CS259344B1 - Anticorrosive highly stable yellow-green pigment - Google Patents

Abstract

The solution concerns the use of dinickel diphosphate as an anti-corrosion thermally highly stable pigment, which is also yellow-green. It is easily applicable to coatings and other protective materials. The pigment is completely stable up to almost 1,400 °C, so it is also usable for special high-temperature purposes. The concentration of pigment in the protective material necessary to achieve sufficient anti-corrosion effects is relatively low. The solution can be used in pigment technology, in the coating industry and other anti-corrosion protective layers.

Description

The invention relates to the use of dinickel diphosphate as an anticorrosive, thermally highly stable yellow-green pigment.

Until recently, the most widely used anti-corrosion pigments were some lead compounds and compounds based on chromene. These were very high-quality and effective pigments, but their use, due to the toxicity of the mentioned substances, entailed hygienic and ecological problems. Therefore, they have recently been replaced by phosphorus compounds, which have the ability to suppress oxygen corrosion in a humid, aqueous environment, especially in iron, steel and cast iron materials. The phosphorus anions contained in them bind iron ions released by corrosion in the form of insoluble phosphate, which then forms a coating, at the same time passivating the metal surface.

The anticorrosive effect of phosphates can also be positively affected by their cations. It is known to use some simple phosphates and also to use or propose to use some condensed phosphates. Among condensed phosphates, these are the so-called polyphosphate glasses /higher linear phosphates/ and most recently, the author of this invention has proposed the use of cyclotetraphosphates of some divalent metals and also the use of some colorless diphosphates - zinc, manganese, copper and also blue-violet dicobalt diphosphate. /The proposal or use of dinickel diphosphates as an anticorrosive pigment is not yet known/.

Of the simple phosphates, the dihydrate of two zinc phosphates - Zn^/PO^/^ 2H ₂ O and CaZn ₂ /PO^/ ₂ .2H ₂ O is currently quite widely used, and the trihydrate of chromium phosphate - CrPO^.3H ₂ O is also used, as well as phosphates of some alkaline earth metals. However, simple phosphates do not reach the level of the best pigments from lead compounds in their anti-corrosion effects. Therefore, it is necessary to apply them to paints in relatively large quantities /concentrations/ so that the anti-corrosion effect is sufficiently effective. Their other disadvantage is based on the fact that they must be used in the form of defined hydrates /i.e. with a certain content of crystal water/, since only these are sufficiently effective.

This also significantly limits their thermal stability /maximum up to temperatures of around 150 °C/ and they cannot be used in anti-corrosion layers - coatings for higher-temperature purposes. In addition, this thermal instability can complicate the final mechanical-thermal operations of pigment treatment or its dispersion into anti-corrosion materials. In some cases of use, another disadvantage of simple phosphates can be their certain solubility in aqueous, especially in not completely neutral media /e.g. due to the action of so-called acid rain/. Over time, coatings can deteriorate due to their partial leaching. With the widespread use of some of these substances as anti-corrosion pigments, this can also lead to certain hygienic and ecological problems /especially in the case of chromium phosphate, and partly also zinc phosphate/; The preparation of simple phosphates, due to the need to obtain them in a relatively pure form and always with an accurate content of crystal water, is not a technologically simple operation.

In addition, they require the use of relatively high-quality raw materials and have a relatively high content of the metal component, which is usually more demanding in terms of raw materials, and which is less effective than the phosphorus component in terms of anti-corrosion action. Most simple phosphates /with the exception of chromium/ are also only white or colorless with only negligible covering properties.

Of the group of condensed phosphates designed or used for anti-corrosion purposes, the so-called polyphosphate glasses are the best known. They are higher linear phosphates, which have phosphorus anions arranged in a polymer chain. As cations, they mostly contain alkali metals /Na, K/, then alkaline earth metals /Ca, Mg/ and in some cases also other cations /Zn, Cd, Al, Fe/.

/The use or design of higher linear nickel phosphates as anticorrosive pigments is not yet known/. However, polyphosphate glasses also have some disadvantages for use as anticorrosive pigments. In terms of their anticorrosive effects, they again do not reach the level of the best lead compounds.

Although their thermal stability is significantly higher than that of simple phosphate hydrates, it is also limited. At temperatures of 400 to 600 °C, they recrystallize - lose their glassy character, and often also lose their anionic character in the form of a higher polymer, so they cannot be used in corrosion-protective layers for even higher temperatures.

When applying higher linear phosphates, their higher solubility and even tendency to get wet, if they are in powder-pigment form, are also a problem. Their particles applied in protective layers can then, under the influence of moisture, convert to dihydrogen phosphates, which are easily soluble and can be easily washed out, thereby destroying the aforementioned layers /e.g. paint films/.

This is disadvantageous from the point of view of the requirement for their long-term anti-corrosion effect, as the layers become permeable to gaseous and liquid media causing corrosion. Moreover, with the widespread use of some of these substances /e.g. with Cd and Zn cations/, certain hygienic and ecological problems may arise. Probably the biggest disadvantage of higher linear phosphates is the energy, material-construction and also technological complexity of their preparation. They must be obtained through the melt, at high temperatures of 800 to 1,300 °C, which is quite aggressive and from which the phosphorus component also leaks to a certain extent. Compared to other types of phosphate pigments, higher linear phosphates are, due to their glassy nature, more demanding in terms of final operations for their treatment into the form of pigment particles /especially crushing and grinding/. Their dispersion into paint or other protective materials is also more complicated. Most polyphosphate glasses are also practically colorless.

Another type of condensed phosphates suitable for use as anticorrosive pigments are recently proposed cyclotetraphosphates of some divalent metals, including nickel. These compounds eliminate most of the shortcomings mentioned for simple phosphates and higher linear phosphates. They are thermally very stable substances, up to their melting temperatures, which for some of them lie in the range of 800 to 1,280 °C. However, above the melting temperature they lose their structure and character of cyclotetraphosphate. They are also chemically very stable and their solubility in aqueous and not entirely neutral media is very low, so their anticorrosive effect is long-term.

However, this can also be a disadvantage in some cases of their use, especially in humid aggressive environments where faster release of phosphoric passivating anions is required. Cyclotetraphosphates have a high proportion of the phosphoric component, which is 2 to 3 times higher than in simple phosphates. This is an advantage of these substances, as it is the most effective component from an anti-corrosion point of view, but in some cases it can also be a more demanding component in terms of raw materials when preparing cyclotetraphosphates. The operations for preparing cyclotetraphosphates are not as technologically, energetically and structurally demanding as those mentioned for other phosphorus compounds, but they are sometimes more difficult to manage in terms of achieving sufficient yields of pure product. Most cyclotetraphosphates are also white or colorless. Dinickel cyclotetraphosphate is colored in a yellow-green shade, which is stable up to a temperature of 1,280 °C. However, its color shade is not very intense.

Another group of condensed phosphates - diphosphates of some metals - recently proposed as anticorrosive pigments further complements the advantages mentioned for cyclotetraphosphates and moves the range of thermal stability to even higher temperatures. Of the diphosphates proposed so far, however, only dicobalt diphosphate is distinctly colored in a blue-violet hue. A diphosphate that has been proposed or used as an anticorrosive thermally stable pigment in a yellow or green hue is not yet known.

The use of dinickel diphosphate as an anticorrosive thermally highly stable yellow-green pigment eliminates the shortcomings mentioned for other diphosphates, complements the advantages for cyclotetraphosphates, especially for dinickel cyclotetraphosphate, and eliminates the shortcomings mentioned for simple phosphates and higher linear phosphates. Ni^P^O^ has basic physical properties - density, specific surface area, oil consumption - corresponding to common inorganic pigments and is easily dispersible into organic binders of paints and other types of binders, including inorganic ones. Its color is intensely yellow-green and is completely stable up to high temperatures. It melts at a temperature of 1,365 °C and even above this temperature its composition does not change /if applied in an inert environment/ and after lowering the temperature below the melting point it returns to the state of solid particles NÍ2P2O7·

The solubility of dinickel diphosphate in aqueous media is slightly higher than that of dinickel cyclotetraphosphate, so it can release phosphoric passivating anions more quickly. However, diphosphate also dissolves gradually and practically in a controlled manner, depending on the degree of corrosive action of the environment. Passivating phosphoric anions are therefore also released in a controlled manner. In the first stage of anti-corrosion action, NijPjO? slowly releases one half of the anions and the rest turns into simple phosphate. This is still in the form of a solid particle, so the paint film or other protective layer in which the phosphate was used as an anti-corrosion pigment is not destroyed in this phase.

In addition, the simple phosphate is again in a yellow-green color and has an anti-corrosion effect, so the overall effect of the diphosphate is of a longer-term nature. Dinickel diphosphate has a molar ratio P/Ni equal to one, which is a higher value and more advantageous from an anti-corrosion point of view than in the case of simple phosphates and, conversely, it is lower than in cyclotetraphosphates, which makes it less demanding in terms of raw materials. The technology for preparing dinickel diphosphate makes it relatively easy to achieve a high yield of a pure product, which has a practically pigmentary form, and at the same time there are no high demands on the quality of the starting raw materials.

It is also possible to use nickel-based waste catalysts for its preparation, and the phosphorus component can also be in the form of diluted, lower-quality (extraction) phosphoric acid.

The following are examples of some of the determined pigment properties of NijPjOy. which roughly correspond to common inorganic pigments. Also given are examples of the determined anti-corrosion-inhibiting properties of dinickel diphosphate, which are better than those of commercial anti-corrosion pigments based on zinc monophosphate dihydrate. Furthermore, the color of the diphosphate and its thermal stability are documented.

Example 1

Some properties of dinickel diphosphate have been determined, relating to its pigmentary use and inhibitory action;

density 3.95 , 3 g/cm specific surface area 2.17 ^m2 /g linseed oil consumption 21.75 g oil/100 g ΝΪ2Ρ2θ· pH of aqueous extract 6.42 - 8 days after inserting the steel sheet 6.75 - 8 days after removing the steel sheet 6.45 inhibitory properties of aqueous extract - corrosion losses of steel after 8 days 5.45 g/ ^m2

immersion in Ni ₂ P ₂ ® ₇ leachate

Example 2

The capabilities of coatings prepared using three oil-based coatings (a, b, c, containing as anticorrosive pigment:

a) nickel diphosphate (NiO?)

b) a commercial core pigment consisting of simple zinc phosphate precipitated on ferric iron (iron red) particles (Zn(PO) ^2H2O3 )

c) commercial core pigment consisting of simple calcium phosphate formed on titanium dioxide particles (titanium white) (Zn ₃ (PO ₄ > ₂ .2 H^O - Tio ₂ ).

The coating material with Ni ₂ P ₂ O ₇ had the following composition (wt. %): 29% linseed oil, 43% iron red pigment, 10% zinc white pigment, 7% talc, 1% siccative (1% octanate; cobalt in gasoline) and 10% Ni 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 O-Fe ₂ O ₃ Zn ₃ (PO ₄ ) ₂ .2H ₂ O-TiC> ₂ Ni^O-,

Corrosion losses of steel sheet ₂ (or sheets with damaged coating in the vicinity of a 100 mm section) (38 mm ² ) in a condensation chamber with SO, after days (ČSN 03 0130)

Corrosion losses of steel sheet ₂ in a chamber with vapors of 18% hydrochloric acid 15.2 g/ml after 8 days

Areas of damaged coating ₂ during accelerated immersion 28 mm ¹ test of resistance to undermining corrosion - according to Mach and Schiffman (ČSN 67 3087)

Areas of damaged coating ₂ (around the longitudinal 100 mm 38.5 mm cut) after 14 days immersed in 1,000 ml of an aqueous solution containing 50 g NaCI and _{ml H2O2}

Relative mass losses of steel.

sheet metal after 21 days of immersion 14.7% in aqueous extracts of the paint film (10% by weight suspension of the paint, film after 14 days of leaching) - related to losses of the steel sheet metal after 21 days in distilled water.

31.6 g/ ^m2 ( ^52.mm2 )

11.9 g/ ^m2 mm ^mm2

10.4 g/ ^m2 (22 ^mm2 )

5.5 g/m ² mm ² mm ²

17.9% 15.86%

Example 3

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

year) exposed to the weather conditions of the East Bohemian chemical-industrial agglomeration. Weight losses due to corrosion (ČSN 03 8140) ranged from 13.9 to 23.1 g/m ² when using a coating with Mg ₂ P ₂ O ₇ after two years, while when using coatings with commercial core pigments, they were 25 to 28 g/m 2 after just one year.

Example 4

Steel plates with coatings prepared according to example 2 from an oil coating material containing 10 wt. % Ni ₂ P ₂ O ₇ were exposed to the weather conditions of the East Bohemian chemical-industrial agglomeration for 2 years. Weight losses due to corrosion (ČSN 03 8140) ranged from 3 to 5 mg/g.

Example 5

The color and thermal stability of dinickel diphosphate were evaluated. The color of the pigment is expressed by the remission curve in Fig.

When assessing the thermal stability of dinickel diphosphate by calcining it in an electric furnace at various temperatures up to 1,500 °C and subsequent analysis of the calcinates using instrumental analysis methods, Ni ₂ P ₂ O^ was completely stable up to 1,365 °C, when it melted, but in terms of composition it was stable up to the monitored temperature of 1,500 °C. After cooling and solidification, it again represented a crystalline diphosphate.

Claims (1)

I will invent the object Use of dicalcium phosphate as an anticorrosive thermally highly stable yellow-green pigment. 1 drawing