A while back I received an email from Harry:

“Have you ever made an ammonium dichromate volcano? They are really popular with parents and teachers and look great daytime or night.”

I responded: “Never learned how to make a volcano. Led a deprived childhood. No way they’re doin’ anything like that in science classes nowadays.”

Making a volcano would, of course, be exactly the sort of school project which would capture the imagination of so many young students.

Harry shot back: “Neat little effect. The ammonium dichromate burns by itself, but you can add other fuels to make more lifelike ‘lava.’ For instance, charcoal 10 or 20-mesh. I imagine there’s some flake titanium, ferro-titanium, etc. that would work as well. You could provide volcano formulas for high school projects.”

Well, I was intrigued. I’ve made 16-inch ball shells and 36-inch girandolas, but never an ammonium-dichromate volcano. I couldn’t let that stand for long. So I asked Harry to send me a few tubs of the ammonium dichromate, and I put it on my to-do list.

In the meantime, I did a little research on the Internet, and also found a couple of paragraphs about the volcano in the Skylighter Project Plans pages.

Warning: So, first off, a bit of a warning: Ammonium dichromate is rated as a hazardous toxic chemical on its MSDS. One should not inhale its dust, but that’s not too tough to avoid since it comes as relatively large orange crystals, not a dust that gets easily airborne.

One should not ingest it. Well, Duh!

One should avoid skin contact. Wear rubber gloves if you’re gonna touch the stuff (which is not necessary to create one of these volcanoes). Avoid eye contact. The stuff can cause cancer.

So, exercise appropriate caution with this chemical. If you’re going to be making a volcano like this for a science fair, perform all actions and experiments with it outdoors, and when the volcano is “erupting” don’t allow anyone to breathe the small amount of smoke and ash, which rises off of it.

Use common sense. I know, I know. Common sense is not in common use nowadays to protect folks from harm. Since everything even remotely dangerous is becoming illegal, folks are increasingly being born with no common sense chip. But, use common sense anyway. There, you see? You got me started.

The scientific stuff: science for kids – old and young

I’m not much of a chemist, but I did find this information interesting, and some other folks might as well.

Ammonium dichromate is sometimes referred to as Vesuvian Fire due to its use in the creation of these small volcano replicas.

Ammonium dichromate’s formula is (NH₄)₂Cr₂O₇.

When it burns, it decomposes according to the following equation:

(NH₄)₂Cr₂O₇ (solid) -> Cr₂O₃
(solid) + N₂ (gas) + 4H₂O (gas)

The gaseous byproducts are simple nitrogen gas and steam, so they are innocuous.

The solid product is chromium (III) oxide. What remains after the volcano burns is this solid, grayish-green ash. The chromium in it is toxic and possibly carcinogenic, so care should be exercised when handling it and disposing of it. Some of this ash flies up into the air when the volcano is burning, so you don’t want anyone close enough to it to breathe the stuff.

The chromium oxide can reportedly be used in a thermite reaction to produce elemental chromium metal, so I’m going to save the chromium oxide ash to try to use it in such a reaction, since I am planning an article on thermite reactions.

A volcano project

I decided to go simple, and make a “volcano” out of a can and heavy-duty aluminum foil. I formed a lip at the bottom of the aluminum foil “cone” to catch the ash as it formed.

I lit the top of the ammonium dichromate with a propane torch, and it burned and created a “volcano” effect, but at times the flame went deep into the orange crystals, down the sides of the can, and propelled some of the crystals up and out of the can, unburnt. I was not completely pleased with the effect that was produced.

So I decided to try a shallow, tuna-fish can, sitting on top of the pop can.

This volcano burned a little better than the first one, but still the flame worked its way down the sides of the can, and the ammonium dichromate did not burn evenly. I still was not satisfied.

I also noticed that igniting the ammonium dichromate with the propane torch was not all that easy. The pressure of the propane blew the crystals out of the way of the flame, and although some of them eventually lit and initiated the desired continuing reaction, the pile did not ignite right at the top of the heap.

So, I decided to try something really simple. I made a “tray” out of flat aluminum foil with the edges turned up to catch the ash. I poured a cone of about a half-pound of the ammonium dichromate in the middle of the foil tray, and inserted a 6-inch length of Visco-fuse into the middle of the pile of orange crystals.

Once the Visco fuse burnt down into the cone of crystals, they ignited and a nice volcano-action formed and burned until only ash remained.

Well, then I thought that the way to get this baby really looking like a volcano, but still burn like it did in this last test, was to form the aluminum foil over the cans, but not cut the opening. I just piled the ammonium dichromate on top of this “mountain” on the flat section and inserted another piece of Visco.

I was really pleased with how this volcano looked and performed.

I think it almost looks like the real thing with glowing, flaming lava flowing down the side of the Mt. St. Gorski.

Making model volcanoes this way uses about 1/4 pound of the crystals per volcano.

Nighttime volcanoes

I thought I’d make a few other versions of the ammonium dichromate volcano at night.

For the first one, I repeated the procedure I followed in the last daytime test. This looked pretty cool as the “lava” burned and flowed down the sides of the “mountain.”

Honestly, I like watching the volcano better in the daytime when I can see the greenish ash being formed and flowing down the sides of the hill.

For the second nighttime volcano, I did the same as above except I stirred in a tablespoon of 36-mesh charcoal to see what sort of effect that would produce.

As this volcano burned, a lot of orange, charcoal sparks rose up into the air above it, creating an effect that was different than the standard, ammonium dichromate-only volcano.

For the third nighttime test, I mixed in about a tablespoonful of medium flake aluminum, and for the fourth and final test I added about a teaspoon of fine spherical titanium.

The addition of these metal fuels seemed to slow down the burning reaction, and did not produce the silver-white sparks, that I was half-expecting. There was an interesting, different sort-of molten flowing effect, as the reaction seemed to almost melt the ammonium dichromate and metal together, causing molten “lava” to flow down the mountain.

As a last offering to the pyro-gods, I simply poured about a half-pound of the ammonium dichromate onto a bare patch of ground and lit it with the propane torch.

This caused the little volcano crystals to ignite from the sides and burn toward the center, and this was probably my favorite effect of the night. (After it, I had to get a shovel and completely clean up the green ash from the area.)

Conclusion

This was a fun little science project. I saved some of the ammonium dichromate for when my grandkids visit, and I’ll introduce them to something they’ll probably never have the chance to see in science class. And there’s enough left to show them how to make a school project volcano just in case that time comes.

I learned something today working on this model volcano, and that’s never a bad thing.

Take care and have fun,

Ned

How to Make a Model Ammonium Dichromate Volcano is a post from: Confessions of a Fireworks Man

Do you really know what those particle sizes really mean? What is really being described? When they say "-325 mesh" and "22 micron", what’s the difference? And why does it matter to you?

Well it can definitely help you to know how the particle "size" ratings get assigned to metal powders. Most of the size ratings come directly from the wholesaler or manufacturer. But every so often we buy surplus materials which may not come with any additional information about the manufacturer, the size or shape of the powder. Recently, we received a surplus lot of magnesium powder, including several drums with almost no information available from the seller. Before we can sell it to you, we need to be able to tell you what it is, so you can figure out if it suits your purposes.

The first step in the identification process is a visual inspection. You may be surprised how much you can tell about a sample just by looking at it. By observing the flow characteristics of a powder, and how it feels between your fingers, you can approximate particle size and shape. If you have experience with metal powders, for instance, you can often tell if a sample is granular (rough feeling), or atomized (round particles, feels smooth, pours and flows quickly and smoothly). If you cannot feel any particles between your fingers, you can assume the powder is probably finer than 200 mesh, or even less than 325 mesh (written as "-325 mesh.")

The next step is to verify those assumptions through quantitative and qualitative testing.

To determine if a material is appropriate to be used in a given formula you’ll need to know the particle’s shape (morphology), size, and distribution (granulometry). Shape is easily determined under a microscope and classified as atomized (spherical or spheroidal), granular, or flake.

Particle size is reported in one of two ways: either by mesh size (large and medium particles, generally larger than 325 mesh) or by microns (very small particles).

Why use two measurements?

US mesh size describes the number of openings per inch in a screen. So if a material is listed as -60 mesh it will all pass though a 60 mesh screen (the minus sign in front of the 60 means that all particles are smaller then 60 mesh). Conversely, if the material is described as +60 mesh, it would mean that all particles would be retained on a 60 mesh screen and are therefore larger than 60 mesh.

But mesh sizes can only go so far. After a point the individual wires that make up the screen are so close together it is no longer practical to measure using screens. In practice, particles smaller than 325 mesh are usually described in microns. A micron is one thousandth of a millimeter, or one millionth of a meter. The unaided human eye can see particles of about 40 microns. Smaller than that, you need magnification.

There is no truly accurate conversion from mesh size to microns, because the wire thicknesses in screens vary all over the place. But approximate conversion tables are commonly used anyway. (In the table below, screen sizes of smaller than 600 mesh are shown, even though they don’t exist in practice.)

"Mass fraction analysis" is used to determine large-to-medium size particle distribution in a sample. The powder is sifted through a set of nesting screens, each with progressively smaller openings (higher mesh numbers). By measuring the percent of material that remains on each screen, we can classify a material by its size distribution.

If you were to sift Skylighter’s #CH2080 Magnesium-Aluminum (described as 180-325 mesh) through a stack of 180 mesh, 200 mesh, and 325 mesh screens, a mass fraction analysis yields a particle size range that looks like this:

If the 180 mesh size was critical to your firework formula, you can interpret this to mean that 26% would remain on the 180 mesh screen (larger then 180 mesh) and 74% would pass through it (be smaller than 180 mesh).

Mass fraction by sieve analysis is a very helpful method of classifying coarse-to-medium particles, but what about the really small stuff?

When the average particle size is around 50 microns, sieve analysis is no longer practical, and doesn’t adequately describe the particle sizes. Several methods are commonly used to measure really fine stuff: gravitational sedimentation, laser light diffraction, optical light microscopes, scanning electron microscopes (SEM) and transmission electron microscopes (TEM). The most accessible method to an amateur is an optical light microscope.

So how is a particle measured with a microscope? Do you need some kind of tiny ruler? As funny as that might sound, that’s exactly how it’s done. The microscope can be fitted with a gizmo called a reticule micrometer. After it is calibrated, it can be used to measure the size of individual particles in a powder sample right down to 1 micron.

But just because you can measure it doesn’t mean it’s a simple task.

Sure, measuring spherical material is fairly straightforward. After all, you’re really just measuring the diameter of little balls. But what about flake, granular, and spheroidal samples? Digital imaging and software can drastically decrease the time needed to perform measurements and reduce error rates. But it appears that most if not all of the automated equipment measures any particle shape as if it is spherical. Because of this, there is not really a standard method for assigning a particle size.

Selecting the method seems to be based mostly on what you’d like your results to state. Below is an imaginary particle and three circles representing different measurement methodologies.

In the first example the measurement is across the smallest dimension of the particle. This method might be used to describe the particle in terms of its reactivity by describing the particle in the smallest possible size. Method B might be used conversely—to describe the particle’s largest dimension. Arguably the most accurate methodology would be using example C, where an average size is calculated.

No matter what method is used, the results would normally be presented to you, the buyer, as an average size (3 micron), a particle range (3 to 15 micron) or a frequency distribution (30% <5 micron, 10% 5-10 micron, 60% 10-15 micron), or some variation thereof.

So why does particle size or shape matter?

Many amateur fireworks makers only consider particle shape and size when a formula calls for a specific material. Even fewer consider particle size distributions. The shape and size of a particle has a huge impact on its reactivity. Flake particles have a large surface area that can be in contact with an oxidizer when compared with a spherical particle. Granular particles often have sharp edges that can ignite more easily than the smooth, round edges of an atomized powder.

Selecting powder with a different particle size or shape can create a wide variety of changes in the pyrotechnic effect, from hang time of a spark to delay of strobing. Even controlling the burn time can be accomplished by altering the particle size and shape.

Look what happens when we change particles in a real example.

The glitter formula below calls for -325 mesh spherical aluminum. Skylighter sells 3 aluminums that are -325 mesh spherical. One is further described as 5 micron (CH0100), one is 12 micron (CH0103) and another is 22 micron (CH0105).

Using the 5 micron aluminum did not produce a usable glitter. Instead it produced a bright star with an unattractive, dense, short-lived flitter-like tail. This aluminum was simply too reactive and started burning both in the flame envelope as well as after, creating poorly defined flashes.

The 12 micron aluminum produced a wonderfully dense, but short tail of fairly evenly-spaced flashes. Because the particle size distribution was within a fairly small range (mostly 6-18 microns), the glitter effect appeared fairly closely behind the star.

The 22 micron produced the best effect of all, creating a long tail that maintained good distribution of flashes over its entire length (with a few long delay pops). The 22 micron contains particles over a very wide range with most particles appearing between 5 to 38 micron.

It is clear from the results of the test above that tracking the average particle size and shape may not be enough to reproduce a specific effect, tracking the particle size distribution (if you know it) may also be worth noting in your formula book.

Brian Paonessa
Skylighter, Inc.

For more information see:

Mesh Sizes and Microns
Skylighter Fireworks Tips
November 26, 2002 — Issue #44

Metal Particle Shapes: What They Mean

Skylighter Fireworks Tips Newsletter
December 2, 2005 — Issue #68

How Particle Size & Shape Is Defined is a post from: Confessions of a Fireworks Man

The Problem:
Electric matches made using Skylighter’s Electric Match Dip Kit (GN5050) and Electric Match Blanks (GN5040) put out a good amount of fire and can directly light visco fuse when connected end-to-end. Visco fuse is the green fuse used in most consumer fireworks (it is also called cannon fuse).  But just taping the electric match to the visco fuse is not 100% reliable, so the connection technique you use is critical. Here’s a little trick that works quite well for me when connecting electric matches to visco fuse and has given me 100% ignition so far.

Materials needed:

• Consumer fireworks
• Electric matches ("ematches")
• Roll of clear packing tape or masking tape.
• Roll of quickmatch (GN3001) or Super-Fast Firecracker Fuse (GN1205)
• Razor blade

Assembly:

Cut visco fuse at an angle. Cut the firework’s visco fuse on a sharp angle (as seen in figure A). This will expose more of the fuse’s black powder core. If your device comes with a long visco fuse attached, you may want to cut it down to about an inch to reduce ignition delay.

Figure A:
Cut visco fuse at an angle

Create a quickmatch sleeve. Using a razor blade, cut a length of quickmatch about 1 inch longer than the fuse supplied with the consumer firework device.

Note: It’s best to cut quickmatch with a razor blade or anvil cutters. Quickmatch can ignite from the friction of scissors cutting through it.

Slide quickmatch over device’s fuse. Carefully slide the device’s fuse into the center of the quickmatch sleeve. Slide the quickmatch sleeve all the way down so it covers the firework’s entire fuse.

Figure B:
Slide quickmatch over fuse

Insert electric match into quickmatch. Outside and away from people, hold the device so it is pointing away from you and any flammable material. Insert an electric match into the open end of the quickmatch to a depth of an inch (as in Figure C). You may need to slide back the electric match’s protective plastic cap.

Note: Removing the electric match’s protective cap may make inserting the ematch easier, but can cause ignition by friction. Insert the ematch’s head slowly and gently.

Figure C:
Insert electric match

Tape quickmatch, and electric match to device. Secure the electric match to the side of the firework with clear packing tape covering both ends of the quickmatch, as in Figure D. Add a couple of extra wraps of tape to secure the electric match in place.

The tape serves two purposes:
1) It confines the burning gasses, increasing the burn rate.
2) It secures the ematch in place.

Tip: If you’ve never done an electrically fired fireworks display, just imagine people moving about in complete darkness with dozens of wires all around. It’s inevitable that if you don’t completely secure each and every electric match someone will trip on "that" wire and pull the electric match free causing a misfire.

Figure D:
Tape electric match in place

How does it work?
When the electric match fires, the ematch sparks for only an instant. If the ematch sparks and fire do not directly hit the visco’s black powder core, the electric match may fail to ignite the firework device. The blackmatch inside the quickmatch sleeve prevents this problem by carrying the fire forward, and increasing the amount of fire given to the visco fuse. This ensures that the slightest spark from your electric match will pass fire to the visco. The quickmatch’s outer paper wrap directs the fire downward through the tube like a flamethrower, lighting everything in its path, including the visco.

"But, I live too far away to pick up quickmatch…"
Having quickmatch on hand does make this process faster, but all you need to make this work is blackmatch and a homemade tube to direct the fire. Skylighter’s GN1205 is a great source of blackmatch, unless you want to make your own.

What is GN1205, Super-Fast Paper Firecracker Fuse?
Well it’s our fastest, shippable fuse. It burns at 1 foot per second! It consists of 3 strands of blackmatch with a light tissue paper wrapping. This tissue paper wrapping gives it a controlled fast burn great for chaining candle batteries, adding leaders to homemade festival balls, even chaining up your finale.

Harvesting blackmatch from GN1205. Gently peel the tissue paper off of the Super-Fast Firecracker Fuse as shown in Figure E.

Figure E:
How to remove blackmatch from Super-Fast Firecracker Fuse

Make a thin walled tube. You’ll need a thin walled paper tube to hold the blackmatch, visco and electric match all in place. For this cut a 3 x 3 piece of copy paper, and roll it on a 3/8th inch dowel or anything about that diameter (a Bic pen works well). Use glue or tape to keep it closed.

Insert blackmatch into thin walled tube. Insert 6 strands of blackmatch into a thin walled paper tube (as seen in Figure F). If the blackmatch is long, cut it flush.

Figure F:
Insert blackmatch into tube

Connecting Electric Matches to Visco (Cannon) Fuse is a post from: Confessions of a Fireworks Man