Homegrown Oxidizers Part One
WSM

Not all of us live in an area friendly to fireworks. Access to these articles of celebration, let alone the materials to produce them may be extremely limited if not completely banned. Reliable information to produce fireworks raw materials is very difficult to find and even consulting professional chemists usually yields little useful information (unless they happen to work in the chlor-alkali industry).

In these articles we’ll try to describe some workable methods of producing fireworks raw materials on a small (hobbyist) scale.

The first material discussed is potassium chlorate. Industry typically produces potassium chlorate by starting with sodium chloride (table salt) and water from which is made sodium chlorate. The solution of sodium chlorate is mixed with a solution of potassium chloride and potassium chlorate (being much less soluble at room temperature) drops out of solution, is washed, dried, powdered and packaged.

With a proper setup, it’s possible to make potassium chlorate directly from potassium chloride and completely avoid any sodium contamination.

Fundamentals

Pyrotechnists generally are concerned with the breakdown of molecules to get the required elements combined in the burning devices to produce the desired effects. To produce the raw materials desired, we need to build up the molecules. This is typically done industrially with electrochemistry.

Electrochemistry uses direct current electricity in solutions of salts to create desired changes in the solutions. Examples of this are electroplating (depositing metals on other materials), electrowinning (getting pure metals from solutions), and anodizing (forming a strong protective oxide layer on aluminum). In our case we are starting with saltwater and producing an oxidizer salt.

The mixture of salt and water (potassium chloride solution in this case) is changed by current through the electrodes by essentially breaking the water down to it’s elemental components, hydrogen and oxygen, driving the oxygen onto the chlorine ions (salts in solution become an ionic mixture) at the anode and the hydrogen collects at the cathode where it bubbles off and out of the solution.

Many amateur chemists have made chlorates successfully using graphite for the anode (positive electrode) and iron or stainless steel for the cathode (negative electrode). Although graphite works, it has drawbacks and limitations to its use. One of the most notable is that it breaks down, leaving a black sludge in the chlorate cell that needs to be removed from the final product before it can be used. Graphite works best at lower temperatures or this breakdown is accelerated.

The state of the art in industry for over 40 years uses a titanium anode coated with MMO, or Mixed Metal Oxides. MMO is a mixture of titanium dioxide and various precious metal oxides such as ruthenium dioxide, iridium dioxide and others in varying amounts to improve the electrical and physical characteristics of the coating.

MMO has some distinct advantages over graphite as an anode:

• Though not physically tough, it is extremely electrically and chemically tough if certain contaminants are absent
• It can operate at much higher temperatures, improving current efficiency (CE)
• It produces a “clean” product requiring minimal processing to be ready for use
• It can operate in a cell for years, where graphite will only last for a month or so
• Though more expensive initially, MMO is more cost efficient due to its longevity
  

Due to the wide use of MMO in industry, new material and surplus stock is available to the amateur electrochemist at reasonable cost.

MMO on titanium anodes come in many shapes, configurations and sizes (as well as formulations). For the purpose of these articles we’ll ultimately discuss the use of an MMO coated titanium mesh anode and titanium sheet metal for the cathode (or cathodes) in the description of a workable amateur chlorate cell.

Where Do We Start?

Most budding electrochemists locate a source of electrodes and develop their system around them. I suggest a better approach is to locate an electric power supply and design the system around it. The best electrical practices dictate that the electrodes demand no more than 80% of the supply’s available current. Less is okay but more tends to overwork our power supply and can lead to premature failure. So what we suggest is get a power supply and tailor the entire system to it.

Our power supply needs are:

• A steady source of “clean” DC power (little or no AC components, AKA ripple)
• Get as high a current output as you can afford (typically, the higher the current output, the more expensive the power supply)
• A variable DC power supply is excellent, especially for experimenting with various setups and conditions, but these tend to be very expensive unless a fortunate find on eBay or an electronics surplus house drops in your lap
  

• For chlorate a minimum voltage of 2.5 Vdc (volts direct current). Industry usually specifies 3.6 Vdc but we’ve successfully used up to 5 Vdc without problems
• Though we’re discussing voltage, the main component of power is the current. Current (measured in Amperes or Amps) is the main influence in our process and the real workhorse. The voltage only needs to be enough to keep the system working. More on the electrical theory later…
  

Many amateur electrochemists have converted computer power supplies to the task and despite the universal availability of them; this author has never used one. Another option, if one has the electrical or electronic know how, is to rewire a microwave oven transformer to supply low voltage Vac (volts alternating current), rectify the output to Vdc and filter the output to remove AC components to yield the required clean DC power.

As most computer power supplies output 12 Vdc and 5 Vdc (our interest is the 5 Vdc portion) and are capable of supplying 30 Amps we will discuss a simple chlorate cell using these parameters.

The chlorate cell information shown can be scaled up or down but scaling up will get more complicated and require tighter control of the minute details of the system. To start, by all means, let’s keep it simple…

Getting Started

We have a power supply (5Vdc, 30 A), now we need the rest of our setup. At a minimum, we need a cell body and the electrodes. The cell body or reaction chamber needs to be compatible with the materials that it’ll be exposed to and secure enough to contain them without spilling or breaking.

In the process of converting salt water to chlorate the steps include hypochlorite (bleach) and hypochlorous ions, with chlorate as the next step. The actual chemistry is quite complicated with many changes happening simultaneously and all affected by each other and a multitude of other factors. These processes have been the subject of scholarly doctoral dissertations but we’ll simplify it with descriptions of practical applications and rules of thumb to be successful (even if we don’t completely understand what’s happening we can still make it happen,… and optimize our yield).

The Reaction Chamber (RC)

Few materials are compatible with our cell but fortunately some of them are common and fairly inexpensive.

• Glass (some but not all will work)
• PVC plastic
• CPVC
• Teflon or PTFE
• Kynar or PVDF
• Viton rubber
  

Typically these materials and similar are completely inert to the cell liquor we’ll create. Other materials can be used but may experience some degradation unless precautions are taken to prevent it (or they’re deemed to be acceptable losses).

• PE or polyethylene
• PP or polypropylene
• XLPE or cross-linked polyethylene
• Silicone rubber
  

With few exceptions we’ll avoid metal containers. For example, some metals would be useful for one of the components but unsuitable for the intermediates.

Glass is attractive because one can see what’s happening in the cell. Seeing is educational when starting out but not required for the process to function correctly (industry uses completely opaque cells, for example). If temperatures are kept in check, PVC is the least expensive option for a reaction chamber. We’ll discuss this more, later.

The author’s first successful chlorate cell was a one gallon glass pickle jar with a 4” PVC pipe cap used for a lid and three holes drilled in the lid for 1) a vent, 2) the anode, and 3) the cathode.


The setup was not ideal and a lot of lessons were learned in the process, but it made several kilos of potassium chlorate crystals that summer. The first run didn’t produce much chlorate but after recharging the depleted liquor with potassium chloride, subsequent runs produced a lot more.

The reason the yield of the first run was small is the bulk of the energy went into creating the precursor ions (hypochlorite and hypochlorous, as well as chlorate) which stays in solution. Once the precursors are developed in the initial run and the liquor is charged with a new batch of chloride, the following runs produce more chlorate and right away.

The anode was an MMO coated CP (commercially pure) titanium rod from a commercial source. The cathode was a CP titanium tube. The spacing wasn’t ideal, the vent was minimal and the power was low, all besides no controls and low efficiency (maybe 40%-50% at best), BUT… it made lots of potassium chlorate.

It should be mentioned, only potassium chlorate was ever produced (the author has yet to bother with sodium chlorate since the potassium salt was the end goal). The whole notion of making potassium chlorate began with the discovery of the availability of potassium chloride water softener salt at the local hardware supply store.

Several problems were noted during those initial runs many years ago:

• Lots of salt crust (salt creep) forming around the lid and around the electrode holes
• The electrode spacing was not optimized
• The electrode sizing wasn’t optimized either
• The power supply was under utilized
• Salt creep affected the electrical connections adversely
• The power connections to the electrode leads (alligator clips) were inadequate for the job
• No cell parameters were measured or controlled
  

The whole thing was a rough attempt… but successful!

Since that time, the author has come a long way and overcome these issues. We will show methods and techniques in an attempt to help the novice electrochemist bypass a lengthy and difficult learning curve to successfully build and operate an effective and efficient chlorate cell.