One method that is used to grow nanowires (nanotubes with solid cores) is to initially deposit a small droplet of a liquid catalyst onto a flat surface. The surface and catalyst are heated and simultaneously exposed to a higher-temperature, low-pressure gas that contains a mixture of chemical species from which the nanowire is to be formed. The catalytic liquid slowly absorbs the species from the gas through its top surface and converts these to a solid material that is deposited onto the underlying liquid-solid interface, resulting in construction of the nanowire. The liquid catalyst remains suspended at the tip of the nanowire. Consider the growth of a 15-nm-diameter silicon carbide nanowire onto a silicon carbide surface. The surface is maintained at a temperature of T s = 2400 K, and the particular liquid catalyst that is used must be maintained in the range 2400 K ≤ T c ≤ 3000 K to perform its function. Determine the maximum length of a nanowire that may be grown for conditions characterized by h = 10 5 W/m 2 ⋅ K and T ∞ = 8000 K . Assume properties of the nanowire are the same as for bulk silicon carbide.
One method that is used to grow nanowires (nanotubes with solid cores) is to initially deposit a small droplet of a liquid catalyst onto a flat surface. The surface and catalyst are heated and simultaneously exposed to a higher-temperature, low-pressure gas that contains a mixture of chemical species from which the nanowire is to be formed. The catalytic liquid slowly absorbs the species from the gas through its top surface and converts these to a solid material that is deposited onto the underlying liquid-solid interface, resulting in construction of the nanowire. The liquid catalyst remains suspended at the tip of the nanowire. Consider the growth of a 15-nm-diameter silicon carbide nanowire onto a silicon carbide surface. The surface is maintained at a temperature of T s = 2400 K, and the particular liquid catalyst that is used must be maintained in the range 2400 K ≤ T c ≤ 3000 K to perform its function. Determine the maximum length of a nanowire that may be grown for conditions characterized by h = 10 5 W/m 2 ⋅ K and T ∞ = 8000 K . Assume properties of the nanowire are the same as for bulk silicon carbide.
Solution Summary: The author explains how nanowires are grown on the flat surface with the help of liquid.
One method that is used to grow nanowires (nanotubes with solid cores) is to initially deposit a small droplet of a liquid catalyst onto a flat surface. The surface and catalyst are heated and simultaneously exposed to a higher-temperature, low-pressure gas that contains a mixture of chemical species from which the nanowire is to be formed. The catalytic liquid slowly absorbs the species from the gas through its top surface and converts these to a solid material that is deposited onto the underlying liquid-solid interface, resulting in construction of the nanowire. The liquid catalyst remains suspended at the tip of the nanowire. Consider the growth of a 15-nm-diameter silicon carbide nanowire onto a silicon carbide surface. The surface is maintained at a temperature of
T
s
=
2400
K,
and the particular liquid catalyst that is used must be maintained in the range
2400
K
≤
T
c
≤
3000
K
to perform its function. Determine the maximum length of a nanowire that may be grown for conditions characterized by
h
=
10
5
W/m
2
⋅
K
and
T
∞
=
8000
K
.
Assume properties of the nanowire are the same as for bulk silicon carbide.
An electrical resistance wire made of tungsten dissipates heat to the surroundings at a constant rate.
Which of the following equations are you going to use to compute for the temperature at any point
within the wire when the temperature throughout the whole wire no longer changes with time? Assume
that the wire can be approximated as a thin cylinder.
a. Fourier-Biot equation
b. Poisson equation
c. Diffusion equation
d. Laplace equation
PROBLEM: IIC - 12
BOOK: ENGINEERING THERMOFLUIDS, M. MASSOUD
A 5.00-ml. sample of blood was treated with trichloroacetic acid to precipitate proteins. Alter centrifugation, the resulting solution was brought to a pH of 3 and was cxtraccd with two 5-mL portions of methyl isobutyl ketone containing the organic lead complexing agent APCD. The extract was aspirated directly into an air-acetylene flame yielding an absorbance of 0.454 at 283.3 nm. Five-milliliter aliquots of standard solutions containing 0.240 and 0.475 ppm Pb were treated in the same way and yielded absorbancc of 0.412 and 0.642. Calculate the concentration Pb (ppm) in the sample assuming that Beer's law is followed.
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