Volatile corrosion inhibitors (VCIs) can efficiently protect a variety of items from environmental attack. Many VCI compounds and compositions are known. This paper describes some of the VCI applications that the authors have witnessed in the last 20 years as well as recently developed corrosion protection systems which are designed to include a combination of inhibitors, desiccants and gases. These new developments increase the efficiency of protection and service life of the material being protected.
More that 20 years of experience with VCI applications makes it possible to design an efficient protection system for ferrous and nonferrous metals
The applications of VCI are very simple in principle. Most of the applications utilize impregnated polyethylene (PE) packaging but a variety of VCI delivery methods have been used [ 1-4].
There exists a need for systems that protect items for a longer period of time than do the well-known current VCI methods. The new methods should retain many of the advantages of the traditional VCI methods. These advantages include self-application of protection as well as almost instant usability of the protected item upon removal from the protection system.
Several VCI compositions with vapor pressures of 102pa (C12 H24 N2 02) to 10+3Pa (C13 H26 NO2), in combination with a gas (N2, pressure > 10+Spa), and a desiccant (CaO, CaC12) were tested. The corrosion rate and surface quality of steel, aluminum, copper and silver specimens were measured. The environment inside the test chamber was as follows:
Chloride - 1.5 mg/m 2 (on test specimen), SO2 - 40 mg/m 3, H2S - 10 mg/m 3, RH - 95-
100%, Temperature: -20°C to +55°C.
RESULTS AND DISCUSSION
Figure 1 shows the relationship between the corrosion protection radius and the vapor pressure of the inhibitor. Below it is the relationship between the vapor pressure of the VCI and the estimated service life of the inhibitor [ 1,2].
A combination of VCI's having a combination of low and high vapor pressure VCI's is probably best in most cases .
Figure 2 shows efficiency and corrosion rate as a function of concentration of VCI and as a function of time after application of the VCI. The concentrations of the VCI, as well as the length of time following application of the VCI, are important variables that must be taken into account when designing a particular VCI system.
The corrosion protection (CP) mechanism depends on the VCI compound (s) used and the characteristics of the metal being protected. These kinds of tests are useful for choosing a suitable CP system for protecting different metals (Figure 3).
The system used in the present study makes it possible to decrease inhibitor concentration, increase the radius of protection and extend the useful life of many metallic and nonmetallic objects. In addition, the protection of metals such as silver, gold and their alloys as well as nonmetal such as precious and semiprecious stones and minerals can be effected. The qualities that are preserved in these cases are ones such as electrical resistance, tarnish (brightness) and color.
Silver is not usually protected from environmental assault . Usually the surfaces are renewed using special washing solutions or by using an abrasive paste. Some alternative preservation methods have been developed to protect decorative silver objects as well as silver for electronic applications.
VCI plastic films, powder, tablets, vapor capsules, and their derivatives are well known. VCIs offer a pathway for reducing ferrous and nonferrous metallic corrosion. However, VCI's have had limitations in s