Principles and applications of CVD powder technology

Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique

Плавный пуск асинхронного двигателя

Актуальность работы. Широкое распространение устройств, называемых Soft Starter, устройств плавного пуска (УПП), а также устройств безударного тока, созданных для ограничения негативной динамики пусковых токов и электромагнитных моментов асинхронного двигателей (АД) с короткозамкнутым ротором, стало результатом эффективного соотношения "цена/качество" для УПП. Однако, проблема реальной, количественной оценки преимуществ и недостатков использования УПП для АД остается актуальной

Origin of two-band chorus in the radiation belt of Earth.

Naturally occurring chorus emissions are a class of electromagnetic waves found in the space environments of the Earth and other magnetized planets. They play an essential role in accelerating high-energy electrons forming the hazardous radiation belt environment. Chorus typically occurs in two distinct frequency bands separated by a gap. The origin of this two-band structure remains a 50-year old question. Here we report, using NASA's Van Allen Probe measurements, that banded chorus waves are commonly accompanied by two separate anisotropic electron components. Using numerical simulations, we show that the initially excited single-band chorus waves alter the electron distribution immediately via Landau resonance, and suppress the electron anisotropy at medium energies. This naturally divides the electron anisotropy into a low and a high energy components which excite the upper-band and lower-band chorus waves, respectively. This mechanism may also apply to the generation of chorus waves in other magnetized planetary magnetospheres

Mining Wastes of an Albite Deposit as Raw Materials for Vitrified Mullite Ceramics

In this work, an examination of mining wastes of an albite deposit in south Spain was carried out using X-ray Fluorescence (XRF), X-ray diffraction (XRD), particle size analysis, thermo-dilatometry and Differential Thermal Analysis (DTA) and Thermogravimetric (TG) analysis, followed by the determination of the main ceramic properties. The albite content in two selected samples was high (65–40 wt. %), accompanied by quartz (25–40 wt. %) and other minor minerals identified by XRD, mainly kaolinite, in agreement with the high content of silica and alumina determined by XRF. The content of Na2O was in the range 5.44–3.09 wt. %, being associated with albite. The iron content was very low (<0.75 wt. %). The kaolinite content in the waste was estimated from ~8 to 32 wt. %. The particle size analysis indicated values of 11–31 wt. % of particles <63 µm. The ceramic properties of fired samples (1000–1350 °C) showed progressive shrinkage by the thermal effect, with water absorption and open porosity almost at zero at 1200–1250 °C. At 1200 °C, the bulk density reached a maximum value of 2.38 g/cm3. An abrupt change in the phase evolution by XRD was found from 1150 to 1200 °C, with the disappearance of albite by melting in accordance with the predictions of the phase diagram SiO2-Al2O3-Na2O and the system albite-quartz. These fired materials contained as main crystalline phases quartz and mullite. Quartz was present in the raw samples and mullite was formed by decomposition of kaolinite. The observation of mullite forming needle-shape crystals was revealed by Scanning Electron Microscopy (SEM). The formation of fully densified and vitrified mullite materials by firing treatments was demonstrated

The role of nano-perovskite in the negligible thorium release in seawater from Greek bauxite residue (red mud)

We present new data about the chemical and structural characteristics of bauxite residue (BR) from Greek Al industry, using a combination of microscopic, analytical, and spectroscopic techniques. SEM-EDS indicated a homogeneous dominant “Al-Fe-Ca-Ti-Si-Na-Cr matrix”, appearing at the microscale. The bulk chemical analyses showed considerable levels of Th (111 μg g−1), along with minor U (15 μg g−1), which are responsible for radioactivity (355 and 133 Bq kg−1 for 232Th and 238U, respectively) with a total dose rate of 295 nGy h−1. Leaching experiments, in conjunction with SFICP- MS, using Mediterranean seawater from Greece, indicated significant release of V, depending on S/L ratio, and negligible release of Th at least after 12 months leaching. STEM-EDS/EELS &amp; HR-STEMHAADF study of the leached BR at the nanoscale revealed that the significant immobility of Th4+ is due to its incorporation into an insoluble perovskite-type phase with major composition of Ca0.8Na0.2TiO3 and crystallites observed in nanoscale. The Th LIII-edge EXAFS spectra demonstrated that Th4+ ions, which are hosted in this novel nano-perovskite of BR, occupy Ca2+ sites, rather than Ti4+ sites. That is most likely the reason of no Th release in Mediterranean seawater

Production of Lightweight Aggregates from Different Types of Boron Wastes

Four boron wastes (BW), named as Sieve (SBW), Dewatering (DBW), Thickener (TBW) and Mixture (MBW) waste, from Kirka plant (Turkey) were investigated for the formation of Artificial Lightweight Aggregates (LWA). The characterization involved chemical, mineralogical and thermal analyses. The bloating behavior was examined by heating microscopy. SBW and DBW expanded in two stages, at 300°C approximately and subsequently at 550°C with concurrent formation of liquid phase. However, at 650-700°C there is excessive liquid phase formed resulting in large, non uniform porosity of irregular shape. On the contrary, in the case of TBW and MBW no noticeable expansion or glassy surface was formed. An optimization route, involved the formation of a mixture with 20wt% clay, 40wt% SBW, 40wt% DBW and one with 20wt% clay, 35wt% SBW, 35wt% DBW, 10wt% quartz sand. The raw aggregates were fired in a rotating crucible at 650°C, 700°C, 710°C and 760°C for 2-5 min. It was observed that the clay addition leads to better plasticity and cohesion between the particles whereas the quartz addition shifts the softening point 50°C higher. Water absorption was 56.8-60.5%, apparent specific gravity 2.3-2.4g/cm and bulk density 0.9-1.1g/cm3. The analysis of microstructure with electron microscopy revealed a glassy phase matrix and an extended formation of both open and closed pores. The results indicate that SBW and DBW boron wastes can be utilized in LWA production

Editorial for Special Issue “Valorization of Metallurgical and Mining Residues and Wastes”

This Special Issue has presented the most recent advances in some of the key aspects of mining and metallurgical waste valorization [...

Production of belite cement using boron and red mud wastes

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Carbon Footprint of the University of Patras in Greece: Evaluating Environmental Culture and Campus’ Energy Management towards 2030

Climate change has already had observable effects due to greenhouse gases (GHG) produced by human activities. Over the years, this becomes more evident as the concentration of GHG released in the atmosphere is concerningly increased as does the earth’s average temperature too. Hence, all countries and many independent organizations are taking actions to reduce the Global Warming phenomenon by setting targets for carbon dioxide emissions. The energy sector is proved to play the most important role in emissions reduction. Greece’s target for this sector is very ambitious in total transformation of energy mixture in the forthcoming years. Universities are also contributing to GHG emissions through their operations and members’ activities. Energy management at the University of Patras in Greece has already started since 2019 by installing energy meters going from manual calculations to an online system. The reliable records and accurate calculations proved as a very important action and a starting point for performing detailed analysis. In this study, there was an effort to calculate the CO2 emissions of the University of Patras using the Carbon Campus Calculator. The results showed that the students commuting is the main source of GHG emissions at the University of Patras and the purchased electricity comes next. These two factors together comprise 60.2% of the total emissions and priority should be given to reducing their footprint. Specific targets were set up for 2030 in compliance with the National Plan for Energy and Climate of Greece. Moreover, an Action Plan managing carbon and energy more efficiently and creating a strong environmental culture among the community is proposed. In the future, the university’s management team should act proactively in every change at Patras University. An assessment on the environmental impact should take place before any decision making. If necessary, extra actions should be defined in order not to deviate from the targets and new standards set