Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the p...Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the presence of a strong reducing agent. Nb2O5, B2O3 and Mg powder blends were milled at room temperature by a high-energy ball mill for different time. Subsequently, undesired MgO phase was removed from the milled powders by HCl leaching to constitute NbB?NbB2?Nb3B4 as final products and they were subjected to an annealing process at 1500 °C for 4 h to observe probable boride transformation. Characterization was carried out by XRD, DSC, PSA, SEM/EDX, TEM and VSM. The effects of milling time (up to 9 h) on the formation, microstructure and thermal behavior of the final products were investigated. Reduction reaction took place after milling stoichiometric powder blends for 2 h. Nano-sized NbB?NbB2?Nb3B4 powders in high purity were obtained in the absence of any secondary phase and any impurity via mechanochemistry by milling for 5 h and leaching with 4 mol/L HCl. After annealing, pure and nano-sized NbB?NbB2?Nb3B4 powders transformed to a single NbB phase without leaving behind NbB2 and Nb3B4 phases.展开更多
In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phas...In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.展开更多
基金financially supported by“The Scientific and Technological Research Council of Turkey(TUBITAK)”with the project title of“Synthesis of Refractory Metal Borides via Three Different Production Methods from Solid,Liquid and Gas Raw Materials for Various Application Areas,Sintering,Characterization,Comparison of Process and Final Products”and with the project number of 112M470
文摘Niobium boride powders having NbB, NbB2 and Nb3B4 phases in various amounts and single phase NbB powders were successfully synthesized by using powder metallurgy methods from related metal oxide raw materials in the presence of a strong reducing agent. Nb2O5, B2O3 and Mg powder blends were milled at room temperature by a high-energy ball mill for different time. Subsequently, undesired MgO phase was removed from the milled powders by HCl leaching to constitute NbB?NbB2?Nb3B4 as final products and they were subjected to an annealing process at 1500 °C for 4 h to observe probable boride transformation. Characterization was carried out by XRD, DSC, PSA, SEM/EDX, TEM and VSM. The effects of milling time (up to 9 h) on the formation, microstructure and thermal behavior of the final products were investigated. Reduction reaction took place after milling stoichiometric powder blends for 2 h. Nano-sized NbB?NbB2?Nb3B4 powders in high purity were obtained in the absence of any secondary phase and any impurity via mechanochemistry by milling for 5 h and leaching with 4 mol/L HCl. After annealing, pure and nano-sized NbB?NbB2?Nb3B4 powders transformed to a single NbB phase without leaving behind NbB2 and Nb3B4 phases.
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.51825103)the National Science Fund for Excellent Young Scholars(No.52222208)+1 种基金the Major science and technology project of Anhui Province(No.008192841048)the HFIPS Director's Fund,CAS(No.BJPY2021B04,YZJJ202202-CX,YZJJKX202202).
文摘In this study,ultrafine HfB_(2) powders with low oxygen were synthesized by a flocculating settling process which yielded ceramic precursors and subsequent carbo/borothermal reduction of the precursors.The liquid phase precursor method can achieve uniform mixing of components at the molecular level through multiple complexation reactions,and then realize the carbo/borothermal reduction reaction at a lower temperature to obtain ultrapure HfB2 powders.The as-resulted quasi-spherical HfB2 powders under the optimum conditions(atomic molar ratio M:B:C=1:2.8:10)calcined at 1500°C for 1 h have an average particle size of 205 nm and an oxygen content of 0.097 wt.%.Detailed analysis of the phase evolution of precursors shows that the formation of HfB2 particles is a mass diffusion mode from the external to internal HfO_(2)cores.We reveal that below 1300°C,HfC is not an intermediate product of HfB2 powder during the transition of precursors.Instead,HfC was formed as a by-product at high temperatures in the carbo/borothermal reduction process.The proposed formation mechanism of HfB_(2) is completely different from the traditional two-step transformation method.After the sintering of the ultrafine powders,the HfB_(2) ceramics show a relative density of 96.1%and superior mechanical properties compared to other works.Furthermore,by simply replacing the initial metal source,chlorinated group IV and V transitional metals(Ti,Zr,Ta,Nb)can also convert into high-purity and ultrafine diborides.This work shows that flocculating settling assisted carbo/borothermal reduction has potential in lot size production of various high-purity and ultrafine boride powders.
