Síntese e caracterização de cobaltita de níquel (NiCo2O4) obtida pelo método dos precursores poliméricos

A cobaltita de níquel (NiCo2O4) de estrutura do tipo espinélio apresenta baixa estabilidade térmica em tornodos 400 °C, que ocasiona a perda de NiO, afetando de maneira significativa as propriedades físicas e estruturaisdo material produzido. Neste trabalho a cobaltita de níquel foi preparada pelo método dos precursorespoliméricos. O material foi calcinado a 350 °C e tratado termicamente nas temperaturas entre 450 – 650 °C.O produto obtido foi caracterizado por Termogravimetria e Calorimetria Exploratória Diferencial (TG/DSC),Difração de Raios X (DRX), Refinamento Rietveld, Espectroscopia Raman, Microscopia Eletrônica de Varredurae caracterização magnética. Os resultados mostraram que é possível se obter a fase cobaltita de níquelindependente do tratamento térmico empregado. As análises magnéticas mostraram um comportamento magnéticodiferente para cada temperatura de tratamento do composto sintetizado.Palavras-chave: Cobaltita de Níquel, Método Pechini, NiCo2O4

Influence of calcium aluminate cement (CAC) on alkaline activation of red clay brick waste (RCBW)

In this paper, the effect of calcium aluminate cement (CAC) additions on the alkali activation of red clay brick waste (RCBW) was studied at room temperature and at 65 C. RCBW was partially replaced with CAC (0e50 wt.%) and blends were activated with NaOH and sodium silicate solutions. The compressive strength evolution was tested on mortars and the nature of the reaction products was analysed by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, microscopic studies and pH measurements. The results show that the use of CAC accelerates the activation process of RCBW so that 50 MPa were obtained in the blended mortars containing 40 wt.% CAC cured for 3 days at room temperature. CAC did not undergo normal hydration and only the C3AH6 phase was identified in the pastes blended with more than 30 wt.% CAC and cured at 65 C, while the main reaction product was a cementitious gel containing Ca and Al from CAC.The authors are grateful to the Spanish Ministry of Science and Innovation for supporting this study through Project GEOCEDEM BIA 2011-26947, and to FEDER funding.Reig Cerdá, L.; Soriano Martínez, L.; Borrachero Rosado, MV.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2016). Influence of calcium aluminate cement (CAC) on alkaline activation of red clay brick waste (RCBW). Cement and Concrete Composites. 65:177-185. https://doi.org/10.1016/j.cemconcomp.2015.10.021S1771856