JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III NON-METALLIC MATERIALS Previous Question Paper (August/September - 2021 - R18)

Metals and non-metallic materials differ significantly in their atomic bonding, physical characteristics, and processing methods. Metals are characterized by metallic bonding, where valence electrons are delocalized in a 'sea of electrons,' providing high electrical and thermal conductivity. In contrast, non-metallic materials, such as ceramics and polymers, rely on covalent or ionic bonding, which typically results in electrical insulation and lower thermal conductivity.

Key differences include:

• Mechanical Properties: Metals are generally ductile and malleable, allowing for plastic deformation. Non-metals are typically brittle (ceramics) or exhibit viscoelastic behavior (polymers).
• Luster and Opacity: Metals possess a characteristic metallic luster and are opaque due to the interaction of light with free electrons. Non-metals vary from transparent to opaque and often have a dull or glassy appearance.
• Corrosion Resistance: Metals are prone to oxidation and corrosion in environmental conditions. Many non-metallic materials, particularly polymers and ceramics, exhibit superior chemical inertness and resistance to corrosion.
• Density: Metals generally have high densities, whereas non-metallic materials like polymers are significantly lighter.

Polyvinyl Chloride (PVC) and Polymethyl Methacrylate (PMMA) are widely used synthetic polymers with distinct properties suited to specific industrial applications.

Polyvinyl Chloride (PVC):

• Properties: PVC is a rigid, durable thermoplastic with excellent chemical resistance, flame retardancy, and low cost. It can be made flexible through the addition of plasticizers.
• Applications: It is extensively used in the construction industry for pipes, window frames, flooring, and cable insulation due to its weather resistance and durability.

Polymethyl Methacrylate (PMMA):

• Properties: Often referred to as acrylic glass, PMMA is characterized by exceptional optical clarity, high light transmission, good UV stability, and moderate impact resistance. It is lightweight and easy to machine.
• Applications: Its primary applications include optical lenses, aircraft canopies, display cases, signage, and medical devices such as intraocular lenses, where transparency and aesthetic finish are critical.