High-purity straight and discrete multiwalled boron nitride nanotubes （BNNTs） were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an...High-purity straight and discrete multiwalled boron nitride nanotubes （BNNTs） were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray （EDX） and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 ℃, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30-50 nm were mostly observed in a temperature range of 1,280-1,320 ℃. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 ℃, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.展开更多
Boron concentrations and isotope compositions have been measured for 93 water samples from the hot springs and drill-holes in the geothermal system in the Yunnan-Tibet Geothermal Belt(YTGB),China.Boron concentrations ...Boron concentrations and isotope compositions have been measured for 93 water samples from the hot springs and drill-holes in the geothermal system in the Yunnan-Tibet Geothermal Belt(YTGB),China.Boron concentrations range from 0.036–472.4ppm,and theδ11B values range from -16.0‰to 13.1‰,indicating the non-marine origin for each geothermal system.We observed a clear binary mixing relationship between the B concentrations and B isotope compositions in Tibet geothermal area.This relationship can be well explained by two sources,i.e.,marine carbonate rocks and magmatic rocks,for the Tibet geothermal water.No evidence supports a mantle contribution to B.In addition,we found that the precipitation only plays a dilution role for B of geothermal waters.δ11B values for the precipitation across the southern Tibetan Plateau area range from -6.0‰ to -6.8‰at least.Due to data scarcity in Yunnan geothermal area,we observed possible different boron sources from the Tibet geothermal system.Comparing it with other geothermal systems in the world,we found that the samples from YTGB have the lowestδ11B values and the largest range of B concentration,which might be related to their special geological background.On the whole,the world geothermalδ11B-Cl/B relation suggests a mixing process between marine and non-marine sources.Additionally,we suggest that B source of B-enriched geothermal waters is mainly from B-enriched crustal country-rocks,instead of mantle.展开更多
文摘High-purity straight and discrete multiwalled boron nitride nanotubes （BNNTs） were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray （EDX） and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 ℃, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30-50 nm were mostly observed in a temperature range of 1,280-1,320 ℃. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 ℃, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.
基金supported by National Natural Science Foundation of China(Grant Nos.41203012,41030317)China Geological Survey(Grant No.1212011085524)
文摘Boron concentrations and isotope compositions have been measured for 93 water samples from the hot springs and drill-holes in the geothermal system in the Yunnan-Tibet Geothermal Belt(YTGB),China.Boron concentrations range from 0.036–472.4ppm,and theδ11B values range from -16.0‰to 13.1‰,indicating the non-marine origin for each geothermal system.We observed a clear binary mixing relationship between the B concentrations and B isotope compositions in Tibet geothermal area.This relationship can be well explained by two sources,i.e.,marine carbonate rocks and magmatic rocks,for the Tibet geothermal water.No evidence supports a mantle contribution to B.In addition,we found that the precipitation only plays a dilution role for B of geothermal waters.δ11B values for the precipitation across the southern Tibetan Plateau area range from -6.0‰ to -6.8‰at least.Due to data scarcity in Yunnan geothermal area,we observed possible different boron sources from the Tibet geothermal system.Comparing it with other geothermal systems in the world,we found that the samples from YTGB have the lowestδ11B values and the largest range of B concentration,which might be related to their special geological background.On the whole,the world geothermalδ11B-Cl/B relation suggests a mixing process between marine and non-marine sources.Additionally,we suggest that B source of B-enriched geothermal waters is mainly from B-enriched crustal country-rocks,instead of mantle.
