In the Universe, chemical reactions occur at very low temperature, very close to 0K. According to the standard Arrhenius mechanism, these reactions should occur with vanishingly small efficiency. However, cold planets...In the Universe, chemical reactions occur at very low temperature, very close to 0K. According to the standard Arrhenius mechanism, these reactions should occur with vanishingly small efficiency. However, cold planets of the solar system, such as Pluto, are covered by a crust composed of ammonia and methane, produced on earth only at very high temperature and pressure, in the presence of catalysts. This observation is incompatible with the predictions of Arrhenius kinetics. Here, we propose a general mechanism to explain the abundance of chemical reactions at very low temperature in the Universe. We postulate that the feedback between mechanical stress and chemical reaction provides, through fracture propagation, the energy necessary to overcome the activation barrier in the absence of thermal fluctuations. The notion described in this work can also be applied to other fields such as explosive-like solid phase transformations and catastrophical geotectonics phenomena (earthquakes).展开更多
Crystalline and nanostructured cobalt （CoFe2O4）, nickel （NiFe2O4）, zinc （ZnFe2O4） and manganese （MnFe2O4） spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, repr...Crystalline and nanostructured cobalt （CoFe2O4）, nickel （NiFe2O4）, zinc （ZnFe2O4） and manganese （MnFe2O4） spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of copredpitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining copredpitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low tem- perature of 75 ℃ and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction （XRPD）, while X-ray photoelectron spectroscopy （XPS） and inductively coupled plasma-atomic emission spectroscopy （ICP-AES） analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy （TEM） observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer （SQUID） revealing hard and soft ferrimagnetic behavior, respectively.展开更多
研究了低于GeCl4挥发温度密闭分解含锗的金合金的技术、KIO3电位滴定常量Ge的方法和提高方法选择性的条件;比较了电位与传统碘淀粉终点指示法对分析结果准确度、精密度,终点稳定性和敏锐度,方法选择性等的影响。结果表明:在优化条件下,...研究了低于GeCl4挥发温度密闭分解含锗的金合金的技术、KIO3电位滴定常量Ge的方法和提高方法选择性的条件;比较了电位与传统碘淀粉终点指示法对分析结果准确度、精密度,终点稳定性和敏锐度,方法选择性等的影响。结果表明:在优化条件下,控制消解温度不超过75℃时,9mL HCl-2 mL H2O2能完全消解0.10 g样品,且无Ge的损失。经蒸馏分离收集锗,消除Au(Ⅲ)及常见共存离子的影响。电位终点指示法与传统碘淀粉终点指示法对锗滴定结果准确度基本一致,电位终点指示法实用性更强。方法用于AuGe12、AuGeNi12-2、AuAgGe18.8-12.5、AuAgGeNi43.8-6-0.2等系列金锗合金中6%～13%锗含量的测定,标准偏差和相对标准偏差分别为0.0214%～0.0450%和0.304%～0.391%,样品加标回收率99.11%～100.99%。展开更多
文摘In the Universe, chemical reactions occur at very low temperature, very close to 0K. According to the standard Arrhenius mechanism, these reactions should occur with vanishingly small efficiency. However, cold planets of the solar system, such as Pluto, are covered by a crust composed of ammonia and methane, produced on earth only at very high temperature and pressure, in the presence of catalysts. This observation is incompatible with the predictions of Arrhenius kinetics. Here, we propose a general mechanism to explain the abundance of chemical reactions at very low temperature in the Universe. We postulate that the feedback between mechanical stress and chemical reaction provides, through fracture propagation, the energy necessary to overcome the activation barrier in the absence of thermal fluctuations. The notion described in this work can also be applied to other fields such as explosive-like solid phase transformations and catastrophical geotectonics phenomena (earthquakes).
文摘Crystalline and nanostructured cobalt （CoFe2O4）, nickel （NiFe2O4）, zinc （ZnFe2O4） and manganese （MnFe2O4） spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of copredpitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining copredpitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low tem- perature of 75 ℃ and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction （XRPD）, while X-ray photoelectron spectroscopy （XPS） and inductively coupled plasma-atomic emission spectroscopy （ICP-AES） analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy （TEM） observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer （SQUID） revealing hard and soft ferrimagnetic behavior, respectively.
文摘研究了低于GeCl4挥发温度密闭分解含锗的金合金的技术、KIO3电位滴定常量Ge的方法和提高方法选择性的条件;比较了电位与传统碘淀粉终点指示法对分析结果准确度、精密度,终点稳定性和敏锐度,方法选择性等的影响。结果表明:在优化条件下,控制消解温度不超过75℃时,9mL HCl-2 mL H2O2能完全消解0.10 g样品,且无Ge的损失。经蒸馏分离收集锗,消除Au(Ⅲ)及常见共存离子的影响。电位终点指示法与传统碘淀粉终点指示法对锗滴定结果准确度基本一致,电位终点指示法实用性更强。方法用于AuGe12、AuGeNi12-2、AuAgGe18.8-12.5、AuAgGeNi43.8-6-0.2等系列金锗合金中6%～13%锗含量的测定,标准偏差和相对标准偏差分别为0.0214%～0.0450%和0.304%～0.391%,样品加标回收率99.11%～100.99%。
