Sciencemadness Discussion Board

Chromium to Chromium (III) oxide

Peter_leyw - 21-1-2019 at 05:23




Hi,


First post in this forum, old timer (i still remember my chemistry basics lessons from 40+ years ago but i have no knowledge on this)

what would be the process to get Cr2O3 from Cr?

I'm looking for pieces (or chunks) of Cr2O3.

I've seen people using (NH4)2Cr2O7 to obtain Cr2O3 (in powder)


Thanks and glad to have found this forum.

[Edited on 21-1-2019 by Peter_leyw]

oberkarteufel - 22-1-2019 at 02:26

Cr2O3 starting from metallic Cr?
I think the best route would be reacting it first with HCl to transform chromium into CrCl3, then adding sodium carbonate (or hydroxide) solution to precipitate Cr(OH)3. Then filtration and rinsing with distilled water. The last step is heating chromium (III) hydroxide, et voilà!

This way you will also get Cr2O3 powder however.

[Edited on 22-1-2019 by oberkarteufel]

Peter_leyw - 22-1-2019 at 09:09



Thank you!

i appreciate the informations even if the result is still powdered Cr2O3

Is there any way to get solid pieces of Cr2O3? (compressing the powder is not an option)

I saw someone mentioning growing crystals (no details)

Any informations on this process?

[Edited on 22-1-2019 by Peter_leyw]

[Edited on 22-1-2019 by Peter_leyw]

Ubya - 22-1-2019 at 13:12

water chemistry will give you just powderer oxide, you can't make an oxide crystal
so you need to press the powder but it's not an option for you, so just work with the powder

Peter_leyw - 22-1-2019 at 15:23



The issue is that the painting and other fine arts ressources book i found (from the 1800's) mention that:

"If you can procure oxide (of chrome) do so in solid form, and not in powder (as pigment) and it cannot be compacted.

Only in solid form (so not wax either) but this form is very hard to find"

Could they have meant crystals?

MrHomeScientist - 30-1-2019 at 06:29

I've never heard of bulk solid chromium oxide as a chemical reagent. What use would a solid chunk have that the powder couldn't do?

Apparently there's a mineral form of Cr2O3, Eskolaite. That'd be about the closest you'd get.

fusso - 30-1-2019 at 06:45

Quote: Originally posted by MrHomeScientist  
I've never heard of bulk solid chromium oxide as a chemical reagent. What use would a solid chunk have that the powder couldn't do?
Polishing?

oberkarteufel - 30-1-2019 at 08:16

Quote: Originally posted by fusso  
Polishing?


I can't imagine anyone using solid/fused chunk of Cr2O3 for polishing. Actually, it's the powder that is mixed with molten wax/fats to get the "green polishing paste". The same way, Fe2O3 is used to make "red polishing paste".

Peter_leyw - 1-2-2019 at 03:49

Quote: Originally posted by MrHomeScientist  
I've never heard of bulk solid chromium oxide as a chemical reagent. What use would a solid chunk have that the powder couldn't do?

Apparently there's a mineral form of Cr2O3, Eskolaite. That'd be about the closest you'd get.



They mention and recommend the solid form (as pigment) on the canvas or specific surfaces for details (this is what the book mention)

Eskolaite is very expensive (and hard to find)

This is probably the source the book mention.

I found the "american elements" site list Chromium (III) oxide as available in powder and "crystals".

The "solid" form could mean that it was melted?



[Edited on 1-2-2019 by Peter_leyw]

[Edited on 1-2-2019 by Peter_leyw]