Properties of metals, ceramics and polymers Knowledge-Based Practice

Questions

1. 1.

   Which of the following structural features is primarily responsible for the superior electrical and thermal conductivity of metals relative to typical ceramics and polymers?

   • A) The presence of directional covalent bonds forming rigid, continuous networks
   • B) The presence of alternating ionic charges that facilitate rapid ion migration at room temperature
   • C) The presence of weak intermolecular secondary forces that allow free molecular rotation
   • D) The presence of delocalized valence electrons that move freely throughout the crystal lattice
2. 2.

   Which factor primarily explains why structural ceramics maintain their rigidity and chemical stability at much higher operating temperatures than both metals and polymers?

   • A) High-energy ionic and covalent bonds resist atomic diffusion and thermal degradation, unlike metallic bonds that allow rapid creep or covalent polymer backbones that undergo chain scission.
   • B) Highly delocalized valence electrons efficiently conduct excess thermal energy away before structural lattice bonds can rupture.
   • C) Weak secondary intermolecular interactions permit dynamic reorganization of crystalline grains without macroscopic loss of strength.
   • D) High molecular weight and chain entanglements stabilize the lattice against thermal softening up to refractory temperatures.
3. 3.

   Which property is uniquely characteristic of polymeric materials compared to conventional crystalline metals and ceramics, resulting directly from their long-chain macromolecular structure?

   • A) High electrical conductivity at room temperature due to free electron transfer
   • B) Sharp, well-defined melting temperatures governed entirely by ionic lattice energies
   • C) High resistance to plastic deformation up to extremely high operating temperatures above 2000 °C
   • D) Viscoelastic behavior exhibiting time-dependent strain and a distinct glass transition temperature
4. 4.

   Which of the following statements accurately explains why crystalline ceramics exhibit brittle fracture rather than the ductile plastic deformation typically observed in metals?

   • A) Ceramics feature delocalized valence electron clouds that restrict atomic movement and lock atoms into rigid positions under shear stress.
   • B) Ceramics consist of flexible macromolecular networks that permanently disentangle and snap upon the application of mechanical load.
   • C) Metallic lattices are held together by highly directional covalent bonds that readily cleave along close-packed crystallographic planes.
   • D) Strong directional covalent and ionic bonds in ceramics hinder dislocation motion because plane slippage forces like-charged ions into repulsive contact.
5. 5.

   Which of the following statements correctly compares the typical physical and mechanical properties of metals, ceramics, and polymers?

   • A) Ceramics generally exhibit the highest hardness and melting temperatures among the three classes, but they are brittle compared to ductile metals.
   • B) Polymers typically display higher thermal and electrical conductivities than metals because of their long macromolecular chains.
   • C) Metals generally have lower densities and lower elastic moduli than polymers due to the presence of delocalized electrons.
   • D) Ceramics readily undergo plastic deformation at room temperature because their ionic and covalent bonds allow easy dislocation motion.

Answers and step-by-step solutions appear after you finish the test.