Juan Antonio Aguilar Garib

Influence of Precursor and Power Irradiation on the Microwave-Assisted Synthesis of ZnS Nanoparticles

Results on the synthesis of ZnS nanoparticles from ZnSO 4 and Zn(CH 3 COO) 2 as precursors under microwave (MW) heating conditions are reported. An MW oven (1650 W) operating at 60 and 100% of the nominal power in periods for 60 s was employed. The obtained dispersions were analyzed by UV-Vis spectroscopy, X-ray diffraction, photoluminescence, and transmission electron microscopy. The results show that the dispersion concentration depends mainly on the applied power, whereas the luminescent properties are related with the employed precursors, because the sulfate ions promote the electronic transition in the ZnS nanoparticles, synthesized with a mean radius of 7.1 nm and possessing a hexagonal morphology.

Editor's message: highlighting research relevance

The aims and scope of a journal are more than a requirement to the authors, they also build the expectations of the readers that finally act as a tough jury, after the reviewers have provided the necessary elements to have an editorial decision regarding acceptance of a submission. It is generally accepted that every author wishes that their research is validated and shared to other interested people by publishing it in prestigious journals; reviewers are chosen based on their good reputation and expertise, so that there is no doubt about their ability to judge a research and find the relevance and novelty in a manuscript, but it could be a mistake to assume that they would dig into a submission to find those elements. Then, it is very important that the contribution of the papers is stated clearly. Nowadays, there are several sources of advice to write papers properly, as well as proofreading and manuscript editing services, but some care more about good writing style, than ensuring that relevance of the hypothesis, pertinence of the literature review, that the research is conducted adequately, interpretation and analysis of the results are correct, and that, indeed, the papers contribute to the advance of the science and the art of the study subject. There are also tips about how to select a suitable journal based on a comparison of published papers in them against a possible submission, and a careful selection of titles and keywords to match the aims and scope of the journal, preferably one with high impact factor. However, these strategies do not always lead to improve the chance of acceptance of a work, but they do increase the load over the journal that would justify every decision made. To overcome these strategies and to not indiscriminately dismiss cases where the journal may receive manuscripts that do not seem to be within its aims and scope, but that actually are, two items were added to the Journal of Microwave Power and Electromagnetic Energy s submission form to retrieve more information that can help in the decision of choosing a manuscript for publication. In the first one, the authors confirm that they have read the aims and scope of the journal, while the second item asks them to provide a few sentences on why the submission is relevant to the journal, as a follow-up to the first item. While all the submitters express their confirmation, many authors dismiss the opportunity to emphasize the importance of their research work when they just post the abstract, provide a self-expertise description, or make unjustified claims of similarity with papers already published, rather than stating clear explanations about why they consider that it is worth to the journal and the readers to publish their papers. Authors seeking for a suitable journal must observe that quality level of a publication is owed to the authors themselves as well as the reviewers, whose criticism, help to solve editorial controversy that might emerge when authors do not strictly follow the instructions

Editor's message: beaming energy from the space

Our society is consuming energy figures which are so large that sometimes they become meaningless when mentioned; electricity alone in 2012 was 20,900 TWH (IEA World energy statistics), 68% from fossil fuels, 11% nuclear and 21% ‘renewable’; the energy that comes from resources that are not significantly depleted by their use, such as sunlight, wind, rain, tides, waves and geothermal heat. It is estimated that energy consumed in the buildings (residential and commercial end users) accounts for 20.1% of this total ([International Energy Outlook 2016). Losses are not considered here, but they are not negligible, either.

Editor's message: reliability of internet sources

Nowadays, publishing is very easy; almost anyone can post anything in the Internet without any supervision regarding reliability or validation of the information presented. If we look for a misspelled word, most probably we will find someone used it in that wrong form, but that could cause in us the confidence that it was used correctly. This lack of supervision is responsible for the spread of myths, either frightening or encouraging. Since the Internet has become a primary source of information for many, it is necessary to design some sort of validation tools or a guidance for readers. Recently, some search engine companies have proposed themselves to help detecting ‘fake news’ to warn people that are searching for information. This is within the concerns of organizations such as The International Microwave Power Institute, among many others, with the purpose to be the most reliable source of information in their respective areas of interest. Many of these organizations offer their documents in the Internet, in competition with pages showing unreliable information that might even be risky. Indeed, at the time of conducting an Internet search, the latter appear in the same lists, sometimes with higher preference because of ranking systems driven by popularity rather than pondering. Considering the above concern, it is worth to analyse the comments presented about the proposals made by the search engine companies in several places, also in the Internet, that could be applicable to science publications against myths. The comments range from having a list of approved sites, and then include that information in the search engine, to implement algorithms that perform crossing information from different sources, confirming that it is not artificially high ranked by being copy– pasted in several sites. For instance, by detecting sentences like ‘scientific studies reveal that...’ without further references, as well as freighting messages that seem to force selling a good or service. What the readers can do first is to identify the source of the material. Anyone can claim, for example, that microwaves and cellular phones cause cancer, while wi-fi does not, and that food processed with microwaves is not nutritional. These claims can be very convincing, so the best is to verify if the claimers are strongly related to that field of knowledge, or if they are just posting something found somewhere else. Therefore, readers should select the most convincing sentences in the text and look for them in the Internet confirming whether they are repeated in several places out of context of the subject, for this is more suspicious than finding them in places in the same field of knowledge. It is better if those sentences are also found in university publications or by recognized organizations. Another aspect is related to common sense and plausibility evaluation. Scholars are not the only ones searching for information, and this evaluation depends on the reader. For the above examples about microwaves, an expert knows that they are not energetic

Editor's message: sustainability and industrial microwave processing

Environmental and social concern as well as economic interests are the motivation for developing technologies that are more energy efficient. Despite this effort, the demand for energy is growing as modern civilization development depends of it. Renewable energies do not exist; it has been defined, by convention, that these energies are those that last longer than any plan that mankind could formulate, then the Sun is the only source that fits into this category. Conventional resources are limited; natural gas and oil will last about 50 years, while coal reserves appear to be large enough for 600 years, so they would satisfy the world energy demand in short term with environmental effects, however, due to the production of CO2, which is a contributor to global warming. Environmental issues lead to alternative sources, which are those that do not affect the environment at the same high levels that fossil fuels do, such as eolic, tidal, hydraulic and biomass, although, these are produced by solar energy. Geothermal energy is another alternative source that consists of taking the heat that is produced in the Earth due to radiative decay. The public is not often aware of its nuclear origin because the term is reserved for the well-known artificial nuclear reactors. Nuclear energy is a real option in progress, even when it is not renewable. There are reserves of uranium for about 100 years, but the potential of regenerative reactors technology, which are a hundred times more efficient, increases this potential to 10,000 years. Notwithstanding, procedures in operation of nuclear plants have demonstrated their high reliability and safety, despite it is necessary to deal with radioactive wastes disposal. We are exposed to radiation from the space, the Earth and even air and food, but reference to it has great impact in safety perception, however, if we mind that accidents are dramatic because of the number of victims and the extend of the affected areas, they are not themselves as threatening as global warming. Ten thousand years is plenty of time to search for other options while natural resources get depleted, so the idea right now is to reduce their exhaustion by increasing devices’ efficiency and make better use of solar energy. This strategy could extend the availability of resources by a few centuries, and combined with reforestation schedules, the CO2 level in the atmosphere could also be reduced. This is a principle behind sustainability. Regarding processes, one step would be to convert those that use fossil fuels to electricity, which in turn is, obviously, generated by some alternative source. This conversion can be achieved by designing furnaces that use electric resistances, electric arc, induction heat, or of course, microwaves, instead of fuel burners. The simplest substitution case is to electric resistances, but in many other cases, it is not as easy as replacing the burners, because not all the materials are susceptible to be heated by electric arc, induction or microwaves.

Editor's message: harvesting and wireless power transmission

Electricity is one of the most useful forms of energy, it can be produced in one place and used in another, transformed into heat, light or work, and it runs most of our facilities. This energy is distributed with an amazing, and sometimes forgotten, electrical network that makes this resource available in many places every day. Most of our apparatus are usually connected to electric outlets; even gadgets and other portable devices are also indirectly connected because their batteries require to be charged. Everything is fine as long as we are at reach of this service, but when far away, we depend upon the batteries that do not last as we wish due to their intensive use. External batteries, charging spots, the use of solar cells and mini crank generators are among the solutions to extend the operational time of the gadgets. However, the idea of harvesting energy from several electromagnetic waves sources, at least in urban areas, such as TV and radio stations, as well as mobile phone services and Wi-Fi, has gained interest. Converting electromagnetic waves into electricity is not a new idea: there is a proposal regarding a satellite with solar panels that beams down the collected energy to the Earth by means of microwaves, which are in turn converted into electricity. In this wireless power transmission method, the beam is aimed to a ground antenna located in a specific place in a system designed for obtaining large amounts of energy and minimizing losses. A basic example of harvesting is the operation of crystal (galena) radios, which run with the power taken from the signal carrying wave, to feed a high impedance earphone and have audio. In this case, the amount of obtained energy is not enough to run other devices, not even a conventional speaker, but other potential applications could emerge with the development of more efficient electronic circuits, including advanced methods for energy storing. Commercial claims of ‘free’ energy and greater efficiency of microwave harvesting devices compared to solar cells could be part of the motivation for getting interest in this possibility, but practical issues must be reviewed in advance to propose this technique as a solution for charging batteries or run devices. Although harvesting could be highly efficient compared to solar cells, the available energy to be harvested is very little; for instance, in terms of energy, indoor light alone is estimated to be 300 times greater than RF sources. Therefore, the applications that have shown certain degree of success are those where the electromagnetic waves are directly aimed to the devices or the source is even in the same room, being rather a wireless power transmission in the range of consumption of devices such as sensor networks and Radio Frequency Identification (RFID) tags. Arithmetically, even very small amounts of energy count, leading to say that charging batteries would be possible, but only for devices that draw less than that energy to run, or

Editor's message: microwave heating courses

Many non-communication microwave applications are related to the heating of systems aiming to provide them the necessary energy for conducting a given process. Therefore, knowledge on this subject is very important. Actually, it is part of the programs of engineering, with syllabus that are centred in the heat equation, which involves conduction and heat gain, such as reaction enthalpy, Joule effect and radioactive decay heating. Solving this equation for microwave heating is difficult since permittivity is often very sensitive to temperature, but while learning about heat transfer in the school, it is common to accept several hypotheses that range from geometrical simple shapes, unidirectional heat transfer, uniform boundary conditions, volumetric heating, constant thermal properties and temperature independent electromagnetic properties, so that the equation is simplified to be manageable by students seeking to exact solutions that provide approximate results. Although such simplification could be acceptable for conventional conduction and convective mechanisms, it is not acceptable for microwave heating because that dependency leads to a loop of affected thermal profile and permittivity so that non-volumetric heating must be considered. Two cases can be taken arbitrarily for discussing about the weight of this simplification. The first case is regarding to situations where the samples are heated with microwaves and the possible process that result from such heating is thermally evaluated. Thermal profiles or heat gain in the sample are not calculated, rather the most important issue is the process itself. The kitchen oven could be the most representative example, where the power supplied by the magnetron is approximately known, but the thermal profile and actual power input to meals is unknown. The second case corresponds to the careful calculation of thermal profiles by solving concatenated differential equations. Reducing the simplification level increases the difficulty for obtaining exact solutions, therefore numerical methods are often employed for this purpose. An important difference with these cases is validation, while in the first case practicality is one of the advantages of the kitchen ovens, effectiveness of heating is given by the cooked food for instance, although other materials heated in system that are alike can be taken here as well. In this second case, although the electric field and thermal profiles are finally provided by the solution of the heat and electromagnetic equations, the difficulties to validate those results come from the challenge of conducting measurements in a microwave field. Temperature can be taken at temperatures in polymers because of their relative low temperature processing, but in the case of ceramics processing there are high thermal gradients, in most cases temperatures are taken optically over the surface. Moreover, the electric field is not actually measured inside the samples.

Recent progress in the shaping and sintering of barium titanate nanoparticles. Application to high permittivity capacitors

The miniaturisation of electronic components required for many devices involves an increase their volumic efficiency. This work focus on the size reduction of capacitors. They are two ways for increasing the capacity of such passive components. One is to find materials with high permittivity, the other is to reduce the thickness of the films used in multilayers ceramics. Barium titanate, BaTiO3 (BT) nanoparticles were sintered using Spark Plasma Sintering (SPS) because the material presents interesting properties when obtained by SPS [1-3]. In this case, very unusual interesting dielectric properties, a so called “colossal” permittivity value up to several thousands. Moreover, no temperature dependence is observed. However, the values of dielectric losses are too high to consider industrial applications. In order to reduce these dielectric losses, different approaches have been proposed to control the chemistry of grain boundaries. We present here the structural, microstructural and electrical properties of ceramics sintered by SPS from BaTiO3 powders elaborated by co-precipitation method. Different routes tested to improve the dielectric properties of the ceramics are presented and discussed.On the other side, thick films of BT have been prepared. The objective of this work was to develop a BaTiO3 material having an accurate particle size to reduce the thickness of sintered films down to 1 μm. The rheological properties of the slurry have been optimized and, thanks to a suitable tape casting process, homogeneous thin films of 1 μm thickness could be obtained. Some properties of the films are described.