Open Access
Issue
Manufacturing Rev.
Volume 7, 2020
Article Number 39
Number of page(s) 6
DOI https://doi.org/10.1051/mfreview/2020037
Published online 24 December 2020

© M. Birdeanu et al., Published by EDP Sciences 2020

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1 Introduction

Corrosion is one of the most studied processes because this affects everything around us. Corrosion inhibition represents a goal due to the damages that corrosion leads to the carbon steel equipment's and installations in a lot of industries, whose remedy implies financial and also time losses. To fight against this process, there were developed methods and techniques as: plating's of the steel's parts or the usage of different organic or inorganic corrosion inhibitors − which are often used to protect materials in different environments [16].

Corrosion inhibitors represent one of the most economical solutions used to prevent the corrosion. In the present paper, the developing and obtaining of corrosion inhibitors as: ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 pseudo-binary oxide nanomaterials are presented. It is known that until present, to obtain ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 pseudo-binary oxides nanomaterials, there were used synthesis methods as: solid-state method [712], sol-gel method [13], molten salt method [14,15], polymerized complex method [16], ceramic method [15,17] or other chemical routes [1820]. The different methods of synthesis, which were used in obtaining these categories of pseudo-binary oxides materials, present some issues like: controlling the particle size and the surface areas, which must be resolved.

The present study presents the obtaining of ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 pseudo-binary oxides nanomaterials by using the hydrothermal method at 250 °C. Also, are presented results regarding structural, morphological, topographical and optical characterizations of the named materials, and the results regarding the corrosion inhibition efficiency for each obtained nanomaterial evaluated in 0.5 M Na2SO4 media.

2 Experimental

2.1 Materials and methods

The hydrothermal synthesis method was used to obtain the pseudo-binary oxide nanomaterials type: ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6. The main challenge, by using this method, was to select the proper hydrothermal parameters (t, T), in order to achieve a successfully morphology and crystalline structure of the materials. Based also on a previously experience in obtaining anticorrosive materials by the hydrothermal method [21,22], the optimal hydrothermal parameters were chosen as it can be seen in Table 1. It was found that the anticorrosive materials ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 can be successfully synthesized at a 1:1 molar ratio of the used precursors for each material, at a temperature of 250 °C for 12 h. The pH values of the synthesis were fixed at 13, using NaOH (97%, Merck), resulting an alkaline medium.

Further, the obtained pseudo-binary oxide nanomaterials were deposited as thin layers (using the drop casting method in acetone medium), in different combinations on carbon steel electrode disks. The carbon steel disks, with 10 mm diameter and 2 mm thick, had the following chemical composition: 93.80% Fe; 4.81% Ni; 0.51% Co; 0.005% Cu; 0.19% P and 0.01% S. Before the drop casting depositions, the carbon steel disks were polished with emery paper and thus rinsed with double distilled water and degreased with ethanol. The modified carbon steel disks were used as working electrodes in the corrosion tests.

Table 1

The starting materials used to obtain pseudo-binary oxide nanomaterials.

2.2 Apparatus

The phase identification of the synthesized nanomaterials was investigated by X-ray diffraction (XRD) on a X'pert Pro MPD X-ray diffractometer with monochromatic Cu Kα (λ = 1.5418 Å) on an incident radiation. For the morphological investigations regarding the obtained pseudo-binary oxides, field emission-scanning electron microscopy (SEM/EDAX) (Model INSPECT S) and atomic force microscopy (AFM) (Model NanoSurfEasyScan 2 Advanced Research) were used. The optical band gap for each pseudo-binary oxide nanomaterial was calculated by recording the difusse reflectance spectra at room temperature using an UV-VIS-NIR spectrometer Lambda 950.

A Voltalab potentiostat (Model PGZ 402) was used to perform the electrochemical measurements. The potentiostat was coupled with a three electrodes electrochemical cell comprising: a platinum wire as a counter electrode, a saturated calomel electrode as the reference electrode and the working electrodes consisting in bare or drop casting modified carbon steel disks (OL). The potentiodynamic polarization measurements were recorded by sweeping the potential from −1.3 to −0.6 V at a scan rate (ν) of 1 mV/s at room temperature (23 °C). Before the polarization, the open circuit potential (OCP) of the modified electrodes was monitored for 30 min. For the corrosion tests a 0.5 M Na2SO4 solution was used.

3 Results and discussion

3.1 Structural and morphological properties

The X-ray diffraction patterns recorded at room temperature in the 2θ range of 10–80° are presented in Figure 1 for: (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6. These patterns are showing that the phases of the materials do appear and the peaks are indexed with: the JCPDS no. 01-076-1826 for ZnTa2O6 where the main diffraction peak appears at 32.56°, JCPDS No. 01-076-1827 for ZnNb2O6 with the main diffraction peak settled at 30.49°, JCPDS No. 01-084-1679 for MgTa2O6 main diffraction peak at 29.37° and JCPDS No. 01-088-0708 for MgNb2O6 where the main diffraction peak is settled at 30.03°. Samples (a), (b) and (d) belong to the orthorhombic space group Pbcn (no. 60), while sample (c) belongs to the tetragonal space group P42/mnm (no. 136).

The morphology of the resulting pseudo-binary oxide nanomaterials (as powders, before the depositions) and the formation of the agglomerates are represented in Figure 2. It is to be mentioned that for the pseudo-binary oxide nanomaterials which contain Ta, are preserved cubic shapes beside irregular shapes (Fig. 2a and 2c, while in the morphology of the pseudo-binary oxides with Nb content, the accicular shapes of the agglomerates is preserved (Fig. 2b and 2d). From the EDAX images for ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 nanomaterials (Fig. 3) it can be observed that only the specific lines for Zn, Mg, Ta, Nb and O are presented.

Topographic analysis for the surface of the obtained nanomaterials was perfomed using atomic force microscopy. The recorded images are presented for each nanomaterial in Figure 4a–d.

To calculate the surface roughness for each sample of material, the NanoSurf EasyScan 2 computer program and the following equations were used [23]:(1)

for the average roughness and(2)

for the mean square root roughness, where N and M represent the number of the crystal axes x and y respectively; z represents the average height of crystallites; xk and yl are the maximum and minimum deviations from the average crystallite.

In Table 2 are presented the calculated values for the measured areas of the obtained nanomaterials. The measurements were taken in the non contact mode using a scan size of 1 μm × 1 μm. The measured area at the surface for each material was 1.30 pm2.

thumbnail Fig. 1

The XRD patterns of: (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 materials prepared through the hydrothermal method.

thumbnail Fig. 2

Scanning electron microscopy images for (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials.

thumbnail Fig. 3

The EDAX images for (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials.

thumbnail Fig. 4

The atomic force microscopy images of: (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6.

Table 2

The calculated Sa and Sq for the measured areas for the obtained nanomaterials.

3.2 Optical properties

Using the Kubelka-Munk equations [24,25], the absorbance was calculated for each obtained pseudo-binary oxide nanomaterial. From the absorption spectra (Fig. 5) can be observed the maximum absorption peak for each sample as it follows: 311 nm for ZnTa2O6, 311 nm for ZnNb2O6, 308 nm for MgTa2O6 and also 308 nm for MgNb2O6. The values are the same for the compounds containing Zn and also the same values for the compounds containing Mg, the presence of Nb or Ta does not seems to influence the absorption. Plotting from each of the absorption spectra: {(k/s) } 2 versus , where k denotes absorption coefficient, s is scattering coefficient and is the photon energy, the optical band gaps were estimated for the obtained materials as it follows: Eg (ZnTa2O6) = 3.6 eV, Eg (ZnNb2O6) = 3.72 eV, Eg (MgTa2O6) = 3.8 eV and Eg (MgNb2O6) = 3.76 eV.

thumbnail Fig. 5

Absorption spectra of (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials. From the inset plot were obtained the optical band gaps.

3.3 Polarisation curves

In Figure 6 are represented the Tafel plots of the investigated OL electrodes recorded after 30 min open circuit potential (OCP) in 0.5 M Na2SO4 solution. The slopes were determined in the Tafel region of the anodic and cathodic curves before and after the corrosion potential (U).

As it can be seen in Table 3, where the calculated parameters from the Tafel plots are summarized, the corrosion potential (Ecorr ) of the OL electrode is −0.916 and the corresponding corrosion current density (icorr ) is 24.08 μA/cm2. The polarization curves were shifted towards the region of lower corrosion current densities in thepresence of ZnNb2O6 and MgTaO6 and the polarization curves shifted towards the region of higher corrosion current densities in the presence of ZnTa2O6 and MgNb2O6.

The inhibition efficiencies (IE%) were calculated based on equation (3) from [26] and for: ZnTa2O6, MgTa2O6 and MgNb2O6 were obtained values of IE% over 50% (see Tab. 3).(3)where and i corr are the corrosion current densities in the absence and in the presence of the pseudo-binary oxide nanomaterials deposited as thin layers on carbon steel electrodes.

In the case of ZnTa2O6, obtained through the hydrothermal method, the IE% of 56.27% is higher than the reported IE% of 48.61% for ZnTa2O6 obtained through the solid state method [10], while in the case of the ZnNb2O6 obtained through the hydrothermal method, the IE% of 37% is lower than for the ZnNb2O6 obtained through the solid state method (52.70%) [10].

The polarization resistance (Rp) increases from 1.53 kΩ cm2 for bare OL to 2.36 kΩ cm2 for MgNb2O6,while in the case of ZnNb2O6 the value of Rp is decreasing to 1.31 kΩ cm2 which also reflects in the IE which is only 37%.

Analyzing the evolution of open circuit potential (OCP) with time for the investigated electrodes (Fig. 7), it can be seen that an exposure time of 30 min leads to a shift in free potential towards more negative values. Comparing the OCP profiles, it can be observed that in almost 20 min, the profile of the untreated electrode presents a decrease in potential until it reaches at the same value as for: ZnNb2O6, MgTaO6 and MgNb2O6.

thumbnail Fig. 6

Tafel representation of polarization curves recorded in 0.5 M Na2SO4 for the studied electrodes: (a) OL, (b)MgTa2O6, (c) ZnNb2O6, (d) ZnTa2O6 and (e) MgNb2O6.

thumbnail Fig. 7

Evolution of open circuit potential with time for investigated electrodes in 0.5 M Na2SO4 electrolyte solution for: (a) OL, (b)MgTa2O6, (c) ZnNb2O6, (d) ZnTa2O6 and (e) MgNb2O6.

Table 3

Tafel parameters of the investigated electrodes after 30 min immersion in 0.5 M Na2SO4 solution.

4 Conclusion

ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 pseudo-binary oxide nanomaterials were obtained through the hydrothermal synthesis method at 250 °C for 12 h. XRD results reveal that the single phase of the obtained pseudo-binary oxide nanomaterials can be obtained through the hydrothermal synthesis at a pH value of 13. The optical band gaps were estimated from the diffuse reflectance spectrum of each materials to be in the range 3.6–3.8 eV. The inhibition efficiency for the obtained materials was calculated and for ZnTa2O6, MgTa2O6 and MgNb2O6 nanomaterials were obtained values of IE% over 50%. Taking into consideration that the tested materials containing Zn and Mg in combination with Ta and Nb did not completely satisfied our expectations, we believe that a further approach using materials containing Mn in combination with Ta and Nb will add a benefit to the efficiency of corrosion, as it was already reported in [27,28].

Acknowledgments

This work was partially financially supported by the project PN III nr. 107 PED / 2017 “Nanostructured anticorrosive hybrid materials based on pseudo-binary oxides and Zn-metalloporphyrins”, partially financially supported as part of the PN 16-14 02 03 and partially project PN III “Hybrid ceramics/porphyrins, deposited by pulsed laser deposition as single and sandwich layers for corrosion inhibition of steels in acid environment”.

This paper was presented at the 3rd International Conference “Emerging Technologies in Materials Engineering EmergeMAT”, organized by the National R&D Institute for Non-ferrous and Rare Metals − IMNR, Romania, 29–30 October 2020.

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Cite this article as: Mihaela Birdeanu, Mirela Vaida, Eugenia Fagadar-Cosma, Hydrothermal synthesis of ZnTa2O6, ZnNb2O6, MgTa2O6 and MgNb2O6 pseudo-binary oxide nanomaterials with anticorrosive properties, Manufacturing Rev. 7, 39 (2020)

All Tables

Table 1

The starting materials used to obtain pseudo-binary oxide nanomaterials.

Table 2

The calculated Sa and Sq for the measured areas for the obtained nanomaterials.

Table 3

Tafel parameters of the investigated electrodes after 30 min immersion in 0.5 M Na2SO4 solution.

All Figures

thumbnail Fig. 1

The XRD patterns of: (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 materials prepared through the hydrothermal method.

In the text
thumbnail Fig. 2

Scanning electron microscopy images for (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials.

In the text
thumbnail Fig. 3

The EDAX images for (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials.

In the text
thumbnail Fig. 4

The atomic force microscopy images of: (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6.

In the text
thumbnail Fig. 5

Absorption spectra of (a) ZnTa2O6, (b) ZnNb2O6, (c) MgTa2O6 and (d) MgNb2O6 nanomaterials. From the inset plot were obtained the optical band gaps.

In the text
thumbnail Fig. 6

Tafel representation of polarization curves recorded in 0.5 M Na2SO4 for the studied electrodes: (a) OL, (b)MgTa2O6, (c) ZnNb2O6, (d) ZnTa2O6 and (e) MgNb2O6.

In the text
thumbnail Fig. 7

Evolution of open circuit potential with time for investigated electrodes in 0.5 M Na2SO4 electrolyte solution for: (a) OL, (b)MgTa2O6, (c) ZnNb2O6, (d) ZnTa2O6 and (e) MgNb2O6.

In the text

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