§20-2 锕系元素The Actinides我们只介绍铀及其化合物的性质。铀的重要化合物 UO2（暗棕色） U3O8（墨绿色） UO3（橙黄色）一、铀的氧化物 1．UO3 (1) amphoteric oxide (2) decomposition 2UO32UO2 + O2 (3) preparation 2UO2(NO3)22UO3 + 4NO2 + O2 2．U3O8 preparation：3U(C2O4)2U3O8 + 8CO + 4CO2 或者：3U + 4O2U3O8 U3O8不溶于水，但溶于酸，生成。二、硝酸铀酰[UO2(NO3)2] 1. Preparation UO3 + 2HNO3UO2(NO3)2 + H2O2. Properties 水解生成 加碱生成 Na2U2O7·6H2O（黄色），加热脱水，生成无水 Na2U2O7，俗称铀黄。3. Structure UO2(NO3)2·2H2O（六角双锥）三、UF6（八面体）1. Preparation UO3 + 3SF4UF6 + 3SOF22. Hydrolysis UF6 + 2H2OUO2F2 + 4HFSuperconductivityFig. 20.1 The structure of UO2(NO3)2·2H2OH. Kammerling Onnes (Nobel Prize for Physics, 1913) discovered superconductivity in Leiden in 1911 when he cooled mercury to the temperature of liquid helium; Many other materials, mostly metals and alloys, were subsequently found to display superconductivity at very low temperatures.Two properties characterize a superconductor:1. It is perfectly conducting, i.e. it has zero resistance.2. It is perfectly diamagnetic, i.e. it completely excludes applied magnetic fields. This is the Meissner effect and is the reason why a superconductor can levitate a magnet. Superconductivity exists within the boundaries of three limiting parameters which must not be exceeded ： the critical temperature (Tc), the critical magnetic field (Hc) and the critical current density (Jc).Until 1986 the highest recorded value of Tc was ~23K for Nb3Ge but in that year Bednorz and Muller, in pioneering work for which they received the 1987 Nobel Prize for Physics, reported Tc=30K in an entirely new Ba-La-Cu-O ceramic system quickly identified as La2-xBaxCuO4.This prompted an examination of other Cu-O systems an...
