A thermal evaporator is used to deposit aluminum. The aluminum charge is maintained at a uniform temperature of 1100 o C. If the the vapor pressure of aluminum is about 1x10-3 torr at that temperature, calculate the evaporation rate of aluminum?

The outer surface of a steel alloy is to be hardened by increasing its carbon content. The carbon is to be supplied from an external carbon-rich atmosphere, which is maintained at an elevated temperature. A diffusion heat treatment at 837°C for 11 min increases the carbon concentration to 0.79 wt% at a position 1.9 mm below the surface. Estimate the diffusion time required at 680°C to achieve this same concentration also at a 1.9 mm position. Assume that the surface carbon content is the same for both heat treatments, which is maintained constant. The preexponential and activation energy values for the diffusion of carbon in the iron are 8.1 x 108 m²/s and 75.9 kJ/mol, respectively. i min

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Calculate the diffusion constant, D, for the process at a diffusion temperature of T=1150 ⁰C given that D0 = 5.5 *10-5 m2/s; Qd = 148,000 J/mol.

At approximately what temperature (in Kelvin) would a specimen of an alloy have to be carburized for 2.5 h to produce the same diffusion result as at 820°C for 16 h? Assume that values for Do and Qd are 1.4 x 104 m?/s and 147 kJ/mol, respectively. T = i K

In boiling water at 1 atm pressure outside a stainless-steel tube with a surface temperature of 410F, the heat-transfer coefficient h in the absence of radiation is 32 Btu/h*ft^2*F. If the emissivity of the stainless steel is 0.8, will radiation significantly augment the rate of boiling (e.g., by more than 5 percent)? Assume that the vapor film is transparent to radiation and the boiling liquid is opaque.

A l-mm sheet of FCC iron is used to contain nitrogen in a heat exchanger at 1200°C. The concentration of N at one surface is 0.04 atomic percent and the concentration at the second surface is 0.005 atomic percent. Determine the flux of nitrogen through the foil in N atoms/cm2's. Hint: The diffusion coefficient D is related to temperature by an Arrhenius-type еquation D = Doexp(-) RT For the diffusion couple N in FCC iron, the activation energy Q is 8.269 kJ/mol and Do is 0.34 mm²/s. R is the gas constant 8.314 J/mol·K.

Carbon is being diffused into chromium at 1400 K (1127°C). The diffusion coefficient at this temperature for the system is 6.25 x 10-11 m/s. Based on this information, calculate the diffusion coefficient of carbon in chromium at a temperature 1300 K (827°C). The activation energy for the diffusion of carbon in chromium is 111,000 J/mol.

What temperature is required to obtain 0.4%C at a distance of 0.3 mm beneath the surface of a 0.22% C steel in 2h, when 1.1% C is present at the surface? Assume that the iron is FCC. (Please see figure 5.12 below for diffusion coefficient data. Please use your notes for a table of erf() function values table of erf() fun Diffusion coefficient D (cm²/s) 10-3 !! ! ! ! ! 10- 10-5 10-9 10-10 10-11 10-12 10-13 10-14 Temperature (°C) 2000 1500 1200 1000 900 800 700 600 wwwwwwwwwwwwwww in graphite Mg in MgO Ca in CaO H in FCC iron Cin FCC iron Fe in FCC iron Fe in BCC iron H in BCC iron 104 T(K) C in BCC iron Fe in FeO 500 10-15 4 5 6 7 8 9 10 11 12 13 Figure 5-12 The diffusion coefficient D as a function of reciprocal temperature for some metals and ceramics. In this Arrhenius plot, D represents the rate of the diffusion process. A steep slope denotes a high activation energy.

Gaseous hydrogen at a constant pressure is to flow within the inside of a thin-walled cylindrical tube of nickel. Consider the steady-state diffusion of hydrogen through the walls of this cylindrical nickel tube. One design calls for a diffusion flux of 5 x 10-8 mol/m2.s, a tube radius of 0.125 m, and inside and outside pressures of 0.5065 MPa (5 atm) and 0.0203 MPa (0.2 atm), respectively; the maximum allowable temperature is 450°C. In case the wall thickness is 2 mm and the yield strength is greater than twice the circumferential stress, what would be the temperature to give this diffusion flux and yet ensure that the tube walls will not experience any permanent deformation? i °C