Abstract Oxides (Al2O3, SiO2, TiO2, ZrO2, Y2O3, CeO2, MgO) are among the most used reinforcements for Aluminum Matrix Composites (AMC); while the combination of Al with Si, Cu and/or Mg excels among the alloying systems used as matrices. Some works in literature study the effects of the reinforcements and the alloying elements on the composites manufacturing, microstructure and mechanical properties. Nevertheless, it is necessary a recompilation of the interactions oxide reinforcement-alloyed matrix, including the reciprocal effects between them. Our search revealed that not only reactions occur at the interfacial regions, but also other phenomena depending on the reinforcement characteristics and the matrix composition, which affect mechanical properties. These phenomena include modifications in the matrix microstructure and its precipitation process, diffusion of elements through the interfaces, change in the reinforcement wettability by the liquid metal, loss of alloying elements, and deterioration of the reinforcement. This work presents the occurrence of these phenomena for Al matrices with different contents of Si, Cu and Mg reinforced with the most used oxides. Its novelty lies in exploring these combinations of conditions, which could serve as a benchmark study and help for a better understanding and selection of the matrix-reinforcement system.

Abstract In this work, we present and discuss results concerning the hard magnetic behavior of rare earth-free MnBi alloys obtained by suction casting technique. The physics of coercivity for these type of alloys is based on the nucleation process of reverse domains, which in turn is determined by the alloy microstructure features such as phase distribution, morphology, grain size and in particular, defects, which are characteristic of real materials. The microstructure of the as-cast alloy presented here comprises the formation of the Low Temperature Intermetallic Phase (LTIP)-MnBi, interspersed within Biand Mn-rich areas. A considerable intrinsic coercivity field of 238 kA/m together with a saturation magnetization of 0.04 T were observed. The nucleation controlled mechanism of this alloy was described in terms of the Kronmüller equation, which incorporates the detrimental effect of microstructure defects through fitting parameters associated to reduced intrinsic magnetic properties at grain size boundaries, interfaces and local demagnetizing fields. A notorious switching of coercivity mechanism associated with domain wall pinning was found to be produced upon annealing of the alloy at 583 K for 24 hrs, yielding a drastic reduction of coercivity (down to 16 kA/m). The key microstructural feature determining the switching of coercivity mechanism is the formation/suppression of Bi-rich areas, which promotes the nucleation and growth of LTIP.

A process for synthesising nanocrystalline hydroxyapatite powders using calcium nitrate tetrahydrated [Ca(NO3)2-4H2O] and phosphorous pentoxide [P2O5] by colloidal solution, is presented and discussed. The powders were washed and calcinated at different temperatures and then characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powder size was compared with the results obtained from TEM and the calculated with the Scherrer's formula.

En este trabajo se presenta un proceso de síntesis por solución coloidal para obtener polvos nanocristalinos de hidroxiapatita usando nitrato de calcio tetrahidratado [Ca(NO3)2-4H2O] y pentoxido de fosforo [P2O5]. Los polvos obtenidos fueron lavados y calcinados a diferentes temperaturas para ser caracterizados empleando difracción de rayos X (DRX), microscopía electrónica de barrido (MEB) y microscopía electrónica de trasmisión (MET). El tamaño de los polvos se obtuvo comparando los resultados obtenidos por MET con los calculados por DRX usando la fórmula de Scherrer.