Metals & Biomedical Applications Flashcards
Common metals used in biomedical appliations
Titanium, Stainless steel 316, Co-Cr-Mo. Also Au, Ag, Cu
biometals are not bioactive
just bioinert and biocompatible within the span of a life time.
Understand the basics of the « virtuous » triangle of Materials Science
Processing, performance, microstructure
Biometals
Mg, Ti, Cr, Co, Ni, Cu
Dental alloys
Silver, Gold, Tin, Mercury
Bonds in metals
A network of positive ions and a moving sea of electrons. Metallic character: conductivity, shiny aspect, formability
Normal metals
Al,Mg,Na: weak bonding
Transition metals
(some covalent character due to unfilled internal electron shells): stronger bonds, higher densities and melting
Crystallization
isothermal evolution with heat evolution
Vitreous transition
gradual transition without heat evolution
Are the solute atoms (ions) located on a periodic lattice?
Yes: ordered (substitutional) solid solutions. No: disordered (substitutional) solid solution.
All structures contain defects, but it’s not always detrimental to performance
A classification of defects by extension: • Point defects (0D), • Linear defects (1D), • Surface defects (2D), • Volumic defects (3D)
Types of defects
vacancies, self-interstitial, substitutional or intersitial solute atom (ion)
For ionic defects
the electrical neutrality has to be ensured: two defects rather than on
Impacts of point defects
Impact on transfer phenomena, matter transfer, electrical conduction
Volumic defects
Pores & cavities, foreign particles, non-desired phases
3D deffects
detrimental. concentrate stresses and may initiate cracking in metals, initiate corrosion
The control of volumic defects is associated with
high additional cost. (high purity materials, controlled atmospheres, clean room processing)
Thermodynamics of materials
–Limited to stable equilibrium situations (time is not a variable), but metastable equilibrium may be considered,
–Chemical thermodynamics, solutions, reactions…
–difficulty in defining simplified system to represent a complex reality
–Numerical models are available, or diagrams
Solid state reaction kinetics
Time is the main variable to describe the evolution of a system:
•Nucleation (surface phenomena),
•Growth limited by diffusion or by interfacial reactions,
Numerical kinetic models also developed, for diffusion controlled reactions
chemical potential of element
i is defined as the derivative of G (and also H ) with respect to the mole content of element i in the phase:
ui is often referred to the
chemical potential
Under equilibrium, the pressure and temperature
homogeneous in all points (phases) of the system (mechanical and thermal equilibrium)
Young-Dupré relationships express
the static contact angle of a liquid drop on a solid substrate, in equilibrium with a gas phase
