Almost all of us are familiar with static electricity because we can see and feel it in the winter. On dry winter days, static electricity can build up in our bodies and cause a spark to jump from our bodies to pieces of metal or other people’s bodies. We can see, feel and hear the sound of the spark when it jumps.
In science class you may have also done some experiments with static electricity. For example, if you rub a glass rod with a silk cloth, rub a plastic comb against a man-made fiber, or if you rub a piece of amber with wool, the glass, plastic and amber will develop a static charge that can attract small bits of paper or plastic.
Static electricity is all around us, especially in the metal and plastic world of the laboratory. Mostly, we can deal with this inconvenience, but when you bring balances into the equation, it becomes tricky.
To understand what is happening when your body or a glass rod develops a static charge, you need to think about the atoms that make up everything we can see. All matter is made up of atoms, which are themselves made up of charged particles. Atoms have a nucleus consisting of neutrons and protons. They also have a surrounding “shell” that is made up electrons. Typically, matter is neutrally charged, meaning that the number of electrons and protons are the same. If an atom has more electrons than protons, it is negatively charged. If it has more protons than electrons, it is positively charged.
Just as the static electricity attracts pieces of paper and plastic, it also attracts metals to one another. This attraction means that a balance which has been calibrated, may weigh differently when say a plastic weighing boat is placed on the platter, The static in the boat will be attracted to the pan and the metal parts of the balance will be attracted to the boat and anything else around it.
A recent study of static electricity present in a plastic weigh boat gave an error of more than 4 grams on a perfectly calibrated, good quality balance. This was a 4 place (0.0001 g) balance, which represents an error of 40,000 divisions. A hopeless situation for weighing.
As many materials are affected by static, such actions as trying to pour powders into a weigh boat on a balance platter can end in disaster as the powder can often be seen to change direction in mid-air and stick to the nearest attracting surface.
There are several options for dealing with the problem of static.
“Static Gun Ionizers”
A simple solution of an Antistatic Gun which generates either a positive charge or a negative charge, depending on if you are squeezing or releasing the trigger. The charges are generated by the excitation of piezoelectric crystals, and by skillful use of the trigger, most static conditions can be neutralized. The Zerostat is cost effective, easy to use, but does have a finite life of approximately 10,000 “Squeeze cycles”. What is more, you have to actively generate negative or positive ions yourself, the unit does not “control” the electrostatic situation, you do.
This is a Polonium 210 element which emits alpha particles (positively charged atoms) which collide with molecules of air, creating a supply of oxygen and nitrogen ions sufficient to neutralize both positive and negative static charges.
They are completely safe as the alpha particles will not pass through the skin, however some people may need to be convinced of that. They are silent, clean and are easy to fit to existing equipment such as balances. They are medium priced, but again, they do decay over time and need to be replaced after a year or so.
The Intelligent Ionizer is an elegant solution to the static problem, however it is more costly than the first two technology examples.
It is an electrically operated DC Corona discharge type. Using high internal voltages, it generates ions with a high parity balance. Completely safe, it is convenient for use in laboratories of all types.
Unlike some electronic solutions, the Intelligent Ionizer does not create a large “wind” or draft, thus reducing the effect on your weighing results of high resolution balances. It is portable, safe, clean and easy to use. It can cover a large area, (up to 700 mm / 27”) away from the unit, making it ideal for laboratories. It has an extremely long life and should not need to be replace in decades, therefore the initial expense can be amortized over a much longer period.