A research team must select a solid material to serve as an electrical insulator inside a high-temperature furnace (operating at 1 200 K). Four candidate solids are under consideration:
1. Magnesium oxide (MgO)
2. Silicon dioxide (SiO2, quartz form)
3. Polyethylene (—CH2— chains in a crystalline molecular solid)
4. Aluminum (Al)
Relevant macroscopic property data collected at 300 K are provided.
Property MgO SiO2 Polyethylene Aluminum
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Melting point / K 3 120 1 990 420 933
Electrical conductivity None None None High
Hardness High Moderate Low Moderate
Assume that relative trends in these properties persist up to 1 200 K unless melting occurs.
(a) From the list, identify the solid that is least suitable for use as the furnace insulator at 1 200 K. Provide two distinct property-based reasons for its elimination.
(b) Between MgO and SiO2, determine which solid is the stronger candidate for the application. Construct a comparative argument that references at least two different macroscopic properties and links each property to the underlying type of bonding or lattice structure.
(c) The team ultimately selects your recommended material and discovers that microscopic cracks form after multiple thermal cycles. Suggest one structural modification or material processing strategy that could mitigate crack formation, and briefly explain the chemical reasoning behind your suggestion.