Sciencemadness Discussion Board

zinc sulfur

tjosephrhodes - 17-3-2011 at 17:42

I am trying to burn some sulfur and zinc for a demonstration and it does not flash and burn, but just sputters and burns blue. Youtube videos and other people say it should burn bright green and very energetically spark and flash. I have tried 2:1 and 6:1 ratio, and I blend them very well with mortar and pestle first. What am I doing wrong?

UKnowNotWatUDo - 17-3-2011 at 18:44

What are you using as your source for sulfur? Is it relatively pure or is it something like gardening sulfur?

tjosephrhodes - 17-3-2011 at 19:20

Its roll sulfur from fisher chemical.

argyrium - 17-3-2011 at 23:06

tjosephrhodes,

Do not be lulled into disrespect for this mixture - it can and has bitten many... and it certainly can behave with a "flash" and not just "sputtering".

simply RED - 17-3-2011 at 23:44

You have to ignite it with something like KNO3/Al/S mix! Not with a match!

Blasty - 18-3-2011 at 10:03

Quote: Originally posted by simply RED  
You have to ignite it with something like KNO3/Al/S mix! Not with a match!


That's not necessary, it will ignite without help from an oxidizer.

tjosephrhodes - 18-3-2011 at 10:13

Most of the people I have seen say they light it with a propane or methane fed bunsen burner, which is exactly what I am using. My mixture just seems to melt and darken and then kind of burn slowly and go out. I can even get it to red hot for minutes without anything dramatic happening. I am doing it in a fume hood with protective gear and nothing flammable around. Not sure what I could be doing wrong.

Blasty - 18-3-2011 at 10:22

Quote: Originally posted by tjosephrhodes  
I am trying to burn some sulfur and zinc for a demonstration and it does not flash and burn, but just sputters and burns blue. Youtube videos and other people say it should burn bright green and very energetically spark and flash. I have tried 2:1 and 6:1 ratio, and I blend them very well with mortar and pestle first. What am I doing wrong?


In a proportion of 6 to 1 it burns pretty fast, but don't get your hopes up if what you are expecting is for it to be some sort of substitute for black powder or flash powder. I have never been able to make it explosively burst a strongly closed container (like kraft paper tubes with both ends tightly shut), like you can with black powder or nitrate/sulfate-based flash powders (chlorate/perchlorate-based flash powders do not need very strong containment to explode.) It always breaks through just some part of the container (usually the area where the hole for the fuse is), giving a rather lame "pop", and propelling it.

Blasty - 18-3-2011 at 10:24

Quote: Originally posted by tjosephrhodes  
Most of the people I have seen say they light it with a propane or methane fed bunsen burner, which is exactly what I am using. My mixture just seems to melt and darken and then kind of burn slowly and go out. I can even get it to red hot for minutes without anything dramatic happening. I am doing it in a fume hood with protective gear and nothing flammable around. Not sure what I could be doing wrong.


Your zinc and sulfur powder also need to be very fine. When I used to tinker with this mix I used a very fine zinc dust and flowers of sulfur.

The WiZard is In - 18-3-2011 at 10:30

Quote: Originally posted by tjosephrhodes  
Most of the people I have seen say they light it with a propane or methane fed bunsen burner, which is exactly what I am using. My mixture just seems to melt and darken and then kind of burn slowly and go out. I can even get it to red hot for minutes without anything dramatic happening. I am doing it in a fume hood with protective gear and nothing flammable around. Not sure what I could be doing wrong.



What ratio of Zink - Sulphur dobe you using?

6 Zn - 1 S by weight seems be de régle.

This is hard to completely mix ... diapering would seem the
best method. Pour on paper and lift ends ad lib to mix.

Byda Shakhashiri's Chemical Demonstrations : A Handbook for
Teachers of Chemistry recommends using a mad hot wire. I
haven't done-did this for 55+ years ---- seems to me I used
a match or a fuse back then. Always worked ... made a heck of a
mess ... but it always worked.

hissingnoise - 18-3-2011 at 10:46

Quote:
This is hard to completely mix ... diapering would seem the
best method. Pour on paper and lift ends ad lib to mix.

Roll the mixture in a ballmill or just put it in a sealed can and roll it around on the ground!
Or better - down a good-sized hill . . .

The WiZard is In - 18-3-2011 at 11:32

Quote: Originally posted by hissingnoise  
Quote:
This is hard to completely mix ... diapering would seem the
best method. Pour on paper and lift ends ad lib to mix.

Roll the mixture in a ballmill or just put it in a sealed can and roll it around on the ground!
Or better - down a good-sized hill . . .

Reminds upon me .... some years ago I bought a bunch of
pyro chemicals from a going out of business (hobby) pyro.
(He got remarried and was pussy whipped.) Said
he ñ when I mixed barium chlorate/shellac for green stars
I put it in a barrel and roll it down el hill.

Twas also told years ago of the professional fwks company
that put la mixture in a barrel and then "Hey Jose ... roll this
barrel around to mix it... were going to town." They drove off
a few ... stopped - read the days paper... then drove back.



djh
----
"Here, where everything is done in a hurry and as cheaply as possible, it
was preferred to transport NG in liquid form, although it was more
dangerous, Many accidents occurred and many live were lost in connection
with NG and as long as most of the workmen were foreigners, especially
Chinese, the industrialists, who care only for profits, did not introduce
any safety regulation until the were forced by the Government after
establishing in 1910 the Bureau of Mines, at Pittsburgh, Pennsylvania."

PATR 2700

The WiZard is In - 18-3-2011 at 13:24

Quote: Originally posted by The WiZard is In  
Quote: Originally posted by tjosephrhodes  
Most of the people I have seen say they light it with a propane or methane fed bunsen burner, which is exactly what I am using. My mixture just seems to melt and darken and then kind of burn slowly and go out. I can even get it to red hot for minutes without anything dramatic happening. I am doing it in a fume hood with protective gear and nothing flammable around. Not sure what I could be doing wrong.



Byda Shakhashiri's Chemical Demonstrations : A Handbook for
Teachers of Chemistry recommends using a mad hot wire. I
haven't done-did this for 55+ years ---- seems to me I used
a match or a fuse back then. Always worked ... made a heck of a
mess ... but it always worked.


Hot metal rod - too.

http://tinyurl.com/6hstmt9

This from Popular Science September 1932, home chemist.
a time before Chemistry became a pejorative and DuPont
was Better things for better living through chemistry.

A classic...

albqbrian - 18-6-2011 at 00:05

I still have Cpt Brinley's book that was published in the mid 1960's using Zn/S as a nice rocket propellant. It was definitely a different time. The book was made to help stop the rash of serious injuries from young men inspired by the early Space Race to make their own. A common, really dangerous "motor" was the heads from wooden matches stuffed into an empty CO2 cylinder. That claimed many a body part.

Brinley had the full support of the Army and came up with a very detailed amateur rocket operation. He was big into making sandbagged structures for protection, remote loading, etc. It covered everything. Except recovery systems! I guess in the 1960s they were too difficult to make. Or they went on the probability path. That a falling rocket and a standing person were unlikely to occupy the same place at the same time. And, of course, you had the sandbags. The book contained detailed descriptions fro two rockets that could attain altitudes of 10K and 20K feet! Steel tubes, no parachute :o Man I miss those days.

OK, back to your question. When used for rocket fuel the recommended ratio is 2 pts Zn to 1 S; by weight. When I did demos I just mixed roughly (eyeballed) equal amounts of each. I then wrapped it in toilet paper and lit the paper. I used this demo to show how to very distinct, different elements transformed into a totally new thing. With lots of flame and smoke. It doesn't flash, but the energetic burning always was a crowd pleaser.

[Edited on 18-6-2011 by albqbrian]

IndependentBoffin - 18-6-2011 at 01:21

Quote: Originally posted by Blasty  
Quote: Originally posted by tjosephrhodes  
I am trying to burn some sulfur and zinc for a demonstration and it does not flash and burn, but just sputters and burns blue. Youtube videos and other people say it should burn bright green and very energetically spark and flash. I have tried 2:1 and 6:1 ratio, and I blend them very well with mortar and pestle first. What am I doing wrong?


In a proportion of 6 to 1 it burns pretty fast, but don't get your hopes up if what you are expecting is for it to be some sort of substitute for black powder or flash powder. I have never been able to make it explosively burst a strongly closed container (like kraft paper tubes with both ends tightly shut), like you can with black powder or nitrate/sulfate-based flash powders (chlorate/perchlorate-based flash powders do not need very strong containment to explode.) It always breaks through just some part of the container (usually the area where the hole for the fuse is), giving a rather lame "pop", and propelling it.


The reason why it doesn't explode is because the reaction (in theory) produces no gaseous products.

Zn(s) + S(s) -> ZnS(s)

Therefore gaseous pressure against a casing to explode it or thrust to propel a rocket can only come from two sources:
1) Vaporisation of the solids
2) Pressure rise from heating of any existing gas

Sulphur has a relatively low vaporisation energy of about 1.75kJ/g. Zinc is a bit higher at 2.34kJ/g. By contrast aluminum has a vaporisation energy of 13.5kJ/g. Therefore sulphur rich compositions are more likely to come close to something resembling a weak "explosion".

Comments: This does not preclude the usage of Zn + S in propellant or explosive applications. To use Zn + S as a propellant you can try to vent high pressure gas into burning Zn + S in the combustion chamber. Best gas for performance to use is one with a high specific heat ratio C<sub>p</sub>/C<sub>v</sub>, e.g. He (expensive) or H<sub>2</sub> (better). For convenience though, CO<sub>2</sub> can be used even though it is a poorer gas as a propellant because of the ease of acquisition in compact containers used in the airgun and soft drink industries.

BTW for those who don't understand the relevance of C<sub>p</sub>/C<sub>v</sub> as a propellant, the explanation is simple: thrust is only provided by linear translational momentum of the exhaust gas. As the degrees of freedom of excitation increase (e.g. polyatomic molecules) then thermal energy of the gas becomes vibrational/rotational energies as well. These energies are wasted from a perspective of rocket thrust. Incidentally this is why all the noble gases (monoatomic particles) have very similar C<sub>p</sub>/C<sub>v</sub> of 1.66 (within 2%)

Conclusion: Zn + S makes a poor propellant and explosive. It is best used for pyrotechnic purposes. Under these circumstances it is relatively safe because it is does not generate copious amounts of gas.

quicksilver - 18-6-2011 at 05:33

LDRS has a "Study of CATO's" that makes for very interesting reading. With more & more serious rocket competition, bodies naturally moved to aluminum & altimeters got much less expensive. The plethora of graphite nozzles made for further strides in the hobby as did inexpensive multi-minutes video cameras (pointed downward through the entire launch: 2-6 minutes would fit on a USB drive).
unfortunately I forgot the name but there is a lot of material dealing with that subject from David Sleeter's huge work "Amateur Rocket Motor Construction" (1st printing '04 - ISBM 0-930387-04-x, it's the "classic" rocket text & IMO should be studied as closely as Davis).