DM308: Lecture 3 Phases and microstructures

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Questions and Answers

What is microstructure?

The very fine, micrometre-scale structure of a material, not visible to the naked eye, that is revealed at magnifications greater than 25X.

How can the term microstructure also encompass the nanostructure of a material?

Some of the structural features can be observed with the naked eye, yet may be smaller than a micrometre, thus including the nanostructure of the material.

What does the microstructure define in conjunction with the crystal structure and chemical composition?

The properties of a material.

What is a phase in the context of materials?

A region of space throughout which all physical properties of a material are essentially uniform. Signup and view all the answers

What can phase diagrams help us understand?

Transitions between phases of a substance/material at different conditions. Signup and view all the answers

What will be the melting point of a 50:50 mixture/alloy of substances A and B?

The melting point will not be the average of the melting points of A and B due to the rule of mixtures. It is not 900°C. Signup and view all the answers

What is crystal structure?

Arrangement of atoms/molecules in a material that obeys translational symmetry Signup and view all the answers

What disrupts the crystal symmetry and has a strong effect on material properties?

Crystalline defects Signup and view all the answers

What are the different properties of diamond and graphite, and what causes these differences?

Diamond is hard, transparent, and an electrical insulator; graphite is soft, opaque, and conducts electricity. The differences are caused by their different crystal structures. Signup and view all the answers

What type of crystals consist of numerous crystals of corundum?

Polycrystalline crystals Signup and view all the answers

What is the difference between microstructure and crystal structure?

Microstructure refers to the structure of a material at the microscopic level, while crystal structure refers to the arrangement of atoms/molecules in a material. Signup and view all the answers

What is the arrangement of atoms/molecules in a material that has no symmetry?

Amorphous Signup and view all the answers

What is the term for the constant temperature state when pure A and B are cooled from the melt to their freezing points?

Thermal arrest Signup and view all the answers

What is responsible for the thermal arrest observed during the formation of new bonds on solidification?

Latent heat of fusion Signup and view all the answers

What is the name of the alloy of mutually soluble A and B that does not show a thermal arrest when solidifying?

Solid solution Signup and view all the answers

What is the freezing range between liquidus and solidus temperatures known as?

Freezing range Signup and view all the answers

What is the term used for the line representing the coexistence of liquid and solid on a cooling curve?

Liquidus + Solidus line Signup and view all the answers

What is the requirement for the atomic radii of the solvent and solute elements according to the relative size factor?

The atomic radii of the solvent and solute elements must be less than 15%. Signup and view all the answers

What happens if the Hume-Rothery rules are not obeyed?

Appearance of miscibility gaps and congruent or eutectic melting points Signup and view all the answers

What is the meaning of 'eutectic' in Greek?

Easy-melting Signup and view all the answers

What is the significance of the eutectic system in binary combinations of elements?

It is quite common and important Signup and view all the answers

What are the metals that satisfy all the solid solution rules except for different atomic radii?

Ni - Nickel. Cu - Copper. Pt - Platinum. Ag - Silver. Au - Gold Signup and view all the answers

What is the requirement for the solute and solvent elements according to the relative valency factor?

The solute and solvent elements must have the same valency Signup and view all the answers

What is the lattice type factor based on?

Crystal structure Signup and view all the answers

What is the requirement for the solute and solvent elements according to the electronegativity factor?

They should have similar electronegativity Signup and view all the answers

What type of phase diagram is quite common due to the difficulty in satisfying all the Hume-Rothery rules?

Eutectic system Signup and view all the answers

What is the eutectic point lower than in a eutectic system?

The melting points of the pure components Signup and view all the answers

Study Notes

Dr. Vassili Vorontsov of the University of Strathclyde discusses crystal structures and material properties.
Crystal structure is the arrangement of atoms/molecules in a material with translational symmetry.
Different crystal structures lead to varying properties for materials. For example, diamond is hard, transparent, and insulating while graphite is soft, opaque, and conductive.
Crystal defects disrupt symmetry and impact material properties. For instance, natural sapphires have impurities that make them blue while man-made sapphires are colorless.
Most materials used in engineering are not single crystals but rather polycrystalline, consisting of numerous crystals within a material.
Microstructure refers to the fine, micrometre-scale arrangement of crystals, phases, and defects within a material. It influences material properties alongside crystal structure and chemical composition.
Understanding the concept of phases is crucial in materials science. A phase is a region of space with uniform physical properties.
Substances A and B have different melting points but form a solid solution when mixed instead of having a defined melting point.
The solidification process releases energy known as the latent heat of fusion.
The Hume-Rothery rules determine the solubility and formation of alloys based on the relative valency, electronegativity, size, and lattice type of elements.
Failure to satisfy these rules can lead to miscibility gaps and congruent or eutectic melting points.
The eutectic system, a common type of phase diagram, features a eutectic point with a lower melting point than the pure components.
Eutectic comes from the Greek word for "easy-melting."

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Test your knowledge about phase diagrams and their representation of the relationships between temperature, composition, and phases of a substance. Explore the concepts of liquidus temperature, solidus temperature, and the formation of solid solutions.