Metals Overview 1 Flashcards
The technical materials used to build most structures are divided into four classes:
- Metals
- Ceramics (including glasses)
- Composites
- Polymers
Biomaterials and biomedical devices are used throughout the human body.
2 Important aspects:
- Functional performance
- Biocompatibility
The material must satisfy it’s design requirements in service:
- 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)
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.
- degrade
- adverse
Properties of Metals (8)
- 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
Metals are widely used as biomaterials due to their
___________ and __________
Strength and thoughness
-
-
- Stainless steel
- Titanium
- Cobalt alloys
Some people are allergic to ions released from these metals.
Major Problem:
-Generation of sine wear particles in service can lead to :
-
-
- Inflammation and
- Implant loosening
Applications (4)
- Bone and joint replacement
- Dental Implants
- Cardiovascular devices
- Surgical instruments
Electronegativity
- Ranges from 0.7 to 4.0
- Large values: tendency to acquire electrons
~Important because of bonding and reactions
Atomic Bonding: Ionic Boding
- Occurs between + and - ions
- Requires _______ transfers
- Large difference in _______required
- Ex. _____
- Predominant bonding in _________
- electron
- electronegativity
- Ex. NaCl
- Ceramics
Covalent Bonding
- Similar _______ - Share electrons
- Bonds determined by ______ - s & p orbitals dominate bonding
- Ex. _______
- electronegativity
- valence
- Ex. CH4
Secondary Bonding
- Arises form interaction between ______
- Fluctuating dipoles
- Permanent dipoles-molecules induced
-dipoles
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
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
Densities of material classes
p_____ > p______ > p_______
p metals > p ceramics > p polymers
Metals have:
- _______-packing (metallic bonding)
- often ______ atomic masses
- close-packing
- large
Ceramics have:
- _____ dense packing
- often ______ elements
- Less
- lighter
Polymers have:
- ____ packing density ( often _______)
- _______ elements
- Low
- amorphous
- Lighter
Composites have
-________ values
-Intermediate
Metals: Energy and Packing
- Non dense , ______ packing
- Dense, _______ packing
- Tend to have _______ energies
~Lower energy state = more stable
- random
- ordered
- lower
Materials and Packing
Crystalline materials
- Atoms pack in periodic, \_\_\_\_ arrays
- Typical of:
-
-
-- 3D arrays
- Metals
- Many ceramics
- Some polymers
Materials and Packing
Non-crystalline materials
- Atoms pack \_\_\_\_ periodic packing
- Occurs for:
-
-- no periodic
- Complex structures
- Rapid cooling
Materials and Packing
__________ = Non-crystalline
-Amorphous
Crystalline solids composed of elemental ________ positively charged ions in a cloud of electrons
-positively
Unit cell:
Smallest repetitive volume which contains the complete lattice pattern of a crystal
Micorstructure of Metals
- Basic atomic architecture is a _________ structures
- Different elements have different crystalline architectures and can combine with ______ partners
- crystal
- different
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
- densely
- one
- radii
- directional
- lower
Simple Cubic Structure (SC)
- ______ due to low packing density (only Po has this structure)
- _____-________ directions are cube edges
- Coordination # = ______
- Rare
- Closed-packed
- 6
Body Centered Cubic Structure (BCC)
- Atoms touch each other along ______ diagonals
- Coordination # = _____
- cube
- 8
Face Centered Cubic Structure (FCC)
- Atoms touch each other along ______ diagonals
- ABCABC…..stacking sequence
- ____ projection
- face
- 2D
X-rays to Determine Crystal Structure
- Incoming X-rays _______ from crystal planes
- Measurement of critical angle, 0c, allows computation of planar spacing, d.
-diffract
X-Ray Diffraction Pattern
- Rectangle
- Square
- Triangle
- (110)
- (200)
- (211)
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
- Solidification
- Nuclei form
- Nuclei grow to form crystals - grain structure
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
- Metallic
- vacancies
- atom
- imperfections
- mechanical
- stress
- dislocations
Types of Imperfections
-Point Defects
-
-
-
-Line Defects
-
- Area Defects
-- Point Defects
- Vacancy atoms
- Interstitial atoms
- Substiutional atoms
- Line Defects
- Dislocations
- Area Defects
- Grain Boundaries
Vacancies:
- Vacant ______ sites in a structure
- Distortion of ______
- atomic
- planes
Self-Interstitials:
- “_____” atoms positioned between atomic sites
- Distortion of ______
- extra
- planes
Dislocations:
- Are ______ defects
- ______ between crystal planes result when ________ move,
- Produce permanent (______) deformation
- line
- Slip
- dislocations
- plastic
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
- Regions
- lattice
- disordered
- Low
