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Biodegradable Materials > Metals Overview 1 > Flashcards

Metals Overview 1 Flashcards

1
Q

The technical materials used to build most structures are divided into four classes:

A
  • Metals
  • Ceramics (including glasses)
  • Composites
  • Polymers
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2
Q

Biomaterials and biomedical devices are used throughout the human body.

2 Important aspects:

A
  • Functional performance

- Biocompatibility

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3
Q

The material must satisfy it’s design requirements in service:

A
  • Load transmission and stress distribution (e.g. bone replacement)
  • Articulation to allow movement (e.g. artificial knee join)
  • Electrical stimuli (e.g. pacemaker)
  • Light transmission (e.g. implanted lenses)
  • Sound transmission (e.g. cochlear implant)
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4
Q

The biomaterials/devices must not ______ in it’s properties within the body( unless this is wanted)

The biomaterials/devices (and any degradation product) must not cause any ________ reaction within the host’s body.

A
  • degrade

- adverse

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5
Q

Properties of Metals (8)

A
  • Lust (shininess)
  • Good conductors of heat and electricity
  • High density (heavy for their size)
  • High melting point
  • Ductile (most metals can be drawn out into thin wires)
  • Malleable (most metals can be hammered into thin sheets)
  • Easily lose electrons
  • Surface reactive
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6
Q

Metals are widely used as biomaterials due to their

___________ and __________

A

Strength and thoughness

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7
Q

-
-

A
  • Stainless steel
  • Titanium
  • Cobalt alloys
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8
Q

Some people are allergic to ions released from these metals.
Major Problem:
-Generation of sine wear particles in service can lead to :
-
-

A
  • Inflammation and

- Implant loosening

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9
Q

Applications (4)

A
  • Bone and joint replacement
  • Dental Implants
  • Cardiovascular devices
  • Surgical instruments
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10
Q

Electronegativity

A
  • Ranges from 0.7 to 4.0
  • Large values: tendency to acquire electrons

~Important because of bonding and reactions

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11
Q

Atomic Bonding: Ionic Boding

  • Occurs between + and - ions
  • Requires _______ transfers
  • Large difference in _______required
  • Ex. _____
  • Predominant bonding in _________
A
  • electron
  • electronegativity
  • Ex. NaCl
  • Ceramics
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12
Q

Covalent Bonding

  • Similar _______ - Share electrons
  • Bonds determined by ______ - s & p orbitals dominate bonding
  • Ex. _______
A
  • electronegativity
  • valence
  • Ex. CH4
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13
Q

Secondary Bonding

  • Arises form interaction between ______
    - Fluctuating dipoles
    - Permanent dipoles-molecules induced
A

-dipoles

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14
Q

Type Bond Energy Comments
Ionic Large! Non-directional (______)
_______ Variable Directional
(semiconductors, ceramics
polymer chains)
Metallic Variable Non-directional (_____)
Secondary _______ Directional
inter-chain (polymer)
inter-molecular

A

Type Bond Energy Comments
Ionic Large! Non-directional (ceramics)
Covalent Variable Directional
(semiconductors, ceramics
polymer chains)
Metallic Variable Non-directional (metals)
Secondary Smallest Directional
inter-chain (polymer)
inter-molecular

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15
Q

Densities of material classes

p_____ > p______ > p_______

A

p metals > p ceramics > p polymers

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16
Q

Metals have:

  • _______-packing (metallic bonding)
  • often ______ atomic masses
A
  • close-packing

- large

17
Q

Ceramics have:

  • _____ dense packing
  • often ______ elements
A
  • Less

- lighter

18
Q

Polymers have:

  • ____ packing density ( often _______)
  • _______ elements
A
  • Low
  • amorphous
  • Lighter
19
Q

Composites have

-________ values

A

-Intermediate

20
Q

Metals: Energy and Packing

  • Non dense , ______ packing
  • Dense, _______ packing
    • Tend to have _______ energies

~Lower energy state = more stable

A
  • random
  • ordered
  • lower
21
Q 
Materials and Packing
Crystalline materials
   - Atoms pack in periodic, \_\_\_\_ arrays
   - Typical of:
          - 
          - 
          -
A
  • 3D arrays
    • Metals
    • Many ceramics
    • Some polymers
22
Q 
Materials and Packing
Non-crystalline materials
   - Atoms pack \_\_\_\_ periodic packing
   - Occurs for:
          - 
          -
A
  • no periodic
    • Complex structures
    • Rapid cooling
23
Q

Materials and Packing

__________ = Non-crystalline

A

-Amorphous

24
Q

Crystalline solids composed of elemental ________ positively charged ions in a cloud of electrons

A

-positively

25
Q

Unit cell:

A

Smallest repetitive volume which contains the complete lattice pattern of a crystal

26
Q

Micorstructure of Metals

  • Basic atomic architecture is a _________ structures
  • Different elements have different crystalline architectures and can combine with ______ partners
A
  • crystal

- different

27
Q

Metallic Crystal Structures

  • Tend to be ______ packed
  • Reasons for dense packing
    • Typically, only _____ element is present, so all atomic _______ are the same.
    • Metallic bonding is not _________.
    • Nearest neighbor distances tend to be small in order to ______ bond energy.
    • Electron cloud shields cores from each other
A
  • densely
  • one
  • radii
  • directional
  • lower
28
Q

Simple Cubic Structure (SC)

  • ______ due to low packing density (only Po has this structure)
  • _____-________ directions are cube edges
  • Coordination # = ______
A
  • Rare
  • Closed-packed
  • 6
29
Q

Body Centered Cubic Structure (BCC)

  • Atoms touch each other along ______ diagonals
  • Coordination # = _____
A
  • cube

- 8

30
Q

Face Centered Cubic Structure (FCC)

  • Atoms touch each other along ______ diagonals
  • ABCABC…..stacking sequence
  • ____ projection
A
  • face

- 2D

31
Q

X-rays to Determine Crystal Structure

  • Incoming X-rays _______ from crystal planes
  • Measurement of critical angle, 0c, allows computation of planar spacing, d.
A

-diffract

32
Q

X-Ray Diffraction Pattern

  • Rectangle
  • Square
  • Triangle
A
  • (110)
  • (200)
  • (211)
33
Q

Formation of Grain Structure
-_________-result of casting of molten material
- 2 Steps
-
-
-Start with a molten material - all liquid
-Crystal grow until they meet each other

A
  • Solidification
  • Nuclei form
  • Nuclei grow to form crystals - grain structure
34
Q

Crystal Defects

  • _______ crystals are not perfect
  • Sometimes there are empty spaces called _______, where an _____ is missing
  • These and other __________, as well as the existence of grains and grain boundaries determine many of the _________ properties
  • When a _____ is applied to a metal, _________ are generated allowing the metal to deform
A
  • Metallic
  • vacancies
  • atom
  • imperfections
  • mechanical
  • stress
  • dislocations
35
Q 
Types of Imperfections
-Point Defects
     - 
     -
     -
-Line Defects
     -
- Area Defects
     -
A
  • Point Defects
    • Vacancy atoms
    • Interstitial atoms
    • Substiutional atoms
  • Line Defects
    • Dislocations
  • Area Defects
    • Grain Boundaries
36
Q

Vacancies:

  • Vacant ______ sites in a structure
  • Distortion of ______
A
  • atomic

- planes

37
Q

Self-Interstitials:

  • “_____” atoms positioned between atomic sites
  • Distortion of ______
A
  • extra

- planes

38
Q

Dislocations:

  • Are ______ defects
  • ______ between crystal planes result when ________ move,
  • Produce permanent (______) deformation
A
  • line
  • Slip
  • dislocations
  • plastic
39
Q

Polycrystalline Materials

  • Interfacial Defects: Grain Boundaries
    • _______ between crystals
    • Transition from ______ of one region to that of the other
    • Slightly _______
    • ____ density in grain boundaries
      - High mobility
      - High diffusivity
      - High chemical reactivity
A
  • Regions
  • lattice
  • disordered
  • Low

Biodegradable Materials (10 decks)

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