Industrial Chemistry: Polymers, Corrosion, and Water Analysis

Posted on Aug 6, 2026 in Chemistry

Preparation and Applications of PMMA

Poly(methyl methacrylate) (PMMA), also known as acrylic glass, is prepared by the addition polymerization (free radical mechanism) of Methyl Methacrylate (MMA) monomers using a benzoyl peroxide initiator at 60°C–80°C.

Reaction:
n[CH2=C(CH3)COOCH3] —Peroxide/Δ→ [—CH2—C(CH3)(COOCH3)—]n

The peroxide decomposes into free radicals, opening the double bond of the MMA to form a linear polymer chain.

Properties: High optical clarity (92% light transmission, superior to glass), lightweight, shatter-proof, and excellent UV and weather resistance.

Applications of PMMA

  • Aviation and Automotive: Aircraft windshields, canopy covers, windows, and tail-light covers.
  • Medical: Hard contact lenses, dental prosthetics, bone cement, and artificial teeth (biocompatible).
  • Displays: Illuminated signboards, commercial displays, skylights, noise barriers, and Lucite panels.
  • Safety: Optical lenses, protective goggles, riot shields, and transparent partitions.

Thermoplastic vs. Thermosetting Plastics

  1. Structure: Thermoplastics have linear or branched polymer chains joined by weak Van der Waals forces. Thermosets have a 3D cross-linked network with strong covalent bonds.
  2. Effect of Heat: Thermoplastics soften on heating and harden on cooling repeatedly without chemical change. Thermosets soften initially but harden permanently on curing due to cross-linking.
  3. Reusability: Thermoplastics can be remolded, reshaped, and recycled multiple times. Thermosets cannot be remolded or reshaped once set; they char or decompose on strong heating.
  4. Physical Properties: Thermoplastics are soft, flexible, soluble in organic solvents, and have lower tensile strength. Thermosets are hard, rigid, brittle, and insoluble in solvents, with high mechanical strength.
  5. Synthesis: Thermoplastics are usually formed by addition polymerization. Thermosets are usually formed by condensation polymerization.
  6. Examples: Thermoplastics: Polyethylene (PE), PVC, Polystyrene, PMMA, and Teflon. Thermosets: Bakelite, Urea-Formaldehyde, Epoxy resins, and Vulcanized rubber.

Dissolved Oxygen and Factors Affecting It

Dissolved Oxygen (DO) is the amount of gaseous oxygen (O2) dissolved in water, expressed in mg/L or ppm. Normal healthy freshwater contains 8–10 ppm DO at 20°C. It is a critical indicator of water quality and supports aquatic life.

Factors Affecting DO Levels

  1. Temperature: Gas solubility decreases as temperature increases. Warm water holds less dissolved oxygen than cold water; therefore, thermal discharge reduces DO.
  2. Organic Waste and BOD: The presence of sewage or effluents increases microbial activity. Aerobic bacteria consume large amounts of DO during organic decomposition, lowering DO levels.
  3. Salinity: High dissolved salt concentration reduces oxygen solubility. Marine or estuarine water holds less DO than freshwater at the same temperature.
  4. Photosynthesis vs. Respiration: Aquatic plants release O2 during daylight via photosynthesis (increasing DO). At night, photosynthesis stops while respiration continues (decreasing DO).
  5. Water Turbulence (Aeration): Fast-flowing, turbulent water mixes with air rapidly, maintaining high DO. Stagnant water suffers from low re-aeration and depleted DO.

Scale and Sludge Formation in Boilers

Sludge is a loose, soft, slimy, non-adherent precipitate formed in the colder parts of a boiler. It can be removed by blow-down operations or wire brushing.

Scale is a hard, sticky, dense, and strongly adherent coating formed on inner boiler walls. It is very difficult to remove.

  • Salts responsible for Sludge: MgCO3, MgCl2, CaCl2, and MgSO4.
  • Salts responsible for Scale: CaSO4, Ca(HCO3)2 (decomposes to CaCO3), CaSiO3, and MgSiO3.

Disadvantages of Scale Formation

  1. Fuel Wastage: Scales are poor thermal conductors. Heat transfer from the furnace to the water decreases, increasing fuel consumption (a 1.25 mm scale can cause ~50% fuel wastage).
  2. Boiler Overheating and Tube Failure: Low heat conductivity causes the boiler’s outer metal to overheat dangerously, reducing tensile strength and causing bulging or bursting.
  3. Decreased Efficiency: Scales partially clog boiler tubes, restricting steam and water flow, which lowers operational output.
  4. Danger of Explosion: Scale cracking allows water to touch red-hot metal, generating sudden high-volume steam that can trigger violent explosions.

Primary vs. Secondary Batteries

Primary Batteries are electrochemical cells where cell reactions are irreversible. Once reactants are consumed, the battery dies and cannot be recharged. Secondary Batteries are electrochemical cells where cell reactions are reversible. They are recharged by passing an external DC current in reverse, enabling multiple charge-discharge cycles.

Key Differences

  • Reversibility: Primary is chemically irreversible; Secondary is chemically reversible.
  • Rechargeability: Primary is non-rechargeable (single-use); Secondary is rechargeable multiple times.
  • Life and Energy Density: Primary has high initial energy density but a short lifespan; Secondary has moderate energy density but a long operational life.
  • Internal Resistance: Primary has high internal resistance; Secondary has low internal resistance.
  • Cost: Primary is cheap initially but expensive per use; Secondary has a high initial cost but is economical long-term.
  • Examples: Primary: Dry cell (Leclanché), Alkaline, and Zinc-Air. Secondary: Lead-Acid, Lithium-Ion, and Ni-Cd.

Water Hardness Calculation

Hardness is caused by Ca2+ and Mg2+ salts, expressed in CaCO3 equivalents (Molecular Weight = 100, Equivalent Weight = 50).

Formula: CaCO3 Eq = Mass of salt (mg/L) × (100 / Mol. Wt. of salt)

Molecular Weights: Ca(HCO3)2 = 162, Mg(HCO3)2 = 146, CaSO4 = 136, MgCl2 = 95, MgSO4 = 120, CaCl2 = 111.

Sample Problem

A water sample contains per liter: Ca(HCO3)2 = 16.2 mg, Mg(HCO3)2 = 14.6 mg, CaSO4 = 13.6 mg, MgCl2 = 9.5 mg, and NaCl = 10.0 mg.

Calculations to CaCO3 Equivalents:

  1. Ca(HCO3)2 = 16.2 × (100 / 162) = 10.0 mg/L (Temporary)
  2. Mg(HCO3)2 = 14.6 × (100 / 146) = 10.0 mg/L (Temporary)
  3. CaSO4 = 13.6 × (100 / 136) = 10.0 mg/L (Permanent)
  4. MgCl2 = 9.5 × (100 / 95) = 10.0 mg/L (Permanent)
  5. NaCl: Non-hardness salt (0.0 mg/L)

Results:

  • Temporary Hardness: 10.0 + 10.0 = 20 mg/L (ppm)
  • Permanent Hardness: 10.0 + 10.0 = 20 mg/L (ppm)
  • Total Hardness: Temporary + Permanent = 20 + 20 = 40 mg/L (ppm)

Conductometric Titration and Conductance

Specific Conductance (κ): The conductance of 1 cm3 of solution between 1 cm2 electrodes placed 1 cm apart. Unit: ohm-1 cm-1. It decreases on dilution due to fewer ions per cm3.

Equivalent Conductance (Λ): The conductance of 1 g-eq of electrolyte in volume V. Λ = (κ × 1000) / N. Unit: ohm-1 cm2 eq-1. It increases on dilution due to higher ionic mobility.

Principle: Ion concentration and mobility dictate conductance. Titration replaces high-mobility ions with low-mobility ions (or vice versa). The endpoint is identified by a sharp break in the conductance vs. titrant volume curve.

Titration Curves

  1. Strong Acid vs. Strong Base (HCl vs. NaOH): (H+ + Cl–) + (Na+ + OH–) → Na+ + Cl– + H2O. Conductance drops sharply as fast H+ is replaced by slower Na+. It hits a minimum at the endpoint (Na+, Cl–) and rises sharply post-endpoint due to free, fast OH– (V-shaped curve).
  2. Weak Acid vs. Strong Base (CH3COOH vs. NaOH): CH3COOH + (Na+ + OH–) → CH3COO– + Na+ + H2O. Initial conductance is low (CH3COOH is poorly ionized). It rises slowly before the endpoint as the strong electrolyte CH3COONa forms, then rises steeply post-endpoint due to excess fast OH– (Inverted L-shape/Hook curve).

Electrochemical Corrosion and Mechanisms

Wet Corrosion occurs when metal comes into contact with a liquid conducting medium or moisture containing dissolved gases (O2, CO2), creating anodic and cathodic zones that form galvanic cells.

Comparison: Dry corrosion involves direct gas attack (O2, Cl2) without moisture, is slow, and forms uniform oxide layers. Wet corrosion requires an electrolyte, is fast, involves ionic flow, and forms rust away from anodic zones.

Mechanism of Oxygen Absorption (Neutral/Alkaline)

This occurs when metal (e.g., Fe) is exposed to water containing dissolved O2.

  1. Anodic Region (Oxidation): Metal dissolves, releasing electrons.
    Anode: Fe → Fe2+ + 2e–
  2. Cathodic Region (Reduction): Dissolved oxygen consumes electrons to form OH– ions.
    Cathode: 1/2 O2 + H2O + 2e– → 2OH–
  3. Rust Formation: Fe2+ and OH– ions diffuse through moisture to form ferrous hydroxide:
    Fe2+ + 2OH– → Fe(OH)2
  4. Oxidation: In excess oxygen, Fe(OH)2 oxidizes to hydrated ferric oxide (Rust):
    4Fe(OH)2 + O2 + 2H2O → 2[Fe2O3 · 3H2O]

Methods of Corrosion Protection

  1. Material Selection and Design: Use pure metals or alloys (e.g., Stainless Steel) and avoid joining dissimilar metals.
  2. Cathodic Protection: Sacrificial Anodic Protection (attach an active metal like Zn or Mg to the anode) or Impressed Current Protection (apply an opposing DC current).
  3. Corrosion Inhibitors: Add chemical agents (chromates, amines) to slow anodic or cathodic reactions.
  4. Protective Coatings: Use organic (paints) or metallic coatings (galvanizing, electroplating).

Electroplating Technique

Electroplating deposits a thin, non-porous layer of corrosion-resistant metal (Ni, Cr, Au) onto a base metal via electrolysis.

  • Anode: Pure bar of coating metal (e.g., Nickel).
  • Cathode: Object to be coated (cleaned base metal).
  • Electrolyte: Aqueous salt solution of the coating metal (e.g., NiSO4).
  • Power: Direct Current (DC) source.

Reactions:
Anode (Dissolution): Ni → Ni2+ + 2e–
Cathode (Deposition): Ni2+ + 2e– → Ni (Deposited on the article surface)

Factors Affecting the Rate of Corrosion

  1. Temperature: The corrosion rate increases directly with temperature because reaction kinetics and ion/oxygen diffusion speeds increase.
  2. pH: Acidic media (pH < 7) cause rapid corrosion due to high H+ ion concentration enabling rapid hydrogen evolution. Basic media (pH > 10) passivate most metals.
  3. Impurities in Metal: Impure metals corrode faster because surface impurities create microscopic cathodic sites, establishing tiny galvanic cells.
  4. Ratio of Anodic to Cathodic Area: A smaller anodic area relative to a larger cathodic area increases the corrosion rate severely due to high localized current density.
  5. Galvanic Series: When two dissimilar metals are connected, the metal higher in the series acts as the anode and corrodes. A larger potential difference accelerates corrosion.
  6. Solubility of Corrosion Products: Insoluble, dense products form a passive barrier. Soluble products dissolve, exposing fresh metal and accelerating corrosion.

Polymer and Plastics Classification

  • Monomer: A small, reactive, low-molecular-weight molecule capable of linking to form macromolecules (e.g., Ethylene).
  • Polymer: A high-molecular-weight macromolecule of repeating structural monomer units linked by covalent bonds (e.g., Polyethylene).
  • Degree of Polymerization (n): The total number of repeating monomer units in a polymer chain. (Polymer Mol. Wt. = n × Monomer Mol. Wt.)
  • Functionality: The number of reactive bonding sites on a monomer. Bifunctional (F=2) forms linear polymers; Trifunctional (F=3) forms 3D cross-linked networks.

Classification of Polymers

  1. Origin: Natural (Rubber, Cellulose, Starch) vs. Synthetic (PE, PVC, Nylon).
  2. Structure: Linear (HDPE, PVC), Branched (LDPE), or Cross-linked/Network (Bakelite).
  3. Mechanism: Addition (chain-growth without byproduct, e.g., PE, PMMA) vs. Condensation (step-growth with elimination of H2O, HCl, e.g., Nylon-6,6, Bakelite).
  4. Thermal Behavior: Thermoplastics (soften on heating, remoldable) vs. Thermosets (permanently rigid cross-links).

Lubrication Principles and Mechanisms

  • Lubricant: A substance introduced between moving metal surfaces to reduce friction and wear.
  • Flash Point: The lowest temperature at which oil vapors ignite momentarily with a flash upon exposure to a flame.
  • Cloud Point: The temperature at which oil turns cloudy due to wax crystallization upon cooling.
  • Functions: Reduces friction, power loss, and surface wear; dissipates heat; seals against dirt; and prevents corrosion.

Lubrication Mechanisms

  1. Hydrodynamic / Fluid Film: A thick lubricant film (≈1000 Å) completely separates surfaces under light loads and high speeds.
  2. Thin Film / Boundary Lubrication: Used under high loads and low speeds where a continuous film cannot be maintained. Polar molecules adsorb onto metal surfaces to form a protective layer.
  3. Extreme Pressure (EP): Used under high load/temperature; additives (S, P, Cl) react with metal to form low-shear protective solid films.

Types and Comparison of Fuels

Comparison of Fuel States

  • Calorific Value: Solid (Low), Liquid (High), Gaseous (Very High).
  • Ignition Temp: Solid (High, hard to ignite), Liquid (Low), Gaseous (Very low, instant ignition).
  • Combustion Control: Solid (Slow, hard to control), Liquid (Easy via valves), Gaseous (Instant, precise control).
  • Smoke and Residue: Solid (Produces smoke, soot, ash), Liquid (Negligible ash/smoke), Gaseous (Zero ash/residue).
  • Efficiency: Solid (Low), Liquid (High), Gaseous (Highest thermal efficiency).

Advantages of Liquid Fuels: Higher calorific value, no solid ash formation, easy flame regulation, and smaller storage volume required.

Advantages of Gaseous Fuels: Highest thermal efficiency due to complete combustion, instant ignition/shutoff, zero smoke emission, and easy transport via pipelines.