CS259344B1 - Anticorrosive thermically high-stable yellow-and-green pigment - Google Patents

Abstract

The solution relates to the use of pyrophosphate dinicell as anticorrosive thermally a highly stable pigment that is extra yellow-green. It is easy to apply to coating and other protective materials. pigment it is completely stable up to almost 1,400 ° C so it is also applicable to special high temperature purposes. Pigment Concentration in the protective material necessary to achieve sufficient anticorrosive effects are relatively low. The solution can be used in pigmentary technology in the paint industry other anticorrosive protective layers.

Description

The invention relates to the use of dinicelium pyrophosphate as an anticorrosive thermally highly stable yellow-green pigment.

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 Therefore, they have recently been replaced by phosphorus compounds which have the ability to suppress oxygen corrosion in a humid, aqueous environment, particularly in iron, steel and cast iron materials.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

Cations may also have a favorable effect on the anticorrosive action of phosphates. It is known, firstly, to use some simple phosphates and to use respectively. the proposed use of some condensed phosphates. Among the condensed phosphates, these are the so-called polyphosphoric glasses (higher linear phosphates) and the most recently proposed use of the cyclotrophosphates of certain divalent metals as well as the use of certain non-color pyrophosphates - zinc, manganese, copper and blue-violet dicobaltate. [The design or use of dinicellous pyrophosphates as an anticorrosive pigment is not yet known].

From simple phosphates is currently quite widespread application of zinc phosphate dihydrate two - ^ Zn / PO ^ / ^ 2H ₂ O ₂ and the connecting rod / PO ^ / ₂ .2H ₂ O and then used as chromium phosphate trihydrate - CTA-.3H ₂ O as well as phosphates of some alkaline earth metals. However, simple phosphates do not attain the level of the best lead pigments by their anticorrosive effects. Therefore, it is necessary to apply them in paints in relatively large amounts (concentrations), so that the anticorrosive effect is sufficiently effective. Their further disadvantage is based on the fact that they have to be used in the form of defined hydrates / i. with a certain content of crystalline water), since only these are sufficiently effective.

This also greatly reduces their thermal stability (up to a maximum of about 150 ° C) and thus cannot be used in anti-corrosion coatings - coatings for high temperature purposes. Moreover, this thermal instability can complicate the final mechanical-thermal operations of treating the pigment or even dispersing it into the anticorrosive materials. In some cases of use, a further disadvantage of simple phosphates, also their certain solubility in aqueous, especially in not completely neutral compositions / e.g. by so - called acid rains. As a result, coatings may degrade over time due to their partial washing. This, with the wide use of some of these substances as anticorrosive pigments, can also lead to certain hygienic and ecological problems (in particular in the case of chromium phosphate, partly also zinc); The preparation of simple phosphates, due to the necessity to obtain them in a relatively pure form and always with an accurate crystal water content, 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 mostly metal-intensive components, which are less effective in terms of anticorrosion than phosphorus. In addition, most simple phosphates (with the exception of chromium) are also only white, respectively. colorless with only faint covering properties.

From the group of condensed phosphates, designed or used for anticorrosive purposes, so-called polyphosphoric glasses are the best known so far. They are higher linear phosphates having phosphoric anions arranged in a polymer chain. As cations, they mostly contain alkali metals (Na, K), alkaline earth metals (Ca, Mg) and in some cases also other cations (Zn, Cd, Al, Fe).

(The case of using or designing higher linear nickel phosphates as anticorrosive pigments is not yet known). However, polyphosphate glasses also have some drawbacks for use as anticorrosive pigments. Again, they do not reach the best of lead compounds before their anticorrosive effects.

Although their thermal stability is significantly higher than that of single phosphate hydrates, it is also limited. They are recrystallized at temperatures of 400 to 600 ° C - they lose their vitreous character and often also lose the character of an anion in the form of a higher polymer, so they cannot be used in corrosion-protective layers for temperatures even higher.

In the application of higher linear phosphates, their higher solubility and even the tendency to moisten also interfere when they are in powder-pigment form. Their particles applied in the protective layers can then be exposed to moisture up to dihydrogen phosphates which are readily soluble and easy to elute. coating films / excite.

This is disadvantageous in view of the requirement for their long-term corrosion resistance, since the layers become permeable to gaseous and liquid corrosive media. Moreover, with the widespread use of some of these substances / e.g. with cations Cd and Zn / some hygienic-ecological problems can arise from this. Obviously, the biggest disadvantage of higher linear phosphates is the energy, material-construction and technological demands of their preparation. They must be obtained via a melt route at high temperatures of 800 to 1300 ° C, which is highly aggressive and from which to some extent the phosphorous component is volatilizing. Compared to the other types of phosphate pigments, in addition, higher linear phosphates are, due to their glassy character, more demanding on the final operations of their treatment into pigment particles (especially crushing and grinding). Their dispersion into paint or other protective materials is also more complicated. Most polyphosphate glasses are also virtually uncoloured.

Another type of condensed phosphate suitable for use as anticorrosive pigments is the recently proposed cyclotetaphosphates of certain divalent metals. including nickel. These compounds overcome most of the drawbacks noted for both single phosphates and higher linear phosphates. They are thermally very stable substances up to their melting point, which for individual of them lies in the interval 800 to 1280 ° C. Above the melting temperature, however, they lose their structure and character of cyclotetaphosphate. They are also very chemically stable and their solubility in aqueous and not completely neutral compositions is very low, so that their anticorrosive action is of long-term character.

However, this may also be a disadvantage in some cases of their use, especially in wet aggressive environments where faster release of phosphorous passive anions is needed. Cyclotrophosphates have a high proportion of phosphorus component, which is 2 to 3 times higher than that of simple phosphates. This is an advantage of these substances, since it is the most effective component from the corrosion point of view, but in some cases it can be even more material intensive in the preparation of cyclotrophosphates. The cyclotetaphosphate preparation operations are not as technologically, energetically and structurally intensive as mentioned for the other phosphorous compounds, but are sometimes more difficult to manage in terms of achieving sufficient yields of the pure product. Also, most of the cyclo-tetraphosphates are white or colorless. The color in the yellow-green hue is dinocellic cyclo-tetraphosphate, which is stable up to a temperature of 1280 ° C. Its color, however, does not have a high intensity.

Another group of condensed phosphates - some metal pyrophosphates - proposed most recently as anticorrosive pigments further complements the advantages stated for cyclo-tetraphosphates and shifts the area of thermal stability to even higher temperatures. Of the pyrophosphates proposed so far, however, only dicobaltate pyrophosphate is markedly colored in bluish violet. The diphosphate which has been designed or used as a corrosion-resistant thermally stable pigment in yellow or green is not yet known.

The use of dinic acid pyrophosphate as an anticorrosive thermally highly stable yellow-green pigment removes the deficiency mentioned for the second pyrophosphates, complements the advantages for cyclotetaphosphates, in particular for dinaphthalic cyclotaphosphate, and eliminates the deficiencies for single phosphates and higher linear phosphates. Ni ^ P ^ O ^ has basic physical properties - density, specific surface area, oil consumption - corresponding to conventional inorganic pigments and is easily dispersible in organic paint binders and other types of binders, including inorganic binders. Its color is intensely yellow-green and is completely stable up to high temperatures. It melts at and above 1365 ° C and does not change in composition (when applied in an inert environment) and, when the temperature is below the melting point, it returns to the solids position Ni2P2O7 ·

The solubility of dinicellous pyrophosphate in aqueous media is somewhat higher than that of dinicellous cyclotrophosphate and thus may release the phosphoric passivating anions more rapidly. However, the diphosphate also dissolves in a stepwise and practically controlled manner, depending on the degree of environmental corrosion. Thus, passive phosphorus anions are also released in a controlled manner. In the first stage of anticorrosive action, NijP? slowly one half of the anions and the rest is converted to a single phosphate. It is still in the form of a solid particle, so that the coating film or film is not destroyed at this stage. another protective layer into which the phosphate has been applied as an anticorrosive pigment.

In addition, the single phosphate is again in a yellow-green color shade and has an anti-corrosion effect, so that the overall action of the pyrophosphate is of a longer-term character. Dicalcium diphosphate has a P / Ni molar ratio equal to one, which is higher and more corrosion-resistant than simple phosphates and, on the other hand, is lower than that of cyclotetaphosphates, which makes it more cost-efficient in this respect. With the preparation of dicalcium phosphate, it is relatively easy to obtain a high yield of a pure product, which is practically pigmented in form, and at the same time there is no great demand on the quality of the starting materials.

Nickel-based waste catalysts may also be used for its preparation, and the phosphorous component may also be in the form of a dilute, lower quality (extractive) phosphoric acid.

The following are examples of some of the determined pigmentary properties of NijPjOy. which roughly correspond to conventional inorganic pigments. Examples of established anticorrosion-inhibiting properties of dinic acid diphosphate, which are superior to those of commercial anticorrosive pigments based on zinc phosphate dihydrate, are also given. Further, the color of the pyrophosphate and its thermal stability are documented.

Example 1

Some properties of dicalcium phosphate related to its pigment use and inhibitory action have been determined;

density 3.95 3 g / cm specific surface 2.17 m ² / g flaxseed oil consumption 21.75 g oil / 100 g ΝΪ2Ρ2θ · pH of aqueous extract 6.42 - 8 days after insertion steel. metal plate 6.75 - 8 days after removal of steel. metal plate 6.45 inhibitory properties of aqueous extract - corrosion loss of steel after 8 days 5.45 g / m ²

immersion in Ni ₂ P ₂ ® ₇ leachate

Example 2

The properties of paints prepared with three oil paints (a, b, c) containing as anticorrosive pigment were compared:

a) dinicellic pyrophosphate (Nijl ^ O ·?)

(b) a commercial core pigment consisting of single zinc phosphate. precipitated on particles of ferric iron (ferric red) (Zn ^ (PO ^) 2 lij® ^ye 2 ° 3>

(c) a commercial core pigment consisting of a simple zirconium phosphate formed on particles of titanium dioxide (titanium dioxide) (n ₃ (PO ₄ > ₂ .2 H 2 O - Thio ₂ )).

The coating composition with Ni ₂ P ₂ O ₇ had the composition (wt.%): 29% linseed oil, 43% ferric red pigment, 10% zinc white pigment, 7% talc, 1% siccative (1% octanate; cobalt in gasoline) and 10% Ni 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 steel sheet thickness of 0.6 mm cold rolled (table).

Table

Coatings with commercial Coatings with core pigments

Zn ₃ (PO ₄ ) ₂ .2H ₂ O-Fe ₂ O ₃ Zn ₃ (PO ₄ ) ₂ .2H ₂ O-TiC> ₂ Ni ^ O-,

Corrosion loss steel. sheet ₂ (or sheets of damaged paint 43.8 g / in smear around 100 mm cut) (38 mm ² ) in condensation chamber with SO, after days (ČSN 03 0130)

Corrosion loss steel. Sheet ₂ in a vapor chamber of 18% acid 15.2 g / ni hydrochloric acid after 8 days

Surfaces of damaged paint ₂ at accelerated immersion 28 mm ¹ test of corrosion resistance - according to Mach and Schiffman (ČSN 67 3087)

Surfaces of damaged paint ₂ (around 100 mm long 38.5 mm section) after 14 days immersion in 1000 ml aqueous solution containing 50 g Naci and ml H ₂ O ₂

Relative mass steel drop.

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

31.6 g / m ² (52 mm ² )

11.9 g / m ² mm mm ²

10.4 g / m ² (22 mm ² )

5.5 g / m ² mm ² mm ²

17.9% 15.86%

Example 3

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

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

Example 4

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

Example 5

The color and thermal stability of dinicellous pyrophosphate was evaluated. The color of the pigment is expressed by the remission curve in FIG.

When assessing the thermal stability of Dicalcium Diphosphate by calcining it in an electric furnace at various temperatures up to 1500 ° C and then analyzing the calcines by methods of instrumental analysis, Ni ₂ P ₂ O ^ was completely stable up to 1,365 ° C when melting but in composition was stable up to the monitored temperature of 1500 ° C. Once cooled and solidified, it again represented crystalline pyrophosphate.

Claims (1)

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