Juliano Katrib

Metal–organic frameworks in seconds via selective microwave heating

Synthesis of metal–organic framework (MOF) materials via microwave heating often involves shorter reaction times and offers enhanced control of particle size compared to conventional heating. However, there is little understanding of the interactions between electromagnetic waves and MOFs, their reactants, and intermediates, all of which are required for successful scale-up to enable production of commercially viable quantities of material. By examining the effect of average absorbed power with a constant total absorbed energy to prepare MIL-53(Al) we have defined a selective heating mechanism that affords control over MOF particle size range and morphology by altering the microwave power. This is the first time a selective mechanism has been established for the preparation of MOFs via microwave heating. This approach has been applied to the very rapid preparation of MIL-53(Al)ta (62 mg in 4.3 seconds) which represents the fastest reported synthesis of a MOF on this scale to date.

A Tool for Predicting Heating Uniformity in Industrial Radio Frequency Processing

Radio frequency energy is utilised for heating in a wide range of applications, particularly in the food industry. A major challenge of RF processing is non-uniform heating in loads of variable and angular geometry, leading to reduced quality and product damage. In this study, the specific effects of geometry on the heating profiles of a range of geometrically variable loads in an industrial scale RF system are analysed, and the understanding used to derive a general tool to predict heating uniformity. Potato was selected as a test material for experimental work; dielectric properties were measured using a 44-mm coaxial probe. Analysis of simulated and experimental surface temperature profiles and simulated power uniformity indices indicates the presence of vertices and edges on angular particles, and their proximity to faces perpendicular to the RF electrodes increases localised heating; faces parallel to the electrodes heated less than those faces perpendicular to them. Comparison of the same geometrical shape in different orientations indicates that overall power absorption uniformity can be better even when localised heating of edges is greater. It is suggested, for the first time, that the rotation of angular shapes within a parallel plate electric field can improve heating uniformity, and that this can be achieved through the design of bespoke electrode systems. A Euler characteristic-based shape factor is proposed, again for the first time, that can predict heating uniformity for solid, dielectrically homogeneous shapes. This gives industry a tool to quickly determine the feasibility for uniform RF heating of different three-dimensional shapes based on geometry alone. This provides a screening method for food technologists developing new products, allowing rapid assessment of potential heating uniformity, and reducing the need for early-stage specialist computational modelling.

Facile Determination of Molecular Structure Trends in Amphiphilic Core Corona Star Polymer Synthesis via Dielectric Property Measurement

The use of dielectric property measurements to define specific trends in the molecular structures of poly(caprolactone) containing star polymers and/or the interbatch repeatability of the synthetic procedures used to generate them is demonstrated. The magnitude of the dielectric property value is shown to accurately reflect: (a) the number of functional groups within a series of materials with similar molecular size when no additional intermolecular order is present in the medium, (b) the polymer molecular size for a series of materials containing a fixed core material and so functional group number, and/or (c) the batch to batch repeatability of the synthesis method. The dielectric measurements are validated by comparison to spectroscopic/chromatographic data.

Four electrode embedded bioimpedance measurement system

A new extension of the AD5933 impedance measurement chip is presented. It allows to use the chip in the four electrode configuration to reduce the artifact effects of interface impedance between the electrode and the sample to be measured. The measurement approach is validated on various test circuits, and the system has been able to measure small physiological samples (50 ul) in a four microelectrode configuration and with a low sensitivity to interface impedances. The system is a good candidate for any embedded bioimpedance measurement system which requires a low sensitivity to interface impedances.

Towards sustainable processing of columbite group minerals: elucidating the relation between dielectric properties and physico-chemical transformations in the mineral phase

Current methodologies for the extraction of tantalum and niobium pose a serious threat to human beings and the environment due to the use of hydrofluoric acid (HF). Niobium and tantalum metal powders and pentoxides are widely used for energy efficient devices and components. However, the current processing methods for niobium and tantalum metals and oxides are energy inefficient. This dichotomy between materials use for energy applications and their inefficient processing is the main motivation for exploring a new methodology for the extraction of these two oxides, investigating the microwave absorption properties of the reaction products formed during the alkali roasting of niobium-tantalum bearing minerals with sodium bicarbonate. The experimental findings from dielectric measurement at elevated temperatures demonstrate an exponential increase in the values of the dielectric properties as a result of the formation of NaNbO3-NaTaO3 solid solutions at temperatures above 700 °C. The investigation of the evolution of the dielectric properties during the roasting reaction is a key feature in underpinning the mechanism for designing a new microwave assisted high-temperature process for the selective separation of niobium and tantalum oxides from the remainder mineral crystalline lattice.

Free-space method for broadband characterization of dielectric properties of materials

Drying materials of all types is of huge importance in industry. Microwave and radiofrequency heating are often utilized for drying; anyway, the design of systems can be very challenging due to a lack of knowledge of the specific dielectric properties of each phase within a multi-phase material. Specifically, one of the key challenges is the measurement of the bulk dielectric properties of heterogeneous material and the ability to distinguish between free and bound water within the material itself.

Implantable cardioverter-defibrillators exposed to low frequency magnetic fields

This paper presents a numerical modeling study of electromagnetic interference (EMI) in implantable cardioverter-defibrillators (ICDs), exposed to low frequency magnetic fields. Initially, an analysis of the standards that consider interference in ICDs was performed, to determine the level of induced voltage that may occur when the device is exposed to such magnetic fields. A Helmholtz coil was used to generate a uniform magnetic field. The magnetic field exposure was performed for the frontal position (front to back). This position presents the worst case scenario. The induced electric fields and voltage were investigated in both a simple homogenous block (brick) and in an anatomical model (virtual phantom). The ICDs sensitivity parameters were adjusted to minimum values (e.g. 0.2 mV for ventricular detection). This maximum sensitivity corresponds experimentally to the worst-case EMI scenarios. The results showed that magnetic fields above 5000 μT were required for the ICD to possibly present a dysfunction in the homogenous block, while they were only 1400μT in the anatomical model. These results could be informative for any proposed standards concerning the safety of ICDs (CENELEC, INCIRP) for workers as well as for the general public.