Most brilliant photo-flash?

[DrJones]

With regards only to radiated brilliance of light, disregarding mixing hazards for the moment, what's the brightest possible photo-flash comprised of? Magnesium? Mg/Al? Al? Ti? Boron? A mixture of metals? Is one oxidizer "better" than another when it comes to amount of light radiated?

Thanks

Edward

[Crazy Swede]

Dried and finely milled sodium nitrate with fine magnesium is very bright and a lot of excess magnesium can be used to react with atmospheric oxgen. Since sodium nitrate wants to attract moisture some dichromate should be added to aviud the risk of spontaneous ignition or the magnesium should be of a passivated quality.

 

To avoid the risks connected to fine magnesium powders fine aluminum powders can be a good substitute.

 

There are even brighter ones but they rely on epensive and even more reactive materials.

 

Edit:

Sodium nitrate is very effective since the sodium atom contributes to visible light. Oxidizers based on potassium do not since potassium radiates mostly outside the visible spectrum.

 

When it comes to fuels the hotter they burn the more light the composition will emit but magnesium has an advantage that it easily turns into vapour that creates a big flame or fire cloud. Zirconium can reach higher temperatures but creates lots of problems connected to accidental ignition.

Edited March 16, 2021 by Crazy Swede

[Arthur]

In the design of the WW2 photo flash bombs (about 250Kg!) the main oxidiser was air! If you try to make a flash with lots of powder it doesn't get brighter linearly with mass unless you spread it out first.

[DrJones]

Thank you, "Crazy Swede" for your informative answer. I suspected but never before confirmed that Na contributes to the visible light spectrum. Might you know if Mg gives "more light" than does Mg/Al or Ti? Thanks again. Edward

[SharkWhisperer]

Thank you, "Crazy Swede" for your informative answer. I suspected but never before confirmed that Na contributes to the visible light spectrum. Might you know if Mg gives "more light" than does Mg/Al or Ti? Thanks again. Edward

Mg is used in US military flares for precisely that reason. The exact formulations are not difficult to locate. Sodium nitrate is extremely hygroscopic and comps and devices using it must be fastidiously segregated from atmospheric water vapor or your comp/device shelf-life will suffer rapidly.

 

Mg has inherent safety and reactivity risks associated with it (many finely powdered or granular pyro metals do), so that must be taken into consideration. It does have utility in fireworking, but has largely been eclipsed by Mg/Al and Al for many purposes.

[Richtee]

Hey Dr..here... http://www.privatedata.com/byb/pyro/pfp/flash.html#Perchlorate/aluminum%20I

[Crazy Swede]

Thank you, "Crazy Swede" for your informative answer. I suspected but never before confirmed that Na contributes to the visible light spectrum. Might you know if Mg gives "more light" than does Mg/Al or Ti? Thanks again. Edward

Yes it does and the reason is that magnesium fulfills the "Glassman criterion" that aluminum and titanium do not.

 

What this means is that since magnesium has a low vaporization temperature (1107°C), which is much lower than its oxide’s decomposition temperature ( ~3200°C), the combustion can take place in an extended metal vapor phase diffusion zone, allowing for a big flame and thus a large radiative area.

 

In practice this means that titanium and aluminium sure creates a lot of heat during their combustion but the flame is smaller and compared to using magnesium as the fuel they will emit less light.

 

Magnalium will be somewhere in between of magnesium and aluminium in efficiency and is therefore sometimes a good choice since the risk of problems connected to corrosion is a lot smaller. BUT, magnalium creates more friction during handling so if someone needs to handle larger amounts of flash powder aluminum is often a better/safer choice, although the output of light will be smaller.

[Crazy Swede]

I have to correct myself!

 

Aluminum actuallys does fulfil the Glassman criteria but I guess the bigger difference between the boling point of magnesium metal and magnesium oxide, compared to the difference between aluminum metal and aluminium oxide, explains why we get bigger and brighter flames with magnesium(?).