CS253098B1 - Anticorrosive pigment - Google Patents

Abstract

Dicarbonate Cyclo-Tetraphosphate As pigment with inhibitory - anticorrosive effects it has better capabilities in paints than commercial anticorrosive pigments based on of simple zinc phosphate. Concentration in paints necessary to achieve sufficient anticorrosive effects can be relatively low, the pigment is chemically and thermally highly stable and is therefore suitable even for special high temperature purposes.

Description

The present invention relates to the use of magnesium di-cyclophosphate as an anticorrosive pigment.

Phosphates of some metals have the ability to have an anti-corrosion effect. They are able to suppress oxygen corrosion especially in ferrous materials in a humid, aqueous environment.

Their phosphate anions react with the iron ions released by corrosion and bind them to the insoluble phosphate, whose coating then also anodizes the metal surface. Metal cations from the phosphate used may also show some inhibitory effects. For example, the beneficial effects of zinc and calcium ions, as well as manganese ions, are reported to increase the effects of zinc ions.

In addition to the beneficial effects of calcium ions and some of the following data, some inhibitory properties of magnesium ions are also expected. In recent years, the use of simple phosphates of some metals has been widespread as anticorrosive pigments, with the aim of replacing the very effective but hygienically and ecologically problematic lead pigments. However, they do not yet achieve the efficacy of lead pigments with their anticorrosive inhibitory properties.

The most widespread is simple zinc phosphate - Ζη ₂ (ΡΟ ^) ₂ · 2 H ₂ O - ev. with admixtures of other bivalent metals (Ca, Mn). It has a relatively high content of zinc component, which is resource intensive and less effective than phosphorus.

Other anticorrosive pigments of the simple phosphate type - chromium and alkaline earth metals - are also known. The production of simple phosphates is not a technologically simple operation, since it is necessary to prepare them in the form of hydrates with an exact content of crystalline water, since they significantly influence the final anticorrosive properties of the products. The demands on the quality of the starting materials are also relatively high. Moreover, anticorrosive pigments of the simple phosphate type are partially soluble in aqueous media, which could have adverse hygienic and ecological consequences when used widely. The need for their use in the form of well-defined hydrates also limits the temperature range of their application; it does not allow their application in paints for coatings resistant to high temperatures and can complicate the final operations of pigment treatment or their dispersion. These compounds also need to be selected with relatively high concentrations in the coating compositions to provide sufficient inhibitory effects.

It is also known to use polyphosphate glasses as anticorrosive agents which contain an anion in the form of a polymeric phosphate chain (the so-called higher linear phosphates). These are systems containing phosphate chain anions and, in addition to alkali metal (Na, K) cations, also some alkaline earth cations (especially Ca, but also systems containing Mg) are known. and other cations - Zn, Cd, Al, Fe. However, these glasses also have some drawbacks due to problems in their preparation and application. It is necessary to obtain a homogeneous melt in the first stage of their preparation and thus to use high temperatures (800-1 300 ° C); furthermore, it is the volatilization of the phosphate component from the melt and the high aggressiveness of the melt, increasing the constructional requirements of the production equipment, and also the relatively difficult grinding of the vitreous product, even with intensive grinding.

After the application of these glasses into paints, their wetting ability is adversely affected. Phosphate chains break down. Due to the content of cations and anions, phosphate glass can thus be converted relatively quickly to simple phosphates corresponding to mostly highly soluble dihydrogen phosphates, which is disadvantageous in view of the long-term inhibitory effect of the coating. These phosphates from the coating are easy to wash out, thereby destroying the coating film, becoming readily permeable to both gaseous and liquid media, and the effect of its protective coating is lost. Again, their higher solubility can lead to certain hygienic-ecological problems that could also arise from their widespread use as in the case of simple phosphates.

Recently, the proposed uses of cyclotetrophosphates - disin (cf. AO 245 071), dimanganate (cf. AO 248 540) and dicalcium (cf. AO 247 844), which most of the drawbacks mentioned for single phosphates and for phosphate glasses, are also known. remove. a certain disadvantage of disodium cyclo-tetraphosphate is the price of zinc, respectively. the manganese component, although their content in these pigments is more than twice as low as in the case of simple phosphates.

Another minor deficiency could also be manifested in the wider use of these pigments in contact with water for direct supply of the population, where ev. the presence of zinc and manganese ions could matter. However, this drawback is negligible in comparison with simple phosphates, in particular due to the several times lower solubility of cyclotetaphosphates and the lower content of these components in these pigments, as well as the possibility of using lower necessary concentrations of pigments in paints.

In the case of dicalcium phosphate as anticorrosive pigment, in some cases its other minor disadvantage may be its somewhat higher solubility than the other cyclo-tetra phosphate. However, only in some cases of use, since, on the one hand, its solubility is considerably lower than that of simple phosphates and phosphate glasses, and in most cases it is favorable that calcium ions increase the alkalinity of the environment. In the case of dicalcium cyclophosphate, it is a problem to master the conditions of its preparation so that its yield is sufficient and there is no loss of the more material-intensive phosphate component.

The thermal stability and hence the temperature range of use of the three cyclotetaphosphates is limited by temperatures of 800 ° C (c-Zn 2 P 2 O 2), 900 ° C (c-Ca 2 P 2 O 2) ^and 950 ° C (c-Mn 2 P). Are temperatures allowing their use as anticorrosive pigments for high temperature purposes and significantly exceed the temperature range of the possible use of both simple phosphates and phosphate glasses; however, for some special applications it would be advantageous to achieve even higher stability temperatures.

These drawbacks are overcome by the invention of the use of magnesium di-cyclophosphate as an anti-corrosion pigment. This substance has favorable pigment properties - density, surface area and oil consumption - for use in paints; It is practically white with about 90% reflectance over the entire visible range of the spectrum and readily dispersible into paints.

Obtaining dicalcium phosphate is not a process technologically demanding for precise adherence to reaction conditions and for the quality of the starting materials as the preparation of some simple phosphates, and is not as energy intensive as the preparation of phosphate glasses. Inexpensive natural magnesium carbonate or certain waste magnesium compounds - hydroxides, carbonates - and inferior (extractive) dilute phosphoric acid can be used. In its synthesis, c-MgP ^O. may be formed either directly in the required powder form, or it can be easily converted into this form by its own dispersion into the paint.

Magnesium cyclotetaphosphate contains the magnesium and phosphorus components in a molar ratio of one to two; this is more favorable in favor of a more efficient phosphorus component. It contains anions in the form of tetraphosphate cycles, consisting of four bound tetrahedra (PO ^).

They are very stable anions advantageous in terms of pigment and anticorrosive properties of cyclo-tetraphosphate. This results in its high thermal stability (up to a melting point of 1,160 ° C) - the highest of all the proposed cyclotetaphosphates. This allows convenient application even in anticorrosive coatings for special high temperature applications.

Another important property is its very difficult, very gradual and gradual solubility in aqueous media. When dissolving the ^{C "M} ^ 2 ^P 4 ° 12 ^tot Iz occur in the first step for hydrolytic cleavage tetrafosforečnanových cycles. When moisture is passed through the coating and the cyclo-tetraphosphate particles are attacked by water molecules, the phosphate ions then enter the soluble form in a slow process. As a result, these passive ions are released virtually in a controlled manner according to the degree of environmental corrosion.

In the first, slowest stage, only one half is gradually released, since the other half remains bound in the form of the magnesium pyrophosphate formed, to which c-Mg ₂ P ₄₀ g ₂ gradually passes. The transition is largely a topochemical event, so that the shape character of the original pigment microparticles remains. This does not create undesirable holes - micropores - in the coating film, which would help further corrosion.

The second stage of possible dissolution of the pigment in the paint is the gradual transition of the resulting pyrophosphate particles, gradually releasing another third of the phosphate-inhibiting anions, to a single magnesium phosphate, which also has some anticorrosive properties.

Below are examples of some of the pigment and inhibitory properties of magnesium di-cyclophosphate and their comparison with commercial phosphate pigments. c-Mg ₂ P _{4 0 2} has favorable pH values of aqueous extracts as well as very good inhibitory properties of this extract towards steel sheet. For steel sheets coated with cyclo-tetrasodium phosphate, less corrosion loss was observed in condensation chamber tests (CSN 03 8131) and in hydrochloric acid vapor chamber (CSN 67 3094) than in sheet metal coatings containing commercial phosphate pigments. The areas of damaged paint with c-Mg ₂ P ₄ 0g ₂ were also smaller in the accelerated immersion test for resistance to corrosion (according to Mach and Schiffman - ČSN 67 3087) as well as in the classification test of paint (ČSN 67 3004) in condensation chamber with vapors. sulfur dioxide and sodium chloride / hydrogen peroxide solution; the relative weight losses of steel sheets in paint film extracts were also smaller (ČSN 67 3004).

Example 1

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

density specific surface 2.85 g / cm ³ 0.27 m ² / g flaxseed oil consumption 23.3 g oil / 100 g pH of aqueous extract c-Mg ₂ ^p 4 ^O 12 - 8 days after inserting the steel sheet 4.87 - 8 days after removal of the steel sheet 5.58 inhibitory properties of aqueous extract 5.10 - corrosion loss of steel after 8 days immersion in extract (mg / g) 2.71

Example 2

Inhibitory properties of coatings prepared using three oil paints containing anticorrosive pigment were compared

- Magnesium cyclo-tetraphosphate (c-Mg ₂ P ₄ 0g ₂ )

- commercial core pigment consisting of a simple zinc phosphate precipitated on ferric oxide particles (Zn ^ (PO ^) ₂ ~ Fe ₂ 0g)

- a commercial core pigment consisting of a single zinc phosphate precipitated on titanium dioxide particles (Zn (PO 4) ₂ - TiO ₂ ).

Coating composition C-Mg ₂ ^P 40 g ₂ had a composition (wt.%), 29% of linseed oil, 43% of pigment red iron oxide, 10% pigment, zinc oxide, 7% talc, 1% driers (1% oktanátu cobalt in gasoline) and 10% c-Mg ₂ P ₄ 0g.

Core pigment paints comprised: 29% linseed oil, 7% talc, 1% siccative and 63% core pigment; the core pigments always contained 16% zinc phosphate, which corresponded to 10% single zinc in the paint.

Corrosion tests (tab.) Were performed with coatings prepared according to ČSN 67 3004 on 0.6 mm cold rolled steel sheet.

Table

Commercial core coatings pigments Coating c-Mg ₂ ^p 4 ^O i2 ^Zn 3 ^<P0 4) 2 ^-Fe 2 ° 3 Zn ₃ ⁽ⁱⁿ 3) 2 ^T i ^O 2 Corrosion loss of steel sheet in condensation chamber after 28 days (CSN 03 8131) Corrosion losses of steel sheet in the chamber with hydrochloric acid vapors 10.65 mg / g 7.39 mg / g 2.35 mg / g after 8 days (ČSN 67 3094) Surfaces of damaged paint during accelerated immersion test 3.30 mg / g 2.58 mg / g 3.02 mg / g against corruption - according to Mach and 2 2 Schiffman (ČSN 67 3087) Classification tests of paint according to ČSN 67 3004: - test A: 28 mm. 18 min 13 mm ⁵ areas of damaged paint in condensation o start the chamber containing S0 _o 38 mm 52 mm 31 mm of (6 points) (7 points) (5 points) - test B: areas of damaged paint 2 2 2 in NaCl solution with H _o 0 38.5 mm 32 mm 14.5 mm - test C: relative weight loss of steel sheet in paint film extracts relative to (6 points) (5 points) (2 points) decreases in distilled water 14.7% 17.9% 9,41% (4 points) (4 points) (3 points) Classification of coating mass CSN 67 3004 CSN 67 3004 CSN 67 3004 Fe-3 Fe-3 Fe-2

SUBJECT OF THE INVENTION

Claims (1)

SUBJECT OF THE INVENTION Use of magnesium di-cyclophosphate as anticorrosive pigment.