Materials Science Exam 1 Review

Radius Ratio

(r/R) or (smaller/larger)

Polar Molecules

-Permanent dipole moments that exist in some molecules due to the asymmetrical arrangment of positively and negatively regions (HCl, H2O). -Can induce dipoles in adjacent non-polar molecules and bond is formed due to the attraction between the permanent and induced dipoles.

Ceramic Structures

-anions larger than metal cations -close packed anions in a lattice (usually FCC) -cations fit into interstitial sites among anions ex) ionically bonded NaCl where Na is significantly smaller in size than Cl.

Permanent Dipole Bonds

-bonds between adjacent polar molecules. -are the strongest among secondary bonds.

Metallic Bonding

-does not lock up their extra electrons by sharing, giving, or accepting them. -in metals, valence electrons are not really owned by one particular atom, but all the atoms. They are free to drift around in a so-called "sea of electrons." Typically for only +1,+2, or +3 valence. -This leaves their nuclei ad filled shells as positive ion cores.

Simple Cubic Structure

-few elements have this structure, Mn -APF = 0.52 -CN = 6 -N = 8*(1/8) = 1 atoms/unit cell

Protons

-has the same mass as neutrons, 1.67x10^-27 kg. -have positive charge (1.6x10^-19 Coulombs) - # of ________ = atomic number (Z)

Neutrons

-has the same mass as protons, 1.67x10^-27 kg. -have no charge -# of ______ defines isotope number

Electrons

-have a mass of 9.11x10^-31 kg -have negative charge (1.6x10^-19 Coulombs)

Face Centered Cubic Structure (FCC)

-numerous elements have this structure: Cr, Fe, Mo, Li, Na... See the table in front cover of text book. -APF = 0.74 -CN = 12 -N = (6*1/2)+(8*1/8) = 4 atoms/unit cell

Secondary or van der Waals Bonding

-results from interaction of atomic or molecular dipoles and is weak, ~0.1 eV/atom or ~10 kJ/mol. ex) Water (H2O). It is covalently bonded, however the charges are not symmetric (hydrogen bonding)

Hexagonal Close-Packed Crystal Structure (HCP)

-six atoms form ______ shape, surrounding one atom in the center. Another plane is situlated halfway up unit cell (c-axis), with 3 additional atoms situated at interstices of __ __ __ planes. -Unit cell has two lattice parameters a and c. Ideal ration c/a = 1.633 -APF = 0.74 -CN = 12 -N = (3*1)+(12*1/6)+(2*1/2) = 6 atoms/unit cell

the Fourteen Bravais Lattices

-the sum of all the structures -named after the French crystallographer who discovered them

Body Centered Cubic Structure (BCC)

-typical metals: α-Fe, V, Cr, Mo, and W -APF = 0.68 -CN = 8 -N = 1+(8*1/8) = 2 atoms/unit cell

Seven Crystal Systems

1) Cubic: simple, body centered, and face centered (3). 2) Tetragonal: simple and body centered tetragonal (2). 3) Orthorhombic: simple, body centered, base centered, and face centered cubic (4). 4) Rhombohedral: simple (1). 5) Hexagonal: simple (1) 6) Monoclinic: Simple and base centered (2). 7) Triclinic: simple (1)

Types of Material (3):

1) Metals: good conductors of electricity, very ductile and deformable, can be quite strong, good thermal conductor 2) Ceramics: poor conductors of electricity, insulating, very hard but very brittle, poor thermal conductor 3) Extremely flexible, good thermal and electrical insulator

Factors that Determine Crystal Structure:

1) Relative Sizes of Ions-formation of stable structures: maximize the # of oppositely charged ion neighbors. (CN and Radius Ratio) 2) Maintenance of Charge Neutrality- net charge in ceramic should be zero.

Coordination Number, CN

= the number of closest neighbors to which an atom is bonded = number of touching atoms

Atomic Weight of an Element

=weighted average of the atomic masses of the atroms naturally occuring isotopes. -is often specified in mass per mole.

Bonding in Polymers

Covalent and Secondary

Bonding in Semiconductors

Covalent or Covalent/Ionic

Primary Interatomic Bonding

Ionic Bond, Covalent Bond, Metallic Bond

Bonding in Ceramics

Ionic/Covalent

Bonding in Metals

Metallic

Defects in Solids

Point Defects, Linear Defects, Planar Defects, Volume Defects

Low Electronegativity

Subshells with one electron

High Electronegativity

Subshells with one missing electron

Electronegativity

a measure of how willing atoms are to accept electrons. -increases from left to right

Lattice Directions

a vector between two points

Interstitial

an extra atom squeezed into the lattice either the same type of atom (self-interstitial) or another kind (impurity interstitial).

Solid Solutions

are made of a host (the solvent or matrix) which disolves the minor component (solute)

Thermal Properties

are related to transmission of heat and heat capacity.

Grain Boundaries

atomic mismatch within the regions where grains meet

Single Crystal

atoms are in a repeating or periodic array over the entire extent of the material

OD, Point Defects

atoms missing or in irregular places in the lattice (lattive vacancies, substitutional and interstitial impurities, self-interstitials)

Crystalline Materials

atoms self-organize in a periodic array

Impurities

atoms which are different from the host

Composition

can be expressed in: -weight percent, ratio of weight of atoms, useful when making the solution -atom percent, ratio of number of atoms, useful when trying to understand the material at the atomic level.

Semiconductors

combination of a metal and a non-metal to create unique electrical properties.

Alloys

combination of two metals to get a combination of their properties.

Composites

combination of two or more types of materials, designed to display a combination of the best properties of each component. ex) fiberglass, glass fiber in a polymer matrix

Polycrystalline Material

comprised of many small crystals or grains

Lattice Positions

coordinates of ______________ where atoms sit in reference to a defined origin.

Ordered Packing =

dense -tend to have lower energies

Amorphous

disordered- lacking a systematic atomic arrangment

Metals

electropositive- they can give up their few valence electrons to become positively charged ions

Materials Engineering

engineering the structure of a material to produce a predetermined property

Plane Density

equals the number of atoms centered on a plane divided by the area of the plane

Linear Density

equals the number of atoms divided by the unit length of the direction vector.

3D, Volume Defects

extended defects (pores, cracks)

Covalent Bonding

extra electrons are shared between atoms. Thus each shared electron belongs to both atoms. ex) CH4

1D, Linear Defects

groups of atoms in irregular positions (screw and edge dislocations)

Anisotropy

having a physical property that has a different value when measured in different directions. -ex) FCC because atoms along the edge of unit cell are more separated than along face diagonal

Isotropic

having a physical property that has the same value when measured in different directions -in some polycrystalline materials, grain orientations are so random, so bulk material properties are ______.

Solvent

in an alloy, the element or compound present in greater amount

Solute

in an alloy, the element or compound present in lesser amount

Chemical Stability

in contact with the environment - corrosion resistance.

Optical Properties

include to absorption, transmission and scattering of light

Materials Science

investigating the relationship that exist between the structures and properties of materials

Polymorphism

materials may exist in more than one crystal structure

Random Packing =

non dense

Atom Percent

number of moles (atoms) of a particular element relative to the total number of moles (atoms) in alloy

Ionic Bonding

occurs between electropositive and electronegative atoms. Basically between metals and non-metals. ex) Sodium Chloride (NaCl)

Substitutional

replacement of an atom on an atomic site with another type of atom

Electrical & Magnetic Properties

response electrical and magnetic fields, conductivity, etc.

Mechanical Properties

response to mechanical force, strength, etc.

Unit Cell

smallest repetitive volume which contains the complete lattice pattern of a crystal.

Solubility

the ability to dissolve

mole

the amount of matter that has a mass in grams equal to the atomic mass in amu of the atoms.

2D, Planar Defects

the interfaces between homogeneous regions of the material (grain boundaries, stacking faults, external surfaces)

Lattice Constants/Lattice Parameters

the lengths of the 3-D sides of a unit cell

Avogadro Number

the number of atoms in a mole. = 6.023 x 10^23 mol^-1*amu/atom= 1 gram/mol

Theoretical Density

the number of atoms/unit cell multiplied by the atomic weight (g/mol) divided by both the volume of the unit cell (cm^3/unit cell and Avagadro's Number (6.023x10^23 atoms/mole)

Close Packed Plane

the plane with the highest packing density

Atomic Packing Factor (APF)

the volume of atoms in the unit cell divided by the volume of the unit cell

Atomic Mass Unit (amu)

used to express atomic weight. 1 ____ is defined as 1/12 of the atomic mass of the most common isotope of carbon atom that has 6 protons (Z=6) and 6 neutrons (N=6).

Vacancy

vacant atomic site in a structure

Weight Percent

weight of a particular element relative to the total alloy weight.

Allotropy

when the material is an elemental solid ex) carbon, which can exist as diamond, graphite, and amophous carbon.