i
PREPARATION AND PROPERTES CHARACTERIZATION OF
P2O5-KNO3-K2O GLASS
MOHD HELMY BIN HASHIM
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Science (Physics)
Faculty of Science
Universiti Teknologi Malaysia
OCTOBER 2005
PSZ 19:16(Pin. 1/97)
UNIVERITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN STATUS TESIS
JUDUL: PREPARATION AND PROPERTIES CHARACTERIZATION OF
P2O5-KNO3-K2O GLASS
SESI PENGAJIAN:
Saya:
2004/2005
MOHD HELMY BIN HASHIM
(HURUF BESAR)
Mengaku membenarkan tesis (PSM/ Sarjana/ Doktor Falsafah)* ini disimpan di
Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti
berikut:
1. Tesis adalah hak milik Universiti Teknologi Malaysia
2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk
tujuan pengajian sahaja.
3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi.
4. **Sila tandakan ()
SULIT
(Mengandungi maklumat yang berdarjah keselamatan
atau kepentingan Malaysia seperti termaktub di dalam
AKTA RAHSIA RASMI 1972)
TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh
organisasi/ badan di mana penyelidikan dijalankan)
TIDAK TERHAD
Disahkan oleh
(TANDATANGAN PENULIS)
(TANDANGAN PENYELIA)
Alamat Tetap: 2, JALAN KEMULIAAN 11,
TAMAN UNIVERSITI,
81300 SKUDAI, JOHOR
Tarikh:
3 OKTOBER 2005
CATATAN: *
**
PROF. DR. MD. RAHIM BIN SAHAR
Tarikh:
3 OKTOBER 2005
Potong yang tidak berkenaan
Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada
pihak berkuasa/ organisasi berkenaan dengan menyatakan seali sebab
dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan
Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja
kursus dan penyelidikan atau Laporan Projek Sarjana Muda (PSM)
“We hereby declare that we have read this thesis and in our opinion
this thesis is sufficient in terms of scope and quality for the
award of the degree of Master of Science (Physics)”
Signature
: __________________
Name of supervisor I
: Prof. Dr. Md. Rahim bin Sahar
Date
: 3 October 2005
Signature
: __________________
Name of supervisor II : Dr. Mohd Nor bin Md. Yusuf
Date
: 3 October 2005
i
ii
I declare that this thesis entitled “Preparation and Properties Characterization of
P2O5-KNO3-K2O Glass” is the result of my own research except as cited in
references. The thesis has not been accepted for any degree and is not concurrently
submitted in candidature of any other degree.
Signature
:
Name
: Mohd Helmy Bin Hashim
Date
: 3 October 2005
iii
Alhamdulillah…
To my mother, Hjh. Halimah Binti Hj Abu Nasir;
To my father, Hj. Hashim Bin Hj. Ibrahim;
To my sister, Nor Haslina and Norliyana Safura;
To my brother-in-law, Jumadi Bin Abdul Shukor;
To my grandfather, Hj. Abu Nasir Bin Hj Abdul Samad;
Thanks for their patience, support and encouragement in numerous ways during the
process of my thesis writing.
To my fiancée, Nurulfadillah Bte Hj. Jais;
And her family,
Hj. Jais Bin Hj. Mohd Bandi;
Hjh. Mestina Binti Hj. Lasiman;
Hjh. Sariah Bintri Hj. Tahir.
Thanks for their understanding, continuous support and encouragement.
Al-Fatihah…
To my late grandfather, Hj. Ibrahim Bin Hj. Abu Bakar;
To my late grandmother,
Hjh. Hitam Binti Othman and Hjh. Roziah Binti Hj. Ali.
iv
ACKNOWLEDGEMENT
In preparing this thesis, I was in contact with many people including
researchers, academicians and practitioners. They have contributed towards my
understanding and thoughts. In particular, I wish to express my sincere appreciation
to my main thesis supervisor, Professor Dr. Md. Rahim Sahar for the encouragement
and guidance, critics and friendship. I am also very thankful to my co-supervisor Dr.
Mohd Nor Md. Yusuf for his guidance, advice and moral support. Without their
continuous motivation and interest, this would not have resulted in the same manner
as it is now.
I would also like to express my gratitude to MOSTE for funding this research
project entitled “Preparation and Properties Characterization of P2O5-KNO3-K2O
Glass” under Contract Research Grant, number 75020. Thanks and appreciations are
also extended to Material Analysis and Non-Destructive Testing Lab Assistant,
Department of Physics, Mr. Jaafar, Mr. Abd. Rahman, Mr. Ahmad Imbar and Mr.
Johari for their technical support during the experimental work.
My deepest gratitude to Mr Zuhairi, Mr Ramli and all of my colleagues in the
materials science unit of the Department of Physics, Faculty of Science, UTM for
their timely and valuable advice and contribution for ideas during the research
program.
I would also like to thank Mr. Adnan for helping on the technical analysis of
the samples by microhardness tester and to Mr. Jefri for sample analysis by
SEM/EDAX at the Faculty of Mechanical Engineering, UTM. To Mr. Lim Keng
Wei, Institut Ibnu Sina, UTM, thanks for XRD technical advice and support.
v
Special thanks to Lab Assistant, Faculty of Environmental Engineering, Mr.
Affendi and Mr. Bakthiar, also Mr. Tarmizi from Faculty of Mechanical
Engineering, respectively of Kolej Universiti Institut Teknologi Tun Hussein Onn
(Kuittho) for the technical analysis of the pH solution and sputter coater facilities.
vi
ABSTRACT
A series of glass based on 50P2O5-xKNO3-(50-x) K2O system where
0 < x ≤ 50 mol % has successfully been prepared using melt-quenched technique.
The glass crystallinity has been confirmed using X-Ray Diffraction (XRD) analysis
while the microhardness is measured using Vickers indenter. It is found that the
microhardness is in the range of 146 Hv to178 Hv as the mol % of KNO3 content
increases. The glass density, which is measured using the digital balance, is found to
be in the range of 2.3820 gcm-3 to 2.4232 gcm-3 as the mol % of KNO3 content
increases. The molecular bond structures and the characteristic of H-OH molecular
vibrations in the glass are investigated using Infrared absorption spectrometer in the
range of 370 cm-1 to 3800 cm-1. It has been found that the nitrogen incorporated into
the glass network by replacing the bridging oxygen. It is also found out that the
increase in the mol % of KNO3 content will cause the corrosion rate of the glass in
pH 1, pH 3, pH 5 and pH 7 solutions to fall from 5.83 x 10-3 gcm-2min-1 to
0.25 x 10-3 gcm-2min-1. All of the solutions experience the increase in pH value after
the 20 minutes corrosion test.
vii
ABSTRAK
Satu siri kaca berasaskan sistem 50P2O5-xKNO3-(50-x) K2O dengan
0 < x ≤ 50 mol % telah berjaya disediakan melalui kaedah pelindapan leburan.
Kehabluran kaca telah dipastikan menggunakan analisis Pembelauan Sinar-X (XRD)
manakala kekerasan mikro telah diukur menggunakan penusuk Vickers. Didapati
bahawa julat kekerasan mikro adalah dari 146 Hv hingga 178 Hv dengan
pertambahan kandungan mol % KNO3. Ketumpatan kaca pula telah disukat
menggunakan penimbang digital dan didapati berada dalam julat 2.3820 gcm-3
hingga 2.4232 gcm-3 dengan pertambahan kandungan mol % KNO3. Struktur ikatan
molekul dan sifat getaran molekul H-OH dalam kaca dikaji menggunakan
spectrometer serapan infra merah dalam julat 370 cm-1 hingga 3800 cm-1. Didapati
bahawa nitrogen masuk kedalam rangkaian kaca dengan menggantikan titian
oksigen. Didapati juga bahawa pertambahan kandungan mol % KNO3 akan
menyebabkan kadar kakisan kaca dalam larutan pH 1, pH 3, pH 5 dan pH 7 menurun
dari 5.83 x 10-3 gcm-2min-1 hingga 0.25 x 10-3 gcm-2min-1. Kesemua larutan tersebut
mengalami kenaikan nilai pH setelah 20 minit ujian kakisan dijalankan.
viii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
vi
ABSTRAK
vii
LIST OF CONTENT
viii
LIST OF TABLES
xi
LIST OF FIGURES
xiii
LIST OF SYMBOLS
xvi
LIST OF APPENDICES
xvii
INTRODUCTION
1.1
General Introduction
1
1.2
Problem Statement
2
1.3
Scope of the Study
2
1.4
Objectives of the Study
3
1.5
Choice of the System
3
1.6
Thesis Plan
4
ix
2
BACKGROUND
2.1
Introduction
6
2.2
The Glassy State
7
2.3
X-Ray Diffraction (XRD)
8
2.4
Glass Structure
11
2.4.1
P2O5 Glass Structure
11
2.4.2
Effect of Alkali to P2O5 Glass
16
2.4.3
Incorporation of Nitrogen to P2O5 Glass
18
2.4.4
Crystallization of Oxynitride Glass
21
2.5
P2O5 Glass Formation Region
22
2.6
Density of Glass
22
2.7
Vickers Hardness
23
2.7.1
24
2.8
2.9
3
Vickers Hardness of P2O5 Glass
Infrared (IR) Absorption Spectra
26
2.8.1
29
Infrared (IR) Absorption of P2O5 Glass
Chemical Durability
29
2.9.1
30
Chemical Durability of P2O5 Glass
EXPERIMENTAL TECHNIQUE
3.1
Introduction
34
3.2
Glass Preparation
34
3.3
X-Ray Diffraction (XRD)
37
3.4
Energy Dispersive Analysis by X-Ray (EDAX)
38
3.5
Density Measurement
38
3.6
Vickers Hardness
40
3.7
Infrared (IR) Spectroscopy
40
3.8
Chemical Durability
42
x
4
RESULTS AND DISCUSSION
4.1
Introduction
46
4.2
X-Ray Diffraction (XRD)
46
4.2.1
46
4.3
Glass Formation Region
Energy Dispersive Analysis by X-Ray (EDAX)
4.3.1
Determination of Nitrogen Content in Final
Glass Compositions
48
4.4
Density
50
4.5
Vickers Hardness
52
4.6
Infrared (IR) Absorption Spectra
54
4.6.1
Molecular Vibrational Peaks
54
4.6.2
Vibration of Hydroxyl Ion, OH-
58
4.7
5
48
Chemical Durability
60
4.7.1
Effect of Compositions
61
4.7.2
Effect of pH Solution
63
4.7.2.1 pH Measurement
64
CONCLUSIONS
5.1
Conclusions
68
REFERENCES
71
APPENDIX A
80
APPENDIX B
85
xi
LIST OF TABLES
TABLE
2.1
TITLE
PAGE
Potential ways nitrogen can be present
in a phosphate glass reacted with ammonia
19
2.2
Density of single oxide glass
23
2.3
Classification of IR radiation
26
4.1
Composition (mol %) and XRD results of
50P2O5-xKNO3-(50-x)K2O glass
4.2
50P2O5-xKNO3-(50-x)K2O; 0<x≤50 glass
composition and density (gcm-3)
4.3
50
50P2O5-xKNO3-(50-x)K2O; 0<x≤50 glass
composition and Vickers hardness (Hv)
4.4
48
55
IR absorption peaks of 50P2O5-xKNO3-(50-x)K2O;
0<x≤50 glass in the region of 1400 cm-1to 370cm-1
57
xii
4.5
Dissolution rate in pH conditions after 20 minutes
Immersion time
4.6
60
Final pH after 20 minutes immersions in pH buffer
solution
65
xiii
LIST OF FIGURES
FIGURE
2.1
TITLE
PAGE
Model of the relationship between volume and
temperature
8
2.2
Spectrum for crystalline phase
9
2.3
Diffuse spectrum for amorphous phase
9
2.4
Bragg’s law for the periodic arrangement atoms
10
2.5
Phosphorus oxide structure (a) PO4 and (b) P4O10 (P2O5)
12
2.6
Phosphate glass tetrahedral network
13
2.7
Phosphate tetrahedral sites that can exist in phosphate
glasses (a) Q3, (b) Q2, (c) Q1 and (d) Q0
2.8
The difference between (a) PO4 glass tetrahedral
(b) SiO4 glass tetrahedral
2.9
2.10
14
14
Excesses charge in phosphorus is compensated by
trivalent aluminum ion to a structure similar to SiO4
15
Linear alkali phosphate chains
16
xiv
2.11
Effect of phosphate structural groups when
alkali oxides are added. (i) In the form of Q2,
(ii) in the form of Q1 and (iii) in the form of Q0
2.12
17
Structure and properties of alkaline phosphate
glass chain network. (a) Before substitute nitrogen
placement and (b) after substitute nitrogen placement
2.13
20
Increasing of network cross-link density.
(a) Small number of cross-linking and
(b) large number of cross-linking
2.14
Vickers hardness measurement imprints
2.15
Two types of stretching vibrations (a) symmetric and
(b) asymmetric
2.16
21
25
28
Bending vibrations. (a) ‘In-plane’ rocking,
(b) ‘in-plane’ scissoring, (c) ‘out-of-plane’ wagging
and (d) ‘out-of-plane’ twisting
2.17
28
Steps of phosphate glass dissolution mechanism
(i) hydration and (ii) network breakage
31
2.18
Asymmetry of p-d orbital overlap between P and O
32
3.1
Glass preparation process
35
3.2
Glass preparation flow chart
36
3.3
Computer-assisted X-Ray (CuKα) Powder Diffractometer
37
3.4
Electronic Balance
39
xv
3.5
Microhardness tester
41
3.6
Fourier Transforms Infrared (FTIR) spectrometer
41
3.7
Cubic shape of glass sample
42
3.8
Chemical durability experiment setup
45
4.1
X-ray diffractogram for 50P2O5-xKNO3-(50-x)K2O system
47
4.2
Nitrogen (wt %) against KNO3 (mol %) of
50P2O5-xKNO3-(50-x)K2O glass
49
4.3
Density (gcm-3) against KNO3 (mol %)
51
4.4
Vickers hardness (Hv) against KNO3 (mol %)
53
4.5
IR spectra of 50P2O5-xKNO3-(50-x)K2O glass
in the region of 370 cm-1 to 1400 cm-1
55
4.6
Effect on P=O band frequency on addition of KNO3
57
4.7
IR spectra of 50P2O5-xKNO3-(50-x)K2O glass in
the region of 1400 cm-1 to 3800 cm-1
59
4.8
Fundamental vibration modes of H-OH
59
4.9
Dissolution rate (gcm-2min-1) against KNO3 (mol %)
61
4.10
Dissolution rate (gcm-2min-1) against pH
63
4.11
Effect of KNO3 content as a function of final pH
values after 20 minutes immersions times in various pH solution
66
xvi
LIST OF SYMBOLS
A
-
Surface area
DR
-
Dissolution Rate
F
-
Load (Force)
f
-
Force constant of molecule bonding
H
-
Ratio of load and surface area
h
-
Height
l
-
Length
l1,l2
-
Diagonal length
m
-
Order of the diffraction peak
m1, m2 -
Mass of atoms in molecule
n
-
Number of bridging oxygen per tetrahedral
OB
-
Bridging oxygen
OT
-
Terminal oxygen (Non-bridging oxygen)
Qn
-
Phosphate tetrahedral group
R
-
Ratio of M2O to P2O5
SA
-
Exposed area
T
-
Transmission
Tc
-
Crystallization Temperature
Tg
-
Glass Transformation Temperature
t
-
Time
W
-
Sample weight before immersion
Wa
-
Glass weight in air
WL
-
Glass weight in liquid
Wo
-
Sample weight after immersion
w
-
Wide
v
-
Vibration frequency
δ
-
Error
xvii
θ
-
Angle
λ
-
Wavelength
µ
-
Reduced mass of molecule system
ρg
-
Density of glass
ρL
-
Density of liquid
xviii
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
THE GLASS PREPARATION
80
B
EDAX SPECTRUM
85
CHAPTER 1
INTRODUCTION
1.1
General Introduction
In the 1950s, interest in amorphous alkali phosphate was stimulated by their
use in a variety of industrial applications, including sequestering agents for hard
water treatments and dispersants for clay processing and pigment manufacturing. By
studying such materials, Van Wazer established the foundations for much of present
understanding about the nature of phosphate glasses [1].
Phosphate glasses are technologically important materials due to their low
melting point and relatively high thermal expansion coefficients, which suit them as
a potential candidate for technological application, such as in medical use on solid
state electrolytes [2]. Phosphate glass also posses low glass transition temperature
and low softening temperature which are increasing interest for many applications
such as glass to metal seals, thick film paste, the molding of optical elements and low
temperature enamels for metals [3,4].
Some other characteristics such as chemical durability, density, IR spectra
and hardness of phosphate glass have also been investigated and attracted many
interests for immobilizing some level nuclear wastes, many of which contain one or
more alkali oxides [5, 6].
Phosphate glasses can also be a good candidate for fertilizer due to their fast
dissolution in aqueous solution [7, 8]. The remarkable bioactivity and compatibility
of the phosphate glasses also attracted the attention of scientists in the fields of
biomedical research to use them as medical materials and potential controlled release
carries of medicine [9-12].
The enormous applications of these glasses are mainly due to the capability to
change their chemical durability character. Day and Reidmeyer produced nitrogencontaining phosphate glasses in the early 1980s by treating the melt in anhydrous
ammonia gas or adding nitrogen compounds to the melt [13]. They found that doubly
and triply coordinated nitrogen ions replace the bridging and non-bridging oxygen
ions in the PO4 tetrahedral.
1.2
Problem Statement
Although there have been many investigation on phosphate based glass, the
effect of nitrogen on their properties such as hardness, glass transition temperature,
Young’s modulus, viscosity and others were not systematically being reported. It is
therefore the aims of this study to prepare and to investigate the physical,
mechanical, optical, and the chemical durability of 50P2O5-xKNO3-(50-x)K2O glass
where 0 ≤ x ≤ 50 mol % will be presented. This study is deemed useful for future
researchers in order to wider understanding and application of phosphate glass. All
the results will be discussed with respective to the composition.
1.3
Scope of the Study
This research study only covers the preparation of multi component
phosphate glass in 50P2O5-xKNO3-(50-x)K2O ternary system which
0 ≤ x ≤ 50 mol % via melt quenching technique and characterization of some
properties of the glass. The characterization of the glass is focusing on:
3
i.
Density based on the structure changers.
ii.
Hardness based on its composition.
iii.
Absorption infrared spectroscopy of glass molecule.
iv.
Chemical durability based on its compositions in the range between pH 1 to
pH 7 conditions.
1.4
Objectives of the Study
The objectives of the study are as follows:
i.
To identify the glass formation range based on 50P2O5-xKNO3-(50-x)K2O
system which 0 ≤ x ≤ 50 mol %.
ii.
To determine the density and correlate with the changing of the glass
structure.
iii.
To correlate the composition and the hardness of the glass.
iv.
To analyze the infrared absorption spectroscopy of the glass.
v.
To observe the effect of composition to chemical durability of the glass and
to evaluate the chemical durability of the glass in pH 1, pH 3, pH 5 and pH 7
conditions.
vi.
To determine the pH changes of solutions in order to understand the behavior
of the glass corrosion.
vii.
To observe the effect of nitrogen to the properties of glass.
1.5
Choice of the System
In this study, phosphate glass based on 50P2O5-xKNO3-(50-x)K2O system
was chosen. This is important especially in view of the effect of nitrogen (with the
nitrate as a source) in alkaline phosphate glasses. The study was done to the glass
sample that was prepared in the range of 0 ≤ x ≤ 50 where x is mol %.
4
P2O5 was chosen as a host because of its low melting point, wide glass
formation region and shows good chemical properties [14, 15]. KNO3 was selected
as the source of nitrogen since it is the simply method to add nitrogen into the glass.
In this study, K2O was used as modifier since it is very active chemically
[16]. It is also useful from the lowest temperature range to the highest [17]. K2O is
very similar to Na2O in its action in glasses. However, there are the couple minor
differences. In the first place, potassium improves the gloss of the glass relative to
soda. Second, in aluminosilicate formulations, the viscosity at given temperature of a
potassium system is higher than of an equivalent soda system.
1.6
Thesis Plan
This thesis is divided into five chapters. The first chapter is a brief of
introduction. In second chapter, reviews of background and current knowledge on
phosphate glass are presented. It will include the general theory on glassy state,
phosphate glass fundamental structure, a special survey on the phosphate glass
formation region, density, Vickers microhardness, infrared absorption spectroscopy,
and chemical durability.
In third chapter, the experimental and theoretical aspects that have been
employed in this research will be described in detail. This will include the
preparation of the glass, X-Ray Diffraction (XRD), observation of nitrogen content
by Energy Dispersive Analysis by X-Ray (EDAX), evaluation of density,
determination of hardness and infrared absorption spectroscopy. The end of the
chapter will discuss the experimental works on the observation of the glass chemical
durability behavior.
The experimental results and findings with discussions will be presented in
fourth chapter. This chapter will give a special attention on the glass properties.
5
Finally, in fifth chapter, some conclusions that may be extracted from this
research are presented. This would also include some suggestions for the future
studies and investigations.
CHAPTER 2
BACKGROUND
2.1
Introduction
Glass is one of the very useful materials. It is an amorphous solid that has no
longer-range order and has attracted many scientists and technologist to study and
further explore on their usage. Among the first to study in more basic way was
Michael Faraday. Michael Faraday was one of those who studied about glass
properties such as electrolysis and conductivity of melts of various glasses [14].
In the 1930s the understanding of the reason why certain molecules are glass
formers, and of the structure of glass, was enlarged by a group of glass researchers
such as Zachariasen and Warren [14]. Then, it was followed by Scott, Winkelmann,
Huggins and Sun [18] who started their works in various fields of glass including
structure, criterion for glass forming substances, gas permeation in glasses, glass
electrode and chemical durability of glasses.
The definition of glass becomes wider since every one can interpret their
ideas in many ways. But for the convenience of this study, glass can be define as a
material that comes from a super cooling process from liquid form without any
continuous state to a matter where a viscosity of the material is increased [19].
7
Glasses are usually inorganic substances formed by the solidification on melt
without crystallization. In the liquid state, the structure of the inorganic substances is
disarranged and the atoms are in continuous motion. With most substances, cooling
down of their melts brings about crystallization at a precisely defined temperature,
and the atoms arranged themselves to a regular network. But, with some substances,
however, the crystallization proceeds very slowly. This is due to a high viscosity of
the melt at the crystallization temperature. If the cooling is suitably rapid, the atoms
are not able to arrange into a crystalline network and only a certain rearrangement of
the neighbouring particles occurs [19, 20].
2.2
The Glassy State
They are many different techniques that can be used to prepare a glass, but
the widely used and certainly the most important historically, is melt quenching
techniques. When changes in specific volume and thermal capacity are investigated
for a glass melt that has been slowly cooled, the result obtained is shown in
Figure 2.1. Starting from the liquids state, as the temperature drops, the specific
volume decreases. Until the point of crystallization temperature (Tc) is reached, an
ordinary liquid releases its fusion heat and changes into a crystal with discontinuous
change in specific volume. Afterward, the volume decreases in accordance with the
expansion coefficient of the crystal. However, a substance, which solidifies into
glassy state, does not crystalline at Tc, but continues as a super cooled liquid until
point glass formation temperature (Tg).
8
Liquid
Specific Volume
Supercooled
Glass
Crystal
Tg
Tc
Temperature
Figure 2.1: Model of the relationship between specific volume and temperature.
2.3
X-Ray Diffraction (XRD)
To determine the amorphous state of the glass, the use of X-Ray Diffraction
technique is a common practice. Diffracted X-Ray waves from different atoms are
capable of interfering with each other and the resultant intensity distribution is
strongly modulated by this interaction. If the atoms are arranged in a periodic
fashion, as in crystals, the diffracted waves will consist of sharp interference
maximal (peaks) with the same symmetrical properties as in the distribution of atoms
(Figure 2.2). Measuring the diffraction pattern therefore allows us to deduce the
distribution of atoms in a material.
However, for the amorphous materials like glass, atoms arrangement is not
periodic [21] and the Bragg’s law is not obeyed. The diffractogram will project a
diffuse spectrum as in Figure 2.3.
9
Intensity
Diffracted peaks
2θ
Diffracted angle
Intensity
Figure 2.2: Spectrum for crystalline phase (Bragg’s law is obeyed)
Haloes peak
Diffracted angle
2θ
Figure 2.3: Diffuse spectrum for amorphous phase (Bragg’s law is
not obeyed)
10
The peaks in an X-Ray Diffraction pattern are directly related to the atomic
distances [21]. The incident and interaction of x-ray beam with the atoms arranged in
a periodic manner in two dimensions is shown in Figure 2.4.
Transmitted beam
Reflected beam
θ
d sin θ
θ
d sin θ
d
Figure 2.4: Bragg’s law for the periodic arrangement atoms.
For a given set of lattice plane with an inter-plane distance of d, the condition
for a diffraction (peak) to occur can be simply written as:
2 d sin θ = mλ
(2.1)
The equation 2.1 above is known as the Bragg's law, after W.L. Bragg, who
first proposed it. In the equation, λ is the wavelength of the x-ray, θ is the diffracted
angle, and m is an integer representing the order of the diffraction peak. The Bragg's
law is one of most important laws used for interpreting X-Ray Diffraction data.
11
2.4
Glass Structure
Briefly, glass is an amorphous solid that is always reflected in the short-range
order with x-ray. It is one of non-crystalline materials which has isotropic physical
properties and reveals no gain structure when it is viewed using an optical
microscope [22]. It is more difficult to know the structure of glass than crystalline
solid. The lacks of translational symmetry of the glass structure make it impossible to
define their unit cell.
The principal characteristic of glassy materials is reflected in the short range
order and the long range disorder [23, 24]. Disorder means mainly that the spatial
arrangement of atoms, ions and molecules do not exhibit three dimensional
periodicity, and the long range order of the crystalline state is destroyed.
The structure disorder of an ideal amorphous state refers to the topological
disorder. Except for some regular arrangement that exists in the nearest neighboring
atoms, some atoms are different from even the nearest neighboring atoms in the
angle of bonding, their strength, and co-ordination number and the structure
arrangement of the next neighboring atoms are all in disorder state. The glass is
regarded as having a disorder structure and there it is an amorphous.
2.4.1
P2O5 Glass Structure
There are three types of phosphorus oxide. They are P2O5, P2O4, and P2O3.
From all of the three types of phosphorus oxide, only P2O5 (phosphorus pentoxide)
can form a glass. The P2O5 (Figure 2.5.b) was built-up by the units of PO4
tetrahedral. This tetrahedral is composed of one phosphorus ion surrounded by four
oxygen ions at the corners (Figure 2.5.a). Adjacent tetrahedral shares three of their
four corner atoms and every tetrahedron has one non-bridging oxygen (NBO) (Figure
2.6). The tetrahedral begins to form as the melt is purposely cooled and becomes
increasingly viscous. The cooling is fast enough to freeze these units in a random
12
fashion, as opposed to the very ordered structure, which should have resulted if the
melt was cooled slowly, allowing crystallization to occur.
The basic structural unit of phosphate [PO4]-3 groups can be attached to a
maximum of three tetrahedral in crystalline state of P2O5. In phosphate glasses, the
PO4 tetrahedral structure is typically described by the Qn groups theory, where n
represents the number of bridging oxygen (BO) per tetrahedral. The number of crosslinking in the polymer is defined as the number of PO4 groups that are attached to
three other through BO [25]. In a pure P2O5 system, the glass is a 3-dimensional
network of branching units (Q3 units) with three BO and one double bonded oxygen
per tetrahedral unit. The addition of modifying alkali cations replaces Q3 units with
Q2 units with the cations creating ionic cross-linking between the phosphate units.
(a)
(b)
Oxygen atom
Phosphorus atom
Figure 2.5: Phosphorus oxide structure (a) PO4 and (b) P4O10 (P2O5) [15]
13
OT
P
OB
OT
OB
OT : Terminal oxygen (Non-bridging oxygen)
OB : Bridging oxygen
P : Phosphorus
Figure 2.6: Phosphate glass tetrahedral network
At a P2O5 concentration of approximately 50 mol%, the Q3 units disappear
and the structure consists of only Q2 units in the form of linear phosphate chains.
Further addition of modifying cations (greater than 50 mol %) begins to convert Q2
units to Q1 units, and finally Q0 units. These structures are shown in Figure 2.7.
It is also well known that the PO4 tetrahedral bonding is totally different from
SiO4. It is because SiO4 tetrahedral would share its four corner BO ions with
neighbors [20] while PO4 tetrahedral would share only three BO ion with neighbors.
This difference is shown in Figure 2.8.
14
Q3
Q2
(a)
(b)
Q1
Q0
(c)
(d)
Figure: 2.7: Phosphate tetrahedral sites that can exist in phosphate
glasses, namely (a) Q3, (b) Q2, (c) Q1 and (d) Q0
(a)
(b)
Figure 2.8: The difference between (a) PO4 glass tetrahedral and (b) SiO4
glass tetrahedral
15
However, the structures of phosphate glasses particularly those with low in
alkali and / or high in aluminum content, exhibit close relationships to those of
silicate glasses because the sizes of P5+ and Si4+ are comparable, and excesses in
charge can be compensated by trivalent Al3+ [26]. In this case, the NBO would share
corners with Al3+ to produce for BO as in SiO4 structures. This structure is as shown
in Figure 2.9.
Figure 2.9: Excesses charge in phosphorus is compensated by trivalent
aluminum ion to a structure similar to SiO4.
Anionic partial substitution of nitrogen for oxygen increases the cross-linking
density of network as well as the similarity to silicates when considering the
following cross-substitution:
P+5 + N-3 = Si+4 + O-2
(2.2)
where, the sign of “=” shows the similarities and not the equilibrium. Thus, the
phosphorus oxynitride, PON, is silica analog in which PO2N2 tetrahedral share their
four corners [27-29].
16
2.4.2
Effect of Alkali to P2O5 Glass
The effect of addition a modifier such as Na2O, K2O or CaO to P2O5 glass
results in cleavage of P-O-P linkages and the creation of (NBO) in the glass. The
alkali phosphate network is believed to consist of linear phosphate chains such as in
Figure 2.10 [30, 31].
Figure 2.10: Linear alkali phosphate chains
As alkali oxide, for example M2O is added to P2O5, the phosphate structural
groups change from Q3 to Q0 as the ratio M2O/P2O5 = R passes from 0 to finally 3.
At each alkali oxide concentration, the relative amounts of the individual
units adjust themselves to satisfy the simultaneous equilibrium as described in Figure
2.11. They can be in the form of Q2, Q1, or Q0.
17
(i)
3
QQ3
QQ22
(ii)
Q22
1
QQ1
(iii)
Q
Q11
Q00
Figure 2.11: Effect of phosphate structural groups when alkali oxides are
added. (i) In the form of Q2, (ii) in the form of Q1 and (iii) in the form of Q0
18
2.4.3
Incorporation of Nitrogen to P2O5 Glass
Interest in oxynitride phosphate glasses stem from their much lower tendency
to devitrify and their considerably higher chemical durability. In addition, the effect
of nitrogen on mechanicals properties is much greater than the effect of cations [32].
According to Wilder, Day and Bunker [33], oxynitride glasses have been
produced by two methods; namely, including compounds such as AlN, Si3N4, Ca3N2,
or Mg3N2 in a batch as a source of nitrogen or remelting a glass in anhydrous
ammonia vapor [34-36]. When a phosphate melts reacts with anhydrous ammonia
vapor, nitrogen can be visualized to be present in an oxynitride glass in at least six
different ways. The first five possibilities listed in Table 2.1 are of little importance
since there are overwhelming evidence [34-40] that nearly all of nitrogen is present
as the N3- ion.
According to the investigation [34-40], numerous of the structure and
properties of phosphorus oxynitride glasses show that the majority of the nitrogen is
present as two N3- ions replacing the three O2- ions in phosphate melts to produce
P-N and P=N bonding. This reaction thus will increase the chain length and crosslinking of the glass chain network. The increasing of the chain and cross-linking can
be shown in Figure 2.12. Further increase of nitrogen content to the glass will
increase the cross-linking density of chain network as was illustrated in Figure 2.13.
19
Table 2.1: Potential ways nitrogen can be present in a phosphate glass reacted
with ammonia
Species
1.
Remarks
NH
(ammonium)
+
4
≡P─O-─NH +4 ammonium ion structurally equivalent to alkali
ion.
N3+ replaces three H+ in chain terminating OH groups P5+ in
2.
NO 3−
(nitrate)
3.
NH 3
(ammonia)
4.
5.
6.
NH −2
(amide)
NH 2 −
(imide)
N 3−
(nitride)
PO 4 group to form ─ O ─ N ─ O ─.
│
O
│
Physically dissolved in ammonia.
Replace terminal OH- to form ≡ P ─NH3.
Replace terminal OH- to form P ─ N ─ P.
│
H
Replace three terminal OH- to form P ─ N ─ P or O2- to form
│
P
P ─ N ─ P or P=N─P.
│
P
20
(a)
(b)
Figure 2.12: Structure and properties of alkaline phosphate glass chain
network. (a) Before substitute nitrogen placement and (b) after substitute
nitrogen placement
21
(a)
(b)
Figure 2.13: Increasing of network cross-linking density. (a) Small number of
cross-linking and (b) large number of cross-linking
2.4.4
Crystallization of Oxynitride Glass
According to Leng-Ward [41] and Hampshire [42], oxynitride glasses may be
crystallized to form oxynitride glass-ceramic materials. The crystalline phase formed
on heat-treatment and the extension of their formation will determine the properties
of the particular material. The phases formed depend on both the composition of the
parent glass and the heat-treatment process. Many glasses require the addition of
nucleating agent to promote the crystallization to occur but, in general, oxynitride
glasses appear to be self-nucleating.
22
2.5
P2O5 Glass Formation Region
According to Andrade et al. [43], for the binary alkali-phosphate system, the
maximum percentage of the modifier (K2O) that allows obtaining a glass sample is
47mol%. It was proven in their structure studies of KNbO3 that with the addition of
5% Fe2O3 on 50%P2O5-50%K2O (based glass composition of the present study) they
were again in the glass formation region and starting to exhibit an amorphous phase.
It was proven since all of them showed a diffuse diffraction in their diffractogram
through the XRD method.
2.6
Density of Glass
Density of glass is being measured to understand their physical properties that
can finally be related to the change in composition. Density is measured in gcm-3
unit. Archimedes method has been used to measure density [44] since it does not
need so much information about the dimension of the glass as well as give more
accurate value. Glass sample is weighted in the air, Wa and in liquid, WL and the
density of the liquid is known as ρL. Density of sample, ρg can be obtained through
this relationship:
ρg =
W a ρL
Wa −WL
(2.3)
For comparison, the densities of selected single oxide glasses are listed in
Table 2.2. As shown in Table 2.2, P2O5 glass has a density around 2.23 gcm-3 [45]
depending on composition.
23
Table 2.2: Density of single oxide glass [45]
2.7
Glass
Density (gcm-3)
SiO2
2.20
GeO2
3.65
B2O5
1.84
As2O3
3.70
SbO3
≥ 5.18
P2O5
≥ 2.23
Vickers Hardness
A hardness of a material is often equated with its resistance to abrasion or
wear and this characteristic is of practical interest since it may determine the
durability of the material used and may also decide the suitability of the material for
special applications.
The hardness of substance can be described as a measure of its resistance to
the penetration of another rigid object [46]. With glass and ceramics, indentation
according to Vickers is usually measured. A suitable hard indenter is pressed into the
surface of the tested material, and the hardness H, is determined as the ratio of the
load, F, and the total surface area A of the permanent indentation that can be related
in equation (2.4).
24
H=
F
A
(2.4)
The Vickers indenter is a diamond pyramid having an angle of 1360 between
opposite pyramid faces [47]. After loading the indenter, pause, and unloading, the
lengths l1 , l 2 of both diagonals of the indentation are measured [19, 46]. The relation
gives the Vickers hardness, Hv [47]:
Hv = 0.1891
where, l =
(l
1
F
l2
(2.5)
+ l 2)
is the average of diagonal length (mm). The measurement imprints
2
of the Vickers hardness is shown in Figure 2.14.
2.7.1
Vickers Hardness of P2O5 Glass
It was reported that the formation of P-O-Cu bonds, which replace P-O---Na+
bonds in P2O5-CuO-Na2O glasses while keeping the same fraction of P-O-P bonds,
increases the cross-linking density in the glass network and therefore, increases the
hardness of the glass [48]. Similarly in phosphate glasses containing nitrogen; their
properties show that the addition of nitrogen also results in an increase of hardness of
the glass [49, 50]. It occurs when nitrogen replaces the oxygen to produce P=N and
P-N, thus enhancing the cross-linking density of the glass network.
25
Figure 2.14: Vickers hardness measurement imprints.
26
2.8
Infrared (IR) Absorption Spectra
The absorption spectra of glasses in the infrared region are largely determined
by the interactions between the material and radiation that excite the atomic
vibration. This may involve oscillatory changes in inter atomic distances (bond
stretching) or in bond angles (bond bending) [51]. It is an easy way to identify the
presence of certain functional groups in molecule. This technique measures the
absorption of various infrared light wavelengths by the material of interest. This
infrared absorption identifies specific molecular components and structure. Infrared
radiations can be divided in to three categories as indicated in Table 2.3.
Table 2.3: Classification of IR radiation [52]
Region
Wavelength range
(µm)
Wave number range
(cm-1)
Near
0.78 - 2.5
12800 - 4000
Middle
2.5 - 50
4000 - 200
Far
50 -1000
200 - 10
For a simple diatomic molecule, absorption of radiation may occur at the
natural vibration frequency of the molecule. This can be calculated using classical
mechanics. If the force constant of the bond is f and the masses of the atoms in the
molecules are m1 and m2, then the vibration frequency is given by [19]:
1
2
ν= π
f
µ
(2.6)
where,
µ=
m1 + m2
m1 m2
(2.7)
27
Although this simple equation cannot be applied to materials as complicated
as in organic glasses, nevertheless it is a general rule that glasses having
compositions based on heavy atoms, bond together by relative weak forces have their
strong infrared absorptions at longer wavelength than glasses consisting of light
atoms bonded together [51].
In order to absorb infrared radiation, a molecule must undergo a net change in
dipole moment as a consequence of its vibration motion. Only under these
circumstances can the alternating electrical fields of the radiation interact with
molecule and cause changing in the amplitude of one of its motion. The dipole
moment is determined by the magnitude of the charge difference and the distance
between the two centers of charge [51]. If the frequency of the radiation matches a
natural vibration frequency of the molecule, this will cause a net transfer of energy
that results change in the amplitude of the molecule vibration, and absorption of the
radiation is the consequence.
The wave numbers of the vibration mode depend on the atomic group,
geometrical arrangement of the atom and internal atom force. With these phenomena,
the atom then can be identified. Vibration mode in different planes may include
symmetrical stretching bond, scissoring, rocking, wagging and twisting mode which
may be accentuated by dangling bonds and other long range disorder of the glass.
The positions of atoms in a molecule are not fixed. They are subject to a
number of different vibrations. Vibrations fall into the two main categories of
stretching shown in Figure 2.15 and bending as shown in Figure 2.16. There are two
types of stretching vibration modes namely, symmetric and asymmetric depending
on the bond length. Meanwhile, there are four types of bending vibration namely in–
plane rocking, in-plane scissoring, out-of-plane wagging and out-of-plane twisting.
28
(a)
(b)
Figure 2.15: Two types of stretching vibrations (a) symmetric and
(b) asymmetric
Near
Near
Near
Far
θ
In-plane rocking In-plane scissoring Out-of-plane wagging Out-of-plane twisting
(b)
(c)
(a)
(d)
Figure 2.16: Bending vibrations. The arrows show the movement of atoms. (a) In
plane bending movement in perpetual angle between two bonds (b) in plane bending
movement due to the changes in angle between two bonds (c) bending movement ‘out
and in’ of plane and (d) twisting movement ‘out and in’ of plane.
29
2.8.1
Infrared (IR) Absorption of P2O5 Glass
According to Salim, Khattak and Hussain [53], the absorption of the P=O
group is around 1282 cm-1 to 1205 cm-1 in polymeric phosphate chains. The
stretching bands of P-O- (NBO) are around 1100 cm-1 to 1110 cm-1 and 1000 cm-1
[54]. Absorptions at 910 cm-1 to 725 cm-1 are due to P-O-P vibrations (BO). The
bands below 500 cm-1 are due to the bending mode of PO4 units in phosphate glass.
IR studies by Corbridge [55] on alkaline and earth alkaline metaphosphate glasses in
the region of 5000 cm-1 to 650 cm-1 showed that IR spectra are essentially related to
the anionic groups, and the cations play a secondary role. According to Pascual and
Duran [56], nitrogen causes shifts and changes in the intensity of IR absorption
bands because of the replacement of oxygen by nitrogen on the P-O-P bonding. This
is evidence that incorporation of nitrogen can occur in phosphate glass network and it
is attributed through Nuclear Magnetic Resonance (NMR) and X-Ray Photoelectron
Spectroscopy (XPS) as studied before [57].
2.9
Chemical Durability
The meaning of ‘chemical durability’ is usually used to express the resistance
offered by a glass against attack by aqueous solution and atmospheric agent [58].
There is no specific method of prediction that one glass is more chemically stable
than other, except after both have experienced a similar experimental condition [59].
Water or its components (OH- and H+) are the most important factors that
involve in the corrosion process. Doremus tried to clarify how water could react with
glass [14]. Later, based on Doremus model, Harvey and Boase [60-62] tried to give a
mathematical expression of glass dissolution kinetic. Many others are also working
in this field as such Xie, He and Xu [63]. Most of them believe that the glass
corrosion is because of a diffusion process.
30
When a glass reacts with water or with an aqueous solution, chemical
changes occur at the surface and may then spread to the whole of the glass depending
on a number of factors. But in this study only several factors will be discuss. They
are:
i. Composition of the glass
ii. pH of the solution.
The initial stage of the chemical reactions has generally been regarded as
those ions exchange between the alkali ions in the glass and the hydrogen ions in the
water (proton).
2.9.1
Chemical Durability of P2O5 Glass
The practical application of phosphate glasses is often limited by their poor
chemical durability. Recently, several phosphate glasses with high aqueous corrosion
resistance have been reported [64]. Bunker published some of the first
comprehensive examination of phosphate glass durability over a range of
compositions and pH values in 1984. Since then, several other reports have been
published on the mechanism of aqueous attack of phosphate glass systems [65-68].
The corrosion rate of phosphate glasses depends on their chemical durability
in relevant medium, which is related to the composition [69], thermal history of the
glass and nature of the media [70]. The nature of solvent along with leaching
experimental conditions comprises the external factors of the release kinetics of
phosphate glasses which depends on the dissolution mechanism of phosphate glass in
aqueous media.
31
According to the generally accepted mechanism of glass dissolution [71-73],
phosphate glasses dissolve in aqueous media in two interdependent steps which are
similar to those of silicate glasses. These steps are as shown in Figure 2.17:
(i)
Ion exchange
Hydration
(ii)
P-O-P breakage
Figure 2.17: Steps of phosphate glass dissolution mechanism (i) hydration
and (ii) network breakage
The first step is the hydration reaction whereby the glass exchanges modifier
cations with the hydrogen ions in water to carry out modifier cations-hydrogen ion
exchange resulting in the formation of hydrated layer on the glass surface at the
glass-water interface.
The second steps involving the network breakage whereby under attack of
hydrogen ions and water molecules, the P-O-P bonds in hydrated layer break up and
result in the destruction of the glass network and release of chains of phosphate with
different degree of polymerization into solution.
32
At high P2O5 concentrations, where the Q3 concentration is high, the
dominant corrosion mechanism is the hydrolysis of the branched tetrahedral (Q3
groups) [67]. These branched tetrahedral are easily attacked by water because the
bonds are strained due to the asymmetry of the p-d orbital overlap [74] as shown in
Figure 2.18. The remaining electron of P is promoted to the 3d orbital, resulting in a
dπ-pπ bonding between P at 3d orbital and O at 2p orbital.
-
+
O
P
-
Phosphorus 3d orbital
-
+
+
Oxygen 2p orbital
Figure 2.18: Asymmetry of p-d orbital overlap between P and O
With the addition of modifying cations and the simultaneous increase in Q2
units, the chemical durability of the glass increases. The addition of cations with high
valence such as Al2+ and Fe3+ which have ionic radius of 0.50 Å and 0.64 Å
respectively will increase the amount of ionic cross-linking within the glass network.
The incorporation of high electrostatic field strength cations can increase the
covalence of the P-O-M bonds and lead to strengthening of the glass matrix. In this
compositional region, the mechanism for dissolution can be explained by the
hydration of the ionic cross-linking, followed by the release of the intact phosphate
chain [74].
33
As a different, with further increase in the concentration of alkali modifiers
with bigger ionic radius such as K+ (1.33 Å), the electrostatic field strength and
phosphate chain length decreases and a simultaneous decrease in chemical durability
occur.
Other compositional variations can also be used to increase the chemical
durability of phosphate glasses. The replacement of a fraction of the oxygen atoms
with anion such nitrogen can also increase the resistance of the glass chain
dissolution by replacing P-O-P bonds with P-N=P or P-N<P bonds [68]. It is
believed that the increasing of the cross-linking chain network produced by existing
of –N= (doubly) and –N< (triply) coordinated nitrogen atoms will reduce the water
diffusion process.
The existing of the –N= and –N< coordinated nitrogen atoms which bonded
to P atoms in alkali phosphorus oxynitride glass was proved by Sauze [57] through
XPS. The results show that the –N= (doubly) and –N< (triply) coordinated nitrogen
atoms have binding energy at 397.9 eV and 399.4 eV respectively compared to -OBO at 533.4 eV which, promote the sharing of electron with phosphorus atoms to
produce the strengthening covalent bond glass chain network thus should also arise
the resistance of chain network hydration.
CHAPTER 3
EXPERIMENTAL TECHNIQUE
3.1
Introduction
In this chapter, all the experimental techniques that have been used will be
described in detail. This would include the glass preparation techniques, X-Ray
Diffraction method, and determination of glass optical, physical and mechanical
properties including the theoretical aspects of the techniques.
3.2
Glass Preparation
The raw materials of P2O5-KNO3-K2O glass were obtained in the powder
form. The P2O5 powder (99% purity derived from Fluka Chemica), KNO3 powder
(99% purity) from Goodrich Chemical Enterprise (GCE) and K2O powder from the
decomposition process of K2CO3 (GCE) chemical powder (99% purity). Upon
heating, K2CO3 decomposed to K2O and released CO2 through the equation (3.1)
below;
K2CO3 (solid)
K2O (solid) + CO2 (gas)
(3.1)
35
All samples were prepared using melt-quenching technique. An appropriate
amount of P2O5, KNO3 and K2CO3 powder were mixed properly in a silica crucible.
The 30 gm batches of mixture were pre heated at 5000C for half an hour and then at
9000C for 2 hours. After the all of composition mixture completely melt, they were
immediately transferred to another furnace to be quenched on moulds of stainless
steel to form 2.5 cm x 2.5 cm x 0.8 cm of bulk rectangular shape for annealing
process at 3000C for one hour. Then, the furnace was switched off to allow the
sample to cool down to the ambient temperature. Glass preparation process and the
flow chart are shown in Figure 3.1 and Figure 3.2 respectively.
Melting
Temperature (0C)
900
Quenching
500
Preheating
Annealing
300
27
0
30
60
90
120
150
180
210
Time (Minutes)
Figure 3.1: Glass preparation process
240
270
36
Well mixed of raw glass composition material was
placed in silica crucible.
The mixture was preheated at 5000C for half an
hour in furnace.
The mixture was melted at 9000C for 2 hours
in furnace.
The melting mixture was poured onto
the stainless steels mould for casting.
The melting mixture was quenched between
two stainless steels and annealed at 3000C
for 1 hour.
Cool down to room temperature
Sample
Figure 3.2: Glass preparation flow chart
37
3.3
X-Ray Diffraction (XRD)
To investigate the amorphous nature of the quenched glass and to identify the
crystalline phase during the changing of KNO3 composition, the samples were
pulverized to analyze in computer-assisted X-Ray (CuKα) Powder Diffractometer
model Bruker D8 Advance, located at Institut Ibnu Sina, Universiti Teknologi
Malaysia (UTM) Skudai. The investigation was done within parameter of
100 < 2θ< 700 in range. All of XRD patterns were obtained at room temperature
(300K) by step scanning of 0.020, one second for each step of counting time at 40 kV
and 25mA. The results were collected and compared for the phase identification
using the American Society for Testing and Materials (ASTM) data cards software.
Figure 3.3 shows an X-Ray Powder Diffractometer that has been used.
Figure 3.3: Computer-assisted X-Ray (CuKα) Powder Diffractometer
38
3.4
Energy Dispersive Analysis by X-Ray (EDAX)
EDAX experiment was done in order to determine the actual compositions of
nitrogen that successfully entered the glass. The EDAX analysis was carried out by
using the Scanning Electron Microscope (SEM) attached EDAX model Philips
XL 40 located at Faculty of Mechanical Engineering, Universiti Teknologi Malaysia
(UTM) Skudai. The samples were polished using SiC abrasive papers grit of 600,
800 and 1200 mesh and kerosene (as lubricant) to produce smooth and clean surface.
To avoid the contamination, the samples were washed in toluene and dried in oven at
33oC. Then, all of samples were coated with a thin layer of gold by sputtering
technique and mounted on an aluminum holder in order to localize the samples
surface target by using SEM for EDAX analysis.
3.5
Density Measurement
Density of the glass was measured by applying a simple Archimedes
principle using electronic balance model Precisa XT 220A located at Department of
Physics, Faculty of Science, Universiti Teknologi Malaysia (UTM), Skudai. A small
piece of glass sample was taken from S2, S3, S4, S5 and S6. To avoid any corrosion
reaction to the sample, toluene was used as an immersion liquid.
The density of the glass was calculated using the equation (2.3) and the
density of toluene is 0.8690 g cm-3 which also known as ρL. Figure 3.4 shows the
electronic balance that has been used during the experiment. From equation (2.3), the
error of density measurement can be deduced as:
δρ g δWa δWa + δWl δρ L
=
+
+
ρg
Wa
Wa − Wl
ρL
(3.2)
39
Since density of toluene ρL is constant, the term of density of toluene is
eliminated and the error of glass density can be written as:
 δW δW + δWl 
 × ρg
δρ g =  a + a
Wa − Wl 
 Wa
Figure 3.4: Electronic balance
(3.3)
40
3.6 Vickers Hardness
Vickers method with microscope (Figure 3.5: Shimadzu
Microhardness tester) model HMV-2T located at Faculty of Mechanical
Engineering, Universiti Teknologi Malaysia (UTM), Skudai was used to
determine the hardness of the glass. All the glass samples were polished using
600, 800 and 1200 mesh SiC abrasive papers and kerosene (as lubricant) to
produce flat and smooth surface. Load with 19.614 N was used in this
experiment.
After the load has been applied, the value of l1 and l2 could be determined.
Then equation (2.5) may be applied. From equation (2.5), the error of hardness
can be defined through equation (3.4):
δHv
Hv
=2
δl
l
+
δF
(3.4)
F
Since force F is constant, the term of force is eliminated and the error of hardness
can be written as:
δHv = 2
3.7
δl
l
× Hv
(3.5)
Infrared (IR) Spectroscopy
The IR spectra of the samples were measured from 370 cm-1 to 1400 cm-1 and
1400 cm-1 to 3800 cm-1 (wave number) by the standard KBr pellet method using
Perkin Elmer spectrometer model GX (Fourier Transforms Infrared) as shown in
Figure 3.6. The FTIR spectrometer located at Institut Ibnu Sina, Universiti Teknologi
Malaysia, Skudai. The sample pellets were prepared by mixing about 1:100 glass
powder to the anhydrous KBr powder. The background for the IR spectra of the glass
samples was calibrated for the spectra KBr.
41
Figure 3.5: Microhardness tester
Figure 3.6: Fourier Transforms Infrared (FTIR) spectrometer
42
3.8 Chemical Durability
The chemical durability of each glass composition was determined by means
of their dissolution rate (DR) in variable pH solution. HCl/ KOH ready made buffer
solution were used as an immersion liquid to form solution pH of 1, 3, 5 and 7.
A portion of cubic shape of glass of approximately 0.5 cm x 0.5 cm x 0.5 cm
were prepared such in Figure 3.7 and their surface are polished using SiC abrasive
papers grit of 320, 600, 800 and 1200 mesh using kerosene as a lubricant, followed
by 120 µm polishing papers in particle size using 3 µm diamond paste. This is in
order to obtain the best polished section glass surface.
SA5
SA4
w
l
SA3
SA6
h
SA1
SA2
Figure 3.7: Cubic shape of glass sample
43
For a cubic shape sample, a total surface area is determined from sum of their
6 surfaces area that were labeled as SA1, SA2, SA3, SA4, SA5, and SA6 respectively. Thus,
the total exposed area (SA) is given by:
S A = S A1 + S A 2 + S A3 + S A 4 + S A5 + S A6
(3.6)
Where S A1 = S A 4 = h × w, S A2 = S A5= w × l and S A3 = S A6 = l × h
(3.7)
l, w and h are the length, wide and height of the sample respectively. From equation
(3.6), the error of the surface area SA should be:
(3.8)
δS A = δS A1 + δS A 2 + δS A3 + δS A 4 + δS A5 + δS A6
Thus, from equation (3.7), the error of SA1, SA2, SA3, SA4, SA5, and SA6 can be deduced
as:
δS A1 = δS A 4 =
δS A 2 = δS A5 =
δh
h
δw
w
δw
+
(3.9)
w
+
δl
(3.10)
l
and
δS A3 = δS A 6 =
δl
l
+
δh
(3.11)
h
The glass samples were then washed with toluene, dried in oven at 33oC for
20 minutes and weighed before being immerse in 50 ml of pH 1, 3, 5 and 7 already
prepared buffer solutions at 27oC for the 20 minutes immersion time in test tubes
using a thread as a hanger. (Because of sample S2 especially in pH 1 and pH 3 has
disappeared in 30 minutes immersion times, this experiment was decided to be done
within 20 minutes immersion times). The experiments were illustrated in Figure 3.8.
44
The samples were taken out from the test tubes after the 20 minutes before
being cleaned up carefully later with smooth tissue to remove the surface layer
(corrosion product) that was produced during the corrosion reaction. Subsequently,
the samples were dried in the oven for 20 minutes and re-weighed.
In this study, the chemical durability of each glass was determined from the
dissolution rate (DR). The DR of bulk samples was calculated from the measured
weight loss, W-Wo (g) where W and Wo are the weights of sample before and after
immersion respectively, sample surface area SA (cm2), and the immersion time, t
(min), using the equation 3.12 [19] :
DR =
W − Wo
S At
(3.12)
The error can be written through equation (3.13):
δDR
DR
=
δ W − W0
W − Wo
+
δS A
+
SA
δt
(3.13)
t
Since the error of time is neglected since it is much smaller compared to the
errors of weight and surface area, equation (3.13) can be written as:
δDR
DR
=
δ W − W0
W − Wo
+
δS A
SA
(3.14)
and the error of dissolution rate:
 δ W − W0
δDR = 
 W − Wo
+
δS A 
 × DR
S A 
(3.15)
45
The changes in pH value notes the chemical reaction may be observed to
study the dissolution characteristic. The pH values of the solutions after the chemical
reaction were observed by using pH meter Horiba F-21 model.
Thread
Test Tube
Sample
pH Solution
Rack
pH 1
pH 3
pH 5
pH 7
Figure 3.8: Chemical durability experimental setup.
CHAPTER 4
RESULTS AND DISCUSSION
4.1
Introduction
The results of all experiments that have been done will be presented in this
chapter. They will be discussed with respect to the composition.
4.2
X-Ray Diffraction (XRD)
X-Ray Diffraction was used to investigate the amorphous nature of the glass.
The diffractogram spectra of samples were shown in Figure 4.1.
4.2.1
Glass Formation Region
As can be seen, the entire sample show an amorphous characteristic with the
exception of sample S1 (50P2O5 - 50K2O) where the KPO3 crystalline phase is easily
identified. It was reported by de Andrade et al. [43], that for the binary alkaliphosphate system, the allowed maximum percentage of the modifier (K2O) for the
formation of glass is 47 mol %.
47
Sample S1, which has 50 mol % of K2O shows evident of crystallization.
However, with the increasing mol % of KNO3, the glass can be easily formed. There
is a strong indication that the addition of KNO3 induces the glass formation. This is
due to the increases in the nitrogen content in the glass [75]. It is true since nitrogen
atoms resulting stronger covalent cross-linking between phosphates chains thus
produce the glass substance a high viscosity during melting and reducing the thermal
expansion coefficient [13, 56]. Rapid cooling process of the viscous melting
substance caused atoms incapable of arranging itself into a crystalline network [19,
20]. Thus, it can be stated that the addition of KNO3 into the glass system reduced
the tendency of the glass to crystallize.
Counts
(A.U)
S6
S5
S4
S3
S2
S1
10
20
40
30
50
60
2-Theta-Scale
Figure 4.1: X-ray diffractogram for 50P2O5-xKNO3-(50-x)K2O glass system.
Glass as in S1 is in crystalline phase
From the pattern of XRD diffractogram as shown in Figure 4.1, the
composition and the crystalline level of the glass can be summarized as in Table 4.1.
As can be seen, the additions of KNO3 clearly decreased the crystallinity state of the
glass.
48
Table 4.1: Composition (mol %) and XRD results of 50 (P2O5)-xKNO3-(50-x)K2O
glass
Sample
4.3
P2O5
KNO3
K2O
(mol %) (mol %) (mol %)
Results
Nitrogen
content
(wt. %)
XRD
S1
50
0
50
Crystalline
-
S2
50
10
40
Amorphous
6.52
S3
50
20
30
Amorphous
7.18
S4
50
30
20
Amorphous
8.67
S5
50
40
10
Amorphous
9.77
S6
50
50
0
Amorphous
10.43
Energy Dispersive Analysis by X-Ray (EDAX)
The EDAX analysis on the amount of glass elements has been conducted and
the results spectrum was shown in Appendix B.
4.3.1
Determination of Nitrogen Content in Final Glass Compositions.
The amount of nitrogen which was inserted is as shown in Table 4.1 and a
plot of nitrogen (wt. %) against the KNO3 compositions (mol %) is presented in
Figure 4.2. It seems from the figure, that the nitrogen content increases as the KNO3
content increases. The increase in nitrogen content is understandable since it comes
from the KNO3 which also increases at the expense of K2O.
49
12
12
S5
Nitrogen (wt. %)
10
10
S6
S4
88
S2
S3
66
44
22
00
00
10
10
20
20
30
30
40
40
50
KNO3 (mol %)
Figure 4.2: Nitrogen (wt. %) against KNO3 (mol %) of
50(P2O5)-xKNO3-(50-x)K2O glass
.
50
4.4
Density
Density of the glass was tabulated in Table 4.2 and a plot of density against
mol % KNO3 is shown in Figure 4.3. From the figure, it can be seen that the density
and KNO3 shows a mutual increment trend. This is quite understandable since the
increase in KNO3 (molecular weight = 101.106 gmol-1) with the reduction of K2O
(molecular weight = 94.203 gmol-1) will most likely result in higher total atomic
weight, thus increase the glass density.
The increase in density along with an increment of KNO3 seems also in
agreement with the results reported by Day [76]. The increasing of nitrogen content
in glasses will increase the density due to the change in the molecule structure caused
by the increasing number of interconnections among the phosphate chains hence
producing more compact and dense glass [56, 76].
Table 4.2: 50P2O5-xKNO3-(50-x) K2O; 0 < x ≤ 50 glass composition and density
(gcm-3)
Glass Composition (Mol %)
Density (gcm-3)
P2O5
KNO3
K2O
50
10
40
2.3820 ± 0.0004
50
20
30
2.3988 ± 0.0005
50
30
20
2.4048 ± 0.0111
50
40
10
2.4170 ± 0.0006
50
50
0
2.4232 ± 0.0002
51
2.440
S5
Density (gcm-3)
2.420
S6
S4
S3
2.400
S2
2.380
2.360
0
10
20
30
40
50
KNO3 (mol %)
Figure 4.3: Density (gcm-3) against KNO3 (mol %)
52
4.5
Vickers Hardness
Vickers hardness of the glass has been determined. The data was tabulated in
Table 4.3. From the table, a plot of hardness against KNO3 was produced and is
shown in Figure 4.4. The figure shows that an increase of nitrate content in the
composition will increase the Vickers hardness. This is true since the increase in
KNO3 would hardened the glass, perhaps due to the forming of P=N- and P-N=
bonding which increase the cross-linking in the glass network [77]. The replacement
also makes the glass structure more covalent especially on the P=N- bonding [49, 57]
thus strengthening the glass network.
Table 4.3: 50P2O5-xKNO3-(50-x) K2O; 0 < x ≤ 50 glass composition and
Vickers hardness (Hv)
Glass Composition (Mol %)
Vickers
Hardness (Hv)
P2O5
KNO3
K2O
50
10
40
146 ± 2
50
20
30
160 ± 2
50
30
20
162 ± 2
50
40
10
174 ± 2
50
50
0
178 ± 2
53
Vickers
Hardness
(Hv)
Vickers
Microhardness
(Hv)
Vickers Hardness (Hv)
200
S5
S3
S4
20
30
S6
S2
150
100
0
10
40
50
mol (%
) KNO3
KNO
3 (mol %)
Figure 4.4: Vickers Microhardness (Hv) against KNO3 (mol %)
54
4.6
Infrared (IR) Absorption Spectra
IR spectroscopy was done and the absorption spectra were obtained. Their
molecular vibrational peaks were investigated in the range of 370 cm-1 to 1400 cm-1
and 1400 cm-1 to 3800 cm-1.
4.6.1
Molecular Vibrational Peaks
IR studies were performed on the 50P2O5-xKNO3-(50-x)K2O glass samples in
the range of 370 cm-1 -1400 cm-1 (Figure 4.5) and the IR peak positions are tabulated
in Table 4.4. As can be seen from Figure 4.5, main bands appearing along the
spectrum range are in the region of 1260 cm-1, 1090 cm-1, 915 cm-1 and 750 cm-1.
According to Pascual and Duran [56], they are due to vibrations of P=O stretching,
P-O- stretching, P-O-P asymmetric stretching and P-O-P bending respectively.
The absorption bands around 999 cm-1 to 1020 cm-1 actually are the overtone
of frequency around 491 cm-1 to 511 cm-1 and is assigned to harmonics of bending
vibration of O=P-O linkages [2].
However, most of the peaks experience some shifts and changes of the
intensity as the KNO3 content increases. The shifts and changes in the intensity of all
bands are due to nitrogen incorporations. This deviation can be considered as
evidence of the vibrations in the bond energies that were produced by the
replacement oxygen by nitrogen [56]. Both the position of the bands and the shifts
produced by increasing nitrogen contain (in nitrate) are similar to those observed in
nitride phosphate glass.
55
750
500
S6
S5
1260
1090 1010 915
%T S
4
(a.u)
S3
S2
1400 1300 1200
1100 1000 900 800 700
Wave Number (cm-1)
600
500
370
Figure 4.5: IR spectra of 50P2O5-xKNO3-(50-x)K2O glass in the region
of 370 cm-1 to 1400 cm-1
Table 4.4: IR absorption peaks of 50P2O5-xKNO3-(50-x)K2O; 0 < x ≤ 50 glass
in the region of 1400 cm-1 to 370 cm-1
Absorption peaks (cm-1)
Sample
S2
1277.27
1090.26
1020.14
906.18
774.69
511.79
S3
1274.35
1085.88
1020.14
913.48
767.39
511.79
S4
1267.04
1085.88
999.68
907.64
752.78
495.64
S5
1259.74
1087.34
999.68
912.02
758.62
494.18
S6
1250.97
1087.34
999.68
929.56
755.70
491.80
56
The common characteristics of IR spectra of the glass could be summarized
as follows:
i. The band assigned to the stretching vibration of the P=O bond, around
1250 cm-1 shifts towards a lower frequencies with the increasing
nitrogen content.
ii. The band around 1090 cm-1, assigned to P-O- ionic stretching and
remains unchanged by the nitrogen incorporation.
iii. Some bands between 915 cm-1 and 750 cm-1, assigned to vibrations of
the P-O-P bonds, broaden and become more diffuse, and even disappear
with the increasing of the nitrogen content.
The shifts of the 1250 cm-1 band to lower frequencies can be regarded as the
replacement of the bridging oxygen by the nitrogen [56]. The stretching vibration of
the phosphoryl group is highly sensitive to changes in the atoms or atom groups
bonded directly to the phosphorus atom [35, 56, 78]. The electronegative atoms or
atoms groups tend to withdraw electrons from the phosphorus atom thus competing
with oxygen which would otherwise have a tendency to form P+-O-, therefore
producing a higher vibration frequency. It can be clearly seen in a plot of P=O
frequency against the additions of KNO3 in Figure 4.6.
When the electronegativity of atoms that attached to the phosphoryl groups
decreases, the band of P=O group shifts to lower frequencies. It is possible since
oxygen and nitrogen atoms have electronegativities of 3.44 and 3.04. Thus, the
replacement by oxygen to nitrogen should destabilize the double bond, as reflected in
the IR spectra. On the other hand, nitrogen presents as =N- replaces the nonbridging, double bond oxygen (P=O). The P=N band is located in range of 1190 cm-1
to 1500 cm-1 [78]. Therefore, a decreasing in intensity and overlapping of the
corresponding band should be observed.
57
1280
1280
S2
S3
Frequency Peaks (cm-1)
1275
1275
S4
1270
1270
1265
1265
S5
1260
1260
S6
1255
1255
1250
1250
00
10
10
20
20
30
30
40
40
50
50
60
KNO3 (mol %)
Figure 4.6: Effect of P=O band frequency on addition of KNO3
The band assigned to P-O- ionic stretching around 1090 cm-1 does not change
with nitrogen content. It can be assumed that this type of oxygen is not been replaced
by the nitrogen atom. The broadening and the disappearing of bands in the P-O-P
vibration range might be attributed to the overlapping bands of P-N bonds and to
lower symmetry of the phosphorus surrounding [56].
The band of P-N bonding starting to appear around 940 cm-1 for S2 and seems
to overlap with P-O-P bonding band around 915 cm-1 and shifts to higher frequency,
before it immersed to O=P-O bending vibration band around 1020 cm-1 with
increasing of nitrogen content. That might be inferred as an effect of the nitrogen
incorporation replacing oxygen in the P-O-P bonding.
The absorption band approximated 929 cm-1 to 906 cm-1 is assigned to the
asymmetric stretching mode of the P-O-P linkage. While the weak absorption band
cited at around 755 cm-1 to 774 cm-1 is attributed to the bending vibration of P-O-P
linkages and diffused with addition of nitrogen [56].
58
From discussion, it can be stated that the IR spectra confirmed that nitrogen
enters the phosphate network, replacing oxygen with =N- and –N< configurations.
The incorporation of nitrogen into the network produces an increase in the bond
density and thus stabilizes the glass.
The vibration band of K+ cations around their network sites cannot be
observed since the vibration band is located at much lower frequency (~ 300 cm-1)
[79].
4.6.2
Vibration of Hydroxyl Ion, OHThe vibration for H-OH content may be represented by the vibration around
3200 cm-1 to 3600 cm-1 and around 1600 cm-1. Thus, the IR spectra in the range of
1400 cm-1 to 3800 cm-1 were performed to observe the modes of water molecules.
This is shown in Figure 4.7.
From Figure 4.7, modes of water molecules for ν1 and ν3 are observed in the
region 3300 cm-1 to 3455 cm-1 while the bending mode of ν2 around 1646 cm-1 to
664 cm-1 [80] (ν1, ν2 and ν3 vibration mode are illustrated in Figure 4.8).
Meanwhile, the bands around 2334 cm-1 to 2374 cm-1 are attributed to P-OH
stretching vibration in meta-phosphate glass [81] and the bands around 3617 cm-1 to
3621 cm-1 are attributed to stretching vibration of free O-H molecules [78].
59
1650
2350
S6
S5
S4
3450
%T
(a.u)
S3
S2
3800 3600
3200
2800
2400
2000
1600
1800
1400
Wave Number (cm-1)
Figure 4.7: IR spectra of 50P2O5-xKNO3-(50-x)K2O glass in the region
of 1400 cm-1 to 3800 cm-1
O
H
O
H
H
O
H
H
H
υ1
υ2
υ3
(a)
(b)
(c)
Figure 4.8: Fundamental vibration modes of H2O [82]. The arrows show the
movement of atoms for (a) bending of symmetrical stretching, (b) symmetrical
bending and (c) bending asymmetrical stretching.
60
4.7
Chemical Durability
The chemical durability of the glass has been determined by means of their
dissolution rate (DR) in a certain pH conditions after 20 minutes immersion time.
The results are shown in Table 4.5. From the table, it can clearly show that the
dissolution rate decrease with increasing pH of the solution except sample S6 which
shows the inconspicuous change. Meanwhile, the dissolution rate of each sample
shows the decreasing trend with the increasing composition of KNO3.
Table 4.5: Dissolution rate in pH solutions after 20 minutes immersion time
pH solutions
Sample
1
3
5
7
Dissolution rate x 10-3 (gcm-2min-1)
S2
(5.83 ± 0.17)
(4.73 ± 0.15)
(4.32 ± 0.11)
(3.74 ± 0.10)
S3
(4.39 ±0.11)
(2.66 ± 0.17)
(2.56 ± 0.07)
(2.00 ± 0.05)
S4
(2.75 ± 0.07)
(1.76 ± 0.03)
(1.57 ± 0.03)
(1.29 ± 0.03)
S5
(2.20 ± 0.05)
(1.29 ± 0.02)
(1.13 ± 0.02)
(1.00 ± 0.02)
S6
(0.38 ± 0.01)
(0.27 ± 0.01)
(0.27 ± 0.08)
(0.25 ± 0.09)
61
4.7.1
Effect of Compositions
From Table 4.5, a plot of dissolution rate against KNO3 content at different
pH conditions after 20 minutes immersion time can be made. This is shown in
Figure 4.9.
7.00E-03
7.00
Dissolution rate ( x 10-3 gcm-2min-1)
6.00
6.00E-03
5.00
5.00E-03
pH1
4.00
4.00E-03
pH3
pH5
3.00
3.00E-03
pH7
2.00
2.00E-03
1.00
1.00E-03
0
0.00E+00
0
10
20
30
40
50
60
KNO3 (mol %)
Figure 4.9: Dissolution rate (gcm-2min-1) against KNO3 (mol %) at different pH
conditions after 20 minutes immersion time
62
As can be seen from Figure 4.9, the dissolution rates decrease with the
increasing of KNO3 content. This is due to the fact that in nitride phosphate glasses,
as nitrogen increase interconnections and cross-linking between phosphate chains,
the water diffusion is reduced, which results in an increasing chemical durability
[49].
The larger cross-linking density of nitride phosphate glass, a greater
covalence of P-N bond compared to P-O bonds, results from =N- and –N< nitrogen
atoms replacing =O and -O- oxygen atoms [49, 57, 64]. These effect combined
together to increase the chemical durability of this glass. Thus, it is can be assumed
that the nitrogen can effectively block up the pathway of H+ diffusing inside the glass
network and slow down the formation of the hydration layer thus, improve the
chemical durability of the glass. It has also been known that nitride glasses have a
lower dissolution rate than their respective non-nitride glasses because of the
presence of nitrogen cross-linking in the glass [49].
63
4.7.2
Effect of pH Solution
From Table 4.5, the relationships of dissolution rate against pH 1, pH 3, pH 5,
and pH 7 solutions at various of KNO3 content after 20 minutes immersion time can
be made. This is shown in Figure 4.10.
7.00E-03
7.00
Dissolution rate ( x 10-3 gcm-2min-1)
6.00E-03
6.00
5.00E-03
5.00
S2
S
2
4.00E-03
4.00
S3
S3
S4
S4
S5
S5
3.00E-03
3.00
S6
S6
2.00E-03
2.00
1.00E-03
1.00
0.00E+00
0.00
00
1
2
3
4
5
6
7
8
pH
Figure 4.10: Dissolution rate (gcm-2min-1) of variable KNO3 content (mol %)
against pH solution conditions after 20 minutes immersion time
64
From Figure 4.10, it can be said that the dissolution rate is in the decreasing
trend as pH values are increased except sample S6 which shows the insignificant
unchanged of dissolution rate.
It was believed that, the resistance to aqueous attack is maxima at neutral pH
and decreases for acidic solutions [83]. It is true since the increase in concentration
of H+ in the solutions, the network will become highly sensitive to break up and
decreasing the pH value of aqueous media could conspicuously increase the
dissolution rate of glass [83]. On the other hand, the lack of nitrogen content will
affect the breakage of glass network in hydrated layer and disentanglement of shortchain polyphosphate into solution with different degree of polymerization because of
the network failure to provide resistant to the H+ attack thus, increase in solubility.
4.7.2.1 pH Measurement
The effect of solution pH to the glass seems can be more understood when a
set of data on the final pH after 20 minutes immersions time in pH buffer solutions
was collected and tabulated in Table 4.6. The final pH solutions after 20 minutes
immersions time against the KNO3 content of the glass can be plotted and is shown
in Figure 4.11.
65
Table 4.6: Final pH after 20 minutes immersions time in pH buffer solution
pH solutions
Sample
1
3
5
7
Final pH solutions
(± 0.01)
S2
2.50
4.40
5.95
7.38
S3
1.87
3.49
5.51
7.29
S4
1.77
3.19
5.20
7.20
S5
1.46
3.20
5.26
7.28
S6
1.19
3.11
5.14
7.16
66
8.00
8.00
7.00
7.00
6.00
6.00
pH
5.00
5.00
pH1
pH3
4.00
4.00
pH5
pH7
3.00
3.00
Init.
pH
2.00
2.00
1.00
1.00
0.00
0.00
0
10
20
30
30
40
40
5050
60
KNO3 (mol %)
Figure 4.11: Effect of KNO3 content as a function of final pH values after 20
minutes immersion times in various pH solutions
67
From Figure 4.11, it can be clearly seen that the final pH decreases with the
increases of KNO3 content. According to Knowles, Franks and Abrahams [84], it is
believed that the pH changes is caused by the K+-H+ ions exchange reaction. The H+
from the buffer solutions penetrated into the bulk glass to form a hydrated layer
replacing the K+ which dissociate from the glasses into the solutions. Thus the final
solution becomes less acidic that the initial solution.
Meanwhile, the reaction of ion exchange is slowed down by the higher
resistant of P-N=P or P-N<P bonds to hydrolysis compared to P-O-P bonds. This
effect is mostly conspicuous by the impenetrable behavior of sample S6 (50 mol %
KNO3) which is enriched with nitrogen to the aqueous attack. Thus, it proves that,
nitrogen-phosphorus network bonds are more stable and much more difficult to
disrupt than P-O-P bonds.
CHAPTER 5
CONCLUSIONS
5.1
Conclusions
From the data analysis and discussion, some conclusion may be summarized
as follows:
In this study, a series of glasses based on 50P2O5-xKNO3-(50-x)K2O where
0 < x ≤ 50 has successfully been made via the melt quenching technique. From the
x-ray diffraction pattern, it suggests that the glasses shows an amorphous
characteristic in 0 < x ≤ 50.
From the EDAX analysis, it is evident that nitrogen content increases with the
increment of KNO3 from 6.52 wt. % for glass containing 10 % KNO3 to 10.43 wt. %
for glass which contains 50 % KNO3. This result indicates that the nitrogen
successfully enters into the glass.
Density measurements for the glass series show an increasing trend with the
increment of KNO3 contents. The increase in density from 2.3820 gcm-3 to
2.4232 gcm-3 is associated with the higher total atomic weight and also due to the
change in the structure caused by the increasing of interconnections among the
phosphate chains.
69
Nitrogen incorporation causes important changes in most properties
measured. The increase of microhardness as a function of mol % KNO3 from 146 Hv
to 178 Hv might be explained by the increase in the cross-linking and strength of the
glass network. It also proves that the mechanical resistance of glasses depends on the
density and strength of bonds in the glass network [56].
The IR absorption spectra show that there are several vibration peaks which
dominated the glass bonding structure. The entering of nitrogen atom into the glass
network with the replacing of bridging oxygen in P-O-P has been shown with the
appearing of P-N stretching absorption band around 940 cm-1 and the shifting of P=O
stretching absorption band towards to the lower frequency cause by the
destabilization of the double bond as reflected in IR absorption spectra in the range
of 1250 cm-1 to 1277 cm-1 wave number. Absorption peaks around 3400 cm-1 and
1600 cm-1 are due to the water peaks, and the peaks around 2350 cm-1 is attributed to
P-OH stretching vibration.
The incorporation of nitrogen into the glass network replaces the oxygen
atoms which increases the branching of the chains resulting in substantial decrease in
the glass dissolution rate. The reduction in dissolution rate might be due to the
increase of nitrogen content and the effect of increasing pH media from pH 1 to pH 7
can be explained by the higher resistance of P=N-P bonds to hydrolysis compared to
P-O-P.
All of pH solutions experience the increase in pH value after the 20 minutes
corrosion test. The increase in pH value indicates the occurrence of proton loss in the
solution due to the K+-H+ glass ions exchange reaction.
Since some of the phenomena are still not well understood, further works
may be carried out so as to better understand the characteristics of the glass. Some
suggestions are summarized as follows:
1. Other characteristics such as thermal properties can also be studied in order to
understand the thermal effect of nitrogen content to the glasses. Such work is
needed to provide more information on these glasses.
70
2. To further understand the corrosion behavior of glasses in aqueous media, it
is suggested that the determination of dissolution rate could be done to the
pH > 7. The types of glass elements including cations, anions and monomers
that dissolve in aqueous solution should also be identified.
3. The study on the corrosion mechanism of these glasses should be carried out.
Such data is very important to be used to improve the more precise glass
composition.
4. Judging from the ability of glass to dissolve in aqueous media, it is suggested
that a study has to be done on the potential of glass to become a ‘controlled
release fertilizer’ since the ions of phosphorus, potassium and nitrogen are
majors elements consumed by plants to grow healthily.
71
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80
APPENDIX A
THE GLASS PREPARATION CALCULATION
81
To prepare M grams of 50P2O5-xKNO3-(50-x)K2O glass, it is need:
α wP O
2 5
w
× M grams of P2O5
sys
β wKNO
3
w
× M grams of KNO3
sys
γ wK O
2
w
× M grams of K2O
sys
where,
w
P2O5
,
w
KNO3
and
w
K 2O
are respectively the molecular weight of P2O5, KNO3
and K2O, while α , β and γ are respectively the mol fraction (mol%) of P2O5, KNO3
and K2O. wsys is the sum of all molecular weight of the system respectively to their
mol fraction.
From a periodic table, molecular weight of every component is;
w
= 141.943 g mol-1
w
= 101.106 g mol-1
w
= 94.203 g mol-1
w
= 138.212 g mol-1
P2O5
KNO3
K 2O
K 2CO3
82
Therefore, to prepare the 50P2O5-xKNO3-(50-x)K2O glass system,
w
sys
should be:
w
= (50% × 141.943) + ( x% × 101.106) + [(50 − x)% × 94.203] g mol-1
w
= α wp2O5 + β wKNO3 + γ
sys
sys
w
K 2O
Thus, to obtain the 30g glass system it requires:
P2O5:
 50% × wP2O5 

 × 30 grams =
W P2O5 grams


wsys 

KNO3:
 x% × wKNO 
3 

× 30 grams = W KNO3 grams


wsys 

K2O:
 (50 − x )% × wK O 
2 

× 30 grams = W K 2O grams


w
sys


but, K2O was obtained from the decompositions process of K2CO3. Thus, it is
important to know the amount of K2CO3 in order to obtain the desired amount of
K2O. From the decompositions process of K2CO3 in equation (3.1), it is clearly
shows that 1 mol of K2CO3 will produce 1 mol of K2O.
83
Therefore,
W
w
K 2CO3
=
K 2 CO3
W
w
K 2O
K 2O
where, W K 2CO3 is the amount of K2CO3. Hence, the calculation is:
W
K 2CO3
=
W
w
K 2O
× wK 2CO3
K 2O
Therefore, to obtainW K 2O , the amount of W K 2CO3 is needed.
For example, to obtained 50P2O5-10KNO3-40K2O glass composition, it should be:
w
sys
= α wp2O5 + β wKNO3 + γ
w
sys
= (50% × 141.943) + (10% × 101.106) + (40% × 94.203) gmol-1
w
sys
w
K 2O
= 118.764 gmol-1
Thus, to obtain the 30g glass system it requires:
P2O5:
 50% × 141.943 

 × 30 grams = 17.928 grams
 118.764

KNO3:
 10% × 101.106 

 × 30 grams = 2.554 grams
 118.764 
84
K2O:
 40% × 94.203 

 × 30 grams = 9.518 grams
 118.764 
but, K2O was obtained from the decompositions process of K2CO3. Thus, it is
important to know the amount of K2CO3 in order to obtain the desired amount of
K2O. From the decompositions process of K2CO3 in equation (3.1), it is clearly
shows that 1 mol of K2CO3 will produce 1 mol of K2O.
Therefore,
W
w
K 2CO3
=
K 2 CO3
W
w
K 2O
K 2O
where, W K 2CO3 is the amount of K2CO3. Hence, the calculation is:
W
K 2 CO3
=
W
w
K 2O
× wK 2CO3
K 2O
W
K 2 CO3
W
K 2 CO3
=
9.518
× 138.212
94.203
= 13.965 grams
Therefore, to obtainW K 2 O = 9.518 grams, the amount of W K 2CO3 = 13.965 grams is
needed.
85
APPENDIX B
EDAX SPECTRUM
86
EDAX spectrum for 50P2O5-10KNO3-40K2O glass
87
EDAX spectrum for 50P2O5-20KNO3-30K2O glass
88
EDAX spectrum for 50P2O5-30KNO3-20K2O glass
89
EDAX spectrum for 50P2O5-40KNO3-10K2O glass
90
EDAX spectrum for 50P2O5-50KNO3 glass