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study help
engineering
the science and engineering of materials
Questions and Answers of
The Science And Engineering Of Materials
Determine the elastic modulus and tensile strength parallel to the fibers of Borsicreinforced aluminum for 25 volume percent fibers. Tensile strength
Explain briefly in what sporting equipment composite materials are used. What is the main reason why composites are used in these applications?
Explain briefly how continuous glass fibers are made.
What is the difference between a fiber and a whisker?
Explain briefly how boron and carbon fibers are made.
If a fiber-reinforced composite contains two separate regions of unidirectional fibers and is tested as shown, what would be the formula for the tensile strength?
What is a coupling agent? What is “sizing” as it relates to the production of glass fibers?
Explain briefly how the volume of fiber, fiber orientation, and fiber strength and modulus affect the properties of fiberreinforced composites.
What do the terms CFRP and GFRP mean?
In a fiber-reinforced composite, what is the role of the matrix?
What fiber-reinforcing materials are commonly used?
In Figure 17-2, find the largest and smallest difference in strength between Borsic and SAP and also the temperatures at which these differences occur. Strength (psi) 150,000 100,000 7075-T6 50,000
What is a fiber-reinforced composite?
If the volume fractions of parts in a composite are all identical (f1 = f2 = … = fn), but the density of each part varies, what does the rule of mixtures become algebraically?
What is a cermet? What is the role of WC and Co in a cermet?
What is a particulate composite?
What is a nanocomposite? How can certain steels containing ferrite and martensite be described as composites? Explain.
What is a dispersion-strengthened composite? How is it different from a particlereinforced composite?
Give two examples for which composites are used for non-structural applications.
Give examples for which composites are used for load-bearing applications.
What do the properties of composite materials depend upon?
Using the rule of mixtures, calculate the density of polypropylene containing 30 vol% talc filler. Compare the calculated density with the typical density for this composite and explain the
Explain the meaning of these terms: creep, stress relaxation, crazing, blushing, environmental stress cracking, and aging of polymers.
Determine the cooling rate for AISI 9310, 4320 and 1080 steels to have the same hardness. (See Figure 13-21.) Rockwell C hardness 70 60 50 40 30 20 0 4340 8640 9310 1080 10 20 Jominy distance (th of
Apparent and Bulk Density. Write a program that will ask the user to provide the information needed to calculate the apparent and bulk density of ceramic parts. The program should also calculate the
Empirical Relationships for Transformations in Steels. Heat treatment of steels depends upon knowing the A1, A3, Acm, Ms, and Mf temperatures. Steel producers often provide their customers with
The density of Al2O3 is 3.96 g/cm3. A ceramic part is produced by sintering alumina powder. It weighs 80 g when dry, 92 g after it has soaked in water, and 58 g when suspended in water. Calculate the
(a) Explain how pure copper is made.(b) What are some of the important properties of copper? (c) What is brass?(d) What is bronze? (e) Why is the Statue of Liberty green?
1. Not all aluminum alloys are easily weldable. Provide a few designations of readily weldable aluminum alloys. List some welding techniques recommended for aluminum alloys.2. List several wrought
Explain the following terms: (a) Quenching; (b) Tempering; (c) Retained austenite; and(d) Marquenching/martempering.
Explain the following: You add 100 mL water to a 500-mL round-bottom flask and heat the water until it is boiling. You remove the heat and stopper the flask, and the boiling stops. You then run cool
Water in an open beaker evaporates over time. As the water is evaporating, is the vapor pressure increasing, decreasing, or staying the same? Why?
Aluminum has an atomic radius of 143 pm and forms a solid with a cubic closest packed structure. Calculate the density of solid aluminum in g/cm3.
For each of the following pairs, predict which substance is more soluble in water.a. CH3NH2 or NH3b. CH3CN or CH3OCH3c. CH3CH2OH or CH3CH2CH3d. CH3OH or CH3CH2OHe. (CH3)3CCH2OH or CH3(CH2)6OHf.
A 1.60-g sample of a mixture of naphthalene (C10H8) and anthracene (C14H10) is dissolved in 20.0 g benzene (C6H6). The freezing point of the solution is 2.81οC. What is the composition as mass
The atomic mass of boron (B) is given in the periodic table as 10.81, yet no single atom of boron has a mass of 10.81 u. Explain.
On the basis of the general solubility rules given in Table 4.1, predict which of the following substances are likely to be soluble in water.a. Aluminum nitrateb. Magnesium chloridec. Rubidium
What are molecular orbitals? How do they compare with atomic orbitals? Can you tell by the shape of the bonding and antibonding orbitals which is lower in energy? Explain.
Describe the bonding in H2S, CH4, H2CO, and HCN using the localized electron model.
Electrons in σ bonding molecular orbitals are most likely to be found in the region between the two bonded atoms. Why does this arrangement favor bonding? In a σ antibonding orbital, where are the
Compare and contrast the MO model with the LE model. When is each useful?
Consider the heteronuclear diatomic molecule HF. Explain in detail how molecular orbital theory is applied to describe the bonding in HF.
The molecules N2 and CO are isoelectronic but their properties are quite different. Although as a first approximation we often use the same MO diagram for both, suggest how the MOs in N2 and CO might
Do lone pairs about a central atom affect the hybridization of the central atom? If so, how?
In the hybrid orbital model, compare and contrast σ bonds with π bonds. What orbitals form the σ bonds and what orbitals form the π bonds? Assume the z-axis is the internuclear axis.
As compared with CO and O2, CS and S2 are very unstable molecules. Give an explanation based on the relative abilities of the sulfur and oxygen atoms to form π bonds.
Compare and contrast bonding molecular orbitals with anti bonding molecular orbitals.
The three NO bonds in NO3- are all equivalent in length and strength. How is this explained even though any valid Lewis structure for NO3- has one double bond and two single bonds to nitrogen?
Use the localized electron model to describe the bonding in H2O.
Use the localized electron model to describe the bonding in CCl4.
Use the localized electron model to describe the bonding in C2H2 (exists as HCCH).
Give the expected hybridization of the central atom for the molecules or ions in Exercises 88 and 94 from Chapter 8. Data in Exercises 94Some of the important pollutants in the atmosphere are
Using the molecular orbital model, write electron configurations for the following diatomic species and calculate the bond orders. Which ones are paramagnetic?a. Li2b. C2c. S2
Using the molecular orbital model, write electron configurations for the following diatomic species and calculate the bond orders. Which ones are paramagnetic? Place the species in order of
Show how two 2p atomic orbitals can combine to form a σ or a π molecular orbital.
Describe the bonding in NO+, NO-, and NO using both the localized electron and molecular orbital models. Account for any discrepancies between the two models.
The transport of O2 in the blood is carried out by hemoglobin. Carbon monoxide (CO) can interfere with O2 transport because hemoglobin has a stronger affinity for CO than for O2. If CO is present,
What type of molecular orbital would result from the in-phase combination of two dxz atomic orbitals shown below? Assume the x-axis is the internuclear axis. z Z X X X
Using molecular orbital theory, explain why the removal of an electron from O2 strengthens bonding, whereas the removal of an electron from N2 weakens bonding.
Using an MO energy-level diagram, would you expect F2 to have a lower or higher first ionization energy than atomic fluorine? Why?
Draw the Lewis structures for SeO2, PCl3, NNO, COS, and PF3. Which of the compounds are polar? Which of the compounds exhibit at least one bond angle that is approximately 120°? Which of the
Draw the Lewis structures for TeCl4, ICl5, PCl5, KrCl4, and XeCl2. Which of the compounds exhibit at least one bond angle that is approximately 120°? Which of the compounds exhibit d2 sp3
A variety of chlorine oxide fluorides and related cations and anions are known. They tend to be powerful oxidizing and fluorinating agents. FClO3 is the most stable of this group of compounds and has
Which of the following statements concerning SO2 is(are) true?a. The central sulfur atom is sp2 hybridized.b. One of the sulfur–oxygen bonds is longer than the other(s).c. The bond angles about the
An unusual category of acids known as superacids, which are defined as any acid stronger than 100% sulfuric acid, can be prepared by seemingly simple reactions similar to the one below. In this
As the head engineer of your starship in charge of the warp drive, you notice that the supply of dilithium is critically low. While searching for a replacement fuel, you discover some diboron, B2.a.
Place the species B2+, B2, and B2- in order of increasing bond length and increasing bond energy.
Determine the molecular structure and hybridization of the central atom X in the polyatomic ion XY3+ given the following information: A neutral atom of X contains 36 electrons, and the element Y
It is possible to balance a paper clip on the surface of water in a beaker. If you add a bit of soap to the water, however, the paper clip sinks. Explain how the paper clip can float and why it sinks
Consider a sealed container half-filled with water. Which statement best describes what occurs in the container? a. Water evaporates until the air is saturated with water vapor; at this point,
Compare and contrast solids, liquids, and gases.
Is it possible for the dispersion forces in a particular substance to be stronger than the hydrogen bonding forces in another substance? Explain your answer.
What is a lattice? What is a unit cell? Describe a simple cubic unit cell. How many net atoms are contained in a simple cubic unit cell? How is the radius of the atom related to the cube edge length
Does the nature of intermolecular forces change when a substance goes from a solid to a liquid, or from a liquid to a gas? What causes a substance to undergo a phase change?
Why do liquids have a vapor pressure? Do all liquids have vapor pressures? Explain. Do solids exhibit vapor pressure? Explain. How does vapor pressure change with changing temperature? Explain.
What is the vapor pressure of water at 100οC? How do you know?
Why is the enthalpy of vaporization for water much greater than its enthalpy of fusion? What does this say about the changes in intermolecular forces in going from solid to liquid to vapor? What do
Which are stronger, intermolecular or intramolecular forces for a given molecule? What observation(s) have you made that support this? Explain.
Why does water evaporate?
Why is N2 a gas at room temperature? Explain why lowering the temperature allows for liquid N2 to form.
White phosphorus and sulfur are both labeled molecular solids even though each is made of only phosphorus and sulfur, respectively. Why are they molecular solids? Why isn’t diamond (which is made
The nonpolar hydrocarbon C25H52 is a solid at room temperature. Its boiling point is greater than 400°C. Which has the stronger intermolecular forces, C25H52 or H2O? Explain.
Hydrogen bonding is a special case of very strong dipole– dipole interactions possible among only certain atoms. What atoms in addition to hydrogen are necessary for hydrogen bonding? How does the
Which gas, CO or N2, is expected to behave more ideally at 10 atm and –50°C?
The conductivity of silicon is enhanced by doping. What is doping?
Atoms are assumed to touch in closest packed structures, yet every closest packed unit cell contains a significant amount of empty space. Why?
Describe what is meant by a dynamic equilibrium in terms of the vapor pressure of a liquid.
A common response to hearing that the temperature in New Mexico is 105οF is, “It’s not that bad; it’s a dry heat,” whereas at the same time the summers in Atlanta, Georgia, are characterized
When a person has a severe fever, one therapy used to reduce the fever is an “alcohol rub.” Explain how the evaporation of alcohol from a person’s skin removes heat energy from the body.
Why is a burn from steam typically much more severe than a burn from boiling water?
When wet laundry is hung on a clothesline on a cold winter day, it will freeze but eventually dry. Explain.
Packaged foods that require cooking in boiling water often contain special directions for use at high elevations. Typically these directions indicate that the food should be cooked longer above 5000
A common prank on college campuses is to switch the salt and sugar on dining hall tables, which is usually easy because the substances look so much alike. Yet, despite the similarity in their
The second-order diffraction (n = 2) for a gold crystal is at an angle of 22.20ο for X rays of 154 pm. What is the spacing between these crystal planes?
Iron has a density of 7.86 g/cm3 and crystallizes in a bodycentered cubic lattice. Show that only 68% of a body-centered lattice is actually occupied by atoms, and determine the atomic radius of
Selenium is a semiconductor used in photocopying machines. What type of semiconductor would be formed if a small amount of indium impurity is added to pure selenium?
What is the formula for the compound that crystallizes with a cubic closest packed array of sulfur ions, and that contains zinc ions in 1/8 of the tetrahedral holes and aluminum ions in 1/2 of the
A certain metal fluoride crystallizes in such a way that the fluoride ions occupy simple cubic lattice sites, while the metal ions occupy the body centers of half the cubes. What is the formula of
Diethyl ether (CH3CH2OCH2CH3) was one of the first chemicals used as an anesthetic. At 34.6οC, diethyl ether has a vapor pressure of 760. torr, and at 17.9οC, it has a vapor pressure of 400. torr.
The molar heat of fusion of sodium metal is 2.60 kJ/mol, whereas its heat of vaporization is 97.0 kJ/mol. a. Why is the heat of vaporization so much larger than the heat of fusion?b. What
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