Effect of additives on microstructures and properties of ceramic compound pipes produced by centrifugal SHS process

7% mass fraction of SiO₂and 2%, 4% and 6% mass fraction of Na₂B₄O₇ were added as additives into the system of A1-Fe₂O₃ to examine their effects on the microstructures and properties of ceramic compound pipes made by centrifugal SHS (self-propagating high temperature synthesis) process. It was found that ceramic layer is mainly composed of α-Al₂O₃, FeAl₂O₄, Al₂SiO₅ and B₂O₃ by XRD analysis. The surfaces on ceramic layer by SEM are much denser than that without additives, and Fe is also found in ceramic layer combined with the EDS analysis. The results show that inner ceramic layer and transition iron layer combine well without any gap observed by metallurgical microscope. It is also found that the shearing strength of the ceramic layer and crushing strength of the composite pipe under 7%SiO₂+4%Na₂B₄O₇(mass fraction) are 22 MPa and 430 MPa, respectively, which are 240% and 22.8% greater than those without additives.