A new species of a solitary coral (Scleractinia, Turbinoliidae) from the San Julián Formation (Upper Oligocene, Santa Cruz) in its stratigraphic and paleoenvironmental context

En depósitos marino-someros de la costa de la provincia de Santa Cruz (Patagonia austral, Argentina), pertenecientes a la Formación San Julián (Oligoceno superior), se hallaron pequeños corales scleractínidos de la familia Turbinoliidae. Las ejemplares descriptos corresponden a Sphenotrochus aff. gardineri y Bothrophoria compressa n. sp. que representa el segundo registro del género. De acuerdo con la asociación de facies y al resto del conjunto de invertebrados, estos corales solitarios y libres (posiblemente semi-excavadores) habrían vivido en aguas templadas a cálidas (Mar Juliense) y sobre substratos arenosos de la plataforma interior-anteplaya superiorA new species of a solitary coral (Scleractinia, Turbinoliidae) from the San JuliánFormation (Upper Oligocene, Santa Cruz) in its stratigraphic and paleoenvironmental context.Small scleractinian corals (Family Turbinoliidae) were collected from the Late Oligocene San Julián Formation, in Santa Cruz province (southern Patagonia, Argentina). The specimens were assigned to Sphenotrochus aff. gardineri and to Bothrophoria compressa n. sp., the second record of the genus. According to the lithofacies association and the remaining fossil invertebrates, these free-living and ahermatypic turbinoliids would have lived in temperate to warm waters (Juliense sea) and in sandy substrates of the inner shelf-upper shoreface.Fil: Erdmann, Silvia. No especifíca;Fil: Bellosi, Eduardo Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Morra, Guillermo A.. No especifíca

HighP–TNano-Mechanics of Polycrystalline Nickel

We have conducted highP–Tsynchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume–pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify “micro/local” yield due to high stress concentration at the grain-to-grain contacts and “macro/bulk” yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under highP–Tconditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 Tm) hardens nanocrystalline Ni, leading to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni

Sinterizzazione di carburo di silicio in fase liquida

Materiali densi a base di carburo di silicio sinterizzato in fase liquida sono stati ottenuti da due polveri (di tipo α-SiC e β-SiC) utilizzando come additivi (Y2O3+Al2O3) Sono state analizzate le densità e la microstruttura dei materiali, in relazione alle caratteristiche e trattamento delle polveri

Improvement offered by coprecipitation of sintering additives on ultra-fine SiC materials

A commercial SiC powder is processed through either conventional ultrasonication or coprecipitation of sintering additives, to obtain dense materials. The coprecipitation process involves a change of the surface properties of SiC particles which concerns the formation of amorphous precipitates (see the figure) deriving from the sintering aids and partial dissolution of the surface silica. These factors lead to microstructural refinement and reduction of the intergranular phase amount in dense samples

The corrosion behaviour of alumina/titanium diboride composites in neutral and acidic chloride solutions

The development of electroconductive ceramic materials to replace conventional metal parts allows the production of high-performance electronic devices, wear parts, electrodes, high temperature heathers, heat exchangers, and so on. In particular the addition of 30% TiB2 on Al2O3 matrix can lower its electrical resistivity down 10-3 Ohm.cm and at the same time can increase its hardness strength and fracture toughness. Since applications require a suitable corrosion resistance, it is important to evaluate the corrosion behaviour of these electroconductive ceramic materials towards common aggressive environments, such neutral or acidic chloride solutions. In this work, two different composites (50%Al2O3-50%TiB2 and 70%Al2O3-30%TiB2) were exposed to 3.5%NaCl solutions at pH 7 and 3; the corrosion was studied by electrochemical tests and chemical analyses and was compared to the behaviour of monolithic TiB2 materia

Studio del comportamento alla corrosione del diboruro di zirconio in soluzioni acquose

Il diboruro di zirconio (ZrB2) sinterizza, con difficoltà, a temperature superiori a 1700°C e in presenza di pressione. La microstruttura del materiale, contenente 2.5% di Si3N4 come additivo di sinterizzazione, è stata studiata con osservazioni al microscopio elettronico (SEM), tramite spettroscopia a dispersione di energia (EDS) e diffrattometria dei raggi X (XRD). Lo studio del suo comportamento alla corrosione è stato condotto in soluzioni acquose acide contenenti anioni diversi, quali cloruri, fluoruri, perclorati, solfati e ossalati, alla temperatura di 45 °C. Le tecniche elettrochimiche utilizzate consistono nella registrazione di curve di polarizzazione e in misure potenziostatiche e sono state affiancate da analisi chimiche delle soluzioni

Corrosion of alumina/titanium diboride composites in neutral and acidic chloride solutions

This research concerns the study of the corrosion behaviour of monolithic titanium diboride and the composites 50%Al2O3/50%TiB2 (50/50) and 70%Al2O3/30%TiB2 (70/30) in 3.5% NaCl solutions, at pH 7 and 3 (adjusted by HCl additions). The test temperature is 45 ± 1°C. Both electrochemical and chemical techniques are applied. Scanning electron microscope (SEM) observations are also used to investigate the corrosion attack morphology. Polarization curve recording evidences that at short immersion times both composites exhibit a passive behaviour. The stability of these passive conditions decreases at increasing volume fractions of titanium diboride in the material and is minimum in the monolithic material. The analyses of the aggressive solutions during 30 days of immersion of 50/50 under free corrosion conditions are in agreement with the hypothesis that at both pH values passivity is due to the presence of a titanium-containing insoluble surface film, probably constituted by hydrated titanium oxide. SEM observations evidence the presence of a third phase in the composites, beside titanium diboride and alumina, that is constituted by an aluminum borate, formed during sinterization. This phase undergoes a chemical attack during exposures to the aggressive solutions, under free corrosion conditions. The relative importance of chemical towards electrochemical corrosion, as assessed by coupling potentiostatic tests and chemical analyses, increases when passive conditions are maintained