Welcome to the lecture on High Temperature Corrosion of Solution Analysis.

So, in this lecture first I will give you a context why do we need high temperature

materials and why do we care about high temperature corrosion.

It gives you a practical understanding of what happens to the material and how it interacts

with the material at high temperature. By high temperature we mean it is more than 0.5 times

the melting point of the given material. Then after establishing this context we will talk

about the fundamentals thermodynamics and kinetics of high temperature corrosion.

Then we will end this lecture with a practical example based on current research that we are

doing. It is also connected to the industry where we are trying to make additively manufactured

thermodynamics centre frame using a nickel based super alloy 247. So, we will see how we can study

It also involves some modelling techniques how we use experiments together with modelling to

understand material behaviour. Coming to the outline of this lecture, first we will talk about

the need for high temperature alloys along with practical applications for high temperature

alloys and then we will talk about general property requirements for high temperature

alloys and how we as engineers and scientists are trying to push the limits of performance by

going to higher and higher temperatures. Then we will talk about the protection against

high temperature environmental degradation. What are all the methods that we use as engineers

and scientists to mitigate the degradation process and then because the extrinsic method

of coating a material is outside the scope of the topic of this class and it is covered in later

class called as surface modification techniques. We will focus mainly on the intrinsic methods,

how by alloying we can tune oxide scale formation and get desired properties. In that we will also

talk about thermodynamics, the Ellingham diagram and other diagrams in thermodynamics for real

life alloys and we will talk about oxide scale formation and growth and some growth loss and

there will be all along there will be an emphasis on the real life examples including some of the

work that we have been currently doing for general electric company. Then we will briefly

talk about the Wagner's criteria for internal versus external oxidation, how we like to have

an external scale to form rather than forming an internal oxide precipitate which might degrade

the mechanical integrity of the components and we will also talk about some alloy development

strategies, some of the challenges and opportunities that lie in this field and how you can contribute

to this field as a corrosion engineer. So that would be the overall outline of the lecture.

So let's jump into the content of the lecture by starting with the need for high temperature alloys.

Coming to the need for high temperature alloys, so what is first high temperature in this context?

In this context as I already mentioned in the first when I was explaining the first two slides,

I was saying it should be above 0.5 times the melting point of material. But in general in

industrial context we usually use the word high temperature application for temperatures which

exceed 500 degree Celsius and we have operating temperatures up to 1200 degree Celsius. In this

case we only use materials that has high melting point not as high melting point like a refractory

material. We can also use some refractory materials for some of the high temperature

applications but most commonly used industrial materials are either iron based materials or

nickel based materials or cobalt based alloys. So in the context of this lecture we will define

anything more than 500 degree Celsius as a high temperature environment and we will talk whatever

material degradation that occurs due to the interaction with the environment at this

temperature as high temperature corrosion. Where do we encounter these high temperature

conditions? One very common example that everybody is familiar with is at least many of you would

have traveled in airplanes. So airplanes usually use something called as a jet engine and in this

at the hottest part of this engine we can even get to temperatures as hot as 1200 degree Celsius

and there is an important industrial process of steam cracking which is used to produce this

hydrocarbon. For example this ethylene pyrolysis these are held in these big tubes that are there

in the picture in the middle. So these can operate at temperatures like 700, 800 degree Celsius and

these if you see the pipes look smaller but these are very heavy and the self weight due to the