![]() And what I want to do is to compare what happens as the microstructure evolves, as we continue through. So that gives you a check as you're going through and you're making your calculations. ![]() Now if you were to take those two at any particular point in terms of temperature, what you would find is that the fraction of solid and the fraction of liquid has got to be equal to 1. And what we're seeing is that is a continuous increase. And once I begin to come into the two phase field, I begin to increase the fraction of solid and it follows the curve that is given on the second diagram. Now what I'm doing is above the liquidous temperature, I have no solid phase. Now, if I were to go ahead and plot the other phase, that is, the solid phase, what I'm going to see is the plot that I have over here. And when I'm at the solidous temperature, effectively, all my liquid is gone and all I have left is the solid. As the temperature begins to drop, I am going to be decreasing the amount of liquid that I have in here, and so the fraction of liquid is continuously dropping until ultimately I reach the solidous temperature. And as the temperature drops, what I'm seeing is liquid from 100% liquid, or a phase fraction of 1, above the liquidous temperature, which is given at 1060. What you can see is I'm plotting the case of the liquid phase. If we take a look at how the fraction of liquid varies as a function of temperature. But what we'll do now is we'll actually summarize some of these results. I would suggest that you actually go ahead through the calculation and determine what the fractions of the phases are as the temperature drops. My suggestion would be to you is to take this data before we go any further. And once we know the compositions at these temperatures, we can then calculate what the fractions of the phases are in that two phase field. We have various temperatures and we have the compositions at each temperature. So, here are the data and what we have in terms of the data. What we'll do now is take the data that I supplied you with in the previous lesson to plot the fraction of the various phases as we go through that two phased field. This first section covers the fundamentals of materials science including atomic structure and bonding, crystal structure, atomic and microscopic defects, and noncrystalline materials such as glasses, rubbers, and polymers. The aim of the course is to help students better understand the engineering materials that are used in the world around them. This is the second of three Coursera courses that mirror the Introduction to Materials Science class that is taken by most engineering undergrads at Georgia Tech. All of these methods work because crystalline regions have different thermal, spectroscopic, or particle scattering properties than amorphous regions.Have you ever wondered why ceramics are hard and brittle while metals tend to be ductile? Why some materials conduct heat or electricity while others are insulators? Why adding just a small amount of carbon to iron results in an alloy that is so much stronger than the base metal? In this course, you will learn how a material’s properties are determined by the microstructure of the material, which is in turn determined by composition and the processing that the material has undergone. % crystallinity can be determined in a lot of ways, but most frequently by discrete scanning calorimetry (DSC) and x-ray diffraction (XRD). So for a polymer manufacturer it's an important quantity to control and measure. Crystallinity is also influenced a lot by how the polymer is processed, chiefly the cooling rate, and also any additives present. The amount of polymer branching, often influenced by the catalyst one uses during synthesis, affects the phase fraction because more branched polymers are less able to form crystalline regions. It is the main reason why high density polyethylene is higher density, stronger, and less porous (better barrier to diffusion) than low density polyethylene. The phase fraction affects the bulk properties quite a bit. So a polymer with phase fraction of 0.5 has 50% of its weight in crystalline phase and 50% of its weight in amorphous phase. The crystalline phase fraction, more usually called just the % crystallinity, is the fraction of the polymer that is crystalline (usually by weight). Crystalline regions tend to be dense, strong, and rigid, whereas amorphous regions are porous. ![]() In amorphous regions, there is no long range order. In crystalline regions, the polymer strands line up in regular, highly ordered ways. Most polymers are semi-crystalline, meaning they have regions where the polymer is crystalline and regions where the polymer is amorphous. ![]()
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