Amalgamation Process / Basic Setting Reaction

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Amalgamation Process/ Basic Setting Reaction

• Low-copper alloys
• High-copper alloys
• admixed alloys
• single composition alloys

Endanus Harijanto
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BASIC COMPOSITION

• A silver-mercury matrix containing filler
  particles of silver-tin
• Filler (bricks)
• Ag3Sn called gamma
• can be in various shapes
• irregular (lathe-cut), spherical,or a
  combination
• Matrix
• Ag2Hg3 called gamma 1
• cement
• Sn8Hg called gamma 2
• voids

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Low-copper Alloys (1)

• When a powder (Ag3Sn, g) is triturated, the Ag
  and Sn in the outer portion of the particles
  dissolve into Hg (mercury).
• Hg also diffuses into the alloy particles.
• Solubility for Ag 0.035 wt, for Sn 0.6 wt

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Low-copper Alloys (2)

• When the solubility is exceeded, crystals of two
  binary metallic compounds precipitate into the
  mercury.
• Ag2Hg3 compound (g1) precipitates first.
• Sn7-8Hg compound (g2) precipitates later.

trituration
condensable, carvable
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Low-copper Alloys (3)

• As the mercury disappears, the amalgam hardens.
  Particles become covered with newly formed
  crystals, mostly g1.

trituration
condensable, carvable
harden, no longer workable
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Low-copper Alloys (4)

• A typical low-copper amalgam is a composite in
  which the unconsumed particles are embedded in g1
  and g2 phases.

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Low-copper Alloys (5)

• In summary,
• Alloy particles (b g) Hg ? g1 g2
  unconsumed alloy particles (b g)
• Physical properties
• g-phase ? strongest, g2 phase ? weakest
• Hardness g gt g1 gtgtgt g2
• g2 ? poor corrosion resistance

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High-Cu Admixed Alloys (1)

• Spherical silver-copper (Ag-Cu) eutectic alloy
  particles are added to lathe-cut low-copper
  amalgam alloy particles (Ag-Sn or g b).
• The final powder is composed of two kinds of
  particles. ? admixed
• Ag-Cu particles act as strong fillers,
  strengthening the amalgam matrix.

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High-Cu Admixed Alloys (2)

• Silver-Copper eutectic alloy
• 71.9 wt Ag, 28.1 wt Cu
• alloy, eutectic,n any combination of metals the
  melting point of which is lower than that of any
  of the individual metals of which it consists. An
  alloy in which the components are mutually
  soluble in the solid state. A eutectic alloy has
  a nonhomogeneous grain structure and is therefore
  likely to be brittle and subject to tarnishing
  and corrosion.

Temperature
Eutectic composition
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High-Cu Admixed Alloys (3)

• Ag dissolves into the Hg from the Ag-Cu alloy
  particles.
• Both Ag and Sn dissolve into Hg from the Ag-Sn
  alloy particles. (same as in low-Cu alloy)
• Sn in solution diffuses to the surface of Ag-Cu
  alloy particles and reacts with the Cu to form
  the h phase (Cu6Sn5) (therefore, the Sn7-8Hg or
  g2 is eliminated)

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High-Cu Admixed Alloys (4)

• A layer of h forms around unconsumed Ag-Cu
  particles.
• g1 phase is the matrix.
• The final structure composes of the g phase,
  Ag-Cu particles, e particles, g1 matrix, and h
  reaction layers.

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High-Cu Admixed Alloys (5)

• In summary
• Alloy particles (b g) Ag-Cu eutectic Hg ?
  g1 h unconsumed alloy of both types of
  particles
• g2 has been eliminated in this reaction, being
  replaced by h.
• The effectiveness in eliminating g2 depends on
  of copper-containing particles.
• (net copper concentration of gt 12 in alloy
  powder)

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High-Cu Single-composition Alloys (1)

• Each particle has the same chemical composition.
• Major components Ag-Cu-Sn

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High-Cu Single-composition Alloys (2)

• Phases found in each single-composition alloy
  particle are b (Ag-Sn), g (Ag3Sn), and e (Cu3Sn).
• h crystals are found as meshes of rod crystals at
  the surfaces of alloy particles (P), as well as
  dispersed in the matrix.

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High-Cu Single-composition Alloys (3)

• In summary
• Alloy particles (Ag-Sn-Cu) Hg ? g1 h
  unconsumed alloy particles
• Little or none of g2 phase can form.