Polyamide Nanofibers Coating by Electrospinning Technique for Anti Corrosion Behavior

-Poly amide (PA-6) nanofiber coatings on aluminum surface using electrospinning technique under two different voltage (24 kV & 34 Kv) were prepared. The coating morphology , roughness and 3D structural properties tested by using Atomic force microscopes (AFM), surface characterized by (SEM) microscopy, and high resolution optical microscopy (HROM) , Contact angle for hydrophobic behavior was tested by shape drop analyzer , and FTIR analysis for changing in crystalline structure was performed .The AFM images showed that the PA coating on the aluminum surface have a tight and twisted nanofiber structure with some beads through its morphology. SEM images shows the morphology beads of surface nanofibers . The electrochemical corrosion of aluminum without and with PA coating studied by subjected it to aerobic solutions of 3.5 wt.% sodium chloride (NaCl) . It has been found that the PA coatings decrease the corrosion currents and corrosion rate as well as increase the corrosion resistance for aluminum in the NaCl solution .


1.Introduction
Electrospinning is a technique to nanofibers prepared with average diameter between (1 nm to some hundreds nm ) by using electrostatic forces .These nanofibers have extra excellent properties such as thinner diameter and a larger surface area than those obtained with other spinning processes.[1].The nanofibers which produce by this method is successfully used in engineering, medicine field , tissue engineering, also it used in industrial application such as coating surface for different applications [2].Recently, electrospinning is the best technique for prepare coating nanofibers compare with other techniques which used to prepare polymer nanofibers; such as : synthesis of the template, drawing, phase separation, and selfassembly [3][4][5][6][7].Electrospun nanofibers coating used to improve the corrosion resistances of the coated materials and can be used in a various industries such as coating of pipes and tanks .In addition that nanofibers textile used in filter media involve (gas, liquid, and molecule) filtrations.[8] Corrosion usually occurs at a rate determined by balance between dissent electrochemical reactions.The first is the anodic reaction, which a metal is corroded.The other is the cathode reaction, where a solution species (often H + or O 2 ) is decreased, striping electrons from the metal.When these two reactions are in balance, the flow of electrons from each reaction is stable , and no obvious electron flow.The two reactions can occurred on one metal or on two various connected metals .We can calculate the corrosion rate from the following equation , also table (1) show the corrosion rate constant .
where, : Icorr = the current of corrosion (Amps) K = a constant according to units of corrosion rate ( = 3272) EW = the equivalent weight (= 9) D = density (2.7 g / cm3) a = area of sample ( cm2 ) = ( 2*2.5 cm2) Our present paper aim to prepare a nanofiber coating of polyamide -6(PA -6) on the aluminum surface using the electrospinning technique.This is for the studying of the effect of PA on the corrosion resistance of aluminum in freely ventilation solutions of 3.5 wt.% (sodium chloride) .Tafil's electrochemical corrosion method used for studding the corrosion behavior of samples (with and without coating) under different preparation conditions.

Experimental Part
I. Electrospinning of nanofibers coatings (0.15 Con.%) wt% of (PA + formic acid) solution was prepared for electrospinning pump.This solution stirring with heating (50 -60 o C) for (24 hr) .Two samples prepared by electrospinning technique under two different voltage (24, 34 ) kV, and other constant conditions " 15cm electrospinning distance, and 0.3 ml/h solution flow rate.The electrospun nanofibers collected on Aluminum foil surfaces Abbreviations and Acronyms Define all the abbreviations and acronyms the first time they appear in the article text.Do not use abbreviations in the paper title unless they are unavoidable.Write zero before the decimal 0.56 and do not write .56 and write cm 3 and do not write cc.For dimensions use 6.5×6.5 cm 2 , and do not write 6.5 cm 6.5×cm.

II. Nanofibers morphological analysis
Surface morphology of electrospun nanofibers coating layers on aluminum surfaces were investigated using optical microscopic with high analysis resolution and atomic force microscopy (AFM).Thickness of coating nanofibers measured by digital micrometer.

III. Corrosion test
A 3.5 wt.% of an aqueous solution of sodium chloride salt used for perform the Tafel's test.The PA aluminum coated and non-coated samples for corrosion measurements were prepared by fixing these samples on glass slide with (2.5 * 3 cm 2 ) area then it connected with insulated copper wire to sample by aluminum conducting tape.The cyclic potentiodynamic polarization (CPP) curves were obtained by sweeping the potential from -1800 mV in the positive direction up to -700 mV vs. corrosion current measured by this test then corrosion rate is calculated from eq. (1).Notice that there are a new bonds create after transformation the PA from macrostructure to nanostructure .Also notice from these figs the PA electrospinning nanofibers have more crystallinity than PA macrostructure , increasing of amorphous structure leads to increase the crystalline peak broadness and intensity.Also the nanofibers with high degree of crystallinity consequently the sample of nanofibers coating show the weakest peak.[9], this is proved by Zimba et al. [10] who observed these peaks more clearly in amorphous PA structure than nanocrystalline structures .
[11] M 3 + + 4Cl ─ = MCl 4 It is also seen from Fig. 5 b&c and Table 1 that the PA coating on aluminum surface decreased the values of j Corr and K Corr which lead to increase the values of RP.Furthermore, the PA coated aluminum electrodes showed less negative values for ECorr.This indicates that PA nanofiber coatings highly prevent the dissolution aluminum via uniform and pitting corrosion in the chloride test solution and the protection efficiency in the order PA under (34kV) > PA (under 24kV).

Conclusion
We conclude from this search the PA electruspune nanofibers is very efficiency for protective the metal surface from corrosion , also the increasing of high voltage for preparation to electrospun nanofibers lead to increase the corrosion resistance of metal surface .
Figs (1 a,b) show the surface morphology for (a) PA coated aluminum under (24 Kv ) and (b) PA coated aluminum under (34 kV).All these images were taken using high resolution optical microscopiy.Notice from Fig. (1.a) that the PA needle structure layers are tight and homogeneously distributed on the surface.Also with (34 kV) condition for preparation the nanofibers coating leads to more homogenously coating than (24 kV).Fig (2 a) show the AFM image for PA coating under (24 kV) and fig (2 b) show the AFM image for PA coating under (34 kV) at three dimensions analysis , notice that the nanofibers which preparation under (24 kV) is about (3 µm) and it is more thick than (34 kV) which about (2.5 µm) but it is less compact than (34 kV)this is because increasing of high voltage in electrospinning technique leads to small nanofibers diameter with beads which leads to more compact coating and more roughness.Fig (3) show the SEM images of electrospune coating under(34 kV).