Structure and Properties of Metals ( l.u . 2/8/10)

1. Structure and Properties of Metals (l.u. 2/8/10)

2. General Material Questions Engr 241 What is passivation? What causes passivation? Is this good or bad? Have you ever seen passivation? What material has a higher stiffness, AL or carbon fiber? What material has a higher tensile strength, carbon fiber or diamond? How would you describe the behavior of lead when compressed at room temperature versus zinc?

3. Strength Problem Engr 241 What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this? What is the pulling force if the rod DIA = .5?

4. Strength Problem Engr 241 What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this? F=pA 1 lb = 4.448 N 1 m = 39.37 in 1 Pa = 1 N/m2 A = πr2

5. Density • Material weight per unit volume, related to atomic weight, radius and packing. • Sometimes expressed in proportion to the density of water (specific gravity = Sg). • SI: kg/m³, USCS: lb/in³ • Specific Strength (strength-to-weight ratio) • Specific Stiffness (stiffness-to-weight ratio) Engr 241

6. Sg H2O (seawater) = 1.03Sg oil (SAE grade) = .87-.89 Engr 241

7. Density Questions Engr 241 What has a higher specific gravity, lead or tungsten? Determine the density of copper in lb/inches cubed? How many ounces per cubic inch is this? What percentage more is the density of Tungsten?

8. Thermal Properties • Temperature: ”the tendency of an object to absorb or dissipate energy in the form of heat" • “Heat is simply another form of energy that can be measured only in terms of the effect it produces” (Tippens, 1992, p. 321) • Heat is not a substance – it is energy that is given up or absorbed • Molecules move differently in different materials Engr 241

9. 9 = ) + o o F ( C 32 5 Thermal Properties • Temperature Conversions (Scales) • Relative: referenced to physical phenomena (freezing-boiling point of water) • SI: Celsius (°C), USCS: Fahrenheit (°F) • scales coincide at -40° Engr 241

10. Thermal Properties • Temperature Conversions (Scales) • Absolute: referenced to minimal achievable temperature (atomic motion ceases) • SI: Kelvin (°K), USCS: Rankine (°R) °K=(°C+273) °R=(°F+460) Engr 241

11. Thermal Properties • Melting Point: “energy required to separate the atoms” • Pure Metals: one defined melting point. • Alloys: wide range of temperatures. • Mercury’s melting point = -39 degrees C Engr 241

12. Thermal Properties where: Q = heat capacity m = mass cp= specific heat T = change in temperature Engr 241 • Specific Heat: “energy required to change the temperature of a unit of mass by 1°” (amount) • The lower the specific heat, the faster the temperature will rise in material. • SI: cal/(g °C), USCS: BTU/(lb °F)

13. Thermal Properties • Thermal Conductivity: “heat flow within the material” (how fast) • Through convection (e.g. ac), conduction (e.g. boil water), and radiation (e.g. sunlight) • Metals: high conductivity • Non-Metals: poor conductivity (e.g. insulators) • SI: cal/s or W, USCS: BTU/s Engr 241

14. Thermal Properties • Using Thermal Conductivity T L Q = kAt Material k (BTU) Silver 1451 Brass 750 Copper 2660 Silver 2870 Steel 320 Brick 5 Concrete 5.6 where: Q = energy transfer rate (BTU) k = thermal conductivity constant (1 W/m K = 6.94 BTU in/ft2 h F) A= area (sq ft) t = time (hr) T = change in temperature (F) L = thickness (in) • Engr 241

15. Thermal Problems Engr 241 What is the r-value of aluminum? A 1 inch thick cooler separates an inside temperature of 8° C and outside temperature of 36° C. How much heat (in BTU’s) is lost through a 10 ft2 area over the course of an hour? Let A represent the area in square feet Let ۲ represent the time of 1 hour Let L be the thickness of the wall in inches Let k be the thermal conductivity constant, for styrofoam = .033 (W/m K)

16. Thermal Properties • Thermal Expansion: “atomic motion linked to temperature gradient” • Constant Mass, Increase in Volume • Thermal Stresses, Fatigue, and Shock • Dimensional Accuracy • Modulus of Elasticity Engr 241

17. Thermal Properties • Thermal Expansion where: L = change in length  = coefficient of expansion L= length T = change in temperature www.concrete.org Engr 241

18. Thermal Expansion Questions Engr 241 What has a higher rate of expansion, steel or tungsten? Calculate the linear expansion (in inches) of a bar of aluminum at 30 degrees C if the initial length of the bar is 10 m at 10 degrees C. What are the equivalent Fahrenheit temperatures for this expansion? Let ∞ represent alpha (coefficient of linear expansion) for aluminum = 23.6x10-6/° C ∆L is the respective change in length in meters ∆t is the change in temperature to cause length change

19. Electric and Magnetic Properties • Conduction: electric flow within the material • SI: 1/ohm-m, USCS: 1/ohm-ft • 1/ohm = mho • Resistivity (dielectrics/insulators) • Superconductors: near zero resistivity at certain temperatures • Semiconductors: solid state devices (impurities/conductivity control) • Common Magnetic metals: Iron, cobalt, nickel Engr 241

20. Material Deterioration • Corrosion: deterioration of metals and ceramics • Degradation: plastics (thermal aging/degradation) • Passivation: protective hard oxide film – chromium in metals • Rust: oxidation of steels or cast iron (magickcanoe.com) Engr 241 (www.landerholm.us)

21. Copper Oxidation (mentaldimensions.files.wordpress.com) Engr 241