Ceria earths

A first crude separation of the ceria earths from the yttria earths is achieved by adding solid oxalic acid to the filtrate from the double sulfate precipitation. Use of a saturated solution of oxalic acid yields a precipitate which is difficult to filter and necessitates further dilution of the solution. 

In 1751 the Swedish mineralogist, A. F. Cronstedt, discovered a heavy mineral from which in 1803 M. H. Klaproth in Germany and, independently, i. i. Berzelius and W. Hisinger in Sweden, isolated what was thought to be a new oxide (or earth ) which was named ceria after the recently discovered asteroid, Ceres. Between 1839 and 1843 this earth, and the previously isolated yttria (p. 944), were shown by the Swedish surgeon C. G. Mosander to be mixtures from which, by 1907, the oxides of Sc, Y, La and the thirteen lanthanides other than Pm were to be isolated. The small village of Ytterby near Stockholm is celebrated in the names of no less than four of these elements (Table 30.1). 

It has been noted that the conductivity and activation energy can be correlated with the ionic radius of the dopant ions, with a minimum in activation energy occurring for those dopants whose radius most closely matches that of Ce4+. Kilner et al. [83] suggested that it would be more appropriate to evaluate the relative ion mismatch of dopant and host by comparing the cubic lattice parameter of the relevant rare-earth oxide. Kim [84] extended this approach by a systematic analysis of the effect of dopant ionic radius upon the relevant host lattice and gave the following empirical relation between the lattice constant of doped-ceria solid solutions and the ionic radius of the dopants. 

Finally, another possibility often discussed in the literature is that cation dopants from the electrode may enhance the electronic conductivity of the gas-exposed surface of the electrolyte in the vicinity of the TPB, thereby extending the reduction zone along the electrolyte surface via mixed conduction. The surface exchange rate of oxygen on both YSZ- and rare-earth-doped ceria (as measured by isotope methods) is only about 1 order of magnitude lower than on LSM at 700 Thus, if there were sufficient... 

Figure 52. Effect of binary gas-phase diffusion on the impedance characteristics of porous mixed-conducting electrodes at low Por (a) zero-bias impedance of LSC on rare-earth-doped ceria at 1 atm and 750 °C as a function of Pq using concentrations and balance gases as indicated. (Reprinted with permission from ref 350. Copyright 2000 Elsevier B.V.) (b) Zero-bias impedance of SSC x= 0.5) on SDC at 800 °C and P02 — 9-91 a function of total...

As an example. Figure 54a shows the zero-bias impedance of LSC electrodes on rare-earth-doped ceria in air at 750 °C measured using a symmetric cell incorporating a traditional reference electrode. Although the two screen-printed electrodes (1 and 2) were processed identically and aligned to an accuracy of 0.1 mm, the cell response is highly asymmetric... 

Figure 54. Measured (a) and simulated (b) effect of electrode misalignment, (a) Total-cell and balf-cell impedances of a symmetric LSC/rare-earth-doped ceria/LSC cell with nominally identical porous LSC x= 0.4) electrodes, measured at 750 °C in air based on tbe cell geometry shown. (b) Finite-element calculation of tbe total-cell and half-cell impedances of a symmetric cell with identical R—C electrodes, assuming a misalignment of the two working electrodes (d) equal to the thickness of the electrolyte (L). ...

Cerium was the first rare-earth element discovered, and its discovery came in 1803 by Jons Jakob Berzelius in Vienna. Johann Gadohn (1760—1852) also studied some minerals that were different from others known at that time. Because they were different from the common earth elements but were all very similar to each other, he named them rare-earth elements. However, he was unable to separate or identify them. In the 1800s only two rare-earths were known. At that time, they were known as yttria and ceria. Carl Gustav Mosander (1797—1858) and several other scientists attempted to separate the impurities in these two elements. In 1839 Mosander treated cerium nitrate with dilute nitric acid, which yielded a new rare-earth oxide he called lanthanum. Mosander is credited with its discovery. This caused a change in the periodic table because the separation produced two new elements. Mosander s method for separating rare-earths from a common mineral or from each other led other chemists to use... 

In the 1800s chemists searched for new elements by fractionating the oxides of rare-earths. Carl Gustaf Mosander s experiments indicated that pure ceria ores were actually contaminated with oxides of lanthanum, a new element. Mosander also fractionated the oxides of yttria into two new elements, erbium and terbium. In 1878 J. Louis Soret (1827—1890) and Marc Delafontaine (1837-1911), through spectroscopic analysis, found evidence of the element holmium, but it was contaminated by the rare-earth dysprosia. Since they could not isolate it and were unable to separate holmium as a pure rare-earth, they did not receive credit for its discovery. 

J, J, Berzelius and his collaborator Wilheim Hisinger, isolated from a heavy mineral found in 1781 in a mine at Bastnas, Sweden, another similar and yet somewhat different "earth". This one was named ceria and the mineral cerite after the then recently discovered planetoid Ceres, It was believed at the time, that both yttria and ceria were single elements, but subsequent study showed each to be a mixture of oxides, the complete separation and identification of which required more than a century of effort. 

The ultimate composition of ceria was established many years after its isolation by C, G, Mosander, a Swedish surgeon, chemist and mineralogist, who was for a time assistant to Berzelius, During the period 1839-1841, Mosander thermally decomposed a nitrate obtained from ceria and treated the product with dilute nitric acid. From the resulting solution, he then isolated first a new earth, "lanthana", and then another new earth, "didymia" (the twin brother of lanthana), of similar chemical but slightly different physical properties, (Figure 1)... 

Jons Jacob Berzelius, 1779-1848. Professor of chemistry and medicine at the Stockholm Medical School. He determined the atomic weights of most of the elements then known, discovered selenium and the earth ceria, and isolated silicon, thorium, and zirconium. Among his students may be mentioned Wohler, Heinrich and Gustav Rose, Mosander, Sefstrom, and... 

The mam object of Berzelius and Hisinger s analysis of cerite was to search for yttria, which might easily have escaped the attention of Scheele and de Elhuyar since it was unknown at the time their investigation was made (29). Although they failed to find yttria, Berzelius and Hisinger discovered instead the new earth ceria. ... 

Cerium in Plants and Animals. Professor Alfonso Cossa, finding the rare earths of the ceria series to be present in many apatites, and realizing the close association in nature between these earths and calcium and phosphorus, tested for them and detected their presence in bone (66). He also detected them in the ash of barley, beech wood, and tobacco. With the aid of C. Schiapparelli and G. Peroni of the University of Turin, he demonstrated their presence in human urine (66, 67, 68). 

Ekeberg (40, 41), M. H Klaproth, and N.-L Vauquelin all investigated Gadolin s new oxide, and it came to be called ijttria, a name derived from Ytterby. In 1803 Klaproth discovered in the mineral cerite another earth which he called terre ochroitebut which is now known as ceria. Berzelius and Wilhelm Hisinger also discovered ceria independently, but upon further investigation neither their yttria nor their ceria proved to be a pure oxide (3). 

In 1839 Mosander heated some cerium nitrate and treated tire partly decomposed salt with dilute nitric acid. In the extract he found a new earth, which he named lanthana, meaning hidden, meanwhile retaining the old name, ceria, for the oxide which is insoluble in dilute nitric acid (7, 28, 45). In the same year, Axel Erdmann, one of Sefstrom s students, discovered lanthana in a new Norwegian mineral, which he named mosan-drite in honor of Mosander. 

Having shown that the earth originally called ceria was composed of ail insoluble portion, ceria, and a soluble portion, lanthana, Mosander investigated yttria in a similar manner (7). In 1843 he showed that yttria from which all the ceria, lanthana, and didymia have been removed contains at least three other earths. These are a colorless oxide, for... 

The following diagrams which Professor James prepared for the Fourteenth Edition of the Encyclopedia Britannica show very clearly the separations by which the original complex earths ceria and yttria were resolved into the simple oxides of the rare earth metals. 

Birth of Wilhelm Hisinger, the discoverer of the earth ceria. Berzelius, Hisinger, and Klaproth all investigated this earth, the latter independently. 

Mar. 17, 1803 1803 Birth of Carl Lowig, independent discoverer of bromine. Klaproth, Berzelius, and Hisinger analyze cerite and discover the earth ceria. 

It is important to calcine at the appropriate temperature to enhance the deactivation and the catalysis for the ceria-modified HM.50,51 The catalyst calcined at 300 °C had no catalytic activity. The activity for the isopropylation of naphthalene appeared over the catalyst calcined at 450 °C and reached the maximum at 550 °C. However, the activity decreased at a temperature of 700 °C. These results show that calcination at an appropriate temperature is necessary to keep the HM pores open. The selectivity for 2,6-DIPN was as high as 70% over the catalysts regardless of their calcination temperature. These phenomena show that the isopropylation proceeds inside HM pores. This selective deactivation of HM pores was limited to modification with ceria. The modification with other rare-earth metal oxides, such as lanthanum and neodymium oxides, also deactivated the external acid sites but choked the HM pore to result in low catalytic activity. The isomerization of 4,4 -DIPB was also prevented by the ceria modification of HM in the isopropylation of biphenyl.49... 

Samarskite occurs in the Ural Mountains, Mitchell County (North Carolina, U.S.A.), Canada, and India. The tantalum content is often small, sometimes nil, and the rare earth oxides, chiefly yttria and ceria, are usually present in considerable number and proportions. The ore is radioactive and contains helium. It forms black, orthorhombic crystals. The density varies from 4-2 to G-2.5 It has been suggested that the niobium and tantalum are disintegration products of compounds of yttrium and cerium with the two higher homologues of manganese,4 masurium, and rhenium. 

Historically, the first rare earth specimen was found by K. A. Arrhenius near Ytterby in 1787. The Finnish Chemist, Johann Gadolin, in 1794, for the first time, successfully separated a new oxide from the mineral found by Arrhenius. This new oxide was named yttria by Ekebero (1797). The mineral was named gadolinite. In 1803 another oxide, very similar to yttria, was discovered independently by Klaproth, and Berzelius and Hisinger. This new oxide was named ceria, and the mineral from which it was isolated was called cerite. 

---