A study of the combustion synthesis of MoSi2 and MoSi2-matrix composites (original) (raw)
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Chemical Engineering Journal, 2008
The possibilities of the synthesis of submicron MoSi 2 and MoSi 2-Si 3 N 4 composite powders were investigated using inorganic salt-assisted combustion synthesis method. Combustion laws in the MoO 3-3Mg-2Si-NaCl and Mo-5Si-NaCl-Si 3 N 4-N 2 systems were studied. The main factors influencing the combustion parameters, phase composition and microstructure of products for both these systems were determined experimentally. Optimum synthesis conditions of submicron MoSi 2 and MoSi 2-Si 3 N 4 composite powders containing 30-40 wt.% of molybdenum disilicide were determined. Compacting conditions for 30 wt.% MoSi 2-70 wt.% Si 3 N 4 composite using the hot pressing technique were found. Compact samples 20 mm in diameter were obtained. Microstructure, phase and chemical compositions of the dense samples were studied.
Combustion Synthesis of Molybdenum Disilicide (MoSi2) Fine Powders
Journal of the American …, 2008
The combustion characteristics of a MoO 3 1SiO 2 1Mg system diluted with sodium chloride have been studied in order to synthesize molybdenum disilicide (MoSi 2) fine powders. The effect of processing variables, including the sodium chloride content and the reactants proportion on the phase composition and microstructure of the final products, was obtained. Both the combustion temperature and the wave velocity decreased with an increase in the amount of sodium chloride. With the appropriate processing parameters, the reacted product consisted of solid crystalline MoSi 2 , and an MgO phase was prepared in the molten sodium halide matrix at 11001-13501C. The final product purification resulted in MoSi 2 powder with a particle size of 100-500 nm. The mechanism of the MoSi 2 formation in the sodium chloride matrix is discussed by analyzing the phase evaluation in the extinguished combustion wave.
Processing, microstructure, properties, and applications of MoSi2-containing composites: a review
Frontiers in Materials
Intermetallic molybdenum disilicide (MoSi2) possesses unique physical, chemical, thermal, and mechanical properties that make it compatible with some ceramics (SiC, Al2O3) and metals (Cu, Al) to manufacture composite materials. Its current applications, chiefly limited to heating elements, can be expanded if its properties are judiciously combined with those of other materials like SiC or Al to produce ceramic- and metal-matrix composites with improved mechanical, thermal, functional, or even multifunctional properties. This review presents a perspective on the feasibility of manufacturing ceramic- and metallic-based MoSi2 composite materials. A comprehensive discussion of the pros and cons of current liquid-state and solid-state processing routes for MoSi2 metal-matrix composites and the resulting typical microstructures is presented. Although MoSi2 has been studied for more than five decades, it was not until recently that industrial applications demanding high temperature and cor...
Frontiers in Materials, 2023
Intermetallic molybdenum disilicide (MoSi2) possesses unique physical, chemical, thermal, and mechanical properties that make it compatible with some ceramics (SiC, Al2O3) and metals (Cu, Al) to manufacture composite materials. Its current applications, chiefly limited to heating elements, can be expanded if its properties are judiciously combined with those of other materials like SiC or Al to produce ceramic- and metal-matrix composites with improved mechanical, thermal, functional, or even multifunctional properties. This review presents a perspective on the feasibility of manufacturing ceramic- and metallic-based MoSi2 composite materials. A comprehensive discussion of the pros and cons of current liquid-state and solid-state processing routes for MoSi2 metal-matrix composites and the resulting typical microstructures is presented. Although MoSi2 has been studied for more than five decades, it was not until recently that industrial applications demanding high temperature and corrosion resistance started utilizing MoSi2 as a bulk material and a coating. Furthermore, beyond its traditional use due to its thermal properties, the most recent applications include it as a contact material in microelectronic components or circuits and optoelectronics. The short-term global growth predicted for the MoSi2 heating elements market is expected to significantly impact possible new applications, considering its potential for reuse and recyclability. A prospective assessment of the application of recycled MoSi2 to composite materials is presented.
NaF-assisted combustion synthesis of MoSi2 nanoparticles and their densification behavior
Journal of Physics and Chemistry of Solids, 2017
The exothermic reduction of oxides mixture (MoO 3 +2SiO 2) by magnesium in NaF melt enables the synthesis of nanocrystalline MoSi 2 powders in near-quantitative yields. The combustion wave with temperature of about 1000-1200°C was recorded in highly diluted by NaF starting mixtures. The by-products of combustion reaction (NaF and MgO) were subsequently removed by leaching with acid and washing with water. The as-prepared MoSi 2 nanopowder composed of spherical and dendritic shape particles was consolidated using the spark plasma sintering method at 1200-1500°C and 50 MPa for 10 min. The result was dense compacts (98.6% theoretical density) possessing submicron grains and exhibiting hardness of 8.74-12.92 GPa.
Effect of mechanical activation on synthesis of ultrafine Si3N4–MoSi2 in situ composites
Materials Science and Engineering: A, 2004
Si 3 N 4 -MoSi 2 in situ composite has been synthesized by reacting powders of molybdenum (Mo) and silicon nitride (Si 3 N 4 ). Mo and Si 3 N 4 powders mixture in a molar ratio of 1:3 were ball milled for 0-100 h. The milled and unmilled powder mixtures were reacted at different temperatures between 1000 and 1600 • C in an argon atmosphere. The effect of mechanical activation (MA) induced by milling has been studied through X-ray diffraction (XRD), differential thermal analysis (DTA), and thermo-gravimetric analysis (TGA). No peaks of Mo in the XRD pattern have been observed after 70 h of milling. The crystallite size of the Mo has been found to be the lowest (41 nm) after milling for 30 h. Similarly, a 100 nm lowest size of crystallite of Si 3 N 4 was observed after milling for 50 h. DTA and TGA results show that the reaction between Mo and Si 3 N 4 enhances with increase in milling time. Milling for 10 h lowers the pyrolysis temperature by 150 • C. Additional milling upto 100 h does not lead to further reduction in the pyrolysis temperature. The intensities of peaks of MoSi 2 in the pyrolysed samples increased with increase in milling time. MoSi 2 particles of size less than 1 m were observed to be uniformly distributed through out the Si 3 N 4 matrix.
Preparation of MoSi2–Al2O3 nano-composite via MASHS route
International Journal of Refractory Metals and Hard Materials, 2012
MoSi 2-Al 2 O 3 nano-composite MASHS PCA In this study, MoSi 2-Al 2 O 3 nano-composite powder was prepared by mechanical alloying. Mixture of MoO 3 , Si and Al powders was exposed to high energy ball milling. Phase compositions and structural evolutions during milling were investigated by X-ray diffraction (XRD) analysis. The morphology of the milled powders was evaluated by scanning electron microscope (SEM). Within short milling times [15, 25 and 60 minutes in ball to powder weight ratios (BPR) of 35:1, 20:1 and 10:1, respectively], a combustion process occurred within the milling powder and the process mechanism was characterized to be mechanically activated self-propagating hightemperature synthesis (MASHS) type. From XRD results it was found that during the combustion process, MoO 3 was completely reduced with Al and the resulting Mo reacted with Si to produce molybdenum disilicide and eventually a MoSi 2-Al 2 O 3 nano-composite powder formed within a short period of time. Further milling resulted in reduced mean crystallite sizes and increased lattice micro strain in the product phases. After 30 hours of milling in BPR of 35:1, the mean crystallite sizes were found to be 10, 9 and 11 nm for Al 2 O 3 , α-MoSi 2 and β-MoSi 2 , respectively. Also, effect of stearic acid addition as a Process Control Agent (PCA) was studied and the results showed that its usage postpones the reaction initiation and reduces mean crystallite sizes.
Synthesis and Properties of in Situ MoSi2/SiC Composites
MRS Online Proceeding Library
This volume is the written proceedings of Symposium F on High Temperature Silicides and Refractory Alloys, which was held in conjunction with the 1993 Fall Materials Research Society Meeting in Boston, Massachusetts, November 28-December 2, 1993. This symposium was very successful with 82 oral presentations, over four days. The first two days were devoted to recent developments in silicides and the last two days to refractory alloys. This response is a reflection of the growing interest in refractory metal based silicides, in particular, MoSi 2 , and the continued development of commercial refractory alloys such as W, Mo, Ta, and Nb-based alloys. The symposium covered synthesis, processing, microstructures, mechanical properties, oxidation behavior, composites, multiphase materials and applications. Significant advances were evident in all these areas. The symposium was sponsored by The Office of Naval Research, Osram-Sylvania Inc., and the General Electric Company. We are very grateful for their support. We are also pleased to acknowledge the support of the staff at MRS for their assistance in assembling both the program and the proceedings. Finally, we would like to thank the session chairs, the manuscript services, the speakers and all those who contributed to the success of this symposium.
Mechanically Activated SHS Compaction of MoSi 2 -Based Composites
MoSi 2 ‒Mo 5 Si 3 composites are promising structural materials for high-temperature oxidizing environments in advanced boilers and turbines. It would be attractive to produce these materials using self-propagating high-temperature synthesis (SHS) as it offers advantages such as low energy consumption and low cost. However, the use of the mixture ratios different from the MoSi 2 stoichiometry decreases the mixture exothermicity, so that ignition without preheating becomes impossible. Another problem is that SHS usually produces porous, low-density materials, which have to be crushed, milled, and hot-pressed. In the present paper, a combination of the mechanically activated SHS with the so-called SHS compaction is used to synthesize MoSi 2 ‒Mo 5 Si 3 composites. More specifically, a mixture of initial powders is first treated in a planetary ball mill, which improves its ignitability. The activated mixture is then ignited in an apparatus for SHS compaction, where the combustion products are subjected to quasi-isostatic pressing immediately after the combustion process, thus producing denser materials and eliminating the need for additional steps. Scanning electron microscopy and X-ray diffraction analysis are used for the product characterization after milling and combustion steps. Compression testing of the product is also conducted.