Flash sintering: New opportunities

It is well know that due to both localized heating and the reduced sintering time in Spark Plasma Sintering (SPS), processing can produce a significant energy saving and metastable microstructures if compared to Hot Pressing [1]. In order to further improve the energy saving we have developed a very rapid sintering technique called Flash SPS (FSPS) with heating rates in the order of 104-105 ᵒC/minute. Unlike the Flash Sintering based on high voltage, FSPS is based on low voltage and it can be up-scaled to samples volumes of several tens of cubic centimeters. Flash SPS allows densification of ZrB2 [2] up to 95% under a discharge time as short as 35 seconds, which results in an energy saving greater than 95% compared to conventional SPS. A novel processing methodology that allows both preheating and FSPS of silicon carbide based materials (both of α and β SiC) has been developed. We were able to densify a SiC disc (Ф 20 mm) from initial density of 53% up to 96% with a discharge time as short as 17s (as shown in the Figure 1). In Figure 1, the rapid densification (i.e. normalized displacement) of SiC by novel FSPS is compared to the conventional SPS process. The developed methodology was scaled up to produce samples as large as 60 mm as shown in Figure 2

From Pit Fire to Ultrafast High-Temperature Sintering (UHS): Shared Features of Ultra-Fast Sintering Techniques

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Development of electric current activated/assisted sintering (ECAS/SPS)

The electric current activated/assisted sintering (ECAS) is an ever growing class of versatile techniques for sintering particulate materials. ECAS was pioneered by Bloxam in 1906. As illustrated in Fig. 1, ECAS development is emblematic of its technological and scientific importance. Nowadays, most of the scientific attention is focused on the Spark Plasma Sintering (SPS) technology originated in 1966 by Dr. Inoue [1]. Essentially, SPS exploits the same punch/die system concept as the more familiar hot pressing (HP) process. The powder is placed in the die and subsequently pressed between two counter-sliding punches. Mechanical loading is normally uniaxial. SPS and HP differ significantly in the heating mode. Specifically, in HP an array of heating elements indirectly heats the punch/powder/die assembly by radiation and eventually by convection and/or conduction. The powder heating rate is controlled by the rate of radiation and/or convection and conduction. Conversely, in SPS, the punches transfer the electricity and Joule heat directly to the powder. As the supplied current density can be very large, the heating rate in the powder can approach 106 Ks−1. The short sintering time, SPS is particularly suitable for: (a) preserving initial powder grain size or nanostructure, (b) consolidating amorphous materials, (c) improving bonding strength between particles and (d) controlling phase reactions or decomposition (in the case of composites). In the SPS process, the measured temperature is not directly related to the sintering temperature. The combined experimental and FEM simulation analysis permitted to obtain the optimum process and mold design which permitted to have direct control of the final microstructure. The electric conductivity of the material plays a fundamental role on the current and temperature distribution inside the sample. The SPS method was successfully applied to electric conductive ceramics such as pure WC, WC-diamond, semiconductors, and low electrical conductive ceramics such as transparent alumina. Here we will summarize future direction and problems in both fundamental research and industrialization of the SPS technology

Ultrafast High-Temperature Sintering of Advanced Ceramics: A Direct Comparison with the State-of-the-Art Techniques

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Measurement of PEEP-induced alveolar recruitment: just a research tool?

For positive end-expiratory pressure (PEEP) to have lung protective efficacy in patients with acute respiratory distress syndrome, it must increase the end-expiratory lung volume through alveolar recruitment while avoiding lung over-inflation. PEEP may increase the end-expiratory lung volume either by increasing the proportion of aerated alveoli at end-expiration or by further inflating already ventilated lung regions. The optimal PEEP regimen is still a matter of debate. In theory, the ability to measure of PEEP-induced alveolar recruitment would be extremely useful in titrating PEEP at the bedside. However, until now this measurement has been confined to clinical research settings. Interesting work by Lu and coworkers, published in the previous issue of this journal, deals with the problem of measuring PEEP-induced alveolar recruitment. The 'gold standard' technique (i.e. the computed tomography method) is compared with the pressure-volume curve method. Because implementation of the latter method at the bedside would be relatively simple, that report, in addition to its intrinsic scientific value, may have important clinical implications

Micro-scale inductorless maximum power point tracking DC-DC converter

In this study, the authors propose a simple maximum power point tracking (MPPT) DC-DC converter amenable for micro-scale photovoltaic applications. The solution avoids the use of inductors and exploits a charge pump as a voltage boost element. To take into account the temperature dependence of the MPP voltage, a passive temperature compensation circuit is also included. To validate the idea a prototype was realised with commercial off-the-shelf components. A system efficiency better than 83% for output power above 90 mW is obtained. The results show the viability of the proposed approach which could be further improved through a full custom integrated-circuit design

Inguinal polypropylene plug: A cause of unusual testicular tumor pelvic metastasis

We report the case of a patient who had undergone polypropylene plug placement 3 years before and referred to our institution with testicular tumor. CT scan demonstrated an enlargement of pelvic lymph nodes on the tumor side while retroperitoneal nodes were normal. Orchifunicolectomy was performed and histopathological examination showed a mixed germ cell tumor involving the tunica vaginalis, rete testis, epididymis and spermatic cord. After surgery the patient was addressed to adjuvant chemotherapy according to PEB scheme. Clinical re-staging showed a decrease of the pelvic bulk disease whereas retroperitoneal nodes were still normal and tumor markers were negative. Left external, internal and common iliac lymphadenectomy as well as left modified template nervesparing retroperitoneal lymph node dissection was performed. Intraoperatively the node bulk was firmly adherent to the external iliac artery and extended until the common iliac bifurcation. In the deeper part of this enlarged and firm lymphatic chain the polypropylene plug placed at the time of hernioplasty was found. Behind the plug all retroperitoneal nodes appeared normal and resulted negative on histopathologic examination. The patient had an unusual metastatization, probably due to the plug

Seismic Microzonation Studies in the City of Ragusa (Italy)

The geotechnical zonation of the subsoil of the city of Ragusa suggests a high vulnerability of the physical environment added to site amplification of the ground motion phenomena. These elements concur on the definition of the Seismic Geotechnical Hazard of the city of Ragusa that should be correctly evaluated, through geo-settled seismic microzoning maps. Based on the seismic history of Ragusa, the following scenario events have been considered: the “Val di Noto” earthquake of January 11, 1693 (M=7.3), the “Etna” earthquake of March 1, 1818 (M=5.9), the 1895 earthquake (IMAX= 7 EMS), the Modica earthquake of January 23, 1980 (MW = 4.63) and the “Sicilian Earthquake” of December 13, 1990 (ML=5.6). Despite of its lower magnitude, a medium size, local earthquake, such as the 1990 “Sicilian” event, has to be accounted for the seismic hazard assessment of Ragusa, since it may cause heavy damage to the most urbanized area. According to historical data, the epicentre of this earthquake was located in the sea. This earthquake is considered a tectonic earthquake and is associated to the strike-slip segment of the Ibleo-Maltese fault system. This fault system is the major seismogenic structure of Eastern Sicily, and it is considered the responsible of the major historical earthquakes which struck this area in the past. According to the response spectra obtained through the application of the 1-D non-linear models, the city of Ragusa has been divided into some zones with different peak ground acceleration at the surface. Shaking maps for the central area of the city of Ragusa were generated via GIS for the scenario earthquakes. The maps represent an important tool for the seismic improvement of the buildings, indispensable for the mitigation of the seismic risk

Topographic Site Effects Evaluation for the Monte Po Hill in the City of Catania (Italy)

The Monte Po Hill is located in the North-eastern part of the city of Catania; this area is prone to high seismic risk due to the presence of several constructions, including a school, in the vicinity of a toe of a slope, characterized by precarious stability conditions. The study has regarded the evaluation of site effects in correspondence of the site, to which corresponds a different value of the Seismic Geotechnical Hazard. In the beginning of 2007 a seismic station has been also located into the school building, with the aim of recording seismic events. Seismograms obtained by the seismic station have been also used to evaluate the ground response analysis at the surface. Finally the 1-D computer code EERA was also used to model the equivalent-linear earthquake site response analyses of layered soil deposits of the hill. The detail with which the hill has been studied has allowed the construction of a detailed 2-D model of its structure. It has been explored the differences between the computed ground motion for different Vs profiles using QUAD4M and QUAKE/W 2-D codes. It has been also possible to compare the results from different 1-D models reflecting current approaches to the determination of site response

Dynamic Geotechnical Characterization of San Giuliano Di Puglia Seismic Area

The city of San Giuliano di Puglia (CB), located in the Molise region in Southern Italy, is prone to high seismic risk. For site characterisation of soil deep site investigations have been undertaken. Borings, static and dynamic in situ tests have been performed. Among them Cone Penetration Tests (CPT), Cross-Hole (C-H) Down-Hole (D-H) and Seismic Dilatometer Marchetti Tests (SDMT) have been carried out, with the aim to evaluate the soil profile of shear waves velocity (Vs). Moreover the following laboratory tests were carried out on undisturbed samples: Oedometer tests, undrained Triaxial tests and Resonant Column tests. The available data enabled one to compare the shear waves velocity profile obtained by empirical correlations, Down Hole tests and Seismic Dilatometer Marchetti Tests. The influence of strain level on G-γ and D-γ curves was evaluated by means of laboratory tests. Two expression to allows the complete shear modulus degradation with strain level and the inverse variation of damping ratio with normalized shear modulus respectively were proposed. Finally after evaluating the synthetic accelerograms at the bedrock, the ground response analysis at the surface, in terms of time history and response spectra, has been obtained by two non-linear models GEODIN and EERA