Anodisation comparator

The average capacitance and specific resistivity of the barrier aluminium oxide films are determined to be 430. .. 470nF/cm and 1.3. .. 2.4 10 " Qcm, respectively. By using the anodisation factor of 1.2 nm/V for the films formed at low formation voltage, dielectric constants of 5.8. .. 6.4 are calculated from the measured capacitance values. The comparatively low dielectric constant is in agreement with the formation of an amorphous anodic aluminium oxide film as discussed above rather than a crystalline structure for which a higher dielec-... 

The thickness of the tubular structure stops increasing when the chemical dissolution rate of the oxide at the mouth of the tube (top surface) becomes equal to the rate of inward movement of the metal/oxide boundary at the base of the tube. Higher anodisation voltages promote the oxidation and field-assisted dissolution and increase the nanotube layer thickness before equilibrium is reached. A slightly different mechanism occurs in aqueous solvents compared with organic solvents in aqueous solvents the process is subtractive (the nanotube array will be less than the... 

Figures 8 and 9 show the Peak Impact Energy of samples moulded at a thickness of 3 and 6 mm in the various moulds using an oven set temperature of 300°C. As the peak internal air temperature of the mouldings increased, the peak impact energy also increased for both the 3 mm and 6 mm mouldings, this is to be expected since higher temperatures reduce the viscosity of the melt and accelerate the rate at which the bubbles diminished over time, thus improving impact resistance. When the impact resistance of the mouldings made from the anodised tool and the impact resistance of the mouldings produced from the Conventional tool were compared, no differences in terms of peak impact energy were observed.

Figure 11 shows the gas consumption used by a conventional A1 tool compared to an Anodised A1 tool to produce a 3mm thick part using an oven set temperature of 300°C. In most cases, the consumption of gas was more for the Conventional A1 moulding compared to the Anodised A1 moulding. 

Following the extensive and detailed investigation into rotomoulding with anodised treated aluminium it was found that typically there is a 20 - 25 % saving on overall cycletime when compared with non-treated Conventional aluminium. There were no differences observed between the two mould materials in terms of impact, shrinkage or surface properties. 

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