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
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
The electron donor properties of Pr6O11 activated at 300, 500 and 800℃ are reported from the studies on adsorption of electron acceptors of various electron affinity (7, 7, 8, 8-tetracyanoquinodimethane , 2. 3. 5. 6-...The electron donor properties of Pr6O11 activated at 300, 500 and 800℃ are reported from the studies on adsorption of electron acceptors of various electron affinity (7, 7, 8, 8-tetracyanoquinodimethane , 2. 3. 5. 6-tetrachloro-1, 4-benzoquin one, p-dinitrobenzene, and m-dinitrobenzcne) in three solvents (acetonitrile, 1,4-dioxan and ethyl acetate). The extent of electron transfer during adsorption is understood from magnetic measurements and ESR spectral data. The corresponding data on mixed oxides of Pr and Al are reported for various compositions. The acid / base properties of these oxides are determined using a set of Hammett indicators.展开更多
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.
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.
文摘The electron donor properties of Pr6O11 activated at 300, 500 and 800℃ are reported from the studies on adsorption of electron acceptors of various electron affinity (7, 7, 8, 8-tetracyanoquinodimethane , 2. 3. 5. 6-tetrachloro-1, 4-benzoquin one, p-dinitrobenzene, and m-dinitrobenzcne) in three solvents (acetonitrile, 1,4-dioxan and ethyl acetate). The extent of electron transfer during adsorption is understood from magnetic measurements and ESR spectral data. The corresponding data on mixed oxides of Pr and Al are reported for various compositions. The acid / base properties of these oxides are determined using a set of Hammett indicators.
