CS259906B1 - Blue-violet thermally highly stable anti-corrosion pigment dicobalt dibasic - Google Patents

Abstract

The solution concerns the use of dicobalt diphosphate as an intensely colored and stable anti-corrosion pigment. C02P2O7 is blue-violet and is thermally completely stable up to 1,250 °C and, under appropriate conditions, even higher. The cobalt content in the pigment is not high and its anti-corrosion properties are very good. The solution can be used in pigment technology, in the paint industry and in the preparation of high-temperature anti-corrosion protective layers.

Description

The present invention relates to the use of dicobaltate pyrophosphate as a thermally stable, anti-corrosion pigment blue-micropile.

In the recent past, some of the lead compounds and zinc chromate-based compounds were the most widely used and also the most effective anti-corrosion pigments. Recently, however, mainly due to hygienic and ecological reasons, they have been replaced by phosphorus compounds. 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 so far more frequently proposed, so-called polyphosphoric glasses (higher linear phosphates) and also the new two types of condensed phosphates - the cyclo-tetrafosphates of certain divalent metals and also zinc, manganese and copper pyrophosphates? however, the proposed pyrophosphates so far are only white, respectively. colorless.

The most commonly used single phosphates used as anticorrosive pigments are two hydrated zinc products - Zn ^ (PO ^ J 2 · 2 ^ 0, CaZn2 (PO ^) 2 ^ 0).

CrO 3, SiO 2 and phosphates of some alkaline earth metals. The main disadvantage of these compounds is that they do not achieve the anticorrosive effects of the best of both lead and chromate pigments and need to be applied to the coating compositions in relatively large amounts (concentrations) in order to satisfy the anticorrosive effects of the coatings. Another disadvantage of these substances is their low thermal stability, which does not allow their application to the corrosion protective layers for temperatures higher than 150 ° C.

This results from their defined hydrated form, which is essential for their anticorrosive action. This lesser thermal stability can also adversely affect 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, especially in not completely neutral, environments may also be a disadvantage. Over time, the pigment particles may be washed out of the protective layer (eg by the action of so-called acid rains), 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 phosphorous component and often more resource intensive, is relatively high. In addition, most single phosphates (with the exception of chromium phosphate) are also only white or white. colorless with little hiding power.

Among the other types of phosphates used or proposed for anticorrosion-inhibiting effect, so-called polyphosphate glasses are still known. They are higher linear condensed phosphates, with anions arranged in the polymer chain. As cations they mostly contain alkali metals (Na, K), alkaline earth metals (Ca, Mg) and in some cases also zinc and other metals (Cd, Al, Fe). Their use as anticorrosive pigments also has some disadvantages. Their anticorrosive effects again do not reach the level of the best lead pigments.

Their thermal stability is considerably higher than that of simple phosphates, but it 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 wet.

In fact, by the action of moisture, the pigment particles can pass into dihydrogen phosphates which are readily soluble and can be washed out of the coating or other protective layers. This is disadvantageous in view of their long-term corrosion resistance, since the layers become permeable to gaseous and liquid corrosive media. In addition, the use of some of these substances (with cations Zn, Cd) can lead to hygienic and ecological problems. Another disadvantage of higher linear phosphates - polyphosphoric glasses is the energetic, technological and also material-construction demands of their preparation, because it is necessary to work in the first stage with a very aggressive phosphate melt, at high temperatures of 800 to 1,300 ° C. volatile phosphorus component. Furthermore, in comparison with the other types of phosphate pigments, due to their vitreous character, they are more demanding in the final operations of their treatment into pigment form (especially crushing and grinding) and the process of their dispersion into paints or other protective materials can be more complicated. As with simple phosphates, most of the proposed phosphor glasses are virtually colorless.

Recently proposed for use as anticorrosive pigments, divalent metal cyclotetrophosphates (including cobalt) eliminates most of the drawbacks noted for single phosphates and higher linear phosphates. They are thermally completely stable up to their melting point. Above this temperature, however, they decompose. Cyclo-tetraphosphates are also chemically very stable, with very low solubility in both aqueous and not completely neutral compositions, so that their anti-corrosion 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.

Cyclotrophosphates have a higher proportion of phosphorus component than simple phosphates and their preparation is not so technologically demanding. Compared to higher linear phosphates, their preparation is not so demanding in terms of energy and construction. Also, most of the cyclo-tetraphosphates are white or colorless. The dicobaltic cyclo-tetraphosphate, which is stable up to 1060 ° C, is the color in blue-violet.

More recently, for use as anticorrosive pigments, the proposed zinc, manganese, and copper pyrophosphates complement the advantages mentioned for the cyclo-tetraphosphates, and in particular shift the thermal stability region to even higher temperatures. Of these three pyrophosphates, however, they are all almost white and none of them are strongly colored.

The use of dicobaltate pyrophosphate as a colored blue-violet thermally highly stable anticorrosive pigment removes the deficiency mentioned for the second uncoloured pyrophosphates as well as the deficiencies mentioned for single phosphates and higher linear phosphates. Co ₂ P ₂ 0 ₇ has basic physical properties suitable for pigment use - density, specific surface area, oil consumption and is easily dispersible into organic binders of paints and other types of binders, including inorganic based binders.

Its color is intensely blue-violet and is completely stable to high temperatures. It melts at 1,250 ° C and even above this temperature, its composition (when applied in an inert binder) does not change, and when the temperature drops below its melting point, it returns to solid particles Co ₂ P ₂ 0 ₇ · Solubility of dicobaltate pyrophosphate the composition is slightly higher than that of cyclo-tetraphosphate and thus releases phosphoric passivating anions more rapidly. However, its solubility is considerably lower than that of simple phosphates and higher linear phosphates;

In the first dissolution step, half of the anions are slowly released and the solid residue corresponds to a single phosphate. Therefore, the impermeability of the coating film and / or of the coating film is still almost not disrupted at this stage. another protective layer to which the pyrophosphate has been applied. The remaining phosphate then again has an anti-corrosion effect, so that overall Co ₂ P ₂ 0 _{7 has} longer-lasting effects. In addition, it is also blue-colored, practically in the same shade as the starting pyrophosphate. Dicobaltous diphosphate has a P / Cu molar ratio equal to 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. With dicobaltate pyrophosphate technology, a relatively high yield of pure product is readily achieved, which is practically in pigment form, yet does not require high quota of raw materials. Waste sludges of cobalt carbonate, wastes from cobalt-based catalysts and also low-quality (extractive) and diluted phosphoric acid can be used for its preparation.

The following are examples of some of the determined pigmentary properties of CO2P2 ° 7> which roughly correspond to the most common inorganic pigments. Examples of the dicobaltate pyrophosphate anticorrosion inhibiting properties are shown, which illustrate its superior abilities in this respect than commercial zinc phosphate based anticorrosion pigments. Further, the color of the pyrophosphate and its thermal stability are expressed.

Example 1

Some properties of dicobaltate pyrophosphate have been determined having: relation to its pigment use and inhibitory effect:

density specific surface area consumption of flaxseed oil pH of aqueous extract

- 8 days after insertion steel. metal plate

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

- corrosion losses of steel after 8 days immersion in leachate C ^ PjO?

3.62 g / cm ³ 3.33 m ² / g

29.0 g oil / 100 g Co ₂ P2 ° 7 6.36 6.65 6.48

11.69 g / m ²

Example 2

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

(a) dicobaltic pyrophosphate (C 1 P 3 Cl 2);

(b) a commercial core pigment consisting of simple zinc phosphate precipitated on ferric oxide particles (ferric red) (Zn ^ / PO ^ / j. 2 I ^ O - Fe2Oj)

(c) a commercial core pigment consisting of a simple zinc phosphate precipitated on titanium dioxide (titanium dioxide) particles (Zn2 / PO2.2H2O-TiCl2).

The coating composition with CO2P ₂ ° 7 had the composition (wt%): 29% linseed oil, 43% iron red pigment, 10% zinc white pigment, 7% talc, 1% siccative (1% cobalt octanate in gasoline) and 10% <2θ2Ρ2θ7 ·

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 673 004 on cold-rolled steel sheet 0.6 mm thick (table).

Table

Coatings with commercial Coating with core pigments with Co ₂ P ₂ 0 _?

Zn ₃ (PO 2) ₂ . Zn ₃ (PO ₄ ) ₂ .

.2H ₂ O, Fe ₂ O ₃ .2H ₂ O-TiO ₂

Corrosion loss steel. sheet (or damaged paint area around 100 mm cut) in condensation chamber with SO ₂ after 21 days (CSN 030 130)

Koroz. steel drop. sheet in a chamber with vapors of 18% hydrochloric acid after 8 days

Surfaces of damaged paint during accelerated immersion test against corrosion - according to Mach and Schiffman (CSN 673 087)

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 of H ₂ O ₂

Relative mass steel drop. sheet after 21 days immersion in aqueous extracts of the paint film (10% by weight of paint suspension, film after 14 days of leaching) - drawn to the loss of steel. sheet after 21 days in dest. water

43.8 g / m (38 mm ² )

31.6 g / m (52?)

5.8 g / m ² (19 mm ² )

15.2 g / m 11.9 g / m

7.9 g / m ² mm mm

-i c 2 16mm

38.5 mm

14.7% mm

17.9% mm

10.85%

Example 3

Steel plates with coatings prepared according to Example 2 from oil paints containing 10 wt. % Co ₂ P ₂ 0 ^, resp. 63% of the core pigments were exposed to the weather conditions of the East Bohemian chemical-industrial agglomeration for 2 years (or 1 year). Corrosion weight loss (CSN 038 140) ranged from 18.5 to 27.8 g / m ² for two years with Co ₂ P ₂ C> ₇ coatings, while for commercial core coatings pigments were 25 to 28 g / m after one year.

He attaches

Color and thermal stability of dicobaltate pyrophosphates were evaluated.

The color Co ₂ P ₂ 0 ₇ in the CIE coordinates of the coloristic triangle (CSN 011 718) is expressed by x = 0.269 and y = 0.260. In the same way, the color of the coating prepared with the coating composition of Example 2 is: x = 0.285 and y = 0.278. Remission of pure CO 2 P 10 O was also determined at wavelengths in the visible light region (CSN 011 718), which is shown in FIG.

In assessing the theoretical stability of dicobaltate pyrophosphate, calcination in an electric furnace at different temperatures and analysis of calcinates by means of instrumental analysis, it turned out that the substance does not undergo chemical, structural or color change after heating up to 1500 ° C.

Claims (1)

OBJECT OF THE INVENTION Use of dicobaltate pyrophosphate as a blue-violet thermally highly stable anticorrosive pigment.