RESUMO
The effect of α-Al2O3 nanoparticles (up to 5 wt.%) on the physical, mechanical, and thermal properties, as well as on the microstructural evolution of a dense magnesia refractory is studied. Sintering temperatures at 1300, 1500, and 1600 °C are used. The physical properties of interest were bulk density and apparent porosity, which were evaluated by the Archimedes method. Thermal properties were examined by differential scanning calorimetry. The mechanical behavior was studied by cold crushing strength and microhardness tests. Finally, the microstructure and mineralogical qualitative characteristics were studied by scanning electron microscopy and X-ray diffraction, respectively. Increasing the sintering temperature resulted in improved density and reduced apparent porosity. However, as the α-Al2O3 nanoparticle content increased, the density and microhardness decreased. Microstructural observations showed that the presence of α-Al2O3 nanoparticles in the magnesia matrix induced the magnesium-aluminate spinel formation (MgAl2O4), which improved the mechanical resistance most significantly at 1500 °C.
RESUMO
Ternary chalcostibite copper antimony sulfide (CuSbS2) is an emerging semiconductor material having applications in photovoltaics, energy storage and optoelectronics due to its high absorption coefficient, suitable bandgap, and it consists of non-toxic and earth abundant elements. CuSbS2 thin films are prepared by combining chemical bath deposition (antimony sulfide (Sb2S3)) and thermal evaporation (copper (Cu)) followed by a heat treatment and their application as visible to near infrared photodetectors is reported. Crystalline structure, elemental composition, chemical state, morphology and optoelectronic properties of the films were characterized by various techniques. The effect of three different Cu thicknesses (CAS 20, CAS 30 and CAS 40 nm) on the photodetection properties are evaluated under illumination using light emitting diodes (LEDs) and a laser. The photodetectors fabricated are successfully tested under different wavelengths, power densities and applied voltage and their photoresponse cyclic stability for each wavelength of illumination was recorded. From the sensitivity calculations, the sample with 20 nm Cu thickness (CAS 20) showed higher detection sensitivity for visible to near infrared wavelengths. Better responsivity results were obtained for CAS 40 because of its improved crystallinity and phase purity. Photodetector properties such as sensitivity and responsivity are evaluated for all the samples. These results are beneficial for cost effective and environment friendly photodetectors and optoelectronic devices based on CuSbS2 thin films.
RESUMO
In this work two systems based on a carbohydrate polymer were studied: inulin as model system and inulin-orange juice as complex system. Both system were stored at different water activity conditions and subsequently characterized. Water adsorption isotherms type II were fitted by the GAB model and the water monolayer content was determined for each system. From thermal analyzes it was found that at low water activities (aw) systems were fully amorphous. As aw increased, crystallinity was developed. This behavior was corroborated by X-ray diffraction. In the inulin-orange juice system, crystallization appears at lower water activity caused by the intensification of the chemical interaction of the low molecular weight species contained in orange juice. Glass transition temperature (Tg), determined by modulated differential scanning calorimeter, decreased with aw. As water is adsorbed, the physical appearance of samples changed which could be observed by optical microscopy and effectively related with the microstructure found by scanning electron microscopy.
