By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been...By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been studied. The experimental results show that, with the increase of the Dy content, the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. For the samples with x=0.20 and 0.30, their magnetic behaviors are abnormal at low temperature, and their resistivities at low temperature have a minimum value. These peculiar phenomena not only come from the lattice effect induced by doping, but also from extra magnetic coupling induced by doping.展开更多
Supergene Mn-oxide deposits are commonly related to thick weathering profiles and form as a result of intense and prolonged weathering of Mn-bearing precursor rocks, processes facilitated by a combination of multiple ...Supergene Mn-oxide deposits are commonly related to thick weathering profiles and form as a result of intense and prolonged weathering of Mn-bearing precursor rocks, processes facilitated by a combination of multiple factors including warm and wet climate, relatively quiescent tectonic environment, and favorable geomorphic setting. Precise age constraints of supergene Mn-oxides may provide valuable information on the climatic, tectonic, and geomorphic conditions prevailing in the geological past. 4~Ar]39Ar laser incremental heating analysis of cryptomelane from the Baye manganese deposit, western Yunnan-Guizhou Plateau, SW China, was conducted to provide numerical constraints on the ages of supergene Mn enrichment and growth rates of Mn-oxide veins. In this study, two Mn-oxide veins of 3-6 cm thickness, termed as Vein A and B, respectively, were col- lected for 4~Ar/39Ar dating. Vein A is subhorizontal and present in fractures parallel to schistosity of the Proterozoic spessartine schists, whereas Vein B is filled in nearly vertical fractures penetrating the schistosity. A combination of optical microscopy, XRD, SEM, and EMP analyses demonstrate that mineral grains extracted from both veins consist of pure, well-crystallized cryptomlane, which has acicular crystal forms and contains 0.96%4.70% K2O. Fourteen cryptomelane subsamples extracted from different growth bands of Vein A yield well-defined plateau ages ranging from 1.35 ± 0.05 to 1.16 ± 0.04 Ma （2or）, whereas seven subsamples obtained from Vein B have plateau ages ranging from 1.23 ±0.05 to 1.01 ± 0.04 Ma （20）. The age results permit estimation for the growth rates of both veins at ca. 115-153 and 34-67 mm Ma-1, respectively. Distinct growth rates between Veins A and B are likely reflective of different fluid pressures during their formation governed by the orientation of the fractures hosting the veins. The growth rates calculated for both veins are 1-2 orders of magnitude higher than the val- ues （〈1-10 mm Ma-l） estimated for Mn-oxide nodules in supergene Mn deposits elsewhere. The high growth rates obtained for the Baye samples are consistent with direct precipitation of tetravalent Mn-oxides from weathering solution in open cavities or fractures, characterized by incremental growth of Mn-oxide bands from the margin to the center of the cavities or fractures. In contrast, Mn-oxide nodules with low growth rates from other deposits formed through self-oxidation and self-catalization, and grow outwards from the nuclei. In addition, prevalence of warm and humid climate and prolonged tectonic uplift in the Yunnan Plateau may have also partly contributed to the rapid growth of Mn-oxides in the Baye deposit.展开更多
The performance and mechanism of manganate preoxidation process for organics removal were investigated in the present paper.The results showed that manganate was a potentially powerful oxidizing agent and could make t...The performance and mechanism of manganate preoxidation process for organics removal were investigated in the present paper.The results showed that manganate was a potentially powerful oxidizing agent and could make the natural organic matter(NOM)concentration of sample solution increase.The process of manganate in combination with ferrous sulphate(FeMnO)was effective for organics removal and with the highest removal rate of 89%when the FeMnO dose was 0.18 mmol/L.The fluorescence analysis showed that the fluorescence intensity values related to hydrophobic acids and model humic acid polymers were the highest and the relative position of the main peak fluorescence intensity was shifted towards lower emission wavelengths,which indicated the reduction in the degree of aromaticity of residual organic matter fraction.展开更多
基金This work was supported by the National Nature Science Foundation of China （No. 19934003） the State Key Project of Fundamental Research of China （No.001CB610604） the Item of Nature Science Research of Anhui （No. 2001kj244）.
文摘By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been studied. The experimental results show that, with the increase of the Dy content, the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. For the samples with x=0.20 and 0.30, their magnetic behaviors are abnormal at low temperature, and their resistivities at low temperature have a minimum value. These peculiar phenomena not only come from the lattice effect induced by doping, but also from extra magnetic coupling induced by doping.
基金supported by National Natural Science Foundation of China(Grant Nos.41202053&40573021)Fok Ying Tong Education Fund(Grant No.101017)+1 种基金Fundamental Research Funds for the Central Universities(Grant No.CUG120102)Program for New Century Excellent Talents in University(Grant No.NCET-05-0665)
文摘Supergene Mn-oxide deposits are commonly related to thick weathering profiles and form as a result of intense and prolonged weathering of Mn-bearing precursor rocks, processes facilitated by a combination of multiple factors including warm and wet climate, relatively quiescent tectonic environment, and favorable geomorphic setting. Precise age constraints of supergene Mn-oxides may provide valuable information on the climatic, tectonic, and geomorphic conditions prevailing in the geological past. 4~Ar]39Ar laser incremental heating analysis of cryptomelane from the Baye manganese deposit, western Yunnan-Guizhou Plateau, SW China, was conducted to provide numerical constraints on the ages of supergene Mn enrichment and growth rates of Mn-oxide veins. In this study, two Mn-oxide veins of 3-6 cm thickness, termed as Vein A and B, respectively, were col- lected for 4~Ar/39Ar dating. Vein A is subhorizontal and present in fractures parallel to schistosity of the Proterozoic spessartine schists, whereas Vein B is filled in nearly vertical fractures penetrating the schistosity. A combination of optical microscopy, XRD, SEM, and EMP analyses demonstrate that mineral grains extracted from both veins consist of pure, well-crystallized cryptomlane, which has acicular crystal forms and contains 0.96%4.70% K2O. Fourteen cryptomelane subsamples extracted from different growth bands of Vein A yield well-defined plateau ages ranging from 1.35 ± 0.05 to 1.16 ± 0.04 Ma （2or）, whereas seven subsamples obtained from Vein B have plateau ages ranging from 1.23 ±0.05 to 1.01 ± 0.04 Ma （20）. The age results permit estimation for the growth rates of both veins at ca. 115-153 and 34-67 mm Ma-1, respectively. Distinct growth rates between Veins A and B are likely reflective of different fluid pressures during their formation governed by the orientation of the fractures hosting the veins. The growth rates calculated for both veins are 1-2 orders of magnitude higher than the val- ues （〈1-10 mm Ma-l） estimated for Mn-oxide nodules in supergene Mn deposits elsewhere. The high growth rates obtained for the Baye samples are consistent with direct precipitation of tetravalent Mn-oxides from weathering solution in open cavities or fractures, characterized by incremental growth of Mn-oxide bands from the margin to the center of the cavities or fractures. In contrast, Mn-oxide nodules with low growth rates from other deposits formed through self-oxidation and self-catalization, and grow outwards from the nuclei. In addition, prevalence of warm and humid climate and prolonged tectonic uplift in the Yunnan Plateau may have also partly contributed to the rapid growth of Mn-oxides in the Baye deposit.
文摘The performance and mechanism of manganate preoxidation process for organics removal were investigated in the present paper.The results showed that manganate was a potentially powerful oxidizing agent and could make the natural organic matter(NOM)concentration of sample solution increase.The process of manganate in combination with ferrous sulphate(FeMnO)was effective for organics removal and with the highest removal rate of 89%when the FeMnO dose was 0.18 mmol/L.The fluorescence analysis showed that the fluorescence intensity values related to hydrophobic acids and model humic acid polymers were the highest and the relative position of the main peak fluorescence intensity was shifted towards lower emission wavelengths,which indicated the reduction in the degree of aromaticity of residual organic matter fraction.
