Introduction to Material Categories Flashcards
_____________ share valence electrons between all the atoms in the solid.
Metals!
____________ are a mixture of two metals in a single phase.
Metal Alloys
Metallic structures are almost exclusively ___________ in nature
Crystalline
The crystals in metals are called ___________.
The edges of these _____ can be seen clearly by treating them with _______ which remove electrons at the edges which are of _______ energy.
The crystals in metals are called _GRAINS_.
The edges of these _GRAINS_ can be seen clearly by treating them with _ACID_ which remove electrons at the edges which are of __HIGHER__ energy.
grain boundaries are shown as _________ between the individual grains because atoms here are at a ______ energy.
grain boundaries are shown as Discontinuities between the individual grains because atoms here are at a Higher energy.
Metals are prone to what two types of corrosion.
Chemical and Electrochemical
What is Chemical Corrosion?
Chemical corrosion occurs by direct chemical reation on the surface of a metal with OXYGEN and other chemicals.
remember: stainless steels are resistant to corrosion because the chromium in them reacts with oxygen at the surface producing a film which prevents the metal underneath from corroding.
What is Electrochemical Corrosion?
occurs when two metals act as electrods of differing structure which being connected by a circuit and an electrolyte. One acts as the Cathode the other as the Anode. The anode is broken down as electrons flow from anode to cathode.
What is a common electrochemical reaction that takes place in the mouth?
Amalgam and Gold restorations interact with each other through saliva (the electrolyte) forming a circuit, which can result in a current being sensed by the pulp (ie: it hurts)
What are Ceramics made of?
Ceramics are substances consisting of metallic and non-metallic elements ionically or covalently bonded to one another.
Ceramics are very ________ to heat
RESISTANT
The three most common ceramics in dentistry are:
1
2
3
SiO2
Al2O2
K2O
What are 3 ceramics that are commonly made from corrosion of metals?
Fe2O3
SnO
Ag2S (from corrosion of amalgams)
When Active metals corrode they form _______products
Active metals corrode to form SOLID CERAMIC products
ie: iron with oxygen froms rust
When Passive metals corrode they ____________
Form Thin Films which prevent further corrosion
ie: In stainless steel chromium reacts with oxygen to form thin layer to protect underlying metal.
Polymers are _____ molecules, made primarily of _______ elements that are chemically bonded via _______ bonds.
Polymers are LONG molecules, made primarily of nonmetallic elements that are chemically bonded via Covalent bonds.
