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Ceramics and Glasses Research Paper

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Ceramics Written Report
Definition of Ceramics
Periodic table with ceramics compounds indicated by a combination of one or more metallic
elements with one or more nonmetallic elements. They are to be most frequently silicates, oxides,
nitrides and carbides, typically insulative to the passage of electricity and heat ,more resistant to high
temperatures and harsh environments than metals and polymers and hard but very brittle.
Ceramic Crystal Structure
Ceramics that are predominantly ionic in nature have crystal structures comprised of charged
ions, where positively-charged (metal) ions are called cations, and negatively-charged (non-metal) ions
are called anions – the crystal structure for a given ceramic depends upon two characteristics:
1. the magnitude of electrical charge on each component ion, recognizing that the overall structure must
be electrically neutral
2. the relative size of the cation(s) and anion(s),which determines the type of interstitial site(s) for the
cation(s) in an anion lattice
Some examples of Crystal structures for Ceramics
• Rock salt structure(AX)
• Fluorite structure (AX
2
)
• Perovskite structure(ABX
3
)
• Spinel structure(AB
2
X
4
)
The size of the ion depends:
1. Coordination number
• Ionic radius tends to increase as the number of nearest neighbor ions of opposite
charge increases
2. Charges of ions
• When an electron is removed from an atom or ion , the remaining valence electrons
become more tightly to the nucleus, which results in decrease in ionic radius
Imperfections of Ceramics
• It includes point defects and impurities
• Non-stoichiometry refers to a change in composition
• the effect of non-stoichiometry is a redistribution of the atomic charges to minimize the energy
• Charge neutral defects include the Frenkel defects(a vacancy- interstitial pair of cations) and
Schottky defects (a pair of nearby cation and anion vacancies)
• Defects will appear if the charge of the impurities is not balanced
Properties of Ceramics
Classifications of Ceramics

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A. Traditional and Modern Ceramics
I. Glasses
The word "Glass" comes from an Indo-European root which means "shiny" and also
has given us the words glare, glow and glaze. Glasses are non-crystalline silicates containing
other oxides, notably CaO, Na
2
O, K
2
O, and Al
2
O
3.
The two prime assets of these materials are
their optical transparency and the relative ease with which they may be fabricated.
Most inorganic glasses can transformed from a non-crystalline state to one that is
crystalline by the proper high-temperature heat treatment in a process called crystallization.
The product is called a glass-ceramic
.
II. Clay Products
Clay is an inexpensive ingredient, found naturally in great abundance, often is used as
mined without any upgrading of quality. When clay and water are mixed in the proper
proportions, a plastic mass that is very amenable to shaping is formed. The formed piece is
dried to remove some of the moisture, after which it is fired at an elevated temperature to
improve its mechanical strength.
Clay products are classified into two categories - the structural clay products and the
whitewares. Most structural clay products are used in construction. Typical structural clay
products are building brick, paving brick, terra-cotta facing tile, roofing tile, and drainage pipe.
Whitewares are white to off-white in appearance and frequently contain a significant vitreous,
or glassy, component. Included in this group are porcelain, pottery, tableware, china, and
plumbing fixtures.
III. Refractories
Refractories are materials that have unusually high melting point and that maintain
their structural properties at very high temperatures. They also have capacity to provide thermal
insulation and remain unreactive and inert when exposed to severe environments. Refractories
are typically used in the metallurgical, glassmaking, and ceramics industries, where they are
formed into a variety of shapes to line the