Heating CaO to create intense light

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Discussion Overview

The discussion centers on the chemistry and physics behind the intense light produced by heating calcium oxide (CaO), particularly in the context of historical applications such as limelight in lighthouses and theatrical productions. Participants explore the mechanisms of light emission, comparisons with other light sources, and the properties of various metal oxides.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that calcium oxide is produced by heating calcium carbonate and questions the notion of "burning" CaO.
  • Another participant explains that heating quicklime to extremely high temperatures can produce an intense glow known as limelight.
  • A comparison is made to the Welsbach mantle, suggesting a modern light source that also relies on high temperatures.
  • One participant claims that the emission of light is purely a physical phenomenon, not a chemical one, stating that anything heated sufficiently will emit light.
  • There is speculation about the reasons for using rare metal oxides in the Welsbach mantle, hinting at their emission spectra.
  • A participant raises a question about whether other oxides, such as barium oxide or strontium oxide, could produce similar effects when heated.
  • Another participant discusses the factors that contribute to the luminosity of certain oxides, mentioning the concepts of black body and grey body radiation, as well as the catalytic properties of some oxides that enhance heat production.
  • One participant reiterates the characteristics of black bodies at high temperatures and their visibility in the spectrum of interest.
  • A later reply clarifies a previous statement regarding the appearance of materials at room temperature.
  • A participant references an experiment related to light emission and radiation, suggesting a connection to the current discussion.

Areas of Agreement / Disagreement

Participants express a range of views on the mechanisms of light emission, with some emphasizing the physical aspects while others highlight chemical properties. There is no consensus on the specific reasons for the luminosity of different oxides or the implications of their properties.

Contextual Notes

Some discussions involve assumptions about the definitions of terms like "black body" and "grey body," as well as the conditions under which various oxides emit light. The discussion does not resolve the complexities of these concepts.

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I saw on TV this morning how Thomas Drummond in 1829 created an intense light for use in a lighthouse in 1829, before electric lights. He heated calcium oxide with alcohol and oxygen to a very high temperature creating what is called limelight, later used in theatrical productions in the 19th century.
What is the chemistry behind this intense light creation by heating CaO?
The TV said the Calcium Oxide was burnt, but I don't see how that is possible.
 
Chemistry news on Phys.org
Calcium oxide CaO is made by heating any material containing calcium carbonate CaCO3 to drive off carbon dioxide. The resulting product is called quicklime, and it will eventually react with the carbon dioxide in the atmosphere and gradually turn back into calcium carbonate.

However, if the quicklime is heated to extremely high temperatures (2400 C), it will give off an intense glow, which is called limelight.

http://en.wikipedia.org/wiki/Calcium_oxide
 
A similar (but more modern) light source is the 'Welsbach mantle' used in street gas lighting until recent times, and still seen in portable gas lamps.
 
There is no chemistry behind the light emitted, just physics - everything heated high enough will emit the light.
 
...and metal oxides can have a high melting point. However, there has to be a special reason for using rare metal oxides in the Welsbach mantle. I suppose that it has something to do with the emission spectrum of thorium...
 
Well anything heated to a very high temp is going to glow. My room is lit up by a tungsten filament glowing at about 2800 C. Is there anything special about CaO?. Can you use BaO , SrO, or a blob of anything that doesn't melt?
 
As I understand it, there are two reasons why some oxides are more apt to get high luminosity than others.
The highest thermal emission in a given frequency range does have a black body, which would appear completely black in the frequency range of interest. A grey body emits less radiation when heated.
Now these oxides have a high emitivity in the visible range and a low one in the infrared (as they are nearly transparent for infrared radiation) so that they get hotter than substances which have high emissions in the IR. I.e. there are less radiation losses in the IR region.
The other reason why to use rather exotic compounds like cerium oxides is that these oxides catalyze the oxidation reactions, so that heat is directly produced at their surface whence they get much hotter than other substances being brought into a flame.
 
DrDu said:
As I understand it, there are two reasons why some oxides are more apt to get high luminosity than others.
The highest thermal emission in a given frequency range does have a black body, which would appear completely black in the frequency range of interest.

A 'black body' in temperatures of the sort we're discussing, 2000-3000 ºC would appear very bright in the frequency range of interest, i.e., in visible wavelengths.
 
Of course. I was referring to it's appearance at room temperature.
 

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