Highly Porous Carbon Materials Derived from Silicon Oxycarbides and Effect of the Pyrolysis Temperature on Their Electrochemical Response.

The design of a material porous microstructure with interconnected micro-meso-macropores is a key issue for the successful development of carbon-derived materials for supercapacitor applications. Another important issue is the nature of these carbon materials. For those reasons, in this study, novel hierarchical micro-meso-macroporous silicon oxycarbide-derived carbon (SiOC-DC) was obtained via chlorine etching of carbon-enriched SiOC prepared via pyrolysis (1100-1400 °C) of sol-gel triethoxysilane/dimethyldiphenysiloxane hybrids. In addition, and for the first time, non-conventional Raman parameters combined with the analysis of their microstructural characteristics were considered to establish their relationships with their electrochemical response. The sample pyrolyzed at 1100 °C showed planar and less-defective carbon domains together with the largest specific surface area (SSA) and the highest volume of micro-meso-macropores, which upgraded their electrochemical response. This sample has the highest specific capacitance (Cs = 101 Fg-1 (0.2 Ag-1)), energy (Ed = 12-7 Wh-1 kg-1), and power densities (Pd = 0.32-35 kw kg-1), showing a good capacitance retention ratio up to 98% after 10,000 charge-discharge cycles at 0.5 Ag-1. At a pyrolysis temperature ≥ 1200 °C, the carbon domains were highly ordered and tortuous with a high degree of interconnection. However, SSA and pore volumes (micro-meso-macropores) were significantly reduced and downgraded the Cs, Ed, and Pd values.

Preparation and Properties of Sustainable Brake Pads with Recycled End-of-Life Tire Rubber Particles.

Sustainable composite brake pads were processed by employing recycled end-of-life tire (ELT) rubber particles obtained by means of cryogenic grinding and ambient grinding. The effect of the grinding mechanism and concentration of ELT rubber particles was then reported. From the friction result test, better behavior in terms of coefficient of friction (COF) was obtained when 3% of ELT rubber particles were introduced into the composite. It was demonstrated that the size of the particles is not as determinant as the friction mechanism in the wear properties of the sustainable brake pads. Whereas, while increasing the ELT rubber particle size acts as detrimental to the COF either in the ambient or cryogenic grinding, at high friction distances, the better adhesion of the particles because of the rough surface of the particles subjected to ambient grinding enhances the long-life behavior of the composite brake pads.

Insights into the Microstructural Evolution Occurring during Pyrolysis of Metal-Modified Ceramers Studied through Selective SiO2 Removal.

Silicon oxycarbide ceramers containing 5% aluminum, zirconium, and cobalt with respect to the total Si amount are prepared from a commercial polysiloxane and molecular precursors and pyrolyzed at temperatures ranging from 500 to 1000 °C. HF etching is carried out to partially digest the silica phase, thus revealing structural characteristics of the materials, which depend upon the incorporated heteroatom. From the structural and textural characterization, it was deduced that when Al enters into the ceramer structure, the crosslinking degree is increased, leading to lower carbon domain size and carbon incorporation as well. On the contrary, the substitution by Zr induced a phase-separated SiO2-ZrO2 network with some degree of mesoporosity even at high pyrolysis temperatures. Co, however, forms small carbidic crystallites, which strongly modifies the carbonaceous phase in such a way that even when it is added in a small amount and in combination with other heteroatoms, this transient metal dominates the structural characteristics of the ceramer material. This systematic study of the ceramer compounds allows the identification of the ultimate properties of the polymer-derived ceramic composites.

Silane coupling agent structures on carbon nanofibers.

Carbon nanofibers (CNFs) are considered ideal materials for reinforcing polymers due to their excellent mechanical properties, among others. In order to obtain composites of optimal properties the clue is to enhance the interaction between reinforcement (CNFs) and polymer matrix. Surface modification of CNFs with silane coupling agents (SCAs) has revealed as one of the most interesting methods. The silanization process has been carried out mixing at room temperature and for one minute the hydrolysed silane with CNFs. We have use four different SCAs: 3-aminopropyltriethoxyxilane (APS), 3-aminopropyltrimethoxysilane (AMMO), N-(2-aminoethyl)-3-(aminopropyltrimethoxysilane) (DAMO), and 3-glycidoxypropyltrimethoxysilane (GLYMO), in order to elucidate the SCA-CNFs interaction and the silane structures formed on CNFs surface. XPS and FTIR-ATR techniques have pointed out that each silane adsorbs on CNFs surface through chemical bonding, forming multilayers. Silane nature determines the structure taken on CNFs surface. APS and AMO silanes adsorb taking vertical structures on CNFs surface, while DMO and GMO adsorb on CNFs taking horizontal structures, stabilized by zwitterions formed through H-bonds with hydroxyl groups from CNFs surface.