Appeal No. 2003-2136 Page 2
Application No. 09/562,952
chip and the metal of the electrode are thereby melted into a molten bond at the
junction.
According to the appellants, because the ratio of the noble metal to the
electrode's metal in the molten bond depends on the energy of the laser beam, the
durability of a spark plug, in turn, depends on the energy of the laser beam. If the chip
is made of iridium ("Ir"), and the electrode is made of nickel ("Ni"), for example, the ratio
of Ir to Ni in the molten bond will be small because the melting point of Ir, viz., 2450°C,
is much higher than that of Ni, viz., 1450°C. (Id. at 2.) Such a ratio, they explain,
cannot alleviate thermal stress at the junction of the chip and the electrode. If the
laser's energy is increased to melt more Ir in a higher ratio, because the melting point of
Ir, infra, and the boiling point of Ni, viz., 2700°C, are not far apart, (id. at 2-3), they add,
the Ni evaporates and makes voids in the molten bond and a large depression is formed
on the periphery of the bond.
In contrast, the appellants form a chip made from an Ir-alloy; the alloy contains a
noble metal such as rhodium ("Rh") that features a lower melting point than Ir. A laser
beam is radiated on a junction of the chip and a Ni electrode to form a molten bond.
The Rh contained in the noble metal chip is melted into the molten bond, forming an
alloy containing Ni, Rh, and Ir. (Id. at 3.) According to the appellants, the molten bond
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