Question

The thermal expansion of aluminum is plotted against temperature in the figure below. Measure the plot at 800 K and see how well the result compares with the data in the table below. (a) (b) (a) The overall thermal expansion (ΔL>L) of aluminum is measurably greater than the lattice parameter expansion (Δa>a) at high temperatures because vacancies are produced by thermal agitation. (b) A semilog (Arrhenius-type) plot of ln (vacancy concentration) versus 1/T based on the data of part (a). The slope of the plot (−EV/k) indicates that 0.76 eV of energy is required to create a single vacancy in the aluminum crystal structure. Values of Linear Coefficient of Thermal Expansion for a Variety of Materials α[mm/(mm⋅ ∘C)×106] Material Temperature = 27 ∘C ( 300 K ) 527 ∘C ( 800 K ) 0 - 1000 ∘C Metals Aluminum 23.2 33.8 Copper 16.8 20.0 Gold 14.1 16.5 Nickel 12.7 16.8 Silver 19.2 23.4 Tungsten 4.5 4.8 Ceramics and glasses Mullite (3Al2O3⋅2SiO2) 5.3 Porcelain 6.0 Fireclay refractory 5.5 Al2O3 8.8 Spinel (MgO⋅Al2O3) 7.6 MgO 13.5 UO2 10.0 ZrO2 (stabilized) 10.0 SiC 4.7 Silica glass 0.5 Soda-lime-silica glass 9.0 Polymers Nylon 66 30-31 Phenolic 30-45 Polyethylene (high-density) 149−301 Polypropylene 68−104 Polytetrafluoroethylene (PTFE) 99

They are in exact agreement.They are in moderate agreement.They are not in agreement.

Answer 1