Comprehensive Studies of the Manganese Effect on Various Physical and Thermal Properties of Sodium Aluminum-Silicate Glasses Containing Sulfur

Beni-Suef University Journal of Applied Sciences 2012; 1(1): 35-48 www.scopemed.org

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Comprehensive Studies of the Manganese Effect on Various Physical and Thermal

Properties of Sodium Aluminum-Silicate Glasses

Containing Sulfur

A. A. Soliman, I. Kashif,* E. M. Sakr and A. Ratep

Physics Department, Faculty of Girls, Ain Shams University, Heliopolis, Cairo, Egypt

*Physics Department, Faculty of Science, Al- Azhar University, Nasr City, Cairo, Egypt

Abstract

The Na2O-SO2-Al2O3-SiO2 glasses containing different amounts of MnO2 ranging from 0.05

to1.0 mol% were prepared and characterized through density, molar volume, non-isothermal

differential thermal analysis (DTA), Vickers hardness, magnetic susceptibility and calculating

the fragility index (Fi), GFA and GS. The results indicate that the variations in density and

molar volume with increase in MnO2 indicate that the structure of glass becomes more open.

Also decrease in glass transition temperature from714 to 619K with increase in MnO2 amount

has been correlated with structural modifications of the network. GFA, GS, Hv and magnetic

susceptibility increased with the addition of MnO2 up to 0·2 mol%. The manganese ions

mostly exist in 2+ state in these glasses when the concentration of MnO2 <0.2 mol% and

above this concentration, these ions seem to exist in 3+ state which enter the glass network as

a modifier and the sulfur ions are entering the glass structure as a ligand around the

manganese octahedral with high spin.

Key Words: non-isothermal DTA; Silicate Glasses Containing Sulfur; fragility and Vickers

hardness; magnetic susceptibility; GFA.

Introduction

The growing importance of many glass

systems as well as their growing potential

and application in industry today enhanced

the necessary for further intensive

research, in attempts to shed more light on

their structure and consequently their

physical properties. So the density of

Na2O-Al2O3-SiO2 glasses (with

Al2O3/Na2O<1) was studied by Doweidar

(1998) to determine the volumes of

structural units. It was found that for

Al2O3/Na2O <1 aluminum ions enter the

structure in the form of AlO4 tetrahedra

with no effect on density and the density

depends on the ratio Na2O/SiO2. The ZnO–

Sb2O3–B2O3 glasses containing different

concentrations of MnO2 ranging from 0

to1.0 mol% were prepared by

Srinivasa et

al. (2006). A number of studies, viz.

optical absorption, infrared and ESR

spectra and magnetic susceptibility, were

carried. The analysis of the results indicate

that manganese ions mostly exist in Mn2+

state in these glasses when the

concentration of MnO2 <0.6 mol% and

above this concentration, these ions seem

to exist in Mn3+

state in the glass network.

Also, the effect of the same range of MnO2

content on Tg, density, hardness, glass

forming ability, stability, fragility,

magnetic susceptibility and the activation

energy of the glass transition of

40SiO2.5Al2O3.55Na2O glasses were

investigated by Soliman et al. (2011). The

result indicates that by increasing MnO up

to 0.4 mol%, manganese ions mostly exist

in the Mn2+

state, occupy network forming

positions in MnO4 structural units and

increase the rigidity of the glass network.

Beyond 0.4 mol%, these ions seem to

exist mostly in the Mn3+

state and occupy

modifying positions. In order to evaluate

the level of stability and GFA of the

glasses, different simple quantitative

methods have been suggested by (Ji Xiu-

Lin and Pan Ye (2009); Du et al. (2007);

Lad et al. (2004); Mondal et al. (2003);


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36

Hrubÿ (1972). They are based on the

characteristic temperatures such as the

glass transition temperature, Tg, the

crystallization temperature, Tp, or the

melting temperature, Tm.

In the present article, the role of the

manganese on the properties of

sodiumaluminosulfosilicate glasses was

investigated by using non-isothermal

differential thermal analysis (DTA),

measuring density, Vickers hardness,

magnetic susceptibility and calculating the

fragility index (Fi), GFA and GS. The

investigated glass samples compositions

contained a constant amount of the sulfur

(4 mol% S2O4 = 8 mol% SO2) as shown in

table (1).

Table .1. Batch composition of glass samples.

Samples

code

The Samples Components (mol %)

SiO

2

Al2O

3 Na2O

Na2S2O

5

MnO

2

S1 40 5

50.9

5 4 0.05

S2 40 5 50.8 4 0.2

S3 40 5 50.6 4 0.4

S4 40 5 50.4 4 0.6

S5 40 5 50.2 4 0.8

S6 40 5 50 4 1

Basics of the samples compositions

Silicon oxide, Aluminum oxide and

manganese oxide were introduced in the

same form. And Sodium oxide was

introduced in the form of crystalline

sodium carbonate which when heated for

preparation gives Na2O according to the

formula

Na2CO3→ Na2O + CO2

This means that one mole of Na2CO3 gives

one mole of Na2O. Also the Sulfur ions

was introduced in the form of crystalline

sodium sulfate which when heated for the

preparation gives SO2 according to the

formula

Na2S2O5→ Na2O + 2SO2,

This means that each mole of the Na2S2O5

gives two moles of SO2 and each glass

sample containing 8mol% SO2 as an

addition as shown in table 1. Glass

powders were first weighed and combined

into 100-gram batches according to the

desired composition with adding 8mol%

SO2. Batched powders were rolled on a

ball mill for 1 hour. Then transferred into

porcelain crucible and heated at 30°C/min

to a temperature of about 1100±20°C and

melted for 2 h bearing in mind that sulfur

could not volatilize for this temperature.

The melts were periodically stirred to aid

with homogenization and the molten

materials were quenched between two steel

plates at room temperature. Due to the

different applied investigations, the

samples were divided into two parts. One

part was powdered to suit the XRD, DTA

and magnetic susceptibility measurements.

The second part was used in its solid form

to suit the hardness and density

measurements.

Basics of the calculations:

Density:

The density of the glass samples were

measured using the Archimed’s technique

which is the most convenient used method.

The samples are weighted in the air and


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37

liquid with known density such as toluene

at room temperature. Then the density of

samples was calculated according to the

equation:

= wa / (wa-wb) .t (1)

Where

is the density of the glass samples

wa is the weight of sample in air

wb is the weight of the sample in toluene

is the density of toluene = 0.8655

gm/cm3)

The molar volume [Vm] was calculated

from molecular weight M, and density

[assuming Mn to be present as MnO2].

Fragility Index:

The dependence of the fragility on the

glass transition temperature, Tg; the

fragility index of the glass, in the

temperature range of glass transition, can

be Approximately evaluated by Durga and

Veeraiah (2003); Kodama and Kojima

(2002) using:·

(2)

Where Tg and Tgend (Te) could be determine

from DTA as shown in figure 1.

Figure.1. Schematic DTA heating curve in the vicinity of glass transition region.

Glass forming ability

According to the Gibbs free energy

between liquid and crystal, a

thermodynamic glass forming ability

(GFA) parameter related to characteristic

temperatures, onset crystallization

temperature (Tx) and liquids temperature

(Tl) was proposed for evaluating the GFA

parameter by Ji Xiu-Lin and Pan Ye, 2009

to be as the following

ω=Tl (Tl+Tx)/ (Tx (Tl-Tx))

(3)

Which is the most reliable and applicable

GFA parameter (Manara et al., 2007;


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38

Ardelean et al., 2002; Greaves, G. N. and

Sen, 2007)

Glass stability

The glass stability, GS, parameter which

can be readily determined via DTA .Glass

stability GS, on the other hand, accounts

for the resistance of a glass towards

devitrification up on reheating. Hrubÿ

(1972) has introduced a parameter KH,

which combines the nucleation and growth

aspects of phase transformation, as an

indicator of the GFA and is given by

KH= (Tx-Tg)/(Tm-Tx) (4)

The large of the KH values, the greater the

stability of the glass against devitrification.

Experimental work

A series of glass samples, of

composition [40 mol% SiO2 +5 mol%

Al2O3 + (51-x) mol% Na2O + 4 mol%

Na2S2O5 + x mol% MnO2] with x=0.05,

0.2, 0.4, 0.6, 0.8 and 1.0 mol% MnO2 were

prepared using chemically pure raw

materials, which were finely pulverized.

The details of the compositions chosen for

the present study are given in Table 1. The

homogeneous mixtures were melted in

porcelain crucibles in an UAF 15/10

Lenton Thermal Designs programmable

electrically heated furnace equipped with

an automatic temperature controller. The

quenched samples were annealed at 300°C

for 20 min, cooled in air to room

temperature, and placed immediately into

vacuum desiccators until used for

measurement. The samples were examined

using a Philips PW 3710 analytical X-Ray

diffraction system with a Cu anode, which

confirmed their amorphous nature. Further

measurements were carried out using

different techniques:

(1) The glass density measurements were

made within the experimental error about

±0·003 g/cm3.

(2) DTA measurements were carried out

using a SHIMADZU DTA-50. The

measurements were carried out between 25

and 1100°C under N2 gas with Al2O3

powder as a reference material, at heating

rates: β= 25K/min.

(3) Vickers hardness was measured using a

Zwick-3270 microhardness tester. The

surfaces of the glass samples were cleaned

in 10% HF aqueous solution for 30 s. The

applied load and the loading time were 4·9

N and 30 s, respectively.

The indentations were observed using a

microscope at room temperature.

(4) Magnetic susceptibility was measured

by applying the Gouy method using a

Faraday electromagnet.

Results

The glass samples [40 mol% SiO2 + 5

mol% Al2O3 + (51-x) mol% Na2O + 4

mol% Na2S2O5 + x mol% MnO2] with

x=0.05, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%

MnO2 were studied by using X-Ray

diffraction, density, differential thermal

analysis, Vickers hardness and magnetic

susceptibility. All the results are presented

as a function of x mol % MnO2 of the

investigated glass samples. It could notes

that our previous work Soliman et al.

(2011), was studied the role of the

manganese on the same glass samples

compositions but without sulfur content.

The investigated glass samples

compositions were contained a constant

amount of the sulfur as addition (4 mol%

S2O4 = 8 mol% SO2) as shown in table (1).

Then, comprehensive studies, concerning

manganese effect on the silicate of the

effect of the manganese on the silicate

glass samples in the presence of the

constant sulfur amount could be done by

using the above mentioned tools.

XRD characterization:

The investigated glass samples were

examined by using the XRD technique as

shown in figure 2. All the samples show a

broad halo peaking at around diffraction

angles (2θ) 32o characteristic of an

amorphous structure and confirming the

absence of crystals in the investigated

samples.


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39

Figure.2. The XRD of the investigated glass samples.

Density and Molar volume:

Figure 3 shows the dependence on

manganese content and the inverse trends

of the density and molar volume of the

glass system: 40 mol% SiO2+ 5 mol%

Al2O3+(51–x) mol% Na2O+x mol% MnO2

+ 4 mol% Na2S2O5 with x = 0.05, 0.2, 0.4,

0.6, 0.8 and 1 mol% MnO2.The density

shows a rapid increase as the mol% of

MnO2 increases for 0.2 mol% followed by

a sharp decrease for 0.4 mol% MnO2 then a

rapid increase for 0.6 mol% MnO2 and then

decreases beyond 0.6 mol% MnO2. In

comparison the variation of the density and

the molar volume of the investigated glass

samples with those in the previous work

Soliman et al. (2011), it shows the same

behaviour with turning the upside down for

the investigated glass samples due to some

shifts of the manganese concentration due

to the presence of sulfur.


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40

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

0 0.2 0.4 0.6 0.8 1 1.2

MnO2 mol%

de

nsity(

g/c

m3)

24.5

25

25.5

26

26.5

27

27.5

28

Vm

(cm

3/m

ol

density(g/cm3)

Vm(cm3/mol)

Figure.3. Density and molar volumes of the investigated glass samples.

DTA measurements:-

The DTA curves from the different

stoichiometries have been measured at a

heating rate of 25K/min as shown in figure

4.

Figure.4. DTA traces in the endothermic and exothermic directions at heating rate of

25K/min for the investigated glass samples.

They exhibited an endothermic peak due to

the glass transition temperature, Tg and

exothermic peak was found by increasing

the temperature that represents the


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crystallization temperature, Tc. The

exothermic peak is followed by a sharp

peak just before the onset melting

temperature, Tm, which may be the eutectic

point of the glass samples and Tm is

followed by the liquid temperature, Tl. The

effect of x mol% MnO2 content on the

thermal transitions data, Tc, Tm and Tl for

the investigated glass samples is shown in

figure 5 as determined from the DTA

traces at a heating rate 25 K/min. The

value of the glass transition temperature,

Tg, of the investigated samples could be

observed almost constant values by

increasing the manganese concentration up

to 0.4 mol% MnO2 followed by increases

up to 0.6 mol% MnO2 and then rapidly

decreases beyond 0.6 mol% MnO2 as

shown in figure 6. Then the maximum Tg,

values were observed for a glass with a

low MnO2 content.

500

550

600

650

700

750

800

0 0.2 0.4 0.6 0.8 1

MnO2 mol%

Tc (

oC

)

905

925

945

965

985

1005

1025

1045

1065

Tm

,Tl (o

C)

TcTmTl

Figure. 5. The thermal transitions data, Tc, Tm and Tl versus MnO2 content for the

investigated glass samples

340

360

380

400

420

440

0 0.2 0.4 0.6 0.8 1

MnO2 mol%

Tg

oc

Figure.6. the glass transition temperature, Tg versus MnO2 content for the investigated glass

samples.


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42

Fragility index:

The fragility index, Fi is measure of the

rate at which the relaxation time decreases

with increasing temperature around Tg.

The fragility index of the glass, in the

temperature range of glass transition, can

be approximately evaluated (Durga and

Veeraiah N (2003); Kodama and Kojima

(2002); Soliman et al. (2010). The

dependence of this quantity on the glass

composition is shown in Figure 7. It shows

that the fragility slightly decreases with

increasing MnO2 content for 0.8 mol%

MnO2 and then increases beyond it.

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1

MnO2 mol%

Hv K

g.m

m-2

12

17

22

27

32

Fra

gili

ty (

Fi)

HvFi

Figure.7. Fragility and Vickers hardness, Hv, versus MnO2 content of the

investigated glass samples

Hardness:

Figure 7 shows the relation between the

hardness and the different concentrations of

manganese in the glass composition [40

mol% SiO2 + 5 mol% Al2O3 + (51-x) mol%

Na2O + 4 mol% Na2S2O5 + x mol% MnO2]

with x=0.05, 0.2, 0.4, 0.6, 0.8 and 1.0

mol% MnO2. It could be shown that the

hardness increases with increasing the

manganese content up to 0.2 mol%.

Beyond 0.2mol% MnO2 the hardness could

be shown as slightly increases (or about

constant behavior) with the increase of

manganese content up to 0.8 mol% and

then rapidly decreases beyond it.

Glass forming ability:

Figure 8 shows the relation between the

calculated values of the glass forming

ability parameter, ω, and the different

concentrations of the manganese content in

the glass samples [40 mol% SiO2 + 5

mol% Al2O3 + (51-x) mol% Na2O + 4

mol% Na2S2O5 + x mol% MnO2] with

x=0.05, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%

MnO2. The calculated values of the GFA

parameter, ω, show a rapid decrease for 0.2

mol% MnO2 and become almost constant

up to 0.8 mol% MnO2 followed by

increase beyond it. Then the investigated

glass samples have a higher GFA for low

manganese oxide contents less than

0.2mol% MnO2, with the best GFA for the

glass sample 0.05mol% MnO2. Indicating

that the concentration region of 0≤×≤0.2

mol % MnO2 is the best glass forming

ability composition region, i.e. the 40mol%

SiO2+5 mol% Al2O3+50.95 mol% Na2O+

4 mol% Na2S2O5 +0.05mol% MnO2 glass

sample has the best GFA.


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43

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

MnO2 mol%

KH

5

5.5

6

6.5

7

7.5

8

8.5

w

KHw

Figure.8. The glass forming ability parameter, ω, and the glass stability parameter, KH

versus MnO2 content for the investigated glass samples

Glass stability

The parameter, KH, Hrubÿ, 1972 is often

used to estimate glass stability, GS. The

larger the KH value, the greater the stability

of the glass against devitrification. The

calculated values of KH in this system are

shown in figure 8. Again the values of KH

decrease with increasing manganese

content up to about 0.2 mol% MnO2 and

beyond 0.2 mol% MnO2 the values of KH

become almost constant indicating a

decrease in GS and it has the same trend as

the GFA parameter. Then a strong

correlation is found between the

parameters of GS, KH, and the GFA are

indicating that the best of GS and GFA at

the concentration region of 0≤×≤0.2 mol %

MnO2 and this result is supported by the

earlier discussion.

Magnetic susceptibility:

The relation between the magnetic

susceptibility and the manganese content of

the investigated glass samples [40 mol%

SiO2 + 5 mol% Al2O3 + (51-x) mol% Na2O

+ 4 mol% Na2S2O5 + x mol% MnO2] with

x=0.05, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%

MnO2 is shown in figure 9. It could be

observed that the increase of the

manganese content up to 0.2 mol% causes

an increase in the magnetic susceptibility

and then decreases reaching minimum at

o.6 mol% MnO2.

Figure. 9. The magnetic susceptibility versus MnO2 content for the investigated glass

samples.


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44

More adding of the manganese content up

to 0.8 mol% MnO2 causes an increase in

the magnetic susceptibility and then

decreases beyond 0.8 mol% MnO2. In

comparison the variation of the magnetic

susceptibility of the investigated glass

samples with the other in the previous work

Soliman et al. (2011), it shows the same

behaviour but with some shifts in the

manganese concentrations. On the other

hand it can be noticed that the maximum

value of the magnetic susceptibility of the

investigated samples is found to be at about

0.2 mol% MnO2 while in the previous

work it was found to be at 0.4 mol% MnO2.

Also the minimum value of the

investigated samples is found to be at about

0.6 mol% MnO2 due to the presence of

sulfur while in the previous work it was

found to be at 0.8 mol% MnO2.

Discussions:

Density and Molar volume:

The variation of density and molar

volume with MnO2 mol% can be

interpreted in terms of the structural

changes which take place in the silicate

networks upon replacing Na2O by MnO2

and the effect of the different oxidation

states of manganese ions, Krishna et al.

(2008); Soliman et al. (2011), since the

SiO2/Al2O3 and SiO2/ S2O4 ratios are

constant in all the samples and the ratios of

SiO2/Na2O and Na2O / S2O4 are depend on

the manganese concentration. There is

unique dependence of density on the ratio

Na2O/SiO2 and the Al2O3 concentration

has no effect on density, Doweidar (1998).

Since for Al2O3/Na2O <1 aluminum ions

enter the structure in the form of AlO4

tetrahedral and such glasses the change in

density due to the structural units in the

silicate network is always compensated

with an opposite and equivalent change

due to the AlO4 groups, Doweidar (1998).

Then the rapid increase of the density as

the manganese content increases from 0.05

to 0.2 mol% MnO2 could be due to

replacing Na2O by MnO2 which causes an

increase in the molecular weight of the

glass samples since the manganese atoms

have a larger molecular weight than the

sodium atoms. While the decrease of the

density with increasing manganese content

up to 0.4 mol% MnO2 may be due to the

manganese ions are present in the form

Mn3+

which enter as a modifier in the glass

composition (Krishna et al. 2008; Durga

and Veeraiah,2003; Soliman et al. 2011),

and in turn leads to a decrease in the

polymerization of the silicate network and

so the structure of the glass network opens

up, leading in turn to decrease in the

density (Deshpande and Deshpande, 2006;

Soliman et al. 2010, 2011). From 0.4 to 0.6

mol% MnO2 the density increases and the

molar volume decreases because the

sulfate groups are incorporated in some

voids available, hindering glinding

movement of the glassy network, another

possible explanation could be sought in a

re-polymerization of the silica network as

Na+2

cations bonding the sulfate anions

according to the reaction( Manara et al.,

2007).

2(Si-0-Na) + +SO4

2- →2(Si-O-Si)

+Na2SO4

Beyond 0.6 mol% MnO2 the density

decreases and the molar volume increases

may be due to the manganese ions around

this concentration being in the form Mn3+

and enter as a modifier in the glass

composition where the sulfur ions enter

around it as a ligand and sodium enter as a

modifier which causes an increase in the

volume of the glass network.

The glass transition temperature, Tg

The variation of Tg values have almost

constant behavior by increasing the

manganese concentration up to 0.4 mol%

MnO2 which may be because Tg values

affected by two factors due to two interval

of manganese concentrations (up to 0.2 and

0.4 mol% MnO2). The first (up to 0.2

mol% MnO2) is due to the presence of the

manganese as Mn2+

ion which enters the

glass network as a former and the second

factor (up to 0.4 mol% MnO2) is due to the

manganese ions may be changed from 2+


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45

to 3+ state and occupy modifying positions

(Krishna et al. 2008; Durga and Veeraiah,

2003; Soliman et al. 2011), where the two

factors are justifying each other producing

almost constant behaviors of Tg values.

Beyond 0.4 mol% MnO2 the Tg value

increases up to 0.6 mol% MnO2 and then

rapidly decreases beyond 0.6 mol% MnO2

as shown in figure 6. Then the increase by

increasing the manganese up to 0.6 mol%

MnO2, may be due to the sulfur enters as

SO4 (former) which causes an increase in

Tg. The decrease of Tg beyond 0.6 mol%

MnO2 may be due to the conversion of the

manganese ions from Mn2+

to Mn3+

which

enters the glass network as a modifier.

Fragility index and Vickers hardness

Figure 7 shows the dependence on

manganese content and the inverse trends

of the fragility index and Vickers hardness

of the glass system: 40 mol% SiO2+ 5

mol% Al2O3+(51–x) mol% Na2O+ x mol%

MnO2 + 4 mol% Na2S2O5 with x = 0.05,

0.2, 0.4, 0.6, 0.8 and 1 mol% MnO2. The

increasing values of Vickers hardness in

the concentration region 0<x≤0·2 mol%

MnO2 may be due to the predominantly 2+

state of the manganese ions, occupying

network forming positions within MnO4

structural units and increasing the rigidity

of the glass network (Krishna et al. 2008;

Durga and Veeraiah,2003; Soliman et al.

2011). Beyond 0·2 mol% MnO2 up to 0.8

mol% could be notice almost constant

behavior of the hardness, that may be due

to the presence of manganese in the form

2+ and 3+ in equivalent effects. While the

fragility slightly decreases by increasing

the manganese concentration up to 0·8

mol% MnO2 which may be due to re-

polymerization of the silica network as

Na+2

cations bonding the sulfate anions

and in turn reducing the fragility of the

glasses network. The decreased values of

Vickers hardness beyond 0·8 mol% MnO2

may be due to the change in state of the

manganese ions to 3+, where they occupy

modifying positions (Durga and

Veeraiah,2003; Soliman et al. 2011) in

turn the number of NBOs increases, which

weakens the glass structure in turn reduces

its rigidity and increases its fragility.

Glass forming ability and glass stability:

Both the glass forming ability, GFA and

the glass stability, GS were decreased up to

0.2 mol% MnO2 and become almost

constant beyond it. Then the glass forming

and stability composition region could be

0.05 <x<0.2 mol% MnO2 and beyond 0.2

mol% MnO2 the ability to form glass does

not change by changing the manganese

content as well as the glass stability. Then

it can be seen that the values of w, have the

same trend as KH and these parameters

exhibit an excellent correlation with the

GFA (Soliman et al. 2010, 2011; Du et al.

2007 ), i.e. the

40SiO2.5Al2O3.50·95Na2O.0·05MnO2

4Na2S2O5 (mol%) glass sample has the

best GFA and thermal stability. In

comparison the variation of the GFA and

the GS of the investigated glass samples

with the those in the previous work

(Soliman et al. 2011), it shows some shifts

in the manganese concentrations. On the

other hand it can be noticed that the

maximum value of the GFA and GS of the

investigated samples is found to be at

about 0.05 mol% MnO2 while in the

previous work it was found to be at 0.4

mol% MnO2 indicating more modification

is happened for the glass network due to

the presence of sulfur, where the sulfur

ions enter around the manganese ions as a

ligand.

Magnetic susceptibility:

The magnetic susceptibility increases

by increasing the manganese for 0.2

mol% and then decreases reaching

minimum for o.6 mol% MnO2 and more

adding of MnO2 causes an increase of the

magnetic susceptibility for 0.8 mol%

MnO2 and then decreases beyond it. It

could be observed that by increasing MnO2

content, the magnetic susceptibility at the

beginning is growing up to 0.2 mol%

where the manganese ion enters as a

former which is present in the form 2+ in

the glass network with both tetrahedral and

octahedral environment (Srinivasa,2006;


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46

Ardelean, 2002). With more addition of

manganese, the magnetic susceptibility

decreases and reached the minimum at 0.6

mol% MnO2 which may be due to the

manganese ions were changed from Mn2+

to Mn3+

. Beyond it, the sulfur ions are

entering the glass structure as a ligand

around the manganese octahedral with high

spin (sulfur present in the first of

electrochemical series) and thus increase

the number of unpaired electron which

causes an increase in magnetic

susceptibility up to 0.8 mol% MnO2. The

magnetic susceptibility decreases beyond

0.8 mol% MnO2 may be due to the

manganese ions are converted from Mn2+

to Mn3+

.

Amass all above

Now we need to assess the mechanical

and thermal properties of the investigated

glasses with the variation of glass

transition temperature. Then the variation

of glass transition temperature, Tg, with the

hardness and fragility of the samples is

shown in Figure 10. Moreover, the

variation of glass transition temperature,

Tg, with the hardness and density of the

samples is shown in Figure 11 where the

linearity is just as a guide for the direction

of changes. It could be deduced that the

hardness changes in the same trend as the

glass transition temperature (Tg,), while the

fragility changing in the opposite direction

of both as shown in figure 10. i.e. the

lowest value of Tg, corresponds to both of

the lowest value of hardness and higher

value of the fragility and vice versa.

15

17

19

21

23

25

27

29

31

340 360 380 400 420 440 460

Tg 0C

Fra

gili

ty

200

250

300

350

400

hard

iness

FiHvLinear (Hv)Linear (Fi)

Figure.10. The variation of the hardness and fragility of the investigated samples with the

glass transition temperature, Tg, (the linearity is just as a guide for the direction of changing)

In the meantime, figure 11 shows that Tg,

Hv and density correlate well.

Furthermore,the higher the glass transition

temperature and hardness, the easier it is to

produce glasses on cooling and the more

stable they are upon reheating. That Tg,

and Hv correlate well proves that glasses

have a higher concentration of glass

formers and a greater stability at low

manganese oxide contents (<0.2mol%

MnO2). Indicate that the structure of glass

becomes more open beyond 0.2mol%

MnO2, the manganese ions change to 3+

which enter the glass network as modifiers

breaking up the connectivity of corner

linked SiO4 tetrahedra with the creation of

nonbridging oxygens (Greaves and Sen

2007) and the sulfur ions enter around the

manganese ions as a ligand.


__________________________________________________________________________

47

2.45

2.5

2.55

2.6

2.65

2.7

2.75

2.8

340 360 380 400 420 440 460 480

Tg 0C

de

nsity

200

220

240

260

280

300

320

340

360

ha

rdin

ess

densityHvLinear (Hv)Linear (density)

Figure.11. The variation of the hardness and density with the glass transition temperature, Tg,(

the linearity is just as a guide for the direction of changing)

Then as compositions beyond 0·2 mol%

MnO2 become more modified, the silica

network is gradually depolymerized, with

reductions in the glass transition

temperature, Tg, indicative of a weakening

of the glass structure as supported by the

density, hardiness and fragility results. It is

possible to suggest that the lower the

manganese content of the glass samples,

the greater is its glass thermal stability and

GFA (Mondal et al. 2003; Soliman et al.

2011).

Then the comparison between the present

results and that from previous work

(Soliman et al. 2011) suggests that the

presence of sulfur give rise to enhancement

in the glass structure and its properties.

Conclusions:

In the present article, the effect of the

manganese on the properties of

sodiumaluminosulfosilicate glasses was

investigated by using non-isothermal

differential thermal analysis (DTA),

density, Vickers hardness, magnetic

susceptibility and calculating the fragility

index (Fi), GFA and GS. The investigated

glass samples compositions were contained

a constant amount of the sulfur as an

addition (4 mol% S2O4 = 8 mol% SO2).

The results indicate that manganese ions

mostly exist in Mn2+

state in these glasses

for the concentration of MnO2 <0.2mol%

and beyond it, these ions seem to exist in

Mn3+

state in the glass network and the

presence of sulfur atoms give rise to

enhancement in the glass structure.

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Comprehensive Studies of the Manganese Effect on Various Physical and Thermal Properties of Sodium Aluminum-Silicate Glasses Containing Sulfur

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