导　　师： 孙艳辉

学科专业： G0304

授予学位： 硕士

作　　者： ;

机构地区： 华南师范大学

摘　　要： 大量研究表明，稀土液态或固态配合物的性质，如稳定常数、分离系数、△<,r>，g<'θ><,m>、△<,r>h<'θ><,m>、△<,r>s<'θ><,m>、晶格常数等，对其原子序数或离子基态作图，则存在如钆断、四分组效应、斜w效应等规律性。但是对于稀土气态配合物klncl<,4>还没有类似的系统研究，其原因是缺少包括全部稀土元素在内的热力学性质数据。 稀土气态配合物已广泛应用于激光材料、发光材料、无水氯化稀土的制备，近期更将其用于火法分离混合稀土。而稀土气态配合物的热力学研究还仅限于少数几个元素，上述应用缺乏理论指导。因此，无论从完善稀土化学理论的角度，还是从为其应用提供理论指导的角度，系统的研究稀土气态配合物的热力学性质都是非常重要的。 本文包括两部分内容。第一部分为用于化学气相传输反应的无水稀土氯化物的制备。本文采用过量氯化铵低温氯化法制备无水稀土氯化物。从保护气氛、装料方式、氯化温度等方面对氯化铵氯化稀土的条件进行探索，得到最佳氯化条件为：采用层铺法的装料方式，温度340℃，在空气气氛中进行氯化焙烧40min。同时探索了稀土氧化物的氯化机理。结果表明ceo<,2>的氯化表现出特殊性，主要反应为ceo<,2>与固态nh<,4>cl之间的复分解反应。其余稀土元素的氯化机理相似，都是氯化铵的热解产物hcl氯化稀土氧化物为该实验的主要反应，同时伴随少量nh<,4>cl直接参与氯化的反应。 第二部分是用化学气相传输法对稀土氯化物与氯化钾生成的气态配合物的反应lncl<,3>(g)+kcl(g)=klncl<,4>(g)(ln=sc～eu)进行研究，在1073～1323k温度范围内选取六个实验温度，由化学气相传输实验数据，可计算出稀土气态配合物klncl<,4>在不同温度的稳定常数及反应的吉布斯自由能变△<,r>，g<,m>，进而通过最小二乘法计算出反应的焓变△<,r>h<'θ><,m>和熵变△<,r>s<'θ><,m>。实验结果显示： (1)配位反应的平衡常数随着温度的升高而降低。表明气态配合物在高温更易分解。 (2)配合反应的△<,r>h<'θ><,m>为负值，说明该类型的配合反应为放热反应。反应熵变△<,r>s<'θ><,m><0。反应的吉布斯自由能变△<,r>g<'θ><,m>随温度的升高而升高，表明气态配合物klncl<,4>的稳定性随温度的升高而降低。 (3)从la～eu，气态配合物的焓变△<,r>h<'θ><,m>和熵变△<,r>s<'θ><,m>先是从la到nd逐渐升高，到sm、eu处出现转折。 (4)和镧系位于同一族的sc和y的气态配合物klncl<,4>的热力学性质表现出明显的差异。如在本研究所有稀土元素中，ksccl<,4>的焓变和熵变最小。kycl<,4>的焓变和熵变接近于重稀土的焓变和熵变。 (5)配合反应能够大幅度提高稀土氯化物lncl<,3>的挥发性但却降低配位体kcl的挥发性。随着温度升高，lncl<,3>的提高系数有降低的趋势，kcl的挥发性降低程度有减小趋势。 It is well known that certain regularities exist in condensed states rareearth complexes when diverse physical chemical properties, such as stabilityconstants, separation factors,△/_rH/_m~θ,△/_rS/_m~θand△/_rG/_m~θare plotted againstthe lanthanide atomic number or the ground electronic state of rare earth ions,known as gadolinium break, tetrad effect and inclined W effect. However, nosimilar systematic analysis has been reported yet for rare earth vapourcomplexes KLnCl/_4 due to the lack of a complete set of property values for allthe rare earth elements. The rare earth vapour complexes KLnCl/_4 have been investigated widelyfor potential applications as laser materials, luminous material, in preparationof anhydrous rare earth chlorides and mutual separation of rare earthelements. But the study on their thermodynamic properties has been onlycarried out for a few elements. Therefore, thermodynamic studies on the rareearth vapour complexes are required to understand the reaction mechanisms. This paper contains two parts. One is the preparation of anhydrate rareearth chlorides for chemical vapor transport reaction by excess NH/_4Cl atlower temperature. In this study, we investigated some influence factors onthe chlorinated yield such as the protect atmosphere, the material loadingmethod, chlorination temperature and time. The results showed that the bestchlorination condition is that the material was loaded by layer spreadmethod and chlorinated by NH/_4Cl at 340℃in air atmosphere for 40 min.More over, the chlorination mechanism of rare earth oxides chlorinated byNH/_4Cl was studied. The results indicated that CeO/_2 show particularity compared with the other rare earth oxides, and the main chlorination ofCeO/_2 is the double decomposition reaction between CeO/_2 and solid NH/_4Cl,while the other rare earth oxides are chlorinated by HCl gas decomposedfrom NH/_4Cl combined with the direct chlorination by NH/_4Cl. The second part is thermodynamic study of vapor complexes KLnCl/_4 bychemical vapor transport reaction, which is the main content of this paper. Inthis study, the reaction LnCl/_3/(g/)+KCl/(g/)=KLnCl/_4/(g/) was studied bychemical vapor transport reaction at 1073～1323 K for Ln=Sc～Eu. Theequilibrium constants and the change of Gibbs free energyΔ/_rG/_m at sixdifferent temperatures were calculated directly from analytical data of thechemical vapor transport experiments. The enthalpy changeΔ/_rH/_m~θ, entropychangeΔ/_rS/_m~θvalues of the reaction were derived from the equilibriumconstants by the method of least squares computation. There are someconclusions for the study as follows: /(1/) The equilibrium constant of forming certain metal halide vaporcomplexes decreases with temperature increasing, which showed the vaporcomplexes are more easy decomposed at higher temperature. /(2/) The enthalpy changeΔ/_rH/_m~θof the reaction is negative, whichshowed the complex reaction is exothermic. The entropy changeΔ/_rS/_m~θisnegative too. In addition, the change of Gibbs free energyΔ/_rG/_m~θof thereaction is increasing with temperature increasing which means the stable ofthe vapor complex KLnCl/_4 is decreasing with temperature increasing. /(3/) The enthalpy changeΔ/_rH/_m~θand the entropy changeΔ/_rS/_m~θof thereaction is increasing from La to Nd firstly and then turn the contrary for Smand Eu. /(4/) Sc and Y, which located at the same group as the lanthanide elements,showed obvious difference from the lanthanide elements for forming vapor complexes KLnCl/_4, that is the enthalpy changeΔ/_rH/_m~θand the entropychangeΔ/_rS/_m~θfor KScCl/_4 are the most least, while those properties forKYCl/_4 are near to that of heavy rare earth vapor complexes. /(5/) The results suggest that the complex reaction enhanced largely thevolatility of lanthanide chlorides but decrease that of potassium chloride, andthe enhancement factor were decreasing with temperature increasing.

关 键 词： 稀土气态配合物 化学气相传输 热力学性质 焓变 熵变

分 类 号： [O614.33 O641.4]

领　　域： [理学] [理学] [理学] [理学]