DE2115427A1 - Corrosion inhibitors and methods of preventing the corrosion of metals - Google Patents

Description

DR. Ic. P (.1SCHFNRIEDFP. Oaae P, 446

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Albright & Wilson Limited, Oldbury near Birmingham, Warwickshire, UK

Corrosion inhibitors and methods of preventing the corrosion of metals

The present invention relates to corrosion preventive agents of the type that are used in low concentrations (e.g., those from 1 to 100 parts per million) can be added to aqueous systems to improve the Prevent corrosion of metals exposed to attack by water. Such inhibitors are used, for example, for the treatment of industrial cooling water systems.

Substances that have heretofore been used for this purpose include certain chromates. The chromates however, have one serious drawback: their toxicity. As a result of this, chromates can only apply to a limited extent. A thing The present invention now consists in developing an agent which is effective as a corrosion inhibitor

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At the same time, however, it is free of chromates and is considerable is less toxic than chromate-containing inhibitors,

It has now been found that from the numerous compounds * which have previously been proposed as corrosion inhibitors and are relatively ineffective have been found * two connections protrude, which can be mixed together to form an agent that has a surprisingly synergistic effect Has corrosion inhibitor. As it was found aeetodiphosphonic acid and zinc sulfate can be used together can be used to effect a synergistic inhibition of corrosion. The mixtures unfold their technically satisfactory prevention of corrosion in the absence of chromates and are proportionate non-toxic.

Accordingly, the present invention relates to a corrosion preventive Agent that is essentially chromate-free and made from acetodiphosphonic acid or an alkali or ammonium salt thereof and consists of zinc sulfate.

The present invention also relates to a method for preventing the corrosion of metals exposed to attack are exposed to corrosive aqueous systems, and this method consists in adding to the water an amount of the agent of the present invention sufficient to prevent corrosion.

Aeetodiphosphonic acid, hereinafter referred to as "ADPA ¹ *, for short, is usually assigned the formula CH-» C.0H (P0, H _o ) _o . It can be obtained by reacting phosphorus trichloride with excess acetic acid

109844 / Ϊ794

and subsequent steam distillation of the reaction product can be produced or also by the action from acetyl chloride and / or acetic anhydride to phosphorous acid. According to the teaching of the present invention as a free acid or as a water-soluble salt, e.g. as a tri- or tetrasodium, potassium or ammonium salt can be used.

The synergistic interaction can be determined within a wide range of mixing ratios. In general, the agents according to the invention can contain 5 to 75 percent by weight, preferably 10 to 60 percent by weight and for example 20 to 50 percent by weight ADPA or a salt thereof and 20 to 95 percent by weight, preferably J> 0 to 85 percent by weight and for example 40 to 80 percent by weight zinc sulfate, and the remainder, if any, may consist essentially of water-soluble, essentially non-toxic, chromate-free corrosion inhibitors, sludge dispersants, or other conventional ingredients of anti-corrosive agents. It has been found that particularly effective agents can be obtained by adding a small amount, for example from 2 to 20 percent by weight, of a copper corrosion inhibitor such as sodium mercaptobenzotriazole, benzimidazole or benzotriazole.

In addition, a sludge dispersant, such as tannin, or a polyelectrolyte, such as polyethyleneimine, and / or a lignosulphonate, e.g. calcium ligninsulphonate, may be present. Preferably they are ADPA and the zinc sulfate are present in substantially equal amounts.

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The compositions of the present invention can be added to aqueous systems at concentrations of from 2 to 100 parts per million, preferably from 5 to 50 parts per million, most preferably from 10 to JO parts per million, e.g. from 20 to 27 parts per million , can be added. The ADPA is preferably present at a concentration of from 2 to 30 parts per million parts, more preferably from 5 to 25 parts per million parts, for example from 10 to 20 parts per million parts. The zinc sulfate is preferably present at a concentration of from 5 to 40 parts per million parts, most preferably from 7 to 30 parts per million parts, for example from 10 to 25 parts per million parts. According to a preferred embodiment of the invention, sodium mercaptobenzotriazole, hereinafter referred to as NaMBT for short, is also present, in an amount of 1 to 5 parts per million.

The present invention will now be illustrated by the following examples. Water, which has a p " of 7.55, is circulated at 25 ° C. for 96 hours over mild steel pipe samples in the presence of sprues (coupons) made of aluminum, cast iron and copper. The total weight loss of the mild steel samples was determined. Assuming that the metal had been removed evenly over the entire exposed surface of the sample, the penetration depth was calculated in mm / year. The results are compiled in the table below.

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example Additive ADPA concentration
(Parts per
Million parts) penetration
in
mm / year Comparison
attempt ADPA 46.7 ti ADPA / ZnSO. 25th 12.2 dd ADPA / ZnSO ^ 5 42.9 1. ADPA / ZnSO ^ / NaMBT
ADPA / ZnSO ^ / NaMBT 25/25 8.4 2. 5/20 8.5 3.
4th 5/20/2
10/10/2 7.7
4.6

In the abbreviations used, ADPA means acetodiphosphonic acid and NaMBT means sodium mercaptobenzotriazole.

109844/1794

Claims (2)

Claims W Chromate-free, corrosion-preventing agent, thereby characterized in that it is made from a combination of acetodiphosphonic acid or a salt thereof in an amount of preferably 5 to 75 percent by weight, e.g. 10 to 60 percent by weight, with zinc sulfate in an amount of preferably 20 to 95 percent by weight, e.g. 30 to 85 percent by weight, and optionally a corrosion inhibitor for copper, such as sodium mercaptobenzotriazole in an amount of preferably 2 to 20 weight percent with the remainder, if any, of essentially non-toxic, chromate-free corrosion inhibitors, sludge dispersants, or others conventional constituents of anti-corrosive agents. 2. Method of preventing corrosion of metals exposed to the action of corrosive aqueous Systems are exposed, characterized in that the corrosive aqueous system 2 to 30 parts per million parts of acetodiphosphonic acid or a salt thereof, 5 to 40 parts per million Zinc sulfate and optionally 1 to 5 parts per million of a copper corrosion inhibitor such as Sodium mercaptobenzotriazole, can be added. 109844/1794