Reflectance of aluminum

Finally, it should be mentioned that neither the ideal metal model nor the damped metal model are able to explain why the actual reflectivity of aluminum is lower than the calculated one (iC >= 1) at frequencies lower than cop. Also, these simple models do not reproduce features such as the reflectivity dip observed around 1.5 eV. In order to account for these aspects, and then to have a better understanding of real metals, the band structure must be taken into account. This will be discussed at the end of this chapter, in Section 4.8. 

The reflectance, dielectric functions, and refractive indices, together with calculations based on the Drude theory, for the common metal aluminum are shown in Fig. 9.11. Aluminum is described well by the Drude theory except for the weak structure near 1.5 eV, which is caused by bound electrons. The parameters we have chosen to fit the reflectance data, hu>p = 15 eV and hy = 0.6 eV, are appreciably different from those used by Ehrenreich et al. (1963), hup = 12.7 eV and hy = 0.13 eV, to fit the low-energy (hu < 0.2 eV) reflectance of aluminum. This is probably caused by the effects of band transitions and the difference in electron scattering mechanisms at higher energies. The parameters we use reflect our interest in applying the Drude theory in the neighborhood of the plasma frequency. 

Figure 9.11 Measured reflectance of aluminum compared with the Drude theory. The dielectric (unction and refractive index are from Hagcmann et al. (1974).

The dielectric function and reflectance of aluminum, which were displayed in Fig. 9.11, are shown over a broader energy range in Fig. 10.2 note that two... 

Figure 10.2 Dielectric functions and reflectance of aluminum (Hagcmann ct al., 1974).

The reflectivity of aluminum coated with lead sulfate is 0.35 for radiation at wavelengths less lhaii 3 prii and 0.95 for radiation greater than 3 pm. Determine the average reflectivity of tliis surface for solar radiation (7 5800 K) and radiation coming from surfaces at room temperature (T 300 K). Also, determine the emissivity and absorptivity of this surface at both temperatures. Do you think litis material is suitable for use in solar collectors ... 

In general, for metals with relatively low reflectivity values (<70%) at room temperature, the reflectivity can be considered to be constant with temperature. This is the case of metals like copper and stainless steel (SS) irradiated at 355 nm ofwavelength showing reflectivity values of 41.5% and 55.6%, respectively. However, aluminum presents a reflectivity of 93.5% at the same wavelength. Experimental observations have shown that the reflectivity of aluminum can reduce to values of 65% during... 

Figure 1.4 Dielectric constant, refractive index and reflectivity of aluminum [from experiments [9]].

Figure 93 Reflectance of aluminum, silver, and gold from 0.2 to 5.0 m Source Bob MeUish. - en Image Metal-reflectance.png http //en.wikipedia.Org/wiki/Reflectivity mediaviewer/File Image-Metal-reflectance.png, Common Cause license Accessed August 2014 at http //creativecommons.Org/licenses/by-sa/3.0/...

The birefringence of substrate materials for optical data storage devices requires special attention, especially in the case of EOD(MOR) disks. Birefringence has no importance for glass substrates (glass does not exhibit any significant birefringence) and is only a subordinate factor for polymeric protective layers of aluminum substrates because of their reflective read/write technique. 

Physical and mechanical properties are given in Table 22 (109,110,112—114). The densities reflect the effect of aluminum the Zn- -27% Al aHoy is ca... 

Fig. 8-2. Background in the determination of aluminum in Alnico. Pulse-height selection facilitates the determination by reducing in importance the background and the lines (in 5th- and 3rd-order reflection) of the matrix elements, nickel and titanium. (After Noreleo Reptr., 3, 78.)...

The appearance of a flake of clay reflects its internal structure, which is something like an untidy stack of papers (Fig. 14.45). Sheets of tetrahedral silicate units or octahedral units of aluminum or magnesium oxides are separated by layers of water molecules that serve to bind the layers of the flake together. Each flake of clay is surrounded by a double layer of ions that separates the... 

Figure 13. Reflectance of a 100 nm thick coating. Dark gold, gray, silver and light gray aluminum.

The enhanced aqueous solubility of aluminum hydroxide in the presence of an acid or alkali is an example where neutralization reaction plays a part. In pure water, the solubility of aluminum hydroxide is low which is very well reflected in the following equation ... 

The linear dependence of the pitting potential on ionic radius is likely a reflection of the similarly linear relationship between the latter and the free energy of formation of aluminum halides.108 It is reasonable to assume that the energy of adsorption of a halide on the oxide is also related to the latter. Hence, one could postulate that the potential at which active dissolution takes place is the potential at which the energy of adsorption overcomes the energy of coulombic repulsion so that the anions get adsorbed. 

Finally, alternatives exist to the use of silver in various materials and processes. These include substitution of aluminum and rhodium for silver in mirrors and other reflecting surfaces tantalum replacement of silver in surgical plates, pins, and sutures stainless steel as an alternative material to silver in the manufacture of table flatware and, in photography, film with reduced silver content (Reese 1991). 

Special consideration of thermal relief for piping exposure to sunlight (solar radiation) needs to be under taken. This is usually accomplished by painting with reflective paint or burial. Hydrocarbon containing piping is usually painted in a reflective color (i.e., aluminum) for advantages of reflection of solar radiation (heat input) to avoid thermal expansion of fluids in blocked systems. 

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