ABSTRACT
Resumen Introducción. Los compuestos con metales de transición en su estructura generan enorme interés por sus propiedades físicas, las más destacadas de las cuales son las magnéticas y las eléctricas. La espinela ZnCr2O4 se ha caracterizado por sus potenciales usos como fotocatalizador y como material empleado para censar CO2, lo cual actualmente es de gran relevancia, y ha motivado conocer nuevos métodos para su obtención y para la justificación de estudios que permitan entender las características termodinámicas para su formación. Objetivo. Estudiar la estabilidad de la fase ZnCr2O4 con la coexistencia de fases secundarias formadas mediante tratamientos térmicos. Materiales y métodos. A partir de la homogeneización de glicina y nitratos (cinc y cromo), se sintetizó por combustión en solución un compuesto amorfo, el cual tras tratamientos térmicos (750, 850 y 950 °C) presentó ordenamiento cristalino. Resultados. Luego de la obtención del compuesto se evaluó la morfología de los polvos empleando microscopía electrónica de barrido (SEM) y evaluando su composición (EDS). Se determinó presencia de material orgánico, se realizó caracterización térmica (TGA y DSC) para definir la temperatura de formación de fases, para luego evaluar y comparar las estructuras mediante difracción de rayos X (DRX), y mediante simulaciones en el programa FactSage( se compararon resultados para verificar el equilibrio de las fases. Conclusión. A través del método de combustión en solución se obtiene una estructura no cristalina conformada por Zn, Cr y O, confirmándose la presencia de C asociado al componente orgánico luego de la combustión.
Abstract Introduction. Compounds with transition metals in their structure generate great interest due to their physical properties, especially their magnetic and electric ones. The spinel ZnCr2O4 has been characterized by its potential uses as photocatalyst and as CO2, sensing material, which has current relevance and has motivated to learn about new methods for obtaining it and for justifying studies that allow to understand the thermodynamic characteristics for its formation. Objective. Study phase stability ZnCr2O4 with the coexistence of secondary phases formed through thermal treatments. Materials and methods. From the homogenization of glycine and nitrates (zinc and chrome), an amorphous compound was synthetized by combustion in solution. After thermal treatments (750, 850 and 950 °C), the compound presented crystalline ordering. Results. After obtaining the compound, the morphology of the powders was evaluated through scanning electronic microscopy (SEM) and their composition was also evaluated (EDS). The presence of organic material was determined and a thermal characterization was made (TGA and DSC) to define the phase formation temperature. Next, the structures were evaluated and compared through X-ray diffraction (XRD). Using simulations in the FactSage( software the results were compared to verify phase equilibrium. Conclusion. Through the solution combustion method, a non-crystalline structure is obtained, formed by Zn, Cr and O, confirming the presence of C associated to the organic component after combustion.
Resumo Introdução. Os compostos com metais de transição na sua estrutura geram enorme interesse por suas propriedades físicas, as mais destacadas das quais são as magnéticas e as elétricas. A espinela ZnCr2O4 se ha caracterizado por seus potenciais usos como fotocatalizador e como material empregado para fazer CO2, o qual atualmente é de grande relevância, e há motivado conhecer novos métodos para sua obtenção e para a justificação de estudos que permitam entender as características termodinâmicas para sua formação. Objetivo. Estudar a estabilidade da fase ZnCr2O4 com a coexistência de fases secundárias formadas mediante tratamentos térmicos. Materiais e métodos. A partir da homogeneização de glicina e nitratos (cinc e cromo), se sintetizou por combustão em solução um composto amorfo, o qual trás tratamentos térmicos (750, 850 e 950 °C) apresentou ordenamento cristalino. Resultados. Logo da obtenção do composto se avaliou a morfologia dos pós empregando microscopia eletrônica de barrido (SEM) e avaliando sua composição (EDS). Se determinou presencia de material orgânico, se realizou caracterização térmica (TGA e DSC) para definir a temperatura de formação de fases, para logo avaliar e comparar as estruturas mediante difração de raios X (DRX), e mediante simulações no programa FactSage( se compararam resultados para verificar o equilíbrio das fases. Conclusão. Através do método de combustão em solução se obtém uma estrutura não cristalina conformada por Zn, Cr y O, confirmando-se a presencia de C associado ao componente orgânico logo da combustão.
ABSTRACT
ABSTRACT In the present work, Cu2+ substituted cobalt ferrite (Co1-xCuxFe2O4, x = 0, 0.3, 0.5, 0.7 and 1) magnetic nanopowders were synthesized via chemical co-precipitation method. The prepared powders were investigated by various characterization methods such as X-ray diffraction analysis (XRD), scanning electron microscope analysis (SEM), vibrating sample magnetometer analysis (VSM) and fourier transform infrared spectroscopy analysis (FTIR). The XRD analysis reveals that the synthesized nanopowders possess single phase centred cubic spinel structure. The average crystallite size of the particles ranging from 27-49 nm was calculated by using Debye-scherrer formula. Magnetic properties of the synthesized magnetic nanoparticles are studied by using VSM. The VSM results shows the magnetic properties such as coercivity, magnetic retentivity decreases with increase in copper substitution whereas the saturation magnetization shows increment and decrement in accordance with Cu2+ substitution in cobalt ferrite nanoparticles. SEM analysis reveals the morphology of synthesized magnetic nanoparticles. FTIR spectra of Cu2+ substituted cobalt ferrite magnetic nanoparticles were recorded in the frequency range 4000-400cm-1. The spectrum shows the presence of water adsorption and metal oxygen bonds. The adhesion nature of Cu2+ substituted cobalt ferrite magnetic nanoparticles with bacteria in reviewed results indicates that the synthesized nanoparticles could be used in biotechnology and biomedical applications.
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Introducción: Se han desarrollado una variedad de sistemas para fijar y artrodesar la columna cervical con las ventajas de reducir del riesgo de seudoartrosis, extrusión y colapso del injerto, así como una mayor precisión en la alineación sagital, por tal motivo requerimos comparar resultados de placa-injerto, caja-placa y caja-PEEK, en pacientes con conducto cervical estrecho. Material y métodos: Estudio prospectivo, de intervención y comparativo, formando tres grupos: grupo I, artrodesis con placa-injerto, grupo II, caja-placa, grupo III, caja-PEEK. La evaluación funcional pre- y postoperatoria con escala de discapacidad cervical y escala visual análoga (EVA) de dolor y radiografías columna cervical. Se analizaron los resultados con pruebas no paramétricas de rangos con signo de Wilcoxon y Kruskal Wallis para comparación entre más de dos grupos. Con nivel de significancia de 0.05. Resultados: Muestra de 37 pacientes para el grupo I con n = 12, con 22 niveles; grupo II con: n = 11, con 19 niveles; grupo III con: n = 14 con 25 niveles. La mayoría de pacientes entre la sexta y octava década de la vida. Al año de postoperados el índice de discapacidad cervical y mejoría del dolor con EVA mostraron mejoría con diferencia estadística en los tres grupos (p = 0.001). Sin embargo, las mediciones radiográficas al año de seguimiento mostraron una mejoría significativa de la lordosis segmentaria (p = 0.02) sólo en pacientes operados con placa-injerto. Conclusiones: El uso de la placa injerto ofrece mejores resultados clínicos y radiográficos en comparación con la caja-placa y caja-PEEK al año de seguimiento.
Introduction: A variety of systems have been developed to fix and perform arthrodesis of the cervical spine, with the advantages of reducing the risk of pseudoarthrosis, extrusion and graft collapse and achieving a more precise sagittal alignment. We therefore need to compare the results of the following approaches to patients with cervical stenosis: plate-graft, cage-plate and PEEK cage. Material and methods: Prospective, interventional, comparative trial involving three groups: group I, arthrodesis with plate-graft; group II, cage-plate, and group III, PEEK cage. The pre- and postoperative assessments included the cervical disability scale, the pain visual analog scale (VAS), and cervical spine X-rays. The results were analyzed with non-parametric tests such as the Wilcoxon sign test and the Kruskal-Wallis test for the comparison of more than two groups. Significance level was 0.05. Results: The sample included a total of 37 patients: n = 12 in group I, with 22 levels; n = 11 in group II, with 19 levels, and n = 14 in group III, with 25 levels. Patient age ranged between 60 and 80. One year after surgery there was an improvement in cervical disability and the pain VAS score, with a statistically significant difference among the three groups (p = 0.001). However, radiographic measurements at that time showed a significant improvement in segmental lordosis (p = 0.02) only in plate-graft patients. Conclusions: The plate-graft approach provides better clinical and radiographic results compared to the cage-plate and PEEK cage techniques, at the one-year follow-up.