You didn't want the free one available here? Oh well.

 

Oh, I also found out that iridium has very high resistance to corrosion, even at very high temperatures. A truly fascinating element, more often than not having arrived from space after the planet formed. Icredibly rare at only 3T mined a year, it is the second densest metal, being pipped only marginally by Osmium. So corrosion resistance is the reason.

 

Spark plug electrodes of any type don't suffer from corrosion.

 

A little while back I was researching which NGK's would be best or my '05 STR, and came up with BKR5EIX-11 (Iridium) as well as IFR5N10 (Iridium laser). The IFR's are more expensive and seem to last forever, while the BKR's appear to be good for 80-100k miles.

Got the BKR's and have been very happy with them. Is the only difference just the cost and expected life-span, and nothing to do with performance or anything else?

 

I suppose there might be some attempted corrosion but I expect he meant erosion. The sparking gradually erodes spark plugs. Platinum resists quite well but I believe iridium is even more resistant.

 

Umm, here's a quote from an NGK tech info FAQ posting:

Abnormal Erosion
Abnormal electrode erosion is caused by the effects of corrosion, oxidation and reaction with lead - all resulting in abnormal gap growth.

 

There's no lead in today's fuels. Hasn't been in 20 (?) years.

 

Quite. Are NGK so backward?

 

I became curious and tracked down the quote phrase. Taken out of context (as above) it does make them seem backwards.

However:

NGK Spark Plugs USA


Ah- that makes sense. The abnormal erosion they discuss would be a result of a malfunctioning engine and/or use of leaded fuel. Nothing to do with the subject at hand.

 

You made that blanket statement, not me. As I read NGK's post, lead was just one cause of erosion, oxidation and corrosion are other causes.

I would suggest that it has everything to do with the subject at hand.

 

OK Robin, in the interests of peace, love and avoiding yet another pedantic hair splitting argument, you win. Speaking of hare, here's a bunny:

The answer to the OP's original question as why modern plugs are made using iridium is obviously to address ABNORMAL wear and nothing to do with extended durability as previously stated.

I'll revise my blanket statement to:

Spark plug electrodes of any type don't suffer from corrosion in engines that are not defective or misfueled in some way resulting in abnormal erosion.

Happy?

 

all base metals corrode in the presence of oxygen and there is certainly oxygen in the fuel air mixture. oxidation is faster at higher temperatures and the cylinder contents certainly get hot

 

Now we're getting somewhere.