The effect of the precursor solution's pretreatment on the properties and microstructure of the SCS final nanomaterials

Nanostructured nickel-based catalysts were produced by solution combustion synthesis and it was found that their properties and structure depended on the pretreatment of the precursor solution. X-ray diffraction, N2 adsorption, and an infrared high-speed camera were used to follow the various synthesis steps and to characterize the obtained catalysts, while their catalytic activity was determined in the hydrogenation of maleic acid. It was determined that the amount of water used and the heating of the precursor solution under mild stirring up to 70 °C influenced the nickel nitrate–glycine–water complexes that were formed in the precursor solution in the form of dendrites. These play a key role in the solution combustion synthesis (SCS) reaction mechanism and in particular in the formation of nickel-based catalysts. Understanding the interrelationships between the processing parameters and the ensuing powder properties allowed an efficient optimization of the catalytic performance

Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions

In this chapter, we present an overview of experimental techniques utilized and kinetic data collected for exothermic self-sustained noncatalytic heterogeneous reactions. The data focuses on five primary experimental techniques: electrothermal explosion, differential thermal analysis, electrothermography, combustion velocity/temperature analyses, and several advanced in situ diagnostics, including time-resolved X-ray diffraction

Nanocrystalline Hydroxyapatite/Si Coating by Mechanical Alloying Technique

A novel approach for depositing hydroxyapatite (HA) films on titanium substrates by using mechanical alloying (MA) technique has been developed. However, it was shown that one-hour heat treatment at 800°C of such mechanically coated HA layer leads to partial transformation of desired HA phase to beta-tri-calcium phosphate (β-TCP) phase. It appears that the grain boundary and interface defects formed during MA promote this transformation. It was discovered that doping HA by silicon results in hindering this phase transformation process. The Si-doped HA does not show phase transition to β-TCP or decomposition after heat treatment even at 900°C

Perovskite-based Catalysts for Direct Ethanol Fuel Cells

Utilizing a screening strategy featuring energy efficient and rapid solution combustion (SC) synthesis technique, and the high throughput NuVant system, a library of conductive perovskites was synthesized and tested as anode electrode in the direct ethanol fuel cell (DEFC) conditions. It was found that a variety of Ru-based perovskites showed considerable electro-catalytic activity for ethanol oxidation. Further, it was demonstrated that the perovskite-platinum catalysts with low noble metal loading prepared directly in by SC method exhibit comparable performance with standard Pt-Ru alloy

Microstructural Transformations And Kinetics Of High-Temperature Heterogeneous Gasless Reactions By High-Speed X-Ray Phase-Contrast Imaging

Heterogeneous gasless reactive systems, including high-energy density metal-nonmetal compositions, have seen increasing study due to their various applications. However, owing to their high reaction temperature, short reaction time, and small scale of heterogeneity, investigation of their reaction mechanisms and kinetics is very difficult. In this study, microstructural changes and the kinetics of product layer growth in the W-Si system was investigated using a high-speed x-ray phase-contrast imaging technique. Using the Advanced Photon Source of Argonne National Laboratory, this method allowed direct imaging of irreversible reactions in the W-Si reactive system at frame rates up to 36 000 frames per second with 4-microsecond exposure and spatial resolution of 1micrometerser. Details of the Si melt and reactions between W and Si, that are unable to be viewed with visible-light imaging, were revealed. These include processes such as the initiation of nucleated melting and other physical phenomena that provide insight into the mixing of reactants and subsequent reaction. Through the use of this imaging technique and future optimization in the imaging process, a model for accurately identifying kinetics of chemical reactions, both spatially and temporally, is also proposed

Mechanochemical Synthesis of Nanocrystalline Hydroxyapatite Coating

A novel approach for depositing of hydroxyapatite (HA) films on titanium substrates by using high energy ball milling (HEBM) has been developed. It was demonstrated that a heat treatment of the mechanically coated HA at 800 °C for one hour leads to partial transformation of HA phase to -TCP. It appears that the grain boundary and interface defects formed during MCS reduce this characteristic transformation temperature. Also, it was shown that Ti incorporation into the HA structure causes the lattice shrinkage and reduction of its grain size as compared to pure HA, but also promote the phase transformation of HA to TCP at high temperature. It is important that doping HA by silicon, while also significantly decrease crystallinity of deposited HA layer, results in hindering of the phase transformation process. The Si-doped HA does not show phase transition or decomposition after heat treatment even at 900 °C. The samples were investigated by X-ray diffraction, scanning electron microscope, Energy dispersive spectroscopy, Atomic force microscopy, Transmission electron microscopy, inductively coupled plasma (ICP) optical emission spectrometer, Vickers microhardness, Electron paramagnetic resonance