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

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

Combustion synthesis: A novel method of catalyst preparation

In this chapter, we summarize work accomplished primarily by the authors on the use of solution combustion synthesis (SCS) in catalysis. Research in combustion synthesis at University of Notre Dame started with the group of Prof. A. Varma, now at Purdue University, in collaboration with Prof. A. Mukasyan and its application to catalysis was pursued jointly with Prof. E. Wolf. Prof. A. Kumar worked on the subject during his graduate studies at Notre Dame and now he is continuing work on the application of combustion synthesis to catalysis at Qatar University. After an introduction to combustion synthesis, we describe reaction pathways involved in the preparation of unsupported and supported catalysts using SCS. The catalytic applications focus on preparation and performance of active and stable catalysts for the hydrogen generation from methanol and ethanol, followed by application to electrocatalysis for fuels cell utilization. - The Royal Society of Chemistry 2019.We gratefully acknowledge the support of this work by grant NPRP-8-509-2-209 from the Qatar National Research Fund (member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Mechanistic Studies Of Combustion And Structure Formation During Combustion Synthesis Of Advanced Materials: Phase Separation Mechanism For Bio-Alloys

Among all implant materials, Co-Cr-Mo alloys demonstrate perhaps the most useful balance of resistance to corrosion, fatigue and wear, along with strength and biocompatibility [1]. Currently, these widely used alloys are produced by conventional furnace technology. Owing to high melting points of the main alloy elements (e.g. Tm.p.(Co) ~1768 K), high-temperature furnaces and long process times (several hours) are required. Therefore, attempts to develop more efficient and flexible methods for production of such alloys with superior properties are of great interest. The synthesis of materials using combustion phenomena is an advanced approach in powder metallurgy [2]. The process is characterized by unique conditions involving extremely fast heating rates (up to 10(exp 6 K/s), high temperatures (up to 3500 K), and short reaction times (on the order of seconds). As a result, combustion synthesis (CS) offers several attractive advantages over conventional metallurgical processing and alloy development technologies. The foremost is that solely the heat of chemical reaction (instead of an external source) supplies the energy for the synthesis. Also, simple equipment, rather than energy-intensive high-temperature furnaces, is sufficient. This work was devoted to experiments on CS of Co-based alloys by utilizing thermite (metal oxide-reducing metal) reactions, where phase separation subsequently produces materials with tailored compositions and properties. Owing to high reaction exothermicity, the CS process results in a significant increase of temperature (up to 3000 C), which is higher than melting points of all products. Since the products differ in density, phase separation may be a gravitydriven process: the heavy (metallic phase) settles while the light (slag) phase floats. The goal was to determine if buoyancy is indeed the major mechanism that controls phase segregation

An active and stable NiOMgO solid solution based catalysts prepared by paper assisted combustion synthesis for the dry reforming of methane

Ni supported on solid solution (NiOMgO) catalysts with different Ni concentration (10, 20 and 30 wt.%) were prepared by a novel paper assisted combustion synthesis (PACS) method, followed by a reduction stage. All as-synthesized materials formed NiOMgO solid solutions, which under optimum PACS conditions exhibited up to about 140 m2/g BET surface area, which is one of the highest reported so far for this type of materials. Solid solutions were not active unless reduced at higher temperatures, causing a fraction of the Ni to segregate to the surface to become the active sites. The activity during the dry reforming of methane was studied as a function of temperature, and time on stream (TOS). The PACS solid solution with 10 wt.% of Ni had the highest surface area and, upon reduction, it was the most active and stable catalyst exhibiting low carbon formation at 600 °C, and no carbon deposition at 700 °C during 24 h TOS. The activity results correlated well with the higher surface area of the starting solid solutions, the smaller Ni crystallite sizes, and the number of Ni2+ and Ni3+ sites on the surface.We gratefully acknowledge the support of this work by grant NPRP-8-509-2-209from the Qatar National Research Fund (member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. We also acknowledged the use of the following Facilities at the University of Notre Dame: Notre Dame Integrated Imaging Center (NDIIC), Notre Dame Materials Characterization Facilities (MCF), and Notre Dame Center for Environmental Science & Technology (CEST).Scopu

In situ XAS and FTIR studies of a multi-component Ni/Fe/Cu catalyst for hydrogen production from ethanol

Multicomponent catalysts containing Ni, Fe, Cu active for ethanol reforming reactions, prepared by solution combustion synthesis are characterized by multiple techniques such as ex situ XRD, XPS, and in situ XAFS and FTIR. XRD results indicate copper to be present in the reduced state as CuNi bimetal while nickel and iron are observed to be partially in a spinel NiFe2O 4 structure. In situ XANES and XAFS analysis show a change in Ni, Fe and Cu oxidation states during reaction. Cu, which was fully reduced before reaction, became partly oxidized upon exposure to ethanol and oxygen. Ni is mostly (75%) reduced and does not seem to change its oxidation state during the reaction. Fe is not present in metallic form after reduction and during the reaction, but some change in the oxidation state from Fe(II) to Fe(III) occurred during the reaction. XPS and SEM images indicate the formation of carbon filament on the spent catalyst. XPS results also indicate the enrichment of surface by Fe and Cu during the reduction of the catalyst. Based on the activity and characterization results obtained, and literature review, the role of predominant phases during ethanol decomposition reaction is proposed.We gratefully acknowledge funding from NSF grant 0730190 for support of this work. This work was also partially supported by Notre Dame Integrated Imaging Facility . Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under contract DE-AC02-06CH11357.Scopu