Electrochemistry and Cement: Principles and Applications
Posted on Dec 18, 2024 in Chemistry
Electrochemistry
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.
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.
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: \(E^\circ_{cell} = 0.34 – (-0.76) = 1.10 \, \text{V}\).
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 \(n = 1, F = 96485, R = 8.314, T = 298\): \(K \approx 3.19\).
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 \(E^\circ_{Fe^{2+}/Fe}\)).
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.
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.
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
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.
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.
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.
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.
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.
Steam Emulsion Number
- Indicates a lubricant’s ability to resist emulsification with steam.
- Important for evaluating lubricants in steam turbines or humid environments.
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.