Introduction

Laboratory studies and case histories have established zirconium as the most corrosion resistant material of construction in many production methods involving organic media. In fact, zirconium plays a pivotal role in production of a wide range of organic materials including formic, acetic, hydroxyacetic, lactic and methacrylic acids, urea, methyl methacrylate, rayon, and various alcohols and phenolic resins. The ability of zirconium to withstand high temperatures and concentrations coupled with the fact that the zirconium ions are colorless allows its use in dye manufacturing and other areas where the color of the final product is critical. Zirconium also appears to be nontoxic and biocompatible.

Corrosion Data

Zirconium has excellent corrosion resistant in most organic media. Exceptions are chlorinated hydrocarbons and organic solutions that contain halogens or halides in the absence of adequate water. Under these conditions zirconium can experience high corrosion rates or suffer from hydriding.

 For corrosion purposes, organic halides can be grouped into three categories. These are water-soluble halides, water-insoluble halides and water-incompatible halides. In the case of water-soluble halides such as aniline hydrochloride, chloroacetic acid and tetrachloroethane, insuring the presence of adequate water or stress relieving after fabrication can significantly reduce the tendency of zirconium to corrode or form hydrides. Water-insoluble halides, such as trichloroethylene and dichlorobenzene are not corrosive to zirconium. Water-incompatible halides, including acetyl chloride, are highly corrosive to zirconium. In each case the presence of adequate water is critical for the formation of the protective oxide layer on the surface of zirconium. Depending upon the solution and operating conditions, the water content needed to maintain zirconium's protective oxide file can be as little as 50 ppm to as much as 2-3%.

Acetic acid

Acetic acid is one of the basic starting materials for a wide range of organic materials. These include acetate esters, acetic anhydride, terephthalic acid, aspirin and other pharmaceuticals. Zirconium is considered the most corrosion resistant material in virtually all acetic acid solutions. As seen in Table 1, the few exceptions include acetic acid containing cupric ions, free chlorine and solutions with insufficient moisture to allow zirconium to reform the protective oxide surface layer. Under highly stressed conditions >650-ppm water is required in acetic acid to prevent stress corrosion cracking. If water addition is not practical, stress relieving may be considered.

Table 1. Corrosion Data for Acetic Acid

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