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.

scholarly journals Peculiarities of Self-Propagating High-Temperature Synthesis and Structure Formation of TiB2-Al2O3 and CrB2-Al2O3 Composites

2011 ◽  
Vol 13 (3-4) ◽  
pp. 161
Author(s):  
Z.A. Mansurov ◽  
D.S. Abdulkarimova ◽  
O. Odawara ◽  
A. Gubarevich ◽  
A.S. Rogachev ◽  
...  
Keyword(s):  
High Temperature ◽  
Combustion Wave ◽  
Xrd Analysis ◽  
Product Formation ◽  
Combustion System ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Different Types ◽  
Combustion Wave Velocity ◽  
Quenching Method

Preparation of TiB2-Al2O3 and CrB2-Al2O3 composites with a broad range of phase composition was  conducted by self-propagating high-temperature synthesis (SHS) involving reaction of different types. The formation of fibrous crystals of aluminum oxide with length of about 10-25 microns and with diameter of 200-500 nm at self-propagating high-temperature synthesis in the system 2B2O3-Cr2O3-6A1 was established. Thermite mixtures of Al-TiO2 and Al-TiO2-B2O3 were incorporated with the Ti-B combustion system to produce the composites of TiB2-Al2O3, within which the increase of the thermite mixture for a higher content of Al2O3 decreased the reaction temperature and combustion wave velocity. This implies that the thermite reaction of Al with TiO2 reduces the exothermicity of the overall SHS process. It was found that adoption of B2O3 as one of the thermite reagents improved the product formation effectively. For investigate the combustion wave in 0.75TiO2-0.25Ti-2B-Al system the «quenching» method was used. The XRD analysis shows that the final products containing diborides and aluminium oxide.

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 SHS robust modes to restore molybdenum by combustion wave in MoO3 – Al system

2020 ◽  
Vol 15 (4) ◽  
pp. 27-32
Author(s):  
Irina V. Milyukova ◽  
Marina P. Boronenko
Keyword(s):  
Spectral Analysis ◽  
High Temperature ◽  
Combustion Wave ◽  
Synthesis Process ◽  
Temperature Synthesis ◽  
Preliminary Heating ◽  
X Ray ◽  
Molybdenum Metal ◽  
High Temperature Synthesis ◽  
Oxide Phases

The work is devoted to the technology for the reduction of molybdenum from oxides by the method of self-propagating high-temperature synthesis in the MoO3 AI system with the addition of aluminum. The experiment was carried out in two modes: in a reactor at different pressures without preliminary heating and in a furnace in air until the initiation of the SH-synthesis process. Samples of molybdenum metal were obtained in different synthesis modes. X-ray phase and X-ray spectral analysis showed that molybdenum is the main phase in the synthesized samples. The presence of slag oxide phases Al2O3 and MoO2 was detected.

scholarly journals Observation of Combustion Wave Propagation during Self-Propagation High-Temperature Synthesis of TiC with Gas Formation.

2000 ◽  
Vol 108 (1255) ◽  
pp. 290-297
Author(s):  
Yasuhiro TANABE ◽  
Nobuko OKADA ◽  
Akira MUKOHFUJIWARA ◽  
Takashi AKATSU ◽  
Eiichi YASUDA
Keyword(s):  
Wave Propagation ◽  
High Temperature ◽  
Combustion Wave ◽  
Temperature Synthesis ◽  
Gas Formation ◽  
High Temperature Synthesis ◽  
Combustion Wave Propagation

Effect of Gravity on Titanium Carbide Foams by Self-propagation High-temperature Synthesis

1999 ◽  
Vol 14 (4) ◽  
pp. 1516-1523 ◽  
Author(s):  
Yasuhiro Tanabe ◽  
Takashi Sakamoto ◽  
Nobuko Okada ◽  
Takashi Akatsu ◽  
Eiichi Yasuda ◽  
...  
Keyword(s):  
High Temperature ◽  
Carbon Black ◽  
Titanium Carbide ◽  
Combustion Wave ◽  
Propagation Velocity ◽  
Temperature Synthesis ◽  
Environmental Pressures ◽  
Environmental Pressure ◽  
High Temperature Synthesis ◽  
Microgravity Conditions

Titanium carbide foams are synthesized by a self-propagation high-temperature synthesis technique using carbon black, which generates gases during the synthesis. The synthesis is performed under terrestrial and microgravity conditions. The effects of gravity on the synthesis are evaluated in this study. The foaming is mainly caused by H2O and CO gases from the carbon black. The elongation of the products increases with decreasing environmental pressure and increasing amount of generated gases. Since the gas flows out along the direction of the combustion wave propagation, the products expand only along this direction. The propagation velocity of the combustion wave increases with increasing amount of generated gases and environmental pressure, which is due to the amount of molten Ti transporting into the reaction/preheat zone. Under higher environmental pressures, thermal convection of the environmental gases mainly affects the propagation velocity. However, at lower pressures, the behavior of the molten Ti has a great effect compared with the gases surrounding the specimens.

Effect of Mg on the Synthesis of TiB2 Powder by a Self-Propagating High-Temperature Synthesis Technique

2013 ◽  
Vol 347-350 ◽  
pp. 1144-1147
Author(s):  
Su Li ◽  
Jun Shou Li ◽  
Fang Zhao ◽  
Ming Hui Ye
Keyword(s):  
High Temperature ◽  
Combustion Synthesis ◽  
Formation Mechanism ◽  
Molar Ratio ◽  
Synthesis Reaction ◽  
Hexagonal Crystal ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Higher Temperature ◽  
Combustion Synthesis Reaction

Micro-nanoTiB2 ceramic was prepared through increasing the molar ratio of Mg and leaching with suitable acid by the combustion synthesis reaction of Mg, TiO2 and B2O3, which could get higher temperature and purer product. The Samples were investigated by XRD and SEM, and the results showed the diameter of the TiB2 was 200 nm ~ 300 nm and the shape of the TiB2 was irregular hexagonal crystal. The diameter of the TiB2 was decreased with the increase of Mg powder. The formation mechanism of TiB2 has been studied.

Reverse burning phenomenon in self-propagating high-temperature synthesis

1998 ◽  
Vol 13 (6) ◽  
pp. 1626-1630 ◽  
Author(s):  
Jou-Hong Lee ◽  
Ai-Yi Lee ◽  
Chien-Chong Chen
Keyword(s):  
High Temperature ◽  
Combustion Synthesis ◽  
External Heat ◽  
The Other ◽  
Green Density ◽  
Temperature Synthesis ◽  
Green Pellet ◽  
High Temperature Synthesis

An interesting reverse burning phenomenon was observed during the combustion synthesis of zirconium-based materials. When an external heat was applied to one end of a green pellet, the ignition was initiated at the other end. Also, the ignition position, measured from the heated end, was proportional to the apparent green density of the compact. The possible explanations for this reverse burning phenomenon are discussed.

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