CERAMIC MATERIALS I Asst. Prof. Dr. Ayşe KALEMTAŞ

[email protected], [email protected], Phone: 211 19 17 Metallurgical and Materials Department INTRODUCTION

MATERIALS

CERAMIC METAL POLYMER COMPOSITE D

CLAY ADVANCED REFRACTORIES ABRASIVES CEMENTS PRODUCTS CERAMICS

Glass- Glasses ceramics

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

HISTORY DEFINITION PROPERTIES APPLICATIONS

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Four of the major technological achievements in which have had the most profound impact on mankind.

. Glass window – which enables sunlight to come into dwelling unit . – opthamics for improved vision, , telescope . Light bulb envelope - lighting . Semiconducting glasses – for computer memory, solar cell, photocopiers

Asst. Prof. Dr. Ayşe KALEMTAŞ Well Known Glass Products

www.whitersstreetglass.com.au Glass splashbacks http://www.wickedreport.com Hirom Glass Violin is a product of Hario www.toxel.com Glass Co. Ltd., . And also, The Glass Bathtub world’s first hand made glass violin.

http://freshome.com http://worlds-interior-design.blogspot.com Superdurable Wall-to-wall glass windows Asst. Prof. Dr. Ayşe KALEMTAŞ Well Known Glass Products

Asst. Prof. Dr. Ayşe KALEMTAŞ Well Known Glass Products

Tempered glass table http://freshome.com http://www.ifjk.org

www.aarticommercial.com/prod www.tripadvisor.com ucts.php Heat resistant Glass sink cabinets in the bathroom Laminated Windscreen Glass glass door

Asst. Prof. Dr. Ayşe KALEMTAŞ Well Known Glass Products

http://www.wolfard.com Classic Wolfard Oil Lamp

Heat resistant glass lid Heat resistant glassware Tempered Glass (microwave safe) Cutting Board Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Any material that exhibits only a short-range order of atoms or ions is an amorphous material; that is, a noncrystalline one.

In general, most materials want to form periodic arrangements since this configuration maximizes the thermodynamic stability of the material. Amorphous materials tend to form when, for one reason or other, the kinetics of the process by which the material was made did not allow for the formation of periodic arrangements.

Glasses, which typically form in ceramic and polymer systems, are good examples of amorphous materials.

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Definitions of Glass

The origin of the word glass is the late Latin term glæsum used to refer to a lustrous and transparent or translucent body.

Glassy substances are also called vitreous, originating from the word vitrum, again denoting a clear, transparent body. Although glass became a popular commodity in the growth of civilization, perhaps because of its transparency, luster (or shine), and durability, the current understanding of glass no longer requires any of these characteristics to distinguish it from other substances.

Glass can be inorganic (non-carbon based) as well as organic (carbon- based), and fusion is not the only method to make a glass.

Thus, the old ASTM definition that glass is an inorganic product of fusion which has been cooled to a rigid condition without crystallizing is not appropriate.

Handbook of Ceramics, Glasses, and Diamonds, Charles A. Harper Editor-in-Chief, Chapter:5, Inorganic Glasses- Structure, Composition and Properties, Arun K.Varshneya and Thomas P. Seward III, McGRAW-HILL Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Methods of Making Inorganic Glasses

The most common method for making glass is to:

. Fuse various raw materials in appropriate proportions together with the application of heat, . Gather and form into useful products, . Cool subsequently at a rate fast enough to avoid distortion of the shape yet slow enough to avoid cracking.

Inorganic glasses may also be obtained by

. Hydrolyzing an alcoholic solution of an organometallic compound, . Stirring the hydrolyzed product to allow rapid chelation to a gel state, . Drying the gel mass to drive off the organics, . Sintering at an elevated temperature to obtain a compact.

This method, called the sol-gel route to glassmaking, is often used to deposit thin films such as antiref lection coatings.

The sol-gel process of making a glass avoids the normally high temperatures employed for the fusion of glass. Chemical vapor deposition is yet another technique which completely avoids fusion of constituent materials.

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

The earliest written records of glass making are some famous clay tablets, dating from around 650 BC, from the library of Assur-bani-pal, but these are incompletely understood because we have no dictionary to explain the technical terms.

Many centuries passed before written accounts of glass making contained any useful insight besides recipes to be followed by rote.

The earliest development in glass making of which we have a reasonably documented description seems to be the invention of glass of by Ravenscroft around 1673-1676.

Asst. Prof. Dr. Ayşe KALEMTAŞ Glass from Nature

Natural Glass

Probably as early as 75,000 B.C.E., long before human beings had learned how to make glass, they had used natural glass to knives, arrowheads, and other useful articles.

The most common natural glass is obsidian, formed when the heat of volcanoes melts rocks such as granite, which then become glassy upon cooling. Other natural glasses are pumice, a glassy foam produced from lava; fulgurites, glass tubes formed by lightning striking sand or sandy soil; and tektites, lumps or of glass probably formed during

http://www.chemistryexplained.com/Ge-Hy/Glass.html#ixzz3G6sDTQBl

Asst. Prof. Dr. Ayşe KALEMTAŞ Glass from Nature

Obsidian

The first glass, used by early man is obsidian. Ryolite lava flows from volcanoes and swiftly cools, impeding the formation of and creating absidian glass. This glass has an irregular structure and, therefore, fractured into smooth curved shapes with finer edges. Around the world, many early cultures discovered these properties and utilized this glass in weapons, tools, and decoration.

Uses of Obsidian as a Cutting Tool

The conchoidal fracture of obsidian causes it to break into pieces with curved surfaces. This type of fracturing can produce rock fragments with very sharp edges. These sharp fragments may have prompted the first use of obsidian by people.

The first use of obsidian by people probably occurred when a sharp piece of obsdian was used as a cutting tool. People then discovered how to skillfully break the obsidian to produce cutting tools in a variety of shapes. Obsidian was used to make knives, arrow heads, spear points, scrapers and many other weapons and tools.

Once these discoveries were made, obsidian quickly became the raw material of preference for producing almost any sharp object. The easy-to-recognize rock became one of the first targets of organized "". It is probably a safe bet that all natural obsidian outcrops that are known today were discovered and utilized by ancient people. http://geology.com/rocks/obsidian.shtml Asst. Prof. Dr. Ayşe KALEMTAŞ Glass from Nature

Obsidian is a popular jewelry stone.

A thin piece of obsidian is often used as a "backing" material for opal doublets and triplets. The black obsidian adds stability to the opal and provides a dark background color that contrasts with the opal's fire.

Mahogany obsidian and snowflake obsidian cabochons set in a sterling silver pendants.

Freshly broken pieces of obsidian have a very high luster. Ancient people noticed that they could see a reflection in obsidian and used it as a .

http://geology.com/rocks/obsidian.shtml Asst. Prof. Dr. Ayşe KALEMTAŞ Glass from Nature

Obsidian in Modern Surgery

Although using a rock as a cutting tool might sound like "stone age equipment", obsidian continues to play an important role in modern surgery.

Obsidian can be used to produce a cutting edge that is thinner and sharper than the best surgical steel.

Today, thin blades of obsidian are placed in surgical scalpels used for some of the most precise surgery.

In controlled studies, the performance of obsidian blades was equal to or superior to the performance of surgical steel.

http://geology.com/rocks/obsidian.shtml Asst. Prof. Dr. Ayşe KALEMTAŞ Glass from Nature

magma fulgurite

obsidian tektites Asst. Prof. Dr. Ayşe KALEMTAŞ Manmade (Synthetic) Glass

When, where, or how human beings discovered how to make glass is not known. Very small dark-colored beads of glass have been dated back to 4000 B.C.E. These may well have been by-products of or pottery glazing.

By 2500 B.C.E. small pieces of true synthetic glass appeared in areas such as , but an actual glass did not appear until about 1500 B.C.E. in . By this time various small vases, cosmetic jars, and jewelry items made of glass had begun to appear.

All the ancient glasses were based on silica (sand), modified with considerable amounts of various metal oxides, mainly soda (Na2O) and lime (CaO). This is still the most common glass being used today. It is known as soda lime glass. However, the ancient glass was usually colored and opaque due to the presence of various impurities, whereas most modern glass has the useful property of transparency.

http://www.chemistryexplained.com/Ge-Hy/Glass.html#ixzz3G6so8r7V

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS

- 4000: Jewel in molted glass -(Phoenicia)

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS -1500: Vases and vessels (Egypt)

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS

Egyptians Romans Middle Ages

• First people to • By Roman times • Main achievements realize what could glass being blown were colored glass be done with glass and molded, cut and windows. when it is hot and engraved, and plastic. painted. • Made vessels for cosmetics and perfumes by forming molten glass around a shaped core.

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

A glass is a that possesses no long-range atomic order and which undergoes the glass transformation from solid to supercooled liquid on heating.

Crystalline materials have a definite structure, whereas amorphous ones do not, and therefore only rather general statements can be made about a material which, when hot, is ductile but when cold is brittle, and fractures if there is a sudden change of temperature.

No melting Resemble point, Amorphous No No long- “frozen a glass structure range order liquids” transition temperature

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Glasses do not solidify at an exact temperature (the melting temperature, Tm,) as is known for crystalline materials, but instead in a rather broad temperature range.

Specifically, upon cooling, a glass becomes increasingly viscous (like honey).

Concomitantly, the specific volume, Vs, of the glass (that is, the volume per unit mass), decreases continuously upon cooling whereas for crystalline Schematic representation of the temperature solids a sudden drop of Vs at dependence of the specific volume, Vs, for a glass the melting temperature is and a crystalline substance. observed.

Understanding , Rolf E. Hummel, Second Edition, Springer, 2004. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

The contraction of glasses during cooling is a combination of two effects.

The first one occurs, as in most crystalline substances, by reducing the interatomic distances.

The second contraction mechanism is due to a rearrangement of atoms. As the glass cools, the atomic rearrangement becomes slower until a temperature is eventually reached at which Schematic representation of the temperature the is so high that any dependence of the specific volume, Vs, for a glass further structural change is and a crystalline substance. nearly impossible.

Understanding Materials Science, Rolf E. Hummel, Second Edition, Springer, 2004. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Below this temperature, Tg, the volume of the glass contracts at a fixed rate that is determined by the present structure.

The intermediate range between Tg and Tm is called the or glass transformation range.

Tg is then defined to be that temperature at which, during cooling, the Vs versus T curve reaches an essentially constant slope.

Above Tg, the material is defined to be a supercooled liquid, or Schematic representation of the temperature eventually a liquid. dependence of the specific volume, Vs, for a glass and a crystalline substance. Below Tg, it is a solid (i.e., a glass).

Understanding Materials Science, Rolf E. Hummel, Second Edition, Springer, 2004. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

For practical reasons, the “melting point” of glasses is defined to be that temperature at which the viscosity is 10 Pa.s.

The intersection of the two straight portions of the Vs versus T curve for glasses is called the fictive temperature, Tf.

Because of the high viscosity of most glasses and the consequential low mobility of the atoms, any crystallization (called deglassing or devitrification) is very sluggish. Nevertheless, extremely slow Schematic representation of the temperature cooling rates or prolonged dependence of the specific volume, Vs, for a glass heating at high temperatures and a crystalline substance. eventually causes devitrification.

Understanding Materials Science, Rolf E. Hummel, Second Edition, Springer, 2004. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

As a matter of fact, glass is a material that has quite a low linear expansion coefficient, which is about 1/5 of that for crystalline silica.

Incidentally, the expansion coefficient of crystalline silica changes abruptly at the temperature at which the allotropic transformation between - to - quartz takes place.

Commercially important is , a whose thermal Comparison of the linear expansion l/l of expansion coefficient is only 1/3 of glass, crystalline silica, and a typical metal that for common soda–lime glass. as a function of temperature

Understanding Materials Science, Rolf E. Hummel, Second Edition, Springer, 2004. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Glass is a very brittle material

Glass is a linear elastic and isotropic material with no plastic behavior at normal temperatures, which can explain its brittle fracture. It follows Hooke’s law.

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Glasses  brittle fracture !!!

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

• Glass has amorphous structure • Crystalline materials have some periodic that results in long term order

Glass is a state of matter. It is a solid produced by cooling molten material so that the internal arrangement of atoms, or molecules, remains in a random or disordered state, similar to the arrangement in a liquid. Such a solid is said to be amorphous or glassy. Ordinary solids, by contrast, have regular crystalline structures.

http://www.chemistryexplained.com/Ge-Hy/Glass.html#ixzz3G6raJsdx

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Two-dimensional illustrations of the structures of (a) crystalline silica, (b) liquid or glassy silica and (c) glassy or vitreous silica containing some sodium oxide

Asst. Prof. Dr. Ayşe KALEMTAŞ General Characteristics of Glasses

Structure is Short range isotropic, so the atomic order but properties are no long-range uniform in all order directions

Soften before Typically good melting, so they electrical and can be formed thermal easily by various insulators forming techniques

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

General properties of glasses . High hardness / brittle . Low density compared to high strength . Low coefficient . Low heat / electrical conductivity . High melting point . Good chemical resistance / chemically inert . Wide range of optical transmission Transparent Translucent Opaque

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Advantages Disadvantages

. Inert . Brittle . Does not corrode . Breakable . Durable . Heavy . Optical transparency . Many forming method . Many composition . Cheap

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Starting ceramic Final product powders

Batching and mixing of raw Homogenisation materials

Batch melting Fining Glass is prepared by cooling from a liquid state without crystallization

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

1. Glass forming oxides: usually the dominant constituent

SiO2, B2O3, P2O5, etc. 2. Fluxes: reduce melting temperatures

Na2O, PbO, K2O, Li2O, etc. 3. Property modifiers: added to tailor chemical durability, expansion, viscosity, etc.

CaO, Al2O3, etc. 4. Colorants: oxides with 3d, 4f electron structures; minor additives (<1 wt%) 5. Fining agents: minor additives (<1 wt%) to help promote bubble removal

As-, Sb-oxides, KNO3, NaNO3, NaCl, fluorides, sulfates

Asst. Prof. Dr. Ayşe KALEMTAŞ ORDINARY GLASS FABRICATION

SAND SODA LIME OTHER GLASS

Percentage of Ingredients in Glass

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION RAW MATERIALS

NETWORK FORMERS

MODIFIERS INTERMEDIATES

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION RAW MATERIALS

The most essential component of any glass batch is always the glassformer. Every glass contains one or more components which serve as the primary source of the structure. If most of the glassformer present in a specific sample is silica, for example, NETWORK that glass is called a silicate. If a significant amount of boric oxide (B O ) is also FORMERS 2 3 present, in addition to silica, the sample is termed a borosilicate glass. The primary

glassformers in commercial oxide glasses are SiO2, B2O3, and P2O5, which all readily form single component glasses.

A large number of other compounds may act as glassformers under certain

circumstances, including GeO2, Bi2O3, As2O3, Sb2O3, TeO2, Al2O3, Ga2O3, and V2O5. With the exception of GeO2 these oxides do not readily form glasses by themselves unless very rapidly quenched or vapor deposited, but can serve as INTERMEDIATES glassformers when mixed with other oxides. The elements S, Se, and Te act as glassformers in chalcogenide glasses. Although halide glasses can be made in many systems, with many different compounds acting as glassformers, the two most common halide glassformers are BeF, and ZrF,.

The degradation in properties is usually countered by addition of property modifiers, which include the alkaline earth and transition metal oxides. While these oxides partially counter the reduction in processing temperature obtained by addition MODIFIERS of fluxes, they also improve many of the properties of the resulting glasses. The properties are thus modified, or adjusted, by careful control of the amount and concentration of these oxides to obtain precisely the desired results. Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION RAW MATERIALS

Division of the oxides into glass formers, intermediates, and modifiers

Glass Formers Intermediates Modifiers

B2O3 TiO2 Y2O3 SiO2 ZnO MgO GeO2 PbO2 CaO P2O5 Al2O3 PbO V2O3 BeO Na2O

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION RAW MATERIALS

COLORANTS AND REFINERS

Colorants are used to control the color of the final glass. In most cases, colorants are oxides of either the 3d transition metals or the 4f rare earths. Uranium oxides were once used as colorants, but their radioactivity obviously reduces their desirability for most applications. Gold and silver are also used to produce colors by formation of colloids in glasses. Colorants are only used if control of the color of the glass is desired, and are usually present in small quantities. Iron oxides, which are common impurities in the sands used to produce commercial silicate glasses, act as unintentional colorants in many products. When colorants are used to counteract the effect of other colorants to produce a slightly gray glass, they are referred to as decolorants.

Fining agents are added to glass forming batches to promote the removal of bubbles from the melt. Fining agents include the arsenic and oxides, potassium and sodium nitrates, NaCl, fluorides such as CaF,, NaF, and Na,AlF,, and a number of sulfates. These materials are usually present in very small quantities (< 1 wt%), and are usually treated as if they have only minor effects on the properties of the final glasses. Their presence, however, is essential in many commercial glasses, which would be prohibitively expensive to produce without the aid of fining agents in reducing the content of unwanted bubbles in the final product.

Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Important temperatures in glasses can be defined by viscosity

Logarithm of viscosity versus temperature for fused silica and three silica glasses. (From E. B. Shand, Engineering Glass, Modern Materials,Vol. 6, Academic Press, New York, 1968, p. 262.) Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

On the viscosity scale, several specific points that are important in the fabrication and processing of glasses are labeled:

1. The melting point corresponds to the temperature at which the viscosity is 10 Pa.s (100 P); the glass is fluid enough to be considered a liquid.

2. The working point represents the temperature at which the viscosity is 103 Pa.s (104 P); the glass is easily deformed at this viscosity.

Logarithm of viscosity versus temperature for fused silica and three silica glasses. (From E. B. Shand, Engineering Glass, Modern Materials,Vol. 6, Academic Press, New York, 1968, p. 262.) Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

3. The softening point, the temperature at which the viscosity is 4x106 Pa.s (4x107 P), is the maximum temperature at which a glass piece may be handled without causing significant dimensional alterations.

4. The point is the temperature at which the viscosity is 1012 Pa.s (1013 P); at this temperature, atomic diffusion is sufficiently rapid that any residual stresses may be removed within about 15 min.

5. The strain point corresponds to the temperature at which the viscosity becomes 3x1013 Pas (3x1014 P); for temperatures below the strain point, fracture will occur before the onset of plastic deformation. The glass transition temperature will be above the strain point.

Logarithm of viscosity versus temperature for fused silica and three silica glasses. (From E. B. Shand, Engineering Glass, Modern Materials,Vol. 6, Academic Press, New York, 1968, p. 262.) Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Most glass-forming operations are carried out within the working range- between the working and softening temperatures.

The temperature at which each of these points occurs depends on glass composition.

Logarithm of viscosity versus temperature for fused silica and three silica glasses. (From E. B. Shand, Engineering Glass, Modern Materials,Vol. 6, Academic Press, New York, 1968, p. 262.) Asst. Prof. Dr. Ayşe KALEMTAŞ INTRODUCTION

Three largest consumers Glass packaging, domestic commodities and construction industry

Glass Consumers

Glass package, 43 % Sheet glass, 30 % Housekeeping, 12 % Electrotechnical needs, 10 % Plant and cunduits, 5 %

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS FAMILIES

Vitreous Commercial glasses are Silica Soda-Lime primarily based on Aluminosilicate silica, but can include any Glass Glass of the other common glass Other Non- formers as well. Lead Silicate Silica-Based Glass Oxide Glasses The properties of these glasses cover as wide a range as those of other Oxyhalide, Oxynitri Other Silica- major types of de and Oxycarbide Based Oxide materials, i.e., metals or Glasses Glasses polymers.

Although soda-lime-silica Chalcogenide and glasses provide the bulk of Amorphous Chalcohalide commercial glasses by Glasses weight, the economic value of other, more Borosilicate Halide specialized commercial Glass Glasses glasses is comparable to Glassy Metals that of the generic soda- lime-silica products.

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Soda-Lime Glass

Soda-lime glass or soda-lime-silicate glass is perhaps the least expensive and the most widely used of all the glasses made commercially.

Most of the beverage containers, glass windows, and incandescent and fluorescent lamp envelopes are made from soda-lime glass.

It has good chemical durability, high electrical resistivity, and good spectral transmission in the visible region.

Because of its relatively high coefficient of thermal expansion (~100x10-7/°C), it is prone to failure, and this prevents its use in a number of applications.

Most of the commercial glass by weight is based on the soda-lime-silica ternary system, with minor additions of other oxides to adjust the properties for specific applications.

Large-scale continuous melting of inexpensive batch materials such as soda ash

(Na2CO3), limestone (CaCO3), and sand at 1400-1500°C makes it possible to form the products at high speeds inexpensively.

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Soda-Lime Glass

Development of soda-lime-silica glass compositions represents a compromise between the outstanding properties of pure silica, and the cost of producing the massive quantities of glass required for windows, containers, and electrical lighting.

Addition of soda to silica results in a large decrease in the temperature required for melting. Unfortunately, large amounts of soda also lead to unacceptably poor chemical durability of the glass.

Replacement of a portion of the soda by lime (CaO), which is not as strong a flux as soda, partially offsets the reduction in chemical durability and results in a glass with a reasonable melting temperature (~1500C), while maintaining acceptable properties for most consumer applications.

Asst. Prof. Dr. Ayşe KALEMTAŞ Borosilicate Glass

Many of these glasses, especially those based on the ternary sodium borosilicate system, rely on the existence of phase separation for their desirable properties, while many others are homogeneous.

As a result, the properties of these glasses also vary over a wide range. In general, however, these glasses are chosen for their applications because they have either better thermal shock resistance, better chemical durability, or higher electrical resistivity than soda-lime-silica glasses.

The improvement in thermal shock resistance results from a lower thermal expansion coefficient, with values for typical borosilicate glasses lying between that of vitreous silica and those of soda-lime-silica glasses.

The improved chemical durability and higher electrical resistivity of these glasses can result from either a carefully planned morphology for the phase separated borosilicate glasses, or the absence of mobile monovalent ions for many of the homogeneous borosilicate glasses.

Asst. Prof. Dr. Ayşe KALEMTAŞ Borosilicate Glass

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Vitreous silica is the most refractory glass in commercial use. In addition to its refractoriness, it has a high chemical resistance to (particularly to acids), a very low electrical conductivity, a near-zero (~5.5 x 10-7/C) coefficient of thermal expansion, and good UV transparency.

Because of the high cost of manufacture, the uses of vitreous silica are mostly limited to astronomical , optical fibers, crucibles for melting high-purity silicon, and high-efficacy lamp envelopes.

In one technique, the glass is obtained by melting high-purity quartz crystals or beneficiated sand at temperatures in excess of 2000°C.

In a second technique, SiCl4 is sprayed into an oxy-hydrogen flame or water-vapour-free plasma. Silica vapors deposit on a substrate and are consolidated subsequently at ~ 1800°C.

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Vitreous Silica

While vitreous silica has many properties which make it desirable for application as a flat, container, or lamp glass, the high melting temperature required to produce vitreous silica (> 2000 C) precludes its application for the more common consumer products, where cost is a driving force behind the choice of glass composition.

Vitreous silica is the generic term used to describe all types of silica glass, with producers referring to the material as either or as Fused Silica. Originally, those terms were used to distinguish between transparent and opaque grades of the material. Fused Quartz products were those produced from quartz crystal into transparent ware, and Fused Silica described products manufactured from sand into opaque ware.

http://www.hebo-glass.com/public/pdf/datasheet_quartz.pdf http://www.technicalglass.com/product_pages/fused_quartz_labware/labware/fused_quartz_labware.html Asst. Prof. Dr. Ayşe KALEMTAŞ Vitreous Silica

Fused quartz tubing Fused quartz rod

Microscope Slides and Cover Slips The quartz heater soaks the shell, the light bulb shell http://www.technicalglass.com/product_pages/fused_quartz_labware/labware/fused_quartz_labware.html Asst. Prof. Dr. Ayşe KALEMTAŞ Lead Silicate Glass

This family of glasses contains PbO and SiO2 as the principal components with small amounts of soda or .

These glasses are utilized for their high degree of brilliance (as stemware or "crystal"), large working range (useful to make art objects and intricate shapes without frequently reheating the glass), and high electrical resistivity (e.g., for electrical feedthrough components).

PbO additions increase the fluidity of glass and its wettability to oxide ceramics.

Hence, high lead borosilicate glasses (generally without any alkali additions) are used extensively in microelectronics (e.g., for conductor, resistor, and dielectric pastes).

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Lead Silicate Glass

Lead Glass • Lime and soda replaced with PbO • High - clarity sparkle • Softer –cut and engrave • Good electrical resistance - electronics

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Lead Silicate Glass

Fundamentals of inorganic glasses, Arun K. Varshneya, ISBN 0-12-714970-8, 1994 by Academic Press, Inc. Asst. Prof. Dr. Ayşe KALEMTAŞ Halide Glasses

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http://www.houzz.com/photos/6186239/50W-Metal-Halide-WP1-Glass-- Wallpack-120V-modernAsst-outdoor. Prof.-lighting Dr. Ayşe KALEMTAŞ Chalcogenide and Chalcohalide Glasses

-Low loss robust chalcogenide fibres for fibre , supercontinuum generation and delivery is glass containing one or more -Fibre end caps and splicing technology for soft glass fibres chalcogenide elements. Modern chalcogenide compounds are Ge, Sb and Te used for CD/DVD http://minerva-project.eu/technology/ http://4textile.blogspot.com.tr/2012/10/226.html

Chalcogenide materials could enable faster data streaming. These materials promise to bridge the gap between glasses such as fibre optics and semiconductors such as silicon — potentially resulting in faster data streaming and more efficient solar cells, among many other applications. ‗With chalcogenides we can form the material into fibres, thin films, microspheres, nanophotonics — anything that you can make glass in to, but they also have the electronic properties of semiconductors, so it‘s almost a marriage of the two worlds,‘

http://www.theengineer.co.uk/more-sectors/electronics/news/chalcogenide- materials-could-enable-faster-data-streaming/1009575.article#ixzz3KitazK11

Asst. Prof. Dr. Ayşe KALEMTAŞ OPTICAL FIBRES

Communications are increasingly based on electro-optic systems in which telephones, and computers are linked by fibre optic cables which carry information by light.

Making glass optical fibres is a highly specialised aspect of glass manufacture. Optical fibres consist of two distinct glasses, core of highly refracting glass surrounded by a sheath of glass with lower refractive index between the two glasses, it is guided by total reflection at the core-sheath interface to the other end of the fibre.

In theory, a wide range of glasses can be used as long as the difference in refractive index is appropriate but the higher the refractive index of the core relative to that of the sheath glass, the greater the carrying capacity of the fibre. A typical system available commercially comprises a germanium doped silica core and a borosilicate cladding.

Asst. Prof. Dr. Ayşe KALEMTAŞ FLAT GLAS

There are two main flat glass methods for producing the basic glass from which all processed glass products are made:

. the drawn glass process and . the process.

Since the introduction of the float process in 1959 by it has gradually replaced other processing techniques.

Annealed glass (ordinary glass) is the end product of the float glass process.

It is carefully cooled through the range of temperatures where the glass solidifies so that no residual stresses develop.

Float glass is made using a bath of molten , where molten glass is floated along the surface. The perfectly flat surface of the tin is transferred to the glass.

Asst. Prof. Dr. Ayşe KALEMTAŞ FLAT GLAS

DRAWING

A solid metal plate is dipped into a bath of molten glass and then slowly withdrawn from the melt. This process would present no problems if we were interested in producing a glass rod. Producing a planar sheet is problematic because the sheet would neck down to a narrow ribbon. This difficulty is overcome by cooling the sheet as it is drawn. These coolers solidify the glass and produce a sheet of fixed width.

Drawing from molten glass: (a) a circular rod; (b) problem of pulling a planar sheet; (c) use of a débiteuse and cooling to allow the formation of a sheet of constant width.

Asst. Prof. Dr. Ayşe KALEMTAŞ FLOAT GLAS

Float glass can be produced in very large sizes with an extremely high flatness. Within the production technique the surface finish is improved and glass sections with visible internal defects are removed.

The production technique requires that residual stresses are introduced. This creates compressive stresses in surface regions which is an advantage in practical use.

Float glass has opened the possibility to use glass in new and demanding applications.

A new series of glass products known as structural glass has been introduced. This type of glass dominates completely today.

Asst. Prof. Dr. Ayşe KALEMTAŞ FLOAT GLAS

Based on float glass various products have • been introduced in the market.

There is a continuous • Heat development regarding • Coated strengthened glass glass products to meet glass new needs on the market.

Some of the mentioned products have been on the market for longer period of time but not being used in structurally demanding applications. • Insulating • Toughened glass glass

Asst. Prof. Dr. Ayşe KALEMTAŞ FLOAT GLAS

http://educationcenter.ppg.com/glasstopics/learn_about_glass.aspx Asst. Prof. Dr. Ayşe KALEMTAŞ FLOAT GLAS

More than 90% of the world‘s flat glass is now made by the float process, where molten glass, at approximately 1000C, is poured continuously from a furnace on to a large shallow bath of molten tin.

The liquid glass floats on the tin, spreads out and forms a level surface. Since the melting point of the tin is much less than that for glass, the glass solidifies as it slowly cools on top of the molten tin.

Thickness is controlled by the speed at which the solidifying glass ribbon is drawn off the bath. Once the glass solidifies, it is fed into an annealing lehr where it is slowly cooled in a process where the residual stresses are controlled.

This process results in the production of an annealed float glass with residual compressive stresses around 8 MPa in the surface. After annealing the glass emerges as a ―fire‖ polished product with virtually parallel surfaces.

This method, in which the glass pane is formed by floating the melt on a bath of liquid tin, revolutionized the manufacture of high quality glass and large sizes. Float glass is available in thicknesses ranging from 2 mm up to 25 mm.

Asst. Prof. Dr. Ayşe KALEMTAŞ ANNEALED GLAS

Advantages

– Cost

Limitations

– Breaks in sharp pieces

– Not as strong as tempered glass

– Size limitations

Asst. Prof. Dr. Ayşe KALEMTAŞ ANNEALED GLAS

Images of annealed glass failure (left), heat-strengthened glass failure (centre), and fully tempered glass failure (right)

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Tempered glass also know as toughened glass is made by quickly cooling the annealed glass when it is heated near compression is formed over the glass surface while tensile formed inside the glass plate. Shatter pattern of tempered glass

Tempered glass is made by heating annealed glass to approximately 700C then cooling the outer surfaces rapidly. This process makes the glass very strong and shock resistant thus Crazed fracture pattern on left in more durable. tempered glass on an elevator wall. Fracture origin is shown above.

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Primary processing is a treatment of the basic glass after its manufacture. Since surface flaws only lead to fracture when a tensile opens them, any method of putting the glass surface into permanent compression is advantageous.

An applied tensile stress would have to overcome this built-in compression before it begins to open up a flaw and hence the glass would be able to resist higher loads. Toughened glass and heat strengthened glass use this principle.

The stress distribution in toughened glass enables it to withstand tensile stresses of much higher levels than ordinary annealed glass. Annealed glass has a residual surface compression stress of around 8-10 MPa, because of production reasons. Any external stress level has to exceed this threshold stress to cause a failure which will be time and size dependent. The thickness of the glass may influence the actual residual compressive stress.

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Toughened glass, or tempered glass as it is also known as, is first cut to its final size and it is edge treated and drilled if required. Afterwards the glass pane is heated to approximately 650C, at which point it begins to soften. Its outer surfaces are then cooled rapidly, creating in them a high compression stress, where the rate of the cooling will determine the amount of built-in compression stress and hence the final strength of that glass.

Its bending strength is usually increased by a factor of 4 or 5 to that of annealed glass and hence a new and raised threshold stress has been achieved. The maximum tensile stress in the middle is half of the surface compressive stress.

When broken, it fractures into small harmless dice and it is known as safety glazing material. Heat strengthened glass is similarly produced, but with strengths approximately half that of toughened glass and without the safety glazing characteristic. Toughened glass cannot be subsequently surface or edge worked or cut because this would initiate a failure.

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

• Resists fractures because surface is compressed • Crumbles when cracked because inside is tense

Advantages – 4 times the stronger than annealed – Breaks into small, harmless pieces. – Qualifies as Safety Glazing

Limitations – Must be cut to size before tempering – Optical distortion (roller wave, strain pattern)

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Tempering glass – Cool outside of glass quickly, outside stiffens while inside is still hot – Shrinking inside compresses outside, compressed outside stretches inside

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Toughened is derived from heating typical flat glass, including patterned, to a plastic like state of around 600-700 C in a specially designed furnace or oven.

After the desired state is achieved it is rapidly cooled with a burst of air to both surfaces.

Different types of glass have different recipes to allow it to be toughened.

Asst. Prof. Dr. Ayşe KALEMTAŞ TEMPERED GLASS

Usage Range of Tempered Glass:  Construction curtain wall  Glass doors & windows Laminated glass is  Support bar of staircases & escalators widely used for  Different types of the glass artdecorations Blaustrading  Location of near the intense heat and the Showerscreens impact severed by the hotcold. Display Cases Revolving Doors Shopfronts Lifts and Foyers Partitions Furniture Pool surrounds, etc.

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

Laminated glass is a kind of which is combined from one or more layers of PVB through heating and pressing processes by autoclave.

2 sheets of glass are bonded with a thin film of plastic such as polyvinyl butyrate under pressure at a temperature of about 100°C

The sandwiched plastic bonds well to the 2 glass surfaces and helps absorb energy in impacts, stops glass shattering and disintegrating if stressed to failure so that it often remains secure and weatherproof.

This provides a high degree of resistance to injury from flying glass in case of impact.

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

Laminated glass absorbs energy Safety of the impact • Ordinary window glass is brittle and breaks into long sharp pieces

Will not shatter

Holds up against

• hurricanes • cyclones • earthquakes

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

Laminated glass is widely used for bullet proof burglar-proof showcase counter aquarium http://www.livingetc.com skylight Glass staircase long corridor www.aarticommercial.com sidelite, etc. Laminated Windscreen Glass If the laminated glass is made from “ordinary” float glass, it is still workable (cutting and drilling is possible) and the PVB helps the fractured glass to stay put inside the construction.

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

Sound Control Application

Another important element of laminated glass is acoustical performance in commercial applications.

Laminated glass reduces noise transmission due to sound damping characteristics of the pvb interlayer.

While glass is inherently a poor acoustical performer, higher performance levels can be achieved by using laminated glass http://qddarley.en.made-in-china.com alone or combined with additional glass plies to form a sealed insulating glass unit.

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

UV Protection

With time, sunlight can cause considerable damage to buildings furnishings, carpets, artwork, photographs, plants and other valuables. These items need special protection from the damaging effects of the sun's (UV) rays.

Laminated glass made with resin can be effective in screening out the harmful UV rays, controlling glare and decreasing solar energy transmittance. Glazing solar control is accomplished in laminated glass by the interlayer ability to reflect and/or absorb and re-radiate much of the solar UV radiation. Laminated glass made with resin screens out more than 99% of damaging UV light.

While protecting buildings from harmful and damaging solar UV radiation, laminated glass made with resin has no adverse affect on the health of indoor plants. In fact, laminated glass is commonly used in greenhouses and atriums to help protect flower color and reproductive development from the damaging effects of UV radiation. Photoreceptors in plants are still able to absorb sunlight the resin interlayer allows to be transmitted.

Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

The City of Arts and Sciences is an entertainment and educational complex that is an amazing work of craftsmanship and design.

Architect Santiago Calatrava primarily designed this gorgeous project.

Laminate glass is widely used not just in the grand windows and ceilings but also found in the planetarium’s floor.

The glass floors are four ply laminated glass that consist of acid etched, anti-slip, 6 mm tempered glass on the top with three 10 mm layers of glass. This keeps right in line with the modern design of the building.

www.homedesignfind.com Asst. Prof. Dr. Ayşe KALEMTAŞ LAMINATED GLASS

BULLETPROOF GLASS

Bulletproof glass is made of laminated glasses and films which have special shielding capability towards bullets.

The different levels of bullet proof glasses are able to shield the bullets from penetration and prevent the broken parts from injuring people. www.bmw-security-vehicles.com They are widely applied in 22-millimetre glass/plastic laminate with a bank, polycarbonate coating on the inside to prevent flying splinters. The 22-millimetre glass protects against: counters of jewelry and gold shops,  cash trucks and • Blunt instruments .44 Magnum with full-jacket flat-nose bullets other regions requiring special safety  .357 Magnum with coned bullets prevention.  9-millimetre Luger with round-nose bullets

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

Choice of Glass Compositions

Choosing a glass composition is a more complicated exercise than may at first appear. One must first establish the properties important to the final user, next consider those properties important to the glass maker, then achieve a balance between these and lastly determine what choice of batch materials will produce either the best quality or, perhaps, the cheapest glass meeting the quality requirements.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

Properties Important to the User

Which properties are important depends very much on the application. From a designer's point of view, strength would nearly always be the first to be considered. However, because the practical strength of glasses is determined more by surface flaws than anything else strength can generally be taken to be weakly dependent on composition and omitted from the specification. So far as strength is concerned commercial glasses can usually be considered as being either pure silica or "the rest" and only two sets of strength data need be considered.

The next most important property, which may not always come immediately to mind, often is resistance to corrosion. Good glasses are generally stable, already being oxides, but can be leached by water or other chemicals, something which is only rarely desirable. Chemical durability is strongly dependent on composition, especially alkali and alumina contents, and thus should always be included. Next we come to the properties essential for the specific application. These may include refractive index, electrical resistivity, thermal expansion, transparency to or absorption of radiation, softening temperature, and so on. These properties fall into two classes, those for which a specific value is needed, like refractive index in an optical glass or thermal expansion for a sealing glass, and those that need to be better than some particular limit, like chemical durability or thermal expansion when thermal shock resistance is important.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

Properties Important to the Glass Maker

Apart from the criteria set by the final user, several properties are very important to the glass manufacturer. The viscosity- temperature characteristic is crucially important to efficient forming.

Also the temperature must be below the temperature at which the melt must be held to begin forming operations. The actual devitrification characteristics may be less important but it can be useful to know whether crystal growth may be rapid if it does occur. The glass manufacturer also wants to have a glass as easy as possible to melt, refine, and homogenize but these factors are not capable of being specified in terms of standard properties.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

Properties Important to the Glass Maker

Some glasses contain significant proportions of elements which can exist in more than one valence state and these may need their oxidation states to be controlled. The most familiar example is the decolorizing of glass in which iron is oxidized, as far as possible, to the ferric state which gives a paler tint than the same concentration of iron reduced to ferrous.

On the other hand, to make a heat absorbing glass one would wish to reduce the iron to ferrous which has a broad absorption peak in the near .

Control of oxidation is generally achieved largely by the selection of oxidizing or reducing materials added to the batch but partly by control of furnace atmosphere.

In small scale laboratory melting oxidation can be controlled by bringing the melt to equilibrium with a specific atmosphere but this is not necessary and would be difficult to achieve in large scale manufacture.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

The batch materials can considerably influence ease of melting, degree of segregation during melting, volatilization losses, refining, and homogeneity of the glass.

Both control of oxidation and overall melting performance can also be affected by minor constituents, that is to say cations or anions added at levels usually below 1%, which control oxidation through mutual interactions or have beneficial effects on melting, refining, and homogeneity.

The interactions between iron and arsenic, antimony or cerium can play an important part in decolorizing. Sulfate is the most commonly used refining agent: arsenic is often efficient but now rarely used because of legal controls on its use and halides can be effective. The glass maker will usually expect to be allowed to modify slightly the user's composition specification to optimize these factors.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS COMPOSITION

Typical composition (wt %) of some of the common commercial glasses

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

By definition, glass-ceramics are materials which are melted and formed using standard glass manufacturing techniques, and then heat treated to produce a highly crystalline material with properties which are very different from those of the original glass.

The most common glass-ceramics are based on either the lithium, sodium, or magnesium aluminosilicate systems.

Although the best known glass- ceramics are used for cookware, applications of glass- ceramics include other consumer products such as electric stove tops and construction materials, and Processing cycle for a glass-ceramic specialty applications such as telescope mirrors, electronic substrates, and missile radomes. Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Production of glass-ceramics usually involves a two-step process.

A small amount of a ―nucleating agent‖ is added to the batch. When heat treated at the proper temperature, this agent will either form very small crystals, i.e., nuclei, or will induce phase separation.

Once this phase has formed, the material is heated to a higher temperature where a second, major phase will grow to yield the final product.

In general, a very fine grained microstructure is desired, since such microstructures produce very strong materials.

Many applications of glass-ceramics are based on their superior resistance to failure due to thermal shock. Since thermal shock resistance is primarily determined by the thermal expansion coefficient of a material, the crystalline phase in these materials should have a low thermal expansion coefficient. A a low thermal expansion coefficient is obtained by a combination of a low expansion crystalline phase and a low expansion residual glass.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Glass-Ceramics • ―Glass-ceramic‖ refers to materials which are fabricated from glass melts by a process of controlled crystalisation. • Glass-ceramis is a partially crystalline material which is fabricated by an incomplete crystallisation (―Ceraming‖) of suitable glasses. • Brands: Ceran, , Robax, Neoceram,

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Crystalline phase in these materials is a lithium aluminosilicate, which is either a -quartz solid solution phase

LAS for Vision, or spodumene for Corningware. A mixture of TiO2, and ZrO2, in the batch results in a very efficient (PYROCERAM nucleation process. Heat treatment below 900C yields very small (<100 nm) particles of the -quartz solid solution phase, which has a refractive index close to the residual glass (very high silica concentration). The ZERODUR resulting material is transparent even though it is highly crystalline. Heat treating the same material at a VISION) temperature > 1000C results in the transformation of the -quartz solid solution. phase into - spodumene, accompanied by grain growth to produce crystals in the 1 to 2 m range.

Machinable glass-ceramics are derived from the K2O–MgO–Al2O3–SiO2 system containing some fluorine. In Macor the crystalline phase is potassium fluorophlogopite [KMg3(AlSi3O10F2)]. Phlogopite is a mica mineral and the plate-like mica crystals are randomly oriented in the glass MACOR phase. Macor can be machined to precise tolerances (±0.01 mm) and into intricate shapes using conventional steel tools: they can be drilled, cut, or turned on a lathe.

Calcium phosphate, Ca3(PO4)2, glasses can be made into glass-ceramics to form a material resembling the mineral part of bone. Since bone is porous, the first step is to produce a foam glass. This is achieved by decomposing APATITE carbonate in the glass melt. The foam glass simultaneously undergoes a controlled crystallization, transforming it into a -ceramic. The dimensions of the interconnections between the pores must be sufficient to allow the ingrowth of living bone tissue, which ensures a permanent joint with the surface of the prosthesis.

Another commercial fluoromica glassceramic called Dicor® has been developed for dental restorations. Dicor has better chemical durability and translucency than Macor. It is based on the tetrasilicic mica, KMg2.5Si4O10F2, which forms fine-grained (∼1μm) anisotropic flakes. Dicor dental restorations are DICOR very similar to natural teeth both in hardness and appearance. They are easy to cast using conventional dental laboratory methods and offer significant advantages over traditional metal–ceramic systems.

Asst. Prof. Dr. Ayşe KALEMTAŞ GLASS-CERAMIC

Zerodur mirror substrates for Glass-ceramic teeth large segmented and monolithic Macor substrates astronomical telescopes

From left to right parent glass, glass ceramic The fracture surface of Macor with 97% crystallinity and glass-ceramic with 50% crystallinity. Grain size is about 20 micrometers.

Edgar Dutra Zanotto, A bright future for glass-ceramics, American Ceramic Society Bulletin, Vol. 89, No. 8 http://www.schott.com/advanced_optics/english/products/optical-materials/zerodur-extremely-low-expansion-glass-ceramic/zerodur/index.html?so=turkey&lang=turkish http://www.ceramic-substrates.co.uk/machinable-ceramics/macor Asst. Prof. Dr. Ayşe KALEMTAŞ Asst. Prof. Dr. Ayşe KALEMTAŞ THE END Thanks for your kind attention

Asst. Prof. Dr. Ayşe KALEMTAŞ Any Questions

Asst. Prof. Dr. Ayşe KALEMTAŞ