Corrosion Inhibiting Synergism by Triazoles in Aqueous Multimetal Systems
Authors: O&apos;Neal Cleveland , Borger Richard N. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
A search for inhibitors of steel corrosion by combining benzotriazole and tolyltriazole with other scale and/or steel inhibitors was conducted. These well-known inhibitors of cuprous metals, are compatible with organic phosphonates and sodium molybdate at effective phosphonates and sodium molybdate at effective low concentrations. Each triazole when combined with these compounds exhibits synergistic corrosion inhibition of steel.

Introduction
For many years the cooling water treatment industry has been seeking corrosion inhibitors that do not aggravate environmental problems. Government restrictions on chromium and zinc ions discharged into streams and lakes has intensified the search. Formulations containing these two heavy metals have been the most effective where protection of ferrous metals was desired. Polyphosphates and organic phosphonates have been frequent partners of zinc phosphonates have been frequent partners of zinc and chromium for both scale prevention and corrosion protection.
With one, two, and four metals immersed in simulated cooling water (S.C.W.); we combined benzotriazole and tolyltriazole with sodium molybdate and two organic phosphonates. A rotating-metal-specimen test apparatus ("spinner rig") was employed. The degree of corrosion was determined by the weight-loss method.
The results indicate that inhibition of steel and aluminum by molybdate is enhanced when small amounts of the triazoles are added. The organic phosphonate/triazole combination provides real synergism on steel in the brass/steel system while the high degree of brass protection is maintained. The triazoles, therefore, are great partners for multi-metal protection in aqueous partners for multi-metal protection in aqueous systems.

Background
Benzotriazole and tolyltriazole have been used for many years as corrosion inhibitors for copper and its alloys. In Figure 1 the structures of these heterocyclic compounds are shown. Pertinent physical properties are given in Table Pertinent physical properties are given in Table 1. One sees that the solubility of TT in water is about 1/4 that of BT. There is no correlation between solubility and performance of the two. Note that both compounds are thermally stable at or above 300 degrees C (572 degrees F).
Benzotriazole (variously called BTA, BTZ, and BT) has been studied considerably more than tolyltriazole (TT).