DK172079B1 - Corrosion inhibitor systems and deicer compsns. - comprising sodium fluorophosphate and/or phosphonic acid deriv. salt - Google Patents

Abstract

Corrosion inhibitor system compr1ses at least one of:-(A) Na fluorophosphate and (B) water-soluble salt of a phosphonic acid deriv. of formula:- RnR'N(CH2PO3H2)2-n where R and R' = alkyl, aminoalkyl or hydroxyalkyl; and n = 0 or 1. Deicer compsn. comprising the above corrosion inhibiting system is also claimed.

Description

DK 172079 B1

The present invention relates to a method for inhibiting corrosion of reinforced iron in ferrous concrete, in particular caused by chloride ions and the like, e.g. corrosion caused by corrosive deicing agents, acid rain and the like. The invention also relates to the inhibition of such corrosion when a deicing agent is also used.

The term "corrosion caused by chloride ions and the like" used in the specification means corrosion caused by e.g. NaCl, CaCl2, other corrosive de-icing agents, or any other products that cause or tend to cause similar corrosion. It also means that systems containing sodium fluorophosphate should not be used to inhibit highly acidic corrosion, such as battery corrosion, since HF can be formed and of course is corrosive.

The present invention also relates to the use of a large number of carriers, such as e.g. gaseous, liquid and solid carriers or diluents, including, for example, but not limited to, deicing agents, sand, solvents, diluents, coatings, paints, emulsions, suspensions, air jet applications and the like, for the corrosion inhibiting system.

The corrosion inhibiting system is one which contains at least sodium fluorophosphate (Na2 PO3F, also known by the name sodium monofluorophosphate).

The invention further relates to a process for the preparation of the corrosion inhibiting systems, methods of using them and the products derived therefrom, which contain at least the remaining amounts of 30 of the corrosion inhibiting systems.

The invention relates in particular to corrosion inhibiting systems for reinforced concrete or iron concrete.

Sodium chloride is widely used as a de-icing agent. Many ways have been proposed to overcome the corrosion problems associated with its use. Eg. For example, the corrosion of reinforcing iron in concrete has been reduced by a prior coating of the reinforcing iron with epoxy before the addition of concrete, or by cathodic protection.

The environment normally reinforced by reinforcing steel by being surrounded by concrete is almost ideally suited to preventing corrosion of the steel. High quality, properly applied, compacted and hardened concrete provides a very alkaline coating of the low permeability steel which protects (passivates) against corrosion 10 and minimizes penetration of corrosion-inducing factors, namely oxygen, water and chloride. However, ingress of moisture, electrolytes and oxygen by diffusion or through fine-grained cracks in the concrete can destroy the passive environment and establish galvanic corrosion cells and eventually destroy the concrete due to the expansive forces provided by the corrosive steel. Chloride salts appear to be the most powerful in providing this type of attack. Concrete structures with lower quality concrete or with insufficient coverage of the reinforcing bars and those exposed to harsh conditions, such as bridge decks exposed to deicing salts, or marine environments, are particularly susceptible to rapid deterioration. The magnitude of this problem and the economic cost of repairing and rebuilding road structures have led to extensive research over the past 15 years regarding the electrochemical behavior of steel in concrete and possible solutions. Past and current research efforts have focused on the importance of factors such as the thickness of the cover, water / cement ratio, coated reinforcement bars, cement inhibitor mixtures, low permeability concrete, etc. in new construction, and monitoring and repair techniques for existing structures. , for example. cathodic protection and membrane coatings.

The low corrosion rate of steel in uncontaminated concrete is due to the formation in the presence of sufficient oxygen of a stable, passive layer of gamma-Fe2 O3 on the steel surface in the high pH environment (12-13). There are two general mechanisms by which this passivating effect can be destroyed: (1) decrease of alkalinity by leaching of basic substances and / or partial reaction with CO 2, and (2) physical and electrochemical action involving chloride. or other aggressive anions. Once the steel's passivity is destroyed, the rate of corrosion increases dramatically with the formation of micro and macro corrosion cells. Oxidation of iron to ferrous ions and formation of oxides 10 occurs at the anode (Equation 1), while reduction of oxygen occurs at the cathode (Equation 2).

(1) Fe - * Fe2 + + 2nd + 02 - »Fe304 (2) 1/2 02 + H2O + 2nd - * 20H"

The anode and cathode regions of the corrosive steel can be widely spaced. They depend on differences in chloride or other anion and oxygen concentrations and are influenced by the pH near the steel / concrete interface.

In Chemical Abstracts, Vol. 102, Abstract No. 189922r, it is stated that a gypsum material 20 can be prepared containing 0.1-5% by weight of sodium monofluorophosphate and does not corrode metal. Gypsum containing 0.1% by weight of sodium monofluorophosphate causes a steel corrosion rate of 0.080 mm per year.

EP-A-0 096 619 describes the protection of 25 metal surfaces in aqueous medium using generally sparingly water-soluble orluorophosphates. A corrosion inhibiting effect of sodium fluorophosphate on metal surfaces is described.

EP-A-0 288 812 discloses replacing sodium sulfate in fluorophosphate detergents for eliminating or reducing the film formed on glass with dishwashing detergents, the film being termed "corrosion".

DE Patent No. 1,771,508 describes the corrosion inhibiting effect of a number of phosphonic acid derivatives on 35 metal surfaces.

It has now been found, according to the invention, surprisingly, that corrosion of reinforced iron in reinforced concrete can be inhibited by the application of a corrosion-inhibiting system containing at least sodium monofluorophosphate, and wherein this substance in contact with water 5 inhibits corrosion of the reinforcing iron; there is nothing in the prior art mentioned above that suggests that a highly effective corrosion protection of reinforced iron in iron concrete can be achieved by simply applying said system to the surface of the iron concrete.

The process according to the invention, which is of the aforementioned kind, is characterized in that a corrosion inhibitor system is provided which contains at least sodium monofluorophosphate and in which the sodium monofluorophosphate in contact with water inhibits the corrosion of the reinforcing iron.

Particularly convenient embodiments of the method of the invention are set forth in claims 2-19.

Generally, at least one deicing agent is also present in the system. Usually at least 50% by weight of deicing agent is present, preferably at least 70% by weight, especially at least 85% by weight and most preferably at least 90%, or even at least 95% by weight, especially when the deicing agent is sodium chloride.

Usually, a deicing agent or deicing agents are selected from sodium chloride, calcium chloride, magnesium chloride and potassium chloride, but it preferably contains sodium chloride.

Generally, at least 0.25% by weight of the corrosion inhibiting system is used. The amount is, of course, to some extent dependent on the amount of deicing agent (and any other materials) that may be present. Preferably, the amount is less than 10% and especially from 2 to 5% by weight.

As noted above, the corrosion inhibiting system contains sodium fluorophosphate. A particularly useful de-icing agent is one which, as a corrosion inhibiting system, contains 3 ± 0.5% by weight of a sodium fluorophosphate system.

It is also possible to use a water-soluble salt of a phosphonic acid derivative, especially selected from a salt of triethylenetetramine hexakismethylene phosphonic acid and ethylhexyl-iminobis-methylene phosphonic acid, in the corrosion inhibiting system.

The corrosion inhibiting material may also contain at least one amide of a fatty acid, especially cocosamide. A particularly useful corrosion inhibiting material is one which contains sodium fluorophosphate, cocosamide and a phosphonic acid derivative.

The corrosion inhibiting material may also contain sodium silicate, usually in a weight ratio of sodium monofluorophosphate to sodium silicate of 1-10: 1-2.5, preferably about 1: 1.

The de-icing agent is usually dissolved in a suitable solvent, often in an aqueous medium, and especially so as to form a substantially saturated solution.

There may also be at least one soil conditioner present in the deicing agent.

Using the procedure! According to the present invention, an outdoor surface can be de-iced by placing a de-icing agent used over the surface of the present invention. Preferably, the de-icing agent is mixed with the corrosion inhibiting system and applied over the concrete surface where the mixing and coating is carried out at substantially the same time.

The corrosion inhibiting system can exert influence on the de-icing agent before it is applied over the concrete surface. The deicing agent or the corrosion inhibiting system can be applied as an aqueous solution in concentrate form.

Particularly preferred deicing agents are (a) one containing at least 85% by weight of deicing agent and at least 35% by weight of a corrosion inhibiting material containing sodium fluorophosphate; (b) one containing sodium fluorophosphate and sodium silicate in a weight ratio of substantially 1: 1; and (c) one in which the deicing agent is a corrosive deicing agent having at least 95% by weight of sodium chloride.

By means of the present invention, reinforced concrete may be provided containing reinforcing iron, the concrete containing at least residual amounts of the de-icing agent.

Particularly preferred deicing agents are: (a) one in which the corrosion inhibiting system is sodium monofluorophosphate; (b) one containing at least 70% by weight of the deicing agent and at least 0.25% by weight of a corrosion inhibiting system containing sodium fluorophosphate; (C) one in which the corrosion inhibiting material contains sodium fluorophosphate and sodium silicate; (d) one containing sodium phosphorus phosphate and sodium chloride; and (e) one in which the corrosion inhibiting material 20 also comprises a water-soluble salt of at least one phosphonic acid derivative as defined above.

By means of the present invention, an outdoor surface may be provided which contains at least residual amounts of a de-icing agent of the kind in question.

According to the invention, a corrosion inhibiting system consisting of at least one substance selected from (a) sodium fluorophosphate may be used, (b) a water-soluble salt of at least one phosphonic acid derivative of the general formula

R n R 'N (CH 2 PO 3 H2) 2-n in which R and R' are independently selected from alkyl, aminoalkyl and hydroxyalkyl, and n means 0 or 1.

Preferably, the system is present in a suitable carrier. It may be dissolved in an aqueous medium, preferably at a concentration which is substantially close to a saturated solution.

The corrosion inhibiting system can e.g. be in a form selected from (1) coatings and paints, especially 5 paints, and (2) emulsions and suspensions. The carrier may be non-aqueous. It may even be true.

The corrosion inhibiting system can e.g. applied to an outdoor surface.

In this embodiment, it is sometimes preferred that at least one component contains sodium fluorophosphate together with sodium silicate. In such a mixture, the weight ratio of sodium fluorophosphate to sodium silicate is preferably 1-10: 1-2.5, especially substantially 1: 1,

The outdoor surface can e.g. is sprayed or painted with the corrosion inhibiting system.

The water allows displacement of the corrosion inhibiting system, such as sodium fluorophosphate, on the iron reinforcements.

Deicing agents are known. By de-icing means, in general, is meant any product capable of lowering the freezing point of water and having the other necessary characteristics necessary not to cause detrimental significant effects on the environment or its intended use. Eg. it must not be greasy if it is to be used for roads. This includes glycols, (e.g., ethylene glycols), calcium magnesium acetate, methanol, calcium chloride, magnesium chloride, urea, sodium formate, and generally other deicing agents generally available. It also comprises corrosive de-icing agents, and the corrosion inhibitors used in the present invention are of particular advantage with such corrosive de-icing agents.

The invention also relates to a corrosion inhibiting system in a large number of suitable carriers. As Examples 35, the carrier may be a suitable gas, liquid or solid phase. It includes, for example, but not limited to, deicing agents, paints, coatings, diluents, emulsions, suspensions, solvents and air jet applications.

Some preferred embodiments include aqueous solutions of sodium fluorophosphate, especially sodium fluorophosphate and sodium silicate, particularly preferred solutions that are actually saturated, i.e. as close to saturation as possible, and then diluted with application. Other preferred embodiments include coatings and paints containing sodium fluorophosphate.

The outdoor surfaces can be dry or wet sprayed, coated, painted or dipped in a container containing the corrosive inhibitory system.

By contrast, in the case of deicing agents, corrosive deicing agents are defined as deicing agents which can cause corrosion and which contain salts such as sodium chloride, calcium chloride, magnesium chloride, potassium chloride, sodium formate and other corrosive deicing agents and other products having ions acting as the chloride ions.

By a corrosion inhibiting system containing fluorophosphate or alternatively a system containing fluorophosphate is meant fluorophosphate alone and in combination with other components such as sodium silicate with or without other additives as desired, e.g. soil conditioners, such as CaSO4, urea, other mineral-containing material, nitrogenous substances and the like, in amounts that do not substantially affect the de-icing characteristics of the de-icing agent as described below.

The invention also relates to products containing at least the remaining amounts of the corrosion inhibiting systems, that is, either in the form of the corrosion inhibiting systems or as a residual amount arising from the effect of the corrosion inhibiting systems on the products or on a component of the products, or from the products. aging, washing, rain, etc. These products generally have outdoor surfaces exposed to air, chloride ions 9 DK 172079 B1 and the like.

Preferably, these are de-icing agents with diminished corrosion characteristics which consist of common salt (NaCl) of at least 0.25% and preferably 2.5 to 5% by weight of a system containing sodium fluorophosphate, with or without sodium silicate. The weight ratio of sodium fluorophosphate to sodium silicate can be, e.g. be 1-10: 1-2.5, but is preferably approx. 1: 1. These deicing agents are particularly preferred since the deicing properties of the common salt are substantially maintained while their corrosive characteristics are inhibited, especially with respect to the reinforcing iron when used in connection with reinforced concrete or iron concrete.

There are many different ways that can be used to apply deicing agents. Eg. For example, deicing agents 15 can be used with sand. The de-icing agent with diminished corrosion characteristics can be dry-blended or wet-blended, whether solid-blended or in-situ blended where needed. Eg. it can be prepared by dry blending sodium chloride with the fluorophosphate-containing system. The fluorophosphate-containing system may also be dissolved, suspended or emulsified in a suitable solvent or diluent for specific end uses, e.g. water, glycols, sand, preferably with the least possible dilution with sufficient water to achieve a viscosity, whereby the system containing sodium fluorophosphate will be easy to spray over the sodium chloride or spray against the sodium chloride, whether on a plant or in a plant. salt and / or sand dispersing carrier, e.g. so that the system exerts influence on the sodium chloride and / or sand before it is applied over a surface such as e.g. a concrete surface. The system can also be sprayed on together with the sodium chloride or the system can be distributed into the sodium chloride by any other method. The sodium chloride may e.g. is supplied by endless conveyor belts such as belt conveyor belts or by other methods. Spraying of the system is carried out so as to achieve the desired levels, e.g. 0.25 to 10% by weight, or if desired higher, and preferably 2 to 5% by weight of the sodium fluorophosphate-containing system in the novel de-icing agent with reduced corrosion characteristics.

This de-icing material, such as salt, and the corrosion inhibiting system having reduced corrosion characteristics nevertheless have the characteristics necessary for a good de-icing agent which is substantially unchanged, such as e.g. friction, freezing point, speed, ice penetration, and ice melting rate.

The de-icing material with corrosion characteristics may contain, instead of sodium chloride, other de-icing agents as stated above, and what has been mentioned about sodium chloride can generally also be said of these other corrosive de-icing agents.

The corrosive de-icing agents need not only contain fluorophosphate with or without sodium silicate, although the corrosive de-icing agents may be less preferably used with or without amides of a fatty acid, e.g. such as those having 20 to 24 C atoms (e.g., cocosamide at an acceptable toxicity level). Although less preferred, salts of phosphonic acid derivatives can also be used as described above. Typical examples of these phosphonic acid derivatives include sodium salt or other compatible soluble salts of triethylenetetramine hexakis (methylene phosphonic acid) and sodium salt of ethylhexyliminobis (methylene phosphonic acid) or a combination thereof.

One method of preparing these phosphonic acid derivatives is to react an amine with formaldehyde and phosphonic acid. The deicing agent can be brought in pellet form if desired.

The corrosion inhibiting systems described above can be used with or without deicing agents to inhibit corrosion. The corrosion inhibiting systems 35 may also be present in a suitable carrier, either a gas, liquid or solid, such as an aqueous or other medium which forms a solution with or without deicing agents, e.g. aqueous saturated solutions, or as a coating, an emulsion, suspension or a paint for some applications. The paint, inheritance, suspension or coating may, if desired, be used for coating metals, such as reinforcing bars, car structures, bridge structures, sanitary pipes, culverts or other outdoor metal surfaces. Air can also be used to disperse the corrosion inhibiting system as well as other suitable gases.

The following examples serve to illustrate particular embodiments of the invention.

Examples 1-4.

The analysis used is ASTM-G-31-72 as adopted 15 again in 1985 for corrosive deicing agents and with the systems described in Table I. The corrosion rate resulting in weight loss is expressed as mm per mm. year. As can be readily seen, systems containing fluorophosphate and silicate have a significant positive effect in reducing corrosion, as shown in the Examples.

12 DK 172079 B1

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Example 5

The following illustrates the effect of pH on the corrosion rate with sodium chloride alone or with the following: A: there is Na2 PO3F, and 5 B: there is Na2PC> 3F: Na2SiC> 3: Na1 ignosulfonate: 1: 1: 1 using the method used. are described in Examples 1 to 4.

Inhibitory pH 6 pH 8 pH 10 pH 12 10 System% 264 t 693 t.

mm / year mm / year mm / year mm / year mm / year (mpy) (mpy) (mpy) (mpy) (mpy) 15 0 0.0498 0.0389 0.0523 (2.36) (1.96 ) (1.84) (1.53) (2.06) 6% A 0.0124 0.0244 0.0320 (-) (0.53) (0.49) (0.96) (1.26) ) 20 4% A 0.0198 0.0310 0.0287 (1.51) (0.41) (0.78) (1.22) (1.13) 2% A 0.0226 0.0325 0, 0264 25 (1.95) (0.68) (0.89) (1.28) (1.04) 6% B 0.0127 0.0086 0.0259 (-) (0.49) (0, 50) (0.34) (1.02) 4% B 0.0132 0.0135 0.0302 (0.68) (0.34) (0.52) (0.53) (1.19) 2% B 0.0226 0.0208 0.0246 (1.49) (1.14) (0.89) (0.82) (0.97) 35

Examples 6-7

The following demonstrates the diminished corrosion characteristics of a system containing sodium chloride using the following procedure:

Reinforcement iron / concrete samples are prepared from 5.08 cm (¾11) reinforcing bars, and concrete with a mixture composition of 1: 1: 5 (Portland cement: water: sand). Sodium chloride is added to the mixing water to form a chloride level 45 in the concrete of 11.87 kg / m 3 Cl-. The concrete deck is 5 mm and the exposed reinforced iron area is 14 cm3. The corrosion rates are measured using the AC impedance measurement method; for sequential alternating current impedance measurements, a fixed-amplitude sine wave, usually of the order of 10 mV, is transmitted to the embedded steel of decreasing 5 frequencies, and both phase shifts and modulus of impedance of the steel are measured as a function of frequency. This is described by F. Manfeld in "Recording an Analysis of AC Impedance Data for Corrosion Studies - I", Corrosion - Nace, Vol. 36, No. 5, pp. 301-307, May 1981, and Vol. 38, No. 11, pages 570-580, November 10, 1982, and K. Hladky, L. Callow, J. Dawson, "Corrosion Rates from Impedance Measurements: An Introduction", Br.

Corro J., Volume 15, No. 1, pp. 20-25, 1980.

Table II

3% 1 s brine

Example Number of days, no. In which the material% of the component is exposed to corrosion 20 in de-icing medium for speed light effect mm / year 6 98 NaCl 85 0.0155

2 Na2 PO3F

7 98 NaCl 75 0.0414 2 phosphonic acid derivative as in Example 4

Sample B 100 NaCl, 85 0.0605

Examples 8-19 35 In the following examples, the corrosion current is followed in a MACROCELL corrosion analysis using reinforced iron sheets as follows:

Two reinforcing iron mats are placed in concrete using average quality air-mixed concrete.

40 Different levels of sodium chloride are blended into several of the top gauge layers to accelerate corrosion and simulate the environment present in old bridge decks. An embankment is placed on top of each plate and the 6% solution of de-icing agent product is dammed to a depth of 1.69 cm. The solutions are replenished every two weeks.

The top and bottom sets of the reinforcing bars are connected electrically and instantaneously on and off in series with a 1.0 Ohm resistor 5 installed between the two mats.

The corrosion current flowing between the top and bottom mats is measured as the voltage drop across the resistor when the button is connected (normal position). The driving force (potential difference) between the top and bottom mats is measured as 10 "instant off" voltage between the two mats (the button is momentarily switched off, · the voltage measurement is made within 2 seconds). Corrosion potentials for the top mats are measured against saturated calomel electrodes with the button in normal "on" position.

In Table III [Cl-], kg of chloride per m3, where the same portion is used in Examples 8, 12 and 16 as with the sample W, etc.

Analysis 20 An analysis of corrosion products on reinforcing iron from Sample C and Example 8 was made.

The corrosion product layer for Sample C is composed mainly of iron oxides / hydroxides with small amounts of sodium and chlorine (from the solution) and silicon (silica from the aggregate mixture) present. The concrete side of the interface shows that calcium is present both as oxides / hydroxides and carbonates.

The corrosion product layer of Example 8 is more complex. The layer is quite thick and has a higher calcium content 30 than the non-inhibited surfaces. Calcium is present as calcium oxide / hydroxide and no indication of the carbonate types present. There is also evidence of the presence of significant amounts of chromium, nitrogen and aluminum in the film.

Traces of phosphorus were also detected.

As a preliminary explanation, it seems that the effect of the inhibitor may be a change in the local environment due to a reaction or prevention of a reaction with the concrete components. The main difference between the inhibited (Example 8) and the uninhibited (Sample C) is the amount and nature of the calcium present in the corrosion product films.

5 Saturation with CO2 of the concrete layer together with the presence of chlorides, an important precursor for corrosion of the steel reinforcement. It was found that the present inhibitor affects this saturation reaction with CO 2 and thus the mechanism of corrosion inhibiting amounts to alter the local environment permitting the maintenance of a stable passive film instead of incorporating the inhibitor compound into the film to form a more protective layer on the surface. .

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Example 2Q

The following will serve to illustrate the diminished corrosion characteristics of a 4% deicing agent solution. The percent inhibition is calculated as a percentage reduction of the corrosion rate relative to the corrosion rate of the same deicing agent solution without the Na2 PO3F system.

Average 10 De-icing% Na2PO3F Corrosion% Inhibitor System Speed mm / year ring 100 CaCl2 0 0.0699 15 94 CaCl2 6 Na2PO3F 0.0307 56 94 CaCl2 6 * 0.0302 56.7 100 MgCl2 0 0.0594 20 94 MgCl2 6 Na2 PO3F 0.0343 42.3 94 MgCl2 6 * 0.0351 41 Example 21

The following example serves to illustrate the effect of the concentration of the Na2 PO3F system over time using a 4% sodium chloride deicing solution as follows:

Defrost% Na2 PO3F Corrosion Rate Mean System 264 t 639 t mm / year mm / year 35 - - - 100 NaCl 0.0599 0.0498 96 NaCl 4 Na2 PO3F 0.0384 0.0104 98 NaCl 2 Na2 PO3F 0.0495 0 , 0173 96 NaCl 4 * 0.0173 0.0086 40 98 NaCl 2 * 0.0290 0.0378 * Na2 PO3F + Na2 SiO3 + sodium lignosulfonate in a weight ratio of 1: 1: 1.

19 DK 172079 B1

Example 22

The following example serves to illustrate the diminished corrosion characteristics of the preferred deicing agent on various metals.

5

NaCl Newspaper- Corrosion Rate- Na2PC> 3F- Soft Galvanized Part Steel Steel Steel Aluminum%% mm / year mm / year mm / year 10 --------- 100 0.0599 0.0665 0, 0180 97.6 0.8 lignosulfonate 0.0193 0.0490 0.0051 15

0.8 Na2 SiO3 0.8 Na2 PO3F

99% 1% lignosul 0.0472 0.0429 0.0168 phonate 99% 1% Na2 SiO3 0.0277 0.0884 0.0246 99% 1% Na2 PO3F 0.0572 0.0307 0.0051

Examples 23-24

The following example serves to illustrate that the diminished corrosion characteristics of de-icing agents with Na2 PO3F and Na2SiO3 and / or lignosulfonate are due to Na2PO3F alone or with Na2SiC> 3 and not the lignosulfonate.

The inhibitor mixture of Na2 PO3F and Na2SiC> 3 is examined for its effect on a sample of soft steel in a saline solution (the corrosion of a reinforcing iron in a small reinforcing iron concrete sample (Example 23)).

23 - Concrete samples

Reinforcement iron / concrete samples are prepared as in Examples 6 and 7 from 1.27 cm (M ") reinforcing sticks and concrete having a composition of 1: 1: 5 (Portland cement: water: sand). The concrete deck is 5 mm and the exposed reinforcing iron area is The samples are exposed to 3% NaCl + inhibitor solutions (at the indicated concentration) for the indicated number of days, after which the analyte (corrosion rate) is analyzed using the AC impedance technique.

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Claims (19)

A method of inhibiting corrosion of reinforcing iron in ferrous concrete, characterized in that a corrosion inhibitor system is provided which contains at least sodium monofluorophosphate at least on the surface of the iron concrete, in which the sodium monofluorophosphate in contact with water inhibits the corrosion of the reinforcement. Process according to claim 1, characterized in that the system is sodium monofluorophosphate. Process according to claim 1 or 2, characterized in that the system is dissolved in an aqueous medium. Process according to claim 1, characterized in that the system contains sodium monofluorophosphate and sodium silicate. Process according to claim 4, characterized in that the system contains sodium monofluorophosphate and sodium silicate in a weight ratio of 1-10: 1-2.5. Process according to claim 5, characterized in that the system contains sodium monofluorophosphate 20 and sodium silicate in a weight ratio of approx. 1: 1. Process according to claim 1, characterized in that the system is sodium monofluorophosphate, coconut amide and a water-soluble salt of at least one phosphonic acid derivative of the general formula RnR1N ^ CH2 PO3H2 ^ 2-n, wherein R and R 1 is independently selected from alkyl, aminoalkyl and hydroxyalkyl, and n is 0 or 1. Process according to claim 1, characterized in that the system is dissolved in a suitable carrier. 9. A process according to claim 1, characterized in that the system contains a non-aqueous carrier. Method according to claim 1, characterized in that the system contains sand. Method according to any one of claims 1-10, characterized in that the surface is an outdoor surface of iron concrete. 12. A method according to claim 11, characterized in that the surface is a reinforced concrete surface of a bridge. Method according to any one of claims 1-12, characterized in that the surface is sprayed with the system. Process according to any one of claims 1-13, characterized in that the system also contains a de-icing agent. Process according to claim 14, characterized in that the de-icing agent is a corrosive de-icing agent containing at least one of the substances sodium chloride, calcium chloride, magnesium chloride and potassium chloride. Process according to claim 14 or 15, characterized in that the corrosive de-icing agent is sodium chloride. Process according to any of claims 14-16, characterized in that the corrosive de-icing agent is mixed with the sodium monofluorophosphate and applied over the concrete surface, the mixing and application being carried out at substantially the same time. Process according to any one of claims 14-16, characterized in that the sodium monofluorophosphate is mixed with the corrosive de-icing agent before it is applied over the concrete surface. Process according to any one of claims 14-17, characterized in that the system is applied as an aqueous solution in concentrate form.