Zhaogang Liu

Preparation of large particle rare earth oxides by precipitation with oxalic acid

Abstract The large particle CeO2 and Y2O3 were prepared using oxalic acid as precipitator. The effects of operational parameters such as stirring velocity, precipitation temperature, feeding speed, aging time, precipitation method, and calcination temperature on particle size and loose density of CeO2 were studied. Under the particular conditions, particle median size of D50 ≥ 30μm, loose density of ≥ 2.0 g/ml of CeO2, and particle median size of D50 ≥ 20 μm of Y2O3 were prepared. This technology had advantages of simple process, less equipment investment, ease of use, and suitability for industrialization products.

Study on separation of rare earth elements in complex system

Abstract The effect of the feed acidity, acetic acid concentration and rare earth concentration on the distribution ratio, separation coefficient and extraction capacity of light rare earth elements were studied in the P204(DEHPA)-HCl system and P507(HEH/EHP)-HCl system both containing acetic acid, respectively. The results showed that the distribution ratio and separation coefficient decreased with increasing of acidity, and increased with increasing of acetic acid concentration and rare earths concentration, and the extraction capacity increased with increasing of acetic acid concentration. When pH value of feed was 2.0, [RE]/[acetic acid] was 1:1 and rare earth concentration 0.35 mol/L, in P204(DEHPA)- HCl system with acetic acid, the maximum separation coefficient( β ) reached to β Ce /La =4.09, β Pr/Ce =1.96 and β Nd/Pr =1.53, and the separation ability of this extraction system was better than P507(DEHPA)-HCl system.

Synthesis of cerium oxide particles via polyelectrolyte controlled nonclassical crystallization for catalytic application

A polyelectrolyte controlled nonclassical crystallization method has been used to synthesize cerium oxide particles with tailored morphology. The results reveal that the as-prepared particles exhibit high specific surface area and enhanced oxygen storage capacity.

Cerium dioxide with large particle size prepared by continuous precipitation

Abstract Cerium dioxide (CeO 2 ) has attracted much attention and has wide applications such as automotive exhaust catalysts, polishing materials for optical glasses and additives for advanced glasses, as well as cosmetic materials. The particle size and its distribution are key factors to the performance of the materials in the functional applications. However, control of particle size is still a challenge in materials synthesis. Therefore, continuous precipitation of cerium oxalate (precursor of ceria) was carried out at different operational conditions such as reactant concentration, agitation speed, feeding rate and reaction temperature, and their effect on the particle size distribution, distribution width and morphology of cerium oxalate were investigated. The optimum conditions for preparing cerium oxalate with large particle size were determined based on orthogonal test as follows: [Ce(NO 3 )]=0.02 mol/L, agitation speed: 200 r/min, feeding rate of solutions of cerium nitrate and oxalic acid: 10 ml/min, reaction temperature: 80 °C. The results showed that the shape of cerium oxalate was sheet and the phase structure was amorphous. The median particle size of the final product was 27.60 μm, the particle size distribution width was very narrow and the micrograph was still sheet-like. Some attempts were made to explain the experimental phenomena in terms of agglomeration, disrupt, and precipitation kinetics.

Effects of neodymium and gadolinium on weathering resistance of ZnO-B2O3-SiO2 glass

The ZnO-B2O3-SiO2 glass doped with Nd2O3 and Gd2O3 was prepared by high temperature melt cooling method. The standard sample of the zinc borosilicate glass was placed in the constant temperature and humidity chamber in order to simulate the atmospheric corrosion process. The surface of the weathered glass was analyzed by scanning electron microscope and energy dispersive spectrometry and the filtrate was analyzed by inductively coupled plasma-atomic emission spectrometry. The results showed that humidity was the most important factor influencing weathering; the morphology of glass surface of altered layer and the product on the surface was observed; the corroding degree of the zinc borosilicate glass doped with Nd or Gd was significantly lighter than that of the base glass. Adding rare earth Nd or Gd in the zinc borosilicate glass could suppress Na, Zn, Si ion release in weathering.

Investigation on phase evolution of the ZnO-B2O3-SiO2 glass ceramics

ZnO-B2O3-SiO2-Al2O3-Na2O glass doped with nucleating agent TiO2 was prepared with melting-quenching method and the effect of nucleating agent on the crystallization behavior and phase evolution of this glass was investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The experimental results show that the glass transition temperature and the first crystallization temperature decrease from 630 °C and 765 °C to 595 °C and 740 °C, respectively, with introduction of TiO2 into glass. There is no diffraction peaks in the XRD pattern but it is no longer transparent for the base glass without nucleating agent after heat treatment, which suggests the serious phase separation occurred, and the observation by SEM indicates that the phase separation is developed by nucleation and growth mechanism. However, there are two different crystals ZnAl2O4 and NaAlSiO4 present in the glass containing TiO2 after heat treating at 575 °C for 2 h and 740 °C for 6 h, respectively. What is interesting is that NaAlSiO4 disappears as the crystallization time at 740 °C increases from 6 h to 12 h, and more ZnAl2O4 crystal is formed, namely, the further formation of ZnAl2O4 is at cost of NaAlSiO4 with increasing crystallization time. And observation of the morphology of glass ceramics shows great difference with increasing crystallization time. Moreover, the ability of ZnO-B2O3-SiO2-Al2O3-Na2O glass ceramics against attacking of 1M HCl solution is increased by the crystals precipitated in heat treatment process.