Electrochemical Synthesis And Characterization Of Nanometer Scale Ceria, Lanthana And Neodymium Rare Earth Oxides

Rare earth oxides, for their special properties, have been used in many fields such as ceramic industry, catalyst and catalyst carrier. What is most important is that they can be reclaimed and cannot corrode the equipment. Because of the wildly used of the rare earth oxides, people focused attention on investigating the methods of its preparation.This thesis has reviewed the resources of rare earth in our country, the markets and the condition of application in domestic and other countries. The fabrication methods of the nanometer CeO2, La2O3, Nd2O3 were comparative analysed. Meanwhile, the method of electrochemical synthesis nanometer scale ceria, lanthana and neodymium rare earth oxides is discussed, and the method of electrochemical synthesis rare earth oxides in a single chamber cell is investigated in details. Different electrolyte solution systems were electrolyzed at a constant current density in a single chamber cell. With the reactions of electrolysis, hydroxide ions are produced or hydrogen ions are consumed in the vicinity of electrode, they causes the increase of local pH at the electrode surface. So the depositions of hydrate or hydrated oxide are obtained. The mechanisms of electrochemical synthesis are proposed and investigated elementarily. Meanwhile, in order to understand the reaction process, electrode-solution interfacial area and the model of electrochemical reactions was introduced in this thesis. Since the evolution of pH value indeed corresponds to the extent of reaction, monitoring the pH change is helpful to comprehend the formation mechanism.The XRD, TEM, SEM, TG-DTA and FT-IR are used to characterize the as products of rare earth oxides, the results are shown as:1. cerium (III) chloride solution was electrolyzed in a single chamber cell, CeO2 was obtained after been calcined at high temperature, it was shown that the ceria powder was spherical in shape with the diameter of 20-50 nm. The mechanism of chlorine oxidation was proposed and investigated elementarily. In addition, the CeO2 particle with the size of 30-50 nm, 20-100 nm is prepared by the used of Ce(NO3)3, CeCl3-KI solution in a single chamber cell respectively. The CeCl3 solution is electrolysed in the double chamber cell, which the anion-exchange membrane is used, and then CeO2 particle with the smaller size of 7-20 nm is prepared.Comparing the products produced by the two methods, the reasons were analyzed. On the size of CeO2 particle, the influences of additives are discussed in this thesis: CeO2 particle with the size of 10-30 nm was prepared by adding ethanol and acetylacetone solution. The group of acac is existed in the precursor by the analyzed of FT-IR. When the SDS is used as the additive, CeO2 particle (10 nm) is obtained. The mix solution of glycol and polyethylene glycol was used as the additive, the CeO2 of flake was obtained.2. La(NO3)3 and LaCl3 solution were electrolyzed with constant current density in a single chamber cell respectively. After the deposition been calcined at 650℃, La2O3 nano-rods with diameters of 20 nm and lengths of about 350 nm and spherical LaOCl with the size of 15-30 nm were prepared. The synthesis mechanism was elementarily investigated in this thesis. Meanwhile, La2O3 nano-rods with diameters of 30 nm and lengths of about 170 nm and spherical LaOCl with the size of 20-45 nm were prepared after the precursor calcined at 800℃. La(NO3)3 solution was electrolyzed in a single chamber cell, the precursor was obtained, after the precursor been calcined at 650℃, XRD patterns reveal that the patterns are the mixed La2O3 and La2CO5 diffraction. Meanwhile, the formed mechanisms of La2O3 and LaOCl are analysed from the view of XRD, TG-DTA and pH data, and the LaOCl synthesis mechanism was proposed in this thesis.3. NdCl3 solution was electrolyzed in a double chamber cell, under the electrolyzing process with constant current density. The pH of the solution is increased in the cathodal cell so that the Nd3+ is hydrolysed and the Nd(OH)3 is formed. Nd2O3 with the size of 30-50 nm is prepared after the deposition calcined at 600℃. After it is calcined at 800℃, Nd2O3 with the size of 30-60 nm is obtained. Furthermore, on the effect of grain size, the current density of 100 A/m2 and 500 A/m2 and the heat treatment of 600℃and 800℃are discussed respectively. In addition, the synthesis mechanism was elementarily investigated in this thesis.