Rafael Kenji Nishihora

Herein, we report the mechanistic investigation of the formation of nickel (Ni) nanocrystallites during the formation of amorphous silicon nitride at a temperature as low as 400 °C, using perhydropolysilazane (PHPS) as a preformed precursor and further coordinated by nickel chloride (NiCl₂); thus, forming the non-noble transition metal (TM) as a potential catalyst and the support in an one-step process. It was demonstrated that NiCl₂ catalyzed dehydrocoupling reactions between Si-H and N-H bonds in PHPS to afford ternary silylamino groups, which resulted in the formation of a nanocomposite precursor via complex formation: Ni(II) cation of NiCl₂ coordinated the ternary silylamino ligands formed in situ. By monitoring intrinsic chemical reactions during the precursor pyrolysis under inert gas atmosphere, it was revealed that the Ni-N bond formed by a nucleophilic attack of the N atom on the Ni(II) cation center, followed by Ni nucleation below 300 °C, which was promoted by the decomposition of Ni nitride species. The latter was facilitated under the hydrogen-containing atmosphere generated by the NiCl₂-catalyzed dehydrocoupling reaction. The increase of the temperature to 400 °C led to the formation of a covalently-bonded amorphous Si₃N₄ matrix surrounding Ni nanocrystallites.

Flat microfiltration mullite (3Al₂O₃2SiO₂) membranes were prepared via phase-inversion tape casting method. The sintering temperature has been reduced from 1700°C to 1450°C by adding 3 wt.% of magnesium oxide (MgO) as a sintering aid. The effect of this compound on the membrane properties was systematically investigated. The presence of MgO promoted at the same time a change in membrane morphology resulting in a symmetric structure, which is opposite to the asymmetrical structure obtained for mullite membranes prepared without this sintering aid. Porosity of 38.9% and average pore size of 2.33 μm was achieved. Water and n-heptane vapor adsorption analysis showed an increment in hydrophilic behavior due to MgO. The reduction of sintering temperature from 1700°C (MgO free) to 1450°C (MgO added) produced mechanical stable samples with flexural strength about 15.3 MPa. The membrane was resistant enough to withstand the water flux permeation test up to 3 bar. Compared to the pure mullite membranes, the MgO containing sample displayed higher water permeation fluxes, which might be related to both the larger superficial pore size and its hydrophilicity.

In the last 20 years, tape casting, a standard wet‐shaping process to produce thin ceramics, has been applied to manufacture polymer‐derived ceramics (PDCs). Si‐based polymers, such as polysiloxanes and polysilazanes, also known as preceramic polymers (PCPs), have been used as precursors/binders replacing conventional raw materials and additives for tape casting process. Thermal processing of PCPs is carried out at lower temperatures in comparison with classical ceramic sintering, particularly of carbides and nitrides. Furthermore, polymeric precursors can be converted into hybrid or composite ceramics, when parts of the polymers remain unreacted. Inert or reactive fillers might be used to reduce both shrinkage and porosity inherently caused by the weight loss occurring during polymer pyrolysis while forming new ceramic phases in the final materials. Alternatively, pore formers might also be added to tailor pore shape, connectivity, and volume (macroporosity). Nevertheless, current equipment and process parameters for tape casting‐based products must be eventually adjusted to fit the characteristics of ceramic precursors. Therefore, the aim of this review is focused on listing and discussing the efforts to produce PDCs using tape casting as a shaping technique. Interactions of system components and effects of treatment, particularly thermal stages, on final microstructure and properties are stressed out. Gaps in the literature concerning processing optimization are pointed out, and suggestions are given for further development of PDCs produced by tape casting.

Mucilages are heteropolysaccharides with rich monosaccharide composition. They are capable of forming films that are brittle and fragile, and in order to obtain flexible materials, plasticizers must be added. The present study aims to evaluate the physicochemical properties of mucilage‐based films produced with Cereus hildmannianus and different glycerol concentrations by the casting technique. Transparent and yellowish films were obtained by the addition of glycerol, which also improved handleability, evidenced by increased elongation, and reduced tensile strength and Young's modulus. Thermal gravimetric analysis and differential thermal analysis revealed that glycerol presence reduced the thermal stability, showing the influence of a plasticizer over the polymer structure. Water absorption capacity and contact angle were reduced with the increase of plasticizer concentration; on the other hand, the water vapor permeability increased, as expected, due to the hydrophilic nature of glycerol. The results indicated the potential application of C. hildmannianus mucilage as a promising material to produce edible films. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45223.