Abstract This study presents the first results of Ni-rich coating growth by the Pechini method on 304 stainless steels fractures, in order to healing fracture surfaces of metallic parts. A series of tests were performed to establish the calcination temperature by differential scanning calorimetry (DSC) at 1300°C using a heating rate of 10°C/min in mixtures of (CH3COO)2Ni•4H2O (Nickel Acetate Tetrahydrate) with HOC(COOH)(CH2COOH)2•H2O (Citric Acid Monohydrate) and precursors: HOCH2CHOHCH2OH (Glycerol) and HOCH2CH2OH (Ethyleneglycol). Results indicate that the Ethyleneglycol precursor is better than the Glycol because it shows a thermal stability at lower temperature of calcination. Subsequently, 304 stainless steel cylindrical fractures (0.6 cm in diameter, 1 cm height) were immersed in a solution of Ethyleneglycol and these samples were gelated at 110°C for 24 h in a muffle furnace. Additionally, these samples were calcined at 660°C for 60 min under an Ar flow of 200 ml/min, using a heating/cooling rate of 5°C/min in order to synthesize the nickel nanoparticles on the fractures. Coating growth on the fractures was carried out at an Ar flow of 220 ml/min at 1100°C for 60 min at a heating/cooling rate of 10°C/ min. By optical and scanning microscopy MEB), it was observed that the coating has a thickness of ~700 μm with a series of cuboidal precipitates larger than 1 μm, as well as laminar phases rich in Ni, Fe and Cr.

Resumen En este estudio se llevó a cabo el crecimiento de recubrimientos ricos en Ni por el método Pechini sobre fracturas de acero inoxidable 304, para sanar superficies de fractura de piezas metálicas. Una serie de pruebas se llevaron a cabo para establecer la temperatura de calcinación por calorimetría de barrido diferencial (DSC) a 1300°C por 10°C/min en mezclas de (CH3COO)2Ni•4H2O (acetato de níquel tetrahidratado) con HOC(COOH)(CH2COOH)2•H2O (ácido cítrico monohidratado) y precursores: HOCH2CHOHCH2OH (glicerol) y HOCH2CH2OH (etilenglicol). Los resultados mostraron que el uso de Etilenglicol es mejor que el Glicerol debido a que muestra una estabilidad térmica a menor temperatura para la calcinación. Posteriormente, fracturas cilíndricas de 0.6 x 1 cm de acero inoxidable 304 se sumergieron en una solución con Etilenglicol y, se gelaron en una mufla a 110°C por 24 h. Adicionalmente, las muestras se calcinaron a 660°C por 60 min bajo un flujo de 200 ml/ min de Ar, a velocidad de calentamiento/enfriamiento de 5°C/min para sintetizar las nanopartículas de Ni sobre las fracturas. El crecimiento del recubrimiento sobre las fracturas se llevó a cabo en un flujo de Ar de 220 ml/min a 1100°C por 60 min a una velocidad de calentamiento/enfriamiento de 10°C/min. Mediante microscopía óptica y de barrido, se observó que el recubrimiento presenta un espesor de hasta 700 μm con una serie de precipitados cuboidales mayores a 1 μm, así como fases laminares ricos en Ni, Fe y Cr.

ABSTRACT Nowadays, iron oxide based magnetic nanoparticles are used in several science and technology applications due to their magnetic properties. Likewise, these materials are used in biomedical applications such as contrast agents for magnetic resonance imaging, magnetic hyperthermia, targeted drug delivery, etc. In this work, the synthesis and characterization of Mg, Zn-containing ferrites with the chemical formula of Mg1-xZnxFe2O4 (0-0,9) were performed. Synthesis was carried out by thermal decomposition method (DT) using metal acetylacetonates (Mg, Zn and Fe) as reactants and oleic acid/phenyl-ether as reaction medium. The obtaining materials were characterized by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The X-ray diffraction patterns of the materials obtained exhibited the formation a single crystalline phase with an inverse spinel structure that corresponds to a magnesium ferrite (JCPDS 88-1935). Magnetic properties of obtained ferrites, such as saturation magnetization (Ms), remanent magnetization (Mr) and coercive field (Hc) were also evaluated by VSM. Ms increased as Zn2+ content was increased, reaching values within 20,22 to 40,03 emu/g, this increase was attributed to the variation of the cations distribution in the spinel structure. FT-IR and TEM results demonstrated that the synthesized nanoparticles have an oleic acid coating, an average size below 10 nm and morphology close to the spherical. According to these results it is possible to incorporate Zn2+ into a crystalline structure of MgFe2O4, by this particular DT method, obtaining ferrites potentially viable for biomedical applications.

RESUMEN Actualmente las nanopartículas magnéticas a base de óxido de hierro son utilizadas en diversas aplicaciones en las áreas de ciencia y tecnología, principalmente por sus propiedades magnéticas. Asimismo, estos materiales son utilizados en aplicaciones biomédicas tales como en la obtención de imágenes por resonancia magnética, hipertermia magnética, liberación de fármacos, etc. En este trabajo se reporta la síntesis y caracterización de ferritas de Mg y Zn con composición química Mg1-xZnxFe2O4 (x=0-0,9) mediante el método de descomposición térmica (DT). Se utilizaron acetilacetonatos metálicos (Mg, Zn y Fe) como reactivos y ácido oleico/feniléter como medio de reacción. Los materiales obtenidos se caracterizaron utilizando las técnicas de difracción de rayos X (DRX), magnetometría de muestra vibrante (MMV), espectroscopia de infrarrojo por transformada de Fourier (FT-IR) y microscopía electrónica de transmisión (MET). Los patrones de difracción de rayos X de los materiales obtenidos muestran la formación de una única fase cristalina con estructura de espinela inversa correspondiente a una ferrita de magnesio (JCPDS 88-1935). Las propiedades magnéticas, tales como magnetización de saturación (Ms), magnetización remanente (Mr) y campo coercitivo (Hc) de las ferritas Mg-Zn fueron evaluadas mediante MMV. Se encontró que la Ms aumenta a medida que se incrementa el contenido de Zn2+ alcanzando valores de 20,22 a 40,30 emu/g, dicho cambio se atribuye a la variación de la distribución de los cationes presentes en la estructura de espinela. Mediante FT-IR y MET se determinó que las partículas sintetizadas poseen un recubrimiento superficial de ácido oleico, una morfología cercana a la esférica y un tamaño de partícula inferior a los 10 nm. De estos resultados se confirma la viabilidad de la incorporación de iones Zn dentro de la estructura cristalina de MgFe2O4 utilizando el método de DT, obteniéndose ferritas potencialmente utilizables en aéreas biomédicas.

ABSTRACT In this work, the synthesis of MgxGa1-xFe2O4 magnetic nanoparticles (MNPs) by sol-gel method is presented. All synthesized samples were identified as a crystalline single phase and the saturation magnetization (Ms) values are within the range of 21,2 to 46,4 emu/g, while coercive field values are less than 100 Oe. The selected samples (x= 0,4 and 0,6) have an average particle size of 14 ± 4 nm, a near spherical shape and by solid state magnetic induction it was possible to demonstrate that a quantity of 6,0 mg of nanoparticles per mL of solution is enough to increase the temperature of the medium (H2O) up to 43,5 °C in less than 10 min. According to the presented results these synthesized nanoparticles are potential materials for their use in cancer treatment by magnetic hyperthermia therapy.

RESUMEN En este trabajo se documenta la síntesis de nanopartículas magnéticas (NPMs) de MnxGa1-xFe2O4, x=0,1 por el método de sol-gel identificando, para cada una de las muestras sintetizadas, la obtención de una única fase cristalina, valores de magnetización de saturación en el rango de 21,2 a 46,4 emu/g y valores de Hc menores a los 100 Oe. Las muestras seleccionadas (x= 0,4 y 0,6) poseen un tamaño promedio de 14 ± 4 nm y una forma cercana a la esférica y mediante la técnica de inducción magnética en estado sólido se encontró que una cantidad de 6,0 mg de nanopartículas por mL de solución es suficiente para incrementar la temperatura del medio (H2O) por encima de los 43,5 °C en un tiempo menor a los 10 min, haciendo a estos materiales potencialmente viables para su uso en el tratamiento del cáncer mediante la terapia de hipertermia magnética.

The sulphoaluminate of strontium, Sr4Al6O12SO4, was synthesized by solid state reaction from mixture of SrCO3, Al2O3 and SrSO4 (3:3:1 molar ratio) as pellets. The kinetics of formation has been studied in the range of temperature between 850ºC and 1100ºC using quantitative X-ray powder diffraction data (XRD) analysis. Likewise, at room temperature, the crystal structure was determined from conventional X-ray powder diffraction data using direct methods and it was refined by the Rietveld method. The kinetics mechanisms that showed the best fit, were identified as geometrical contraction at grain boundary (R1.1) and nucleation and growing by energy law (P1.1). The activation energy values obtained were 145.47KJmol-1 (R1.1) and 151.35KJmol-1 (P1.1), respectively. The resulting crystal structure was orthorhombic type (a: 13.32802Å, b: 13.34430Å and c: 9.38704Å). The observed adjustment parameters were RB: 0.0985, Rwp: 0.137, Rp: 0.0925 and Chi2: 1.94.

Calcium sulphoaluminate cement (CSAC) is an attractive candidate for biomedical applications due to its appropriate mechanical properties and high calcium content. In vitro bioactivity and hemocompatibility of calcium sulphoaluminate cement were assessed. The cement was prepared from a mixture of calcium sulphoaluminate (CSA) clinker, gypsum and water. Cement samples were immersed in a simulated body fluid (SBF) at 37 °C for different periods of time (7, 14 and 21 days). The analyses of these samples after their immersion in SBF revealed the formation of a bonelike apatite layer on their surface. The hemolytic activity was assessed by measuring hemoglobin released from erythrocytes when they were exposed to the cement. The results showed that the cement is hemocompatible.