Arc Thermal Spray Process Research Articles

Investigating the corrosion resistance of Zn and Al coating deposited by arc thermal spraying process

Carbon steel is commonly used as a structural material in offshore windmill towers. The bases of these towers, which are located in tidal and submerged zones, often face corrosion challenges in marine environments. In this study, protective Zn and Al coatings were applied to S355J2 + N carbon steels by twin-wire arc spraying. The corrosion resistance of these coatings was evaluated by immersing them in various saline solutions, including NaCl solutions, sea salt solutions, and seawater. Corrosion tests were conducted for up to 1600 h. The results indicated that the corrosion rates of the Zn coatings and the accumulation of corrosion products on the Al coatings increased with higher concentrations of the testing solutions. The corrosion products of Zn coatings tested in sea salt solutions or seawater were mainly gordaite (NaZn4(SO4)(OH)6Cl(H2O)6), whereas those tested in NaCl solutions were mainly simonkolleite (Zn5(OH)8Cl2H2O). After testing in 5 wt% sea salt solutions for 1600 h, the Zn coatings exhibited interlayer decohesion owing to the formation of an oxide layer within the laminar structure. By contrast, the Al coatings displayed a well-mixed microstructure, ensuring strong adhesion and reducing susceptibility to interlayer decohesion in saline solutions. Consequently, in the current study, the Al-coated specimens demonstrated superior performance to that of the Zn-coated specimens in saline solutions.

Application of Arc Thermal Spray Process in Corrosion Protection of Steels and Electromagnetic Pulse Shielding

In the present work, an overview has been discussed on the application of arc thermal spray technology. This process used in erosion, corrosion and electromagnetic pulse (EMP) shielding. The Al coating exhibits excellent corrosion properties in simulated weathering i.e., Society of Automotive Engineers (SAE) J2334 as well as 3.5 wt.% NaCl solution at long run of application. However, weathering condition possesses Cl- and CO3-- ions, which simultaneously influence in the deterioration of Al coating. Once the Zn is alloyed with Al in coating, it enhances the corrosion attributed to the formation of severe defects and galvanic coupling between Al and Zn. The stainless steel and Ti coatings have been used on the concrete surface to reduce the corrosion of waste water reservoir where Ti is exhibited more corrosion resistance due to dense and uniform morphology as well as on the surface of Ti coating during exposure in acidic solution, it forms rutile and anatase, which further provide corrosion protection. Moreover, the Zn has beneficial properties in regards of EMP shielding rather than iron and Cu plate. Zn with copper has excellent EMP shielding compared to pure Cu. As the thickness is increased, the EMP shielding properties are increased. From this review article, it is suggested to reduce the porosity of arc thermal sprayed coating using some chemical post treatment.

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process.

The corrosion of steel structures in coastal areas is a major issue. Therefore, in the present study, the protection against the corrosion of structural steel is carried out by depositing 100 μm thick Al and Al-5 Mg coatings using a plasma arc thermal spray process, immersing them in 3.5 wt.% NaCl solution for 41 days (d). To deposit such metals, one of the best known processes, arc thermal spray, is frequently used, but this process has severe defects and porosity. Thus, to minimize the porosity and defects of arc thermal spray, a plasma arc thermal spray process is developed. In this process, we used normal gas to create plasma instead of argon (Ar) and nitrogen (N2) with hydrogen (H) and helium (He). Al-5 Mg alloy coating exhibited uniform and dense morphology, where it reduced more than four times the porosity compared to Al, where Mg fills the voids of the coating, resulting in greater bond adhesion and hydrophobicity. The open circuit potential (OCP) of both coatings exhibited electropositive values due to the formation of native oxide in Al, while in the case of Al-5 Mg, the coating is dense and uniform. However, after 1 d of immersion, both coatings showed activation in OCP, owing to the dissolution of splat particles from the corner where the sharp edges are present in the Al coating, while Mg preferentially dissolved in the Al-5 Mg coating and made galvanic cells. Mg is galvanically more active than Al in the Al-5 Mg coating. Due to the capacity of the corrosion products to cover the pores and defects, both coatings stabilized the OCP after 13 d of immersion. The total impedance of the Al-5 Mg coating is gradually increased and is higher than the Al, which can be attributed to the uniform and dense coating morphology where Mg dissolves and agglomerates to form globular corrosion products and deposit over the surface, thereby causing barrier protection. The defect bearing corrosion products on Al coating led to the cause having a higher corrosion rate than the Al-5 Mg coating. A total of 5 wt.% mg in the Al coating improved the corrosion rate by a rate of 1.6 times compared to the pure Al in the 3.5 wt.% NaCl solution after 41 d of immersion.

Effects of Surface Treatment Conditions on the Bonding Strength and Electromagnetic Pulse Shielding of Concrete Using the 85Zn-15Al Arc Thermal Metal Spraying Method.

The surface treatment of concrete enhances the bonding of its metal coatings. Therefore, in the present study, on the concrete surface, prior to the deposit of an 85Zn-15Al coating via an arc thermal spraying process, different surface treatments were considered for the effective electromagnetic pulse (EMP) shielding properties of the concrete. However, the direct coating on a concrete surface possesses lower bond adhesion, therefore it is of the utmost importance to treat the concrete surface prior to the deposition of the metal coating. Moreover, to obtain better bond adhesion and fill the defects of the coating, the concrete surface is treated by applying a surface hardener (SH), as well as a surface roughening agent (SRA) and a sealing agent (SA), respectively. The metal spraying efficiency, adhesion performance, and bonding strength under different concrete surface treatment conditions were evaluated. The EMP shielding effect was evaluated under the optimal surface treatment condition. The proposed method for EMP shielding exhibited over 60% of spraying efficiency on the treated surface and a bonding strength of up to 3.9 MPa for the SH-SRA-SA (combining surface roughening and pores/defects filling agents) specimen compared to the control one, i.e., 0.8 MPa. The EMP shielding values of the surface-treated concrete with surface hardener, surface roughening agent, and sealing agent, i.e., SH-SRA-SA specimens, exhibited 96.6 dB at 1000 MHz. This was about 12 times higher than without coated concrete.

Deposition of Different Metallic Coatings as Repair Materials for Concrete by Using a Twin-Wire Arc Thermal Spray Process

Using a concrete surface, the ingress of aggressive ions and the initiation of the corrosion reaction of an embedded steel rebar were studied. To reduce the corrosion reaction of the embedded steel rebar, either a coating on the steel rebar or a repair material was used on the concrete surface. Therefore, in the present study, 200 µm thick Cu, Ti, and 85Zn-15Al were used as repair materials, and their coatings were deposited on the concrete surface using a twin-wire arc thermal spray process. Different experiments such as bond adhesion, water permeability, immersion in a 5 wt.% NaCl solution, and accelerated carbonation were performed to assess the durability of the coatings, and the characterization of the coatings was performed by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Cu and 85Zn-15Al coatings exhibited severe defects and porosity; therefore, these coatings exhibited very low bond adhesion, whereas the Ti coating showed a dense and compact morphology, and its bond adhesion value was 11 times greater than that of the Cu coating. The NaCl immersion results can be used to determine the extent of the deterioration of different coatings in coastal areas; based on these results, the Cu coating exhibited delamination, while 85Zn-15Al showed white rust deposition. By contrast, there was no detrimental effect of NaCl immersion on the Ti coating during the 28 days under study, and the coating exhibited characteristics identical to those observed after deposition. The Ti coating reduced the carbonation depth by 1.5–2 times that of the Cu and 85Zn-15Al coatings after four and eight weeks of exposure. The present study suggests that Ti can be the potential metal used as a repair material for concrete to enhance the durability of buildings and infrastructure.

Morphological and corrosion studies of ammonium phosphate and caesium nitrate treated Al coating deposited by arc thermal spray process

In the present studies, the Al coating deposited by arc thermal spraying process was treated with different concentrations of ammonium phosphate mono basic ((NH4)H2PO4) and caesium nitrate (CsNO3) to improve the morphology and corrosion characteristics of the coating. As coated (AC) sample exhibits pores and defects onto the surface but once the treatment was carried out, the coating shows reduction in porosity as observed by scanning electron microscopy (SEM). The treated coatings contain caesium aluminum oxide (CAO: Cs2Al2O3) and ammonium aluminum hydrogen phosphate hydrate (AHP: (NH4)3Al5H6(PO4)8.18H2O) as composite oxides identified by X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) results reveal that as the exposure periods are increased, the resistance to coating/treatment (Rc/t) and charge transfer resistance (Rct) of AC and 0.5 M NH4H2PO4 and 0.0025 M CsNO3 (CN2) are increased with exposure periods in artificial ocean water solution. The improvement in total impedance values at 0.01 Hz of AC sample is attributed to formation of corrosion products which fill the pores/defects of coating while CN2 sample owing to the treatment film i.e. AHP and CAO and transformation of AHP into stable form. As the amount of NH4H2PO4 and CsNO3 is increased up to 1 M and 0.005 M i.e. CN3, the AHP film dissolved and enhances the corrosion reaction. Thus, cracking is observed in corrosion products. The enhancement in corrosion resistance of CN2 sample is attributed to the formation of α-Al(OH)3 (bayerite) and Al3(PO4)2(OH)3(H2O)5 (Aluminium hydroxide phosphate hydrate: AHPH) in greater amount as corrosion products. These corrosion products of CN2 sample are stable, sparingly soluble and protective.

Electromagnetic Shielding Performance of Different Metallic Coatings Deposited by Arc Thermal Spray Process.

Advancement in electronic and communication technologies bring us up to date, but it causes electromagnetic interference (EMI) resulting in failure of building and infrastructure, hospital, military base, nuclear plant, and sensitive electronics. Therefore, it is of the utmost importance to prevent the failure of structures and electronic components from EMI using conducting coating. In the present study, Cu, Cu-Zn, and Cu-Ni coating was deposited in different thicknesses and their morphology, composition, conductivity, and EMI shielding effectiveness are assessed. The scanning electron microscopy (SEM) results show that 100 µm coating possesses severe defects and porosity but once the thickness is increased to 500 µm, the porosity and electrical conductivity is gradually decreased and increased, respectively. Cu-Zn coating exhibited lowest in porosity, dense, and compact morphology. As the thickness of coating is increased, the EMI shielding effectiveness is increased. Moreover, 100 µm Cu-Zn coating shows 80 dB EMI shielding effectiveness at 1 GHz but Cu and Cu-Ni are found to be 68 and 12 dB, respectively. EMI shielding effectiveness results reveal that 100 µm Cu-Zn coating satisfy the minimum requirement for EMI shielding while Cu and Cu-Ni required higher thickness.

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

The adhesion of coatings on a given substrate has fundamental importance on a coating/substrate system's functionality. The current paper presents the adhesion strength results of FeCr and CoCr-based deposits produced by the electric arc thermal spray process on carbon steel, with an intermediate layer of 95Ni5Al. Three chemical compositions were tested for coating deposition and were characterized using plate and tube specimens made of carbon steel UNS G10200 to result in a screening of performance. Microstructural evaluation by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were performed. Coating strength was measured using the standard pull-off test method. The corrosion resistance was analyzed with salt spray exposure, electrochemical polarization, and impedance spectroscopy (EIS) tests. The adhesion strength of FeCr and CoCr alloy coatings shows an overall average tensile strength of 27.2 MPa. All sealed conditions presented low corrosion and the samples with epoxy sealant exhibited a high resistance against corrosion. The X-ray diffraction results have revealed alpha and gamma FeCr alloys and chromite as deposited phases after the coating process.

Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

Aluminum coating was deposited by arc thermal spraying process onto the steel substrate for the corrosion protection in aggressive environment. However, the arc thermal sprayed coating possesses defects in the coating. Thus, it is important to reduce the defects and enhance the corrosion resistance properties of the deposited coating using post-treatment. In the present study, we have used different concentrations of sodium phosphate mono basic (NaH2PO4) with 0.1 molar (M) calcium nitrate [Ca(NO3)2] as post-treatment solution to fill out the defects of the Al coating. It was observed by scanning electron microscopy (SEM) that 1 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample exhibited 71% reduction in defects compared to as coated samples. X-ray diffraction (XRD) was performed to determine the phases formed on the coating surface after treatments. XRD confirms the formation of sodium aluminum hydrogen phosphate (Na3Al(OH)(HPO4)(PO4)) and brushite (Ca(HPO4)(H2O)2) as composite oxides on the Al coating. Electrochemical results show that 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample has exhibited the highest charge transfer resistance and the lowest corrosion current density after 89 days of exposure in 3.5 wt.% NaCl solution. The enhancement in corrosion resistance of 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample attributed to the formation of adherent, sparingly soluble, and stable corrosion products. The volume fraction result of the corrosion products formed on 0.5 M NaH2PO4 with 0.1 M Ca(NO3)2 treated sample after 89 days of exposure in 3.5 wt.% NaCl using XRD confirms the highest amount of Bayerite (α-Al(OH)3) deposition, thus, the corrosion rate of this sample was the lowest.

Sodium Phosphate Post-treatment on Al Coating: Morphological and Corrosion Study

The coatings deposited by arc thermal spraying process possess defects and pores within the coating, which must be filled using a proper pore sealing agent. In the present study, we have deposited an Al coating on a steel substrate using arc thermal spraying. Post-treatment with different concentrations of sodium phosphate monobasic (NaH2PO4) salt solution was then carried out to fill the pores in the Al coating. The scanning electron microscopy results show that NaH2PO4 (SP) at 0.5 M concentration significantly reduces the porosity. When the concentration of NaH2PO4 is less than 0.5 M, the coating contains some pores and defects, whereas post-treatment with 1 M NaH2PO4 leads to the formation of a brittle film with wide cracks on the coating surface. The x-ray diffraction results of the treated coating confirm the formation of sodium aluminum hydrogen phosphate (Na3Al(OH)(HPO4)(PO4) film (SAHP). Electrochemical results obtained in artificial ocean water solution (ASTM D1141) show that treatment of the coating with 0.5 M NaH2PO4 enhanced the corrosion resistance properties for up to 7 days of exposure, but once the exposure periods are extended, the treated coatings exhibited deterioration because SAHP film started to dissolve in aggressive ions, i.e., artificial ocean water solution which makes the solution acidic owing to the formation of hydrogen phosphate and phosphoric acid. The AC sample shows protection after 60 days of exposure in artificial ocean water solution owing to the formation of protective, adherent, and uniform α-Al(OH)3 as corrosion products.

Study on the deposition of stainless steel on polymeric substrates by arc electric thermal spraying

It is known that application areas of plastics can be enlarged by imparting special features such as higher electrical and thermal conductivity by surface metallization of these materials. Still, there are very limited studies on the metal deposition on polymeric substrates by thermal spray process due to various limitations and problems associated with this aspect, although some reports are available on the fabrication and characterization of bonding layers using low melt temperature materials. With this background, this study was taken up with the objectives of deposition of 309L stainless steel on some polymeric substrates (PP, Nylon 66 and PVC) by electric arc thermal spray process through a prior development of a bond coating. This bond coating was based on epoxy resin/micro silica with scattered and packed metal particles anchored over it, which changed the nature of the substrate surface creating a favorable topology for adhesion and scattering of the sprayed particles. Coatings having an average thickness of 129.06 μm of stainless steel and 259.06 μm of bonding layer (epoxy/micro silica) were obtained over a polyvinyl chloride (PVC) substrate, which had the smaller difference of coefficient of thermal expansion with the bond coat. Obtained coating showed good electrical conductivity value. This kind of favorable metallization of plastics could expand its application areas and might be potential candidate to replace expensive metallic or ceramic materials in special applications.

Corrosion mechanism and kinetics of Al-Zn coating deposited by arc thermal spraying process in saline solution at prolong exposure periods

Steel structures significantly degrades owing to corrosion especially in coastal and industrial areas where significant amounts of aggressive ions are present. Therefore, anodic metals such as Al and Zn are used to protect steel. In the present study, we provide insights for the corrosion mechanism and kinetics of Al-Zn pseudo alloy coating deposited on mild steel plate via an arc thermal spraying process in 3.5 wt.% NaCl solution in terms of its improved corrosion resistance properties at prolonged exposure durations. Electrochemical studies including open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) on the deposited coating at longer exposure durations revealed enhanced corrosion resistance properties while the morphology of corrosion products through field emission-scanning electron microscopy (FE-SEM) indicated their compactness and adherence. Furthermore, atomic force microscopy (AFM) confirmed reduced roughness when compared with that of unexposed coating. Additionally, X-ray diffraction (XRD) and Raman spectroscopy results confirmed the formation of protective, adherent, and sparingly soluble Simonkolleite (Zn5(OH)8Cl2.H2O) after 55 d of exposure in 3.5 wt.% NaCl solution. A schematic is proposed that explains the corrosion process of Al–Zn pseudo alloy coating in 3.5 wt.% NaCl solution from the deposition of coating and initiation of corrosion to longer exposure durations.

The microstructures and anti-corrosion behavior of the thermal sprayed Hastelloy C276 coating on substrate of Q235 steel

Hastelloy C276 coating was prepared on the substrate of Q235 steel by arc thermal spraying process. The microstructure, microhardness, thermal shock resistance and anti-corrosion of the coating were investigated. The coating exhibits a layered buildup structure with some pores and unmelted particles appearing. There is a distinct and rough interface between the coating and the substrate which increases the contact area between the coating and the substrate. The coating and the substrate were meshed to each other in the boundary, showing a strong bonding. The coating exhibited a strong thermal shock resistance with the substrate of Q235 steel at 600 °C. The microhardness of the surface of the coating is much higher than the microhardness of the surface of the substrate. Uniform corrosion method of laboratory semi-immersion test was used to test the corrosion resistance of C276 coating. The coating exhibited good corrosion resistance in concentrated HCl with a concentration of 36.5%.

Influence of calcium nitrate on morphology and corrosion characteristics of ammonium phosphate treated Aluminum coating deposited by arc thermal spraying process

In present study Al coating was deposited by arc thermal spraying process thereafter treated with different concentration of Ammonium phosphate mono basic (NH4H2PO4) and 0.1 M calcium nitrate [Ca(NO3)2] to fill the porosity. Impedance values of treated coating was increased at longer duration of exposure in artificial ocean water due to transformation of Brushite and Ammonium Aluminum hydrogen phosphate hydrate into metastable and sparingly soluble gypsum and Aluminum phosphate. 0.1 M Ca(NO3)2 has positive influenced with 1 M NH4H2PO4 on formation of compact and crystalline morphology as well as corrosion resistance of Al coating.

Influence of Zn and Mg Alloying on the Corrosion Resistance Properties of Al Coating Applied by Arc Thermal Spray Process in Simulated Weather Solution

In this study, Al–Zn and Al–Mg coatings were deposited on steel substrates by an arc thermal spray process. X-ray diffraction and scanning electron microscopy were used to characterize the deposited coatings and corrosion products. Open circuit potential (OCP), electrochemical impedance spectroscopy, and potentiodynamic studies were used to assess the corrosion characteristics of these coatings after exposure according to the Society of Automotive Engineers (SAE) J2334 solution of varying durations. This solution simulates an industrial environment and contains chloride and carbonate ions that induce corrosion of the deposited coatings. However, the Al–Mg alloy coating maintained an OCP of approximately − 0.911 V versus Ag/AgCl in the SAE J2334 solution even after 792 h of exposure. This indicates that it protects the steel sacrificially, whereas the Al–Zn coating provides only barrier-type protection through the deposition of corrosion products. The Al–Mg coating acts as a self-healing coating and provides protection by forming Mg6Al2(OH)16CO3 (Al–Mg layered double hydroxides). Mg6Al2(OH)16CO3 has interlocking characteristics with a morphology of plate-like nanostructures and an ion-exchange ability that can improve the corrosion resistance properties of the coating. The presence of Zn in the corrosion products of the Al–Zn coating allows dissolution, but, at the same time, Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3 are formed and act to reduce the corrosion rate.

Deposition of Coating to Protect Waste Water Reservoir in Acidic Solution by Arc Thermal Spray Process

The corrosion characteristics of 304 stainless steel (SS) and titanium (Ti) coatings deposited by the arc thermal spray process in pH 4 solution were assessed. The Ti‐sprayed coating exhibits uniform, less porous, and adherent coating morphology compared to the SS‐sprayed coating. The electrochemical study, that is, electrochemical impedance spectroscopy (EIS), revealed that as exposure periods to solution were increased, the polarization resistance (Rp) decreased and the charge transfer resistance (Rct) increased owing to corrosion of the metallic surface and simultaneously at the same time the deposition of oxide films/corrosion on the SS‐sprayed surface, while Ti coating transformed unstable oxides into the stable phase. Potentiodynamic studies confirmed that both sprayed coatings exhibited passive tendency attributed due to the deposition of corrosion products on SS samples, whereas the Ti‐sprayed sample formed passive oxide films. The Ti coating reduced the corrosion rate by more than six times compared to the SS coating after 312 h of exposure to sulfuric acid‐ (H2SO4‐) contaminated water solution, that is, pH 4. Scanning electron microscope (SEM) results confirmed the uniform and globular morphology of the passive film on the Ti coating resulting in reduced corrosion. On the other hand, the corrosion products formed on SS‐sprayed coating exhibit micropores with a net‐like microstructure. X‐ray diffraction (XRD) revealed the presence of the composite oxide film on Ti‐sprayed samples and lepidocrocite (γ‐FeOOH) on the SS‐coated surface. The transformation of TiO and Ti3O into TiO2 (rutile and anatase) and Ti3O5 after 312 h of exposure to H2SO4 acid reveals the improved corrosion resistance properties of Ti‐sprayed coating.

Corrosion behavior in seawater of arc thermal sprayed Inconel 625 coatings with sealing treatment

In this study, zinc powder (Zinc), inorganic ceramic (Ceramic), and organic-inorganic composite ceramic (Hybrid) sealing processes were applied to improve the corrosion resistance of arc thermal sprayed Inconel 625 coatings. The Inconel 625 coating in seawater solution showed poor corrosion resistance due to its porosity and Cr depletion resulting from Cr oxide formation during the arc thermal spraying process. Zinc sealing formed a stable cathodic protection, but the local corrosion damage occurred largely in the anodic polarization experiment caused by an excessive dissolution reaction and a weak bonding force between the zinc particles. Hybrid sealing gave a better sealing effect, but surface corrosion damage appeared due to interconnected micro-crack defects on the surface. Ceramic sealing gave the best corrosion protection due to a high sealing efficiency and a lower surface damage tendency resulting from effectively blocked defects of the Inconel 625 coating.

An effective and novel pore sealing agent to enhance the corrosion resistance performance of Al coating in artificial ocean water

A new technique was accepted to fill the porosity of Al coating applied by arc thermal spray process to enhance corrosion resistance performance in artificial ocean water. The porosity is the inherent property of arc thermal spray coating process. In this study, applied coating was treated with different concentrations of ammonium phosphate mono basic (NH4H2PO4: AP) solution thereafter dried at room temperature and kept in humidity chamber for 7d to deposit uniform film. The corrosion resistance of Al coating and treated samples have been evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic techniques with exposure periods in artificial ocean water. Electrochemical techniques, X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) indicated that phosphate ion would have been retarding corrosion of Al coating effectively. The formation of AHP (Ammonium Aluminum Hydrogen Phosphate Hydrate: NH4)3Al5H6(PO4)8.18H2O) on Al coating surface after treatment with AP is nano sized, crystalline and uniformly deposited but after exposure them in artificial ocean water, they form AHPH (Aluminum hydroxide phosphate hydrate Al3(PO4)2(OH)3(H2O)5) that is very protective, adherent, uniform and plate like morphology of corrosion products. The AHPH is sparingly soluble and adherent to surface and imparted improved corrosion resistance.

Protection of Reinforced Concrete Structures of Waste Water Treatment Reservoirs with Stainless Steel Coating Using Arc Thermal Spraying Technique in Acidified Water.

Waste water treatment reservoirs are contaminated with many hazardous chemicals and acids. Reservoirs typically comprise concrete and reinforcement steel bars, and the main elements responsible for their deterioration are hazardous chemicals, acids, and ozone. Currently, a variety of techniques are being used to protect reservoirs from exposure to these elements. The most widely used techniques are stainless steel plating and polymeric coating. In this study, a technique known as arc thermal spraying was used. It is a more convenient and economical method for protecting both concrete and reinforcement steel bar from deterioration in waste water treatment reservoirs. In this study, 316L stainless steel coating was applied to a concrete surface, and different electrochemical experiments were performed to evaluate the performance of coatings in different acidic pH solutions. The coating generated from the arc thermal spraying process significantly protected the concrete surface from corrosion in acidic pH solutions, owing to the formation of a double layer capacitance—a mixture of Cr3+ enriched with Cr2O3 and Cr-hydroxide in inner and Fe3+ oxide on the outer layer of the coating. The formation of this passive film is defective owing to the non-homogeneous 316L stainless steel coating surface. In the pH 5 solution, the growth of a passive film is adequate due to the presence of un-dissociated water molecules in the aqueous sulfuric acid solution. The coated surface is sealed with alkyl epoxide, which acts as a barrier against the penetration of acidic solutions. This coating exhibits higher impedance values among the three studied acidic pH solutions.

Pore blocking characteristics of corrosion products formed on Aluminum coating produced by arc thermal metal spray process in 3.5 wt.% NaCl solution

Arc thermal metal spray coating is very efficient process to protect the steel from corrosion in industrial, humid and saline/coastal environments. This paper incorporates the experimental results for the performance of Aluminum coating deposited on mild steel substrate by arc thermal metal spray. Different electrochemical techniques, FE-SEM, Raman spectroscopy and XRD were used to assess the performance of deposited coating. Electrochemical studies revealed the enhanced corrosion resistance properties of coating in 3.5wt.% NaCl solution. The formation of α-Al(OH)3 on coating substrate during exposure periods block the pores of coating and impede the penetration of corrosive species to react with substrate.