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Glassceramics are polycrystalline materialscomposed of at least one crystalline phase and avitreous matrix phase, which is produced by thecontrolled crystallization. Wideranging propertiesof glassceramics can be modified in a predictableway by controlling the chemical compositions andheat treatment scheduleE163. AlzO3SiOzZrOz system is seldom reported due to the high meltingtemperature. ZrOz, TiOz and PzO5 are commonnucleating agents. In glassceramics, ZrO2 is an effective nucleating agent due to the characteristicsof high electrovalency and electric field intensity,which facilitate the accumulation of glass fabric,but the solubility of ZrOz in silicate glass system islow ( ~ 5 % , mass fraction). Chen et al¢781 reported that ZrO2 in glassceramics improved the mechanical properties, especially fracture toughnessKlc and wear resistance. But Liu et alE93 pointedout that ZrO2 used as nucleating agent individuallydid not induce bulk crystallization in KzOMgOSiO2 system. PiersonE1°3found that the solubility ofTiO2 was so high (2%20°~) that lots of hypomicrons were precipitated during reheating or cooling, and the hypomierons facilitated the mainphase to be precipitated from glass matrix. Doherty et alEu3 pointed out that TiO2 was beneficial tophase separation and the subsequent formation of

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Effects of nano silica on synthesis and properties of glass ceramics in

Debasis Pradip Mukherjee, Sudip Kumar Das ⁎

Department of Chemical Engineering, University of Calcutta, 92, A P C Road, Kolkata, 700 009, India

a b s t r a c t

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

Glass ceramics of composition 34SiO2–29Al2O3–25CaO–12CaF2(wt.%) was made by conventional melting and quenching process using either normal or nano-SiO2respectively 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-SiO2addition, 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-SiO2containing glass is lower than the normal SiO2containing 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

1 Introduction

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 CaF2as 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-SiO2in

concrete improved its mechanical properties[6–14] The nano-SiO2

has a uniform size and shape The use nano-SiO2may 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

2 Experimental procedure 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 0.014μ, 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 inter-nal 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

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

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

⁎ Corresponding author Tel.: +91 9830638908.

E-mail address: drsudipkdas@vsnl.net (S.K Das).

Contents lists available atSciVerse ScienceDirect Journal of Non-Crystalline Solids

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j n o n c r y s o l

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withα-Al2O3powder as reference material to evaluate the glass

crystal-lization 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

diffrac-tometers (PANalytical PW3040/60, The Netherlands) with Niﬁltered

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

rectan-gular 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

shrink-age 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],

Hv¼ 1:8544 P

where Hv is the Vickers hardness number (VHN) in kg/mm2, P is

the normal load in kg, and d is the average diagonal length of the

indentation in mm

3 Results and discussion

3.1 Differential thermal analysis (DTA)

The DTA curves for two different specimens BS and BNS at a heating

rate of 10 °C/min are shownFig 1(a)–(b) respectively One exothermic

peak was observed in both the specimens The exothermic peak

corresponds to wollastonite, anorthite and gehlenite Nano-SiO2affected

the glass transition temperature (Tg) and the crystallization peak

tem-perature (Tp) as shown inFig 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],

− ln 1−xð Þ ¼ ktð Þn

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

the reaction rate constant which is related to the absolute temperature

T, as given by Arrhenius type equation,

k¼ ν exp −RTE

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],

lnT

2

β ¼

E

where, Tpis 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(Tp/β) versus 1/Tpfor two glass samples are shown inFig 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 inTable 2 From the value of activation energy E, the Avrami parameter (n) is calculated by using the Augis–Bennett equation[22],

n¼2ΔT:5RT

2

Table 1

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

4.05 4.10 4.15 4.20 4.25 4.30

o C

-5 0 5 10 15 20 25 30

a

13.70 13.75 13.80 13.85 13.90

Temperature(oC)

895.14 o C b

-15 -10 -5 0 5 10 15

20

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

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

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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

dimen-sional 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 referenceﬁles 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 inFig 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),

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 inFig 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)

10.2 10.4 10.6 10.8 11.0 11.2 11.4

10.0

10.5

11.0

11.5

12.0

12.5

13.0

BNS BS

2 p

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

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›

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

Anorthite (CaAl2Si2O8) — A 00-70-0287 Gehlenite (Ca2Al2SiO7) — G 00-35-0755 Wollastonite (CaSiO3) — W 00-76-0186

a

850oC

950oC

1050oC

1150oC A

A A A A

W W

G G G

G G

2 (o)

A-Anorthite G-Gehlenite W-Wollastonit e

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

1150oC

1050oC

850oC

950oC

W

W A W A

WAW W

A W A

A-Anorthite G-Gehlenite W-Wollastonite

G

A WA

b

2 (o)

Fig 3 (a)–(b) X-ray diffraction patterns of the glass batches after heat treated at different

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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

tonite phase increased along with anorthite and gehlenite More

wollas-tonite 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],

where K = 0.94 (the Scherrer constant), λ = wavelength of the

X-ray radiation (Cu Kα = 0.154 nm), B = full width at half

maxi-mum (FWHM) andθ = Bragg angle of the XRD peak.Fig 4presents

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 theFig 5that 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-SiO2into the glass system (BNS) the

mean crystallite sizes is comparatively small other than the normal

Silica

3.3 Fourier transform infrared spectroscopy (FTIR)

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

ma-trix composed of SiO4tetrahedral connected at the corners to form a

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 ob-served at 3424 cm–1which may be due to the O–H stretching of the surface water and the peak at 1638 cm–1may be due to the deforma-tion 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 ab-sorption peak might be due to chemiab-sorptions of atmospheric CO2on the surface The peaks at 1144 cm–1and 1024 cm–1are assigned to the asymmetric stretching vibrations of the silicate tetrahedral network The peak at 1090 cm–1is attributed to the symmetric stretching vibra-tion of the Si\O\Si bonds, the band at 800 cm–1is associated symmet-ric 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 ob-served near 940 cm–1 is assigned to the stretching vibration of the

Si\O bond in the Si(OAl/Ca)2group 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–1to 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–1are attributed

to the spectrum of both the specimens with the presence of CaF

10

20

30

40

50

60

BS

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.

Wavenumbers (cm-1)

a

b

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

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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.

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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–1corresponds to the Si\O\Ca

bonds containing non-bridging oxygen and at 819 cm–1corresponds to

the stretching mode of the O\Si\O bonds[29–31]

3.4 Scanning electron microscopy (SEM)

Figs 6(a)–(d) and7(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

3.5 Physical measurements Fig 8showed 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/cm3respectively (Table 4) For sample BS, density increased with increasing in heat treatment temperature But sample BNS, den-sity 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 9andTable 4depict the shrinkage (%) and water absorption (%)

of the samples sintered in the temperature range of 850 °C–1150 °C, re-spectively 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 Tpthe glassy phase would have enough time for viscousﬂow and it leads to complete densiﬁcation[36]

3.6 Chemical measurements Fig 10shows 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 theﬁgure 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

2.90

2.92

2.94

2.96

2.98

3.00

3.02

3)

Temperature(oC)

BNS BS

Fig 8 Variation of density with different ceramization temperature of the glass

batches BS and BNS soaked for 1 h.

Table 4

Physical and mechanical measurement values of glass samples heat treated at different temperature.

0 2 4

BS

Temperature (oC)

10 12 14

16

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

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3.7 Mechanical measurements

Fig 11shows the hardness of the heat-treated glass ceramic

spec-imens 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 fromTable 4that Vickers hardness

values decrease with heat treatment temperature and reaches

mini-mum 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

4 Conclusions Glass ceramic systems of 34SiO2–29Al2O3–25CaO–12CaF2have been prepared by used normal SiO2and 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 crystal-lite sizes of wollastonite (CaSiO3) were in the range from 17 to 49 nm for nano-SiO2and for normal SiO2range from 23 to 63 nm Increasing the heat treated temperature from 850 to 1150 °C resulted in an in-crease of crystallite size for both the cases The nano-SiO2containing 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

Acknowledgments The authors would like to thank the UPE scheme of University Grants Commission and the Center for Research in Nanoscience and Nanotech-nology (CRNN), University of Calcutta for theﬁnancial 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

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0.2

0.4

0.6

0.8

1.0

1.2

BNS BS

Temperature (oC)

1.0 1.1 1.2 1.3 1.4

Fig 10 Chemical resistance of the two glass batches and dependence on the composition

and the heat treatment temperature: NaOH and HCl.

5.0

5.2

5.4

5.6

5.8

6.0

Temperature (oC)

BNS BS

Fig 11 Variation of Vickers hardness (Hv) with different heat treatment temperature

for BS and BNS samples.

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