This paper explains the phenomena which occur in commercially available laboratory microwave equipment, and highlights several situations where experimental observations are often misinterpreted as a 'microwave effect'. Electromagnetic simulations and heating experiments were used to show the quantitative effects of solvent type, solvent volume, vessel material, vessel internals and stirring rate on the distribution of the electric field, the power density and the rate of heating. The simulations and experiments show how significant temperature gradients can exist within the heated materials, and that very different results can be obtained depending on the method used to measure temperature. The overall energy balance is shown for a number of different solvents, and the interpretation and implications of using the results from commercially available microwave equipment are discussed.
A microwave/conventional hybrid furnace has been used to sinter three ceramics with different microwave absorption characteristics under pure conventional and a range of microwave/conventional hybrid heating regimes. The precursor powder particle size was also varied for each material. In each case it was ensured that every sample within a series had an identical thermal history in terms of its temperature/time profile. An increase in both the onset of densification and the final density achieved was observed with an increasing fraction of microwave energy used during sintering, the effect being greatest for the materials that absorbed microwaves most readily. Twenty‐three percent greater densification was observed for submicron zinc oxide powder, the material with the largest microwave absorption capability, when sintered using hybrid heating involving 1 kW of microwave power compared with pure conventional power under otherwise identical conditions. For the ceramic with the lowest microwave absorption characteristic, alumina, the increase in densification was extremely small; partially stabilized zirconia, a moderate microwave absorber, was intermediate between the two. Temperature gradients within the samples, a potential cause of the effect, were assessed using two different approaches and found to be too small to explain the results. Hence, it is believed that clear evidence has been found to support the existence of a genuine “microwave effect.”
This paper reports results on the shielding effectiveness parameter of laminated epoxy composites with carbon fibre reinforcements. Measurements of shielding effectiveness were carried out with a coaxial transmission line testing chamber according to ASTM 4935 standard and epoxy-matrix composites with continuous carbon-fibres were proven to be an excellent electromagnetic interference shielding material, where a composite slab made of 4 layers of prepregs provided more than 99.9% of electromagnetic attenuation. It was found that the reflection mechanism of the shielding material was mainly influenced by the fibre volume ratio, and that an increase in the number of layers of the composite resulted in higher shielding effectiveness due to a greater absorption mechanism. Calculations of the shielding effectiveness parameter of the material used were made by means of commercial electromagnetic simulation tools, having determined experimentally the overall resistivity of the composite. The findings presented in this work suggest that in presence of a greater number of interfaces at different impedance the separate modelling of matrix and fibres at mesoscopic scale must be taken into account.
Synthetic materials are an everyday component of modern healthcare yet often fail routinely as a consequence of medical‐device‐centered infections. The incidence rate for catheter‐associated urinary tract infections is between 3% and 7% for each day of use, which means that infection is inevitable when resident for sufficient time. The O'Neill Review on antimicrobial resistance estimates that, left unchecked, ten million people will die annually from drug‐resistant infections by 2050. Development of biomaterials resistant to bacterial colonization can play an important role in reducing device‐associated infections. However, rational design of new biomaterials is hindered by the lack of quantitative structure–activity relationships (QSARs). Here, the development of a predictive QSAR is reported for bacterial biofilm formation on a range of polymers, using calculated molecular descriptors of monomer units to discover and exemplify novel, biofilm‐resistant (meth‐)acrylate‐based polymers. These predictions are validated successfully by the synthesis of new monomers which are polymerized to create coatings found to be resistant to biofilm formation by six different bacterial pathogens: Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus.
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