ABSTRACT

Glass ceramics, a new family of polycrystalline materials produced by the controlled
crystallization of glass has many uses cutting across all spheres of life from domestic appliances
through medical devices to space exploration. The production process, just like that of other
pyrotechnic products, takes a high toll on energy demand as a high temperature process. The best
example can be drawn from the US economy where the annual energy bill for the glass industry as
a multibillion-dollar industry is put at more than 1.3 billion USD.
In the present study, an attempt is made to find alternative route for ceramic glass production in
the Nigeria that is cost effective in terms of energy input. In the process, a novel route outside the
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two usual routes employed in glass ceramic production was adopted in fabricating a product
which when subjected to some physical tests showed every attribute of glass ceramics. Although
the process, which involved the sintering crystallization of glass and crystalline composites, has
no preference to any particular glass composition or crystalline material, a low melting glass
composition was used in the experiment to situate the process within the many limitations of the
experiment. In this case an ophthalmic glass composition was selected, partially melted at
1200oC, fritted and remixed with a fresh batch and sintered at 1000oC. The percentage water
absorption, porosity bulk density and specific gravity were evaluated using by the Archimedes’
Principle (ASTM C373). The evaluation of these properties has a direct bearing to the ultimate
characteristics of the glass-ceramic product.
The values obtained were 0.176 % for water absorption, 0.268% for porosity, 1.528 for specific
gravity and 1.53gcm-3 for density. The density is indicative of a lightweight material relative to
the properties of the derivative materials. The XRD analysis shows the main crystalline phase in
the material to be cristobalite and nephline. Optical microscopy obtained confirmed the presence
of crystalline phases in a glassy matrix, which is conclusive of the fact that the product is indeed
glass ceramic.
With further improvement the product of the experiment is a candidate for application as an
electronic spacer as a lightweight material. However if substitute can be found for the Pb content,
which is considered a toxic substance, its future use will extend to utility objects.

 

 

TABLE OF CONTENTS

 

Cover page. ……. ……. …… ……. ……. `…… …… …… ….. i
Title page. ……. ……. …… ……. ……. ……. ……. …… ii
Declaration …… …… …… …… …… …… …… …… iii
Certification. ……. ……. …… ……. ……. ……. ……. ……. …… iv
Acknowledgement. ……. ……. ……. ……… …….. ……. ……. v
Abstract. ……. ……. …….. …….. …….. ………. …….. ……. vii
Content page. …… ……. ……. ……. ………. …….. …….. ix
List of Tables. …. …. …… …… …… …… …… ……. . xiii
List of Plates. …. …… …… ……. ……. ……. …… ……. …… xiv
List of Figures. ……. ……. ……. ……. ……. ……. …….. ……. xv
List of Appendices …… …… …… ……. …… ……. ……. xvi
Dedication …… …… …….. ……. …… …… ……. ……. . xvii
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Definition of Special Terms …… …… ……. …… ……. …… xviii
CHAPTER ONE
1 INTRODUCTION 1
.1. Background of the study……………………………..……………. 1
.2. Definition of Glass…………………………………….…………… 3
.3. Problem of the Study…………………………………………..…… 5
.4. Research Questions …………………………………………….….. 5
.5. Objectives of the study……………………………………………… 6
.6. Justification………………………………………………….…….. 6
.7. Significance of the study…………………………………….…….. 9
Page
.8. Limitation of the study…………………………………………….. 10
.9. Scope………………………………………………….…………… 10
CHAPTER TWO
4.5 LITERATURE REVIEW 12
2.1 Development of Glass Ceramic…………………………………………. 12
2.2 Glass Formation Versus Crystallization………………………………… 13
2.3 Devitrification………………………………………………………..…. 15
2.2.1 Solid/Solubility…………………………………………….…… 19
2.2.2 Nucleation and crystal growth……………………………….… 25
2.3 Glass ceramics composition system…………………………………… .. 27
2.3.1 Glass ceramic types and Nucleating agents……………………. 27
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2.4 Glass and Glass-ceramic matrix composites……………………..…….. 34
2.5 Properties of Glass-ceramic materials………………………..………… 35
2.6 Applications of Glass ceramics…………………………………….…… 37
2.6.1 Dental Applications……………………………………….…… 37
2.6.2 As Bearings…………………………………………………….. 37
2.6.3 Cookware………………………………………………………. 38
2.6.4 Heat exchangers………………………………………………… 39
2.6.5 Neutron absorbing materials……………………………………
39
2.6.6 As sealing and Bonding medium or thermosetting elements…… 39
2.6.7 Electrical Insulators…………………………………………..…. 40
Page
2.7 Stages in the glass ceramic process………………………………………………… 40
2.7.1 Raw materials selection and processing………………………… 40
2.7.2 Melting and forming……………………………………………. 43
2.7.3 Conversion into polycrystalline solid……………………….….. 44
2.8 Annealing……………………………………………………………….. 47
2.9 Established Routes for glass ceramic production………………….….. … 50
2.10 Glass sand deposits in Nigeria…………………………………………… 51
CHAPTER THREE
3 METHODOLOGY 54
3.1 The silica source…………………………………………………. 54
3.2 Field sampling……………………………………………………. 54
3.3 Chemical Analysis………………………………………………… 54
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3.4 Raw Material processing and particle characterization……………. 55
3.5 Choice of Glass composition………………………………………. 56
3.6 Batching and melting………………………………………………. 57
3.7 Product Characterization…………………………………………… 58
CHAPTER FOUR
4 RESULTS AND ANALYSIS 60
4.1. Chemical analysis…………………………………………….. 60
4.2. Choice of glass composition…………………………………. 61
Page
4.3. Batching and melting………………………………………….. ……… 61
4.4. Produce characterization……………………………………………….. 62
4.4.1 Water absorption, porosity and specific gravity……………… 62
4.4.2 X-Ray analysis and optical microscopy……………………… 63
4.5 Cost Analysis………………………………………………………….. 68
CHAPTER FIVE
5. SUMMARY, CONCLUSION AND RECOMMENDATIONS 69
5.1. Summary…………………………………………………….. 69
5.2. Conclusion…………………………………………………… 70
5.3. Recommendations…………………………………………..… 71
REFERENCES………………………………………………………….. 72

 

CHAPTER ONE

1.1 BACKGROUND
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Glass ceramics, a family of polycrystalline materials prepared by the controlled crystallization of
glasses, constitute an essential part of modern living. From their simplest use as cookware,
through critical but still familiar uses in dental restoration to the even more critical use as missile
radomes, they are yet to find complete replacements in the face of stiff competition from synthetic
products such as plastics and other lightweight materials, in a world increasingly moving away
from reliance on naturally sourced materials. The several advantages offered by glass over other
materials, which has served to reinforce its competitiveness over a long period of use spanning
several centuries, include exceptional chemical durability, multi-faceted optical properties and
complete recycling capability in an era of heightened environmental consciousness.
Although glass ceramics, like conventional ceramics, contain a substantial refractory crystalline
component, the difference between the two classes of materials stems from the fact that a glass
ceramic starts out as a pure glass in which finely dispersed crystalline structures are made to
“grow” within the glass matrix by a process of controlled crystallization. The presence of the so
called ‘home groomed’ microstructure, in addition to enhancing the strength of the glass,
increases its flexibility, with the consequential minimal presence of the severe microcracks that
act as stress concentrators in the event of brittle failure but also simultaneously preventing the
deterioration of less severe flaws thus acting as crack inhibitors.
Due to the fact that the size and distribution of the crystalline substructure within the glass can be
accurately controlled, the resulting crystals confer on the end product various characteristics such
as lack of porosity and extremely low coefficient of thermal expansion which can all be precisely
controlled to suit specific applications but often the crystal chemistry is much different from that
of the original or residual glass.
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That Science is at odds in finding complete substitutes to glass products generally,
notwithstanding the long history of use, spanning several millennia, is a factor attributable to
what Rao (1981) describes as the twin freedom enjoyed by materials in the glassy state vis-à-vis
“freedom from the restraints of periodicity and freedom from the requirements of stoichiometry”.
This peculiar nature of glassy materials has generated a lot of research interest in Glass Science
especially since the early 60s referred to, in the annals of history, as “the Golden Age of Glass
Science” (Doremus, 1983). Professor N. F. Molt earned the Nobel Prize “for having done so
much to transfer glass science from the archives to the forefront of solid state” (Rao, 1981). This
acknowledgement serves as a pointer to the flurry of activities in present day glass research.
As a non-stoichiometric substance, a single glass composition can accommodate as many as 60
elements at once. Michael Faraday, long ago, in recognition of the special attributes of glass,
preferred to call it a “solution’ rather than a compound (Doremus, 1983). This position, largely,
holds sway to the present day. New glass forming systems are being developed everyday. Thus
the same glass, which can be made stronger than steel as symbolized by fibreglasses valued as
structural reinforcers, can by way of alteration of composition be made to dissolve in water as
typified by sodium silicate composition (water glass). Again as illustrated by the Li2O-Al2O-SiO2
family of compositions, by way of modification of composition, glass can be made to have
negative or zero expansion coefficients within some ranges of temperature.
In spite of the usefulness of glass ceramics as a modern material, there is no form of productive
activity in Nigeria relating to glass ceramics or record of any research effort directed at its
development by the dozen or so research institutes in the country that engage in industry related
activities as an extension of their mandates. It is therefore reasonable to state that any research
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directed at an important branch of glass usage such as glass ceramics, especially in a country with
huge potentials for industrial growth as Nigeria, cannot be in any way exhaustive, at least not at
this stage of her development.
An attempt will be made in this study to explore the possibility of production of glass ceramics
from local raw materials with particular reference to low energy input varieties. The energy
dimension is chosen as the focus of study, partly as a response to the unsteady global energy
situation and also because Nigeria’s precarious energy infrastructure calls for steps, in her path of
industrial take off, with inbuilt guarantee of sustainability.
1.2 DEFINITION OF GLASS
The versatility of glass has infused some dynamism into the term “glass” to the extent that
numerous definitions have been proposed for it over its many years of history. The one most
frequently quoted definition of glass proposed in 1945 by the American Society for Testing and
Materials (ASTM) refers to it as an inorganic product of fusion which has cooled to rigid
condition without crystallizing (Rawson, 1980). Although this “traditional” definition
accommodates the majority of glasses, which are usually inorganic with one known mode of
production materials, i.e. cooling to rigidity from the melt, it is considered too restrictive in the
sense that it cannot account for organic polymers and other materials with glassy structures made
by methods other than cooling from the melt. For instance amorphous thin glassy coatings made
by sputtering directly from the vapour state have every claim to being called glasses just as
sodium silicate glass can be made by two methods, one by cooling from the melt and the other by
preparing an aqueous solution of sodium silicate and evaporating to dryness.
These changes in the material world prompted a committee of the US National Research Council
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to come up a broader definition in 1976 without recourse to mode of production or constituent
materials. The broader outlook refers to glass as “an x-ray amorphous solid, which exhibits the
glass transition, that being defined as that sudden change in the derivative thermodynamic
properties from crystal-like to liquid-like values”. Its rigidity must approach that of an ideal
elastic solid i.e. it should be at least 1013.7 Pa s on the viscosity scale and when examined by x-ray
diffraction it should have the structural attribute of liquids, which is a short range order. Critics of
the newer definition rest their case on the fact that only a few materials referred to as “borderline
cases” do not fit into the ASTM definition which they regard as the classical definition of glass.
1.3 THE PROBLEM OF THIS STUDY
According to Hoover (1964), an important consideration in the location of industries is the
disposition of a country’s mineral and energy resources. Nigeria on this basis has all it takes to
become an industrial nation. Available statistics based on studies carried out by the relevant
agency, the Raw Materials Research and Development Council (RMRDC), shows that the raw
materials for glass making exist in great abundance in the country (RMRDC, 1997). The
existence of commercially exploitable deposits hosted by rock of the basement complex around
Egbe, Udiaraku, Okene and Lokoja has been reported (RMDC, 2003). A number of other deposits
located in Kenyi/Madakiya in Kaduna State and Gworza in Borno State have been covered in
isolated studies with sketchy details regarding their glass forming ability (Malgwi, 1989; Jekada,
1997). These findings are in agreement with the assertion of Pincus (1967) to the effect that glass
raw materials are among the cheapest and most abundant of all industrial raw materials the world
over.
While the raw material need of the glass industry can be said to be met with some degree of
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certainty, the same assertion cannot be made for the energy requirement not withstanding the fact
that Nigeria is the world’s sixth largest producer of fossil fuels. The country’s weak energy
infrastructure remains the stumbling block to the maximum utilization of the country vast oil and
gas resources. Apart from the fact that Nigeria is a net importer of refined petroleum products,
long queue of vehicles are not uncommon sights at gasoline stations due to poor storage facilities.
The matter is made worse by the fact that regions of petroleum resources have remained the
hotbed of global sociopolitical instability against the mounting energy cost of global output of
glass products the use of fossil fuels. Electricity power generation required for glass melting is
also in short supply in the country.
According to the US Department of Energy (2000), the total energy bill of the glass industry is
more than $1.3 billion. Representing an important segment of the country’s economy the industry
engages more than 150, 000 people in skilled jobs and generating more than 21 million tonnes of
consumer products each year at an estimated value of $22 billion.
The approach to be adopted in tackling the energy issue in glass production as the problem of this
study is to explore ways of producing glass ceramics with low energy input.
1.3 RESEARCH QUESTIONS
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I. What would be the economic implications of such an approach?
II. How would it fit into the Nigerian situation of the weak energy infrastructure of the country?
III. How would it contribute to solving the global energy crises?
1.4 OBJECTIVES OF THE STUDY
The precise objectives are to:
I. Identify a source of raw material suitable for glass ceramic production in Nigeria.
II. Carry out chemical analysis on samples of the raw material to ascertain the chemical
constituents.
III. Identify the appropriate glass formula with the least energy input.
IV. Explore the most appropriate route for conversion of the raw material into glass ceramic with
respect to the energy demand of the product.
V. Test-melting the batch.
VI. Characterize the product of the experiment as the basis for further development.
1.5 JUSTIFICATION.
Glass ceramics fall under the category of glasses valued for high technology and specialty
applications, in addition to their common uses in domestic appliances. Specialty glasses differ
from traditional glasses in the contents of specific additives, or may be of entirely different
compositions. Novel processes have also been exploited in developing many of these
compositions.
According to a report by Business Communications Company, Incorporated (BCC),
(www.bccresearch.com), the North American market for advanced and specialty glasses reached
$2.3 billion in 2002 and with a projected growth rate of 7.8% would reach $3.3 billion by 2007.
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The global market was estimated at $8.5 billion in 2002, and at an expected growth rate of 8.3%
would reach $12.6 billion by 2007.
The largest market for advanced and specialty glasses according to the report are concentrated in
electronics displays, which include liquid crystal displays (LCDs) and gas and vacuum discharge
displays. This market in North America was worth approximately $1.3 billion in 2002 and was
expected to have reached almost $2 billion by the year 2007. The global market was expected to
grow from $4.8 billion in 2002 to $7.8 billion in 2007.
Over 60% of the total market according to the survey is for electronic applications. The combined
electronics segment market for North America was put at $1.4 billion in 2002 and was expected to
increase to $2.2 billion by 2007. The medical/dental market is expected to witness a relatively
strong growth, as demand for dental aesthetics increases and new products find their ways to the
market. The applications that would fuel this growth include glass-ceramic crowns and DNA
microanalysis. On the whole, the demand for advanced glasses is expected to maintain the growth
level as new applications in these various segments come on the market.
In the aspect of global competition, North America is in the lead in several areas, since the US
glass company, Corning Inc. has the largest market share in these areas. Japan follows closely
behind in the two market segments, for the reason that a number of Japanese companies are also
major producers of specialty glasses. In the same manner the German multinational, Schott Glas
AG, makes Europe another strong competitor, as a major player in most EU countries.
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Glass ceramics manufacture holds great potential for employment generation in a country like
Nigeria as it is becoming increasingly evident that no country can afford to insulate itself from the
effects of the global marketplace. Glass demand, as stated by Limbs (2002), remains strong and
growing, exceeding worldwide gross domestic product, and will continue to grow with the focus
of growth shifting to Asia, especially China as her rising economic fortune is raising a new crop
of consumer population. For instance, the Chinese share of global demand for glass, which
reached 4 billion square meters in 2003, was put at 30 percent while the overall annual increase in
global demand for glass products between 1990 to 2003 was put at 4 percent per year, is 1.2
percent higher than the worldwide average GDP of 2.8 percent a year, within that same period.
Judging from the experience of India and China, Nigeria’s huge population translates into a
considerable consumer market for any local industry that specializes in glass ceramics products.
This market potential is further boosted by the realizable dream of a common market within the
West African sub region under the aegis of West African Economic Community (ECOWAS).
According to a report in the UNIDO Quarterly, Africa has a high potential for investment in
untapped human and natural resources (Punch, February 9, 2000). The report states that many
investors are discovering that Africa provides high returns from carefully selected investments
even in conflict-infested regions. The same report adds that Africa enjoys many advantages in the
global market place and this includes the benefits of locating projects on the continent to supply
the U. S., Europe and Japan. Furthermore, a joint poll by the United Nations Conference on Trade
and Development (UNCTAD) and the International Chamber of Commerce (IICC) released in
Bangkok in February 2000 placed Nigeria top among four countries on the continent that would
likely benefit from increased transnational activities in the next five years. (Punch, February 18,
2000).
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The glass ceramics industry is certain to benefit from the attendant capital inflow to Africa by
virtue of the groundwork being laid by this study. It is therefore timely to embark on a study that
will develop the basis for glass ceramics manufacture in Nigeria and the present study is set to
establish that framework.
1.6 SIGNIFICANCE OF THE STUDY
The significance of this study hinges on the attempt to improve the economic situation in Nigeria
via the production of low energy input glass ceramics. Although energy costs in the glass industry
according to the US based Manufacturing Energy Consumption Survey (MECS), do not vary
substantially across glass sectors as a cost item, it does account for 6-12% of total production costs
(Dohn, 2000). The same survey revealed that in the United States, the glass industry consumed 206
trillion B.T.U. of energy worth about $1.4 billion on energy in 1998. About 8% of the energy
supply came from fossil fuels. Apart from its being physically limited, the use of fossil fuels
constitutes a threat to our health and environment. In addition to its contribution to global
warming, burning fossil fuel releases chemicals and particulates that can cause cancer, brain and
nerve damage, birth defects, lung injury, and respiratory problems to mention a few.
Those that might question the relevance of a research directed at energy reduction at this stage in
our national life, given that Nigeria, a major exporter (sixth largest in the world) will for a long
time to come have enough petroleum oil to satisfy local consumption, must take a cue from the
transformations that turned the United States into a modern industrial nation. In 1950, the U.S. was
producing half the world’s oil but fifty years on, the country no longer produce half her own oil
need. Moreover, the world’s burgeoning population has other uses for petroleum products that
extend to fertilizer such that it is feared that demands will outstrip production unless some
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alternative is found for petroleum fuels.
1.7.0 LIMITATIONS OF THE STUDY
This form of research should ideally attract funding from government or the business community.
The financial constraint has undoubtedly placed a heavy limitation on the outcome of this highly
practical work.
Another limitation placed on this study is the vast size of the country and the lack of updated
geological information regarding the country’s mineral resources. The only mineral map
currently in use in the country dates as far back as the early 60s. This weak database of the
country’s mineral resources is most likely to affect the outcome of this and related studies.
Another obvious impediment in the way of a successful completion of the work is the level of
infrastructure needed to sustain the work. The researcher is unaware of any assembly of
laboratory facility needed to carry this work to a successful end. This situation calls for
improvisations that may have compromised the standard of the outcome.
1.8 SCOPE
Within the scope of this study, local raw materials has a restricted meaning limited to quartz,
quartzite or glass sand because glass ceramics as other raw materials used in the experiment as a
control measure are in analytical grades. More so because glass ceramics as value added products
require the use of analytical grades of other raw materials/chemicals as supplements to silica as
the main raw material.
The laboratory aspect of the present work was limited in scope to the sequence of procedures
followed in converting the raw batch to a molten glass and annealing it to the required
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specification in physical characteristics. The work stops at any form of operation carried out on
the products of the experiment to transform them into testable samples but not beyond that.
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