DE1159731B - Vapor phase inhibitors to protect iron and its alloys against atmospheric corrosion - Google Patents

Description

Vapor phase inhibitors for the protection of iron and its alloys against atmospheric corrosion It is known that with the help of so-called vapor phase inhibitors Can appreciate metals against rust attack. Their effectiveness is due to the formation of a anti-corrosive atmosphere. Because of this special behavior they are mainly used where storage or shipping is required of machines, tools, etc., since they represent the presence of an omnidirectional in an enclosed space to maintain the protective conditions. as proved suitable for this z. B. firmly closable containers made of metal, plastic or wood. Metal foils and paper can also be used as packaging material, Cardboard or fabric covered with wax, rubber, plastics, asphalt or the like Materials are coated or impregnated.

The use of these rust protection inhibitors can in principle can be done in two different ways, once by separating them added to the packaging, for example in the form of tablets or an aerosol, and on the other hand, by using packaging material impregnated with it brings. In both cases, the protective substance passes into the surrounding area as a result of evaporation Atmosphere, which triggers the protective effect against the metal.

The invention describes volatile salts of hydrazoic acid which are useful as vapor phase inhibitors. Volatile salts for the purposes of the invention are those compounds in which the hydrazoic acid is bound to inorganic or organic nitrogen bases. They correspond to the general formula in which R denotes hydrogen which, however, can be partially or completely replaced by aliphatic, alicyclic, aromatic or heterocyclic radicals.

The azides suitable as inhibitors can be built up, for example, on the basis of the following amines: Inorganic: ammonia and hydrazine. Organic: 1. Primary amines: methylamine, ethylamine, isopropylamine, tertiary butylamine, cyclohexylamine, benzylamine, ethanolamine, etc.

2. Secondary amines: dimethylamine, diisopropylamine, dicyclohexylamine, N-methylbenzylamine, etc.

3. Tertiary amines: trimethylamine, N, N-dimethyl-benzylamine, etc. 4. Quaternary ammonium bases: tetramethylammonium, Tetraäthylammoniumhydroxyd, Methylpyridiniumhydroxyd ETC. 5. Heterocyclic bases: piperidine, piperazine, morpholine, etc. Amines with a dissociation constant below Kb = 10-11 are no longer able to form stable azides and are therefore eliminated as salt formers. This also includes all compounds with an amphoteric character, such as. B. acetamide, betaine, etc.

With a few exceptions, ammonium azides are white crystalline substances, all of which are more or less soluble in water. This creates the prerequisite that they guarantee perfect protection against corrosion even if condensation occurs inside the packaging, since it is possible for the inhibitor to pass into the aqueous phase and also to become effective there. In order for the ammonium azides to be able to exert a satisfactory protection even in a possibly acidic environment, the simultaneous one has to . The presence of a more or less large excess of free amine is advisable, since even small amounts of free hydrazoic acid are corrosive. The ratio of the free amine to ammonium azide can of course vary within wide limits, but an excess of 0.1 to 25 "is generally sufficient.

Corresponding to their use as vapor phase inhibitors, the vapor pressure of the ammonium azides at 20 ° C. should not be less than 10-4 Torr ', since otherwise perfect protection against corrosion is no longer guaranteed as a result of insufficient volatility. In general . Such compounds are used which have a vapor pressure between 10-2 and 10-3 Torr. In specially stored cases, however, it may be advisable to use even more volatile substances.

The amount of ammonium azides required for the intended purpose, which is necessary to maintain the protective effect, can vary within wide limits depending on the requirements made and the compounds used. For packaging material, -0, 1- # to 50 g / m 2, preferably 2 to 25 g / m 2, a useful protection, while the vapor concentration, based on the 'space, 0.5 to 500 g / m 3, preferably 10 to 60 g / m3.

To achieve a perfect corrosion protection, it is not necessary to use the pure Ammoniumazide .. Rather, the same success can be achieved when On - moniumsatze whose acid residue should be as a non-corrosive anion, brings together with an alkali or Erdalkaliazid used. Phosphates, oxalates and benzoates, for example, are suitable for this. It is irrelevant whether the starting materials are volatile or not, since in these mixtures in the presence of water, as a result of the establishment of an equilibrium, protective ammonium azide is formed, e.g. B.

(NH4), HPO, + 2 NaN, Na2HPO, + 2 NH, N, The composition of these mixtures should be such that they have a pH of 6 to 12, but preferably 7 to 10, in aqueous solution.

The ammonium azides described here were found to be highly effective Vapor phase inhibitors and show in comparison to the known ammonium nitrites Flawless protective effect even in a considerably lower concentration.

Example 1 BlechstreifenausFlußstahlinderGröße25x50mm were suspended after thorough cleaning in test tubes of about 175 cm3 contents, which were then sealed with a cotton plug. They each contained 25 cm3 of a 0.1 molar aqueous solution of the corresponding inhibitors. The duration of the test was 7 days in all cases, with test conditions being adhered to which enabled a corrosion investigation under changing temperature conditions. For this purpose, the metal strips were exposed to a temperature of 38 ° C. for 8 hours within a 12 hour period and then slowly cooled to about 20 ° C. over a period of 4 hours. The weight loss under these conditions can be seen in the table below. Weight Inhibitor decrease in mg Water .............................. 32.9 Ammonium azide ....................... 1,2 n-butylammonium azide ................ 0.5 Di-n-butylammonium azide ............... 01.9 Tetraethylammonium azide ............. 0.9 Ethanolammonium azide ................ 1.3 Benzylammonium azide .......> ... ...... 0.8 Morpholine azide ........... * ............ 1.6 Cyclohexylammonium azide .. ............. 1.1 Dieyelohexylammonium azide . .......... 0.9 Example 2 The in - results listed in the table below have been obtained under the same terms and conditions as described in Example l 'closer. The salt mixtures were dissolved in 25m3 water. Weight Inhibitor decrease in mg 0.8 g sec. Ammonium phosphate ......... 0.9 0.8 g sodium azide ..................... 0.8 g ammonium oxalate ..... 1.0 0.8 g sodium azide .................... 1.5 g sec.n-butylammonium phosphate .... 0.7 0.8 g sodium azide .................... 3 2 g di-n-butylammonium benzoate ..... 0.8 0: 8 g sodium azide .................... 2.2 g of secondary tetraethylammonium phosphate 0.9 0.8 g sodium azide .................... 2.3 g of ethanol ammonium benzoate ....... 1.1 0.8 g sodium azide .................... 1.8 g cyclohexylammonium oxalate ...... 0.9 0.8 g sodium azide .................... Example 3 The experimental set-up corresponded to the two previous examples, with the difference that, instead of the inhibitor solution, impregnated paper (11 × 17 cm) was examined. This was arranged in the upper part of the test container and did not come into contact with the metal samples. 10 cubic meters of water were used to generate the necessary moisture. Inhibitor weight co # zentra! ion appearance after days increase in mg in g "m- 2 3 1 4 1 5 6 7 after 7 days 1. Dicyclohexylammonium azide 0.1 ++ ++ 1 ++ 13.8 0.5 (b 0+ 0, 3.0 1 to 20 0 0 0 0 0 0 0 0.0 2. Dicyclohexylammonium Nitrite (VPI) 1 ++ ++ ++ ++ ++ ++ ++ 46.2 3 + ++ ++ ++ ++ ++ 21.6 5 G + ++ ++ ++ ++ ++ 19.0 10 and 20 0 0 0 0 0 0 0 0.0 Explanation of symbols: ++ strong rust formation; + Rust formation; (#) Traces of rust; (D stainless.

Claims (2)

PATENT CLAIMS: 1. Use of inorganic or organic ammonium azides of the general formula in which R denotes hydrogen, which, however, can be partially or completely replaced by aliphatic, alicyclic, aromatic or heterocyclic radicals whose vapor pressure at 20'C is not less than 10-4 Torr, optionally in conjunction with excess free amine, as vapor phase Inhibitors for protecting objects made of iron and its alloys from corrosion. 2. Use of ammonium azides according to claim 1, which have been formed from a mixture of ammonium salts with alkali or alkaline earth azides by double reaction.