Flash sintering of TCP bioceramics: Effect of particle size and influence on β→α transition

In this work, sintering behavior of tricalcium phosphate ceramics under the effect of an external electrical field (in Flash sintering configuration) was analyzed to obtain dense bio-resorbable components. The aim was to understand whether the application of the external E-field, which allows to reduce drastically sintering time and temperature, limits also the undesired β→α-TCP phase transition. TCP powders were synthesized by solid state reaction and by wet synthesis though precipitation from aqueous solutions, this allowing to obtain amorphous calcium phosphate nano-particles, which were crystallized into nano β-TCP by thermal treatment. Then, cold-pressed green pellets were prepared and their sintering behavior was studied by dilatometry under different E-field at constant rate heating. The presence of α-TCP and the microstructure were investigated by XRD and SEM techniques. It is shown that a Flash phenomenon takes place for both TCP powders morphology below 1000°C it being more evident at higher E-fields and when smaller particles were used. Moreover, although β→α transition occurs at ~1150°C for pure TCP, the detection of both polymorphs indicates a local higher temperature, which could be correlated to Joule effect induced by the current flow along the material

Calcium Phosphate Powders for Biomedical Applications: Synthesis, Thermal Behavior and Non-Conventional Sintering

The present work was focused on the synthesis of three different calcium phosphate powders with possible application as bioceramics, their chemical, structural and thermal characterization, and finally their consolidation into dense compounds by conventional and flash sintering techniques. In the first part, Mg-doped (0 - 2 mol% Mg2+) tricalcium phosphate powders with micrometric size were produced by solid state reaction, and the influence of dopant on their sintering behavior and, specifically, on the β→α phase transition was studied. It was shown that magnesium stabilizes β-phase and ensures, after conventional sintering, much better densification and final mechanical properties. Moreover, annealing treatments on sintered compounds are suitable to convert the retained α- into β-TCP only in presence of Mg. Un-doped β-TCP was additionally subjected to flash sintering, thus obtaining dense microstructure at temperatures lower than 1000°C in just 10 min and avoiding any phase transition. A specific physical model based on of thermal-balance equations was considered to investigate the flash sintering process in detail; it was possible to point out that thermal runaway is the main mechanisms that triggers the process, which could be described also in terms of electric behavior of the material, real sample temperature and flash onset. Moreover, the observed blackening effect and the development of an additional resistance contribution at the electrodes were taken into account and discussed. In the second part of the work, Mg-doped (0 - 5 mol% Mg2+) tricalcium phosphate nanometric (~ 20 nm) powders were synthetized by chemical precipitation, thus obtaining highly-defected CDHA easily convertible into β-TCP at 750°C. Magnesium doping was found to inhibit the first crystallization and to promote β-TCP formation directly. The nanopowders were conventionally sintered to produce dense (~90%) β-TCP with sub-micrometric gran size. Flash sintering was also carried out on the nanopowders, demonstrating that the flash event can occur only after CDHA→β-TCP reaction, since the precursor is too resistive for allowing the electrical current flow. A non-linear electrical behavior was found for the β-phase, associated with the grain growth. Flash sintering was also applied in isothermal mode, producing dense sub-micrometric β-TCP at 900°C in just few seconds. It was also possible to build two maps relating the processing parameters for flash sintering on the basis of thermal model and the material behavior. Finally, hydroxyapatite nanopowders were synthesized by chemical precipitation with different amount of Sr2+ replacing Ca2+ into the apatite structure (0 - 100 mol%). The nanopowders were deeply characterized from a morphological, chemical and structural point of view (SEM, TEM, ICP, XRD, FT-IR, 31P-NMR, 1H-NMR, N2 sorption) finding a relation between the experimental evidences and the amount of Sr

Viscous flow flash sintering of porous silica glass

For the first-time compacts of porous glass particles (95 wt% SiO2, 2.3% Na2O, 1.6% Al2O3) exhibiting macro-, meso- and micro-pores were densified by flash sintering, using DC electric field in the range 1000–3000 V cm− 1. The results point out the applicability of this sintering technology to glasses characterized by viscous flow sintering mechanisms. Excluding the anodic region, the specimens resulted well densified using a current limit of 2 mA mm− 2 and a dwelling time of 30 s. The obtained microstructure at the anode and at the cathode side is asymmetric, the former being characterized by the formation of Na-enriched region, the latter by the local formation of large pores (hundreds of microns). The mechanism, which triggers the flash event, appears to be associated to dielectric breakdown.Fil: Prado, Miguel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Biesuz, Mattia. University of Trento; ItaliaFil: Frasnelli, Matteo. University of Trento; ItaliaFil: Benedetto, Franco Emmanuel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Sglavo, Vincenzo M.. University of Trento; Itali

Virological Investigation of Avian Influenza Virus on Postglacial Species of Phasianidae and Tetraonidae in the Italian Alps

Land-based birds, belonging to Galliformes order are considered to be potential intermediaries in the emergence of new strains of influenza A viruses (AIVs), but the viral circulation in these birds remains largely unknown. To gain insights into the circulation of AIV in the wild Galliformes populations in Italian Alps, we conducted a virological survey on rock partridge (Alectoris graeca saxatilis) belonging to Phasianidae family and on tetraonids including rock ptarmigan (Lagopusmutus helveticus) and black grouse (Tetrao tetrix tetrix). In 2003 and 2004, during the hunting seasons, 79 wild Galliformes, categorised into age and sex classes, were hunted in the Sondrio Province (Central Alps). Cloacal swabs were collected from 11 rock partridges and from 68 tetraonids including 23 alpine rock ptarmigans and 45 black grouses.We tested cloacal swabs by a high sensitive reverse transcription- (RT-) PCR detecting thematrix gene of AIV.No AIV was detected in the investigated samples, thus, suggesting the lack of AIV circulation in these relict populations in the study period. In terms of threatened species conservation, during wildlife management activities, it is very important to exclude the introduction of AIV-carrier birds in shared territories, a fact representing a health risk for these populations

Outbreak of Eimeria kofoidi and E. legionensis coccidiosis in redlegged partridges (Alectoris rufa)

An outbreak of coccidiosis occurred in red-legged partridges is reported. At the post-mortem examination the birds showed a mucous haemorrhagic enteritis, mostly in the duodenal intestinal tract. Direct microscopic examination of intestinal content revealed the presence of a high number of oocysts. After incubation, on the basis of the morphological features, two species of coccidia were identified: Eimeria kofoidi and E. legionensis

Case report of a pustular dermatitis outbreak in sheep: Clinical and food safety considerations

The objective of this report is to describe an outbreak of pustular dermatitis in a flock of about 200 sheep, its clinical evolution and food safety implications. The onset of the symptoms was sudden and the lesions spread very quickly from ewe to ewe, so that in about 3 days almost all of the lactating sheep were stricken. Pustules from 5 different animals, six milk samples, two cheese samples, teat cup samples from the milking machine and farmer’s hands were analysed. A pure culture of Staphylococcus aureus, producing staphylococcal enterotoxin (SE) C, was isolated from pustules. Milk and cheese showed a contamination by coagulase positive staphylococci <15 and 30 colony forming units respectively and the absence of SE. Farmer’s hands and teat cups samples resulted negative for coagulase positive staphylococci. Therapy with daily topical medicaments was prescribed and a prophylactic intervention was suggested by the administration of an autovaccine. The low level of milk and cheese contamination and the absence of SE in cheese supported the decision to not advise the farmer to recall cheese produced with milk from affected animals

Long-Term Serological Investigations of Influenza A Virus in Free-Living Wild Boars (Sus scrofa) from Northern Italy (2007&ndash;2014)

Influenza A viruses (IAV) have been repeatedly demonstrated to circulate in wild suid populations. In this study, serum samples were collected from 2618 free-ranging wild boars in a protected area of Northern Italy between 2007 and 2014, and firstly screened by enzyme-linked immunosorbent assay (ELISA) for the presence of antibodies against IAV. The ELISA-positive samples were further tested by hemagglutination inhibition (HI) assays performed using antigen strains representative of the four major swine IAV (sIAV) lineages circulating in Italy: avian-like swine H1N1, pandemic-like swine H1N1, human-like swine H1N2 and human-like swine H3N2. An overall seroprevalence of 5.5% (145/2618) was detected by ELISA, with 56.7% (80/141) of screened sera tests positive by HI assay. Antibodies against H1N1 subtypes were the most prevalent beginning in 2009&mdash;with the highest detection in the first quarter of the year&mdash;until 2013, although at a low level. In addition, antibodies to H3N2 subtype were found during six years (2007, 2009, 2010, 2011, 2012 and 2014) whereas H1N2 antibodies were detected in 2012 only. Of the HI-positive samples, 30% showed reactivity to both H1N1 and H3N2 subtypes. These results provide additional insight into the circulation dynamics of IAV in wild suid populations, suggesting the occurrence of sIAV spillover events from pigs to wild boars

Case report of a pustular dermatitis outbreak in sheep: Clinical and food safety considerations

The objective of this report is to describe an outbreak of pustular dermatitis in a flock of about 200 sheep, its clinical evolution and food safety implications. The onset of the symptoms was sudden and the lesions spread very quickly from ewe to ewe, so that in about 3 days almost all of the lactating sheep were stricken. Pustules from 5 different animals, six milk samples, two cheese samples, teat cup samples from the milking machine and farmer’s hands were analysed. A pure culture of Staphylococcus aureus, producing staphylococcal enterotoxin (SE) C, was isolated from pustules. Milk and cheese showed a contamination by coagulase positive staphylococci <15 and 30 colony forming units respectively and the absence of SE. Farmer’s hands and teat cups samples resulted negative for coagulase positive staphylococci. Therapy with daily topical medicaments was prescribed and a prophylactic intervention was suggested by the administration of an autovaccine. The low level of milk and cheese contamination and the absence of SE in cheese supported the decision to not advise the farmer to recall cheese produced with milk from affected animals