Terras raras no Brasil: histórico, produção e perspectivas

This contribution introduces a brief discussion about the properties and applications of the rare earth elements, with a focus on their current status in Brazil. The general chemical properties, main applications and historical background of the chemistry of these elements are presented, and special attention is devoted to the development of the exploitation and both academic and industrial activities involving rare earths in Brazil. A discussion of the current world scenario ensues and some perspectives regarding the prospection, market and government policy concerning the rare earth elements in Brazil are given.

Defects in Persistent Luminescence Materials

Persistent luminescence materials can store energy from solar radiation or artificial lighting and release it over a period of several hours without a continuous excitation source. These materials are widely used to improve human safety in emergency and traffic signalization. They can also be utilized in novel applications including solar cells, medical diagnostics, radiation detectors and structural damage sensors. The development of these materials is currently based on methods based on trial and error. The tailoring of new materials is also hindered by the lack of knowledge on the role of their intrinsic and extrinsic lattice defects in the appropriate mechanisms. The goal of this work was to clarify the persistent luminescence mechanisms by combining ab initio density functional theory (DFT) calculations with selected experimental methods. The DFT approach enables a full control of both the nature of the defects and their locations in the host lattice. The materials studied in the present work, the distrontium magnesium disilicate (Sr₂MgSi₂O₇) and strontium aluminate (SrAl₂O₄) are among the most efficient persistent luminescence hosts when doped with divalent europium Eu²⁺ and co-doped with trivalent rare earth ions R³⁺ (R: Y, La-Nd, Sm, Gd-Lu). The polycrystalline materials were prepared with the solid state method and their structural and phase purity was confirmed by X-ray powder diffraction. Their local crystal structure was studied by high-resolution transmission electron microscopy. The crystal and electronic structure of the nondoped as well as Eu²⁺, R^2+/3+ and other defect containing materials were studied using DFT calculations. The experimental trap depths were obtained using thermoluminescence (TL) spectroscopy. The emission and excitation of Sr₂MgSi₂O₇:Eu²+,Dy³⁺ were also studied. Significant modifications in the local crystal structure due to the Eu²⁺ ion and lattice defects were found by the experimental and DFT methods. The charge compensation effects induced by the R³⁺ co-doping further increased the number of defects and distortions in the host lattice. As for the electronic structure of Sr₂MgSi₂O₇ and SrAl₂O₄, the experimental band gap energy of the host materials was well reproduced by the calculations. The DFT calculated Eu²⁺ and R^2+/3+ 4fn as well as 4f^n-15d¹ ground states in the Sr₂MgSi₂O₇ band structure provide an independent verification for an empirical model which is constructed using rather sparse experimental data for the R³⁺ and especially the R²⁺ ions. The intrinsic and defect induced electron traps were found to act together as energy storage sites contributing to the materials’ efficient persistent luminescence. The calculated trap energy range agreed with the trap structure of Sr₂MgSi₂O₇ obtained using TL measurements. More experimental studies should be carried out for SrAl₂O₄ to compare with the DFT calculations. The calculated and experimental results show that the electron traps created by both the rare earth ions and vacancies are modified due to the defect aggregation and charge compensation effects. The relationships between this modification and the energy storage properties of the solid state materials are discussed.

Harvinaisten metallien talteenotto epäorgaanisista jätevirroista

Taloudellisesti tärkeiden metallien varannot ja tuotanto eivät ole jakautuneet tasaisesti. Maantieteelliset alueet, joilla ei ole omia varantoja ovat riippuvaisia muualta tuoduista raaka-aineista. Euroopan komissio ja USA:n energiaministeriö ovat luokitelleet tietyt metallit kriittisiksi niiden taloudellisen merkittävyyden ja saatavuuteen liittyvien epävarmuustekijöiden johdosta. Tällaisten metallien saatavuutta voitaisiin mahdollisesti parantaa lisäämällä niiden talteenottoa jätteistä. Tutkimuksessa kartoitettiin Euroopan komission kriittiseksi luokittelemien metallien pitoisuuksia eräissä jätevirroissa. Kartoitetut jätteet olivat teollisissa poltto-prosesseissa syntyneitä polttojätteitä, prosessiteollisuuden jätesakkoja ja sähkö- ja elektroniikkajätteitä. Kartoituksen perusteella valittiin lupaavimmat jätteet ja suoritettiin niille talteenottokokeita. Talteenottokokeita suoritettiin kolmelle jätteelle. Yhdestä jätesakasta liuotettiin indiumia rikki- ja suolahapoilla. Kahden eri polttojätteen seoksesta liuotettiin galliumia rikkihapolla. Käytettyjen loisteputkien käsittelyprosessista peräisin olleesta sakasta liuotettiin maametalleja rikki- ja suolahapoilla sekä rikki- ja typpihapon seoksella. Indium liukeni heikosti (korkeintaan 25 %) huoneenlämmössä rikkihapolla. Suolahapolla se liukeni paremmin (68 %). Polttojätteen liuotuskokeissa galliumin talteenottoasteen todettiin riippuvan käytetyn liuottimen määrästä. Loisteputkijätesakasta liukeni yttriumia ja europiumia kaikilla käytetyillä happoliuoksilla noin 70–100 %. Käytetyillä happokonsentraatioilla ei havaittu suuria eroja yttriumin ja europiumin liukoisuuksissa. Näitä metalleja voitaisiin mahdollisesti ottaa talteen tämän tyyppisestä sakasta liuottamalla ne happoliuoksella ja saostamalla oksalaattina. Tarvittaessa liuokset voitaisiin puhdistaa tai metallit erottaa toisistaan neste–nesteuutolla, joka on tärkein maametallien tuotantoon käytetty hydrometallurginen menetelmä.

Use of nuclear technique in samples for agricultural purposes

The concern related to environment is growing. Due to this, it is needed to determine chemical elements in a large range of concentration. The neutron activation technique (NAA) determines the elemental composition by the measurement of artificial radioactivity in a sample that was submitted to a neutron flux. NAA is a sensitive and accurate technique with low detection limits. An example of application of NAA was the measurement of concentrations of rare earth elements (REE) in waste samples of phosphogypsum (PG) and cerrado soil samples (clayey and sandy soils). Additionally, a soil reference material of the International Atomic Energy Agency (IAEA) was also analyzed. The REE concentration in PG samples was two times higher than those found in national fertilizers, (total of 4,000 mg kg-1 ), 154 times greater than the values found in the sandy soil (26 mg kg-1 ) and 14 times greater than the in clayey soil (280 mg kg-1 ). The experimental results for the reference material were inside the uncertainty of the certified values pointing out the accuracy of the method (95%). The determination of La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu in the samples and reference material confirmed the versatility of the technique on REE determination in soil and phosphogypsum samples that are matrices for agricultural interest.

NIR-Vis Up-Conversion Luminescence in the Yb3+,Er3+ Doped Y2O2S, ZrO2, and NaYF4 Nanomaterials

Since the discovery of the up-conversion phenomenon, there has been an ever increasing interest in up-converting phosphors in which the absorption of two or more low energy photons is followed by emission of a higher energy photon. Most up-conversion luminescence materials operate by using a combination of a trivalent rare earth (lanthanide) sensitizer (e.g. Yb or Er) and an activator (e.g. Er, Ho, Tm or Pr) ion in a crystal lattice. Up-converting phosphors have a variety of potential applications as lasers and displays as well as inks for security printing (e.g. bank notes and bonds). One of the most sophisticated applications of lanthanide up-conversion luminescence is probably in medical diagnostics. However, there are some major problems in the use of photoluminescence based on the direct UV excitation in immunoassays. Human blood absorbs strongly UV radiation as well as the emission of the phosphor in the visible. A promising way to overcome the problems arising from the blood absorption is to use a long wavelength excitation and benefit from the up-conversion luminescence. Since there is practically no absorption by the whole-blood in the near IR region, it has no capability for up-conversion in the excitation wavelength region of the conventional up-converting phosphor based on the Yb3+ (sensitizer) and Er3+ (activator) combination. The aim of this work was to prepare nanocrystalline materials with high red (and green) up-conversion luminescence efficiency for use in quantitative whole-blood immunoassays. For coupling to biological compounds, nanometer-sized (crystallite size below 50 nm) up-converting phosphor particles are required. The nanocrystalline ZrO2:Yb3+,Er3+, Y2O2S:Yb3+,Er3+, NaYF4:Yb3+,Er3+ and NaRF4-NaR’F4 (R: Y, Yb, Er) materials, prepared with the combustion, sol-gel, flux, co-precipitation and solvothermal synthesis, were studied using the thermal analysis, FT-IR spectroscopy, transmission electron microscopy, EDX spectroscopy, XANES/EXAFS measurements, absorption spectroscopy, X-ray powder diffraction, as well as up-conversion and thermoluminescence spectroscopies. The effect of the impurities of the phosphors, crystallite size, as well as the crystal structure on the up-conversion luminescence intensity was analyzed. Finally, a new phenomenon, persistent up-conversion luminescence was introduced and discussed. For efficient use in bioassays, more work is needed to yield nanomaterials with smaller and more uniform crystallite sizes. Surface modifications need to be studied to improve the dispersion in water. On the other hand, further work must be carried out to optimize the persistent up-conversion luminescence of the nanomaterials to allow for their use as efficient immunoassay nanomaterials combining the advantages of both up-conversion and persistent luminescence.

Cost Reduction of Permanent Magnet Synchronous Machines

Electrical machine drives are the most electrical energy-consuming systems worldwide. The largest proportion of drives is found in industrial applications. There are, however many other applications that are also based on the use of electrical machines, because they have a relatively high efficiency, a low noise level, and do not produce local pollution. Electrical machines can be classified into several categories. One of the most commonly used electrical machine types (especially in the industry) is induction motors, also known as asynchronous machines. They have a mature production process and a robust rotor construction. However, in the world pursuing higher energy efficiency with reasonable investments not every application receives the advantage of using this type of motor drives. The main drawback of induction motors is the fact that they need slipcaused and thus loss-generating current in the rotor, and additional stator current for magnetic field production along with the torque-producing current. This can reduce the electric motor drive efficiency, especially in low-speed, low-power applications. Often, when high torque density is required together with low losses, it is desirable to apply permanent magnet technology, because in this case there is no need to use current to produce the basic excitation of the machine. This promotes the effectiveness of copper use in the stator, and further, there is no rotor current in these machines. Again, if permanent magnets with a high remanent flux density are used, the air gap flux density can be higher than in conventional induction motors. These advantages have raised the popularity of PMSMs in some challenging applications, such as hybrid electric vehicles (HEV), wind turbines, and home appliances. Usually, a correctly designed PMSM has a higher efficiency and consequently lower losses than its induction machine counterparts. Therefore, the use of these electrical machines reduces the energy consumption of the whole system to some extent, which can provide good motivation to apply permanent magnet technology to electrical machines. However, the cost of high performance rare earth permanent magnets in these machines may not be affordable in many industrial applications, because the tight competition between the manufacturers dictates the rules of low-cost and highly robust solutions, where asynchronous machines seem to be more feasible at the moment. Two main electromagnetic components of an electrical machine are the stator and the rotor. In the case of a conventional radial flux PMSM, the stator contains magnetic circuit lamination and stator winding, and the rotor consists of rotor steel (laminated or solid) and permanent magnets. The lamination itself does not significantly influence the total cost of the machine, even though it can considerably increase the construction complexity, as it requires a special assembly arrangement. However, thin metal sheet processing methods are very effective and economically feasible. Therefore, the cost of the machine is mainly affected by the stator winding and the permanent magnets. The work proposed in this doctoral dissertation comprises a description and analysis of two approaches of PMSM cost reduction: one on the rotor side and the other on the stator side. The first approach on the rotor side includes the use of low-cost and abundant ferrite magnets together with a tooth-coil winding topology and an outer rotor construction. The second approach on the stator side exploits the use of a modular stator structure instead of a monolithic one. PMSMs with the proposed structures were thoroughly analysed by finite element method based tools (FEM). It was found out that by implementing the described principles, some favourable characteristics of the machine (mainly concerning the machine size) will inevitable be compromised. However, the main target of the proposed approaches is not to compete with conventional rare earth PMSMs, but to reduce the price at which they can be implemented in industrial applications, keeping their dimensions at the same level or lower than those of a typical electrical machine used in the industry at the moment. The measurement results of the prototypes show that the main performance characteristics of these machines are at an acceptable level. It is shown that with certain specific actions it is possible to achieve a desirable efficiency level of the machine with the proposed cost reduction methods.

Blue and Uv-Emitting Upconversion Nanoparticles: Synthesis and (Bio) Analytical Applications.

Rare-earth based upconverting nanoparticles (UCNPs) have attracted much attention due to their unique luminescent properties. The ability to convert multiple photons of lower energy to ones with higher energy through an upconversion (UC) process offers a wide range of applications for UCNPs. The emission intensities and wavelengths of UCNPs are important performance characteristics, which determine the appropriate applications. However, insufficient intensities still limit the use of UCNPs; especially the efficient emission of blue and ultraviolet (UV) light via upconversion remains challenging, as these events require three or more near-infrared (NIR) photons. The aim of the study was to enhance the blue and UV upconversion emission intensities of Tm3+ doped NaYF4 nanoparticles and to demonstrate their utility in in vitro diagnostics. As the distance between the sensitizer and the activator significantly affect the energy transfer efficiency, different strategies were explored to change the local symmetry around the doped lanthanides. One important strategy is the intentional co-doping of active (participate in energy transfer) or passive (do not participate in energy transfer) impurities into the host matrix. The roles of doped passive impurities (K+ and Sc3+) in enhancing the blue and UV upconversions, as well as in influencing the intense UV upconversion emission through excess sensitization (active impurity) were studied. Additionally, the effects of both active and passive impurity doping on the morphological and optical performance of UCNPs were investigated. The applicability of UV emitting UCNPs as an internal light source for glucose sensing in a dry chemistry test strip was demonstrated. The measurements were in agreement with the traditional method based on reflectance measurements using an external UV light source. The use of UCNPs in the glucose test strip offers an alternative detection method with advantages such as control signals for minimizing errors and high penetration of the NIR excitation through the blood sample, which gives more freedom for designing the optical setup. In bioimaging, the excitation of the UCNPs in the transparent IR region of the tissue permits measurements, which are free of background fluorescence and have a high signal-to-background ratio. In addition, the narrow emission bandwidth of the UCNPs enables multiplexed detections. An array-in-well immunoassay was developed using two different UC emission colours. The differentiation between different viral infections and the classification of antibody responses were achieved based on both the position and colour of the signal. The study demonstrates the potential of spectral and spatial multiplexing in the imaging based array-in-well assays.

Evolution of an Archean greenstone belt in the Stormy Lake - Kawashegamuk Lake area (stratigraphy, structure and geochemistry) - Western Wabigoon Subprovince, Northwest Ontario /

330 km 2 of the easter-n part of the Archean Manitou Lakes - Stormy Lake metavolcanic - metasedimentary belt have been mapped and sampled. A large number of rocks ~.vere analyzed for the major and trace constituents including the rare-earth elements (REE). The Stormy Lake - Kawashegamuk Lake area may be subdivided into four major lithological groups of supracrustal rocks 1) A north-facing mafic assemblage, consisting of pillowed tholeiitic basalts and gabbro sills characterized by flat REE profiles, is exposed in the south part of the map area and belongs to a 8000 m thick homoclinal assemblage outside the map area. Felsic pyroclastic rocks believed to have been issued from a large central vent conformably overlie the tholeiites. 2) A dominantly epiclastic group facing to the north consists of terrestrial deposits interpreted to be an alluvial fan deposit ; a submarine facies is represented by turbiditic sediments. 3) The northeastern part of the study area consists of volcanic rocks belonging to two mafic - felsic cycles facing to the southuest ; andesitic flows with fractionated REE patterns make up a large part of the upper cycle, whereas the lower cycle has a stronger chemical polarity being represented by tholeiitic flows, with flat REE, which a r e succeeded by dacitic and rhyolitic pyroclasti cs. iii 4) A thick monotonous succession of tholeiitic pillmled basalt f lows and gabbro sills with flat REE represent the youngest supracrustal rocks. TIle entire belt underwent folding, faulting and granitic plutonism during a tectono-thermal event around 2700 Ma ago. Rocks exposed in the map area were subjected to regional greenschist facies metamorphism, but higher metamorphic grades are present near late granitic intrusions. Geochemical studies have been useful in 1) distinguishing the various rock units ; 2) relating volcanic and intrusive rocks 3) studying the significance of chemical changes due to post magmatic processes 4) determining the petrogenesis of the major volcanic rock types. In doing so, two major volcanic suites have been recognized : a) a tholeiitic suite, mostly represented by mafic rocks, was derived from partial melting of upper mantle material depleted in Ti, K and the light REE ; b) a calc-alkalic suite which evolved from partial melting of amphibolite in the lower crust. The more differentiated magma types have been produced by a multistage process involving partial melting and fractional crystallization to yield a continuum of compos i t i ons ranging from basaltic andesite to rhyolite. A model for the development of the eastern part of the Manitou Lakes - Stormy Lake belt has been proposed.

Structural, Magnetic and Thermal Studies of Ce1-xEuxCrO3 Nano-Powders

A new series of nano-sized Ce1-xEuxCrO3 (x = 0.0 to 1.0) with an average particle size of 50 - 80 nm were synthesized using a solution combustion method. Nano-powders Ce1-xEuxCrO3 with the canted antiferromagnetic property exhibited interesting magnetic behaviours including the reversal magnetization and the exchange bias effect. The effect of europium doping as the ion with the smaller radius size and different electron con figuration on structural, magnetic and thermal properties of Ce1-xEuxCrO3 were investigated using various experimental techniques, i.e. DC/AC magnetic susceptibility, heat capacity, thermal expansion, Raman scattering, X-ray photoemission spectroscopy, transmission/scanning electron microscopy, X-ray powder diffraction and neutron scattering. An exchange bias effect, magnetization irreversibility and AC susceptibility dispersion in these samples confirmed the existence of the spin disorder magnetic phase in Ce1-xEuxCrO3 compounds. The exchange bias phenomenon, which is assigned to the exchange coupling between glassy-like shell and canted antiferromagnetic core, showed the opposite sign in CeCrO3 and EuCrO3 at low temperatures, suggesting different exchange interactions at the interfaces in these compounds. The energy level excitation of samples were examined by an inelastic neutron scattering which was in good agreement with the heat capacity data. Neutron scattering analysis of EuCrO3 was challenging due to the large neutron absorption cross-section of europium. All diffraction patterns of Ce1-xEuxCrO3 showed the magnetic peak attributed to the antiferromagnetic Cr3+ spins while none of the diffraction patterns could detect the magnetic ordering of the rare-earth ions in these samples.

Geochemistry and Minerology of Chaliyar River Sediments with Special Reference to the Occurrence of Placer Gold

The present work deals with the texture, mineralogy and geochemistry of bedload sediments of the main stream of the Chaliyar basin, a typical small drainage system of the tropics enjoying heavy rain fall and moderate climate, located essentially in the Northern Kerala and flowing over the crystalline rocks (and their laterized duricrust) of the South Indian granulite terrain. As the Chaliyar is the major river draining the Wynad Gold Fields and is known for its placer gold occurrences, the thesis gives special emphasize on understanding the nature and distribution of detrital gold in sediments of the basin, while attempting to infer the provenance characteristics and factors involved in the evolution of sediments in general. Minerologically the chaliyar basin sands are quartzose. The quartz and feldspar contents in the coarse sand fraction of the basin range from 64 to 86% and 2 to 16% respectively. The Q/F ration ranges from 4 to 38 with a slight decrease in the lower reaches. Other minerals present include, hornblende, pyroxene and heavy minerals like opaques, garnet, rutile, biotite, spene, silliminite, zircon, apatite and monazite some of which are seen as inclusions in quartz. The major element composition of Chaliyar bedload sediments in the main channel and the headwater tributaries is related to the mineralogical and textual characteristics of sediments.

Tailoring the microwave dielectric properties of BaRE2Ti4O12 and BaRE2Ti5O14 ceramics bycompositional variations

Ceramic dielectric resonators in the BaO-RE2O3-TiO2 (RE=rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the Q decreased. The temperature coeffecient of the resonant frequency improved with bismuth addition.

Tailoring the Microwave Dielectric Properties of BaRE2Ti4012 and BaRE2Ti5014 Ceramics by Compositional Variations

Ceramic dielectric resonators in the BaO-RE2O3-TiO2 (RE = rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the 0 decreased. The temperature coefficient of the resonant frequency improved with bismuth addition

Synthesis,Characterization and Properties of [REI_xREX]TiNb06 Dielectric Ceramics

Dielectric ceramics based on solid solution phases of [RE1_x= REr]TiNb06, where REI_s = Nd, Pr, Sm and RE' = Dy, Gd and Y, were prepared by the conventional solid-state ceramic route for values of x. The ceramic samples are characterized by X-ray diffraction and microwave methods. Ceramics based on RE (Pr, Nd and Sm) belonging to aeschynite group shows positive value of Tf and those based on RE (Gd, Dy and Y) belonging to euxenite group show negative value of r f. The solid solution phases between the aeschynite and the euxenite group shows intermediate dielectric constant and r f values. The results indicate the possibility of tailoring the dielectric properties by varying the composition of the solid solution phases. The range of solid solubility of euxenite in aeschenite and aeschenite in euxenite are different for different rare earth ions