 So, most of the time chemical characterization is done to understand the chemical properties of the material, where XRF is done XI fluorescence technique this is a set up which is XRF do not think that this is a washing machine. It is a XRF set up from our IID Bombay at XF very expensive equipment costing more than I think 2, 2.5 crores. Then second unit is ICP inductively coupled plasma unit which gives you the concentration of trace elements. Then pH value we study cation exchange capacity and then pore solution analysis. So, these are the pallets of X-ray you can imagine if half mm thick half centimeter thick aluminum disc which is normally used. And half of this disc is filled up with cellulose state and the material for which chemical composition is to be obtained. And this makes a bond you cover it apply some load. So, that becomes a pallet and this pallet in this form goes into the XRF machine to get the fractions of oxides which are present in it. Now, this is the inductively coupled plasma unit where you can find out the trace elements which are present in the file mass up to the P P T level part per trillion. So, this instrument which is on our lab can be used up to P P D or P P M part per million part per billion. But then this equipment can be used for finding out the concentrations up to P P T level part per trillion. Now, these are the results of different materials which have been analyzed. You will notice that the calcium is present in the chalk sample and 26.5 percent is present in GGBFS. And in your normal white clay the calcium is only insignificant 0.27. The fly ashes are also very poor 0.11 except for one type of fly ash which might be a different type of source of coal. So, this is the reason why your GGBFS is very active that has more calcium. This is what is known as elemental analysis of different oxides. Well, this type of study becomes very important to see how the pH of the material changes over a period of time. So, you have to establish first whether the soil or the geomaterial is acidic or basic and how this acidity or basicity changes over a period of time. So, this type of studies are normally done particularly by people who are in associated with concrete technology that how easily the system becomes acidic or basic. The commonsense says that you cannot use the material which is acidic in making concrete. So, you may see the alteration in the response of the material. It may dip for the and then again pick up in terms of a pH. So, these type of studies are done to study the response of the material over a prolonged duration. And the last scheme of characterization of the materials for their chemical properties is known as cation exchange capacity. So, by definition cation exchange capacity is the concentration of calcium ions which is present in certain volume of the extract divided by the equivalent weight of the cation. Now, these cations are nothing but the cations which are replaced by calcium ions. So, that is the reason why we call it as a cation exchange capacity. How easily the cations can be exchanged from the soil mark by the contaminant. So, here you have to treat the soil sample repeatedly by sodium hydroxide and calcium hydroxide. And then see by every trial how many calcium ions are replacing sodium ions. So, this is a sort of a reactivity. So, for different materials you will notice that the cation exchange capacity units are milli-equivalent for 100 grams. This varies and you will find that for different type of soils the values are quite less. However, for blast furnace flag you cannot do this as analysis because the moment you add water it forms a thick gel. It sets for this type of water cannot be the basic idea of doing SEM is to get a very detailed idea about the material. Particularly, where you stop by simple optical imaging this is where SEM begins or this is where the domain of SEM begins. So, for obtaining very detailed images at much higher magnification and resolution approximately 10 power 5 times if you want to study any sample or a specimen then you can adopt for SEM. And this is the improvement over simple light microscopy. The beauty is that SEM images the surface structure of bulk specimens. And nowadays SEM analysis is becoming very very common in different types of studies related to biological sciences, particularly tissue concern if you are interested in studying in medical sciences, material sciences, earth sciences. And in civil engineering also we are using it because we treat geomaterial as a natural material or man made material. So, what is essentially done here is that you create a image using electrons instead of the light waves. So, in a simple photography you use light waves for capturing a photograph. However, in SEM we use electrons of certain energy. So, basically the entire SEM spectroscopy or microscopy is based on the fact that you use electrons of different energy and the scattering. The beauty of this technique is that images have a greater depth of field and resolution than optical micrographs. And that is why it becomes an ideal technique for studying the fracture surfaces or the particulate material, is it not? Where you have more of particles arrangement which you want to study and the fracture surfaces are irregular, not very shining, broken and so on. Now, this is a recent development where EDS is normally used, this is known as energy dispersive spectrometer. And when you add this along with SEM, so this becomes EDSEM edax. So, this allows elemental analysis also. That means, you can do the analysis of sodium to uranium. However, you cannot study lanthanides, actinides and the gases if they are happening to be less than 0.1 percentage of the weight. So, this is the beauty of the technique. Another good technique, another good implementation of this technique is the X-ray mapping is also possible in SEM. And we show the distribution of elements in the material. So, if you want to do the elemental analysis, SEM becomes a very good tool. Remember in XRF also you have done elemental analysis X-ray fluorescence technique, where you can get the composition of oxides by weight. This is a chemical characterization of the material. Another interesting point is that it can do line scanning. So, X-ray line scans will show you the concentration of the elements along a line of the in the material. So, how the elemental composition is varying from one point to another point can also be studied. I will not go much in details of these topics, because then it comes a you know subject itself. But I am just giving you again some idea about what SEM is, what are the beauties of this technique and what are the limitations. What is the working principle? The working principle is you have a beam of energetic electrons which is falling on the sample. Sometimes we call it as a specimen also and then interpretation is done by using again collection of X-ray beam or the electrons which are getting generated in the system. And what we study essentially is the interaction of the electrons and this transformation is done on a 3D image to obtain a topographical, morphological, compositional and crystallographic information. So, this is the beauty of this technique. This figure shows you how sample is bombarded with an incident beam of electron. So, basically when the electron beam is tries the sample both photon and electron signals are emitted. Now, what is that you want to collect and what is that you want to analyze is an art. So, if you consider this as a sample on which there is a beam of electrons falling and then there is a scattering. So, you can have X-rays, you can have auger electrons, you can have primary backsteaded scattered electrons which we want to collect for our analysis and this will depend upon the atomic number and topographical information. Then we can have cathodolum luminescence that means, how electrical information can be obtained from this type of a finger print of the material. And then if you can collect secondary electrons you can get the topographic information. So, this is how you can do 3-D tomography of the system by using a scanning electron microscopy. This is a general outline of how SEM works. It takes time to analyze the samples and sample preparation. So, this I will be discussing in the subsequent slides. Now, this is a topic on which SUCHIT is working, determination of fabric structure of fine-grained soils using SEM. So, this is one of the applications of scanning electron microscopy and he has gone one step further where he is amalgamating SEM with MIP that is mercury and region porous initri. So, most of the slides I have taken from his presentations for during the different stages. The first thing is you create a sample of compacted soil. So, this is a cylindrical triaxial sample and I want to let us understand what is the fabric structure. When we talk about fabric structure basically this is a grain structure and their arrangement which we are interested in finding out. I can I hope that you will appreciate that this type of studies cannot be done just by simple optical photography. In previous lecture I had talked about 2-D confocal microscopy and 3-D photography is it not surface photography. So, those techniques cannot be used here. Those techniques are used for morphological examination. So, this is the model which has been developed by Suchit. He extrudes a sample which is known as a cubic specimen from this sample and then he studies the orientation of the grains or the fabric structure in the 2 perpendicular planes. Now, what are the challenges which are associated with the specimen preparation? We call this as specimen small country and this is a sample of the file and it is understood that this specimen happens to be representative of the entire sample. So, one of the topics one which we are working right now is we are trying to simulate nature how sedimentation takes place in oceans. So, you can imagine if you have a sample of 6 centimeter length based on the sedimentation process, how grain structure is getting formed can be studied by taking out a sample under in situ conditions as a form of a UDF sample undisturbed sample and then taking out this specimen and analyzing it for SEM. So, once you have taken out this cubic specimen you have to answer few challenges or you have to gear up for handling these challenges. The first challenge is this sample is going to have lot of pore fluids is it not. So, how to get rid of this pore fluid? So, the first challenge is removal of the pore fluid from the specimen without disturbing its microstructure. Do you think that there is any technique by which you can remove the pore structure from the soil mass apart from the techniques which should be adopted for this type of a work? The most ideal situation would be if I can squeeze the sample just by applying some pressure which is what is done in a pressure membrane extractor. If you remember the other day when you came to the lab I had shown you a device by which you can extract pore solution, but then it will be very difficult to maintain the microstructure if you are applying external pressure. So, this is where we go for freeze drying technique. We had shown you liquid nitrogen gas. So, if you dip the sample in this liquid nitrogen you can get it of the liquid phase and the entire structure gets frozen. Now, unfortunately this technique is not suitable for all type of soils. This is very much suitable for the soils which are swelling and shrinking type of the soils. But suppose if you are dealing with the soils which are ordinary soils which are very passive materials. So, this is where you can use air drying technique. You can dry the sample in the air and you can remove the pore solution which is present in the soil mass. Another challenge is that specimen should be able to withstand the vacuum which is present in the microscope. That means, should be stiff enough and should not get broken. Now, each one deals with development of a technique. So, that is why I said that SEM is also a very intricate method of doing the analysis. Another challenge is that as illumination is with electrons a specimen should be made to conduct electricity. But you will agree with the fact that most of the materials in are in the powder form and they are the oxides including soil which are not good conductor of electricity. So, that means, you have to give some treatment to the specimen before you can do SEM analysis. So, this is where some coating is to be done. And this coating is either of gold or of carbon depending upon the requirements. So, these specimens are coated with a thin layer of gold or carbon which is also known as a sputter coating or a quarter is the name of the machine. But when should you use a gold thin film or when should you use a carbon thin film it all depends upon what is that you want to do. So, gold coating film will absorb X ray signals generated into this specimen. And for obtaining X ray spectrum of non conducting sample a coating material very transparent to the X ray like carbon should be used. So, there could be a situation when you are taking SEM photograph and the sample may not show you any response. So, this is where you have to switch over from gold to normally carbon coating. So, again this comes from your experience and the type of material which you are handling. This is do you wanted these details? Geotechnical engineering is an art you know most of the experiments which geotechnical engineers do they are done as an artist. What this indicates is making a sample of 6 centimeter length may take you 2 days or 3 days. Taking a specimen out of the sample may take you 1 week you know it is a very very slow process and very you have to be very patient. That is the only answer is this correct such as or you will like to add something that is what I say it is not a challenge it is a temperament. Somebody may do this test somebody may not do this test you may not be able to take out a sample out of specimen out of a sample. So, it is basically a temperament nothing else. So, when you do direct shear test the tendency is you pour the sand and just fill it and in 2 minutes your sample is ready. Truly speaking when we work on our direct shear splitters and the samples we take at least 18 to 20 hours to make a direct shear sample. We just go by grain by grain and by grain and grain and grain and so on. So, we arrange the sample based on the granular element we just do not pour the sand and do the test like this. So, that is what I say that our subject is more of an art and most of the philosophies are you know included in the subject. It is not mathematics where you put a plus b and say it is equal to c it is a science it is an art. But yes your question is very correct challenge is there, but then I have not included in this list. But to make you happy we can say yes the first point should be how a specimen should be retrieved out of the soil sample, but that is not a very big deal I suppose or it is so you can answer his point. So, that is why geotechnical engineering is you know too much research oriented and one should have a temperament to do research. Research cannot be forced. Now, another answer to your question will be why means this challenge is not included in this. So, the thing is basically in this study we wanted to know the structure of the you know particles or the arrangement of the particles in two different directions. Okay, so that is why that is the this is the need for this particular study. So, generally whenever you do the SEM means you need not to be very you know cautious about the taking out the samples means just you are interested in the you know topmost surface, but here I am I was interested in not only the topmost surface the horizontal surface I was interested in the perpendicular surface also. So, that is why I took a lot of time to you know cut the sample with the help of a knife properly and then keep it for the drying purpose. So, that is why this challenge is I would say this is for this particular study, but if you want to know general about the specimens just you can take out the sample and just cut some part of it and keep it under microscope. So, like in case of let us say polymers or concrete, but even concrete samples are also very tough to you know extrude from a sample, but then you have to device away. You cannot say that this cannot be done. Okay, are you satisfied or not? Say that this cannot be done alright. So, these are the challenges and of course what you say Gen that can also be included in the list. Well, this is the typical face to face interaction which normally you know is depicted in the text books and you have been studying in your undergraduate. But did you have a question to see this literally that whether this structure really exists or not? So, I will try to show what such it is obtained in his studies. Now, this is what actually we got by doing a SEM analysis of the sample here you can see this platelet and this is just sitting above another plate. Can you appreciate this? It is clear or no? Now, if you enlarge this view this is what you get. So, this is one platelet and there are so many other plates you know which are underlying these are sheets. So, this is how you say face to face contact. I will show you another photograph where it becomes much more easy to visualize. Is the figure clear or no? A little bit hazy, contrast is less. So, this also a problem with the researchers they get too much bias by their own findings. So, we start seeing everything in our own doing you know others may not observe, but you can see the stratification over here. So, these are the stratification you know she is formation layer wise. Is this clear? You can add something if you want. Basically the first two figures now they these photographs are taken from the top and the third figure is taken from the sides. So, if you understand now from this left figure face to face interaction that if I take it from the top I can get you know the layers and if I see from the sides I can get those stratifications. Yeah, this one is clear you know you can see this sheet lying over the other sheets. So, basically in SEM what I have to do first of all I have to keep the sample in one direction I have to take the photographs and then just change its face and again take the photograph. This is a much better picture of kaolin. So, here you can see the packs of the sheets of kaolin you know. So, this is exactly face to face arrangement of the grains of kaolin. Of course, this is at 4000 magnification. So, this proves the granular structure of the or the particulate structure of the soil mass. Another reason could be that you are working on marine clays I suppose. So, marine clays will show you lot of you know impurities and because of that there may be some haze. However, this was a pure mineral on which we have performed the test. So, these are the sheetings of the kaolin which are very clear and you know it gives you a feel of how face to face interaction can be really defined and what causes this type of interaction and ultimately how material properties are going to get altered. Now, my question to you is why these studies are required till now you have been doing only compaction curve is it not without bothering about what really is happening to the soil mass when you move on from dry of optimum to the wet of optimum crossing over the OMC. So, for that you have to wait for some time and when he present his results in his annual progress seminar then you should come and see that there is a transition of the orientation of the grains from dry to the wet of optimum and he has literally captured all these things beautifully. And then he is trying to give assign an electrical number associated to the arrangement of the grains and that number tells you what type of fabric structure is present in the soil mass. So, this is his PhD topic. How much time normally you take to complete one sample analysis? So, preparation of sample take at least you know one day or half day means for each specimen I would say and then taking the photographs and analyzing it. So, at least it takes a week for 4 to 5 samples. It gives you a fair idea about the grain structure. Look at the second type of structure which you have been studying in undergraduate phase 2 edge and edge to edge interactions is it not. This is what how do you call this as the structure, flocculated structure. Truly speaking this is really is this a flocculated structure or not? How would you define this structure? This is a dispersed structure. Truly speaking it is not a real flock, it is a card house structure, it is a pack of cards. Now, if you look at the micrographs you have a grain here and you have a grain here. So, this is you know edge to edge interact arrangement. Is this clear? Switch it, is this clear on the program? And again now if you see these 3 photographs 1, 2, 3. The first one it is taken on the dry of optimum on the compaction curve. The second one is you know near the optimum water content and the next one is weight of optimum. So, you can see the grain structure or the fabric structure changes as we move on the compaction curve and the basically why the particles are getting compacted or why we are getting dry density more as we go for higher water content and up to certain water content. So, it is because the particle packing or the density of the particles it is increasing. So, that is the reason. How much time it takes to analyze this photograph? Suppose, if this photograph is given to you, how much time normally takes to analyze the photograph to make out something out of it? Basically it depends on the judgment basically and intuition. So, given a chance you may not find any interesting mechanism happening here. That is what actually I am telling you that it requires a third eye to observe what is happening here. Look at these two grains you know they are just sitting over the edges these are not the flakes as compared to the previous photograph where the flakes were there. So, if you compare this this is only edge and edge of the particles magnified to almost 4 to 5000 magnification. But by the time you come over here it has become more amalgamated. So, these type of studies can be done with the help of SEM. So, that is the beauty of finding out this structure and you know why do we need to study the grain structure so that we can correlate it to the hydraulic conductivity. So, the best way to make models for hydraulic conductivity would be the models which are based on scanning electron micro copy results and the orientation of the grains if you can quantify them. Anyway, this is of more of a such importance. Anything else which you want to add on SEM? That is good enough. Can I talk about something about limitations and it is basically. So, as you said this interpretation of the results is a again I can say it is a challenge. So, how do you observe means how many micrographs till now you have gone through. So, from that you get an idea that how researchers you know they study the SEM micrograph from that you can get that I should go in this direction I should study each and every particle and its arrangement. So, that gives you more feeling. So, again that interpretation at what magnification you are taking that is that again some matter matters a lot because if you are taking photographs at say 500 magnification and 4000 magnification. So, same photograph but at different magnifications they will give you something different information. So, that also matters a lot. So, so many things are there you know to for interpretation for proper interpretation of the photograph micro. It is just like zooming in and zooming out of a picture to get the information of your requirement.