Studying the effect ZnO NP Deposited on ST37-2 by Pulse Laser Depositions Technique for Corrosion Protection Using in Oil Storage Applications.

In the study, zinc oxide nanoparticles (ZnO NP ) were coated on carbon steel substrates via pulse laser deposition (PLD) process, in order to achieve passive layers of nanocoating. ST37-2 a type of steel is used in the manufacture of tanks that are used in oil applications, which suffers from corrosion, this will lead a large losses. Electrochemical technique (Tafel polarization completion) has been carried out for study the corrosion behavior of this steel coating type. The specimens of steel were examined in aqueous solution containing about 3.5 wt. % NaCl using polarization method, with power of hydrogen (pH) held to value 4.0, in order to evaluated the corrosion rate. ZnO NP. Characteristics and topographic nanocoating by PLD technique were evaluated by Field Emission Scanning Electron Microscope (FESEM) and X-ray Diffraction (XRD) tests. Where semi uniform nanoparticles of ZnO NP were achieved with a nanoscale approximately ranging from 33-56 nm, While XRD pattern indicated the presence of ZnO NP with different crystal structures. In other side the input parameters of (PLD) technique were substrate temperature, number of pulse and fluencies energy have been examined, in order to study their influence on the rate of corrosion reduction. The results indicate that number of shoots pulse has a significant effect the corrosion rate in operation of PLD technique, which is highest among the contributions of the other parameters. Enhancement about 56% is achieved of ST37-2 coated with (ZnO NP ) deposition, as compared with uncoated steel.


Introduction
The corrosion problem is one of the most important industrial problems in oil sectors, which costs money, maintenance, effort and time, in addition to monitoring [1].Oil and gas transport pipelines and tanks are exposed to damage due to corrosion, which draws great attention from researchers, educational and research institutions, in addition to private companies [2].Particular in Iraq, due to the types of soil and cruel climatic conditions, large parts of oil and gas transport pipelines and tanks are exposed to damage [3].Carbon steel, whether was medium or low, is commonly used in oil applications such as, pipelines or tanks, because of its good properties and availability, in addition to low cost [4].It is very common to use ST37-2 in tanks and drums in Iraqi Factories and Petroleum refinery [5].This type of metals are affected by corrosion, especially the external areas, so precautions, must be taken to maintain [5].Unluckily oil or gas tanks life can be dramatically limited by corrosion and this represented a serious problem for many years [6].Many researchers have drawn a big attention to this topic and implanted many conditions conventional corrosion protection systems such as coatings, cathodic protection, and inhibitors and even are not active enough, having a short service life, or cannot be applied.E. Ya.Lyublinski et al [7] applied cathodic protection combination with soluble corrosion inhibitors.M. J. Kadhim et al [8] deposited titanium oxide on the surface of the steel type A106-B which, commonly used as an oil pipe via PLD technique.On the other side, the importance of nanotechnology rise as a hope representing the new era in the protection of petroleum applications [8,9].This paper describes impact of ZnO NP on ST37-2 to obtain a distinctive and nano textured implanted by PLD technique that, gives good surface characteristics to protect against corrosion.

Material and processes 1.1 Base Metal
The material substrate that used in this work St37-2carbon steel has been analyzed in the (Al-Nabaa Co. Engineering Services Ltd.) using spectrometer type (Pmi Master Pro) optical emission spectrometer (OES) (S.N52Q0089) robust mobile model, German manufacturing under conditions at the temperature of 20 ºC and the humidity of 63%.The results of the analysis have been illustrated in the Table (1), which includes the stander and actual and measured values of chemical compositions belong to material substrate.Remaining.

Carbon steel (ST37-2) microstructure test
The microstructure examination of the base metal was carried out in steps represented by following stages.The first, which was the process of grinding the surface, this operations via abrasive sand papers with different number of grains per square inch including 120, 320, 500, 1000 and 2000 grit .While the second stage was polishing using alumina particles with soft cloth, until the surface sample becomes somehow similar to mirror.Then the microstructure is should applied to a chemical treatment known as etching process using Nital (2% HNO3 + 98% Alcohol), then microstructure imaging using an optical microscope (carlzeiss jena) type with a digital camera arrangement.The microstructure represented by areas of dark color   Color and Form off-white powder -While temperatures of evaporation and melting belong to nanomaterial under various circumstances are listed in Table (3).

Fig. (3): Illustrates the uniaxial press instrument
After that the pellet is sintered at 450 °C, in furnace for 1 hour in order to be used as a target for the PLD.

Pulse Laser Deposition (PLD) system
The PLD unit included vacuum system consists from vacuum pump and vacuum chamber constructed from high temperature Pyrex-glass.The pulse laser source is Nd :YAG laser with a frequency second radiation at 1064 nm at fluencies energy 1 J/cm 2 .The distance kept constant between ZnO target and laser source by 5 cm.where the other PLD working conditions illustrate in the Table (4).Figure (5) shows the photograph of the excremental work unit with PLD system.Then, the chamber was evacuated using a rotary pump with the aid of a turbo molecular pump to arrive the required operating pressure, until the pressure reaches 0.00075 torr, which is equivalent to 1×10 -3 millibars (mbar).While the time required for depositions with this technique at rate one pulse for every second.The average number of pulses was applied on the ZnO disc are 300.
The films were grown on the substrate of the ST37-2 material.During coating process the substrate temperatures was 300 º C. On the other hand, the repetition rate was 5 Hz and the operating pressure was kept constant at 10 -2 mbar.Temperature at 300 ºC, number of shoots are 300, and fluencies energy 1000 mJ/cm 2 considered as optimal conditions to minimize corrosion rate are.

Surface morphology results
The surface prepared by PLD technique was investigated by FESEM in order to know, more details about the shape and size of nanoparticles. Figure (9) imaging the morphology, of the surface topography, after, the PLD, coatings.Based on the substrate surface characteristics and the conditions of PLD process, like (substrate temperature, number of shoots, and fluencies energy, it was observed that the surface topography appear as valley and hill with spread of hillock.Thus affected the increase in the collision between the nanoparticles of the deposited ZnO, a small grains formed from those particles to accumulate together to become so larger grains.a dense layer is distinguished on the surface topography also, noted that a small semi spherical nanoparticles are observed homogeneously and uniformly distributed over the ST37-2 surface area.Figure (9) demonstrated the topography of ZnO NP surfaces.Aggregations of zinc oxide particles were also observed, with sizes ranging from approximately 33-56 nm, Due to the nature of deposition by the PLD method, the mechanism is based on the ablation of the metal atoms not evaporating them, from the metal target in non-equilibrium state, in addition to the fact that the target is zinc oxide, not pure zing element, which causes accumulations and gatherings in some areas.

Corrosion rate results
Results of corrosion examine at PLD parameters of ZnO NP coated on ST37-2 are showed in Table (5).While the corrosion behavior of uncoated sample, as compared with coated sample clearly observed, and the corrosion characteristics including corrosion current, corrosion rate and corrosion resistance are illustrated in the Table (5), clearly improvement in the corrosion resistance was noted about 56% .The corrosion resistance of all prepared coated samples ,demonstrated higher values than that of the parent metal (ST37-2).Figure (10) illustrates the comparison between them.

Conclusions
In this study, zinc oxide nanoparticles were deposited on carbon steel of type 37-2 by PLD technique and under working conditions substrate temperature at 300 ºC, number of shoots is 300, and fluencies energy 1000 mJ/cm 2 .
A homogeneous and regular texture was obtained from zinc oxide nanoparticles with nano size ranging from 33-56 nm, which led to an improvement in the surface characteristics of corrosion resistance at a rate compared to the base metal, where the results showed a clear improvement about 56%.
known as Pearlite phase ( +  3 C), and, on the other side were more bright colored areas founded are known as ferrite (α-Iron phase), and through the volume fraction, it clear that this type of carbon steel is medium, and the Figure (1) depicted that friction area consists of ferrite to pearlite.
depicted the temperatures of melting and evaporation, which refers to ZnO NP .NP Powder X-Ray diffraction of ZnO NP Powder is presented in Figure (2) based on comparing the results obtained from miller indices and angles of the XRD, corresponding to the strong peaks of the zinc oxide nano powder.The values are stated in according to standard numbered card # 36-1451 issued by the Joint Committee on Powder Diffraction Standards, (JCPDS) (the new name is international center for diffraction data, ICDD) [Ref.].The results were well matched in terms of miller indices with a slight match in the diffraction angle values.The crystal does not exceed the same angle value for a number of distinctive peak positions, as shown in Table (3).These peaks are belonged to zinc oxide.the crystalline structure of ZnO NP denoted the recognize peaks at angles 31.88°,34.57°, 36.35,47.70°,56.602°and 62.862° refer to the nano oxide zinc powder with structure (100), (002), (102),(110) and (103) respectively [ref].

Fig. ( 6 ): Polarization instrument used in this work 3 . Results and Discussion 3 . 1 (
Fig. (6): Polarization instrument used in this work3.Results and Discussion3.1 (ZnO) nanocoatingThe effect of PLD conditions including (substrate temperature, number of shoots and fluencies energy) on formation of ZnO NP thin film growth have been analyzed.It was noted; that the numbers of pluses shooting of the PLD process have the most influencing factor on the substrate is determined by the time duration of the PLD.In other hand the appearance of the coating seemed uniform and dark, with a color that, tends to gray as shown in the Figure(7).