Content Revision Flashcards
What is the definition of a particle?
An individual item without size limitations, only constraint being that it is small relative to its surroundings.
Define inter-particle strength.
Strength of a granule. Related to how particles of a granule interact with eachother.
Define intra-particle strength.
Strength of a single particle. Related to how constituents of a single particle resist deformation and fracture, depends on the structure of the particle.
Define granulation.
Process by which smaller particles are fused together to form larger masses in which the original particles can still be identified.
Discuss liquid bridges.
Presence of small amounts of liquid on the particle surface affects the interparticle forces.
Smoothing effect on surface imperfections.
Reduces inter-particle distance.
Discuss solid bridges.
Binder bridges formed when liquid binder between particles solidifies.
Crystalline bridges formed when dissolved material crystallises from solution present in the gap between particles.
Discuss electrostatic forces.
Occur due to friction during particle collisions and rubbing of particles against equipment surfaces.
Strength of force is related to the charge of the particles.
Act over long distance in comparison to adhesion forces.
Discuss three different segregation mechanisms.
Trajectory: Small particles whose drag force is governed by Stoke’s Law are projected horizontally. Larger particles decelerate slower than small particles.
Elutriation: Powders containing particles with radius 50u are charged in a vessel, air is displaced upwards. Fine particles remain in suspension, large particles fall to the bottom.
Percolation: Brazil Nut effect. Disturbance of particles causes spaces to be created. Large particles move up, small particles move down.
Discuss metallic bonding.
Metal atoms give up their valence electrons to form positive ions. This creates a sea of de-localized electrons. Electrostatic attraction between metal ions and electrons hold metal together.
Discuss ionic bonding.
Metal ion transfers its valence electron to a non-metal ion. Electrostatic attraction between the positive and negative ion creates an ionic bond.
Discuss covalent bonding.
Non metal atoms share valence electrons to fill the outer shell of both atoms with 8 electrons, this gives a stable configuration and forms a covalent bond between the two atoms.
Discuss plastic deformation of crystalline solids.
Occurs through the movement of structural defects called dislocations.
Discuss Permanent Dipole-Permanent Dipole interactions.
Some atoms are d+, some are d-. This occurs as atoms such as O are more electronegative than C, therefore the O atoms attract more electrons becoming d-, and carbon d+. These partial charges can be permanently in place, a PD-PD interaction occurs when two PD molecules interact with eachother.
Discuss Permanent Dipole-Induced Dipole interactions.
Symmetrical molecules are non-polar as the partial charges cancel. However, when in close proximity, a polar molecule can induce a temporary dipole in a symmetrical molecule. In doing so, this creates a PD-ID interaction.
Discuss Induced Dipole-Induced Dipole interactions.
Non-polar still have electron movement, due to their random nature. An instantaneous uneven distribution of electrons can produce temporary charges in a molecule. These temporary charges can then induce temporary charges in neighbouring molecules. This creates an ID-ID interaction.
Discuss Hydrogen bonding.
Formed when a H atom attached to a very electronegative atom (NOF) is attracted to another very electronegative atom (NOF).
What is CED?
Cohesive Energy Density. Amount of energy required to separate the constituent molecules of the material to an infinite distance.
What is permittivity?
Measure of resistance encountered when forming an electric field.
Why do we granulate?
Improve flow
Improve homogeneity
Improve bulk density
Improve wettability.
