Sciencemadness Discussion Board

Does CaO evaporate at 1000 °C?

vmelkon - 13-3-2016 at 17:15

I have some CaCO3.
I am heating it to perhaps 1000 °C with a air-propane torch since I want to convert it to CaO.

It glow bright white. Candoluminescent effect.
It looks also as if it is evaporating. When I take away the flame, I see some white smoke coming off it. Does this make sense?

The metal surface on which the CaCO3 was placed, is getting covered by a white film that I can scratch off with a spatula. The metal surface is a hard disk platter.

blogfast25 - 13-3-2016 at 18:04

Quote: Originally posted by vmelkon  
I have some CaCO3.
I am heating it to perhaps 1000 °C with a air-propane torch since I want to convert it to CaO.

It glow bright white. Candoluminescent effect.
It looks also as if it is evaporating. When I take away the flame, I see some white smoke coming off it. Does this make sense?

The metal surface on which the CaCO3 was placed, is getting covered by a white film that I can scratch off with a spatula. The metal surface is a hard disk platter.


With a BP of 2850 C, you're so far away of it that the vapour pressure of CaO is still negligible.

Other possibilities are:

* mechanical entrainment of some CaCO3 by escaping CO2
* some lower-boiling contaminant in the CaCO3 evaporating

macckone - 14-3-2016 at 16:05

Using a blow torch directly could evaporate CaO. But not much. That is how a flame test works. Most likely a contaminant. Either from the container or the calcium carbonate. Zinc oxide is used as a whitener in various forms of 'chalk'. You could also have calcium sulfate in the mix. It will produce sulfur dioxide and trioxide.

blogfast25 - 14-3-2016 at 18:12

Quote: Originally posted by macckone  
Using a blow torch directly could evaporate CaO. But not much. That is how a flame test works.


CaO's about the worst material for flame tests though. Usually chlorides give much better results, due to higher volatility. Calcium's lines are weak at best anyway.

[Edited on 15-3-2016 by blogfast25]

macckone - 14-3-2016 at 21:36

Agree with blogfast25. Calcium is a poor candidate for a flame test. I am leaning towards sulfate in the OPs mixture due to the fuming.

vmelkon - 17-3-2016 at 10:19

Thanks guys.
The source was from calcium hyprochlorite from Walmart. I think the brand is HTC and it is for "pool shocking".
I used it to make chloroform. The byproducts are Ca(OH)2 and calcium acetate.
I filtered the byproducts to get Ca(OH)2 and I washed with water.
I used the Ca(OH)2 to heat with urea to make ammonia.
The leftover should contain a lot of CaCO3.

So I was wondering if some urea byproducts were left with the CaCO3.

deltaH - 18-3-2016 at 11:42

Calcium hydroxide reacts with urea to make calcium cyanurate and ammonia. The white calcium cyanurate decomposes to isocyanic acid which is volatile and condenses to make cyanuric acid, another white powder. This might be the white stuff you see.

Heated to a very high temperature, calcium cyanurate eventually decomposes to calcium cyanamide by loss of lots of CO2. There's an excellent paper on this forum called cyanuric acid and cyanurates or something like that. Try a Google site search to find it or in my site in the articles about the fire fighting plaster. Link in my signature.

The calcium cyanamide will oxidise at high temperature exposed to air to form calcium oxide, even more CO2 and N2.

[Edited on 18-3-2016 by deltaH]