No abstract

No abstract

Ni-Co ferrites are magnetostrictive ceramics that have potential application in magnetostrictive/ magnetoelastic sensors, as well as in magnetoelectric composites. Ni-rich Ni-Co spinel ferrite samples were processed by the ceramic method and bulk samples were sintered at 1350 ºC in the solid state and at 950 ºC with Bi2O3 liquid phase. The sintered samples were characterized by light microscopy, scanning electron microscopy, Raman spectroscopy, vibrating sample magnetometry and capacitance dilatometry. With Bi2O3 additions as small as 0.6 mol% it was possible to sinter the Ni-Co ferrite at 950 ºC, obtaining high-density samples; however, such liquid-phase sintered samples presented iron oxide particles. The studied samples presented magnetoelastic sensitivities very close to CoFe2O4, with significantly lower magnetic hysteresis. The results thus indicate that the magnetic properties of the samples analyzed are suitable for applications in magnetomechanical sensors.

Supermartensitic is a new class of stainless steels in development and consolidation as commercial products. Significant changes on chemical composition of conventional martensitic stainless steels, such as the reduction of the carbon content to ,0?03 wt-%, and the addition of Ni and Mo, marked the development of this new group of alloys. New grades containing higher amounts of Cr and small additions of Ti and/or Nb were developed recently. As a result, supermartensitic steels offer an interesting combination of high strength, toughness, weldability and corrosion resistance. In this work, the pitting corrosion resistance of a 15Cr supermartensitic steel with Ni, Mo and Cu additions was studied. It is well known that the mechanical properties and corrosion resistance of martensitic steels are adjusted by the final tempering treatment. Several single tempering treatments in the 300-650uC range and double tempering treatments were performed in order to obtain different microstructures. The pitting corrosion resistance was investigated by electrochemical test in 3?5%NaCl solution. It was found that the pitting potential slightly decreased with the increase in temperature and time of tempering. The analysis of pits formed during the corrosion tests showed that ferrite islands are more corrosion resistant than the martensitic matrix due to the higher Cr and Mo contents.

INTRODUÇÃORecentemente, devido ao esgotamento dos recursos fósseis e ao aumento das preocupações ambientais, muitos estudos estão à procura de combustíveis limpo e/ou renová-veis para complementar e substituir os combustíveis fósseis tradicionais. O biodiesel é considerado como um dos potenciais combustíveis alternativos, uma vez que contém menos enxofre e aproximadamente carbono neutro, é renovável e biodegradável [1][2][3]. O biodiesel é geralmente produzido por transesterificação devido à maior disponibilidade de matérias -primas ricas em triglicerídeos, mas o processo de esterificação tem sua importância por ser um processo alternativo que possibilita a utilização de matérias-primas ricas em ácidos graxos livres presentes em resíduos e subprodutos de processamentos industriais da biomassa, destacando os óleos brutos, óleos usados em frituras e ainda produtos de origem animal, como banha ou sebo [4][5][6]. Os catalisadores ácido/base heterogêneos são econômicos e benéficos ao meio ambiente, porque eles podem ser recuperados e reutilizados em reações catalíticas para produção do biodiesel [7][8][9][10]