Effect of Nano-Ceria on Physiognomies of Aluminum-5% Zinc Sacrificial Anode

Sacrificial anodes possessing higher electrochemical efficiency is the demand of marine, oil and gas industries. Due to high energy capability and long life light weight aluminum based anodes are more favorable as compare to magnesium and zinc based anodes to protect the engineering structures from corrosion. In present study an attempt was made to develop Al-5% Zn based composite with nano-ceria. The effect of nano-ceria on physiognomies of Al-5% Zn anode was determined through weight loss, CPR (Corrosion Penetration Rate) and emf study in CCP (Close Circuit Potential) conditions. The results indicated that by incorporating the ceria in the matrix of Al-5% Zn anode the corrosion inhibition efficiency and hardness were increased significantly.

Although, by addition of 5% Zn the sacrificial tendency of Al was improved sufficiently, even though Al-5% Zn anodes have not gain much industrial attraction because of its non-columbic loss and microbiologically induced corrosion attack in aqueous environments. Shibli et. al. [9][10][11] observed that addition of various metal oxides (such as IrO 2 , RuO 2 , CeO 2 and ZnO-Al 2 O 3 ) could decrease noncolumbic loss and microbiologically induced corrosion of the Al-5% Zn anodes. Among these oxides, addition of nano CeO 2 (ceria) has been considered more effective [11][12]. Anodic efficiency highly depend on the concentration of ceria in Al-5% Zn anodes. Aziz et. al.
[13] and Rivera et. al. [14] studied the effect of higher concentration of CeO 2 in Al-5% Zn alloys. They noted that when such material is exposed to the environment a barrier layer of CeO 2 is formed on its surface and its anodic efficiency is decreased appreciably. The effect of particle size of ceria on the efficiency of Al-5% Zn anode is rarely studied.
In Pakistan, marine, oil and gas structures are being protected by ICCP despite the limitations of higher installation and maintenance cost along with stray current problems. Another issue concerned with SACP is the use of magnesium and zinc as sacrificial anodes which have less energy capabilities as compared to Al-5% Zn-anodes.
Keeping in view the current research trend in the field of SACP and problems related marine, and oil and gas sectors in Pakistan an attempt is made to develop Al-Zn-CeO 2 sacrificial anode.The effect of particle size and concentration of CeO 2 on the anodic efficiency of Al-5% Zn are investigated.

MATERIALS AND METHOD
To manufacture Al-5%Zn-ceria anode, Al and Zn ingot of 99% purity along with Merck-grade cerium nitrate (Ce(NO 3 ) 3 .6H 2 O) were used. The nano-ceria was synthesized using precipitation method, whereas Al-5%Zn anode was manufactured by traditional casting technique. The detailed procedure involved in the synthesis of nano-ceria and manufacturing of Al-5% Zn anode is described elsewhere [15]. Effect of Nano-Ceria on Physiognomies of Aluminum-5% Zinc Sacrificial Anode loss and CPR in CCP conditions. The detail of method used for percentage weight loss and CPR is reported [15].
The hardness of the anode was also determined by measuring the VHN (VickerHardness Number) at 1Kg f test load.

Characterization of Nano-Ceria
The XRD pattern of nano-ceria synthesized at different time intervals is shown in Fig. 1. XRD results indicates that the intensity of the ceria peaks were increased with increasing the precipitation time. D

Sacrificial Tendency of Anodes
Sacrificial tendency of Al-5% Zn-ceria anodes was determined through monitoring the variation in emf for 168h in CCP system. Fig. 3 indicates that for period of 168h wide fluctuation in the emf of AZ1, AZ2, AZ3, AZ4 and AZ10 anodes, whereas emf of AZ4, AZ5, AZ7, AZ8 and AZ9 was remained quite stable. The anodes which do not maintain their emf below -0.9V would not compensate the loss of electrons of cathode efficiently, thus corrosion inhibition by the use of AZ1, AZ2, AZ3, AZ4, AZ8 and AZ10 could not be anticipated.
The performance of the anodes deduced from their emf values was further validated by monitoring the emf and CPR of the cathode. The variation in the emf of mild steel cathode while coupling it with AZ1 to AZ10 anodes via CCP system is shown in Fig. 3. The utmost feature of the results shown in Fig. 4 is the significant contrast in the initial emf values of the cathode when it was coupled with AZ1, AZ3 and AZ10 hereinafter referred as Group-A anodes and AZ2, AZ4, AZ5, AZ6 and AZ9 hereinafter referred as Group-B anodes. It can be seen in Fig. 4   Hardness result of Al-5% Zn anode as a function of ceria concentration is shown in Fig. 7, which demonstrates that hardness is also improved with addition of the ceria and improvement in the hardness is dependent on the size and concentration of nano ceria particles. Substantial increase in hardness with addition of ceria can be explained by correlating with physico-mechanical properties of ceria. Since ceria belongs to ceramic family, so by the addition of ceria increase in hardness of Al-5% Zn anode can be anticipated [16]. Moreover, the enhancement in the anode life can also be substantiated from the substantial improvement in the hardness.