view of the work of lee et al 12 the rate of coating growth was typically in the range of 5 to 10 u03bcm h as shown in fig1 a the x ray diffraction xrd pattern of an aln coating deposited on si 3 n 4 indicated that the coating was highly textured with a strong preferred orientation to the 002 direction the coating was about 20 u03bcm thick the underlying si 3 n 4 substrate was not detected by the xrd analysis the weight of the coated sample was 0 3966 g in order to evaluate the corrosion resistance of the coated sample the sample was loaded with 13 4 mg cm 2 of na 2 so 4 and subsequently subjected to a flowing o 2 environment for 100 hours at 850 u00b0 c and 101 kpa after the exposure to the corrosion treatment the weight of the sample was 0 4086 g the xrd pattern of the corroded sample shown in fig1 b crystalline na 2 so 4 sample was covered with a layer of crystalline na 2 so 4 the aln coating underneath the na 2 so 4 layer was also detected in the xrd pattern when the sample was ultrasonically washed in warm distilled water the na 2 so 4 layer was dissolved in the water as evidenced by the disappearance.