Lectures 1-2 Flashcards
Ceramics are
non-metallic, inorganic materials
Most ceramics are composed of
Si, C, or metal elements combined with O, C or N.
Crystalline ceramics have a —– arrangement of atoms
regular
Amorphous ceramics have an —– arrangement of atoms
irregular
Bonded ceramics are … . Includes examples of …. .
a combination of crystalline and amorphous structures, clay materials
Ceramics usually have a —- Young’s Modulus.
high
Ceramics are better in —– rather than in —–.
compression, tension
Ceramics have —– melting points
high
Ceramics, due to their melting points, are useful in what type of application
high temp applications
Ceramics do not have —— bonds, so are useful as —-
metallic, insulators
Ceramics often have —– —— conductivity
poor thermal
Ceramics are often environmentally —–, meaning they do not —— or ——-
stable, corrode, degrade
Crystalline ceramics with an edge dislocation. Why are they difficult to dislocate?
Due to the extra bonds with the ions that are between the larger atoms, unlike a simple crystalline metal.
Glass is used when talking about
a non-crystalline (amorphous) solid
Metals can form amorphous structures if they are….
cooled extremely rapidly, or processed carefully
Crystalline sillica forms a —— shaped structure
tetrahedral
Crystalline silica can form three structures;
quartz, crystabolite, and tridymite
Amorphous forms of silica are called
silica glasses
Pure forms of amorphous silica are…. (two)
fused silica or vitreous silica
Viscosity is a measure of
the resistance of a fluid to flow
Viscosity can be defined as the ratio of the
applied shear stress to the shear strain rate.
Increasing temperatures in a material, the viscosity becomes —-
lower (more flowy)
On a Volume-temp graph for a crystalline material solidification, the upper gradient represents …..
a low viscosity fluid aka liquid
On a Volume-temp graph for a crystalline material solidification, the middle vertical line represents …..
the material solidifying and gaining a regular structure
On a Volume-temp graph for a crystalline material solidification, the lower gradient line represents ….. . The upper end of the lower gradient represents …… and the lower end of the lower gradient represents …… .
the material becomes a solid
a solid at a high temperature
a solid at a low temperature
On a Volume-temp graph for an amorphous material, the upper gradient line represents …..
liquid at a high temperature
On a Volume-temp graph for an amorphous material, the lower gradient line represents ….. (two things)
lower temperature above T g => less compact structure
lower temperature below T g => more compact structure
T g for Amorphous materials is the
glass transition temperature
At the T g, what happens to the appearance of the material?
becomes glassy
What features does the material below the T g have in terms of properties?
- brittle
- relatively hard
Glass at a high temperature has a —- viscosity
high
“frozen-in” used in the context of glass cooling is talking about the
atoms having insufficient time to diffuse and the disordered structure (amorphous) is “frozen-in”
Glass does not have a definite …
temperature where it transforms from a solid to a liquid
A glass material becomes —- and —–, without ——-
hard, rigid, crystallising
Glass materials are often considered as ———- liquids
supercooled
The strain point is
the temp at which internal stress is relieved within several hours
The annealing point is
temperature at which internal stress is relieved within a few minutes
What approx. viscosity does the softening point have
4 x 10^6
Melting point for a glass is not when it becomes fully liquid, but is when the glass has a ….
low viscosity t
How does the glass react when it is at the softening point
glass slumps under its own weight
Working point for a glass means
it is soft enough to be formed into shape
Point defects in ceramics example
vacancies
—– can be found in ceramics but —— is extremely difficult due to the …
dislocations, slip, repulsion of ions with the same charge in the crystal structure
A thermal shock in a ceramic is caused by
uneven rapid cooling and heating
What happens when thermal shock is induced in a ceramic
the exterior cools more rapidly than the interior, placing the exterior under tension
The tension in the exterior of the ceramic through thermal shock can lead to
crack initiation and rapid fracture
In a clay, there are —— which contain strong —- and —– bonds but the layers are bonded together by ….
layers, ionic covalent, weaker van der waals forces
How does the water make the clay moldable?
The water molecules get in between the layers of the clay
Diffusion is a —— / —— depenedent phenomenon
time / temp
Higher temperature = —— diffusion
faster
If a material is loaded in tension it can begin to … . This is due to the process of ——
plastically deform over time, creep
In a ceramic, edge dislocations are more likely to become —– than —— deforming.
fractures, plastically
How would they commonly use a ceramic eg tungsten carbide for a tougher blade/drill? Why do they use it in this quantity?
A small section that is attached onto the edge where the blade/drill will come into contact with the material being worked, only used in small quantities as the ceramic is tough but brittle so could cause whole blade to fracture
By adding different elements to the initial composition of glass, the material becomes …. (two points)
- more easy to work
- lower working temp
With an amorphous glass material, the solidification process follows what sort of trend?
It is less defined and happens over a longer period of time compared to a crystalline which solidifies at a defined temperature
Creep is faster at (2)
- higher temp
- higher applied stress
Creep rate =
C σ^n exp ( -Qc / R T )
C - constant
n - constant
σ - stress
R - gas constant
Qc - activation energy for creep
T - temp
Fatigue is when a material is
subjected to repeated application and removal of stress below its yield strength
After fatigue has set in, failure is typically ——– to the stress direction
perpendicular
Ntoches, scratches and indentations are classed as —– —–
stress raisers
Wear occurs when
components are in contact and there are only a small contact points that take the whole load
Adhesive wear is
when the asperties are plastically deformed and welded together, which leads to them being torn away from the surfaces
Asperities are
the small contact points between components
Abrasive wear occurs when
hard particles of grit are between the surfaces which cause material to be removed
Corrosive wear is
chemical or electrochemical damage of the material surface combined with adhesive or abrasive wear
