Obtenção de scaffolds metálicos com presença de fases quasicristalinas dos sistemas Al-Cu-Fe e Al-Cu-Fe-Cr

Abstract

Since the discovery of quasicrystals (QCs), the scientific community has extensively studied this class of materials due to their structural characteristics and physical properties. One of the main structural characteristics of these phases is their translational quasiperiodicity. Their primary physical and chemical properties include low electrical and thermal conductivity, high hardness and Young's modulus values, and low surface energy, among others. Despite this unique set of properties, QCs have many limitations in terms of applications due to their intrinsic fragility. However, they have great potential for application, such as reinforcing agents in composites, coatings in tribological systems, thermal insulators, agents for increasing the corrosion resistance of various materials, catalytic systems etc. The present work aims to produce porous architectures that present quasicrystalline phases in their structures from two distinct routes. The first one was via dynamic freeze-casting from a quasicrystalline alloy Al62,5Cu25Fe12,5 (%at), produced by gas atomization. This route enabled the production of scaffolds with high porosity values (62.4%), with open and interconnected pores. The second route was via leaching of an Al85Cu6Fe3Cr6 alloy (%at), produced via spray forming. In other words, starting from a solid deposit, the pore formation stage resulted from exposing the samples to a concentrated NaOH solution. The effect of leaching time on the evolution of sample porosity was evaluated. The results indicated that the longer the leaching time, the greater the depth of chemical attack, reaching 376.4 ± 40.0 µm after 48 hours of leaching. Furthermore, the impact of leaching time on the adsorption capacity of these materials was evaluated, using Congo red dye (CR) as a contaminant to be removed from a solution. Its removal occurred through adsorption on the surface of the leached alloy. The sample leached for 30 minutes showed the highest CR removal efficiency, largely due to its slightly positive surface charge (zeta potential of +7.2 ± 4.2 mV), which promotes favorable electrostatic interactions with the anionic dye molecules. It was observed that the adsorption capacity decreases at longer leaching times, such as 48 hours, where the formation of oxides and hydroxides on the surface generates a negative surface charge and blocks active sites. Cycling tests demonstrated that the material can be reused as an adsorbent, despite a slight decrease in adsorption capacity after each cleaning cycle, indicating that some active sites remain occupied. CR was also used to evaluate, under the best leaching condition evaluated, its use as a catalysts in the presence of sodium borohydride (reducing agent). Catalytic tests revealed that the characteristic absorption peaks of CR disappeared or shifted to shorter wavelengths in just 10 minutes of immersion in the presence of NaBH4, confirming the efficient catalytic degradationof the dye. FTIR analyses reinforced these results, showing the breakage of azo bonds and the formation of by-products, validating the material's catalytic potential. The second route made it possible to produce porous samples with a quasicrystalline phase, which can be used in adsorption and catalysis systems, with the advantages of being handled and recovered effortlessly.