for the time indicated below a about 1450 u00b0 f for about 5 minutes to give a coating thickness of less than 1 mil b about 1450 u00b0 f for about 15 minutes to give a coating thickness of about 2 mil c about 1550 u00b0 f for about 5 minutes to give a coating thickness of about 2 mil d about 1650 u00b0 f for about 5 minutes to give a coating thickness of about 3 mil e about 1750 u00b0 f for about 2 minutes to give a coating thickness of about 2 mil 5 gradually remove the screens from the furnace tube and allow the screens to cool to room temperature after the screens have cooled to room temperature the screens are immersed in a solution containing about 20 by weight sodium hydroxide in water for about one hour at about 200 212 u00b0 f to leach out most of the aluminum from the coating 6 after the leaching step the coated screens are rinsed in water and then immersed in hot water for about one hour at about 180 212 u00b0 f 7 after the rinsing and soaking step described in paragraph 6 the coated screens are immersed in a solution containing about 2 to 5 hydrogen peroxide in water for about one hour at about 75 u00b0 f and then the screens are rinsed in water and dried in air at room temperature the coated screens should not be pyrophoric when exposed to air the weight gain for the screen in a was only about 0 4 mg sqcm for the screens in b e the weight gain was about 5 6 mg sqcm the photomicrographs shown in fig3 and 5 are typical of.