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Latihan Soal Difusi Padatan
1. A sheet of steel 1, 5 mm thick has nitrogen atmospheres on both sides at
1200C and is permitted to achieve a steady-state diffusion condition. The
diffusion coefficient for nitrogen in steel at this temperature is 6 x 10-11 m2/s,
and the diffusion flux is found to be 1,2 x 10-7 kg/m2s. Also, it is known that
the concentration of nitrogen in the steel at the high pressure surface is 4 kg/m3.
How far into the sheet from this high-pressure side will the concentration be 2,0
kg/m3? Assume a linear concentration profile.
2. Determine the carburizing time necessary to achieve a carbon concentration of0.45 wt% at a position 2 mm into an ironcarbon alloy that initially contains
0.20 wt% C. The surface concentration is to be maintained at 1.30 wt% C, and
the treatment is to be conducted at 1000C. (D0 = 2,3 x 105 m2/s)
3. At what temperature will the diffusion coefficient for the diffusion of copper in
nickel have a value of 6.5 10-17 m2/s. Use the diffusion data (tabulasi data
difusi).4. The diffusion coefficients for iron in nickel are given at two temperatures:
T (K) D (m2/s)
1273 9.4 1016
1473 2.4 1014
a. Determine the values of D0 and the activation energy Qd.
b. What is the magnitude of D at 1100C (1373 K)?
.
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Jawaban Latihan Soal
J = DCA CB
xA xB
1. Gunakan rumus laju difusi steady state
xB = xA + DCA CB
J
xA = 0 (pada permukaan)
D = 6 x 1011
m2
/sCA = 4 kg/m
3
CB = 2 kg/m3
J = 1,2 x 107 kg/m2.s
Jadi, xB = 1 mm
2. Gunakan rumus laju difusi non steady state
Cx C0Cs C0
= 1 erfx
2 Dt
Cx = 0,45
C0 = 0,20
Cs = 1,30
x = 2 mm = 2 10-3 m
erfx
2 Dt
= 1 0.2273 = 0.7727
z = 0,854 (hasil interpolasi)
z = 0.854 =x
2 Dt
Jadi, t = 7.1 104 s = 19,7 h
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Jawaban Latihan Soal
3. Gunakan rumus hubungan koefisien difusi dengan temperatur
T = QdR(lnD lnD0)
D0 = 2,7 10-5 m2/sQd = 256000 J/mol
D =6.5 10-17 m2/s
Gunakan R = 8,31 J/mol.K
Jadi, T = 1152 K
4. Gunakan rumus hubungan koefisien difusi dengan temperatur
Qd = RlnD1 lnD2
1
T1
1
T2
D0 = D1 exp
Qd
RT1
Qd
= 252400 J/mol
D0 = 2,2 x 10-5 m2/s
D (saat 1100C) = 5,4 x 10-15 m2/s
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