When will a material burn if a laser is shone on it?

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Discussion Overview

The discussion centers around the conditions under which a material, specifically Alumina, will burn when exposed to a high power laser for a brief duration. Participants explore the implications of temperature, oxidation, and material properties in the context of a mechanical engineering dissertation project.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant, Alex, describes modeling Alumina in Ansys Icepak and reports a temperature increase to 4700 degrees C for a duration of 20ns, questioning whether this would cause the material to burn.
  • Another participant suggests that the reason for the inquiry determines its validity, implying that context matters.
  • Alex clarifies that the inquiry is for a dissertation in Mechanical Engineering, emphasizing the need for the material to convert laser light into IR radiation without burning, as it will be pulsed weekly for a year.
  • One participant advises that books may be more beneficial than forum inquiries for this type of question.
  • Another participant outlines conditions for burning: the material must be oxidizable, there must be a source of oxygen, and the temperature must be sufficient for a reaction. They note that Alumina is difficult to oxidize due to its high oxidation state.
  • A concern about ablation is raised, highlighting the importance of ensuring the melting point of the material is higher than the achieved temperature.

Areas of Agreement / Disagreement

Participants express varying perspectives on the inquiry's validity and the conditions for burning, with no consensus reached on the specific outcomes for Alumina under the described conditions.

Contextual Notes

The discussion does not resolve the assumptions regarding the material's properties, the specific environmental conditions, or the precise definitions of burning and ablation.

alex111888
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Hi there,

This may sound like a silly question, but I'm looking at shining a high power laser onto a target material for a fixed period of time.

I have modeled Alumina in Ansys Icepak, and the temperature increase has come to 4700 degrees C. This maximum temperature is only reached for approximately 20ns, so an extrememly short period of time. How can I calculate if the ceramic will burn, as the surface finish needs to remain as perfect as possible.

Thanks

Alex
 
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Whether it's silly or not depends on your reason for doing it.
 
Dr Lots-o'watts said:
Whether it's silly or not depends on your reason for doing it.

It is for a dissertation for my Masters in Mechanical Engineering, so the reason is not so silly!

I need the material to 'convert' the laser light into IR radiation which can be picked up by an IR detector. My reason for wanting to know whether the material will burn is simple- the material will be pulsed say once a week, but needs to last a year. Sorry I cannot give away more details.

Alex
 
May I make the suggestion that, for this sort of thing:

books > asking a forum
 
The material will burn if:
a) it is oxidizable
b) there is a source of oxygen
c) the temperature is high enough for it to react.

Alumina isn't easy to oxidise since its in quite a high oxidation state already.

Ablation is another worry; make sure your melting point is higher than the temperature you're going to achieve.
 

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