CS236014B1 - Mixed metal corrosion inhibitor for closed water systems - Google Patents

Abstract

The inhibitor according to the invention contains 10 to 30 wt. % sodium benzoate, 0.1 to 5 wt. % 1, 2, 3 benzotriazole, 30 to 65 wt. % alkali metal phosphates, for example disodium hydrogen phosphate, 5 to 25 wt. % sodium tetraborate and 0.001 to 0.5 wt. % caprolactam. It is intended for ensuring anti-corrosion protection and functional capability of closed cooling and heating water systems, the parts of which are made of various types of metals

Description

(54) Mixed metal corrosion inhibitor for closed water systems

The inhibitor according to the invention comprises 10 to 30 wt. % sodium benzoate, 0.1 to 5 wt. % 1,2,3 benztriazole, 30 to 65 wt. % of alkali metal phosphates, for example disodium hydrogen phosphate, up to 25 wt. % sodium tetraborate and 0.001 to 0.5 wt.% caprolactam.

It is intended to provide anticorrosive protection and functional capability of closed cooling and heating water systems whose parts are made of different types of metals.

236 014 Int. Cl. 'C 23 F 11 / Ϊ0

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The present invention relates to a mixed metal corrosion inhibitor for closed water systems. It is intended for metals from which cooling systems or combined cooling and heating systems with circulating water or aqueous solutions are constructed, in particular steel, cast iron, copper, aluminum, lead and tin. Typical examples of such systems are the cooling and heating circuits of motor vehicles. Their individual parts are made of various materials, mainly metal, which are connected directly or by means of non-metallic connectors. The cooling water or aqueous solution is corrosive to the individual parts of the system depending on the type of material, their interconnection and design. The type and degree of corrosion depends on the composition of the aqueous medium, the flow of the liquid, the temperature and the heat transfer. The use of untreated or inadequately treated aqueous solutions causes corrosion on various parts of the system, resulting in corrosion products. Corrosion shortens the life and deteriorates functional properties such as tightness and strength. Corrosion products deteriorate the hydraulic properties, heat transfer and hence heat exchange efficiency. Particularly dangerous are the uneven corrosion of steel and cast iron parts, the local zinc coating of brass exchangers, the pitting of aluminum alloy parts as well as the breakdown of the soldered joints and the local corrosion caused by the operation of electrical macro-cells. Corrosion attack occurs during operation mainly due to elevated temperature and flow, but also in non-operational time at rest under deposits, at the interface of liquid and gaseous phases.

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Water of varying composition is used as a cooling medium, especially in periods when there is no risk of freezing or antifreeze, such as aqueous glycol solutions, all year round or only in winter. If water and aqueous solutions are not treated with corrosion inhibitors, they act aggressively and cause the above mentioned faults. This also applies to pure distilled water or condensate.

Chromates, nitrites, phosphates, silicates, borates, benzoates, monoethanolamine, triethanolamine, mercaptobenzthiazole, benztriazole and the like are known and used as corrosion inhibitors in aqueous solutions. for antifreeze glycol fluids. The disadvantages of the additives used so far are their low activity on some metals, the need for high concentration and poor solubility in theode. The additives do not always allow a smooth transition from the winter season with antifreeze to the summer season with water.

The disadvantages of the prior art in this field are largely overcome by the mixed metal corrosion inhibitor for closed

The aqueous systems according to the invention are characterized in that the inhibitor comprises 10 to 30 wt. % sodium benzoate, 0.1 to 5 wt. %

1, 2, 3 benztriazole, 30 to 65 wt. % alkali metal phosphates, for example disodium hydrogen phosphate, 5 to 25 wt. % of sodium tetraborate and 0.001 to 0.5% by weight of caprolactam.

The mixed inhibitor according to the invention has a high inhibitory activity which, by the synergistic action of all components, achieves more than 95% in condensate, demineralized or distilled water in the tests according to CSN 668910 compared to water without inhibitor. They do not form turbidity or deposits. It can be dosed directly into the system, but also a stock solution of high concentration can be prepared and added in the required amount. Without flushing, the mixed inhibitor can be added to water in a system that was operated with antifreeze glycolovone liquid in the winter season.

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The mixed inhibitor is dosed in water or aqueous solutions of the cooling systems in an amount of 1 to 10 g / ^l and the pH of the treated water is 7 to 8.5. Addition of bromothymol blue alcoholic solution may be used as an indicator of mixed corrosion inhibitor in the circuit. The blue color also indicates that the pH value has not fallen below the critical value. After addition of the constituents, the pH is adjusted as necessary with phosphoric acid. The pH is checked with indicator papers. The inhibitor content can be controlled by the concentration of the phosphate component by a colorimetric method to produce phosphomolybdate blue.

The invention, its applications and effects are explained in more detail below by way of example of a specific embodiment thereof.

Example 1

600 g of a mixed corrosion inhibitor containing 30 wt.% (180 g) of sodium benzoate, wt. % (12 g) of 1,2,3-benzotriazole, 32 wt. % (192 g) disodium hydrogenphosphate, 22 wt. % (132 g) sodium tetraborate, 13.99 wt.% (83.94 g) sodium nitrite, and 0.01 wt. % (0.06 g) of ε-caprolactam.

After stirring the solution, 85% phosphoric acid was added dropwise until the pH reached 8.2. Inhibitory corrosion efficiency of the mixture under laboratory conditions was 98% for steel, 97% for cast iron, 99% for silicon, 98% for brass, Pb-Sn solder for 99%, 100% for copper.

Example 2

The vessel is filled with 10 L of distilled water and 10 g of a mixed corrosion inhibitor containing 20 wt. % (2g) sodium benzoate, 0.1 wt. % (0.01 g) benztriazole, 65 wt.% (6.5 g) mono-sodium dihydrogen phosphate, 5 wt. % (0.5 g) sodium tetraborate, 9.89 wt. % (0.989 g) sodium nitrite, 0.001 wt. % (0, OOC 1 g) of β-caprolactam. After mixing

238 014 checks the pH with indicator papers to be in the range of 7 - 8.5. The solution is poured into the radiator of a motor vehicle. Inhibitory corrosion efficiency of the mixture under laboratory conditions was higher than 95% for cast iron, steel, silicon, brass, copper and solder.

Example 3

3000 L of demineralized water was added to the storage tank and 12,000 g of a mixed corrosion inhibitor containing 10 wt. % (1200 g) sodium benzoate, 1 wt.% 120 g) 1,2,3 benztriazole, 55 wt. % (6600 g) disodium hydrogen phosphate, 23 wt. % (2760 g) sodium tetraborate, 10.98 wt. % (1317.6 g) sodium nitrite, 0.02 wt.% (2.4 g) of β-caprolactam. The solution is mixed with air. After mixing, the pH is controlled and 85% phosphoric acid is added in mls as necessary to achieve a pH of 8.0. By adding 900 ml of a 0.1% alcoholic aqueous solution (20% alcohol) of bromothymol blue, the water becomes blue. The inhibited water prepared in this way is used to fill the cooling systems of motor vehicles - buses, trucks. The blue color indicates the use of treated water in individual vehicles. Corrosion inhibition efficiency fully complies with the requirements of ČSN 668910 Coolants with low freezing point ”as proved by laboratory tests.

Example 4

1000 l of demineralized water or condensate are introduced into the storage tank and a 10% mixed inhibitor stock solution is prepared by pouring in portions 100 kg of a 20 wt. % (20 kg) sodium benzoate, 5 wt. % (5 kg) 1,2,3 benztriazole, 44.5 wt. % (44.5 kg) disodium hydrogen phosphate, 25 wt. % (25 kg) sodium tetraborate, 5 wt. % (5 kg) of sodium nitrite, 0.5 wt.% (0.5 kg) of ε-caprolactam. When all the ingredients have been dissolved by stirring, 85% phosphoric acid is added after the pH has been determined, eg by indicator papers,

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8.0 - 8.5. 3000 ml of a 0.1% solution of bromothymol blue in 20% alcohol are then added and the stock solution turns blue. For engine cooling systems, eg. In the case of motor vehicles, 10% of the volume of the stock solution and 90% of the volume of low evaporator water, demineralized water, condensate and anchors are mixed with the pump in the system. Randomly determine the pH of the indicator paper, not below 7.5. The efficiency of the treated cooling water from the cooling system was checked under laboratory conditions. The inhibition efficiency was higher than 95% and the corrosion values of individual metals complied with ČSN 668 910.

The inhibitory corrosion activity of the mixed inhibitor of the invention was evaluated by control tests under laboratory and operating conditions. Under laboratory conditions, weight loss of metal specimens was determined after exposure in test environments, at dissolution, at 80 ° C and for 7-14 days. The tests were carried out in accordance with ČSN 668910. The values of corrosion losses in distilled water with a corrosion inhibitor were well below the permissible values.

The invention is intended to provide anticorrosive protection and the necessary service life and performance of closed cooling and heating water systems whose parts are made of different metals. In particular, it can be used for cooling circuits of motor vehicles, locomotives, diesel engines, where water is used as a cooling medium.

Claims (1)

BACKGROUND OF THE INVENTION 238 014 Mixed metal corrosion inhibitor for closed water systems comprising 10 to 30 wt. % sodium benzoate, 0.1 to 5 wt. % 1,2,3 benztriazole, 30 to 65 wt. % alkali metal phosphates, e.g., disodium hydrogen phosphate, 5 to 25 wt. % sodium tetraborate, 5 to 15 wt. % sodium nitrite and 0.001 to 0.5 wt. % Of caprolactam. Printed by Moravian Printing Works, Price: CZK 2,40 with operation 12, cl. Lidove milici 3, Olomouc