120

Chapter -4

Studies of Borate Glasses Doped with Transition Metal

Ion (Fe, Cu and TiO2)

1.1 Introduction

Recent technological applications have generated more interest in the studies

of different types of glasses. In the recent developments of novel compositions [1-6]

of

superior physical and chemical properties such as high thermal expansion coefficients

[7], low melting and softening temperatures and high ultra-violet and far infrared

transmission [8,9]

, make these glasses potential candidates for many technologically

applications, such as sealing materials, medical use [10]

, and solid state electrolytes [11]

.

Also because of their unusually high chemical durability and low processing

temperature, iron phosphate glass are being considered for vitrifying certain nuclear

wastes that are poorly suited for borosilicate glasses [12,13]

. Phosphate glasses are also

becoming important in optical technology such as in high energy laser application [11]

,

fiber and optical lenses [14, 15]

. The relationship between the structure of the host glass

and the properties of the doped ions is useful for designing the glasses for different

applications.

Transition metals ions (TMI) doped borate glasses have many applications in

microelectronics, optical glasses and solid state laser [16-18]

. Phosphate glasses

containing transition metal oxides (TMO) are of continuing interest because of their

applicability in memory switching, electrical threshold, and optical switching devices,

etc [19-21]

.

Glasses with high TiO2 content are of great interest in basic research and

technologic applications because of their optical properties and good chemical

resistance [22]

. Also, the titanate glasses are interesting for obtaining of glass-ceramics

with crystalline phases of barium and lead titanates, which present good dielectric

properties, by techniques such as quenching and heat treatment [23, 24]

or glass

irradiated by laser pulse [25]

. The main problem is the production of stable glasses,

since it is well known that TiO2 into glasses increases spontaneous crystallization

tendency during the cooling [26]

, however, it is reported that additions of glass

modifiers and formers SiO2 and B2O3 [27]

, Al2O3 and Na2O [28]

, B2O3, K2O, Cs2O and

121

BaO [29]

, PbO and P2O5 [30]

, etc., into the glassy network, stabilizes it against bulk or

superficial crystallization.

On one hand, glass ceramics based on titanate glasses, containing crystalline

phases of K2Ti6O13 [31]

, and/or perovskites of BaTiO3 [32]

, are very promising in

structural and electronic applications. The crystals of K2Ti6O13 have a fibrous tunnel-

like structure and exhibit high thermal insulation, mechanical and chemical resistance

[33]. Potassium hexatitanate whiskers are used as reinforcing agent for plastics and

metallic alloys because of their price ranges from one-tenth to one-twentieth of the

cost of SiC whiskers [34]

. On the other hand, BaTiO3 is used most extensively in

manufacturing of ceramic capacitors because of its high dielectric properties [35]

.

Vitrification and crystallization processes of titanate glasses, using melting-casting

technique have been studied in a few systems, such as K2O-TiO2 [36]

, K2O-Al2O3-TiO2

[37] and BaO-PbO-TiO2- B2O3-Al2O3

[38].

However, the aim of the present study was to investigate the effect of

transition metal ion Fe, Cu and TiO2 concentration on optical properties and the glass

forming characteristics of mixed alkali borophosphate glasses. Glasses of the general

composition 15Li2O – 15Na2O – 37.5B2O3 – 25P2O5 – (7.5 –x) ZnO – xTMI, with

different concentration of Fe, Cu, TiO2 were prepared by conventional melt-quench

method.

1.2 Experimental

Borate Glasses doped with Transition Metal Ion glasses having the following

compositions were prepared, using analytical grade compounds as the starting

materials following the procedure described in chapter 2.

122

Sr.

No.

Glass

Code

Composition Mole % (x)

1 V 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5

–x)ZnO -xFe

X=0.5, 1.0, 1.5,

2.0, 2.5.

2 VI 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5

–x)ZnO -xCu

X=0.5, 1.0, 1.5,

2.0, 2.5.

3 VII 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5

–x)ZnO –xTiO2

X= 1, 1.5, 2.0,

2.5, 3.

The initial constituents used were of 99.5% purity. These chemicals were

thoroughly mixed and ground for 30-40 min in a mortar pestle. The charge (30gm)

was calcined in an alumina crucible by considering the decomposition temperatures of

their initial compounds.

The calcined charge was then melted using muffle furnace. The melting

temperature was optimized at temperatures 9000C to 1100

0C for respective

composition. The charge was melt for 2-3 hrs. Under these conditions the melt was

thoroughly homogenized and attained desirable viscosity for pouring. The pouring

was done on a flat metallic plate.

The glass was then annealed at appropriate temperatures. The optimized

annealing temperatures were found to be 3500C

- 400

0C and the time to about 4 hrs,

for the present series of glass samples. For a lesser annealing temperature and dwell

time, cracking of the glass was observed.

123

4.3 Studies of Mixed Alkali Borophosphate Glass Doped with Fe

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xFe

The structures and properties of glasses in the mixed alkali (MA)

borophosphate glass doped with Fe system i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xFe have been investigated.

V-1 V-2 V-3 V-4

Photographs of investigated mixed alkali borophosphate glasses doped with Fe

4.3.1 Characterization

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xFe

The detailed characterization procedure of density, molar volume, X-ray

diffraction, UV transmission, infrared absorption spectra, TGA-DTA, dielectric

properties, conductivity, micro hardness, refractive index and chemical degradation

studies are given in chapter 2.

4.3.2 Results and Discussion

4.3.2.1 Density Measurements

The calculated values of density (ρ) and molar volume (Vm) for all the mixed

alkali borophosphate glasses doped with Fe samples under the investigation have been

displayed in table 4.3.1. Variation of density (ρ) and molar volume (Vm) with Fe

mole% for all glass samples is shown in fig. 4.3.1.

124

Table 4.3.1.Variation in physical properties with composition 15Li2O – 15Na2O –

37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xFe

Sr.

No.

Glass

Code

Glass composition (Mol %)

Molar

Mass

(gm)

Density

(g/cm3)

Molar

Volume

(cc/mol)

Li2O Na2O

B2O3 P2O5 ZnO Fe

1 V-1 15 15 37.5 25 7.0 0.5 81.32 1.98 41.07

2 V-2 15 15 37.5 25 6.5 1.0 81.19 1.92 42.28

3 V-3 15 15 37.5 25 6.0 1.5 81.07 1.84 44.05

4 V-4 15 15 37.5 25 5.5 2.0 80.94 1.76 45.98

5 V-5 15 15 37.5 25 5.0 2.5 80.81 1.70 47.53

The density of glass decreases from 1.98 to 1.70 g/cm3

and molar volume

increases from 41.07 to 47.53 cc/mol. It may be due to the smaller atomic weight of

the Fe samples as compared to the other samples in the system. The molar mass of the

samples decreases with increasing Fe composition as shown in figure 4.3.1.

The molar volume increases with increasing Fe composition, it indicate that

replacement of B2O3 by Fe increasing the molar volume causing shrinkage of the

glass network resulting decreases the density. It means that decreasing molecular

weight of oxide ions used in the glass, replacing B2O3 by Fe might be expected

decrease the density of these glasses.

The decrease of the modifier contents i.e. Fe acts as glass modifier in the pure

B2O3 results in the initial formation of four co-ordinated boron atoms where increased

modifier contents induce the formation of non-bridging oxygen containing borate

triangles.

This phenomenon is widely known as the ‘boron anomaly’. The increase in

density observed is attributed to increase in the rigidity of glass. In general the density

of glass system is explained in terms of between the masses and sizes of the various

structural units present in glass. In other words, the density is related to how tightly

the ions or ionic groups are packed closely in the structure. From fig. 4.3.1 it is

observed that the density decreases gradually with increase in Fe content in the

125

present glass system. The relationship between density and glass composition (x) can

be explained in terms of an apparent volume Vm occupied by 1 gm of oxygen. In this

case it is observed that molar volume increases monotonically with increase of Fe

content which indicates that the topology of the network is significantly changed with

composition.

0 2

1.70

1.75

1.80

1.85

1.90

1.95

2.00

Density

Molar Volume

MOl % Fe

Den

sity

(g/

cm3 )

40

42

44

46

48

MolarV

olum

e (cc/mol)

Fig.4.3.1.Variation of density and molar volume with mol% of Fe ion

4.3.2.2 XRD Analysis

Powder X-ray diffraction patterns of all the mixed alkali borophosphate

glasses doped with Fe (TMI) (15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x)

ZnO -xFe) glass samples showed broad peaks characteristics of glass structure.

Representative XRD pattern is shown in fig. 4.3.2. It confirms the amorphous nature

of the investigated glass samples.

126

20 30 40 50 60 70 80

600

800

1000

1200

1400

1600

1800

2000

2200

Inte

nsity

(a.u

.)

2(degree)

V-3

Fig.4.3.2. XRD pattern of a mixed alkali borophosphate glasses doped with x=1.5%

of Fe sample.

4.3.2.3 Infrared Transmission

The IR spectra of the mixed alkali borophosphate glasses doped with Fe

(15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -xFe) glass samples are

shown in fig. 4.3.3 and fig. 4.3.4.

Fig.4.3.3. IR spectra of the mixed alkali borophosphate glasses doped with x=0.5%

Fe.

127

Fig.4.3.4.IR spectra of the mixed alkali borophosphate glasses doped with x=2.0%

Fe.

Table 4.3.2.IR peaks and their assignments for mixed alkali borophosphate

glasses

Sr.

No.

Wave No. Assignments

1 650 – 1500cm-1

Vibrational modes observed are

mainly due to the phosphate

network which appears in the range

2 650 – 900cm-1

Characteristic of the vibrations of

bridging P-O-P groups

3 900 – 1156.88cm-1

Characteristic of terminal P-O and

PO3 groups

4 1156.88 to

1500cm-1

Characteristic of vibrations of non

bridging PO2 groups

5 1341cm-1

and

1741cm-1

B2 and B4 additional sharp peaks

The absorption bands of the mixed alkali borophosphate glasses doped with Fe

(15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -xFe) glass samples were

good agreement with reported literature [39]

.

128

4.3.2.4 UV- Visible Spectroscopy

Transmission characteristics for different glass composition having different

thickness are shown in fig. 4.3.5. Transmission in the range 300-800 nm is found to

be 45-65% in these glasses.

100 200 300 400 500 600 700

0

100

200

300

400

500

600

700

800

% T

ran

sm

itan

ce

Wavelength (nm)

V-1

V-2

V-3

V-4

Fig.4.3.5. UV spectra of mixed alkali borophosphate glasses doped with Fe ion

Table.4.3.3. Band gap of different mixed alkali borophosphate glasses doped with

Fe ion.

Sr.

No

Sample

Code

Composition

X mole %

% T UV cut

off

(nm)

Band

Gap in

eV

1 V-1 0.5 213.36 359.28 3.46

2 V-2 1.0 0.6144 374.83 3.31

3 V-3 1.5 13.59 434.54 2.85

4 V-4 2.0 0.523 438.26 2.83

Figure 4.3.5 reveals the variation of transmittance spectra of mixed alkali

borophosphate glasses doped with Fe. It can be observed that UV cut off point

increases with increasing doping of Fe ions and these values are listed in table 4.3.3.

129

The energy band gap of mixed alkali borophosphate glasses doped with Fe samples

decreases with increasing Fe %. This can be attributed to the structural changes that

are taking place with introduction of transition metal ions.

4.3.2.5 TGA – DTA Analysis

The characteristic temperatures of the obtained glass were determined by

thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The

TGA-DTA curves that were obtained for the as quenched glasses (powder)

corresponding to the compositions x=0.5% , 1.0% , 1.5% and 2.0% of Fe content are

shown in figs. 4.3.6, 4.3.7, 4.3.8 and 4.3.9, respectively.

Fig.4.3.6. TGA-DTA curve and characteristic temperature determined for the

compositions x=0.5% of Fe glass at heating rate of 40oC/min.

130

Fig.4.3.7. TGA-DTA curve and characteristic temperature determined for the

compositions x=1.0% of Fe glass at heating rate of 40oC/min.

Fig.4.3.8. TGA-DTA curve and characteristic temperature determined for the

compositions x=1.5% of Fe glass at heating rate of 40oC/min.

131

Fig.4.3.9. TGA-DTA curve and characteristic temperature determined for the

compositions x=2.0% of Fe glass at heating rate of 40oC/min.

The glass transition temperatures (Tg) and crystallization temperature (Tc) of

the various 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -xFe glass

samples are listed in table 4.3.3.

Table.4.3.4 Transition temperatures of mixed alkali borophosphate glasses doped

with Fe system indicated by TGA - DTA curves.

Sr.

No.

Glass

code

Mole %

Fe

Tg (oC) Tc (

oC)

1 V-1 0.5 438.18 508.84

2 V-2 1.0 442.99 516.38

3 V-3 1.5 442.62 512.04

4 V-4 2.0 447.88 512.38

From table 4.3.4 it indicates for higher mol % Fe glass transition temperature

(Tg) increases drastically but at lower mol % effect is less because of realignment of

network structure. However, the crystallization temperature (Tc) increases with

132

increasing Fe content of the mixed alkali borophosphate glasses doped with Fe

samples. It means that larger changes in glass structure occur.

4.3.2.6 Microhardness

The microhardness of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x)

ZnO -xFe glasses is 2.5203 GPa for 0.5%, 3.6874 GPa for 1.5% and 3.5010 GPa for

2.0% of Fe. From these values indicates the formation of more rigid structure.

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO –xFe glasses for 0.5%, 1.5% and 2.0% of Fe content are shown in figs.

4.3.10.

Fig. 4.3.10 Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xFe glasses for 0.5% of Fe

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –

x) ZnO –xFe glasses for 1.5% of Fe content is shown in fig. 4.3.11

133

Fig.4.3.11. Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xFe glasses for 1.5% of Fe

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –

x) ZnO –xFe glasses for 2.0% of Fe content is shown in fig. 4.3.12.

Fig.4.3.12. Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 –

25 P2O5 – (7.5 –x) ZnO -xFe glasses for 2.0% of Fe

4.3.2.7 Refractive Index

The refractive indices of the prepared 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xFe glasses were measured by travelling microscope. The

measured refractive index has been 1.5382 for 0.5% Fe and 1.4210 for 1.0% Fe

content doped the glasses and it agreed well with the reported value of El-Alaily et. al.

134

is 1.5731[40]

. However, the refractive index of our investigated samples are in the

range of 1.4210 – 1.5382. These values are good agreement to the reported by Alaily

et. al.

4.3.2.8 Dielectric Properties and Conductivity

The dielectric properties and a.c. conductivity measured to all glasses with

varying frequency at room temperature using impedance analyser LCR-Q meter

(Model HIOKI3532-50 LCR Hi- Tester) in the frequency range 100 Hz to 5MHz with

accuracy 0.001Hz. The impedance analyser was interfaced to a personal computer

using GPIB add on card and the recorded data was stored on the computer.

Measurements of capacitor and dissipation factor tanδ with varying frequency.

Using this value we have calculated dielectric constant (ε’), dielectric loss (ε”) and

dielectric loss tangent (tanδ) using following relation [41]

.

ε’= Cpd / ε0 A (1)

ε”= ε’tanδ (2)

Fig.4.3.13. Dielectric constant with log frequency

135

Where d is thickness of glass, A area of glass and ε0 permiviity of free space,

The dielectric properties of glasses arise due to ionic motion. Fig 4.3.13 shows

the frequency dependence of dielectric constant with room temperature of the studied

samples. From fig 4.3.13 all samples show the same behaviour is observed. Dielectric

constant decreases with increase in frequency up to a certain frequency and beyond

this frequency that remains fairly constant the similar behaviour is reported by

investigations [42]

. At certain frequency dielectric constant increases with increases in

Fe ion. This behaviour indicates that ferroelectric behaviour of all samples. This

variation of dielectric constant attributed to polarized space charge. Since grains or

grain boundaries are absent in glasses, the dielectric constants of glasses are usually

low, generally 5-12 dielectric properties are governed by conductions mechanism in

glasses at low frequency the dielectric constant is high this behaviour can explained

on the basis of polarization process.

Fig.4.3.14.Dielectric loss with log frequency

136

Fig.4.3.15.Dielectric loss tangent with log frequency

Fig 4.3.14 shows that dielectric loss in each glass is same behaviour. Fig

4.3.15 show the dielectric loss tangent with frequency of all samples. Fig 4.3.15

dielectric loss tangent increases with increase in frequency. The similar behaviour is

obtained all glass samples.

The a.c. conductivity obtained from following equation.

σa.c = ω ε0ε’tanδ (3)

When a low frequency ac fields applied across a material, the free charges in

the material can follow the field, giving rise to energy losses.

137

Fig.4.3.16. A.C. conductivity with log frequency

Thus ac conductivity can be considered is losses due to bound charges

whereas there should be no such losses under a dc field. In the present study, the ac

electrical conductivity (σa.c.) showed frequency dependence, (σa.c.) Increase with

frequency as show in fig 4.3.16. Even though, the origin of the frequency dependence

on conductivity is controversial. The a.c. conductivity increase with increase in

frequency and Fe ion similar type of behaviour is reported in a V2O5 doped glass [43]

.

4.3.2.9 Chemical Degradation

The result of the corrosion test for the polished samples of mixed alkali

borophosphate glasses doped with Fe system was carried out in 10% NaOH and 10%

HCl solutions at room temperature for 1hrs to 6 hrs of exposure are shown in tables

4.3.5 and 4.3.6.

The dissolution rate was seen to be higher in acidic medium as compared to

alkaline medium.

In 10% HCl solution, the rate of dissolution for glass V-4 i.e. 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 2.0Fe is maximum and for glass V-1

138

i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 0.5Fe is less in all the

studied glass samples of mixed alkali borophosphate glasses doped with Fe glasses.

In 10% NaOH solution, the dissolution rate is very slow, for V-1 glass than the

other. From the studies of chemical degradation it came to notice that the rate of

dissolution of V-1 glass in both i.e. in 10% HCl and in 10% NaOH is low in

comparison to other investigated mixed alkali borophosphate glasses doped with Fe

system.

In 10% HCl solution, the rate of dissolution for glass V-4 i.e. 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 2.0Fe is maximum and for glass V-1

i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 0.5Fe is less in all the

studied glass samples of mixed alkali borophosphate glasses doped with Fe glasses..

The investigated glasses contain group I (Periodic Table) fluxes i.e. Na and

glass former B2O3, which help to improve the chemical resistance hence the rate of

dissolution in NaOH solution is slower than in HCl. The result of the corrosion test

for the polished samples of mixed alkali borophosphate glasses doped with Fe system

was carried out in 10% NaOH and 10% HCl solutions at room temperature for 1hrs to

6 hrs of exposure are shown in figures 4.3.17 and 4.3.18.

Table.4.3.5. Weight loss observed in 10% HCl for 1 to 6 hrs of exposure of 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xFe glasses.

Sr.

No.

Glass

Code

Composition

X mole% of

Fe

Wt. loss in 10% HCl g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 V-1 0.5 0.42 0.63 0.78 0.85 0.99 0.90

2 V-2 1.0 0.38 0.60 0.71 0.86 0.96 0.89

3 V-3 1.5 0.31 0.58 0.69 0.81 0.92 0.90

4 V-4 2.0 0.35 0.60 0.68 0.82 0.93 0.91

139

Table.4.3.6. Weight loss observed in 10% NaOH for 1 to 6 hrs of exposure of

15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xFe glasses.

Sr.

No.

Glass

Code

Composition

X mole% of

Fe

Wt. loss in 10% NaOH g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 V-1 0.5 0.011 0.016 0.032 0.053 0.074 0.088

2 V-2 1.0 0.015 0.025 0.050 0.071 0.082 0.097

3 V-3 1.5 0.013 0.033 0.048 0.065 0.080 0.099

4 V-4 2.0 0.012 0.028 0.040 0.062 0.079 0.098

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Wt.

lo

ss in

10%

HC

l g

/cm

2

Mol % of Fe

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.3.17. Plot of weight loss versus Fe content at various time of exposure in 10%

HCL.

140

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

Wt.

lo

ss in

10%

NaO

H g

/cm

2

Mol % of Fe

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.3.18. Plot of weight loss versus Fe content at various time of exposure in 10%

NaOH.

141

4.4 Studies of Mixed Alkali Borophosphate Glasses Doped with Cu

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -xCu

The structures and properties of glasses in the mixed alkali (MA) borate glass

doped with Cu system i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -

xCu have been investigated.

VI-1 VI-2 VI-3 VI-5

Photographs of investigated mixed alkali borophosphate glasses doped with Cu.

4.4.1 Characterization

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –x Cu

The detailed characterization procedure of glass samples studies are given in

chapter 2.

4.4.2 Results and Discussion

4.4.2.1. Density Measurements

It is an important tool to explore the structural compactness, softening, the

change in geometric configuration and co-ordination etc. [44]

. The density and molar

volumes of mixed alkali borophosphate glasses doped with Cu ions under the

investigations have been given in table 4.4.1. In the present glass, Na2O – ZnO – B2O3

content remain constant while the CuO content varies from 5 to 15 % by replacing

P2O5 content.

142

Table.4.4.1. Chemical composition (mol %), density values and molar volume of

mixed alkali borophosphate glasses doped with Cu ions. (15Li2O – 15Na2O – 37.5

B2O3 – 25 P2O5 – (7.5 –x) ZnO –xCu)

Sr.

No.

Glass

Code

Glass composition (Mol %)

Molar

Mass

(gm)

Density

(g/cm3)

Molar

Volume

(cc/mol)

Li2O Na2O B2O3 P2O5 ZnO Cu

1 VI-1 15 15 37.5 25 7.0 0.5 81.36 1.68 48.42

2 VI-2 15 15 37.5 25 6.5 1.0 81.27 2.00 40.63

3 VI-3 15 15 37.5 25 6.0 1.5 81.19 2.34 34.69

4 VI-4 15 15 37.5 25 5.5 2.0 81.1 2.41 33.65

5 VI-5 15 15 37.5 25 5.0 2.5 81.00 2.49 32.53

From the graph it is shown that with addition of Cu there is initial increase in

density is observed. This is may be due to compactness of glass network formation.

The molar mass of the samples decreases with increasing Cu composition, the density

of glass increases from 1.68 to 2.49 g/cm3

and molar volume decreases from 48.42 to

32.53 cc/mol as shown in fig 4.4.1.

143

0 2

1.6

1.8

2.0

2.2

2.4

2.6

Density

Molar volume

Mol % Cu

Den

sity

(g/

cm3 )

32

34

36

38

40

42

44

46

48

50M

olar Volu

me cc/m

ol

Fig.4.4.1. Variation of density and molar volume with mol% of Cu ion

4.4.2.2. XRD Analysis

Powder XRD patterns of all the 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO -xCu glass samples showed broad peaks characteristics of glass

structure, amorphous nature of glass. A representative XRD pattern is shown in fig

4.4.2.

144

20 30 40 50 60 70 80

200

400

600

800

1000

1200

1400

1600

1800

Inte

nsity

(a.u

.)

2 (degree)

VI-2

Fig 4.4.2.XRD pattern of a mixed alkali borophosphate glasses doped with Cu

(15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO -xCu)

The broad peak obtained at 2θ range of 200 – 30

0 implies the non crystalline

nature of the glass.

4.4.2.3. Infrared Transmition

Fig.4.4.3. IR spectra of the mixed alkali borophosphate glasses doped with x=1.0%

Cu.

145

Table 4.4.2.IR peaks and their assignments for mixed alkali borophosphate glasses

doped with Cu.

Sr.

No.

Wave No. Assignments

1 962cm-1

Characteristic of the vibrations of

bridging P-O-P groups

2 1680cm-1

Assigned to water, OH

3 620cm-1

P-O-Cu stretching vibrations being

modified into the P-O-Cu-O-Zn

bands.

IR transmission spectra are shown in fig. 4.4.3, which represent the

characteristics of the various phosphate glass samples i.e. VI-2 of % CuO doped glass.

The absorption bands appear in the range 700 – 1500 cm-1

are mainly due to the

phosphate network. The pyrophosphate groups are predominant structure units in all

these glasses. The identical IR spectra for all these glasses clearly indicate that the

structure of PO4 chains doesn’t get affected by Cu+1

and Cu+2

ions in the glass. These

strong bands of the phosphate glass samples i.e. VI-2 of % CuO doped glass is similar

to the reported work [45-47]

.

4.4.2.4. UV- Visible Spectroscopy

The fundamental optical band gap of the glasses has been calculated using UV-

Vis transmittance spectra to understand their optically induced transition. The UV-VIS

transmittance spectra of a mixed alkali borophosphate glasses doped with Cu are

shown in figure 4.4.4.

The wavelength of mixed alkali borophosphate glasses doped with Cu glasses

samples increases with increasing the % of Cu. It was also confirmed that energy band

gap decreases with % of Cu increases. Figure 4.4.4 reveals the variation of

transmittance spectra of mixed alkali borophosphate glasses doped with Cu samples.

146

Table.4.4.3.Band gap of different mixed alkali borophosphate glasses doped with

Cu ion.

Sr.

No

Glass Code %T UV cut off

(nm)

Band Gap

in eV

1 VI-1 25346.80 520.08 2.39

2 VI-2 17121.79 529.41 2.35

3 VI-3 15548.88 554.95 2.24

200 300 400 500 600 700

0

5000

10000

15000

20000

25000

30000

%T

ran

sm

itta

nce

Wavelength (nm)

VI-1

VI-2

VI-3

Fig 4.4.4.UV transmission spectra of xLi2O – (30-x) Na2O – 37.5 B2O3

– 25 P2O5 – (7.5 –x) ZnO -xCu glasses

4.4.2.5. TGA – DTA Analysis

The characteristic temperatures of the obtained glass were determined by

TGA-DTA curves that were obtained for the as quenched glasses (powder)

corresponding to the compositions x=0.5%, 1.0% and 1.5% of Cu content are shown

in figs. 4.4.5, 4.4.6 and 4.4.7, respectively.

147

Fig.4.4.5. TGA-DTA curve and characteristic temperature determined for the

compositions x=0.5% Cu glass at heating rate of 40oC/min.

Fig.4.4.6. TGA-DTA curve and characteristic temperature determined for the

compositions of x=1.0% Cu glass at heating rate of 40oC/min.

148

Fig.4.4.7. TGA-DTA curve and characteristic temperature determined for the

compositions of x=1.5% Cu glass at heating rate of 40 o

C/min.

The glass transition temperatures (Tg) and crystallization temperature (Tc) of

the various 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xCu glass

samples are listed in table 4.4.4. Metwalli et. al. [48]

found that the glass transition

temperature (Tg) is 344oC for 50B2O3 – 45 PbO –5CuO glass samples.

Table.4.4.4. Transition temperatures of mixed alkali borophosphate glasses doped

with Cu system indicated by TGA - DTA curves.

Sr.

No.

Glass

code

Mole %

Cu

Tg (oC) Tc (

oC)

1 VI-1 0.5 441.92 502.33

2 VI-2 1.0 447.83 514.94

3 VI-3 1.5 444.20 515.08

From table 4.4.4 it indicates that the glass transition temperature changes with

increasing the Cu content. It may be due to the change in network structure; the

149

material become soft of the mixed alkali borophosphate glasses doped with Cu

samples.

4.4.2.6. Microhardness

The microhardness of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x)

ZnO -xCu glasses is 2.4517 GPa for 0.5% and 3.6285 GPa for 1.0% and 2.7459 GPa

for 1.5% of Cu content. It indicates the formation of more rigid structure. Miura et. al.

[49] found that the microhardness are in the range of 4.3 to 2.7 GPa for yCuO x(100-y)

P2O5 of glass samples. The values are good agreement with the reported values.

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO –xCu glasses for 0.5% of Fe content is shown in fig. 4.4.8.

Fig.4.4.8.Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xCu glasses for 0.5% of Cu content

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO –xCu glasses for 0.5% of Fe content is shown in fig. 4.4.9.

150

Fig.4.4.9.Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO –xCu glasses for 1.0% of Cu content

The Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO –xCu glasses for 0.5% of Fe content is shown in fig. 4.4.10.

Fig.4.4.10.Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xCu glasses for 1.5% of Cu content

4.4.2.7. Refractive Index

The refractive indices of the prepared 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO –xCu glasses were calculated a simple technique by travelling

microscope. The refractive index 1.237 for 0.5% Cu, 1.262 for 1.0% Cu and 1.283 for

1.5% Cu doped glasses.

151

4.4.2.8. Chemical Degradation

In the determination of degradation mechanisms, it is important to outline the

types of reaction that may take place between acid/alkali and phosphate glasses.

Polished samples of mixed alkali borophosphate glasses doped with Cu

glasses were exposed for 1 to 6 hrs of exposure.

The plot of weight loss observed and a content of CuO listed in table 4.4.5 and

4.4.6. The dissolution rate for Cu ion doped mixed alkali borophosphate glasses was

seen to be low as compared with previous glasses. It results that introduction of Cu

and Zn ions increase the chemical durability.

From the observed result, it is noticed that weight loss in HCl is more than

NaOH. The weight loss of investigated glass samples in NaOH is increase with

increases in CuO content up to 15%; but in HCl initially the weight loss is rapidly

upto 15%. Plot of weight loss versus Cu content at various time of exposure in 10%

HCL are shown in figure 4.4.11. Plot of weight loss versus Cu content at various time

of exposure in 10% NaOH is shown in figure 4.4.12.

Table.4.4.5.Weight loss observed in 10% HCl for 1 to 6 hrs of exposure of 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xCu glasses

Sr.

No.

Glass

Code

Composition

X mole% of

Cu

Wt. loss in 10% HCl g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 VI-1 0.5 0.50 0.71 0.79 0.84 0.99 1.07

2 VI-2 1.0 0.47 0.69 0.75 0.81 0.95 1.05

3 VI-3 1.5 0.39 0.61 0.69 0.75 0.89 1.00

152

Table.4.4.6. Weight loss observed in 10% NaOH for 1 to 6 hrs of exposure of

15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xCu glasses

Sr.

No.

Glass

Code

Composition

X mole% of

Cu

Wt. loss in 10% NaOH g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 VI-1 0.5 0.015 0.025 0.040 0.051 0.062 0.075

2 VI-2 1.0 0.021 0.037 0.051 0.072 0.091 0.110

3 VI-3 1.5 0.030 0.045 0.058 0.078 0.098 0.126

0.4 0.6 0.8 1.0 1.2 1.4 1.6

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Wt.

loss

in 1

0% H

Cl g

/cm

2

Mol % of Cu

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.4.11. Plot of weight loss versus Cu content at various time of exposure in 10%

HCL.

153

0.4 0.6 0.8 1.0 1.2 1.4 1.6

0.02

0.04

0.06

0.08

0.10

0.12

Wt.

loss

in 1

0% N

aOH

g/c

m2

Mol % of Cu

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.4.12. Plot of weight loss versus Cu content at various time of exposure in 10%

NaOH.

154

4.5 Studies of Mixed Alkali (MA) Borophosphate Glasses Doped

with TiO2

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xTiO2

The structures and properties of glasses in the mixed alkali borophosphate

glasses doped with TiO2 system i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –

x) ZnO –xTiO2 have been investigated.

VII-1 VII-2 VII-3 VII-4

Photographs of investigated mixed alkali borophosphate glasses doped with TiO2

4.5.1 Characterization

15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –x TiO2

The detailed characterization procedure is given in chapter 2.

4.5.2 Results and Discussion

4.5.2.1 Density Measurements

The mixed alkali borophosphate glasses doped with TiO2 ions under the

investigations have been displayed in table 4.5.1.

155

Table 4.5.1- density and molar volume of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO –x TiO2 glass system

Sr.

No

Glass

Code

Glass composition (Mol %)

Molar

Mass

(gm)

Density

(g/cm3)

Molar

Volume

(cc/mol)

Li2O Na2O

B2O3 P2O5 ZnO TiO2

1 VII-1 15 15 37.5 25 6.5 1.0 81.44 1.65 49.35

2 VII-2 15 15 37.5 25 6.0 1.5 81.44 1.66 49.06

3 VII-3 15 15 37.5 25 5.5 2.0 81.43 1.68 48.47

4 VII-4 15 15 37.5 25 5.0 2.5 81.42 1.74 46.79

5 VII-5 15 15 37.5 25 4.5 3.0 81.42 1.82 44.73

From the table for glass samples indicates the density of glass increases from

1.65 to 1.82 g/cm3

and molar volume decreases from 49.35 to 44.73cc/mol as noted in

a table and plotted density vs. content of TiO2 is as shown in fig 4.5.1. Increased in

modifier contents introduce the formation of NBO containing borate triangles [50-52]

.

With addition of TiO2 the topology of the network is changes. The increase of the

modifier contents i.e TiO2 acts as glass modifier. These results are found in good

agreement with results reported earlier [53-55]

.

156

0 2 4

1.64

1.66

1.68

1.70

1.72

1.74

1.76

1.78

1.80

1.82

1.84

Density

Molar volume

Mol % TiO2

Den

sity

(g/c

m3 )

44

46

48

50M

ola

r Volu

me (cc/m

ol)

Fig.4.5.1.Variation of density and molar volume with mol % of TiO2 ion

4.5.2.2. XRD Analysis

The XRD patterns of all the mixed alkali borophosphate glasses doped with

TiO2 samples show no sharp peak, but only a broad diffuse hump around low angle

region, this is clear indication of glass structure. Representative XRD pattern is shown

in fig 4.5.2, which confirms the amorphous nature of the investigated glass samples.

157

20 30 40 50 60 70 80

200

400

600

800

1000

1200

1400

1600

1800

Inte

nsity

(a.u

.)

2 (degree)

VII-1

Fig.4.5.2.XRD pattern of a mixed alkali borophosphate glasses doped with TiO2

(15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xTiO2) samples

4.5.2.3. Infrared Transmition

Fig.4.5.3. IR Spectra of mixed alkali borophosphate glasses doped with x=1.5%

TiO2

158

Table 4.5.2.IR peaks and their assignments for mixed alkali borophosphate glasses

doped with TiO2

Sr.

No.

Wave No. Assignments

1 1713cm-1

Asymmetric stretching vibration of

PO2 groups

2 1548 and 1417

cm-1

Asymmetric and symmetric

stretching of PO3 groups

3 1016cm-1

Asymmetric stretching of P-O-P

bridges

4 591 and 571cm-1

Symmetric stretching of P-O-P

bridges

5 518cm-1 P-O bonds

Symmetric stretching mode of PO3 units is due to weak band at 1016cm-1

these band is a characteristic absorption of BO4 structural units and band observed

1417 cm-1

is a characteristic absorption of BO3 structural units [56-58]

.

4.5.2.4. UV- Visible Spectroscopy

The glasses with and without TiO2 doping have been characterized with UV –

visible spectrophotometer and it has shown interesting results. Fig. 4.5.4 represents

the transmittance spectra of the x=1.0% and x=1.5% TiO2 doped polished glass

samples.

159

100 200 300 400 500 600 700

0

50

100

150

200

250

300

350

% T

ran

smit

ance

Wavelength (nm)

VII-1

VII-2

Fig.4.5.4. UV spectra of mixed alkali borophosphate glasses doped with TiO2

(15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x) ZnO –xTiO2) glass samples.

Table 4.5.3.Band gap of different mixed alkali borophosphate glasses doped with

TiO2

Sr.

No

Sample

Code

Composition

X mole %

% T UV cut

off

(nm)

Band

Gap in

eV.

1 VII-1 1.0 14.56 414.92 2.99

2 VII-2 1.5 172.53 434.82 2.86

The UV-VIS transmittance spectra of a mixed alkali borophosphate glasses

doped with TiO2 are shown in figure 4.5.4.

The wavelength of mixed alkali borophosphate glasses doped with TiO2

glasses samples increases with increasing the % of TiO2. It was also confirmed that

energy band gap decreases with % of TiO2 increases. Figure 4.5.4 reveals the variation

of transmittance spectra of mixed alkali borophosphate glasses doped with TiO2

160

samples. This can be attributed to the structural changes that are taking place with

introduction of TiO2 ions.

4.5.2.5. TGA-DTA Analysis

The TGA-DTA curves that were obtained for the as quenched glasses

(powder) corresponding to the compositions x=1.0% and 1.5% of TiO2 are shown in

figs. 4.5.5 and 4.5.6, respectively.

Fig.4.5.5. TGA-DTA curve and characteristic temperature determined for the

compositions of x=1.0% TiO2 glass at heating rate of 40oC/min.

161

Fig.4.5.6. TGA-DTA curve and characteristic temperature determined for the

compositions of x=1.5% TiO2 glass at heating rate of 40oC/min.

The Tg and Tc of the various 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –

x) ZnO - xTiO2 glass samples are listed in table 4.5.4. Shaim et. al. [59]

reported that

the glass transition temperature (Tg) is 440oC for Na2O –Bi2O3 –P2O5 –TiO2 samples.

This value is consistent with our values of the samples.

Table.4.5.4. Transition temperatures of mixed alkali borophosphate glasses doped

with TiO2 system indicated by TGA - DTA curves.

From table 4.5.4 Tg increase with increasing the TiO2 content. It may be due

the material become soft of the sodium borate glass samples. However, the

crystallization temperature (Tc) increases with increasing TiO2 content of the mixed

alkali borophosphate glasses doped with TiO2 samples it indicates larger changes in

glass structure occur.

Sr.

No.

Glass

code

Mole %

TiO2

Tg (oC) Tc (

oC)

1 VII-1 1.0 460.73 525.16

2 VII-2 1.5 462.98 525.87

162

4.5.2.6. Microhardness

The microhardness of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 – (7.5 –x)

ZnO - xTiO2 glasses is 3.1382 GPa for 1.0% and 2.9000 GPa for 1.5% of TiO2. It

indicates the formation of more rigid structure.

Vickers indentation image of 15Li2O –15Na2O –37.5 B2O3 –25 P2O5 –(7.5 –x)

ZnO -xFe glasses for 1.0% of TiO2 content as shown in figure 4.5.7.

Fig.4.5.7. Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25 P2O5 –

(7.5 –x) ZnO -xFe glasses for 1.0% of TiO2 content

Vickers indentation image of 15Li2O –15Na2O–37.5 B2O3–25 P2O5 –(7.5 –x)

ZnO -xFe glasses for 1.5% of TiO2 content as shown in figure 4.5.8.

Fig.4.5.8. Vickers indentation image of 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO -xFe glasses for 1.5% of TiO2 content

163

4.5.2.7. Refractive Index

The refractive indices of the prepared 15Li2O – 15Na2O – 37.5 B2O3 – 25

P2O5 – (7.5 –x) ZnO –xTiO2 glasses were calculated by simple technique of travelling

microscope. The measured refractive index has been 1.662 for 1.0% TiO2 and 1.521

for 1.5% TiO2 doped glasses.

4.5.2.8. Chemical Degradation

The result of the corrosion test for the polished samples of mixed alkali

borophosphate glasses doped with TiO2 glasses were carried out in 10% NaOH and

10% HCl solutions at room temperature for 1 hrs to 6 hrs of exposure are shown in

table 4.5.5 and 4.5.6.

The dissolution rate was seen to be higher in acidic medium as compared to

alkaline medium.

In 10% HCl solution, the rate of dissolution for glass VII-3 i.e. 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 2.0TiO2 is maximum and for glass

VII-1 i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 1.0TiO2 is less in

all the studied glass samples of mixed alkali borophosphate glasses doped with TiO2

glasses.

In 10% NaOH solution, the dissolution rate is very slow, for VII-1 glass than

the other. From the studies of chemical degradation it came to notice that the rate of

dissolution of VII-1 glass in both i.e. in 10% HCl and in 10% NaOH is low in

comparison to other investigated sodium borate glasses.

NaOH attack the borate skeleton; it does not attack on the alkali ions of the

glasses. Due to breaking the borate skeleton more alkali released to join the attack on

the glass. In 10% HCl solution, the rate of dissolution of for glass VII-3 i.e. 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 2.0TiO2 is maximum and for glass

VII-1 i.e. 15Li2O – 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – 1.0TiO2 is less in

all the studied glass samples of mixed alkali borophosphate glasses doped with TiO2

glasses.

The investigated glasses contain group I (Periodic Table) fluxes i.e. Na and

glass former B2O3, which help to improve the chemical resistance hence the rate of

dissolution in NaOH solution is slower than in HCl. Plot of weight loss versus TiO2

content at various time of exposure in 10% HCL is shown in figure 4.5.9. Plot of

164

weight loss versus TiO2 content at various time of exposure in 10% HCL is shown in

figure 4.5.10.

Table.4.5.5. Weight loss observed in 10% HCl for 1 to 6 hrs of exposure of 15Li2O –

15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xTiO2 glasses

Sr.

No.

Glass

Code

Composition

X mole% of

TiO2

Wt. loss in 10% HCl g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 VII-1 1.0 0.40 0.49 0.80 0.92 0.99 1.09

2 VII-2 1.5 0.48 0.51 0.84 0.90 0.97 1.05

3 VII-3 2.0 0.53 0.54 0.81 0.88 0.94 1.01

Table 4.5.6.Weight loss observed in 10% NaOH for 1 to 6 hrs of exposure of 15Li2O

– 15Na2O – 37.5 B2O3 – 25P2O5 – (7.5 – x) ZnO – xTiO2 glasses

Sr.

No.

Glass

Code

Composition

X mole% of

TiO2

Wt. loss in 10% NaOH g/cm2

1 hrs 2 hrs 3 hrs 4 hrs 5 hrs 6 hrs

1 VII-1 1.0 0.06 0.018 0.032 0.049 0.058 0.081

2 VII-2 1.5 0.011 0.020 0.035 0.053 0.062 0.085

3 VII-3 2.0 0.014 0.021 0.040 0.055 0.068 0.092

165

1.0 1.2 1.4 1.6 1.8 2.0

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Wt.

loss

in 1

0% H

Cl g

/cm

2

Mol % of TiO2

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.5.9. Plot of weight loss versus TiO2 content at various time of exposure in

10% HCL.

1.0 1.2 1.4 1.6 1.8 2.0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Wt.

loss

in 1

0% N

aOH

g/c

m2

Mol % of TiO2

1 hr

2 hrs

3 hrs

4 hrs

5 hrs

6 hrs

Fig.4.5.10. Plot of weight loss versus TiO2 content at various time of exposure in

10% HCL.

166

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