quiz3fall2000 - ENSC 3313,Fall 2000 Answer any 4 Questions...

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ENSC 3313, Fall 2000 Answer any 4 Questions only, 1 point each 8; The micrograph below shows the crystal grains in a metal at ~. Please determine the ASTM grain size number . ~ rJ "" - '-> "" ,." lJ ~ ~ The magnification is 200, so I will see only a quarter of those I would see in 1" x 1 " at 100x, so either I can draw my 1" x 1 " unit and multiply by - -4 or draw a 2" x 2" unit, as here. I count = 128 N = 2n-l = 128 = 27 and n -8 ~ 2. If 1 lattice site in 10,000 of a particular metal is vacant at 1000°K and 1 lattice site in 100,000 is vacant at 900°K, what proportion of lattice sites are vacant at 800°K? Recollect that the number varies exponentially with temperature. Exponential decay Let ~ = Ce-K/T where C and K are constant~ o Substituting 10-4 = Ce-K/l000 10-5 = Ce-K/900 Hence, K = 20, 727 and C -105, Repeating NT = lO5e-20.727/800 NT = 5.6 x 10-7 Rare Earth -Cobalt magnets are being considered for surgically implantable motors. An important example is SmCo which is 65 w/o Co and 35 w/o Sm. The atomic masses of Co and Sm are 58.93 amu
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quiz3fall2000 - ENSC 3313,Fall 2000 Answer any 4 Questions...

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