Are Gas Mantles Thermoluminescent or something else?

[CC]

Hi:

How does a gas mantle, or "Welsbach mantle" composed of Thoria and Ceria
(or the new ones without Th) on an ash mesh and heated by a
methane+air, propane+air, or white gas+air flame work?

For instance, a stoichiometric propane+air flame at 1 atm and 300K burns
at about 2268K. This temperature is only sufficient to produce dull red
heat for any object that reaches this temp. Thus, the gas mantle must
be doing something else than black body radiation to produce its
brilliant greenish-white light.

I have been involved in a discussion with someone on the Candle Power
Forums who believes the emission of light from a mantle is due to
"thermoluminescence." I am not convinced this is correct, but am not
sure. I researched this subject and the explanation I have found is
that it is a phenomenon used for dating. A material that has been
exposed to ionizing radiation (therefore a source of energy that can
produce a non-Boltzman population distribution) basically gets some of
its electrons displaced and trapped in higher energy, but stable states.

These states become unstable when the material is heated, releasing the
stored energy as visible light. This can be integrated and related to
the age of the material.

From my reading of thermoluminescent dating, there are two facts: 1. it
is a release of stored energy, thus must be temporary (a finite number
of photons will be emitted, then the material will no longer emit
photons). 2. an energy source other than thermal is responsible for
generating the excited states.

For the gas mantle to radiate more light than a 2268K object by
thermoluminescence, assuming it could reach the maximum temperature of
the propane+air flame, would mean that it would have to be possible for
a non-Boltzman population of energy states to be reached via the input
of 2268K thermal energy alone. This is the point where my cursory
knowledge of statistical thermodynamics poops out. I had a long
discussion with a very high-level combustion scientist yesterday about
this, and he convinced me that this is just not possible.

If that is correct, then there must be some other non-thermal mechanism
which permits energy to be transfered to the mantle. This might allow
the mantle to reach a higher temperature than 2268K and thus be able to
radiate as a blackbody at a much higher temperature than the flame in
air temp. Such a mechanism might be catalytic oxidation of oxidizable
species at the surface of the mantle. Alternatively, direct non-thermal
transfer of energy such as from excited chemical species from the
combustion reaction to the mantle materials, could generate excited
states in the rare-earth oxides, resulting in a release of non-blackbody
visible radiation.

Which is it? Or is there some other mechanism?

There are currently comments on sci.engr.lighting suggesting that the
emission is thermoluminescent:

davidlee...@dont.use.this.bit.hotmail.com wrote: "It isn't
"incandescent" in the normal sense of a filament lamp. The light
is due to thermoluminescence - thermal excitation and photon emission on
return to the ground state - so it isn't a black body. Even tungsten isn't
truly a black body emitter - tungsten at a physical temperature of 3600K
emits light with an effective colour temperature of 3754K (according to the
"Rubber Book")."

But how can a purely thermal input generate non-thermal population
distributions?

The explanation of someone who truly can explain how a mantle emits
would be greatly appreciated.

Thanks for input.

Good day!

--
_____________________
Christopher R. Carlen
cr...@bogus-remove-me.sbcglobal.net
SuSE 9.1 Linux 2.6.5

[Sbharris[atsign]ix.netcom.com]

COMMENT:

I believe that "thermoluminescence" of the type seen from a flame and
mantle (also called candoluminescence) is indeed merely a sort of
higher-frequency fluorescence from metal ions, which is pumped by heat.
In this way, the wavelength can be considerably shorter than the
standard "incandescence" which is blackbody spectrum.

This is not all that odd a phenomenon: are you not used to seeing a
green flame from copper salts heated by a bunsen burner? The color
temperature of that green flame is considerably "hotter" than the flame
itself. Now, suppose you found some salt that put out a UV spectral
band, instead of green? You could then use that to make white light in
the same way it's done inside mercury vapor fluorescent tubes.

Cerium, I believe, radiates a band in the UV, and this is picked up and
downshifted into the visible blue-white by thorium ions in the classic
Welsbach mantle (or nowadays, the Th function is done by yittrium or
zirconium ions). The metal nitrates are impregnated into fiber mantles
which burn away, leaving a loose ash of oxides which then convert heat
from the flame into shorter wave light.

"Limelight" from calcium oxide heated by an Ox-hydrogen flame was an
early example of thermoluminescense used for lighting. But the
temperature needed there was much higher than the 1000 C gas
temperature of the Welsbach mantle. The latter is really a quite
remarkable invention.

http://en.wikipedia.org/wiki/Candoluminescence

SBH

[salm...@sbcglobal.net]

On 12/2/05 5:48 PM, in article
1133574526....@o13g2000cwo.googlegroups.com,

"Sbharris[atsign]ix.netcom.com" <sbha...@ix.netcom.com> wrote:

> I believe that "thermoluminescence" of the type seen from a flame and
> mantle (also called candoluminescence) is indeed merely a sort of
> higher-frequency fluorescence from metal ions, which is pumped by heat.
> In this way, the wavelength can be considerably shorter than the
> standard "incandescence" which is blackbody spectrum.
>
> This is not all that odd a phenomenon: are you not used to seeing a
> green flame from copper salts heated by a bunsen burner? The color
> temperature of that green flame is considerably "hotter" than the flame
> itself. Now, suppose you found some salt that put out a UV spectral
> band, instead of green? You could then use that to make white light in
> the same way it's done inside mercury vapor fluorescent tubes.
>
> Cerium, I believe, radiates a band in the UV, and this is picked up and
> downshifted into the visible blue-white by thorium ions in the classic
> Welsbach mantle (or nowadays, the Th function is done by yittrium or
> zirconium ions). The metal nitrates are impregnated into fiber mantles
> which burn away, leaving a loose ash of oxides which then convert heat
> from the flame into shorter wave light.
>
> "Limelight" from calcium oxide heated by an Ox-hydrogen flame was an
> early example of thermoluminescense used for lighting. But the
> temperature needed there was much higher than the 1000 C gas
> temperature of the Welsbach mantle. The latter is really a quite
> remarkable invention.

I turns out that I am very interested in this subject. Nernst concluded, and
I now tend to agree, that the relatively high light output from a mantle is
because of selective radiation. The thoria mesh that is at the heart of the
classic mantle. Thoria is transparent at most of the wavelengths in the near
infrared region, and as can be seen by its whiteness, a good deal of the
visible spectrum as well.

Because of such low emissivity, the temperature of the mantle more closely
approaches that of the flame than a metal mesh would. That makes it possible
for emission by ceria, added to the mantle to provide visible emission, to
be greater than that of a black body cooled down by radiation at all
wavelengths.

In recent years, because of radiation phobia, yttria has been substituted
for thoria. It is an almost colorless rare earth oxide that give the same
selective properties.

Because electrical lighting replace gas lighting, there is no real economic
incentive to study mantle science. For amateurs, who have access to
relatively high power CO2 lasers or the like, one could try looking at the
emission from laser heated mantles compared to flame heated manuals to see
if the spectra are much different.

Please let me know of other real mantle information is available.

Bill

-- Ferme le Bush

[Gregg]

CC wrote:
> Hi:
>
> How does a gas mantle, or "Welsbach mantle" composed of Thoria and Ceria
> (or the new ones without Th) on an ash mesh and heated by a
> methane+air, propane+air, or white gas+air flame work?
>
> For instance, a stoichiometric propane+air flame at 1 atm and 300K burns
> at about 2268K. This temperature is only sufficient to produce dull red

"Dull red?" -

- This isn't a scientific reply - just a common observation.
Have you ever looked into a kiln operating at 2000 C?
- You need cobalt glasses to protect your eyes - it's white hot.
Even at 1500 C it's white hot and difficult to look at - I did not
calculate or look up the black body spectrum, but the old optical
pyrometers used a heated filament - the current in the filament was
increased until the color matched the heated surface. - They were
calibrated against a black body source. At 2000 C you need filters in
front of the pyrometer to protect your eyes.

The light from such source may distort color perception, but they
certainly appear bright - too bright to look at for extended periods.
(Tungsten light sources and mantle lanterns also distort color
perception when compared to sunlight)

Gregg

[Mark Thorson]

salm...@sbcglobal.net wrote:
>
> Because electrical lighting replace gas lighting, there is no real
> economic incentive to study mantle science. For amateurs, who have
> access to relatively high power CO2 lasers or the like, one could
> try looking at the emission from laser heated mantles compared to
> flame heated manuals to see if the spectra are much different.

With advances in plastics, etc., how cold
could a material be that emits a brilliant
white light?

Could it happen in boiling water at 1 atm?

[The Ghost In The Machine]

In sci.physics, Mark Thorson
<nos...@sonic.net>
wrote
on Sat, 03 Dec 2005 10:24:14 -0800
<4391E2CE...@sonic.net>:

Define "brilliant", the amount of material, and if necessary,
the distance to said material.

:-)

The amount of energy per unit frequency per unit volume, if I'm
using this equation correctly, in a blackbody scenario is

8 * pi * h * f^3 / (c^3 * (exp(h * f / (k * T) ) - 1))

where pi = 3.14159..., h = Planck's Constant = 6.626 * 10^-34 J-s,
f is the frequency, k is Boltzmann's constant = 1.3807 * 10^-23 J/K,
c = lightspeed = 299792458 m/s, and T is the temperature in Kelvin.

(The units are J-s/m^3, of course.)

>
> Could it happen in boiling water at 1 atm?

It could. The amount of energy per unit frequency per unit
volume at 600 THz for boiling water at 373.15 K
would be 4.104 * 10^-47 J-s/m^3 ... which is darned small.
However, the generation of light from collapsing bubbles is
probably not that well explained by this equation anyway,
and I'm not all that up on this stuff.

Note that the classical prediction gives a far higher value:
1.730 * 10^-13 J-s/m^3, which might make for a possible test
if one can get a water tank big enough -- something on the
order of Superkamiokande...

http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html

--
#191, ewi...@earthlink.net
It's still legal to go .sigless.

[salm...@sbcglobal.net]

On 12/3/05 10:24 AM, in article 4391E2CE...@sonic.net, "Mark Thorson"
<nos...@sonic.net> wrote:

> With advances in plastics, etc., how cold
> could a material be that emits a brilliant
> white light?
>
> Could it happen in boiling water at 1 atm?

I do not understand your question. Certainly it is possible to use
fluorescence at multiple wavelengths to simulate a white light source. In
most fluorescent emitters, different particles are at different
temperatures. For example, the states in a laser often are said to have a
negative temperature because those states are not in thermal equilibrium. It
is just about impossible to heat with a flame so as to avoid equilibrium.

[donald haarmann]

"CC" <some...@overthe.rainbow.net>

| Hi:
|
| How does a gas mantle, or "Welsbach mantle" composed of Thoria and Ceria
| (or the new ones without Th) on an ash mesh and heated by a
| methane+air, propane+air, or white gas+air flame work?
|

[snip]

-----------
This from Ullmann's 5th A 27 p.31 Thorium and Thorium Compounds

9.2 Conventional Applications

9.2.1 Illuminants

The most important application of thorium followed the discovery by Auer Von Welsbach
in 1892 that some rare earth oxides and thorium oxide, when introduced in the form of
woven yarn into a gas flame, considerably increased the luminous efficacy of the flame.
The emission of light is excited by cathode rays, heat, and UV radiation. Although pure
cerium oxide converts the UV fraction of an oxidizing gas flame into visible light more
efficiently than ThO23, it is not used in principle because so much light is emitted in the
IR region that "cooling" of the gas flame occurs. Excitation of cerium oxide gives a gas
flame temperature of only 1500o C, whereas thorium oxide gives 1930o C. Maximum
luminous efficacy occurs at 1 % cerium oxide in ThO2. [40]

&c.

[40] F. Möglich, Angew. Chem. 53 (1940) 405-409.

"By World War II, total consumpption [of thorium] worldwide amounted to ca. 8000 t, [metric]
mainly for the production of gas mantles, reaching 250 t in some years."

Thorium oxide was used in fluorescent lamps, thus the old ones were somewhat toxic.
Modern ones still contain a small amount of Hg.

Thorpe's - Dictionary of Applied Chemistry (various editions) devotes several pages to gas mantles.

--
donald j haarmann
----------------------------
There is no higher or lower knowledge,
but one only, flowing out of experimentation.
Leonardo