Talk:Aluminium oxide

Organize page

Thie page is in need of some organization, even if its a short article. I put the industrial fabrication stuff on the bottom with a header. Fresheneesz 02:08, 25 November 2005 (UTC)

IS Al2O3 ionic or covalent?

Suppliers

Altough a category "Suppliers" exists in other pages, Aldrich is here linked in the section for normal links. How can I decide, if this link is advertisment, neutral or that someone has been paid for adding this link?

http://en.wiki.x.io/wiki/User_talk:213.188.227.119

Best regards

Break down

Does anyone know how to break this stuff down without using a thermic lance?

Depends how much you want to break down. If you just want to break down the surface oxide on the metal to make the metal react you can just place it in a weak salt (NaCl) solution!

Health risks

I am curious as to the health risk with aluminium oxide. We probably all have heard the stories about aluminium pans and rhubarb. I saw a mention that aluminium pans haven't been confirmed as a health risk at all in the Al. page.

Actually I hadn't heard about the Al pans and the rhubarb. According to this material safety data sheet, no adverse health effects are known due to ingestion of aluminium oxide. According to this public health guidance note, the only known adverse health effects are at the extreme dosage rate of 30mg intravenously, three times per week. There is a reference made to a "controversy" involving dementia -- are these the stories to which you refer? -- Tim Starling 11:55, Nov 3, 2003 (UTC)

Well, seems the story is common here in Sweden atleast: The acidity of rhubarbs makes the oxide give away from the pan and get eaten ("Have you noticed just how _clean_ the aluminium gets when you've made rhubarb pie?"), and everyone I've heard this from says it very toxic. I even had a chemistry teacher in high school tell us about this in a very serious tone for like ten minutes. -- sandos

Sounds like rubbish to me. There's some interesting information about this at [1] -- it just goes to show how people are prepared to ignore scientific evidence and take notice of every specious rumour, even to the point of pressing the authorities for a ban. -- Tim Starling 07:07, May 29, 2005 (UTC)

• Inhaling fine dusts of aluminium oxide would probably cause respiratory problems, and maybe even diseases similar to silicosis. Otherwise, the oxide is very unreactive and difficult to transform into soluble aluminium salts (for which there is some concern on the health effects, but controversial). Physchim62 12:13, 26 October 2005 (UTC)

When was Alumina first discovered?

When was aluminium oxide first dicovered or first made, i just need to know dates and names! pls...

Grinding wheels . . .
have been around since man first used them to convert wheat into flour . . .
and aluminum is an integral part of its history . . .
This was the best source I could find about the history of the aluminum as grinding material and probably as close as you will ever get to the truth about the originators of aluminum . . .

grinding wheels @ Answers Dot Com

Morehugh 19:16, 16 January 2007 (UTC)

Merge suggestion

No! This is a chemistry article about the chemical, corundum is a mineralogy article about the naturally occurring mineral. Vsmith 15:32, 8 January 2006 (UTC)

Oppose merger I agree with the above poster. Would an article about diamond or charcoal be merged with an article about carbon?--24.217.183.224 08:21, 9 January 2006 (UTC)

Oppose merge: there is (potentially) more than enough material to justify two articles; minerals and chemical compounds are usually treated seperately on WP. Physchim62 (talk) 09:14, 9 January 2006 (UTC)

Suggested Additions

Maybe I will get to this sometime but if someone else wants to distill the below to add it might be good.

- What about the various phases of alumina (alpha, gamma, etc) and what temps they form at

- What about its uses in the field of catalyst research, ceramics, biomedicine, and pottery

hi

sources:

 http://ceramic-materials.com/cermat/material/41.html
 http://ceramic-materials.com/cermat/oxide/al2o3.html
 http://www.azom.com/details.asp?ArticleID=52

I would like to see more about the Crystal Structure and bonding. Also Alumina has a very high melting point and therefore it is commonly used as a refractory material.

Thermal conductivity of pure alumina should be around 25-35 W/(m.K).

Picture

This picture of Al2O3-based plastics seems like a poor addition to the article. It doesn't show the common mineral form, and it's a poorly-taken photo to boot. Any objections to removing it? Anyone have a better example?Alvis 06:15, 2 August 2006 (UTC) (moved to bottom of page Dirk Beetstra ^{T C} 07:19, 2 August 2006 (UTC))

support remove picture, there must be better ones around. --Dirk Beetstra ^{T C} 07:19, 2 August 2006 (UTC)

Two people showing support (2 weeks), I have removed the image. Too bad no better image is available. --Dirk Beetstra ^{T C} 16:10, 16 August 2006 (UTC)

Cubic or HCP

From the article:

The most common form of crystalline alumina, α-aluminum oxide, is known as corundum and has a hexagonal close packed (HCP) lattice structure. The table on this page lists it as cubic, which is incorrect.

... if the sidbar is wrong, why isn't it corrected. This might need some attention from some wikipedians (I'm just a passer-by.) 129.241.129.67 13:15, 6 May 2007 (UTC)

Thermal Conductivity

In the Properties section I'm surprised by the statement:

Aluminium oxide is a good thermal insulator and electrical insulator.

I thought that alumina was a relative good conductor of heat for an electrical insulator. See for example http://www.accuratus.com/alumox.html (from the numbers given for the thermal conductivity appears to be very sensitive to impurities). 155.198.213.89 09:49, 26 September 2007 (UTC)

Alumina fiber is a good thermal insulator.

Thermal conductivity of pure alumina should be around 25-35 W/(m.K).

Bauxite?

It says in this article that "aluminium oxide is the main component of bauxite". However, the bauxite article says that "It consists largely of the minerals gibbsite Al(OH)3, boehmite and diaspore AlOOH, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2." No aluminium oxide there. So which is correct?--BillFlis 06:56, 27 October 2007 (UTC)

Those are just hydrated aluminum oxides. Chemists will count them as equal. If you heat them up enough, you drive off the water until they are just anhydrous oxide. Gah4 (talk) 18:30, 29 March 2022 (UTC)

Bayer Process Description

The description of the bayer process chemistry in the alumina article is inconsistent with the description in the bayer process article. In particular, the alumina article claims that both the aluminium oxides and the silicon dioxide (ie quartz ) disolve in the NaOH solution, wheras the bayer process article does not claim that the SiO2 dissolves. The latter is probably correct. I don't think common sand dissolves in caustic soda even at 175 C. Eregli bob (talk) 04:27, 15 December 2007 (UTC)

Outside the context of these industrial processes, silica does indeed dissolve in alkali. That's one of the mechanisms by which a base bath (sat. KOH/NaOH in IPA/EtOH) cleans laboratory glassware - it removes a thin film of the glass by dissolving silica to give silicates. --Rifleman 82 (talk) 13:56, 15 December 2007 (UTC)

Alundom

Is "alundom" also alumina? I see it mentioned in old texts, but cannot find a defintion of what it is. DonPMitchell (talk) 01:38, 16 July 2008 (UTC)

Oh did find it in 1930's edition of the Critical Tables. It is alumina. —Preceding unsigned comment added by DonPMitchell (talk • contribs) 01:45, 16 July 2008 (UTC)

Zero-Point of Charge

Anyone know the zero-point of charge of alumina? Need to perform SEM. —Preceding unsigned comment added by Bottiglieri1 (talk • contribs) 20:07, 30 July 2008 (UTC)

Warnings!

This product should not be used for polishing titanium products, as it will cause corrosion. —Preceding unsigned comment added by 81.130.21.26 (talk) 12:27, 1 September 2009 (UTC)

File:Corundum-3D-balls.png

MC Escher?

like this?

that model doesn't make sense, it looks like a hundred times that M. C. Escher thing :-) I can't imagine how this looks in reality. --androl (talk) 18:10, 5 October 2009 (UTC)

I've replied here. Apologies for not noticing this discussion sooner!

Ben (talk) 21:18, 10 March 2010 (UTC)

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Colour confusion

The table to the right of the article says it's white, but abrasive paper and old aluminium cookware surface 'oxide' appears very much dark grey, so i'm confused. — Preceding unsigned comment added by 79.66.215.175 (talk) 17:39, 9 August 2012 (UTC)

Most oxides are intrinsically colorless, and their powders are white because of light scattering on grains. However, their industrial forms are impure and thus colored - very little concentrations can induce colors, well below 1%. Materialscientist (talk) 23:39, 9 August 2012 (UTC)

Thermal expansion coefficient of Aluminum Oxide

Hi I guess that it will be useful to enter " Thermal expansion coefficient of Aluminum Oxide " in this article with the same units of measure in " Aluminum " article .

Thermal Expansivity, 20 - 1000 C : 8.0 um/mK (reference: http://www-ferp.ucsd.edu/LIB/PROPS/PANOS/al2o3.html)

the article name is obnoxious

I looked up alumina, not "aluminia," so why does this article use the hypercorrection "aluminium oxide" instead of plain aluminum oxide? 96.231.17.143 (talk) 18:45, 2 August 2014 (UTC)

It's not obnoxious, and it's not a hypercorrection. As explained at Aluminium > Etymology, the 2 forms of the element's name, aluminium and aluminum, are both widely used in English around the world; which one predominates depends on which country you are in. Quercus solaris (talk) 22:05, 2 August 2014 (UTC)

The only obnoxious thing here is the American ignorance (re: Aluminum). — Preceding unsigned comment added by 84.253.34.177 (talk) 14:13, 13 March 2017 (UTC)

Citation info

According to Chemical Abstracts, 608,616 reports mention alumina, of which 23347 appeared since the year 2018, of which 265 were reviews (i.e. suitable for WP:SECONDARY). Preliminary conclusion: citations to primary literature are not feasible or suitable.--Smokefoot (talk) 22:18, 9 April 2018 (UTC)

Sapphire Ring Company in USA , sapphire-education

This comment, posted by Sapphireringco was completely unrelated to the article, and appeared to be a promotion for a company. Deleted by Dinithi2 (talk) 01:58, 8 October 2018 (UTC)

does it become an electrical conductor when molten

Does it become an electrical conductor when molten ? if so, why/how ? - Rod57 (talk) 14:44, 20 October 2018 (UTC)

My guess is that alumina is insulating even above its (very high) melting point. It is difficult to find sources that give data on things that dont happen, so it would be difficult to support for my assertion with a ref. Generally however, colorless of white materials, Al2O3, LiF, NaCl, are insulators. --Smokefoot (talk) 14:56, 20 October 2018 (UTC)

Absolutely. Molten salts are broken into ions, therefore they conduct electricity. That's the whole premise of the electrolysis of molten alumina and other molten salts. Lajoswinkler (talk) 13:07, 21 January 2021 (UTC)

I suspect that molten pure aluminum oxide is an insulator, and not an ionic liquid. If you add other ions, like sodium or potassium, then it will be a conductor as, at least partially, an ionic liquid. Gah4 (talk) 18:36, 29 March 2022 (UTC)

Hardness

I came to this article looking for the hardness of aluminium oxide, as it is an abrasive. There are passing mentions, but I cannot find anything like a clear statement of its hardness. Please would someone knowledgeable add this information or clarify the subject ? Many thanks ! Darkman101 (talk) 06:15, 1 January 2019 (UTC)

Exactly what I wanted to ask. ––Nikolas Ojala (talk) 16:16, 11 January 2019 (UTC)

Boiling point

There's a boiling point listed for Al₂O₃, and it's not listed as "decomposes", but I recall this from John D. Clark's book "Ignition":

"As an example of the first, calculations were made for years on systems containing aluminum, using thermodynamic data on gaseous Al₂O₃ calculated from its assumed structure. And the results didn't agree too well with the experimental performances. And then an inconsiderate investigator proved that gaseous Al₂O₃ didn't exist. Red faces all over the place."

I've also not seen any reference to gaseous Al₂O₃ in modern literature regarding the topic (e.g. regarding the ongoing attempts to develop a working carbothermic method of refining aluminium metal, which due to the extreme temperatures involved must consider gaseous species such as aluminium vapour and Al₂O).

Should it therefore be listed as "decomposes"? Magic9mushroom (talk) 03:46, 24 August 2019 (UTC)

dielectric strength

The article does mention its use in capacitors, and otherwise as an insulator, but doesn't give its dielectric strength. That is, the volts per (length unit) that it can stand before dielectric breakdown. And specifically the hydrated form in electrolytic capacitors. Gah4 (talk) 18:39, 29 March 2022 (UTC)