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Development of, Cadmium free, Silver based Electrical Contact Materials

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Develop cadmium-free silver based internally oxidized cost ... Indium oxide. Zinc oxide. Gallium oxide. Copper oxide. Nickel Oxide. Iron Oxide. Magnesium Oxide ... – PowerPoint PPT presentation

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Title: Development of, Cadmium free, Silver based Electrical Contact Materials


1
Development of, Cadmium free, Silver based
Electrical Contact Materials
Satyanarayana Emani
emansat_at_iit.edu
Philip Nash
nashp_at_iit.edu
Engineered materials solutions
www.emsclad.com
2
Objective
  • Develop cadmium-free silver based internally
    oxidized cost effective electrical contact
    material with good performance.

3
Manufacturing Procedure
  • Melting and Casting Induction Melting in a
    graphite crucible.

  • Horizontal continuous cast.
  • Forming Cold rolling ( 60
    70 reduction).
  • Oxidation Internally
    oxidized at 900 F under 3 atm

  • pressure of Oxygen for one week.
  • Cold rolling
  • Stamping



4
Necessary properties for Electrical Contact
Materials
  • High conductivity Conduct current.

  • Prevent resistive current rise.

  • Dissipate maximum heat.
  • High melting point Resists contact welding.

  • Resists arc erosion.
  • High hardness Resists contact
    welding(sticking).

  • Resists mechanical wear.
  • Corrosion resistance No films to increase
    electrical-

  • -resistance.

5
Application
  • Medium duty appliance controls and switches
    (10 60 amps / 12 120 V a.C).
  • Ex coffee makers, Owens.
  • General modes of failure of contacts
  • 1) Welding Melting of the surface caused by
    the arc.
  • Sticking of the contact
    in the make operation.
  • 2) Erosion Stirring action of the arc.
  • Splatter caused by the
    stirring.

6
Why not pure Silver?
  • 1) Easily welded
  • 2) High erosion.
  • Due to low hardness and low melting point.
  • Reasons for alloying and oxidation
  • 1) Increase hardness - Decrease in welding and
    wear
  • 2) Increase in viscosity - Decrease in erosion
  • Why not Ag-CdO ?
  • 1) Dissociation of CdO into Cd and O2.
  • 2) Vaporization of Cadmium.
  • 3) Cadmium vapors detrimental to the
    environment.

7
Properties of Ag-CdO contacts
  • Low erosion rate.
  • Low welding tendency.
  • Maintains stable electrical resistance.
  • Easily produced by internal oxidation.
  • Good formability.

8
Mechanisms by which properties are achieved in
Ag-CdO contacts
  • Arc-quenching effect dissociation of CdO.
  • Splatter reduction effect increase in
    viscosity.
  • Anti welding effect ceramic nature of CdO.
  • Self cleaning effect vaporization of Cd.
  • Greater affinity for oxygen than silver.
  • High diffusion of oxygen in Cd than in Ag.
  • Uniform particle distribution.

9
Process parameters governing alloy development
  • Material must be developed by wrought alloy
    process( powder metallurgy is not to be used).
  • Material developed must have good ductility so as
    to permit the use of metal forming operations
    such as cold rolling (60 70 reduction) and
    stamping.
  • Material developed must not be hazardous to the
    environment
  • Material developed must be produced at a cost
    that is comparable to or less than the existing
    costs for silver cadmium oxide.
  • Material developed must have performance
    comparable to or better than Ag-CdO contacts.

10
Possible replacements
  • Silver - Tin oxide
  • Silver - Tin oxide - ternary additives

  • Indium oxide

  • Zinc oxide

  • Gallium oxide

  • Copper oxide

  • Nickel Oxide

  • Iron Oxide

  • Magnesium Oxide
  • Silver - Nickel
  • Silver - Zinc
  • Silver - Carbon
  • Silver - Tungsten carbide

11
Disadvantages of Ag-SnO2 Contacts
  • Very high diffusion of Tin in Silver.
  • Additions above 4 wt of tin cause external
    oxidation.
  • Formation of resistive layer on oxidation, on the
    surface, attributed too high thermal stability of
    the tin oxide.
  • Formation of precipitate free pure silver layer
    on the surface.
  • Poor wettability of SnO2 by molten silver.
  • Low ductility.

12
Role of ternary additives
  • Preferentially oxidize over Tin and act as
    nucleation sites for Tin oxide formation, there
    by improving internal oxidation and dispersion of
    oxides.
  • Reduce the diffusion of Tin in Silver.
  • Improve the wettability of Tin Oxide by molten
    Silver and prevent the oxide slag formation.
    (Which ever oxide wets the silver easily will
    enhance the wetting angle of Tin Oxide).
  • Improve the ductility by changing the morphology
    of the size and shape of the oxide precipitate.
  • Render the oxide particles fine and improve the
    dispersion.

13
Determination of wetting angles
part 1
  • Electroplating of metal sheet which has a higher
    melting point than silver with various alloying
    elements.
  • Electrolyte 5 HCl aqueous
    solution.
  • Anode Metal
    sheet(Ni-Fe-Mo).
  • Cathode Alloying element(Sn,
    Zn, In).
  • Oxidation of electroplated sheet
  • Furnace Muffle furnace.
  • Temperature range 500 800 C.
  • Atmosphere Air
  • Fe, Cu, Ni oxides are directly prepared by
    heating the metal sheets in the furnace in
    atmosphere air.

14
Determination of wetting angles
part 2
  • The oxidized sheet is kept in the tube furnace at
    1000 C in vacuum.
  • A small silver bead is kept on the oxide layer.
  • The furnace is closed with a Quartz window on one
    side for inside vision.
  • After the silver melts pictures of the molten
    silver are taken by using a Traveling Microscope
    with an attached camera.
  • The pictures are analyzed and the wetting angles
    are determined.

15
Determination of wetting angles

Tube furnace
Fused silica glass window
Oxide substrate
Liquid metal
Image analyzer
Traveling microscope
thermocouple
Wetting angle ?
Computer
Oxide substrate
Liquid metal
16
Work Done
  • Sn, In, Zn oxide substrates are prepared.
  • The alloys with the following composition which
    will yield 12 percent volume of oxide upon
    oxidation are prepared.
  • Ag - 4.44 Sn - 2 Cu (wt)
  • Ag - 4.20 Sn - 2 Zn (Wt)
  • Ag - 4.75 Sn - 2 In (wt)
  • Melting is done in a graphite crucible in a
    controlled Nitrogen atmosphere in a muffle
    furnace.
  • Experimental instruments necessary (Tube furnace,
    Fused silica window, Traveling microscope,
    computer aided image analyzer) to perform the
    sessile drop Experiments are set up.

17
Zn
18
In
19
Sn
20
SnO2
21
ZnO
22
Work in progress
  • Preparation of Fe, Ni, Cu oxide substrates.
  • Microstructure analasys of the prepared alloys.
  • Preparation of Ag-Sn-Fe, Ag-Sn-Ni, Ag-Sn-Mg,
    Ag-Sn-Ga alloys.
  • Forming (cold rolling) of the alloys prepared.
  • Internal oxidation of the alloys.
  • Determination of the wetting angles for the
    oxides prepared.

23
Future plan of work
  • Determine the wetting angles of different metal
    oxides by Silver melt by using sessile drop
    technique. And understand the mechanisms by which
    the wettability is improved.
  • Metallurgical analysis (Metallography, S.E.M,
    T.E.M,X-Ray) to characterize diffusion and
    oxidation properties.
  • Understand the mechanism by which Tin imparts
    brittleness to Silver and find processes by which
    it can be reduced.
  • Find processes by which the diffusion of Tin in
    Silver is reduced.
  • Determine the erosion characteristics and weld
    force of the alloys developed by using endurance
    tests.

24
THANK YOU
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