Cathodic Protection of Steels using CNT's

There seems to be a lot happening in the CNT arena, where it can be used in coatings to protect mild steel or they can also use in in concrete where it helps with cathodic protection, where the CNT's in the concrete act as one of the conductors for this purpose, so it would seem that there is another string in the bow for CNT uses?


http://iopscience.iop.org/article/10.1088/2043-6254/aa5cf8


Advances in Natural Sciences: Nanoscience and Nanotechnology

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Effect of coating mild steel with CNTs on its mechanical properties and corrosion behaviour in acidic medium

Mahmud Abdulmalik Abdulrahaman¹, Oladiran Kamaldeeen Abubakre^1,4, Saka Ambali Abdulkareem^2,4, Jimoh Oladejo Tijani^3,4, Ahmed Aliyu² and Ayo Samuel Afolabi⁵
Published 3 March 2017 •  © 2017 Vietnam Academy of Science & Technology
Advances in Natural Sciences: Nanoscience and Nanotechnology, Volume 8, Number 1
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Abstract

The study investigated the mechanical properties and corrosion behaviour of mild steel coated with carbon nanotubes at different coating conditions. Multi-walled carbon nanotubes (MWCNTs) were synthesized via the conventional chemical vapour deposition reaction using bimetallic Fe–Ni catalyst supported on kaolin, with acetylene gas as a carbon source. The HRSEM/HRTEM analysis of the purified carbon materials revealed significant reduction in the diameters of the purified MWCNT bundles from 50 nm to 2 nm and was attributed to the ultrasonication assisted dispersion with surfactant (gum arabic) employed in purification process. The network of the dispersed MWCNTs was coated onto the surfaces of mild steel samples, and as the coating temperature and holding time increased, the coating thickness reduced. The mechanical properties (tensile strength, yield strength, hardness value) of the coated steel samples increased with increase in coating temperature and holding time. Comparing the different coating conditions, coated mild steels at the temperature of 950 °C for 90 min holding time exhibited high hardness, yield strength and tensile strength values compared to others. The corrosion current and corrosion rate of the coated mild steel samples decreased with increase in holding time and coating temperature. The lowest corrosion rate was observed on sample coated at 950 °C for 90 min.
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1. Introduction

Mild steel remains an important engineering material frequently applied in construction, chemical, power production, automobile and electrochemical industries due to its abundance at relatively low production cost. Above all, mild steel possesses unique and remarkable mechanical properties such as good strength, toughness, ductility, formability and weldability which confirm its suitability as a better construction material in comparison to other engineering materials [1–3].
In fact, most fabricators and machinists consider mild steel as a favourite raw material in the production of engineering components such as gears, cams, shafts, keys, hand tools among others. Some of these engineering components must have strong and hard surface along with soft and tough core for their durability, reliability and safe operations depending on the operational conditions. These aforementioned properties are however lacking in mild steel, thus causing simultaneous wear at the surface and subsequently breakage upon impact during operations [4, 5]. Furthermore, mild steels are sometimes susceptible to ravages and failure depending on the environmental conditions causing deterioration of material surfaces, a phenomenon called corrosion. Corrosion causes gradual weakening and failure of material properties which can sometimes lead to human injury, loss of life and collateral damage [6]. In fact, William and David [2] and Singh et al [7] independently found that about 5% income of the developed nations were spent on corrosion prevention and maintenance and/or replacement of products lost due to the effect of corrosion. It should however be mentioned that, corrosion of steels in acidic aqueous solution is evident in most industries where acids are used in pickling, industrial cleaning, descaling and oil well acidizing processes [8].
On the other hand, several metals and non-metals, ceramics including polymers have been applied as coating on mild steel to improve their hardness, wear, fatigue and corrosion resistance in order to suit many applications [9, 10]. Montemor [9] reported that utilizing conductive fillers such as carbon black, graphite, fullerene, metallic particles and carbon nanotubes should improve the surface properties of materials.
Of all these coating materials or conductive fillers, carbon nanotubes (CNTs) are considered the most promising nanomaterials to improve the surface properties of existing materials due to its exceptional electrical, mechanical, chemical and thermal properties [10, 11]. Several synthesis approaches such as electrical arc discharge, laser ablation, pyrolysis, plasma enhanced, thermal or catalytic chemical vapour deposition have been explored to produce high quality CNTs of different length and diameter. However, catalytic chemical vapour deposition (CCVD) is considered more versatile and prominent than other methods for obtaining large-scale and high quality CNTs at comparatively low cost [12]. A typical CCVD technique involves decomposition of carbon sources (acetylene or methane gas) at a temperature above 600 °C on metals such as Fe, Co, Mo, Ni or their mixtures placed on a quartz boat in a horizontal quartz tube inside furnace at a predetermined time. Sometimes, these metallic particles are supported on conventional substrates such as CaCO₃, SiO₂, MgO, Al₂O₃, TiO₂, zeolites, activated carbon, and clay to produce the CNTs. Conversely, purification of CNTs grown on substrates remains a challenge after production, which often involves several steps. Different purification methods have been utilised still concentrated HNO₃ or mixture HNO₃–H₂SO₄ remains most frequently used. Although, this purification method has certain drawbacks limiting the purified CNTs from fulfilling all require technical processing.
Furthermore, the choice of CNTs as a coating material includes ultra-strength and ability to tolerate large strain as reinforcing materials in polymer composites [13]. Chen et al [14] revealed that the surfaces of metals possess defects, cracks, gaps, crevices and micro holes, which behave as active sites for initiation of fatigue and dissolution of metal during corrosion. Thus, CNTs can easily be made to enter and fill in these micro holes acting as a physical barrier to propagation of cracks and corrosion processes. Poole and Owens [15] found that the tensile strength of steel incorporated with 30% CNTs was seven times higher than the original steel without CNTs. The service conditions of many engineering materials make it necessary for them to possess a very strong and solid surface to resist wear, leaving a softer and more plastic core to absorb shock upon impact during operations [16, 17].
Furthermore, many surface treatment methods have been developed and applied to enhance the surface properties of components produced from mild steel. For instance, the surface properties of mild steel can be improved via the diffusion of carbon, nitrogen, carbon nitride or cyanide onto the surface of mild steel at austenitising temperature and/or lower temperature. Although, Qi et al [17] highlighted several limitations of diffusion methods to include: time and energy consumption, complex heat treatment schedules, wider heat affected zone, lack of solid solubility limited and slower kinetics. Besides, the method is not environmentally friendly. In addition, metals such as zinc, chromium, titanium and their alloys have been deposited as coating on mild steel to improve its surface properties. Marder [18] found zinc to be less ductile compared to the substrate it protects thus compromising the coating intension during deformation. Chromium because of its desired properties has been used to coat mild steel but this method was restricted due to health and environmental concerns [19]. Deposition of ceramics and their composites as coating on mild steel have been reported to enhance the surface properties of mild steel. However, ceramic coatings have certain limitations such as high cost of equipment, low coating adherence, large porosity, requirement of controlled environment (such as vacuum) and line of site. Moreover, complex procedures are often involved during operations [20].
In view of the associated deficiencies and challenges with the existing coating methods to improve the performance of mild steel, it is imperative to develop simple, scalable, cheap and environmental friendly method for the surface treatment of mild steel that will impact superior surface properties. Therefore, this study investigated the influence of CNTs at different coating conditions on the mechanical properties and corrosion behaviour of mild steel in acidic medium.



https://www.researchgate.net/public...re_solutions_in_the_presence_of_chloride_ions


Abstract
This study investigates the electrochemical characterization of carbon nanotube and zinc-rich epoxy primers (CNT-ZRPs) on carbon steel in simulated concrete pore (SCP) solutions in the presence of chloride ions. The mechanistic performance of CNT-ZRPs was characterized by adding different zinc content. The electrochemical results indicated a dominant barrier protection effect for the coating with 60 wt% Zn while there was a mixed corrosion protection mechanism for the coating with 70 wt% Zn and a dominant cathodic protection mechanism for coatings with higher zinc content (80 wt% and 90 wt% Zn). These barrier and cathodic protection control mechanisms were characterized quantitatively by electrochemical and high-resolution techniques.


https://www.astm.org/DIGITAL_LIBRARY/JOURNALS/TESTEVAL/PAGES/JTE20160062.htm

Volume 45, Issue 5 (September 2017)

Effects of Carbon Nanotube-Carbon Fiber Cementitious Conductive Anode for Cathodic Protection of Reinforced Concrete

(Received 31 January 2016; accepted 29 June 2016)
Published Online: 2016
CODEN: JTEVAB

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Zuo, J., Yao, W., Xu, J., Chen, Y., and Liu, X., "Effects of Carbon Nanotube-Carbon Fiber Cementitious Conductive Anode for Cathodic Protection of Reinforced Concrete," Journal of Testing and Evaluation, Vol. 45, No. 5, 2017, pp. 1777-1786, https://doi.org/10.1520/JTE20160062. ISSN 0090-3973
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mce-anchorAbstract
Carbon nanotube-carbon fiber/cement-based composites used as auxiliary anode for cathodic protection of reinforced concrete were explored in this paper. Cathodic protection was applied with impressed current and its efficiency was verified by corrosion potential, corrosion current, and AC impedance spectroscopy. Results showed that cement composites containing 0.4 wt. % carbon fiber and 0.5 wt. % carbon nanotubes exhibit the optimum electrical and mechanical properties. Effective protection on steel re-bars can be expected due to a sufficient negative potential shift by the applied electric current. Compared with a carbon fiber cementitious conductive anode system, a decrease of corrosion current of steel re-bars was observed for the carbon nanotube-carbon fiber cementitious conductive anode system. During cathodic protection, both capacitive loop radius of a Nyquist plot in the intermediate frequency region and the charge transfer resistance increased with time. A detailed mechanism analysis of the efficiency of cathodic protection using the carbon nanotube-carbon fiber cementitious conductive anode is also included.

Author Information:
Zuo, J.
Shanghai Construction Group Co., Ltd., Shanghai,
Yao, W.
Key Laboratory of Advanced Civil Engineering Materials, Tongji Univ., Ministry of Education, Shanghai,
Xu, J.
Key Laboratory of Advanced Civil Engineering Materials, Tongji Univ., Ministry of Education, Shanghai,
Chen, Y.
Key Laboratory of Advanced Civil Engineering Materials, Tongji Univ., Ministry of Education, Shanghai,
Liu, X.
College of Mechanics and Materials, Hohai Univ., Nanjing,

Stock #: JTE20160062
ISSN:0090-3973
DOI: 10.1520/JTE20160062