BIOMATERIALS EXAM 1 - STRUCTURE AND BONDING

lectures 2-3

structure - function relationship

structure of a material ultimately decides its properties and as a result, its function

• more order → mechanical properties improve

example of structure affecting function:

water and ice: atoms are the same but they are arranged differently

ice - crystalline structure, hydrogen bonds hold molecules together

water - liquid state, not crystalline

• mechanical properties change

what kind of atomic bonding is there?

primary and secondary

what bonds are primary?

ionic, covalent, metallic

what bonds are secondary?

hydrogen, vander waals

rank the types of bonds from weakest to strongest

hydrogen/van der waals < covalent < metallic < ionic

rank the types of bonds from strongest to weakest

ionic > metallic > covalent > hydrogen/van der waals

what is the strongest bond

ionic

what is the weakest bond

hydrogen/van der waals

what is stronger, covalent or metallic?

metallic

what is weaker, covalent or metallic?

covalent

ionic bonding:

• strong, electrostatic between anions and cations

• bonding energy between 600 and 1500 kJ/mol

• thermal and electric insulator

  • high strength and high melting temp

covalent bonding:

• sharing electrons between two atoms

• bonding energy between 17.94 and 71.77 kJ/mol

  • directional, high bonding energy possible

• low electrical conductivity

metallic bonding:

• cations that interact with floating electrons

• bonding energy between 70 and 850 kJ/mol

• thermal and electric conductor, good mechanical properties including ductility

which materials have which bonds?

ionic - ceramics

covalent - polymers

metallic - metals

hydrogen bonding:

attractive force between a hydrogen atom covalently bonded to a very electronegative atom (such as N, O, or F) and another very electronegative atom

• more H bonds = higher viscosity

van der waals bonding:

• forces created by atomic or molecular dipoles

• a bond or molecule whose ends have opposite charges

• between biomaterials and proteins

crystallography

• crystalline materials are arranged in an ordered fashion

• type of crystal structure affects properties

• only looking at the first three in picture

crystalline structure

atoms arranged in a repetitive fashion in a 3D structure over large atomic distances

• opposite is amorphous

• more order = stronger/stiffer material

  • think plastic balls in a bucket

  • even carbon has graphite and diamond

unit cell

smallest repeating unit of a crystalline material

• repeated in 3 dimensions to form final material

coordination number

the number of atoms or ions immediately surrounding a central atom in a complex or crystal

atomic packing factor (APF)

fraction of the volume of a unit cell that is occupied by atoms or ions

• sum of the sphere volumes of all atoms within a unit cell divided by the unit cell volume

• dimensionless

APF formula:

this DO BETTER LATER

APF for FCC:

74%

derivation of FCC APF

[(8*1/8 + 6*1/2) * 4/3 pi r³] / (2root2r)³ = 0.740 = 74%

APF for BCC:

68%

derivation of BCC APF:

(1/8*8+1)*4/3 pi r^3/(4/root3r)^3=0.68 or 68%

APF for simple cubic

52%

derivation for simple cubic APF:

skip lol

what are the cubic structures called?

lattice systems

what is a lattice?

an ordered array of points describing the arrangement of particles that form a crystal

miller indices in lattice structures

group of three numbers that indicates the orientation of a plane or set of parallel planes of atoms in a crystal

what does APF affect

mechanical properties

what do miller indices/orientation of planes affect

chemistry/chemical properties

miller indices notation

(h k l) represent a point

• negative numbers and directions are denoted by a bar on top of the number

how to determine miller indices:

• determine the points at which the plane intersects the x, y, and z axes.

  • If the plane is parallel to an axis, the intercept for that axis is taken to be ∞

• take the reciprocal of the intercepts

• multiply by an integer to clear fractions if needed

• record integer indices in parentheses with no commas (h k l)

  • negative numbers are indicated by a bar over the integer