Lecture 01, 2

• What is the definition of crystallisation?

  A solid-liquid separation process forming crystals
• What is the role of supersaturation in crystallisation?

  It drives nucleation and crystal growth
• What is a crystalline material?

  Molecules packed in a defined order
• What is the internal structure of a crystal called?

  The unit cell
• What is the melting point characteristic of crystalline materials?

  They have a defined melting point
• How are molecules held within a crystal?

  By intermolecular forces
• Why are crystals used in pharmaceutical products?

  They provide high purity and stability
• What is crystallisation?

  A process forming a solid from a liquid
• What happens during the crystallisation process?

  Molecules organise to form a solid crystal
• What is nucleation in crystallisation?

  Formation of a small mass for crystal growth
• What is the Gibbs free energy change (∆G) during crystallisation?

  It indicates the energy available for phase change
• What is supersaturation?

  More dissolved solute than in saturation
• What is the degree of supersaturation formula?

  Degree = Concentration / Solubility
• What happens when a solution reaches saturation?

  It cannot dissolve more solute
• What is the effect of increasing temperature on solubility?

  It increases solubility
• What is primary homogeneous nucleation?

  Spontaneous nucleation without phase boundary
• What is the significance of secondary nucleation?

  It is common in industrial crystallisation
• What is Ostwald’s rule of stages?

  Transition occurs to a more stable state
• What is the effect of cooling rate on crystallisation?

  It affects supersaturation generation
• What is the role of seeding in crystallisation?

  It bypasses the nucleation stage
• What is the rate-limiting step of crystal growth?

  Diffusion of molecules to the impingement site
• What are the stages of crystal growth?

  1. Transport of growth unit to crystal surface
  2. Adsorption at the impingement site
  3. Diffusion to a growth site
  4. Incorporation into the crystal lattice
• What factors affect controlling crystallisation?

  • Nucleation control
  • Crystal growth control
  • Thermodynamic, kinetic, and process controls
• What mechanisms are involved in secondary nucleation?

  • Initial breeding
  • Needle breeding
  • Polycrystalline breeding
  • Collision breeding
• What are the characteristics of polymorphs?

  • Different crystal arrangements
  • Varying stability, melting point, and solubility
• What is the significance of controlling polymorphism?

  • Ensures desired crystal form
  • Affects stability and solubility
• What is the importance of temperature in crystallisation?

  • Affects polymorph formation
  • Influences solubility and supersaturation
• How does stirring rate affect crystallisation?

  • Influences crystal size and habit
  • Affects supersaturation generation
• What is the relationship between dissolution and crystal growth?

  • Rate of dissolution equals rate of growth at saturation
  • Supersaturation drives crystal growth
• What is the significance of Gibbs free energy in crystallisation?

  • Indicates stability of phases
  • Lower Gibbs free energy favours crystallisation
• What is the effect of impurities on nucleation?

  • Lower free energy of nucleation
  • Facilitate heterogeneous nucleation
• What is the significance of the super-solubility diagram?

  • Illustrates stability zones for crystallisation
  • Guides nucleation and growth conditions