Welcome to the lecture on complementary corrosion measurement techniques.

In this lecture we will be talking about two complementary methods that can be used to

monitor corrosion including the atomic emission spectrochemistry, spectro electrochemistry

and respirometric method. But this lecture is going to be done in a different way.

I don't know if you are familiar with the initiative called as Corozum that is organized

by Professor Gerald Frankel from the Ohio State University who was also my PhD advisor

when I was a PhD student. There we have two interesting lectures on the respirometric

methods by Professor Sana Bartanen who is my advisor currently and by Professor Kevin

Ogle on the atomic emission spectro electrochemistry. So they give a rather detailed tutorial on these

methods over two lectures and I will post the links for those two lectures. So why am I talking

here now? I am giving you an introduction to the topic so that you can jump right into the lectures

or the seminars by Professor Kevin Ogle and Professor Robert Frankel at your own pace. But

I would advise you to complete watching this lecture before the next class. So why do we need

these complementary techniques? I gave a detailed introduction about detailed lecture on electrochemical

methods that are used including EIS, Potential Dynamic Polarization, Linear Polarization

Resistance, several methods to monitor corrosion. So why are we in need of these complementary

methods? The reason is rather simple. When we are dealing with the corrosion of an alloy,

what we basically assume that okay when we are doing anodic polarization, we assume that okay

there is not a lot of cathodic reaction happening and the film formation does not take a lot of

current. This is the oxide formation current and this is the cathodic current and we get the

high dissolution. And usually we assume that okay if you have a given alloy with let us say

18% chromium and 10% nickel, a model austenitic stainless steel, what happens is that we assume

that okay the dissolved electrolyte, dissolved ions will be consistent with the alloy composition

which means that we are expecting a congruent dissolution. But often it is not, we do not know

how much current is coming from the ion dissolution and chromium dissolution and the nickel dissolution.

So we can, we need to deconvolute how in a different in a given alloy how different elements,

the constituents of the dissolving, we need to understand that. That is one need and in open

circuit, let us take an open circuit condition, the you cannot the total net current is 0,

we do not know okay the dissolution rate or the cathodic current rate. So what we can do is we

can also monitor this cathodic reaction which is going to be hydrogen evolution reaction or

the oxygen reduction reaction using the respirometric methods either monitoring the pressure changes for

a constant volume or at a constant pressure change in volume. So there are two methods,

volumetric method and the manometric method of respirometry. So we can use this to monitor

the cathodic reaction and okay then it should equal, so let us assume this oxide formation

current is negligible, then it should equal the dissolution current and then we can decompose

what is the individual contribution from the different alloying elements present. So the key

questions that can be answered with this ASIC method is does the element and current correspond

to the alloy composition which basically means that is the dissolution congruent or is there

selective dissolution of certain alloying elements beyond the alloy chemistry, maybe we have 10%,

but the current corresponding to nickel might be only 5% and the chromium we have 18% chromium

maybe it might corrode more than the alloy composition like there might be a depletion

of chromium in the alloy due to dissolution and the enrichment of nickel because it's also it's

possible because nickel is a more mobile element when compared to chromium but there is also this

oxide formation. So if we can calculate the dissolution current then we can also calculate

whether there is significant oxide formation current or the corrosion product formation and

this respirometric method is not only useful to monitor the cathodic reaction, the gas evolution

reactions or the oxygen reduction reaction, the gas evolution reaction in the cathodic

the G means only hydrogen evolution reaction but when we are above the oxygen the water

stability potential we can also have oxygen evolution reaction and it should add up so you

can probably what would happen if I am above the water stability potential I have this I or OER