Chemical heterogeneities in nanometric titanomagnetites prepared by soft chemistry and studied ex situ : evidence for fe-segregation and oxidation kinetics

Nanocrystalline Fe-based spinels with composition Fe3-xTixO4 are synthesized using soft chemistry. Two steps are involved:  precipitation in an aqueous solution followed by thermal annealing under a reducing mixture of N2/H2/H2O gases. Fe-segregation is found inside stoichiometric particles when the powders are studied ex situ; they exhibit a strong surface iron enrichment. This heterogeneity is related to kinetic effects linked to the difference of mobility between Fe2+ and Ti4+ cations during the partial oxidation of cations occurring ex situ. Stresses in the grains induced by oxidation govern the oxidation kinetics and lead to an abrupt compositional variation inside each particle. These…

Mechanically Activated Self-Propagating High Temperature Synthesis (MASHS) Applied to the MoSi<sub>2</sub> and FeSi<sub>2</sub> Phase Formation

Design of a reactor operating in supercritical water conditions using CFD simulations. Examples of synthesized nanomaterials

International audience; Direct information about fluids under supercritical water conditions is unfeasible due to the engineering restrictions at high pressure and high temperature. Numerical investigations based on computational fluid dynamics (CFD) calculations are widely used in order to get extensive information on the fluid behavior, particularly to help the design of a new reactor. This paper presents the numerical investigations performed on an original supercritical water device, especially in the level of the reactor. CFD calculations allow to design and optimize the present reactor described in this study. Currently, this process produces some nanometric oxide powders in continuou…

Evidence for H2S gas as an intermediate species in the reaction mechanism of trapping hydrogen by cobalt disulfide

Cobalt sulfide prepared by aqueous precipitation using Na2S and a Co(II) salt is known to trap hydrogen at room temperature and low pressure. The importance of oxidation of the primary CoS precipitate with atmospheric oxygen with respect to its efficiency as a hydrogen absorber is demonstrated. This stage of oxidation produces a mixture of two solid phases: a partially crystallized cobalt hydroxide Co(OH)2 and an amorphous cobalt sulfide CoS2 with a Co(OH)2/CoS2 molar ratio of 1 as predicted by thermodynamics. This biphasic product is probably the basic cobalt sulfide CoSOH considered in older and even more recent work. This product traps molecular hydrogen with a H2/Co molar ratio of 0.5 w…

Time-resolved XRD experiments for a fine description of mechanisms induced during reactive sintering

The control of Mechanically Activated Field Activated Pressure Assisted Synthesis hereafter called the MAFAPAS process is the main objective to be achieved for producing nanostructure materials with a controlled consolidation level. Consequently, it was essential to develop characterization tools "in situ" such as the Time Resolved X-ray Diffraction (TRXRD), with an X-ray synchrotron beam (H10, LURE Orsay) coupled to an infrared thermography to study simultaneously structural transformations and thermal evolutions. From the 2003 experiments, we took the opportunity to modify the sample-holder in order to reproduce the better synthesis conditions of the MAFAPAS process, but without the conso…

Anomalous Valence Contrast of Metal Transition in Nanocrystalline Ferrite

New insight on the lithium hydride–water vapor reaction system

Abstract The reaction of lithium hydride (LiH) powder with pure water vapor (H2O and D2O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 μm. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li2O). Then, both Li2O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li2O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li2O at the LiH/Li2O interface and through the consumption of Li2O and the formation of LiOH at the Li2O/LiOH interface. Above 10 hPa, only the monohydrate LiOH·H2O is formed. T…

Spark plasma sintering of cobalt ferrite nanopowders prepared by coprecipitation and hydrothermal synthesis.

International audience; Cobalt ferrite exhibits a high coercivity at room temperature and a strong magnetic anisotropy compared to the other spinel ferrites and, consequently appears as an interesting material for permanent magnets and high-density recording. The magnetic properties depend also on the crystallite size. In order to keep the powder properties in a bulk material, dense nanostructured cobalt ferrite has to be sintered. A field activated sintering process like spark plasma sintering (SPS) may be promising for such challenge. The present paper deals with: (i) the preparation of cobalt ferrite by two methods: coprecipitation and hydrothermal synthesis in supercritical water; (ii) …

Synthesis of FeAl Hetero-Nanostructured Bulk Parts via Spark Plasma Sintering of Milled Powder

AbstractSpark plasma sintering (SPS) has been used in order to introduce nanocrystalline grains within fully dense FeAl consolidated parts. Hetero-nanostructured parts, consisting of nano, ultrafine and micrometric grains, have been successfully processed when milled - Y2O3 reinforced - FeAl powder was used. The large temperature differences that are spontaneously generated during the SPS process as well as the use of milled powder account for the formation of such interesting structures. The grain size distribution - that is suggested to be very potent to improve both strength and ductility - could be significantly modified by a proper selection of sintering temperature and holding time.

Experimental Equipment for Studying the Residual Stresses Developed During High Temperature Reactions by X-Ray Diffraction

This paper describes a device dedicated to studyng, by X-ray diffraction the residual stresses developed on surface samples as a function of temperature and atmosphere conditions. The setup consists of : a.) an horizontal axis goniometer which allows the programmed positionning of the sealed X-ray source and of the linear detector. b.) a high temperature controlled atmosphere chamber Particular attention has been paid to the thermal stability up to 1200°C and the accurate position on the sample.

In-situ time resolved X-ray diffraction study of the formation of the nanocrystalline NbAl3 phase by mechanically activated self-propagating high-temperature synthesis reaction

The mechanically activated self-propagating high-temperature synthesis (MASHS) technique was used to produce a NbAl3 intermetallic compound. This process results from the combination of two steps: a mechanical activation of the Nb 3Al powder mixture which is followed by a self-propagating high-temperature synthesis (SHS) reaction, induced by the exothermal character of the reaction Nb3Al. An original experiment was designed to study in-situ the formation of the NbAl3 phase in the combustion front: time-resolved X-ray diffraction coupled with an infrared imaging technique and a thermocouple measurement were performed to monitor the structural and thermal evolution during the SHS reaction. Ow…

Phénomènes de ségrégation dans les ferrites de titane nanométriques : apports complémentaires de différentes techniques expérimentales (DRX, XPS, EXAFS ...)

Grâce a la complementarite de diverses techniques deux phenomenes de segregation ont ete mis en evidence dans les ferrites de titane nanostructures: une segregation cinetique (dite dynamique) et une segregation thermodynamique. Par des techniques d'analyse locales (MET, XPS) et statistiques (DRX...), des heterogeneites au sein des grains de poudre contenant des cations Fe 2+ ont ete mises en evidence lors de leur etude a l'air. Leur origine est cinetique et decoule d'une oxydation incomplete des cations Fe 2+ . Des affinement de Rietveld de diagrammes de diffraction des rayons X et diffraction de neutrons ont permis de montrer quant a eux que le titane ainsi que toutes les lacunes creees lo…

Dense nanostructured materials obtained by spark plasma sintering and field activated pressure assisted synthesis starting from mechanically activated powder mixtures

The preparation of highly dense bulk materials with a grain size in the range of a few to a few hundreds nanometers is currently the objective of numerous studies. In our research we have achieved a measure of success in this regard by using the methods of mechanically-activated, field-activated, pressure-assisted synthesis, MAFAPAS, which has been patented, and mechanically-activated spark plasma sintering, MASPS. Both methods, which consist of the combination of a mechanical activation step followed by a consolidation step under the simultaneous influence of an electric field and mechanical pressure, have led to the formation of dense nanostructured ceramics, intermetallics, and composite…

In-situ time-resolved X-ray diffraction experiments applied to self-sustained reactions from mechanically activated mixtures

Resume . Le procede MASHS (Mechanically activated self-propagating high-temperature synthesis) apparait etre un procede alternatif interessant pour elaborer des materiaux tels que des ceramiques, des composites ou des intermetalliques. La formation au cours d'une reaction de combustion autoentretenue d'intermetalliques, tels que NbAlj et M0S12, a ete suivie in-situ et en temps reel en couplant la diffraction des rayons X, produits par le rayonnement synchrotron (Ligne D43, LURE - Orsay) et, une thermographie infrarouge. A partir de temps d'acquisition tres courts (de 30 ms a 100ms par diffractogrammes), il a ete possible de determiner simultanement les evolutions structurales et thermiques.…

Experimental investigation on lithium borohydride hydrolysis

Abstract Lithium borohydride, one of the highest energy density chemical energy carriers, is considered as an attractive potential hydrogen storage material due to its high gravimetric hydrogen density (19.6%). Belonging to borohydride compounds, it presents a real issue to overcome aims fixed by the U.S. Department of Energy in the field of energy, and so crystallizes currently attention and effort to use this material for large scale civil and military applications. However, due to its important hygroscopicity, lithium borohydride is a hazardous material which requires specific handling conditions for industrial aspects. In order to understand much more the reaction mechanism involved bet…

Oxidation resistance of Ti 3 AlC 2 and Ti 3 Al 0.8 Sn 0.2 C 2 MAX phases: A comparison

Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phase powders are densified using Spark Plasma Sintering technique to obtain dense bulk materials. Oxidation tests are then performed over the temperature range 800-1000°C under synthetic air on the two different materials in order to compare their oxidation resistance. It is demonstrated that, in the case of the Ti3Al0.8Sn0.2C2 solid solution, the oxide layers consist in TiO2, Al2O3 and SnO2. The presence of Sn atoms in

Cation Distribution in a Titanium Ferrite Fe2.75Ti0.25O4Measured byin-SituAnomalous Powder Diffraction Using Rietveld Refinement

Many ferrites contain different cations with various valence states and location in the spinel structure. In compounds such as these, only a combination of different techniques such as Mussbauer spectroscopy, IR analysis, and thermogravimetry allows the distribution of cations to be obtained. For very complicated distributions, the mathematical decomposition of derivative thermogravimetric curves (DTG) leading to quantitative distribution is uncertain. In this paper, we present an alternative technique based on resonant diffraction. The anomalous scattering of each cation in the crystalline material is used to determine its amount and position by Rietveld refinement. Since the energy for su…

Synthesis of nanocrystalline NbAl3 by mechanical and field activation

Abstract The mechanically-activated, field-activated, and pressure-assisted synthesis (MAFAPAS) process, which combines the simultaneous synthesis and densification of nanophase materials, was utilized to produce nanocrystalline NbAl3 material from Nb+3Al mechanically activated powders. Nb+3Al elemental powders were co-milled for a short time in a specially designed planetary ball mill to obtain nanoscale distributed reactants but to avoid the formation of any product phases. These were then subjected to high AC currents (1500–1650 A) and uniaxial pressures (56–84 MPa). Under these conditions, a reaction is initiated by field activation and completed within a short period of time (3–6 min).…

Synthesis of YAG nanopowder by the co-precipitation method: Influence of pH and study of the reaction mechanisms

International audience; YAG nanopowders with an average grain size of 30 nm have been successfully synthesized by the co-precipitation method using nitrates with precipitant of ammonium hydrogen carbonate. The influence of precipitation conditions such as pH, aging time and calcination temperature on the formation of secondary phases has been studied. The accurate control of pH value at every stage of precipitation process is crucial to avoid the presence of YAM (Yttrium Aluminium Monoclinic, Y4Al2O9) and yttrium oxide (Y2O3) after calcination. The reaction mechanisms have been investigated using different techniques such as infrared spectroscopy, x-ray diffraction and thermal analyses. The…

Dense Mosi2 produced by reactive flash sintering: Control of Mo/Si agglomerates prepared by high-energy ball milling

The objective of this work is to determine the influence of the agglomeration state of the MA mixture on the microstructure and the chemical composition of SPS end-products. In order to produce MoSi2 with a microstructure and a density perfectly controlled via reactive sintering implying an SHS reaction, the characteristics of Mo/Si mechanically activated (MA) powder mixtures were investigated. Indeed, the MA powders have been characterized in terms of their surface specific area, size, phase composition and microstructure. The high-energy milling allows the formation of agglomerates (0.8 to 800 μm) composed of nanometric crystallites of molybdenum and silicon, as a consequence of a continu…

Effect of coherency of domain walls on X-ray diffraction diagrams: Case a crystal with a low tetragonality

Les diagrammes de diffraction des rayons X d'une poudre ou d'une ceramique de BaTiO 3 tetragonal ont ete etudies. Une correlation entre les caracteristiques des profils des raies de diffraction (intensite, forme, position,...) et la microstructure en domaines ferroelectriques a ete mise en evidence. A partir d'une approche numerique, le calcul des diagrammes de diffraction montre que la modification des profils des raies de diffraction du compose tetragonal est fortement dependante de la microstructure en domaines ferroelectriques. Ce a du prendre en compte l'existence d'un certain degre de coherence dans les murs de domaines entre deux domaines a 90° adjacents. Il a par ailleurs ete mis en…

Reactive Sintering of molybdenum disilicide by Spark Plasma Sintering from mechanically activated powder mixtures: Processing parameters and properties

Abstract Dense molybdenum disilicide with a nano-organized microstructure was synthesized by mechanical activation, by producing nanostructured agglomerates of a 1:2 mixture of Mo and Si, followed by the synthesis/consolidation in one step using SPS technology. In order to synthesize a dense molybdenum disilicide with a perfectly controlled microstructure, an investigation of the influence of Spark Plasma Sintering processing parameters (temperature, heating rate, mechanical pressure and holding time) on the chemical composition and the microstructure characteristics has been performed. The present work shows also that the so-obtained materials present better oxidation resistance in compari…

Sintering of copper nanopowders under hydrogen: an in situ X-ray diffraction analysis.

Abstract The reduction by hydrogen gas of the cuprite layer on copper nanocrystals and the subsequent sintering of the nano-particles were studied using in-situ X-ray diffraction and dilatometry. Spherical nanocrystals produced by evaporation and condensation have an average size of 35 nm, exhibiting a large surface curvature. Each nanoparticle is coated with a 3.5 nm layer of Cu 2 O, which is rough and disordered, as revealed by high-resolution electron microscopy. Reduction by hydrogen of this curved cuprite layer occurs at 363 K, which is ≈65 K lower than is observed on a layer supported by micrometer-sized or bulk copper with a flat surface. The reduction process and its effect on the s…

Continuous hydrothermal synthesis of inorganic nanopowders in supercritical water: towards a better control of the process

International audience; A hydrothermal synthesis process working in supercritical conditions (T > 374 °C, P > 22 MPa) and in a continuous mode has been developed for inorganic nanopowder synthesis. This paper presents a review of the past 5 years of research conducted on this process. Numerous materials (oxides: ZrO2, TiO2, Fe2O3..., ferrites: Fe2CoO4..., or BaZrO3) were obtained with specific features. Some technical issues have been solved, that are presented here. Heat transfer was studied, leading to a more efficient design of the reactor. Future developments have been examined through process engineering, in which our group is engaged, especially through CFD modelling.

Sources d'hétérogénéité d'un assemblage par soudage par diffusion homogène de tôles en acier austénitique inoxydable

Ce document presente un apercu des heterogeneites de microstructure aux interfaces qui peuvent etre rencontrees lors du soudage par diffusion homogene d'un assemblage de toles. Un assemblage homogene a finalement ete realise avec l'obtention de proprietes mecaniques tres satisfaisantes. Pour finir, une piste de reflexion est apportee afin d'ameliorer les proprietes des assemblages.

Electrochemical behavior of nanocrystalline iron aluminide obtained by mechanically activated field activated pressure assisted synthesis

Abstract The corrosion behavior of nanocrystalline iron aluminide obtained by mechanically activated field—activated pressure—assisted synthesis was investigated in sulphuric acid media using potentiodynamic curves. The effect of microstructure on the electrochemical corrosion resistance was investigated by examining samples which were heat treated to effect a change in crystallite size and microdistorsion.

Spark Plasma Sintering tool design for preparing alumina-based Functionally Graded Materials

Abstract A way to produce Functionally Graded Materials (FGM) is by means of Spark Plasma Sintering (SPS) and specifically designated tools. These new tools permit a current density modulation and therefore a temperature variation along the z-axis. The key feature relies on a varying die section. FEM modelling has given the suitable range of die dimensions between the top and the bottom to obtain a given temperature gradient (around 300 °C) out of roughly a 15 mm height. Experiments conducted in different configurations (with or without samples) and the measurement of the associated thermal gradient led to improvements of the mould (in particular the introduction of a counter-piston). By th…

Influence of Twinning Microstructure of Crystals with Low Tetragonality on a X-Ray Diffraction

The intensity distributions of the X-rays scattered in the tetragonal single crystal, which represent a complex of the twin domains separated by the coherent parallel boundaries, are simulated. The calculations are performed by using the Monte Carlo method within the framework of a kinematical approach. The thickness distributions of the twin domains are defined according to the geometrical, Gaussian and log normal functions. ‘Critical’ effects of the X-ray scattering are found, namely there is transformation of the tetragonal doublet into singlet or multiplet. As demonstrated, each of characteristics of the tetragonal doublet profile depends on a few parameters of the twin microstructure o…

Bulk FeAl nanostructured materials obtained by spray forming and spark plasma sintering

Abstract This paper examines the efficiency of two consolidation processing techniques high velocity oxy-fuel (HVOF) spray forming and spark plasma sintering (SPS) which allow to obtain bulk dense nanostructured materials. An oxide dispersion strengthened (ODS) Fe–40Al (at.%) based milled powder (with a nanostructure

Cation Distribution in Ferrites with Spinel Structure Measured by Anomalous Powder Diffraction

Spark Plasma Sintering of Metallic Glasses

Spark plasma sintering (SPS) of metallic glasses (MG) can be quite different from sintering crystalline metallic alloys. Indeed, MG behave differently with increasing temperature, as they encounter a glass transition and devitrification. Their shaping can thus be compared to what can be performed on thermoplastic polymers. SPS is a promising way to prepare bulk parts from amorphous powders, since it allows very fast heating and cooling rates. It gives an advantage to avoid or limit devitrification of the amorphous phase upon the thermal cycle. However, diffusion mechanisms, which generally control densification, are activated at temperatures that are not compatible with MG structural integr…

Utilisation de la diffraction résonnante pour déterminer la distribution cationique d'un ferrite de titane nanométrique

Les proprietes magnetiques des ferrites de structure spinelle dependent, entre autres, de la distribution cationique dans la maille. La connaissance de cette repartition a pu etre obtenue dans le cas d'un ferrite substitue au titane en utilisant la diffraction anomale de poudre couplee avec un affinement structural de type Rietveld, methode qui est le fruit des dernieres avancees effectuees autour du rayonnement synchrotron.

Simultaneous Synthesis and Consolidation of Nanostructured MoSi2

A new process combining electric field activation and the imposition of pressure from mechanically activated powder mixtures is demonstrated as a means to simultaneously synthesize and densify nano-MoSi2 in one step. Nanophase reactants (Mo + 2Si) produced by mechanical activation are reacted by field activation with the simultaneous application of a uniaxial pressure. Mo + 2Si powders were comilled in a specially designed planetary mill to obtain nanometric reactants but to avoid formation of any product phases. These were then subjected to high alternating currents (1600 A) and pressures of 106 MPa. Under these conditions, a reaction is initiated and completed within a short period of tim…

Experimental investigation of the grain size dependence of the hydrolysis of LiH powder

International audience; The hydrolysis reaction of LiH powder has been investigated in order to determine the products, rates and mechanisms of this reaction and the influence of the experimental parameters. Raman spectroscopy, X-ray diffraction and gravimetric analysis were used. It was shown that the product of hydrolysis was the hydroxide of lithium (LiOH) for low partial pressure of water (≈50 Pa) and LiOH*H2O for a higher partial pressure of water (>2000 Pa). Moreover, data obtained using gravimetric analysis inside a glove box containing a controlled partial pressure of water (500 ppmv/50 Pa at 25 °C) were used to determine the rate of the reaction versus particle size. The experiment…

Sintering of lead phospho-vanadate by spark plasma sintering

International audience

Enhancement of self-sustaining reaction by mechanical activation: case of an FeSi system

Mechanical high energy ball milling of an Fe2Si elemental powders mixture was used to activate a self sustaining combustion reaction or so-called self-propagating high-temperature synthesis (SHS) to form iron disilicide, a reaction for which the thermodynamic criterion is not favorable. A complete characterization of the milled powders before reaction was performed with energy dispersive X-ray spectrometry, specific surface measurements and X-ray diffraction profile analysis. Thermal and structural information describing the combustion front initiated by heating up a sample to 400°C in a Fe‐Si system is communicated. In order to isolate the phases involved in the gasless reaction, a time-re…

Combustion synthesis of MoSi2 and MoSi2–Mo5Si3 composites: Multilayer modeling and control of the microstructure

International audience; In this work, we present a multilayer modeling for the formation of molybdenum silicides in the exothermic reaction between Mo and Si under the influence of a temperature pulse. The heating rate can either be a well-controlled ramp or be generated spontaneously by the propagation of a combustion synthesis front. The model addresses the specific situation above the melting point of silicon and describes the solid–liquid reaction taking place in a single representative particle of molybdenum surrounded by the melt of silicon. We obtain a set of kinetic equations for the propagation of the interfaces between the different layers (Mo/Mo5Si3 and Mo5Si3/MoSi2) in the solid…

Production of dense nanostructured materials using FAPAS and SPS techniques

International audience

Mechanically Activated SHS Reaction in the Fe-Al System: In Situ Time Resolved Diffraction Using Synchrotron Radiation

The Mechanical Activation Self propagating High temperature Synthesis (M.A.S.H.S.) processing is a new way to produce nanocrystalline iron aluminide intermetallic compounds. This process is maily the combination of two steps ; in the one hand, a mechanical activation where the Fe - Al powder mixture was milled during a short time at given energy and frequency of shocks and in the other hand, a Self propagating High temperature Synthesis (S.H.S.) reaction, for which the exothermicity of the Fe + Al reaction is used. This fast propagated MASHS reaction has been in -situ investigated using the Time Resolved X - Ray Diffraction (TRXRD) using a X - ray synchrotron beam and an infrared thermograp…

One-Step Synthesis and Consolidation of Nanophase Iron Aluminide

The simultaneous synthesis and densification of nanophase iron aluminide is investigated. Elemental nanophase reactants produced by mechanical activation were reacted by field activation with the simultaneous application of uniaxial pressure. The process was demonstrated in this work by the synthesis of dense nanometric FeAl. Iron and aluminum powders were co-milled in a specially designed planetary mill to obtain nanometric reactants and to avoid formation of any product phases. These powders were then subjected to high AC currents (1250–1500 A) and pressures in the range of 70–106 MPa. Under these conditions, a reaction was initiated and completed within a short period of time (2.5–3.5 mi…

Synthesis of niobium aluminides using mechanically activated self-propagating high-temperature synthesis and mechanically activated annealing process

The mechanically activated self-propagating high-temperature synthesis (MASHS) technique and the mechanically activated annealing process (M2AP) were used to produce NbAl3 intermetallic compound. The MASHS process results from the combination of two steps: first, a mechanical activation of the Nb 3Al powders mixture; second, a self-propagating high-temperature synthesis (SHS). The M2AP process also results from the combination of two steps: the first is the same; the second consists of the annealing of as-milled powders. Based on X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDXS), the as-milled powders, MASHS, and M2AP end-pr…

Influence of the pH on the ZnO nanoparticle growth in supercritical water: Experimental and simulation approaches

Abstract In order to improve the knowledge on the nucleation and the growth mechanisms of metal oxides nanoparticles produced in supercritical water domain, ZnO was used as a “model” material. A continuous process of hydrothermal synthesis was employed to synthesize ZnO nanopowders ( T  = 410 °C and P  = 305 bar) from Zn(NO 3 ) 2 and KOH solutions with different values of [KOH]/[Zn(II)] ratio from 0 to 8 in order to investigate the pH effect on the growth of ZnO nanocrystallite in terms of size and morphology. The samples were characterized by X-Ray Diffraction and Transmission Electronic Microscopy. ZnO crystal was considered as a cylindrical crystallite with a diameter D and height H . Es…

Correlation between ball milling conditions and planar effects on Cu-nanostructured powders

It is most often proposed that the process of ball milling introduces a variety of defects (vacancies, dislocations, grain boundaries, stacking faults,...) which raise the free energy of the system making it possible to produce metastable phases. But there are very few investigations that deal with the characterization and quantification of the defects produced in milled powders. XRD is really a valuable technique for a characterization in terms of size and morphology of crystallites and imperfections. In this paper, a new line profile analysis method is proposed in order to take into account the dependence of the crystallite size, of the residual strains as well as of the planar defects, o…

Advanced Usage of SPS Technology for Producing Innovative Materials

MoSi2 Formation Mechanisms during a Spark Plasma Synthesis from Mechanically Activated Powder Mixture

Mechanical Activation as a New Method for SHS

The use of mechanical activation (the elemental powder mixture is milled for a short time at given frequency and impact energy) as a precursor to self-propagating high-temperature synthesis (SHS) results in the formation of nanostructured porous materials. The mechanical activation step was found necessary (i) to modify the thermal parameters of the combustion front (i.e. combustion front velocity, thermal heating rate…) in the cases of Mo-Si, Fe-Al, Ni-Si (ii) to initiate a combustion front in the case of systems having a low exothermicity. Nevertheless, the control of the mechanically activated mixture characteristics and, the understanding of the mechanical activation role on the SHS par…

Diffraction anomale et composition cationique d'une titanomagnétite nanométrique

Les ferrites substitues au titane constituent des materiaux interessants pour aller vers la comprehension des reactions d'oxydo-reduction qui ont lieu dans ces composes de structure spinelle. Ces composes synthetises par chimie douce on ete etudies in-situ par diffraction anomale dans diverses conditions. Dans le cas particulier du compose Fe 2.5 Ti 0.5 O 4 , les premiers resultats montrent que cette methode de synthese ne permet pas d'elaborer directement le ferrite avec la composition esperee. En effet l'analyse structurale met en evidence un taux de titane bien inferieur a 0.5 alors que d'autres techniques,(analyse ICP, methode de Poix), confirment ce taux de substitution.

Powder metallurgy processing and deformation characteristics of bulk multimodal nickel

cited By 7; International audience; Spark plasma sintering was used to process bulk nickel samples from a blend of three powder types. The resulting multimodal microstructure was made of coarse (average size ∼ 135 μm) spherical microcrystalline entities (the core) surrounded by a fine-grained matrix (average grain size ∼ 1.5 μm) or a thick rim (the shell) distinguishable from the matrix. Tensile tests revealed yield strength of ∼ 470 MPa that was accompanied by limited ductility (∼ 2.8% plastic strain). Microstructure observation after testing showed debonding at interfaces between the matrix and the coarse entities, but in many instances, shallow dimples within the rim were observed indica…

Microstructure-oxidation resistance relationship in Ti3AlC2 MAX phase

International audience; Spark Plasma Sintering and Hot Isostatic Pressing were used to synthesize coarse-grained and fine-grained Ti3AlC2 specimens. Moreover, Spark Plasma Sintering processing parameters were modified in order to vary the TiC, Al2O3 and TixAly impurity and the porosity contents in the fine-grained samples. The influence of the Ti3AlC2 microstructure on the oxidation resistance was assesed. It is demonstrated that the grain size can drastically modify the oxidation resistance. The higher density of grain boundaries, in fine-grained specimens, increases the number of Al diffusion paths and leads to the formation of a protective alumina scale. In coarse-grained sample, Al diff…

The mechanically activated combustion reaction in the Fe–Si system: in situ time-resolved synchrotron investigations

Mechanical high-energy ball milling of Fe+2Si elemental powder mixtures was used to activate self sustaining combustion reaction in the case of iron disilicide synthesis. The reaction path as well as the influence of the microstructural parameters on phase transformation have been investigated in detail. Time-resolved X-ray diffraction (TRXRD) using the fast recording kinetics offered by the synchrotron radiation was coupled to an infrared camera in order to study the internal structure of the combustion wave. The crystallite size and the amount of mechanically induced phases play an important role during the combustion; the reaction path and the end product composition mainly depend on the…

Synthesis of bulk FeAl nanostructured materials by HVOF spray forming and Spark Plasma Sintering

Abstract This paper examines the efficiency of two consolidation processing techniques: High Velocity Oxy-Fuel (HVOF) spray forming and Spark Plasma Sintering (SPS) to obtain bulk nanostructured materials from an Y 2 O 3 reinforced Fe–40Al (at.%) milled powder. The microstructures of the sintered end-products were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) in order to gain new insights in their microstructure formation mechanisms. HVOF spray forming is more effective to retain fine nanograins, in particular within retained unmelted powder particles. The drawbacks of this technique are that it inevitably leads to a high fraction of porosity…

Caractérisation de poudres de zircone synthétisées par voie hydrothermale

La synthese hydrothermale permet la realisation de poudres fines cristallisees et desagglomerees Ces qualites sont appropriees a l'elaboration de composites fins oxyde/oxyde par synthese simultanee des deux phases. Nous avons developpe ce protocole pour la realisation de nanocomposites ahrmine/zircone (Q). Nous presentons ici plus particulierement le travail effectue sur la zircone, Les conditions de traitement hydrothermal et d'un traitement thermique modere supplementaire sont analysees en relation avec les caracteristiques des poudres synthetisees. Differentes techniques complementaires sont utilisees pour ces poudres de zircone: diffraction des rayons X (% de la phase quadratique, taill…

CFD simulation of ZnO nanoparticle precipitation in a supercritical water synthesis reactor

International audience; Continuous hydrothermal flow synthesis process has shown great advantages concerning the control of particle size and morphology through the optimization of supercritical water processing parameters. In particular, micromixing is a key issue of the process for controlling the nucleation mechanism. A Computational Fluid Dynamics (CFD) model is suggested for nanoparticle size determination using a population balance approach. Models for reaction kinetics, thermodynamics, nucleation and growth are presented. The effects of base concentration and hydrodynamics are investigated. Results show that the CFD may be valuable simulation tool for controlling the size and the sha…

Hydrothermal growth of ZnO nanostructures in supercritical domain: Effect of the metal salt concentration (Zn(NO3)2) in alkali medium (KOH)

Abstract The metal salt concentration effect on the size and morphology of ZnO NPs was highlighted through its synthesis thanks to a continuous one-step method at 401 ± 15 °C and 306 ± 8 bar. Experiments were performed from Zn(NO3)2 and KOH as reactants in concentration ranges of 10–480 mM and 40–1920 mM, respectively. A constant [KOH]/[Zn(NO3)2] ratio of 4 was fixed in order to maintain a constant pH value between 12.5 and 13.0. The as-prepared NPs were characterized by X-ray diffraction and (high-resolution) transmission electron microscopy. Based on Louer's method, ZnO crystal exhibiting a hexagonal structure was considered as cylinder with a diameter D and a height H. The D/H parameter …

Mechanical, thermal and electrical properties of nanostructured CNTs/SiC composites

International audience; Dense SiC-based nanostructured composites reinforced by well-distributed carbon nanotubes (CNTs) were elaborated for the first time by spark plasma sintering (SPS) without sintering additive. Microstructures of materials containing different amounts of CNTs – up to 8.0 vol% – were correlated with their mechanical, electrical and thermal properties. A continuous decrease of the SiC grain size was observed when the amount of CNT was increased, while the evolution of density showed a different behavior that could be explained by the particular combination of SPS technique with the electrical resistivity evolution of the green bodies. Optimal effect of CNTs addition on h…

Enhancement of self-sustaining reaction Cu3Si phase formation starting from mechanically activated powders

Mechanical high-energy ball milling of an 3Cu Si elemental powders mixture was used to activate a self-sustaining combustion reaction or so-called self-sustaining high-temperature synthesis (SHS) to form the copper silicide phase, a reaction for which the thermodynamic criterion proposed by Munir for self-propagation reaction is not favorable. A complete characterization of the end-products was performed with X-ray diffraction analysis and scanning electron microscopy. Thermal and structural information describing the combustion front initiated by heating up a sample to 180°C in a Cu:Si system is communicated. This paper clearly shows that the mechanically activated self-sustaining high-tem…

Peculiarities of X-Ray Diffraction in Crystals with Diffuse Boundaries of Twin on System {011}, <011>

Investigation of mechanically activated field-activated pressure-assisted synthesis processing parameters for producing dense nanostructured FeAl

The parameters of the mechanically activated field-activated pressure-assisted synthesis (MAFAPAS) process, which were recently developed and patented for producing dense nanostructured materials, were studied in the case of the B2-FeAl intermetallic. Based on x-ray diffraction (XRD) experiments, residual stresses XRD analysis, relative density measurement, and secondary-electron microscopic observations, the optimal synthesis conditions (time, current intensity, and pressure) were studied. Fe + Al powders were comilled in a specially designed planetary mill to obtain a mixture of reactants at the nanoscale without the formation of any product. The milled mixtures were then subjected to a h…

Mechanical activation conditions of the Fe2O3 and V2O3 mixture powders in order to obtain a nanometric vanadium spinel ferrite

Abstract Co-milling of iron and vanadium oxides allows to obtain an intimate oxides mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500°C and 10−25 Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with the only spinel phase. The characterization of the powders is achieved by X-ray diffraction (XRD), scanning electron microscopy, infrared (IR) spectrometry, thermogravimetry and calorimetry. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain size.

Développements récents de l'étude en temps réel par diffraction des rayons X couplée à une thermographie infrarouge : application au suivi de la réaction MASHS dans les systèmes FeAl, et MoSi2

La formation au cours d'une reaction de combustion autoentretenue et mecaniquement activee (MASHS) d'intermetalliques nanometrique, tels que les composes FeAl et MoSi 2 , a pu etre observee in-situ et en temps reel en couplant la diffraction des rayons X, produit par rayonnement synchrotron, et une thermographie infrarouge. La mise en oeuvre d'une telle experience est indispensable en raison de la vitesse importante (10 mm/s) de propagation du front de combustion. Des developpements recents realises au niveau des systemes de detections permettent d'obtenir des temps d'acquisition tres courts (quelques dizaines de millisecondes) et de reveler des etapes intermediaires au cours de la transfor…

Characteristics of LiFePO4 obtained through a one step continuous hydrothermal synthesis process working in supercritical water

International audience; The olivine-like material LiFePO4 was prepared via a continuous hydrothermal synthesis process working from subcritical to supercritical water conditions. The influence of some processing parameters–temperature and reaction time–was investigated in terms of material purity, grain size and morphology. Supercritical conditions were found to be attractive to synthesize in one step a well-crystallized material without impurities. The primary particles size was in the nanometric range. They showed a natural tendency to form micron size agglomerates, which were supposed to be the cause of the limited capacity, as demonstrated through a cross study using laser particle size…

Microstructural study of titanium carbonitride elaborated by combustion synthesis

Abstract The self-propagating high-temperature synthesis (S.H.S.) process, which is promising for the fabrication of ceramic materials, was chosen to elaborate titanium carbonitride materials. The influence of parameters such as nitrogen gas pressure and carbon ratio on the microstructure was studied. A single phase product of Ti(C,N) is obtained for a carbon ratio under 15 at.% and a nitrogen pressure of 36 MPa. The increase of the carbon ratio corresponds to a decrease of the maximum temperature reached during the synthesis. Time resolved X-ray diffraction measurements (TRXRD) with the synchrotron radiation were used to determine the reaction mechanisms. We could observe that the synthesi…

Investigation of the SHS mechanisms of titanium nitride by in situ time-resolved diffraction and infrared thermography

Abstract The self-propagating high-temperature synthesis (SHS) or combustion synthesis is a promising process to produce advanced ceramics due to the high purity of the elaborated materials and the very short synthesis time. Titanium nitride has been synthesised from pressed titanium powder and a nitrogen gas flow under a 0.1 MPa pressure. The influence of the addition of a TiN diluent was investigated. For the first time, SHS reaction mechanisms were determined from in situ time-resolved X-ray diffraction (TRXRD) experiments using the synchrotron radiation. These experiments were coupled with infrared thermography to study the propagation of the combustion reaction. It appeared that the in…

Original Supercritical Water Device for Continuous Production of Nanopowders

Well-crystallized ZnO, ZrO2, TiO2, CeO2, Y2O3 and La2O3 nanoparticles are synthesized under supercritical water conditions (T > 647 K and P > 22.1 MPa) using a home-made continuous process. At room temperature, metallic salts with or without aqueous hydroxide solution (KOH or NaOH) are pressurized to 25–30 MPa. Then, the reactant(s) is/are rapidly heated to 673–773 K by mixing with the supercritical water in a patented reactor. Residence time is in the range from 2 to 8 s. XRD, TEM and surface area analyses highlight the production of pure and well-crystallized nanoparticles with a uniform size distribution.

Role of the Microstructure on the High Temperature Oxidation Properties of the Intermetallic Compound NbAl<sub>3</sub>

The influence of the NbAl 3 microstructure on its oxidation mechanism was investigated in air under atmospheric pressure over the temperature range 500-1080°C. Different processing techniques as induction melting and mechanically-activated annealing processes (M2AP) were used to produce the intermetallic compound NbAl 3 . A protective external alumina scale grew only on Al-enriched NbAl 3 between 700 and 1080°C. Stoichiometric NbAl 3 exhibited the pesting phenomenon between 550-900°C, whereas a non protective lamellar oxide scale formed above 900°C. The proposed oxidation mechanism explains these observations which are in agreement with the oxidation study of powders with different crystall…

Deposition and characterization of cold sprayed nanocrystalline NiTi

International audience; Binary 50Ni–50Ti mixture was prepared by mechanical alloying from elemental powders. After 48 h of milling, the nanocrystalline B2-NiTi powder was produced. Then, this as-milled powder was deposited by cold spraying in order to produce a target which can be used to create thin films by magnetron sputtering technique. The objective is to improve the electrical characterizations of the NiTi/SiO2/Si M.O.S structures. Themorphology evolution of the powder particles, the phase identification and the alloying evolution process as function of milling time were studied using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. In addition, th…

Correlation between milling parameters and microstructure characteristics of nanocrystalline copper powder prepared via a high energy planetary ball mill

The microstructure evolution of Cu-nanostructured powders versus the ball milling conditions was investigated by whole peak profile powder pattern modeling method. This method allows defining in some approach the characteristics of as-milled Cu powder microstructure in terms of crystallite size, type and density of dislocations and twin faults density. It is shown that the change of microstructure characteristics of as-milled Cu powder versus the ball milling conditions (under constant time of the ball milling) depend on only some energy parameters of the milling, for example, average size of crystallite is uniquely defined by energy of the shock, whereas the portion of edge and screw compo…

Nanocrystalline FeAl Synthesis by MASHS with <i>In Situ</i> and Post Mortem Characterizations

From nanostructured powders to dense nanostructured materials: Mechanically activated powder metallurgy

Residual Stresses and Reactivity of Solids. Determination and Part Plaid in the Reaction Mechanisms

Thermal-electrical-mechanical simulation of the nickel densification by Spark Plasma Sintering. Comparison with experiments

Abstract Spark Plasma Sintering is a non-conventional process of the powder metallurgy field which uses a high electrical current to rapidly produce fully dense materials. In the present paper, a thermal-electrical-mechanical model developed on ABAQUS Software is proposed to simulate the densification of a nickel disk. A compaction model, studied in [Wolff, C., Mercier, S., Couque, H., Molinari, A., 2012. Modeling of conventional hot compaction and spark plasma sintering based on modified micromechanical models of porous materials. Mechanics of Materials 49 (0), 72–91. URL http://www.sciencedirect.com/science/article/pii/S0167663611002195 ], has been used to reproduce the densification of t…

In situ study of the sintering of a lead phosphovanadate in an Environmental Scanning Electron Microscope

cited By 3; International audience; The in situ sintering of a powder of Pb3(VO4) 1.6(PO4)0.4 composition was performed in an Environmental Scanning Electron Microscope. The electric current induced by the electron beam was found to reduce the effective temperature of sintering as well as to accelerate the kinetics of shrinkage of a cluster composed of sub-micrometric grains of material. The presence of the residual current flow in the cluster during observation for in situ experiments helps to reduce the apparent sintering temperatures from 50 to 150 °C compared to conventional heating conditions without current. © 2011 Elsevier B.V. All rights reserved.

Assisted self-sustaining combustion reaction in the Fe–Si system: Mechanical and chemical activation

Abstract This work presents original investigations carried out to improve the activated self-propagating high-temperature synthesis (SHS) process in the Fe–Si system: different ignition modes are tested (volume heating as opposed to a local ignition source), and the use of additive is considered in order to enhance the SHS type reactivity in the Fe–Si system. When 20 wt.% of KNO 3 is added to the reactive mixture, the fast (>20 mm s −1 ), stable and self-sustaining combustion reaction produces a very fine FeSi + α-FeSi 2 structure. Infrared thermography (IR) as well as post-mortem analysis (SEM, EDXS, XRD) was used to understand the mechanism behind the chemical activation process when KNO…

Utilisation de la technique de frittage flash pour la synthèse et la densification d'iodoapatites

"Reactivity of Cu3Si of different genesis towards copper(I) chloride"

Abstract A comparative study of the reactivity between copper(I) chloride and three types of Cu 3 Si obtained in a molten medium (Cu 3 Si-Ref) and from mechanical activation following an annealing process (Cu 3 Si-M2AP) or a self-propagating high-temperature synthesis (Cu 3 Si-MASHS) was performed by thermogravimetry under vacuum using non-isothermal and isothermal methods of kinetic measurement. It was established that for the three Cu 3 Si/CuCl systems, the acceleration and decay stages in the temperature range 145–215°C are very closely approximated by an equation of the Prout–Tompkins type where an autocatalytic process was proposed. The lower apparent activation energy obtained for the…

In Situ Determination of the Residual Stress Field Induced by Air Oxidation, up to 1000 °C, in a 20% Cr 5% Al Ferritic Steel, by X-Ray Diffraction

Structure and composition heterogeneity of a FeAl alloy prepared by one-step synthesis and consolidation processing and their influence on grain size characterization.

Abstract This paper aims to characterize a bulk dense FeAl (47 at.%) alloy synthesized and consolidated by one-step current-activated pressure-assisted processing of nanocrystalline elemental powders. The end-product was analyzed using a combination of scanning (SEM) and transmission electron microscopies (TEM), electron back-scattering diffraction (EBSD) as well as electron probe microanalysis (EPMA). Special attention was paid to verify the grain size (32–89 nm) previously determined by X-ray diffraction peak profile analysis. It has been found that this material displays equiaxed grains (0.8–4 μm in size) and contains limited structural defects like subgrains and dislocations. The EPMA r…

Combustion wave structure during the MoSi2 synthesis by Mechanically-Activated Self-propagating High-temperature Synthesis (MASHS): In situ time-resolved investigations

Abstract In situ synchrotron time-resolved X-ray diffraction experiments coupled with an infrared imaging camera have been used to reveal the combustion wave structure during the production of MoSi2 by Mechanically Activated Self-propagating High-temperature Synthesis (MASHS). The fast combustion front exhibits a form described as an ‘equilibrium structure’ where the chemical reaction is the sole major driving force. In the MASHS process, oxide-free interfaces between Mo and Si nanocrystallites enhance the reaction Mo+2Si→MoSi2. Exhaustive time-resolved investigations show a possible solid-state process in the first second of the reaction within the combustion front. If preheating is added,…

Hydrothermal Synthesis of ZnO Crystals from Zn(OH)2 Metastable Phases at Room to Supercritical Conditions

The originality of this work is to highlight the effect of temperature and pressure on the size and morphology of hydrothermal ZnO particles from ambient to supercritical conditions (T > 374 °C and P > 221 bar) using a unique continuous one-step process. Experiments were carried out from zinc nitrate (Zn(NO3)2) and potassium hydroxide (KOH) solutions in the ranges of 1–300 bar and 30–400 °C. The as-prepared particles of ZnO (flower, ellipsoid, and sphere) and e-Zn(OH)2 (polyhedral) sized from nano to micrometers were characterized by X-ray diffraction and electronic microscopy. The wulfingite phase (e-Zn(OH)2) was detected inside some powders especially at room temperature for higher pressu…

Tin-based mesoporous silica for the conversion of CO2 into dimethyl carbonate.

Sn-based SBA-15 was prepared by reacting di-n-butyldimethoxystannane with SBA-15 pretreated with trimethylchlorosilane (TMCS) to cap the external hydroxyl groups. Small-angle X-ray diffraction (SXRD), infrared spectroscopy (IR), nitrogen adsorption/desorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and inductively coupled plasma atomic emission (ICP-AES) measurements allow us to propose that the organotin species are located within the pore channels of the mesoporous host. This novel material catalyzes selectively the coupling of CO(2) with methanol to dimethyl carbonate (DMC). The reaction time-conversion dependence shows that a turnover number (TON) of 1…

Effect of Microstructure on the High Temperature Oxidation and Pesting Behaviour of MoSi<sub>2</sub>

New Ceramics for the Information Storage: Nanoparticles of Titanium Ferrites. Influence of Oxidation and Reduction Reactions upon the Coercivity

Spark plasma synthesis from mechanically activated powders: a versatile route for producing dense nanostructured iron aluminides

Abstract The possibility of mechanically activated spark plasma sintering (MASPS) to perform simultaneously within a very short period of time the synthesis and the consolidation of nanophase iron aluminide from mechanically activated powders of Fe and Al in two different ratio (Fe53 at.% and Fe60 at.%) were confirmed in this work.

Spark Plasma Sintering à partir de poudres mécaniquement activées : compréhension des transitions de phase au cours d'un frittage réactif

International audience; À " basse température " (entre 400 et 600 ◦C), l'oxydation de MoSi2 entraîne sa désintégration en poudre (phénomène de " peste "). De récents travaux ont montré que l'utilisation de MoSi2 dense et nano-organisé permettrait de ralentir ce phénomène de " peste ". Le défi de produire des matériaux denses et nano-organisés peut être relevé par le frittage " flash " réactif sous champ électrique à partir des poudres mécaniquement activées (Mechanically-Activated Spark Plasma Sintering, MASPS). Le contrôle de la composition et de la microstructure du composé intermétallique MoSi2 nécessite de déterminer les paramètres du frittage SPS (température, rampe de montée en tempér…

Investigations of the formation mechanism of nanostructured NbAl3 via MASHS reaction

Abstract The nanostructured NbAl3 intermetallic compound was synthesized using the mechanically-activated self-propagating high-temperature synthesis (MASHS) technique. This process results from the combination of two steps: a short duration ball-milling of a pure elemental Nb+3Al powder mixture followed by a self-propagating high-temperature synthesis (SHS) reaction induced by the Nb+3Al reaction exothermicity. Synchrotron time-resolved XRD coupled with a 2D infrared camera were used to investigate the structural and thermal evolutions during the SHS reaction, and to study in situ the mechanism of NbAl3 formation. The influence of the incoming heat flux and the mechanical activation effect…

Simultaneous IR and time-resolved X-ray diffraction measurements for studying self-sustained reactions.

Self-propagating high-temperature synthesis provides an attractive practical method for producing advanced materials such as ceramics, composites and intermetallics. This kind of reaction has been investigated in situ using time-resolved X-ray diffraction, with an X-ray synchrotron beam (D43 beamline, LURE, Orsay) coupled to simultaneous IR thermography to study structural transformations and thermal evolution. With short acquisition times (30 ms per pattern) it has been possible to observe several steps before obtaining compounds. Two different compound formations have been described: (i) the different steps of reaction, aluminium melting, subsequent temperature increase and fast reaction …

Mechanical activation effect on the self-sustaining combustion reaction in the Mo–Si system

Abstract Nanostructured molybdenum disilicide (MoSi2) was synthesized using an alternative route called MASHS (mechanically activated self-propagating high-temperature synthesis). This original process combines a short duration ball milling (MA) with a self-sustaining combustion (SHS). These two steps were investigated. The microstructure evolution of the powder mixture during mechanical activation was monitored using XRD profile analysis and TEM investigations. Short duration ball milling of (Mo+2Si) powder produces Mo and Si nanocrystallites into micrometric particles. It was demonstrated that pure α-MoSi2 with nanometric structure (DMoSi2=88 nm) could be produced via a very fast combusti…

Processing conditions, microstructure and mechanical properties of hetero-nanostructured ODS FeAl alloys produced by spark plasma sintering

International audience; Spark plasma sintering (SPS) has been used to sinter a milled oxide dispersion-strengthened (ODS) FeAl powder in order to prepare dense nanostructured parts. The effect of processing conditions including sintering temperature, holding time and degassing treatments on the microstructure and mechanical properties of the as-sintered materials was investigated. A hetero-nanostructure that contains nano, ultrafine and micrometric grains was confirmed to be developed whatever the processing window, due to the large temperature difference generated during the SPS process itself. The grain size distribution can be tailored by selecting a combination of sintering temperature …

In situ synchrotron characterization of mechanically activated self-propagating high-temperature synthesis applied in Mo–Si system

Abstract An original experiment was designed to monitor structural and thermal evolutions during the MASHS (Mechanically Activated Self-propagating High-temperature Synthesis) process in the Mo–Si system. Time-Resolved X-Ray Diffraction (TRXRD) coupled with an infrared imaging technique was performed to study, in situ, the formation of the α-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractograms, no intermediate phase was observed during the passage of the combustion front. The only reaction responsible for the self-sustentation is Mo+2Si→MoSi2 in the primary zone inside the combustion wave. The mechanical activation was found to i…