REACTION OF FREON TO REFRIGERATION MATERIALS
Metals
Most of the commonly used construction metals, such as steel, cast iron, brass, copper, tin, lead, and alu- minum, can be used satisfactorily with Freon compounds under normal conditions of use. At high temper- atures some of the metals may act as catalysts for the breakdown of the compound. The tendency of metals to promote thermal decomposition of Freon compounds is in the following general order, with those metals that least promote thermal decomposition listed first:
The above order is only approximate. Exceptions may be found with individual Freon compounds or for special conditions of use.
Magnesium alloys and aluminum containing more than 2 percent magnesium are not recommended for use in systems containing Freon compounds if water may be present. Zinc is not recommended for use with Freon 113. Experience with zinc and other Freon compounds has been limited, and no unusual reactivity has been observed. However, it is more chemically reactive than other common construction metals, so it would seem wise to avoid its use with the Freon compounds unless adequate testing is carried out.
Some metals may be questionable for use in applications requiring contact with Freon compounds for long periods of time or unusual conditions of exposure. These metals, however, can be cleaned safely with Freon solvents. Cleaning applications are usually for short exposures at moderate temperatures.
Most halocarbons may react violently with highly reactive materials, such as sodium, potassium, and bar- ium in their free metallic form. Materials become more reactive when finely ground or powdered. In this state, magnesium and aluminum may react with fluorocarbons, especially at higher temperatures. Highly reactive materials should not be brought into contact with fluorocarbons until a careful study is made and appropriate safety precautions are taken.
Plastics
A brief summary of the effect of Freon compounds on various plastic materials follows. However, compati- bility should be tested for specific applications. Differences in polymer structure and molecular weight, plas- ticizers, temperature, and pressure may alter the resistance of the plastic toward the Freon compound:
• Teflo-TFE-fluorocarbon: no swelling observed when submerged in Freon liquids, but some diffusion found with Freon 12 and Freon 22
• Polychlorotriflororoethylene: slight swelling, but generally suitable for use with Freon compounds
• Polyvinyl alcohol: not affected by the Freon compounds but very sensitive to water; used especially in tubing with an outer protective coating
• Vinyl: resistance to the Freon compounds depends on vinyl type and plasticizer, and considerable variation is found; samples should be tested before use
• Orlon-acrylic fiber: generally suitable for use with the Freon compounds
• Nylon: generally suitable for use with Freon compounds but may tend to become brittle at high temperatures in the presence of air or water; tests at 250 degrees F (121 degrees C) with Freon 12 and Freon 22 showed the presence of water or alcohol to be undesirable, so adequate testing should be carried out
• Polyethylene: may be suitable for some applications at room temperatures; however, it should be thoroughly tested since greatly different results have been found with different samples
• Lucite®-acrylic resin (methacrylate polymers): dissolved by Freon 22 but generally suitable for use with Freon 12 and Freon 114 for short exposure; with long exposure it tends to crack, craze, and become cloudy; use with Freon 113 and Freon 11 may be questionable
• Cast Lucite acrylic resin: much more resistant to the effect of solvents than extruded resin; can probably be used with most of the Freon compounds
• Polystyrene: Considerable variation found in individual samples but generally not suited for use with Freon compounds; some applications might be acceptable with Freon 114
• Phenolic resins: usually not affected by Freon compounds but composition of resins of this type may be quite different; samples should be tested before use
• Epoxy resins: resistant to most solvents and entirely suitable for use with the Freon compounds
• Cellulose acetate or nitrate: suitable for use with Freon compounds
• Delrin-acetal resin: suitable for use with Freon compounds under most conditions
• Elastomers: considerable variation is found in the effect of Freon compounds, depending on the particular compound and elastomer type, but in nearly all cases a satisfactory combination can be found; in some instances the presence of other materials, such as oils, may give unexpected results, so preliminary testing of the system involved is recommended