induced cracks the thickness of the tbc ceramic layer can be varied according to the temperature drop required the reduction in surface temperature which can be obtained using zro 2 8 y 2 o 3 tbc with 20 porosity at the heat flux and surface temperature which is typical of an operating drying cylinder has been measured at 6 u00b0 c per 100 u03bcm of tbc thickness the preferred thickness of the tbc layer is varied between 0 and 400 u03bcm depending on the surface temperature drop required in the cross direction profile of the drying cylinder the preferred surface roughness of the bond layer is 7 12 u03bcm which is controlled by selecting suitable size powders for spraying and optimizing the spraying parameters the roughness of the bond layer is important in determining the adhesion strength between the bond layer and the tbc layer the preferred adhesion of the tbc layer is in excess of 8 mpa the surface roughness of the tbc layer is maintained below 7 u03bcm by controlling the size of the powders used and the operating parameters during spraying excessive surface roughness of the tbc layer may damage the paper contacting the cylinder both the bond coat and the ceramic coating can be applied on dryer cylinders using.