http://www.diva-portal.org

This is the published version of a paper published in Journal of Asian Ceramic Societies.

Citation for the original published paper (version of record):

Mukherjee, D P., Kumar Das, S. (2016)

Influence of TiO2 content on the crystallization and microstructure of machinable glass-ceramics.

Journal of Asian Ceramic Societies, 4(1): 55-60

http://dx.doi.org/10.1016/j.jascer.2015.11.004

Access to the published version may require subscription.

N.B. When citing this work, cite the original published paper.

Permanent link to this version:http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-50171

Im

DD

a

ARRAA

KMHGTM

1

tcimnfncPcarha

oS

(

C

h2

Journal of Asian Ceramic Societies 4 (2016) 55–60

Contents lists available at ScienceDirect

Journal of Asian Ceramic Societies

HOSTED BY

j ourna l ho me page: www.elsev ier .com/ loca te / jascer

nfluence of TiO2 content on the crystallization and microstructure ofachinable glass-ceramics

ebasis Pradip Mukherjee ∗, Sudip Kumar Dasepartment of Chemical Engineering, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India

r t i c l e i n f o

rticle history:eceived 24 August 2015eceived in revised form 22 October 2015ccepted 10 November 2015vailable online 4 December 2015

eywords:icrostructure-finalardness

a b s t r a c t

Glasses based on the SiO2–Al2O3–MgO–K2O–B2O3–MgF2 system added with TiO2 were synthesizedand characterized by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. The resultsshowed that by increasing the TiO2 content, glass transition temperature (Tg), both the crystallizationpeak temperature (Tp

I and TpII) and activation energy (E) increased. The interconnected large blocky

card-like crystals were identified as fluorophlogopite as a major crystalline phase for all three glass-ceramic specimens by (XRD) and subsequently confirmed by SEM. The Vickers hardness (Hv) value forglass-ceramic specimens decreases with progressively increasing TiO2 content (1–10 wt%) and Titania

lass ceramicsiO2

achinability

containing MGT-3 glass-ceramic specimen with interconnected large blocky card-like fluorophlogopitemica crystals possess lower Hv (4.26 GPa) as well as good machinability (m = 0.12) useable for machinableapplications. The study shows that Titania promoted initial crystallization of glass and can be used as aneffective nucleting agent.

© 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by

. Introduction

Glass-ceramics materials are polycrystalline solids, prepared byhe controlled crystallization technique. After crystallization pro-ess of the mica composition based glass through heat treatment,nterconnected mica crystals are developed in whole the glass

atrix where the main crystalline phase is synthetic fluormica,amed fluorophlogopite. Crystallization is a thermodynamically

avorable and kinetically controlled process [1]. The variousucleating agents are generally added into the glass to inducerystallization. Beall and his research group [2] used TiO2, ZrO2,2O5, Ta2O5, Fe2O3, and F as heterogeneous nucleating agents forrystallization of various silicate glass systems. These nucleatinggents either accrues in a specific microphase of the phase sepa-ated base glass or support the phase separation. Cormier et al. [3]ave studied the role of different amount of TiO2 in magnesiumluminosilicate glass. Peixin et al. [4] have studied the influence

∗

Corresponding author. Present address: Glass Technology Group, Departmentf Built Environment and Energy Technology, Linnaeus University, SE-351 95 Växjö,weden. Tel.: +46 769920147.

E-mail addresses: drdebasispmukherjee@gmail.com, debasis.mukherjee@lnu.seD.P. Mukherjee).

Peer review under responsibility of The Ceramic Society of Japan and the Koreaneramic Society.

ttp://dx.doi.org/10.1016/j.jascer.2015.11.004187-0764 © 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Produc

Elsevier B.V. All rights reserved.

of TiO2 and ZrO2 on the crystallization of glass with the chemicalcomposition of 45MgO–20B2O3–35SiO2 (wt%). Crystallization pro-cess is generally affected by nucleating agent via two mechanisms.At first, it can support the crystallization by forming a metastableliquid–liquid phase separation, which have to be the starting pointfor the internal crystallization of glass [1]. Secondly, small crys-talline precipitates containing titanium ion or zirconium ion canalso act as heterogeneous nucleation sites for further crystallizationof the glass matrix [1,5]. Cheng et al. [6] studied the crystallizationkinetics of a glass based on one type of mica, NaMg3AlSi3O10F2,with the addition of TiO2 as nucleating agent. After crystallizationprocess of the mica composition based glass system through heattreatment, interconnected mica crystals are developed in wholethe glass where the main crystalline phase is synthetic fluormica,named fluorophlogopite. Peixin et al. [4] have been establishedthat the crystallization of 45MgO–20B2O3–35SiO2 (wt%) glass ledto the formation of a major Mg2B2O5 phase, and minor crystallinephases Mg3B2O6 and Mg2SiO4. According to their [4] findings,both TiO2 and ZrO2 promoted the phase separation during theannealing process above the glass transition temperature (Tg). Inthe earlier work [7–11], authors had studied the kinetics as well as

crystallization behavior, microstructure and mechanical propertiesof different glass system using CaF2, TiO2 as a nucleating agentsand also using nano silica. Authors [12] had studied the kinetics aswell as crystallization behavior and microstructure with respect

tion and hosting by Elsevier B.V. All rights reserved.

5 f Asian

tbttaptg

2

2tpKpwesiftfa

iniwGtmad

ouc(a

cwwp

tnp2

TC

it surrounded by both bridging oxygen and non-bridging oxygen.These oxygen isolate the network-modifier cations from each otherby providing screens that mask the positive charge. Besides this,modifier cations that are partly or wholly coordination by bridging

6 D.P. Mukherjee, S.K. Das / Journal o

o B2O3 content in the barium fluorophologopite glass-ceramicsased on the SiO2–Al2O3–MgO–BaO–MgF2 system. The aim ofhe present work is to investigate the possible role of TiO2 inhe SiO2–Al2O3–MgO–K2O–B2O3–MgF2 glass system. In order tochieved the improvement of hardness and machinability. Titaniaromoted initial crystallization of glass and can be used as an effec-ive nucleting agent to generate fluorophlogopite mica in theselass-ceramics useable for solid oxide fuel cell (SOFC) applications.

. Experimental procedure

Table 1 shows the composition of all glass batches (MGT-1, MGT- and MGT-3). The glasses have been labeled in accordance withheir respective TiO2 contents (wt%). The raw materials used torepared the glasses are SiO2 (99.8%), Al2O3 (99.3%), MgO (99.9%),2CO3 (98%), H3BO3 (99.5%), MgF2 (99.9%), and TiO2 (99.5%) sup-lied by M/S Merck Specialties Private Limited, India. All batchesere melted at 1500 ◦C for 2 h in an alumina crucible in air in an

lectrically heated raising hearth furnace followed by pouring on ateel plate. After release from the plate, the resultant glasses weremmediately transferred to an annealing furnace operating 630 ◦Cor 2 h to remove the internal stress and then cooled down slowlyo room temperature. The anneal glasses were sized as requiredor different experimentations and subsequently heat-treatmentt different temperature.

Differential scanning calorimetry of the glass powders weigh-ng near about 50 mg in an alumina crucible were carried out initrogen atmosphere from room temperature to 1000 ◦C at heat-

ng rate 10 ◦C/min using �-alumina powder as a reference materialith the help of a DSC instrument (Model STA 449C; NETZSCH-erätebau GmbH, Selb, Germany) to determine the glass transition

emperature (Tg) and crystallization peak temperature (Tp) with aeasurement error of ±1 ◦C. DSC of glass powders were carried out

t four different heating rates (ˇ) such as 5, 10, 15 and 20 ◦C/min toetermined the crystallization kinetics.

The amorphous nature of glasses and qualitative analysisf crystalline phases in the glass-ceramics were investigatedsing a conventional Bragg–Brentano diffractometer (PANalyti-al PW3040/60, The Netherlands) with Ni-filtered Cu-Ka radiation� = 1.5406 A) at 40 kV and 30 mA. The scan range was 5◦–80◦ with

step size of 0.05◦.Fourier transform infrared transmission spectra (FTIR) of glass-

eramics were recorded in the wave number range 400–2000 cm−1

ith the help of FTIR spectrometer (Alpha FTIR, Bruker, Germany)ith a resolution of ±1 cm−1, in order to identify different bondsresent in the glass ceramics and crystals structure.

The crystallization characteristics and microstructural studies ofhe heat-treated glass-ceramics samples were examined by scan-

ing electron microscope (ZEISS EVO-MA 10, Germany). For thisurpose the heat-treated and polished samples were etched with

vol.% HF aqueous solution for 6 min.

able 1hemical compositions of base glass.

Glass SiO2 Al2O3 MgO K2O B2O3 MgF2 TiO2

MGT-1wt% 42.90 16.10 12.00 10.00 6.00 12.00 1.00mol% 35.59 7.94 14.96 5.34 4.33 31.75 0.62

MGT-2wt% 38.90 16.10 12.00 10.00 6.00 12.00 5.00mol% 32.54 7.94 14.96 5.34 4.33 31.75 3.15

MGT-3wt% 37.90 12.10 12.00 10.00 6.00 12.00 10.00mol% 31.60 5.94 14.96 5.34 4.33 31.75 6.27

Ceramic Societies 4 (2016) 55–60

The hardness of the all glass-ceramic specimens was measuredby micro-indentation on the polished surface of the specimens.Micro-indentations were taken using 160 microhardness testers(Carl Zeiss Jena, Germany) equipped with a conical Vickers indenterat an indent load of 40 g. Ten indents were taken for each samplewith identical loading condition and average of this was used tocalculate the hardness using the standard equation for the Vickersgeometry.

Hv = 1.8544 × P

d2(1)

where Hv is the Vickers hardness number (VHN) in kg/mm2, P is theapplied load in kg, and d is the mean of the lengths diagonals of theindentation in mm. Baik et al. [13,14] introduced the machinabilityparameter m as,

m = 0.643 − 0.122Hv (2)

The machinability parameter m is an important tool to characterizemachinable glass-ceramics.

3. Results and discussion

3.1. DSC analysis results

The glass to glass-ceramic conversion, the desired crystallinephases is a phase transformation process that requires control heattreatment. The heat treatment temperatures were selected fromdifferential scanning calorimetry (DSC) study and the results havebeen demonstrated in Fig. 1. The endothermic minima correspondto glass transition while the two exothermic peaks correspondto the crystallization into the glass. Two exothermic peaks wereobserved for all the batches. Fig. 1 showed that by increasing theTiO2 content (1–10 wt%), the glass transition temperature (Tg) andboth the crystallization peak temperature (Tp

I and TpII) increased.

The Tg obtained for MGT-1 glass specimen is 705 ◦C, whereas MGT-2 and MGT-3 have Tg value of 708 and 723 ◦C respectively. After theTg two exothermic peaks were observed and they corresponds tostat the crystallization process. These exothermic peaks started forMGT-1 glass specimen were at 874 ◦C (Tp

I) and 938 ◦C (TpII) whereas

for MGT-2 and MGT-3 glass specimens 882 ◦C (TpI) and 959 ◦C (Tp

II);902 ◦C (Tp

I) and 980 ◦C (TpII) respectively. Agarwal [15] proposed

that when a modifier cation is added in silica containing glass melt,

0 300 600 90 0 120 0

MGT-1

MGT-2

MGT-3

Endo

E

xo

Tempera tur e (oC)

980oC(TpII)

902oC(TpI)

723oC(Tg)

959oC(TpII)882oC(Tp

I)

708oC(Tg)

938oC(TpII)874oC(Tp

I)

705oC(Tg)

Fig. 1. DSC thermogram of different glasses heat treated at 10 ◦C/min.

D.P. Mukherjee, S.K. Das / Journal of Asian Ceramic Societies 4 (2016) 55–60 57

9.0 9.6 10 .2 10. 8 11.4 12.010.4

10.8

11.2

11.6

12.0

MGT-1 TpI

MGT-2 TpI

MGT-3 TpI

MGT-1 TpII

MGT-2 TpII

MGT-3 TpII

ln(T

p2 /β)

(1/Tpx104)

FM

otbi[tTim

(tctamm

l

wpccgva(e

n

whi

TA

8070605040302010

KF

KF

F

F

F

F

FKF

KF

F

F

KF

KF KF

KF

KFC

F

FF

KFKF

KF

FC

C

KFKF

KF- JCPDS f ile No. 10-0 494F- JCPDS f ile No. 80-0 783C- JCPDS f ile No. 82-1 884

C- Mg2(Al4Si5O18)

F- Mg2(SiO4)

KF- KMg3(Si3AlO10)F2

MGT-3

MGT-2

MGT-1Rel

ativ

e In

tens

ity (a

.u.)

2θ (d egrees)

ig. 2. Variation of ln(Tp2/ˇ) vs. 1/Tp of all the glass specimens (MGT-1, MGT-2 and

GT-3) for first and second crystallization peak (TpI and Tp

II) temperature.

xygen are poorly shielded from each other’s influence becausehe oxygen are mainly bonded to Si4+ cations by strong covalentond. When metal oxide is added in the glass system, such as TiO2

n this case, the interaction of units will be accelerated by groupTiO4] due to its higher negative attractive force to some posi-ive cations such as Mg+ and K+ under some suitable conditions.he result of this linking is that some different phase contain-ng Mg+ and K+ can be observed by different characterizations

ethods.DSC was performed for MGT-1, MGT-2 and MGT-3 glasses

nucleating agent-doped as 1–10 wt% TiO2) at different heating rateo determine the activation energy of crystallization and types ofrystal growth occurs. The variations of TiO2 on the crystalliza-ion kinetics of the glass specimens under a given thermal cyclere essential to predict their behavior in practical applications. Theodel was developed by Matusita and Saka [16] using the followingodified form of the Kissinger equation.

nT2

p

�= E

RTp+ C (3)

here is the heating rate, Tp is the crystallization peak tem-erature of the DSC maximum exotherm, R is the universal gasonstant, E is the activation energy for crystallization and C is aonstant. From the slope and intercept of the plot ln(Tp

2/ˇ) vs. 1/Tp

iven by Eq. (3), one can derived the E. The linear plots of ln(Tp2/ˇ)

s. 1/Tp for first and second crystallization peak temperature (TpI

nd TpII) are shown in Fig. 2. From the value of activation energy

E), the Avrami exponent (n) was calculated using Augis–Bennettquation [17].

= 2.5�T

× RT2p

E(4)

here, �T is the full width of the exothermic DSC peak at thealf maximum intensity. The calculated E and n values are listed

n Table 2. It can be seen that E for both first and second crystalliza-

able 2ctivation energy (E) and Avrami parameter (n) of the glass specimens.

Batch no. E (kJ/mol) Avrami exponent (n)

TpI Tp

II TpI Tp

II

MGT-1 299.99 385.12 2.91 2.61MGT-2 345.14 391.63 2.74 2.84MGT-3 370.09 428.07 3.02 3.08

Fig. 3. XRD patterns of MGT-1, MGT-2 and MGT-3 glass specimens heat treated at1080 ◦C for 2 h.

tion peak temperature (TpI and Tp

II) increased from ∼299 kJ/mol to∼370 kJ/mol for Tp

I and ∼385 kJ/mol to ∼428 kJ/mol for TpII upon

addition of 1–10 wt% TiO2. According to Johnson–Mehl–Avramitheory, Avrami exponent (n) depends on the crystallization man-ner [12]. In present cases the values of Avrami exponent for firstTp

I were 2.91, 2.74 and 3.02 and second TpII were 2.61, 2.84, and

3.08 for the glass specimens MGT-1, MGT-2 and MGT-3 respectively(Table 2). The n values for the Tp

I and TpII suggest that the crystal

growths are two-dimensional in nature at the time of crystalliza-tion process.

3.2. XRD analysis results

Fig. 3 shows the X-ray diffraction patterns of each glass-ceramicspowder heat treated at 1080 ◦C. From this figure, it was clearlynoted that the major or predominant crystalline phase for all spec-imens were fluorophlogopite mica, KMg3(AlSi3O10)F2 (Monoclinicsystem, with space group C2/m(12), JCPDS file no. 10-0494) alongwith forsterite [Mg2SiO4 – orthorhombic system, with space groupPbnm(62), JCPDS file no. 80-0783] and cordierite [Mg2Al4Si5O18 –hexagonal system, with space group P6/mcc(192), JCPDS file no.82-1884] appeared as minor or secondary crystalline phases. Theintensity and the number of this phases increase with increase inheat treatment temperature from 800 ◦C to 1080 ◦C as representedin Fig. 3. In the MGT-1 specimen, heat treated at 1080 ◦C, peaksof forsterite at 22.6◦, 34.1◦, 36.0◦ and 71.2◦ (2�) appeared alongwith the fluorophlogopite mica at 30.2◦, 39.8◦, 41.3◦ and 60.3◦ (2�)as a major crystalline phase. In the MGT-2 specimen, at the sameheat treated temperature, five new peaks of fluorophlogopite micaappeared at 8.9◦, 26.7◦, 28.4◦, 31.2◦ and 62.8◦ (2�) and one new peakof cordierite at 11.3◦ (2�) along with the fluorophlogopite. In MGT-3 (10 wt% TiO2) specimen heat treated at 1080 ◦C, two new peaks ofcordierite appeared at 19.3◦, 45.6◦ (2�) and one peak of cordieriteat 11.3◦ and fluorophlogopite at 62.8◦ (2�) disappeared along withthe all crystalline phases. From this analysis it was clearly observedthat at the high heat treated temperature and higher amount of TiO2

(10 wt% TiO2) the glass specimens were crystallized completelyto form glass-ceramic and this is an irreversible ceramizationprocess.

58 D.P. Mukherjee, S.K. Das / Journal of Asian

400800120016002000

1259

1227

1074

1011

951 85

1 721

685

649

507

472

142916

31

Tran

smitt

ance

(%)

Wavenu mbers (c m-1)

MGT-1MGT-2MGT-3MG wit hout TiO

2

Fig. 4. FTIR spectra of glass-ceramics specimens without TiO2 and with TiO2 (MGT-1to MGT-3) heat treated at 1080 ◦C for 2 h.

Fig. 5. SEM photomicrograph of (a) MGT-1, (b) MGT-2 and (c) MGT-3 etched (by immersat 1080 ◦C for 2 h.

Ceramic Societies 4 (2016) 55–60

3.3. FTIR analysis results

The FTIR transmission spectra in the range of 400–2000 cm−1 ofthe glass-ceramics specimens containing TiO2 (1–10 wt%), whichare heat treated at 1080 ◦C for 2 h are depicted in Fig. 4. The glass-ceramics specimens are shown a peak at 472 cm−1, which is dueto Si O Si bending vibration modes of [SiO4] unit along with thepresence of Ti O Ti-stretching vibration in this region [18–20].The transmission peak at 508 cm−1 may be attributed to the bend-ing vibration of O Si O and Si O Si bond of [SiO4] units [21].The band at 649 cm−1 for all the spectra is assigned to Al O Alstretching vibration of [AlO6] units [22]. It is known that bandsin-between at 660–690 cm−1 are due to vibration in [TiO4] tetra-hedron [23]. The dissolved Ti4+ cations in silico-oxide networkmay lead the transmission band to shift toward high wavenumber.So the transmission peak at 685 and 721 cm−1 for all the spectraof Fig. 4 are due to stretching vibration of O Si O in [SiO4]

tetrahedron as well as stretching vibration of Si O Ti between[SiO4] and [TiO4] of the network. The peak near 851 cm−1 is acharacteristic band for Al O stretching vibration of [AlO4] units[22]. The band position at 951 cm−1 is due to the B O stretching

ion in 2 vol% HF aqueous solution for 6 min) glass-ceramic specimens heat treated

D.P. Mukherjee, S.K. Das / Journal of Asian

Table 3Mechanical measurement properties of glass-ceramic specimens heat treated atdifferent temperature.

Batch no. Heat treatmenttemperature (◦C)

Microhardness (Hv)in GPa

Machinabilityparameter (m)

MGT-1 800 5.33 ± 0.01 −0.007900 5.27 ± 0.02 0.0006

1000 5.23 ± 0.02 0.0041080 5.17 ± 0.01 0.012

MGT-2 800 5.19 ± 0.02 0.009900 5.12 ± 0.02 0.018

1000 5.01 ± 0.02 0.0361080 4.89 ± 0.02 0.046

MGT-3 800 4.73 ± 0.01 0.066900 4.62 ± 0.01 0.079

vTovBtaSibabrow

3

ci1gflM(2lmgggavcc

3

ttrhhtT8

1000 4.33 ± 0.01 0.1151080 4.26 ± 0.02 0.123

ibration of [BO4] units in tri, tetra, and penta borate groups [24].he sharp peak observed at 1011 cm−1 corresponds to the fluorphl-gopite. This peak is assigned to Si O Si asymmetric stretchingibration [18–20]. This intense peak was due to the presence of2O3. This sharp broadening peak at 1011 cm−1 corresponds tohe B O stretching vibration of [BO4] units [12,25,26]. The bandt 1074 cm−1 is for the anti-symmetric stretching vibration ofi O Si of [SiO4] unit [21,24]. The peak position at 1227 cm−1

s attributed to B O stretching vibration of trigonal BO4 units inoroxol rings [27]. The peak position at 1259 cm−1 is assigned tonti-symmetric stretching vibration of Si O Si of [SiO4] unit. Theand position attributed at 1429 cm−1 is due to the B O vibrationelated to tri-[BO3], tetraborate [BO4] groups. The peak positionbserved at 1631 cm−1 is due to the H O H bending vibration forater molecule [19].

.4. SEM analysis results

Scanning electron microscopy photomicrographs of the glass-eramic specimens heat treated at 1080 ◦C for 2 h are representedn Fig. 5. Fig. 5(a)–(c) depicts the microstructure of MGT-

(TiO2–1 wt%), MGT-2 (TiO2–5 wt%) and MGT-3 (TiO2–10 wt%)lass-ceramic, respectively. All these photomicrographs showuorophlogopite crystal dispersed throughout the glass matrix.GT-1 glass-ceramic contains blocky card like mica flake crystals

Fig. 5(a)). When TiO2 (5 wt%) is added as a nucleating agent in MGT-, uniform and dense blocky microstructure obtained where strand

ike fluorophlogopite mica crystal phase develops throughout theatrix (Fig. 5(b)). The crystal sizes are about 5–6 �m for all the

lass-ceramic specimens. In Fig. 5(c), i.e., 10 wt% TiO2 containinglass-ceramic, interconnected large blocky card-like fluorophlo-opite mica crystals predominant. This type of microstructurerrangements into the glass matrix has sufficient tendency to pre-ent the generation and growth of crack. The appearance of blockyrystals might be due to the formation of fluorophlogopite micarystals for all the glass-ceramic specimens concerned.

.5. Mechanical properties

Table 3 shows the machining properties of the specimen’s heatreatment in the temperature range 800–1080 ◦C for 2 h. Accordingo Table 3, the hardness values reduce slightly on formation of fluo-ophlogopite mica crystal. The glass-ceramic specimen MGT-1 hasardness value of 5.33 GPa (at 800 ◦C) which falls to 5.17 GPa after

eat treatment at 1080 ◦C for 2 h. Hence, when the heat treatmentemperature progressively increases, Hv values gradually decrease.he glass-ceramic specimen MGT-3 has hardness value 4.73 GPa (at00 ◦C) which reduces to 4.26 GPa after heat treatment at 1080 ◦C

[[[

Ceramic Societies 4 (2016) 55–60 59

for 2 h. The large reduction of hardness value may be interpreted bythe formation of interlocking blocky house of cards like microstruc-ture [28,29]. Table 3 also shows the machinability parameters (m)calculated from hardness values after heat treatment at differ-ent temperatures (800–1080 ◦C for 2 h). According to the resulttable, MGT-1 glass-ceramic specimen has the Hv value 5.17 GPa (at1080 ◦C/2 h), but it does not have the machinability (m = 0.012) asit shows only surface crystallization into the glass matrix. By theheat treatment at 1080 ◦C for about 2 h, glass-ceramic specimenMGT-3 shows a lowest hardness value 4.26 GPa, indicating goodmachinability (m = 0.123). The above discussion clearly indicatedthat, as the TiO2 content increased (1–10 wt%) the machinablity ofthe specimens increased.

4. Conclusions

The effect of TiO2 on properties of SiO2–Al2O3–MgO–K2O–BaO–MgF2 glass system has been investigated in this study in orderto establish their applicability as machinable application. Thevariation in TiO2 content (1–10 wt%) has a marked influence oncrystallization as well as crystal morphology. From DSC study, Tg

and both the crystallization peak temperature (TpI and Tp

II) of theglass specimens were increased with the addition of TiO2 con-tent (1–10 wt%) due to the high field strength of Ti4+ ion. Thecrystals formed were largely homogeneous and two-dimensionalin nature for all the glass-ceramic specimens concern. The XRDanalysis indicated the formation of fluorophlogopite mica crys-tal as a predominant phase along with forstertite and cordieriteminor phases. The FTIR analysis confirmed the presence of Si O Sibending vibration modes of [SiO4] unit along with the presence ofTi O Ti-stretching vibration in the 472 cm−1 wave number region.The aspect ratio of fluorophlogopite mica crystals increased withincrease of heat treatment temperature and higher TiO2 contentin the composition of glass specimens as also identified by XRDand SEM study. The Hv value for glass-ceramic specimens decreaseswith progressively increasing TiO2 content and Titania containing(10 wt%) mica glass-ceramic with interconnected large blocky card-like fluorophlogopite mica crystals. It possess lower Hv (4.26 GPa) aswell as good machinability (m = 0.12) which results in easy machin-ing. TiO2 promoted initial crystallization of glass and can be usedas an effective nucleating agent for machinable applications.

Acknowledgements

The authors would like to thank the UPE scheme of Univer-sity Grants Commission (UGC) and the Center for Research inNanoscience and Nanotechnology (CRNN), University of Calcuttafor financial support. One of the authors, Debasis Pradip Mukherjeethanks the Center for Research in Nanoscience and Nanotechnol-ogy (CRNN), University of Calcutta, Kolkata, India, for providing theSenior Research Fellowship (SRF).

References

[1] D.G. Grossman, J. Am. Ceram. Soc., 55, (9) 446–449 (1972).[2] W. Höland and G. Beall, Glass-Ceramic Technology, The American Ceramic

Society, Westerville (2002).[3] L. Cormier, O. Dargaud, N. Menguy, G.S. Henderson, M. Guignard, N. Trcera and

B. Watts, Cryst. Growth Des., 11, (1) 311–319 (2011).[4] Z. Peixin, S. Zhitong and Z. Jianhua, Chin. J. Mater. Res., 12, 303 (1998).[5] G. Carl, T. Höche and B. Voigt, Phys. Chem. Glasses, 43C, 256–258 (2002).[6] K. Cheng, J. Wan and K. Liang, J. Am. Ceram. Soc., 82, (5) 1212–1216 (1999).[7] D.P. Mukherjee and S.K. Das, Ceram. Int., 39, (1) 571–578 (2013).

[8] D.P. Mukherjee and S.K. Das, J. Non-Cryst. Solids, 368, 98–104 (2013).[9] D.P. Mukherjee, T. Datta and S.K. Das, AIP Conf. Proc., 1536, 625–626 (2013).10] D.P. Mukherjee, J.K. Sinha and S.K. Das, AIP Conf. Proc., 1536, 639–640 (2013).11] D.P. Mukherjee and S.K. Das, Ceram. Int., 40, (3) 4127–4134 (2014).12] D.P. Mukherjee and S.K. Das, Ceram. Int., 40, (8) 12459–12470 (2014).

6 f Asian

[

[

[[[[

[[[

[

[

[

[

[

[27] I. Ardelean, F. Ciorcas, M. Peteanu, I. Bratu and V. Ioncu, Mod. Phys. Lett. B, 14,

0 D.P. Mukherjee, S.K. Das / Journal o

13] D.S. Baik, K.S. No, J.S. Chun, Y.J. Yoon and H.Y. Cho, J. Mater. Sci., 30, 1801–1806(1995).

14] D.S. Baik, K.S. No, J.S. Chun and H.Y. Cho, J. Mater. Process. Technol., 67, 50–54(1997).

15] A. Agarwal and M. Tomozawa, J. Am. Ceram. Soc., 78, (3) 827–829 (1995).16] K. Matusita and S. Saka, J. Non-Cryst. Solids, 39, 741–746 (1980).17] J.A. Augis and J.E. Bennett, J. Therm. Anal. Calorim., 13, 283–292 (1978).18] J. Yu, X. Zhao, J. Yu, G. Zhong, J. Han and Q. Zhao, J. Mater. Sci. Lett., 20, 1745–1748

(2001).

19] N.A. Shafi and M.M. Morsi, J. Mater. Sci., 32, 5185–5189 (1997).20] V.L. Burdick and D.E. Day, J. Am. Ceram. Soc., 50, (2) 97–101 (1967).21] G. Fuxi, Optical Spectroscopic Properties of Glass, Springer-Verlag, Berlin

(1992).22] V. Stubican and R. Roy, Am. Mineral., 46, 32–51 (1961).

[[

Ceramic Societies 4 (2016) 55–60

23] P. González, S. Serra, S. Liste, S. Chiussi, B. León and M. Pérez-Amor, J. Non-Cryst.Solids, 320, (1–3) 92–99 (2003).

24] E.I. Kamitsos, M.A. Karakassides and G.D. Chryssikos, J. Phys. Chem., 91, (5)1073–1079 (1987).

25] G. Pal Singh, P. Kaur, S. Kaur and D.P. Singh, Mater. Phys. Mech., 12, 58–63(2011).

26] M.R. Reddy, S.B. Raju and N. Veerraiah, Bull. Mater. Sci., 24, (1) 63–68(2001).

653 (2000).28] A.C. Fischer-Cripps, J. Am. Ceram. Soc., 84, (11) 2603–2606 (2001).29] A. Goel, D.U. Tulyaganov, V.V. Kharton, A.A. Yaremchenko, S. Agathopoulos and

J.M.F. Ferreira, J. Am. Ceram. Soc., 90, (7) 2236–2244 (2007).