Materials Science Forum Vols. 798-799

Abstract: The sensing elements for humidity has been vastly researched to be applied in several areas, since automotive and food industries up to automation in the agricultural production and in the environmental monitoring. In this work, ceramic material are focused, owing to their unique structure, consisting of grains, grain boundaries, surfaces and pores, the control of which allow to obtain suitable microstructure to be used as humidity sensors. In this work, the influence of the relative humidity on the electrical conductivity of the ceramic sensing elements of ZrO₂ and of TiO₂, under specific climatic conditions, is investigated. In this sense, the ceramics used as humidity sensing elements were manufactured through conventional ceramic processing. The sintered ceramics were characterized through X-ray diffractometry techniques, scanning electron microscopy, apparent density by the Archimedes principle and linear retraction. The results showed the development of a solid solution of ZrO₂-TiO₂. The microstructures presented a homogeneous distribution of pores. The ceramic tablets, sintered at 1100 °C, evidenced a linear behaviour in the curves capacitance versus environment humidity.

Abstract: In this work, compacting powders of different ZrO₂(Y₂O₃) are investigated relating the particle size, compaction pressure, and use of binders. Powders of ZrO₂ stabilized with 3mol % Y₂O₃ with an average particle size of 0.15 to 0.7μm presence of both bonding and 0.15μm without addition of binder, were uniaxially compacted with pressures of 30 to 115MPa. Green density between 40% and 50% were obtained. The results indicate that powders sized less densification above 1400°C, while the larger sizes only after reaching full densification above 1500°C. Crystallographic characterization indicates that the powders have a percentage of monoclinic phases in the range of 15% to 26%, but only after sintering tetragonal phase is identified.

Abstract: In this work, silver nanoparticles were incorporated in four different concentrations into rice husk ash (RHA) to promote an antimicrobial effect. The suspension was magnetic stirred and dried at 80°C for 24 h. The samples were characterized by scanning electron microscopy (SEM), specific surface area and zeta potential measurements. Microbiological analyses were conducted test the efficiency of the material in the elimination of the bacteria Escherichia coli. SEM results revealed a homogeneous dispersion of silver nanoparticles on the substrate, surface area values similar to those found in the literature and effective antimicrobial activity at low silver concentration.

Abstract: Polymers nanocomposites are composed by nanometrical particles embedded in a specific matrix. Additions of small amount of nanoparticles of inorganic material in specific matrixes can greatly improve mechanical properties. The high specific surface area of the inorganic materials nanoparticles promotes its dispersion in the polymeric matrix, and the obtained properties are strongly related to the homogeneity of the dispersion. In the present work, nylon 6.12 nanocomposites with different concentrations of pseudoboehmite obtained by sol-gel process were prepared with different concentrations of octadecylamine. The pseudoboehmite was characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis and thermo gravimetric analysis. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite reduces the melting flow, evidencing the interaction of pseudoboehmite with the polymeric matrix probably modifying its crystalline structure.

Abstract: In this work, the effect of the addition of an organophilic smectite clay on the properties of polypropylene (PP) was evaluated. The clay was a commercial natural montmorillonite treated with ammonium quaternary salt (Cloisite 20A^®). The composites were prepared by extrusion, and contain 5 wt.% of clay. The materials were characterized by: tensile and impact strength, oxygen permeability tests, optical microscopy, thermal analysis and X-ray diffraction analysis. The mechanical properties of the PP were decreased due to the clay addition. The composites presented a microstructure predominantly intercaleted, with fine and homogeneous dispersion of the clay layers within the matrix. The composite showed an increase of about 30% in the oxygen barrier property of the PP, which is an interesting result when considering the application of the composite as a packaging material.

Abstract: In this work, the effect of the incorporation of a sodium smectite clay (Brasgel) in Nylon-6 toughened with Poly (vinyl butyral) film (PVB film) was evaluated. The composites contain 60 wt.% of Nylon-6, 40 wt.% of PVB film and 5 wt.% of clay, relative to the total weight of the mixture. The clay was previously purified by sedimentation, and dried in a spray-dryer at 150°C. The composites were obtained by extrusion, in two steps: step 1 - mixture of nylon-6 with clay (called master of nylon-6) and step 2 - mixture of master of nylon-6 with PVB film. The clay was characterized by X-ray diffraction and X-rayfluorescence. The composites were characterized by mechanical tests (tensile and notched Izod impact strength), X-ray diffraction and scanning electron microscopy (SEM). The composites showed significant increase in the values of the notched Izod impact strength, when compared to the ones for pure nylon-6, and kept the stiffness of the matrix phase.