Week 12: Ceramics Flashcards
What are the 5 different types of ceramics?
- Glasses - lime soda glass
- Clay - bricks
- Refractories - fireclay
- Abrasives - si carbide, al oxide
- Cement - concrete
Is glass an amorphous or crystalline ceramic?
Amorphous
What is another way of saying non-crystalline?
Amorphous, short-range order
Crystalline Ceramic
An ordered structure with unit cells
What’s an example of a crystalline ceramic?
Quartz
What bonding is present in crystalline and non-crystalline ceramics?
Ionic and covalent
Why do ceramics have a lower density?
Because atoms are different sizes so they’re packed less efficiently
What does the bonding mean in ceramics?
- High strength
- High melting temp
- Low ductility
- Low electrical conductivity
Why aren’t there many slip planes in ceramics?
Because of the strong covalent and ionic bonding
What does a lower number of slip planes mean?
Little to no plastic deformation occurs, so the material will be brittle
Supercooled Liquid
Amorphous ceramic above Tg
What happens when the bonding of electrons are shared equally?
%IC is 0, so it’s fully covalent bonding
What happens when the bonding of electrons are shared unequally?
%IC isn’t 0, so there’s some form of ionic bonding
What is another way of saying crystalline?
Long-range order
What are silicate ceramics made of?
Silicon & Oxygen
What are examples of silicate ceramics?
Naturally occurring
Eg: soils, sand, rock, gravel, clay
How do we form a crystal material?
Heat above Tm and cool slowly
Why is glass non-crystalline?
When it moves from supercooled to glass, it doesn’t have enough time to reorder its crystals
What crystal structure is present in diamonds?
Sp3
What crystal structure is present in graphite?
Sp2
What crystal structure is present in graphene?
Sp2
What are 3 methods to make ceramics?
- Glass forming
- Firing
- Cementation
Which concrete test method isn’t standardised?
Tensile test
Why do you add more water to concrete than needed?
To increase workability and put it into moulds
What test method is used for finding fracture toughness?
4 point bend test with notch
What test method is used for finding E?
3 point bend test
Thermal Toughening
Heating between Tg and softening point, then quenching with air jets quickly
Chemical Toughening
Adding element in ceramic where diffusion takes place
Laminating
Placing glass between polymer and laminating
Glazing
Applying a material to surface and firing until solid
Concrete
What is the filler and matrix?
A composite material
Filler: Water, gravel & sand (aggregate)
Matrix: Portland cement
Hydration
The process of creating cement and triggering the reaction
How do voids form in concrete?
Voids or holes in cement that form due to excess water after reaction
Why are pores bad?
They lead to lower fracture toughness because of lower cross-sectional area
How to test concrete?
Compression and flexural testing (3 point)
In a compression test, what leads to a higher strength?
Lower temperature and higher strain rate
Reinforced Concrete
Putting steel reinforcements into steel to increase toughness
Pres-stressed Concrete
Creating tension in reinforcement then releasing when pouring concrete
Creates compressive strength in concrete
Geopolymer Concrete
Matrix of cement and thermosetting polymer
Pros and cons of geopolymer concrete?
+ High TS, FS, CS
+ Lighweight
+ Corrosion resistance
- Expensive
- Dangerous to human skin
