ot: wikipedia at its finest. not.

because if you had worked in a technical field, you'd understand why you need to be accurate and specific on this stuff. if your seat belt manufacturer specified "um, some kind of stringy stuff", no tensile resistance, no u.v. resistance, no moisture/oil resistance, etc, your response indicates that it wouldn't bother you.

it was rhetorical. the /evidence/ is that you didn't do that.

yeah, but opinion is opinion, it's not fact. the guys bleating about spark plug ceramics are expressing their opinions as if they were fact, even though the real facts contradict them. as they'd know if they bothered to read [and could comprehend] any of the cites they insist on.

That is right . Porcelain has been used as a generic name for the insulator on spark plugs from the earliest days of the spark ignition engine.

not when the clowns on wikipedia are claiming the insulator is made of two-parts, one being alumina, the other your grandmother's kitchen crockery. if they're trying to be technically specific, they should be /accurately/ technically specific.

oh, and historically, early plug uppers /were/ porcelain. these really were two piece, and the hot part was mica. that kind of construction hasn't been used since the 1930's.

I looked at what it says. It says the insulator has two parts. The external part is glazed and the inside part is not. I think the glaze would melt if it was used on the inside.

then it's been changed yet again. modern [post 1930's] insulators are single piece. the upper is glazed for flashover resistance. no point doing that inside. even inside, plugs don't get hot enough to melt glaze unless there's something wrong like severe detonation, or pre-ignition. [this is one of the reasons you use alumina, not porcelain - not only is much more heat resistant - refractory - it's a much better thermal conductor and this helps keep that kind of thing from happening, along with electrodes being more stable, while still being able to work at temperatures high enough to allow self-cleaning to occur. and while being a much more electrically stable material that's also cheap to manufacture.]

That makes a lot of sense. Fussing about different ceramics does *nothing* to enhance understanding of how spark plugs work. You are pole vaulting over mouse turds when you split hairs that thin. Ben

if you're looking at a spark plug as a single unit rather than trying to understand how it works, then you can gloss over some of the details. but if you're trying to explain how it works and why, which is what this wikipedia page purports to do, then it should at least attempt to be accurate. and it's not like the accurate information isn't easily available!

to put it another way, seeing the "hivemind wikiborg" try to distort reality and ignore easily available authoritative sources like this is [i imagine] like you listening to someone tell you the 911 turbo is fwd, front engine, and has a 1300cc 4-banger in it. if you've never seen that vehicle before, you don't know much about automotive principles, and you're 100m away from it, all you can say for sure is that it's a car with 4 wheels, front wheel steering, two seats, and it doesn't appear to have a place to hitch the donkey. but you /do/ know cars and you /do/ know this person's description is hopelessly inaccurate. the only question then is whether or not you're going to actually say something when this person tries to repeat the same misinformation to someone else...

For some reason the OP feels it vastly important that people know the chemical composition of the ceramic material. The spark plug is made of several components yet evidently, what they're made of doesn't matter.

It is called porcelain. Some of the better quality dinner plates are also made with aluminum oxide porcelain.

only by people that don't know what they're talking about. nobody in the industry calls it that, and that word shouldn't be used if you have any intention of trying to convey technical accuracy.

1. if you're talking ceramics, it's called "alumina". just like silica or titania.
2. yes, made /with/ alumina, but they're not made /of/ alumina. the firing temperature for alumina is too high to get vitrification. that's why spark plug insulators are "sintered", a solid state diffusion process.

so can we assume that you'd see no problems trying to use a chocolate tea pot? or does the material matter in that application? how about rubber bearing balls - would they be ok to use in a car's wheel bearing? how about a wooden muffler?

that's not an accurate representation of my position. the materials of those other components matter, but those parts are [more or less] accurately described, so there's nothing to comment on.

My point is that the metal case is described as being made of "metal" and the seals are made of "metal and glass." Does the material matter in that application?

You are the poster child for People who don't know what they are talking about The auto parts sales industry typically refers to the insulator on spark plug as porcelain.

You are trying to create a distinction without difference. the average clay flower pot is "sintered"

All that means for a ceramic is it is fired at a temperature below the melting point. If it was fired to the melting point you would have a puddle of melted clay instead of a pot. The glaze on the surface of the glazed part of spark plug porcelain is fired above the melting point of the glaze. In other words, the glaze has lower melting temp.

The distinction between porcelain and ordinary pottery is not sintering. The difference has to do with its material properties and appearance

yes, you definitely have a point. but i think "general principle" is the objective here. you could conceivably specify a chocolate composition, a tea temperature, and a usage timeframe that could make it feasible to use a chocolate tea pot. but you can't take that specific application and say that all chocolate teapots are useful as a general principle.

general principle is that alumina has the necessary thermal, electrical and economic qualifications for the job. as do nickel alloys for electrodes. practically any bolt-grade steel will do for the jacket if plated for corrosion resistance, but there are a bunch of different seal materials that could work, so "general principle" defined as "metal glass mix" i think is about as far as it goes. just like you're not getting into detail about the particle sizes and distribution, or even morphology with the pre-sinter aluminum powder.

fortunately, auto parts sales people don't /make/ what they sell, so we can all relax safe in the knowledge that our stuff will work despite their ignorance.

no, it's "fired". "fired" means some degree of vitrification - i.e. sub-melting of some phases that fuse other particles together sufficiently for them not to fall apart again. sintering is a solid state process that doesn't involve sub-phases or their sub-melting.

that is true, the glaze does indeed melt, but melting is not sintering!

indeed. but not for the reasons you're trying to imply! porcelain is a type of pottery. technical ceramics are not pottery. spark plug insulators are a technical ceramic.

"appearance" is so irrelevant, that statement beggars belief. an insulator being white and shiny tells you NOTHING about its composition, and DEFINITELY not that it's ANY relative of a vitrified porcelain. unbelievably stupid thing to say.

Firing means putting in a kiln and heating. Firing is part of the process for making sparkplug insulators.

An average flower pot is also sintered.

Nobody said it tells the composition. That is your fetish. Names may be descriptive, but that doesn't mean they are required to tell the composition.

I didn't call it "vitrified porcelain". Porcelains can be made by sintering

no. this post started with me complaining about wikipedia inaccuracy, and here we are full circle back to the same thing because you've obviously read wikipedia connecting sintering and pottery, but it's incorrect. pottery vitrification involves a liquidus phase. sintering does not. "solid state diffusion" - look it up.

you keep on reading the ink on urinals dude - it's just the kind of definitive education you need to help you design the next space shuttle.