Síntese pelos métodos de combustão e Pechini e caracterização de ferrita de níquel para aplicação como dispositivos de sensor de umidade.

Abstract

In this study, nickel ferrite (NiFe204) plus nickel oxide (NiO) nanocomposites were synthesized by chemical routes: combustion reaction at 500 0 C, and Pechini method at 700, 900 and 1100 0 C. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to the structural and morphological characterizations. Hysteresis curves at room temperature were obtained using a vibrating sample magnetometer (VSM). Also, the electrical resistance versus relative humidity of the composites (adsorption and desorption) in the form of fims were obtained. These measurements characterized the samples for application as humidity sensor devices. Rietveld refinement of the XRD patterns possibly to identify and quantify the presence of crystalline nickel ferrite and nickel oxide (in smaller concentration) phases. The crystallite mean size for the samples obtained by the Pechini method grows with increasing temperature from 700 to 900 ° C, being stable from 900 to 1100 ° C. The images obtained by SEM showed good morphology for the nanoparticles, which favors the formation of pores for all samples. However, the number of pores and volume of pores seems to be different for all samples, showing influences on the electrical properties (qualities of the humidity sensor). It was also observed an increase in the average grain size of samples with increasing heat treatment temperature, probably due to the coalescence between crystallites favored at higher temperatures. The magnetization curves for the samples showed low coercivity and high saturation magnetization, which classify it as a soft ferromagnet (or ferrimagnet). For the electrical resistance versus relative humidity curves, it was observed that the sample obtained by combustion reaction method showed a shorter response time, when compared to the Pechini reaction ones. In addition, samples obtained by Pechini reaction at 700 ° C showed greater sensibility to humidity and smaller recover time, both related to good performance in humidity sensor applications.