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Materials Sem 2 > Ceramics and Glasses > Flashcards

Ceramics and Glasses Flashcards

1
Q

What are Crystalline Ceramics?

A

Based on regular arrangements of atoms/ions

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2
Q

What are Amorphous Ceramics?

A

Atoms/ions are not arranged in a regular long range structure

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3
Q

What are Bonded Ceramics?

A

Based on crystalline and amorphous structures bonded together

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4
Q

Name some ceramics properties

A 
Low toughness
Poor in tension
High hardness
High melting point
Insulators
Environmentally stable
Typically ionic or covalently bonded
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5
Q

What is ‘Powder Processing’?

A

Way to bond ceramics with high melting temps. Heat and pressure is applied to ceramic in powder for which fuses into a matrix. Can create unwanted pores

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6
Q

What is meant by a ‘Supercooled Liquid’?

A

Often refers to amorphous (glass) materials . Amorphous structure is ‘frozen in’ when glass cools.

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7
Q

What is the chemical form of Silica Based ceramics?

A

SiO2

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8
Q

What is the Silicon solid state structure?

A

Tetrahedral shape

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9
Q

What are the Crystalline Silica structures?

A

Quartz
Crystabolite
Tridymite

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10
Q

What are the Amorphous Silica structures?

A

Fused silica

Vitreous silica

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11
Q

What are the effects of adding oxides to amorphous silica?

A

Disrupts bonds reducing Tg

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12
Q

What occurs in Crystalline material solidification?

A

Clear change in volume during solidification

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13
Q

What occurs in Amorphous material solidification?

A

Does not have a definite temperature where it transforms from liquid to solid

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14
Q

What is the Strain point?

A

Temperature at which internal stress is relieved within several hours

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15
Q

What is the Annealing point?

A

Temperature at which internal stress is relieved within a few minutes

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16
Q

What is the Softening point?

A

Viscosity of approx. 4x106 Pa-s, glass slumps under its own weight

17
Q

What is the Working point?

A

Soft enough to be formed into shape

18
Q

What are some of the Defects of ceramics?

A

Vacancies
Dislocations
Pores
Grain boundaries - smaller grain size increases strength

19
Q

What is ‘Thermal shock’?

A

Uneven rapid heating or cooling can create stresses due to the difference in the expansion pf the interior and the exterior of the ceramic

20
Q

Describe the effects of Annealing

A

Heating around the annealing point allows stresses to be relieved

21
Q

What is ‘Thermal Tempering’?

A

Glass is heated above the Tg (but below the softening T)
Exterior is cooled rapidly with air or oil
As interior cools it shrinks placing exterior in compression

Materials Sem 2 (6 decks)

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