nm and more preferably from 10 to 100 nm a diamond layer 130 is coated on the porous substrate 100 as illustrated in fig2 the coating process may be performed using conventional methods suitable for the deposition of diamond on a substrate examples of such coating or deposition processes are but not limited to chemical vapour deposition cvd physical vapour deposition pvd arc jet based cvd hot filament cvd hfcvd microwave assisted chemical vapor deposition mwcvd microplasma radio frequency plasma chemical vapour deposition rfpcvd direct current plasma chemical vapor deposition dc pcvd electron cyclotron resonance ecr plasma cvd ecr pcvd combustion flame cvd and epitaxy deposition in a preferred embodiment the deposition and growth of the diamond is performed using the chemical vapour deposition the process is preferably performed a pressure ranging from 10 to 100 torr at a temperature raging from 300 to 1500 u00b0 c preferably from 700 to 1300 u00b0 c in another preferred embodiment of the present invention hydrocarbon gases such as methane ch 4 or acetylene c 2 h 2 are used as a source or precursor for depositing and growth of diamond layer the injection of hydrocarbon gas is preferably performed using a mixture of said hydrocarbon gas with hydrogen gas the preferred ratio of said gas mixture is from 1 to 10 of the hydrocarbon gas with respect to hydrogen gas by injecting more than 10 of hydrocarbon.