Direct Filling Gold

sheets Also called as fibrous gold.
Standard no. 4 gold foil is supplied in 100 x 100 mm ( 4x 4 inch ) sheets that weight 4 grains( 0.259 grams) and 0.51 micro meter in thickness.
3 foil--- 3 grains in weight ( 0.194 grams) and 0.38 micrometer in thickness.

Produced by rolling cut segments of no. 4 foils into a desired width –
- 2 mm
- 8 mm
- 4 mm

Two sheets of no. 4 pure gold foil and a layer of pure platinum foil sandwiched between them can be hammered until the thickness of no. 4 foil is achieved.

Microcystalline gold powder formed electrolytic precipitation– also called crystalline, mat or sponge.
Mat gold is electrolytically precipitated crystalline form that is sandwiched between sheets of gold foil and formed into strips.
Alloyed electrolyte precipitate
- Granular gold alloyed with 0.1% calcium.
- Calcium increases the strength.

Fine powder is formed by chemical precipitation or atomizing the metal. Particle size ---maximum 74 micrometer and average particle size is 15 micrometer.
Foil forms an effective container for the powdered metal and forms pellets of 1- 2 mm in diameter
Each pellet contains ten times more more metal by volume than are comparable sized pellet of gold foil.

For cold – welding gold should have a clean surface free from impurities. Gold attract gases eg. Oxygen, to its surface and any adsorbed gas film prevents cohesion of individual increments of gold, during their compaction.
Cohesive gold --- manufacturer therefore supplies the gold essentially free of surface contaminants, and thus inherently cohesive.
Non – cohesive gold---- Manufacturer can subject the foil to a volatile agent such as ammonia, which is adsorbed on surface of gold. This volatile substance acts as a protective film to prevent adsorption of non volatile materials and premature cohesion of pellets in their container.

Pure gold is soft, malleable and ductile and does not oxidize under the normal atmospheric conditions.
It has rich yellow colour and strong metallic lusture.
Brinnel hardness number of gold is 25. this makes it very soft. During compaction the hardness increases.
Gold is the noblest of all the metals. It does not undergo tarnish and corrosion in the oral environment.
ability to be cold welded at room temperature.
Gold exhibits excellent marginal integrity and biocompatibility with the oral tissues.
Coefficient of thermal expansion of gold is 14.4 8* 10-6 which is close to that of tooth structure 11.4* 106 .

1. Powdered gold is_______?

A. Made by a combination of chemical precipitation and atomization

B. Made by electrolytic precipitation

C. Made by beating pure gold at high temperatures

D. Made by milling pure gold ingots