103 final

What are ceramics made of?

cations (metals) + anions (non-metals) (many exceptions)

What type of bonding do ceramics mostly have?

mixed primary bonds (ionic and covalent)

What is a key requirement for ions in ionic crystal structures?

ions must be touching (contacting each other)

What is the critical radius ratio formula for ionic structures?

rₘ / rₓ (radius of cation / radius of anion)

What is a simple ionic crystal structure formula and its possible structures?

AX type: FCC or simple cubic structure, same number of cations and anions

What is the structure of Fluorite type ceramics?

AX₂ type: simple cubic structure

What is the Perovskite structure formula and type?

ABX₃ type: FCC structure

What is the Spinel structure formula and type?

AB₂X₄ type: FCC structure

What type of structure do covalent ceramics have?

more open structures

Give examples of carbon-based covalent ceramics.

Diamond: carbon bonded to 4 others (tetrahedral); Graphite: layers of hexagonally arranged carbons; Fullerenes (C₆₀): dome-like structure; Buckyballs: fullerenes with cations inserted inside

What is the basic formula for silicates?

SiO₄

What types of bonding are found in silicates?

both covalent and ionic bonds

Describe the sheet structure in silicates.

closely packed sheets with ionic bonds connecting them

What are non-crystalline ceramics called?

amorphous ceramics

Example of a non-crystalline ceramic?

glass (usually silica-based)

What type of bonding is mainly present in glass?

mostly ionic bonding

Do non-crystalline ceramics have a sharp melting point?

no, they have no clear melting point

What is Tg and Tm in non-crystalline ceramics?

Tg: temperature where melting starts (glass transition temp); Tm: temperature where fully melted

What types of defects can occur in crystalline ceramics?

vacancy, interstitial, dislocation, grain boundary

What are Schottky and Frenkel defects in ceramics?

Schottky defect: missing cation and anion; Frenkel defect: cation displaced to interstitial site; both cause disturbance in electro-neutrality

What is sintering?

a high-temperature process that bonds ceramic particles together without fully melting them

How does sintering work?

ceramic powder is heated below melting point, particles fuse at contact points, reducing porosity and increasing strength

Why is sintering important?

it densifies ceramics, making them strong and usable for structural applications