Síntese e caracterização de TaC e óxido misto de tântalo e cobre nanoestruturados a partir do precursor oxálico de tântalo através de reações gás-sólido e sólido-sólido a baixa temperatura

The research and development of nanostructured materials have been growing significantly in the last years. These materials have properties that were significantly modified as compared to conventional materials due to the extremely small dimensions of the crystallites. The tantalum carbide (TaC) is an extremely hard material that has high hardness, high melting point, high chemical stability, good resistance to chemical attack and thermal shock and excellent resistance to oxidation and corrosion. The Compounds of Tantalum impregnated with copper also have excellent dielectric and magnetic properties. Therefore, this study aimed to obtain TaC and mixed tantalum oxide and nanostructured copper from the precursor of tris (oxalate) hydrate ammonium oxitantalato, through gas-solid reaction and solid-solid respectively at low temperature (1000 ° C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Spectroscopy X-Ray Fluorescence (XRF), infrared spectroscopy (IR), thermogravimetric (TG), thermal analysis (DTA) and BET. Through the XRD analyses and the Reitiveld refinement of the TaC with S = 1.1584, we observed the formation of pure tantalum carbide and cubic structure with average crystallite size on the order of 12.5 nanometers. From the synthesis made of mixed oxide of tantalum and copper were formed two distinct phases: CuTa10O26 and Ta2O5, although the latter has been formed in lesser amounts

Structural and mechanical properties of La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co, Ni and Cu) perovskites

La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La0.6Sr0.4FeO3-δ perovskite were studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La0.6Sr0.4M0.1Fe0.9O3−δ with mixed rhombohedral and orthorhombic structures. Substitution of Cu decreases the melting point of La0.6Sr0.4FeO3-δ. The results of mechanical characterizations show that La0.6Sr0.4Co0.1Fe0.9O3−δ and La0.6Sr0.4Ni0.1Fe0.9O3−δ have ferroelastic behavior and comparable elastic moduli, however, subtitution of Ni shows higher hardness and lower fracture toughness than Co in Bsite doping

Síntese e caracterização de CuNb2O6 e CuNbC através de reação sólido- sólido e gás- sólido a baixa temperatura

The refractory metal carbides have proven important in the development of engineering materials due to their properties such as high hardness, high melting point, high thermal conductivity and high chemical stability. The niobium carbide presents these characteristics. The compounds of niobium impregnated with copper also have excellent dielectric and magnetic properties, and furthermore, the Cu doping increases the catalytic activity in the oxidation processes of hydrogen. This study aimed to the synthesis of nanostructured materials CuNbC and niobium and copper oxide from precursor tris(oxalate) oxiniobate ammonium hydrate through gas-solid and solid-solid reaction, respectively. Both reactions were carried out at low temperature (1000°C) and short reaction time (2 hours). The niobium carbide was produced with 5 % and 11% of copper, and the niobium oxide with 5% of copper. The materials were characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF), infrared spectroscopy (IR), thermogravimetric (TG) and differential thermal analysis (DTA , BET and particle size Laser. From the XRD analysis and Rietveld refinement of CuNbC with S = 1.23, we observed the formation of niobium carbide and metallic copper with cubic structure. For the synthesis of mixed oxide made of niobium and copper, the formation of two distinct phases was observed: CuNb2O6 and Nb2O5, although the latter was present in small amounts

Redução aluminotérmica do óxido de tântalo usando uma tocha de plasma como ignitor

In this work was used a plasma torch of non transferred arc with argon as work gas, using a power supply with maximum DC current of 250 A and voltage of 30 V to activate the plasma and keep it switched on. The flame temperature was characterized by optical emission spectroscopy, through Boltzmann-plot-method. The torch has been used like igniter in the aluminothermic reduction of the mixture tantalum oxide and aluminum, seeking to obtain metallic tantalum. In heating of the reagents only one particle will be considered to study interactions between plasma-particle, seeking to determinate its fusion and residence time. The early powders were characterized by laser granulometry, scanning electron microscopy (SEM) and X-ray diffraction analysis. The final product of this reaction was characterized by SEM and X-ray diffraction. Crystallite size was calculated by the Scherrer equation and microdeformation was determined using Willamsom-Hall graph. With Rietveld method was possible to quantify the percentile in weight of the products obtained in the aluminothermic reaction. Semi-quantitative chemical analysis (EDS) confirmed the presence of metallic tantalum and Al2O3 as products of the reduction. As was waited the particle size of the metallic tantalum produced, presents values in nanometric scale due the short cooling time of those particles during the process

Personnalité, fonctionnement réflexif et ajustement conjugal dans un contexte de traumas en enfance: Associations avec les pratiques parentales et la désorganisation de l’attachement de l’enfant

Le présent mémoire s’est intéressé à la contribution respective de la gravité des traumas vécus en enfance, des traits de la personnalité, du fonctionnement réflexif et de l’ajustement conjugal des survivants, à la sensibilité et à la négativité (i.e., hostilité et intrusion) des pratiques parentales adoptées et à la prédiction de la désorganisation de l’attachement de leur enfant à 17 mois. Dans cette perspective, 100 mères ayant vécu des mauvais traitements en enfance et de faible statut socio-économique ont été recrutées à l’hôpital Rosemont-Maisonneuve de Montréal à l’aide du Parental Bonding Instrument. Des analyses corrélationnelles menées sur l’ensemble des variables ont permis de mettre en évidence des associations significatives entre la sensibilité maternelle et l’ajustement conjugal et le FR-G ainsi qu’entre les comportements maternels négatifs et la gravité du trauma subi en enfance, le FR-G et la désorganisation de l’attachement de l’enfant. De plus, les variables corrélées à la désorganisation de l’attachement à 17 mois ont été incluses dans un modèle de régression logistique hiérarchique afin de tester leur contribution à sa prédiction. Les résultats indiquent qu’un modèle significatif de prédiction de l’organisation de l’attachement de l’enfant inclut le FR-T et l’insensibilité maternelle et explique environ 43 % de la variance de cette dernière. Selon ce modèle, l’augmentation de 1 point de FR-T diminue de 1,7 fois le risque que l’attachement de l’enfant soit désorganisé et l’augmentation de 1 de l’indice d’insensibilité maternelle augmente de 1,4 fois ce même risque. Ces résultats s’inscrivent dans le raffinement de la compréhension des pratiques maternelles sensibles et négatives dans un contexte d’historique de trauma en enfance ainsi que de la désorganisation de l’attachement de l’enfant et ils sont discutés en fonction de la littérature à ce sujet.

Infección por virus sincitial respiratorio y su relación con valores de IGG en niños críticos

Antecedente: La infección por el virus sincitial respiratorio (VSR) representa una elevada morbimortalidad, y en algunos casos necesidad de manejo en unidades de cuidado intensivo pediátrico (UCIP). La respuesta inmunológica influye de manera directa en la expresión de la severidad y pronóstico de los pacientes con infección respiratoria. Metodología: Estudio de una cohorte retrospectiva de pacientes con infección respiratoria grave secundaria a VSR, sin historia de inmunodeficiencia, atendidos en la UCIP del Hospital Universitario Clínica San Rafael. Se realizó análisis descriptivoglobaly de acuerdo a la categorización de las prueba de IgG. Resultados: De 188 pacientes que ingresaron a la UCIP, 13% presentaron infección por VSR (24), con una edad promedio de 7,3 (DE=3,6) meses. Pertenecían al sexo masculino79,83%. Se encontró que 12,5% tenían un valor de IgGbajo para su edad, 58,33% tenían valores en límite inferior y el 29,17% dentro de rangos normales para su edad. En los pacientes con IgG baja, fue mayor la presentación de choque séptico que no responde a líquidos (100 vs 92 vs 86%), la mediana de días de ventilación mecánica fue mayor (8 vs 6 vs 5 respectivamente), así como la mortalidad (67 vs 7,1 vs 0%). Conclusión: Nuestra serie encontró que aquellos pacientes con niveles bajos o valores en el límite inferior de IgG sérica tuvieron mayor compromiso sistémico, mayor duración de ventilación mecánica y mayor mortalidad. Se necesitan estudios prospectivos que relaciones niveles bajos de IgG con severidad y pronostico en estos pacientes con infección grave por VSR.