Optimisation of the Flame Spheroidisation Process for the Rapid Manufacture of Fe3O4-Based Porous and Dense Microspheres

The rapid, single-stage, flame-spheroidisation process, as applied to varying Fe3O4:CaCO3 powder combinations, provides for the rapid production of a mixture of dense and porous ferro-magnetic microspheres with homogeneous composition, high levels of interconnected porosity and microsphere size control. This study describes the production of dense (35-80 µm) and highly porous (125-180 µm) Ca2Fe2O5 ferromagnetic microspheres. Correlated backscattered electron imaging and mineral liberation analysis investigations provide insight into the microsphere formation mechanisms, as a function of Fe3O4/porogen mass ratios and gas flow settings. Optimised conditions for the processing of highly homogeneous Ca2Fe2O5 porous and dense microspheres are identified. Induction heating studies of the materials produced delivered a controlled temperature increase to 43.7 °C, indicating that these flame-spheroidised Ca2Fe2O5 ferromagnetic microspheres could be highly promising candidates for magnetic induced hyperthermia and other biomedical applications

Flame spheroidisation of dense and porous Ca2Fe2O5 microspheres

Compositionally uniform magnetic Ca2Fe2O5 (srebrodolskite) microspheres created via a rapid, single-stage flame spheroidisation (FS) process using magnetite and carbonate based porogen (1:1 Fe3O4:CaCO3) feedstock powders, are described. Two types of Ca2Fe2O5 microsphere are produced: dense (35 - 80 µm), and porous (125 - 180 µm). Scanning electron microscopy (SEM) based techniques are used to image and quantify these. Complementary high-temperature X-ray diffraction (HT-XRD) measurements and thermogravimetric analysis (TGA) provide insights into the initial process of porogen feedstock decomposition, prior to the coalescence of molten droplets and spheroidisation, driven by surface tension. Evolution of CO2 gas (from porogen decomposition) is attributed to the development of interconnected porosity within the porous microspheres. This occurs during Ca2Fe2O5 rapid cooling and solidification. The facile FS-processing route provides a method for the rapid production of both dense and porous magnetic microspheres, with high levels of compositional uniformity and excellent opportunity for size control. The controllability of these factors make the FS production method useful for a range of healthcare, energy and environmental remediation applications

Rapid synthesis of magnetic microspheres and the development of new macro–micro hierarchically porous magnetic framework composites †

Magnetic framework composites (MFCs) are a highly interesting group of materials that contain both metal–organic frameworks (MOFs) and magnetic materials. Combining the unique benefits of MOFs (tuneable natures, high surface areas) with the advantages of magnetism (ease of separation and detection, release of guests by induction heating), MFCs have become an attractive area of research with many promising applications. This work describes the rapid, scalable synthesis of highly porous magnetic microspheres via a flame-spheroidisation method, producing spheres with particle and pore diameters of 206 ± 38 μm and 12.4 ± 13.4 μm, respectively, with a very high intraparticle porosity of 95%. The MFCs produced contained three main iron/calcium oxide crystal phases and showed strong magnetisation (Ms: 25 emu g−1) and induction heating capabilities (≈80 °C rise over 30 s at 120 W). The microspheres were subsequently surface functionalised with molecular and polymeric coatings (0.7–1.2 wt% loading) to provide a platform for the growth of MOFs HKUST-1 and SIFSIX-3-Cu (10–11 wt% loading, 36–61 wt% surface coverage), producing macro–micro hierarchically porous MFCs (pores > 1 μm and <10 nm). To the best of our knowledge, these are the first example of MFCs using a single-material porous magnetic scaffold. The adaptability of our synthetic approach to novel MFCs is applicable to a variety of different MOFs, providing a route to a wide range of possible MOF–microsphere combinations with diverse properties and subsequent applications

Detección de nanopartículas magnéticas en diferentes substratos para un sensor de efecto Hall

En la actualidad uno de los mayores retos de la Ingeniería Biomédica es desarrollar herramientas que ayuden a disminuir la elevada tasa de mortalidad debido a enfermedades cronicodegenerativas. Lo anterior se debe a que los métodos convencionales no permiten conocer el desarrollo de la enfermedad a un nivel molecular o celular, además de ser poco compactos, de respuesta lenta, poco precisa y elevado costo. Por ello, el desarrollo de dispositivos compactos capaces de diagnosticar dichas enfermedades en una etapa temprana con respuesta rápida y de bajo costo se ha convertido en la prioridad de numerosas empresas médicas, así como de diversos investigadores alrededor del mundo. Una de las áreas prometedoras de particular interés en investigación en el desarrollo de dispositivos de detección es el desarrollo de biosensores que utilicen micro o nanopartículas magnéticas como etiquetas para interacciones biomoleculares específicas [1]. Los biosensores magnéticos detectan la dispersión del campo magnético basándose en efectos galvanomagnéticos que ocurren cuando un material por el cual fluye una corriente eléctrica es expuesto a un campo magnético externo [2] y entre ellos se encuentran la magnetoresistencia y el efecto Hall. Entre los materiales reportados con más interés son las películas delgadas de arseniuro de indio y antimoniuro de indio, los cuales cuentan con las propiedades electromagnéticas necesarias para lograr el desarrollo de un dispositivo de efecto Hall [3]. Investigadores de instituciones como la Universidad Autónoma de Ciudad Juárez, la Universidad de Texas en Dallas, la Universidad de California en Berkeley [4], la Universidad de Aveiro en Portugal [5], el Instituto de Tecnología en Tokio [6], entre otras, se encuentran trabajando en el desarrollo de biosensores de efecto Hall para detección de partículas magnéticas con posible aplicación en el área de Ingeniería Biomédica. El presente proyecto de investigación surge en el 2015 en la Universidad Autónoma de Ciudad Juárez como propuesta de un proyecto de titulación por parte de la Dra. Perla E. García Casillas. Forma parte de una serie de proyectos del área de nanomedicina cuyo tema de interés es el desarrollo de dispositivos compactos, de respuesta rápida, precisa y de bajo costo encaminados a la detección temprana y tratamiento de enfermedades cronicodegenerativas como el cáncer

Low-voltage differential voltage follower for WTA and fully differential applications

A low-voltage differential version of a high performance voltage follower is presented. The proposed circuit is very compact, and symmetric with respect to the input devices. Both differential input devices are enhanced by local shunt feedback, increasing the gain and, thus, reducing the output resistance for higher precision. The circuit has proved useful as a winner-take-all (WTA) circuit. It also features operation as a fully differential amplifier with low supply voltage requirements close to a transistor's threshold voltage. Experimental results verifying the operation of the proposed structure are provided.Consejo Nacional de Ciencia y Tecnologí

Optimisation of the Flame Spheroidisation Process for the Rapid Manufacture of Fe3O4-Based Porous and Dense Microspheres

The rapid, single-stage, flame-spheroidisation process, as applied to varying Fe3O4:CaCO3 powder combinations, provides for the rapid production of a mixture of dense and porous ferromagnetic microspheres with homogeneous composition, high levels of interconnected porosity and microsphere size control. This study describes the production of dense (35–80 µm) and highly porous (125–180 µm) Ca2Fe2O5 ferromagnetic microspheres. Correlated backscattered electron imaging and mineral liberation analysis investigations provide insight into the microsphere formation mechanisms, as a function of Fe3O4/porogen mass ratios and gas flow settings. Optimised conditions for the processing of highly homogeneous Ca2Fe2O5 porous and dense microspheres are identified. Induction heating studies of the materials produced delivered a controlled temperature increase to 43.7 °C, indicating that these flame-spheroidised Ca2Fe2O5 ferromagnetic microspheres could be highly promising candidates for magnetic induced hyperthermia and other biomedical applications.</jats:p