材料科学与工程专业(第四版)英语翻译(1,2,3,5,6,7单元)(4)

1.3 What are some of the important properties of each of the five main classes of engineering materials? Answer1.3: Metallic Materials

? many are relatively strong and ductile at room temperature ? some have good strength at high temperature

? most have relatively high electrical and thermal conductivities

Polymeric Materials

? generally are poor electrical and thermal conductors ? most have low to medium strengths ? most have low densities

? most are relatively easy to process into final shape ? some are transparent Ceramic Materials

? generally have high hardness and are mechanically brittle ? some have useful high temperature strength

? most have poor electrical and thermal conductivities

Composite Materials

? have a wide range of strength from low to very high

? some have very high strength-to-weight ratios (e.g. carbon-fiber epoxy materials) ? some have medium strength and are able to be cast or formed into a variety of sha (e.g. fiberglass-polyester materials)

? some have useable strengths at very low cost (e.g. wood and concrete)

Electronic Materials

? able to detect, amplify and transmit electrical signals in a complex manner ? are light weight, compact and energy efficient

1.8 What are nanomaterials? What are some proposed advantages of using nanomaterials over their conventional counterparts?

Answer1.8: Are defined as materials with a characteristic length scale smaller than 100 nm. The length scale could be particle diameter, grain size in a material, layer thickness in a sensor, etc. These materials have properties different than that at bulk scale or at the

molecular scale. These materials have often enhanced properties and characteristics because of their nano-features in comparison to their micro-featured counterparts. The structural, chemical, electronic, and thermal properties (among other characteristics) are often enhanced at the nano-scale.

Homework 2

Chapter 3, Problem 4

What are the three most common metal crystal structures? List five metals that have each of these crystal structures. Chapter 3, Solution 4

The three most common crystal structures found in metals are: body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP). Examples of metals having these structures include the following. BCC:

??iron,vanadium, tungsten, niobium, and chromium.

FCC: copper, aluminum, lead, nickel, and silver. HCP: magnesium,

Chapter 3, Problem 5

For a BCC unit cell, (a) how many atoms are there inside the unit cell, (b) what is the coordination number for the atoms, (c) what is the relationship between the length of the side a of the BCC unit cell and the radius of its atoms, and (d) APF = 0.68 or 68%

Chapter 3, Solution 5

(a) A BCC crystal structure has two atoms in each unit cell. (b) A BCC crystal structure has a coordination number of eight. (c) In a BCC unit cell, one complete atom and two atom eighths touch each other along the cube diagonal.

This geometry translates into the relationship

Chapter 3, Problem 6

For an FCC unit cell, (a) how many atoms are there inside the unit cell, (b) What is the coordination number for the atoms, (c)

??titanium,zinc, beryllium, and cadmium.

?4R.

a?

4R2

, and (d) what is the atomic packing factor?

Chapter 3, Solution 6

(a) Each unit cell of the FCC crystal structure contains four atoms. (b) The FCC crystal structure has a

coordination number of twelve. (d) By definition, the atomic packing factor is given as:

Atomic packing factor?

volume of atoms in FCC unit cell

volume of the FCC unit cell

These volumes, associated with the four-atom FCC unit cell, are

?4?16

Vatoms?4??R3???R3

?3?3

and Vunit cell

?a3

, where a represents the lattice constant.

Substituting

a?

Vunit cell

3

?a?

3

The atomic packing factor then becomes,

?16?R3?APF (FCC unit cell)???=0.74 ??3??32R?

Chapter 3, Problem 7

For an HCP unit cell (consider the primitive cell), (a) how many atoms are there inside the unit cell, (b) What is the coordination number for the atoms, (c) what is the atomic packing factor, (d) what is the ideal c/a ratio for HCP metals, and (e) repeat a through c considering the “larger” cell.

Chapter 3, Solution 7

The primitive cell has (a) two atoms/unit cell; (b) The coordination number associated with the HCP crystal structure is twelve. (c)the APF is 0.74 or 74%; (d) The ideal c/a ratio for HCP metals is 1.633; (e) all answers remain the same except for (a) where the new answer is 6.

Homework 3 Chapter 3, Problem 25

Lithium at 20?C is BCC and has a lattice constant of 0.35092 nm. Calculate a value for the atomic radius of a lithium atom in nanometers.

Chapter 3, Solution 25

For the lithium BCC structure, which has a lattice constant of a = 0.35092 nm, the atomic radius is, …… 此处隐藏：2720字，全部文档内容请下载后查看。喜欢就下载吧 ……