Abstract Palygorskite (Pal) is a natural clay mineral with fibrous morphology and high surface area. Depending on the geological origin, it presents impurities, such as quartz and carbonates, which can harm some of its properties. Therefore, this work seeks to define a viable methodology for the purification of a Brazilian Pal. Two types of mixing processes (sonication and milling) and two types of dispersing agents (sodium silicate and sodium polyacrylate) were investigated. In addition, a subsequent acid activation with hydrogen peroxide and sulfuric acid was performed for complete purification. The viability of the purification of Pal was confirmed by X-ray diffraction, X-ray fluorescence, and thermogravimetric analyses. The sonication mixture process and the use of sodium polyacrylate as a dispersing agent were more effective. In addition, BET analysis showed an increase in the surface area of Pal, and scanning electron microscopy confirmed the permanence of its fibrous morphology after the purification steps.

Resumo Nanocompósitos de alumina/nanotubos de carbono e alumina tenacificada com zircônia (ZTA)/nanotubos de carbono foram desenvolvidos por rota cerâmica convencional utilizando sinterização sem pressão para aplicação balística. Os nanotubos de carbono de parede múltipla (NTC) foram funcionalizados por reação de oxidação com ácido nítrico. Além disso, os surfactantes dodecil sulfato de sódio e goma arábica foram utilizados para promover uma distribuição homogênea de NTC na matriz cerâmica. Os pós cerâmicos foram preparados com alumina pura, alumina com adição de 20% em massa de zircônia tetragonal/ítria, alumina/NTC e ZTA/NTC com adição de 0,1 e 0,5% em massa de NTC. A morfologia dos nanocompósitos foi caracterizada por MEV-FEG. As propriedades mecânicas das amostras sinterizadas foram avaliadas por ensaio de flexão, microdureza Vickers e tenacidade à fratura pelo método SEVNB. A adição de NTC na cerâmica e no compósito causou aumento geral na densificação, dureza, resistência à flexão e tenacidade à fratura. O compósito ZTA com adição de 0,1% de NTC obteve os melhores resultados.

Abstract Toughened and hardened alumina/carbon nanotubes and zirconia-toughened alumina (ZTA)/carbon nanotubes nanocomposites were developed by conventional ceramics route using pressureless sintering for the ballistic application. The multiwall carbon nanotubes (CNT) were functionalized with nitric acid oxidation reaction. Moreover, the surfactants sodium dodecyl sulphate and gum arabic were used to promote a homogeneous distribution of CNT in the ceramic matrix. Ceramic powders were prepared with pure alumina, alumina with the addition of 20 wt% of tetragonal zirconia/yttria, alumina/CNT and ZTA/CNT with the addition of 0.1 and 0.5 wt% of CNT. The morphology of nanocomposites was characterized by SEM-FEG. The mechanical properties of sintered samples were evaluated by flexural bending, Vickers microhardness and fracture toughness by SEVNB method. The addition of CNT in the ceramic and composite caused a general increase in densification, hardness, flexural strength and fracture toughness. ZTA composite with the addition of 0.1 wt% of CNT yielded the best results.