Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
21 Cards in this Set
- Front
- Back
|
How much tin silver in amalgam?
|
65%
|
|
|
How much tin in amalgam?
|
29%
|
|
|
How much copper in amalgam?
|
6%
|
|
|
How much zinc in amalgam?
|
2%
|
|
|
Setting reaction of amalgam?
|
Hg + γ -> γ + γ1 + γ2 + Hg
|
|
|
Why is there an expansion of amalgam?
|
Crystal growth of γ1 and γ2
|
|
|
Structure of amalgam?
|
Residual γ cores with a matrix of γ1, γ2 and excess Hg
|
|
|
Which phase of amalgam is to blame for marginal breakdown and creep?
|
γ2
|
|
|
Which phase of amalgam is most electrochemically active and therefore most to blame for corrosion?
|
γ2
|
|
|
What is changed in amalgams composition to reduce the amount of γ2?
|
Eutectic composition of Ag-Cu added to original alloy
|
|
|
What is the setting reaction of non γ2 amalgam?
|
Before
Hg + γ -> γ + γ1 + γ2 + Hg But after this the added Ag- Cu reacts with γ2 to give γ2 + AgCu -> γ1 + η So overall γ + Hg + Cu -> γ + γ1 + η + Hg |
|
|
What affect does Pd have on amalgam
|
Improves corrosion and creep
|
|
|
What affect does the copper have on amalgam?
|
Increases hardness and strength
|
|
|
Why is zinc used in production of amalgam?
Why is it best to try and not get any in the powder? Which technique of producing amalgam particles uses no zinc? |
A scavenger, at high temps in production other metals would oxidise, but if zinc is added this oxidises instead to produce a slag
If it is left in the powder then it causes delayed expansion of amalgam due to reacting with water and creating hydrogen Spherical (firing molten metals into an inert gas column) to form spheres doesnt need zinc |
|
|
2 ways of producing particles of amalgam
|
Lathe cut - make an ingot and cut up with a lathe to make either fine or coarse flakes
Spherical - fire molten metals into an inert gas column, forms spheres |
|
|
Heat Txs for lathe cut amalgam?
|
Ingot homogenised at 420 degrees to get rid of coring
Then once it's all been cut up it is heated to 100 degrees to relieve stresses caused by lathe cutting |
|
|
Heat Txs for spherical amalgam?
|
Homogenised to get rid of coring
|
|
|
What is fluid going down the side of an amalgam filling called?
|
percolation
|
|
|
Which type of amalgam adapts to pins best and can be condensed under lowest force?
|
Spherical
|
|
|
What is the purpose of carving?
|
Shape the restoration and remove mercury rich layer
|
|
|
What is the Bielby layer?
|
Amorphous surface layer produced by polishing
|
