Question

Q2B / Complete the following: ( 15 marks)

1-Advanced materials are ............ , .......... , ............. , and ...............

2-As the atomic number is increased, the melting point is ..................

3 -Covalent bond is very strong because ..................

4- The relationship between vacancies number and tem.is .................

5- Nano- fibers are used for ............., .............., and ...............

6-The difference between soft and permanent magnets is ......................

7- Cast iron has lower toughness than steel because ..................

8-Cobalt has density of ......, melting temp. of ...... and can be classified to........

9- Cermets mean ..................

10-Exrinisic has energy gap of .................ev

Answer 1

1. Advanced materials are  light metals (titanium and aluminium)  ,  composites of  carbon fiber and Kevlar , steels (trip steels and dual phase steels) .

2. As the atomic number of elements increases, the melting point increases because there are more electrons around the nucleus, which creates a stronger negatively-charged force.

3.Covalent bonds are very stronger because they are formed by the sharing of electrons. Because this effects completes the outer, valence shells of both atoms leading to a stable configuration.

4.The relationship between vacancies number and temperature is

where n_v - equilibrium concentration of vacancies .

T - Temperature

ΔGv -  change in Gibb’s free energy

the above equation says that a crystal to be in equilibrium it has to contain a certain concentration of vacancies. The typical formation energy of vacancies in metals is of the order of 1 eV. For example, a copper metal contains an equilibrium vacancy density of 1.85 x10⁵ per cubic centimeter at 293 K. The equilibrium density increases to 1.41 x 10¹⁹ per cubic centimeter at its melting point. The increase in vacancy with temperature increases.

5.Nano- fibers are used for tissue engineering, drug delivery, cancer diagnosis, lithium-air battery, optical sensors and air filtration.

6.The difference between a permanent magnet and a soft magnet is in their atomic structures. Permanent magnets have their atoms aligned all the time. Soft magnets have their atoms aligned only while under the influence of a strong external magnetic field.

7.Cast iron has lower toughness than steel because cast Iron has high compression strength than steel ,hence doesn't looses shape.

8.Cobalt has density of 8.86 grams/cm³, melting temp. of 1,495 ^oC ( 2,723 ^oF )  and can be classified as Transition Metal which are located in Groups 3 - 12 of the Periodic Table.

9. Cermets means a class of heat-resistant materials made of ceramic and sintered metal.

10.Exrinisic has energy gap of nearly equal to 1 eV .