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engineering
the science and engineering of materials
Questions and Answers of
The Science And Engineering Of Materials
A magnetic material has a coercive field of 167 Aym, a saturation magnetization of 0.616 tesla, and a residual inductance of 0.3 tesla. Sketch the hysteresis loop for the material.
A magnetic material has a coercive field of 10.74 A/m, a saturation magnetization of 2.158 tesla, and a remanance induction of 1.183 tesla. Sketch the hysteresis loop for the material.
Give the electron configuration of the pure elements in Table 20-3. Material Gadolinium Nd₂Fe₁2B Nickel BaO 6Fe₂O3 Co-Sm . Curie Temperature (°C) 16 312 358 469 747 Material Iron Alnico
Using Figure 20-17, determine the following properties of the magnetic material: remanance, saturation magnetization, coercive field, initial permeability, maximum permeability, and power (maximum BH
In Figure 20-9(b), what materials have the highest and lowest saturation magnetizations and coercivities? Square loop for computer applications Inductance (a) Soft magnet for electrical
Use the data in Table 20-4 to correlate maximum permeability with coercivity. Is there a potential trend? Name Ingot iron Low-carbon steel Silicon iron, unoriented Silicon iron, grain-oriented 4750
Sketch the M-H loop for Fe at 300 K, 500 K, and 1000 K.
Define the terms soft and hard magnetic materials. Draw a typical M-H loop for each material.
Use the data in Table 20-6 to see if there is a possible relationship between BHmax and the Curie temperature. Material Fe-Co Fe-Co-Al-Ni BaFe
What important characteristics are associated with soft magnetic materials?
Estimate the power of the Co5Ce material shown in Figure 20-14. Co-Sm Cosce -8,000 -6,000 -4,000 -2,000 Demagnetizing field (oersted) 10,000 8,000 6,000 4,000 2,000 Magnetization (gauss)
Are materials used for magnetic data storage magnetically hard or soft? Explain.
Give examples of materials used in magnetic recording.
What are the advantages of using Fe- Nd-B magnets? What are some of their disadvantages?
What is the maximum magnetic power for Co-γ-Fe2O3?
A multi-layer capacitor is to be designed using a relaxor ferroelectric formulation based on lead magnesium niobate (PMN). The apparent dielectric constant of the material is 20,000. Calculate the
Calculate the capacitance of a parallelplate capacitor containing five layers of mica for which each mica sheet is 1 cm x 2 cm x 0.005cm. The layers are connected in parallel.
For the 14 materials with both a dielectric strength and resistivity listed in Table 19-7, plot the dielectric strength as a function of resistivity. Assume log average values for the resistivity
Define the following terms: electrostriction, piezoelectricity (define both its direct and converse effects), and ferroelectricity.
Suppose we are able to produce a polarization of 5 x 10-8 C/m2 in a cube (5 mm side) of barium titanate. Assume a dielectric constant of 3000. What voltage is produced?
A 2-mm-thick alumina dielectric is used in a 60 Hz circuit. Calculate the voltage required to produce a polarization of 5 x 10-7 Cym2.
Calculate the displacement of the electrons or ions for the following conditions: (a) Electronic polarization in nickel of 2 x 10-7 C/m2;(b) Electronic polarization in aluminum of 2 x
With respect to mechanical behavior, we have seen that stress (a cause) produces strain (an effect). What is the electrical analog of this?
Can polymers be semiconducting? What would be the advantages in using these instead of silicon?
How do the touch screen displays on some computers work?
What are ionic conductors? What are their applications?
Calculate the electrical conductivity of a fiber-reinforced polyethylene part that is reinforced with 20 vol % of continuous, aligned nickel fibers.
If we want the resistivity of a nylon to be 104 ohm · cm, what weight percent carbon fibers should be added?
Silicon is the material of choice for the substrate for integrated circuits. Explain why silicon is preferred over germanium, even though the electron and hole mobilities are much higher and the
Investigate the scaling relationship known as Moore’s Law. Is it expected that this trend will continue to be followed in the future using established microelectronics fabrication techniques? If
How can we make LEDs that emit white light (i.e., light that looks like sunlight)?
Design a light-emitting diode that will emit at 1.12 micrometers. Is this wavelength in the visible range? What is a potential application for this type of LED?
When a voltage of 5 mV is applied to the emitter of a transistor, a current of 2 mA is produced. When the voltage is increased to 8 mV, the current through the collector rises to 6 mA. By what
At room temperature, will the conductivity of silicon doped with 1017 cm-3 of arsenic be greater than, about equal to, or less than the conductivity of silicon doped with 1017 cm-3 of
Determine the electrical conductivity of silicon when 0.0001 at% antimony is added as a dopant and compare it to the electrical conductivity when 0.0001 at% indium is added.
Calculate the electrical conductivity of silicon doped with 1018 cm-3 boron at room temperature. Compare the intrinsic carrier concentration to the dopant concentration.
Calculate the intrinsic carrier concentration for GaAs at room temperature. Given that the effective mass of electrons in GaAs is 0.067me, where me is the mass of the electron, calculate the
Determine the amount of arsenic that must be combined with 1 kg of gallium to produce a p-type semiconductor with an electrical conductivity of 500 ohm-1 · cm-1 at 25°C. The lattice
Estimate the electrical conductivity of silicon doped with 0.0002 at% arsenic at 600°C, which is above the plateau in the conductivity-temperature curve.
We would like to produce an extrinsic germanium semiconductor having an electrical conductivity of 2000 ohm-1 · cm-1. Determine the amount of phosphorus and the amount of gallium required to
Report the temperature range (in°C) for which the sample in Figure 19-15 behaves as an extrinsic semiconductor. Intrinsic 1 Extrinsic Slope =-Eg/2kB) Intrinsic (n;) 2 High temperatures 1000/T
For germanium and silicon, compare the temperatures required to double the electrical conductivities from the room temperature values.
For germanium and silicon, compare, at 25°C, the number of charge carriers per cubic centimeter, the fraction of the total electrons in the valence band that are excited into the conduction band,
What is radiative and nonradiative recombination? What types of materials are used to make LEDs?
Explain the following terms: semiconductor, intrinsic semiconductor, extrinsic semiconductor, elemental semiconductor, compound semiconductor, direct bandgap semiconductor, and indirect bandgap
The electrical resistivity of a beryllium alloy containing 5 at% of an alloying element is found to be 50 x 10-6 ohm · cm at 400° C. Determine the contributions to resistivity due to
(a) Copper and nickel form a complete solid solution. Draw a schematic diagram illustrating the resistivity of a copper and nickel alloy as a function of the atomic percent nickel. Comment on why the
Find the resistivity of palladium at 443°C if it has a defect contribution of 1.02 x 10-7 ohm · cm.
After finding the electrical conductivity of cobalt at 0°C, we decide we would like to double that conductivity. To what temperature must we cool the metal?
The electrical resistivity of pure chromium is found to be 18 x 10-6 ohm . cm. Estimate the temperature at which the resistivity measurement was made.
Calculate the electrical conductivity of nickel at 250°C and at 1500°C.
Calculate the electrical conductivity of platinum at 2200°C.
Calculate the resistivities of cobalt and beryllium at 505 K.
A typical thickness for a copper conductor (known as an interconnect) in an integrated circuit is 250 nm. The mean free path of electrons in pure, annealed copper is about 40 nm. As the thickness of
Draw a schematic of the band structures of an insulator, a semiconductor, and a metal. Use this to explain why the conductivity of pure metals decreases with increasing temperature, while the
In a welding process, a current of 400 A flows through the arc when the voltage is 35 V. The length of the arc is about 0.1 in., and the average diameter of the arc is about 0.18 in. Calculate the
We apply 10 V to an aluminum wire 2 mm in diameter and 20 m long. If 10% of the valence electrons carry the electrical charge, calculate the average drift velocity of the electrons in km⁄h and
A current density of 5000 A⁄cm2 flows through a magnesium wire. If half of the valence electrons serve as charge carriers, calculate the average drift velocity of the electrons.
If the current density is 1.25 A⁄cm2 and the drift velocity is 107 cm⁄s, how many charge carriers are present?
Ag has an electrical conductivity of 6.80 x 105 Ω–1 · cm-1. Au has an electrical conductivity of 4.26 x 105 Ω-1 · cm-1. Calculate the number of charge carriers per unit volume
We would like to produce a 5000-ohm resistor from boron-carbide fiber having a diameter of 0.1 mm. What is the required length of the fiber?
A current density of 100,000 A⁄cm2 flows through a gold wire 50 m in length. The resistance of the wire is found to be 2 ohm. Calculate the diameter of the wire and the voltage applied to the
Of the metals listed in Table 19-1, which are the most and least conductive? Material Superconductors Hg, Nb3Sn YBa₂Cu3O7-x MgB₂ Metals Alkali metals Na K Alkali earth metals Mg Ca Group 3B
The power lost in a 2-mm-diameter copper wire is to be less than 250 W when a 5 A current is flowing in the circuit. What is the maximum length of the wire?
A 0.5-mm-diameter fiber, 1 cm in length, made from boron nitride is placed in a 120-Ω circuit. Using Table 19-1, calculate(a) The current flowing in the circuit; and(b) The number of electrons
A current of 10 A passes through a 1-mmdiameter wire 1000 m long. Calculate the power loss if the wire is made from(a) Aluminum and(b) Silicon Material Superconductors Hg,
A wire two microns in diameter is made from 10 cm silver, 0.1 cm gallium, and 10 cm silver all joined end to end (i.e., in series). Assume the joints are perfect and have no additional resistance.
Find the resistance of a fiber with a crosssectional area of 1.34 mm2 and length of 10 cm that is subjected to a voltage of 225 V for which the current density is 1.25 A⁄cm2. Assume the resistor is
1. Calculate the resistivity of pure iridium at 673 K using its temperature resistivity coefficient.2. Electrical conductivity is sometimes given in the units of %IACS. What does IACS stand for?
Concrete Canoe Design. Describe what novel materials can be used to make a concrete canoe.
The binder used in producing asphalt has a density of about 1.3 g/cm3. Design an asphalt, including the weight and volumes of each constituent, that might be suitable for use as pavement. Assume that
We would like to produce a concrete sculpture. The sculpture will be as thin as 3 in. in some areas and should be light in weight, but it must have a 28-day compressive strength of at least 2000 psi.
We would like to produce a concrete that is suitable for use in building a large structure in a sulfate environment. For these situations, the maximum water-cement ratio should be 0.45 (by weight).
Design a wood floor that will be 50 ft by 50 ft and will be in an environment in which humidity changes will cause a fluctuation of plus or minus 5% water in the wood. We want to minimize any
A wooden structure is functioning in an environment controlled at 65% humidity. Design a wood support column that is to hold a compressive load of 20,000 lb. The distance from the top to the bottom
We plan to prepare 10 yd3 of concrete using a 1:2.5:4.5 weight ratio of cement–sand–coarse aggregate. The water–cement ratio (by weight) is 0.45. The sand contains 3 wt% water; the coarse
We have been asked to prepare 100 yd3 of normal concrete using a volume ratio of cement–sand–coarse aggregate of 1:2:4. The water–cement ratio (by weight) is to be 0.5. The sand contains 6 wt%
Calculate the amount of cement, sand, aggregate, and water needed to create a concrete mix with a 28-day compressive strength of 34 MPa for a 10 m x 10 m x 0.25 m structure given the following
Determine the amounts of water, cement, and sand in 10 m3 of concrete if the cement–sand–aggregate ratio is 1:2.5:4.5 and the water–cement ratio is 0.4. Assume that no air is entrained
What is the maximum water to cement ratio acceptable for a structure that must have a final compressive strength of at least 5 ksi? Compressive strength (psi) 8000 6000 4000 2000 0.3 28 days 7 days 3
A wall 30 feet long is built using radial longitudinal cuts of 5-in. wide pine with the boards arranged in a vertical fashion. The wood contains a moisture content of 55% when the wall is built;
Boards of maple 1 in. thick, 6 in. wide, and 16 ft long are used as the flooring for a 60 ft x 60 ft hall. The boards were cut from logs with a tangential-longitudinal cut. The floor is laid when the
Boards of oak 0.5 cm thick, 1 m long, and 0.25 m wide are used as flooring for a 10 m x 10 m area. If the floor was laid at a moisture content of 25% and the expected moisture could be as high as
Use Table 18-1 to determine if there is a relationship between density and the elastic modulus of the woods listed. Wood Cedar Pine Fir Maple Birch Oak Density (for 12% Water)
Determine the expansion in the radial direction of cedar when it changes from 12% to 27% water content. The initial dimension is 1 ft.
Table 18-1 lists the densities for typical woods. Calculate the densities of the woods after they are completely dried and at 100% water content. Wood Cedar Pine Fir Maple Birch Oak Density (for
A green wood with a density of 0.82 g/cm3 contains 150% water. The compressive strength of this wood is 27 MPa. After several days of drying, the compressive strength increases to 41 MPa. What is the
The density of a sample of oak is 0.90 g/cm3. Calculate(a) The density of completely dry oak and(b) The percent water in the original sample.
A sample of wood with the dimensions 3 in. x 4 in. x 12 in. has a dry density of 0.35 g/cm3.(a) Calculate the number of gallons of water that must be absorbed by the sample to contain 120% water.(b)
1. What is the difference in lignin content between hardwood and softwood species? What is the chemical structure of lignin?2. The equilibrium moisture content of wood is the moisture content at
Calculate the steepest and the shallowest apparent (i.e., linear) slopes of the lines in Figure 17-26 and identify the materials to which they belong. Specific strength (x 106
Properties of a Laminar Composite. Write a computer program (or use spreadsheet software) to calculate the properties of a laminar composite. For example, if the user provides the value of the
What factors will have to be considered in designing a bicycle frame using an aluminum frame and a frame made using C-C composite?
Design an electrical-contact material and a method for producing the material that will result in a density of no more than 6 g/cm3, yet at least 50 vol% of the material will be conductive.
Design the materials and processing required to produce a discontinuous, but aligned, fiber-reinforced fiberglass composite that will form the hood of a sports car. The composite should provide a
What is a laminar composite?
Find the materials with the highest numerical values for each of the following six properties in Table 17-2: (a) Density; (b) Tensile strength;(c) Elastic modulus; (d) Melting
Determine the ratio of the cross-sectional area of fiber to filament in both images in Figure 17-18. DOO( (a) (b)
What are the advantages of using ceramicmatrix composites?
Plot seven equally spaced points from the curve in Figure 17-11 and find a non-polynomial equation to fit the line that has an R2 value of at least 0.900. Tensile strength
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