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Microstructural study of Crofer 22 APU-glass interface forSOFC application

Bhupinder Kaur, K. Singh, O.P. Pandey*

School of Physics and Materials Science, Thapar University, Patiala, Punjab 147004, India

a r t i c l e i n f o

Article history:

Received 14 March 2011

Received in revised form

22 April 2011

Accepted 23 April 2011

Available online 11 June 2011

Keywords:

Crystallization kinetics

Hurby parameter

Microstructure

X-ray methods

* Corresponding author. Tel.: þ919888401777E-mail address: oppandey@thapar.edu (O

0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2011.04.160

a b s t r a c t

Glasses of composition (60�x)SiO2e15CaOe10Al2O3e(10 þ x)Na2Oe5TiO2 (x ¼ 0, 5, 10, 15)

were prepared. The crystallization kinetics of prepared glasses were investigated by

differential thermal analyzer, dilatometer and X-ray diffraction techniques. In order to

check the applicability of the prepared glasses as a sealant in solid oxide fuel cell, these

were deposited on Crofer 22 APU steel by slurry technique and thermally treated. The

interface of the glassesteel composites was further analyzed under scanning electron

microscope in conjunction with energy-dispersive X-ray spectroscopy and X-ray dot

mapping. All glass samples exhibit phase separation. The phase separation tendency

increases with increasing content of Na2O in glasses. The N-10 glass containing 10% Na2O

shows good adhesion with Crofer 22APU.

Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction [6e11]. Moreover, these reported compositions of sealing

Solid oxide fuel cells (SOFCs) are energy conversion devices

that can convert chemical energy of the fuel directly into

electrical energy. This process is eco-friendly and efficient one

[1e3]. SOFCs have received great attention as a promising new

technology for power generation because they are able to

utilize a wide variety of hydrocarbon fuels. A planar design of

SOFC is simple, produces higher power densities with high

efficiency than other designs.

The typical design of planar SOFC requires hermetic seals

to prevent fuel-oxidant mixing and also electrical insulation

to the stack [4]. Glass and glass ceramics have been widely

used for sealing different components of SOFC. First and the

foremost requirements of a glass to be used as a seal is to

have excellent thermo-chemical and thermo-mechanical

stability in stringent oxidizing and reducing environments of

fuel cell [5]. Lanthanum containing borosilicate glasses have

been extensively studied as sealing materials for SOFC

..P. Pandey).2011, Hydrogen Energy P

glasses are mostly confined to composition where silica acts

as a glass former. Al2O3 in glasses acts as intermediate,

which behaves as a network former and network modifier in

the glass system. B2O3 is added in most of the glasses to

decrease viscosity and increase the wettability with other

components of SOFC. However, it also decreases the stability

of seal as it leads to phase separation in borosilicate glasses.

Furthermore, the presence of La2O3 additive in the glass

matrix leads to formation of the devitrified phase at

operating temperature of SOFC and the amount of that

phase increases with high temperature aging [12]. Apart

from B2O3, alkali metal oxide (Na2O) is used as a modifier to

increase the wettability of glasses. It leads to decrease in

glass transition temperature while the thermal expansion

coefficient increases in hydrothermal conditions of SOFC

[13]. This causes poor chemical stability of Na2O-SiO2 glasses

in SOFC environment. However, addition of CaO in a Na2O-

SiO2 glass increases the chemical resistance to water

ublications, LLC. Published by Elsevier Ltd. All rights reserved.

Table 1 e Glass compositions (mol %) with their label.

Glass label SiO2 Al2O3 TiO2 CaO Na2O

N-25 45 10 5 15 25

N-20 50 10 5 15 20

N-15 55 10 5 15 15

N-10 60 10 5 15 10

400 600 800 1000 1200

-50

-40

-30

-20

-10

0

Tp2

Tp2

Tp2

Tp2

Tp1Tp1

Tp1

End

o D

own

V

Temperature ( C)

N-10

N-20

N-15

N-25

Tp1

Tm

Tm

Tm

Tm

Fig. 1 e DTA curves of prepared glasses at the heating rate

of 10 �C/min.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 73840

induced phase separation [14,15]. Moreover, Al2O3 hinders the

formation of the hydrated open network structure surface

layer in a Na2OeCaOeSiO2 glasses [16]. Addition of polar

oxides such as PbO and transition metal oxides such as ZrO2

and TiO2 in these glasses improves the chemical stability [15].

The stability of glass sealant depends on the inter-diffusion

distance at the interface of glass-SOFC components, which

should be less than 10 mm. The diffusion distance of Cr from

ferritic steel into BaO-CaO borosilicate glasses increases from

10 to 15 mm with the thermal treatment time (from 10 h to

200 h) at 800 �C [17]. Conversely, a Na2O-CaO-silicate glass

reacts with pre-oxidized AISI 430 alloy and forms Cr, Mn, Fe

and O enriched interface layer of 1e2 mm thickness in

reducing atmosphere at 800 �C after 200 h [18]. Smeacetto

et al. [19] in their recent publication have also demonstrated

that glasses containing a low amount of sodium oxide can

be used as sealing material for SOFC.

Based on these studies, soda lime aluminosilicate glass has

been chosen in the present investigation as basic glass. TiO2

which acts as nucleating agent is added to improve the

chemical stability [20]. In the present work, Na2OeCaOe

Al2O3eSiO2eTiO2 glass system has been investigated in

detail. To estimate the applicability of these glasses as

sealants, their thermal properties, crystallization behavior,

thermal expansion coefficient after heat treatment and the

overall bonding characteristics of the glass with metallic

(Crofer22APU) interconnect were investigated.

2. Materials and methods

2.1. Glass preparation

Selected glass compositions for present study with their

designationaregiveninTable1.Glassesweresynthesizedusing

conventional splat quenching technique. Theminimumpurity

of all the ingredientsused to synthesize theseglasseswas99.8%.

For the synthesis of glasses, required amount of ingredients

were taken. These ingredients were ground in ball mill (Retsch

PM100) for 2 h in dry media. The ball milled mixtures were

melted at 1500 �C in a recrystallized alumina crucible.

Table 2 e Activation energy (kJ/mol) for the glass transition an

Sample identity Mahadevan method Kis

Eg Ep1 Ep2 Eg

N-25 271.11 386.11 215.55 254.86

N-20 58.80 51.29 68.45 43.17

N-15 149.38 216.61 124.04 134.40

N-10 100.77 142.73 167.32 83.78

The glass ingots after casting were kept in a preheated

furnace at 400 �C for 12 h to remove the stresses of the

quenched glasses.

2.2. Phase identification

The amorphous nature of samples was characterized by X-ray

diffraction (XRD) using X’Pert Pro, PAN alytical model of Phi-

lips, Netherlands. During the experiment, the scan speed was

0.02�/min. The crystalline phases obtained after heat treat-

ment was identified by the Joint Committee on Powder

Diffraction Standards (JCPDS-ICDD) files. Thermal behavior

and crystallization kinetics of the glass was investigated by

Differential Thermal Analysis (DTA) (DTA-TG, Perkin Elmer,

USA) using powder samples with alumina as a reference

material. For crystallization kinetics, 15 mg of glass samples

were scanned by DTA in nitrogen at different heating rates (a)

of 5, 10, 15, 20 �C/min from50 �C to 1200 �C. Thermal expansion

coefficient of the glasses was measured using Netzsch DIL 402

PC, UK, at the heating rate of 5 �C/min in the air environment.

2.3. Activation energy calculations

The activation energy of the glass transition (Eg) and crystal-

lization (Ec) can be obtained by the following relationship [21]:

ln a ¼ � ERT

þ constant (1)

d crystallizations with various methods.

singer method Augis and Bennett method

Ep1 Ep2 Eg Ep1 Ep2

369.21 196.47 262.98 265.03 258.59

33.92 48.14 242.57 236.49 263.59

199.99 104.96 260.47 260.76 255.27

124.07 146.77 249.55 254.84 256.42

1 .0 0 1 .0 1 1 .0 2 1 .0 3 1 .0 4

1 .5

2 .0

2 .5

3 .0

-1 2 .0

-1 1 .5

-1 1 .0

-1 0 .5-5 .5

-5 .0

-4 .5

-4 .0

1 .0 0 1 .0 1 1 .0 2 1 .0 3 1 .0 4ln

()

1 0 0 0 /T g (K -1)

a

ln (

/ Tg2 )

b

ln (

/Tg)

c

Fig. 2 e Activation energy plot with (a) Mahadevan (b)

Kissinger and (c) Augis and Bennett methods for N-25

glass.

10 15 20 25

0.5

1.0

1.5

2.0

2.5

3.0

3.5

S (K

)

Na2O (mol%)

Fig. 4 e The graphical representation of S parameter with

respect to Na2O (mol %) at heating rate 10 �C/min.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 7 3841

where E is the activation energy and R is the gas constant.

The second approach to evaluate the activation energy of

the glass transition (Eg) and crystallization (Ec) is Kissinger

equation as given below [22]:

ln

�a

T2

�¼ � E

RTþ constant (2)

10 15 20 25

0.6

1.2

1.8

15 C/min 10 C/min5 C/min

Na O content (mol%)2

Hr

Fig. 3 e The graphical representation of Hruby parameter

with respect to Na2O (mol %).

The slope of the plot ln (a=T2) versus 1=T (K�1) gives the value

of activation energy.

Additionally, activation energy was also calculated using

the method proposed by Augis and Bennett [23]:

ln�aT

�¼ � Ec

RTpþ ln Ko (3)

The activation energy of the glass transition and the crystal-

lization processes are calculated and compared with the

values as obtained from the Kissinger and Mahadevan

models.

From the point of view of technological application, the

glass should be thermally stable. A parameter usually

employed to estimate the glass stability is the thermal

stability (DT) [21], which is defined by the following equation:

DT ¼ Tc � Tg (4)

The larger difference between Tc and Tg, the higher is the

kinetic resistance to crystallization. In other words, the glass

is thermally stable.

100 200 300 400 500 600 700 800

0.000

0.001

0.002

0.003

0.004

0.005

0.006 N -25 N-20 N-15 N-10 N -10 GC Crofer

dL

/d

Lo

X

10

-6

K

-1

Temperature ( C)

Fig. 5 e Thermal expansion curves of prepared glasses,

N-10 glass ceramic and Crofer steel.

Table 3 e Properties of glasses and steel.

Properties

Sampleidentity

DTA data Dilatometric data

Glass transitiontemperature, Tg (�C)

Crystallizationtemperature, Tp (�C)

Glass transitiontemperature, Tg (�C)

Softeningtemperature, Ts (�C)

TEC (K�1) in the rangeof 200e550 �C

N-25 692 741, 864 562 589 8.88 � 10�6

N-20 616 705, 915 572 629 8.31 � 10�6

N-15 607 711, 910 628 657 8.34 � 10�6

N-10 708 831, 965 654 709 8.19 � 10�6

Heat treated N-10 e e e e 8.27 � 10�6

Crofer 22APU e e e e 8.42 � 10�6

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 73842

Another thermal stability parameter, S, proposed by Saad

and Poulain [24], is given by Eq. (5)

S ¼ �Tp � Tc

��Tc � Tg

��Tg (5)

The thermal stability parameter, S, reflects the resistance to

devitrification after the formation of the glass. (Tp-Tc) is

20 40 60 80

0

400

800

Inte

nsity

(Cou

nts)

2 (Deg.)

(a)

(b)

(c)

AlNa ( SiO4 )

SiO2

Fig. 7 e XRD patterns of (a) N-10 glass, (b) N-10 heat treated

glassat 900 �Cand (c)N-10heat treatedglassat 950 �C for 1h.

10 20 30 40 50 60 70 80 90 1000

400

800

1200

1600

N-10

N-15

N-20

Inte

nsit

y (C

ount

s)

2 (Deg.)

N-25

Fig. 6 e XRD patterns of prepared glasses.

related to the rate of devitrification transformation of the

glassy phases, while a high value of (Tc-Tg) delays the nucle-

ation process.

Hurby [25] has given a factor which combines both

nucleation and growth aspects of glass transformation and

is given by

Hr ¼ Tc � Tg

Tm � Tc(6)

Where Tm is the melting temperature of glass.

Fig. 8 e (a): SEM micrograph of interface between N-10

glass and Crofer steel showing the overall view of inter-

face. (b): Back scattered electron micrograph of interface

between N-10 glass and Crofer steel.

Fig. 9 e (a): EDS spectrum analyses of the glass of the diffusion couple marked 1 in Fig. 8(b). (b): EDS spectrum analyses of the

interface of the diffusion couple marked 2 in Fig. 8(b). (c): EDS spectrum analyses of the steel of the diffusion couple marked 3

in Fig. 8(c).

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 7 3843

2.4. Formation of the diffusion couple

The steel plates (Crofer) were cut in 1 � 1 cm2 to prepare the

diffusion couple. This piece was degreased by ultrasonic

cleaner in acetone media. After that, these pieces were dip in

a solution of 5% HNO3 for 5 min to dissolve any oxide layer

formation on the surface. The glass coating was applied onto

the cleaned substrate surface by a slurry method. The thick-

nessof the glass coating layerwas1mm.For coating, the slurry

was prepared from the mixture of the glass powder dispersed

in 5%PVA.Thediffusioncouplewas thermally treatedat 900 �Cfor 1 h, to check adhesion of the glass with Crofer 22APU. The

heat treated diffusion couple was characterized by scanning

electron microscopy (SEM, JEOL6400, Japan) to study the

interface in conjunction with energy-dispersive X-ray spec-

troscopy (EDS). The sample was mounted in epoxy resin and

ground flat by using 240, 400, 800 and 1200 grit abrasive papers

consecutively and then polished with diamond paste of one

mm to achieve a mirror-like surface finish. The sample was

etched with 0.05 N HCl solution containing few drops of HF for

1min before an examination under SEM. In order to check any

variation in chemical composition before and after heat

treatment, N-10 glass was further subjected to heat treatment

at 900 �C for 1 h. EDS analysis on polished surface of the heat

treated glass was carried out.

3. Results and discussion

3.1. Thermal properties of glass and glasseceramic

Fig. 1 shows the DTA curves of all the glasses. DTA curves

exhibit two exothermic peaks, which indicate phase

separation in the glasses. Basically phase separation occurs

due to the formation of a second glass matrix within the

glass matrix. Higher modifier contained glasses, in general,

exhibit phase separation tendency [26]. The glass transition

temperature (Tg) of glasses is observed in the range of

600e800 �C followed by two exothermic peaks, which

belongs to crystallization of the glasses. Endothermic peaks

Fig. 10 e X-ray dot mapping of Na, Al, Si, Cr and Fe of the interface of the diffusion couple.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 73844

at around 1050e1200 �C are denoted for melting of the glasses

(Fig. 1). As a modifier (Na2O) increases the Tg, Tc and Tm

decrease in the present glasses. These observations are

similar to that of reported in sodium silicate glasses [27].

Based on the DTA results, the theoretical calculations were

made using different models as described in experimental

section. Calculated activation energy of these glasses with

various models is summarized in Table 2.

Kissinger and Mahadevan methods give nearly same value

of activation energy but Augis and Bennet’s method gives

relatively large value as compared to others. The average

value of activation energy of glasses except N-20 is large as

compared to another borosilicate system [9]. From Table 2, it

can be observed that N-20 glass shows very less value of

activation energy. It is well reported in literature that with

the increase of the modifier content the network weakens,

which will decrease the value of activation energy [26]. But

the value of activation energy follows the opposite trend in

this system. This anomaly arises due to the presence of

minor amount of SiO2 (Zeolite) phase in the microcrystalline

glass matrix containing higher Na2O. The increase in Na2O

content with a decrease of SiO2 content increases the phase

separation tendency in glasses as observed in Fig. 1. It can

be explained on the basis of the diffuse and broad

exothermic/endothermic peaks in DTA curve. However, the

trend observed for activation energy of all the glasses is

same. Fig. 2 depicts such variation for N-25 glass.

Asmentioned in experimental part, the difference between

Tg and Tc also indicate the thermal stability of the glasses.

According to this approach, N-10 glass is more stable as

compared to the other glasses as is evident from Fig. 1.

Fig. 3 shows the variation in Hr parameter for the second

crystallization peak of different compositions at different

heating rates. The Hr parameter of N-10 glass is higher than

other glasses as shown in Fig. 3. In general, the modifier

weakens the glass network and decreases the glass

transition temperature so the less content of Na2O in glass

composition shows better thermal stability [28]. Similarly,

Saad and Poulain have suggested a criterion to check the

stability of the glasses. According to this approach, N-10

glass exhibit higher S value which indicates the higher

stability of this particular glass. The S parameter with

respect to the Na2O is shown in Fig. 4.

The dilatometer studywas performed to know the variation

in a thermal expansion coefficient of all the pristine glasses,

which is shown in Fig. 5. N-10 glass shows a lower thermal

expansion coefficient as compared to the other glasses. The

thermal expansion coefficient originated due to asymmetric

potential well of the solids [29]. In the present glasses, the

observed TEC decreases as the modifier content decreases

except N-20. But the increasing trend of Ts value is observed

(Table 3). It is evident in XRD pattern of pristine glass as

shown in Fig. 6. The XRD pattern of higher modifier

containing glasses exhibits a sharp hump around 30� which is

due to zeolite phase [30]. The presence of this phase may lead

to decrease the TEC of the glasses since TEC of zeolite (SiO2) is

very low (0.5 � 10�6/K). In addition to TEC measurement on

pristine glasses, TEC of steel is also measured under a similar

condition to check the compatibility between selected N-10

glass and steel. The difference in TEC values of glasses and

steel is less than 1 � 10�6 which is necessary during SOFC

operation (Table 3). During SOFC operation glass gets

Fig. 11 e (a): Back scattered electronmicrograph of the N-10

glass. (b): EDS spectrum analyses of the glass marked in

Fig. 11(a).

Fig. 12 e (a): Back scattered electronmicrograph of the N-10

heat treated glass at 900 �C for 1 h (b): EDS spectrum anal-

yses of the glasseceramic marked in Fig. 12(a).

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 7 3845

converted to the glass ceramics. The presence of these

crystalline phases in the glass matrix changes the TEC.

Therefore, before the interfacial study, the selected glass was

heat treated for different duration and temperature. The heat

treatment is required to facilitate the maximum

crystallization for diffusion to occur. Ultimately, this will lead

to achieve good adhesion between steel and glass. Many

researchers have reported that phase separation leads less

activation energy of the crystallization, which is essential for

good adhesion with other metallic materials [31]. The peak

crystallization temperatures Tp1 and Tp2 of N-10 glass are

observed at 780 �C and 925 �C, respectively. Based on the

analysis of crystallization kinetics of the N-10 glass, the heat

treatment temperature selected for present study was 900 �C,which is just below the second crystallization temperature of

this particular glass. The heat treated glass exhibits two

different crystalline phases, i.e. aluminum sodium silicate

(JCPDS #00-002e0625) and zeolite (JCPDS #01-073e3414) as

shown in Fig. 7. The formation of zeolite (SiO2) phase in glass

ceramic is harmful to SOFC application since it has low

thermal expansion. However, overall thermal expansion

of glass ceramic increases slightly as compared to pristine

glass. As shown in Table 3, the variation in TEC values of glass

and glass ceramic with steel is within the limit (<2%). This

indicates that the glass may be useful for interfacial study

with Crofer [32]. Based on the experimental and theoretical

results, N-10 glass was selected to make the diffusion couple

between Crofer 22APU steel and N-10 glass.

The detailed microstructural study of the interface

between N-10 glass and Crofer 22APU steel was done to get

more insight about the adhesion and interfacial mechanism.

3.2. Analysis of glassesteel interface

To study the interfacial phenomenon, glassesteel interface

was analyzed under SEM. Cross-sectional microstructure of

the interface between N-10 glass and Crofer 22APU is shown

in Fig. 8 (a & b). The interface between glass and steel shows

good adhesion (Fig. 8(a)). However, some voids and porosity

are observed at the areas away from the interface (Fig. 8(b)).

The EDS analysis at the marked area as shown in Fig. 8(b)

was done to understand the diffusion and inter-diffusion of

the elements. This is shown in Fig. 9(a)e(c) for the areas

marked as 1, 2 and 3, respectively.

As observed from the EDS analysis, the maximum diffu-

sion of Cr has taken place from the steel side. On the other

hand, only Al3þ has diffused from the glass side to the inter-

face which is very less in amount. Basically, the interface

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 73846

contained Cr3þ rich layer. Though its diffusion is within the

permissible limit, but it has got a higher tendency as

compared to other elements. The overall analysis indicates

that layers of chromium oxide and a reaction layer of Cr

diffusion into the glass identified by EDS were found at the

interface between the glass and the steel. For confirmation of

the diffusion from steel to glass and vice-versa, X-ray

elemental dot mapping of the interface was done. These

results are shown in Fig. 10. The SEM image of the interface

provides good adhesion of glass with steel as can be seen in

Fig. 10(a). The X-ray dot mapping of Na, Al, Si, Cr and Fe are

shown in Fig. 10(bef) respectively. These results further

confirmed the diffusion of Cr3þ which is more prominent

than other elements. However, the interface is smooth and

free from porosity, which is required for good sealing.

EDS analysis of as prepared and heat treated glass are

shown in Fig. 11(a and b) and Fig. 12(a and b), respectively. The

weight percentage of Na content in both the cases is about 4%.

There is no major change in the weight percentage of sodium

content before and after thermal treatment i.e. sodium is

present in the glass network.

4. Conclusions

Differential Thermal Analysis of all the glasses showed two

crystallization peaks due to phase separation in glasses. N-10

glass exhibitmaximum thermal stability as compared to other

glass compositions.

The TEC of N-10 glass ceramic is higher than the pristine

glass.

Heat treated glass (N-10) exhibit sodium rich (aluminum

sodium silicate) and sodium free (zeolite) phases which are

not detrimental for SOFC applications.

The diffusion couple between Crofer and glass (N-10) shows

the good and smooth interface which is formedmainly by the

diffusion of Cr3þ and Al3þ ions. Naþ ions are not present at the

interface.

Acknowledgment

The authors gratefully acknowledge the financial support

provided by UGC for this research work.

r e f e r e n c e s

[1] Steele BCH, Heinzel A. Materials for fuel-cell technologies.Nature 2001;414:345e52.

[2] Yamamoto O. Solid oxide fuel cells: fundamental aspects andprospects. Electrochim Acta 2000;45:2423e35.

[3] Kim Yongmin, Hong Seong-Ahn, Nama Suk Woo, Seo Seok-Ho, Yoo Young-Sung, Lee Sang-Houck, Development of 1 kWSOFC power package for dual-fuel operation. Int J Hydrogenenergy; doi:10.1016/j.ijhydene.2010.10.056.

[4] Fergus JW. Sealants for solid oxide fuel cells. J Power Sources2005;147:46e57.

[5] MahapatraMK, LuK. Glass-based seals for solid oxide fuel andelectrolyzer cells e a review. Mater Sci Eng R 2010;67:65e85.

[6] Xie X, Gao H. Calorimetric studies on the crystallization ofLi2SeB2O3 glasses. J Non-cryst Solids 1998;240:166e76.

[7] Yin Cheng, Hanning Xiao, Wenming Guo, Weiming Guo.Structure and crystallization kinetics of PbOeB2O3 glasses.Ceramics Int 2007;33:1341e7.

[8] Meinhardt KD, Kim DS, Chou YS, Weil KS. Synthesis andproperties of a barium aluminosilicate solid oxide fuel cellglasseceramic sealant. J Power Sources 2008;182:188e96.

[9] Arora Anu, Singh Kulvir, Pandey O.P., Thermal, structuraland crystallization kinetics of SiO2eBaOeZnOeB2O3eAl2O3

glass samples as a sealant for SOFC, Int J Hydrogen Energy;doi:10.1016/j.ijhydene.2011.03.036.

[10] Vishal Kumar, Anu Arora, Pandey OP, Singh K. Studies onthermal and structural properties of glasses as sealants forsolid oxide fuel cells. Int J Hydrogen Energy 2008;33:434e8.

[11] Yeong-Shyung Chou, Stevenson Jeffry W, Prabhakar Singh.Effect of aluminizing of Cr-containing ferritic alloys on theseal strength of a novel high-temperature solid oxide fuelcell sealing glass. J Power Sources 2008;185:1001e8.

[12] Sohn SB, Choi SY, Kim GH, Song HS, Kim GD. Suitable glass-ceramic sealant for planar solid-oxide fuel cells. J Am CeramSoc 2004;87:254e60.

[13] Tomozawa M, Takata M, Acocella J, Watson EB, Takamori T.Thermal properties of Na2O$3SiO2 glasses with high watercontent. J Non-cryst Solids 1983;56:343e8.

[14] Singh P, Vora SD. Vapor phase silica transport during SOFCoperation at 1000�C. Ceram Eng Sci Proc 2005;26:99e110.

[15] Scholze H, Nature Glass. Structure and properties. New York:Springer Verlag; 1991.

[16] Wassick TA, Doremus RH, Langford WA, Burman C.Hydration of soda-lime silicate glass, effect of alumina.J Non-cryst Solids 1983;54:139e51.

[17] Ghosh S, Sharma AD, Kundu P, Basu RN. Glass-Ceramicsealants for planar IT-SOFC: a bilayered approach for joiningelectrolyte and metallic interconnect. J Electrochem Soc2008;155:B473e8.

[18] Smeacetto F, Salvo M, Ferraris M, Casalegno V, Asinari P,Chrysanthou A. Characterization and performance of glass-ceramic sealant to join metallic interconnects to YSZ andanode-supported-electrolyte in planar SOFCs. J Eur CeramSoc 2008;28:2521e7.

[19] Smeacetto F, Salvo M, D’Herin Bytner FD, Leone P, Ferraris M.New glass and glass-ceramic sealants for planar solid oxidefuel cells. J Eur Ceram Soc 2010;30:933e40.

[20] Bahadur D, Lahl N, Singh K, Singheiser L, Hilpert K. Influenceof nucleating agents on the chemical Interaction ofMgOeAl2O3eSiO2eB2O3 glass sealants with components ofSOFCs. J Electrochem Soc 2004;151:A558e62.

[21] Mahadevan S, Giridhar A, Singh AK. Calorimetricmeasurements on as-sb-se glasses. J Non-Cryst Solids 1986;88:11e34.

[22] Kissinger HE. Reaction kinetics in differential thermalanalysis. Anal Chem 1957;29:1702e6.

[23] Augis JA, Bennett JE. Calculation of the Avrami parametersfor heterogeneous solid state reactions using a modificationof the Kissinger method. J Therm Anal 1978;13:283e92.

[24] Saad M, Poulain M. Glass forming ability criterion. Mater SciForum 1987;19-20:11e8.

[25] Hruby A. Evaluation of glass-forming tendency by means ofDTA. Czech J Phys B 1972;22:1187e93.

[26] Lahl N, Singh K, Singheiser L, Hilpert K. Crystallizationkinetics in AOeAl2O3eSiO2eB2O3 glass (A¼Ba, Ca, Mg).J Mater Sci 2000;35:3089e96.

[27] Ruzha Harizanova. Volksch Gunter, Russel Christian,crystallization and microstructure of glasses in the systemNa2O/MnO/SiO2/Fe2O3. Mater Res Bull 2011;46:81e6.

[28] Ma Mingsheng, Ni Wen, Wang Yali, Wang Zhongjie,Liu Fengmei. The effect of TiO2 on phase separation and

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 7 ( 2 0 1 2 ) 3 8 3 9e3 8 4 7 3847

crystallization of glass-ceramics in CaOeMgOeAl2O3

eSiO2eNa2O system. J Non-Cryst Solids 2008;354:5395e401.[29] Raghavan V., Materials science and engineering: a first

course, 5th edn.[30] Criado M, Fernandez-Jimenez A, Torre AG, de la,

Aranda MAG, Palomo A. An XRD study of the effect of theSiO2/Na2O ratio on the alkali activation of fly ash. CementConcrete Res 2007;37:671e9.

[31] Park J, Ozturk A. Effect of TiO2 addition on the crystallizationand tribological properties of MgOeCaOeSiO2eP2O5eFglasses. Thermochim Acta 2008;470:60e6.

[32] Ghosh S, Das Sharma A, Kundu P, Mahanty S, Basu RN.Development and characterizations ofBaOeCaOeAl2O3eSiO2 glasseceramic sealants forintermediate temperature solid oxide fuel cell application.J Non-Cryst Solids 2008;354:4081e8.