scholarly journals Formation of Mo5Si3/Mo3Si–MgAl2O4 Composites via Self-Propagating High-Temperature Synthesis

Molecules ◽  
2019 ◽  
Vol 25 (1) ◽  
pp. 83 ◽  
Author(s):  
Chun-Liang Yeh ◽  
Yin-Chien Chen
Keyword(s):  
High Temperature ◽  
Combustion Velocity ◽  
Ceramic Composites ◽  
Minor Amount ◽  
Metallothermic Reduction ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Molybdenum Silicides ◽  
Spinel Mgal2o4 ◽  
A Minor

In situ formation of intermetallic/ceramic composites composed of molybdenum silicides (Mo5Si3 and Mo3Si) and magnesium aluminate spinel (MgAl2O4) was conducted by combustion synthesis with reducing stages in the mode of self-propagating high-temperature synthesis (SHS). The SHS process combined intermetallic combustion between Mo and Si with metallothermic reduction of MoO3 by Al in the presence of MgO. Experimental evidence showed that combustion velocity and temperature decreased with increasing molar content of Mo5Si3 and Mo3Si, and therefore, the flammability limit determined for the reaction at Mo5Si3 or Mo3Si/MgAl2O4 = 2.0. Based upon combustion wave kinetics, the activation energies, Ea = 68.8 and 63.8 kJ/mol, were deduced for the solid-state SHS reactions producing Mo5Si3– and Mo3Si–MgAl2O4 composites, respectively. Phase conversion was almost complete after combustion, with the exception of trivial unreacted Mo existing in both composites and a minor amount of Mo3Si in the Mo5Si3–MgAl2O4 composite. Both composites display a dense morphology formed by connecting MgAl2O4 crystals, within which micro-sized molybdenum silicide grains were embedded. For equimolar Mo5Si3– and Mo3Si–MgAl2O4 composites, the hardness and fracture toughness are 14.6 GPa and 6.28 MPa m1/2, and 13.9 GPa and 5.98 MPa m1/2, respectively.

scholarly journals Metallothermic Reduction of MoO3 on Combustion Synthesis of Molybdenum Silicides/MgAl2O4 Composites

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4800
Author(s):  
Chun-Liang Yeh ◽  
Min-Chia Chen
Keyword(s):  
High Temperature ◽  
Combustion Synthesis ◽  
Xrd Analysis ◽  
Metallothermic Reduction ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Molybdenum Silicides ◽  
Front Temperature ◽  
In Situ Production

Combustion synthesis involving metallothermic reduction of MoO3 by dual reductants, Mg and Al, to enhance the reaction exothermicity was applied for the in situ production of Mo3Si–, Mo5Si3− and MoSi2–MgAl2O4 composites with a broad compositional range. Reduction of MoO3 by Mg and Al is highly exothermic and produces MgO and Al2O3 as precursors of MgAl2O4. Molybdenum silicides are synthesized from the reactions of Si with both reduced and elemental Mo. Experimental evidence indicated that the reaction proceeded as self-propagating high-temperature synthesis (SHS) and the increase in silicide content weakened the exothermicity of the overall reaction, and therefore, lowered combustion front temperature and velocity. The XRD analysis indicated that Mo3Si–, Mo5Si3– and MoSi2–MgAl2O4 composites were well produced with only trivial amounts of secondary silicides. Based on SEM and EDS examinations, the morphology of synthesized composites exhibited dense and connecting MgAl2O4 crystals and micro-sized silicide particles, which were distributed over or embedded in the large MgAl2O4 crystals.

scholarly journals Intermetallic/Ceramic Composites Synthesized from Al–Ni–Ti Combustion with B4C Addition

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 873
Author(s):  
Chun-Liang Yeh ◽  
Chih-Yao Ke
Keyword(s):  
Combustion Velocity ◽  
Ceramic Composites ◽  
The Other ◽  
X Ray Diffraction ◽  
Temperature Synthesis ◽  
Reaction Systems ◽  
X Ray ◽  
High Temperature Synthesis ◽  
In Situ Formation

The fabrication of intermetallic/ceramic composites by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) was investigated in the Al–Ni–Ti system with the addition of B4C. Two reaction systems were employed: one was used to produce the composites of xNiAl–2TiB2–TiC with x = 2–7, and the other was used to synthesize yNi3Al–2TiB2–TiC with y = 2–7. The reaction mechanism of the Al–Ni–Ti system was strongly influenced by the presence of B4C. The reaction of B4C with Ti was highly exothermic, so the reaction temperature and combustion velocity decreased due to increasing levels of Ni and Al in the reactant mixture. The activation energies of Ea = 110.6 and 172.1 kJ/mol were obtained for the fabrication of NiAl- and Ni3Al-based composites, respectively, by the SHS reaction. The XRD (X-ray diffraction) analysis showed an in situ formation of intermetallic (NiAl and Ni3Al) and ceramic phases (TiB2 and TiC) and confirmed no reactions taking place between Ti and Al or Ni. The microstructure of the product revealed large NiAl and Ni3Al grains and small TiB2 and TiC particles. With the addition of TiB2 and TiC, the hardness of NiAl and Ni3Al was considerably increased and the toughness was also improved.

Self-Propagating High-Temperature Synthesis (SHS) of Advanced High-Temperature Ceramics

2008 ◽  
Vol 395 ◽  
pp. 15-38 ◽  
Author(s):  
Suman K. Mishra ◽  
Lokesh C. Pathak
Keyword(s):  
High Temperature ◽  
Ceramic Composites ◽  
Research Field ◽  
Advanced Materials ◽  
Temperature Synthesis ◽  
Advantages And Disadvantages ◽  
High Temperature Synthesis ◽  
Large Numbers ◽  
Material Preparation

Over the years, the self-propagating high-temperature synthesis (SHS) has become an interesting research field to prepare a large numbers of advanced materials. Recently, the demands for high temperature advanced ceramics have further intensified the research on SHS for efficient material preparation. Several reviews, large numbers of papers and patents on various aspects of material production by SHS are available in literature. These are scattered and it is desirable to have a comprehensive review of the literatures that not only helps the researchers but also guide the beginners in this area. In this paper, we have emphasized our contributions on synthesis of various advanced high temperature ceramics, the borides, carbides, oxides and their composites by SHS processes. Several advantages and disadvantages of the SHS technique for advanced high temperature (HT) materials are highlighted. The preparation of nano-sized powders and finegrained in-situ high temperature ceramic composites through SHS is specially mentioned.

scholarly journals Combustion Synthesis of NbB2–Spinel MgAl2O4 Composites from MgO-Added Thermite-Based Reactants with Excess Boron

Crystals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 210 ◽  
Author(s):  
Chun-Liang Yeh ◽  
Yin-Chien Chen
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Combustion Synthesis ◽  
Combustion Wave ◽  
Xrd Analysis ◽  
Activation Energies ◽  
Temperature Synthesis ◽  
Reaction Systems ◽  
High Temperature Synthesis ◽  
Spinel Mgal2o4

The formation of NbB2–MgAl2O4 composites from the MgO-added thermite-based reaction systems was investigated by self-propagating high-temperature synthesis (SHS). Two thermite mixtures, Nb2O5/B2O3/Al and Nb2O5/Al, were, respectively, adopted in Reactions (1) and (2). The XRD analysis confirmed the combination of Al2O3 with MgO to form MgAl2O4 during the SHS process and that excess boron of 30 atom.% was required to yield NbB2–MgAl2O4 composites with negligible NbB and Nb3B4. The microstructure of the composite reveals that rod-shaped MgAl2O4 crystals are closely interlocked and granular NbB2 are embedded in or scattered over MgAl2O4. With the addition of MgAl2O4, the fracture toughness (KIC) of 4.37–4.82 MPa m1/2 was obtained for the composites. The activation energies Ea = 219.5 ± 16 and 167.9 ± 13 kJ/mol for Reactions (1) and (2) were determined from combustion wave kinetics.

Microstructure of intermetallic-matrix composites produced in situ by self-propagating high-temperature synthesis

1994 ◽  
Vol 52 ◽  
pp. 708-709
Author(s):  
C. P. Doğan ◽  
D. E. Alman
Keyword(s):  
High Temperature ◽  
Exothermic Reaction ◽  
Ceramic Composites ◽  
Matrix Composites ◽  
Temperature Synthesis ◽  
Intermetallic Matrix ◽  
High Temperature Synthesis ◽  
Wide Range ◽  
Intermetallic Matrix Composites

Self-propagating, high-temperature synthesis (SHS) is one method of material production in which elemental constituents are ignited, initiating a self-sustaining, exothermic reaction that results in their transformation into intermetallic and ceramic compounds. In addition, several reactions can be initiated within a single body to form intermetallic-intermetallic, intermetallic-ceramic, or ceramic-ceramic composites in situ. The driving force for the reactions is the negative heats of mixing of the forming compounds, which results in the liberation of heat. The obvious advantages of SHS processing are that it presents an opportunity to produce near net-shape advanced materials and composites with a high level of purity in a relatively low-cost and energy efficient manner.At the U.S. Bureau of Mines, we are actively involved in the SHS processing of a wide range of singlephase intermetallic and intermetallic-matrix composites: TiAl, TiAl+TiB2, TiAl+TiC, TiAl+Ti5Si3, MoSi2+SiC. One key element of our study is a thorough understanding of the effect of processing variables, such as composition, temperature, pressure, time, powder morphology, etc., on the microstructure, and hence the properties, of these materials.

Self-propagating high-temperature synthesis of ZrB2-B4C composites with the dispersed phase as hollow shells

2019 ◽  
Vol 485 (2) ◽  
pp. 190-193
Author(s):  
V. A. Shcherbakov ◽  
A. N. Gryadunov ◽  
M. I. Alymov
Keyword(s):  
High Temperature ◽  
Ceramic Composites ◽  
Dispersed Phase ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Ceramic Binder

The formation of the microstructure of ZrB2-B4C ceramic composites produced by SHS pressing has been studied. It has been shown that the exothermic interaction in a mixture of Zr, B, and C powders gives an equilibrium SHS product containing ZrB2 as a dispersed phase and B4C – as a ceramic binder. The effect of the ceramic binder (B4C) content on the formation of the microstructure of SHS composites has been studied. It is shown, at content of B4C 10-20 wt% homogeneous SHS composites were formed consisting monolithic the ZrB2 particles with a size of 10-12 pm, and at content of B4C 20-40 wt% – hollow shells consisting of the ZrB2 particles.

Fabrication of Aluminum-Ceramic Composites with TiC-Ni Skeleton by SHS Pressing Method

2016 ◽  
Vol 684 ◽  
pp. 371-378
Author(s):  
A.F. Fedotov ◽  
Evgeniy I. Latukhin ◽  
Vladislav A. Novikov
Keyword(s):  
Experimental Study ◽  
High Temperature ◽  
Molten Aluminum ◽  
Ceramic Composites ◽  
Structure And Properties ◽  
Temperature Synthesis ◽  
Pressing Method ◽  
High Temperature Synthesis ◽  
Infiltration Pressure ◽  
Porous Skeleton

One-stage technology of obtaining aluminum-ceramic skeleton composites by combining the processes of self-propagating high-temperature synthesis (SHS) of the porous skeleton and its infiltration under pressure with molten aluminum (method SHS-pressing) was considered. Experimental study of the effect of the pressure of infiltration on the distribution of the content of aluminum over the height and radius of the disk-shaped sample with SHS skeleton made of a cermet of TiC-Ni was performed. Mechanisms of the formation of structure and properties of the composite depending on the infiltration pressure were described.

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