Houshang Alamdari

Iron–manganese: new class of metallic degradable biomaterials prepared by powder metallurgy

Abstract An Fe–35 wt-%Mn alloy, aimed to be used as a metallic degradable biomaterial for stent applications, was prepared via a powder metallurgy route. The effects of processing conditions on the microstructure, mechanical properties, magnetic susceptibility and corrosion behaviour were investigated and the results were compared to those of the SS316L alloy, a gold standard for stent applications. The Fe35Mn alloy was found to be essentially austenitic with fine MnO particles aligned along the rolling direction. The alloy is ductile with a strength approaching that of wrought SS316L. It exhibits antiferromagnetic behaviour and its magnetic susceptibility is not altered by plastic deformation, providing an excellent MRI compatibility. Its corrosion rate was evaluated in a modified Hanks solution, and found superior to that of pure iron (slow in vivo degradation rate). In conclusion, the mechanical, magnetic and corrosion characteristics of the Fe35Mn alloy are considered suitable for further development of a new class of degradable metallic biomaterials.

Clear microstructure-performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis.

Microstructural properties of mixed oxides play essential roles in their oxygen mobility and consequently in their catalytic performances. Two families of mixed oxides (perovskite and hexaaluminate) with different microstructural features, such as crystal size and specific surface area, were prepared using the activated reactive synthesis (ARS) method. It was shown that ARS is a flexible route to synthesize both mixed oxides with nano-scale crystal size and high specific surface area. Redox properties and oxygen mobility were found to be strongly affected by the material microstructure. Catalytic activities of hexaaluminate and perovskite materials for methane oxidation were discussed in the light of structural, redox and oxygen mobility properties.

Characterization of a Full Scale Prebaked Carbon Anode using X-Ray Computerized Tomography

In the conventional Hall-Heroult electrolysis process, the carbon anode is formed either by pressing or by vibro-compaction. The final properties of an anode are influenced by many parameters such as raw materials properties and manufacturing process. Presently, the aluminium producers have to deal with continuous variation of raw materials properties. To minimize the effects of the raw materials variations on the final product quality, numerical modeling of the forming process is of great interest. However, it is imperative to collect data on real anodes in order to calibrate these models. Some of the most valuable data are the density and porosity distribution of a full-scale baked anode obtained with computed tomography (CT). To test the method, three cored samples of 300 mm in diameter were taken from an industrial anode and scanned with an X-Ray tomograph. Calibration standards were also used to fit the CT scan results with the experimental data.

Solvent free synthesis of nanocrystalline hexaaluminate-type mixed oxides with high specific surface areas for CO oxidation reaction

Nanocrystalline hexaaluminate-type mixed oxides having crystallite sizes of around 20 nm and high surface areas (>77 m2 g−1) were synthesized using an original mechanosynthesis technique. These nanocrystalline materials were evidenced to be highly active heterogeneous catalysts compared to the conventional parent materials.

Co-Cu Metal Alloys from LaCo1-xCuxO3 Perovskites as Catalysts for Higher Alcohol Synthesis from Syngas

The specific surface area of ground perovskites is strongly dependent on the synthesis and pretreatment conditions. Calcining the ground LaCo1-xCuxO3-? perovskites at 5000C causes a decrease of their specific surface, but the further reductive pretreatment of the calcined sample in hydrogen leads to only a minor change in the specific surface area.The introduction of extra- and intra-perovskite lattice copper has different effects on the structure stability, reducibility and catalytic properties of LaCoO3 perovskites. Under the same pretreatment conditions the basic structure of both LaCoO3 and Cu2O/LaCoO3 samples is retained at the reduction temperature of 5000C (90 min) while that of Co-Cu based perovskites is completely collapsed producing a high dispersion of bimetallic metals and Co-Cu alloys supported on amorphous La2O3. For a series of LaCo1-xCuxO3 samples, increasing the copper content in the perovskite structure leads to an increase in the metal surface area of the reduced phase. The pretreated catalysts were tested for CO dissociation and for alcohol synthesis from syngas. The results indicated that the copper sites neighboring with cobalt atoms in the reduced perovskites decrease the activity in CO dissociation and increase the rate of higher alcohol synthesis while extra-perovkite lattice copper tends to produce methanol, methane and CO2. The overall activity in syngas conversion and higher alcohol productivity are proportional to the Co-Cu metal surface. The role of dual sites of Co and Cu for the synthesis of higher alcohols is discussed. The catalytic activity and alcohol productivity as well as product distribution depend strongly on reaction temperature and pretreatment conditions. The highest productivity of alcohols in the present study is about 73 mg/gcat/h for sample LaCo0.7Cu0.3O3.

Waste-free scale up synthesis of nanocrystalline hexaaluminate: properties in oxygen transfer and oxidation reactions

Synthesis of nanocrystalline hexaaluminate is reported using an original activated reactive synthesis process. Starting from a classical ceramic solid, exhibiting low surface area and a micrometric crystal size, a two-step grinding process allows reduction of the crystal size down to a few nanometers and development of high surface areas. The synthetic process was then used to produce transition metal- and noble metal-doped structures. The effects of (i) morphological and structural properties and (ii) substitution on oxygen transfer properties and catalytic properties in CO and CH4 oxidation reactions were studied. Crystal size was shown to be a key parameter in controlling the bulk oxygen transfer. Study of the catalytic properties in low and high temperature oxidation reactions also shows the crucial effect of the morphological parameters. Highest activities were achieved over nanocrystalline high surface compositions. Finally, even if less active than classical palladium supported solids, these new structures exhibited extremely high thermal stability.

Effects of Physical Properties of Anode Raw Materials on the Paste Compaction Behavior

The current study investigates the effects of coke particle characteristics and paste formulation on the flowability and the compression behavior of anode pastes. Shape factor and texture of different fractions of cokes were characterized using an image analysis system where the characteristics of each coke were correlated to its vibrated bulk density (VBD). A compression test was designed to study the effects of particle characteristics and paste recipe on the compactability of pastes. The test was applied on four anode pastes, prepared from different coke types, particle size distributions and pitch contents. It was observed that the compression test is significantly sensitive to any changes in raw materials characteristics and formulations. Consequently, the compression test may be used as a tool for evaluating anode quality in relation with material variations.

Tribo-Mechanical Properties of HVOF Deposited Fe3Al Coatings Reinforced with TiB2 Particles for Wear-Resistant Applications

This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load. This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF) technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load.

Air and CO2 Reactivity of Carbon Anode and Its Constituents: An Attempt to Understand Dusting Phenomenon

Carbon anode, used in the Hall-Heroult process, is subject to both air oxidation and carboxy gasification by CO2. These reactions are considered as being the main causes of dusting phenomenon in the electrolysis bath. More precisely, it is believed that CO2 and O2 preferentially attack the baked pitch (pitch coke) resulting in detachment of coke and butt particles in the form of dust. The present work aims at elucidating this phenomenon by studying the air and CO2 reactivities of the prebaked carbon anode and also of its constituents. The air and CO2 reactivities were evaluated using thermo-gravimetric analysis and the standard reactivity test of R&D Carbon, ISO Standard 12981-1. The microstructural features of the samples, i.e. real density, crystallite size and specific surface area, were measured. The reactivity of the anode and its constituents was assessed separately and their effect on dusting phenomenon was discussed.

Role of Mn+ cations in the redox and oxygen transfer properties of BaMxAl12−xO19−δ (M = Mn, Fe, Co) nanomaterials for high temperature methane oxidation

BaMxAl12−xO19−δ (M = Mn, Fe, Co, x = 1, 2) hexaaluminate nanomaterials were successfully prepared using the ARS (Activated Reactive Synthesis) process, a top-down and solvent free original synthesis route. The crystal sizes of the nanomaterials range at 24 ± 2 nm, which allows them to display high surface area (from 60 to 100 m2 g−1). The role of Mn+ cations in the redox and oxygen transfer properties of the nanomaterials was studied by H2-TPR and 18O/16O isotopic exchange, respectively. The nature of the transition metal as well as its content is observed to play a key role in the oxygen transfer properties. The catalytic properties of the nano-hexaaluminates, evaluated for methane oxidation, a reaction involving severe conditions (high temperature), resulted from multiple factors including oxygen transfer properties and transition metal valence and concentration on the surface.