51
Is the tip in the
made of pure iridium?
We use
a new iridium alloy
developed at DENSO.
Q
10
A
Melting point(
°
C)
Element
Oxidation resistance
3410
2610
2454
Tungsten (W)
Molybdenum (Mo)
Iridium (Ir)
1769
Platinum (Pt)
1453
Nickel (Nl)
1063
Gold (Au)
960
Silver (Ag)
Bad
Bad
Good
Better
Good
Better
Better
Iridium is characterized by a higher melting point than either nickel or platinum.
Therefore, it wears very well when subject to electrical discharge. However, at
high temperatures it oxidizes a little too much and so we are unable to use
pure iridium for spark plug electrodes.
DENSO studied many additives with a view to improving the corrosion
resistance of iridium and has now developed a new iridium alloy (the alloy of
iridium and rhodium) highly suitable for use in spark plug electrodes. This new
product is covered by the following DENSO patents; JP2877035, GB2302367;
and other patents pending in USA, Germany, Canada, Italy and South Korea.
The following photographs compare the durability of the new iridium alloy and
pure iridium when used in an engine under the same conditions.
New DENSO iridium alloy
Pure iridium
Test engine: 90 cc 4-cycle 1-cylinder Test conditions:Full
X
9000rpm
X
30h
Part of the pure iridium material was shed and corroded. The new DENSO iridium
alloy showed no corrosion on the electrode and mainfained good condition.
(The above is analyzed in DENSO.)