Reprinted from the ACJ - October, 1992
The "Merc Index" for chemical classification states that it acts as a deodorant and a disinfectant, preserves wood, cleans metal, etches quarry stone and helps in treating ulcers. It slices, dices and makes mounds of coleslaw just as easily. Irving Sax, in the "Hazardous Chemical Desk Reference" states it is a poison, a mutagen, a teratogen, can cause dermatitis and gastrointestinal problems. With such disparity, it could be penicillin or it could be bubonic plague. What the devil am I talking about? Zinc chloride.
Liquids, powders, pastes—chances are, you can probably see a zinc chloride flux right now from where you are reading this magazine. Since the beginning of time, give or take an eon, zinc chloride fluxes have been the most widely used, best accepted and most practical soldering fluxes available. They are inexpensive and very effective, which is probably why they are still the standard, even today.
Zinc chloride (abbreviated as ZnC12) is usually found in conjunction with ammonium chloride and a small amount of wetting agent when compounded into a flux. Both zinc chloride and ammonium chloride are excellent reducing agents and clean metal very efficiently in the temperature range necessary for soldering.
This affinity for capturing oxygen means ZnC12 fluxes will pull oxygen not only from metal, but also from many sources such as your lung tissue, mucous membranes and skin tissue. So, some amount of caution should be taken when using ZnC12 fluxes.
A somewhat unique feature of ZnC12 is its hygroscopic nature. Dry ZnC12 crystals have a very strong desire to attract water. This ability to pull water from the air is probably very familiar to you, especially if you have ever left a jar of powdered ZnC12 flux open, only to return to a flux brick, or worse yet, a jar of flux soup.
This desire for water adds another hazard to the moist body tissues we discussed earlier, as ZnC12 will dry out most body parts in short order. As is the case with most chemicals, hygiene is the key to safe use.Zinc chloride, ammonium chloride as well, can get into your body by inhalation and by ingestion. Skin absorption into your blood stream is unlikely, but skin contact is a concern as we will discuss shortly. Avoiding inhalation of ZnC12 or the other flux components can be accomplished fairly easily. The flux fumes generated during soldering will be taken up the local exhaust system you installed, after reading last month's column, to handle leaded solder fumes.
If you didn't rush right out and install an exhaust system, or if circumstances make local exhaust impractical, half mask respirators do an excellent job of capturing flux fumes. Cartridges are available which not only filter out acidic chloride fumes, but are mounted in conjunction with a High Efficiency Particulate (HEPA) type of filter to capture lead and metal fumes as well. So the safety equipment folks are looking out for you.
If you use a powdered ZnC12, a simple OSHA-approved dust mask will do the trick while handling the powder. But realize as soon as the powder melts and vaporizes during soldering, you will need the exhaust or half mask respirator to trap the fumes. A dust mask just won't cut it.
To avoid ingestion of ZnC12, the same rules and precautions stated above apply. It's kind of a two-for-one deal. But ingestion by a secondary means is possible, so let's talk about skin contact.
ZnC12 absorption through your skin isn't likely, but absorption onto your skin is highly likely. This is due to the desire of ZnC12 to be wet. It will cling to the water molecules in the cracks of your skin, and once there, it holds on tight.
Even after several hand washes, some ZnC12 may still be present. It can dry out your hands, sometimes severely, and can be transferred to cigarettes, sandwiches, etc., and ingestion of ZnC12 can occur by this sneaky means. The simple fix for this hazard is to wear impermeable gloves, thus avoiding chapped hands and contamination when handling ZnC12 fluxes.
The hygroscopic nature of ZnC12 also adds a new dimension to the physical hazards around the shop. If flux is left on tool handles, tabletops, doorknobs or spilled on the shop floor (especially powders), it will suck up water and become very slippery. Your boots can track it onto stairways and ladder rungs, setting up a dangerous fall scenario. Routine floor washing and cleaning of spills rapidly will help you avoid injuries.
The aggressive nature of ZnC12 fluxes helps in radiator repair, but also corrodes most metals in record time. If the fumes are not all going out the stack, corrosion may occur around the shop. Occasionally inspect the brackets and/or chains supporting things in your shop for deterioration. This is best done before the roof-mounted exhaust fan falls through the roof of a customer's car. Cleanup around the shop can be done easily with soap and lots of water to dissolve the ZnC12.
For all the good things ZnC12 has done for the world, and ZnC12 fluxes have done for radiator repair, the hazards seem relatively minor and are easily dealt with. Shop exhaust, personal protective equipment and good personal hygiene will go a long way to keeping the zinc chloride on the work piece, off the shop floor, and out of your hair, lungs and skin.
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
JOHNSON MANUFACTURING COMPANY
114 Lost Grove Road / PO Box 96 / Princeton, Iowa 52768-0096
Phone 563-289-5123 or Fax 563-289-3825