CS259341B1 - Anticorrosive thermically stable pigment - Google Patents

Abstract

The solution relates to the use of pyrophosphate as a corrosion-resistant thermic a stable pigment. CU2P2O7 is stable to high temperatures and is anti-corrosive when used in paints and in others types of corrosion protection layers including inorganic binders for high temperature purposes. The solution can be used in pigmentary technology and in the paint industry and heat resistant materials.

Description

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

The most effective anticorrosive pigments are some lead compounds and zinc chromene compounds. Recently, however, they have been replaced by phosphorus compounds for hygienic and ecological reasons.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.

Of the phosphorus compounds, resp. designed for use as simple phosphates as anticorrosive pigments. The second group is condensed phosphates. These include the so-called polyphosphoric glasses (higher linear phosphates), which have been proposed so far, and the recently proposed cyclotrophosphates of some divalent metals, and more recently also zinc and manganese pyrophosphates.

Of the simple phosphates, two zinc products in the form of dihydrates are the most widespread so far - Zn2 (PO4) j2.114, CaZnj (PO4) j2H10. It is also known to use CrPO4SH3O and phosphates of some alkaline earth metals. The main disadvantage of these compounds is that they do not yet achieve the best corrosion effects of both lead and chromate pigments and need to be applied to paints in relatively large amounts (concentrations) in order to have satisfactory corrosion effects. 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 corrosion protective coatings for higher temperatures (above 150 ° C). Their lower thermal stability can also complicate the final mechanical-thermal operations of pigment preparation and treatment 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 agents (eg by 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 breaking 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 and often more material intensive, is relatively high.

Also the so-called polyphosphoric glasses and their use as anticorrosive 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 ferric (the case with copper cations (not yet known). Although it is significantly higher than that of simple phosphates, it is also limited, since they do not recrystallize in the temperature range of 400 to 600 ° C and usually lose the character of the higher polymer anion and therefore cannot be used in corrosion protective layers above these temperatures. and if they are powder-pigmented, they even tend to get wet.They are gradually converted to dihydrogenphosphates by the action of moisture, which are then easily soluble, can easily (washed out of the protective layers, thus breaking up and becoming permeable for corrosive media.

Higher linear phosphates are not anticorrosive in the long term, despite the fact that their use on a large scale (especially Cd and Zn products) can lead to hygienic and ecological 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 (80 to 1300 ° C), which are very aggressive and partly also aggressive phosphorous fumes. The products have a glassy character and are therefore quite demanding

final operation of their modification into powder - pigment form and dispersion into paint or other material.

The recently proposed series of divalent metal cyclotetrophosphates (including 1 copper) eliminates most of the drawbacks mentioned for both single phosphates and higher linear phosphates. They are thermally very stable up to their melting point (copper product up to 8990 ° C).

Above this temperature, however, they decompose. Cyclo-tetraphosphates are also very chemically stable, with very low solubility in both aqueous and not completely neutral media, so that their anticorrosive action has a long-term character. However, in some cases their use, especially in damp, aggressive environments, may be a disadvantage, since a faster release of phosphoric passivating anions is needed.

Cyclo-tetraphosphates 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. The preparation of cyclo-tetraphosphates is not as technologically and structurally demanding as the preparation of the latter.

However, some products are more difficult to manage to obtain sufficient yield.

The drawbacks mentioned for simple phosphates and for higher linear phosphates eliminate them and the advantages mentioned for cyclotrophosphates are complemented by the use of dibasic pyrophosphate as an anticorrosion thermally stable pigment.

CUjPjO? It has suitable basic pigment properties - density, specific surface area, oil consumption, is almost white with a light blue tint and easily dispersible into organic and inorganic binders. The solubility of dibasic pyrophosphate is higher than that of dibasic cyclohexaphosphate and thus releases phosphoric passivating ions more quickly. Again, however, in a gradual and practically regulated way, depending on the degree of corrosive environmental impact. In the first step, half of the anions are slowly released and the solid residue corresponds to a single phosphate. Therefore, the impermeability of the coating film, respectively, is virtually not impaired at this stage. another protective layer to which the pyrophosphate has been applied.

The remaining phosphate then has an anti-corrosion effect again, so that it has a total CuCl2? longer-term effects. It is also completely stable up to a melting point of 1050 ° C and is still stable even after reaching this temperature. The diphosphate has a P / Cu molar ratio equal to one, which is a higher value and, from an anti-corrosion point of view, lower than that of simple phosphates, and vice versa is lower, and thus less expensive in terms of raw materials than cyclotetrafosphates.

With the preparation of dibasic pyrophosphate, a relatively high yield of the pure product is easily achieved, which is practically in pigmented form, while at the same time not demanding on the quality of the starting materials.

The following are examples of some of the determined pigmentary properties of CuCl2O2 which roughly correspond to the most common inorganic pigments. The following are examples of the determined anticorrosion-inhibiting properties of dibasic pyrophosphate, which illustrate its superior abilities in this respect than commercial anticorrosive pigments based on zinc phosphate dihydrate.

Example 1

Some properties of copper pyrophosphate related to its pigment use and inhibitory action have been determined:

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

- 8 days after insertion steel. 6,39 w

- 8 days after removal of steel. Inhibition properties of aqueous extract

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

Example 2

The ability of coatings prepared with three oil paints (a, b, c) containing as anti-corrosion pigment was compared:

a) Copper (II) pyrophosphate

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

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

The coating composition with CuCl 3 O 2 had a composition (wt%) of 29% linseed oil, 43% ferric red pigment, 10% zinc white pigment, 7% talc, 1% siccative (1% cobalt octanate in gasoline) and 10% Cu ₂ P ₂ O ₇ ·

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

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

Table

Coatings with commercial Coatings with core pigments

Zn ₃ (P0 _{4) 2} .2H ₂ 0-Fe ₂ 0 ₃ Zug (PO _{4) 2} .2H ₂ O-TiO ₂ Cu ^ O

Corrosion loss steel. sheet (or damaged paint area around 100 mm cut) in condensation chamber with SO ₉ after 21 days (ČSN 03 0130) ^í 43.8 g / m '(38 mm ² ) Corrosion loss steel. plate in vapor chamber 18 6 acid. 15.2 g / m ' hydrochloric acid after 8 days surface of damaged paint at accelerated draft 28 mm ² Corrosion resistance test - according to Mach and Schifman (ČSN 67 3087) Damaged paint surfaces (around 100 mm longitudinal) 38.5 mm ² after 14 days of immersion in 1000 ml of an aqueous solution containing 50 g of NaCl and 10 ml of H ₂ O ₂ . steel drop. sheet after 21 days immersion 14.7% to aqueous extracts of the paint film (10% by weight: suspension of paint, film after 14 days of leaching (-related to the loss of steel sheet after 21 days in dist. water)

31.6 g / m ² (52 mm ² )

11.9 g / m ² mm ² min

5.1 g / m ² (24 mm ² )

8.2 g / m ²

12.25 mm ² nun

17.9% 10.44%

Example 3

Steel plates with coatings prepared according to Example 2 of 10% oil paints. % Cu ₂ P ₂ O ₇ resp. 63% of the core pigments were for 2 years (resp.

year) exposed to weather conditions of the East Bohemian chemical and industrial agglomeration. The weight loss due to corrosion (CSN 03 8140) ranged from 9.2 to 16.2 g / m ₂ for 2 years with Cu ₂ P ₂ O ₇ , while for commercial core pigments it was already 25 to 28 g / m ² per year.

He attaches

The thermal stability of copper pyrophosphate was evaluated by calcination in an electric furnace at various temperatures, followed by analysis of calcines by methods of instrumental analysis. Cu ₂ P ₂ O ₇ is completely stable up to its melting point at 1050 ° C.

Claims (1)

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