Eu Mossbauer spectra of BaFBr:Eu phosphor are reported for the first time.The results show that f(Eu(2+) )<f(Eu(3+)) or <x2>Eu(2+)><x2>Eu(3+),which indicates that the attraction between phonons and E...Eu Mossbauer spectra of BaFBr:Eu phosphor are reported for the first time.The results show that f(Eu(2+) )<f(Eu(3+)) or <x2>Eu(2+)><x2>Eu(3+),which indicates that the attraction between phonons and Eu(2+) is stronger than that between phonons and Eu(3+),this may cause a faster increase of f(Eu=(2+)vs f(Eu(3+)) when temperature decreases as observed in the experiments.It is also found from Mossbauer investigation that when temperature decreases,the relative content of Eu(2+) decreases, while that of Eu(3+) increases.The temperature dependent Mossbauer spectra provide evidence for electron exchange or hopping between Eu(2+) or Eu(3+) sites in BaFBr lattice. The Mossbauer results are discussed and compared with the results of XPS and Photoluminescence studies.展开更多
Reduction behavior of preoxidized synthetic ilmenite was studied by means of Mossbauer spectra. In the course of reduction, iron component in the samples is reduced in stepwise: Fe 3+ →Fe 2+ →Fe 0, and some...Reduction behavior of preoxidized synthetic ilmenite was studied by means of Mossbauer spectra. In the course of reduction, iron component in the samples is reduced in stepwise: Fe 3+ →Fe 2+ →Fe 0, and some intermediate compounds, such as Fe 3O 4, Fe 2TiO 4 etc . and their solid solution may be generated besides Fe 2O 3 and FeTiO 3. If the reduction temperature is higher than 1173 K, the metallization needs only half time of the case when the temperature is lower than 1073 K.展开更多
The spatial occurrence of iron in kaolinite of coal measures west of Beijing was studied by using the Mossbauer spectroscopy technique and a step-by-step method of fitting. The results show that there are three kinds ...The spatial occurrence of iron in kaolinite of coal measures west of Beijing was studied by using the Mossbauer spectroscopy technique and a step-by-step method of fitting. The results show that there are three kinds of spatial occurrence in kaolinites： tetra-coordination Fe（3＋） in Si-O tetrahedrons, sexa-coordination Fe（3＋） in A1--O octahedrons and sexa-coordination Fe（2＋） in A1-O octahedrons, respectively occupying 51.72 %, 37.25 % and 11.03 %, Neither foreign matter of magnetic Fe mineral nor superparamagnetic goethite exists in kaolin concentrates. Fe in kaolin concentrates cannot be removed by conventional methods, which is significant for both theoretical research on kaolinite minerology and practical use of the kaolinites of coal measures west of Beijing.The research also illustrates that the Mossbauer spectroscopy is an effective method in studying the micro-superfine Fe in kaolin.展开更多
An Fe-based nanocrystalline alloy powder is important for application in microwave absorption,and the particle size has a critical impact on the electromagnetic microwave parameters.Therefore,it is necessary to study ...An Fe-based nanocrystalline alloy powder is important for application in microwave absorption,and the particle size has a critical impact on the electromagnetic microwave parameters.Therefore,it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Febased nanocrystalline powers.In this study,Fe-B-P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment.We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe-B-P particles.The experimental results indicate that the Fe-B-P particles synthesized through an aqueous chemical reduction are amorphous spheres.Fe-B-P particles with an original particle size of 200-1200 nm can be milled into an irregular shape with the size reduced to\500 nm after 0.5 h of ball milling,and subsequently,the particles become smaller with increases in the milling time,with traces of Fe2O3 generated on the particle surface.The results of the Mo¨ssbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property.The volume proportions of the superparamagnetic component increase from 13.1 to 15.8%as the treatment time increases.We measured the permittivity and permeability spectra of Fe-B-P particles within the frequency range of 2-18 GHz.The reflection loss(RL)is-10 dB for an absorber thickness of 1.7-5.0 mm.The RL is-20 dB for an absorber thickness of 1.9-2.7 mm.The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency,which will broaden the bandwidth of the absorption as well.展开更多
文摘Eu Mossbauer spectra of BaFBr:Eu phosphor are reported for the first time.The results show that f(Eu(2+) )<f(Eu(3+)) or <x2>Eu(2+)><x2>Eu(3+),which indicates that the attraction between phonons and Eu(2+) is stronger than that between phonons and Eu(3+),this may cause a faster increase of f(Eu=(2+)vs f(Eu(3+)) when temperature decreases as observed in the experiments.It is also found from Mossbauer investigation that when temperature decreases,the relative content of Eu(2+) decreases, while that of Eu(3+) increases.The temperature dependent Mossbauer spectra provide evidence for electron exchange or hopping between Eu(2+) or Eu(3+) sites in BaFBr lattice. The Mossbauer results are discussed and compared with the results of XPS and Photoluminescence studies.
文摘Reduction behavior of preoxidized synthetic ilmenite was studied by means of Mossbauer spectra. In the course of reduction, iron component in the samples is reduced in stepwise: Fe 3+ →Fe 2+ →Fe 0, and some intermediate compounds, such as Fe 3O 4, Fe 2TiO 4 etc . and their solid solution may be generated besides Fe 2O 3 and FeTiO 3. If the reduction temperature is higher than 1173 K, the metallization needs only half time of the case when the temperature is lower than 1073 K.
基金Project 3042013 supported by Natural Science Foundation of Beijing
文摘The spatial occurrence of iron in kaolinite of coal measures west of Beijing was studied by using the Mossbauer spectroscopy technique and a step-by-step method of fitting. The results show that there are three kinds of spatial occurrence in kaolinites： tetra-coordination Fe（3＋） in Si-O tetrahedrons, sexa-coordination Fe（3＋） in A1--O octahedrons and sexa-coordination Fe（2＋） in A1-O octahedrons, respectively occupying 51.72 %, 37.25 % and 11.03 %, Neither foreign matter of magnetic Fe mineral nor superparamagnetic goethite exists in kaolin concentrates. Fe in kaolin concentrates cannot be removed by conventional methods, which is significant for both theoretical research on kaolinite minerology and practical use of the kaolinites of coal measures west of Beijing.The research also illustrates that the Mossbauer spectroscopy is an effective method in studying the micro-superfine Fe in kaolin.
基金supported by the National Natural Science Foundation of China (Nos. 51401049, U1704253)Natural Science Foundation of Zhejiang Province (No. LR18E010001)Key Research and Development Program of Zhejiang Province (No. 2019C01121)
文摘An Fe-based nanocrystalline alloy powder is important for application in microwave absorption,and the particle size has a critical impact on the electromagnetic microwave parameters.Therefore,it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Febased nanocrystalline powers.In this study,Fe-B-P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment.We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe-B-P particles.The experimental results indicate that the Fe-B-P particles synthesized through an aqueous chemical reduction are amorphous spheres.Fe-B-P particles with an original particle size of 200-1200 nm can be milled into an irregular shape with the size reduced to\500 nm after 0.5 h of ball milling,and subsequently,the particles become smaller with increases in the milling time,with traces of Fe2O3 generated on the particle surface.The results of the Mo¨ssbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property.The volume proportions of the superparamagnetic component increase from 13.1 to 15.8%as the treatment time increases.We measured the permittivity and permeability spectra of Fe-B-P particles within the frequency range of 2-18 GHz.The reflection loss(RL)is-10 dB for an absorber thickness of 1.7-5.0 mm.The RL is-20 dB for an absorber thickness of 1.9-2.7 mm.The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency,which will broaden the bandwidth of the absorption as well.
