MT2

• Tafel plot


  Equation in electrochemical kinetics relating the rate of electrochemical reaction to the overpotential
• Tafel equation


  1. M ↔ M Z+ + ze−

  2. η = a ± b log|i|
• Nernst diffusion layer


  Split into two diffusion layers, with the pulsating diffusion layer having metal ion concentration pulsating with the frequency of the pulsating current
• Current efficiency


  Number of coulombs required for a reaction divided by the total number of coulombs passed
• At the anode, the pH becomes low due to the formation of hydrogen ions, and at the cathode the pH increases due to the formation of OH- ions
• Faraday's law


  W=ZQ, where W is the weight of deposit, Z is the electrochemical equivalent, and Q is the electric charge passed
• Substrate cleaning


  Designed to remove contamination on the substrate surface, involving open tanks, cleaning solutions, rinsing, and electrodeposition
• Leveling


  Progressive reduction of surface roughness during deposition, through preferential adsorption of a leveling agent on high points to inhibit deposition
• Corrosion protection of Fe by Zn coating

  Zinc has a more negative standard potential than iron, so it acts as a sacrificial anode to protect the iron
• Electroless and displacement deposition

  No power supply is necessary, with electrons supplied by a reducing agent (electroless) or the substrate (displacement)
• Advantages and disadvantages of electrodeposition and electroless deposition

  • [Not provided]
• Electrodeposition of alloys


  Requires the metals to have similar deposition potentials and be present in the electrolyte, with metal ions replenished in proportion to their deposition rates

  
• Electrodeposition of multilayer alloys

  Involves switching between two potentials to deposit pure layers of one metal and layers of the other metal with traces of the first
• Conductive polymers


  Properties: Electroactivity, Conductivity, Chemical stability, Flexible, Lightweight

  Applications: Advanced materials, Polymer batteries, Electric devices, Sensors, Biomedical implants, Protective coatings
• Strong and weak polyelectrolytes


  [Not provided]
• Cathodic and anodic deposition of polymers

  Anodic: Dissolution, Local pH decrease, Electrodeposition of insoluble film

  Cathodic: Protonation and dissolution, Cathodic base generation, Deposition of insoluble film
• Electrophoretic deposition (EPD)


  Fabrication of stable suspensions, Electrophoretic motion of particles/molecules, Coagulation and film formation at the electrode surface

  
• Hamaker equation


  Deposition yield = (μSEt/C) = (μSEt(Cs/Cc-Cs))
• Cathodic and anodic electrosynthesis of oxides and hydroxides

  Cathodic: M^n+ + ne- → M, H2O + 2e- → H2 + 2OH-

  Anodic: M^2+ + 2H2O → MO2 + 4H+ + 2e-
• Advantages and disadvantages of electrophoretic deposition and electrosynthesis of oxides

  • [Not provided]
• Materials fabrication using hydrometallurgy

  Preliminary operations

  2. Leaching

  3. Separation of leach liquor, purification

  4. Recovery of materials/metals (electrolysis)
• Flotation mechanisms


  Separating particles by treatment with chemicals to make some adhere to air bubbles and rise to the surface
• Direct and reverse flotation

  Direct: Mineral transferred to froth, leaving gangue in pulp

  Reverse: Gangue separated into float fraction
• Collectors for flotation


  Organic molecules with an ionic end that adsorbs on the mineral surface and a hydrophobic organic chain
• Flotation additives: conditioners and activators


  Conditioners: pH regulators

  Activators: Permit collector adsorption
• Flotation additives: depressants and frothers


  Depressants: Prevent collector adsorption on specific ions

  Frothers: Heteropolar molecules that absorb at the air-water interface and create stable bubbles
• Magnetic applications


  • Fe3O4
  • CoPt alloys
• Corrosion protection


  • Zn
  • Ni
• Capacitors


  • PZT
  • BST
• Piezoelectric devices


  • PZT
  • Quartz
• Biomedical implants


  • TiO2
  • Al2O3
• Why is material design (microstructure) important for advanced applications

  • Example 1: alpha Fe2O3 is non-magnetic vs gamma Fe2O3 is magnetic
  • Example 2: BaTiO3 -> is cubic above 120C (dielectric) vs BaTio3 is tetragonal below 120C (piezoelectric)
• Solid solutions


  The properties of materials can be improved by changing order of magnitude using the solid solutions
• Improve magnetic ability


  • MnFe2O4 vs (Mn0.5Zn0.5)Fe2O4
• Improve electric properties


  • BaTiO3/SrTiO3 vs (Ba1-x Srx)TiO3
• Solid state synthesis method for the fabrication of complex oxides


  1. Powder prep (using ball mills)

  2. Powder characterization (particle size and surface are)

  3. Pressing

  4. Synthesis

  5. Milling

  6. Powder Characterization (particle size, componstion and phase analysis)
• Solid state synthesis reactions

  • Al2O3(s)+TiO2(s)→Al2TiO5(s)
  • SrCO3(s)+TiO2(s)→SrTiO3(s)+CO2(g)
• Ideal powder characteristics for synthesis of complex oxides

  • Small particle size (<1um)
  • Low synthesis temperature
  • Small particle size in product
  • Homogenous composition in product
  • Narrow size distribution in particle size
  • Homogeneous composition in product
  • Dispersed particles
  • Spherical shape of particles
  • High purity
• Ideal powder characteristics for sintering of oxides

  • Small particle size (<1um)
  • Low sinter temperature
  • Small grain size in product
  • Dense product with low porosity
  • Narrow (or bimodal) size distribution in particle size
  • Dense product with low porosity
  • Dispersed particles
  • Spherical shape of particles
  • High purity
  • homogeneous composition
• Wet chemical precipitation method for production of oxides

  1. Precipitate

  2. Anneal at 500 °C to produce the particles with smaller size