The Preparation Research Of Nb And Nb/Si Powder Surface Coating Modification

Nb/Nb₅Si₃ composite material composed of Nb and Nb₅Si₃, has excellent strength-toughness and long-term stability in high temperature, is considered as one of the promising metals for ultra-high temperature structural materials. However, the poor oxidation resistance of pure Nb in high temperature has been a major barrier to the preparation of Nb/Nb₅Si₃ composite under aerobic condition. In this paper, the surface of the Nb powder and Nb/Si composite was modified, forming a protective layer on the particle surface. Then the coated powder was made into a coating by thermal spraying, and the high-temperature oxidation resistant of the coating was studied.Firstly, Na₂SiO₃·9H₂O was chosen as raw materials, and SiO₂-coated Niobium powder was achieved by sol-gel method. By controlling the different reaction parameters (such as material ratio, aging time, pH, heating temperature and so on), the influence of different reaction conditions on the coating was studied, and the structure and performance of coated powders were also researched. Finally, the best coating conditions were obtained: m(SiO₂)/m(Nb)=1.5% or 3%, aging time was 120 minute, pH=9.5, the heating temperature was 100℃.Micron Nb is hard to be coated under the room temperature due to its inertia. Considering this, TEOS was chosen as raw materials, and TEOS-coated Niobium powder was achieved by pretreatment method. The parameters, such as reaction time, temperature, pretreatment, material ratio, ect, and the structure as well as performance of coated powders were studied. The optimal process for TEOS coated micron Nb powder was got as follows: n(Nb)/n(TEOS)=1:6, the reaction time was 2 hours and the temperature was 80℃.On this basis, still using TEOS as raw material, the TEOS-coated Nb/Si composite powder was achieved with the optimum conditions in the pretreatment method. The materials were characterized by XRD, FT-IR, SEM and TG-DTA. The results revealed that the high-temperature antioxidant property of the TEOS-coated sample got improved significantly, and the synthesis of Nbss/Nb₅Si₃ composites in air will be possible.