The main raw material of coal fly ash was obtained from…….. The composition of fly ash is shown in the table. Sodium hydroxide was purchased from HPLC Pvt. Ltd. Mumbai, India. Molybdic acid and calcium chloride were purchased from CDH Pvt. Ltd. New Delhi, India. Zinc chloride was purchased from MERCK Ltd. Mumbai, India. The solvent used in preparing the coating i.e. xylene was purchased from Avantor Performance Material India Ltd. The acrylic resin and epoxy resin with its hardener were obtained from Atul Polymers, India. The other chemicals used in this work were AR and LR.3.2 grades. Techniques3.2.1 Electrochemical Impedance Spectroscopy (EIS) The electrochemical impedance spectroscopy (EIS) technique is a useful method for studying the corrosion mechanism and the fundamental parameters of electrochemical reactions. EIS technique is a very popular technique, the reasons for its popularity can be explained as follows :1. The technique uses only very small perturbation signals without disturbing the properties of the electrode being measured.2. It can obtain charge transfer resistance and double layer capacitance data in the same measurement.3. Measurements can be made in solution with low conductivity while, under similar conditions. DC techniques are subject to significant errors due to large ohmic drops.4. The equipment is relatively inexpensive and it is very easy to obtain large amounts of data quickly.3.2.1.1. The basic principles of electrochemical impedance spectroscopy (EIS). For any electrical circuit, consisting of various passive elements (i.e. resistors, capacitors and inductors), the behavior of the entire circuit at an applied AC voltage depends on both behaviors... .... center of paper ..... .i-cerchi [30]. Therefore, in these cases, interpretation of the impedance data is usually difficult and care must be taken when doing so. 2) Finally, measurements obtained using electrochemical impedance spectroscopy (EIS) are sequential; for example, each frequency point is considered in turn, which means that to obtain frequency spectra, say from 10 KHz to 10 mHz, it takes some time depending on the power of the impedance machine. This can be a long time for systems that corrode rapidly and whose reaction rate changes rapidly. Furthermore, at low frequencies, the system may be subject to noise "pick-up" which can lead to frequency dispersion on the impedance graph. Despite these drawbacks, electrochemical impedance spectroscopy (EIS) has proven to be a valuable technique and can provide important information about the nature of corrosion processes in many systems. [31].