finalspr2000 - FINAL ENGSC 3313, Spring 2000 I. Name An...

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¥ Name ENGSC 3313, Spring 2000 FINAL An important radioactive isotope is strontium-90 because it is absorbed by bone (The Sr substitutes for Ca in Ca3(pO4)2). It has a half life of 30 years. What proportion would have decayed after 70 years? I. We have exponential decay = e-tl!. . where !. . is a constant, Ao = initial amount ( ~ Ao Substituting 0.5 = e-30/A and J. = 43.5 years A7o Ao - Repeating e-70/43.5 = Q.2Q Hence, proportion decayed is 1- 0.20 = ~ Sun bums are caused by ultraviolet (U.V.) light. One strategy in developing sun screens is to look for compounds with permissible electron shifts that correspond to the energy of U. v. light. Please determine the energy of the electron shift required to absorb a photon of u. v. light with a wave length of 300 nm. R = 8.31 J/mole-K, h = 0.62 x 10-33 J-s, k = 13.8 x 10-24 J/K. 2, c \)=- A L\E = hu = 6.62 x 10-19 J Draw the 5 ~ of symmetry in a tetragonal unit cell. 3. 3 Planes thru middle of faces and perpendicular to axes. , " , 2 Planes that are face diagonals of ~ 'c' surface (drawn) , " , " , , ... " ... ,
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z t ~y x 5 What is the packing factor for the ionic compound KI that has the NaCl type FCC crystal structure? The ionic radii are K = 0. I 33nm, I = O.22Onm. FCC compound, so 4 of each type per cell and 2Rl + 2R2 = a Hence: P.F. = =0.62 23(0.133 + 0.220)3 6 Please predict the relative solubility of Cobalt (Co) and Titanium (Ti) in iron (Fe), (i.e., which is more soluble?) Please defend your answer. Rad., nm 0.1241 0.146 0.125 Cry. Type BCC HCP HCP Density, g/cc 7.87 4.51 8.83 Valence 2+ 4+ mass. aInU 55.85 47.90 Electroneg. 1.8 1.5 1.8 Fe Ti Co 58.93 2+ Cobalt is closer to Fe in size, valence, and electronegativity. Crystal type is a toss up. Atomic mass and density are not part of the Hume-Rothery rules. Therefore, we would expect Co to be more soluble than Ti in Fe.
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7 8. Mechanical properties matter. Handbooks will quote at least 4 properties obtained from a tensile test. Name 4! yield strength tensile strength elastic modulus % elongation --and maybe % reduction in area. Given a cold drawn iron wire of diameter 2.0 mm. Reguired, an iron wire of diameter 1.6 mm having a hardness of at least 125 BHN, a strength of at least 350 MPa and a ductility of at least 30% (on 2"). Specify a processing sequence! ~ ~ rJ, u c 'E (U :c ~ c o ~ ~ .fo'pperl --~i I ; 0 2l D /~ 60 Cold work, % j I (c) ...30 ,..'(7}. Required for hardness and strength, above 22% CW Required for ductility, below 30% CW Choose -25% CW do2 -df2xlOO .. OJnrw =
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finalspr2000 - FINAL ENGSC 3313, Spring 2000 I. Name An...

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