Rough diamond coatings

BDD electrodes are semiconductor electrodes with microcrystalline structure and relatively rough surfaces on the micrometric scale. Diamond-coated electrodes used for disinfection are chemically, mechanically, and thermally very resistant and show very low corrosion even under high electric charge. Diamond electrodes present no surface redox processes as known from other carbon electrodes (for example glassy carbon). 

Diamond like coatings are basically amorphous and therefore smooth whereas diamond coatings are polycrystalline and hence rough. As a result, the diamond like coating experiences lower sliding friction in wear resistance applications and tends to provide better protection than a diamond coating inspite of the comparatively lower hardness. 

In general, previous studies confirmed the notion that regardless of grain size, diamond coatings with a smooth surface finish provide very low friction coefficients to mating surfaces. Figure 9 illustrates the close relationship between surface roughness and friction coefficients of diamond films. 

Apart from physical roughness and chemical passivation effects, phase transformation or structural changes can also play a major role in the friction and wear performance of diamond coatings.The extent of such changes may be dominated by environmental species or by ambient temperature. 

Diamond Coatings Come Out of the Rough, Design Engineering, January 1991, pp. 72-78. 

The same skepticism applies to nanocrystalline diamond that is reported to be harder than diamond single crystals (Sumiya and Irifune, 2007). Other cases in which rough surfaces may have skewed the measurements are TiN/SiN coatings (Kauffmann et al., 2005) and (AlMgB14 + TiB2) mixtures (Cook et al., 2000). 

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