A solid ternary mixture consisting of NaF,silicon and one metal oxide such as La2O3,CeO2,Pr6O11,Nd2O3,and Y2O3 was prepared and usedas de-fluorinated reagent for CF4 decomposition.The results show that 90% conversion ...A solid ternary mixture consisting of NaF,silicon and one metal oxide such as La2O3,CeO2,Pr6O11,Nd2O3,and Y2O3 was prepared and usedas de-fluorinated reagent for CF4 decomposition.The results show that 90% conversion of CF4 can be reached initially over NaF-Si-La2O3,NaF-Si-CeO2,NaF-Si-Nd2O3,and NaF-Si-Y2O3 at 850 C.The fresh and used reagents were characterized using XRD and XPS techniques.It was found that the active components of NaF and metal oxides in NaF-Si-CeO2,NaF-Si-Pr6O11,NaF-Si-Nd2O3,and NaF-Si-Y2O3 weretransformed into inert phases of mixed metal fluorides and silicates,respectively,resulting in an ineffective utilization of these de-fluorinatedreagents,whereas no inert phases from NaF and La2O3 can be observed in the used NaF-Si-La2O3,indicating the NaF-Si-La2O3 reagent couldbe utilized more efficiently than the other reagents in CF4 decomposition.展开更多
The present work investigates the effect of high praseodymium oxide(Pr6O11)content on the microstructure and phase formation of mullite(3Al_(2)O_(3)·2SiO_(2))precursor by means of the spark plasma sintering proce...The present work investigates the effect of high praseodymium oxide(Pr6O11)content on the microstructure and phase formation of mullite(3Al_(2)O_(3)·2SiO_(2))precursor by means of the spark plasma sintering process.30 wt%Pr6O11was added to a mullite precursor consisting of aluminum nitrate nonahydrate and tetraethyl orthosilicate through a high energy mixer mill in ethanol media.The spark plasma sintering was performed at a te mperature of 1200℃under 23 Pa vacuum co nditions by applying initial and final pressure of 10 and 30 MPa,respectively.XRD analysis confirms the existence of mullite,alumina,Pr6O11,Pr2O3and quartz as the only crystalline phases.FESEM images reveal an interesting deposition of hexagonal-shaped Al_(2)O_(3)particles on polished surfaces and complex oxide phases of the fiber network adhering to alumina particles in the form of tails seen on the fracture surfaces.Moreover,the bending strength of 213±21 MPa,Vickers hardness of 9.3±0.1 MPa and fracture toughness of6.21±0.12 MPa·m1/2are obtained for the prepared composite.展开更多
PrrOll nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant. The calcination process was affected, for ...PrrOll nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant. The calcination process was affected, for 1 h in static air atmosphere, at 400-700 ℃ temperature range. The different samples were characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM）, field emission scanning electron microscopy （FE-SEM）, thermogravimetric analysis （TGA）, in situ electrical conductivity, and N2 adsorption/desorption. The obtained results demonstrated that nano-crystalline Pr6O11, with crystallites size of 6-12 nm, started to form at 500 ℃. Such value increased to 20-33 nm for the sample calcined at 700℃. The as-synthesized PrrOll nanoparticles presented high electrical conductivity due to electron hopping between Pr（III）-Pr（IV） pairs.展开更多
The non-isothermal kinetics of mullite formation from both non-mixed and mixed with different rare earth oxides（Pr6O11 and Er2O3） kaolinite were studied by comprehensive thermal analysis technologies and X-ray diffr...The non-isothermal kinetics of mullite formation from both non-mixed and mixed with different rare earth oxides（Pr6O11 and Er2O3） kaolinite were studied by comprehensive thermal analysis technologies and X-ray diffraction（XRD）. Meanwhile, Kissinger equation, Ozawa equation and JMA modified equation（I） and（II） were employed for analysis of the effects of Pr6O11 and Er2O3 on the kinetics of kaolinite in phase transformation at high temperatures. The results showed that the addition of two kinds of rare earth oxides influenced the crystallization kinetic parameters of kaolinite. Crystallization activation energies and frequency factors of the kaolinite mixed with Pr6O11 were obviously decreased compared with the kaolinite with none, but the kaolinite mixed with Er2O3 weakly decreased. Crystallization behaviors were not changed, belonging to volume crystallization. Mullite formation from kaolinite was suppressed while generation of cristobalite was promoted by Pr6O11, and effect of Er2O3 on mullite formation from kaolinite under high temperature was not evident.展开更多
基金supported by the National Natural Science Foundation of China (No. 20976149)
文摘A solid ternary mixture consisting of NaF,silicon and one metal oxide such as La2O3,CeO2,Pr6O11,Nd2O3,and Y2O3 was prepared and usedas de-fluorinated reagent for CF4 decomposition.The results show that 90% conversion of CF4 can be reached initially over NaF-Si-La2O3,NaF-Si-CeO2,NaF-Si-Nd2O3,and NaF-Si-Y2O3 at 850 C.The fresh and used reagents were characterized using XRD and XPS techniques.It was found that the active components of NaF and metal oxides in NaF-Si-CeO2,NaF-Si-Pr6O11,NaF-Si-Nd2O3,and NaF-Si-Y2O3 weretransformed into inert phases of mixed metal fluorides and silicates,respectively,resulting in an ineffective utilization of these de-fluorinatedreagents,whereas no inert phases from NaF and La2O3 can be observed in the used NaF-Si-La2O3,indicating the NaF-Si-La2O3 reagent couldbe utilized more efficiently than the other reagents in CF4 decomposition.
文摘The present work investigates the effect of high praseodymium oxide(Pr6O11)content on the microstructure and phase formation of mullite(3Al_(2)O_(3)·2SiO_(2))precursor by means of the spark plasma sintering process.30 wt%Pr6O11was added to a mullite precursor consisting of aluminum nitrate nonahydrate and tetraethyl orthosilicate through a high energy mixer mill in ethanol media.The spark plasma sintering was performed at a te mperature of 1200℃under 23 Pa vacuum co nditions by applying initial and final pressure of 10 and 30 MPa,respectively.XRD analysis confirms the existence of mullite,alumina,Pr6O11,Pr2O3and quartz as the only crystalline phases.FESEM images reveal an interesting deposition of hexagonal-shaped Al_(2)O_(3)particles on polished surfaces and complex oxide phases of the fiber network adhering to alumina particles in the form of tails seen on the fracture surfaces.Moreover,the bending strength of 213±21 MPa,Vickers hardness of 9.3±0.1 MPa and fracture toughness of6.21±0.12 MPa·m1/2are obtained for the prepared composite.
文摘PrrOll nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant. The calcination process was affected, for 1 h in static air atmosphere, at 400-700 ℃ temperature range. The different samples were characterized using X-ray diffraction （XRD）, transmission electron microscopy （TEM）, field emission scanning electron microscopy （FE-SEM）, thermogravimetric analysis （TGA）, in situ electrical conductivity, and N2 adsorption/desorption. The obtained results demonstrated that nano-crystalline Pr6O11, with crystallites size of 6-12 nm, started to form at 500 ℃. Such value increased to 20-33 nm for the sample calcined at 700℃. The as-synthesized PrrOll nanoparticles presented high electrical conductivity due to electron hopping between Pr（III）-Pr（IV） pairs.
基金supported by the National Natural Science Foundation of China(NSFC)(51264009)the Natural Science Foundation of Jiangxi Province of China(20122BAB206023)
文摘The non-isothermal kinetics of mullite formation from both non-mixed and mixed with different rare earth oxides（Pr6O11 and Er2O3） kaolinite were studied by comprehensive thermal analysis technologies and X-ray diffraction（XRD）. Meanwhile, Kissinger equation, Ozawa equation and JMA modified equation（I） and（II） were employed for analysis of the effects of Pr6O11 and Er2O3 on the kinetics of kaolinite in phase transformation at high temperatures. The results showed that the addition of two kinds of rare earth oxides influenced the crystallization kinetic parameters of kaolinite. Crystallization activation energies and frequency factors of the kaolinite mixed with Pr6O11 were obviously decreased compared with the kaolinite with none, but the kaolinite mixed with Er2O3 weakly decreased. Crystallization behaviors were not changed, belonging to volume crystallization. Mullite formation from kaolinite was suppressed while generation of cristobalite was promoted by Pr6O11, and effect of Er2O3 on mullite formation from kaolinite under high temperature was not evident.
