Materials Science for Engineering MET 161-3
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Questions and Answers

What defines a material with short-range order?

  • Atoms are arranged in layers with no specific bonding pattern.
  • The special arrangement of atoms extends only to the nearest neighbors. (correct)
  • It has a uniform arrangement of atoms extending over at least 100 nm.
  • Its atomic arrangement is completely random throughout the material.

    • Which characteristic is associated with long-range order in materials?

  • The atoms form clusters with no specific arrangement.
  • Atoms are arranged symmetrically with no directional preference.
  • The special atomic arrangement extends over lengths larger than 100 nm. (correct)
  • The atomic arrangement is random and unordered.

    • In which material type would you expect to find no order?

  • Polymeric materials
  • Crystalline solids
  • Metals
  • Monoatomic gases (correct)

    • Which of the following statements about crystalline and non-crystalline materials is correct?

    <p>Crystalline materials show long-range order in atomic arrangement.</p> Signup and view all the answers

    What is a characteristic feature of non-crystalline materials?

    <p>They have a random atomic arrangement with no long-range order.</p> Signup and view all the answers

    What aspect differentiates materials within the engineering context?

    <p>Their mechanical and electrical properties.</p> Signup and view all the answers

    Which of the following best describes the arrangement of atoms in a typical gas?

    <p>They have no orderly arrangement.</p> Signup and view all the answers

    What key property distinguishes materials with short-range order from amorphous materials?

    <p>The order extends to the nearest neighbors in short-range order.</p> Signup and view all the answers

    What defines a lattice in a crystal structure?

    <p>An arrangement of points in a periodic pattern.</p> Signup and view all the answers

    What is the basis in the context of crystal structures?

    <p>A collection of atoms associated with lattice points.</p> Signup and view all the answers

    How many Bravais lattices exist in three-dimensional arrangements?

    <p>14</p> Signup and view all the answers

    Which crystal system is characterized by atoms at each corner and one atom in the center?

    <p>Body-Centered Cubic (BCC)</p> Signup and view all the answers

    In Simple Cubic (SC) lattice, how many atoms are associated with each unit cell?

    <p>1</p> Signup and view all the answers

    What happens to a lattice point located at a corner of a unit cell?

    <p>It is counted as contributing to multiple unit cells.</p> Signup and view all the answers

    What is the atomic hard-sphere model used for?

    <p>To represent atomic distances in crystalline solids.</p> Signup and view all the answers

    What is the primary purpose of defining unit cells in crystallography?

    <p>To describe the repetitive patterns in crystal structures.</p> Signup and view all the answers

    What distinguishes single crystal materials from polycrystalline materials?

    <p>Single crystals contain only one large crystal.</p> Signup and view all the answers

    Which of the following best describes the atomic arrangement in amorphous materials?

    <p>Completely random atomic structure.</p> Signup and view all the answers

    What type of order do liquid crystals exhibit?

    <p>Liquid-like behavior with special order.</p> Signup and view all the answers

    In polycrystalline materials, what are the smaller crystals referred to as?

    <p>Grains.</p> Signup and view all the answers

    How do crystalline materials differ from amorphous materials regarding melting points?

    <p>Crystalline materials possess a defined melting point.</p> Signup and view all the answers

    Which statement is true regarding grain boundaries in polycrystalline materials?

    <p>They are points of misalignment between individual grains.</p> Signup and view all the answers

    Which characteristic is NOT associated with crystalline materials?

    <p>Random atomic structure.</p> Signup and view all the answers

    What triggers the alignment of certain polymer molecules in liquid crystals?

    <p>External stimuli such as electric fields.</p> Signup and view all the answers

    What is the formula to calculate the packing factor?

    <p>Packing Factor = Volume of atoms in a unit cell / Volume of unit cell</p> Signup and view all the answers

    How is the atomic radius for BCC and FCC structures determined?

    <p>By determining the lattice parameter and assigning atomic radii along the correct direction</p> Signup and view all the answers

    What factor is crucial in calculating the theoretical density of a material?

    <p>Number of atoms per unit cell and atomic mass</p> Signup and view all the answers

    In crystallographic points, what do the fractional indices q, r, and s represent?

    <p>The coordinates of a specific lattice position</p> Signup and view all the answers

    What is the relationship between lattice parameters and atomic radius for FCC structures?

    <p>Atomic radius is half the lattice parameter</p> Signup and view all the answers

    What does a higher packing factor indicate about a crystal structure?

    <p>More efficient use of space by atoms</p> Signup and view all the answers

    How many atoms are typically present in a simple cubic (SC) unit cell?

    <p>1</p> Signup and view all the answers

    What is the significance of specifying crystallographic directions?

    <p>To describe the arrangement and behavior of atoms in the crystal</p> Signup and view all the answers

    What is the first step in determining the u, v, and w indices for a direction vector?

    <p>Construct a right-handed x-y-z coordinate system</p> Signup and view all the answers

    Which of the following equations represents the calculation of the u index?

    <p>$u = \frac{x_2 - x_1}{a}$</p> Signup and view all the answers

    What is done to the coordinate differences after they are calculated?

    <p>Normalized by dividing with respective lattice parameters</p> Signup and view all the answers

    What indicates that a crystallographic plane has an infinite intercept along an axis?

    <p>The plane is parallel to that axis</p> Signup and view all the answers

    After obtaining the reciprocals of the intercepts for the h, k, and l indices, what is the next step?

    <p>Normalize the values</p> Signup and view all the answers

    What is the purpose of adjusting the indices to the smallest integer values?

    <p>To comply with crystallographic notation</p> Signup and view all the answers

    Which statement is true regarding the direction indices and the plane indices?

    <p>They differ in the initial coordinate system setup</p> Signup and view all the answers

    What is the first choice of action when a plane intersects the chosen origin?

    <p>Construct a parallel plane within the unit cell</p> Signup and view all the answers

    Study Notes

    Course Overview

    • Focus on crystalline and non-crystalline materials in engineering.
    • Covers material evolution, classification, structures, properties, and failure analysis.

    Material Classification

    • Materials are classified based on atomic order:
      • No Order: Atoms in monoatomic gases or plasma without orderly arrangement.
      • Short-Range Order: Arrangement extends to nearest neighbors (e.g., glasses).
      • Long-Range Order: Order exists over larger distances (over 100 nm).

    Crystalline Materials

    • Composed of atoms arranged in a regular, repeating pattern.
    • Can be classified into:
      • Single Crystal Materials: Entire material exists as one large crystal.
      • Polycrystalline Materials: Made up of many small crystals (grains) with varying orientations.

    Liquid Crystals

    • Polymer materials demonstrating unique ordering.
    • Exhibit liquid-like behavior but can align under external stimuli (e.g., electric fields).

    Properties Comparison

    • Crystalline Materials: Ordered arrangement, specific melting points, definite geometrical shapes.
    • Amorphous Materials: Random atomic structure, glass transition temperature, irregular shapes.

    Crystal Structures

    • A lattice is a periodic array of points corresponding to atomic positions.
    • A basis consists of one or more atoms associated with each lattice point.
    • Crystal structures are formed by placing the atoms of the basis on every lattice point.

    Unit Cells and Bravais Lattices

    • Crystal structures can be divided into unit cells, the smallest repeating units.
    • There are 14 Bravais lattices corresponding to 7 crystal systems.

    Atom Counting in Unit Cells

    • Specific arrangements yield a set number of lattice points per unit cell.
    • Shared points among adjacent unit cells must be accounted for in calculations.

    Packing Factor

    • Defined as the fraction of space occupied by atoms in a unit cell.
    • Calculated as the ratio of the volume of atoms to the volume of the unit cell.

    Density Calculation

    • Theoretical density can be determined using the number of atoms per unit cell and atomic mass.
    • Formula: Density = (Number of atoms per unit cell × Atomic mass) / (Volume of unit cell × Avogadro constant).

    Crystallographic Points, Directions, and Planes

    • Points within a unit cell are denoted using fractional coordinates.
    • Crystallographic Direction: A vector between two points, represented by three indices indicating proportions of lattice parameters.
    • Miller Indices: Used to define orientations of crystallographic planes, derived from intercepts with coordinate axes.

    Summary of Concepts

    • Atomic arrangement determines material properties and classifications.
    • Understanding these concepts is essential for selection and application in engineering materials.

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    Quiz Team

    Description

    Explore the intricacies of crystalline and non-crystalline materials in this quiz based on the MET 161-3 course. Understand the evolution and classification of engineering materials to enhance your knowledge in materials science.

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