Question

(a) For the solidification of pure gold compute the critical radius r and the activation energy AG* if nucleation is homogeneous. Values for the latent heat of fusion and surface energy are -1.16x109 J/m3 and 0.132 J/m2 respectively. AT for gold is 230°c from Table 11.1, Tm for gold is 1064°C (b) Calculate the number of atoms found in a nucleus of critical size. Assume a lattice parameter of 0.413 nm for solid gold at its melting temperature.

Answer 1

Im oxdento evaluate the qinen by 2 Tm mumber d atom Criti cal Radius a im a mucleu of Cri-Hcal si2e, it j fiyst AHE datermine the numbn meceasaruy to the unit cells, which them Guiven O132 T O64 +273 = 1337 K atoms Per Cell mumber unit AT T-T =230+273 = 503 K A3 it i Fcc CuystalStrueture, AHE = -.1G x to'J/3 umit Cells T 3 2X6.132 X1337 (--1G 109) 503 Givern O 413 mmm 2X0.132 x133 amd We got = 0.6mm 1C x 503 = 0-6mm O.G0 x169m umit cells (06)3 Co413)3 farticle Activation emengy 16T 3 AHE (T)* umit Cells 12 IC TE (0132)(37) 3xU.IC)1 50 4 atoms are Fcc unit cde aiociated with 0-20 x 10 => Total muumber d atoms Pesn critical mudeus t, - umitcells/oriticalmudeusX atoms cs Scanned with CamScanner Scanned with CS CamScne48 otomscritical nuedes