The Influence of Surface Anisotropy Crystalline Structure on Wetting of Sapphire by Molten Aluminum
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Scanning Electron Microscope EDAX Analyses of the 1020 Aluminum (wt pct)
Fe
Cu
Mn
Mg
Cr
Zn
Ti
Ni
0.003
0.00
0.00
0.001
0.00
0.00
0.00
0.00
METALLURGICAL AND MATERIALS TRANSACTIONS A
Al (min) 99.995
VOLUME 44A, MAY 2013—2301
III.
RESULTS
Figure 4 illustrates the effects of temperature and time on the Al contact angle (/) on polished ‘‘c’’ (0001), ‘‘a’’ ð10 10Þ, and ‘‘m’’ ð11 20Þ planes. As time increased, the contact angle (/) decreased linearly. Higher temperatures have a tendency to promote wetting. The values of /o and ð@/=@tÞT from Figure 4 are summarized in Table II. It is evident that there exist two distinct regimes of ð@/=@tÞT at ~1273.15 K (~1000 C). For the higher temperatures, the ð@/=@tÞT is about twice that for the lower temperatures. A transition exist for both /o and ð@/=@tÞT that resembles the transition for the "c"-plane
Contact Angle, φ (degrees)
110 108 105
1073 K
φ = 107.3 - 0.05 t
1173 K
φ = 105.2 - 0.08 t
1273 K
103
φ = 102.6 - 0.11 t
100
1373 K
φ = 97.6 - 0.11 t
98 95
1473 K
φ = 93.2 - 0.11 t
93 90 0
2
4
6
8
10
12
14
16
18
20
Time (min)
"a"-plane Contact Angle, φ (degrees)
100
1073 K
φ = 100 - 0.10 t
98
φ = 98 - 0.12 t
95
φ = 96 - 0.15 t
1273 K
φ = 93 - 0.19 t
1373 K
1173 K
93 90 88
φ = 89 - 0.2 t
1473 K
85
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
Time (min) "m"-plane
Contact Angle, φ (degrees)
100
1073 K
φ = 99.7-0.06 t
1173 K
98
A. Variation of cos / with clv for ‘‘c’’ Plane (0001)
φ = 98-0.07 t 95
φ = 97.7-0.11 t
93
1273 K
φ =91.0-0.12 t 1373 K
90 88
φ = 87.0 - 0.13 t 1473 K
85
0.0
2.5
5.0
(0001) ‘‘c’’ plane reported by Champion et al.[8] and Shen et al.[9,10] Figure 5 is a linear plot of the contact angles at zero time, /o, as a function of temperature. The results confirm the presence of two distinct temperature regimes divided at T = 1273.15 K (1000 C), the same as previous studies.[1–4] The ð1120Þ plane has almost the same profile as for the ð1010Þ plane; both are more wetted by Al than the (0001) plane. The low-temperature slopes d/=dT are almost identical to those previously reported by Champion et al.[8] and Shen et al.[11] Both reported distinctive slope changes transitions for the contact angle (/) vs temperature for molten aluminum on ‘‘c’’ plane (0001) of sapphire. These transitions are shown in Figures 6[8–11] and 7 and occur within some difference degrees of variation ~100 K (~100 C) of variation, respectively. Champion et al.[8] observed a slope change at ~1298.15 K (~1025 C). At higher temperatures >1298.15 K (1025 C), they reported a steeper, more negative slope of –0.20 (deg/K). However, the Shen et al.[11] transition is at ~1373.15 K (~1173 C) and had a lesser slope, not a greater one at the higher temperature. Similarly, Shen et al.[11] reported transitions at ~1373.15 K (~1173 C) for the ‘‘r’’ plane ð0112Þ and the ‘‘m’’ planeð1120Þ. However, their results are different than those observed in this study about some difference degrees of variation ~100 K (~100 C) higher a
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