CS260487B1 - Anti-corrosion thermally stable pigment - Google Patents

Abstract

The solution concerns the use of dimagnesium diphosphate as an anticorrosive thermally stable pigment. MgzP2O/ has very good anticorrosive inhibitory effects even at a relatively low concentration in a coating or other binder. It is thermally completely stable up to high temperatures, so it can also be used for high-temperature purposes. It contains a relatively high proportion of the raw material-available magnesium component, which in addition has a positive effect on the alkalinity of wet aggressive media, possibly penetrating through a coating or other protective layer. The solution can be applied in pigment technology, in the coating industry and in the preparation of high-temperature protective layers.

Description

The invention relates to the use of magnesium pyrophosphate as an anti-corrosion thermally stable pigment. MgzP2O / has very good anticorrosive inhibitory effects even at a relatively low concentration in the paint or other binder. It is thermally stable to high temperatures, so it can be used for high temperature purposes. It contains a relatively high proportion of raw material magnesium, which in addition positively affects the alkalinity of wet aggressive media, eventually permeable through the coating or other protective layer. The solution can be used in pigment technology, in the paint industry and in the preparation of high temperature protective coatings.

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The present invention relates to the use of magnesium pyrophosphate as an anti-corrosion thermally stable pigment.

Some lead compounds and zinc chromate based compounds are effective anticorrosive pigments. Recently, however, they have been replaced by phosphorus compounds for hygienic and ecological reasons. Phosphates suppress oxygen corrosion in a humid, aqueous environment, especially in ferrous materials (steel, cast iron), where they bind iron ions due to corrosion, into insoluble phosphate. This then creates a coating that also passivates the metal surface. Phosphate cations may also have a beneficial effect on anticorrosive effects. In accordance with the beneficial effects of calcium ions and some of the data below, some inhibitory properties are also expected for magnesium ions. Of the phosphorus compounds, resp. designed for use as anticorrosive pigments in particular simple phosphates. The second group is condensed phosphates. This includes both the so-called polyphosphoric glasses (higher linear phosphates), which have been proposed so far, and the recently proposed cyclotetaphosphates of certain divalent metals, including magnesium and more recently also pyrophosphates of zinc, manganese, copper, cobalt and nickel.

Of the simple phosphates, zinc phosphate in the form of dihydrate - Zn3 (PO4) 2 is the most widespread so far. 2H2O. The use of CrPOt is also known. 3H2O and phosphate salts of some alkaline earth metals, especially calcium. In addition, double calcium-zinc phosphate - CaZn2 (PO4) 3.2H2O has recently been used. Calcium ions will have an effect on corrosion pigments, even if they are in admixture. They effectively increase the alkalinity of the moisture, eventually permeate through the coating or generally by an anticorrosive protective layer. Again, a similar effect can be expected for magnesium ions. The use of simple phosphates as anticorrosive pigments has a number of disadvantages. The main disadvantage of these compounds is that they do not yet have the anticorrosive effects of the best pigments of both lead and chromate and need to be applied to the coating compositions in relatively large amounts (concentrations) so that their anticorrosive effects are satisfactory. A further disadvantage of simple phosphates is the relatively low thermal stability of these substances resulting from their defined hydrated form, which is essential for their anticorrosive action. Therefore, they cannot be used in anti-corrosion protection layers for higher temperatures (above 150 ° C). Their lower thermal stability can also complicate the final mechanical-thermal operations of preparation and treatment of the pigment as well as its dispersion into the anticorrosive mass. In view of the long-term anticorrosive effect of simple phosphates, their partial solubility in aqueous, not completely neutral environments (eg the action of so-called acid rain) may also be a disadvantage. Over time, the pigment particles may be washed out of the protective layer, thereby damaging its impermeability to corrosive media. Also, the technology of preparing simple phosphates is not a simple operation due to the need to obtain a precisely defined hydrate. It also requires high-quality raw materials and the content of the metal component, which is less effective than the phosphorus component, is relatively high.

The first group of condensed phosphates designed or used as anticorrosive pigments is called polyphosphoric glass. These higher linear condensed phosphates contain anions in the form of a polymer chain. They are designed with various sodium, potassium and magnesium cations in addition to calcium; sometimes also with zinc, cadmium, clay or iron.

Again, polyphosphoric glasses do not reach the level of the best lead pigments by their anticorrosive effects. Their thermal stability is considerably higher than that of simple phosphates, but is also limited, since they recrystallize in the temperature range of 400 to 600 ° C and mostly lose the character of the higher polymer anion. Therefore, they cannot be used in corrosion protection layers above these temperatures.

Higher linear phosphates are also partially soluble and, when in powdered-pigment form, even tend to be wetted. By the action of moisture they gradually progress to dihydrogen phosphates, which are then readily soluble, can be easily washed out of the protective layers, which thus break up and become permeable to corrosive media. Higher linear phosphates are then not anticorrosive in the long term, despite the fact that their use on a large scale (especially Cd and Zn products) can also lead to hygienic and environmental problems.

A further disadvantage of these compounds is the high demands on their preparation, especially from an energy and construction point of view. They are prepared from melt at high temperatures (800 to 1300 ° C), which are considerably aggressive and from which some aggressive phosphorus products are already volatile. The products have a glassy character and so the final operations of their preparation into powder - pigment form and dispersion into paint or other mass are also quite demanding.

Recently proposed for use as anticorrosive pigments, cyclo-tetraphosphates of some divalent metals (including magnesium) overcome most of the drawbacks noted for single phosphates and higher linear phosphates. They are thermally very stable up to their melting point (magnesium product up to 1160 ° C). Above this β

however, they decompose by temperature. Cyclotrophosphates are also chemically very stable, with very low solubility in aqueous and not completely neutral environments, so that their anticorrosive action is long-lasting; however, this may be a disadvantage, since a faster release of phosphoric passivating anions is needed.

Cyclotrophosphates have a high proportion of phosphorous anticorrosive active ingredient, which is 2 to 3 times higher than that of simple phosphates. However, for some products, this component may be more material intensive than the cationic component. This is especially true for dicalcium and di-magnesium cyclotetaphosphate, where the cationic component is very inexpensive and it would be advantageous to increase its proportion in the pigment in this respect, while maintaining the character of the condensed phosphate anion (for example as with pyrophosphates). The preparation of cyclo-tetraphosphates is not as technologically and structurally demanding as the preparation of the latter.

Recently, zinc, manganese, copper, cobalt and nickel pyrophosphates have also been proposed as anticorrosive pigments, in addition to the advantages mentioned for cyclotrophosphates. They have an even higher thermal stability, are somewhat faster acting and have a slightly lower content of raw material-intensive, albeit anti-corrosion, very effective phosphorous components. However, the content of the cationic -, divalent metal - component, which, in most cases, of the pyrophosphates proposed so far, is not higher in terms of raw materials. From this point of view, the use of pyrophosphates with some cheap cation, eg magnesium, seems to be very effective.

The use of magnesium pyrophosphates as an anticorrosive thermally stable pigment therefore removes the drawbacks mentioned for single phosphates and for higher linear phosphates, complements the advantages mentioned for (and also removes some of the drawbacks) for cyclo-tetraphosphates and for second pyrophosphates.

Mg2P2O7 has suitable basic pigment properties - density, specific surface area, oil consumption, is completely white and easily dispersible into organic and inorganic binders.

The solubility of magnesium pyrophosphates is higher than that of magnesium pyrophosphate, thus releasing phosphoric passivating ions more rapidly. Again, however, in a gradual and practically regulated way, depending on the degree of corrosive environmental impact. In the first stage, one-third of the anions are slowly released and the solid residue corresponds to a single phosphate. Therefore, the impermeability of the coating film or of the other protective layer to which the pyrophosphate has been applied is still almost not disrupted at this stage.

The remaining phosphate then has an anti-corrosion effect again, so that the Mg2P2O2 generally has longer-lasting effects. The magnesium ions released thereby effectively increase the alkalinity of the attacking wet, aqueous medium; their action in this direction proves higher than in the case of calcium ions. Magnesium diphosphate is also completely stable up to its melting point of 1185 ° C and is still stable after reaching this temperature. The diphosphate has a molar P / Mg ratio of one. This is a higher value and more favorable from an anticorrosive point of view than for simple phosphates and, on the contrary, it is lower and thus less expensive in terms of raw materials than for cyclotetaphosphates.

The content of the cheap magnesium component is twice that of dicalcium cyclotaphosphate. In the process for preparing magnesium pyrophosphates, it is easy to achieve a relatively high yield of pure product, which is practically in pigmented form, while not requiring high quality raw materials. Natural magnesite, waste magnesium carbonate or various magnesium sludge and lower quality (extractive) dilute phosphoric acid may be used.

The following are examples of some of the determined pigmentary properties of Mg 2 P 2 O 7, which roughly correspond to the most common inorganic pigments.

The following are examples of established anticorrosion-inhibiting properties of magnesium pyrophosphate, which illustrate its superior abilities in this respect than commercial anticorrosive pigments based on simple zinc phosphate dihydrate.

He did

Some properties of magnesium pyrophosphates related to its pigment use and inhibitory action have been determined:

density specific surface consumption of flaxseed oil pH of aqueous extract - 8 days after insertion steel. - 8 days after removal of steel. sheet inhibiting properties of water leachate - corrosion loss of steel after 8 days immersion in leachate MgzP2O7

3.15 g / cm ³ 5.38 m ² / g 32.5 g oil per

Mg2P2O7 100 g MgaP2O7 9.9

8.8

12.0 g / m ²

Example 2

The ability of coatings prepared with three oil paints (a, b, cj containing as anticorrosive pigment) was compared:

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(a) Magnesium pyrophosphate (MgaP2O7)

(b) a commercial core pigment consisting of simple zinc phosphate precipitated on ferric oxide particles (ferric red) [Zn3 (PO4) 2.2 H2O - Ρβ2θ3]

(c) a commercial core pigment consisting of simple zinc phosphate precipitated on titanium dioxide (titanium dioxide) particles [ZU3 (PO4) 2]. 2 H2O-TiO2]

The paint with Mg2P2O7 had the composition (wt.%):

% linseed oil,% iron red pigment,% zinc white pigment,% talc,

i. _

Γ '

T a b for 1k a% dessicant (1% cobalt octanate in gasoline) and% MgaP2O7.

Coatings with core pigments contained:

% linseed oil,% talc,% siccatives and% core pigment;

the core pigments always contained 16% zinc phosphate, which corresponded to 10% single zinc phosphate in the coating composition,

Corrosion tests were performed with coatings prepared according to ČSN 67 3004 on a steel sheet thickness of 0.6 mm cold rolled (table).

Coatings with commercial core pigments

Zns (PO4) 2.2H2O - Zn3 (PO4) 2.2 H2O -, Coating with Mg2P2O7 - Fe2O3 - T1O2

Corrosion loss steel. sheet (or areas of damaged paint around 100 mm cut)

in condensation chamber with SO2 after 21 days (CSN 03 0130) 43.8 g / m ² (38 mm ² ) 31.6 g / m ² (52 mm ² ) 12.9 g / m ² (31 mm ² ) Corrosion loss steel. sheet in a chamber with vapors of 18% hydrochloric acid after 8 days .15.2 g / m ² 11.9 g / m ² 11.1 g / m ² Surfaces of damaged paint iprl accelerated immersion test for resistance to corrosion - acc Mach and Schiffman (ČSN 67 3087) 28 mm ² 18 mm ² 14.25 mm ² Surfaces of damaged paint (around 100 mm longitudinal section) after 14 days immersion in 1000 ml of an aqueous solution containing 50 g of NaCl and 10 ml H2O2 38.5 mm ² 32 mm ² 18.5 mm ² Relative mass steel drop. after 21 days immersion in aqueous extracts of the coating film (10% by weight of coating suspension, film after 14 days of leaching) - based on steel losses. sheet after 21 days in dest. water 14.7% 17.9% 9.57%

and

Claims (1)

Example 3 Steel plates with coatings prepared according to Example 2 - 10% oil paints. ° / o Mg2P2O7, respectively. 63% of the core pigments were exposed to weather conditions of the East Bohemian chemical-industrial agglomeration for 2 years (or 1 year). Weight loss due to corrosion (CSN 03 8140) ranged from 13.9 to 18.5 g / m ² for two years with Mg2p2O7 coating, while for commercial core pigments it was 25 to 28 after one year g / m ² . Example 4 The thermal stability of di-magnesium pyrophosphate was calculated by calcination in an electric furnace at different temperatures, followed by analysis of the calcines by methods of instrumental analysis. Mg 2 P 2 O 7 is completely stable up to its melting point at 1185 ° C and is also stable in composition up to the monitored temperature of 1500 ° C; Once cooled and solidified, it again represented crystalline diphosphate. I will invent the subject Use of dicalcium phosphate as an anti-corrosion thermally stable pigment.