CHEMICAL STRENGTHENING OF LITHIUM
ALUMINO SILICATE GLASS-CERAMICS
Ion Exchange by mobile alkali Ions (Li,Na,K)
Acar Bertan ANĞAN
MLZ 463 Project Preparition of Materials Science and Engineering
Report 1
Advisor:Dr.Öğretim Üyesi Emrah DÖLEKÇEKİÇ
Content
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Scope of the Report
Introduction
Definition of Glass
Definition of LAS Glass Ceramics
Application areas of LAS glass-ceramics
Strengthening Methods
Chemical Strengthening
Why we choose Chemical Strengthening?
Scope of the report
What is a glass and glass-ceramic material,.What is a strengthening,which properties we
want to increase.How we can reach our desired properties with an special treatments and
why we choose chemical strengthening to achieve desired properties.
Introduction
In this thesis we examine Lithium alumino silicate glass-ceramics strengthening by chemical
process called Ion Exchange.Aim of this process changing lithium ions exchange by bigger
alkali ions such as Na,K in molten salt bath and creating compressive layer on surface.This
compressive layer provide suppressing of surface flaws under static or dynamic load. In this
process compressive layer depht play an important role and can be varied with process
route like salt type,salt bath time and surface properties before salt bath.Flexural strength
and impact resistance can be increased 4-6 times.Better scratch properties gain.Also crystal
particles size should be small enough if we want transperency.
Definition of Glass
Glass, an inorganic solid material that is usually transparent or translucent as well as hard,
brittle, and impervious to the natural elements. Glass has been made into practical and
decorative objects since ancient times, and it is still very important in applications
as disparate as building construction, housewares, and telecommunications. It is made by
cooling molten ingredients such as silica sand with sufficient rapidity to prevent the
formation of visible crystals.
Definition of Glass-Ceramıcs and LAS Glass-Ceramics
Glass ceramics are produced through controlled crystallization. Typically, a glass material is formed
through a typical manufacturing process, and then the material is cooled and then reheated to force
crystallization. During this process, nucleating additive agents are often added to the composition to
improve control during the crystallization process. Due to this unique manufacturing process, glass
ceramics offer outstanding properties that have made them especially useful materials for glass-tometal sealing. Glass ceramics have the unique ability to exhibit key properties of both glasses and
ceramics, offering several advantages for manufacturers.Some of the important properties of
LAS glass ceramics; has a strong negative coefficent of thermal expansion (CTE)
LAS glass ceramics(Li2O 3-6%, Al2O3 18-25%, SiO2 58-75%) offer several advantageous
thermomechanical properties, including an adjustable coefficient of thermal expansion, high
temperature resistance, improved chemical durability, and zero or very low open porosity.
Application Areas of LAS Glass-Ceramics
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Cookware
Radomes
Military armour applications
Dental applications
Honeycomb mounts for satellite mirrors
X-ray telescopes
Strengthening Methods
Strengthening glass can be done via two primary processes; tempering, thermal
strengthening and chemical strengthening in order to increase the heat resistance and overall
strength of the glass.
I.
II.
Heat tempering
Chemically strengtheing
Chemical Strengthening
Chemically strengthened glass is a type of glass that has increased strength as a result of a
post-production chemical process.
Main application area of chemical strengthening based on the exchange of smaller alkali
ions in the glass matrix ( Na+ or Li+) for larger alkali ions delivered to the surface,
respectively, K+ or Na+. This will result in a near surface molar volume expansion that,
because of the constraint of the unexpanded inner portion of the glass body, will generate
strong compression stress on the surface balanced by a tensile stress in the inner glass
body.We called this compression area,compression layer. mechanical properties are
dependent on the stress level at the surface (CS) and the depth of penetration of the
bigger ion(comprasion layer depht).
According to its nature ion exchange is not a thermodynamic equilibrium process, the
flux of ions inward and outward glass matrices is a kinetic process driven by gradients in the
electrochemical potentials of the involved ionic species.
In glass ceramics the mechanisms are much more complex than in glasses because of their
polycrystalline nature: IOX(Ion Exchange) generally takes place mostly in one phase
(crystalline phase or residual glass). In some cases, the mechanism is similar to what is
observed in glasses with the replacement of an ion by another in the structure; while in
other cases, this IOX leads to microstructural modifications (for example, amorphization or
phase change of a crystalline phase).
Why We Choose Chemical Strengthening?
Chemical strengthening can create a high-performance glass with no notable distortion and
a very shallow surface layer of strengthened, alkali-rich material. The added strength of this
specialized glass makes it ideal not only for harsh environments but also for highperformance applications in conductors, semiconductors, energy, medicine, and more.
Chemical Strengthening can be performed on much thinner glass than heat tempering.
REFERENCES
https://www.elantechnology.com/glass/glass-materials/las-glass-ceramics/
https://abrisatechnologies.com/2014/11/glass-strengthening-methods/
https://www.researchgate.net/publication/306415546_Ion-Exchange_in_Glass-Ceramics
wikipedia
https://www.britannica.com/technology/glass
https://www.researchgate.net/publication/319471996_CHEMICAL_STRENGTHENING_OF_GLASS_BY
_ION-EXCHANGE