F-f. Chen et aL Engineering Failure Analysis 37(2014)29-41 ig. 4. Black deposit on the outer wall of titanium tubes and its distribution(a) position near the support plate(b) deposit at the bottom. 2Theta [deg J Fig. 5. XRD results of the black deposit on the surface of titanium tubes. 2.2. XRD analysis of the black deposit Black deposit was found at the bottom and the contact part with the support plates of nearly all failure tubes, shown in Fig 4. We scraped some and conducted XRD for composition analysis. The results are shown in Fig. 5. The black deposit inly consists of Fe3 Oa according to the standard powder diffraction file(pDf)card. The Fe3 O4 mainly came from the galvanic corrosion of support plates made of carbon steel under xygen-dehcient con- ditions. But why did it dominantly appear at the contact part between the tubes and the support plates? It can be deduced2.2. XRD analysis of the black deposit Black deposit was found at the bottom and the contact part with the support plates of nearly all failure tubes, shown in Fig. 4. We scraped some and conducted XRD for composition analysis. The results are shown in Fig. 5. The black deposit mainly consists of Fe3O4 according to the standard powder diffraction file (PDF) card. The Fe3O4 mainly came from the galvanic corrosion of support plates made of carbon steel under oxygen-deficient con￾ditions. But why did it dominantly appear at the contact part between the tubes and the support plates? It can be deduced Fig. 4. Black deposit on the outer wall of titanium tubes and its distribution (a) position near the support plate (b) deposit at the bottom. Fig. 5. XRD results of the black deposit on the surface of titanium tubes. 32 F.-J. Chen et al. / Engineering Failure Analysis 37 (2014) 29–41