Appeal No. 96-1087
Application 08/068,700
a center electrode supported by said insulator;
a housing secured to an outer periphery of said insulator;
an earth electrode arranged on said housing and facing to said
center electrode; and
a narrowed portion disposed on a tip of an electrode material of at
least one of said center electrode and said earth electrode, said
narrowed portion including a projection formed by extending said
electrode material and a discharge layer firmly connected to a top
end of said projection;
wherein said discharge layer is provided with a noble metal chip
arranged on a discharging side and a relaxing layer arranged on
another side of said projection;
said electrode material being made of nickel-base heat resisting
alloy, said noble metal chip being made of a Pt-Ir alloy essentially
consisting, by weight, of 90-100% Pt and 0-10% Ir, or made of an
alloy obtained by dispersing 0.01-2% zirconia or yttria in said Pt-Ir
alloy of 98 to 99.99%;
said relaxing layer being made of a Pt-Ni alloy essentially consisting,
by weight, of 70-90% Pt and 10-30% Ni; and
a diameter D of said narrowed portion being in a range of 0.6-1.2
mm, and a length L of said narrowed portion provided with said
discharge layer being in a range of 0.8-1.5 mm, a thickness S of said
relaxing layer being not less than 0.05 mm, and the relationship
between a thickness T of said discharge layer and said length L of
said narrowed portion being 0.2L # T# L.
The prior art references of record relied upon by the examiner in rejecting the
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