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From: ornitz@kodak.kodak.com (Barry Ornitz)
Newsgroups: rec.pyrotechnics
Subject: Re: Help for beginner
Keywords: rocket fuel, safety, caramel candy
Message-ID: <1990Oct23.174126.12857@kodak.kodak.com>
Date: 23 Oct 90 17:41:26 GMT
I agree wholeheartedly with Doug Gwyn when he encourages experimenters to stay
away from toxic fuels for home built rockets. However, I disagree as to the
safety of the caramel candy (melted sucrose)/saltpeter (potassium nitrate) fuel
he suggests.
The melting point of sucrose is approximately 185 deg C or 365 deg F. It
cannot be melted over a double boiler. This is unfortunate since a double
boiler can give such good temperature control (essentially the boiling point
of water - 100 deg C at 1 atmosphere). This is important since most home
experimenters have no means of accurately controlling elevated temperatures.
The problem is that the autoignition point of the melted sucrose/potassium
nitrate mixture is only slightly higher than the melting point of the sucrose.
If memory serves, it is between 200 to 230 C depending on the water content
of the potassium nitrate crystals. Considering that the molten sucrose is
very viscous, it is very difficult to melt the sucrose without having excessive
overheating at the walls of the vessel it is being melted in. With such a small
safety margin, you are really taking chances trying this over a stove at home.
I am not very sure of the absolute numbers on the autoignition temperature,
but I remember when trying this fuel over 25 years ago, I used an accurately
calibrated electric skillet with a redundant candy thermometer. I had some
some tense moments when localized heating got portions of the mixture rather
close to the danger point.
Unless you have the specialized equipment to control the temperature extremely
well, I would avoid this fuel for home built rockets.
Barry
-----------------
| ___ ________ | Dr. Barry L. Ornitz WA4VZQ
| | / / | | Eastman Kodak Company
| | / / | | Eastman Chemical Company Research Laboratories
| |< < K O D A K| | Process Instrumentation Research Laboratory
| | \ \ | | P. O. Box 1972, Building 167B
| |__\ \________| | Kingsport, TN 37662 615/229-4904
| | INTERNET: ornitz@kodak.com
-----------------
From: ornitz@kodak.kodak.com (Barry Ornitz)
Newsgroups: rec.pyrotechnics
Subject: Re: Help for beginner
Message-ID: <1990Oct29.213028.18754@kodak.kodak.com>
Date: 29 Oct 90 21:30:28 GMT
In article <90298.143116FQV@psuvm.psu.edu> FQV@psuvm.psu.edu
(jim bowers) writes:
>Well, the melting point of sucrose is 185C but a powdered mixture of both
>sugar and sodium nitrate will have a melting point less than sugar (organic
>chemistry lesson). Also, you can make a double boiler using mineral oil
>which has a much higher boiling point. Use a hot plate and use it outside.
What do you know? Another smug answer on wreck.pyrotechnics from another
wannabe chemist!
The melting point of this mixture has very little depression. The calculations
are based on solution thermodynamics, organic chemistry has little to do with
the situation. You have taken physical chemistry and thermodynamics haven't
you? What you are actually seeing is the effect of water of hydration of the
sodium nitrate. Potassium nitrate shows less of an effect in this. In making
caramel candy, you add water to make the mixture melt at a lower temperature.
For making rocket fuel, you do not want this water present, so you start with
anhydrous nitrates and sucrose. The water of hydration lowers the performance
of the fuel considerably.
As far as the double boiler goes - don't you know how one works? What oil are
you going to use? The aromatic mineral oils such as Mobiltherm Light (Socony
Mobil Oil Co.) cannot be used in an open system in contact with the air as its
boiling point (~204C) is well above its flash point (121C). Dowtherm E would
be a good choice for its boiling temperature if you can stand the toxicity of
o-dichlorobenzene and can handle its flash point of 68C (boiling point 177C).
Use a hot plate if you dare. I discussed the effects of localized overheating
in my original post. In a viscous mixture like this, hot spots are difficult
to avoid. Ask any cook about trying to keep thick puddings and gravies from
scorching.
There are much safer fuels than this one. Why temp fate?
Barry
-----------------
| ___ ________ | Dr. Barry L. Ornitz WA4VZQ
| | / / | | Eastman Kodak Company
| | / / | | Eastman Chemical Company Research Laboratories
| |< < K O D A K| | Process Instrumentation Research Laboratory
| | \ \ | | P. O. Box 1972, Building 167B
| |__\ \________| | Kingsport, TN 37662 615/229-4904
| | INTERNET: ornitz@kodak.com
-----------------
From: ornitz@kodak.kodak.com (Barry Ornitz)
Newsgroups: rec.pyrotechnics
Subject: Re: Help for beginner
Keywords: fuels, propellents
Message-ID: <1990Nov1.160846.22055@kodak.kodak.com>
Date: 1 Nov 90 16:08:46 GMT
In article <14280@smoke.brl.mil> gwyn@smoke.brl.mil (Doug Gwyn) writes:
>In article <1990Oct29.213028.18754@kodak.kodak.com> ornitz@kodak.kodak.com
(Barry Ornitz) writes:
>>There are much safer fuels than this one. Why temp fate?
>
>Because nobody has yet explained what the safer fuels are..
About the safest fuel I ever used was a mixture of potassium perchlorate and
powdered shellac. The two ingredients are mixed wet with alcohol, eliminating
most of the spark hazard. The mixture is loaded wet into the rocket case too
(using non-sparking tools of course). Once dry, the engine becomes a rock-hard
mass. It must be primed with meal powder for reliable ignition.
The black-powder based conventional rocket fuel described in most texts on
pyrotechnics is probably the safest fuel for beginners that uses easily
obtained ingredients. Remember for a rocket fuel, the proportion of charcoal
to sulfur is much greater than in black powder for primitive weapons. This
fuel should again be charged wet into the rocket case with the correct ramming
tools. It must dry thoroughly before use.
Much of the confusion over the potassium nitrate/sucrose fuel has to do with
the water of crystallization of both the sucrose and the nitrate. For optimum
performance, both materials must be DRY. The water of crystallization is a
diluent which lowers the maximum temperature achieved by the exhaust gases.
With enough water, sucrose and potassium nitrate will "melt" together at room
temperature - but you wouldn't have much of a fuel.
Barry
-----------------
| ___ ________ | Dr. Barry L. Ornitz WA4VZQ
| | / / | | Eastman Kodak Company
| | / / | | Eastman Chemical Company Research Laboratories
| |< < K O D A K| | Process Instrumentation Research Laboratory
| | \ \ | | P. O. Box 1972, Building 167B
| |__\ \________| | Kingsport, TN 37662 615/229-4904
| | INTERNET: ornitz@kodak.com
-----------------
Potassium nitrate/sugar fuel which is made from dry ingredients takes much
higher temperatures to melt. Its performance is quite good. _BUT_, the actual
temperatures needed are only slightly below the autoignition temperature. The
high viscosity of the molten mixture makes it difficult to control the temp-
erature accurately, especially for the home experimenter without access to
fancy (and safe) equipment. An electric skillet is not enough!
As I have said before, there are many other fuels that are safer to use and
make that perform as well. The potassium nitrate and charcoal fuels (with
small amounts of sulfur - much smaller amounts than in black powder) have been
used successfully by fireworks manufacturers for years. Made and loaded while
damp, this fuel is quite safe when loaded with non-sparking tools. Consult
most classic pyrotechnics texts for details. Of course, the finished rocket
engines have to dry before use.
Barry
-----------------
| ___ ________ | Dr. Barry L. Ornitz WA4VZQ
| | / / | | Eastman Kodak Company
| | / / | | Eastman Chemical Company Research Laboratories
| |< < K O D A K| | Process Instrumentation Research Laboratory
| | \ \ | | P. O. Box 1972, Building 167B
| |__\ \________| | Kingsport, TN 37662 615/229-4904
| | INTERNET: ornitz@kodak.com
-----------------
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