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

General Material Questions What is passivation? What causes passivation? Is this good or bad? Have you ever seen passivation? 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 stiffness, AL or carbon fiber? What material has a higher tensile strength, carbon fiber or diamond? 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? How would you describe the behavior of lead when compressed at room temperature versus zinc? 1Engr 241

Strength Problem What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this? 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? What is the pulling force if the rod DIA =.5? 2Engr 241

Strength Problem What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this? 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 F=pA 1 lb = N 1 lb = N 1 m = in 1 m = in 1 Pa = 1 N/m 2 1 Pa = 1 N/m 2 A = π r 2 A = π r 2 3Engr 241

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

5Engr 241 Sg H2O (seawater) = 1.03 Sg oil (SAE grade) =

Density Questions What has a higher specific gravity, lead or tungsten? 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? 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? 6Engr 241

7 Thermal Properties Temperature: ”the tendency of an object to absorb or dissipate energy in the form of heat" 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 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 Heat is not a substance – it is energy that is given up or absorbed Molecules move differently in different materials Molecules move differently in different materials

8Engr 241 Temperature Conversions (Scales) Temperature Conversions (Scales) Relative: referenced to physical phenomena (freezing-boiling point of water) Relative: referenced to physical phenomena (freezing-boiling point of water) SI: Celsius (°C), USCS: Fahrenheit (°F) SI: Celsius (°C), USCS: Fahrenheit (°F) scales coincide at -40° scales coincide at -40° Thermal Properties oo FC  (

9Engr 241 Thermal Properties Temperature Conversions (Scales) Temperature Conversions (Scales) Absolute: referenced to minimal achievable temperature (atomic motion ceases) Absolute: referenced to minimal achievable temperature (atomic motion ceases) SI: Kelvin (°K), USCS: Rankine (°R) SI: Kelvin (°K), USCS: Rankine (°R) °K=(°C+273)°R=(°F+460)

10Engr 241 Melting Point: “energy required to separate the atoms” Melting Point: “energy required to separate the atoms” Pure Metals: one defined melting point. Pure Metals: one defined melting point. Alloys: wide range of temperatures. Alloys: wide range of temperatures. Mercury’s melting point = -39 degrees C Mercury’s melting point = -39 degrees C Thermal Properties

11Engr 241 Thermal Properties where: Q= heat capacity m= mass c p = specific heat  T= change in temperature Specific Heat: “energy required to change the temperature of a unit of mass by 1°” (amount) 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. The lower the specific heat, the faster the temperature will rise in material. SI: cal/(g °C), USCS: BTU/(lb °F) SI: cal/(g °C), USCS: BTU/(lb °F)

12Engr 241 Thermal Conductivity: “heat flow within the material” (how fast) Thermal Conductivity: “heat flow within the material” (how fast) Through convection (e.g. ac), conduction (e.g. boil water), and radiation (e.g. sunlight) Through convection (e.g. ac), conduction (e.g. boil water), and radiation (e.g. sunlight) Metals: high conductivity Metals: high conductivity Non-Metals: poor conductivity (e.g. insulators) Non-Metals: poor conductivity (e.g. insulators) SI: cal/s or W, USCS: BTU/s SI: cal/s or W, USCS: BTU/s Thermal Properties

13Engr 241 Using Thermal Conductivity Using Thermal Conductivity Thermal Properties where: Q= energy transfer rate (BTU) k= thermal conductivity constant (1 W/m K = 6.94 BTU in/ft 2 h F) A= area (sq ft) t = time (hr)  T= change in temperature (F) L= thickness (in) Q = kAt TLTL Materialk (BTU) Silver 1451 Brass 750 Copper 2660 Silver 2870 Steel 320 Brick 5 Concrete 5.6

Thermal Problems What is the r-value of aluminum? 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 ft 2 area over the course of an hour? 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 ft 2 area over the course of an hour? Let A represent the area in square feet Let A represent the area in square feet Let ۲ represent the time of 1 hour Let ۲ represent the time of 1 hour Let L be the thickness of the wall in inches Let L be the thickness of the wall in inches Let k be the thermal conductivity constant, for styrofoam =.033 (W/m K) Let k be the thermal conductivity constant, for styrofoam =.033 (W/m K) 14Engr 241

15Engr 241 Thermal Expansion: “atomic motion linked to temperature gradient” Thermal Expansion: “atomic motion linked to temperature gradient” Constant Mass, Increase in Volume Constant Mass, Increase in Volume Thermal Stresses, Fatigue, and Shock Thermal Stresses, Fatigue, and Shock Dimensional Accuracy Dimensional Accuracy Modulus of Elasticity Modulus of Elasticity Thermal Properties

16Engr 241 Thermal Expansion Thermal Expansion Thermal Properties where:  L= change in length  = coefficient of expansion L= length  T= change in temperature Materialα (Alpha) /°C Aluminum2.4 Brass1.8 Concrete Copper1.7 Glass/Pyrodex.3 Iron1.2 Lead3 Silver2.0 Steel1.2 Zinc2.6

Thermal Expansion Questions What has a higher rate of expansion, steel or tungsten? 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? 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 Let ∞ represent alpha (coefficient of linear expansion) for aluminum = 23.6x10 -6 /° C ∆L is the respective change in length in meters ∆L is the respective change in length in meters ∆t is the change in temperature to cause length change ∆t is the change in temperature to cause length change 17Engr 241

18Engr 241 Electric and Magnetic Properties Conduction: electric flow within the material Conduction: electric flow within the material SI: 1/ohm-m, USCS: 1/ohm-ft SI: 1/ohm-m, USCS: 1/ohm-ft 1/ohm = mho 1/ohm = mho Resistivity (dielectrics/insulators) Resistivity (dielectrics/insulators) Superconductors: near zero resistivity at certain temperatures Superconductors: near zero resistivity at certain temperatures Semiconductors: solid state devices (impurities/conductivity control) Semiconductors: solid state devices (impurities/conductivity control) Common Magnetic metals: Iron, cobalt, nickel Common Magnetic metals: Iron, cobalt, nickel

19Engr 241 Material Deterioration Corrosion: deterioration of metals and ceramics Corrosion: deterioration of metals and ceramics Degradation: plastics (thermal aging/degradation) Degradation: plastics (thermal aging/degradation) Passivation: protective hard oxide film – chromium in metals Passivation: protective hard oxide film – chromium in metals Rust: oxidation of steels or cast iron Rust: oxidation of steels or cast iron (magickcanoe.com ) (

Copper Oxidation 20Engr 241 (mentaldimensions.files.wordpress.com)