Ceramics Flashcards
Define a ceramic.
An inorganic compound of 1 metal and 1 or more non-metals. [Ionic and covalent bonding possible.]
Define silica
SiO2, main ingredient in most glass products.
Define alumina
Al2O3, used in abrasives and fake bones
Define hydrous aluminum silicate
Main ingredient of clay
What are the main properties of ceramics
High hardness Electrical and Thermal Insulators Chemically Stable High Melting Temps Brittle No ductility Sometimes translucent
Define the three categories of ceramics.
Traditional: Clay, abrasives, cement
New Ceramics: oxides, carbides (better mechanical properties than traditional)
Glasses: based on silica, noncrystalline
Why can’t ceramics absorb stresses like metals can?
Ionic&covalent bonding vs metallic bonding - no slip
How do you strengthen ceramics?
Make starting materials uniform Decrease grain size Decrease porosity Introduce compressive surface stresses Use fiber reinforcement Heat treat
Are all ceramics insulators?
No - large range of electrical conductivities, but generally lower than metals.
Describe thermal expansion in ceramics
Less than in metals, but more damaging because of brittleness
What are traditional ceramics made of?
Mineral silicates, silica, alumina, and other clay and cements found in nature. Glass is sometimes defined as a traditional ceramic because it is also a silica product.
Where do you get silica naturally?
Quartz, from sandstone. It’s low cost, hard, and chemically stable.
Where do you get alumina from?
Bauxite and corundum. It has good hot hardness, low thermal conductivity, and good corrosion resistance.
What differentiates new ceramics from traditional?
Chemically simpler, and developed synthetically.
Define glass, first as a state of matter, and then as a ceramic.
As a state of matter, glass is the amorphous structure of a solid material. It occurs when molten materials are cooled into solids to fast to become crystalline.
As a ceramic, glass is a compound that cools to a rigid condition without crystallizing.
Why is silica used for glass?
It naturally cools to it’s glassy state rather than crystallizing.
Why are there other ingredients besides silica in glass?
They promote fusion during heating, they increase fluidity in molten glass, they improve chemical resistance to acids bases and water, they add colour, and alter optic index of refraction.
How are glass-ceramics formed?
Heat treatment. They use smaller grains. (makes them stronger than original ceramics). Are generally opaque, not clear.
What are the advantages of glass ceramics?
Close dimensional control over final shape
High strength (stronger than glass)
Low porosity and thermal expansion
High resistance to thermal shock
What are the elements that act like ceramics?
Carbon
Silicon
Boron
What is the relationship in ceramics between strength and porosity?
UTS = UTSo e^-nP
P = porosity
n is an exponent factor
As porosity goes up, strength goes down. Exponentially.
Is carbon conductive? Graphene oxide?
Carbon - yes
Graphene Oxide - no
