Sintering Of Precursors Research Articles

(Invited) Metal Oxide Mixed Sulphide of Controlled Crystal Structure As Catalysts for Two-Electron Water Oxidation

Conventional catalysts based on noble metals (Pt, Ru) are often used for production of oxygen during water electrolysis in four-electron pathway as they can decrease gas evolution overpotential. Another possible valuable product from water oxidation is hydrogen peroxide obtained via two-electron process. Currently, transition metal oxides, are readily employed to catalyse this reaction. Although they display certain activity, it is still not satisfactory for mass production of H2O2, therefore further optimisations are needed. We suggest in this work, in addition to typical nanostructure modifications of metal oxides (MoO2) such as doping or structural engineering, an application of transition metal dichalcogenides (MoS2). Consequently, the oxide is partially replaced by sulphur. The selection of molybdenum as a centre atom ensures sufficient electrical conductivity of material as an electrode active layer. This combination is intended to provide the benefits thanks to layered materials of tuned interlayer spacing as well as controlled number of active sites. It enables selective adsorption of intermediate products of water oxidation (O∗, OH∗, and OOH∗), and therefore increased preference towards two-electron pathway.Various chemical approaches are considered to synthesize this material, especially hydrothermal treatment in autoclave and high-temperature sintering of precursors. The catalytic activity of the nanostructured metal oxide is further enhanced by its deposition on conductive high surface area support made of carbon/graphite particles of strictly defined textural parameters and surface chemistry. The final composite is obtained using hydrophobic binders (PVDF and PTFE) to form the electrode and improve the catalyst stability. The measurements are carried out in flow electrolyser unit with an alkaline electrolyte. The amount of produced H2O2, H2 as well as quantity and quality of evolved gases are assessed in terms of faradaic efficiency, pressure and overvoltage measurements.

Morphology of Aluminum Alloy Foams Produced with Dolomite via Partial Sintering of Precursors.

Highly expanded, low-cost aluminum-based foams were successfully produced via powder metallurgy using dolomite as foaming agent. Nickel additions (5–15 wt.%) were explored in order to reduce the temperature disparity between dolomite decomposition and the melting range of the metallic matrix. Specific Al–Ni compositions provide appropriate viscosities for effective encapsulation of CO2 gas released during dolomite decomposition. A partial sintering step of compacted precursors was introduced prior to foaming, which resulted in high porosity levels (~86%) and significant volume expansion (~250%) in the final product. The partial sintering technique was a key determining factor in obtaining stable, highly expanded cellular structures with homogeneous pores, averaging 3 mm in size and being morphologically comparable with ALPORASTM foams.

EVOLUTION AND CHARACTERIZATIONS OF AURIVILLIUS BISMUTH TITANATE BY MODIFIED SOLID STATE PROCESSING

Mild agate mortar activation followed by sintering of precursors, in resemblance to modified solid state process, was studied for synthesis of the aurivillius bismuth titanate. Hand on mill activation was carried out for eight hours followed by annealing treatment at 1000°C for 12 hours in presence of air atmosphere to obtain the proper phase. Scherrer’s formula was utilized to estimate crystallite size along with planes of orientation. Crystallite size was about 65nm while prominent peaks of orientations were (-117), (006), (111), (200) and others. FESEM and TEM studies were carried to obtain the morphology and estimated grain size of the synthesized aurivillius compound. Morphological features execute the material system to be nanocrystalline in nature as estimated from grain size measurement in correspondence with XRD crystallite size estimation. FTIR analysis confirms M-O coordinations of synthesized modified perovskite (aurivillius) sample. Optical property was evaluated from UV-VIS analysis with prominent absorption spectra in the visible region. Tauc plot was used to estimate the band gap to be about 2.86eV & 2eV for both direct and indirect transitions.