Papers by Author: Heberto Balmori-Ramírez

Abstract: Cordierite has been synthesized by heating mixtures of kyanite and talc, using kyanite powders of two different sizes. The reaction is studied by thermogravimetric and differential thermal analysis. Phase changes are followed by X-Ray diffraction of samples fired between 750 °C and 1400 °C. The evolution of the reaction starts with the dehydration of talc at approximately 880 °C. The kyanite decomposes at approximately 1140 °C. The first traces of α-cordierite appear at around 1200 °C. The influence of the kyanite particle size on the kinetics and microstructure is analyzed.

Abstract: Elemental powder mixtures of Co and Ti were subjected to high-energy ball milling in order to produce mechanically alloyed powders with nominal compositions Co64Ti36, Co67Ti33, Co70Ti30, Co73Ti27, Co76Ti24 and Co85Ti15. The mechanically alloyed powders were treated during 30 minutes in inert atmosphere at temperatures in the range 300 – 700 °C. Both the as-milled powders as well as those subjected to heat treatments have been characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectrometry and differential thermal analysis. As-milled products consist mostly of agglomerated powders with a size between 10 and 80 µm which give an amorphous-like diffraction pattern, except for the Co85Ti15 sample whose pattern presents the characteristic peaks of the Co3Ti intermetallic phase. The transformation of the asmilled powders occurs at temperatures in the range of about 530 – 670 °C with clearly observed exothermic events. The Co3Ti phase is found in all heat treated samples, together with fcc-Co (in Co76Ti24 and Co85Ti15) or the hexagonal Co2Ti intermetallic phase (in Co64Ti36, Co67Ti33 and Co70Ti30); the Co73Ti27 sample was essentially single-phase Co3Ti after heating to 700 °C. Our results suggest the occurrence of crystallization of an amorphous phase in two overlapping stages during heating of the mechanically alloyed powders.