Chrysotile:cement roofing sheets were milled with and without K2HPO4. As indicated by X-ray diffraction (XRD), the samples crystallinities were reduced with the increasing milling time. The same tendency was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with disaggregation of the chrysotile fiber bundles and formation of non-fibrous micrometric agglomerate particles. After milling for 16 min, most of the phases present in the cement and chrysotile were transformed into amorphous materials, except quartz, in which the structure integrity was preserved, and calcium carbonate, where the particles were reduced to nanometric size. Both milled samples were submitted to release experiments in water, where the characteristics of a potential slow release fertilizer and acid soil conditioner were observed. The process is a viable alternative not only to eliminate the hazard of chrysotile fibers without the need to remove them from the cement matrix, but also as aggregation value to the milled almost amorphous mixture.

In this paper, we present an alternative method to obtain thin films for coating protection on the surface of the AA2524-T3 Al-alloy by using the Layer-by-Layer (LbL) technique. The LbL films were fabricated by alternated immersion of the Al-alloy into a poly(styrene sulfonate) (PSS) and polyaniline nanoparticles (PAni-NPs) solutions, obtaining a PAni-NPs/PSS bilayer architecture. The LbL films were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), electrochemical and micro-abrasive wear tests. The results show that the number of bilayers promotes shifts to less negative potentials, indicating an optimized system, in which the best performance was observed for a 15-bilayer PAni/PSS LbL film. The pitting potential (Epit) values shifted 130 mV (from -610 mV to -480 mV) in comparing a bare Al-alloy. The predominantly wear mechanism for AA2524-T3 with PAni-NPs/PSS bilayers was scratching whereas for the bare material there was an equivalence between scratching and rolling mechanisms. The results proved that the incorporation of PAni-NPS by the LbL method may be propitious as protective coating against corrosion in AA2524-T3 alloy.

Rice husk ash (RHA) is a waste material produced in large quantities in many regions worldwide, and its disposal can be problematic. This work describes a method for using RHA to synthesize silicon and potassium slow-release fertilizer. The extraction of silica from RHA was accomplished by alkaline leaching with KOH. Different KOH concentrations and reaction times were evaluated and the best production of K2SiO3 solution was achieved using 6 mol L-1 and 6 h, respectively. The fertilizer was synthesized by the reaction of K2SiO3 with KAlO2 in aqueous medium, followed by calcination at 500 °C. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses indicated that the fertilizer composition was similar to mineral kalsilite. Solubility essays indicated lower K+ and Si4+ release percentage in neutral medium. Kinetic mechanisms of release tests can be well explained by the pseudo-second order model. The proposed synthesis seems to be a viable process offering economic and environmental benefits.