апрель 2019

The new «smart» corrosion protective pigment based on tripolyphosphate-intercalated Zn-Al layered double hydroxide: synthesis and characterisation

Rusakevich S. R., Коваленко В. Л. Коваленко В. Л. , Коток В. А. Коток В. А.
Химия и современные технологии
Abstract / Full Text

Paint coatings are widely used in the modern world, especially for corrosion protection of the metal with simultaneously formation decorative image. But the main disadvantage of pain coating is a passive type of corrosion protection. The current research project aim is to determine the possibility of synthesis of “smart” pigment, based on inhibitor-intercalated layered double hydroxide (LDH), with high pigments properties and active metal protection with water presence. Zn4Al LDH as a nanocontainer and tripolyphosphate as an intercalating inhibitor was selected for “smart” pigment. Pigment samples were synthesized by direct co-precipitation at the equilibrium pH and characterized by PXRD, DTG, DSC, SEM, EDX, IR, Color Comparator and anodic voltammogram of mild steel without and with pigment extract.

By PXRD, TG, DSC, EDX, and IR it was established that samples are bi-phase (high crystalline ZnO+XRD-amorphous Zn-Al- P3O10 LDH).

Fig. 1. XRD pattern of Zn-Al-Tripolyphosphate LDH sample

Advanced pigment properties (manual grindingeasiness and particle diameter <2 μm) are shown. Extra whiteness of pigment (coefficient of diffusion reflection 90%, lightness L=96.1, color purity 1%) was detected by color measurements. Anodic voltammogram curves exhibited the high corrosion-protective activity of the synthesized pigment: the presence of the pigment extract leads to a reduction inthe current density of steel corrosion by 3.2 times.

Table 1 − Different color parameters of Zn-Al-Tripolyphosphate pigment

Coefficient of diffusion reflection, % Spectral Tone Color Purity Chromaticity Coordinates
1 2 3 Medium λ, nm Р, % x Y z
90.49 89.46 90.26 90.07 560*` 1 99.52 90.15 31.63
CIE Lab   Color Strength   Chromaticity Coordinates of Light Source
a* b* L*   S   X0 Y0 Z0
0.800 0.902 96.097   1.206   109.85 100 35.582

Fig 2. Zn-Al-Tripolyphosphate pigment


Conclusion.1) Zn-Al LDH as a base and tripolyphosphate as an anion-inhibitor for construction of the new type of corrosion-prospective pigment; 2) Zn-Al-tripolyphosphate pigment samples have been synthesized. 3) By means of XRD analysis it has been demonstrated that sample pigment is bi-phase and consists of high crystalline Zn-Al layered double oxide (with the crystal lattice of ZnO) and low crystalline Zn-Al-Tripolyphosphate LDH (with the crystal lattice of Zn(OH)2); 4) Color characteristics of synthesized pigment have been investigated. It has been shown that the pigment has an extra high level of whiteness (coefficient of diffusion reflection more than 90%, color purity only 1%, lightness more than 96%). This pigment could be used for change titania. High pigment properties of the sample (grinding easiness and softness) have been indicated. 5) By mean of anodic voltammogram, the high corrosion-protective activity of pigment sample has been proving: corrosion current density of steel in the presence of pigment water extract has decreased in 5.63 times (compared one without pigment extract).” Smart” behavior of synthesized pigment has been shown. Without paint layer damage obtained sample play the only role of “white pigment”. But in the case of the presence in the paint the cracks or holes, and simultaneously in the presence of water, pigment shows the anticorrosion properties.