Manufacture of Alloy Powder

1
Manufacture of Alloy Powder

• Lathe-cut (Irregular) powder
• Atomized (Spherical) powder
• Particle size v.s. Properties

Endanus Harijanto
2
Lathe-cut (Irregular) Powder

• Metal ingredients ?heated ?poured into a mold ?
  ingot (Ag3Sn (g) some b, e, h)
• Ingot ? homogenizing anneal
• An annealed ingot of alloy is place in a machine
  and is fed into a cutting tool.
• 60-120 µm in length, 10-70 µm in width

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Atomized (Spherical) Powder

• Made by melting the desired elements together
• The liquid metal is atomized into fine spherical
  droplets of metal by being sprayed under high
  pressure of an inert gas.
• ? Spherical powders 2- 43 µm
• Also have heat treatment and are
• usually washed with acid.

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Homogenizing Anneal

• The ingot is placed in an oven and heated at a
  temperature below the solidus (at 400C) for
  sufficient time (6-8 hours) to allow diffusion of
  the atoms to occur and the phases to reach
  equilibrium.

5
Particle Treatments

• Acid-washed amalgam powders
• tend to be more reactive.
• Stress-relief process after particle cutting
• annealing cycle at 100C for several hours
• aging process

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Lathe-cut v.s. Atomized alloys

• Lathe-cut or admixed powders resist condensation
  better than spherical powders.
• Spherical alloys require less mercury than
  typical lathe-cut alloys because of the smaller
  surface area per volume.
• Amalgams with a low mercury content generally
  have better properties.

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Particle Size

• A powder containing tiny particles requires a
  greater amount of mercury to form an acceptable
  amalgam.
• A small-to-average particle size ? a more rapid
  hardening and a greater early strength
• Particle size distribution can affect the
  character of the finished surface.
• The larger particles may be pulled out during
  carving ? a rough surface ? corrosion

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Amalgam Alloy Composition

• ANSI/ADA Spec. 1 (ISO 1559) requires that
  amalgam alloys be predominantly silver (Ag) and
  tin (Sn).
• containing Zn gt 0.01 ? Zinc Containing
• containing Zn lt 0.01 ? nonzinc

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Classification

• Low-copper (Conventional) amalgam alloy
• (at least 65 wt Ag, 29 wt Sn, lt 6 wt Cu)
• lathe-cut (irregular) powder or spherical
  particles or mixed
• Ag-Sn
• High-copper amalgam alloy
• (6-60 wt Cu)
• (1) Admixed (Ag-Sn Ag-Cu)
• A mixture of irregular and spherical particles of
  different or same composition
• (2) Unicomposition or Single composition
  (Ag-Sn-Cu)
• All spherical particles

? 90 of the dental amalgams currently placed