CS259734B1 - Blue-and-violet thermically atable pigment with anticorrosive properties - Google Patents

Abstract

The present invention relates to the use of cyclo-tetraphosphate long-color as color a a stable anti-corrosion pigment. C-C02P4- O12 has a distinctive blue-violet shade, is thermally completely stable up to 1060 "C and has effective anticorrosion capabilities. Content cobalt in pigment is relatively low and is smaller than the other cobalt pigments. The solution can be used in pigmentary technology and in the paint industry

Description

The present invention relates to the use of dicobaltic cyclotrophosphate as a blue-violet pigment with anticorrosive properties.

Some metal phosphates have the ability to inhibit corrosion, since they inhibit, in particular, ferrous materials, oxygen corrosion in a humid, aqueous environment. Corrosion-released iron ions are bound to the insoluble phosphate, which at the same time anodically passivates the metal surface. Cations can also have a beneficial effect on the anticorrosive action of phosphates.

At present, the use of some simple phosphates as anticorrosive pigments has been extended, replacing the otherwise very effective, but for hygienic and ecological reasons, pigments based on lead compounds. However, simple phosphates do not achieve the anticorrosive properties of the best and most widely used lead pigments. So far, simple zinc phosphate in the form of - Zn3 (PO4) 2.2 H2O dihydrate has been used on a larger scale. It has a relatively high content of a divalent metal component, which is resource intensive and at the same time less effective in terms of anticorrosion than the phosphorus component.

Chromium phosphate is also known as an anticorrosive pigment but for which the same disadvantages apply as for zinc phosphate. The use of alkaline earth phosphates is also known. However, the production of these simple phosphates is not a technologically simple operation since they need to be prepared in the form of certain hydrates, i.e. with an exact content of crystalline water, which significantly affects their anticorrosive properties. The precipitation reactions of their preparation also require starting materials of relatively high purity.

Simple phosphates are also partially soluble in aqueous, not completely neutral environments, which, in addition to the possible degradation of the coating over time, can cause adverse hygienic and environmental problems in their widespread use. Their close correlation of anticorrosive efficiency with the content of crystal water significantly limits the temperature range of their use and does not allow their application in paints for high temperature purposes.

This may also complicate the final mechanical-thermal operations of treating pigments or dispersing them into the paint. A further disadvantage is also the need to apply them to the coating compositions in relatively high concentrations in order to obtain sufficient anticorrosive effects of the coatings. In addition, most simple phosphates are also only white or colorless, with only slight opacity and none have a distinctive color shade.

It is also known to use glass products of the type of higher linear condensed phosphates having anions in the form of a polymeric phosphate chain. They also contain alkali metal cations (Na, KJ and some alkaline earth metals (Ca, Mg), possibly also cations of other metals (Zn, Cd, Al, Fe). However, these glasses also have some drawbacks. containing iron ions are again virtually colorless, which can be a disadvantage for some applications, it is a technological difficulty of their preparation (necessity to start from the melt at temperatures of 800 to 1 300 degrees Celsius, its high aggressiveness, volatilization of phosphate component from melt) ) and, when applied, their solubility and wetting ability.

In fact, pigment particles of higher linear phosphates applied in the coating composition can be converted to dihydrogen phosphates by the action of moisture. These are then readily soluble, and can be easily washed out of the coatings, thereby destroying the coating film. This is disadvantageous from the viewpoint of the long-term protective effect of the coating, since the coating becomes permeable to both gaseous and liquid corrosive media. Again, the higher solubility of these products can lead to certain hygienic-ecological problems in the wider application of this type of pigment.

The proposed use as anticorrosion pigments of cyclo-tetrafosphates of certain divalent metals is also known. (No. AO No. 253 192) and di-magnesium (No. AO No. 253 098), which overcome most of the drawbacks mentioned for both simple phosphates and ipolyphosphate glasses.

However, they are all white, respectively. colorless (except beige c-Fe2P40i?). However, the anticorrosive pigment, which would excel in its high thermal and chemical stability and was intensely colored in blue or purple, is not yet known. Although it is known to use some cobalt compounds (oxide, silicate as thermally stable pigments in blue-violet color shade. In terms of anticorrosive effects, they are practically inert in nature, their main disadvantage is relatively high content of deficient cobalt (especially in the case of oxide). energy intensity of their preparation.

These drawbacks are overcome by the invention of using dicobaltic cyclo-tetraphosphate as a blue-violet thermally stable pigment with anticorrosive properties. This substance has suitable basic pigment properties - density, specific surface, oil consumption, it is intensely blue-violet and easily dispersible in organic paints and other types of binders, including inorganic-based binders. X

Its preparation is not as technologically expensive as a one-year process for accurate adherence to reaction conditions and for the quality of the raw materials, as is the preparation of some simple phosphates and is not as energy and structurally demanding as the preparation of phosphate glasses. It is also not as energy and resource intensive as preparing other blue-violet pigments of the cobalt compound type. The cobalt content of the cyclo-tetraphosphate is only 27.3% by weight. % and also waste carbonate sludge processed in the glass industry can be used to prepare the pigment.

Low-quality (extractive) and diluted phosphoric acids can also be used as sources of phosphorous component. This component is then in the pigment in the form of tetrafosphate cycles, consisting of the four tetrahedra (—PO4—) linked together. These very strong anions are then the main carriers of the thermal and chemical stability of the pigment and its anticorrosive properties.

The pigment is stable up to a melting point of 1060 [deg.] C., which is the highest thermal stability of all of the compounds of this type proposed hitherto after magnesium di-cyclophosphate. It allows the application of pigment also in anticorrosive protective layers for special high-temperature applications.

In terms of chemical stability, C-CO2PO4012 is the most stable of the hitherto proposed cyclotrophosphates. It is most difficult to dissolve in all aqueous environments, both acidic and alkaline, so its effective anticorrosive action is indeed of long-term character. Moreover, its dissolution is, as with other compounds of this type, a stepwise process, with all the intermediates at each dissolution stage also in intense blue-violet tint and also having anti-corrosion effects. When dissolving C-CO2P4O12, the anions of the tetrafosphate cycles must first undergo hydrolytic cleavage.

When moisture passes through the coating and the attack of the cyclotrophosphate particles with water molecules, the phosphate passivating ions then enter the soluble form in a slow process. They are thus released practically in a controlled way according to the degree of environmental corrosion.

Thus, in the first, slowest stage, only one half is gradually released, as the other half remains bound in the form of the dicobaltate pyrophosphate formed, to which C-CO2P4O12 passes. The transition is in part a topochemical event, so that the shape character of the original pigment microparticles remains. This avoids the formation of undesirable holes - micropores - in the coating film, which would help further corrosion. The color shade of the coating is practically preserved, as the particles of pyrophosphates are intensely blue-violet.

The second stage of possible dissolution of the pigment in the coating is the gradual transition of the resulting pyrophosphate, new particles with the gradual release of another third of the phosphate inhibiting anions to a single cobalt phosphate, which also has some anticorrosive properties and is also a bluish violet hue.

Examples of some pigmentary properties and anticorrosion-inhibiting properties of dicobaltic cyclo-tetraphosphate are given below. C-CO2P4012 has intensive color in blue-violet shade, high thermal stability, favorable pH values of aqueous extracts and very good inhibitory effects of this extract to steel sheet.

For steel sheets coated with dicobalt cyclo-tetraphosphate, lower (or at least comparable) corrosion mass losses were recorded in condensation chamber tests (CSN 03 8131) and in chambers with hydrochloric acid vapors than for paint plates containing commercial anticorrosive pigments. based on simple zinc phosphate. Also the corrosion loss of steel sheets with a coating containing cyclo-tetraphosphate during long-term weather tests in conditions of the East Bohemian chemical-industrial agglomeration were favorable and they document very good anticorrosive capacity of C-CO2P4O12.

Example 1

Some properties of dicobaltic cyclo-tetraphosphate related to its pigment use and inhibitory action have been determined:

density 3.46 g / cm ³ specific surface 0.75 m ² / g flaxseed oil consumption 20.0 g oil / 100 g C-CO 2 P 4 O 12 pH of aqueous extract 4.82 - 8 days after inserting the steel sheet 5.64 - 8 days after removal of steel sheet 5,02 inhibitory properties of water leachate - corrosion losses of steel after 8 days immersion of 9.1 g / m ² into leachate C-CO02P4012

Example 2

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

(a) Long-tetrachloride cyclotetrophosphate (C-CO 2 P4012)

(b) a commercial core pigment consisting of poisonous zinc phosphate precipitated on ferric oxide particles <(ferric red) [Zn3 (PO4) 2].

. 2 H2O-Fe2O3]

(c) a commercial core pigment consisting of a simple zinc phosphate precipitated on titanium dioxide particles (titanium dioxide) [Zu3 (PO4) 2, 2 H2O - T1O2].

The paint with C-CO2P4O12 had the composition (wt.%):

% linseed oil,% ferric red pigment,% zinc zinc pigment,% talc,% desiccant (1% cobalt octane in gasoline) and% C-CO2P4O12.

Coatings with core pigments contained:

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

the core pigments each contained 10% 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 steel sheet thickness of 0.6 mm cold rolled (table).

Table

Coatings with commercial Coatings with C-CO2P4O12 core pigments

Zn3 (PO4) 2.2 H2O - ΖΠ3 (ΡΟ4) 2. 2H2O - - Fe2O3 - Τ1Ο2

Corrosion loss steel. sheet in the condensation chamber after 16.8 g / m ² days (ČSN 03 0131)

Corrosion loss steel. sheet in a chamber with 18% hydrochloric acid vapors 15.2 g / m ² after 8 days

Example 3

Steel plates with coatings prepared according to Example 2 of 10% oil paints. % C-CO2P4012, respectively. 63% of core pigments were exposed to weather conditions of the East Bohemian chemical-industrial agglomeration for 2 years (or 1 year). The weight loss due to corrosion (CSN 03 8140) ranged from 18.5 to 23.1 g / m ² for two years when using C-CO2P4O12, whereas for commercial core pigments, after one year 25 up to 28 g / m ² .

Example 4

The color and thermal stability of dicobaltic cyclo-tetraphosphate was evaluated.

13.2 g / m ² 6.56 g / m ²

11.9 g / m ² 15.6 g / m ²

Color C-CD2P4O12 in CIE coordinates of coloristic triangle (ČSN 011718) is expressed by values of x = 0.274 and y = 0.260. In the same way, the color of the paint prepared with the coating composition of Example 2 is: x = 0.290 and y = 0.282. Remission of pure C-CO21P4O12 was also determined at wavelengths in the visible range (ČSN 011718), which is shown in the figure.

In assessing the thermal stability of dicobaltic cyclo-phosphate, calcination in an electric furnace at various temperatures and analysis of calcinates by means of instrumental analysis and leaching with an aqueous solution of 0.3 N HCl (according to the author's certificate no. 232 090), it turned out that melting point of 1 060 ° C does not undergo any chemical, structural or color change.

Claims (1)

The use of dicobaltic cyclo-tetraphosphate as a blue-violet thermally stable bile pigment with anticorrosive properties.