DE1771525C3 - Corrosion-inhibiting salt mixtures - Google Patents

Description

Sodium, calcium and magnesium chlorides are known to be in solid form as thawing salts for Ice and snow cover used on roads, these salts go into solution. Next find solutions These salts are used as cooling brines and as dust binders, especially in coal mining as well on streets and sports fields. In all areas of application, the or Forming solutions of these salts with metal parts, such as steel parts, in contact and cause undesirable corrosion there, of which so-called "pitting corrosion" is particularly easy leads to lasting uselessness of the attacked metal parts. A limited, but strong corrosive effect on limited areas of the metal parts, the surrounding ones Areas of the metal parts are not or only slightly attacked.

The corrosive effects of these salts and their solutions, which are used in various applications have the most varied of concentrations, is also still of this concentration dependent. In general, more dilute solutions are more corrosive than more concentrated ones.

For this reason, the salts are corrosion inhibitors such as chromates, phosphates, zinc salts, Sodium nilrite, added, some of which are not physiologically harmless. However, these are inhibitors only effective for some of the areas of application and show in sodium and calcium chloride solutions often a different solubility. The selection of the suitable inhibitor is not just a matter of course according to the type of salt, but also according to the concentration of the salt to be used or the application resulting solution of the salts and is also dependent on the concentration of the inhibitor in question. Numerous series and comparative tests are necessary to determine the If necessary, find out a suitable corrosion inhibitor in each case. In many cases, several inhibitors are also required can be combined with each other to achieve the intended effect.

Therefore, the search for as universally applicable and effective inhibitors as possible or for such Salt mixtures containing inhibitors sought.

There were salt mixtures, the calcium chloride, magnesium chloride or their mixtures as well as one Containing corrosion inhibitor, found. These salt mixtures are characterized in that they are as

35

40

45

55

60 corrosion inhibitor contain 12 to 15 percent by weight alkali, ammonium or alkaline earth formate.

In the case of aqueous solutions of salt mixtures, which predominantly consist of calcium chloride or only from Calcium chloride and formate exist, the corrosion-inhibiting effect extends to practically all of them Concentrations of the solutions of calcium chloride. Apparently this effect is soluble with in the good The formates can also be used in concentrated calcium chloride solutions justified. For example, in a 30% calcium chloride solution at room temperature 4.6 percent by weight calcium formate and in a 10% calcium chloride solution ^ percent by weight Calcium formate soluble. A corresponding corrosion-inhibiting effect of alkali, Ammonium and other alkaline earth formates are also found in solutions containing sodium or magnesium chloride contained alone or in a mixture with one another and with calcium chloride. Likewise, the mentioned formates are used in a mixture with one another.

In the case of salt mixtures, which mainly consist of calcium or sodium chloride, the corrosion-inhibiting The effect of the formates is increased when the salt mixtures are still 0.25 to 1.0 percent by weight contain calcium hydroxide or sodium hydroxide. The one made from these salt mixtures, or Aqueous solutions resulting from use have a pH of 9 to 10. These are alkaline Reaction is desirable because iron and steel in these solutions are less likely to be attacked by corrosion than in neutral or weakly acidic solutions.

It has surprisingly been found that the solubility of calcium hydroxide in calcium chloride-containing Solutions by the addition of Forniiaterc is increased considerably. Common salt mixtures, which mainly consist of calcium chloride and do not contain any formates, only up to Contain 0.25 percent by weight of calcium hydroxide, otherwise the solubility limit in the concentrated solutions of calcium hydroxide is exceeded. In addition, at lower temperatures, the Aqueous solutions of these salt mixtures deposited calcium oxychloride, the pipelines and pumps clogged by refrigeration units or distribution devices. It has surprisingly been shown that salt mixtures, which consist mainly of calcium chloride and according to the invention 12 to 15 percent by weight alkali, ammonium or alkaline earth formates contain, nor up to i percent by weight calcium hydroxide can be added without that the solubility limit of the calcium hydroxide is exceeded in their concentrated solutions. 0.5 percent by weight calcium hydroxide can be added without being at low temperatures Calcium oxychloride is precipitated. This results in another advantage. If namely the formiat- and calcium hydroxide-free calcium, sodium or magnesium chloride solutions carbon dioxide from the atmosphere can absorb, they react after a short time neutrally or slightly acidic. By such a A decrease in the pH value strongly promotes corrosion.

Due to the increasing solubility of calcium hydroxide, alkali, ammonium or alkaline earth formates, which is also given at low temperatures. can contain calcium chloride Salt mixtures correspondingly larger

genes of calcium or sodium hydroxide can be added. Those produced from such salt mixtures Solutions retain their alkaline reaction even in contact with air containing carbon dioxide considerably longer periods of time than solutions of corresponding, but formate-free salt mixtures. at Solutions of salt mixtures, which consist to a noticeable extent of magnesium chloride, forbids alkalization due to the poor solubility of the magnesium hydroxide.

The by the addition of calcium or sodium ormate The strong corrosion inhibition caused is evident in both calcium, sodium and magnesium chloride solutions different concentration. L in particularly good corrosion protection is used in solutions ; s achieved that 10 to 25 percent by weight of the invention Contains salt mixes. This is where the alternation tests through these solutions lie ..η iron and steel caused annual wear below 0.1 mm, while it is considerable in non-inhibited, appropriately composed solutions !. is higher. Above all, however, the dreaded "pitting corrosion" on iron and steel parts is caused by the The addition of formats has been reduced considerably. In solutions of the salt mixtures according to the invention the "pitting corrosion" always remains below the measurable limit, which is the case with a mechanical measuring device (needle punch) is 0.01 mm. In contrast to this, "pitting corrosion" always occurs in non-inhibited solutions, whereby the average depth of the holes is 0.1 mm.

The established good for calcium, sodium and magnesium chloride solutions of different Concentration of the formates' universal anti-corrosive effect is surprising, since the previously known Inhibitors showed only limited effects. This is all the more true since in J. appl. Chem. 4, July 1954, 384 ff., It is established that the corrosion protection brought about by salts of aliphatic acids solely on the Presence of the salts is based on long-chain acids, while the short-chain acids have no such effect show.

Compared to some other inhibitors, the formulations are characterized by their great chemical resistance out. There is also no reaction with iron. After a four-month trial period, the initial one was the first Formate concentration in iron barrels has been preserved.

The technical implementation of the process according to the invention is very simple. It depends on whether the chlorides are used in solid or dissolved form. Solid salts should be used the components are mixed before or when they are used. Such a mixture can z. B. from:

85 percent by weight ground

CaCl ₂ 82/85%,
14 weight percent technical

Calcium formate,
1 percent by weight hydrated lime powder

55

60

85 percent by weight of ground rock salt

(Road salt quality),
14 weight percent technical

Calcium formate,
1 percent by weight of potassium hydroxide powder

For many purposes, the hygroscopic salts are preferred in their flake form. MgCl is almost exclusively commercially available in this form as a hexahydrate with 46% MgCl _{2 content.} Since it is possible that mixtures of these flakes with the finely crystalline Ca formate and the hydrated lime powder will separate, it is advantageous to dose the additives per sack with the instruction that only the contents of complete sacks are dissolved or scattered.

These mixtures advantageously contain, for example:

85 percent by weight CaCli flakes

with 77/80% CaCl ₂ ,

14 percent by weight of technical Ca formate,
1 percent by weight hydrated lime powder

exist.

86 weight percent MgCJ ₂ flakes
with 46% MgCl ₂ .

14 percent by weight of technical Ca formate

84 percent by weight CaCl ₂ flakes
with 77/80% CaCl ₂ ,

15 percent by weight of technical sodium formate,
1 percent by weight hydrated lime powder.

The mixtures given here and having similar compositions are direct for many purposes operational, e.g. B. as de-icing salts for road winter service, to clear roads and dust Places to stabilize earthbound paths.

For some uses, e.g. B. for cooling brines or spray solutions to remove dust from coal, Coke, etc., high proof solutions are preferred. The production of these solutions from the salt mixtures is possible without difficulty with the help of a stirring or pumping tank.

For dust control applications, it is advantageous to dissolve the specified CaCl ₂ mixtures in a weight ratio of 1: 2 with water, because the concentrations of the resulting solutions are approximately in equilibrium with the average relative humidity of the air. In the case of the flakes _{containing MgCl 2} , the solution ratio is expediently 1: 1 with water because of the high water of crystallization content of this salt. Of course, other solution ratios can also be used.

If the solutions of Ca (OH) ₂ containing CaCl ₂ mixtures are exposed to low temperatures, e.g. B. as cooling brines or when storing outdoors in winter, e.g. B. on coal stations, it is advisable to reduce the calcium hydroxide addition in the above recipes to 0.5 percent by weight to avoid the crystallization of calcium oxychloride. If the inhibited solutions of the two hygroscopic salts are to be used to make coal, coke, briquettes, etc. dust-free at the colliery or at the coal dealer, the goal can only be optimally achieved if the spray solutions contain wetting agents. Non-ionic wetting agents, e.g. B. Alkylarylphenolpolyglykoläther, since these do not enter into poorly soluble compounds with the alkaline earth chlorides. The wetting agents are either added to the solutions or, to make things easier for the consumer, to the salt mixtures, if the latter prefers solid goods. In the case of mixtures containing CaCl ₂ or MgCl ₂ flakes, the network can

means in a particularly simple manner in a rotating drum before mixing with the others Components are sprayed on in an amount of 0.2 to 2.0%. With only powdery substances the wetting agent is advantageously sprayed on in an intensive mixer.

It has been shown that the inhibiting effect of the formates even in the presence of wetting agents preserved.

If the two alkaline earth chlorides are present in the form of commercially available concentrated alkalis, it is possible without difficulty to inhibit these alkalis in the sense according to the invention. To z. B. to inhibit a CaCl ₂ liquor with 36 ° Bc, corresponding to about 35 percent by weight CaCl ₂ , are dissolved in 100 kg, ₅ corresponding to 75 1 of this liquor after adding 40 liters of water one after the other with stirring:

7.5 kg technical calcium formate,

0.6 kg callchydrate powder.

If such solutions are to be used to remove dust from coal, they are expediently 0.1 to 1.0% of a nonionic wetting agent was added.

The anti-corrosion effect of the formates in the salt mixtures according to the invention was tested in alternating immersion tests Tested in the laboratory and, in order to get closer to the conditions in practice, in the open air under the influence of industrial air. Included the following aspects were decisive:

1. The tests extended over a longer period of time, because this is the only way to draw conclusions about the practice in which corrosion damage becomes noticeable, possibly only after years. On the other hand, the results of corro- sion can _3S tests under severe conditions while shortening time experience has shown that only with great reservations evaluate for the practice. A second reason for the long duration of the tests is that the dreaded pitting corrosion can only be recognized after a long test period.

The laboratory tests ran for two months and the outdoor tests for four months.

2. To show the wide range of effects of the formates, a concentration range of 25 or 23 percent by weight to 1 percent by weight, based on the anhydrous chloride, detected. It was proceed in such a way that first the highest percentage solutions are prepared and from them the low percentage solutions by adding the calculated amounts of water. This way of working means a deliberate aggravation compared to other corrosion tests published in the literature because as the solution is diluted, the concentration of the inhibitor also decreases, in extreme cases to V25 of the initial value. Of course it is The inhibitor's protective effect is greater when its concentration is diluted with the chloride solution does not decrease in the same proportion. The reason for the self-imposed aggravation is that in In practice there are cases where concentrated solutions are applied and a dilution through Rainwater can be done, such. B. in the manner described on coal yards. It should be shown that even in those cases where the limited solubility of the inhibitor in the concentrated Solutions, a protective effect is still present in the diluted solutions is.

Experiments in the laboratory

The test material used blank, 320-grit and pierced plates of size 80 x 20 χ 2 mm made of sheet metal St 10.03, which were hung in the solutions prepared from the salt mixtures according to the invention on Giashooks for 22 hours per day so that they were completely covered. The platelets hung in the laboratory air for 2 hours every working day. The salt concentration was kept constant by the occasional addition of water. The solutions were kept at a temperature of 25 ° C. After 60 days, the rust loosely adhering to the iron flakes was lightly brushed off and the firmly adhering rust layer was removed by dipping the flakes in 10% hydrochloric acid containing 1.5 g / l of the Dowell A 74 inhibitor from Dow Chemical Corp. contained and a temperature of 8O ⁰ C had. The flakes were then dried and reweighed, and the weight loss found was converted to g / m ² · day. In Table 1 a, the compositions of the individual salt mixtures are given in percent by weight, from which the high-percentage "stock solutions" were first prepared and the lower-percentage solutions were prepared by diluting them with water. For the composition of the “stock solutions”, see Table 1 b.

The total of eight dilution series also includes the three zero test series in which the solutions of the three salts tested: CaCl ₂ , MgCl ₂ and NaCl were used without the addition of formate, but partly with the addition of calcium hydroxide at the same chloride concentration as in the inhibited solutions.

The results of the tests are given in Table 2. In the columns, from left to right:

the concentrations of anhydrous chloride in the solutions,

the pH values at the end of the experiment,

the weight loss per platelet in g / m ² day,

the corrosion protection values (abbreviated Korr.-Sch.) in percent by weight, calculated according to the formula

Here, α means the decrease in weight in the non- inhibited solution and b means the decrease in weight in the inhibited solution.

The corrosion protection values show that the inhibitory power of the formates _{is highest in CaCl 2} solutions, it being quite irrelevant whether Ca or Na formate is used. The protective effect in the concentrated solutions down to a concentration of approx. 10% CaCl _{2 is} approx. 80%, in the more diluted solutions it decreases to 48 or 45%. A satisfactory protective effect was achieved in the two highest concentrations in NaCl solutions. In order to also inhibit the 5 and 1% solutions satisfactorily, the addition of formate should have been increased. The same applies to the MgCl ₂ solutions, in which 55% protection was achieved only in the 5% solution. Since the MgCl ₂ solutions could not be made alkaline like the other two, the conclusion that formate works particularly well at an initial alkaline concentration is reasonable.

From the pH values of test series III, at which the two "stock solutions" contained the same _{amounts of Ca (OH) 2} , it can be seen that formate has an alkaline effect.

Try in barrels outdoors under a rain canopy

Each attempt took two. Iron barrels, open at the top, of 1001 each, placed on the front, of which one was a step higher so that the solution could flow out of this into the lower one. Out the latter could be pumped into the higher one. The solution was in a day in that one, the next in the other barrel. The cycle extended over a period of 4 months. The barrels were in the open, only protected from the rain by a roof. This made the aggressive Industrial air free access to the barrels and the small iron plates suspended in them, which can only be found in the barrels the size (80 χ 100 χ 2 mm) of those for the laboratory tests used differentiated.

The tests were carried out only with CaCL solutions, each time a zero test and an inhibition test side by side. The solutions were made from the same salt mixtures as the solutions of the Laboratory tests produced | s. Table I a, row I a and Ib, calcium formate as inhibitor). Additionally included this time the mixtures still contain 0.6% of a non-ionic wetting agent.

The experiments were carried out in two concentration ranges. The higher concentration range resulted from dissolving the two salt mixtures in double the amount of water (practice rule). The solutions in the lower concentration range were adjusted _{to 13% CaCl 2 by diluting the higher percentage solutions.} The composition of the solutions is given in Table 3 and the result of the experiments is given in Table 4.

In the inhibited concentrated solution, the corrosive attack of 0.17 g / m ² day is just as high as in the correspondingly concentrated solution in the laboratory tests. Because the corrosion in the non-inhibited solution was only half as strong as in the laboratory tests, there is now only a corrosion protection of 53%.

In contrast to the concentrated solutions, the platelets became significant in the diluted solutions more attacked than in the laboratory tests. The corrosion protection was now 64%.

Table 1 a Applied Chloric for the Corrosion tests Ca-F. Na-F. Ca (OH,) Composition of the solid material mixtures Art - - % CaCl ₂ 77/80% ') 14th - 0.25 Test type CaCl ₂ 77/80% ') % - 14.7 1.00 Test series CaCl ₂ 77/80% ') 99.75 10.5 - 1.00 Zero verse CaCl ₂ 77/80% ') 85.00 - - 1.00 Yes Inhib. Vers. MgCl ₂ 46% ') 84.3 9 - - Ib Inhib. Vers. MgCl ₂ 46% ') 88.5 - - - Ic Inhib. Vers. NaCl 95% ² ) 100.00 17th - 1.00 Id Zero verse NaCl 95% ² ) 91.00 1.00 Ha Inhib. Vers. 99.00 Man Zero verse 82.00 IUa Inhib. Vers. Formate IHb % ') In scale form. ² I rock salt.

Table 1b Composition of the stock solutions for the alternating immersion tests in beakers

Test series Test type chloride
^ Formate
% Ca (ol Yes Zero verse 25 CaCl ₂ - 0.08 Ib Inhib. Vers. 25 CaCl ₂ 5.2 Ca-F. 0.32 Ic Inhib. Vers. 25 CaCl ₂ 5.5 Na-F. 0.32 Id Inhib. Vers. 25 CaCl ₂ 3.7 Ca-F. 0.35 Ha Zero verse 23 MgCl ₂ - _. Man Inhib. Vers. 23 MgCl ₂ 4.9 Ca-F. purple Zero verse 23 NaCl 0.24 IHb Inhib. Vers. 23 NaCl 5.0 Ca-F. 0.29

309 083

i 77 1 525 9 "10

Table 2 Results of the alternating immersion tests in the laboratory, test duration 60 days, t = 25 ° C

chloride

a) pH zero test ')

Weight decrease gm ² days

b) addition of Ca-l ^; i> rmiai

pH ¹ )

Gew.-Ahn. g no

Corr.-Sch.

■ ι

c) Addition of Na Foimial

pH ¹ )

Cjew.-Abn.
gnr ■ day

Corr.-Sch.

d) addition of calcium

.. ,, Wt.
Π " ¹ green day

Test series la to 1 d: CaCU solutions

7.3 0.65 10.2 0.17 74 10.4 0.17 74 10.1 0.45 7.0 0.8 8.5 0.17 79 8.3 0.18 78 8.4 0.6 6.8 3.0 7.4 0.55 82 7.3 0.72 76 7.3 2.05 6.7 5.7 6.9 3.0 48 6.8 3.8 33 6.9 4.6 6.5 6.9 6.8 3.8 45 6.6 3.9 44 6.7 5.4

l-orinial Corr.-Sch.

30.8 25.0 31.6 19.3

21.7

Test series Ha and 11b; MgCU solutions

7.2 0.21 7.0 0.16 24 7.2 1.2 7.3 0.7 42 7.4 4.9 7.5 2.2 55 7.3 5.6 7.3 4.6 18th

Experimental series purple and IHb: NaCl solutions

8.2 0.7 9.1 0.16 77 7.5 4.0 8.1 1.8 55 7.5 5.4 7.5 3.4 37 7.8 6.0 8.2 4.3 28

¹ ) Measured at the end of the test.

Table 3 Composition of the solutions fin the alternating immersion tests in iron barrels

% CaCl ₂

% Ca formate.

VoCa (OH) ₂ % wetting agent.

pH b. Vers.-Ende Weight decreases of the

Tile

g / m ² ■ day

Average g / m ² % corrosion protection ..

Day.

Concentrated solutions

Zero verse

26th

0.08 0.2 Inhib. Vers.

22nd
4.5
0.33
0.2

Diluted solutions Il-verse. 3 Inhib. Vers _ 0.04 0.1 13th 2.7 0.2 0.1

Table 4 Results of the alternating immersion tests in barrels

Concentrated solutions zero verse.

0.36; 0.33 0.36; 0.41

0.365

ungen Diluted solutions lnhib. vers. Zero verse lnhih.-ver 8.8 5.9 7.8 0.41; 0.16
0.22; 0.15 4.6; 5.2
5.0; 5.4 1.8; 1.8
1.7; 1.8 0.17
53 5.0 1.8
64

Ua?

Claims (2)

I 771 claims: 1. Salt mixtures, the calcium chloride, magnesium chloride or their mixtures as well as a Contain corrosion inhibitor, characterized in that they are used as a corrosion inhibitor Contain 12 to 15 percent by weight alkali, ammonium or alkaline earth formate. 2. Salt mixtures containing calcium chloride or sodium chloride and a corrosion inhibitor contain, characterized in that they contain 12 to 15 percent by weight as a corrosion inhibitor Alkali, ammonium or alkaline earth formate and 0.25 to 1.0 percent by weight calcium or sodium hydroxide contain.