An overview of natural polymers as reinforcing agents for 3D printing

Three-dimensional (3D) printing, or additive manufacturing, is a group of innovative technologies that are increasingly employed for the production of 3D objects in different fields, including pharmaceutics, engineering, agri-food and medicines. The most processed materials by 3D printing techniques (e.g., fused deposition modelling, FDM; selective laser sintering, SLS; stereolithography, SLA) are polymeric materials since they offer chemical resistance, are low cost and have easy processability. However, one main drawback of using these materials alone (e.g., polylactic acid, PLA) in the manufacturing process is related to the poor mechanical and tensile properties of the final product. To overcome these limitations, fillers can be added to the polymeric matrix during the manufacturing to act as reinforcing agents. These include inorganic or organic materials such as glass, carbon fibers, silicon, ceramic or metals. One emerging approach is the employment of natural polymers (polysaccharides and proteins) as reinforcing agents, which are extracted from plants or obtained from biomasses or agricultural/industrial wastes. The advantages of using these natural materials as fillers for 3D printing are related to their availability together with the possibility of producing printed specimens with a smaller environmental impact and higher biodegradability. Therefore, they represent a “green option” for 3D printing processing, and many studies have been published in the last year to evaluate their ability to improve the mechanical properties of 3D printed objects. The present review provides an overview of the recent literature regarding natural polymers as reinforcing agents for 3D printing

Examining the thermal properties of unirradiated nuclear grade graphite between 750 and 2500 K

This study presents the first high temperature measurements (between 750 K and 2500 K) of thermal conductivity, thermal diffusivity, specific heat and spectral emissivity of virgin graphite samples (type IM1-24) from advanced gas-cooled reactor (AGR) fuel assembly bricks. Scanning electron microscope (SEM) and X-ray computed tomography (XRT) techniques were used to verify the presence of Gilsocarbon filler particles (a characteristic microstructural feature of IM1-24 graphite). All thermal properties were investigated in two orthogonal directions, which showed the effective macroscopic thermal conductivity to be the same (to within experimental error). This can be linked to the morphology of the filler particles that consist of concentrically aligned graphitic platelets. The resulting spherical symmetry allows for heat to flow in the same manner in both macroscopic directions. The current thermal conductivity results were compared to other isotropic grade graphite materials. The significant discrepancies between the thermal conductivities of the individual grades are likely the result of different manufacturing processes yielding variations in the microstructure of the final product. Differences were identified in the filler particle size and structure, and possibly the degree of graphitization compared to other reported nuclear graphites

LINGUA PER COMUNICARE E LINGUA PER STUDIARE: GLI ALUNNI NON ITALOFONI NELLA SCUOLA ITALIANA. PERCORSI DI AVVICINAMENTO E COMPRENSIONE DI UN TESTO DI STORIA

Secondo il MIUR, nell’anno scolastico 2006-2007, gli studenti stranieri nella scuolaitaliana, provenienti da circa 190 paesi, hanno superato, anche se di poco, quota 500.000(circa il 5,6% degli studenti).Il percorso verso l’integrazione scolastica è tortuoso: in difficoltà appaiono lestrutture che li accolgono e gli stessi insegnanti, che devono gestire un gruppo-classe diitalofoni secolarizzati e di studenti stranieri da un profilo ben poco delineato.I dati sui comportamenti linguistici di questi allievi rivelano quanto siano diversi itempi dell’acquisizione dell’italiano per la comunicazione quotidiana e interpersonale,rispetto a quella per lo studio.Come evidenziato da Cummins, le abilità comunicative di base (BICS) e lacompetenza linguistica cognitivo-accademica (CALP) si sviluppano in tempi molto diversi:le prime dai 6 mesi ai due anni; le seconde, invece, in un periodo che va dai 5 ai 7 anni. Percomprendere e usare la L2 per lo studio, l’apprendente straniero deve acquisire competenzediverse, di tipo linguistico, testuale, culturale, oltre che di tipo cognitivo e informativo.E’ qui che si inserisce il nostro lavoro, tentativo di esplorare strategieglottodidattiche e pedagogiche capaci di rinforzare le abilità dell’allievo rispetto ai compiticognitivi e linguistici richiesti dallo studio delle discipline scolastiche. L’obiettivo è far sìche l’allievo raggiunga, attraverso l’italiano, una buona autonomia nello studio e in tuttiquei casi in cui dovrà affrontare testi complessi in contesti extra-scolastici

TENSILE BEHAVIOUR OF T91 STEEL OVER A WIDE RANGE OF TEMPERATURES AND STRAIN-RATE UP TO 10^4 s^-1

High cromium ferritic/martensitic steel T91 (9% Cr, 1% Mo), on account of its radiation resistance, is a candidate material for nuclear reactor applications. Its joining by an impact method to create a cold joint is tested in the realm of scoping tests towards the safe operation of nuclear fuels, encapsulated in representative T91 materials. Hitherto, T91 mechanical characterisation at high strain rates is relatively unknown, particularly, in relation to impact joining and also to nuclear accidents. In this study, the mechanical characterization of T91 steel was performed in tension by varying the strain-rate (10-3 up to 104 s-1) and temperature (20-800°C) on dog-bone specimens, using standard testing machines or Hopkinson Bar apparati. As expected, the material is both temperature and strain-rate sensitive and different sets of parameters for the Johnson-Cook strength model were extracted via a numerical inverse procedure, in order to obtain the most suitable set to be used in this field of applications

Tensile Behavior of T91 Steel Over a Wide Range of Temperatures and Strain-Rate Up To 104 s1

High chromium ferritic/martensitic steel T91 (9% Cr, 1% Mo), on account of its radiation resistance, is a candidate material for nuclear reactor applications. Its joining by an impact method to create a cold joint is tested in the realm of scoping tests toward the safe operation of nuclear fuels, encapsulated in representative T91 materials. Hitherto, T91 mechanical characterization at high strain rates is relatively unknown, particularly, in relation to impact joining and also to nuclear accidents. In this study, the mechanical characterization of T91 steel was performed in tension by varying the strain-rate (1023 up to 104 s21) and temperature (20-800C) on dog-bone specimens, using standard testing machines or Hopkinson Bar apparati. As expected, the material is both temperature and strain-rate sensitive and different sets of parameters for the Johnson-Cook strength model were extracted via a numerical inverse procedure, in order to obtain the most suitable set to be used in this field of applications.JRC.E.4-Nuclear Fuel Safet

Zirconium carbonitride pellets by internal sol gel and spark plasma sintering as inert matrix fuel material

Inert matrix fuel is a fuel type where the fissile material is blended with a solid diluent material. In this work zirconium carbonitride microspheres have been produced by internal sol gel technique, followed by carbothermal reduction. Material nitride purities in the produced materials ranged from Zr(N0.45C0.55) to Zr(N0.74C0.26) as determined by X-ray diffraction and application of Vegard's law. The zirconium carbonitride microspheres have been pelletized by spark plasma sintering (SPS) and by conventional cold pressing and sintering. In all SPS experiments cohesive pellets were formed. Maximum final density reached by SPS at 1700 C was 87% theoretical density (TD) compared to 53% TD in conventional sintering at 1700 C. Pore sizes in all the produced pellets were in the mm scale and no density gradients could be observed by computer tomography