tailieunhanh - The Materials Science of Coatings and Substrates Part 8

Tham khảo tài liệu 'the materials science of coatings and substrates part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 176 Electrodeposition 4 8 12 15 20 26 28 32 36 40 72 98 Time days Figure 31 Change with time at room temperature of the intensity of texture components in copper elecưodeposits. Adapted from reference 73. 130 120 110 Knoop hartfnoM 100 o 80 70__ __ __ __ 38 45 55 65 75 111 Figure 32 Relationship between Knoop hardness and the 111 content of copper foil. Adapted from reference 64. Structure 177 Figure 33 a Electrodeposited clusters about 5 mm long photographed 15 min. after the beginning of the growth b A diffusion-limited aggregate computed with a random walker model. The digitized images in both a and b have about X 104 boundary sites. From reference 74. Reprinted with permission of the American Physical Society. additives and Figure 33b a fractal tree grown by a computer algorithm called diffusion-limited aggregation. An interesting observation is that Figure 33b bears a striking resemblance to trees or dendrites produced by elecholysis in simple salt solutions 74 . A fractal is an object with a sprawling tenuous pattern 75 . Magnification of the pattern would reveal repetitive levels of detail a similar structure would exist on all scales. For example a fractal might look the same whether viewed on the scale of a meter a millimeter or a micrometer. Examples of fractals in nature include formation of mountain ranges fems coastlines hees branching patterns of rivers and turbulent flow of fluids or air 75 76 . In the human body fractal like shuctures abound in networks of blood vessels nerves and ducts. Airways of the lung shaped by evolution and embryonic development resemble fractals generated by a computer 77 . 178 Electrodeposition Although the entire field of fractals is still in its infancy in many instances applying either theoretical fractal modeling and simulations or performing fractal analysis on experimental data has provided new insight on the relation between geometry and activity by virtue of the very ability to quantitatively link the two 78 . .