollastonite (CaSiO3)
appeared as major phases. The intensity and amount of this phases
increases with increasing sintering temperature as shown in Fig. 3(a).
At 950 °C, several peaks of anorthite at 23.7° (d = 3.7389 Å), 27.2°
(3.2737 Å), 28.0° (3.1949 Å), 31.1° (2.8775 Å), 39.1° (2.2992 Å), 43.0°
(2.1076 Å) due to diffractions from the triclinic form (cell constants
a = 8.186 Å, b = 12.876 Å, c = 14.182 Å; JCPDS Card No. 70-0287)
wollastonite at 29.3° (3.0363 Å), 29.9° (2.9901 Å), 43.9° (2.0720 Å),
48.9° (1.8661 Å) due to diffractions from the triclinic form (a = 7.94 Å,
b = 7.32 Å, c = 7.07 Å; JCPDS Card No. 76-0186) and a new phase,
gehlenite (Ca2Al2SiO7) at 10.2° (8.6844 Å), 17.7° (4.9930 Å), 59.5°

(1.5650 Å), and 67.9° (1.3790 Å) due to diffractions from the tetragonal
form (a = 7.6858 Å, c = 5.0683 Å; JCPDS Card No. 35-0755) appeared.
At 1050 °C, peaks of anorthite at 24.1° (3.6369 Å), 27.3° (3.2672 Å),

Table 2
DTA for the two glass specimen at different heating rates.
Batch no

Heating rate
(β) (°C/min)

Crystallization
peak temperature
(Tp) (K)

Activation
energy
(kJ mol−1)

Avrami
exponent (n)

‹n›

BS

5
10
15
20

5
10
15
20

931.05
951.03
963.06
971.01
883.12
895.14
904.11
911.09

293.17

2.50
2.57
2.63
2.67
2.66
2.73
2.78
2.83

2.69

BNS

305.21

Crystal phase

JCPDS reference no

Anorthite (CaAl2Si2O8) — A
Gehlenite (Ca2Al2SiO7) — G
Wollastonite (CaSiO3) — W

00-70-0287
00-35-0755
00-76-0186

27.9°(3.1920 Å), 31.0° (2.8782 Å), 39.5° (2.3013 Å), 42.9° (2.1061 Å)
wollastonite at 29.4° (3.0381 Å), 29.8°(2.9893 Å), 43.6° (2.0730 Å),
47.8° (1.8645 Å) and gehlenite at 10.8° (8.7139 Å), 18.0° (5.0035 Å),
21.4°(4.1431 Å), 57.9° (1.5926 Å), 60.1° (1.5202 Å), 68.3° (1.3767 Å)
appeared along with the anorthite and wollastonite. At 1150 °C, there
are no such changes in the peak intensity but the sharpness of the
peaks has been increased.
In BNS, at 850 °C, peaks of anorthite (CaAl2Si2O8) and wollastonite
(CaSiO3) appeared at 38.3° (2.3607 Å) and 44.5° (2.1445 Å) as a major
phase as shown in Fig. 3(b). At 950 °C, peaks of gehlenite (Ca2Al2SiO7)
appeared at 10.2° (8.6844 Å), 24.6° (3.6315 Å), 61.0° (1.5189 Å) and
68.1° (1.3770 Å) along with anorthite and wollastonite. At 1050 °C,
one fresh peak of wollastonite at 22.0° (3.9369 Å) appeared along with
anorthite, wollastonite and gehlenite but a peak of gehlenite at 10.2°
disappeared. From 1050 °C to 1150 °C, there are changes in the intensity
of the peaks of wollastonite at 16.2° (5.4668 Å), 29.1° (3.0733 Å), 37.1°
(2.4122 Å), 52.2° (1.7579 Å) and anorthite at 17.4° (5.0921 Å), 19.9°

(4.4129 Å), 24.0° (3.7206 Å), 36.9° (2.4385 Å), 44.3° (2.0445 Å)
W

a
G

Intensity (a.u.)

BNS
BS

12.5

G G

W
A A
A A

A-Anorthite
G-Gehlenite
W-Wollastonit e
A W
A W

GG

G
o

1150 C

o

1050 C
o

950 C
o

850 C

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

2 (o)
W

b
WA A

A-Anorthite
G-Gehlenite
W-Wollastonite

A W
W
AW
G A W A WAWW

G

G
o
1150 C

Intensity (a.u.)

100

o
1050 C

o

950 C
o
850 C

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
2.85

2 (o)
Fig. 3. (a)–(b) X-ray diffraction patterns of the glass batches after heat treated at different
temperature soaked for 1 h (a) BS and (b) BNS.


D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

Kλ
B cosθ

ð5Þ

where K = 0.94 (the Scherrer constant), λ = wavelength of the
X-ray radiation (Cu Kα = 0.154 nm), B = full width at half maximum (FWHM) and θ = Bragg angle of the XRD peak. Fig. 4 presents
the calculated mean crystallite sizes with acceptable errors, as a
function of temperature of the BS and BNS samples after heat treated
for 1 h. It is clear from the Fig. 5 that at 850 °C, minor quantities of
small crystal with sizes of approximately 23 nm and 17 nm for BS and
BNS respectively have been observed. After heat treated at temperature
950 °C, a number of much larger crystals with the average size of 31 nm
of sample BS and 21 nm of sample BNS are observed. After heat treated
at temperature 1050 °C and 1150 °C, the crystallite size increased with
increase in the heat treated temperature with sizes in range 42 to
63 nm for sample BS and 27 to 49 nm of sample BNS within the limits
of errors.
In the whole temperature range studied, a steady increase of the
crystallite size with the heat treated temperature is observed and
it is observed that using nano-SiO2 into the glass system (BNS) the
mean crystallite sizes is comparatively small other than the normal
Silica.
3.3. Fourier transform infrared spectroscopy (FTIR)

Mean crystallite size (nm)

BNS
BS

60
50

40
30
20
10
800

900

1000

1100

1400

1200

1000

800

600

400

Wavenumbers (cm-1)
o

b

850 C

o
950 C
o
1050 C
o
1150 C

1400

1200

1000

800

600

400

Wavenumbers (cm-1)
Fig. 5. (a)–(b) FTIR spectra of glass batches after heat treatment at different temperature
soaked for 1 h (a) BS and (b) BNS.

Fourier transform infrared spectroscopy (FT-IR) was carried out in
order to obtain more structural information on both the specimen BS
and BNS. The silica-based glass structure is generally viewed as a matrix composed of SiO4 tetrahedral connected at the corners to form a

70

o

850 C
o
950 C
o
1050 C
o
1150 C

Transmittance (%)

d¼

a

Transmittance (%)

appeared along with gehlenite. At 1150 °C, there are no changes in
intensity, as sintering temperature increased the sharpness of the
peaks has been increased.
The formations of anorthite and wollastonite are major phases in BS
and BNS respectively, but both the phases appeared simultaneously
along with gehlenite. In general the gehlenite phase appears at a higher
crystallization peak temperature containing glass ceramics. In BS the
crystalline peak temperature is higher than that of BNS. Similar results
are also observed by another researcher [26]. In BNS, with the increased
in sintering temperature, the formation of high peak intensity wollastonite phase increased along with anorthite and gehlenite. More wollastonite crystal phases in BNS indicated higher mechanical strength [27].
In order to determine the mean crystallite sizes of the wollastonite
(CaSiO3) phases calculated by Scherrer equation [28],

101

1200

Temperature(oC)
Fig. 4. Mean crystallite sizes calculated by Scherrer equation from XRD-line broadening as
a function of the temperature of the samples BS and BNS, heat treated at 850–1150 °C
soaked for 1 h.

continuous tri-dimensional network with all bridging oxygen (BOs).
Fig. 5(a)–(b) illustrates the FTIR spectra of the specimen BS and BNS
sintered at various temperatures. At 850 °C–950 °C, the peak was observed at 3424 cm –1 which may be due to the O–H stretching of the
surface water and the peak at 1638 cm –1 may be due to the deformation mode of H\O\H bond or due to the bending of the surface O-H
group [29]. The small absorption peaks at about 1550 and 1610 cm –1
are related to CO group and molecular water, respectively. The CO absorption peak might be due to chemisorptions of atmospheric CO2 on
the surface. The peaks at 1144 cm–1 and 1024 cm–1 are assigned to the
asymmetric stretching vibrations of the silicate tetrahedral network.
The peak at 1090 cm–1 is attributed to the symmetric stretching vibration of the Si\O\Si bonds, the band at 800 cm–1 is associated symmetric stretching vibration of Si\O\Si and one at around 464 cm–1 is
assigned as rocking vibration Si\O\Si bonds [30–32]. The peak observed near 940 cm–1 is assigned to the stretching vibration of the
Si\O bond in the Si(OAl/Ca)2 group containing non bridging oxygen.
The Si(OAl/Ca)2 group is a silicon-oxygen tetrahedral that has two
corners shared with aluminum-oxygen or calcium-oxygen polyhedral
[33,34]. The peaks at 1030 cm–1 to 1080 cm –1 is identified to the
vibration of the Si(OAl/Ca) group. The presence of wollastonite in the
(BS and BNS) specimens is indicated by the spectra of 1060 cm–1,
900 cm–1, 560 cm–1. The peaks at 650 cm–1,648 cm–1 are attributed
to the spectrum of both the specimens with the presence of CaF2


102

D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

Fig. 6. (a)–(d) SEM micrograph of BS glass after heat treatment at different heat treatment temperature (a) 850 °C, (b) 950 °C, (c) 1050 °C and (d) 1150 °C soaked for 1 h.

Fig. 7. (a)–(d) SEM micrograph of BNS glass after heat treatment at different heat treatment temperature (a) 850 °C, (b) 950 °C, (c) 1050 °C and (d) 1150 °C soaked for 1 h.


D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

103

3.02

16

Water Absorption (%)

2.98
2.96
2.94

6

BNS
BS

14
4
12

2

BNS
BS

2.92

Shrinkage (%)

Density (gm/cm3)

3.00

10
0

2.90
800

900

1000

1100

800

1200

1000

Temperature

Temperature(oC)
Fig. 8. Variation of density with different ceramization temperature of the glass
batches BS and BNS soaked for 1 h.

900

1100

1200

(oC)

Fig. 9. Properties of the two glass batches and dependence on the composition and the
heat treatment temperature: water absorption and shrinkage.

3.5. Physical measurements
components of wollastonite [35]. At 1050 °C and 1150 °C in BNS
specimen, new vibration bands appeared at 975 cm –1, 915 cm–1, and
819 cm–1. Band of 975 cm –1 and 915 cm–1 corresponds to the Si\O\Ca
bonds containing non-bridging oxygen and at 819 cm–1 corresponds to
the stretching mode of the O\Si\O bonds [29–31].

3.4. Scanning electron microscopy (SEM)
Figs. 6(a)–(d) and 7(a)–(d) show the micrograph of specimen BS
and BNS after heat treated at 850 °C to1150°C temperatures for 1 h.
The sample BS formed large size of needle like crystals at 1050 °C
(Fig. 6(c)) and also showed the surface cracks. Similar observations

were reported by other researchers [26,27]. Fig. 6 (d) showed that,
at 1150 °C specimen BS are crystallized, and that many acicular grains
with long axis were observed. This acicular characteristic, a typical
microstructural morphology in wollastonite is clear in specimen BS.
The microstructure of BNS specimens at low temperature (850 °C)
heat treatment showed very small inter-stars phase or small white
spheres like crystal structures distributed around the surface of the
glass sample, the crystallization is observed to start at surface. Sample
BNS heated at 850 °C–1150 °C for 1 h exhibited a large number of
slightly bigger inter-stars phase crystals (Fig. 7(b), (c), (d)) compared
to that of at 850 °C (Fig. 7(a)). As the higher temperature the conditions
for nucleation and formation of new crystalline phase, i.e. gehlenite is
favorable and microstructure with good crystallinity appear. Fig. 7(d)
showed the gehlenite crystal. As the temperature increased from 850 °C
to 1150 °C, the crystal size increased along with the aspect ratio, similar
observations also observed by Scherrer calculation in connection with
XRD analysis.

Fig. 8 showed the densities of as prepared glass ceramuics, BS
and BNS, heat treated at 850–1150 °C for 1 h were about 3.01 and
2.92 g/cm 3 respectively (Table 4). For sample BS, density increased
with increasing in heat treatment temperature. But sample BNS, density achieves the maximum value (2.99 g/cm3) at 1050 °C, beyond this
the density decreased with increasing the heat treatment temperature.
The decrease in density may be attributed to the formation of gehlenite
crystalline phase and propagation of a large number of slightly bigger
inter-stars phase crystals interlocked with each other accompanied by
crystal growth. This has been proofed by the SEM observations.
Fig. 9 and Table 4 depict the shrinkage (%) and water absorption (%)
of the samples sintered in the temperature range of 850 °C–1150 °C, respectively. It can be noted that the increase in sintering temperature
from 850 °C–1150 °C reduced the linear shrinkage of the both samples,

which is probably due to volatility of these glass ceramics. In BS the
crystallization peak temperature (Tp) is more than compared to BNS,
hence the sinterability depends on the Tp, i.e., with increase in Tp the
glassy phase would have enough time for viscous flow and it leads to
complete densification [36].

3.6. Chemical measurements
Fig. 10 shows the chemical resistance, i.e., percentage of weight loss
in NaOH and HCl test of glass specimen BS and BNS after sintered at
different temperature. It is clear from the figure that BNS is more acid
resistant than BS whereas BS is more alkali resistant than BNS. Being
more acid resistant of BNS is due to presence of more wollastonite
phases.

Table 4
Physical and mechanical measurement values of glass samples heat treated at different temperature.
Batch no

BS

BNS

Temperature

Density

Water absorption

Shrinkage

Microhardness (Hv)

(°C)

(g/cm3)

(%)

(%)

(GPa)

850
950
1050
1150
850
950
1050
1150

2.92
2.95
2.97
3.01
2.93
2.97
2.99
2.98

6.25
4.12
1.51
0.53
5.091
1.925
0.26
0.04

±
±
±
±
±
±
±
±

0.002
0.002
0.003
0.002
0.003
0.003
0.003
0.003

±
±
±

±
±
±
±
±

0.31
0.20
0.07
0.02
0.25
0.19
0.01
0.01

10.012
12.098
12.568
12.992
15.235
15.623
15.931
15.986

±
±
±
±
±
±

±
±

0.13
0.12
0.19
0.21
0.15
0.16
0.16
0.16

5.57
5.41
5.29
5.45
5.94
5.81
5.78
5.87

±
±
±
±
±
±
±
±

0.03
0.03
0.02
0.02
0.03
0.03
0.04
0.03


104

D.P. Mukherjee, S.K. Das / Journal of Non-Crystalline Solids 368 (2013) 98–104

1.2

4. Conclusions
BNS
BS 1.4

1.0

1.2

0.6

1.1

0.4
0.2

800

HCL

NaOH

1.3
0.8

900

1000

1100

1.0
1200

Temperature (oC)
Fig. 10. Chemical resistance of the two glass batches and dependence on the composition
and the heat treatment temperature: NaOH and HCl.

Microhardness, Hv, (GPa)

Acknowledgments
The authors would like to thank the UPE scheme of University Grants
Commission and the Center for Research in Nanoscience and Nanotechnology (CRNN), University of Calcutta for the financial support. One of
the authors, Debasis Pradip Mukherjee thanks the Center for Research
in Nanoscience and Nanotechnology (CRNN), University of Calcutta,
Kolkata, India, for providing the fellowship.

6.0

5.8
BNS
BS

5.6

References
[1]
[2]
[3]
[4]
[5]

5.4

5.2

5.0
800

Glass ceramic systems of 34SiO2–29Al2O3–25CaO–12CaF2 have been
prepared by used normal SiO2 and nano-SiO2. The glass crystallization
peak temperature (Tp) is lowered in nano silica containing glass system.
XRD analysis conclusively proved that introduction of nano silica in the
glass ceramic system wollastonite and anorthite crystal phases are
more than the glass ceramic containing normal silica. The mean crystallite sizes of wollastonite (CaSiO3) were in the range from 17 to 49 nm
for nano-SiO2 and for normal SiO2 range from 23 to 63 nm. Increasing

the heat treated temperature from 850 to 1150 °C resulted in an increase of crystallite size for both the cases. The nano-SiO2 containing
glass ceramics gives superior physical and mechanical properties, and
also showed the improvement of microstructure properties, hence is
suitable for industrial building, internal and external wall facing and
tiles applications.

900

1000

1100

1200

Temperature (oC)
Fig. 11. Variation of Vickers hardness (Hv) with different heat treatment temperature
for BS and BNS samples.

[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]

3.7. Mechanical measurements

Fig. 11 shows the hardness of the heat-treated glass ceramic specimens BS and BNS are measured by acquiring micro-indentation at an
indent load of 40 g and the average diagonal length of the hardness
impression is calculated. It is clear from Table 4 that Vickers hardness
values decrease with heat treatment temperature and reaches minimum at 1050 °C and then increases with temperature at 1150 °C.
But it is lower than the 850 °C values for both the cases. At lower
temperature formation of anorthite and wollastonite phases is due to
the higher Vickers hardness values. At 1150 °C the Vickers hardness
increases might be due to the ghelenite crystal phase. The maximum
hardness of 5.9 GPa and 505 GPa is observed in for BNS and BS samples
at 850 °C heat treatment temperature.
3.8. Uses
Nano-SiO2 containing glass gives superior physical, chemical
and mechanical properties, hence is suitable for industrial building,
internal and external wall facing and tiles applications.

[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]

[31]
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