6.1 Introduction

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From the course by Georgia Institute of Technology

Material Behavior

293 ratings

Georgia Institute of Technology

Material Behavior

293 ratings

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. This is the first of three Coursera courses that mirror the Introduction to Materials Science class that is taken by most engineering undergrads at Georgia Tech. The aim of the course is to help students better understand the engineering materials that are used in the world around them. 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.

From the lesson

Noncrystalline and Semicrystalline Materials [Level of Difficulty: Medium || Student Effort: 2hrs 30mins]

In this module, we discuss materials that are not fully crystalline, such as polymers, rubbers, and glasses. You will learn how the absence of crystallinity affects the behavior of these materials and what factors affect their formation and properties. Lessons include discussions of the microstructure and defects in amorphous materials, partial cystallinity in polymers, and demonstrations of materials exhibiting ductile and brittle behavior at different temperatures.

6.1 Introduction3:52

Meet the Instructors

Thomas H. Sanders, Jr.
Regents' Professor
School of Materials Science and Engineering

Welcome back.

We're now introducing a new module,

the module on non-crystalline and semi-crystalline materials.

If you recall back when we described module four, we introduced for

the first time a structural defect.

And we talked about those structural defects in your currents in all types of

materials, and that defect we were talking about was a vacancy.

Later on, we've introduced other types of defects

which include line defects like dislocations.

Now, what we're going to do in this chapter is to talk about

a material which is essentially non-crystalline.

It looks like an amorphous structure so it's totally defected.

When we talk about materials that are at room temperature

glass-like, what we have to do is we have to

understand the concept of something called a glass-transition temperature.

We're going to talk about viscous deformation.

We'll be describing the structure and property first of oxide glasses.

Then we'll talk about structure and

properties of amorphous and semi-crystalline polymers.

We'll talk about structure and properties of rubbers and elastomers, and

lastly, we're going to talk about metallic crystals.

And yes, metals can be made into the glassy state.

So far, we've been emphasizing crystalline materials.

Now what we're going to talk about are other types of engineering materials that

lack long range translational periodicity of a typical crystalline material.

These non-crystalline materials are referred to as either amorphous,

glassy, or super-cooled liquids.

Now, we can also refer to them as being a solid.

And when we use the term solid, we have to be careful whether or

not we mean a crystalline or a non-crystalline solid.

Theoretically, any material can form an amorphous structure

when you have sufficiently high enough rates of cooling.

In this module we're going to be emphasizing the structural considerations

that facilitate the development of an amorphous structure.

Now there are a number of important materials that happen

to be able to be formed in the non-crystalline state.

And there are a number of elements which include sulfur, selenium and phosphorus.

There are examples of halides, sulfides, selenides and

tellurides, all of which, various compounds that are listed on this table,

can be produced as non-crystalline.

It also happens that there are a number of nitrides and

sulfates as well as carbonates that can be produced using,

and produce and develop a non-crystalline state of matter.

Oxides, which include the important oxide, SiO2,

which is the basis of the glasses that we see on a regular basis.

Polymers certainly are able to form non-crystalline states, and

as I said earlier, metallic alloys, they can be cooled at a sufficient

rate at which they can be produced in a non-crystalline form.

Thank you.

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