THE OPTICAL PROPERTIES OF Pr3+ EMBEDDED IN THE RARE EARTH BOROGERMANATE MATRICES: REBGeO5

The luminescent properties of the trivalent praseodymium ion in the trigonal borogermanate matrice PrBGeO5 have been analysed. The energy level schemes are deduced from the absorption and emission spectra and reproduced with 14 crystal field parameters (cfps) according to the local point symmetry occupied by the rare earth element in the matrix.The luminescent properties of the trivalent praseodymium ion in the trigonal borogermanate matrice PrBGeO5 have been analysed. The energy level schemes are deduced from the absorption and emission spectra and reproduced with 14 crystal field parameters (cfps) according to the local point symmetry occupied by the rare earth element in the matrix

Evaluation of point defect concentrations in B2-FeAl intermetallic compound

Thermal defects are studied for three compositions (49, 50 and 52 at.%Fe) of the intermetallic compound FeAl with B2 structure. Magnetic measurements are used to determine the thermal defect concentrations. These concentrations are determined from fitting the experimental curves of magnetic susceptibility, obtained during an isochronal annealing after a quench. Next we have evaluated theoretically the concentrations of different point defects that exist in this compound. The used model is based in the Bragg-Williams approximation assuming the nearest-neighbour interaction. The calculated concentrations describe well the experimental values.Thermal defects are studied for three compositions (49, 50 and 52 at.%Fe) of the intermetallic compound FeAl with B2 structure. Magnetic measurements are used to determine the thermal defect concentrations. These concentrations are determined from fitting the experimental curves of magnetic susceptibility, obtained during an isochronal annealing after a quench. Next we have evaluated theoretically the concentrations of different point defects that exist in this compound. The used model is based in the Bragg-Williams approximation assuming the nearest-neighbour interaction. The calculated concentrations describe well the experimental values

Magnetic properties of LaFe1-xCrxO3 and Fe2-2xCr2xO3 mixed oxides

Mixed oxides with formula LaFe1-xCrxO3 and Fe2-2xCr2xO3, where 0≤x≤1, are studied. The samples have been prepared using solid state reaction technique in air. The X-ray diffraction spectra indicated that the samples crystallize in a corundum phase with space group ( R3c ) for Fe2-2xCr2xO3 and in the perovskite structure for LaFe1-xCrxO3. Many techniques have been used to explore the magnetic properties of the systems. High field, ZFC and FC magnetization vs. temperature, d.c. susceptibility and Mössbauer spectroscopy were carried out. High temperature magnetic susceptibility measurements and high field magnetic magnetization (H ≤ 20 T) show that the behavior of the susceptibility and the magnetization are complex. Mössbauer spectra of the solid solutions have been measured at 4.2 K and in the temperature range 77 K to 300 K. The shapes of spectra are unusual, showing strong relaxation phenomena in a wide temperature range as recently observed for many frustrated systems. The results are discussed by establishing the existence of various magnetic structures, inducing intermediate magnetic phases between the antiferromagnetic and the paramagnetic states. Preliminary magnetic phase diagrams of the systems have been established.Mixed oxides with formula LaFe1-xCrxO3 and Fe2-2xCr2xO3, where 0≤x≤1, are studied. The samples have been prepared using solid state reaction technique in air. The X-ray diffraction spectra indicated that the samples crystallize in a corundum phase with space group ( R3c ) for Fe2-2xCr2xO3 and in the perovskite structure for LaFe1-xCrxO3. Many techniques have been used to explore the magnetic properties of the systems. High field, ZFC and FC magnetization vs. temperature, d.c. susceptibility and Mössbauer spectroscopy were carried out. High temperature magnetic susceptibility measurements and high field magnetic magnetization (H ≤ 20 T) show that the behavior of the susceptibility and the magnetization are complex. Mössbauer spectra of the solid solutions have been measured at 4.2 K and in the temperature range 77 K to 300 K. The shapes of spectra are unusual, showing strong relaxation phenomena in a wide temperature range as recently observed for many frustrated systems. The results are discussed by establishing the existence of various magnetic structures, inducing intermediate magnetic phases between the antiferromagnetic and the paramagnetic states. Preliminary magnetic phase diagrams of the systems have been established

Caracterización fisicoquímica del yeso natural de Mauritania

Gypsum from "Nderhamcha", a region in Mauritania, has been studied through three techniques: thermo-gravimetry, thermo-differential analysis, and X ray diffraction. It has been proved that the dehydration of this material happens in two stages, characterized by the closeness of their temperature. The thermal study as certains the two transformations due to the gypsum dehydration and those due to soluble and insoluble anhidrite.El yeso de Mauritania, de la región "Nderhamcha", ha sido estudiado a través de tres técnicas instrumentales: termogravimetría, análisis térmico-diferencial y difracción de rayos X. Se comprueba que la deshidratación de este material se efectúa en dos etapas, caracterizadas por temperaturas muy próximas. En el estudio térmico se comprueban las dos transformaciones debidas a la deshidratación del yeso y las debidas a la anhidrita soluble e insoluble

Formación de hidroxiapatita, Ca5(PO4)3∙OH, en presencia de silicatos

Hydroxyapatite Ca5(PO4)3OH (HAp) is a crystalline phase which has several applications within the domain of special cements. This phase takes an important role in the cement reactions for the reconstruction of skeletal functions (medical domain). It is used also to improve properties of dental material. On the other hand, it is investigated to develop chemically bonded ceramics. In this paper we study the formation of HAp with β-C2S and C5PS, using some compositions in the rich lime portion of the system CaO-SiO2-P2O5-H2O (at atmospheric pressure and open system). These compositions lie in the range of: CaO: 67-71 %; SiO2: 3-18%; P2O5: 9-29% (Wt%). The preparations are made using solid state reactions, with thermal treatment at open system. The identification of phases was carried out using X-ray diffraction, Infra-Red absorption and Differential Thermal Analysis. We delimit a spectroscopy little domain lies in the range of CaO-69,5-70%; P2O5-16,2-19,5%; SiO2-11,1-13,6%. Within this domain, the crystalline phases solid state compatibility at temperature near 1000ºC are HAp, β-C2S, C5PS.La hidroxiapatita, Ca5(PO4)3OH (HAp), es una fase cristalina que tiene diversas aplicaciones en el ámbito de determinados cementos especiales. Esa fase juega un importante papel en las reacciones de cementos utilizados en medicina para la reconstrucción defunciones del esqueleto. Se utiliza también para mejorar propiedades de materiales de aplicación odontológica. Por otra parte, se está estudiando para desarrollar conglomerantes cerámicos. En el presente trabajo se estudia la compatibilidad en estado sólido de la HAp con β-C2S y C5PS utilizando, a presión atmosférica y recinto abierto, composiciones en la zona rica en cal del sistema CaO-SiO2-P2O5-H2O dentro de los límites siguientes. CaO: 67-71 %; SiO2: 3-18%; P2O5: 9-29% (en peso). El tratamiento térmico se realizó en estado sólido y en atmósfera abierta. La identificación de las fases se realizó a través de Difracción de Rayos X, Espectroscopia de Absorción Infrarroja y Análisis Térmico Diferencial. Se define una pequeña zona del diagrama de composición: CaO=69,5-70%; P2O5=16,2-19,5%; SiO2=11,1-13,6%. En este campo las fases cristalinas compatibles en estado sólido, formadas a 1.000ºC, son HAp, β-C2S y C5PS

Crescimento e respostas hematológicas de tambaquis alimentados com diferentes quantidades de mandioca (Manihot esculenta)

Tambaqui,Colossoma macropomum is a fish of primary importance in Brazilian aquaculture and in the Amazon region in particular. The aim of this work is to analyze the combined effects of physical training and levels of dietary cassava (Manihot esculenta) on the hematological parameters, food intake, conversion efficiency, growth ratio and swimming performance of this fish. A diet for tambaqui consisting of 30% cassava caused decreases in weight gain and specific growth rate compared with the control group. Diets containing 15% or 45% cassava did not affect these indices and did not cause hematological changes in tambaqui juveniles, indicating that some amount of cassava can be used as an alternative energy source for this important aquaculture species.Tambaqui Colossoma macropomum, é um peixe de importância fundamental na aquicultura do Brasil e, em particular, na Região Amazônica. O objetivo deste trabalho foi analisar o efeito combinado do treinamento físico com diferentes níveis de macaxeira (Manihot esculenta) na dieta, sobre os parâmetros hematológicos, ingestão alimentar, eficiência de conversão, taxa de crescimento e performance natatória desses peixes. A dieta com 30% de cassava causou diminuição no ganho de peso e na taxa de crescimento específico quando se comparou ao grupo controle. Dietas contendo 15% e 45% de cassava não apresentaram efeito sobre estes índices e não causaram alterações hematológicas significativas em indivíduos juvenis de tambaqui, indicando que estas quantidades de cassava podem ser administradas como alternativa de fonte de energia para essa importante espécie na aquicultura