|WikiProject Glass||(Rated Start-class, Top-importance)|
Info from the de:-Wikipedia. I'm not an expert on glass-ceramic and I am confused a bit: if glass-ceramic has such a low heat conduction coefficient, why does the plate get hot at all? Is it the infrared radiation heating the pot, which then heats the surface? How does this thing work? Lupo 12:15, 28 Jun 2004 (UTC)
heat conduction coefficient means how much heat the material transmits by conduction; metals tend to have high coefficients (100's of W/m/K) while glass and ceramics have low ones (SiO2 ceramic has 1.04 W/m/K at 200 deg C). Low doesn't mean zero, so the material does transmit slightly, but I would guess (no expert) a lot of the heating occurs by absorption of the infra red radiation by the ceramic just above the heating elements. This is because there must be some infra red absorption (about 15% from the CERAN article).
The German CERAN article says CERAN Platten haben eine hohe Hitzedurchlässigkeit und praktisch keine Wärmeausdehnung. which says that they have a high heat transmission ability (not the same as conductance) and practically no heat expansion. -Wikibob | Talk 21:48, 2004 Oct 5 (UTC)
- So you're saying that the plate gets hot because of this 15-20% absorbtion of infrared radiation emitted by the burner? Plus maybe by the hot pot above? And the pot itself is heated primarily by the other 80-85% going through the glass-ceramic? Hmmm... the plates get really hot, even if there is no pot on them. (In the first type, using a burner, not in an induction stove.) Time to e-mail Schott? Lupo 07:54, 6 Oct 2004 (UTC)
Why does the glass plate heat up?
The original question was: "If glass-ceramic has such a low heat conduction coefficient, why does the plate get hot at all?"
- The plate heats up because the conduction coefficient is not zero, as stated above. If you put a hot object on top of the plate, the plate would eventually heat up. A low conduction coefficient just means that it would take a long time for it to heat up. This is a good thing - you want the pot to heat up, not the stove itself. There's no point to heat up the stove surface because it would just be a waste of energy.
So, this leads us to the next question: "Is it the infrared radiation heating the pot, which then heats the surface?"
- Yes, this is the primary reason why the glass plate heats up. It also heats up because of the infared radiation. However, this contribution is constructed so that it is less. The stove is manufactured so that most of the infared radiation heats the pot, and not the stove surface!
- All right. Then see my follow-up remark: the plate also gets really hot (didn't measure it, but I sure don't want to touch it!) when there's no pot on the plate. That must then come from these 15-20% of infrared radiation that are absorbed, mustn't it? Or is it just an illusion? I mean, do I only think the plate got hot because when I put my hand above the plate and feel it's hot, my hand gets hit by the other 80-85% that do get through? Hmmm... I think I'll have to buy some kind of thermometer and try to measure the surface temperature of the stove right after switching a plate off, without ever having placed a pot on it. Lupo 08:05, 11 Jun 2005 (UTC)
Finally, the last question: "How does this thing work?"
- Let's look a microwave oven first. If you placed a metal object in a microwave oven, and started the machine, the metal object would heat up - in fact, it would heat up quite a bit! The technology for stoves with induction coils is an application of this phenomena. Think of the stove as a sort of "open microwave". Hope this helps! --HappyCamper 02:19, 11 Jun 2005 (UTC)
- Phenomena is plural!
- Sorry, I don't get that analogy at all. The physics involved between a microwave oven and an induction stove are quite different, I thought. My question on "how does this thing work" was more a short-hand of saying "how does the heat get to the food, and wat heats up the plate". I wasn't asking about an induction stove; I can understand more or less how these work. Thanks for the answers! Lupo 08:05, 11 Jun 2005 (UTC)
Induction ranges & corningware: clearing up some confusion
On to induction ranges: these actually work by hysteresis losses (the current article is wrong about this, btw), also a source of inefficiency in transformer cores. What ultimately heats the food is the energy dissipated when a ferromagnetic pot (austenitic stainless steel, copper, aluminum, and glass pans don't work on iduction ranges unless they're built with a ferritic steel insert) is magnetized in one direction, then the other, 50 to 60 times a second (usually 50 Hz, since they're more popular in Europe). If the coil heats up without any pot on it, chances are very good that your cooktop is of the type with halogen lamps or ohmic heating elements underneath, that work like an Easy-Bake Oven or a normal electric range, respectively. If it glows white, it's halogen; red (only on high heat), and it's a normal heating element that heats the ceramic by conduction. Keep in mind how much thinner a plate is top-to-bottom as opposed to side-to-side.--Joel 23:14, 17 Jun 2005 (UTC)
Hi! Sorry, I am new at wikipedia and I just came across the glass-ceramic (gc) article, which is, I am afraid, in some parts quite wrong. However, I am not familiar enough with wiki (I will try to become :) to change it. But some general remarks: ß-spodumen is NOT the major phase in gc. (I suppose you are speaking of the LAS-System, which is only ONE gc system) Exactly speaking there is even no so called ß-spodumen but keatite solid solution. And this keatite s.s. is only existing in gc's which are translucent or opaque, which is the minor amount of gc's used today. For the LAS-System (Li-Al-Si) which is the most used one today, ß-Eucryptite is the major phase. This gc's are transparent and used in cooktops and telescopes, and projectors. If this gc is heated up above ca. 900°C for some time, the ß-Eucryptite changes to ß-keatite (or wrongly saying ß-spodumene). But in general, this phase transformation is NOT wanted (just in some special cases)
BUT also: There are many other Gc's systems which are e.g. MAS (Mg-Al-Si-System), Phlogopit, ZAs (Zn-...), Lithium-Disilikate, ...
There are some other points which are not really good, but I am afraid to change them. Any suggestions?
Best regards Lagodefroy (talk) 14:21, 24 June 2009 (UTC)
Changes to page
ok, nobody complained about my remarks about the errors, so now I wil try to correct the page step by step. As I said, I am new with wiki and unfortunetly I do not have so much time as I want to. Please lets discuss if there is anything you do not agree with!
I made a lot of changes and rewrote the article carefully. However, I am no native English speaker, so please advice here. In addition, the part about the stoves does not fit in my opinion, however I did not delete it. Please advice again.
I have reviewed the article again, and deleted the passage about "vaseline glass" as there is no evidence in the linked article that vaseline glass is a glass-ceramic (which I also doubt strongly). Lagodefroy (talk) 12:03, 27 January 2010 (UTC)
"so called nucleation agents"
Why "so called nucleation agents"? The wording seems to imply that the additives are not nucleation agents, although they are so called. Because if they were nucleation agents, they'd simply be called "nucleation agents", not "so-called nucleation agents". -- Wegesrand (talk) 14:32, 6 January 2011 (UTC)
yep, you're right. It should mean more like "additions which are called nucleation agents"... but I see that it is misleading. I deleted "so called". Lagodefroy (talk) 10:27, 28 January 2011 (UTC)lagodefroy