Synthesis Of MoSi Research Articles

Effect of Mechanical Alloying Time and Ball-Powder Weight Ratio on Synthesis of MoSi<SUB>2</SUB>–Mo<SUB>5</SUB>Si<SUB>3</SUB> Nanocomposite

Effect of Mechanical Alloying Time and Ball-Powder Weight Ratio on Synthesis of MoSi<SUB>2</SUB>–Mo<SUB>5</SUB>Si<SUB>3</SUB> Nanocomposite

Synthesis of MoSi 2–TiC nanocomposite powder via mechanical alloying and subsequent annealing

MoSi 2–30 wt.% TiC nanocomposite powder was successfully synthesized by ball milling and following heat treatment. Effect of milling time and annealing temperature were investigated. The products synthesis and reactions progress were characterized by XRD. Morphology and microstructure of milled powders were monitored by SEM and TEM, respectively. Results showed that the synthesis of this composite begins after 10 h of milling and progresses gradually up to 30 h of milling. MoSi 2–TiC composite was completely synthesized after annealing of 30 h milled powder at 900 °C. On the basis of Reitveld refinement method, the mean grain size and microstrain of 13.2 nm and 0.44% were obtained, respectively for 30 h milled powder that is in consistent with TEM image. In the spite of grain growth and strain release, this nanocomposite powder maintained its nanostructure after annealing.

Activated combustion features in the Mo–Si–C-promoter system and synthesis of MoSi 2–SiC composite powders

Opportunities on combustion synthesizing the MoSi 2–SiC ceramic composites in a wide range of compositions under the chemical activated mode were studied. Molybdenum, silicon powders and carbon black were used as initial reagents, and Teflon was used as an activating additive. It was established that Teflon displays a dual (kinetic and thermal) impact on the interaction between reagents. The phasic character of the combustion process evolution, being characterized by low- and high-temperature regimes, was revealed. The end-products were subjected to SEM, XRD and chemical analyses.

Synthesis of MoSi 2–Al 2O 3 nanocomposite by mechanical alloying

MoSi 2–Al 2O 3 nanocomposite was synthesized by mechanical alloying (MA) of MoO 3, SiO 2 and Al powder mixture. The structural evolution of the powders was studied by X-ray diffraction (XRD). Both β-MoSi 2 and α-MoSi 2 were obtained after 3 h of milling. The spontaneous formation of β-MoSi 2 during milling proceeded by a mechanically induced self propagating reaction (MSR), analogous to that of the self propagating high temperature synthesis (SHS). After 70 h of milling the β-phase transformed to α-phase. The crystallite size of α-MoSi 2 and Al 2O 3 after milling for 100 h was 12 and 17 nm, respectively. Residual Mo and Si in the 3 and 70 h milled samples formed β-MoSi 2 and Mo 5Si 3 during heating at 1000 °C, respectively.

Effect of mechanical alloying on combustion synthesis of MoSi2

Characteristics of the combustion synthesis of MoSi2 using elemental Mo and Si powder mixtures prepared by mechanical alloying were investigated. The mechanical alloying resulted in powders of pseudolamellar structure and a partial conversion of the elemental powders to hexagonal MoSi2 phase. Combustion reaction of the mixture was ignited around 670 °C, which is much lower than that with the powder prepared by low-energy ball milling. A mathematical model was developed to demonstrate the possibility of the ignition of the combustion reaction of the lamellar structure via a solid-state diffusional process. On the basis of model, effects of mechanical alloying time on the ignition temperature and combustion temperature are discussed.

Synthesis and oxidation resistance of MoSi2-SiC composites

Synthesis of fully dense MoSi 2 -SiC composites without SiO 2 -inclusions was performed, and oxidation behavior of the composites was studied. For the fabrication of MoSi 2 and MoSi 2 -SiC composites, the mixed powders consisting of elemental Mo, Si and C were sintered at 1673 or 1873 K with a spark plasma sintering method. Namely, in-situ synthesis of MoSi 2 and SiC and sintering of the compounds were simultaneously performed. As the result, fully dense MoSi 2 and MoSi 2 composites which little contain SiO 2 inclusions were fabricated. Oxidation tests of the sintered bodies were carried out in air at 773 K in the accelerated oxidation region and 1773 K in the passive oxidation region. In the composites, occurrence of simultaneous oxidation of Mo and Si in the accelerated oxidation region was remarkably suppressed. In oxidation at 1773 K, the composites show outstanding oxidation resistance by a formation of a protective SiO 2 layer.

Micropyretic synthesis of MoSi2 powders through an aluminothermic reaction

An aluminothermic reaction starting with inexpensive MoO3, SiO2, and Al powders was utilized to prepare molybdenum disilicide (MoSi2) powders by the micropyretic/combustion synthesis process and leaching. The combustion-synthesized product was porous and could readily be crushed into powders. X-ray diffraction (XRD) analysis revealed that the product of such a reaction consisted of α–Al2O3, MoSi2, and a small amount of Mo(Si,Al)2 and Mo5Si3. The reason for the formation of Mo(Si, Al)2 phase is discussed. MoSi2 powders were obtained by leaching out the Al2O3 from the synthesized powder mixtures in boiling phosphoric acid solution. The synthesized MoSi2 powders, including a small amount of Mo(Si, Al)2 and Mo5Si3, were very fine with an average particle size of about 1 μm.

Novel synthesis of MoSi<SUB>2</SUB> and MoSi<SUB>2</SUB>-Al<SUB>2</SUB>0<SUB>3</SUB> ultrafine powders

Novel synthesis of MoSi<SUB>2</SUB> and MoSi<SUB>2</SUB>-Al<SUB>2</SUB>0<SUB>3</SUB> ultrafine powders

金属間化合物の粉末冶金と諸物性 パルス通電加圧−燃焼合成法によるＭｏ‐Ｓｉ系金属間化合物の作製

In this study, Mo-Si and Mo-Si-Nb system were fabricated by the pulse discharge pressure-combustion synthesis method (Nb was added into Mo-Si, in order to improve ductility at room temperature and high temperature strength). During the synthesis of Mo-Si and Mo-Si-Nb mixed powders, samples abruptly shrunk at 1323K. It is clear that combustion reaction occurred at this temperature and compounds were formed by combustion reaction. The relative density of fabricated samples was 96 to 98% and no internal defects were foundby ultrasound images in the samples. The formed phases of the fabricated samples were as follows;only MoSi2 phases were formed for Mo:Si=1:2 mixed powders, and, for the Nb added samples, MoSi2, Nb5Si3 and Mo5Si3 phases were formed and unreacted Nb remained. Young's modulus and the bending strength of fabricated samples showed similar results. Monolithic MoSi2 sample had the highest value of Young's modulus and bending strength, and for Nb added samples, Young's modulus and bending strength decreased with the increase in Nb content.

Synthesis of MoSi 2 powder by mechanical alloying

Systematic investigations were carried out on the synthesis of MoSi 2 powders by using a combination of mechanical alloying (MA) and vacuum heat treatment techniques. MA was conducted by two different high-energy ball mills under various milling conditions. The mechanically alloyed powders were characterized by X-ray diffraction and scanning electron microscopy as well as differential scanning calorimetry. The results showed that the preparation of MoSi 2 phase is not successful for all the mechanically alloyed powders after being milled with a less energetic planetary ball mill. However, the low-temperature α-MoSi 2 phase and the high-temperature β-MoSi 2 phase were formed when the same powder mixtures were mechanically alloyed with a more energetic shaker ball mill after a long milling time. Microstructural investigation indicates that cold welding behavior of Mo and Si powders during MA treatment has a pronounced effect on the formation of MoSi 2 phases. Vacuum heat treatment can also promote the formation of MoSi 2 phases in mechanically alloyed powders which are processed with shaker ball mill.