Electrochemistry and Cement: Principles and Applications

Electrochemistry

  1. What is EMF, and What is its Significance in Electrochemistry?

    • EMF (Electromotive Force) is the potential difference between two electrodes when no current flows. It drives the redox reaction in an electrochemical cell.
    • Significance:
      • Determines the spontaneity of a reaction (\(\Delta G^\circ = -nFE^\circ_{cell}\)).
      • Measures the energy available for work.
      • Helps calculate thermodynamic parameters like the equilibrium constant and Gibbs free energy.
  2. Working Principle and Reactions in a Glass Electrode

    • The glass electrode measures pH based on the potential difference developed across a pH-sensitive glass membrane due to \(H^+\) ion exchange.
    • Reactions:
      • At the inner surface: \(H^+_{internal} + Na^+_{glass} \leftrightarrow Na^+_{internal} + H^+_{glass}\).
      • At the outer surface: \(H^+_{solution} + Na^+_{glass} \leftrightarrow Na^+_{solution} + H^+_{glass}\).
    • The potential is proportional to \(\log [H^+]\), giving the pH value.
  3. Standard EMF of the Cell: \(Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)\)

    • \(E^\circ_{cell} = E^\circ_{cathode} – E^\circ_{anode}\).
    • \(E^\circ_{Cu^{2+}/Cu} = 0.34 \, \text{V}, \, E^\circ_{Zn^{2+}/Zn} = -0.76 \, \text{V}\).
    • Calculation: \(E^\circ_{cell} = 0.34 – (-0.76) = 1.10 \, \text{V}\).
  4. Equilibrium Constant for \(Fe^{2+} + Ag^+ \rightarrow Fe^{3+} + Ag\)

    • Given: \(E^\circ_{Fe^{3+}/Fe^{2+}} = 0.77 \, \text{V}, \, E^\circ_{Ag^+/Ag} = 0.80 \, \text{V}\).
    • \(E^\circ_{cell} = 0.80 – 0.77 = 0.03 \, \text{V}\).
    • Using \(K = e^{\frac{nFE^\circ_{cell}}{RT}}\):
      Substitute \(n = 1, F = 96485, R = 8.314, T = 298\): \(K \approx 3.19\).
  5. Voltage for \(Fe | Fe^{2+} || Mn^{2+} | Mn\)

    • \(E_{cell} = E^\circ_{Mn^{2+}/Mn} – E^\circ_{Fe^{2+}/Fe} – \frac{0.0591}{n} \log \frac{[Mn^{2+}]}{[Fe^{2+}]}\).
    • Substitute known values to calculate the voltage (requires data for \(E^\circ_{Mn^{2+}/Mn}\) and \(E^\circ_{Fe^{2+}/Fe}\)).
  6. Advantages of Li-ion Batteries for Electric Vehicles

    • High energy density for compact storage.
    • Long cycle life and high charge/discharge efficiency.
    • Lightweight, reducing vehicle weight.
    • Environmentally safer compared to lead-acid batteries.
    • Low self-discharge rate, preserving charge longer.
  7. Construction and Working of a Calomel Electrode

    • Construction: Contains mercury and mercurous chloride in contact with a KCl solution.
    • Working: It provides a stable reference potential via the reaction:
      \(Hg_2Cl_2 + 2e^- \leftrightarrow 2Hg + 2Cl^-\).
    • The potential depends on KCl concentration, commonly saturated for constancy.
  8. Factors Affecting Electrode Potential

    • Concentration of ions in the solution (Nernst equation).
    • Temperature affects potential linearly.
    • Gas pressure for gas-involved electrodes.
    • Electrode surface condition, such as cleanliness or passivation.

Portland Cement and Lubrication

  1. Portland Cement and Rotary Kiln Zones

    • Definition: A construction material made by heating limestone and clay.
    • Zones in rotary kiln:
      • Drying zone: Removes water.
      • Calcination zone: Decomposes calcium carbonate to calcium oxide and \(CO_2\).
      • Clinkering zone: Forms clinker (main compounds like \(C_3S, C_2S\)).
      • Cooling zone: Solidifies and stabilizes clinker.
  2. Setting and Hardening of Cement; Role of Gypsum

    • Setting: Stiffening of cement paste due to hydration of \(C_3A\) and \(C_3S\).
    • Hardening: Strength development as C-S-H and calcium hydroxide form.
    • Gypsum: Controls the setting time by preventing flash setting due to rapid \(C_3A\) hydration.
  3. Lubrication Mechanisms

    • Fluid-film lubrication: A thin film of fluid prevents contact between surfaces, reducing wear.
    • Boundary lubrication: A protective molecular layer or additive minimizes friction when the fluid film breaks down.
  4. Emulsification in Lubrication

    • Definition: Formation of oil-water mixtures.
    • Significance: Determines lubricant stability and performance in water-contaminated environments, such as marine or industrial machinery.
  5. Viscosity Index (VI)

    • High VI indicates minimal change in viscosity with temperature.
    • Ensures proper lubrication at high temperatures and prevents excessive resistance at low temperatures.
  6. Steam Emulsion Number

    • Indicates a lubricant’s ability to resist emulsification with steam.
    • Important for evaluating lubricants in steam turbines or humid environments.
  7. Flash and Fire Points of Lubricating Oil

    • Flash point: Temperature where vapor ignites briefly.
    • Fire point: Temperature where vapor burns continuously.
    • Pensky-Martens Apparatus: Heated oil releases vapor; a flame is applied to measure these points.