CS259341B1 - Anticorrosion stable pigment - Google Patents

Abstract

The solution concerns the use of disodium diphosphate as an anticorrosive thermally stable pigment. CU2P2O7 is stable up to high temperatures and is effective against corrosion when used in coatings and other types of anticorrosive protective layers, including inorganic binders for high-temperature purposes. The solution may have applications in pigment technology and in the coating and heat-resistant materials industry.

Description

The invention relates to the use of diporpous diphosphate as an anti-corrosion thermally stable pigment.

The most effective anti-corrosion pigments are some lead compounds and compounds based on zinc chromene. However, recently they have been replaced by phosphorus compounds for hygienic and ecological reasons. Phosphates suppress corrosion by oxygen in a humid, aqueous environment, especially in ferrous materials (steel, cast iron), where they bind iron ions resulting from corrosion into insoluble phosphate. This then forms a coating that also passivates the metal surface. Phosphate cations can also have a positive effect on the anti-corrosion effects.

Of the phosphorus compounds, the most commonly used or proposed for use as anti-corrosion pigments are mainly simple phosphates. The second group is represented by condensed phosphates. This group includes, on the one hand, the so-called polyphosphate glasses (higher linear phosphates), which have been proposed more frequently so far, and, on the other hand, the cyclotetraphosphates of some divalent metals, which have been proposed by the author of this invention, and most recently, also zinc and manganese diphosphates.

Of the simple phosphates, the two most widely used are zinc products in the form of dihydrates - Zn^(PO^)j.21^0, CaZnj(PO^)j.íHjO. The use of CrPO^.SHjO and phosphates of some alkaline earth metals is also known. The main disadvantage of these compounds is that they do not yet achieve the anticorrosive effects of the best lead and chromate pigments and they need to be applied to paint materials in relatively large quantities (concentrations) for their anticorrosive effects to be satisfactory. Another disadvantage of simple phosphates is the relatively low thermal stability of these substances, resulting from their defined hydrated form, which is necessary for their anticorrosive effect. They cannot therefore be used in anticorrosive protective 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 and also its dispersion into the anticorrosive material.

From the point of view of the long-term anti-corrosion effect of simple phosphates, their partial solubility in aqueous, not completely neutral media (e.g., by the action of so-called acidic solutions) can also be a certain disadvantage. Over time, pigment particles can be washed out of the protective layer, thereby breaking its impermeability to corrosion-causing media. The technology of preparing simple phosphates is also not a simple operation, due to the need to obtain a precisely defined hydrate. It also requires high-quality raw materials, while the content of the metal component, which is less effective than the phosphorus component and is often more demanding in terms of raw materials, is relatively high.

Also, the so-called polyphosphoric glasses and their use as anti-corrosion pigments have certain disadvantages; These higher linear condensed phosphates contain anions in the form of a polymer chain. They are designed with various cations - sodium, potassium, calcium, magnesium and sometimes also zinc, cadmium, aluminum or iron (the case with copper cations (not yet known). Polyphosphoric glasses do not reach the level of the best lead pigments in terms of their anti-corrosion effects. Their thermal stability is significantly higher than that of simple phosphates, but it is also limited, because in the temperature range of 400 to 600°C they recrystallize and usually lose the character of the higher polymer anion. Therefore, they cannot be used in anti-corrosion protective layers above these temperatures. Higher linear phosphates are also partially soluble and, if they are in powder - pigment form, they even tend to get wet. Under the influence of moisture, they gradually turn into dihydrogen phosphates; these are then easily soluble, can be easily (washed out of protective layers, which are thus destroyed and become permeable to corrosive media.

Higher linear phosphates are not effective in the long term as anti-corrosion agents, not to mention the fact that their use on a large scale (especially Cd and Zn products) can lead to hygiene and ecological problems. Another disadvantage of these compounds is the high complexity of their preparation, especially from an energy and construction point of view. They are prepared from melts at high temperatures (80 to 1,300 °C), which are quite aggressive and from which aggressive phosphorus products also partially evaporate. The products have a glassy character and are therefore also relatively demanding

the final operation of their processing into powder - pigment form and dispersion into a paint or other substance.

Recently proposed series of cyclotetraphosphates of divalent metals (including 1 copper) eliminate most of the shortcomings mentioned for simple phosphates and for higher linear phosphates. They are thermally very stable up to their melting point (copper product up to 890 °C).

Above this temperature, however, they decompose. Cyclotetraphosphates are also chemically very stable, with very low solubility in aqueous and not completely neutral environments, so their anticorrosive action is long-term. In some cases, their use, especially in humid, aggressive environments, however, can be their disadvantage, because then a faster release of phosphorous passivating anions is required.

Cyclotetraphosphates have a high proportion of the more effective phosphoric anticorrosive component, which is 2 to 3 times higher than in simple phosphates. However, in the case of some products, this component may be more demanding in terms of raw materials than the cationic component. The preparation of cyclotetraphosphates is not as technologically and structurally demanding as the preparation of the latter phosphates.

However, for some products it is more difficult to manage to achieve sufficient yield.

The disadvantages mentioned for simple phosphates and for higher linear phosphates are eliminated and the advantages mentioned for cyclotetraphosphates are supplemented by the use of diporpous diphosphate as an anticorrosive thermally stable pigment.

CUjPjO? has suitable basic pigment properties - density, specific surface, oil consumption, ' is almost white with a faint blue tint and easily dispersible in organic and inorganic binders. The solubility of dicopper diphosphate is higher than that of cyclo-tetracopper diphosphate, and so the phosphoric passivating ions are released from it faster. However, again in a gradual and practically regulated manner, according to the degree of corrosive action of the environment. In the first stage, half of the anions are gradually released and the solid remainder corresponds to simple phosphate. Therefore, in this phase, the impermeability of the paint film, or other protective layer to which the diphosphate was applied, is almost not violated.

The remaining phosphate then also acts as an anti-corrosion agent, so overall CUjPjO? has longer-term effects. It is also completely stable up to its melting point of 1,050 °C and is still partially stable after reaching this temperature. The diphosphate has a molar ratio of P/Cu equal to one, which is a higher value and more advantageous from an anti-corrosion point of view than simple phosphates, and conversely, it is lower, and therefore less demanding in terms of raw materials than cyclotetraphosphates.

The technology for preparing diporpic diphosphate easily achieves a relatively high yield of pure product, which is practically in pigment form, and there are no high demands on the quality of the starting raw materials.

The following are examples of some of the determined pigment properties of Cu2P2O3, which roughly correspond to the most common inorganic pigments. The following are examples of the determined anti-corrosion-inhibitory properties of dicopper diphosphate, which document its better capabilities in this respect than commercial anti-corrosion pigments based on zinc monophosphate dihydrate.

Example 1

Some properties of diporpous diphosphate have been determined, related to its pigmentary use and inhibitory action:

density 4.15 g/cm specific surface 1.38 m /g linseed oil consumption 19.2 g oil/100 g CU2P2®7 pH of aqueous extract 5.04

- 8 days after inserting the steel sheet 6.39 w

- 8 days after removing the steel sheet 5.48 inhibitory properties of the aqueous extract

- corrosion losses of steel after 8 days of immersion in the leachate 8.18 g/m

Example 2

The capabilities of coatings prepared with the help of three oil-based coatings (a, b, c) containing as anti-corrosion pigment:

a) diporpic acid (Cu(II) phosphate)

b) commercial core pigment consisting of simple zinc phosphate precipitated on iron oxide particles (ferric red) (Zn ₃ (P0 ₄ ) ₂ .2H ₂ O-Fe ₂ O ₃ )

c) a commercial core pigment consisting of simple zinc phosphate precipitated on titanium dioxide particles (titanium white) (Zn ₃ (P0 ₄ ) ₂ .2H ₂ O-TiO ₂ ).

The coating material with CUjPjO^ had a composition (wt. %) of 29% linseed oil, 43% iron red pigment, 10% zinc white pigment, 7% talc, 1% siccative (1% cobalt octanate in gasoline) and 10% Cu ₂ P ₂ O ₇ ·

The coatings with core pigments contained: 29% linseed oil, 7% talc, 1% siccatives and 63% core pigment; the core pigments always contained 16% zinc phosphate, which corresponded to 10% simple zinc phosphate in the coating.

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

Table

Coatings with commercial Core pigment coating

Zn ₃ (P0 ₄ ) ₂ .2H ₂ 0-Fe ₂ 0 ₃ ZUg (PO ₄ ) ₂ .2H ₂ O-TiO ₂ Cu^O,

Corrosion losses of steel sheet (or damaged coating area around 100 mm of the section) in a condensation chamber with SO ₉ after 21 days (ČSN 03 0130 ⁾ 43.8 g/m2 (38 ^mm2 ) Corrosion losses of steel sheet in a chamber with 18 6 acid vapors. 15.2 g/m2 hydrochloric acid after 8 days areas of damaged paint during accelerated immersion 28mm ² test for resistance to undercutting corrosion - according to Mach and Schifman (ČSN 67 3087) Areas of damaged paint (around the longitudinal 100 mm 38.5mm ² section) after 14 days of immersion in 1,000 ml of an aqueous solution containing 50 g NaCl and 10 ml H ₂ O ₂ Relative mass losses of steel sheet after 21 days of immersion 14.7% into aqueous leaches of the paint film (10% by weight: suspension of the paint, film after 14 days of leaching (-related to losses of steel sheet after 21 days in distilled water

31.6 g/ ^m2 (52 ^mm2 )

11.9 g/m ² mm ² min

5.1 g/ ^m2 (24 ^mm2 )

8.2 g/ ^m2

12.25 mm ² nun

17.9% 10.44%

Example 3

Steel plates with coatings prepared according to example 2 from oil coatings containing 10 wt. % Cu ₂ P ₂ O ₇ , or 63 % core pigments, were exposed to the sun for 2 years (or

year) exposed to weather conditions of the East Bohemian chemical-industrial agglomeration. Weight losses due to corrosion (ČSN 03 8140) ranged from 9.2 to 16.2 g/m2 when using coating 2 with Cu ₂ P ₂ O ₇ after two years, while when using coatings with commercial core pigments they were 25 to 28 g/ ^m2 after just one year.

Attached

The thermal stability of diporpous diphosphate was assessed by calcination in an electric furnace at various temperatures, followed by analysis of the calcinates by instrumental analysis methods. Cu ₂ P ₂ O ₇ is completely stable up to its melting point of 1,050 °C.

Claims (1)

Use of copper diphosphate as an anti-corrosion thermally stable pigment.