Effect of rare earth oxides on the thermal decomposition of barium oxalate

Catalytic activity of rare earth oxides (REO); La₂O₃, Sm₂O₃, Gd₂O₃ and Ce₂O₃ on the isothermal decomposition of barium oxalate has been studied at 723 K. The α?t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La₂O₃>Sm₂O₃>Gd₂O₃ >Ce₂O₃. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process.     

Derivatographic study of the thermal behaviour of 13 rare earth element oxides

The simultaneous TG-DTG-DTA thermoanalytical curves of 13 rare earth (4f) element oxides, namely, CeO₂, Dy₂O₃, Er₂O₃, Gd₂O₃, HfO₂, Ho₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃, Tb₄O₇, Tm₂O₃, Yb₂O₃ and Y₂O₃, were recorded with a MOM derivatograph under static air atmosphere over the temperature range from ambient to 1050°C. Only HfO₂, Nd₂O₃, Pr₆O₁₁, Sm₂O₃ and Tb₄O₇ showed appreciable weight losses due to the liberation of small amounts of oxygen. X-ray diffractometry was used to identify the thermal degradation products and their precursors.     

纳米晶稀土复合氧化物Dy~1~-~xSr~xCoO~3~-~y 3: 固相反应 动力学的研究

依据固相反应动力学模型,研究了纳米晶Dy~1~-~xSr~xCoO~3~-~y的固相反应过程。结果表明,纳米晶稀土复合氧化物Dy~1~-~xSr~xCoO~3~-~y的固相反应是扩散控制过程,反应活化能为120kJ.mol^-^1,从823-973K温度,其反应速率常数在0.302×10^-^6～4.50×10^-^6之间。通过固相反应在700℃获得了粒径在5-15nm的纳米晶粉体,这源于纳米晶的表面和界面效应。     

纳晶稀土复合氧化物Dy~1~-~xSr~xCoO~3~-~yⅡ: 固相烧结动力学研究

研究了纳晶氧化物Dy~1~-~xSr~xCoO~3~-~y(x=0.6)的等温烧结动力学,计算了烧结激活能, 结果表明: 在烧结初期, 致密化机制主要为蒸发-凝聚传质; 在烧结中期, 致密化机制转为晶界控制。烧结过程的激活能为5.255×10^4J·mol^-^1。较小的激活能体现了纳米粒子的尺寸效应。快速运动的晶界, 导致晶界与气孔的运动速度不匹配, 造成纳晶氧化物密度低, 最终形成纳米海绵态网络结构。     

Study of the thermal decomposition kinetics of some rare earth carbonates,fluorocarbonates and fluorooxalates

The thermal transformations of Pr and La carbonates, La, Ce, Pr, Nd, Sm, Eu and Gd fluorocarbonates, and La, Nd, Dy and Ho fluorooxalates were investigated. A Derivatograph Q-1000 (MOM, Hungary) was used for thermal analysis. The kinetics of the processes was studied in a flow reactor. The activation energies and preexponential factors for dehydration and decarbonization were calculated. Samples of Pr fluorocarbonate, Ho fluorooxalate, and Pr and La carbonates were exposed to γ-irradiation (dose from 6.2·10⁶ to 6.1·10⁷ rad). The influence of the irradiation dose upon the kinetic parameters (E _a andA) of the processes was investigated.     

辉光放电质谱法测定稀土矿中的15种稀土元素

利用高纯铜粉与稀土矿石粉末均匀混合压片制样.混合15种高纯稀土氧化物制样建立标准工作曲线,校正15种稀土元素相对灵敏度因子,再进行定量分析.结果 表明,稀土元素工作曲线的线性方程相关系数R2均大于0.996,相对标准偏差(RSD)小于5％,满足定量分析要求.测定结果与电感耦合等离子体质谱法(ICP-MS)和电感耦合等离...     

The catalytic effect of rare earth oxides on the thermal decomposition of ammonium perchlorate

The kinetics of the decomposition of ammonium perchlorate (AP) in the presence of rare earth oxides, yttrium oxide (Y₂O₃) and lanthanum oxide (La₂O₃) as catalysts have been investigated. The Prout-Tompkins and contracting-cube equations have been found to fit the isothermal thermogravimetry data of catalysed AP decomposition. Gases evolved during catalytic decomposition of AP were analysed by infrared spectroscopy by matrix isolation technique. The mechanism of the catalysed thermal decomposition of AP has also been discussed in terms of an electron transfer process.

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Zusammenfassung Es wurde die Reaktionskinetik der thermischen Zersetzung von Ammoniumperchlorat (AP) in Gegenwart der Seltenerdenoxide Yttriumoxid (Y₂O₃) und Lanthanoxid (La₂O₃) als Katalysatoren untersucht. Zum Fitting der isothermen thermogravimetrischen Daten der katalysierten Zersetzung von AP läßt sich die Prout-Tompkins- und die Schrumpfwürfelgleichung erfolgreich anwenden. Die bei der katalytischen Zersetzung von AP freigesetzten Gase wurden durch IR-Spektroskopie untersucht. Der Mechanismus der katalytischen thermischen Zersetzung wurde auch vom Gesichtspunkt eines Elektronentransferprozesses aus besprochen.

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Determination of rare earth elements in mineral raw materials and rare earth industry products by neutron activation analysis

To determine REE in mineral raw materials, high purity RE metals and their compounds, neutron activation analysis with extraction chromatographic REE separation has been developed. Combination of the developed RE extraction and separation procedures with subsequent -spectrometric analysis of the RE radionuclides allows to determine their content with the lower detection limit –10^–5–10^–8%. The relative standard deviation is 0.2–0.3.     

Determination of rare earth elements in phosphorites by neutron activation analysis

Fourty three phosphorite rocks from Western Iraq were analyzed for eleven REE as well as uranium by NAA using IRT Reactor with a neutron flux of 2.3·10¹³ n·cm^–2·s^–1. The gamma activity from each sample was counted with a Ge(Li) and well-type HPGe, each detector connected to an on-line computer. Uranium fission products and different reaction interferences were assessed and allowed for. The results were also checked against international reference materials.     

Valence change in rare earth cluster oxides

Rare earth clusters of europium, thullium and ytterbium were generated by gas aggregation technique and probed by photoionization mass spectrometry. Their relative intensities in mass spectra have shown that their stabilities are governed by compact geometrical structures. The addition of oxygen gas in the nucleation region was used to produce the reactive nucleation. Several stages of oxidation were observed as a function of oxygen pressure up to saturation. For the maximal degree of oxidation the observed oxide ion compositions enable one to follow the valence of metal atom in its oxide as cluster size increases. This exhibits a divalent to trivalent valence change with cluster size. Moreover it emerges from the data that the divalent to trivalent transition for Tm, Yb, and Eu occurs at different size values.     

X-ray absorption spectroscopy of rare earth intermediate oxides

The M_IV–V and L_III absorption spectra (between 850 and 7500 eV) of intermediate rare earth oxides (Pr₇O₁₂ and Pr₉O₁₆) were studied. These oxides required careful preparation and handling in order to assure their composition.The spectra are characterized by multiplet features that are interpreted as having contributions from both trivalent and tetravalent sites. In the M_IV–V spectra the appearance of distinct multiplet lines and additional weaker features demonstrate clearly the increasing ratio of the tetravalent sites as the oxygen content increases from Pr₇O₁₂ to PrO₂. Similar behavior has been observed for the CeO_x and TbO_x systems. These observations show that in these oxides, the trivalent and tetravalent sites are inequivalent and that the evidence of valence transition is seen in the appearance of the complex spectral features originating from the tetravalent sites.     

Oxide melt solution calorimetry of rare earth oxides

Key to the evaluation of the long-term durability and reactivity of REE-materials is the accurate determination of their thermodynamic properties. High-temperature oxide melt solution calorimetry offers an effective methodology for the determination of enthalpies of formation for REE-materials. Calorimetric techniques and crosschecks are summarized that demonstrate that consistent and correct thermodynamic data can be generated using lead borate and sodium molybdate solvents. A summary of recent calorimetric studies of REE-orthophosphates and REE-oxyapatites illustrates the successful application of our techniques in quantifying formation enthalpies and elucidating energetic trends. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of rare earth elements in bauxites by instrumental neutron activation analysis

The instrumental neutron activation analysis method was used for determination of 12 rare earth elements in red and white bauxites. Consideration was given to those systematic errors which in a relative method of analysis can result from the effects of neutron self-shielding, photon self-absorption and fission interfering reactions, due to different chemical composition of bauxite samples and the standard of silicate rock. Also presented is the characteristics “V” shaped chondrite normalized rare earth pattern of white bauxites.     

Stuffed rare earth pyrochlore solid solutions

Synthesis and crystal structures are described for the compounds Ln₂(Ti_2−xLn_x)O_7−x/2, where Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0 to 0.67. Rietveld refinements of X-ray powder diffraction data indicate that in the Tb and Dy titanate pyrochlores, the extra Ln³⁺ cations mix mainly on the Ti⁴⁺ site with little disorder on the original Ln³⁺ site. For the smaller rare earths (Ho-Lu), stuffing additional lanthanide ions results in a pyrochlore to defect fluorite transition, where the Ln³⁺ and Ti⁴⁺ ions become completely randomized at the maximum (x=0.67). Initial magnetic characterization for the fully stuffed x=0.67 samples for Ln=Tb-Yb shows no long range ordering down to 2 K, and only partial saturation of the full expected magnetic moment under applied fields up to 5 T. In all of these Ln-Ti-O pyrochlores, the addition of magnetic Ln³⁺ in place of non-magnetic Ti⁴⁺ adds edge sharing tetrahedral spin interactions to a normally corner sharing tetrahedral network of spins. The increase in spin connectivity in this family of solid solutions represents a new avenue for investigating geometrical magnetic frustration in the rare earth titanate pyrochlores.     

DBC-偶氮氯膦固相光度法测定稀土元素铈,铕,钇

在2 mol/L HCl介质中,Ce(Ⅲ),Eu(Ⅲ),Y(Ⅲ)与DBC-偶氮氯膦形成的络合物吸附到201×7型强碱性苯乙烯阴离子树脂上。最大吸收波长Ce(Ⅲ)络合物为648 nm,Eu(Ⅲ)络合物为650 nm,Y(Ⅲ)络合物为650 nm。Ce(Ⅲ)络合物表观摩尔吸光系数为6ε48 nm=9.6×104L.mol-1.cm-1,Eu(Ⅲ)络合物表观摩尔吸光系数为6ε50 nm=1.51×105L.mol-1.cm-1,Y(Ⅲ)络合物表观摩尔吸光系数为6ε50 nm=5.6×104L.mol-1.cm-1。固相光度法测定Ce(Ⅲ),Eu(Ⅲ),Y(Ⅲ)质量浓度在0~0.48μg/mL范围内与吸光度值呈良好线性关系。该法可用于分子筛中Ce的测定。