JNTU B.Tech III NON-METALLIC MATERIALS Previous Question Paper (February/March - 2022 - R18)

Metals and non-metallic materials exhibit fundamental differences in their atomic structure, bonding, and physical properties, which dictate their respective engineering applications.

The key differences are summarized as follows:

1. Atomic Bonding: Metals consist of positive ions in a sea of delocalized electrons, allowing for high electrical and thermal conductivity. Non-metals rely on shared (covalent) or transferred (ionic) electrons, resulting in localized bonding that restricts charge carrier movement.
2. Mechanical Behavior: Metals are characterized by their ability to undergo plastic deformation due to dislocation motion within the crystal lattice. In contrast, non-metals like ceramics are typically brittle, as their rigid ionic or covalent bonds prevent dislocation movement, leading to fracture under stress.
3. Optical and Thermal Properties: Metals are opaque because free electrons absorb and re-emit light across the spectrum. Non-metals can be transparent, translucent, or opaque depending on their band gap and atomic arrangement. Metals generally have high thermal conductivity, whereas non-metals often serve as thermal insulators.
4. Chemical Stability: Metals are prone to oxidation and corrosion when exposed to environmental elements. Non-metallic materials, particularly ceramics and certain polymers, often exhibit superior chemical inertness and resistance to environmental degradation.

Polyvinyl Chloride (PVC) and Polyacrylonitrile (PAN) are two significant thermoplastic polymers with distinct chemical structures, properties, and industrial applications.

Polyvinyl Chloride (PVC)

PVC is produced by the polymerization of vinyl chloride monomer. It is inherently rigid due to the presence of chlorine atoms, which introduce strong dipole-dipole interactions between polymer chains.

Properties:

• High chemical resistance to acids, bases, and salts.
• Excellent flame retardancy due to its chlorine content.
• Good electrical insulation properties.
• Versatility: Can be made rigid (uPVC) or flexible by adding plasticizers.
• High durability and weather resistance.

Applications:

• Construction: Pipes, conduits, window frames, and flooring.
• Medical: Blood bags and tubing.
• Electrical: Cable insulation and jacketing.
• Packaging: Blister packs and bottles.

Polyacrylonitrile (PAN)

PAN is a synthetic, semi-crystalline organic polymer resin. It is characterized by a high glass transition temperature and significant intermolecular forces due to the polar nitrile (-CN) groups.

Properties:

• High thermal stability and chemical resistance.
• High tensile strength and stiffness.
• Excellent resistance to ultraviolet (UV) radiation and sunlight.
• Low solubility in common organic solvents.
• Ability to be processed into high-performance fibers.

Applications:

• Precursor for Carbon Fiber: PAN is the primary raw material used to produce high-strength carbon fibers through controlled oxidation and carbonization.
• Textiles: Used in the production of acrylic fibers for clothing, sweaters, and carpets due to its wool-like feel.
• Filtration: Used in industrial membrane filters for water treatment.
• Outdoor fabrics: Used in awnings and boat covers due to superior weather resistance.