NEW DEVELOPMENTS FOR CERAMIC PIGMENTS

In the last years, the development of pigments for the production of tiles, ceramic coatings or cosmetics has become a need, because the aesthetic aspect and the color frequently represent the parameters of interest [1]. Color is an optical property that takes to countless applications. A good ceramic pigment has indispensable
requirements, such as high temperature stability, reproducibility and chemical inertia [2]. The final color of each pigment is due to the addition of a chromophore ion (usually transition metals) into an inert matrix, or this ion may be part of the own matrix, as in the case of ferrite [3].
Among the pigment classes, one of the most important is the spinel group, AB2O4, due to its capacity of accommodating different cations, leading to a variety of colors and tonalities. Among spinels, this work evaluated the behavior of barium
monoferrite, BaFe2O4. Spinel ferrites combine interesting soft magnetic properties with rather high electrical resistivities. Some ferrites have also been applied as brown pigments, as catalytic materials, magnetic materials and wave absorption
materials [4].
Numerous studies have been done on the phase relations in Ba–Fe–O ternary system. Three stable phases were reported, namely, Ba2Fe2O5, BaFe2O4 and the hexagonal BaFe12O19 [5,6].
In spite of this, many apparently contradictory results have been found, with the hexagonal BaFe2O4 phase usually being reported as coexisting with BaFe12O19 and Fe2O3, along with other metastable phases. BaFe12O19 and a-BaFe2O4 are
mutually insoluble in each other as solids, and both coexist up to 1000 8C, after which point a third phase, the metastable hexagonal Ba2Fe6O11, can also develop until the ternary mixture reaches its liquid point at 1175 8C, reverting to
BaFe12O19 and a-BaFe2O4 on cooling [7]. Fine-particle spinel ferrites, such as BaFe2O4, are useful for the low temperature preparation of high-density ferrites and as
suspension materials for ferromagnetic liquids. Nanoparticles of BaFe2O4 demonstrate a resonance anomaly near 125 K that could indicate the presence of a magnetic phase. On the other hand, hexagonal magnetic hard ferrites such as BaFe12O19 are
magnetic materials of great scientific and technological interest due to their relatively strong anisotropy and moderate, but still interesting magnetization. They are applied as permanent magnets, in microwave devices or in perpendicular magnetic recording. Another application is in catalysis area [4,8–11].
Different synthesis methods have been evaluated, such as coprecipitation [12,13], aerosol [14,15] or sol–gel [16,17]. In this work, the polymeric precursor method (Pechini) [17] was used in BaFe2O4 synthesis, for application as ceramic
pigment.

2. Experimental procedure
The polymeric precursor was prepared by the Pechini method, which has been used to synthesize polycationic powders. Precursors used were citric acid (Vetec), iron III
nitrate (Vetec) and barium acetate (Reagen), to synthesize the metallic citrate, which was polymerized using ethylene glycol (Synth).
Fig. 1 schematically presents the BaFe2O4 synthesis. After the primary calcination, the polymeric precursor was obtained, which was calcined between 500 and 1100 8C, with a heating rate of 10 8C min 1 in air atmosphere.
The determination of the crystalline phases was carried out by X-ray diffraction (XRD) with Siemens D-5000 Diffractometer with Cu Ka radiation (l = 1.5406 A ° and 2u = 208–708), at room temperature. Cell volume was calculated using the
Rede 93 program, based on the least square method, developed at the Chemistry Institute of Unesp, at Araraquara, SP, Brazil [18]. Quartz was used as an external standard.
Infrared spectra were obtained using KBr pellets, in the range of 2000 to 400 cm 1 (spectrophotometer BOMEM, model MB–102).
The surface area measurements of the pigments were accomplished by a Micromeritics ASAP 2000 equipment, using N2 as the adsorption/desorption gas. The particle average
diameter was calculated using the BET method, dBET. Scanning electron microscopy (ZEISS DSM, 940) was used to characterize the pigment morphology. In the laboratory test, pigments were applied on ceramic pieces. A mixture of glaze (commercial glaze—GERBI, Brazil) and 3% of sieved pigment was used (mass ratio). The mixture
was homogenized in a ball mill during 10 min. The slip was poured on the ceramic biscuits obtaining an uniform glaze layer, which was then heat treated up to 500 8C with heating rate of 10 8C min 1, which was then increased to 15 8C min 1
up to 1000 8C for 1 h. Than, the furnace was cooled back to room temperature at 10 8C min 1.
Colorimetric parameters (L*, a* and b*) and diffuse reflectance of powders and glazed samples were measured with the Gretac Macbeth Color-eye spectrophotometer 2180/2180 UV, from 300 to 800 nm, using the D65 illuminant withmeasurement at 88. The CIE-L*a*b* colorimetric system,recommended by the CIE (Commission Internationale de l’Eclairage) [19] was followed. In this system, L* is the lightness axis (where black is equal to 0 and white to 100), b*represents the color varying from blue (negative axis) to yellow (positive axis), a* represents the color varying from green
(negative axis) to red (positive axis).

3. Results and discussion
Fig. 2 illustrates the XRD patterns of the materials synthesized by the Pechini method, calcined at different temperatures.







The samples present a single phase above 700 8C, identified as an orthorhombic spinel like phase space group-Bb21m (36), according to the index card JCPDS 46–0113, whose lattice parameters are: a = 19.042 A ° , b = 5.3838 A ° and c = 8.4445 A ° .
At 500 8C, a non-identified intermediate phase is also observed, which disappears at 700 8C. Castro et al. synthesized barium monoferrite, using the combustion method. Fe3O4, Ba(NO3)2 and BaCO3 were found as intermediate phases. After calcination at 700 8C, Fe3O4 and BaCO3 can still be found [5].
BaFe2O4 shows a tunnel structure with iron having a tetrahedral coordination. Corners of the FeO4-tetrahedra change their directions blockwise in one layer parallel to the a/b-plane. As a result, large and long tunnels are created by 12
FeO4-tetrahedra in the tetrahedra network of orthorhombic- BaFe2O4. Each of the large tunnels contains two Ba2+ (Ba(1)) atoms (double tunnels). In addition, smaller compressed quadrangular tunnels exist containing exclusively Ba2+
(Ba(2)) (single tunnels) and those tunnels which are too small for an intercalation of Ba2+ (vacant tunnels). The sequence double tunnel–single tunnel–vacant tunnel–single tunnel repeats along the a-axis. Ba(1) shows a monocapped trigonal
prismatic oxygen surrounding in the large tunnels. Along the tunnel direction there are no connections between these BaOpolyhedra.
The surrounding of Ba(2) is different, as soon as it shows edge-sharing BaO-polyhedra resulting in [BaO]-chains along the tunnels [20].



The BaFe2O4 structure leads to a different ligand field for
iron, when compared to usual hematite pigments. For hematite,
iron is surrounded by six oxygens in octahedral coordination. In
barium monoferrite, iron is in tetrahedral coordination. As a
consequence a different splitting of the five d orbitals is
observed, leading to different colors [21].
Table 1 presents the values of the lattice parameters and the
unit cell volume of the system in study. It is observed that the
unit cell volume increases with temperature in a more effective
way from 700 to 800 8C, getting almost constant above this
temperature.
The absorption vibrations of the system BaFe2O4, Fig. 3,
consist of well-defined bands, as follows:
Bands at 1460 and 850 cm 1, which decrease their intensity
with temperature increase, while bands at 1753, 1060 and
700 cm 1 disappear at 1000 8C. According to literature
results, BaCO3 presents bands at 1750, 1460, 1060, 860 and
700 cm 1 [22], while FeCO3 presents bands at 1523, 876 and
736 cm 1 [23,24]. These results indicate the presence of
carbonates in the present material. These carbonate bands
were not observed in XRD patterns, due to their low
resolution.
Bands at 600 and 450 cm 1 get well defined at higher
temperatures. These bands are assigned to v1 and v2
vibrations of spinels [25–27], which belong to the same
T1u representation [28,29]. Similar results were obtained by
Gonza´lez-Carren˜o et al. [14], which found bands at 586 and
434 cm 1, for hexaferrite BaFe12O19.
Results of crystallite size and particle diameter (BET), as a
function of temperature, are also presented in Table 1. An
increase of both parameters with temperature is observed, but
while crystallite size increases 70%, particle size increases
400%. This result is evidenced by the number of crystallites in
each particle, which increases from 4.8 to 14.5, indicating the
particle sintering. This is confirmed by SEM analysis (Fig. 4),
whose photomicrographs indicate the presence of aggregates,
with particle coalescence.
The color analysis of BaFe2O4, calcined at different
temperatures, was obtained correlating the results of reflectance
in the visible region (reflected wavelength) with colorimetric
coordinates (tonality variation, brightness and saturation).
Fig. 5 illustrates the diffuse reflectance of the pigments
before and after laboratory test. All curves present higher
reflection from 650 to 750 nm. It may be observed that
reflectance increases from 600 to 800 8C, probably due to
carbonate amount decrease, as observed by infrared spectroscopy
(Fig. 3). The decrease in reflectance observed at higher
temperatures is probably due to the sintering among particles,
observed in BET (Table 1) and SEM (Fig. 4) results.
It should be observed that curve profile is different from
other ferrite results. Ferrite reflectance usually presents a band
between 650 and 780 nm [3,30]. For BaFe2O4, there is no high
reflectance plateau. Otherwise, reflectance increases continuously
up to 750 nm. This may be due to the iron ligand field. For
the other ferrites, Fe2+ and Fe3+ are present in octahedral and
tetrahedral coordination, while, in barium ferrite, iron is only in
tetrahedral coordination. It should be emphasized that
octahedral ligand field leads to a higher splitting of d orbitals
than tetrahedral one. Consequently, electron transition occurs
with a higher energy absorption (or a smaller wavelength) [21].
As a consequence, the resulting color is a direct evidence of
Fe3+ or Fe2+ ions coordinated by oxygen [31,32]. This result
may also be observed in Fig. 6, which presents the colorimetric
coordinates of pigments before and after laboratory test. After
laboratory test, the ceramic pieces presented a good aesthetic
aspect, without defects as bubbles, superficial texture, among
others.
Results presented in Fig. 6 indicate that L* and b*
coordinates increase up to 700 8C, decreasing at higher
temperatures. As stated before, for diffuse reflectance results,
the increase may be due to carbonate elimination, while the
decrease may be due to sintering among particles. A continuous
decrease with temperature was observed for a* parameter.
According to Garcı´a et al. [33], the iron (III) oxides suffer a
reduction to Fe2+ ion, promoted by the emission of molecular
oxygen according to Eq. (1), when fired at high temperature or
when in the presence of unoxidized organic material. In the
present case, this unoxidized organic material is in the form of
carbonate and may lead to Fe3+ reduction, changing the
pigment color.
3Fe2O3!2Fe3O4 þ 1
2O2 (1)
The laboratory test, done with pigment calcined at 1000 8C
(Figs. 5 and 6), indicates that the pigment is chemically and
thermally stable, as no surface defects were observed.
Comparing the colorimetric coordinates of the pigment
calcined at 1000 8C before and after laboratory test, a small
change in tonality may be observed (DH* = 2.8) while the
saturation decrease (DC* = 4.4) and the lightness increase
(DL* = 5.3) are more important.
4. Conclusion
The pigment BaFe2O4 was obtained by the polymeric
precursor method, with single phase and brown color. Diffuse
reflectance and chromatic coordinates results indicate that
carbonate presence as well as sintering among particles change
the color, leading to its variation as a function of the heat
treatment of the pigment precursor. Differences between UV–
vis spectra of BaFe2O4 and other ferrites are probably due to the
iron ligand field—while the former presents iron in tetrahedral
sites, the latter present iron in octahedral and tetrahedral sites.
The pigment presents a suitable technological behavior without
reactions between glaze and pigment, indicating that powders
are chemically and thermally inert up to 1000 8C.

LA INDUSTRIA DEL AZULEJO EN CASTELLON

Documento interesante que planteaba las posibilidades futuras de la industria castellonense del azulejo, como podemos ver aboga por una fuerte y pronta internacionalizacion, algo que no se hizo en su momento de un modo suficientemente consistente y ahora se estan sufriendo los daños generados por esto. Pegadle un vistazo esta realmente bien...

Azulejos flexibles ... y rentables

La industria azulejera de Castellón es una de las pocas, por no decir la única, de las industrias españolas que aparecieron en el ya clásico estudio sobre la riqueza competitiva de las naciones que M. Porter publicó hace ya once años. Este profesor de escuela de negocios de Harvard señalaba en su estudio que “aproximadamente el 90% de la producción española de pavimentos cerámicos se concentraba en Castellón, en el noreste de España al norte de Valencia” y señalaba que a pesar de su pujanza “su amenaza a la industria italiana de la cerámica no era aún inminente”. El estudio presentado por KPMG hace algunos días sobre la comparación de las empresas cerámicas de Castellón y las italianas muestra como esta última afirmación de M. Porter se ha quedado desfasada.

Ya hace diez años estaba claro que la posición competitiva de la industria cerámica de Castellón contaba con muchos elementos favorables. El clima y la tradición hacen de España una de las mayores consumidoras de azulejos por persona. Además la red de depósitos arcillosos contiene menos residuos orgánicos que la arcilla italiana lo que favorece que hallan menos defectos de producción, tiempos de cocción menores y, por tanto, mayor calidad y competitividad. La decisiva inversión en nuevas tecnologías durante el final de los años 80 y los años 90 y las mejoras en el aprovisionamiento de gas fortalecieron todavía más a la industria que, en estos momentos, puede competir en condiciones de igualdad con el gigante italiano.

Todas estas condiciones han favorecido que la industria azulejera castellonense sea mucho más rentable que la italiana a pesar de que la producción de las 21 mayores empresas españolas sea la mitad de las 21 primeras empresas italianas.
En concreto la rentabilidad de las principales empresas azulejeras de Castellón fue del 7,6% de las ventas frente al 2,6% de las empresas italianas. Y esto a pesar de que se ha producido una pequeña caída de la rentabilidad en las empresas cerámicas que el año anterior se situaba en el 8,5% y la previsión es que el margen continúe reduciéndose ante la mayor competencia internacional.
En cualquier caso el margen de maniobra de las empresas azulejeras castellonenses es muy superior al de sus homónimas italianas que seguirán viendo como el transporte de las materias primas y, en menor medida, sus mayores costes laborales, lastran sus cuentas de resultados.

Dada esta situación sería importante que las empresas azulejeras castellonenses hicieran frente al único reto que todavía se les resiste: la internacionalización. Es cierto que las exportaciones de las empresas cerámicas españolas han aumentado desde el 37% de la producción de 1987 al 51% del año pasado. Sin embargo la industria italiana exporta el 70% de su producción, lo que le permite seguir dominando el mercado internacional. Aumentar el peso de los mercados internacionales es una estrategia todavía más importante si se tiene en cuenta que la capacidad de absorción de la producción por parte del sector de la construcción español va a disminuir ante la previsible reducción de la producción de viviendas que se espera para los próximos años.
Sin embargo esta estrategia de mayor apertura de los mercados internacionales debería realizarse de forma que se prestara atención a una adecuada diversificación de los clientes. Las empresas italianas ya han aprendido la lección con la desaceleración reciente de la economía de Estados Unidos. Por suerte hasta el momento la diversificación de las azulejeras castellonenses les ha permitido hacer frente a la caída de la demanda proveniente de Norteamérica con las ventas al este de Europa y Arabia Saudita. Además su menor tamaño es también una ventaja en este aspecto pues facilita una mayor flexibilidad a las empresas azulejeras de Castellón.
Por último se debe insistir en la importancia de la creación de marca en la internacionalización. El “made in Italy” vende todavía mucho en los mercados internacionales a pesar de que la calidad y el nivel de innovación de la cerámica de Castellón es tan alta o superior a la de sus competidoras italianas. Por eso es también fundamental promocionar la producción española en el mundo hasta situar el “made in Castellón” en el lugar que le pertenece.


Liberalización, ¿qué liberalización?

La Cumbre de Barcelona ha vuelto a poner en el centro de las discusiones de política económica la cuestión de la liberalización de los mercados. Sin embargo no todos los países de la Unión Europea tienen la misma visión sobre la cuestión. París y Berlín forman un eje que intenta alzarse con la medalla de “defensores de la economía social” y opositores a la liberalización. Sin embargo, al mismo tiempo, se muestran contrarios a aumentar la ayuda al desarrollo. Por su parte en España, donde el gobierno saca pecho diciendo que la liberalización avanza más rápido que los compromisos europeos, la misma es más nominal que real como se puede comprobar en los sectores eléctrico, de gas o en las líneas aéreas. Sin embargo nadie habla del terrible efecto de la política agraria común sobre la competencia mundial, la liberalización efectiva de los mercados internacionales y el desarrollo de los países del tercer mundo.
La realidad es que el mundo está viviendo un nuevo episodio de proteccionismo comercial, una práctica que se creía ya superada. El Gobierno de Estados Unidos pretende imponer aranceles al acero, la agricultura y los semiconductores además de las subvenciones a sus líneas aéreas. La Unión Europea se queja y pide represalias cuando a su vez subvenciona también a sus propias líneas aéreas. Es una auténtica ceremonia de la confusión. Muchos liberalismo de boquilla y poca libertad económica. Los mercados internacionales de muchos productos siguen atados de pies y manos ante el control que ejercen los grandes bloques económicos que no pueden renunciar a la protección de sus ineficientes productores. El señor Bové sigue luchando contra la globalización mientras cobra sustanciales cantidades de la Unión Europea que subvenciona de forma escandalosa la producción de muchos productos agrarios y ganaderos y empobrece a los países productores de materias primas del tercer mundo. Mientras la Política Agraria Común siga en pie hablar de liberalización y de libre comercio mundial es simplemente una entelequia. Es una forma de calmar la propia conciencia que tienen los “pseudo liberales” para justificar su adjetivo mientras, mediante al recurso del “y tu más”, aumentan el proteccionismo y dificultan la auténtica competencia.
Otra cosa queda clara en esta guerra comercial reciente. Depende de que sector sea el perjudicado la reacción es más pronta e intensa o menos. La Unión Europea no ha tardado en responder con represalias a la amenaza de imponer altos aranceles al acero lanzada por Bush desde Estados Unidos. Las exportaciones alemanas y francesas peligraban. Sin embargo cuando las mandarinas valencianas son excluidas del mercado norteamericano sin una justificación clara las cosas llevan otro ritmo.

Moraleja: en esta época de creciente lucha comercial lo mejor es tener una representación directa en la Unión y no dejar en manos de otros nuestros legítimos intereses comerciales.

RARE EARTH ELEMENTS

Determination of Rare Earth Elements (REEs) in Environmental Samples
By
Türker PASİNLİ

A Dissertation Submitted to the
Graduate School in Partial Fulfillment of the
Requirements for the Degree of

MASTER OF SCIENCE
RARE EARTH ELEMENTS (REEs)

1.1. Introduction to Rare Earth Elements (REEs)

The term rare earth was suggested by Johann Gadolin in 1794. "Rare" because when the first of the REEs was discovered they were thought to be present in the earth's crust only in small amounts, and "earths" because as oxides they have an earthy appearance. Because of chemical similarities among the REEs, their complete isolation and classification took more than a century from their discovery (Evans 1997).

The REEs lie in the last rows of Mendeleev’s periodic table, comprising both lanthanide and actinide series (Figure 1.1). The REE term is mostly employed in chemistry as a synonym of the lanthanide series.

The REEs have similar physicochemical properties, which change periodically with the atomic number. They range from La to Lu (atomic numbers between 57 and 71: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Th), ytterbium (Yb), and lutetium (Lu). Yttrium (atomic number 39) a Group IIIB transition metal, although not a lanthanide is generally included with the REEs as it occurs with them in natural minerals and has similar chemical properties. For the same reason, scandium (atomic number 21) is also included with the REEs. The REEs are usually divided into three groups: light REEs, from La to Pm, the medium REEs, from Sm to Ho, and the heavy REEs, from Er to Lu.




Figure 1.1. Periodic table with REEs and scandium, yttrium and thorium.


Although lanthanides are termed rare-earth elements, they are not rare in nature. Their levels in the earth’s crust are often equal to or higher than some physiologically significant elements, such as iodine, cobalt, silver, gold, platinum and selenium (Brzyska 1996). Cerium (68 mg/kg) and lanthanum (32 mg/kg) are the most common. Lutetium and thulium are the rarest (about 0.5 mg/kg) while the concentrations of the remainder range from 1 to 9 mg/kg. Promethium is an artificial radioactive element with no stable isotopes.

The REEs have similar chemical and physical properties and behave relatively coherently as a group. Chemically, REEs are strong reducing agents and their compounds are generally ionic. REEs are never found as free metals in the earth's crust.
All their naturally occurring minerals consist of mixtures of various REEs and nonmetals. Bastnaesite [(Ce,La)(CO3)F], monazite [(Ce,La,Nd,Th)(PO4)] [(REE)PO4] and xenotime [YPO4] are the three most significant minerals of REEs. The REEs are definitely electropositive metals with the oxidation number of +3. Only cerium, terbium and praseodymium with an oxidation number of +4 and samarium, europium and ytterbium with the oxidation number of +2 form stable compounds. Europium and cerium are the most reactive elements of the REEs (Evans 1997).


1.2. Uses of Rare Earth Elements

Lanthanide compounds frequently have magnetic, catalytic and optic properties and therefore are widely used in industry. Their industrial uses are outlined in Table 1.1.




Table 1.1. Industrial uses of REEs (Pedreira et al. 2002)

In the last twenty years new technologies have been introduced in metallurgical, optical and electronic industries, which increased the role of artificial lanthanide compounds with special physicochemical properties.

At present, metallurgy utilizes about 37% of lanthanides and their compounds which is used to remove oxygen and to enrich steel. Thirty percent of lanthanides are used for catalytic converters, 29% in ceramic industry, and 1% in other industries.
Pure lanthanide compounds are used in electronics and optoelectronics to produce luminophores (oxides of lanthanum, gadolinium, europium and terbium), lasers (e.g., halogens of neodymium, holmium and erbium), optical fibers, components of magnetic memories (e.g., gadolinium-gallium garnet, GGG), permanent magnets (alloys of samarium and neodymium) and high-temperature superconductors.
Also they are used as magnetic resonance imaging (MRI) contrast reagents in medicine, and also lanthanum chloride (LaCl3) is added to chemical fertilizers in China (Liang et al. 1991, Gorbunov et al.1992, Sloof et al. 1993, Brzyska 1996, Evans 1997, Shuai et al. 2000, Liang et al. 2001).

1.3. Biological Effects of Rare Earth Elements

Rare earth elements are released into the environment as a result of their industrial uses (Gorbunov et al. 1992). Continuous exposure to low concentrations of REEs could cause adverse health effects because of their bioaccumulation along the food chain.
Although there is so far no reported incidence of intoxication due to the intake of REEs through the food chain, several deleterious effects due to occupational and environmental exposure to REEs have been reported (Sabbioni et al.1982, Sax 1984).

According to these reports, rare earth elements have both positive and negative effects on human health. For example rare earth elements show benefit in the liver where gadolinium selectively inhibits secretion by Kupffer cells and decrease cytochrome P450 activity in hepatocytes, thereby protecting liver cells against toxic products of xenobiotic biotransformation. Praseodymium ion (Pr3+) produces the same protective effect in liver tissue cultures.
On the other hand, cytophysiological effects of lanthanides appear to result from the similarity of their cationic radii to the size of Ca2+ ions, their high degree of ionic bonding and their donor atom affinities. Trivalent lanthanide ions, especially La3+ and Gd3+, block different calcium channels in human and animal cells. Lanthanides can affect numerous enzymes. Dy3+ and La3+ block Ca2+-ATPase and Mg2+-ATPase, while Eu3+ and Tb3+ inhibit calcineurin. In neurons, lanthanide ions regulate the transport and release of synaptic transmitters and block some membrane receptors, e.g. GABA and glutamate receptors (Palasz et al.2000).

It is likely that lanthanides significantly and uniquely affect biochemical pathways, thus altering physiological processes in the tissues of humans and animals.

1.4. Determination of Rare Earth Elements

As the demand for high purity rare earth compounds is increasing and for environmental protection, the development of new precise and accurate analytical methods for the determination of REEs is required at trace levels.
For many years, the most common analytical techniques for measuring REEs have been neutron activation analysis (NAA) (Orvini et al. 2000, Figueiredo et al. 2002, Minowa et al. 2003) and isotope dilution mass spectrometry (IDMS) (Hoyle et al. 1983, Greaves et al. 1989, and Noemia et al. 1990). These methods are, however, time consuming and require very sophisticated equipment, unviable to most laboratories. The inductively coupled plasma optical emission spectrometry (ICP-OES) is one of the most effective multi-element techniques for the quantitative determination of many trace elements with widely varying matrices, and is often used in the determination of the REEs. Instrumental detection limits are stated to be on the order of 50.0 µg/L (Djingova et al. 2002). The more recent inductively coupled plasma mass spectroscopy (ICP-MS) technique is a powerful method for the direct determination of REEs (detection limits, in the order of 2.0 µg/L (Pedreira et al. 2002), but the equipment is still too expensive for many laboratories.

1.4.1. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)

Inductively coupled plasma optical emission spectrometry (ICP-OES) is an important analytical tool in a wide range of scientific disciplines. It is used for simultaneous determination of over 70 elements in virtually any sample in less than 2 minutes. Concentrations from parts per billion to weight % can be determined without preconcentration or dilution. The ICP-OES method enables multi-element determination with high levels of precision and accuracy for most elements (<1% RSD). Also it offers low detection limits, rapid analytical procedure, a large dynamic range (four or more orders of magnitude), and complete removal of the analyte from its original matrix in order to minimize interferences with lower matrix background (Settle 1997).

ICP-OES is based on the fact that atoms are promoted to higher electronic energy levels when heated to high temperatures. In fact, the plasma temperature is sufficient to ionize most atoms. For about three-quarters of the elements amenable to the technique, the most sensitive line arises from an ion rather than an atom. As the excited species leave the high-temperature region, the absorbed energy is released as ultraviolet and visible photons when the excited atoms decay to lower energy levels or the ground electronic state. Useful emission lines generally occur in the region between 160 and 900 nm. Atomic and ionic emission lines are very narrow, typically less than 5 pm, and their wavelengths follow well-understood selection rules (Settle 1997).

The ICP is estimated to produce a typical temperature of 6500 0K and this high temperature is sufficient to break virtually all chemical bonds in a sample. Consequently, the emitting atoms and ions are virtually independent of one another. As a result, the technique exhibits high sensitivity, a linear range of four or more orders of magnitude, and much reduced chemical interference relative to AAS or arc/spark emission techniques (Settle 1997).

In an ICP-OES determination, the samples are most commonly introduced into the plasma as aerosols. A wide variety of devices are available for sample introduction. Pneumatic nebulizers are the least expensive and most commonly used in commercial devices. The aerosol produced by the nebulizer is generally passed through a spray chamber to remove large droplets and produce a more homogeneous aerosol. While passing through the plasma, the aerosol is vaporized, atomized, perhaps ionized, and then electronically excited. After leaving the plasma, the sample emits photons, which are sampled through a narrow entrance slit and dispersed with grating monochromotor. The resolved radiations are measured with a photomultiplier tube or array detectors (such as a charge coupled device, CCD or charge injection device, CID), which converts the optical signal into an electrical signal. An electronic interface converts the signal into an appropriate form for measurement and storage by a dedicated computer (Settle 1997).

ICP-OES has been widely used in the determination of trace REEs. For example; Liang et al. (2001) used ICP-OES for the determination of La, Y, Yb, Eu, Dy after preconcentration step with nanometer-sized titanium dioxide micro-column. The technique was used by Shuai et al. (2000) for the determination of rare earth impurities in high-purity lanthanum oxide, by Iwasaki (1986) and Rucandio (1992) for the determination of lanthanides and yttrium in rare earth ores; and by Crock et al. (1982) for determination of rare earth elements in geological materials.

1.4.2. Preconcentration and Separation of Rare Earth Elements

Inductively coupled plasma optical emission spectrometry, as mentioned, offers one of the most suitable techniques for REEs determination. However, the low level of REEs in samples is not compatible with the detection limits exhibited by this technique. Also major constituents, such as organic compounds and inorganic salts, cause matrix effects. In order to achieve accurate and reliable results, efficient preconcentration of REEs and their separation from matrix is required.
One of the most widely used techniques for the separation and preconcentration of trace REEs has been co-precipitation. For example, Roychowdhury et al. (1989) precipitated REEs and Y as oxalates using calcium as a carrier. In another study Greaves et al. (1989) employed a precipitation step with hydrated iron (III) oxide followed by a purification procedure using a single cation-exchange column after which the sorbed species were eluted with hydrochloric and nitric acids. Liquid-liquid extraction is another efficient separation technique used in the studies related with REEs. Wang et al. (2004) applied the technique in the separation of Y from heavy REEs using a novel organic carboxylic acid, s-Nonylphenoxy acetic acid, as extractant in the presence of several other complexing agents such as EDTA, DTPA, or HEDTA. Ion exchange procedures have also been applied successfully for the separation of REEs from geological materials [Navarro et al. 2002]. In this study, the researchers separated REEs with a cation exchange resin; then they eluted the sorbed species with a nitric acid-oxalic acid mixture. Zhu et al. (1998) utilized an ion-exchange microcolumn prepared with Diol silica consisting of a acrylic acid/acrylamide copolymer. Elution of REEs from the microcolumn was realized with 0.25 M HNO3. Möller et. al (1992) used Chelex 100 chelating resin for preconcentration of REEs in sea water by ion exchange chromatography. High performance liquid chromatography (HPLC) was also applied in the determination of REEs. In one such study, Qin et al. (2000) used a 2-ethylhexylhydrogen 2-ethylhexylphosphonate resin as the stationary phase and dilute nitric acid as the mobile phase for the separation of REE impurities in high purity cerium oxide.

1.4.2.1. Solid-Phase Extraction (SPE)

In addition to the preconcentration / separation techniques mentioned above, the solid-phase extraction (SPE) technique has become increasingly popular in recent years (Grebneva et al. 1996, Vicente et al. 1998, Dev et al. 1999, Liang et al. 2001, Hirata et al. 2002). It is an extraction method that uses a solid phase and a liquid phase to isolate one, or one type, of analyte from a solution. It is usually used to clean up a sample before using a chromatographic or other analytical method to quantitate the amount of analyte(s) in the sample. The solid phase extraction technique has several advantages; (i) it is simple to implement, (ii) high preconcentration factors can be obtained by SPE , (iii) it enables rapid phase separation, and (iv) it can be combined with different techniques. The general procedure is to load a solution onto the SPE phase, wash away undesired components, and then wash off the desired analytes with another solvent into a collection tube.

The solid phase extraction method is widely used in chromatographic preconcentration studies that can be performed in two distinct forms, the batch and the column methods. In our project we used the batch method. In the batch mode, a quantity of the chromatographic stationary phase (or sorbent) is added to the sample and the mixture is then shaken for some time. If the conditions are suitable, the analytes of some interest become bound to the sorbent and are then separated from the sample solution by filtration.

Column preconcentration can be performed either off-line or on-line. In the former case, the sample is passed through a suitable column after which the enriched analyte is desorbed from the column and the resultant solution is analyzed by an appropriate procedure. In the on-line method, the sorbent column is coupled directly to the analytical instrument so that the sample enrichment, desorption, and analysis steps can be carried out at the same run automatically.

Why ceramic tile?

Why Ceramic Tile? Top Ten Benefit of Choosing Tile

When deciding on a home improvement project, you have lots of options, and while ceramic tile is only one of those options, the following are ten facts that set ceramic apart from others. The decorator effect of tile has only recently taken hold in homes of all styles; from contemporary to colonial, tile has a design and style to fit all applications. Tile is widely adaptable and can be used in an array of settings, from kitchens and baths to dining rooms and living rooms. Whether it’s a stone finish you're after or a traditional glazed finish, there’s a style to suit every taste.

 Ease of Maintenance. While no surface remains entirely maintenance free, ceramic tile comes about as close at it can to being service free. Short of the application of the occasional sealant, applied once every four years or so, tile requires only the regular cleaning that any flooring surface would require. With the installation of grout, tile becomes almost impervious to water damage, and can be virtually hosed off if necessary. Many specialty products are currently available that assist greatly in tile maintenance and upkeep, all of which can be found in nearly any home goods provider or supermarket.

 Adaptability. There is a tile option for nearly any application, and your imagination and creativity are your only limitations when installing tile. From porticos in a dining room to a tiled hearth in front of a fireplace, you can adapt tile to nearly any surface, indoors or out. Tile’s adaptability has been exploited throughout Europe, and examples for tile floors can be seen in kitchens, living rooms, dining rooms and even bedrooms. In some destinations abroad, it is not uncommon to find an entire house tiled wall to wall, in an effort to keep cool, and provide a versatile flooring surface.

 Cost Effectiveness. Dollar for dollar, tile still remains one of the most cost effective home improvements on the market today. When considering initial costs versus longevity, it becomes quite clear that ceramic tile overall offers the best "dollar per mile" of any surface. Ceramic tile's limited upkeep and maintenance adds to its value even further. Square footage material costs stay in check with most other alternatives, and while the initial installation costs may be slightly higher, it's important to consider all the long term costs and value when judging overall cost effectiveness.

 Installation Variety. While your installation options are only limited by your imagination, there are a number of ideas already in place to get your creative juices flowing. Although flooring has always been the number one usage of ceramic tile, you aren't limited to just floors. Backsplashes, porticos, murals and countertops can all be tiled in an artistic manner, subject to your décor. You can match your floor to your tile walls, or contrast the two to make your project stand out even more.

 Durability. The ancient Romans saw the benefit of tile in its durability, and this fact is not lost on us modern folks. Tile is great for high traffic situations thanks to its strength and resiliency to staining and wear. The ancient Romans originally used tile in a utilitarian manner, but it was soon obvious even to them that a decorative element could be introduced to tiling. While not extremely impact resistant, the wear ability of tile is the reason for its durability.

 Ease of Repair. Even though ceramic is strong, there is still the opportunity for breakage, as with any earthenware. When a breakage does occur, repairing tile is far simpler than fixing hardwood or plank flooring. Simply remove the broken pieces, clean the area, reinstall replacement tiles and regrout the repaired area. Completing tile repairs typically takes less time than repairing a wood floor, or even a composite flooring surface. It is important to keep several pieces of tile left over from your installation for these repair needs.

 Style. As always, style counts, and tile is no exception to that rule. Tile has a finish and style to adapt to any décor; from southwest to cosmopolitan, there is a color and a texture to fit every need. There is an unlimited variety to tile, from bright vibrant colors to muted tones and everything in between, and a brief trip to any tile house or home improvement retailer will prove this point. While colors and textures can vary greatly between manufacturers, virtually any combination of color and texture can be found on today's market.

 Design Flexibility. Thanks to the variety of sizing options of ceramic tiles, design flexibility is drastically improved. You can opt for smaller 6" x 6" tiles, all the way up to the 24" x 24", as well as the squaring options, such as "brick and block" or "Flemish" style joints. All these choices add to the design characteristics that are perfect for your application.

 Capital Improvement. In many cases, adding a tile to your home will increase its potential resale value tremendously. Potential buyers will certainly take notice of a well installed and designed tile enhancement. With its attractive style and impressive presentation, a good tile job can add thousands of dollars in potential value to prospective customers.

Not tweet

Yes I know my followers that we're not tweeting last days, but we have much work to do, and that's really good news these days.... I promise that we're going to tweet more the following days, I will keep all of you updated about my trip to Russia, Ukraine and Uzbekistan... I'm sure after many months working there we're going to have a really good trip in business terms!

March 2010

March just have arrived, we left back Cevisama 2010 and Qualicer and now we have to continue working in our possibilities. This month we're going to share information about new markets and new business opportunities mixed with technical information very interesting for technicians and laboratory people.

Stay online with us! we have many things to show you!